Biomedical subjects

J A Timbrell

Publications and source records attributed to J A Timbrell.

At least 37 records · Page 2Linked to original sources

PubMed1995

The in vivo and in vitro protective properties of taurine.

1. Taurine is a ubiquitous, free amino acid found in mammalian systems. 2. The biological functions of taurine are unclear. 3. Various in vivo data suggest that taurine has a variety of protective functions and deficiency leads to pathological changes. 4. Depletion in rats of taurine increases susceptibility to liver damage from carbon tetrachloride. 5. Susceptibility to a variety of hepatotoxicants correlates with the estimated hepatic taurine level. 6. In vitro data suggest that taurine can protect cells against toxic damage. 7. Taurine protects isolated hepatocytes against carbon tetrachloride, hydrazine and 1,4-naphthoquinone but not against allyl alcohol, alpha-naphthylisothiocyanate (ANIT) or diaminodiphenyl methane (DAPM) cytotoxicity. 8. The mechanisms of protection are unclear but may include modulation of calcium levels, osmoregulation and membrane stabilization.

Animals↗

PubMed1995

In vitro microsomal metabolism of hydrazine.

1. It has been demonstrated that hydrazine is metabolized by rat liver enzymes located in the microsomal fraction. This metabolism was reduced in the absence of oxygen or NADPH and was increased by NADH in the presence of NADPH. 2. Microsomal enzyme inhibitors, piperonyl butoxide and metyrapone, significantly inhibited hydrazine metabolism but glutathione had no affect and was not depleted. 3. In addition to P450, flavin monooxygenase may also be involved in catalysing the microsomal metabolism of hydrazine. 4. Liver microsomes prepared from either beta-naphthoflavone, acetone or the isoniazid-pretreated rat did not show a significant increase in hydrazine metabolism compared with microsomes from the control rat. However, although phenobarbitone pretreatment increased overall microsomal hydrazine metabolism this was not increased relative to P450 content. 5. Hydrazine metabolism was 20-70% lower in human microsomes prepared from three individuals compared with the control rat. 6. Hydrazine is also metabolized by rat liver mitochondria but the monoamine oxidase inhibitors clorgyline and pargyline do not significantly decrease this.

Adolescent↗

PubMed1995

Role of cytochrome P450 in hydrazine toxicity in isolated hepatocytes in vitro.

1. Hepatocytes, isolated from the control, diethyldithiocarbamate (DEDC), acetone, isoniazed and hydrazine pretreated rat, were incubated with hydrazine (8-20 mM) for 3 h. Hydrazine caused a dose-dependent loss of viability, leakage of LDH, depletion of GSH and ATP and an inhibition of the incorporation of 3H-leucine into protein. 2. Pretreatment with DEDC increased, whereas hydrazine and acetone pretreatments decreased the cytoxicity and biochemical effects of hydrazine. Pretreatment with isoniazid slightly increased hydrazine cytotoxicity. Acetone pretreatment reduced the inhibition of protein synthesis caused by hydrazine compared to the control. 3. 4-Nitrophenol hydroxylase activity (P4502E1) correlated with viability, LDH leakage, ATP and GSH depletion in cells from the control, DEDC, acetone and hydrazine pretreated rats. 4. The activities of PROD (P4502B1) and EROD (P4501A1/1A2) also correlated with the above parameters for all treatments. The results suggest that three isoenzymes may be involved in the detoxication of hydrazine. Protein synthesis inhibition did not correlate with the activities of any of the enzymes measured.

Acetone↗

PubMed1994

Effect of acute and repeated exposure to low doses of hydrazine on hepatic microsomal enzymes and biochemical parameters in vivo.

A single dose of hydrazine (3 mg.kg-1 i.p.) caused hepatic accumulation of triglycerides and depletion of ATP in rats after 9 h. Repeated exposure of rats to hydrazine (approximately equal to 2.5 mg.kg-1 per day) for 10 days resulted in depletion of hepatic reduced glutathione (GSH) and triglycerides. Repeated exposure to hydrazine also caused a significant (time dependent) induction of p-nitrophenol hydroxylase (NPH) activity together with changes in other hepatic microsomal enzymes. These included 7-pentoxyresorufin O-deethylase (PROD) and 7-ethoxyresorufin O-de ethylase (EROD) activity, total cytochrome P450, cytochrome b5 and cytochrome P450 reductase activity. Repeated exposure to lower levels of hydrazine (approximately equal to 0.250 mg.kg-1 per day) caused no significant hepatic biochemical or microsomal changes after 5 or 10 days except for an increase in NPH activity (17%) and liver ATP (15%) after 5 days.

Animals↗

PubMed1994

Influence of inducers and inhibitors of cytochrome P450 on the hepatotoxicity of hydrazine in vivo.

Hydrazine hepatotoxicity in vivo, as manifested by triglyceride accumulation, depletion of ATP and reduced glutathione (GSH) was shown to be dose related. The effect of pretreatment of rats with various inhibitors and inducers of cytochrome P450 on these dose-response relationships was investigated. Pretreatment with the inhibitor piperonyl butoxide increased triglyceride accumulation whereas pretreatment with the inducers phenobarbital and beta-naphthoflavone (BNF) resulted in reduced triglyceride accumulation. Pretreatment with the inducers acetone and isoniazid also enhanced triglyceride accumulation. Only phenobarbital pretreatment also significantly reduced GSH and ATP depletion. A linear correlation was found between hepatic glutathione and ATP levels in non-pretreated animals given various doses of hydrazine. However, exponential relationships were found between hepatic triglycerides and both hepatic ATP and glutathione. The results suggest that i) the hepatotoxicity of hydrazine can be modulated by inducing or inhibiting particular isoenzymes of cytochrome P450, ii) ATP and GSH depletion may not be directly involved in the development of fatty liver.

Acetone↗

PubMed1994

Studies on the muscle toxicant 2,3,5,6-tetramethyl p-phenylenediamine: effects on various biomarkers including urinary creatine and taurine.

The effect of the specific muscle toxicant, 2,3,5,6-tetramethyl p-phenylenediamine (TMPD), on urinary creatine and taurine, markers of testicular and liver dysfunction, respectively, has been investigated in male Sprague-Dawley rats. Damage to the gastrocnemius and soleus muscles was accompanied by a rise in serum creatine kinase (predominantly the muscle-specific isoenzyme, CK-MM), alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Increases in serum alpha-hydroxybutyrate dehydrogenase (HBDH) and total lactate dehydrogenase (LDH) (mainly isoenzymes, LDH1 and LDH2), occurred but only minor damage to the heart and no rise in CK-MB, (heart muscle isoenzyme) was seen. Damage to stage XIV tubules in the testis was evident histologically after the highest dose. This was accompanied by an increase in LDH-C4 testis-specific isoenzyme and a decrease in serum testosterone. Apart from reduced serum albumin, no other serum parameters indicated liver damage and there was only slight liver steatosis in some animals at the highest dose. Urinary taurine was not significantly raised after any dose of TMPD, but there was a significant increase in urinary creatine after the highest dose. It can be concluded that in the presence of discrete muscle damage, the use of urinary taurine and urinary creatine as markers of liver and testicular dysfunction, respectively, is not confounded. However, a variety of different markers should be used in conjunction to fully delineate the tissue damage due to toxic chemicals.

Animals↗

PubMed1993

Depletion of total non-protein sulphydryl groups in mouse tissues after administration of d-amphetamine.

A study of total non-protein sulphydryl groups (TNPSH) depletion was performed in male Charles River CD1 mice (25-30 g) isolated or housed in pairs. The mice were injected intraperitoneally with d-amphetamine (5, 20 and 80 mg/kg), kept at 20 +/- 1 degrees C, sacrificed at different times (between 0 and 120 min) and TNPSH in brain, lungs, heart, liver, kidney and spleen was quantified. d-Amphetamine significantly reduced the TNPSH levels in the liver and kidney, the reduction being more pronounced in the latter organ. In the other organs assayed no depletion was observed. Housing in pairs increased depletion of TNPSH both in the liver and in the kidney. The dose of 20 mg/kg caused a higher TNPSH depletion in paired mice than the dose of 80 mg/kg did in isolated mice. Rectal temperatures (RT) were also determined in the different times for the same doses of d-amphetamine. For the two lowest doses temperature values were similar in isolated and paired mice and were inversely proportional to TNPSH depletion in kidney. The administration of 80 mg/kg induced the highest TNPSH depletion in kidney and liver, but the hyperthermic effect was lower than that elicited by 20 mg/kg. No proportion was observed between RT and TNPSH depletion in liver. These results suggest that d-amphetamine changes TNPSH homeostasis in mouse liver by a temperature independent mechanism. In kidney, the hyperthermic effect may have some influence. Housing mice in pairs increases TNPSH depletion, but has no influence in the hyperthermic effect of d-amphetamine, with this experimental protocol.

Animals↗

PubMed1993

Taurine protects against the cytotoxicity of hydrazine, 1,4-naphthoquinone and carbon tetrachloride in isolated rat hepatocytes.

Exposure of rat hepatocytes to hydrazine, carbon tetrachloride or 1,4-naphthoquinone results in cytotoxicity determined as uptake of Trypan blue and leakage of lactate dehydrogenase (LDH). After exposure of hepatocytes to hydrazine and 1,4-naphthoquinone, ATP was also measured and was found to be depleted. Addition of the beta-amino acid taurine to the hepatocyte incubation buffer partially protects the cells against the cytotoxicity of these three different cytotoxic compounds, as indicated by Trypan blue uptake and LDH leakage. Taurine also reduces the depletion of ATP caused by 1,4-naphthoquinone but not hydrazine. It is suggested that taurine may have a cytoprotective effect in vitro and may be a useful tool for the investigation of mechanisms of cytotoxicity.

Animals↗

PubMed1993

The correlation between urinary and liver taurine levels and between pre-dose urinary taurine and liver damage.

Analysis of data from several studies has shown that urinary taurine levels are highly significantly correlated with liver taurine concentration in control rats. Furthermore, urinary taurine levels measured before dosing with various hepatotoxic agents are significantly correlated with serum AST and ALT values measured after dosing with hepatotoxicants. That is, animals with low urinary taurine values and therefore low liver taurine concentrations tend to show greater hepatic damage. These data suggest that taurine may have a protective function in the liver.

Alanine Transaminase↗

PubMed1993

Reduction of liver taurine in rats by beta-alanine treatment increases carbon tetrachloride toxicity.

Treatment of rats with beta-alanine increases the urinary taurine levels and markedly reduces the concentration of taurine in the liver. Dosing with carbon tetrachloride (CCl4) during treatment with beta-alanine results in a marked decrease in urinary taurine concomitant with a decrease in food intake. Treatment of animals with beta-alanine increases the hepatotoxicity of single doses of CCl4 as determined histologically and by measurement of serum alanine transaminase (ALT) and aspartate transaminase (AST) levels. Urinary creatine is also raised significantly after the administration of CCl4 in beta-alanine-treated animals. However, the accumulation of triglycerides (TRIG) in the liver caused by dosing with CCl4 was not influenced by beta-alanine treatment. The data suggest that liver taurine levels may be an important factor in determining the degree of CCl4-induced cellular necrosis but not hepatic triglyceride accumulation.

Alanine Transaminase↗

PubMed1993

Effect of various non-hepatotoxic compounds on urinary and liver taurine levels in rats.

Administration of compounds which alter protein synthesis or sulphur amino acid metabolism in rats results in changes in the excretion of urinary taurine. Treatment with diethylmaleate (DEM) or phorone, which will deplete glutathione (GSH), reduces taurine excretion, whereas treatment with buthionine sulphoximine (BSO), which will inhibit glutathione synthesis, increases taurine excretion. Treatment with cycloheximide, an inhibitor of protein synthesis, increases taurine excretion, whereas pretreatment with phenobarbital, which will increase protein synthesis, decreases taurine excretion. Administration of agents which damage organs other than the liver such as the kidney, heart and testes, does not increase urinary taurine.

Animals↗

PubMed1993

Investigations into the effects of various hepatotoxic compounds on urinary and liver taurine levels in rats.

The effect of various hepatotoxicants on urinary taurine and urinary creatine has been studied in the rat. Several hepatotoxic agents, carbon tetrachloride, thioacetamide, galactosamine and allyl alcohol which all caused hepatic necrosis (sometimes accompanied by steatosis), resulted in a rise in urinary taurine and in some cases creatine, when administered to rats. Ethionine and hydrazine also raised urinary taurine but caused only steatosis and did not raise urinary creatine. Therefore urinary taurine and possibly creatine may be useful markers of liver injury and dysfunction. Liver taurine levels were also affected by some of the hepatotoxicants but in those cases where there was a rise in urinary taurine this could not be accounted for by the loss in liver taurine. It is suggested that the increase in urinary taurine is partly due to changes in protein synthesis and hence in sulphur amino acid metabolism caused by hepatotoxic agents. However, bromobenzene did not increase urinary taurine and alpha-naphthylisothiocyanate and lithocholate caused reduced levels. It is suggested that this lack of increase in urinary taurine may be due to depletion of glutathione or interference with the biliary system.

1-Naphthylisothiocyanate↗

PubMed1992

Determination of hydrazine in biofluids by capillary gas chromatography with nitrogen-sensitive or mass spectrometric detection.

Plasma and liver levels of hydrazine were determined at 10, 30, 90 and 270 min in rats given 0.09, 0.27, 0.84 and 2.53 mmol of hydrazine per kg body weight orally by capillary gas chromatography-mass spectrometry of its pentafluorobenzaldehyde adduct (DFBA, m/z 388) using selected ion monitoring with 15N2-labelled hydrazine as the internal standard (adduct, m/z 390). The mean half-life for hydrazine in the plasma was approximately 2 h but varied with dose. Urinary excretion (0-24 h) of hydrazine and its metabolite acetylhydrazine were determined employing nitrogen-phosphorus detection of the adducts utilising a novel internal standard, pentafluorophenylhydrazine, the adduct of which structurally resembles DFBA. The fraction of the original dose excreted as hydrazine (and acetylhydrazine) declined with increasing dose.

Animals↗

PubMed1992

Proton NMR spectroscopic studies on the metabolism and biochemical effects of hydrazine in vivo.

The metabolism and disposition of hydrazine and its effects on endogenous metabolites has been studied in rats by the use of high resolution proton NMR spectroscopy of urine. Several metabolites of hydrazine were detected, notably acetyl- and diacetylhydrazine and a cyclised metabolite which results from a hydrazone formed from 2-oxoglutarate and hydrazine. Effects of hydrazine on endogenous metabolites in urine and plasma were also observed; notably a dose-related increase in urinary taurine, a dose-related increase in urinary and plasma lactate, increases in urinary alpha-alanine, beta-alanine, methylamine and a decrease in urinary 2-oxoglutarate. This study has indicated the utility of using high resolution proton NMR spectroscopy to analyse urine for both metabolites and endogenous compounds after exposure of animals to toxic substances.

Animals↗

PubMed1992

A biochemical and NMR spectroscopic study of hydrazine in the isolated rat hepatocyte.

Using isolated rat hepatocytes the biochemical effects of hydrazine have been investigated using both conventional assay techniques and high resolution proton NMR. High resolution proton NMR revealed that hydrazine caused a significant increase in alanine and lactate levels in the incubation buffer, whereas levels of beta-hydroxybutyrate were decreased. NMR also detected metabolites of hydrazine notably acetylhydrazine and a cyclised hydrazone formed with alpha-ketoglutarate. Changes were detected in NADH and NADPH, ATP, succinate dehydrogenase (SDH) and total non-protein sulphydryl groups (TNPSH). However, the changes in pyridine nucleotides occurred at higher concentrations than those affecting succinate dehydrogenase and ATP. Similarly, the depletion of TNPSH occurred at a higher concentration and with a different time course to that seen with ATP depletion and inhibition of succinate dehydrogenase.

Adenosine Triphosphate↗

PubMed1992

Urinary creatine profiles after administration of cell-specific testicular toxicants to the rat.

Cell-specific testicular toxicants have been used to examine the distribution of creatine within the rat testis, and to examine the potential use of creatinuria as a non-invasive indicator of testicular damage. Groups of rats were administered single doses of various toxicants: a germ cell toxicant (methoxyacetic acid, MAA), one of two Sertoli cell toxicants (di-n-pentyl phthalate, DPP or 1,3-dinitrobenzene, 1,3-DNB), or a Leydig cell toxicant (ethane-1,2-dimethane sulphonate, EDS). Urinary creatine and creatinine levels were monitored in 24 h periods over the following 48 h, after which time the testes were removed, weighed and, after processing, sections were examined by light microscopy. All four treatments resulted in reductions in relative testis weight (RTW) and produced morphological changes similar to those which have been previously reported. In addition, MAA, DPP and 1,3-DNB all caused significant elevations in urinary creatine excretion and the urinary creatine:creatinine ratio (Cr/Crn) within 24 h. EDS had no such effect. We conclude that creatine is associated with the cells of the seminiferous epithelium, and that elevated urinary excretion of creatine may serve as a non-invasive marker for damage to these cells in vivo.

Acetates↗

PubMed1992

Studies on the disposition and metabolism of hydrazine in rats in vivo.

1. Rats were given various doses of hydrazine orally and their plasma and liver hydrazine levels were determined (at various times up to 270 min after dosing) by gas chromatography/mass spectrometry. 2. The increase in the peak plasma level and in the area under the plasma concentration-time curve (AUC) were not directly proportional to the dose. 3. The ratio of plasma to liver hydrazine varied with dose suggesting saturation of an uptake mechanism might be occurring. 4. In a separate experiment hydrazine was still detectable in the plasma and liver 24 h after dosing with hydrazine i.p. 5. Rats were given the same doses of hydrazine and urine was collected for 24 h after dosing and assayed for hydrazine and acetylhydrazine. The proportion of hydrazine and acetylhydrazine excreted declined with dose. 6. Liver samples were taken for histopathological examination 96 h after dosing. Only after the highest dose (81 mg kg-1) was there evidence of fatty liver, 96 h after a single dose, and a reduction in both liver and body weight.

Animals↗

PubMed1991

Identification of novel hydrazine metabolites by 15N-NMR.

15N-NMR has been used to study the metabolism of hydrazine in rats in vivo. Single doses of [15N2]hydrazine (2.0 mmol/kg: 98.6% g atom) were administered to rats and urine collected for 24 hr over ice. A number of metabolites were detected by 15N-NMR analysis of lyophilized urine. Ammonia was detected as a singlet at 0 ppm and unchanged [15N2]hydrazine was present in the urine detectable as a singlet at 32 ppm. Peaks were observed at 107 and 110 ppm which were identified as being due to the hydrazido nitrogen of acetylhydrazine and diacetylhydrazine, respectively. A resonance at 85 ppm was ascribed to carbazic acid, resulting from reaction of hydrazine with carbon dioxide. A singlet detected at 316 ppm was thought to be due to the hydrazono nitrogen of the pyruvate hydrazone. The resonance at 56 ppm was assigned to 15N-enriched urea, this together with the presence of ammonia indicates that the N-N bond of hydrazine is cleaved in vivo, possibly by N-oxidation, and the resultant ammonia is incorporated into urea. A doublet centred at 150 ppm and a singlet at 294 ppm were assigned to a metabolite which results from cyclization of the 2-oxoglutarate hydrazone. Therefore 15N-NMR spectroscopic analysis of urine has yielded significant new information on the metabolism of hydrazine.

Ammonia↗