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Biomedical subjects

T J Gray

Publications and source records attributed to T J Gray.

At least 73 records · Page 4Linked to original sources
PubMed1984

The effect of hypolipidaemic agents on peroxisomal beta-oxidation and mixed-function oxidase activities in primary cultures of rat hepatocytes. Relationship between induction of palmitoyl-CoA oxidation and lauric acid hydroxylation.

A study was conducted of the effects of 10 hypolipidaemic agents on peroxisomal and microsomal enzyme activities in primary cultures of rat hepatocytes. Treatment with compounds such as Wy-14,643, tiadenol, nafenopin, BR-931, clofibrate and mono-(2-ethylhexyl)phthalate induced cyanide-insensitive palmitoyl-CoA oxidation (a specific peroxisomal marker enzyme), a polypeptide with a molecular weight of 80,000 associated with peroxisome proliferation, and carnitine acetyltransferase activity, after 70 h of culture. These compounds also maintained hepatocyte cytochrome P-450 levels and markedly induced lauric acid hydroxylation, whereas little effect was observed on 7-ethoxycoumarin O-deethylase. Studies with metyrapone, which also maintains cytochrome P-450, suggested that treatment with the hypolipidaemic agents resulted in the formation of different form(s) of cytochrome P-450 to those present in control cultures. Regression analysis demonstrated a high correlation between the induction of the peroxisomal parameters and lauric acid hydroxylation. The results indicate that hypolipidaemic agents which stimulate hepatic peroxisomal enzyme activities also induce novel form(s) of cytochrome P-450 with high specificity towards lauric acid hydroxylation. Both these processes may depend therefore on common receptor(s) which are retained in primary cultures of rat hepatocytes.

Animals↗
PubMed1983

Induction of lauric acid hydroxylation and maintenance of cytochrome P-450 content by clofibrate in primary cultures of rat hepatocytes.

The hypolipidemic agent clofibrate at a concentration of 0.5 mM in the culture medium maintained the cytochrome P-450 content of rat hepatocytes for up to 96 hr. This effect was associated with a marked induction of lauric acid hydroxylation whereas little effect was observed on the metabolism of three other cytochrome P-450 dependent mixed function oxidase substrates. The results suggest that clofibrate induces similar form(s) of cytochrome P-450 in cell culture to those observed in vivo and that primary cultures of rat hepatocytes may be useful for studies on both the peroxisomal and microsomal effects of hypolipidemic agents.

Animals↗
PubMed1983

Peroxisome proliferation in primary cultures of rat hepatocytes.

Primary cultures of rat hepatocytes were exposed to a range of chemicals known to cause peroxisome proliferation in vivo. Peroxisomal palmitoyl-CoA oxidation and carnitine acetyltransferase (CAT) activity were increased within 12 to 24 hr of adding 0.5 mM clofibrate to the culture medium, reaching about 20 times control levels after 72 hr. Stimulation of CAT activity was dose related over a concentration range of 0.05 to 2 mM clofibrate and 0.02 to 0.2 mM mono-2-ethylhexylphthalate (MEHP). Higher concentrations of MEHP were cytotoxic. The stimulation of CAT activity and palmitoyl-CoA oxidation produced by clofibrate and MEHP was inhibited by cycloheximide. In further studies with clofibrate and a range of other known peroxisome proliferators (nafenopin, tiadenol, BR-931, Wy-14,643, and acetylsalicylic acid), induction of CAT and palmitoyl-CoA oxidation was observed with no increase in activity of another peroxisomal enzyme, D-amino acid oxidase. This differential effect on peroxisomal enzyme activity is typical of that seen in vivo. Furthermore, the relative potencies of the different peroxisome proliferators in vitro agreed well with what is known from studies in vivo. Mitochondrial and microsomal marker enzymes showed little change in activity. Electron microscopy of treated cultures revealed increased numbers of peroxisomes, some of which lacked the characteristic nucleoid. The results indicate that primary cultures of rat hepatocytes provide a rapid, sensitive means of identifying chemicals that cause peroxisome proliferation and a potentially valuable system for studies aimed at clarifying the toxicological significance of this phenomenon.

Animals↗
PubMed1983

Peroxisomal effects of phthalate esters in primary cultures of rat hepatocytes.

Primary rat hepatocyte cultures were used to compare the effects of some alkylphthalate esters on peroxisomal enzyme activities and morphology. Linear diesters from methyl to n-octyl and their constituent monoesters and alcohols were compared with the branched chain 2-ethylhexyl derivatives. Carnitine acetyltransferase activity was increased 9.5-fold by mono-2-ethylhexylphthalate (MEHP) and 5.5- and 7-fold by mono-n-pentyl- and mono-n-octylphthalate (MNOP), the 2 most potent of the linear monoesters. Activity of the specific peroxisomal marker, cyanide-insensitive palmitoyl-CoA oxidation decreased with time in control cultures. Whereas MEHP produced a time related increase over the initial level of palmitoyl-CoA oxidation, MNOP treatment only maintained the initial level of activity. The peroxisome proliferation-associated 80 000 mol. wt polypeptide was induced by MEHP but not MNOP. Similarly, MEHP produced increased numbers of peroxisomes, many without a nucleoid, whereas MNOP and mono-n-pentylphthalate had no such effect. 2-Ethylhexanol was less potent as an inducer of carnitine acetyltransferase than MEHP and the linear alcohols had no effect on this enzyme. Studies with diesters indicated that induction of carnitine acetyltransferase required hydrolysis of the diester. It is concluded that the straight-chain phthalates studied have little effect on hepatic peroxisomes compared with the 2-ethylhexyl ester and that hepatocyte cultures provide a rapid means of comparing the peroxisomal effects of different phthalates.

Animals↗
PubMed1982

Peroxisome proliferation in cultured rat hepatocytes produced by clofibrate and phthalate ester metabolites.

Adult rat hepatocytes cultured for 48 h in the presence of 0.2 mM clofibrate, mono-(2-ethylhexyl)-phthalate (MEHP) or 2-ethylhexanol (2-EHA) contained increased numbers of peroxisomes. In keeping with the effects of these compounds in vivo, the peroxisome proliferation was associated with marked increases (up to 15-fold) in the activity of carnitine acetyltransferase. No such effects were produced by n-hexanol or two microsomal enzyme inducers, phenobarbital and 1,2-benzanthracene. These results suggest that cultured hepatocytes may provide a useful model system for studying chemically induced peroxisome proliferation.

Animals↗
PubMed1982

Species differences in the testicular toxicity of phthalate esters.

Oral administration of di-n-butylphthalate (DBP) produced uniformly severe seminiferous tubular atrophy in rats and guinea pigs but caused only focal atrophy in mice. Hamsters showed no testicular changes with DBP and only minor changes in response to di-(2-ethylhexyl)phthalate (DEHP) and di-n-pentylphthalate (DPP). The rate of intestinal monohydrolysis of DEHP was slower in hamsters than in rats and this may be important, as mono-(2-ethylhexyl)phthalate (MEHP) did cause focal seminiferous tubular atrophy in hamsters. However, mono-n-butylphthalate (MBP) had no such effect. The decrease in testicular zinc concentration and enhancement of urinary zinc excretion produced in rats by DEHP and DPP was not observed in hamsters. Thus, species differ widely in their sensitivity to the testicular toxicity of phthalate esters.

Animals↗
PubMed1980

Testicular atrophy produced by phthalate esters.

In a 90-day toxicity study in rats, di-(2-ethylhexyl)phthalate (DEHP) produced testicular atrophy. To characterise further the testicular toxicity of phthalate esters the effect of age on the induction of testicular atrophy has been examined as well as the reversibility of the lesions and the effects of certain other phthalate esters. Seminiferous tubular atrophy, comprising a loss of spermatids and spermatocytes, resulted when 4-week-old rats were given 10 daily doses of DEHP. In similarly treated 10-week old rats up to 50% of tubules were atrophic while the remainder were unaffected. No testicular damage was produced in 15 week-old rats. The lesion produced in 4-week-old rats was reversible whether treatment was stopped prior to, or continued until after the control rats had reached sexual maturity. Normal testicular weight and histology were restored within 12 and 20 weeks respectively. Of a series of di-n-alkyl phthalates from dimethyl to di-n-octyl, the butyl, pentyl and hexyl esters produced testicular lesions similar to DEHP. The testicular effects of DEHP were not influenced by simultaneous administration of testosterone or follicle stimulating hormone (FSH). The mechanism by which phthalate esters exert their effects is discussed in the context of a possible action on Sertoli cell function.

Aging↗