Effectiveness of methyrapone in the treatment of acetaminophen toxicity in mice

Tenebrio molitor as a Simple and Cheap Preclinical Pharmacokinetic and Toxicity Model

The progression of drugs into clinical phases requires proper toxicity assessment in animals and the correct identification of possible metabolites. Accordingly, different animal models are used to preliminarily evaluate toxicity and biotransformations. Rodents are the most common models used to preliminarily evaluate the safety of drugs; however, their use is subject to ethical consideration and elevated costs, and strictly regulated by national legislations. Herein, we developed a novel, cheap and convenient toxicity model using Tenebrio molitor coleoptera (TMC). A panel of 15 drugs-including antivirals and antibacterials-with different therapeutic applications was administered to TMC and the LD50 was determined. The values are comparable with those already determined in mice and rats. In addition, a TMC model was used to determine the presence of the main metabolites and in vivo pharmacokinetics (PK), and results were compared with those available from in vitro assays and the literature. Taken together, our results demonstrate that TMC can be used as a novel and convenient preliminary toxicity model to preliminarily evaluate the safety of experimental compounds and the formation of main metabolites, and to reduce the costs and number of rodents, according to 3R principles.

Studies on preventive and curative effects of berberine on chemical-induced hepatotoxicity in rodents

Berberis aristata is an edible plant employed in the South Asian Traditional Medicine, particularly its fruits being used as a tonic remedy for liver and heart. In this investigation, berberine, a known compound from this plant, was studied for its possible antihepatotoxic action in rats. Pretreatment of animals with berberine (4 mg/kg; orally twice daily for 2 days) prevented the acetaminophen- or CCl4-induced rise in serum levels of alkaline phosphatase (ALP) and aminotransaminases (AST and ALT), suggestive of hepatoprotection. Post-treatment with three successive oral doses of berberine (4 mg/kg every 6 h) reduced the hepatic damage induced by acetaminophen, while CCl4-induced hepatotoxicity was not modified, suggesting a selective curative effect against acetaminophen. Pretreatment of animals with a single oral dose of berberine (4 mg/kg) induced prolongation of the pentobarbital (60 mg/kg, i.p.)-induced sleeping time as well as increased strychnine (0.3 mg/kg; i.p.)-induced toxicity, suggestive of inhibitory effect on microsomal drug metabolizing enzymes, cytochrome P450s (CYPs).

Potentiation of paracetamol and carbon tetrachloride-induced hepatotoxicity in rodents by the food additive vanillin

The potential of vanillin to potentiate the paracetamol and carbon tetrachloride (CCl4)-induced hepatotoxicity was investigated in rats. Vanillin when given alone (15 mg/kg, orally), did not modify liver function in rats as the values of serum enzymes of alkaline phosphatase (ALP) and aminotransaminases (AST and ALT) were found similar to those in the normal animals. However, when given repeatedly before the administration of the subtoxic dose of paracetamol (500 mg/kg) or CCl4 (1 ml/kg), vanillin caused liver damage, as manifested by the significant increase in the serum levels of hepatic enzymes. When tested for its possible interaction with pentobarbital (75 mg/kg, i.p.) and strychnine (0.9 mg/kg, i.p.), it caused reduction in pentobarbital-induced sleep in mice as well as preventing the animals against the lethal effect of strychnine, suggestive of an induction of microsomal drug metabolizing enzymes. These results indicate that vanillin potentiates the hepatotoxic potential of paracetamol and CCl4 in rats probably through an enzyme induction process.

Studies on protective effect of DA-9601, Artemisia asiatica extract, on acetaminophen- and CCl4-induced liver damage in rats

The hepatoprotective effect of DA-9601, a quality-controlled extract of Artemisia asiatica, on liver damage induced by acetaminophen (APAP) and carbon tetrachloride (CCl4) was investigated by means of serum-biochemical, hepatic-biochemical, and histopathological examinations. Doses of DA-9601 (10, 30, or 100 mg/kg) were administered intragastrically to each rat on three consecutive days i.e. 48 h, 24 h and 2 h before a single administration of APAP (640 mg/kg, i.p.) or CCl4 (2 ml/kg, p.o.). Four h and 24 h after hepatotoxin treatment, the animals were sacrificed for evaluation of liver damage. Pretreatment of DA-9601 reduced the elevation of serum ALT, AST, LDH and histopathological changes such as centrilobular necrosis, vacuolar degeneration and inflammatory cell infiltration dose-dependently. DA-9601 also prevented APAP- and CCl4-induced hepatic glutathione (GSH) depletion and CCl4-induced increase of hepatic malondialdehyde (MDA), a parameter of lipid peroxidation, in a dose-dependent manner. These findings suggest that pretreatment with DA-9601 may reduce chemically induced liver injury by complex mechanisms which involve prevention of lipid peroxidation and preservation of hepatic GSH.

Selective protective effect of an extract from Fumaria parviflora on paracetamol-induced hepatotoxicity

1. The hepatoprotective activity of an aqueous-methanolic extract of Fumaria parviflora was investigated against paracetamol- and CCI4-induced hepatic damage. 2. Paracetamol (1 g/kg; orally) produced 100% mortality in mice; pretreatment of animals with the plant extract (500 mg/kg; orally) reduced the death rate to 50%. 3. Pretreatment of rats with plant extract (500 mg/kg, orally twice daily for 2 days) prevented (P < 0.001) the paracetamol (640 mg/kg)-induced rise in serum enzymes alkaline phosphatase (ALP) and transaminases (GOT and GPT), whereas the same dose of the extract was unable to prevent (P > 0.05) the CCI4-induced rise in serum enzyme levels. 4. Posttreatment with 3 successive doses of the extract (500 mg/kg, 6 hourly) also restricted the paracetamol-induced hepatic damage. 5. The plant extract (500 mg/kg; orally) caused significant prolongation in pentobarbital (75 mg/ kg)-induced sleep as well as increased strychnine-induced lethality in mice (P < 0.05), suggestive of an inhibitory effect on microsomal drug metabolizing enzymes (MDME). 6. It is conceivable therefore, that Fumaria parviflora extract exhibits a selective protective effect against paracetamol-induced hepatotoxicity, probably mediated through MDME inhibition.

Preventive and curative effects of Artemisia absinthium on acetaminophen and CCl4-induced hepatotoxicity

1. Effect of aqueous-methanolic extract of Artemisia absinthium (Compositae) was investigated against acetaminophen- and CCl4-induced hepatic damage. 2. Acetaminophen produced 100% mortality at the dose of 1 g/kg in mice while pretreatment of animals with plant extract (500 mg/kg) reduced the death rate to 20%. 3. Pretreatment of rats with plant extract (500 mg/kg, orally twice daily for two days) prevented (P < 0.01) the acetaminophen (640 mg/kg) as well as CCl4 (1.5 ml/kg)-induced rise in serum transaminases (GOT and GPT). 4. Post-treatment with three successive doses of extract (500 mg/kg, 6 hr) restricted the hepatic damage induced by acetaminophen (P < 0.01) but CCl4-induced hepatotoxicity was not altered (P > 0.05). 5. Plant extract (500 mg/kg) caused significant prolongation (P < 0.05) in pentobarbital (75 mg/kg)-induced sleep as well as increased strychnine-induced lethality in mice suggestive of inhibitory effect on microsomal drug metabolizing enzymes (MDME). 6. These results indicate that the crude extract of Artemisia absinthium exhibits hepatoprotective action partly through MDME inhibitory action and validates the traditional use of plant in hepatic damage.

The influence of disulfiram on acetaminophen metabolism in man

1. Acetaminophen clearance and its partial clearance to its major metabolites has been determined before and after 5 days treatment with the anti-alcohol abuse agent disulfiram (200 mg daily). The study was conducted in 10 subjects, five without liver disease and five with alcoholic cirrhosis of the liver. Acetaminophen was given i.v. at a dose of 500 mg. Plasma samples were obtained up to 8 h after injection and urine collected for 24 h. 2. Across all subjects acetaminophen plasma clearance was reduced from 0.249 +/- 0.061 to 0.217 +/- 0.066 l/min after disulfiram treatment (mean +/- SD, P less than 0.05). Thus no change in acetaminophen dosage would be required in patients treated with disulfiram. 3. The partial clearance of acetaminophen to its glucuronide, sulphate and glutathione derivatives (i.e. cysteine and N-acetyl cysteine) was not significantly changed by disulfiram treatment. Thus it seems unlikely that the previously observed protective effects of disulfiram against acetaminophen-induced hepatotoxicity in animals due to inhibition of metabolism will be seen in man.

Comparison of the effects of ascorbyl palmitate and L-ascorbic acid on paracetamol-induced hepatotoxicity in the mouse

The effects of ascorbyl palmitate (ASCP) and free L-ascorbic acid (LAA) on the hepatotoxicity of paracetamol (acetaminophen) and the in vivo covalent binding of reactive paracetamol metabolites to hepatic proteins has been studied in male MF1 mice. The oral administration of [3H(G)]paracetamol (600 mg/kg) resulted in covalent binding to hepatic proteins, a depletion of hepatic non-protein sulphydryl (NPS) groups after 2 h, and a marked elevation of plasma alanine aminotransferase (ALAT) activity after 24 h. The co-administration of paracetamol and ASCP (1412 mg/kg, equivalent to 600 mg/kg free LAA), but not paracetamol and LAA (600 mg/kg), significantly reduced covalent binding of paracetamol metabolites at 2 and 4 h after treatment. In addition ASCP, but not LAA, significantly reduced the depletion of NPS groups and the elevation of plasma ALAT activity. ASCP also completely prevented the 35% mortality observed at 24 h in paracetamol treated mice. These results demonstrate that ASCP, but not LAA, when co-administered orally with the analgesic is an effective inhibitor of paracetamol-induced hepatotoxicity in the mouse. The mechanism by which ASCP prevents liver injury appears to involve destruction of reactive paracetamol metabolites which is associated with a sparing action on hepatic reduced glutathione levels.

Pharmacokinetic consequences and toxicologic implications of metyrapone-induced alterations of acetaminophen elimination in man

This study examined the effect of metyrapone on the elimination rate of acetaminophen and on the apparent formation rate of acetaminophen metabolites in man. Metyrapone treatment, 1.5 g, increased the half-life of acetaminophen, decreased the fraction of the dose recovered in the urine as the glucuronide and increased the fraction of the dose recovered in urine as the sulfate and mercapturate conjugates. The apparent rate constant for the formation of acetaminophen glucuronide was significantly decreased by metyrapone while the apparent rate constants for the formation of the sulfate and mercapturic acid metabolites were unchanged or slightly increased, respectively. These data indicate that metyrapone inhibits acetaminophen glucuronidation and possibly enhances the oxidation of acetaminophen to its quantitatively minor yet highly toxic reactive metabolite. The extent to which the parallel pathways of acetaminophen elimination are also affected by inhibitors of cytochrome P-450-mediated oxidation will limit the efficacy of these types of potential antidotes for the treatment of acetaminophen overdose.

Hamster hepatocytes in culture as a model for acetaminophen toxicity studies with inhibitors of drug metabolism

A hamster hepatocyte system was developed for use in studying the toxicity of acetaminophen (APAP). The cells were isolated and placed in culture conditions in petri dishes containing a film of collagen. Hepatocytes, after attachment to collagen, were exposed for various periods of time to different concentrations of APAP. Hepatocytes exposed to APAP exhibited concentration- and time-dependent GSH depletion followed by cytoplasmic enzyme leakage and an increase in malondialdehyde content (TBA-reactive material). These effects were reduced by the drug metabolism inhibitors metyrapone, piperonyl butoxide, and dithiocarb. Removal of APAP and its unbound metabolites from cells prior to 1.5 hr followed by culture in drug-free medium resulted in no observable damage to the cells over a 24-hr period. Removal of drug after longer exposure times followed by culture in fresh medium resulted in eventual cell damage. This finding showed that deleterious changes caused by APAP occurred over a 1.5-hr period after which eventual hepatocyte damage could not be reversed by removal of the drug. Further experiments showed that metyrapone and dithiocarb had some protective effect when added after APAP had been completely removed from damaged cells. This result indicates that these agents have a protective action separate from, and in addition to, their ability to inhibit APAP oxidation via cytochromes P-450.