The pharmacokinetics of dabigatran in a rat model of hyperlipidemia induced by poloxamer 407

Various pharmacokinetic changes have been reported in experimental hyperlipidemic (HL) animal models. To evaluate whether P-glycoprotein (P-gp) activity was affected in HL rats, we assessed the pharmacokinetics of dabigatran after oral administration of dabigatran etexilate (DABE); this is a dabigatran prodrug and a well-known P-gp substrate.HL and control rats exhibited similar area under the plasma concentration-time curve (AUC), total body clearance (CL), and steady state volume of distribution (Vss) values following intravenous administration of dabigatran (1 mg/kg). This suggested that the distribution and elimination of dabigatran were similar in control and HL rats.The hepatic and intestinal P-gp protein levels did not differ significantly between control and HL rats. The dabigatran AUC and extent of absolute oral bioavailability (F) values were similar in control and HL rats following oral administration of DABE (10 mg/kg as dabigatran). Therefore, there was no apparent change in intestinal P-gp activity in HL rats compared to control rats.This study revealed no significant change in P-gp expression or activity in the intestine or liver of HL rats, and similar pharmacokinetics of dabigatran. Hyperlipidemia may not directly affect the oral absorption of P-gp substrate drugs.

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.

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.

Population Semiphysiologic Kinetic Modeling and Simulation of Plasma Triglyceride Levels After Soybean Oil-Based Intravenous Lipid Emulsion Administration in Rats

BACKGROUND

Soybean oil-based intravenous lipid emulsion (SO-ILE) has clinical utility as an energy source and in lipid rescue therapy. However, an excessive infusion rate of SO-ILE in routine use and in lipid rescue therapy may cause serious side effects. There is little information about plasma triglyceride (TG) kinetics following SO-ILE administration. The present study aimed to develop a population semiphysiologic kinetic model of TG and to predict the TG kinetics even at extremely high concentrations in rats.

MATERIALS AND METHODS

TG concentration profiles after intravenous bolus (0.1, 0.25, 0.5, 1.0, 1.5, and 2.0 g/kg) or infusion (3.0 g/kg/h for 1 hour) of SO-ILE to rats were analyzed by a kinetic model constructed with 4 pathways: apolipoprotein acquisitions, zero-order catabolism, first-order uptake to storage sites, and zero-order secretion from storage sites. The developed model was subjected to internal and external validation.

RESULTS

Plasma TG concentrations appeared to decline in a biphasic manner with nonlinear TG kinetics. The developed kinetic model was well validated and found to accurately predict the external validation data.

CONCLUSIONS

The proposed kinetic model accurately described TG concentrations after SO-ILE administration at various infusion rates, including a lipid rescue regimen. The maximum acceptable infusion rate of SO-ILE in routine use should correspond to the maximum velocity of the apolipoprotein acquisition: 0.619 g/kg/h in rats. The prediction of TG kinetics at extremely high concentrations will provide useful information for lipid rescue therapy.

Induction of suicidal erythrocyte death by nelfinavir

The HIV protease inhibitor, nelfinavir, primarily used for the treatment of HIV infections, has later been shown to be effective in various infectious diseases including malaria. Nelfinavir may trigger mitochondria-independent cell death. Erythrocytes may undergo eryptosis, a mitochondria-independent suicidal cell death characterized by cell shrinkage and phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include oxidative stress and increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i). During malaria, accelerated death of infected erythrocytes may decrease parasitemia and thus favorably influence the clinical course of the disease. In the present study, phosphatidylserine abundance at the cell surface was estimated from annexin V binding, cell volume from forward scatter, reactive oxidant species (ROS) from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, and [Ca²⁺]_i from Fluo3-fluorescence. A 48 h treatment of human erythrocytes with nelfinavir significantly increased the percentage of annexin-V-binding cells (≥5µg/mL), significantly decreased forward scatter (≥2.5µg/mL), significantly increased ROS abundance (10 µg/mL), and significantly increased [Ca²⁺]_i (≥5 µg/mL). The up-regulation of annexin-V-binding following nelfinavir treatment was significantly blunted, but not abolished by either addition of the antioxidant N-acetylcysteine (1 mM) or removal of extracellular Ca²⁺. In conclusion, exposure of erythrocytes to nelfinavir induces oxidative stress and Ca²⁺ entry, thus leading to suicidal erythrocyte death characterized by erythrocyte shrinkage and erythrocyte membrane scrambling.

Antiretroviral bioanalysis methods of tissues and body biofluids

Research in the many areas of HIV treatment, eradication and prevention has necessitated measurement of antiretroviral (ARV) concentrations in nontraditional specimen types. To determine the knowledgebase of critical details for accurate bioanalysis, a review of the literature was performed and summarized. Bioanalytical assays for 31 ARVs, including metabolites, were identified in 205 publications measuring various tissues and biofluids. 18 and 30% of tissue or biofluid methods, respectively, analyzed more than one specimen type; 35-37% of the tissue or biofluid methods quantitated more than one ARV. 20 and 76% of tissue or biofluid methods, respectively, were used for the analysis of human specimens. HPLC methods with UV detection predominated, but chronologically MS detection began to surpass. 40% of the assays provided complete intra- and inter-assay validation data, but only 9% of publications provided any stability data with even less for the prevalent ARV in treatments.

Pharmacokinetics of verapamil and its metabolite norverapamil in rats with hyperlipidaemia induced by poloxamer 407

In this study, the pharmacokinetics of verapamil and its active metabolite norverapamil were evaluated following intravenous and oral administration of 10 mg/kg verapamil to rats with hyperlipidaemia (HL) induced by poloxamer 407 (HL rats). The total area under the plasma concentration time curve (AUC) of verapamil in HL rats following intravenous administration was significantly greater (by 11.2%) than in control rats due to their slower (by 11%) non-renal clearance. The oral AUC of verapamil in HL rats was also significantly greater (by 116%) compared with controls, with a larger magnitude than the data observed following intravenous administration. This may have been a result of the decreased intestinal metabolism of verapamil in HL rats. The AUC of norverapamil and AUC(norverapamil)/AUC(verapamil) ratios following intravenous and oral administration of verapamil were unchanged in HL rats. Assuming that the HL rat model qualitatively reflects similar changes in patients with HL, the findings of this study have potential therapeutic implications. Further studies in humans are required to determine whether modification of the oral verapamil dosage regimen in HL states is necessary.

Effects of poloxamer 407-induced hyperlipidemia on the pharmacokinetics of carbamazepine and its 10,11-epoxide metabolite in rats: Impact of decreased expression of both CYP3A1/2 and microsomal epoxide hydrolase

The pharmacokinetics of carbamazepine (CBZ) and its active 10,11-epoxide metabolite (CBZ-E) were evaluated after intravenous and oral administration of 5 mg/kg CBZ to rats with hyperlipidemia induced by poloxamer 407 (HL rats) and controls. The total area under the plasma concentration-time curve (AUC) of CBZ in HL rats after intravenous administration was significantly greater than that in controls due to their slower non-renal clearance (CL(NR)). This was due to slower hepatic CL(int) for metabolism of CBZ to CBZ-E in HL rats via CYP3A1/2. This result was consistent with a previous study indicating reduced hepatic CYP3A1/2 expression in HL rats. Interestingly, the AUC of CBZ-E was also increased in HL rats, while AUC(CBZ-E)/AUC(CBZ) ratios remained unchanged. These results suggested that further metabolism of CBZ-E to the inactive metabolite trans-10,11-dihydoxyl-10,11-dihydro-CBZ (CBZ-D) via microsomal epoxide hydrolase (mEH) was also slowed in HL rats. The significantly reduced hepatic mRNA level and expression of mEH protein in HL rats compared to controls confirmed the above hypothesis. Similar pharmacokinetic changes were observed in HL rats after oral administration of CBZ. These findings have potential therapeutic implications assuming that the HL rat model qualitatively reflects similar changes in patients with hyperlipidemia. Caution is required regarding pharmacotherapy in the hyperlipidemic state in cases where drugs that are metabolized principally by CYP3A1/2 or mEH and have a narrow therapeutic range are in use.

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.

Effects of obesity induced by high-fat diet on the pharmacokinetics of nelfinavir, a HIV protease inhibitor, in laboratory rats

The effect of obesity induced by a high-fat diet on the pharmacokinetics (PK) of nelfinavir (NFV) was investigated, focusing on the change of distribution and elimination caused by dyslipidemia and hepatic steatosis.The plasma unbound fraction (f(u)) of NFV in obese rats (0.61+/-0.03%) was significantly lower than in the control (1.10+/-0.09%), caused by increasing the plasma triglyceride-rich lipoprotein level. After intravenous (i.v.) administration of NFV, the marked decrease of the distribution volume and slower total clearance (39.5% and 69.1% of the control, respectively) caused by the lower f(u) were the main reasons for the significantly higher area under the blood concentration versus time curve (AUC) in obese rats (145.3% of the control). The absorption of NFV after intraduodenal (i.d.) administration in obese rats was significantly greater than in the control (AUC; 170.4% of the control). The increased bile in obese rats was the main reason for the increasing absorption of NFV, and the lower expression of intestinal P-glycoprotein was also considered. On the other hand, although higher AUCs in obese rats were shown, unbound AUCs in the obese rats were slightly lower than in the control, namely, the plasma NFV concentration in obese rats to obtain the same pharmacological effect was higher than in the control, suggesting the difficulty of drug monitoring. These results suggest that it is necessary to pay further attention to therapeutic drug monitoring of NFV in patients manifesting metabolic syndrome, such as dyslipidemia and visceral fat accumulation, including hepatic steatosis.