Effect of dietary oil intake on hepatic cytochrome P450 activity in the rat

Elucidation of the Intestinal Absorption of para-Aminobenzoic Acid, a Marker for Dietary Intake

para-Aminobenzoic acid (PABA) has long been used as an indicator of the completeness of 24-h urine collection by determination of total urinary excretion of PABA and its metabolite, N-acetyl-PABA. N-Acetyl-PABA is formed by human arylamine N-acetyltransferase 1 (NAT1) in liver and intestine. This intestinal metabolism may reduce the urinary recovery of PABA due to secretion of N-acetyl-PABA into the intestinal lumen. In the present study, the effect of intestinal metabolism of PABA on its absorption was quantitatively evaluated by the in situ single-pass perfusion method using rat intestine expressing rat arylamine N-acetyltransferase 2 (Nat2), which is similar to human NAT1. PABA was taken up in a linear fashion in the intestinal mucosa and its effective permeability coefficient indicated 100% absorption. The metabolism of PABA to N-acetyl-PABA reached saturation and substrate inhibition was observed at higher PABA concentrations. These phenomena were also observed in an in vitro study using the intestinal S9 fraction. Interestingly, N-acetyl-PABA was transported more quickly into the vein than into the intestinal lumen. Both the substrate inhibition of Nat2 and transporter-mediated efflux of N-acetyl-PABA into veins result in low secretion levels of N-acetyl-PABA into the intestinal mucosa over a wide range of PABA concentrations.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Pharmacokinetics of dibutyl phthalate (DBP) in the rat determined by UPLC-MS/MS

Dibutyl phthalate (DBP) is commonly used to increase the flexibility of plastics in industrial products. However, several plasticizers have been illegally used as clouding agents to increase dispersion of aqueous matrix in beverages. This study thus develops a rapid and validated analytical method by ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) for the evaluation of pharmacokinetics of DBP in free moving rats. The UPLC-MS/MS system equipped with positive electrospray ionization (ESI) source in multiple reaction monitoring (MRM) mode was used to monitor m/z 279.25→148.93 transitions for DBP. The limit of quantification for DBP in rat plasma and feces was 0.05 μg/mL and 0.125 μg/g, respectively. The pharmacokinetic results demonstrate that DBP appeared to have a two-compartment model in the rats; the area under concentration versus time (AUC) was 57.8 ± 5.93 min μg/mL and the distribution and elimination half-life (t_1/2,α and t_1/2,β) were 5.77 ± 1.14 and 217 ± 131 min, respectively, after DBP administration (30 mg/kg, i.v.). About 0.18% of the administered dose was recovered from the feces within 48 h. The pharmacokinetic behavior demonstrated that DBP was quickly degraded within 2 h, suggesting a rapid metabolism low fecal cumulative excretion in the rat.

An examination of the potential effect of lipids on the first-pass metabolism of the lipophilic drug anethol trithione

In this study, an examination of the potential effect of lipids on the first-pass metabolism of anethol trithione (ATT) was investigated. ATT is metabolized rapidly and extensively in liver into 4-hydroxy-anethole trithione (ATX), which was confirmed using the rat intestinal perfusion with the mesenteric cannulation model. Male Sprague-Dawley rats were orally administered of the lipid-based formulations (prepared by medium chain triglycerides (MCT)), the cyclodextrin formulation and the suspension formulation, respectively. For 6.75 mg/kg groups, ATX/ATT area under the plasma concentration-time curve (AUC) ratio decreased by 87% and 76% after administration of the MCT-based formulations and the cyclodextrin formulation, when compared with the suspension formulation (p < 0.05), respectively; for 2.25 mg/kg groups, it decreased by 53% in the MCT group when compared with the cyclodextrin group (p < 0.05). The saturation of pre-system metabolism of ATT was observed after administration of the MCT-based formulations and the cyclodextrin formulation, likely as a result of enhanced absorption and therefore presentation of higher drug concentrations to liver, when compared with the suspension formulation. A trend toward lower systemic metabolite to parent ratios was evident after administration of the lipid formulations, when compared with the cyclodextrin formulation; however, this was not statistically significant. Further studies on the potential for lipids to inhibit hepatic metabolism are therefore warranted.

Olive oil protects rat liver microsomes against benzo(a)pyrene-induced oxidative damages: an in vitro study

Benzo(a)pyrene (B(a)P), a member of the polycyclic aromatic hydrocarbon family is present ubiquitously in the environment. One of its toxic effects is induction of oxidative stress (mediated by the enzyme B(a)P hydroxylase) which leads to various diseases like cancer. Olive oil (OO) that consists of many antioxidant compounds is reported to have many beneficial properties including protection against cancer. The objective of the present study is to evaluate the effect of OO on B(a)P hydroxylase enzyme and further elucidate the antioxidant capacity of OO against B(a)P-induced toxicity. Rat liver microsomes were divided into three groups: vehicle control, B(a)P treated group, and OO + B(a)P co-incubated group. Antioxidant enzymes which were decreased and protein carbonyl content and lipid peroxidation products which were increased on exposure to B(a)P was attenuated to near normal on OO exposure. B(a)P hydroxylase enzyme was very low in OO incubated group which may be due to inhibition of the enzyme by OO or high utilization for the metabolism of B(a)P. Further, no B(a)P metabolites (3-OH B(a)P and B(a)P 7,8-dihydrodiol) were identified in HPLC during B(a)P + OO exposure. The results prove the protective role of OO against B(a)P-induced oxidative damage.

METABOLIC INTERACTION BETWEEN CYCLOSPORINE AND SIROLIMUS

BACKGROUND

When the immunosuppressants cyclosporine (CsA) and sirolimus (SRL) are co-administered to transplant patients, lower doses are used than when either drug is given alone. Since both drugs share similar transport and metabolic pathways, there is the potential for an interaction leading to unpredictable effects. Furthermore, both drugs affect the activity of cytochrome P450 3A1/2 (CYP3A1/2), the rat parallel to human CYP3A4, and the multidrug transporter P-glycoprotein (Pgp).

METHODS

To clarify the role of metabolic enzymes and membrane transporters involved in the disposition of both drugs, we examined hepatic CYP3A1/2, Pgp, and multidrug resistance gene (mdr) mRNA during chronic therapy with CsA and SRL in salt-depleted rats. Specifically, rats were given intravenous doses of CsA 2.5 mg/kg and SRL 1 mg/kg, alone or in combination, for two weeks via constant rate intravenous infusion.

RESULTS

CsA treatment inhibited hepatic CYP3A1/2 protein expression, catalytic activity, and mRNA levels. SRL dosing suppressed CYP3A1/2 protein expression and catalytic activity, without affecting mRNA. With combined dosing, however, there was a much greater reduction. Hepatic Pgp protein levels were elevated after treatment with either drug alone, as well as with combined dosing. Compared to controls, there were significant increases in mdr1a and mdr1b mRNA levels in all treatment groups, with the combined drugs causing the greatest increase.

CONCLUSIONS

Both CYP3A1/2 and Pgp participate in the disposition of CsA and SRL in rats. Changes in the individual activities of CYP3A1/2 and Pgp may contribute to an interaction between CsA and SRL resulting in unanticipated effects during chronic therapy.