Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Enzyme Induction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed1985

Metabolic changes in elicitor-treated bean cells. Selectivity of enzyme induction in relation to phytoalexin accumulation.

Treatment of cell suspension cultures of Phaseolus vulgaris c.v. Immuna with an elicitor preparation heat-released from the cell walls of the phytopathogenic fungus Colletotrichum lindemuthianum resulted in rapid accumulation of the prenylated 5-hydroxyisoflavanone phytoalexin kievitone followed by later accumulation of the pterocarpan-derived phytoalexin phaseollin. Kievitone formation was preceded by rapid transient increases in the extractable activities of the enzymes L-phenylalanine ammonia-lyase and chalcone synthase. The extractable activities of 15 enzymes were measured in the cell cultures during the period of kievitone accumulation. The results suggest a highly selective induction of enzymes associated directly with the phytoalexin pathway. No induction of enzymes of pathways diverging from or providing substrates for the phenylpropanoid----isoflavonoid pathway was observed. The increase in glutamate dehydrogenase activity in control cultures was prevented by elicitor application. A comparison of enzyme activities in control and Colletotrichum-infected bean hypocotyls provided further evidence of the selective induction of enzymes of phytoalexin synthesis, although peroxidase, glutamate dehydrogenase and glutamate synthase activities were higher in infected than in healthy hypocotyls. It is concluded that the major enzymic changes occurring in elicitor-treated bean cells are probably those directly associated with defence mechanisms such as the formation of isoflavonoid phytoalexins (this paper) or accumulation of phenolic compounds and hydroxyproline-protein in the cell walls [Bolwell, G. P. et al. (1985) Eur. J. Biochem. 148, 571-578].

Acyltransferases↗
PubMedDate not supplied

Liver enzyme induction and serum lipid levels after replacement of carbamazepine with oxcarbazepine.

We evaluated liver P450 enzyme system induction and serum lipid levels in a prospective follow-up study in 12 male patients with epilepsy after replacing carbamazepine (CBZ) medication with oxcarbazepine (OCBZ). Antipyrine(t1/2) increased and antipyrine(CL) decreased 2 months after the medication was changed, reflecting normalization of liver P450 enzyme system function. Furthermore, serum total cholesterol levels decreased, but serum concentrations of high-density lipoprotein (HDL)-cholesterol and triglycerides (TG) were unchanged. OCBZ may be the preferable antiepileptic drug (AED) with regard to the effects of the medication on lipid metabolism.

Adult↗
PubMed1978

Enzyme induction by drugs. Its relevance to clinical biochemistry.

The properties of the hepatic microsomal, drug detoxicating, enzyme system are reviewed with particular reference to its inducibility. Induction is modified by various factors of which the diet is particularly important. A theoretical model system for induction has been proposed and this is discussed. There are a number of methods for assessing microsomal enzyme induction in man, none of which is ideal. Nevertheless, induction is a well recognized phenomenon in man and has a bearing on the metabolism of a number of endogenous substances. The effect of induction on steroid metabolism and the relationship between inducers, vitamin D, and metabolic bone disease is discussed. Bilirubin metabolism is affected by changes in microsomal enzyme activity and inducers have been used therapeutically in some cases of hyperbilirubinaemia. The relationship between drugs and the hepatic porphyrias is reviewed. The hepatic microsomal enzyme system is but one of many inducible enzymes and the role of induction in general in metabolic regulation is emphasised.

Animals↗
PubMed1999

Effect of cryopreservation on cytochrome P-450 enzyme induction in cultured rat hepatocytes.

In the present study, we evaluated the inducibility of cytochrome P-450 (CYP) CYP1A, CYP2B, CYP3A, and CYP4A by beta-naphthoflavone, phenobarbital, dexamethasone, and clofibric acid, respectively, in primary hepatocyte cultures prepared from both fresh and cryopreserved rat hepatocytes. Rat hepatocytes were successfully thawed and cultured after cryopreservation in liquid nitrogen for up to 1 month. Percentage of total recovery, viable cell recovery, and final viability of the cells were 68%, 72%, and 85%, respectively. Regardless of whether they were cryopreserved or not, cultured hepatocytes exhibited near-normal morphology. Treatment of cryopreserved hepatocytes with beta-naphthoflavone caused an 8-fold increase in 7-ethoxyresorufin O-dealkylase (CYP1A1/2) activity, with an EC50 of 1.5 microM; treatment with phenobarbital caused a 26-fold increase in 7-pentoxyresorufin O-dealkylase (CYP2B1/2) activity, with an EC50 of 10 microM; treatment with dexamethasone caused a 10-fold increase in testosterone 6beta-hydroxylase (CYP3A1/2) activity, with an EC50 of 1.3 microM, whereas treatment with clofibric acid caused a 3-fold increase in lauric acid 12-hydroxylase (CYP4A1-3) activity, with an EC50 of 170 microM. The induction of CYP1A, CYP2B, CYP3A, and CYP4A enzymes by these inducers was confirmed by Western immunoblotting. The patterns of P-450 induction in cryopreserved rat hepatocytes, in terms of concentration response, reproducibility, magnitude, and specificity of response, were similar to those observed in freshly isolated hepatocytes. Additionally, the magnitude and specificity of induction was similar to that observed in vivo in rats. In conclusion, under the conditions examined, cryopreserved rat hepatocytes appear to be a suitable in vitro system for evaluating xenobiotics as inducers of P-450 enzymes.

Animals↗
PubMed1979

The effect of enzyme induction on diazepam metabolism in man.

1 The elimination and metabolism of diazepam in man was investigated following the induction of the liver microsomal enzyme system by antipyrine. 2 Seven healthy volunteers were given 1200 mg antipyrine as an inducing agent for a period of 14 days. Before and after the induction period the elimination of diazepam and desmethyldiazepam was measured in the plasma by gaschromatography. As parameters of liver microsomal enzyme activity, antipyrine elimination and gamma-glutamyl-transpeptidase in the plasma, D-glucaric acid and 6-beta-hydroxycortisol urinary excretion were measured on both occasions. 3 Following the induction period most parameters of microsomal enzyme activity measured were significantly changed indicating an increase of the microsomal enzyme system. The elimination of diazepam was significantly altered having a half-life of 37 h before and 18 h afterwards combined with a significant increase in total body clearance after the induction period, although the volume of distribution remained unaltered. The formation of the main metabolite N-desmethyldiazepam was not changed, but its elimination was increased having a half-life of 139 or 58 h respectively. 4 The elimination of unchanged diazepam and desmethyldiazepam is significantly increased by the induction of the liver microsomal enzyme system using antipyrine as an inducing agent in healthy volunteers, which might be important under certain clinical conditions.

17-Hydroxycorticosteroids↗
PubMed2001

The role of enzyme induction and inhibition on cypermethrin hepatotoxicity.

Cypermethrin at different concentrations (100, 200, 400 and 800 ng ml(-1)) was incubated with a primary culture of rat hepatocytes. Cypermethrin was cytotoxic to rat hepatocytes at concentrations of 200 ng ml(-1)or greater. Toxicity was measured by a decrease in cell viability and leakage of ALT and AST enzymes into the culture medium. The role of cytochrome P450 in the hepatotoxicity of cypermethrin insecticide was investigated in fresh hepatocytes isolated either from phenobarbital pretreated rats or control rats and coincubated with SKF525A. Pretreatment with phenobarbital strongly protected the hepatocytes against the cypermethrin induced loss of cell viability percentage and increased enzyme leakage percentage. Coincubation of the hepatocytes with SKF525A, a well-known cytochrome P450 inhibitor, substantially potentiated the effect of cypermethrin on cell viability and enzyme leakage. These results suggest that the cytocidal hepatotoxicity of cypermethrin in primary hepatocyte culture depends on its parent compound and phenobarbital, as a cytochrome P450 inducer, could be of therapeutic value.

Alanine Transaminase↗
PubMed1979

The development of a "Microtitre" fluctuation test for the detection of indirect mutagens, and its use in the evaluation of mixed enzyme induction of the liver.

The "Microtitre" Fluctuation test recently introduced for the detection of direct mutagens has been adapted for the detection of indirect mutagens through the incorporation of an "S9-mix" metabolic system. It compares favourably with Greens' original method for the detection of a range of chemical mutagens. The technique has been employed in the evaluation of mixed enzyme induction using phenobarbitone and beta-naphthoflavone (benzoflavone), as a safe substitute for Aroclor-1254. The post-mitchondrial preparations from rats induced with the combined inducers had a similar "metabolic competence" to those derived from Aroclor induced animals. Such a combination would therefore provide a useful alternative to Aroclor-1254 for routine screening. It was found that the level of "S9" present in the metabolic system greatly affected the quantitative mutagenic response. This varied considerably from chemical to chemical and underlined the need for such preliminary investigations in routine screening.

Animals↗
PubMed1990

[Influence of thyroid status on microsomal and peroxysomal enzyme induction by fibrates in rats].

The influence of thyroid hormones upon the inductive effects on microsomal enzymes and the hepatic proliferation produced by different fibrates was studied in the male rat. A pharmacological dose of triiodo-L-thyronine significantly lowers the total cytochrome P450 content induced by some equi-effective doses of clofibrate, ciprofibrate, bezafibrate and fenofibrate. The ethoxycoumarin O-deethylase activity (ECOD) is concomitantly decreased. On the contrary, L-T3 accentuates the specific inductive effect of fibrates on bilirubin-UDPGT activity. Hypothyroid has little or no influence upon the effect of fibrates towards cytochrome P450 content and ECOD activity. On the other hand, this thyroid status significantly lowers the CN- palmitoyl coenzyme A dehydrogenase, which is a marker enzyme of the peroxisome proliferation caused by the different fibrates. These results indicate a possible modulation of thyroid hormones within the fibrates induction mechanism in the rat.

Acyl-CoA Dehydrogenase↗
PubMed1968

Tyrosine aminotransferase: enzyme induction independent of adenosine 3', 5'-monophosphate.

The importance of adenyl cyclase and adenosine 3',5'-monophosphate in the induction of tyrosine aminotransferase by adrenocorticosteroids has been tested in HTC cells derived from a rat hepatoma and grown in tissue culture. Adrenocorticosteroids cause a 10-to 15-fold increase in the rate of synthesis of tyrosine aminotransferase in these cells. Under various experimental conditions, with or without glucocorticoids, neither adenyl cyclase nor cyclic adenosine mono-phosphate could be detected in HTC cells. In addition, neither the cyclic nucleotide nor N(6), O(2')-dibutyryl cyclic adenosine monophosphate caused increased activity of the transaminase in HTC cells. We conclude that induction of tyrosine aminotransferase by glucocorticoids is not mediated by the adenyl cyclase-cyclic adenosine monophosphate system.

Adenine Nucleotides↗