Quercetin reduced the formation of N-acetyl-p-benzoquinoneimine, a toxic metabolite of paracetamol in rats and isolated rat hepatocytes.

N-acetyl-p-benzoquinoneimine (NAPQI) is toxic metabolite of paracetamol formed primarily by cytochrome P4502E1 (CYP2E1) metabolic pathway when administered at therapeutic doses or overdose. The influence of quercetin (flavonoid) on the bioactivation of paracetamol to NAPQI was investigated using rat liver microsomes and rats in vivo. Paracetamol (80 mg/kg) was administered orally without or with silymarin (100 mg/kg), a known inhibitor of CYP2E1, CYP3A4 and quercetin (10 and 20 mg/kg) to rats for 15 consecutive days. Area under the plasma concentration-time curve (AUC0-∞ ) and the peakplasma concentration (Cmax ) of paracetamol were dose-dependently increased with quercetin (10 and 20 mg/kg) compared to paracetamol control group (p < 0.001). On the other hand, the AUC0-∞ and Cmax of NAPQI were decreased significantly with quercetin. The same results were observed with silymarin also. The elevated liver and kidney functional enzymes/compounds were significantly reduced by quercetin and silymarin compared to paracetamol control group. The formation of NAPQI was reduced in the incubation samples in presence of quercetin in experiment using isolated rat hepatocytes. The presentstudy results revealed that quercetin might be inhibited the CYP2E1-mediated metabolism of paracetamol; thereby decreased the formation of NAPQI and protected the liver and kidney.

Pharmacokinetic interaction study between flavanones (hesperetin, naringenin) and rasagiline mesylate in wistar rats.

Cytochrome P-450 (CYP) enzymes and P-glycoprotein (P-gp) play an important role in the oral bioavailability and first-pass-metabolism (FPM) of many drugs. Rasagiline is a selective, monoamine oxidase-B inhibitor and it undergoes significant FPM in the liver prior to excretion by CYP1A2. Hesperetin and naringenin are naturally occurring flavanones and are reported as modulators of CYP enzymes and P-gp. The objective of the present investigation was to evaluate the effect of hesperetin and naringenin on the pharmacokinetics (PK) of rasagiline in rats. Rats were treated orally with rasagiline (2 mg/kg) alone and co-administered with hesperetin and naringenin (12.5 and 25 mg/kg) for 15 consecutive days. Blood samples were collected from tail vein on the 1st day in a single dose PK study (SDS) and on 15th day in the multiple dose PK study (MDS). Hesperetin and naringenin co-administration significantly enhanced the area under the curve (AUC), maximum plasma concentration (Cmax) and elimination half life (t1/2) of rasagiline with a concomitant reduction in clearance (CL/F) in both SDS and MDS. Rasagiline concentrations were significantly increased when co-administered with hesperetin and naringenin in the brain. No significant difference was found in rasagiline transport from mucosal to serosal side in the presence of hesperetin and naringenin ex vivo (rat everted gut sacs used). Our findings suggested that hesperetin and naringenin enhanced the systemic exposure of rasagiline might be through the inhibition of CYP1A2 but not P-gp. Further studies are needed on CYP1A2 and P-gp over expressed cells to confirm this interaction at cellular level.