Loganin Ameliorates Acute Kidney Injury and Restores Tofacitinib Metabolism in Rats: Implications for Renal Protection and Drug Interaction.

Tofacitinib, a Janus kinase (JAK) inhibitor used to treat rheumatoid arthritis, is metabolized through hepatic cytochrome P450 (CYP), specifically CYP3A1/2 and CYP2C11. Prolonged administration of rheumatoid arthritis medications is generally associated with an increased risk of renal toxicity. Loganin (LGN), an iridoid glycoside, has hepatorenal regenerative properties. This study investigates the potential of LGN to mitigate acute kidney injury (AKI) and its effects on the pharmacokinetics of tofacitinib in rats with cisplatin-induced AKI. Both intravenous and oral administration of tofacitinib to AKI rats significantly increased the area under the plasma concentration-time curve from time 0 to infinity (AUC) compared with control (CON) rats, an increase attributed to the decelerated non-renal clearance (CLNR) and renal clearance (CLR) of tofacitinib. Administration of LGN to AKI rats, however, protected kidneys from severe impairment, restoring the pharmacokinetic parameters (AUC, CLNR, and CLR) of tofacitinib to those observed in untreated CON rats, with partial recovery of kidney function, as evidenced by an increase in creatinine clearance (CLCR). Possible interactions between drugs and natural components should be considered, especially when co-administering both a drug and a natural extract containing LGN or iridoid glycosides to patients with kidney injury.

Effects of Hyperlipidemia on the Pharmacokinetics of Tofacitinib, a JAK 1/3 Inhibitor, in Rats.

Tofacitinib, an inhibitor of Janus kinases (JAKs) 1 and 3, has been shown to be effective in the treatment of rheumatoid arthritis. The incidence of hyperlipidemia has been found to be higher in patients with rheumatoid arthritis. The present study therefore investigated the pharmacokinetics of tofacitinib after its intravenous (10 mg/kg) or oral (20 mg/kg) administration in poloxamer-407-induced hyperlipidemic (PHL) rats. The area under the plasma concentration-time curve from zero to infinity (AUC0-∞) after intravenous administration of tofacitinib was 73.5% higher in PHL than in control rats, owing to slower time-averaged nonrenal clearance (CLNR) in the former. Evaluation of in vitro metabolism showed that the intrinsic clearance (CLint) of tofacitinib was 38.6% lower in PHL than in control rats, owing to the decreased protein expression of hepatic cytochrome P450 (CYP) 3A1/2 and CYP2C11 in PHL rats. Similar results were observed in PHL rats after oral administration of tofacitinib. These results were likely due to the decreased CLNR, CLint, and P-glycoprotein (P-gp) expression in the intestines of PHL compared to control rats. Overall, these findings indicated that hyperlipidemia slowed the metabolism of tofacitinib, increasing its plasma concentrations, and that this reduced metabolism was due to alterations in expression of the proteins CYP3A1/2, CYP2C11, and P-gp in the liver and/or intestines of PHL rats.

Effects of Isosakuranetin on Pharmacokinetic Changes of Tofacitinib in Rats with N-Dimethylnitrosamine-Induced Liver Cirrhosis.

Tofacitinib, a Janus kinase 1 and 3 inhibitor, is used to treat rheumatoid arthritis. It is mainly metabolized by the cytochromes p450 (CYP) 3A1/2 and CYP2C11 in the liver. Chronic inflammation eventually leads to cirrhosis in patients with rheumatoid arthritis. Isosakuranetin (ISN), a component of Citrus aurantium L., has hepatoprotective effects in rats. This study was performed to determine the effects of ISN on the pharmacokinetics of tofacitinib in rats with N-dimethylnitrosamine-induced liver cirrhosis (LC). After intravenous administration of 10 mg/kg tofacitinib to control (CON), LC, and LC treated with ISN (LC-ISN) rats, the total area under the plasma concentration-time curves (AUC) from time zero to infinity increased by 158% in LC rats compared to those in CON rats; however, the AUC of LC-ISN rats decreased by 35.1% compared to that of LC rat. Similar patterns of AUC changes were observed in the LC and LC-ISN rats after oral administration of 20 mg/kg tofacitinib. These results can be attributed to decreased non-renal clearance (CLNR) and intestinal intrinsic clearance (CLint) in the LC rats and increased intestinal and hepatic CLint in the LC-ISN rats. Our findings imply that ISN treatment in LC rats restored the decrease in either CLNR or CLint, or both, through increased hepatic and intestinal expression of CYP3A1/2 and CYP2C11, which is regulated by the induction of pregnane X receptor (PXR) and constitutive androstane receptor (CAR).

Effects of Dextran Sulfate Sodium-Induced Ulcerative Colitis on the Disposition of Tofacitinib in Rats.

Tofacitinib, a Janus kinase 1 and 3 inhibitor, is mainly metabolized by CYP3A1/2 and CYP2C11 in the liver. The drug has been approved for the chronic treatment of severe ulcerative colitis, a chronic inflammatory bowel disease. This study investigated the pharmacokinetics of tofacitinib in rats with dextran sulfate sodium (DSS)-induced ulcerative colitis. After 1-min of intravenous infusion of tofacitinib (10 mg/kg), the area under the plasma concentration-time curves from time zero to time infinity (AUC) of tofacitinib significantly increased by 92.3%. The time-averaged total body clearance decreased significantly by 47.7% in DSS rats compared with control rats. After the oral administration of tofacitinib (20 mg/kg), the AUC increased by 85.5% in DSS rats. These results could be due to decreased intrinsic clearance of the drug caused by the reduction of CYP3A1/2 and CYP2C11 in the liver and intestine of DSS rats. In conclusion, ulcerative colitis inhibited CYP3A1/2 and CYP2C11 in the liver and intestines of DSS rats and slowed the metabolism of tofacitinib, resulting in increased plasma concentrations of tofacitinib in DSS rats.

Inhibition of imrecoxib on mRNA and protein expression of CYP2C11 enzyme in rats.

To evaluate the effect of imrecoxib on CYP2C11 enzyme activity, mRNA, and protein expression, a UPLC method was established. Tolbutamide was selected as the CYP2C11 enzyme-specific probe drug and incubated with imrecoxib in rat liver microsomes. The yield of 4-hydroxytolbutamide was measured using UPLC to investigate the effect of imrecoxib on CYP2C11 enzyme activity. Imrecoxib (10 mg/kg) was administered intragastrically twice daily. After 1, 7, and 14 days of administration, the liver tissues were analyzed. The expression of CYP2C11 enzyme mRNA was determined using reverse transcription-polymerase chain reaction, and its protein expression was determined using Western blot analysis. Imrecoxib concentration was inversely proportional to the production of 4-hydroxytolbutamide in liver microsomes. Imrecoxib demonstrated a dose-dependent inhibitory effect on CYP2C11 activity with IC50 = 74.77 µM. After administration, reverse transcription-polymerase chain reaction showed CYP2C11 enzyme mRNA expressions were 65% (P < 0.05), 35%, and 34% of the control group, respectively (P < 0.01). Western blot analysis showed CYP2C11 enzyme protein expressions were 80, 37, and 34% of the control group, respectively (P < 0.01). Imrecoxib can reduce mRNA and protein expression of CYP2C11 enzyme in rat liver and inhibit the activity of CYP2C11 enzyme in a dose-dependent manner. However, it does not produce clinically significant drug interactions.

Modulatory effects of Benjakul extract on rat hepatic cytochrome P450 enzymes.

Benjakul, a traditional Thai formulation, has been used as a carminative and adaptogenic drug. It consists of five plants, Piper chaba Hunter, Piper sarmentosum Roxb., Piper interruptum Opiz., Plumbago indica Linn., and Zingiber officinale Roscoe, in equal ratios. Some individual herbs present in Benjakul were reported to modulate cytochrome P450 (CYP) enzymes. This study aimed to investigate the effects of Benjakul extract on the activities and mRNA expression levels of hepatic CYP2C11 and CYP3A1 in rats. Adult male rats were orally administered 200, 400, or 600 mg/kg BW Benjakul extract for 28 days. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN) and creatinine levels were assayed. CYP2C11 and CYP3A1 activities were analyzed using cytochrome P450 assay kits. The mRNA expression of CYP2C11 and CYP3A1 was measured using a quantitative real-time PCR assay. Benjakul treatment significantly increased the serum ALT and BUN levels. At doses of 200, 400, and 600 mg/kg BW, Benjakul treatment increased hepatic CYP3A1 activity and CYP3A1 mRNA expression. CYP2C11 mRNA expression was unchanged by treatment with Benjakul extract; however, treatment with the high and middle doses of Benjakul extract increased CYP2C11 activity. Treament with Benjakul extract induced CYP2C11 and CYP3A1 activity in rats. Concurrent use of Benjakul with conventional drugs should be considered to potentially induce herb-drug interactions.

Acute Peripheral Inflammation Increases Plasma Concentration of Hypoglycemic Agent Nateglinide with Decreased Hepatic Drug-Metabolizing Activity in Rats.

The effects of inflammation on hypoglycemic agents were evaluated in male rats with acute peripheral inflammation (API). Nateglinide (NTG) was utilized as a model compound, since it is a hepatically-metabolized compound and its metabolism is mainly mediated by CYP 2C11 enzyme. In the experiments, rats were subjected to carrageenan injection into their hind paws for API induction, and the plasma concentration profiles of NTG were then examined. In addition, pooled liver microsomes were prepared from control and API rats, and the hepatic drug-metabolizing activity toward NTG and the hepatic expression of CYP2C11 protein were evaluated. It was shown that the plasma concentration of NTG following its intravenous administration decreases at a slower rate in API rats than that in control rats. It was also indicated in the incubation study with the liver microsomes that the hepatic drug-metabolizing activity toward NTG decreases in API rats. Additionally, it was revealed in Western immunoblotting that the hepatic expression of CYP2C11 protein decreases in API rats. These findings suggest that inflammation occurring in peripheral tissues brings about a decrease in hepatic NTG metabolism by suppressing the hepatic expression of CYP2C11 protein, causing an alteration of the plasma concentration profile of NTG with its impaired elimination.

Neuroinflammation is able to downregulate cytochrome P450 epoxygenases 2J3 and 2C11 in the rat brain.

Cytochrome P450 (CYP) epoxygenases have been considered the main producers of epoxyeicosatrienoic acids (EETs) through the oxidation of arachidonic acid (AA). EETs display various biological properties, notably their powerful anti-inflammatory activities. In the brain, EETs have proven to be neuroprotective and to improve neuroinflammation. However, it is known that inflammation could modify CYP expression. We have previously reported that an inflammatory process in astrocytes is able to down-regulate CYP2J3 and CYP2C11 mRNA, protein levels, and activity (Navarro-Mabarak et al., 2019). In this work, we evaluated the effect of neuroinflammation in protein expression of CYP epoxygenases in the brain. Neuroinflammation was induced by the intraperitoneal administration of LPS (1 mg/kg) to male Wistar rats and was corroborated by IL-6, GFAP, and Iba-1 protein levels in the cortex over time. CYP2J3 and CYP2C11 protein levels were also evaluated in the cortex after 6, 12, 24, 48, and 72 h of LPS treatment. Our results show for the first time that neuroinflammation is able to downregulate CYP2J3 and CYP2C11 protein expression in the brain cortex.

Exploring the biotransformation of N-(2-hydroxyphenyl)-2-propylpentanamide (an aryl valproic acid derivative) by CYP2C11, using in silico predictions and in vitro studies.

OBJECTIVES: N-(2-hydroxyphenyl)-2-propylpentanamide (HO-AAVPA), a derivative of valproic acid (VPA), has been proposed as a potential anticancer agent due to its improved antiproliferative effects in some cancer cell lines. Although there is evidence that VPA is metabolized by cytochrome P450 2C11 rat isoform, HO-AAVPA CYP-mediated metabolism has not yet been fully explored. Therefore, in this work, the biotransformation of HO-AAVPA by CYP2C11 was investigated. METHODS: Kinetic parameters and spectral interaction between HO-AAVPA and CYP were evaluated using rat liver microsomes. The participation of CYP2C11 in metabolism of HO-AAVPA was confirmed by cimetidine (CIM) inhibition assay. Docking and molecular dynamics simulations coupled to MMGBSA methods were used in theoretical study. KEY FINDINGS: HO-AAVPA is metabolized by CYP enzymes (KM  = 38.94 µm), yielding a hydroxylated metabolite according to its HPLC retention time (5.4 min) and MS analysis (252.2 m/z). In addition, CIM inhibition in rat liver microsomes (Ki  = 59.23 µm) confirmed that CYP2C11 is mainly involved in HO-AAVPA metabolism. Furthermore, HO-AAVPA interacts with CYP2C11 as a type I ligand. HO-AAVPA is stabilized at the CYP2C11 ligand recognition site through a map of interactions similar to other typical CYP2C11 substrates. CONCLUSION: Therefore, rat liver CYP2C11 isoform is able to metabolize HO-AAVPA.

CYP2C11 played a significant role in down-regulating rat blood pressure under the challenge of a high-salt diet.

BACKGROUND: Arachidonic acid (AA) is oxidized by cytochrome P450s (CYPs) to form epoxyeicosatrienoic acids (EETs), compounds that modulate ion transport, gene expression, and vasorelaxation. Both CYP2Cs and CYP2Js are involved in kidney EET epoxidation. METHODS: In this study, we used a CYP2C11-null rat model to explore the in vivo effects of CYP2C11 on vasorelaxation. For 2 months, CYP2C11-null and wild-type (WT) Sprague-Dawley rats were either fed normal lab (0.3% (w/w) sodium chloride) or high-salt (8% (w/w) sodium chloride) diets. Subsequently, an invasive method was used to determine blood pressure. Next, western blots, quantitative PCR, and immunohistochemistry were used to determine renal expression of CYPs involved in AA metabolism. RESULTS: Among CYP2C11-null rats, a high-salt diet (females: 156.79 ± 15.89 mm Hg, males: 130.25 ± 16.76 mm Hg, n = 10) resulted in significantly higher blood pressure than a normal diet (females: 118.05 ± 8.43 mm Hg, P < 0.01; males: 115.15 ± 11.45 mm Hg, P < 0.05, n = 10). Compared with WT rats under the high-salt diet, western blots showed that CYP2C11-null rats had higher renal expression of CYP2J2 and CYP4A. This was consistent with the results of immunohistochemistry and the qPCR, respectively. The two rat strains did not differ in the renal expression of CYP2C23 or CYP2C24. CONCLUSION: Our findings suggested that CYP2C11 plays an important role in lowering blood pressure under the challenge of a high-salt diet.

Effects of CYP2C11 gene knockout on the pharmacokinetics and pharmacodynamics of warfarin in rats.

1. CYP2C11 is the most abundant isoform of cytochrome P450s (CYPs) in male rats and is considered the main enzyme for warfarin metabolism. 2. To further access the in vivo function of CYP2C11 in warfarin metabolism and efficacy, a CYP2C11-null rat model was used to study warfarin metabolism with both in vitro and in vivo approaches. Prothrombin time (PT) of warfarin was also determined. 3. The maximum rate of metabolism (Vmax) and intrinsic clearance (CLint) of liver microsomes from CYP2C11-null males were reduced by 37 and 64%, respectively, compared to those in Sprague Dawley (S-D) rats. The Km of liver microsomes from CYP2C11-null males was increased by 73% compared to that of S-D rats. The time to reach the maximum plasma concentration (Tmax) of warfarin in CYP2C11-null males was significantly delayed compared to that in S-D males, and the CL rate was also reduced. The PT of CYP2C11-null rats was moderately longer than that of S-D rats. 4. In conclusion, the clearance rate of warfarin was mildly decreased and its anticoagulant effect was moderately increased in male rats following CYP2C11 gene knockout. CYP2C11 played a certain role in the clearance and efficacy of warfarin, while it did not seem to be essential.

Effects of shuanghuanglian injection on the activities of CYP1A2, 2C11, 2D1 and 3A1/2 in rats in vivo and in vitro.

Shuanghuanglian Injection (SHLI), one of the most popular herbal prescription in China, has been commonly used to treat pneumonia, tonsillitis, and other respiratory diseases caused by bacterium and virus. This study is to investigate the effects of SHLI on the activities of Cytochrome P450 (CYP) 1A2, 2C11, 2D1 and 3A1/2 in rats. Sixteen rats were randomly divided into two groups (SHLI-treated and blank control). They were administered SHLI or physiological saline for consecutive seven days. On day eight, 16 animals were administrated cocktail drugs as probe substrates of the four CYP in vivo. In addition, other four probe drugs were added, respectively, into incubation systems of rat liver microsomes (RLM) to assess the effects of SHLI on the four CYP isoforms in vitro. SHLI exhibited an inductive effect on CYP2C11 in vivo by decreasing Cmax, t1/2 and AUC0-∞ of tolbutamide, while the main pharmacokinetic parameters of caffeine, metoprolol and dapsone have no significant changes. In vitro study, SHLI showed no significant effects on the activities of CYP1A2, 2D1 and 3A1/2, but increasing the metabolism of tolbutamide in RLM. SHLI induced the activities of CYP2C11, but had no significant effects on the activities of CYP1A2, CYP2D1 and CYP3A1/2 in rats.

Growth hormone: a newly identified developmental organizer.

The sexually dimorphic expression of cytochromes P450 (CYP) drug-metabolizing enzymes has been reported in all species examined. These sex differences are only expressed during adulthood and are solely regulated by sex differences in circulating growth hormone (GH) profiles. Once established, however, the different male- and female-dependent CYP isoform profiles are permanent and immutable, suggesting that adult CYP expression requires imprinting. As the hormone that regulates an adult function is likely the same hormone that imprints the function, we selectively blocked GH secretion in some newborn male rats, whereas others received concurrent physiologic replacement of rat GH. The results demonstrate that adult male GH activation of the signal transduction pathway regulating expression of the principal CYP2C11 isoform is obligatorily dependent on perinatal GH imprinting, without which CYP2C11 and drug metabolism would be permanently and profoundly suppressed. As there are other adult metabolic functions also regulated by GH, pediatric drug therapy known to disrupt GH secretion could unintentionally impair adult health.

In vitro and in vivo evaluation of cucurbitacin E on rat hepatic CYP2C11 expression and activity using LC-MS/MS.

This study explored the effects of cucurbitacin E (CuE), a bioactive compound from Cucurbitaceae, on the metabolism/pharmacokinetic of tolbutamide, a model CYP2C9/11 probe substrate, and hepatic CYP2C11 expression in rats. Liquid chromatography-(tandem) mass spectrometry (LC-MS/MS) assay was used to detect tolbutamide as well as 4-hydroxytolbutamide, and then successfully applied to the pharmacokinetic study of tolbutamide in rats. The effect of CuE on CYP2C11 expression was determined by western blot. CuE (1.25-100 µmol L-1) competitively inhibited tolbutamide 4-hydroxylation (CYP2C11) activity only in concentration-dependent manner with a K i value of 55.5 µmol L-1 in vitro. In whole animal studies, no significant difference in metabolism/pharmacokinetic of tolbutamide was found for the single pretreatment groups. In contrast, multiple pretreatments of CuE (200 µg kg-1 d-1, 3 d, i.p.) significantly decreased tolbutamide clearance (CL) by 25% and prolonged plasma half-time (T 1/2) by 37%. Moreover, CuE treatment (50-200 µg kg-1 d-1, i.p.) for 3 d did not affect CYP2C11 expression. These findings demonstrated that CuE competitively inhibited the metabolism of CYP2C11 substrates but had no effect on rat CYP2C11 expression. This study may provide a useful reference for the reasonable and safe use of herbal or natural products containing CuE to avoid unnecessary drug-drug interactions.

Effects of phillyrin and forsythoside A on rat cytochrome P450 activities in vivo and in vitro.

1. Phillyrin and forsythoside A are two important active ingredients in Forsythia suspensa. However, the effects of phillyrin and forsythoside A on the activities of cytochrome P450 (CYP450) remain unclear. 2. This study aimed to investigate the effects of phillyrin and forsythoside A on the activities of CYP1A2, CYP2C11, CYP2D1 and CYP3A1/2 by cocktail probe drugs in rats both in vivo and in vitro. 3. Many pharmacokinetic parameters of caffeine and metoprolol in phillyrin pretreatment group, caffeine and tolbutamide in forsythoside A pretreatment group were affected significantly. In rat liver microsomal incubation system, the concentrations of acetaminophen and dextrophan in the phillyrin pretreatment group are higher than blank control group by 207.69% and 125.00%, however, the concentrations of 4-hydroxytolbutamide and 6ß-hydroxytestosterone were not significantly altered. The concentrations of acetaminophen and 4-hydroxytolbutamide in the forsythoside A pretreatment group are higher than blank control group by 223.07% and 154.16%, whereas the concentrations of dextrophan and 6ß-hydroxytestosterone were not significantly altered. 4. These results indicated that Phillyrin had potential inductive effects on rat CYP1A2 and CYP2D1 activities, without affecting CYP2C11 and CYP3A1/2 activities. Moreover, forsythoside A had inductive effects on the activities of CYP1A2 and CYP2C11, without affecting CYP2D1 and CYP3A1/2 activities.

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate.

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

Effects of Guanxinning injection on rat cytochrome P450 isoforms activities in vivo and in vitro.

1. We aimed to investigate the regulatory effects of Guanxinning injection (GXNI) on activities of cytochrome P1A2 (CYP1A2), CYP2C11, CYP2D1 and CYP3A1/2 by probe drugs in rats in vivo and in vitro. 2. GXNI-treated and blank control groups were administered GXNI and physiological saline by caudal vein for 14 days consecutively, then they were given the probe drugs of caffeine (10 mg/kg), tolbutamide (10 mg/kg), metoprolol (20 mg/kg) and dapsone (10 mg/kg) by intraperitoneal injection. The blood samples were collected at different times for ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis. Changes of the pharmacokinetics parameters between the GXNI-treated and the blank control groups were used to evaluate the effects of GXNI on the four CYP450 isoforms in rats in vivo. After blood collection, the livers of rats were taken and made microsomes for in vitro tests. The relevant metabolites of phenacetin, tolbutamide, dextromethorphan and testosterone were analyzed quantitatively by high-performance liquid chromatography (HPLC) after microsome incubation. The statistical differences between the two groups were observed to detect the effects of GXNI on the four CYP450 isoforms in rats in vitro. 3. The in vivo and in vitro results demonstrated that GXNI could induce CYP1A2 activity in rats, but had no significant effects on CYP2C11, CYP2D1 and CYP3A1/2.

Pharmacokinetics of tolbutamide and its metabolite 4-hydroxy tolbutamide in poloxamer 407-induced hyperlipidemic rats.

Under hyperlipidemic conditions, there are likely to be alterations in the pharmacokinetics of CYP2C11 substrates following decreased expression of CYP2C11, which is homologous to human CYP2C9. The pharmacokinetics of tolbutamide (TB) and its metabolite 4-hydroxy tolbutamide (4-OHTB) were evaluated as a CYP2C11 probe after intravenous and oral administration of 10 mg/kg tolbutamide to poloxamer 407-induced hyperlipidemic rats (HL rats). Changes in the expression and metabolic activity of hepatic CYP2C11 and the plasma protein binding of tolbutamide in HL rats were also evaluated. The total area under the plasma concentration-time curve (AUC) of tolbutamide in HL rats after intravenous administration was comparable to that in controls due to their comparable non-renal clearance (CLNR ). The free fractions of tolbutamide in plasma were comparable between the control and HL rats. The 4-hydroxylated metabolite formation ratio (AUC4-OHTB /AUCTB ) in HL rats was significantly smaller than that in the control rats as a result of the reduced expression of hepatic CYP2C11 (by 15.0%) and decreased hepatic CLint (by 28.8%) for metabolism of tolbutamide to 4-OHTB via CYP2C11. Similar pharmacokinetic changes were observed in HL rats after oral administration of tolbutamide. These findings have potential therapeutic implications, assuming that the HL rat model qualitatively reflects similar changes in patients with hyperlipidemia. Since other sulfonylureas in clinical use are substrates of CYP2C9, their hepatic CLint changes have the potential to cause clinically relevant pharmacokinetic changes in a hyperlipidemic state.