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

Paracetamol (N-acetyl-para amino phenol) is the most commonly used analgesic and antipyretic around the world. Its causes hepatotoxicity and nephrotoxicity at overdose or even at therapeutic doses. It is primarily metabolized by glucuronidation and sulfate conjugation. It is also metabolized by cytochrome-P450 system (CYP2E1, CYP1A2 and CYP 3A4), leading to the formation of N-acetyl-p-benzoquinoneimine (NAPQI). The present study was planned to investigate the influence of chrysin (known CYP2E1 and CYP3A4 inhibitor) on the bioactivation of paracetamol to NAPQI using rat liver microsomes in vitro and rats in vivo. Paracetamol (80 mg/kg) was administered orally without or with silymarin (100 mg/kg), a known CYP2E1 inhibitor and chrysin (100 and 200 mg/kg) to rats for 15 consecutive days. The area under the plasma concentration-time curve (AUC0-∞) and the peak plasma concentration (Cmax) of paracetamol were dose-dependently increased with chrysin (100 and 200 mg/kg) compared to paracetamol control group. On the other hand, the AUC0-∞ and Cmax of NAPQI were decreased significantly with chrysin (100 and 200 mg/kg). The elevated liver and kidney function markers were significantly reduced by chrysin and silymarin compared to paracetamol control group (P < 0.01). Histopathological studies of liver and kidney also well correlated with liver and kidney function tests. Chrysin also reduced the formation of NAPQI in the incubation samples of rat hepatocytes. The present study (both in vivo and in vitro) results revealed that chrysin might be inhibited the CYP2E1, CYP1A2 and CYP3A4-mediated metabolism of paracetamol; thereby decreased the formation of NAPQI and protected the liver and kidney.

Systemic exposure of Paracetamol (acetaminophen) was enhanced by quercetin and chrysin co-administration in Wistar rats and in vitro model: risk of liver toxicity.

Intestinal P-glycoprotein (P-gp) and drug-metabolizing enzymes (DMEs) play an important role in the first-pass-metabolism (FPM) and pharmacokinetics (PK) of majority of drugs. Paracetamol is primarily metabolized by conjugation reactions and a little amount (∼15%) undergoes cytochrome P450 (CYP2E1)-mediated oxidative metabolism produces a hepatotoxic metabolite, N-acetyl-p-benzoquinonimine (NAPQI). Quercetin and chrysin are naturally occurring flavonoids, reported as modulators of P-gp and DMEs. Therefore, the objective of this study was to evaluate the effects of quercetin and chrysin on the pharmacokinetics of paracetamol using rats and non-everted gut sacs in vitro. Paracetamol was given orally (100 mg/kg) to rats alone and in combination with quercetin (5, 10 and 20 mg/kg) and chrysin (50, 100 and 200 mg/kg) once daily for 21 consecutive days. Blood samples were collected on the 1st day in single dose pharmacokinetic study (SDS) and on the 21st day in multiple pharmacokinetic studies (MDS). The plasma concentrations of paracetamol were determined by HPLC and PK parameters were calculated by using Kinetica (Version 5.1). The maximum plasma concentration (Cmax) and area under the curve (AUC0-12) of paracetamol was significantly increased by quercetin and chrysin co-administration in SDS and MDS. In non-everted rat gut sac method, the absorption of paracetamol was increased by presence of P-gp inhibitors (verapamil, quinidine and ketoconazole), quercetin and chrysin (50 µg/mL). Our findings suggested that the quercetin and chrysin might be inhibited the P-gp and metabolism of paracetamol; thereby increased the systemic exposure of paracetamol. Further studies are needed to evaluate whether the quercetin or chrysin are involved in the formation of NAPQI by CYP2E1 or not on isolated rat hepatocytes or using cell lines.

Quercetin declines plasma exposure of metoprolol tartrate in the rat model.

The study was undertaken to evaluate the effect of quercetin on the pharmacokinetics of Metoprolol tartrate. A single dose in vivo pharmacokinetic study was carried out in rat models. In this study, rats were treated with quercetin (10 mg/kg) and metoprolol tartrate (20 mg/kg) orally and blood samples were collected 0, 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 8, 12 h post treatment. Plasma concentration of metoprolol tartrate was estimated using reverse phase-high-performance liquid chromatography method. Area under the plasma concentration-time curve (AUC0-12) of metoprolol has significantly (P < 0.001) decreased by 9.8 times in the metoprolol and quercetin combination group (9434.65 ± 3525.02) when compared with AUC0-12 metoprolol of metoprolol-alone treated group (962.17 ± 242.81). AUC0-∞ of metoprolol has significantly (P < 0.001) decreased by 14.9 times in the combination group (16670.79 ± 12129.06) in comparison to AUC0-∞ of metoprolol of metoprolol-alone treated group (1113.68 ± 441.83). the results obtained herein indicate that quercetin remarkably declines the plasma exposure of metoprolol when concomitantly administered by oral route.

Pharmacokinetic interaction study between quercetin and valsartan in rats and in vitro models.

Valsartan is a potent, orally active non-peptide tetrazole derivative and selectively inhibits angiotensin II receptor type 1 which causes reduction in blood pressure and is used in treatment of hypertension. The risk of heart disease mortality decreased significantly as flavonoid intake increased. Interestingly, the flavonoid-containing foods contain a high amount of Quercetin. The objective of this study was to evaluate the influence of quercetin on the pharmacokinetics of valsartan. In vivo studies were performed on rats. Rats were treated with quercetin (10 mg/kg) and valsartan (10 mg/kg), blood samples were collected at 1, 1.5, 2, 2.5, 3, 3.5, 4, 6 and 8 h. Plasma concentration of valsartan was estimated by Reverse Phase (RP-HPLC). Quercetin significantly increases the plasma concentration of valsartan and peak concentration (70.45 µg/mL) was achieved at 3.5 h. In vitro studies were performed on rat intestinal everted sacs. The transport of valsartan from serosal side to mucosal side decreased from 53.12 ± 1.27 to 40.15 ± 0.45 µg/mL in the presence of quercetin and from 53.12 ± 1.27 to 28.68 ± 0.31 µg/mL in the presence of verapamil (standard P-glycoprotein (P-gp) inhibitor) at 120 min. Verapamil is a potent P-gp and CYP3A4 inhibitor. Quercetin is a P-gp inhibitor and may be an inhibitor of CYP3A4. The simultaneous administration of quercetin significantly increases the intestinal absorption and decreases the efflux of valsartan. The observed effect may be beneficial to develop oral valsartan dosage forms using safe P-gp inhibitor (quercetin) to improve its oral bioavailability.