Abstract
Erectile dysfunction (ED) is a global public health issue affecting approximately 150 million men of all ages. The ED prevalence in South Africa is 65% of adult males attending a primary care facility. In South Africa, several aphrodisiac plants were traditionally used to treat and manage ED. Therefore, the review sought to scientifically validate the use of aphrodisiac plants in the treatment of ED. Secondary data were extracted from previous articles, which were obtained from Google Scholar, ScienceDirect, and ResearchGate databases. Diverse aphrodisiac plants including S. longepedunculata A. vera, E. capensis, M. oleifera, M. serrata, Z. officinale, M. angustifolia, V. unguiculata, A. sativum, and W. somnifera exhibited many phytonutrients and secondary metabolites. Phytonutrients comprised vitamins (A, B1-4, B6, B9, B12, C, E) and minerals (iron, copper, selenium, potassium, calcium, zinc, magnesium, etc) while secondary metabolites comprised polyphenols, phenols, flavonoids, alkaloids, tannins, and others. Those phytoconstituents exhibited antioxidant, anti-inflammatory, antidiabetic, anti-obesity, vasodilatory, antihyperlipidemic, antiatherosclerosis, antithrombotic, antihyperglycemic, anti-sickling, and antihypertension properties. As explained in the body of text, plant extracts, phytoconstituents, and pharmacological properties demonstrated, through various ways, their commendable potential to stimulate erectile function in animal models by increasing sexual drive, testosterone, and blood flow. But some aphrodisiac plants, E. tirucalli, C. tomentosa, E. lysistemon, A. senegal, S. madagacariensis, R. communis, A. vera, B. natalensis, P. Africana, K. africana, A. sativum, C. edulis, and C. sativa, were found to be toxic when administered to animal models. Overall findings explain the use of those aphrodisiac plants in the treatment and management of ED by local communities. However, these findings are inconclusive because they are mostly based on in vitro and in vivo studies. Therefore, clinical trials are recommended to determine efficacy and safety in terms of standardising optimal dosages for humans with ED.
Keywords
Introduction
Erectile dysfunction (ED) is defined as the inability to consistently achieve and maintain an erection sufficient to permit satisfactory sexual intercourse.1–3 This is a result of the impairment of vascular system supplying blood to the erectile tissues of the penis, which are three cavernous, two corpora cavernosa, and corpus spongiosum.4,5 It is a worldwide public health problem that affects men of all age groups including under 40 years and above (up to 70 years).2,3 The prevalence of ED increases with age, rising from 2%-9% in men aged 40 to 49 years to 20%-40% in men aged 60 to 69 years and 50%-100% in men over 70 years.6,7 At a global scale, approximately 150 million people are affected by this condition, and by 2025, that number is expected to rise to around 320 million. 6 The ED prevalence in South Africa is 65% of adult males attending a primary care facility. 8 Although this condition is evidently widespread, it is still undertreated. 6
The ED condition may be triggered by physiological, psychological, or hormonal (testosterone deficiency) disturbances in the nervous, cardiovascular, endocrine, or reproductive systems.5,6,9 Baker et al 10 have classified the main causes of ED as vascular, neurological, and hormonal, This condition disrupts sequence of events comprising nerve impulses in the brain, spinal column, area around the penis, and the response in muscles, fibrous tissues, veins, and arteries in and near the corpora cavernosa. The cardiovascular system is at risk of impairment by ageing, chronic diseases (atherosclerosis, heart diseases, atherosclerosis, hypertension, diabetes mellitus, and obesity), and a lifestyle of alcoholism, cigaret smoking, and lack of physical activity.1,4,11 Between 35% and 50% of men with diabetes have experience ED 12 while 98% of male patients with chronic illnesses in South Africa had ED symptoms. 8 Ageing and poor lifestyle in particular are associated with metabolic impediments to nitric oxide (NO) production, fewer smooth muscle cells, and increased fibrosis within the corpora cavernosa, which prevent adequate penile engorgement and pressure on the penile veins. 11
The phosphodiesterase type-5 (PDE-5) enzyme present in the walls of blood vessels catalyzes the breakdown of the smooth muscle-relaxing agent (cyclic guanosine monophosphate [cGMP]), which is a second messenger of NO. 13 Consequences of ED are reduced self-esteem, compromised well-being and limited interpersonal relationships, which could result in a loss of emotional and physical intimacy and at times divorce. 1 The inhibition of PDE-5 increases cGMP levels, reduces intracellular calcium (Ca2+) and induces vasodilation to promote penile erectile. 14 Blocking PDE-5 causes blood vessels to relax and widen, which increases blood flow to certain areas of the body including penis. Mainstream pharmacological treatments for ED are PDE-5 enzyme inhibitors [sildenafil citrate (Viagra), tadalafil (Cialis), vardenafil (Levitra), avanafil, lodenafil, udenafil, mirodenafil, and vardenafil] as well as intracavernosal injection therapy of vasoactive substances, vacuum erection devices, and penile prosthesis implants.2,4 Challenges associated with traditional PDE-5 inhibitors are side effects, failure by some patients to respond, addressing only symptoms, and high costs. Inhibitors for ED produce life-threatening toxic effects because PDE-5 gets expressed throughout the entire body. 15
Plant-based aphrodisiacs have been used throughout the history to enhance libido, maintain penile erections, and improve sexual desire and endurance. 15 Africa and other developing nations have been using plant-based aphrodisiacs more than conventional remedies.6,16 In South Africa alone, over 130 plant species were found to be traditionally used as aphrodisiacs to treat and manage ED or impotence. 17 Plant-based products are preferred to conventional remedies because of easy access, affordability, cultural and spiritual legitimacy, effectiveness, safety (minimal or no side-effects), and understanding of preparations and applications.2,6 Inadequate accessibility to modern medicines and drugs in middle- and low-income countries, especially in Africa, has largely contributed to the widespread use of traditional medicines especially in poor households. 18 However, there is still dearth of scientific information to validate traditional uses of aphrodisiac plants.16,19
Therefore, the review sought to scientifically validate the use of aphrodisiac plants used in South Africa for the treatment of ED.
Results and Discussion
Aphrodisiac Plants Traditionally Used to Treat ED
The review study identified about 41 plant species that belonged to 26 families for which there was reasonable amount of information to scientifically validate their use as aphrodisiac (Table 1). Except for exotic and cultivated Citrus sinensis (sweet oranges), Zingiber officinale (ginger), and Allium sativum (garlic), the remaining 38 plant species were native to South Africa. Fabaceae, Euphorbiaceae, Asteraceae or Malvaceae families were represented by seven, four, and two plant species being used as aphrodisiacs for ED, respectively, while most families had one representative each. In another study, 20 Fabaceae had the highest number of representative plant species with medicinal value in the sub-Saharan Africa. Furthermore, Fabaceae has an extensive range of distribution across all biomes of the world. 21 Apart from ED, which is the focus of this review, plant species are also being used to treat 3-15 other ailments (Table 1).
Scientific Validation of Aphrodisiac Plants Traditionally Used for the Treatment of Erectile Dysfunction.
Preparations and Administration of Herbal Medicines
Traditional use of plants to treat ED and other ailments is a common practice in Africa, especially in the Southern (South Africa, Zimbabwe, Botswana), Western (Nigeria), Eastern (Ethiopia, Kenya, Tanzania, Uganda), and Central (Democratic Republic of Congo, Cameroon) Africa (Table 1). Plant parts used for traditional remedies for ED were leaves, shoots, flowers, stems, roots, stem and root bark, bulbs, tubers, rhizomes, seeds, latex (milky substances), and gels. Those remedies were either taken orally either through chewing and swallowing exudates or through drinking decoctions (mix of herbal products with boiled milk or water) and infusions (herbal products soaked in milk or water). Sometimes remedies were taken as inhaled fumes or smokes. In another study, 104 medicinal products are added to or mixed with a traditional beer, porridge, fermented corn, and tea. Crushed root or bark was mixed with honey, porridge or other herbal products, and taken orally before breakfast. Latex and powdered root paste each mixed with butter were applied topically on the shaft and glans of the penis, respectively. Some information on the preparations of herbal remedies was provided for, including periods for boiling decoctions and treatments as well as dosages, which is corroborated by another study on commercialization of herbal products. 104 Although packaging and presentation of those products are modern, they lack scientific safety and quality controls. All this information can be used as a baseline for developing and standardising herbal medicines for African Traditional Medicine (ATM). 105
Phytoconstituents of Aphrodisiac Plants to Alleviate Erectile Dysfunction
This review established some promising phytoconstituents (secondary metabolites or phytochemicals, phytonutrients and pharmacological properties), which could possibly alleviate ED (Table 1). For instance, extracts of almost all the identified plant species including Securidaca longepedunculata Aloe vera, Ekebergia capensis, Moringa oleifera, Morella serrata, Zingiber officinale, Monsonia. angustifolia, Vigna unguiculata, A. sativum, and Withania somnifera exhibited many phytonutrients and secondary metabolites. Phytonutrients included vitamins (A, Bs, C, E) and minerals (iron, copper, selenium, potassium, calcium, zinc, copper, etc) while secondary metabolites comprised polyphenols, phenols, flavonoids, alkaloids, tannins, glycosides, saponins, polysaccharides, xanthones, and terpenoids. Collectively, those phytoconstituents exhibited antioxidant, anti-inflammatory, antidiabetic, anti-obesity, vasodilatory (vasorelaxant), lipolytic (antihyperlipidemic), antiatherosclerosis, antithrombotic, antihyperglycemic, anti-sickling, and antihypertension properties. Those phytoconstituents together with their pharmacological properties have potential to promote blood flow in arteries and veins of the body and penis, and therefore penile erectile. This finding is supported by various studies21,106–108 citing that secondary metabolites enhance erectile function by ensuring blood circulation and supply to penile tissues. To qualify the finding, mechanisms of action of plant extracts and their phytoconstituents on how they alleviate ED are unpacked below.
Mechanisms of Action of Plants in Treating and Managing Erectile Dysfunction
In several in vitro and in vivo studies, Mondia whitei, Kigelia Africana, E. capensis, M. serrata, Bulbine natalensis, M. angustifolia extracts were fed to rats, mice and African catfish to see if their induced ED could be alleviated (Table 1). Those plant extracts increased sexual activity serum testosterone levels and luteinising hormone, sexual desire (libido), penile reflexes, penile erection, penile ejaculation, intromission, mounting frequency, testicular weight, sperm count, sperm motility, quick flips, long flips, and fertilization ability of mice or rats. Precursors of sexual function such as testosterone level, libido, and penile erection are linked to the presence of aphrodisiac activity of medicinal plants. 109 The abovementioned plant extracts exhibited polyphenols, phenols, flavonoids, alkaloids, tannins, terpenoids, coumarins, sterols, saponins, glycosides, anthraquinones, carotenoids, anthracyanosides, and steroids, which could have played a role in alleviating ED in those animal models. Aphrodisiac action of various plants including Carica papaya were also found to be attributed to the presence of tryptophan, carotenoid, vitamins, flavonoids (quercenin, kaempferol), some minerals, and amino acids (arginine). 109 Minerals such as potassium, calcium, zinc, and magnesium play an important role in the processes that promote penile erection. 109 In some studies,110,111 minerals (e.g. zinc) and vitamins were found to stimulate the synthesis and release of testosterone by regulating luteinising hormone and testosterone-degrading enzymes in animal models. In other studies,19,109 phytoconstituents that exhibit antioxidant properties played an important role in enhancing male reproductive function. A. sativum extracts increased sexual behavior of male rats through the activity of phytoconstituents such as steroids, flavonoids, phenolics, and allicin, which increased blood flow to sexual organs through nitric oxide synthase. 109 Erythrina lysistemon flavonoids also improved blood flow and vascular health for erectile function. W. somnifera root extract also improved the production of nitric oxide (NO) signaling the pathway at the penile site in mice. 112 M. oleifera extracts were able to alleviate sexual dysfunction via the inhibition of cleaving enzymes monoamine oxidase type B and PDE-5 in male rats. The inhibition of PDE-5 increases the production of cGMP, reduces intracellular calcium (Ca2+), and induces vasodilation in the inner walls of blood vessels resulting in increased blood flow to prolong penile erection.14,15,113 The penis is composed largely of a sponge-like smooth muscle called the corpus cavernosum. During arousal, blood fills the lacunar spaces in the smooth muscle. The result of sexual stimulation is a release of the smooth muscle relaxant property, nitric oxide (NO), from the endothelial cells by the enzyme NO synthase (eNOS) that uses L-arginine as its substrate. NO diffuses into the smooth muscle cells of the corpus cavernosum where it binds to and activates guanylate cyclase. A. sativum (garlic) extracts also activated guanylate cyclase enzyme by increasing the production of cGMP in the body, stimulated sexual desire or libido, and mediated relaxation of smooth muscle cells to dilate or widen blood vessels, which yielded increased blood flow into penile tissues resulting in an erection. 114 A. vera also proved to be a natural vasodilator as its extracts fed to rats increased the amount of nitrogen (converted to nitric oxide or NO) produced in the body, which loosened and widened walls of blood vessels, thereby allowing blood flow to the entire body and penile tissues. Furthermore, Allium sativum extracts facilitated the release of endothelial nitric oxide synthase (eNOS) or neuronal NOS (nNOS), which converts L-arginine to L-citrulline to form or synthesise NO in vascular smooth muscle.115,116 As such, the therapeutic effect of A. sativum extracts on the improvement of erectile function was found to be comparative to or even better than that of Viagra. S. longepedunculata xanthones stimulate the relaxation of corpus cavernosum smooth muscle of the penis by 97% in comparison to Viagra at 1.8 × 10−5 mg/mL. 109 Annona senegalensis extracts also exhibited anticonvulsant property that could help relax corpus cavernosum smooth muscles. Antimicrobial and immunomodulatory properties of several aphrodisiac plants in Table 1 have enabled the body to treat or prevent pathogenic infections, which also enhances vascular endothelial function to increase blood flow in the body and penile tissues. This augments the immune response to prevent pathogenic infection in states of immunodeficiency, to fight pathogenic infections and to mitigate risks of chronic diseases including cancer. These findings are indicative of pro-sexual stimulatory potential of aphrodisiac plants, which could alleviate ED. Although undertaking clinical trials remain a challenge, Malviya et al 19 have presented several other plants that have scientifically been validated for the management and treatment of ED. The influence of secondary metabolites and pharmacological properties on vascular system (vascular endothelium) and erectile function is unpacked as follows.
Since oxidative stress and inflammation contribute to ED, antioxidant and anti-inflammatory properties might indirectly support erectile health. Free radicals [reactive oxygen species (ROS) and reactive nitrogen species (RNS)] cause cellular oxidative stress and inflammation that damage the inner lining of arteries and veins within the body and penis resulting in vascular endothelial dysfunction and cardiovascular complications such as hypertension and atherosclerosis.5,115,117 Free radicals linked to inflammation react with NO to form peroxynitrite that increases the degradation of NO, which leads to a reduced NO production and availability. 113 This impairs vasodilation, which increases vascular resistance marked by vasoconstriction (narrowing of the lumen or walls of blood vessels) and conversion to a prothrombotic, atherosclerosis and proinflammatory state. 118 Endothelial dysfunction primarily causes ED because of the decreased blood flow to penile tissue and the inability to achieve or maintain an erection. 117 It must however be noted that a reduced lumen diameter of the artery could also cause cardiovascular disease such as hypertension (HTN) due to the development of high blood pressure (HBP). Inflammation is also regarded as a major factor in the development of metabolic abnormalities that contribute to ED due the production of pro-inflammatory cytokines (IL-1, IL-6, IL-12, TNF-α), which too damage endothelium. Therefore, antioxidant and anti-inflammatory properties in extracts of many plants in this review were critical as they scavenged free radicals (ROS and RNS) and inhibited the production of pro-inflammatory cytokines, respectively. For instance, extracts of A. vera, E. capensis, B. natalensis, K. africana, M. serrata, Z. officinale, M. angustifolia, A. sativum, and M. whitei fed to male rats sequestered free radicals and inhibited the secretion of proinflammatory factors to boost endothelial cells lining blood vessels to enhance the stimulation of NOS activity to produce NO to increase blood flow. A. vera extracts decreased inflammation by 48% and 37% in a rat adjuvant induced arthritic inflammatory model and croton oil-induced edema, respectively. Ricinus communis extracts exhibiting flavonoids fed to mice reduced induced edema by 26% and 58% due to a good anti-inflammatory activity. Furthermore, R. communis extracts exhibiting flavonoids and tannins, which are strong antioxidants, fed to mice had promising free radical scavenging activity. Cytokine modulation increases the production of NO in Baker et al, 10 which demonstrates the potential therapeutic utility of anti-inflammatory property in the management and prevention of ED. Zhu et al 113 also found that the elevated compound dietary antioxidant Index (CDAI) levels were closely linked with a reduced risk of ED while the CDAI was significantly reduced in ED patients. Antioxidant and anti-inflammatory properties support healthy testosterone levels and protect endothelial cells from oxidative stress by neutralizing free radicals. Antioxidant activity also reduces the injury effect or structural damage and apoptosis (cell death) on the endothelium of capillary and artery by quenching free radicals through bioactive components such as superoxide dismutase (SOD), minerals (zinc2+, selenium), vitamins (A, Bs, C, E), secondary metabolites (flavonoids, phenolics, polysaccharides, polyphenols, and saponins).107,119 In this review study, phenolics, flavonoids, tannins, terpenoids, carotenoids, and anthocyanins, characterized by antioxidant and anti-inflammatory, reduced atherosclerosis formation and risk of developing cardiovascular disease (hypertension or high blood pressure) and decreased inflammatory biomarkers levels. Scavenging free radicals that cause oxidative stress prevent the onset of chronic diseases, which can impair cardiovascular system. 120 Reduced atherosclerosis activity means a decrease in the buildup of plague, which widens the lumen size of arteries to increase blood flow. Extracts of several other plants in Owaba et al 109 used as aphrodisiacs also exhibited secondary metabolites (flavonoids, xanthones), vitamins (A, B1, B2, B3), and minerals (zinc, iron, potassium, phosphorus, copper) characterized by antioxidant and anti-inflammatory properties, which could protect organs from oxidative stress caused by free radicals and cytokines. Flavonoids of S. longepedunculata, Erythrina lysistemon, and other plant extracts improved vascular health and blood flow, which are crucial for erectile function. Those phytoconstituents and the associated pharmacological properties heightened libido, increased the level of serum testosterone, inhibited lipid peroxidation, stimulated the relaxation of corpus cavernosum smooth muscle, and dilated arteries or blood vessels in the penis. Habitual intake of specific flavonoid-rich foods was also found to be associated with reduced ED incidence.121,122 Healthy endothelial cells in corpus cavernosa of the penis regulate erectile function by releasing NO and other vasoactive agents to promote vasodilation and relaxation of corpus cavernosum smooth muscle cells to increase blood flow to facilitate penile erection.7,123 In preclinical and clinical studies, 112 natural products rich in polyphenols also exhibited therapeutic potential in ED because of their anti-inflammatory and antioxidant properties that had increased intracavernous blood flow by enabling smooth muscle cell to relax leading to an improvement in erectile function. Another study 124 had established that antioxidant treatment with α-tocopherol (vitamin E) improved the impairment of relaxation in the corpus cavernosum by enhancing neuronal NO action as well as endothelial function. Furthermore, anti-inflammatory activity in rats normalized the expression of vascular endothelial growth factor and decreased tumor necrosis factor-α (TNF-α) in the lumen of the blood vessels of the organ, which proved effective in preserving erectile function in a rat model of neurogenic ED. 125 Anti-inflammatory activity treatment before cavernous nerve (CN) injury in rats also improved erectile recovery and vascular regeneration, and preserved the micro-architecture of the corpus cavernosum. 125 Secondary metabolites and phytonutrients of plants also increase the amount of nitrogen produced in the body to form NO, which loosens and widens blood vessels, thereby allowing more blood flow to the penis. Since oxidative stress was prevalent in ED patients,126,127 scavenging free radicals may prevent risks of the onset of ED. In a clinical study based on men over 50 years old, 7 antioxidant supplementation significantly improved erectile function compared to placebo. This is because antioxidant and anti-inflammatory therapy are a useful tool for preventing smooth muscle dysfunction and fibrosis in ED condition. 128 Most ED patients were found to have high levels of pro-inflammatory cytokines such as tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6), and interleukin-8 (IL-8). 129 Inflammation and diabetes mellitus are linked with ED male patients in various studies.130–133 Since inflammation is associated with ED, 130 the above stated anti-inflammatory properties of plant extracts have potential to indirectly support erectile function. Plant-based anti-inflammatory activity of the identified plants promises to prevent the onset of ED condition in men by reducing the production of pro-inflammatory cytokines due to therapeutic effects of sterols, flavonoids, phenolics, alkaloids, some vitamins, and other phytoconstituents. M. oleifera sterols were also found to inhibit the secretion of inflammatory factors. Other botanical drugs showed promising therapeutic effects on ED in clinical studies without significant adverse effects in particular study. 14
Diabetic condition has an influence on vascular system and ED. The presence of hyperglycemia and insulin resistance in diabetes mellitus makes metabolic processes of the endothelial cell undergo excessive oxidative stress, which causes endothelial cell injury and early development of atherosclerosis. 134 Endothelial cell injury results in endothelial dysfunction, which impairs the availability of NO and therefore vasodilatation that slows or blocks blood flow to the body and penile tissues. Atheroscslerosis also reduces the flow of blood due to a build-up of plague (fats, cholesterols, calcium deposits), which narrows the lumen of vessels. Glycation end-products and ROS derived from a hyperglycemic state also accelerate endothelial dysfunction by lowering NO bioavailability, and the essential stimulus of relaxation on the smooth muscles. 135 Several aspects of altered metabolism in individuals with type-2 diabetes may compromise the penile vasculature structure and functions, thus exacerbating the imbalance between smooth muscle contractility and relaxation. 135 This is the reason ED prevalence increases in patients with long-lasting diabetes and of greater severity.136,137 Diabetic patients are even less responsive to medical therapy than non-diabetic patients both with ED. 4 Therefore, inhibiting diabetic condition is also likely to prevent the onset of ED. In this review, A. vera, Z. officinale, S. longepedunculata, R. communis, K. africana, and V. unguiculata extracts exhibited great antidiabetic (antihyperglycemic) and antiatherosclerosis properties by lowering serum glucose and build-up of plague (cholesterol and triacylglycerol) under preclinical and clinical trials, respectively. R. communis extracts fed to mice resulted in the elevated level of insulin and better lipid profile, which resulted in the decreased levels of glucose from 390 mg/dL to 148 mg/dL (ie, 62% reduction). Sterols emanating from M. oleifera extracts also reduced the absorption of cholesterol by the intestines. Rats fed with A. vera extracts containing some polysaccharides and vitamin Bs significantly reduced the level of phospholipids along with the elevation in the level of high-density lipoprotein (HDL) known as good cholesterol. A. vera vitamin Bs also help lower the level of lipoprotein cholesterol in the bloodstream. The prevention of the build-up of plague may help to reduce the development of atherosclerosis while widening lumen of arteries and increasing blood flow in the body and penis. As such, lowering of serum cholesterol, which when elevated accelerates the deposition of fatty materials in arteries, including the coronary arteries of the heart, could minimize risks of hypertension and the onset of cardiovascular diseases in humans. Antidiabetic and anti-obesity properties of those plants were attributed to various secondary metabolites such as xanthones, essential oils, polysaccharides, flavonoids, alkaloids, polyphenols, S-allyl cysteine, and carotenoids.107,108,119 Polyphenolic compound, pycnogenol, improved erectile function in patients with ED and diabetes mellitus (DM) group by 45%, in non-diabetes mellitus (NDM) group by 22%, in lowering of total and low-density lipoprotein cholesterol by 20% and 21% and glycemia by 22% in DM patients. 138 This compound inhibited arginase, acetylcholinesterase, angiotensin converting enzyme (ACE), rhokinase II; activated endothelial and neuronal nitric oxide synthase (nNOS); decreased synthesis of luteinizing hormone and testosterone reduction; activated silent information regulator 2-related enzymes (sirtuin1) and inhibited free radical/reactive oxygen species. 139 Essentials oils of certain plants exhibited hypoglycemic properties that hindered glucose production, increased glucose uptake, and improved insulin sensitivity. 122 Essential oils also increased antioxidant effects by regulating antioxidant enzymes, scavenging ROS, and decreasing lipid peroxidation. 122 In another study, 140 intake of plant-based polysaccharides was also found to have improved glucose metabolism and reduced bodyweight in animal models of obesity. Glucose- and cholesterol-lowering properties (antiatherosclerosis) of plants improve endothelial dysfunction and preserve endothelial cell viability, which stimulate NO production and the relaxation of vessels to increase blood flow in the body and penis. 135 A. sativum S-allyl cysteine had enabled restoration of erectile function or reversed ED in diabetic rats by inhibiting ROS formation via modulation of nicotinamide adenine dinucleotide phosphate (NADP) oxidase subunit expression in penile tissue.
As was briefly explained above, a build-up of plague (atherosclerosis) is one of the major causes of ED in men as it clogs the blood vessels. This, in turn, affects the flow of blood into the penile area, resulting in ED. Coronary heart disease (hypertension) associated with build-up plague on the lining of the arteries is still one of the major causes of death in the Western world. In this review, antihyperlipidemic, antihypercholesterolemic, antiatherosclerosis or anti-dyslipidemia property of many plants such as A. sativum, A. vera, V. anguiculata, and Z. officinale in in vitro and in vivo (animals and humans) studies inhibited lipid peroxidation (causing oxidative degradation of lipids) and lowered the build-up of plaque or the accumulation of cholesterol and calcium deposits on inner walls of blood vessels. Continuing feeding plant extracts exhibiting such properties to rats also reduced the absorption of dietary cholesterol to widen walls or lumen of arteries and increase blood flow in the body and penile tissues. Flavonoids, polyphenols, polysaccharides and alkaloids as well as vitamins (B4, B9, B12) were found to be responsible for this due to their antiatherosclerosis properties.107,108 V. unguiculata leaf extracts possessed flavonoids that were characterized by antihyperlipidemic activity. Inhibition of lipid peroxidation prevents overproduction of ROS, which could cause oxidative stress to damage endothelial cell integrity. Antiatherosclerosis activity may also alleviate hypertension by opening clogged arteries (ie, widening the lumen of arteries) to promote blood flow throughout the body and to enable penile erection. This is also likely to reverse vasculogenic ED, which usually occurs when arteries and veins supplying blood to and from corpora cavernosa of the penis are blocked by cholesterol. 4 A. vera vitamin Bs also helped with lowering the level of lipoprotein cholesterol on inner walls of vessels. Vasodilatory (vasorelaxant) activity of Eriosema kraussianum and Cleome gynandra enabled the relaxation of vascular system to widen walls of vessels to increase blood flow, which could be ascribed to the presence of NO. NO converted from V. unguiculata L-arginine in the body enabled the corpus cavernosum smooth muscles in the penis to relax, which allowed chambers inside the penis to open wide and fill up with blood triggering an erection. Anticonvulsant activity of A. senegalensis is a muscle relaxer that affects smooth muscle cells of mice. Anti-thrombotic activity of C. gynandra and A. sativum also prevented the formation of blood clots in vessels to widen lumen and increase blood flow.
Sickle cell disease (SCD), especially the sickle cell anemia (SCA) is also associated with ED. This is a condition in which red blood cells take a shape of a sickle. 141 Those sickle cells are rigid or inflexible and they stack one over another preventing them from flowing in the vessels.142,143 This condition is associated with overproduction of ROS, which promotes intravascular oxidative stress and inflammation in endothelial cells disrupting NO homeostasis. 144 All this reduces or blocks the flow of blood from vessels to vital organs including penis, which may cause thrombosis.141,142 This explains why ED is more prevalent among men with this SCD than those without it. 145 In this review, anti-sickling or anti-anemic activity of Ziziphus mucronate, A. vera, V. unguiculata, A. sativum, C. papaya, and Citrus sinensis had alleviated or reversed the anemic condition in mice. This activity is able to prevent the sickling of healthy red blood cells caused by microvascular occlusion. 31 For instance, 92% of sickle cells in control (in the presence of hydroxyurea) was considerably reduced to 29%, 42%, 33%, 38%, and 48% when treated with Cajanus cajan seed, C. cajan leaf, Zanthoxylum zanthoxyloides leaf, and C. papaya leaf extracts, respectively. 146 Nutritional preparation of C. cajan fruit with proven anti-sickling properties is already being used in the management of sickle cell disease in Nigeria. 147 Additional fruit preparations from Persia americana and C. sinensis in the same country were also found to possess promising anti-sickling properties in an in vitro study. A. sativum (exhibiting S-allyl cysteine and fructosyl arginine compounds), 148 as well as V. unguiculata and A. senegalensis extracts also exhibited great anti-sickling activities. 149 Anti-sickling properties are ascribed to phytoconstituents such as anthocyanin, essential oils, flavonoids, carotenoids and nitrogenous substances. 147 These compounds are also characterized by strong antioxidant activities. Antioxidant activities have potential to be used as therapeutic management of sickle cell disease by providing a shield against lipid peroxidation in red blood cells.150,151 Overall, anti-sickling property reduces the destruction of red blood cells, which promotes the flow of healthy blood to vital organs including penile tissues.
Safety and Toxicity of Herbal Medicines
About 29 aphrodisiac plants were screened for safety and toxicity in this review (Table 2). The screening studies were largely dominated by animal models (93%) with only 7% representing clinical trials. Of all those plants, 13 or approximately 45% showed varying nature of toxicity while the remaining majority (16 or 56%) did not. Those plants were Euphorbia tirucalli, Capparis tomentosa, E. lysistemon, Acacia senegal, S. madagacariensis, R. communis, A. vera, B. natalensis, Peltophorum Africana, K. africana, A. sativum, Catha edulis, and Cannabis sativa. Strychnos spp. alkaloids (especially tropane, nicotine, pyrrolizidine, lupin) and R. communis ricin and agglutinin were found to be highly toxic in nature and showed severe effects on animal and human health. 106 A. sativum extracts exhibited side effects and toxicity that were found to be less than those of Viagra. 114 It is however noted that animal models are poor indicators of drug safety in humans. 15
Safety and Toxicity of Some Aphrodisiac Plants (Data Extracted from Table 1).
Conclusion
Extracts of many aphrodisiac plants traditionally used for the treatment of ED and other ailments in South Africa possessed diverse secondary metabolites, phytonutrients, and pharmacological properties. Those phytoconstituents stimulated erectile function in animal models as a result of the increased sex drive (libido), testosterone, and amount of blood flowing in the penis. Furthermore, about 13 aphrodisiac plants were found to be toxic to the tested animal models. To an extent, these findings justify the use of aphrodisiac plants in the treatment and management of ED by local communities. But efficacy and safety of the phytoconstituents cannot be guaranteed for human consumption because these findings are mostly based on in vitro and animal-based in vivo studies. Therefore, efficacy and safety of those phytoconstituents are to be tested through clinical trials to establish optimal doses to be administered to people suffering from ED. Outcomes of such trials could provide leads for the development of new plant-based drugs for ED treatment and management in South Africa.
Materials and Methods
The review was based on secondary data searched from relevant literature, which was sourced and accessed from electronic databases that included Google Scholar, ScienceDirect, and ResearchGate. The following terms and combinations thereof were used to collect information: aphrodisiac plants OR aphrodisiacs, ED OR sexual impotence AND erectile function, secondary metabolites OR phytochemicals OR bioactive compounds, botanicals OR ethnobotanicals OR ethnomedicinal, pharmacological property OR biological activity, traditional medicine OR herbal medicine, cytotoxicity AND toxicity. Articles that were included in this review were those covering keywords and published in English language from anywhere in the world during the 2000-2024 period. Articles that were excluded comprised those partially accessed (abstract only), with missing author names, covering plants not found in South Africa, and with non-English full text. About 134 articles were selected and searched for information. The required information was packaged in terms of scientific name, family, traditional uses, parts used and preparations as well as phytochemical and pharmacological data (see Table 1). Gathered information and data were analysed manually to yield findings and results as reported in the body of text.
Footnotes
Declaration of Conflicting Interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethical Approval
Ethical Approval is not applicable for this review manuscript.
Funding
The author received no financial support for the research, authorship, and/or publication of this article.
Statement of Human and Animal Rights
This review does not contain any studies with human or animal subjects.
Statement of Informed Consent
There are no human subjects in this article and informed consent is not applicable.
