Sage Journals: Discover world-class research

Abstract

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.

Keywords

diabetes dipeptidyl peptidase 4 herbal natural compounds

Introduction

According to the statistics from International Diabetes Federation (IDF), there were 425 million diabetes mellitus (DM) patients in 2017 worldwide, and that number is expected to increase to 629 million by 2045.¹ Abnormally high blood glucose caused by insulin insufficiency or insensitivity can lead to severe complications such as chronic renal failure, microvascular complication, cerebrovascular accident, and infarction induced by high glycated serum and blood vessel proteins.^2,3 Moreover, insufficient insulin signal leads to the decreased glucose uptake from the blood that, in turn, can result in ulcers, gangrene, diabetic retinopathy, and neuropathy.² Recent DM treatment is inclined to maintain the blood glucose level within normal limits by (e.g. nutritional therapy and physical management) and medication due to the incurable nature of DM.^4,5 Diabetic medications can be characterized into five strategies based on their acting mechanisms: raising insulin secretion (e.g. sulfonylurea and meglitinide analogs), reducing intestinal glucose absorption (e.g. acarbose), triggering insulin-independent glucose uptake signaling (e.g. thiazolidinedione and biguanide), reducing urinal glucose reabsorption (e.g. gliflozins), and prolonging insulin sensitive [e.g. dipeptidyl peptidase 4 (DPP-4) inhibitor and glucagon-like peptide 1 (GLP-1) receptor agonists] [American Diabetes Association, 2019b]. These antidiabetic drugs help DM patients to maintain their blood glucose levels with various adverse effects (Table 1), such as urine-tract infection, lactoacidosis, hypoglycemia, and obesity. These drug-related adverse effects can deteriorate the quality of life of DM patients and create unsurmountable difficulties for proper dosing regimens in a clinical setting. It has been observed that DPP-4 inhibitors can exert a similar efficacy in reducing blood glucose levels without severe adverse effects such as hypoglycemia as compared with sulfonylurea.⁶ Nevertheless, various adverse side effects associated with the current DPP-4 inhibitor can still be observed that, in turn, can severely limit their practical application. As such, there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis and botanic sources containing herbs and plants with fewer side effects. In this article, we have reviewed various approaches including in silico, in vitro enzymatic and cell assays, and in vivo animal tests in the search for natural DPP-4 inhibitors for the treatment of type 2 diabetes.

Table 1.

Current hypoglycemic agents and their side effect.⁷

Class	Name	Mechanism	Side effect	Reference
Sulfonylurea	Glimepiride, Glyburide, Gliclazide	Insulin secretion	Hypoglycemia, obesity	Deacon and Lebovitz⁸
Meglitinides agonist	Repaglinide, Nateglinide	Insulin secretion	Hypoglycemia, obesity	Grant et al.⁷
Thiazolidinedione	Pioglitazone, Rosiglitazone, Lobeglitazone	Increase insulin sensitivity	Obesity, edema	Kung and Henry⁹
DPP-4 inhibitors	Sitagliptin, Vildagliptin, Saxagliptin	Increase insulin sensitivity	Indigestion, rash	Chin et al.¹⁰
Biguanide	Metformin	Reduce gluconeogenesis	Lactoacidosis, indigestion	Defronzo et al.¹¹
Amylase/glucosidase inhibitors	Acarbose, Miglitol, Voglibose	Inhibit starch digestion	Diarrhea, flatulence	Zhang et al.¹²
Sodium/glucose transporter inhibitors	Dapagliflozin, Canagliflozin, Empagliflozin	Reduce urine glucose re-absorption	Urinary and genital tract infection	Lupsa et al.¹³

Overview of DPP-4 and its biological function

Two forms of DPP-4

DPP-4, which is a 88 kDa serine protease, contains one region of cytoplasmic region (amino acids 1–6) coupled with transmembrane domain (amino acids 7–28) and extracellular region (amino acids 29–766) with the main catalytic domain.¹⁴ There are two DPP-4 isoforms in the body: membrane-bound DPP-4 (mDPP-4) composed of full-length DPP-4 peptide; and soluble DPP-4 (sDPP-4), whose cytoplasmic and transmembrane regions are absent.¹⁴ Both forms can exert various biological activities in regulation of physiology and pathology.¹⁵

Biological function of soluble form DPP-4

sDPP-4 is secreted by lymphocytes, circulates in the blood,¹⁶ and shows high concentration in kidney.¹⁷ It has been observed that sDPP-4 plays various roles in improving skeleton muscle activity, immunocyte activation, chemotaxis, and homeostasis. sDPP-4 can secrete into serum via the response of skeletal muscle cells upon acute physical activities or feeding protein hydrolysate.¹⁸ Secreted sDPP-4 can reduce vasoconstriction that is caused by neuropeptide Y (NPY) and subsequently increase the arteriolar diameter of skeletal muscle that provides a physiological explanation for raising training efficiency caused by sDPP-4.^19,20 In addition to arteriolar diameter of skeletal muscle, secreted sDPP-4 acts as myokine, which stimulates inflammation in smooth muscles from blood vessel through activating protease-activated receptor 2 (PAR2)/ERK/NF-κB signaling pathway, increasing proinflammatory cytokine release and finally stimulating smooth muscle cell proliferation.²¹ However, sDPP-4-induced smooth muscle inflammation is not always good to the body. For instance, Romacho et al. reported sDPP-4 might cause microvascular endothelial dysfunction, which is the cause of chronic kidney disease in elders, through the same signaling with smooth muscle inflammation.^22,23 Thus, Dubé et al. illustrated that cardiovascular inflammation can be attenuated by DPP-4 inhibitor in the process of HIV treatment, and that leads to diminish cardiovascular morbidity of HIV treatment.²⁴ In T-cell activation, sDPP-4 can activate T-cell proliferation via co-stimulation with T-cell receptor (TCR) signaling and Toll-like receptor, whose activation is neither associated with its enzymatic activity nor with adenosine deaminase binding.^25–28 On the other hand, sDPP-4 can upregulate the expressions of IL-6 and TNF-α in monocyte through caveolin-1/ERK/NF-κB/c-Fos signaling, which is involved in monocyte proliferation.²⁹ It is noteworthy that Tansi et al. proved the interaction between DPP-4 and HIV-1 transcription regulator Tat (HIV-1-Tat).³⁰ Markedably, the effect on DPP-4/HIV-1-Tat in viral infection and proliferation needs further investigative attention. The role of sDPP-4 in chemotaxis regulation is related to the degradation of chemokine. Hematopoietic stem cell homing is attracted by stromal cell-derived factor 1 (SDF-1/CXCL12) and colony-stimulating factors (CSFs), which are substrates of both sDPP-4 and mDPP4.^15,31 Accordingly, sDPP-4 inhibition can improve success rate of transplantation after analyzing the relationship between sDPP-4 activity and hematopoietic stem cell transplantation.³² The known DPP-4 (both soluble and membrane-bound forms) substrates include numerous homeostatic hormones such as GLP-1, NPY, glucagon, peptide Y, and secretin, which accurately regulate blood sugar homeostasis.¹⁵ GLP-1 is involved in insulin sensitivity and secretion, food reward, and appetite through ghrelin and leptin, and cellular metabolism with adiponectin.^15,33–35 NPY blocks melanocortin-4 receptor signaling and leads to the reduction of energy consumption and possibility of obesity.^36,37 After secretion from intestinal L cell, GLP-1 is rapidly degraded by sDPP-4 into inactive GLP-1 amide, in which half-life is shorter than 2 min.³⁸ In dysglycemic patients, active GLP-1 content can be further decreased and cause more severe hyperglycemia.³⁹ Accordingly, inhibiting sDPP-4 activity can keep more active GLP-1 and NPY in serum and thus improve insulin efficiency.⁴⁰ Other biological activities including nonimmunodeficient virus infection are also explored. It has been demonstrated by the case study of Middle East respiratory syndrome coronavirus (MERS-CoV) infection that sDPP-4 can potentially function to block viral infection.^41,42 Truncated C-X-C chemokine 10 (CXCL10) secretion in persistent infection of hepatitis C is essential,⁴³ implying that DPP-4 may play a role in HCV persistent infection as manifested by a case report, in which a DM patient complicated with HCV infection showed HCV replication reduction after sitagliptin treatment.⁴⁴ sDPP-4 is essential for maintaining immune activity and chemotaxis, especially in inflammatory regulation, based on all available information of its biological activities. Thus, the serum activity of sDPP-4 can be an indicator of physiological or immunological stages.

The effect of serum sDPP-4 activity can be classified into several categories: infection related damage, transplantation or autoimmune disease, respiratory disease, and response to diabetic medications and complications, as discussed in detail in the following. Serum sDPP-4 activity in HIV infection is referred to the HIV-induced intestinal damage that is caused by Th17 cell depletion.^45,46 It has been observed that rheumatoid arthritis and multiple sclerosis patients have lower serum sDPP-4 activity than healthy people,^47,48 whereas HIV patients have higher serum sDPP-4 activity.⁴⁹ Moreover, Leicht et al. analyzed sDPP-4 activity in end-stage renal disease patients before and after kidney transplantation, and sDPP-4 activities were found to decrease after kidney transplantation.⁵⁰ These results suggest that serum sDPP-4 activity can be a potential biomarker for monitoring the progress of autoimmune disease and the prognosis of organ transplantation. Interestingly, serum sDPP-4 activity can be associated with the progress of chronic obstructive pulmonary disease (COPD),⁵¹ which is highly correlated with respiratory inflammation, obviously indicating the relationship between serum sDPP-4 activity and COPD progression.⁵² However, the prognosis of malignant pleural mesothelioma (MPM), which is a rare pulmonary malignancy, can be predicted by sDPP-4 activity in pleural fluid.⁵³ The pathological correlation between sDPP-4 activity and MPM prognosis is still veiled. These reports provide interesting suggestions about sDPP-4 levels as the biomarkers of various diseases, which are not easy to monitor in serum or other body fluid.

Biological function of membrane-bound DPP-4

Remarkably, mDPP-4 can be found mainly in the kidney, gastrointestinal tract, T lymphocytes, and reproductive organs.^54,55 Biological activities of mDPP-4 include the regulation of immune response and blood vessel function.¹⁵ mDPP4, also named CD26, is a T-cell co-stimulator of T-cell receptor responding to antigen-presenting cells.⁵⁶ Thus, mDPP-4 recently has been considered as a potent target in treatment of transplantation and autoimmune disease. Dolanbay et al. reported an interesting study about the impact of mDPP-4 inhibition in early pregnancy that can be important in treating recurrent implantation failure.⁵⁷ In hematopoietic stem cell transplantation, graft-versus-host disease (GVHD) is a common complication, which is critical in survival rate after transplantation.⁵⁸ Zhang et al. proved the association between Th17 cells and GVHD and which Th17 cell can be regulated by mDPP-4 inhibition that indicates current DPP-4 inhibitors can help ameliorating the onset of GVHD.⁵⁹ The impact of mDPP-4 in immune regulation is also implicated in autoimmune disease and hypersensitivity. mDPP-4 expression levels in CD8⁺ T cells of Hashimoto’s thyroiditis patients are significantly lower than healthy subjects that is plausibly attributed to disease progression.⁶⁰ In contrast, mDPP-4 levels are almost 11-fold higher in psoriatic skin than in normal skin, asserting the involvement of mDPP-4 in psoriatic development.⁶¹ mDPP-4 plays a positive role in asthma progress through promoting T-cell activation.⁶² These reports have unequivocally demonstrated the positive role played by mDPP-4 in immune regulation. mDPP-4 acts on both endothelial and epithelial cells in regulation of blood vessel function,. In addition to endothelial inflammation caused by sDPP-4, the role of mDPP-4 in endothelial generally involves the endothelial migration, angiogenesis, and proliferation under hypoxia status, which can be found in the development of endometriosis.⁶³ Xu et al. have pointed out that DPP-4 inhibitors that can alleviate pulmonary artery remodeling and, finally, delay the development of pulmonary hypertension.⁶⁴ In the regulation of cardiovascular function, mDPP-4 inhibition can reverse diastolic left ventricular dysfunction via inhibiting mDPP-4/SDF-1α related angiogenesis.⁶⁵ mDPP-4 involves in epithelial-mesenchymal transition (EMT) for epithelial cell,⁶⁶ suggesting the potential implication of mDDP-4 in promoting cancer development. In fact, breast cancer metastasis can be triggered by DPP4 inhibition through CXCL12/CXCR4/mTOR pathway.⁶⁷ However, DPP-4 inhibitor shows the opposite activity in non-small cell lung cancer, which suppresses cancer cell growth via macrophage-mediated natural killer (NK) cell activation.⁶⁸ Collectively, these studies have furnished comprehensive descriptions of mDPP-4 biological functions in the whole body and further manifest that DPP-4 inhibition (sDPP-4 or mDPP-4) can produce unexpected side effects.

Role of DPP-4 in diabetes treatment

The endocrinological impact of DPP-4 is more prominent in the mediation of blood glucose. DPP-4 inhibition is a predominant approach for treating diabetes because of prolonged incretin half-lives within serum, especially in type 2 DM.⁶⁹ In addition, it has been suggested that sitagliptin can preserve pancreatic β-cell function and subsequently stabilize insulin secretion as shown by two 4-year clinical trials, in which sitagliptin was adopted to treat slowly progressive type 1 DM (SPTIDDM) and latent autoimmune diabetes adult (LADA).^55,70 In addition to clinical treatment, DPP-4 levels can be used as a biomarker. For instance, high serum sDPP-4 levels can be referred to the elevated glycation end products, which subsequently evoke endothelial cell damage and diabetic nephropathy incidence.^71,72 In addition, high serum sDPP-4 levels also indicate worse drug response to DPP-4 inhibitor and hyperglycemia, which are the indicators of poor glycemic control and advanced disease progress.^73,74 The above information emphasizes the effect of DPP-4 inhibition and monitoring in DM treatment. The method of screening DPP-4 inhibitor and the recent known natural DPP-4 inhibitors are presented in the following.

Methods for screening novel DPP-4 inhibitors

In silico screening of DPP-4 inhibitors

Virtual screening has been seamlessly integrated into drug discovery and development⁷⁵ and its success significantly relies on compound library,⁷⁶ especially the structural diversity of compound library.⁷⁷ For instance, microalgal metabolites were screened for DDP-4 inhibitors.⁷⁸ Compared with the synthesized chemicals, natural compound libraries generally consist of more structurally diverse compounds than their synthetic counterparts,⁷⁹ providing a better screening resource. As such, numerous studies have adopted various natural compound libraries to find novel DDP-4 inhibitors as listed in Table 2.

Table 2.

Natural compound libraries adopted by various studies.

Natural compound library	Reference
Traditional Chinese Medicine Database (TCM Database@Taiwan)	Chen⁸⁰
Naturally Occurring Plant-based Anti-cancer Compound-Activity-Target database (NPACT)	Mangal et al.⁸¹
Natural Products subset of the ZINC database	Irwin and Shoichet et al.⁸²
The Binding Database (BindingDB)	Liu et al.⁸³
Antidiabetic natural compounds database (ADNCD)	Khatoon et al.⁸⁴
Phenol-explorer	Rothwell et al.⁸⁵
In-house natural products database (NPD)	Zhang et al.⁸⁶
The NuBBE Database (NuBBEDB)	Nguyen et al.⁸⁷

It is not uncommon to observe that docking studies were carried out based on a single DDP-4 crystal structure, despite the fact that a great number of DDP-4-inhibitor co-complex structures have been deposited in the Protein Data Bank (PDB). Deng et al.⁸⁸ for instance, docked a series of synthesized triazole-based uracil derivatives into the linagliptin-DDP4 co-complex structure (PDB code: 2RGU) using the standard precision (SP) Glide (Schrödinger, Inc.), which places internally generated ligand conformations with various positions and orientations into the binding pocket. Deng et al.⁸⁹ employed Gold (Cambridge Crystallographic Data Center), which is a genetic algorithm (GA)-based scheme to explore the conformational flexibility of ligand and the rotational flexibility of receptor, to dock synthesized pyrazolo inhibitors into the quinazolinone-DDP4 co-complex structure (PDB code: 2ONC).⁹⁰ It should be noted that both Glide and Gold are flexible docking algorithms.⁹¹ Nevertheless, DDP-4 is unrestrained per se as manifested by the fact that DDP-4 consists of various binding subsites, namely S₁, S’₁, S₂, S’₂, and extensive S₂, etc., to which the corresponding amino acids of the DDP4 substrate peptide designated by P₁, P’₁, P₂, P’₂, etc. from the nearest to the farthest cleavage point can bind as shown in Figure 1,⁹² and S₂, which is composed of various hydrophobic residues, namely GLU205 and GLU206 dyad and ARG125, is highly plastic.⁹³ Furthermore, Nabeno et al. categorized inhibitors into three different classes (Figure 1) based on the interactions between inhibitor and DDP-4 subsites as listed in Table 3, from which it can be observed that inhibitors of different classes bind to different DDP-4 subsites, and S₁ and S₂ are the common binding subsites.⁹² In fact, the root means square deviation (RMSD) between alogliptin-bound protein conformation (PDB: 3G0B) and teneligliptin-bound one (PDB: 3VJK) is 1.07 Å, denoting the promiscuous nature of DDP-4 that can be further demonstrated by Figure 2, in which the six DDP4 co-complex structures (PDB codes are 3W2T, 1X70, 3BJM, 2RGU, 3VJK, and 3G0B) are superimposed. Moreover, the diverse structures of inhibitors can also manifest the plasticity of DPP4. Lee et al. for instance, analyzed the chemical structures of those launched DDP-4 inhibitors and divided them into different classes⁹⁴ that, in turn, can be further noticeable the promiscuity of target protein.⁹⁵ As such, the promiscuity of DDP-4 cannot be fully taken into account unless more sophisticated structure-based ensemble docking schemes such as SVM-Pose/SVM-Score combinatorial ensemble docking⁹⁶ or analog-based pharmacophore ensemble schemes such as pharmacophore ensemble/support vector machine⁹⁷ can be adopted. It can be argued that molecular dynamics (MD) can be used to address the flexibility of DDP4 as illustrated by the study of Liu et al.⁹⁸ Nevertheless, the lengthy MD calculation will substantially increase computational time and expense, making it impractical to be carried out in a high-throughput fashion, let alone the more resource-demanded quantum mechanical (QM)/molecular mechanics (MM) algorithm.⁹⁹

Figure 1.

Nomenclature of substrate inhibitor residues and their corresponding subsites in the binding pocket of enzyme and the concept of three classes of inhibitors based on their subsites.

Table 3.

Three classes of inhibitors based on their subsites, their corresponding Protein Data Bank (PDB) entry, and references.

Inhibitor	PDB code	Class	Reference
Vildagliptin	3W2T	1	Nabeno et al.⁹²
Saxagliptin	3BJM	1	Metzler et al.¹⁰⁰
Alogliptin	3G0B	2	Zhang et al.¹⁰¹
Linagliptin	2RGU	2	Eckhardt et al.¹⁰²
Sitagliptin	1X70	3	Kim et al.¹⁰³
Teneligliptin	3VJK	3	Yoshida et al.¹⁰⁴

Figure 2.

The superposition of six DDP4 co-complex structures, whose PDB codes are 3W2T (color-coded in green), 1X70 (gray), 3BJM (purple), 2RGU (orange), 3VJK (brown), and 3G0B (red). The ligand alogliptin is shown in colors.

Direct test of compounds against DPP-4

There are four types of assay methods for screening DPP-4 inhibitors for direct testing: direct enzymatic assay, in vitro cell assay, ex vivo assay, and in vivo animal tests. DPP-4 and tested compounds are mixed in the direct enzymatic assay, followed by adding specific substrate peptides such as gly-pro-p-nitroanilide. The chemical p-nitroanilide will be released from peptides and the amount is determined by optical absorption at 405 nm at noninhibition state.¹⁰⁵ This method is fast for analysis and can be used to evaluate the inhibition pattern from calculated K_i values. However, the minimum changes within direct enzymatic assay cannot be directly translated into the actual bioactivity in cells and animals.¹⁰⁶ Ex vivo assay can simulate the biological interaction within body, whereas it needs fresh serum or tissue sample as the source of DPP-4.^107,108 Moreover, previous studies reported that mucosal DPP-4 inhibition can be possibly related to the onset of coeliac disease, which is an autoimmune disorder due to the immune response to gluten.^109,110 However, a modern version of DPP4 activity assay needs to homogenize the whole intestinal biopsy that, in turn, can lead to mucosal DPP-4 inhibition.¹⁰⁸ Yazbeck et al. have derived a new DPP4 substrate with ¹³C isotope that can be released upon reaction with DPP-4.¹¹¹ As such, the requirement to homogenize the biopsy is completely exonerated, leading to higher correlation as compared with its conventional counterparts.¹¹¹

Myocytes and pancreatic cells are often used in the cell-based assays to discover DPP-4 inhibitors. Because β-cells in pancreatic islet is an important GLP-1 target, the downstream signaling of GLP-1 in pancreatic cells can be an indicator or biomarker of DPP-4 activity.¹¹² In addition, GLP-1 attenuates lipopolysaccharide (LPS)-induced cardiomyocyte inflammation. The variations of inflammatory signaling including NF-κB, ERK, and TNF-α within LPS-induced cardiomyocyte can indirectly gauge DPP-4 activity.¹¹³ Nevertheless, the results of cell-based assay can be an authentic representative of the realistic situation mainly due to the fact that they do not consider in vivo pharmacodynamic and pharmacokinetic factors. Nevertheless, direct action upon target cells can be very helpful in detailing intracellular dynamics prior to clinical or animal tests.

DPP-4 inhibitors have been highlighted as potential regimen for autoimmune-disease based on the characteristics in T-cell activation and inflammation.⁵⁵ Notably, autoimmune animal model becomes a platform for testing in vivo efficacy of DPP-4 inhibitors in long-term administration.¹¹⁴ Alternatively, in vivo assay of DPP-4 inhibitory efficacy can be verified by diabetic animal model despite the fact that DPP-4 can degrade GLP-1, leading to insulin desensitization and secretion decrease.¹¹² The most unvanquished limitation of in vivo test is that only end-point effect can be observed in pre-testing drug candidate despite the fact that it is more related to clinical situations. The data retrieved from in vitro and direct enzymatic assay can be synergistically essential for understanding the conceivable hypoglycemic mechanism.

Natural compounds as novel DPP-4 inhibitors

The effects of DPP-4 studies were mainly focused on immune, endocrine, and neuron system from the end of 1990s to early of 2000s.^115–117 A study reported in 2006 that incretin was the molecular target of DPP-4, suggesting the implication of DPP-4 inhibitor in diabetes treatment. Consequently, the diabetic research has turned into a new paradigm for searching for antidiabetic DPP-4 inhibitors.¹¹⁸ To date, only very limited natural DPP-4 inhibitors from various sources/origins have been reported (Table 4). Natural DPP-4 inhibitors from different origins using different approaches for screening the compound to reach the target are summarized as follows. In addition to plant source, DPP-4 inhibitors from animals and microbes are single-subclasses, in which DPP-4 inhibitors from animals and microbes are peptides and macrolides, respectively. Interestingly, the most predominant subclasses of DPP-4 inhibitors are terpenoids, peptides, phenolics, and flavonoids. These findings have implicated that alkaloids are not suitable as DPP-4 inhibitors or their applications in DDP4 inhibition have not been well explored. In addition to pure compounds, some crude extracts of natural materials or protein hydrolysates can exert DPP-4 inhibition as well. For instance, the DPP-4 inhibition activities of methanol extracts of Ficus benghalensis, Syzigium cumini, Ocimum sanctum, and Eucalyptus sp. have been demonstrated.^119,120 The hypoglycemic efficacy of traditional Chinese antidiabetic medicines decoction of Schizandra chinensis Baill., Coptis chinensis, Psidium guajava L., and Morus alba L. has been verified by DPP-4 inhibition by in vivo test.¹²¹ The protein hydrolysates from whey, barbel, and yam can reduce the DPP-4 activity in enzymatic measurements.^122–125 Through partition by molecular sieve, the highest inhibition peptide sequences of DPP-4 such as Ala-Pro, Leu-Pro-Val-Pro-Gln, Trp-Ser-Gly, and Phe-Ser-Asp have been found.^126–128 Nevertheless, these results from in vitro enzymatic assays cannot guarantee a promising future since physiological regulation of DPP-4 is far more complicated than bench-top experiments. Therefore, the results from direct enzymatic assay for new candidates or hits require further validation such as in vivo investigations to confirm their actual therapeutic values when compared with clinical medicines.

Table 4.

Natural DPP-4 inhibitors from different origins.

Structure subclass	Compound name	Source	Testing method	Reference
Plant origin
Alkaloids	Ephedrine	Ephedra spp.	Enzymatic	Ojeda-Montes et al.¹²⁹
	Berberine	Coptis chinensis	Enzymatic	Al-Masri et al.¹³⁰
Diarylheptanoid	Calebin A	Curcuma longa	Enzymatic	Oliveira et al.¹³¹
Flavonoids	Chrysin	Passiflora caerulea	In vitro	Kalhotra et al.¹³²
	Kaempferol, Kaempferol 7-O-Α-L-Rhamnoside, Vitexin, Lepidoside, Rutin	Smilax china L.	Enzymatic	Zhao et al.¹³³
	Aspalathin	Aspalathus linearis	In vivo	Muller et al.¹³⁴
Glycoside	Linustatins A, Linustatins B, Linustatins C, Linustatins D, Linustatins E	Linum usitatissimum L.	Enzymatic	Yang et al.¹³⁵
Peptide	Soybean hydrolysate	Glycine max	Ex vivo	Lammi et al.¹⁰⁸
	Lupin hydrolysate	Lupinus spp,	Ex vivo	Lammi et al.¹⁰⁸
	AP peptide, IPA Peptide	Euphausia superba	Enzymatic	Ji et al.¹²⁸
Phenolics	Emodin	Rheum palmatum Linn	In vivo	Wang et al.¹³⁶
	Salvianolic Acid C	Xiaokean formula	Enzymatic	Wu et al.¹³⁷
	(+)-Vitisin A	Vitis thunbergii var. taiwaniana	Enzymatic	Lin et al.¹³⁸
	(–)-Vitisin B
	Syringic Acid 4-O-Β-D-Glucopyranosyl-(1→5)-Α-L-Rhamnopyranoside, Eight phenolic glycosides, Two phenolic acids	Magnolia officinalis	Enzymatic	Yan et al.¹³⁹
Sterol	Stigmasterol	Fagonia cretica	Enzymatic	Saleem et al.¹⁴⁰
Terpenoids	16-hydroxycleroda-3,13-dien-15,16-olide	Polyalthia longifolia	In vivo	Huang et al.¹⁴¹
	Quinovic Acid, Quinovic acid-3Β-O-Β-D-glycopyranoside	Fagonia cretica	Enzymatic	Saleem et al.¹⁴⁰
	Quinovic acid-3Β-O-Β-D-glucopyranosyl-(28→1)-Β-D-glucopyranosyl ester
	Ginsenoside Rg, Timosaponin AI	Xiaokean formula	Enzymatic	Wu et al.¹³⁷
	Two norsesquiterpenoids	Magnolia officinalis	Enzymatic	Yan et al.¹³⁹
	Lupeol	Hedera nepalensis	Enzymatic	Saleem et al.¹⁴⁰
Xanthonoid	Mangiferin	Magnifera indica	In vivo	Suman et al.¹⁴²
Animal origin
Peptide	LPVPQ peptide, IPM peptide	milk	Enzymatic	Nongonierma et al.¹²⁶
	WSG peptide, FSD peptide	Barbus sp.	Enzymatic	Sila et al.¹²⁷
Microbial origin
Macrolide	Grassypeptolide A	marine	In vitro	Kwan et al.¹⁴³

FSD, Phe-Ser-Asp; IPM, Ile-Pro-Met; LPVPQ, Lys-Pro-Val-Pro-Gln; WSG, Trp-Ser-Gly.

Caution of using DPP-4 inhibitors

Previous sections have described the biological functions, assay methods, and known natural DPP-4 inhibitors, which are purported to treat DM. However, DPP-4 inhibition can possibly cause unexpected sequela owing to its entanglement with immune response and endothelial functions. In fact, the roles of DPP-4 in tumorigenesis and progression, respectively, have been reviewed recently.^144,145 In lung cancer and pancreatic cancer, DPP-4 inhibitor can assuredly reduce cancer progression and promote the overall survival.¹⁴⁶ However, in breast cancer, prostate cancer, and endometrial carcinoma, DPP-4 inhibition would cause the opposite consequence which promotes cancer progression.^67,147,148 The role of DPP-4 inhibition in cancer treatment is inconclusive, but it is certain that DPP-4 inhibition in tumorigenesis and tumor development in site-specific tumor should be considered.^144,145 In addition to cancer development, opportunistic infection is another issue of DPP-4 inhibition. Anno et al. reported a 69-year-old DM patient, who developed fever after taking vildagliptin for 1 week owing to hypercytokinemia.¹⁴⁹ It is obvious that numerous chemokines such as CXCL3, CXCL4, CXCL 5, and CXCL10 can also function as DPP-4 substrates.⁵⁶ Chen et al. have found that DM patients with short-term DPP-4 inhibitor treatment are at higher risk of herpes zoster infection as compared with non-DPP-4 treatment patients after surveying the Longitudinal Health Insurance Database 2000.¹⁵⁰ The development of Hashimoto’s thyroiditis and celiac disease are inversely correlated with DPP4 levels (vide supra), suggesting that DPP-4 inhibition can promote disease progression. Inflammatory bowel disease (IBD), which is a general term for Crohn’s disease and ulcerative colitis, is caused by opportunistic infection or immune cell infiltration.^151,152 A meta-analysis published by Radel et al. has indicated that DPP-4 inhibition can increase the risk of Crohn’s disease.¹⁵³ In conclusion, DPP-4 inhibitors can be used to treat DM, whereas their complications with other immune disease or cancer should be seriously considered.

Perspectives and future research

The effect of virtual screening via computational biology or informatics further combined with in vitro enzymatic and cell assay, and in vivo animal tests offer a promising approach to discover candidates or hits for expediting the preclinical development process (Figure 3). Nevertheless, poor or ill drug absorption, distribution, metabolism, excretion, and toxicity (ADME/Tox) properties make substantial contributions to drug attritions,¹⁵⁴ and little effort has been dedicated to profiling ADME/Tox properties of DDP-4 inhibitors. As such, it is necessary to predict ADME/Tox parameters in the process of virtual screening, which should be carried by adopting schemes that can consider the unstructured nature of DDP-4, to minimize the late-stage failures.

Figure 3.

Effect of natural products in DPP-4 inhibition and the screening methods.

Footnotes

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Conflict of interest statement

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

ORCID iD

Ching-Feng Weng

References

Cho

Shaw

Karuranga

, et al. IDF diabetes atlas: global estimates of diabetes prevalence for 2017 and projections for 2045. Diabetes Res Clin Pract 2018; 138: 271–281.

Dodds

The how-to for type 2: an overview of diagnosis and management of type 2 diabetes mellitus. Nurs Clin North Am 2017; 52: 513–522.

Park

Kang

Jeon

, et al. Recent advances in the pathogenesis of microvascular complications in diabetes. Arch Pharm Res 2019; 42: 252–262.

American Diabetes Association a. 5. Lifestyle management: standards of medical care in diabetes-2019. Diabetes Care 2019; 42: S46–S60.

American Diabetes Association b. 9. Pharmacologic approaches to glycemic treatment: standards of medical care in diabetes-2019. Diabetes Care 2019; 42: S90–S102.

Zhou

Bai

Wang

, et al. The benefits and risks of DPP4-inhibitors vs. sulfonylureas for patients with type 2 diabetes: accumulated evidence from randomised controlled trial. Int J Clin Pract 2016; 70: 132–141.

Grant

Graven

LJ.

Progressing from metformin to sulfonylureas or meglitinides. Workplace Health Saf 2016; 64: 433–439.

Deacon

Lebovitz

HE.

Comparative review of dipeptidyl peptidase-4 inhibitors and sulphonylureas. Diabetes Obes Metab 2016; 18: 333–347.

Kung

Henry

RR.

Thiazolidinedione safety. Expert Opin Drug Saf 2012; 11: 565–579.

10.

Chin

Nam

Lee

, et al. Comparative safety for cardiovascular outcomes of DPP-4 inhibitors versus glimepiride in patients with type 2 diabetes: a retrospective cohort study. Medicine (Baltimore) 2017; 96: e7213.

11.

Defronzo

Fleming

Chen

, et al. Metformin-associated lactic acidosis: current perspectives on causes and risk. Metabolism 2016; 65: 20–29.

12.

Zhang

Chen

, et al. Alpha-glucosidase inhibitors and hepatotoxicity in type 2 diabetes: a systematic review and meta-analysis. Sci Rep 2016; 6: 32649.

13.

Lupsa

Inzucchi

SE.

Use of SGLT2 inhibitors in type 2 diabetes: weighing the risks and benefits. Diabetologia 2018; 61: 2118–2125.

14.

Lambeir

Durinx

Scharpe

, et al. Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV. Crit Rev Clin Lab Sci 2003; 40: 209–294.

15.

Mulvihill

Drucker

DJ.

Pharmacology, physiology, and mechanisms of action of dipeptidyl peptidase-4 inhibitors. Endocr Rev 2014; 35: 992–1019.

16.

Casrouge

Sauer

Barreira

Silva

, et al. Lymphocytes are a major source of circulating soluble dipeptidyl peptidase 4. Clin Exp Immunol 2018; 194: 166–179.

17.

Hasan

Hocher

Role of soluble and membrane-bound dipeptidyl peptidase-4 in diabetic nephropathy. J Mol Endocrinol 2017; 59: R1–R10.

18.

Neidert

Mobley

Kephart

, et al. The serine protease, dipeptidyl peptidase IV as a myokine: dietary protein and exercise mimetics as a stimulus for transcription and release. Physiol Rep 2016; 4: e12827.

19.

Just

Cooper

Delorey

DS.

Sympathetic vasoconstriction in skeletal muscle: adaptations to exercise training. Exerc Sport Sci Rev 2016; 44: 137–143.

20.

Neidert

Al-Tarhuni

Goldman

, et al. Endogenous dipeptidyl peptidase IV modulates skeletal muscle arteriolar diameter in rats. Physiol Rep 2018; 6: e13564.

21.

Wronkowitz

Gorgens

Romacho

, et al. Soluble DPP4 induces inflammation and proliferation of human smooth muscle cells via protease-activated receptor 2. Biochim Biophys Acta 2014; 1842: 1613–1621.

22.

Romacho

Vallejo

Villalobos

, et al. Soluble dipeptidyl peptidase-4 induces microvascular endothelial dysfunction through proteinase-activated receptor-2 and thromboxane A2 release. J Hypertens 2016; 34: 869–876.

23.

Seliger

Salimi

Pierre

, et al. Microvascular endothelial dysfunction is associated with albuminuria and CKD in older adults. BMC Nephrol 2016; 17: 82.

24.

Dube

Chan

Lake

, et al. A randomized, double-blinded, placebo-controlled trial of sitagliptin for reducing inflammation and immune activation in treated and suppressed HIV infection. Clin Infect Dis. Epub ahead of print 10 December 2018. DOI: 10.1093/cid/ciy1051.

25.

Kim

Nian

Mcintosh

CH.

Sitagliptin (MK0431) inhibition of dipeptidyl peptidase IV decreases nonobese diabetic mouse CD4⁺ T-Cell migration through incretin-dependent and -independent pathways. Diabetes 2010; 59: 1739–1750.

26.

Slaitini

Gysbers

, et al. Soluble CD26/dipeptidyl peptidase IV enhances human lymphocyte proliferation in vitro independent of dipeptidyl peptidase enzyme activity and adenosine deaminase binding. Scand J Immunol 2011; 73: 102–111.

27.

Lee

Alam

, et al. Soluble DPP-4 up-regulates toll-like receptors and augments inflammatory reactions, which are ameliorated by vildagliptin or mannose-6-phosphate. Metabolism 2016; 65: 89–101.

28.

Kitagawa

Hamaguchi

Majima

, et al. Dipeptidyl peptidase-4 inhibitors have adverse effects for the proliferation of human T Cells. J Clin Biochem Nutr 2018; 63: 106–112.

29.

Ikeda

Kumagai

Iwata

, et al. Soluble CD26/dipeptidyl peptidase IV enhances the transcription of IL-6 and TNF-α in THP-1 cells and monocytes. PLoS One 2013; 8: e66520.

30.

Tansi

Blanchard

Berger

, et al. Interaction of human dipeptidyl peptidase IV and human immunodeficiency virus type-1 transcription transactivator in Sf9 cells. Virol 2010; 7: 267.

31.

Mortier

Gouwy

Van Damme

, et al. CD26/dipeptidylpeptidase IV-chemokine interactions: double-edged regulation of inflammation and tumor biology. J Leukoc Biol 2016; 99: 955–969.

32.

Broxmeyer

HE.

Counteracting the enzymatic activity of dipeptidylpeptidase 4 for potential therapeutic advantage, with an emphasis on cord blood transplantation. Korean J Intern Med 2013; 28: 639–645.

33.

Ronveaux

Tome

Raybould

HE.

Glucagon-like peptide 1 interacts with ghrelin and leptin to regulate glucose metabolism and food intake through vagal afferent neuron signaling. J Nutr 2015; 145: 672–680.

34.

Hayes

Schmidt

HD.

GLP-1 influences food and drug reward. Curr Opin Behav Sci 2016; 9: 66–70.

35.

Achari

Jain

SK.

Adiponectin, a therapeutic target for obesity, diabetes, and endothelial dysfunction. Int J Mol Sci 2017; 18: e1321.

36.

Kuhnen

Krude

Biebermann

Melanocortin-4 receptor signalling: importance for weight regulation and obesity treatment. Trends Mol Med 2019; 25: 136–148.

37.

Lotta

Mokrosinski

Mendes

Oliveira

, et al. Human gain-of-function MC4R variants show signaling bias and protect against obesity. Cell 2019; 177: 597–607.e599.

38.

Sharma

Verma

Vaidya

, et al. Recent updates on GLP-1 agonists: current advancements & challenges. Biomed Pharmacother 2018; 108: 952–962.

39.

Singh

AK.

Glucagon-like peptide 1 and dysglycemia: conflict in incretin science. Indian J Endocrinol Metab 2015; 19: 182–187.

40.

Nadkarni

Chepurny

Holz

GG.

Regulation of glucose homeostasis by GLP-1. Prog Mol Biol Transl Sci 2014; 121: 23–65.

41.

Inn

Kim

Aigerim

, et al. Reduction of soluble dipeptidyl peptidase 4 levels in plasma of patients infected with Middle East respiratory syndrome coronavirus. Virology 2018; 518: 324–327.

42.

Letko

Miazgowicz

Mcminn

, et al. Adaptive evolution of MERS-CoV to species variation in DPP4. Cell Rep 2018; 24: 1730–1737.

43.

Riva

Laird

Casrouge

, et al. Truncated CXCL10 is associated with failure to achieve spontaneous clearance of acute hepatitis C infection. Hepatology 2014; 60: 487–496.

44.

Yanai

Dipeptidyl peptidase-4 inhibitor sitagliptin significantly reduced hepatitis C virus replication in a diabetic patient with chronic hepatitis C virus infection. Hepatobiliary Pancreat Dis Int 2014; 13: 556.

45.

Paiardini

Muller-Trutwin

HIV-associated chronic immune activation. Immunol Rev 2013; 254: 78–101.

46.

Ploquin

Casrouge

Madec

, et al. Systemic DPP4 activity is reduced during primary HIV-1 infection and is associated with intestinal RORC⁺ CD4⁺ cell levels: a surrogate marker candidate of HIV-induced intestinal damage. J Int AIDS Soc 2018; 21: e25144.

47.

Ulusoy

Kamanli

Ilhan

, et al. Serum levels of soluble CD26 and CD30 and their clinical significance in patients with rheumatoid arthritis. Rheumatol Int 2012; 32: 3857–3862.

48.

Tejera-Alhambra

Casrouge

De Andres

, et al. Low DPP4 expression and activity in multiple sclerosis. Clin Immunol 2014; 150: 170–183.

49.

Mahmoudi

Hedayat

Aghamohammadi

, et al. Soluble CD26 and CD30 levels in patients with common variable immunodeficiency. J Investig Allergol Clin Immunol 2013; 23: 120–124.

50.

Leicht

Shipkova

Klett

, et al. CD26/dipeptidyl peptidase IV: a comparative study of healthy persons and kidney transplant recipients before and early after transplantation. Clin Biochem 2013; 46: 1383–1388.

51.

Somborac-Bacura

Buljevic

Rumora

, et al. Decreased soluble dipeptidyl peptidase IV activity as a potential serum biomarker for COPD. Clin Biochem 2012; 45: 1245–1250.

52.

Cho

Lee

Kim

LK.

COPD as a disease of immunosenescence. Yonsei Med J 2019; 60: 407–413.

53.

Fujimoto

Ohnuma

Aoe

, et al. Clinical significance of soluble CD26 in malignant pleural mesothelioma. PLoS One 2014; 9: e115647.

54.

Uhlen

Fagerberg

Hallstrom

, et al. Proteomics. Tissue-based map of the human proteome. Science 2015; 347: 1260419.

55.

Wang

Zheng

Huang

, et al. Dipeptidyl peptidase-4(DPP-4) inhibitors: promising new agents for autoimmune diabetes. Clin Exp Med 2018; 18: 473–480.

56.

Ohnuma

Dang

Morimoto

Revisiting an old acquaintance: CD26 and its molecular mechanisms in T cell function. Trends Immunol 2008; 29: 295–301.

57.

Dolanbay

Yardimoglu

Yalcinkaya

, et al. Expression of trophinin and dipeptidyl peptidase IV in endometrial co-culture in the presence of an embryo: a comparative immunocytochemical study. Mol Med Rep 2016; 13: 3961–3968.

58.

Shokouhi

Bray

Bakhtiyari

, et al. Effects of AGVHD and CGVHD on survival rate in patients with acute myeloid leukemia after allogeneic stem cell transplantation. Int J Hematol Oncol Stem Cell Res 2015; 9: 112–121.

59.

Zhang

Chu

, et al. Cellular and molecular mechanisms in graft-versus-host disease. J Leukoc Biol 2016; 99: 279–287.

60.

Liu

Gong

, et al. CD26 expression is down-regulated on CD8⁺ T cells in patients with hashimoto’s thyroiditis. Int Immunopharmacol 2018; 54: 280–285.

61.

Van Lingen

Van De Kerkhof

Seyger

, et al.CD26/dipeptidyl-peptidase IV in psoriatic skin: upregulation and topographical changes. Br J Dermatol 2008; 158: 1264–1272.

62.

Nieto-Fontarigo

Gonzalez-Barcala

San Jose

, et al. CD26 and asthma: a comprehensive review. Clin Rev Allergy Immunol 2019; 56: 139–160.

63.

Tan

Lee

Tan

, et al. CD26/DPPIV down-regulation in endometrial stromal cell migration in endometriosis. Fertil Steril 2014; 102: 167–177.e169.

64.

Wang

, et al. Dipeptidyl peptidase IV (DPP-4) inhibition alleviates pulmonary arterial remodeling in experimental pulmonary hypertension. Lab Invest 2018; 98: 1333–1346.

65.

Shigeta

Aoyama

Bando

, et al. Dipeptidyl peptidase-4 modulates left ventricular dysfunction in chronic heart failure via angiogenesis-dependent and -independent actions. Circulation 2012; 126: 1838–1851.

66.

Peng

Yang

Chan

, et al. Hibiscus sabdariffa polyphenols alleviate insulin resistance and renal epithelial to mesenchymal transition: a novel action mechanism mediated by type 4 dipeptidyl peptidase. J Agric Food Chem 2014; 62: 9736–9743.

67.

Yang

Takagaki

Yoshitomi

, et al. Inhibition of dipeptidyl peptidase-4 accelerates epithelial-mesenchymal transition and breast cancer metastasis via the CXCL12/CXCR4/mTOR axis. Cancer Res 2019; 79: 735–746.

68.

Jang

Janker

De Meester

, et al. The CD26/DPP4-inhibitor vildagliptin suppresses lung cancer growth via macrophage-mediated NK cell activity. Carcinogenesis 2019; 40: 324–334.

69.

Luo

Liu

, et al. The effects of novel antidiabetic drugs on albuminuria in type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. Clin Drug Investig 2018; 38: 1089–1108.

70.

Awata

Shimada

Maruyama

, et al. Possible long-term efficacy of sitagliptin, a dipeptidyl peptidase-4 inhibitor, for slowly progressive type 1 diabetes (SPIDDM) in the stage of non-insulin-dependency: an open-label randomized controlled pilot trial (SPAN-S). Diabetes Ther 2017; 8: 1123–1134.

71.

Ishibashi

Matsui

Maeda

, et al. Advanced glycation end products evoke endothelial cell damage by stimulating soluble dipeptidyl peptidase-4 production and its interaction with mannose 6-phosphate/insulin-like growth factor II receptor. Cardiovasc Diabetol 2013; 12: 125.

72.

Zheng

Liu

Qin

, et al. Increased plasma dipeptidyl peptidase-4 activities are associated with high prevalence of diabetic nephropathy in Chinese patients with newly diagnosed type 2 diabetes: a cross-sectional study. Diab Vasc Dis Res 2016; 13: 127–136.

73.

Aso

Ozeki

Terasawa

, et al. Serum level of soluble CD26/dipeptidyl peptidase-4 (DPP-4) predicts the response to sitagliptin, a DPP-4 inhibitor, in patients with type 2 diabetes controlled inadequately by metformin and/or sulfonylurea. Transl Res 2012; 159: 25–31.

74.

Aso

Terasawa

Kato

, et al. The serum level of soluble CD26/dipeptidyl peptidase 4 increases in response to acute hyperglycemia after an oral glucose load in healthy subjects: association with high-molecular weight adiponectin and hepatic enzymes. Transl Res 2013; 162: 309–316.

75.

Fara

Oprea

Prossnitz

, et al. Integration of virtual and physical screening. Drug Discov Today Technol 2006; 3: 377–385.

76.

Hajduk

Galloway

Spring

DR.

Drug discovery: a question of library design. Nature 2011; 470: 42–43.

77.

Muegge

Oloff

Advances in virtual screening. Drug Discov Today Technol 2006; 3: 405–411.

78.

Selvaraj

Kaliamurthi

Cakmak

, et al. Computational screening of dipeptidyl peptidase IV inhibitors from micoroalgal metabolites by pharmacophore modeling and molecular docking. Phycol Res 2016; 64: 291–299.

79.

Harvey

AL.

Natural products in drug discovery. Drug Discov Today 2008; 13: 894–901.

80.

Chen

CY.

TCM Database@Taiwan: the world’s largest traditional Chinese medicine database for drug screening in silico. PLoS One 2011; 6: e15939.

81.

Mangal

Sagar

Singh

, et al. NPACT: naturally occurring plant-based anti-cancer compound-activity-target database. Nucleic Acids Res 2013; 41: D1124–D1129.

82.

Irwin

Shoichet

BK.

Zinc–a free database of commercially available compounds for virtual screening. J Chem Inf Model 2005; 45: 177–182.

83.

Liu

Lin

Wen

, et al. BindingDB: a web-accessible database of experimentally determined protein-ligand binding affinities. Nucleic Acids Res 2007; 35: D198–D201.

84.

Khatoon

Rashid

Shaikh

, et al. ADNCD: a compendious database on anti-diabetic natural compounds focusing on mechanism of action. 3 Biotech 2018; 8: 361.

85.

Rothwell

Perez-Jimenez

Neveu

, et al. Phenol-Explorer 3.0: a major update of the Phenol-Explorer database to incorporate data on the effects of food processing on polyphenol content. Database (Oxford) 2013; 2013: bat070.

86.

Zhang

Liu

, et al. Fast and effective identification of the bioactive compounds and their targets from medicinal plants via computational chemical biology approach. Med Chem Commun 2011; 2: 471–477.

87.

Nguyen

Munnier

Souce

, et al. Novel alginate-based nanocarriers as a strategy to include high concentrations of hydrophobic compounds in hydrogels for topical application. Nanotechnology 2015; 26: 255101.

88.

Deng

Han

Zhou

, et al. Discovery of triazole-based uracil derivatives bearing amide moieties as novel dipeptidyl peptidase-IV inhibitors. Bioorg Chem 2017; 75: 357–367.

89.

Deng

Shen

Zhu

, et al. Surrogating and redirection of pyrazolo[1,5-a]pyrimidin-7(4H)-one core, a novel class of potent and selective DPP-4 inhibitors. Bioorg Med Chem 2018; 26: 903–912.

90.

Feng

Zhang

Wallace

, et al. Discovery of alogliptin: a potent, selective, bioavailable, and efficacious inhibitor of dipeptidyl peptidase IV. J Med Chem 2007; 50: 2297–2300.

91.

Pagadala

Syed

Tuszynski

Software for molecular docking: a review. Biophys Rev 2017; 9: 91–102.

92.

Nabeno

Akahoshi

Kishida

, et al. A comparative study of the binding modes of recently launched dipeptidyl peptidase IV inhibitors in the active site. Biochem Biophys Res Commun 2013; 434: 191–196.

93.

Leiting

Pryor

, et al. Catalytic properties and inhibition of proline-specific dipeptidyl peptidases II, IV and VII. Biochem J 2003; 371: 525–532.

94.

Lee

Kim

, et al. Unique binding mode of evogliptin with human dipeptidyl peptidase IV. Biochem Biophys Res Commun 2017; 494: 452–459.

95.

Gao

Skolnick

A comprehensive survey of small-molecule binding pockets in proteins. PLoS Comput Biol 2013; 9: e1003302.

96.

Leong

Syu

Ding

, et al. Prediction of N-methyl-D-aspartate receptor GluN1-ligand binding affinity by a novel SVM-pose/SVM-score combinatorial ensemble docking scheme. Sci Rep 2017; 7: 40053.

97.

Leong

MK.

A novel approach using pharmacophore ensemble/support vector machine (PHE/SVM) for prediction of hERG liability. Chem Res Toxicol 2007; 20: 217–226.

98.

Liu

Huan

, et al. Establishment of a selective evaluation method for DPP4 inhibitors based on recombinant human DPP8 and DPP9 proteins. Acta Pharm Sin B 2014; 4: 135–140.

99.

Bersuker

Leong

Boggs

, et al. A method of combined quantum mechanical (Qm)/molecular mechanics (Mm) treatment of large polyatomic systems with charge transfer between the Qm and Mm Fragments. Int J Quantum Chem 1997; 63: 1051–1063.

100.

Metzler

Yanchunas

Weigelt

, et al. Involvement of DPP-IV catalytic residues in enzyme-saxagliptin complex formation. Protein Sci 2008; 17: 240–250.

101.

Zhang

Wallace

Feng

, et al. Design and synthesis of pyrimidinone and pyrimidinedione inhibitors of dipeptidyl peptidase IV. J Med Chem 2011; 54: 510–524.

102.

Eckhardt

Langkopf

Mark

, et al. 8-(3-(R)-aminopiperidin-1-Yl)-7-but-2-ynyl-3-methyl-1-(4-methyl-quinazolin-2-ylme thyl)-3,7-dihydropurine-2,6-dione (Bi 1356), a highly potent, selective, long-acting, and orally bioavailable DPP-4 inhibitor for the treatment of type 2 diabetes. J Med Chem 2007; 50: 6450–6453.

103.

Kim

Wang

Beconi

, et al. (2r)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)- yl]-1-(2,4,5-trifluorophenyl)butan-2-amine: a potent, orally active dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes. J Med Chem 2005; 48: 141–151.

104.

Yoshida

Akahoshi

Sakashita

, et al. Discovery and preclinical profile of teneligliptin (3-[(2s,4s)-4-[4-(3-methyl-1-phenyl-1h-pyrazol-5-yl)piperazin-1-yl]pyrrolidin-2-y lcarbonyl]thiazolidine): a highly potent, selective, long-lasting and orally active dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes. Bioorg Med Chem 2012; 20: 5705–5719.

105.

Liu

Sun

Zhao

Investigating the contributions of residues to dipeptidyl peptidase-IV inhibitor binding by molecular dynamics simulation. Lett Drug Des Discov 2014; 11: 886–893.

106.

Walters

Namchuk

Designing screens: how to make your hits a hit. Nat Rev Drug Discov 2003; 2: 259–266.

107.

Al-Awar

Almasi

Szabo

, et al. Novel potentials of the DPP-4 inhibitor sitagliptin against ischemia-reperfusion (I/R) injury in rat ex-vivo heart model. Int J Mol Sci 2018; 19: E3226.

108.

Lammi

Bollati

Ferruzza

, et al. Soybean- and lupin-derived peptides inhibit DPP-IV activity on in situ human intestinal caco-2 cells and ex vivo human serum. Nutrients 2018; 10: E1082.

109.

Detel

Persic

Varljen

Serum and intestinal dipeptidyl peptidase IV (DPP IV/CD26) activity in children with celiac disease. J Pediatr Gastroenterol Nutr 2007; 45: 65–70.

110.

Lebwohl

Sanders

Green

PHR

. Coeliac disease. Lancet 2018; 391: 70–81.

111.

Yazbeck

Jaenisch

Squire

, et al. Development of a (13)C stable isotope assay for dipeptidyl peptidase-4 enzyme activity a new breath test for dipeptidyl peptidase activity. Sci Rep 2019; 9: 4906.

112.

Rohrborn

Wronkowitz

Eckel

DPP4 in diabetes. Front Immunol 2015; 6: 386.

113.

Lin

CC.

Sitagliptin attenuates inflammatory responses in lipopolysaccharide-stimulated cardiomyocytes via nuclear factor-kB pathway inhibition. Exp Ther Med 2016; 11: 2609–2615.

114.

Petersen

A methodological review of induced animal models of autoimmune diseases. Autoimmun Rev 2018; 17: 473–479.

115.

Clark

Kupper

TS.

IL-15 and dermal fibroblasts induce proliferation of natural regulatory T cells isolated from human skin. Blood 2007; 109: 194–202.

116.

Frerker

Raber

Bode

, et al. Phenotyping of congenic dipeptidyl peptidase 4 (DP4) deficient dark agouti (DA) rats suggests involvement of DP4 in neuro-, endocrine, and immune functions. Clin Chem Lab Med 2009; 47: 275–287.

117.

Klemann

Schade

Pabst

, et al. CD26/dipeptidyl peptidase 4-deficiency alters thymic emigration patterns and leukcocyte subsets in F344-rats age-dependently. Clin Exp Immunol 2009; 155: 357–365.

118.

Drucker

Nauck

MA.

The incretin system: glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors in type 2 diabetes. Lancet 2006; 368: 1696–1705.

119.

Dey

Mitra

Katakam

, et al. Exploration of natural enzyme inhibitors with hypoglycemic potentials amongst eucalyptus Spp. by in vitro assays. World J Diabetes 2014; 5: 209–218.

120.

Bhandari

Singla

, et al. Chemometrics optimized extraction procedures, phytosynergistic blending and in vitro screening of natural enzyme inhibitors amongst leaves of Tulsi, Banyan and Jamun. Pharmacogn Mag 2015; 11: S522–S532.

121.

Wang

Chiang

BH.

Anti-diabetic effect of a traditional Chinese medicine formula. Food Funct 2012; 3: 1161–1169.

122.

Lacroix

Li-Chan

EC.

Inhibition of dipeptidyl peptidase (DPP)-IV and α-glucosidase activities by pepsin-treated whey proteins. J Agric Food Chem 2013; 61: 7500–7506.

123.

Konrad

Anna

Marek

, et al. The evaluation of dipeptidyl peptidase (DPP)-IV, α-glucosidase and angiotensin converting enzyme (ACE) inhibitory activities of whey proteins hydrolyzed with serine protease isolated from Asian pumpkin (Cucurbita ficifolia). Int J Pept Res Ther 2014; 20: 483–491.

124.

Shih

Lin

, et al. Effects of yam dioscorin interventions on improvements of the metabolic syndrome in high-fat diet-induced obese rats. Bot Stud 2015; 56: 4.

125.

Sila

Martinez-Alvarez

Haddar

, et al. Recovery, viscoelastic and functional properties of Barbel skin gelatine: investigation of anti-DPP-IV and anti-prolyl endopeptidase activities of generated gelatine polypeptides. Food Chem 2015; 168: 478–486.

126.

Nongonierma

Fitzgerald

RJ.

Structure activity relationship modelling of milk protein-derived peptides with dipeptidyl peptidase IV (DPP-IV) inhibitory activity. Peptides 2016; 79: 1–7.

127.

Sila

Alvarez

Haddar

, et al. Purification, identification and structural modelling of DPP-IV inhibiting peptides from barbel protein hydrolysate. J Chromatogr B Analyt Technol Biomed Life Sci 2016; 1008: 260–269.

128.

Zhang

Purification, identification and molecular mechanism of two dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from Antarctic krill (Euphausia superba) protein hydrolysate. J Chromatogr B Analyt Technol Biomed Life Sci 2017; 1064: 56–61.

129.

Ojeda-Montes

Ardid-Ruiz

Tomas-Hernandez

, et al. Ephedrine as a lead compound for the development of new DPP-IV inhibitors. Future Med Chem 2017; 9: 2129–2146.

130.

Al-Masri

Mohammad

Tahaa

MO.

Inhibition of dipeptidyl peptidase IV (DPP IV) is one of the mechanisms explaining the hypoglycemic effect of berberine. J Enzyme Inhib Med Chem 2009; 24: 1061–1066.

131.

Oliveira

Martinez

Nagabushnam

, et al. Calebin A: analytical development for pharmacokinetics study, elucidation of pharmacological activities and content analysis of natural health products. J Pharm Pharm Sci 2015; 18: 494–514.

132.

Kalhotra

Chittepu

Osorio-Revilla

, et al. Structure(-) activity relationship and molecular docking of natural product library reveal chrysin as a novel dipeptidyl peptidase-4 (DPP-4) inhibitor: an integrated in silico and in vitro study. Molecules 2018; 23: E1368.

133.

Zhao

Nguyen

, et al. PTP1B, α-glucosidase, and DPP-IV inhibitory effects for chromene derivatives from the leaves of Smilax china L. Chem Biol Interact 2016; 253: 27–37.

134.

Muller

Joubert

De Beer

, et al. Acute assessment of an aspalathin-enriched green rooibos (Aspalathus linearis) extract with hypoglycemic potential. Phytomedicine 2012; 20: 32–39.

135.

Yang

Song

Zhang

, et al. Cyanogenetic glycosides and simple glycosides from the linseed meal. Fitoterapia 2015; 106: 78–83.

136.

Wang

Yang

Fan

, et al. Screening of a natural compound library identifies emodin, a natural compound from Rheum palmatum Linn that inhibits DPP4. PeerJ 2017; 5: e3283.

137.

Wang

Zhao

XP.

Screening and identification of DPP-4 inhibitors from Xiaokean formula by a fluorescent probe. Zhongguo Zhong Yao Za Zhi 2016; 41: 1241–1245.

138.

Lin

Chen

, et al. Anti-α-glucosidase and anti-dipeptidyl peptidase-IV activities of extracts and purified compounds from vitis thunbergii var. Taiwaniana. J Agric Food Chem 2015; 63: 6393–6401.

139.

Yan

Liu

Zhang

, et al. Phenolic glycosides and other constituents from the bark of Magnolia officinalis. J Asian Nat Prod Res 2014; 16: 400–405.

140.

Saleem

Jafri

Ul Haq

, et al. Plants Fagonia cretica L. and Hedera nepalensis K. Koch contain natural compounds with potent dipeptidyl peptidase-4 (DPP-4) inhibitory activity. J Ethnopharmacol 2014; 156: 26–32.

141.

Huang

Lin

Riyaphan

, et al. Polyalthia clerodane diterpene potentiates hypoglycemia via inhibition of dipeptidyl peptidase 4. Int J Mol Sci 2019; 20. pii: E530.

142.

Suman

Mohanty

Maheshwari

, et al. Natural dipeptidyl peptidase-IV inhibitor mangiferin mitigates diabetes- and metabolic syndrome-induced changes in experimental rats. Diabetes Metab Syndr Obes 2016; 9: 261–272.

143.

Kwan

Liu

Ratnayake

, et al. Grassypeptolides as natural inhibitors of dipeptidyl peptidase 8 and T-cell activation. ChemBioChem 2014; 15: 799–804.

144.

Overbeek

Bakker

Van Der Heijden

, et al. Risk of dipeptidyl peptidase-4 (DPP-4) inhibitors on site-specific cancer: a systematic review and meta-analysis. Diabetes Metab Res Rev 2018; 34: e3004.

145.

Banerjee

Kumar

SKA

, et al. Critical role of dipeptidyl peptidase IV: a therapeutic target for diabetes and cancer. Mini Rev Med Chem 2019; 19: 88–97.

146.

Bishnoi

Hong

Shah

, et al. Dipeptidyl peptidase 4 inhibitors as novel agents in improving survival in diabetic patients with colorectal cancer and lung cancer: a Surveillance Epidemiology and Endpoint Research Medicare study. Cancer Med 2019; 8: 3918–3927.

147.

Yang

Zhang

, et al. DPPIV promotes endometrial carcinoma cell proliferation, invasion and tumorigenesis. Oncotarget 2017; 8: 8679–8692.

148.

Russo

Gao

Bhasin

, et al. Downregulation of dipeptidyl peptidase 4 accelerates progression to castration-resistant prostate cancer. Cancer Res 2018; 78: 6354–6362.

149.

Anno

Kaneto

Kawasaki

, et al. Drug fever and acute inflammation from hypercytokinemia triggered by dipeptidyl peptidase-4 inhibitor vildagliptin. J Diabetes Investig 2019; 10: 182–185.

150.

Chen

Lin

Yeh

, et al. Short-term dipeptidyl peptidase-4 inhibitor use increases the risk of herpes zoster infection in Asian patients with diabetes. QJM 2016; 109: 91–95.

151.

Inflammatory Bowel Disease Group, Chinese Society of Gastroenterology and Chinese Medical Association. Evidence-based consensus on opportunistic infections in inflammatory bowel disease (republication). Intest Res 2018; 16: 178–193.

152.

Lee

Kwon

Cho

ML.

Immunological pathogenesis of inflammatory bowel disease. Intest Res 2018; 16: 26–42.

153.

Radel

Pender

Shah

SA.

Dipeptidyl peptidase-4 inhibitors and inflammatory bowel disease risk: a meta-analysis. Ann Pharmacother 2019; 53: 697–704.

154.

Van De Waterbeemd

Gifford

ADMET in silico modelling: towards prediction paradise?

Nat Rev Drug Discov 2003; 2: 192–204.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Abstract

Keywords

Introduction

Overview of DPP-4 and its biological function

Two forms of DPP-4

Biological function of soluble form DPP-4

Biological function of membrane-bound DPP-4

Role of DPP-4 in diabetes treatment

Methods for screening novel DPP-4 inhibitors

In silico screening of DPP-4 inhibitors

Direct test of compounds against DPP-4

Natural compounds as novel DPP-4 inhibitors

Caution of using DPP-4 inhibitors

Perspectives and future research

Footnotes

Funding

Conflict of interest statement

ORCID iD

References