Current Drug Metabolism - Volume 17, Issue 5, 2016

Introduction: The kynurenine pathway includes several neuroactive compounds, including kynurenic acid, picolinic acid, 3-hydroxykynurenine and quinolinic acid. The enzymatic cascade of the kynurenine pathway is tightly connected with the immune system, and may provide a link between the immune system and neurotransmission. Main Areas Covered: Alterations in this cascade are associated with neurodegenerative, neurocognitive, autoimmune and psychiatric disorders, such as Parkinson’s disease, Huntington’s disease, Alzheimer’s disease, multiple sclerosis, amyotrophic lateral sclerosis, migraine or schizophrenia. Highlights: This review highlights the alterations in this metabolic pathway in the physiological aging process and in different disorders. A survey is also presented of therapeutic possibilities of influencing this metabolic route, which can be achieved through the use of synthetic kynurenic acid analogues, enzyme inhibitors or even nanotechnology.

Background: ABCB1 is a key ABC efflux transporter modulating the pharmacokinetics of a large percentage of drugs. ABCB1 is also a site of transporter mediated drug-drug interactions (tDDI). It is the transporter most frequently tested for tDDIs both in vitro and in the clinic. Objective: Understanding the limitations of various in vitro and in vivo models, therefore, is crucial. In this review we cover regulatory aspects of ABCB1 mediated drug transport as well as inhibition and the available models and methods. We also discuss protein structure and mechanistic aspects of transport as ABCB1 displays complex kinetics that involves multiple binding sites, potentiation of transport and probe-dependent IC50 values. Results: Permeability of drugs both passive and mediated by transporters is also a covariate that modulates apparent kinetic values. Levels of expression as well as lipid composition of the expression system used in in vitro studies have also been acknowledged as determinates of transporter activity. ABCB1-mediated clinical tDDIs are often complex as multiple transporters as well as metabolic enzymes may play a role. This complexity often masks the role of ABCB1 in tDDIs. Conclusion: It is expected that utilization of in vitro data will further increase with the refinement of simulations. It is also anticipated that transporter humanized preclinical models have a significant impact and utility.

Background: Hepatic transporters, including efflux transporters and uptake transporters, have been recognized to play an important role in the disposition of various drugs. These membrane transporters show extensive substrate specificity with an abundance of overlap, implying the probability of transporter involved in the drugdrug interactions with other drugs. Thus reliable techniques are taken into consideration to evaluate the role of transporter-mediated drug disposition and possible effects on pharmacokinetics in the research. Methods: An electronic search of PubMed database from inception to December, 2015 was conducted. In addition, we searched the reference lists of included studies and carried out a citation search for the included studies via Web of Science to find other potentially relevant studies. Results and Conclusion: The function of membrane transporters could be evaluated in vitro, in situ and in vivo, employing models spanning from cell-based assay to transgenic mouse. Each technique has its own application with specific advantages and limitations. The readers will gain insight into techniques applied to evaluate the drug clearance mediated by hepatic transporters. In addition, this review focuses particularly on the in vitro-in vivo extrapolation of hepatic transporter-mediated drug clearance. The challenges and gaps of the extrapolation are further discussed. The increased understanding of this knowledge would improve the capability to predict the in vivo situation.

Background: Over the decade, miRNAs are the most important molecules for the biopharmaceutical industry due to their relation with several human diseases. Presently, the phase-II clinical trial has been initiated for the first miRNA-based therapeutics (“Miravirsen”) to treat HCV infection. It has been expected that many more miRNA-based therapeutics will enter the clinical trials. Therefore, it is important to develop different kinds of novel delivery systems with better efficacy and more efficiency, but fewer side effects. Methods: We have undertaken a structured search of bibliographic databases for peer-reviewed research literature to solve our review question. Literature survey was performed widely to write this review article. Results: In this review, we have discussed the various types of miRNA delivery systems such as viral vectors, lipid-based systems, nanocarriers, and LNA-customized DNA delivery without any delivery-mediated agent. Current status, technical support, and the future challenges for miRNA-based delivery are also discussed. Conclusion: Recent development and understanding of miRNA had shown the therapeutic potentiality of miRNA.

Background: Nanoparticles have shown great potential in biomedical applications such as imaging probes and drug delivery. However, the increasing use of nanoparticles has raised concerns about their adverse effects on human health and environment. Reproductive tissues and gametes represent highly delicate biological systems with the essential function of transmitting genetic information to the offspring, which is highly sensitive to environmental toxicants. This review aims to summarzie the penetration of physiological barriers (blood-testis barrier and placental barrier), distribution and biological effects of nanoparticles in the reproductive system, which is essential to control the beneficial effects of nanoparticles applications and to avoid their adverse effects on the reproductive system. Methods: We referred to a large number of relevant peer-reviewed research articles about the reproductive toxicity of nanoparticles. The comprehensive information was summarized into two parts: physiological barrier penetration and biological effects of nanoparticles in male or female reproductive system; distribution and metabolism of nanoparticles in the reproductive system. The representative examples were also presented in four tables. Results: The in vitro and in vivo studies imply that some nanoparticles are able to cross the blood-testis barrier or placental barrier, and their penetration depends on the physicochemical characteristics of nanoparticles (e.g., composition, shape, particle size and surface coating). The toxicity assays indicate that nanoparticles might induce adverse physiological effects and impede fertility or embryogenesis. Conclusion: The barrier penetration, adverse physiological effects, distribution and metabolism are closely related to physicochemical characteristics of nanoparticles. Further systematic and mechanistic studies using well-characterized nanoparticles, relevant administration routes, and doses relevant to the expected exposure level are required to improve our understanding of biological effects of nanoparticles on the reproductive system.

Background: Diabetic nephropathy (DN) is currently the most common cause of end-stage renal disease (ESRD). Although nowadays much is known about its classification, pathogenesis, clinical manifestations and evolution, to date we are not yet able to stop the natural progression of nephropathy in diabetic patients. Methods: Treatment options are: lifestyle change with close blood pressure monitoring and tight glycemic control. The most common therapies adopted for this condition are Angiotensing Converting Enzyme-inhibitors (ACEi). However these drugs are able to block the progression of renal damage only in a small proportion of patients. In the remaining, DN progresses and may evolve into ESRD. Conclusion: The purpose of this review is to summarize the “state of art” of current novel therapeutic strategies to stem this debilitating kidney disease.

Background: Circadian clocks are endogenous timing systems that regulate various aspects of mammalian metabolism, physiology and behavior. Traditional chronotherapy refers to the administration of drugs in a defined circadian time window to achieve optimal pharmacokinetic and therapeutic efficacies. In recent years, substantial efforts have been dedicated to developing novel small-molecule modulators of circadian clocks. Methods: Here, we review the recent progress in the identification of molecular targets of small-molecule clock modulators and their efficacies in clock-related disorders. Specifically, we examine the clock components and regulatory factors as possible molecular targets of small molecules, and we review several key clock-related disorders as promising venues for testing the preventive/therapeutic efficacies of these small molecules. Finally, we also discuss circadian regulation of drug metabolism. Results: Small molecules can modulate the period, phase and/or amplitude of the circadian cycle. Core clock proteins, nuclear hormone receptors, and clock-related kinases and other epigenetic regulators are promising molecular targets for small molecules. Through these targets small molecules exert protective effects against clock-related disorders including the metabolic syndrome, immune disorders, sleep disorders and cancer. Small molecules can also modulate circadian drug metabolism and response to existing therapeutics. Conclusion: Small-molecule clock modulators target clock components or diverse cellular pathways that functionally impinge upon the clock. Target identification of new small-molecule modulators will deepen our understanding of key regulatory nodes in the circadian network. Studies of clock modulators will facilitate their therapeutic applications, alone or in combination, for clock-related diseases.

Backround: Parkinson’s disease is a pathology involving the progressive degeneration of dopaminergic neurons in the substantia nigra of the brain. L-DOPA combined with an inhibitor of DOPA decarboxylase, a pyridoxal 5’-phosphate-dependent enzyme, is still the most effective treatment for symptoms of Parkinson's disease. LDOPA increases synaptic dopamine, while the inhibitor of peripheral DOPA decarboxylase reduces the conversion of L-DOPA to dopamine in the systemic circulation, allowing for greater L-DOPA distribution into the central nervous system. CarbiDOPA and benserazide are the inhibitors currently used in Parkinson's disease treatment. However, carbiDOPA and trihydroxybenzylhydrazine, the active metabolite of benserazide, are substrate analogues both endowed with a hydrazine function, which irreversibly bind not only to DDC but also to free pyridoxal 5’-phosphate and pyridoxal 5’-phosphate-dependent enzymes. Therefore, the lack of DOPA decarboxylase specificity, responsible for various side effects and adverse reactions, is a negative factor in such treatment of the disease. Results and Conclusion: Aim of this review is to report on the most recent investigations regarding new DOPA decarboxylase inhibitors that could represent the starting point for possible Parkinson's disease drugs development. We focused on the common chemical features among all the identified inhibitors in order to seek shared structural motifs that could be involved in inhibition. Then, we highlighted the extent of inhibition, measured by means of in vitro and/or cell-based assays. Finally, we pointed out the state of the art in the metabolism of such classes of compounds, and discussed the possible advances in Parkinson's disease pharmacological treatment.