Pharmacokinetic interaction between oltipraz and dimethyl-4,4‘-dimethoxy-5,6,5′,6’-dimethylene dioxybiphenyl-2,2′-dicarboxylate (DDB) after single intravenous and oral administration to rats

An active metabolite of oltipraz (M2) increases mitochondrial fuel oxidation and inhibits lipogenesis in the liver by dually activating AMPK

BACKGROUND AND PURPOSE

Oltipraz, a cancer chemopreventive agent, has an anti-steatotic effect via liver X receptor-α (LXRα) inhibition. Here we have assessed the biological activity of a major metabolite of oltipraz (M2) against liver steatosis and steatohepatitis and the underlying mechanism(s).

EXPERIMENTAL APPROACH

Blood biochemistry and histopathology were assessed in high-fat diet (HFD)-fed mice treated with M2. An in vitroHepG2 cell model was used to study the mechanism of action. Immunoblotting, real-time PCR and luciferase reporter assays were performed to measure target protein or gene expression levels.

KEY RESULTS

M2 treatment inhibited HFD-induced steatohepatitis and diminished oxidative stress in liver. It increased expression of genes encoding proteins involved in mitochondrial fuel oxidation. Mitochondrial DNA content and oxygen consumption rate were enhanced. Moreover, M2 treatment repressed activity of LXRα and induction of its target genes, indicating anti-lipogenic effects. M2 activated AMP-activated protein kinase (AMPK). Inhibition of AMPK by over-expression of dominant negative AMPK (DN-AMPK) or by Compound C prevented M2 from inducing genes for fatty acid oxidation and repressed sterol regulatory element binding protein-1c (SREBP-1c) expression. M2 activated liver kinase B1 (LKB1) and increased the AMP/ATP ratio. LKB1 knockdown failed to reverse target protein modulations or AMPK activation by M2, supporting the proposal that both LKB1 and increased AMP/ATP ratio contribute to its anti-steatotic effect.

CONCLUSION AND IMPLICATIONS

M2 inhibited liver steatosis and steatohepatitis by enhancing mitochondrial fuel oxidation and inhibiting lipogenesis. These effects reflected activation of AMPK elicited by increases in LKB1 activity and AMP/ATP ratio.

Contribution of a significant first-pass effect of dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate in the liver to its poor bioavailability in rats

Objectives

The objective of this study was to investigate the mechanism responsible for the poor oral bioavailability of dimethyl-4′,4′-dimethoxy-5,6,5′,6′-dimethylene dioxy-biphenyl-2,2′-dicarboxylate (DDB), a hepatoprotective agent, in rats.

Methods

DDB was intravenously administered to rats at doses of 0.2-1 mg/kg. To determine the hepatic first-pass effect in rats, DDB (1 mg/kg) was administered via the pyloric vein and the femoral vein. Direct measurement of intestinal permeability was attempted using Caco-2 cell monolayers and rat intestinal epithelium.

Key findings

A moment analysis indicated that the volume of distribution and clearance remained unchanged with the magnitude of the dose, indicating that DDB exhibited linear pharmacokinetics. When the area under the curve for DDB after administration to the pyloric vein was compared with that after femoral vein administration, the ratio (FH) was found to be 0.294, indicating a significant first-pass effect for DDB. The permeability of DDB was high in the rat intestine (1.78 ± 0.229 × 10−5 cm/s) and in Caco-2 cell monolayers (6.8 ± 0.70 × 10−5 cm/s), suggesting that DDB, in soluble form, was readily permeable across the intestinal epithelium.

Conclusions

These observations indicated that despite the fact that DDB was readily permeable to the intestinal epithelium, a significant first-pass metabolism was associated with its pharmacokinetics in rats.

Therapeutic potential of dithiolethiones for hepatic diseases

Comprehensive studies support the notion that oltipraz [4-methyl-5-(2-pyrazynyl)-1,2-dithiole-3-thione] and its congeners exert cancer chemopreventive effects by the prevention, inhibition or reversal of carcinogenic processes. Recently, it was found that dithiolethione compounds had the activities to prevent or treat fibrosis, insulin resistance, and mitochondrial protective effects in the liver by a mechanism involving AMP-activated protein kinase (AMPK) and/or 70-kDa ribosomal protein S6 kinase 1 (S6K1). Moreover, chemical regulation of the AMPK-S6K1 pathway was found to affect Liver X receptor (LXR) activity and lipogenesis, leading to the identification of AMPK and S6K1 as targets for treating hepatic steatosis. These biological activities of dithiolethiones may offer a novel approach to pharmaceutical intervention. This review focuses on the interaction between oltipraz and the AMPK-mTOR-S6K1 pathway, which regulates genes that confer hepatocyte protection from intoxication, disrupted energy metabolism, and inflammation. In terms of therapeutic potential, the findings reviewed here demonstrate a new therapeutic potential for dithiolethiones, which function in a unique manner, and offer the possibility of new treatments for hepatic diseases.

Pharmacokinetics of 7-carboxymethyloxy-3',4',5-trimethoxy flavone (DA-6034), a derivative of flavonoid, in mouse and rat models of chemically-induced inflammatory bowel disease

The pharmacokinetics (including distribution in the gastrointestinal tract) of 7-carboxymethyloxy-3',4',5-trimethoxy flavone (DA-6034) has been investigated in several mouse and rat models of chemically-induced inflammatory bowel disease (IBD). In the female ICR mouse model, IBD was induced by dextran sulfate and the mice administered 30 mg kg(-1) DA-6034 intravenously or orally. In the male SJL mouse model of IBD induced by oxazolone, 30 mg kg(-1) DA-6034 was administered orally. In the male Sprague-Dawley rat model of IBD induced by trinitrobenzene sulfonic acid (TNBS), 10 mg kg(-1) DA-6034 was administered intravenously and orally. After intravenous administration, the total area under the plasma concentration-time curve from time zero to the last measured time, t, in plasma (AUC(0-t)) values were comparable between control and dextran sulfate-induced IBD mice, and between control and TNBS-induced rats. This suggested that the disposition of DA-6034 was not affected considerably by dextran sulfate in mice and TNBS in rats. However, after oral administration in mice and rats with IBD, the AUC(0-t) values were greater compared with the respective controls. This could have been due to an increase (slow) in the gastrointestinal transit time (in IBD mice and rats, the percentages of the oral dose recovered from the rinsing fluid of the small intestine and large intestine as unchanged drug were greater and smaller, respectively), and an increase in intestinal permeability.

Interspecies pharmacokinetic scaling of oltipraz in mice, rats, rabbits and dogs, and prediction of human pharmacokinetics

Dose-independent pharmacokinetics of oltipraz after intravenous and/or oral administration at various doses to mice, rats, rabbits and dogs were evaluated. After both intravenous and/or oral administration of oltipraz to mice (5, 10 and 20 mg/kg for intravenous and 15, 30 and 50 mg/kg for oral administration), rats (5, 10 and 20 mg/kg for intravenous and 25, 50 and 100 mg/kg for oral administration), rabbits (5, 10 and 30 mg/kg for intravenous administration) and dogs (5 and 10 mg/kg for intravenous and 50 and 100 mg/kg for oral administration), the total area under the plasma concentration-time curve from time zero to time infinity (AUC) values of oltipraz were dose-proportional in all animals studied. Animal scale-up of some pharmacokinetics parameters of oltipraz was also performed based on the parameters after intravenous administration at a dose of 10 mg/kg to mice, rats, rabbits and dogs. Linear relationships were obtained between log time-averaged total body clearance (Cl) x maximum life-span potential (MLP) (1 year/h) and log species body weight (W) (kg) (r=0.999; p=0.0015), log Cl (l/h) and log W (kg) (r=0.979; p=0.0209), and log apparent volume of distribution at steady state (V(ss)) (l) and log W (kg) (r=0.999; p=0.0009). The corresponding allometric equations were ClxMLP=49.8 W(0.861), Cl=5.20 W(0.523) and V(ss)=4.46 W(0.764). Interspecies scale-up of plasma concentration-time data for the four species using pharmacokinetic time of dienetichron resulted in similar profiles. In addition, concentrations of oltipraz in a plasma concentration-time profile for humans predicted using the four animal data fitted to the dienetichron time transformation of animal data.

Effects of acute renal failure on the pharmacokinetics of oltipraz in rats

Pharmacokinetic parameters of oltipraz were compared after intravenous and oral administration at a dose of 30 mg/kg to control rats and rats with U-ARF. After intravenous administration to rats with U-ARF, the AUC was significantly greater (1100 versus 1730 microg x min/mL) than that in control rats, and this could be due to significantly slower CL (27.2 versus 17.3 mL/min/kg). The slower CL could be mainly due to significantly slower CL(NR) (27.2 versus 17.3 mL/min/kg), and this could be supported by significantly slower in vitro CL(int) (32.1 versus 13.2 mL/min/whole liver) in the rats. The Vss was significantly larger in rats with U-ARF (4050 versus 5680 mL/kg), and this was not due to a significant increase in free fractions (unbound in plasma proteins) of oltipraz in the rats because the free fractions were 17.0 and 15.7% for control rats and rats with U-ARF, respectively. Unexpectedly, after oral administration to rats with U-ARF, the AUC of oltipraz was significantly smaller than that in control rats (329 versus 149 microg x min/mL), and this could be mainly due to a decrease in the absorption of oltipraz from the gastrointestinal tract in the rats (95 and 72% of the oral dose were absorbed in control rats and rats with U-ARF, respectively).

Pharmacokinetic changes of oltipraz after intravenous and oral administration to rats with liver cirrhosis induced by dimethylnitrosamine

Pharmacokinetic changes of oltipraz were investigated after intravenous and oral administration at a dose of 30 mg/kg to control Sprague-Dawley rats and rats with liver cirrhosis induced by dimethylnitrosamine. After intravenous administration in rats with liver cirrhosis, the area under the plasma concentration-time curve from time zero to time infinity (AUC) was significantly greater (1490 microg min/ml versus 2840 microg min/ml) than that in control rats. This was due to significantly slower total body clearance (CL) (20.2 ml/(min kg) versus 10.6 ml/(min kg)) in the rats. The slower CL was due to significantly slower CL(NR) (20.1 ml/(min kg) versus 10.5 ml/(min kg)) in rats with liver cirrhosis. The significantly slow CL(NR) was due to slower hepatic blood flow rate and significantly slower in vitro intrinsic oltipraz disappearance clearance (CL(int), 77.2 ml/min per whole liver versus 11.5 ml/min per whole liver) because the free (unbound in serum proteins) fraction of oltipraz was significantly greater (15.1% versus 31.3%) in the rats. After oral administration in rats with liver cirrhosis, the AUC was also significantly greater (354 microg min/ml versus 812 microg min/ml) and this was not due to increased absorption in the rats. This also could be due to slower hepatic blood flow rate and significantly slower CL(int) in the rats.