Interaction of serum proteins with CYP isoforms in human liver microsomes: inhibitory effects of human and bovine albumin, alpha-globulins, alpha-1-acid glycoproteins and gamma-globulins on CYP2C19 and CYP2D6

Combined impact of hypoalbuminemia and pharmacogenomic variants on voriconazole trough concentration: data from a real-life clinical setting in the Chinese population

Voriconazole (VRC) displays highly variable pharmacokinetics impacting treatment efficacy and safety. To provide evidence for optimizing VRC therapy regimens, the authors set out to determine the factors impacting VRC steady-state trough concentration (Cmin) in patients with various albumin (Alb) level. A total of 275 blood samples of 120 patients and their clinical characteristics and genotypes of CYP2C19, CYP3A4, CYP3A5, CYP2C9, FMO3, ABCB1, POR, NR1I2 and NR1I3 were included in this study. Results of multivariate linear regression analysis demonstrated that C-reactive protein (CRP) and total bilirubin (T-Bil) were predictors of the VRC Cmin adjusted for dose in patients with hypoalbuminemia (Alb < 35 g/L) (R2 = 0.16, P < 0.001). Additionally, in patients with normal albumin level (Alb ≥ 35 g/L), it resulted in a significant model containing factors of the poor metabolizer (PM) CYP2C19 genotype and CRP level (R2 = 0.26, P < 0.001). Therefore, CRP and T-Bil levels ought to receive greater consideration than genetic factors in patients with hypoalbuminemia.

Pleiotropy of Progesterone Receptor Membrane Component 1 in Modulation of Cytochrome P450 Activity

Progesterone receptor membrane component 1 (PGRMC1) is one of few proteins that have been recently described as direct modulators of the activity of human cytochrome P450 enzymes (CYP)s. These enzymes form a superfamily of membrane-bound hemoproteins that metabolize a wide variety of physiological, dietary, environmental, and pharmacological compounds. Modulation of CYP activity impacts the detoxification of xenobiotics as well as endogenous pathways such as steroid and fatty acid metabolism, thus playing a central role in homeostasis. This review is focused on nine main topics that include the most relevant aspects of past and current PGRMC1 research, focusing on its role in CYP-mediated drug metabolism. Firstly, a general overview of the main aspects of xenobiotic metabolism is presented (I), followed by an overview of the role of the CYP enzymatic complex (IIa), a section on human disorders associated with defects in CYP enzyme complex activity (IIb), and a brief account of cytochrome b5 (cyt b5)'s effect on CYP activity (IIc). Subsequently, we present a background overview of the history of the molecular characterization of PGRMC1 (III), regarding its structure, expression, and intracellular location (IIIa), and its heme-binding capability and dimerization (IIIb). The next section reflects the different effects PGRMC1 may have on CYP activity (IV), presenting a description of studies on the direct effects on CYP activity (IVa), and a summary of pathways in which PGRMC1's involvement may indirectly affect CYP activity (IVb). The last section of the review is focused on the current challenges of research on the effect of PGRMC1 on CYP activity (V), presenting some future perspectives of research in the field (VI).

Inhibitory effects of type 2 diabetes serum components in P450 inhibition assays can potential diagnose asymptomatic diabetic mice

Human cytochrome P450 (or CYP) inhibition rates were investigated in sera from high fat diet (HFD)-induced type 2 diabetes (T2D), T2D recovered, and asymptomatic mice models to verify whether P450 inhibition assays could be used for the detection of disease, evaluation of therapeutic effect, and early diagnosis of T2D. In T2D mice, the blood glucose levels markedly increased; while blood glucose levels of recovered mice exceeded 200 mg dL^-1, these eventually returned to the levels seen in control mice. In asymptomatic mice fed with short term HFD (stHFD), no changes in blood glucose levels were observed. The inhibition rates of CYP1A2, CYP2A13, and CYP2C18 in T2D mice significantly increased. Whereas in recovered mice, these changes returned to the same levels noted in the control mice. Changes in the inhibition rates of CYP2A13 and CYP2C18 in stHFD mice were similar to those in T2D mice. A receiver operating characteristic (ROC) curve analysis showed high area under the ROC curve (AUC) values (0.879-1.000) of CYP2A13 and CYP2C18 in T2D and stHFD mice, indicating their high diagnostic accuracy. Collectively, this study validates the P450 inhibition assay as a method for the therapeutic evaluation and early diagnosis of T2D mouse models.

An ex vivo approach to botanical-drug interactions: a proof of concept study

ETHNOPHARMACOLOGICAL RELEVANCE

Botanical medicines are frequently used in combination with therapeutic drugs, imposing a risk for harmful botanical-drug interactions (BDIs). Among the existing BDI evaluation methods, clinical studies are the most desirable, but due to their expense and protracted time-line for completion, conventional in vitro methodologies remain the most frequently used BDI assessment tools. However, many predictions generated from in vitro studies are inconsistent with clinical findings. Accordingly, the present study aimed to develop a novel ex vivo approach for BDI assessment and expand the safety evaluation methodology in applied ethnopharmacological research.

MATERIALS AND METHODS

This approach differs from conventional in vitro methods in that rather than botanical extracts or individual phytochemicals being prepared in artificial buffers, human plasma/serum collected from a limited number of subjects administered botanical supplements was utilized to assess BDIs. To validate the methodology, human plasma/serum samples collected from healthy subjects administered either milk thistle or goldenseal extracts were utilized in incubation studies to determine their potential inhibitory effects on CYP2C9 and CYP3A4/5, respectively. Silybin A and B, two principal milk thistle phytochemicals, and hydrastine and berberine, the purported active constituents in goldenseal, were evaluated in both phosphate buffer and human plasma based in vitro incubation systems.

RESULTS

Ex vivo study results were consistent with formal clinical study findings for the effect of milk thistle on the disposition of tolbutamide, a CYP2C9 substrate, and for goldenseal׳s influence on the pharmacokinetics of midazolam, a widely accepted CYP3A4/5 substrate. Compared to conventional in vitro BDI methodologies of assessment, the introduction of human plasma into the in vitro study model changed the observed inhibitory effect of silybin A, silybin B and hydrastine and berberine on CYP2C9 and CYP3A4/5, respectively, results which more closely mirrored those generated in clinical study.

CONCLUSIONS

Data from conventional buffer-based in vitro studies were less predictive than the ex vivo assessments. Thus, this novel ex vivo approach may be more effective at predicting clinically relevant BDIs than conventional in vitro methods.

Role of protein-protein interactions in cytochrome P450-mediated drug metabolism and toxicity

Through their unique oxidative chemistry, cytochrome P450 monooxygenases (CYPs) catalyze the elimination of most drugs and toxins from the human body. Protein–protein interactions play a critical role in this process. Historically, the study of CYP–protein interactions has focused on their electron transfer partners and allosteric mediators, cytochrome P450 reductase and cytochrome b5. However, CYPs can bind other proteins that also affect CYP function. Some examples include the progesterone receptor membrane component 1, damage resistance protein 1, human and bovine serum albumin, and intestinal fatty acid binding protein, in addition to other CYP isoforms. Furthermore, disruption of these interactions can lead to altered paths of metabolism and the production of toxic metabolites. In this review, we summarize the available evidence for CYP protein–protein interactions from the literature and offer a discussion of the potential impact of future studies aimed at characterizing noncanonical protein–protein interactions with CYP enzymes.

Effect of uremic serum and uremic toxins on drug metabolism in human microsomes

There is increasing evidence that renal impairment modifies nonrenal drug clearance through drug metabolizing cytochrome P450 (CYP) enzymes. In this study, the direct inhibitory effect of serum from chronic renal failure (CRF) patients receiving dialysis was evaluated in CYP3A4 (testosterone) and CYP2B6 (bupropion) metabolism assays. Human liver microsomes were incubated with ultrafiltered serum collected pre- and post-hemodialysis from ten CRF patients. Additionally, several uremic toxins were evaluated in the CYP3A4 assay. In only three patients was there a significant decrease or increase in testosterone or bupropion metabolism post-dialysis. Urea, mannitol, guanidine, homocysteine, uridine and creatinine had no effect on CYP3A4 metabolism. CMPF, hippuric acid and p-cresol had IC50 values that fell within CRF patient plasma concentrations. The IC50 values for indoxyl sulfate and indole-3-acetic acid were greater than CRF plasma concentrations. The lack of a consistent effect on CYP3A4 or CYP2B6 metabolism by uremic serum may be due in part to the frequency of hemodialysis in these patients which reduced the accumulation of uremic toxins. CMPF, hippuric acid and p-cresol have the ability to inhibit CYP3A4 metabolism at clinical concentrations which may correspond to reports of changes in hepatic metabolism in some CRF patients.

Herb-drug interaction of 50 Chinese herbal medicines on CYP3A4 activity in vitro and in vivo

The purpose of this study is to evaluate the effects of Chinese herbal medicines on the enzymatic activity of CYP3A4 and the possible metabolism-based herb-drug interactions in human liver microsomes and in rats. Fifty single-herbal preparations were screened for the activity of CYP3A4 using human liver microsomes for an in vitro probe reaction study. The enzymatic activity of CYP3A4 was estimated by determing the 6β-hydroxytestosterone metabolized from testosterone performed on a liquid chromatography-tandem mass spectrometry (LC-MS/MS). Huang Qin (Scutellaria baicalensis Geprgi), Mu Dan Pi (Paeonia suffruticosa Andr.), Ji Shiee Terng (Spatholobus suberectus Dunn.) and Huang Qi (Astragalus membranaceus [Fisch] Bge) have been demonstrated to have remarkable inhibiting effects on the metabolism of CYP3A4, whereas Xi Yi Hua (Magnolia biondii Pamp.) exhibited a moderate inhibition. These five single herbs were further investigated in an animal study using midazolam. Mu Dan Pi, Ji Shiee Terng and Huang Qi were observed to have greatly increased in the C(max) and AUC of midazolam. This study provides evidence of possible herb-drug interactions involved with certain single herbs.

Gene expression profiles in liver of pigs with extreme high and low levels of androstenone

BACKGROUND

Boar taint is the unpleasant odour and flavour of the meat of uncastrated male pigs that is primarily caused by high levels of androstenone and skatole in adipose tissue. Androstenone is a steroid and its levels are mainly genetically determined. Studies on androstenone metabolism have, however, focused on a limited number of genes. Identification of additional genes influencing levels of androstenone may facilitate implementation of marker assisted breeding practices. In this study, microarrays were used to identify differentially expressed genes and pathways related to androstenone metabolism in the liver from boars with extreme levels of androstenone in adipose tissue.

RESULTS

Liver tissue samples from 58 boars of the two breeds Duroc and Norwegian Landrace, 29 with extreme high and 29 with extreme low levels of androstenone, were selected from more than 2500 individuals. The samples were hybridised to porcine cDNA microarrays and the 1% most significant differentially expressed genes were considered significant. Among the differentially expressed genes were metabolic phase I related genes belonging to the cytochrome P450 family and the flavin-containing monooxygenase FMO1. Additionally, phase II conjugation genes including UDP-glucuronosyltransferases UGT1A5, UGT2A1 and UGT2B15, sulfotransferase STE, N-acetyltransferase NAT12 and glutathione S-transferase were identified. Phase I and phase II metabolic reactions increase the water solubility of steroids and play a key role in their elimination. Differential expression was also found for genes encoding 17beta-hydroxysteroid dehydrogenases (HSD17B2, HSD17B4, HSD17B11 and HSD17B13) and plasma proteins alpha-1-acid glycoprotein (AGP) and orosomucoid (ORM1). 17beta-hydroxysteroid dehydrogenases and plasma proteins regulate the availability of steroids by controlling the amount of active steroids accessible to receptors and available for metabolism. Differences in the expression of FMO1, NAT12, HSD17B2 and HSD17B13 were verified by quantitative real competitive PCR.

CONCLUSION

A number of genes and pathways related to metabolism of androstenone in liver were identified, including new candidate genes involved in phase I oxidation metabolism, phase II conjugation metabolism, and regulation of steroid availability. The study is a first step towards a deeper understanding of enzymes and regulators involved in pathways of androstenone metabolism and may ultimately lead to the discovery of markers to reduce boar taint.

Pharmacokinetics of Oltipraz in Mutant Nagase Analbuminemic Rats

Pharmacokinetic parameters of oltipraz were compared after intravenous (10 mg/kg) and oral (50 mg/kg) administration to control male Sprague-Dawely rats and mutant Nagase analbuminemic rats (NARs). In NARs, the expression and mRNA level of CYP1A2 increased, and oltipraz was mainly metabolized via CYP1A1/2, 2B1/2, 2C11, 201, and 3A1/2 in male rats. Hence, it may be expected that the CL of oltipraz would be significantly faster in NARs. This was proven by the following results. After intravenous administration, the CL of oltipraz was significantly faster in NARs (125% increase) than controls due to significantly greater free fractions (unbound to plasma proteins) of oltipraz (197% increase) and significantly faster CL(int) for the disappearance of oltipraz (11.4% increase) in NARs, since oltipraz is an intermediate hepatic extraction ratio drug in rats. The V(ss) was significantly larger in NARs (109% increase) and this could be due to significant increase in free fractions of oltipraz in NARs. After oral administration, the AUC of oltipraz was also significantly smaller in NARs (61.9% decrease). This could also be due to significant increase in free fractions of oltipraz and significantly faster CL(int) in NARs. However, this was not due to decrease in absorption in NARs.

The comparative interaction of human and bovine serum albumins with CYP2C9 in human liver microsomes

The effect of human serum albumin (HSA), in its endogenous, free fatty acid free (FAF) and globulin free (GF) form, on the activity of CYP2C9 was studied in human liver microsomes using tolbutamide as the substrate. The widely used BSA was included to assess the differential effect of BSA and HSA. CYP2C9 activity was expressed as CLint (Vmax/Km). HSA(FAF) and BSA showed a concentration-dependent and biphasic (activation and inhibition) interaction with CYP2C9 activity. HSA(GF) and HSA exhibited an inhibitory effect, with an inhibition constant, Ki, of 19.9 microM (0.13% albumin) and 42.2 microM (0.35% albumin), respectively. Enzyme-kinetics revealed that the activation is accompanied by a decrease in Km values, while with inhibition Km values increased. A simplified method to calculate clearance, utilizing a single slope (V/S) determination based on V over the lowest linear range of [S] (designated as CLone) was assessed. Virtually identical values were obtained for CLint and CLone. The free-drug hypothesis was tested by comparing ratios of relative CLint/unbound fraction (FDH Test ratio). The FDH Test ratio for HSA was about 1, indicating that HSA binding of tolbutamide reduced the CYP2C9 activity in accord with the free-drug hypothesis. The FDH Test ratios for BSA and HSA(FAF) were 3.7 and 3.0, revealing a monophasic activation of CYP2C9. For 2%HSA(GF) the ratio of 0.3 confirmed inhibition. As revealed by their removal, free fatty acids and globulins, significantly alter the interaction of HSA with CYP2C9. In addition, HSA and BSA showed different effects on the oxidation of tolbutamide by CYP2C9.