Enzyme Activity of Natural Products on Cytochrome P450

Drug-metabolizing enzymes, particularly the cytochrome P450 (CYP450) monooxygenases, play a pivotal role in pharmacokinetics. CYP450 enzymes can be affected by various xenobiotic substrates, which will eventually be responsible for most metabolism-based herb–herb or herb–drug interactions, usually involving competition with another drug for the same enzyme binding site. Compounds from herbal or natural products are involved in many scenarios in the context of such interactions. These interactions are decisive both in drug discovery regarding the synergistic effects, and drug application regarding unwanted side effects. Herein, this review was conducted as a comprehensive compilation of the effects of herbal ingredients on CYP450 enzymes. Nearly 500 publications reporting botanicals’ effects on CYP450s were collected and analyzed. The countries focusing on this topic were summarized, the identified herbal ingredients affecting enzyme activity of CYP450s, as well as methods identifying the inhibitory/inducing effects were reviewed. Inhibitory effects of botanicals on CYP450 enzymes may contribute to synergistic effects, such as herbal formulae/prescriptions, or lead to therapeutic failure, or even increase concentrations of conventional medicines causing serious adverse events. Conducting this review may help in metabolism-based drug combination discovery, and in the evaluation of the safety profile of natural products used therapeutically.

Temperature Effects on Tuber Production and Carbohydrates Partitioning in Different Cultivars During Consecutive Stages of Potato (Solanum tuberosum L.) Growth

The main objective of this study was to assess responses of mid-early (Spunta) and mid-late (Bellini) potato cultivars to different temperature regimes during subsequent stages of potato growth. The impact of high temperature (25/22°C day/night), low temperature (18/16°C day/night) and intermediate temperature (20/18°C day/night) was evaluated for different growth stages. Data were obtained for photosynthesis, carbohydrates in leaves, stems and tubers as well as production parameters. Enzyme activities were determined for sucrose-phosphate synthase in leaves, acid invertase in stems and acid and neutral invertases in tubers. Gene expression levels of relevant sugar metabolizing enzymes was quantified.A detailed correlation analysis revealed a strong impact of the expression level of sugar metabolizing enzymes in leaves on the final number of tubers per plant.Whereas total tuber yield increases with temperature, the number of tubers per plant was highest under low temperature conditions. Our data suggest an important role of the temperature on the length of the different growth stages.

Puromycin-based purification of cells with high expression of the cytochrome P450 CYP3A4 gene from a patient with drug-induced liver injury (DILI)

Background Many drugs have the potential to induce the expression of drug-metabolizing enzymes, particularly cytochrome P450 3A4 (CYP3A4), in hepatocytes. Hepatocytes can be accurately evaluated for drug-mediated CYP3A4 induction; this is the gold standard for in vitro hepatic toxicology testing. However, the variation from lot to lot is an issue that needs to be addressed. Only a limited number of immortalized hepatocyte cell lines have been reported. In this study, immortalized cells expressing CYP3A4 were generated from a patient with drug-induced liver injury (DILI). Methods To generate DILI-derived cells with high expression of CYP3A4, a three-step approach was employed: (1) Differentiation of DILI-induced pluripotent stem cells (DILI-iPSCs); (2) Immortalization of the differentiated cells; (3) Selection of the cells by puromycin. It was hypothesized that cells with high cytochrome P450 gene expression would be able to survive exposure to cytotoxic antibiotics because of their increased drug-metabolizing activity. Puromycin, a cytotoxic antibiotic, was used in this study because of its rapid cytocidal effect at low concentrations. Results The hepatocyte-like cells differentiated from DILI-iPSCs were purified by exposure to puromycin. The puromycin-selected cells (HepaSM or SI cells) constitutively expressed the CYP3A4 gene at extremely high levels and exhibited hepatocytic features over time. However, unlike primary hepatocytes, the established cells did not produce bile or accumulate glycogen. Conclusions iPSC-derived hepatocyte-like cells with intrinsic drug-metabolizing enzymes can be purified from non-hepatocytes and undifferentiated iPSCs using the cytocidal antibiotic puromycin. The puromycin-selected hepatocyte-like cells exhibited characteristics of hepatocytes after immortalization and may serve as another useful source for in vitro hepatotoxicity testing of low molecular weight drugs.

Pharmacokinetics-based Chronotherapy

Dosing time-dependency of pharmacokinetics (or chronopharmacokinetics) has been long recognized. Studies in recent years have revealed that diurnal rhythmicity in expression of drug-metabolizing enzymes and transporters (DMETs) are key factors determining chronopharmacokinetics. In this article, we briefly summarize current knowledge with respect to circadian mechanisms of DMETs and discuss how rhythmic DMETs are translated to drug chronoeffects. More importantly, we present our perspectives on pharmacokinetics-based chronotherapy.

Piecing together human adult comparative pharmacokinetic trials and rodent studies: What happens to drug clearance in obesity?

In many comparative trials examining the effects of adult obesity on pharmacokinetics of drugs, conclusions were made based on values that were either not adjusted to total body weight or adjusted to non-obese body mass (e.g., ideal or lean body weight). In many cases these values were higher in the obese subjects. We have reviewed the data from comparative human trials, and it is apparent that in examining clearance normalization to total body weight (as typically done in studies involving pediatric obese patients), the clearances are often reduced in the obese. We have also reviewed the results of experimental obese versus non-obese rodent models. Those studies have mostly found that the systemic exposures to the same dose per body weight are increased, with obesity-related decreases in clearance. Furthermore, the expression of a number of important drug metabolizing enzymes are reduced in the experimental obese state. There is also evidence that obesity causes increases in the measured mass of eliminating organs such as liver and kidney. Human clearance normalized to total body weight appears to better reflect the underlying changes reported in the expression of protein and functional activity of drug clearance mechanisms.

Methanolic Extract of Myrsine africana Leaf Ameliorates Hyperglycemia and Dyslipidemia in Alloxan-Induced Diabetic Albino Mice

Background. Diabetes mellitus is one of the leading public health problems globally, and its prevalence is increasing in Ethiopia. The current drugs for people with diabetes are costly, less effective, and less safe with a challenging administration method. Thus, globally, the need for alternative herbal antidiabetic medicines is increasing. In the previous studies, antioxidant activities have been seen in crude extracts of M. africana leaves, which is an auspicious sign of antidiabetic property. Accordingly, this study has evaluated the antidiabetic and antidyslipidemic activities of methanolic extract of M. africana leaves. Methods. Hypoglycemic and antihyperglycemic activities of the three doses (250 mg/kg, 500 mg/kg, and 1000 mg/kg) of crude methanolic extract of M. africana leaf were studied on normoglycemic, oral glucose-loaded, and alloxan-induced diabetic mice models. The effect of the extract on diabetic dyslipidemia, insulin and glycated hemoglobin levels, carbohydrate-metabolizing enzymes, and body weight was also studied in alloxan-induced diabetic mice. Glibenclamide (5 mg/kg) was used as a standard drug in all cases. Data analysis was carried out using mixed-design ANOVA. A P value of ≤0.05 was considered a statistically significant difference. Results. The methanolic extract of M. africana leaf did not show acute toxicity up to the dose of 5000 mg/kg and showed better glucose utilization in the oral glucose tolerance test. After 14 days of treatment, M. africana leaf extract decreased the blood glucose level, glycated hemoglobin, glucose-6-phosphatase, and fructose-1-6-bisphosphatase in diabetic mice. In contrast, it increased hexokinase and insulin levels in diabetic mice. Moreover, weight loss and dyslipidemia profiles have been corrected significantly in diabetic mice. Conclusion. M. africana leaves showed antihyperglycemic and antidyslipidemic effects in alloxan-induced diabetic mice. That suggests M. africana may be a potential treatment option for diabetes in the future. However, further molecular studies are required to analyze the mechanisms.

The Nuclear Receptor PXR in Chronic Liver Disease

Pregnane X receptor (PXR), a nuclear receptor known for modulating the transcription of drug metabolizing enzymes and transporters (DMETs), such as cytochrome P450 3A4 and P-glycoprotein, is functionally involved in chronic liver diseases of different etiologies. Furthermore, PXR activity relates to that of other NRs, such as constitutive androstane receptor (CAR), through a crosstalk that in turn orchestrates a complex network of responses. Thus, besides regulating DMETs, PXR signaling is involved in both liver damage progression and repair and in the neoplastic transition to hepatocellular carcinoma. We here summarize the present knowledge about PXR expression and function in chronic liver diseases characterized by different etiologies and clinical outcome, focusing on the molecular pathways involved in PXR activity. Although many molecular details of these finely tuned networks still need to be fully understood, we conclude that PXR and its modulation could represent a promising pharmacological target for the identification of novel therapeutical approaches to chronic liver diseases.

Vitamin D effects on androgen levels in men

Background. Accumulating evidence from animal and human studies suggests that vitamin D is involved in many functions of the reproductive system. Considering the potential link between vitamin D and human fertility, authors performed this review summarizing current literature on vitamin D and possible mechanisms explaining the link of vitamin D with androgen metabolism in men. The purpose of this review was to provide an overview on the effects of vitamin D on androgen metabolism in men. Methods. Author performed a systematic literature search in PubMed for relevant English language publications published from January 2011 until September 2021. Results. The vitamin D receptor and vitamin D-metabolizing enzymes are found in reproductive tissues. In men, vitamin D status has been associated with androgen levels and hypogonadism. Further, there is some evidence for a favorable effect of vitamin D supplementation on testosterone concentrations, although others failed to show a significant effect on testosterone levels. Vitamin D might play an important role in androgen metabolism. Existing evidence from available trials evaluating the effect of vitamin D supplementation on androgen levels in men is insufficient to recommend measurement of 25(OH)D levels or vitamin D supplementation in hypogonadal men. We cannot exclude vitamin D effects on androgen levels in men with low TT levels or in men with severe vitamin D deficiency. This question remains to be answered in future investigations. Conclusions. Vitamin D deficiency is associated with adverse fertility outcomes including hypogonadism, but the evidence is insufficient to establish causality. High-quality trials are needed to further evaluate the effects of vitamin D supplementation on androgen levels in men.