Variation in Expression of Cytochrome P450 3A Isoforms and Toxicological Effects: Endo- and Exogenous Substances as Regulatory Factors and Substrates

The CYP3A subfamily, which includes isoforms CYP3A4, CYP3A5, and CYP3A7 in humans, plays important roles in the metabolism of various endogenous and exogenous substances. Gene and protein expression of CYP3A4, CYP3A5, and CYP3A7 show large inter-individual differences, which are caused by many endogenous and exogenous factors. Inter-individual differences can cause negative outcomes, such as adverse drug events and disease development. Therefore, it is important to understand the variations in CYP3A expression caused by endo- and exogenous factors, as well as the variation in the metabolism and kinetics of endo- and exogenous substrates. In this review, we summarize the factors regulating CYP3A expression, such as bile acids, hormones, microRNA, inflammatory cytokines, drugs, environmental chemicals, and dietary factors. In addition, variations in CYP3A expression under pathological conditions, such as coronavirus disease 2019 and liver diseases, are described as examples of the physiological effects of endogenous factors. We also summarize endogenous and exogenous substrates metabolized by CYP3A isoforms, such as cholesterol, bile acids, hormones, arachidonic acid, vitamin D, and drugs. The relationship between the changes in the kinetics of these substrates and the toxicological effects in our bodies are discussed. The usefulness of these substrates and metabolites as endogenous biomarkers for CYP3A activity is also discussed. Notably, we focused on discrimination between CYP3A4, CYP3A5, and CYP3A7 to understand inter-individual differences in CYP3A expression and function.

A Bioequivalence Study of Avanafil in Healthy Chinese Male Subjects Under Fasting and Fed Conditions: Results of a Randomized, Open-Label, Single-Dose, 2-Sequence, 2-Period Crossover Study

This bioequivalence study was conducted to determine the pharmacokinetics and safety profiles of an originator and a generic avanafil formulation in Chinese male subjects under fed and fasting conditions. Each eligible subject was initially randomly given avanafil (200 mg) in a test‐reference or reference‐test order, before being switched to another study drug sequence after 7 drug‐free days. The bioequivalence of test and reference avanafil were determined if the 90%CIs of the geometric mean ratio (GMR) for the area under plasma concentration‐time curve (AUC) from time 0 to infinity (AUC_0‐∞), AUC from time 0 to the last detectable concentration (AUC_0‐t), and the maximum plasma concentration (C_max) fell within the range 80%‐125%. Under fasting/fed conditions, the 90%CIs of GMR for AUC_0‐∞, AUC_0‐t, and C_max were 98.9% to 109.5%/96.0% to 101.2%, 99.6% to 110.3%/96.6% to 102.4%, and 99.3% to 116.8%/94.3% to 106.7%, respectively, which were all within the 80%‐125% range. Adverse events (AEs) occurred in 20.8% of subjects under fasting conditions and 20.7% of subjects under fed conditions, with a severity of grade 1. No significant difference was found in the rate of occurrence of AEs and drug‐related AEs in the test and reference‐avanafil groups (all P > .05). We concluded that the test and reference avanafil were bioequivalent in healthy Chinese male subjects under fasting and fed conditions.

Effects of gut microbiota on in vivo metabolism and tissue accumulation of cytochrome P450 3A metabolized drug: Midazolam

The link between drug‐metabolizing enzymes and gut microbiota is well established. In particular, hepatic cytochrome P450 (CYP) 3A activities are presumed to be affected by gut microbiota. However, there is no direct evidence that the gut microbiota affects CYP3A metabolism or the clearance of clinically relevant drugs in vivo. Our purpose was to evaluate the effects of gut microbiota on in vitro and in vivo drug metabolism and on the clearance of midazolam, which is a standard CYP3A metabolized drug. Hepatic Cyp3a activity and in vitro midazolam hydroxylase activity were compared using specific pathogen‐free (SPF) and germ‐free (GF) mice. In a pharmacokinetics (PK) study, SPF and GF mice were intraperitoneally injected with 60 mg/kg of midazolam, and plasma and tissue concentrations were measured. Hepatic Cyp3a activity and midazolam hydroxylase activity were significantly lower in GF mice than in SPF mice. Notably, in the PK study, the area under the plasma concentration–time curve from time zero to infinity and the elimination half‐life were approximately four‐fold higher in GF mice compared with SPF mice. Furthermore, the concentration of midazolam in the brain 180 min after administration was about 14‐fold higher in GF mice compared with SPF mice. Together, our results demonstrated that the gut microbiota altered the metabolic ability of Cyp3a and the tissue accumulation of midazolam.

Coordinated cytochrome P450 expression in mouse liver and intestine under different dietary conditions during liver regeneration after partial hepatectomy

Liver resection is performed to remove tumors in patients with liver cancer, but the procedure's suitability depends on the regenerative ability of the liver. It is important to consider the effects of exogenous factors, such as diets, on liver regeneration for the recovery of function. The evaluation of drug metabolism during liver regeneration is also necessary because liver dysfunction is generally observed after the operation. Here, we investigated the influence of a purified diet (AIN-93G) on liver regeneration and changes in the mRNA expression of several cytochrome P450 (CYP) isoforms in the liver and small intestine using a two-thirds partial hepatectomy (PH) mouse model fed with a standard diet (MF) and a purified diet. Liver regeneration was significantly delayed in the purified diet group relative to that in the standard diet group. The liver Cyp2c55 and Cyp3a11 expression was increased at 3 day after PH especially in the purified diet group. Bile acid may partly cause the differences in liver regeneration and CYP expression between two types of diets. On the other hand, Cyp3a13 expression in the small intestine was transiently increased at day 1 after PH in both diet groups. The findings suggest that compensatory induction of the CYP expression occurred in the small intestine after attenuation of drug metabolism potential in the liver. The present results highlight the importance of the relationship between liver regeneration, drug metabolism, and exogenous factors for the effective treatment, including surgery and medication, in patients after liver resection or transplantation.

Skeletal Muscle Interleukin-6 Regulates Hepatic Cytochrome P450 Expression: Effects of 16-Week High-Fat Diet and Exercise

High-fat diet (HFD) induces several changes to the pathways regulating energy homeostasis and changes the expression of the hepatic cytochrome p450 (Cyp) enzyme-system. Despite these pervious findings, it is still unclear how the effects of HFD and especially HFD in combination with treadmill running affect hepatic Cyp expression. In this study, we investigated the mRNA and protein expression of selected Cyp's in mice subjected to 16 weeks of HFD and treadmill running. To understand the regulatory mechanisms behind the exercise-induced reversion of the HFD-induced changes in Cyp expression, we used a model in which the exercise-induced myokine and known regulator of hepatic Cyp's, interleukin-6 (IL-6), were knocked out specifically in skeletal muscle. We found that HFD increased the mRNA expression of Cyp1a1 and Cyp4a10, and decreased the expression of Cyp2a4, Cyp2b10, Cyp2e1, and Cyp3a11. HFD in combination with treadmill running reversed the HFD increase in Cyp4a10 mRNA expression. In addition, we observed increased Cyp1a and Cyp3a protein expression as an effect of exercise, whereas Cyp2b expression was lowered as an effect of HFD. IL-6 effected the response in Cyp3a11 and Cyp1a expression. We observed no changes in the content of the aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, or peroxisome proliferation activator receptor alpha. In conclusion, we show that both HFD and exercise in HFD-fed animals can regulate hepatic Cyp expression and that changes in Cyp3a in response to HFD and exercise are dependent on skeletal muscular IL-6.

Drug metabolism enzymes in a steatotic model of rat treated with a high fat diet and a low dose of streptozotocin

Herein we have characterized CYPs and antioxidant enzymes in a new steatotic rat model induced with a high fat diet (HFD) combined with a low dose of streptozotocin (STZ). This model was recently put forward in order to better replicate the NAFLD human pathology. HFD/STZ rats developed hyperglycemia, hypercholesterolemia and overt steatosis. The treatment also caused liver damage, but not lipid peroxidation, suggesting this damage was due to hepatic fat deposition and excess formation of toxic free fatty acids, rather than to oxidative stress. In the HFD/STZ group, a significant rise in total CYP content was found, in conjunction with increased activity and protein levels of CYP2E1 and CYP4A, the latter also up-regulated at the transcriptional level. A significant decrease of CYP2C11 was observed at the transcriptional and protein level, whereas CYP3A2 did not change in response to HFD/STZ treatment. In our experimental conditions, the activity of the HO-1 and NQO1 enzymes, whose genes are regulated by Nrf2, were not affected, and nor were the antioxidant enzymes SOD and CAT, confirming the lack of oxidative stress. Our HFD/STZ treatment, which established overt steatosis and changes in CYPs expression, but not oxidative stress, likely reflects an early stage of NAFLD.