Hepatic Drug-metabolizing Enzyme Activities Research Articles

Non-alcoholic fatty liver disease changes the expression and activity of hepatic drug-metabolizing enzymes and transporters in rats

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, which can cause serious complications and gradually increase the mortality rate. However, the effects of NAFLD on drug-metabolizing enzymes and transporters remain unclear, which may cause some confusion regarding patient medication. In this study, a NAFLD rat model was constructed by feeding rats with methionine and choline deficiency diets for 6 weeks, and the mRNA and protein levels of drug-metabolizing enzymes and transporter were analyzed by real-time fluorescent quantitative PCR and Western blot, respectively. The activity of drug-metabolizing enzymes was detected by cocktail methods. In the NAFLD rat model, the mRNA expression of phase I enzymes, phase II enzymes, and transporters decreased. At the protein level, only CYP1A1, CYP1B1, CYP2C11, and CYP2J3 presented a decrease. In addition, the activities of CYP1A2, CYP2B1, CYP2C11, CYP2D1, CYP3A2, UGT1A1, UGT1A3, UGT1A6, and UGT1A9 decreased. These changes may be caused by the alteration of FXR, HNF4α, LXRα, LXRβ, PXR, and RXR. In conclusion, NAFLD changes the expression and activity of hepatic drug-metabolizing enzymes and transporters in rats, which may affect drug metabolism and pharmacokinetics. In clinical medication, drug monitoring should be strengthened to avoid potential risks.

Dysregulation of the mRNA Expression of Human Renal Drug Transporters by Proinflammatory Cytokines in Primary Human Proximal Tubular Epithelial Cells.

Proinflammatory cytokines, which are elevated during inflammation or infections, can affect drug pharmacokinetics (PK) due to the altered expression or activity of drug transporters and/or metabolizing enzymes. To date, such studies have focused on the effect of cytokines on the activity and/or mRNA expression of hepatic transporters and drug-metabolizing enzymes. However, many antibiotics and antivirals used to treat infections are cleared by renal transporters, including the basal organic cation transporter 2 (OCT2), organic anion transporters 1 and 3 (OAT1 and 3), the apical multidrug and toxin extrusion proteins 1 and 2-K (MATE1/2-K), and multidrug resistance-associated protein 2 and 4 (MRP2/4). Here, we determined the concentration-dependent effect of interleukin-6 (IL-6), IL-1β, tumor necrosis factor (TNF)-α, and interferon-γ (IFN-γ) on the mRNA expression of human renal transporters in freshly isolated primary human renal proximal tubular epithelial cells (PTECs, n = 3-5). PTECs were exposed to either a cocktail of cytokines, each at 0.01, 0.1, 1, or 10 ng/mL or individually at the same concentrations. Exposure to the cytokine cocktail for 48 h was found to significantly downregulate the mRNA expression, in a concentration-dependent manner, of OCT2, the organic anion transporting polypeptides 4C1 (OATP4C1), OAT4, MATE2-K, P-glycoprotein (P-gp), and MRP2 and upregulate the mRNA expression of the organic cation/carnitine transporter 1 (OCTN1) and MRP3. OAT1 and OAT3 also appeared to be significantly downregulated but only at 0.1 and 10 ng/mL, respectively, without a clear concentration-dependent trend. Among the cytokines, IL-1β appeared to be the most potent at down- and upregulating the mRNA expression of the transporters. Taken together, our results demonstrate for the first time that proinflammatory cytokines transcriptionally dysregulate renal drug transporters in PTECs. Such dysregulation could potentially translate into changes in transporter protein abundance or activity and alter renal transporter-mediated drug PK during inflammation or infections.

Citrus depressa Hayata peel ameliorates nonalcoholic fatty liver and modulates the activity of hepatic drug-metabolizing enzymes and transporters in rats fed a high-fat diet.

Citrus depressa Hayata is a small, green citrus fruit native to Taiwan and Japan. Citrus peel contains polymethoxylated flavones, including nobiletin and tangeretin, and may exhibit strong antioxidant and anti-inflammatory activities. A preliminary study revealed that Citrus depressa Hayata peel (CDHP) ethanolic extract reduced fat accumulation and the concentration of reactive oxygen species in human HepG2 cells exposed to oleic acid. The effects of CDHP on the activity of hepatic drug-metabolizing enzymes and membrane transporters in high-fat (HF) diet-induced fatty liver were investigated. Male rats were fed a low-fat diet, a HF diet, and a HF diet containing 4% CDHP for 11 weeks. The low-fat and HF diet respectively contained 13.5% and 38.1% of daily total calories from dietary fat. CDHP supplementation reduced the HF diet-induced accumulation of triglycerides in the liver and lowered hepatic fatty acid synthase activity. Higher faecal excretions of cholesterol, triglycerides, and total bile acids were observed after CDHP treatment. CDHP lowered the HF diet-induced increase in the mRNA expressions of nuclear factor erythroid 2-related factor 2, aryl hydrocarbon receptor, pregnane X receptor, and peroxisome proliferator-activated receptor-α and the activities of cytochrome P-450 (CYP)1A1, 1A2, 2B, and 2E1. However, increased hepatic CYP3A activity was observed in rats fed the HF diet containing CDHP. A higher hepatic multidrug resistance-associated protein 2 level was observed after CDHP treatment. After CDHP administration (1 g per kg body weight) for 1 h, nobiletin was found in plasma and various tissues and was abundant in the liver. An in vitro study revealed that the activity of various CYP enzymes in liver microsomes was inhibited by CDHP ethanolic extract and nobiletin, with IC50 values ranging from 18.5 to 54.4 μg ml-1 and from 13.0 to 33.2 μM, respectively. The results of this study suggest that CDHP might reduce hepatic steatosis and alter drug-metabolizing enzymes and transporters in HF diet-induced nonalcoholic fatty liver diseases.

Pharmacogenomics testing in patients with liver transplant and potential impact on prospective management.

Aim: Pharmacogenomics (PGx) tests are performed on whole-blood or saliva specimens. In patients with a transplanted liver, PGx results may be discordant with hepatic drug metabolizing enzyme activity. We evaluate the incidence and impact of PGx testing in liver transplant recipients, detail potential errors and describe clinical decision support (CDS) solution implemented. Materials & methods: A retrospective cohort study of liver transplant recipients at Mayo Clinic who underwent PGx testing between 1January 1996 and 7October 2019 were characterized. Impact of a CDS solution was evaluated. Results: There were 129 PGx tests in 117 patients. PGx testing incidence increased before (per year incidence rate ratio=1.45, 95% CI: 1.20-1.74, p<0.001) and after transplant (incidence rate ratio=1.48, 95% CI: 1.27-1.72, p<0.001). Three erroneous PGx tests were avoided 6 months following CDS implementation. Conclusion: Incidence of PGx testing in liver transplant recipients is increasing, leading to erroneous therapeutic decisions. CDS interventions and education are needed to prevent errors.

PBPK modeling of CYP3A and P-gp substrates to predict drug-drug interactions in patients undergoing Roux-en-Y gastric bypass surgery.

Roux-en-Y gastric bypass surgery (RYGBS) is an effective surgical intervention to reduce mortality in morbidly obese patients. Following RYGBS, the disposition of drugs may be affected by anatomical alterations and changes in intestinal and hepatic drug metabolizing enzyme activity. The aim of this study was to better understand the drug-drug interaction (DDI) potential of CYP3A and P-gp inhibitors. The impacts of RYGBS on the absorption and metabolism of midazolam, acetaminophen, digoxin, and their major metabolites were simulated using physiologically-based pharmacokinetic (PBPK) modeling. PBPK models for verapamil and posaconazole were built to evaluate CYP3A- and P-gp-mediated DDIs pre- and post-RYGBS. The simulations suggest that for highly soluble drugs, such as verapamil, the predicted bioavailability was comparable pre- and post-RYGBS. For verapamil inhibition, RYGBS did not affect the fold-change of the predicted inhibited-to-control plasma AUC ratio or predicted inhibited-to-control peak plasma concentration ratio for either midazolam or digoxin. In contrast, the predicted bioavailability of posaconazole, a poorly soluble drug, decreased from 12% pre-RYGBS to 5% post-RYGBS. Compared to control, the predicted posaconazole-inhibited midazolam plasma AUC increased by 2.0-fold pre-RYGBS, but only increased by 1.6-fold post-RYGBS. A similar trend was predicted for pre- and post-RYGBS inhibited-to-control midazolam peak plasma concentration ratios (2.0- and 1.6-fold, respectively) following posaconazole inhibition. Absorption of highly soluble drugs was more rapid post-RYGBS, resulting in higher predicted midazolam peak plasma concentrations, which was further increased following inhibition by verapamil or posaconazole. To reduce the risk of a drug-drug interaction in patients post-RYGBS, the dose or frequency of object drugs may need to be decreased when administered with highly soluble inhibitor drugs, especially if toxicities are associated with plasma peak concentrations.

Acute Kidney Injury Pharmacokinetic Changes and Its Impact on Drug Prescription.

Acute kidney injury (AKI) is a common problem in hospitalized patients that is associated with significant morbid-mortality. The impact of kidney disease on the excretion of drugs eliminated by glomerular filtration and tubular secretion is well established, as well as the requirement for drug dosage adjustment in impaired kidney function patients. However, since impaired kidney function is associated with decreased activity of several hepatic and gastrointestinal drug-metabolizing enzymes and transporters, drugs doses adjustment only based on kidney alteration could be insufficient in AKI. In addition, there are significant pharmacokinetics changes in protein binding, serum amino acid levels, liver, kidney, and intestinal metabolism in AKI, thus the determination of plasma drug concentrations is a very useful tool for monitoring and dose adjustment in AKI patients. In conclusion, there are many pharmacokinetics changes that should be taken into account in order to perform appropriate drug prescriptions in AKI patients.

123I-iomazenil whole-body imaging to detect hepatic carboxylesterase drug-metabolizing enzyme activity.

Drugs are mainly metabolized by hepatic enzymes, the activity of which can differ between individuals. Although it is ideal to measure the hepatic clearance of liver-targeted drugs in individualized medicine, blood enzyme tests typically measure metabolic drug clearance in the entire body, and not just in the liver. We investigated whether I-iomazenil imaging can directly assess and quantify the activity of hepatic drug-metabolizing enzymes. Hepatic enzymes that metabolize I-iomazenil were identified by thin-layer chromatography in mouse liver homogenates with bis(4-nitrophenyl) phosphate (BNPP) inhibitor for carboxylesterase enzymes and nicotinamide adenine dinucleotide phosphate (NADPH) generator for cytochrome P450 enzymes. Whole-body images of mice were acquired using I-iomazenil with and without BNPP, and the distribution was also obtained. The metabolism of I-iomazenil in the blood, liver, gall bladder, and bladder was investigated by thin-layer chromatography. From the in-vitro metabolism of I-iomazenil using BNPP, the enzyme converting I-iomazenil to I-R-COOH was identified as carboxylesterase, and that converting I-iomazenil to M2 was identified as cytochrome P450 in experiments with and without an NADPH generator. The biological distribution and whole-body imaging showed increased accumulation in the liver of mice administered BNPP compared with normal mice, but decreased levels in the gall bladder and small intestine. The main fraction in bile and urine was I-R-COOH, with two unknown metabolites (M1 and M2), I, and I-iomazenil also being present. I-iomazenil whole-body imaging has good possibility of direct measurement of hepatic carboxylesterase activity as accumulation of I-R-COOH in the gall bladder through bile and in the bladder through urine.

Difference in the Pharmacokinetics and Hepatic Metabolism of Antidiabetic Drugs in Zucker Diabetic Fatty and Sprague-Dawley Rats

The Zucker diabetic fatty (ZDF) rat, an inbred strain of obese Zucker fatty rat, develops early onset of insulin resistance and displays hyperglycemia and hyperlipidemia. The phenotypic changes resemble human type 2 diabetes associated with obesity and therefore the strain is used as a pharmacological model for type 2 diabetes. The aim of the current study was to compare the pharmacokinetics and hepatic metabolism in male ZDF and Sprague-Dawley (SD) rats of five antidiabetic drugs that are known to be cleared via various mechanisms. Among the drugs examined, metformin, cleared through renal excretion, and rosiglitazone, metabolized by hepatic cytochrome P450 2C, did not exhibit differences in the plasma clearance in ZDF and SD rats. In contrast, glibenclamide, metabolized by hepatic CYP3A, canagliflozin, metabolized mainly by UDP-glucuronosyltransferases (UGT), and troglitazone, metabolized by sulfotransferase and UGT, exhibited significantly lower plasma clearance in ZDF than in SD rats after a single intravenous administration. To elucidate the mechanisms for the difference in the drug clearance, studies were performed to characterize the activity of hepatic drug-metabolizing enzymes using liver S9 fractions from the two strains. The results revealed that the activity for CYP3A and UGT was decreased in ZDF rats using the probe substrates, and decreased unbound intrinsic clearance in vitro for glibenclamide, canagliflozin, and troglitazone was consistent with lower plasma clearance in vivo. The difference in pharmacokinetics of these two strains may complicate pharmacokinetic/pharmacodynamic correlations, given that ZDF is used as a pharmacological model, and SD rat as the pharmacokinetics and toxicology strain.

Role of Adaptor Protein Toll-Like Interleukin Domain Containing Adaptor Inducing Interferon β in Toll-Like Receptor 3- and 4-Mediated Regulation of Hepatic Drug Metabolizing Enzyme and Transporter Genes.

The expressions and activities of hepatic drug-metabolizing enzymes and transporters (DMETs) are altered during infection and inflammation. Inflammatory responses in the liver are mediated primarily by Toll-like receptor (TLR)-signaling, which involves recruitment of Toll/interleukin (IL)-1 receptor (TIR) domain containing adaptor protein (TIRAP) and TIR domain containing adaptor inducing interferon (IFN)-β (TRIF) that eventually leads to induction of proinflammatory cytokines and mitogen-activated protein kinases (MAPKs). Lipopolysaccharide (LPS) activates the Gram-negative bacterial receptor TLR4 and polyinosinic:polycytidylic acid (polyI:C) activates the viral receptor TLR3. TLR4 signaling involves TIRAP and TRIF, whereas TRIF is the only adaptor protein involved in the TLR3 pathway. We have shown previously that LPS-mediated downregulation of DMETs is independent of TIRAP. To determine the role of TRIF, we treated TRIF(+/+) and TRIF(-/-) mice with LPS or polyI:C. LPS downregulated (∼40%-60%) Cyp3a11, Cyp2a4, Ugt1a1, Mrp2 mRNA levels, whereas polyI:C downregulated (∼30%-60%) Cyp3a11, Cyp2a4, Cyp1a2, Cyp2b10, Ugt1a1, Mrp2, and Mrp3 mRNA levels in TRIF(+/+) mice. This downregulation was not attenuated in TRIF(-/-) mice. Induction of cytokines by LPS was observed in both TRIF(+/+) and TRIF(-/-) mice. Cytokine induction was delayed in polyI:C-treated TRIF(-/-) mice, indicating that multiple mechanisms mediating polyI:C signaling exist. To assess the role of MAPKs, primary hepatocytes were pretreated with specific inhibitors before treatment with LPS/polyI:C. We found that only the c-jun-N-terminal kinase (JNK) inhibitor attenuated the down-regulation of DMETs. These results show that TRIF-independent pathways can be involved in the downregulation of DMETs through TLR4 and 3. JNK-dependent mechanisms likely mediate this downregulation.

Changes in the pharmacokinetics of glibenclamide in rats with streptozotocin-induced diabetes mellitus

The aim of this study was to investigate the pharmacokinetics of glibenclamide (Gli) administrated orally and intravenously to normal and diabetic rats. The AUC(0–720min) of orally administered Gli in diabetic rats (321.24mgmin/L) was greater than that (57.752mgmin/L) in normal rats. CL (0.019L/min/kg) was significantly slower than that (0.092L/min/kg) of normal rats. The AUC(0–480min) of intravenous Gli in diabetic rats (1528.280mgmin/L) also was significantly greater than that (509.523mgmin/L) in normal rats, and CL was decreased approximately 3-fold. No significant difference in intestinal absorption of Gli was observed between normal and diabetic rats as determined by in situ single-pass intestinal perfusion. The clearance of Diclofenac (a substrate of CYP2C9) was determined to evaluate changes in hepatic drug-metabolizing enzyme activity in rats. The CL in diabetic rats was significantly lower (42.43% decrease) than that in normal rats. Hepatic protein expression of CYP2C9 was measured using Western blot analysis; compared with normal rats, the hepatic protein expression of CYP2A9 was decreased in diabetic rats. Therefore, the slower clearance of Gli in diabetic rats can be attributed primarily to the lower expression of hepatic CYP2C9.

Effect of the triazolobenzodiazepine estazolam on hepatic drug-metabolizing enzyme activity in rats.

Oral doses of the sedative/hypnotic estazolam (500 mg kg-1 day-1) to rats for 21 days caused statistically significant increases in liver weight, ascorbate excretion, cytochrome P-450 concentrations, and in aniline hydroxylase, ethylmorphine N-demethylase and glutathione S-transferase activities, as did approximately equivalent doses of flurazepam hydrochloride. Histologically, the centrilobular hepatocytes were enlarged. Some of these parameters were also increased after doses of estazolam of 100 mg kg-1 day-1, but not after 5 mg kg-1 day-1, which is about 50-fold greater than a clinical dose. Estazolam was a much less potent enzyme inducer than phenobarbitone under the conditions of these studies.

Time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic drug-metabolizing enzyme activity in rats.

The time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic cytochrome P450-dependent drug-metabolizing capacity (cytochrome P450 and b5 content, activity of aminopyrine N-demethylase, p-nitroanisole O-demethylase, aniline hydroxylase and benzphetamine N-demethylase) and on the pharmacokinetics of antipyrine have been determined in rats. Measurement of enzyme activity and antipyrine (after intravenous injection of 20 mg kg(-1)) were performed 2, 24 and 96 h after a single intraperitoneal injection of endotoxin (1 mg kg(-1)) and after repeated doses (once daily for 4 days). The contribution of tumour necrosis factor alpha (TNFalpha) to the endotoxin-induced changes was also examined in rats pretreated with granulocyte colony-stimulating factor (G-CSF). The systemic clearance of antipyrine and the activity of hepatic cytochrome P450-dependent drug-metabolizing enzymes were dramatically reduced 24 h after a single injection of endotoxin, but had returned to control levels by 96h. The magnitudes of these decreases in these measurements after repeated doses of endotoxin were similar to those seen 24h after the single dose. The systemic clearance of antipyrine correlated significantly with cytochrome P450 content and aminopyrine N-demethylase activity. In histopathological experiments, moderate hypertrophy of Kupffer cells was observed, with no evidence of severe liver-tissue damage. G-CSF pretreatment suppressed the increased plasma concentrations of TNFalpha produced 2 h after single endotoxin injection, but did not eliminate the endotoxin-induced decrease in the systemic clearance of antipyrine, suggesting that TNFalpha is not the sole component responsible for the reduction of cytochrome P450-mediated drug-metabolizing enzyme activity. These results provide evidence that a single intraperitoneal injection of 1.0 mgkg(-1)K. pneumoniae endotoxin in rats reduces hepatic P450 and b5 levels, and reduces the activity of various cytochrome P450-mediated drug-metabolizing enzymes without causing severe liver-tissue damage. This suggests that the effect of endotoxin on hepatic cytochrome P450-mediated drug-metabolizing isozymes is non-selective.

Hormonal Regulation of Hepatic Drug-Metabolizing Enzyme Activity During Adolescence

Activities of drug-metabolizing enzymes (DMEs) are known to change throughout the course of physical and sexual maturation, with the greatest variability noted during infancy and adolescence. The mechanisms responsible for developmental regulation of DME are currently unknown. However, the hormonal changes associated with puberty/adolescence provide a theoretical framework for understanding the biochemical regulation of DME activity during growth and maturation. Important information regarding potential influences of growth and sex hormones can also be extrapolated from studies that evaluate changes in activities of DMEs occurring as a consequence of physiological, pathological, and/or pharmacological hormonal fluctuations. Collectively, current data support the hypothesis that isoform-specific alterations in DME activity during adolescence are mediated by sex and/or growth hormones. Characterization of the underlying biochemical alterations responsible for developmental changes in DME activity will require additional studies in which relationships between DMEs and important hormonal axes are evaluated during the course of pubertal development.

Effect of the organophosphorus pesticide diazinon on glucose tolerance in type 2 diabetic rats

We have reported that the toxicity of the organophosphorus pesticide diazinon (DZN) and its metabolites is increased in streptozotocin-induced diabetic rats (type 1 diabetic rats). In the present study, we have investigated the effect of DZN on glucose tolerance in genetic type 2 diabetic rats, Goto-Kakizaki (GK) rats. Oral glucose tolerance test (OGTT) (2 g/(5 ml kg)) was assessed before, and 1 and 2 weeks after intraperitoneal injection of DZN (6.5 mg/kg) in Wistar and GK rats. DZN significantly increased the levels of glucose in plasma at designated blood sampling points in GK rats. The activity of hepatic drug-metabolizing enzymes and expression of hepatic cytochrome P450 (CYP) 1A2, CYP3A2 and CYP2D1, which oxidize DZN to DZN-oxon, a potent ChE inhibitor, were measured before DZN injection. There were no significant differences in the activity and expression of CYPs between both rat groups, indicating that the ability of metabolic activation might be almost the same in Wistar and GK rats. DZN dramatically decreased the activity of cholinesterase (ChE) in plasma by approximately 40% in both Wistar and GK rats. However, no significant differences in the activity of ChE in plasma were observed between Wistar and GK rats for 5 days after DZN injection. No massive necrotic and apoptotic areas, leukocyte infiltration and immunoreactive insulin-positive cells (β-cells) were observed in pancreas 2 weeks after DZN injection. Moreover, DZN might not affect plasma insulin levels in Wistar and GK rats. These results suggest that DZN deteriorates the glucose tolerance in GK rats. It is unlikely that this phenomenon is due to differences in ChE activity and/or DZN-oxon production levels between Wistar and GK rats.

2-(2’-Hydroxy-3’,5’-di-tert-butylphenyl)benzotriazole (HDBB)の毒性 ―血中濃度及び肝薬物代謝酵素活性に対する影響

2-(2’-Hydroxy-3’,5’-di-tert-butylphenyl)benzotriazole (HDBB)の毒性 ―血中濃度及び肝薬物代謝酵素活性に対する影響

Low Folate Status Enhanced Benzene-Induced Cytogenetic Damage in Bone Marrow of Mice: A Relationship Between Dietary Intake and Tissue Levels of Folate

We examined the protective effect of dietary folate on benzene-induced chromosomal damage in bone marrow of mice regarding folate levels in diet and tissue. Male mice were fed either a deficient, basal, or high folate diet (0, 2, or 8 mg/kg diet, respectively) for 4 wk followed by a single dose of benzene. Plasma folate levels corresponded to those of dietary intake. Meanwhile, bone marrow, erythrocyte, and liver folate were decreased to 40% in the deficient group and almost saturated in the high group. Plasma homocysteine levels negatively correlated to levels of tissue folate. Chromosomal damage, evaluated by micronucleus assay, was not affected by folate status alone but was markedly enhanced by benzene, particularly in the deficient group (P < 0.05 vs. the basal and high groups). The activities of hepatic drug-metabolizing enzymes did not enhance benzene metabolism in the deficient groups, indicating that enhanced chromosomal damage was solely due to the low folate status. These results suggest that a low folate status can increase the risk of benzene-induced chromosomal damage in bone marrow, but excess folate intake does not enhance protection, as it is saturated in tissue.

Toxicity of diazinon and its metabolites increases in diabetic rats

The effect of diazinon (DZN) on the activities of cholinesterase (ChE) in plasma and acetylcholinesterase (AChE) in erythrocyte and brain was investigated in normal and streptozotocin-induced diabetic rats. Hepatic drug-metabolizing enzyme activity was also estimated by measuring the systemic clearance of antipyrine, and the expression of hepatic cytochrome P450 (CYP) 3A2 and CYP1A2, which is closely related to the metabolism from DZN to DZN-oxon, a strong inhibitor of both ChE and AChE. No significant differences in the activities of ChE in plasma and AChE in erythrocyte were observed between normal and diabetic rats. Treatment with DZN significantly decreased these activities in diabetic rats more than in normal rats 6 h after injection (6.5 mg/kg). Treatment with DZN significantly decreased the activity of AChE in brain of diabetic rats than normal rats 3 h after injection (65 mg/kg), although no significant difference in the activity was found between normal and diabetic rats. The urinary recovery of diethylphosphate (DEP), a metabolite of DZN-oxon, was significantly increased in diabetic rats, but that of diethylthiophosphate (DETP), a metabolite of DZN, was unchanged. Significant increases in the systemic clearance of antipyrine and protein levels of hepatic CYP1A2, not CYP3A2, were observed in diabetic rats. These results suggest the possibility that a metabolite of DZN, DZN-oxon, causes higher toxicity in diabetic rats due to the enhancement of hepatic CYP1A2-mediated metabolism of DZN.

LBOVI-B-4Recombinant human growth hormone (rhGH) has no effect on activities of hepatic cytochrome P4501A2 (CYP1A2), N-acetyltransferase 2 (NAT2), xanthine oxidase (XO) or cytochrome P4502D6 in children with idiopathic growth hormone (GH) deficiency

BACKGROUND Growth hormone (GH) is a known modulator of hepatic drug metabolizing enzyme activity. However, previous investigations have used polyfunctional enzyme substrates and the effect on GH on individual hepatic enzyme isoforms remains unknown. This investigation assessed the activities of CYP1A2, NAT-2, XO and CYP2D6 in children receiving GH replacement using the specific probe substrates caffeine and dextromethorphan (DM). METHODS Pre-pubertal children (4–14y, n=12) with idiopathic GH deficiency received DM (0.5mg/kg) and caffeine (11.5mg) prior to and 3 and 6 months following initiation of rhGH therapy. Urine was collected for 8 hours and analyzed via HPLC. Blood was also obtained for CYP2D6 genotyping. The following molar ratios and 95% CI estimation for the mean Δ were calculated: AFMU+1X+1U/17U(CYP1A2), AFMU/AFMU+1X+1U(NAT2), 1U/1U+1X(XO), DM/DX(CYP2D6). Mean baseline ratios were also compared to those obtained at 3 and 6 months using the Student's t-test. RESULTS Mean (95% CI) ratio and Δ values in NAT-2 slow acetylators and CYP2D6 EMs were as follows: (See Table) Ratio Baseline 3 months p Δ 3 months 6 months p Δ 6 months CYP1A2 (n) 5.1 (4.7, 5.6) (11) 5.6 (4.6, 6.6) (11) 0.42 0.47 (−0.33, 1.27) 5.9 (3.9, 7.9) (9) 0.37 0.97 (−0.80, 2.7) NAT2 (n) 0.07 (0.03, 0.11) (11) 0.06 (0.03, 0.10) (11) 0.81 −0.01 (−0.02, 0.01) 0.07 (0.02, 0.12) (9) 0.98 0.07 (0.02, 0.12) XO (n) 0.69 (0.65, 0.73) (11) 0.71 (0.67, 0.75) (11) 0.52 0.02 (−0.02, 0.06) 0.72 (0.66, 0.78) (9) 0.33 0.04 (−0.03, 0.01) CYP2D6 (n) 0.015 (−0.008, 0.037) (10) 0.015 (−0.003, 0.033) (10) 0.97 0.00 (−0.01, 0.01) 0.019 (0.000, 0.039) (8) 0.91 0.002 (−0.03, 0.03) CONCLUSION rhGH does not appear to alter the activities of hepatic CYP1A2, NAT-2, XO or CYP2D6 in children with idiopathic GH deficiency. Altered clearance of drugs in this patient population are likely isoform-specific and thus apparent for selected compounds that are substrates for enzymes other than CYP1A2, NAT-2, XO or CYP2D6. Clinical Pharmacology & Therapeutics (2005) 79, P84–P84; doi: 10.1016/j.clpt.2005.12.300

Hepatic CYP Isoforms and Drug-Metabolizing Enzyme Activities in Broiler Chicks

Day-old chicks were raised for four - six weeks in pens using different bedding materials (wire, paper, corn cobs, hardwood, rice hulls, cedar, and pine) to determine if these beddings have any effect on hepatic drug metabolizing enzyme activities, cytochrome P450 isoforms, and the disposition of enrofloxacin, a drug previously approved for use in chickens. Cytochrome P450 (CYP) isoforms from the major P450 isoform families (1A, 2A, 2B, 2C, 2D, 2E, 3A, and 4A) and their corresponding hepatic drug metabolizing enzyme activities were measured in subcellular fractions obtained from 4-and 5-week-old birds. Five week- old birds were treated with medicated water containing Baytril at 50 ppm enrofloxacin for five consecutive days and then withdrawn for two days prior to sacrifice. There were no significant differences in P450 - mediated reactions or levels of CYP isoforms between any of the different test groups. The marker residue for enrofloxacin was barely detectable in the marker tissue (breast muscle) of the treated birds. The major metabolites of enrofloxacin, namely, ciprofloxacin, desethylenyl-enrofloxacin, and desethylenyl ciprofloxacin, were detectable in extracts of liver homogenates of the treated birds. However, the levels were below the level of quantification.

Endotoxin from various gram-negative bacteria has differential effects on function of hepatic cytochrome P450 and drug transporters

The differential effects of endotoxin derived from Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli on hepatic cytochrome P450 (CYP)-dependent drug-metabolizing enzyme activity and on the expression of hepatic CYP3A2, CYP2C11, P-glycoprotein and multidrug resistance-associated protein 2 (Mrp2) was investigated in rats. Endotoxin from all three different pathogens significantly decreased the systemic clearance of antipyrine, reflecting reduced hepatic drug-metabolizing enzyme activity 24 h after intravenous injection (0.5 mg/kg). The degree of the decreased systemic clearance by P. aeruginosa endotoxin was smaller than that by both K. pneumoniae and E. coli endotoxin. Western blot analysis revealed that the down-regulation of CYP3A2 by K. pneumoniae and E. coli endotoxin was greater than that by P. aeruginosa endotoxin. However, the down-regulation of CYP2C11 by all three different endotoxin was almost the same. Both K. pneumoniae and P. aeruginosa endotoxin significantly down-regulated P-glycoprotein, but did not down-regulate Mrp2. E. coli endotoxin had no effect on the expression of either P-glycoprotein or Mrp2, probably due to the low dose used. The down-regulation of CYP3A2 by endotoxin was parallel to the decreased systemic clearance of antipyrine. These results suggest that endotoxin has a differential effect on the hepatic CYP-mediated drug-metabolizing enzyme activity, and on the protein levels of hepatic CYP3A2 and P-glycoprotein, probably due to bacterial source-differences in the production of some proinflammatory mediators. Endotoxin appears to regulate coordinately CYP3A2, CYP2C11 and P-glycoprotein, but not Mrp2.