The effect of experimental hyperlipidemia on the stereoselective tissue distribution, lipoprotein association and microsomal metabolism of (±)-halofantrine

Effects of Hyperlipidemia on the Pharmacokinetics of Tofacitinib, a JAK 1/3 Inhibitor, in Rats

Tofacitinib, an inhibitor of Janus kinases (JAKs) 1 and 3, has been shown to be effective in the treatment of rheumatoid arthritis. The incidence of hyperlipidemia has been found to be higher in patients with rheumatoid arthritis. The present study therefore investigated the pharmacokinetics of tofacitinib after its intravenous (10 mg/kg) or oral (20 mg/kg) administration in poloxamer-407-induced hyperlipidemic (PHL) rats. The area under the plasma concentration-time curve from zero to infinity (AUC0-∞) after intravenous administration of tofacitinib was 73.5% higher in PHL than in control rats, owing to slower time-averaged nonrenal clearance (CLNR) in the former. Evaluation of in vitro metabolism showed that the intrinsic clearance (CLint) of tofacitinib was 38.6% lower in PHL than in control rats, owing to the decreased protein expression of hepatic cytochrome P450 (CYP) 3A1/2 and CYP2C11 in PHL rats. Similar results were observed in PHL rats after oral administration of tofacitinib. These results were likely due to the decreased CLNR, CLint, and P-glycoprotein (P-gp) expression in the intestines of PHL compared to control rats. Overall, these findings indicated that hyperlipidemia slowed the metabolism of tofacitinib, increasing its plasma concentrations, and that this reduced metabolism was due to alterations in expression of the proteins CYP3A1/2, CYP2C11, and P-gp in the liver and/or intestines of PHL rats.

Pharmacokinetic alterations in poloxamer 407-induced hyperlipidemic rats

1. Plasma lipid profile abnormalities in hyperlipidemia can potentially alter the pharmacokinetics of a drug in a complex manner. To evaluate these pharmacokinetic alterations in hyperlipidemia and to determine the underlying mechanism(s), poloxamer 407-induced hyperlipidemic rats (HL rats), a well-established animal model of hyperlipidemia have been used. 2. In this review, we summarize findings on the pathophysiological and gene expression changes in drug-metabolizing enzymes and transporters in HL rats. We discuss pharmacokinetic changes in drugs metabolized primarily via hepatic cytochrome P450 (CYPs) in terms of alterations in hepatic intrinsic clearance (CL^'_int), free fraction in plasma (f_u) and hepatic blood flow rate (Q_H), depending on the hepatic excretion ratio, as well as drugs eliminated primarily by mechanisms other than hepatic CYPs. 3. For lipoprotein-bound drugs, increased binding to lipoproteins resulted in lower f_u values and volumes of distribution, with some exceptions. Generally, slower non-renal clearance (or total body clearance) of drugs that are substrates of hepatic CYP3A and CYP2C is well explained by the following factors: alterations in CL^'_int (due to down-regulation of hepatic CYPs), decreased f_u and/or possible decreased Q_H. 4. These consistent findings across studies in HL rats suggest more studies are needed at the clinical level for optimal pharmacotherapies for hyperlipidemia.

Influence of body composition on disposition of the highly fat distributed compound as analysed by physiologically based pharmacokinetic (PBPK) modeling and simulation

A recent study suggested that the pharmacokinetics (PK) of highly fat distributed compounds can be affected by acute changes in the volume of adipose tissue. The present study investigates possible influences of body composition on the disposition of the highly lipophilic compound TAK-357 in two rat strains. Physiologically based PK (PBPK) modeling and simulation was applied on single and multiple dose PK data of TAK-357 in obese Wistar fatty rats and Wistar lean rats having approximately 45% and 13% body fat, respectively. The observed effects of an elevated fat mass in Wistar fatty rats on the plasma concentrations appeared to be partly compensated for by other differences between the two rat strains. A decrease in the tissue to blood partition coefficients under high body fat conditions was identified as another factor contributing to the difference in PK. A higher lipid content in the plasma in high body fat animals may result in relatively lower tissue to blood partition coefficients. PBPK-based simulations indicate that the plasma concentrations of lipophilic compounds in high body fat conditions can differ by up to two-times at steady-state. This confirms that there is only a small impact of body composition change on the plasma concentration of highly lipophilic drugs and that the need for therapeutic dose adjustments may be limited.

Pharmacokinetics of metformin in the rat: assessment of the effect of hyperlipidemia and evidence for its metabolism to guanylurea

Metformin pharmacokinetics are highly dependent upon organic cationic transporters. There is evidence of a change in its renal clearance in hyperlipidemic obese patients, and no information on its metabolic fate. To study some of these aspects, the influence of poloxamer 407 (P407)-induced hyperlipidemia on metformin pharmacokinetics was assessed. Control and P407-treated adult male rats were administered 30 mg/kg metformin intravenously (i.v.). The pharmacokinetic assessments were performed at 2 time points, 36 and 108 h, following the intraperitoneal dose of P407 (1 g/kg). mRNA and protein expressions of cationic drug transporters were also measured. There was no evidence of a change in metformin pharmacokinetics after i.v. doses as a consequence of short-term hyperlipidemia, and a change in transporter mRNA but not protein expression was observed in the P407- treated rats 108 h after P407 injection. Urinary recovery of unchanged drug was high (>90%) but incomplete. Presumed metabolite peaks were detected in chromatograms of hepatocytes and microsomal protein spiked with metformin. Comparative chromatographic elution times and mass spectra suggested that one of the predominant metabolites was guanylurea. Hyperlipidemia by itself did not affect the pharmacokinetics of metformin. Guanylurea is a putative metabolite of metformin in rats.

Effects of serum lipoproteins on cyclosporine A cellular uptake and renal toxicity in vitro

In-vitro studies were performed to shed light on previous findings that showed increased uptake of cyclosporine A in the kidneys and liver of hyperlipidemic rats, and increased signs of kidney toxicity. Hepatocytes were obtained from rats, cultured, and exposed to a diluted serum from hyperlipidemic rats. Some cells were also exposed to lipid-lowering drugs. After washing out the rat serum or lipid-lowering drugs, cells were exposed to cyclosporine A embedded in serum lipoproteins. Pretreatment with hyperlipidemic serum and lipid-lowering drugs was associated with an increased uptake of cyclosporine A. As expected, atorvastatin caused an increase in low density lipoprotein receptor and a decrease in MDR1A mRNA in the hepatocytes. A decrease in NRK-52E rat renal tubular cellular viability caused by cyclosporine A was noted when cells were preincubated with diluted hyperlipidemic serum. This was matched with evidence of hyperlipidemic-serum-associated increases in the NRK-52E cellular uptake of cyclosporine A and rhodamine-123. The findings of these experiments suggested that in hyperlipidemia the expression and (or) the functional activity of P-glycoprotein was diminished, leading to greater hepatic and renal uptake of cyclosporine A, and renal cellular toxicity.

Effect of rat serum lipoproteins on mRNA levels and amiodarone metabolism by cultured primary rat hepatocytes

Hyperlipidemia can significantly increase amiodarone (AM) in vivo liver uptake and decrease its velocity of microsomal metabolism. Here, hepatocytes isolated from normolipidemic (NL) and hyperlipidemic rats were incubated with AM in the presence or absence of diluted NL or hyperlipidemic serum. The serum was added either as preincubation before drug, or concurrently with drug; incubations without rat serum were used as controls. The hepatocyte levels of mRNA for several proteins and enzymes were also measured. Disappearance of AM was seen up to 72 h. There was little difference between hepatocytes from NL or hyperlipidemic animals in intrinsic clearance (CL(int) ) of AM. The effect of hyperlipidemic rat serum, either before or with AM, was profound, causing a significant reduction in the CL(int) . Reductions were seen in mRNA for cytochrome P450 1A1, 3A2, and 2D1, some transporters, and low-density lipoprotein receptors after exposure of hepatocytes to lipoprotein-rich sera. In conclusion, exposure of isolated hepatocytes to hyperlipidemic serum caused decreases in AM CL(int) and lower mRNA levels for some proteins involved in the uptake and metabolism of AM. When coincubated with serum, an additional effect of increased binding to lipoproteins seemed to further contribute to a reduced CL of AM.

Effect of experimental hyperlipidaemia on the electrocardiographic effects of repeated doses of halofantrine in rats

BACKGROUND AND PURPOSE

Halofantrine can cause a prolongation of the cardiac QT interval, leading to serious ventricular arrhythmias. Hyperlipidaemia elevates plasma concentration of halofantrine and may influence its tissue uptake. The present study examined the effect of experimental hyperlipidaemia on QT interval prolongation induced by halofantrine in rats.

EXPERIMENTAL APPROACH

Normolipidaemic and hyperlipidaemic rats (induced with poloxamer 407) were given 4 doses of halofantrine (i.v., 4-40 mg·kg(-1)·d(-1)) or vehicle every 12 h. Under brief anaesthesia, ECGs were recorded before administration of the vehicle or drug and 12 h after the first and last doses. Blood samples were taken at the same time after the first and last dose of halofantrine. Hearts were also collected 12 h after the last dose. Plasma and heart samples were assayed for drug and desbutylhalofantrine using a stereospecific method.

KEY RESULTS

In the vehicle group, hyperlipidaemia by itself did not affect the ECG. Compared to baseline, QT intervals were significantly higher in both normolipidaemic and hyperlipidaemic rats after halofantrine. In hyperlipidaemic rats, plasma but not heart concentrations of the halofantrine enantiomers were significantly higher compared to those in normolipidaemic rats. Despite the lack of difference in the concentrations of halofantrine in heart, QT intervals were significantly higher in hyperlipidaemic compared to those in normolipidaemic rats.

CONCLUSIONS AND IMPLICATIONS

The unbound fraction of halofantrine appeared to be the controlling factor for drug uptake by the heart. Our data suggested a greater vulnerability to halofantrine-induced QT interval prolongation in the hyperlipidaemic state.

Pharmacokinetics of clomipramine, an antidepressant, in poloxamer 407-induced hyperlipidaemic model rats

Objective

This study was undertaken to investigate the effects of hyperlipidaemia on the pharmacokinetics of clomipramine, an antidepressant, particularly addressing the change of clomipramine distribution to plasma components in poloxamer 407-induced hyperlipidaemia model rats.

Methods

Clomipramine pharmacokinetic studies in hyperlipidaemic rats were performed with clomipramine continuous infusion. Furthermore, clomipramine protein binding and distribution to the brain and plasma components such as lipoproteins were investigated.

Key findings

Mean plasma concentration of clomipramine at steady state during continuous infusion (17.5 µg/min/kg) in hyperlipidaemic rats (0.45 ± 0.01 µg/ml) was significantly higher than that in the control rats (0.30 ± 0.02 µg/ml). However, the amount of clomipramine in the brain in hyperlipidaemic rats (0.31 ± 0.06 µg/g) was dramatically lower than in the control rats (1.89 ± 0.13 µg/g). However, the plasma unbound fraction in hyperlipidaemic rats (0.98 ± 0.05%) was significantly lower than that of the control rats (6.51 ± 0.62%).

Conclusions

Lower distribution to the brain and lower plasma clearance of clomipramine in hyperlipidaemic rats resulted from lower plasma unbound fraction because of higher lipid-rich protein contents in blood. Results of this study provide useful information for dosage adjustment of clomipramine in hyperlipidaemia.

Effect of hypertriglyceridemia on the pharmacokinetics and blood-brain barrier penetration of clozapine and norclozapine following administration to rats

There is a long-term discussion in the literature concerning the possible link between the improved efficacy of clozapine treatment and elevated plasma triglyceride levels, but no mechanistic studies have been performed to date. The aim of this work was to investigate whether the postprandial hypertriglyceridemia affects the pharmacokinetics and brain distribution of clozapine and norclozapine. Experimental hypertriglyceridemia in rats was induced by oral administration of peanut oil and the pharmacokinetic parameters and brain penetration of clozapine and norclozapine following administration of clozapine were compared to normotriglyceridemic control animals. Moderately increased clearance of clozapine was found in hypertriglyceridemic animals compared to control group. No changes were found in penetration of compounds across the blood-brain barrier (BBB). Taken together, the results do not support the hypothesis that hypertriglyceridemia improves the effect of clozapine by altered pharmacokinetics of clozapine and norclozapine and their increased penetration across the BBB.