Effects of glucose on the pharmacokinetics of intravenous chlorzoxazone in rats with acute renal failure induced by uranyl nitrate

Regulation of X-Ray Irradiation on the Activity and Expression Levels of CYP1A2 and CYP2E1 in Rats

The objective of this study was to investigate the regulation of X-ray irradiation and its effect on the activity and protein and mRNA expression levels of CYP1A2 and CYP2E1 in rats. Rats were randomly divided into 0 Gy (control), 1 Gy (low-dose irradiation), and 5 Gy (high-dose irradiation) groups. CYP1A2 and CYP2E1 activity was evaluated from changes in pharmacokinetic parameters of caffeine and chlorzoxazone, respectively. The plasma concentrations of the probe drugs were determined by high-performance liquid chromatography (HPLC). Enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (PCR) tests were used to analyze the protein and mRNA expression levels of CYP1A2 and CYP2E1, respectively. The AUC_0-12 of caffeine was decreased by 1.7- and 2.5-fold, and the CL was increased by 1.8- and 2.6-fold in the 1 Gy and 5 Gy groups, respectively, compared to the 0 Gy group. The AUC_0-10 of chlorzoxazone was 1.4- and 1.8-fold lower, and the CL was 1.4- and 1.9-fold higher in the 1 Gy and 5 Gy groups, respectively, compared to the 0 Gy group. The metabolism of caffeine and chlorzoxazone increased under X-ray irradiation as CL levels increased and AUC levels decreased, suggesting that CYP1A2 and CYP2E1 activity is enhanced in rats after X-ray irradiation. Compared to that of the 0 Gy group, the protein expression level of CYP1A2 was measured as 28.3% and 38.9% higher in the 1 Gy and 5 Gy groups, respectively. The protein expression level of CYP2E1 was 48.4% higher in the 5 Gy group compared to the 0 Gy group, and there was no statistically significant difference between 0 Gy and 1 Gy. Compared to the 0 Gy group, the mRNA expression level of CYP1A2 was 200% and 856.3% higher in the 1 Gy and 5 Gy group, respectively, whereas the mRNA expression level of CYP2E1 was 89.0% and 192.3% higher in the 1 Gy and 5 Gy groups, respectively. This study reveals significant changes in the activity and protein and mRNA expression levels of CYP1A2 and CYP2E1 in rats after exposure to X-ray irradiation.

Effects of Radiation on Drug Metabolism: A Review

BACKGROUND

Radiation is the fourth most prevalent type of pollution following the water, air and noise pollution. It can adversely affect normal bodily functions. Radiation alters the protein and mRNA expression of drugmetabolizing enzymes and drug transporters and the pharmacokinetic characteristics of drugs, thereby affecting drug absorption, distribution, metabolism, and excretion. Therefore, it is important to study the pharmacokinetic changes in drugs under radiation.

METHODS

To update data on the effects of ionizing radiation and non-ionizing radiation caused by environmental pollution or clinical treatments on the protein and mRNA expression of drug-metabolizing enzymes and drug transporters. Data and information on pharmacokinetic changes in drugs under radiation were analyzed and summarized.

RESULTS

The effect of radiation on cytochrome P450 is still a subject of debate. The widespread belief is that higherdose radiation increased the expression of CYP1A1 and CYP1B1 of rat, zebrafish or human, CYP1A2, CYP2B1, and CYP3A1 of rat, and CYP2E1 of mouse or rat, and decreased that of rat's CYP2C11 and CYP2D1. Radiation increased the expression of multidrug resistance protein, multidrug resistance-associated protein, and breast cancer resistance protein. The metabolism of some drugs, as well as the clearance, increased during concurrent chemoradiation therapy, whereas the half-life, mean residence time, and area under the curve decreased. Changes in the expression of cytochrome P450 and drug transporters were consistent with the changes in the pharmacokinetics of some drugs under radiation.

CONCLUSION

The findings of this review indicated that radiation caused by environmental pollution or clinical treatments can alter the pharmacokinetic characteristics of drugs. Thus, the pharmacokinetics of drugs should be rechecked and the optimal dose should be re-evaluated after radiation.

Clients and Oncogenic Roles of Molecular Chaperone gp96/grp94

As an endoplasmic reticulum heat shock protein (HSP) 90 paralogue, glycoprotein (gp) 96 possesses immunological properties by chaperoning antigenic peptides for activation of T cells. Genetic studies in the last decade have unveiled that gp96 is also an essential master chaperone for multiple receptors and secreting proteins including Toll-like receptors (TLRs), integrins, the Wnt coreceptor, Low Density Lipoprotein Receptor-Related Protein 6 (LRP6), the latent TGFβ docking receptor, Glycoprotein A Repetitions Predominant (GARP), Glycoprotein (GP) Ib and insulin-like growth factors (IGF). Clinically, elevated expression of gp96 in a variety of cancers correlates with the advanced stage and poor survival of cancer patients. Recent preclinical studies have also uncovered that gp96 expression is closely linked to cancer progression in multiple myeloma, hepatocellular carcinoma, breast cancer and inflammation-associated colon cancer. Thus, gp96 is an attractive therapeutic target for cancer treatment. The chaperone function of gp96 depends on its ATPase domain, which is structurally distinct from other HSP90 members, and thus favors the design of highly selective gp96-targeted inhibitors against cancer. We herein discuss the strategically important oncogenic clients of gp96 and their underlying biology. The roles of cell-intrinsic gp96 in T cell biology are also discussed, in part because it offers another opportunity of cancer therapy by manipulating levels of gp96 in T cells to enhance host immune defense.

KCa channels as therapeutic targets in episodic ataxia type-2

Episodic ataxia type-2 (EA2) is an inherited movement disorder caused by mutations in the gene encoding the Ca(v)2.1alpha1 subunit of the P/Q-type voltage-gated calcium channel that result in an overall reduction in the P/Q-type calcium current. A consequence of these mutations is loss of precision of pacemaking in cerebellar Purkinje cells. This diminished precision reduces the information encoded by Purkinje cells and is thought to contribute to symptoms associated with this disorder. The loss of the precision of pacemaking in EA2 is the consequence of reduced activation of calcium-dependent potassium channels (K(Ca)) by the smaller calcium current and in vitro can be pharmacologically restored by K(Ca) activators. We used a well established mouse model of EA2, the tottering (tg/tg) mouse, to examine the potential therapeutic utility of one such Food and Drug Administration (FDA)-approved compound, chlorzoxazone (CHZ). Compared with wild-type Purkinje cells, we found the firing rate of tg/tg Purkinje cells in acutely prepared cerebellar slices to be very irregular. Bath application of CHZ successfully restored the precision of pacemaking in a dose-dependent manner. Oral administration of CHZ to tg/tg mice improved their baseline motor performance and reduced the severity, frequency, and duration of episodes of dyskinesia without producing any adverse effects. We propose the use of CHZ, which is currently FDA approved as a muscle relaxant, as a safe and novel treatment of EA2.

Faster clearance of omeprazole in rats with acute renal failure induced by uranyl nitrate: contribution of increased expression of hepatic cytochrome P450 (CYP) 3A1 and intestinal CYP1A and 3A subfamilies

It has been reported that omeprazole is mainly metabolized via hepatic cytochrome P450 (CYP) 1A1/2, CYP2D1 and CYP3A1/2 in male Sprague-Dawley rats, and the expression of hepatic CYP3A1 is increased in male Sprague-Dawley rats with acute renal failure induced by uranyl nitrate (U-ARF rats). Thus, the metabolism of omeprazole would be expected to increase in U-ARF rats. After intravenous administration of omeprazole (20 mgkg−1) to U-ARF rats, the area under the plasma concentration-time curve from time zero to infinity (AUC) was significantly reduced (371 vs 494 μg min mL−1), possibly due to the significantly faster non-renal clearance (56.6 vs 41.2 mL min−1 kg−1) compared with control rats. This could have been due to increased expression of hepatic CYP3A1 in U-ARF rats. After oral administration of omeprazole (40 mg kg−1) to U-ARF rats, the AUC was also significantly reduced (89.3 vs 235 μg min mL−1) compared with control rats. The AUC difference after oral administration (62.0% decrease) was greater than that after intravenous administration (24.9% decrease). This may have been primarily due to increased intestinal metabolism of omeprazole caused by increased expression of intestinal CYP1A and 3A subfamilies in U-ARF rats, in addition to increased hepatic metabolism.

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus

Objectives

In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration–time curve from time zero to time infinity (AUC) of metabolites, AUCmetabolite/AUCparent drug ratios, or the time-averaged nonrenal and total body clearances (CLNR and CL, respectively) of parent drugs as reported in the literature have been compared.

Key findings

After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CLint) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster.

Summary

Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Time-dependent effects of Klebsiella pneumoniae endotoxin on the pharmacokinetics of chlorzoxazone and its main metabolite, 6-hydroxychlorzoxazone, in rats: restoration of the parameters in 96 hour in KPLPS rats to control levels

It has been reported that chlorzoxazone (CZX) was primarily metabolized via hepatic Cyp2e1 to form 6-hydroxychlorzoxazone (OH-CZX) in rats, and the activity of aniline hydroxylase (a Cyp2e1 marker) in the liver was significantly decreased in rats at 24 h after pretreatment with lipopolysaccharide derived from Klebsiella pneumoniae (24 h KPLPS rats), whereas the levels were not changed at 2 h and 96 h in the KPLPS rats. Thus, the time-dependent pharmacokinetic parameters of CZX and OH-CZX were evaluated after the intravenous administration of CZX (20 mg/kg) to control rats, and the 2 h, 24 h and 96 h KPLPS rats along with the time-dependent changes in the protein expression of hepatic Cyp2e1. After the intravenous administration of CZX to 24 h KPLPS rats, the AUC(0-2 h) of OH-CZX and AUC(OH-CZX, 0-2 h)/AUC(CZX) were significantly smaller (by 40.5% and 71.2%, respectively) than those of controls due to the significant decrease (by 75.3%) in the protein expression of hepatic Cyp2e1. However, in 96 h KPLPS rats, the pharmacokinetic parameters of both CZX and OH-CZX were unchanged compared with controls due to the restoration of the protein expression of hepatic Cyp2e1 to control levels. These observations highlighted the existence of the time-dependent effects of KPLPS on the pharmacokinetics of CZX and OH-CZX in rats.

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: Do adenosine A1antagonists (selective/non-selective) normalize the altered topotecan kinetics in ARF?

A series of exploratory investigations with multiple agents was carried out in normal rats and in rats with uranyl nitrate-induced acute renal failure to understand the disposition characteristics of intravenous topotecan (TPT) used as a model substrate. The disposition of TPT was unaltered in normal rats when treated with methotrexate, whereas treatment with probenecid increased the systemic exposure of TPT. In case of uranyl nitrate-induced acute renal failure (UN-ARF) rats, the systemic exposure of TPT was increased when compared with normal rats, whereas in UN-ARF rats treated with probenecid a further reduction in renal clearance of TPT was noted as compared with that of UN-ARF induced rats. Thus, TPT may be involved in the tubular secretory pathway when a passive glomerular filtration pathway for elimination was not possible. The disposition of TPT did not normalize in UN-ARF rats when treated with caffeine, a non-selective adenosine A1 receptor antagonist, whereas the selective adenosine A1 receptor antagonist (1,3-dipropyl-8-phenylxanthine, DPPX) normalized TPT pharmacokinetic disposition by improving renal function. Renal excretion studies demonstrated that CLR improved by almost fivefold following DPPX treatment in ARF rats. In addition, the qualitative stability/metabolism pattern of TPT in liver microsomes prepared from various groups of rats (normal rats, UN-ARF rats, rats treated with DPPX, and UN-ARF rats treated with DPPX) was found to be similar. In summary, using a pharmacokinetic tool as a surrogate, it has been shown that the pharmacokinetic disposition of TPT improved considerably upon treatment with DPPX, a selective adenosine A1 antagonist.

Effects of water deprivation on drug pharmacokinetics: correlation between drug metabolism and hepatic CYP isozymes

Male Sprague-Dawley rats deprived of water for 72 h (a rat model of dehydration) showed no change in protein expression of the hepatic microsomal cytochrome P450 (CYP) 1A2, 2B1/2, 2C11, or 3A1/2, but an increase in protein expression (3-fold) and mRNA level (2.6-fold) of CYP2E1. Glucose feeding instead of food normalized CYP2E1 protein expression during dehydration. Here, we review how dehydration can change the pharmacokinetics of drugs reported in the literature via changing CYP isozyme levels. We also discuss how dehydration changes the pharmacokinetics of drugs that are metabolized via renal DHP-I, or are mainly excreted in the urine and bile, and form conjugates.

Pharmacokinetics of chlorzoxazone in rats with diabetes: Induction of CYP2E1 on 6-hydroxychlorzoxazone formation

Pharmacokinetic parameters of chlorzoxazone (CZX) and its main metabolite, 6-hydroxychlorzoxazone (OH-CZX), were compared after intravenous (20 mg/kg) and oral (50 mg/kg) administration of CZX in rat model of diabetes induced by alloxan (DMIA) or streptozotocin (DMIS), and their respective control rats. In both rat models of diabetes, the expression and mRNA level of CYP2E1 increased, and CZX was metabolized to OH-CZX via CYP2E1 in rats. Hence, it could be expected that formation of OH-CZX increased in both rat models of diabetes. As expected, after intravenous (80.5% and 74.4% increase in rat models of DMIA and DMIS, respectively) and oral (55.6% and 70.5% increase, respectively) administration of CZX, the AUC of OH-CZX was significantly greater than their respective control rats. Since, CZX is an intermediate hepatic extraction ratio drug, the greater AUC values of OH-CZX (the significantly faster CL(NR) of CZX) in both rat models of diabetes could be supported by significantly faster CL(int) for the formation of OH-CZX (75.9% and 129% increase for rat models of DMIA and DMIS, respectively) and significantly greater free fractions of CZX in plasma (51.9% and 58.9% increase, respectively). Also it was reported that hepatic blood flow rate was faster in male Wister rat model of DMIS.

Effects of glucose supplementation on the pharmacokinetics of intravenous chlorzoxazone in rats with water deprivation for 72 h

It was reported that in rats with water deprivation for 72 h with food (dehydration rat model), the expression of CYP2E1 was 3-fold induced with an increase in mRNA level and glucose supplementation instead of food during 72-h water deprivation (dehydration rat model with glucose supplementation) inhibited the CYP2E1 induction in dehydration rat model. It was also reported that chlorzoxazone (CZX) is metabolized to 6-hydroxychlorzoxazone (OH-CZX) mainly via CYP2E1 in rats. Hence, the effects of glucose supplementation on the pharmacokinetics of CZX and OH-CZX were investigated after intravenous administration of CZX at a dose of 25 mg/kg to control male Sprague-Dawley rats and dehydration rat model and dehydration rat model with glucose supplementation. Based on the above mentioned results of CYP2E1, it could be expected that increased formation of OH-CZX in dehydration rat model could decrease in dehydration rat model with glucose supplementation. This was proven by the following results. In dehydration rat model with glucose supplementation, the AUC of OH-CZX was significantly smaller (1900 versus 1050 microg min/ml), AUC(OH-CZX)/AUC(CZX) ratio was considerably smaller (105 versus 34.3%), C(max) was significantly lower (20.6 versus 8.08 microg/ml), total amount excreted in 24-h urine as unchanged OH-CZX was significantly smaller (62.3 versus 42.7% of intravenous dose of CZX), and in vitro V(max) (2.18 versus 1.20 nmol/min/mg protein) and CL(int) (0.0285 versus 0.0171 ml/min/mg protein) were significantly slower than those in dehydration rat model.

Hepatic Disposition of the Cytochrome P450 2E1 Marker Chlorzoxazone and its Hydroxylated Metabolite in Isolated Perfused Rat Livers

The steady-state disposition of chlorzoxazone (CZX) and its hydroxylated metabolite 6-hydroxychlorzoxazone (HCZX) was determined in a single-pass isolated perfused rat liver (IPRL) model using constant CZX concentrations of 10-200 microM. The concentrations of CZX, HCZX, and/or HCZX glucuronide in the perfusate, bile, and liver tissues were measured and kinetic parameters calculated. Upon an increase in CZX inlet concentrations from 10 to 200 microM, its extraction ratio sharply declined from 0.681 to 0.087. This was associated with a saturable formation of HCZX, which was rapidly and completely metabolized to its glucuronide conjugate. Whereas the biliary excretion of CZX was negligible, that of HCZX was substantial (up to 40% of the generated metabolite). Overall, 79-93% of the CZX dose (10-200 microM) was recovered in our model as CZX and HCZX. Additionally, HCZX accounted for 56% (200 microM) to 71% (10 microM) of the extracted CZX dose. Further, a preliminary study using the preformed HCZX showed a complete (100%) recovery of the metabolite as its conjugate. Therefore, the unrecovered portion of CZX dose in our study (7-21% of the administered dose or 29-44% of the extracted dose at inlet CZX concentrations of 10-200 microM) is most likely due to parallel metabolism of CZX to other metabolites.

Effects of acute renal failure on the pharmacokinetics of oltipraz in rats

Pharmacokinetic parameters of oltipraz were compared after intravenous and oral administration at a dose of 30 mg/kg to control rats and rats with U-ARF. After intravenous administration to rats with U-ARF, the AUC was significantly greater (1100 versus 1730 microg x min/mL) than that in control rats, and this could be due to significantly slower CL (27.2 versus 17.3 mL/min/kg). The slower CL could be mainly due to significantly slower CL(NR) (27.2 versus 17.3 mL/min/kg), and this could be supported by significantly slower in vitro CL(int) (32.1 versus 13.2 mL/min/whole liver) in the rats. The Vss was significantly larger in rats with U-ARF (4050 versus 5680 mL/kg), and this was not due to a significant increase in free fractions (unbound in plasma proteins) of oltipraz in the rats because the free fractions were 17.0 and 15.7% for control rats and rats with U-ARF, respectively. Unexpectedly, after oral administration to rats with U-ARF, the AUC of oltipraz was significantly smaller than that in control rats (329 versus 149 microg x min/mL), and this could be mainly due to a decrease in the absorption of oltipraz from the gastrointestinal tract in the rats (95 and 72% of the oral dose were absorbed in control rats and rats with U-ARF, respectively).