Experimental Biology and Medicine

Bax is an essential mediator of mitochondria-dependent programed cell death. Bax belongs to the Bcl-2 family of proteins and its activities are regulated through interaction with other member proteins in the Bcl-2 family. To date, several apoptosis-inducing drugs activating Bax have been developed, and some of them are already in the market as therapeutics against cancer. However, at present, there are no clinically effective pharmacological Bax inhibitors protecting essential cells. Previously, we developed Bax-Inhibiting Peptides (BIPs) that belong to the peptide group of Cell-Penetrating Peptides (CPPs). CPPs have the ability to deliver cargo molecules into the cell. In this review, we will describe the mechanism of action of BIPs together with the recent applications of BIPs in disease models in vitro and in vivo. However, BIPs have several limitations in their use to treat human diseases, and other types of Bax inhibitors need to be developed for future therapeutics. Recently, several groups reported the successful development of novel small compounds inhibiting Bax. We will review these Bax inhibitors to discuss current strategies to develop pharmacological Bax inhibitors.

The advent of successful solid organ transplantation is undoubtedly among the most significant medical achievements of the 20th century. Despite advances in the field of transplantation since its inception over 50 years ago, our approach to donor organ preservation outside of the body remains unchanged. Recently, attempts have been made to replace static cold storage with more sophisticated ex vivo machine perfusion. Rather than cooling the organ on ice to slow metabolic processes, machine perfusion aims to support normal metabolic function in a near-physiologic environment and to provide a platform on which the organ can be evaluated, preserved, and recovered. Ex vivo machine perfusion devices have demonstrated early success with respect to transplant outcomes in heart, lung, and liver, with perfusion times limited to several hours. The continued development of more advanced perfusion systems is likely to extend the duration of ex vivo organ support to days or even weeks, and enable recovery of initially unsuitable donor organs. In this review, we discuss recent clinical and pre-clinical studies, state-of-the-art organ preservation technologies, existing limitations, and a perspective on future developments.

Hyperphosphatemia is nearly universal in patients with advanced chronic kidney disease and end stage renal disease. Given the considerable negative sequelae associated with hyperphosphatemia, i.e. increased cardiovascular disease, hastening of renal failure and death, reducing serum phosphate is a goal of therapy. In the absence of sufficient renal function, intestinal phosphate absorption is the remaining target to reduce plasma phosphate levels. Much work has been done with respect to understanding transcellular phosphate absorption. Both animal studies using inducible or intestinal NaPi-2b knockout mice and specific NaPi-2b inhibitors revealed this transporter as the primary mechanism mediating transcellular phosphate absorption in the intestine. However, this has not translated into effective phosphate lowering therapies in patients with kidney disease. More recently, it was observed that inhibition of the epithelial sodium hydrogen exchanger, sodium–hydrogen exchanger isoform 3 (NHE3), or its genetic deletion, decreases intestinal phosphate absorption. The mechanism mediating this effect is through increased transepithelial resistance and reduced paracellular phosphate permeability. Thus, NHE3 inhibition reduces paracellular phosphate permeability in the intestine. The transepithelial potential difference across intestinal epithelium is lumen negative and phosphate commonly exists as a divalent anion. Further, consumption of the typical Western diet provides a large lumen to blood phosphate concentration gradient. Based on these observations we argue herein that the paracellular phosphate absorption route is the predominant pathway mediating intestinal phosphate absorption in humans.

This review provides a summary of recent discoveries in choline transport and the proteins mediating it with a specific focus on the choline transporter-like proteins (CTL)/solute carriers 44 A (SLC44A) and their role in phospholipid metabolism. Since its initial cloning, particularly, the CTL1/SLC44A1 transporter has been investigated further and its ubiquitous expression characterized in various cells and tissues of mouse, rat, and human origin. We describe the role of this choline transporter both in the plasma membrane and in the mitochondria and summarize novel aspects of choline transport regulation in the muscle, nervous system, and cancer.

Although better science and technology has been linked with better health care, however, reality is much different. Although America and most of Europe are equipped with most advanced science and technology, paradoxically cancer incidence is highest in the world. This indicates that science and technology alone is not sufficient in treating diseases like cancer. It is also now well recognized that more than 95% of the drugs/compounds that kill either cancer cells in culture or regress the tumors in animals, fail in phase I clinical trials in humans, indicating that most pre-clinical models of cancer are inadequate. In addition, most of the anticancer drugs that are approved by the regulatory agencies such as FDA either has no effect on the overall survival of the cancer patient or may provide an increase in few months in overall survival. This is despite the fact that most targeted therapies that are currently available are highly expensive; thus suggesting the lack of affordability. This review is meant to focus on some of these problems in detail and then provide potential solutions since most cancers are caused by multiple genes, and thus multi-targeted therapies are needed such as natural products which are inexpensive, safe and have been used for thousands of years for both prevention and treatment of cancer.

Based on evidence extracted from a cross-sectional review of the literature, we sought to advance a novel conceptual framework that the physiology of hemorrhagic shock from exsanguination and maximal oxygen uptake ( V ˙ O₂max), induced by physical exercise, shares key common features. As such, this review focuses on the notion that intolerance to inadequate oxygen delivery (DO₂) resulting from associated states of hypovolemia appears to be a common physiological link that “connects” hemorrhagic shock to the physiology that limits maximal aerobic capacity. Our approach focuses on the similarities in a complex cascade of cardiopulmonary, metabolic and autonomic compensatory responses during hemorrhage and maximal physical exertion that ultimately function to avoid critical levels of DO₂ (DO_2crit) and are manifested by elevation in blood lactate levels. We introduce a paradigm of absolute (i.e. hemorrhage) versus relative (i.e. exercise) hypovolemia as a primary physiological factor that contributes to reaching DO_2crit, and define the concept of “O₂ deficit” to replace the clinical concept of O₂ debt. Using the peer-reviewed literature, we provide human data obtained from patients who suffered hemorrhagic shock from severe blood loss and compare it to healthy subjects who performed maximal exercise. We include a novel conceptual framework of the continuum of metabolic relationship between DO₂ and V ˙ O₂ that is manifested as the final step during both progressive blood loss leading to hemorrhagic shock and at V ˙ O₂max. We present evidence to support the contribution of utilizing “O₂ extraction reserve” as the initial mechanism for developing an O₂ deficit, and the notion of individual variability in compensatory responses. In the absence of reversing inadequate DO₂, an increased reliance on O₂ extraction reserve, cellular anaerobic glycolysis, and phosphocreatine stores to supplement the energy required by the tissues for normal function will deplete a finite capacity for compensation. In the end, acidity reflected by a blood pH ≤ ∼7.0 leads to disturbance of normal cell functioning of metabolic machinery manifested by irreversible shock in the case of hemorrhage or physical exhaustion when V ˙ O₂max is reached.

Pharmaceutical drug development and clinical testing is associated with billions of dollars, and often the time and money spent does not result in a viable drug formulation. The pharmaceutical industry has long relied on animal models for testing efficacy, toxicity and specificity of novel drugs. However, the studies cannot be fully relied upon, as animal models are not reflective of human pathophysiology and drug response, which results in drugs being pulled from development as late as at stage IV, after billions of dollars have already been invested in such an effort. With the advent of adult-induced pluripotent stem cell technology, came an era which offered the potential of pursing human relevant developmental and pathogenesis research and drug testing on patient-induced pluripotent stem cell-derived differentiated cells, consciously reflecting human responses with regard to drug safety, toxicity, efficacy, and side effects. Specifically, human-induced pluripotent stem cell-derived hepatobiliary cells and tissues may be a more human-relevant model system to address the biggest barrier to drug safety and approval: hepatotoxicity. In this review, we address the potential of human-induced pluripotent stem cell-based hepatobiliary differentiation technology as a means to study human liver development and hepatic cell fate determination, and to model liver diseases in an effort to develop a new human-relevant preclinical platform for drug development.

Integral membrane proteins comprise a large proportion of drug targets, yet are challenging to study in vitro due to their amphiphilic nature. Conducting useful functional in vitro studies requires an artificial membrane that can mimic the lipid environment of the biogenic membrane. Droplet interface bilayer technology provides a method to form artificial bilayers with a robustness and physicochemical complexity that has not previously been possible, facilitating more sophisticated in vitro studies of membrane proteins. This mini-review examines functional studies of membrane proteins that utilize droplet interface bilayers to date and comments on possible directions of future research. Observations from our own laboratory regarding the study of a flippase protein in droplet interface bilayers are also presented.