C.J. Paul

Effect of a concomitant single dose of ethanol on the hepatotoxicity and metabolism of acetaminophen in mice

A concomitant single dose of ethanol (1 g/kg) protected mice from hepatic injury induced by acetaminophen (250 mg/kg) as evidenced by the lowering of plasma transaminases. Pharmacokinetic studies with [14C]acetaminophen indicated that ethanol enhanced the initial blood concentrations of radiolabel and its rate of elimination. A tissue distribution study suggested that these effects were probably due to an ethanol-induced inhibition of the biliary clearance of acetaminophen from the blood. Examination of the urinary and biliary metabolites indicated that ethanol inhibited the excretion of the degradation products derived from the glutathione-deactivated hepatotoxic acetaminophen intermediate. The decrease in acetaminophen induced hepatotoxicity was therefore attributed to an inhibitory effect of ethanol on the biotransformation of acetaminophen to the toxic intermediate.

Pathways of disposition of acetaminophen conjugates in the mouse.

After a single dose of [14C]acetaminophen (50 mg/kg) was administered orally to bile duct cannulated mice, 13.9% of the radioactivity was recovered in the bile while 41.2% was found in the urine in the first 3 h after administration. Analyses of biles revealed that the major biliary metabolite was acetaminophen glutathione (AG) conjugate which was derived from the hepatotoxic acetaminophen intermediate. Examination of urines showed that they contained mostly glucuronide and sulfate conjugates with no AG or its degradation products (cysteine and mercapturate). Analysis of urines collected from non-cannulated animals at 4 h showed that they contained glucuronide, sulfate, cysteine and mercapturate metabolites. Our results suggest that after formation in the liver, the majority of the glucuronide and sulfate conjugates were directly eliminated by the kidney. On the other hand, the pathway for the disposition of the glutathione conjugate was first into the bile, then reabsorption, and finally disposition into the urine as cysteine and mercapturate metabolites.

Enalapril cytotoxicity in primary cultures of rat hepatocytes. I. Effects of cytochrome P450 inducers and inhibitors

Enalapril maleate (EN) incubated with primary cultures of rat hepatocytes was cytotoxic in concentrations of 0.5 mM or greater. Toxicity was measured by release of lactate dehydrogenase (LDH) into the culture medium at 24 h. SKF525A, alpha-naphthoflavone (alpha NF) and metyrapone (MTP) reduced the toxicity of EN. In vivo pretreatment with phenobarbital (PB) and beta-naphthoflavone (beta NF) had minor protective effects on the responses of hepatocytes to EN exposure. However, in vivo pretreatment with pregnenolone-16 alpha-carbonitrile (PCN) substantially potentiated EN cytotoxicity. These results suggest that the cytocidal hepatotoxicity of EN in primary culture depends to some degree on metabolic activation by a cytochrome P450 species.

Effect of acetylsalicylic acid on a toxic dose of acetaminophen in the mouse

Abstract The effect of acetylsalicylic acid (ASA) on the toxicity and metabolism of [14C]acetaminophen was studied in the mouse. Pretreatment with ASA did not affect lethality, but hepatotoxicity as determined by plasma transaminases was reduced by ASA pretreatment. The blood concentration profiles of radioactivity were altered by ASA following po and ip administration. It was suggested that ASA reduced the rate of acetaminophen absorption and inhibited elimination. Paper chromatography of urine showed that following ip dosing ASA reduced the excretion of sulfate conjugate but increased the excretion of total catabolites of the glutathione conjugate. In the po study a similar inhibition of sulfation was observed, but excretion of total glutathione degradation products was not altered statistically even though excretion of mercapturate was statistically elevated by ASA pretreatment. An attempt was made to correlate the excretion of glutathione degradation products (an estimate of the toxic pathway) with toxicity. A direct correlation could not always be demonstrated, and it was concluded that factors additional to toxic metabolite formation modified acetaminophen-induced hepatotoxicity in the mouse.

Interaction of cannabinoids with pentobarbital in rats

The effect of cannabidiol (CBD), cannabigerol (CBG), cannabinol (CBN), Δ8-tetrahydrocannabinol (Δ8-THC), and Δ9-tetrahydrocannabinol (Δ9-THC) on the in vivo metabolism of [14C]pentobarbital (14C-P) was investigated in rats. The cannabinoids were administered ip (20 mg/kg) 30 min prior to either oral or iv treatment with 14C-P. When 14C-P was given po, the 14C blood concentrations were initially depressed and later elevated by CBG and CBD, increased by Δ8-THC and Δ9-THC and unaffected by CBN. When 14C-P was injected iv, the blood 14C values were elevated by CBD and unchanged by CBG, Δ8-THC or Δ9-THC. Urinary excretion of total 14C and the metabolites of P was decreased by CBD, CBG and Δ8-THC during the first 6 hr following treatment. The effect of CBD on the blood concentration and urinary excretion of 14C was dose-related. In rats treated with CBD + P, the liver and serum concentrations of P metabolites were significantly lower and the liver, serum and brain concentrations of unmetabolized P were significantly higher than in P-treated rats. Pentobarbital induction and sleeping times were potentiated by CBD and Δ9-THC and antagonized by CBG. It was concluded that CBD delayed P metabolism, CBG decreased the rate of P absorption and excretion. Δ8-THC and Δ9-THC decreased elimination of P and CBN had little effect on P absorption, metabolism or excretion. The effect of CBD + P on sleeping time was correlated with brain P concentrations.

N-acetylcysteine-induced inhibition of gastric emptying: A mechanism affording protection to mice from the hepatotoxicity of concomitantly administered acetaminophen☆

Swiss Webster male mice, 22 +/- 3 g, killed 17-18 h following the concomitant oral administration of acetaminophen (350 mg/kg) and N-acetyl-cysteine (NAC, 100-500 mg/kg, treated) had statistically significant lower plasma transaminases (GOT and GPT) than control mice (acetaminophen + water). Possible mechanisms underlying this protective effect of NAC were examined. NAC (500 mg/kg) reduced [14C]acetaminophen-derived radioactivity in the blood and tissues but increased the percentage of the dose in the gastrointestinal tract. Depletion of hepatic sulphydryl compounds below 75% of the control value was prevented by NAC treatment, whereas urinary excretion of mercapturate and sulfate, metabolites derived from sulphydryls, were proportionally increased and excretion of unchanged drug was decreased by NAC. Absorption of acetaminophen from the small intestine was prevented by NAC and this was attributed to an inhibition in gastric emptying. Since all changes observed following NAC treatment could be attributed to inhibition of gastric emptying, it was considered the major mechanism responsible for affording in mice protection from acetaminophen-induced hepatocellular damage following concomitant oral administration.

Effect of sodium salicylate on the fate of warfarin in the rat

Abstract Salicylate (88.9 mg/kg, po) decreased the blood level of radioactivity emanating from [ 14 C]warfarin (1 mg/kg, iv and po) during the 24 hr following drug administration, reduced the area under the blood radioactivity vs time curve, and shortened the half-life for elimination of radioactivity from the blood. During the first 6 hr after drug administration, salicylate increased the biliary excretion of radioactivity, which resulted in enhanced fecal excretion of warfarin and its metabolites. Salicylate administration initially increased and later decreased the amount of radioactivity in the liver, and increased the proportion of warfarin metabolites to unchanged warfarin in this organ. It did not affect the proportion of unchanged warfarin to metabolites in the blood, bile and urine, or the total amount of radioactivity excreted during 48 hr in the urine and feces. In vitro, salicylate decreased the binding of [ 14 C]warfarin to rat serum proteins in a linear manner. It is concluded that, in the rat, salicylate competes with warfarin for serum protein binding sites, thereby facilitating its uptake by the liver. Second, through a combination of its choleretic action and effect on membrane transport, salicylate enhances the biliary excretion of warfarin and its metabolites, thus accounting for the decreased concentration in the blood and lowered antiboagulant action.

Enalapril cytotoxicity in primary cultures of rat hepatocytes. II. Role of glutathione

The cytotoxicity of enalapril maleate (EN) in primary cultures of rat hepatocytes, at concentrations of 0.5 mM or greater, was measured by the release of lactate dehydrogenase (LDH) into the culture medium. Pretreatment of the hepatocytes with L-buthionine-(S,R)-sulfoximine (BSO) and diethyl maleate (DEM) potentiated the toxicity whereas N-acetyl-L-cysteine (NAC) provided protection. EN produced a dose-dependent reduction in intracellular glutathione (GSH) concentration. This was an early effect, apparent after only 1 h of exposure to the drug, whereas loss of cell viability occurred after 6-18 h. These results suggest that the mechanism of EN cytotoxicity involves a GSH-dependent detoxification pathway.

Effect of ethanol on the pharmacokinetics of 2-14C-methaqualone in the rat.

Abstract Blood concentrations of radioactivity at 2, 3 and 4 hr and tissue concentrations at 4 hr following 2- 14 C-methaqualone (25 mg/kg po) administration, were statistically higher in rats simultaneously dosed with ethanol (3 gm/kg po) than in controls receiving only methaqualone. The major route of elimination was biliary excretion and ethanol inhibited the biliary clearance of carbon-14. An inhibition of metabolism by ethanol could not be demonstrated and reduced clearance was attributed to a depression of active secretory processes by ethanol. Consequently, an elevation of plasma concentrations of free drug and an increased uptake of methaqualone into lipoid tissues such as the brain occurred offering an explanation for reports of potentiation following administration of the ethanolmethaqualone combination.

Use of a discrete diode array spectrophotometer for the quantitative and qualitative analysis of cytochrome P-450

Cytochrome P-450, the hemoprotein located in the endoplasmic reticulum of mammalian cells and responsible for the metabolism of xenobiotics, was qualitatively and quantitatively analyzed using the HP-8450A diode array spectrophotometer. The diode array instrument was compared to a conventional spectrophotometer and the advantages of the diode array instrument over conventional spectrophotometry with respect to the analysis of cytrochrome P-450 were discussed.