Current Drug Metabolism - Volume 19, Issue 11, 2018

Background: Despite the therapeutic use of peptides is limited because of their metabolism in vivo, there are no systematic reviews explaining degradation of peptides by peptidases. This review summarizes peptidases present in the tissues and metabolic characteristics of peptides, and provides recent strategies for improving the metabolic stability of peptides. Method: We reviewed a number of peptidases including their functional groups, tissue localization and cleavage specificity. Given the broad distribution of peptidases in the body, several tissues, such as the liver, kidney, lung, blood, nasal epithelial cells, placenta and skin, have the capacity to metabolize peptides. We compared the metabolic characteristics of peptides in these tissues and then summarized strategies for improving peptide stability. Results: In addition to the primary organs including liver, kidney, gastrointestinal tract and blood involved in peptide metabolism, other organs such as the lung, skin, placenta and nasal mucosa may also play a role in peptide degradation. At present, the main measures to improve the stability of the peptide include N- and/or C-terminal modification or substitution, D-amino acid or unnatural amino acid substitution, cyclization, backbone modification, nanoparticle formulations and increased molecular mass. Conclusion: This review summarized the key in vivo peptidases and their tissue distribution characteristics, and presented strategies to improve the metabolic stability and bioavailability of peptide drugs. These viewpoints will benefit the further development and utilization of peptide drugs.

Background: Metronidazole (MTZ) is a synthetic derivative of nitroimidazole that has been widely used for the treatment of several bacterial and parasitic infections including trichomoniasis, amoebiasis, giardiasis, liver abscess, gingivitis, syphilis and phagedena. Scientists have evaluated its carcinogenicity in preclinical in vitro and in vivo studies. Method: Google scholar and Pubmed search engines were used to construct historic timeline after discovery of MTZ with a journey of ~3 decades of research. Similar search was conducted for its in vivo carcinogenic activities, further extended to elaborate its role in carcinogenicity in humans. Results: In addition to preclinical in vitro validation of DNA damage, MTZ has been reported to induce cancer in a variety of animal models including lung cancer, malignant lymphomas, breast cancer, hepatocellular carcinoma, pituitary tumors, testicular neoplasms and uterine cancer. Several retrospective cohort studies have reported MTZ as a potential risk factor for lung cancer (n = 771), cervical cancer (n = 2500), breast cancer (n = 2), cholangiocarcinoma (n = 1), and neuroblastoma (n = 28). So far, all the reported data have confirmed MTZ carcinogenicity in animals; however it is still controversial in humans. Based on previous observations, the oxidative metabolites from MTZ are shown to have more carcinogenic effects than the parent drug itself. Conclusion: Due to potent carcinogenic behaviour, use of MTZ for animals' treatment and its uses in animal food products is prohibited in USA and European countries; however its clinical use in human population is still increasing. Therefore, regular research studies are required to explicate its mechanism/s involved in carcinogenesis.

Background: Psoriasis is a chronic disease of inflammatory nature. It involves autoimmune mechanism and the systemic diseased state is created by the interaction of immune system, autoantigens and variety of environmental triggers. It is a complex skin disease which involves participation of numerous factors, making it multifactorial in nature. The main characteristics include proliferation of keratinocytes, increase in dermal vascularity and infiltrated immune cells. Among all factors, vascular alterations present a significant feature of the disease and angiogenesis seems to have an important role in giving rise to psoriasis phenotype. In the early phases of psoriasis there occurs sprouting of new blood vessels which disappear with disease clearance. Psoriatic lesions show highly altered vascular network in the form of numerous enlarged, tortuous and hyperpermeable cutaneous blood vessels. Secretion of various pro-angiogenic growth factors promote the expansion of vascular network in psoriatic skin cells. In addition to pro-angiogenic growth factors, pro-inflammatory cytokines also contribute to this process by activating endothelial cells and exerting pro-angiogenic action as well. Angiogenesis, in psoriasis display a close association of vascular endothelium activation, angiogenesis, inflammation and lesional skin, as is demonstrated by in vivo models. Objective: The present review discusses angiogenesis as the central process in the evolution of psoriasis and summarizes various angiogenic mediators and their respective roles in the development of psoriasis. Conclusion: Anti-angiogenic therapies targeting vasoproliferation may represent a valid approach for the development of anti-psoriatic drugs and further development in this field can pave way to new fields of treatment. Such therapies could be at par to those directly targeting inflammation.

Background: Cytochrome P450 2S1 (CYP2S1) is one of the ‘orphan’ CYPs, which is expressed primarily among extra-hepatic tissues and it is inducible by dioxin. Although the contribution of extra-hepatic CYPs in drug metabolism is considered less significant, they play more important roles in leading to in situ toxicity in organs with higher expression. Method: A non-systemic search was performed to review articles relevant to CYP2S1 in literature. This review will update the findings related to the expression and regulation of CYP2S1 gene and protein, substrate profiles and metabolism mechanisms, genetic polymorphisms, and their association with diseases. Results: The expression of CYP2S1 was mainly in the epithelium of portal of entry organs such as respiratory and gastrointestinal tract. Aryl Hydrocarbon Receptor (AHR) is believed to be partly involved in the induction of CYP2S1. CYP2S1 was found to activate and deactivate pro-drugs which resulted in toxicity and detoxification of carcinogens. The current knowledge of the endogenous functions of CYP2S1 is largely related to cell proliferation and lipid metabolisms. Several polymorphic alleles of CYP2S1 have been reported and documented to date. Conclusion: Molecular-based investigations should be performed to better understand the regulation mechanism of CYP2S1 in various cells and tissues. It is pivotal to establish optimum expression and incubation systems in vitro to elucidate the substrate specificity of CYP2S1 and characterise the genetic consequences of variant CYP2S1 in vitro.

Background: Drug Metabolism and Pharmacokinetic (DMPK) studies of Taxus natural products, their semi-synthetic derivatives and analogs are indispensable in the optimization of lead compounds and clinical therapy. These studies can lead to development of new drug entities with improved Absorption, Distribution, Metabolism, Excretion and Toxicity (ADME/T) profiles. To date, there have been no comprehensive reviews of the DMPK features of Taxus derived medicinal compounds. Natural and semi-synthetic taxanes may cause and could be affected by Drug-drug Interaction (DDI). Hence ADME/T studies of various taxane-containing formulations are important; to date these studies indicate that the role of cytochrome p450s and drug transporters is more prominent than phase II drug metabolizing enzymes. Mechanisms of taxane DMPK mediated by nuclear receptors, microRNAs, and single nucleotide polymorphisms are being revealed. Method: Herein we review the latest knowledge on these topics, as well as the gaps in knowledge of the DMPK issues of Taxus compounds. Results and Conclusion: DDIs significantly impact the PK/pharmacodynamics performance of taxanes and coadministered chemicals, which may inspire researchers to develop novel formula. While the ADME/T profiles of some taxanes are well defined, DMPK studies should be extended to more Taxus compounds, species, and Taxus - involved formulations, which would be streamlined by versatile omics platforms and computational analyses. Further biopharmaceutical investigations will be beneficial to the translation of bench findings to the clinical applications.

Background: Hypoxia can alter the Pharmacokinetic (PK) characteristics of drugs, thereby affecting drug absorption, distribution, metabolism, and excretion. Environmental characteristics at high altitude include but are not limited to hypobaric hypoxia, low temperature, high solar radiation, and arid climate, all of which can adversely affect normal bodily functions. Therefore, it is important to study the pharmacokinetic changes of drugs at high altitude. Method: A systematic review of published studies was carried out to investigate the effects of hypoxia on the metabolic characteristics of some drugs and the activity and expression of drug-metabolizing enzymes in high-altitude hypoxic environments, and discussed the relevant mechanisms. Results: The metabolism of most drugs decreases in high-altitude hypoxia, whereas Mean Residence Time (MRT), Half Time (T1/2), and Area Under the Curve (AUC) increase and Clearance (CL) decrease in this environment. The effect of hypoxia on CYP450 enzymes in animals is still a subject of debate. With the exception of CYP2C11 and CYP2C22, the widespread belief is that high-altitude hypoxia decreased the activity and expression of CYP1A1, CYP1A2, CYP2E1, and CYP3A1, and increased those of CYP3A6 and CYP2D1 in rats. The changes in the activity and expression of drug metabolizing enzymes are consistent with the changes in pharmacokinetics of some enzyme substrates in the high-altitude hypoxia environment. Conclusion: The findings of this review have indicated that hypoxia may play a key role in the PK changes of drugs at high altitude. It is suggested that patient living at or traveling to high altitude should be closely monitored, and the dosages of some drugs metabolized should be reduced.