Current Drug Metabolism - Volume 16, Issue 10, 2015

Cytochrome P450 (CYP450) enzymes are the most important metabolizing enzyme family exists among all organs. Apart from their role in the deactivation of most endogenous compounds and xenobiotics, they also mediate most procarcinogens oxidation to ultimate carcinogens. There are several modes of CYP450s activation of procarcinogens. 1) Formation of epoxide and diol-epoxides intermediates, such as CYP1A1 and CYP1B1 mediates PAHs oxidation to epoxide intermediates; 2) Formation of diazonium ions, such as CYP2A6, CYP2A13 and CYP2E1 mediates activation of most nitrosamines to unstable metabolites, which can rearrange to give diazonium ions. 3) Formation of reactive semiquinones and quinines, such as CYP1A1 and CYP1B1 transformation of estradiol to catechol estrogens, subsequently formation semiquinones; 4) Formation of toxic O-esterification, such as CYP1A1 and CYP1A2 metabolizes PhIP to N2-acetoxy-PhIP and N2-sulfonyloxy-PhIP, which are carcinogenic metabolites. 5) Formation of free radical, such as CYP2E1 is involved in activation tetrachloromethane to free radicals. While for CYP2B6 and CYP2D6, only a minor role has been found in procarcinogens activation. In addition, as the gene polymorphisms reflected, the polymorphisms of CYP1A1 (-3801T/C and -4889A/G), CYP1A2 (- 163C/A and -2467T/delT), CYP1B1 (-48G/C, -119G/T and -432G/C), CYP2E1 (-1293G/C and -1053 C/T) have been associated with an increased risk of lung cancer. The polymorphisms CYP1A1 (-3801T/C and -4889A/G), and CYP2E1 (PstI/Rsa and 9-bp insertion) have an association with higher risk colon cancers, whereas CYP1A2 (-163C/A and -3860G/A) polymorphism is found to be among the protective factors. The polymorphisms CYP1A1 (-3801T/C and -4889A/G), CYP1B1 -432G/C, CYP2B6 (-516G/T and -785A/G) may increase the risk of breast cancer. In conclusion, CYP1A1, CYP1A2, CYP1B1, CYP2A6, and CYP2E1 are responsible for most of the procarcinogens activation, and their gene polymorphisms are associated with the risk of cancers.

The type 2 diabetes or T2D mellitus has turn into an epidemic throughout the globe in recent years. Various forms of treatment modalities have been available for patients with T2D with some major classes of approved drugs that include Sulfonylureas, Meglitinides, Biguanides, Thiazolidinedione, Alpha-glucosidase inhibitors, GLP-1 analogs, DPP-4 Inhibitors, and SGLT2 inhibitors. This review focuses on the drug metabolizing enzymes (DME), gene polymorphisms, and inter-individual variability in therapeutics including adverse reaction effects involving Phase-I DME and Phase-II in general. This review also covers some key anti-diabetic drugs with respect to their pharcogenomics.

The recent identification of the interplay between metabolizing enzymes and BCRP has drawn more and more attention from people. BCRP, a transporter belonging to ATP-binding cassette (ABC) family, has been hypothesized to play roles in many aspects including protecting the human body against therapeutics because it is expressed in the tissues that function as barriers in vivo. Efficient coupling of BCRP and metabolizing enzymes enables rapid elimination of foreign compounds from the body because BCRP could facilitate the excretion of metabolites catalyzed by phase I and II enzymes into bile, urine and feces. Without BCRP coupling, pass through the cell membrane may be difficult for them by passive diffusion because of the increment of the molecular weight and water solubility. Thus the metabolism-efflux alliance has extraordinary importance to drug metabolism, distribution, pharmacological effect, toxicity and elimination. In this manuscript, a brief discussion about the interplays of BCRP and metabolizing enzymes in liver, intestine, kidney, lung and other organs were presented and summarized. Many endogenous and exogenous compounds belong to different chemical groups, for instance, the dietary flavonoids and the steroidal hormones were involved. Clarifying the cooperation mechanisms of BCRP and enzymes could lead to a better prediction of drug clearance in vitro.

The liposome delivery system has been intensively explored as novel drug delivery system (DDS) for antitumor drugs, due to its safety, selective cytotoxicity, long circulation and slow elimination in blood, which is favorable for cancer therapy. The liposome-based chemotherapeutics are used to treat a variety of cancers to enhance the therapeutic index of antitumor drugs. Here, the author reviewed the important targets for cancer therapy and the pharmacokinetic behavior of liposomal drugs in vivo, as well as the application of the targeting liposomal system in cancer therapy. Considering further application for clinical use, the great challenges of the liposome-based delivery system were also proposed as follows: 1) prepare stealth liposome with steric stabilization and further enhance the therapeutic effects and safety; 2) explore more safe clinical targets and complementary or different types of targeting liposome; 3) thirdly, more investment is needed on the research of pharmacokinetics of the elements such as the ligands (antibody), PEG and lipids of liposome delivery system as well as safety evaluation. Considering the complex process of the liposomal encapsulation drugs in vivo, the author inferred that there are maybe different forms of the encapsulation drug to be internalized by the tumor tissues at the same time and space, although there are little reports on it.

Many herbal medicines and drugs are available in the clinic as potent hepatoprotective agents for the treatment of commonly occurring liver diseases. Recently, herbal medicines such as silymarin and curcumin have gained more attention and popularity for the treatment of various liver diseases because of their safety and efficacy profiles. Some of them are related to transporters for drug disposition processes, therapeutic efficacy and/or adverse drug reactions. Currently, herbal medicines and diet supplements made from natural products are widely used in patients who are being treated with conventional prescription medicines, which are related to an increasing risk of herbal-drug interactions (HDIs) and/or drug–drug interactions (DDIs). The purpose of present review is to summarize the contemporary knowledge of transporter-mediated HDIs or DDIs for herbal medicines/drugs focusing on hepatoprotective compounds. Several herbal medicines/drugs are discussed in detail in this review.

The major aim of current pharmacokinetic studies is to investigate the drug absorption, disposition, metabolism and excretion in animals and humans. The time courses of plasma concentrations are usually characterized and linked to the pharmacodynamic effect to evaluate drug efficacy. However, under certain circumstance, site of action is located in tissues rather than in circulation, which requires direct measurement of tissue concentrations instead of plasma concentrations. Microdialysis is one of those techniques that have been demonstrated to be feasible for measurement of free drug concentration in many tissues, and is capable of being applied in most pharmacokinetic studies to enhance drug efficacy and reduce the unnecessary side effects. This paper reviews this technique from the perspective of theoretical background including the history of development, basic principle, components and their functions. Moreover, the relative recovery of microdialysis and the key factors are discussed, followed by calibration methods available to reduce the systemic bias. In addition, microdialysis is compared with conventional tissue sampling technique for superiorities and limitations. At last, the application of microdialysis in pharmacokinetic study is summarized, especially in assessment of drug efficacy and safety in different tissues. So far, microdialysis is a valuable tool in drug development and will play an unique role in a variety of pharmacokinetic and pharmacodynamic studies in future.

With the recent advancement in nanoscience and nanotechnology, there is a growing demand for assessment of the toxicological effects of nano materials to humans and other biological systems. And a predictive toxicology approach that uses in vitro screening assays in conjunction with in vivo study results are widely employed in nano safety evaluation. In recent years stem cells have gained wide attention in the scientific community owing to their potential benefits for various applications in health care systems. Stem cells are undifferentiated cells that have high replicative potential and multilineage differentiation capacity. And therefore, stem cells could be exploited for developing in vitro model systems to study nanomaterials interaction with the biological systems and a potential tool to predict toxicity in humans. The details provided in this article will give an overview of optimizing stem cell technology in predicting the toxicity of nano materials the essential features of the article.

Background/Aims: Idiopathic short stature (ISS) is defined as short stature of unknown origin. Responses to growth hormone (GH) in children with ISS are highly variable and dose-dependent, and the optimal treatment is controversial. This study was performed to compare the effects of GH treatment in prepubertal children with ISS versus growth hormone deficiency (GHD). Methods: This retrospective study was conducted at Ajou University Hospital, Korea. Children with GHD (n = 38) or ISS (n = 22) were treated with GH (0.23 mg/kg/week, 6 times a week) for 2 years. All subjects were prepubertal during the study period. The auxological parameters and growth outcome of the two groups were compared. The association of initial clinical characteristics and first-year height standard deviation scores (Δ height SDS) was analyzed. Results: No differences were observed in the baseline auxological parameters between the ISS and GHD groups. Growth outcomes in the first and second years were similar in both groups. Age was negatively associated with first-year change in Δ height SDS in both groups. Conclusions: GH treatment was effective in both children with ISS and those with GHD. Early intervention with GH is the most appropriate therapeutic option in both ISS and GHD.