Sang G. Kim

Effects of cysteine on amino acid concentrations and transsulfuration enzyme activities in rat liver with protein–calorie malnutrition

The changes in amino acid concentrations and transsulfuration enzyme activities in liver were investigated after 4-week fed on 23% casein diet (control group) and 5% casein diet without (protein-calorie malnutrition, PCM group) or with (PCMC group) oral administration of cysteine, 250 mg/kg (twice daily, starting from the fourth week) using rats as an animal model. By supplementation with cysteine in PCM rats (PCMC group), cysteine level was elevated almost close to the control level, and glutathione (GSH), aspartic acid and serine levels were restored greater than the control levels. The measurement of transsulfuration enzyme activities exhibited that gamma-glutamylcysteine ligase (gamma-GCL) activity was up-regulated in rats with protein restriction (PCM group), and cysteine supplementation (PCMC group) down-regulated to the control level. One-week supplementation of cysteine (PCMC group) significantly down-regulated the cysteine sulfinate decarboxylase activity. These results indicate that the availability of sulfur amino acid(s) especially cysteine appears to play a role in determining the flux of cysteine between cysteine catabolism and GSH synthesis.

Effects of cysteine on the pharmacokinetics of intravenous clarithromycin in rats with protein-calorie malnutrition.

Effects of cysteine on the pharmacokinetics of clarithromycin were investigated after intravenous administration of the drug at a dose of 20 mg/kg to control rats (4-week fed on 23% casein diet) and rats with PCM (protein-calorie malnutrition, 4-week fed on 5% casein diet) and PCMC (PCM treated with 250 mg/kg for oral cysteine twice daily during the fourth week). Clarithromycin has been reported to be metabolized via hepatic microsomal cytochrome P450 (CYP) 3A4 to 14-hydroxyclarithromycin (primary metabolite of clarithromycin) in human subjects. It has also been reported that in rats with PCM, CYP3A23 level decreased to 40-50% of control level, but decreased CYP3A23 level in rats with PCM completely returned to control level by oral cysteine supplementation (rats with PCMC). Human CYP3A4 and rat CYP3A23 proteins have 73% homology. In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity, AUC (567, 853 and 558 microg min/ml for control rats and rats with PCM and PCMC, respectively) and percentage of clarithromycin remaining after incubation with liver homogenate (69.6, 83.9 and 71.7%) were significantly greater than those in control rats and rats with PCMC. Moreover, in rats with PCM, the total body clearance, CL (35.3, 23.4 and 35.8 ml/min/kg), nonrenal clearance, CL(NR) (21.3, 15.2 and 24.1 ml/min/kg) and maximum velocity for the disappearance of clarithromycin after incubation with hepatic microsomal fraction, V(max) (351, 211 and 372 pmol/min/mg protein) were significantly slower than those in control rats and rats with PCMC. However, above mentioned each parameter was not significantly different between control rats and rats with PCMC. The above data suggested that metabolism of clarithromycin decreased significantly in rats with PCM as compared to control due to significantly decreased level of CYP3A23 in the rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters of clarithromycin (AUC, CL, CL(NR) and V(max)) were restored fully to control levels because CYP3A23 level was completely returned to control level in rats with PCMC.

Effects of enzyme inducers or inhibitors on the pharmacokinetics of intravenous parathion in rats.

In order to find what form of hepatic cytochrome P450 (CYP) is involved in the metabolism of parathion to form paraoxon, rats were pretreated with the enzyme inhibitors, such as SKF 525‐A and ketoconazole or enzyme inducers, such as dexamethasone, isoniazid, phenobarbital, and 3‐methylcholanthrene. Parathion, 3 mg/kg, was infused in 1 min via the jugular vein. In rats pretreated with SKF 525‐A or ketoconazole, nonspecific CYP inhibitors, the area under the plasma concentration–time curve from time zero to time infinity (AUC) and total body clearance (Cl) of parathion were significantly greater and slower, respectively, than those in respective control rats, suggesting that parathion was metabolized by CYPs. In rats pretreated with dexamethasone (CYP3A23 inducer), the AUC was significantly smaller (41.5 compared with 52.5 µg min/mL), Cl was significantly faster (72.2 compared with 57.1 mL/min/kg), and the amounts and/or tissue‐to‐plasma ratios of parathion was significantly (or tended to be) smaller than those in control rats. However, the pharmacokinetic parameters of parathion were not significantly different after pretreatment with other enzyme inducers compared with respective control rats. The above data suggested that parathion was metabolized to paraoxon by dexamethasone‐inducible CYP3A23, the induction of which was confirmed by Western blot analysis. This was supported by in vitro intrinsic clearance (Clint) of parathion to form paraoxon in hepatic microsomal fraction; the Clint in rats pretreated with dexamethasone was significantly faster (0.0900 compared with 0.0290 mL/min/mg protein) than that in control rats. Copyright

Effects of E. Coli lipopolysaccharide on the pharmacokinetics of ipriflavone and its metabolites, M1 and M5, after intravenous and oral administration of ipriflavone to rats: Decreased metabolism of ipriflavone due to decreased expression of hepatic CYP1A2 and 2C11

It was reported that ipriflavone was primarily metabolized via hepatic CYP1A1/2 and 2C11 in rats. In the present study, the expression of CYP1A2 and 2C11 decreased in the liver, but increased in the intestine in rats pretreated with E. coli lipopolysaccharide (ECLPS; an animal model of inflammation). Thus, pharmacokinetic parameters of ipriflavone and its metabolites, M1 and M5, were evaluated in ECLPS rats. After intravenous administration (20 mg/kg) to ECLPS rats, the AUC of ipriflavone was significantly greater (26.7% increase) and CL(NR) of ipriflavone was significantly slower (19.9% decrease) than in the controls. This could have been due to decreased expression of hepatic CYP1A2 and 2C11 compared to the controls. After oral administration (200 mg/kg) to ECLPS rats, the AUC of ipriflavone was also significantly greater (130% increase) than in the controls. Although the expression of intestinal CYP1A2 and 2C11 increased in ECLPS rats, contribution of this increase to the significantly greater AUC of ipriflavone after oral administration of ipriflavone to ECLPS rats was not considerable. This could have also been due to a significantly decreased expression of hepatic CYP1A2 and 2C11 in ECLPS rats. The formation of M1 and M5 could be mediated via CYP1A2 and/or 2C11 in rats.

Influence of 4-week and 8-week exercise training on the pharmacokinetics and pharmacodynamics of intravenous and oral azosemide in rats

Cytochrome P450 expression was determined in the livers of control, 4-week exercised (4WE) and 8-week exercised (8WE) rats. Even though the 4-week and 8-week exercise training caused 53 and 25% increases, respectively, in total cytochrome P450 contents in the liver, exercise training did not cause any changes in the levels of P450 1A2 (which primarily metabolizes azosemide), 2E1 and 3A23 in the liver, as assessed by both Western and Northern blot analyses. Also, exercise training failed to alter the activity of NADPH-dependent cytochrome P450 reductase. The plasma concentrations of norepinephrine and epinephrine were significantly (2 to 3 folds) higher in 4WE rats than in controls, presumably due to physical stress, but the catecholamine levels in 8 WE rats returned to control levels. After intravenous administration (10 mg/kg of azosemide), the amount of unchanged azosemide excreted in 8-h urine (Ae(Azo, 0-8 h)) was significantly greater (46% increase) in 4WE rats than that in control rats. This resulted in a significantly faster (82% increase) renal clearance of azosemide. However, the nonrenal clearances were not significantly different between control and 4WE rats. The significantly greater Ae(Azo, 0-8 h) in 4WE rats was mainly due to a significant increase in intrinsic active secretion of azosemide in renal tubules and not due to a decrease in the metabolism of azosemide. After oral administration (20 mg/kg), Ae(Azo, 0-8 h) was also significantly greater (264%) in 4WE rats and this again was due to a significant increase in intrinsic active renal secretion of azosemide and not due to an increase in gastrointestinal absorption. After both intravenous and oral administration, the 8-h urine output was not significantly different between control and 4WE rats although Ae(Azo, 0-8 h) increased significantly in 4WE rats. This could be due to the fact that the urine output reached a plateau at 10 mg/kg after intravenous administration and 20 mg/kg after oral administration of azosemide to rats and possibly due to increase in plasma antidiuretic hormone levels and aldosterone production in 4WE rats.