Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “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 973 records · Page 54Linked to original sources
PubMed1989

Remission induction in children with acute non-lymphocytic leukemia using cytosine arabinoside and doxorubicin or daunorubicin: a report from the Childrens Cancer Study Group.

Four hundred ninety evaluable patients were treated on an induction regimen consisting of two to four courses of cytosine arabinoside plus an anthracycline. Overall, 78% of patients went into remission, 10% died during induction, and 12% were induction failures. For the first 152 patients, courses consisted of 7 days continuous infusion with cytosine arabinoside (Ara-C, 100 mg/m2) and 3 days of doxorubicin (30 mg/m2). Because of unacceptable toxicity, particularly for children less than 3 years of age, the anthracycline was changed to daunorubicin, and the doses of both induction drugs for children under 3 was reduced. For children aged 3 years and older the change in anthracycline was associated with a significant increase in induction failures (7% to 16%, P = .04) and a decrease in deaths (15% to 8%, P = .09). For younger children, for whom doses were also changed, the effect was greater; Mortality decreased from 29% to 1% (P less than .0001), and the remission induction rate increased from 66% to 88% (P = .005). The therapy modifications also influenced survival following remission induction: Daunorubicin-treated patients, aged 3 years and over, did significantly better than those given doxorubicin (P = .03), but the opposite was seen in younger children (P = .06). Gastrointestinal and skin toxicities and septicemia were significantly more common when doxorubicin was being used, but the extent of myelosuppression was similar for the two anthracyclines.

Age Factors↗
PubMed1998

Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells.

Treatment of human lung epithelial (A549) cells with crocidolite asbestos resulted in the induction of the inducible form of nitric oxide synthase (iNOS), production of NO, and a dramatic decrease in intracellular reduced glutathione (GSH). Iron, mobilized from the crocidolite fibers (27% iron by weight), and the formation of NO were required for the formation of 2'-deoxy-7-hydro-8-oxoguanosine in the DNA of the A549 cells, but not for the decrease in GSH. Therefore, we investigated the role of GSH and iron in the induction of iNOS in A549 cells by crocidolite. Iron was required for the induction of iNOS by crocidolite. A fivefold higher amount of chrysotile asbestos (3% iron by weight) was required to cause a similar decrease in intracellular GSH and induction of iNOS. In the absence of asbestos, treatment with either buthionine sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, or ferric ammonium citrate (FAC), a soluble form of iron, did not result in induction of iNOS. However, iNOS was induced when A549 cells were treated simultaneously with BSO and FAC. The presence of 5 mM N-acetylcysteine prevented induction of iNOS in crocidolite-treated A549 cells. These observations suggest that the induction of iNOS resulted from a decrease in intracellular GSH and the presence of iron from the asbestos fibers.

Asbestos↗
PubMed1995

Co-induction of arginase and nitric oxide synthase in murine macrophages activated by lipopolysaccharide.

In view of studies showing that not only nitric oxide synthase (NOS) activity but arginase activity is induced in rodent macrophages by lipopolysaccharide (LPS), the objective of this study was to investigate the co-induction of these two enzymes and to ascertain whether common mechanisms are involved. RAW 264.7 cells were activated by 2 micrograms LPS/ml and incubated for up to 48 hr. Inducible NOS (iNOS) and inducible arginase II (AII) activities were monitored, respectively, by measuring NO2-/NO3- accumulation in cell culture media and formation of urea (as CO2) from L-arginine by cell lysates. AII activity increased linearly up to at least 48 hr, whereas NO2-/NO3- formation reached a plateau well before 48 hr. Immunoprecipitation experiments revealed that AII accounted for 90-100% of arginase activity in LPS-activated macrophages. The inhibitor of NF-kappa B activation, pyrrolidine dithiocarbamate, inhibited the induction of iNOS but not AII. Moreover, whereas IFN-gamma caused iNOS induction, AII induction was nearly abolished by IFN-gamma, perhaps by inhibiting transcription of the AII gene. These observations indicate that co-induction of iNOS and AII occurs by distinct transcriptional mechanisms, AII induction could diminish NO production by decreasing L-arginine availability, and IFN-gamma can prevent AII induction.

Amino Acid Oxidoreductases↗
PubMed1996

Cytochrome P4501A induction in avian hepatocyte cultures: a promising approach for predicting the sensitivity of avian species to toxic effects of halogenated aromatic hydrocarbons.

Concentration-dependent effects of halogenated aromatic hydrocarbons (HAHs) on cytochrome P4501A (CYP1A) induction in primary hepatocyte cultures prepared from embryos of chickens (four breeds), pheasants, turkeys, ducks (three breeds), and herring gulls were determined. CYP1A activity was estimated by measuring ethoxyresorufin O-deethylase (EROD) activity and the concentration of immunodetectable CYP1A was estimated using mouse monoclonal antibody 1-12-3 that was prepared against scup (Stenotomus chrysops) CYP1A1. The HAHs studies were 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4'-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 3,4,4',5-tetrachlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), 2,3,3',4,4'-pentachlorobiphenyl (PCB 105), and 2,3',4,4',5-pentachlorobiphenyl (PCB 118). Two general types of comparisons were made: (1) relative potencies of compounds within a species (expressed relative to TCDD as induction equivalency factors, IEFs) and (2) relative sensitivity of each species to EROD induction by each compound. Three methods for estimating potency were compared. These were: (1) the concentration of inducer that produced a half-maximal (EC50) EROD response, (2) the concentration producing a response equivalent to 10% of the maximal response produced by TCDD (ECTCDD 10%), and (3) a slope ratio method. For each method, the rank order in potency was TCDD > or = TCDF > PCB 126 > PCB 81 > PCB 77 > PCB 169 in chicken, pheasant, and turkey hepatocytes. The rank order was similar in duck and herring gull hepatocytes with the following exceptions: TCDF was approximately 2- to 4-fold more potent than TCDD in duck hepatocytes; PCB 169 induced EROD in gulls, but PCB 77 had no measurable effect in this species. PCB 118 was a relatively weak EROD inducer in most species/breeds, but it did not induce EROD in Pekin ducks or gulls. PCB 105 was a weak inducer in White Leghorn chicken and turkey hepatocytes, but it did not induce EROD in other species. The EC50, ECTCDD10% and slope ratio methods for estimating potencies generally gave similar IEFs for compounds that produced a maximal response that was at least 60% of the maximal response produced by TCDD. For compounds that caused a response that was 50% or lower than that produced by TCDD, EC50-based IEFs were greater (10- to 100-fold) than ECTCDD10%-based IEFs or slope-ratio-based IEFs. Among species, the rank order in sensitivity to EROD induction was chicken > pheasant > turkey > or = duck > or = herring gull. The relative sensitivity of avian hepatocyte cultures to EROD induction by PCB 77 was similar to the relative sensitivity of these species (reported elsewhere) to lethality after in ovo injection of PCB 77. Chicken hepatocyte cultures were 5-10 times more sensitive to EROD induction by TCDD than were pheasant hepatocyte cultures, which is identical to the difference in sensitivity of these species to the lethal effect of TCDD after in ovo injection. Measuring the sensitivity of hepatocyte cultures to EROD induction might be useful for estimating the sensitivity of avian species (including rare or endangered species, where it is impossible to conduct in vivo studies) to the embryotoxic effects of TCDD, non-ortho substituted PCBs, and other aryl hydrocarbon receptor agonists.

Animals↗
PubMed1988

Mechanisms involved in ornithine decarboxylase induction by 12-O-tetradecanoylphorbol-13-acetate, a potent mouse skin tumor promoter and an activator of protein kinase C.

ODC, the first enzyme in mammalian polyamine biosynthesis, is rapidly induced in response to a wide variety of growth stimuli. However, there is no single mechanism which may explain the rapid turnover of ODC activity. ODC activity has been shown to be regulated at the level of synthesis and degradation, and also by post-translational modifications and an interaction with macromolecules. Our results indicate that TPA-induced ODC activity is regulated at the transcriptional level. An initial signal in ODC induction by TPA is not clear. We have suggested that TPA-increased accumulation of epidermal prostaglandins is required, but not sufficient, for ODC induction by TPA. Others have suggested the role of lipoxygenase product(s) in ODC induction. The role of the microtubule-containing system in regulation of ODC induction has been shown. The involvement of cyclic nucleotides in ODC induction by TPA is controversial. Also, generation of free radicals appears to be involved in ODC induction by TPA. Data summarized in this chapter indicate that activation of PKC may be an initial step in ODC induction by TPA.

Animals↗
PubMed1994

Characterization of cytochrome P4501A induction in medaka (Oryzias latipes) by samples generated from the extraction and processing of coal.

The objective of this study was to characterize cytochrome P4501A induction in medaka liver as a biomarker for detecting polyaromatic hydrocarbon (PAH)-type compounds in samples of processed coal or petroleum. Ethoxyresorufin-O-deethylase (EROD) activity in individual medaka livers was used to asses induction of P4501A following the addition of various samples to aquaria water. Samples included a known P4501A inducer, beta-naphthoflavone, and various processed coal samples, as well as a petroleum-pitch. The sensitivity of detecting significant EROD induction by adding samples to aquaria water was approximately 0.1 mg/L for most samples; however, a coal-tar pitch significantly increased EROD activity at 0.01 mg/L. Different samples induced EROD activity to different extents. All samples elicited a concentration-dependent increase in EROD activity, with maximum EROD induction 2 days after a single administration of xenobiotics to aquaria water. Western blot studies established that induction of EROD activity by all xenobiotics tested was associated with corresponding increased amounts of immunoreactive P4501A. EROD induction was not influenced by gender, by single or multiple xenobiotic exposures, nor by feeding or fasting animals during the course of xenobiotic exposure. The ability of xenobiotics to induce EROD activity in medaka liver did not always correlate with their genotoxic potential determined by bacterial mutagenesis assays. Induction of P4501A in medaka liver appears to provide a convenient, economical, reliable and sensitive indicator for the presence of PAH-type compounds in coal- or petroleum-derived samples.

Animals↗
PubMed1993

Induction of extracellular arabinases on monomeric substrates in Aspergillus niger.

The induction of extracellular arabinases by pentose sugars and polyols generated by the metabolic pathway of L-arabinose and D-xylose catabolism in Aspergillus niger was investigated. Induction occurred with L-arabinose and L-arabitol but not with D-xylose or xylitol. L-arabitol in particular was found to be a good inducer for alpha-L-arabinofuranosidase and endo-arabinase activities. Western blotting analysis showed both alpha-L-arabinofuranosidase A and B to be present. No induction was observed using D-arabitol. Unlike the wild type A. niger N402 strain, the A. niger xylulose kinase negative mutant N572 also showed induction of alpha-L-arabinofuranosidases A and B and endo-arabinase activity on D-xylose and xylitol. This is due to metabolic conversion of these compounds leading to the accumulation of both xylitol and L-arabitol in this mutant, the latter of which then acts as inducer. The induction of the two alpha-L-arabinofuranosidases and endo-arabinase is under the control of two regulatory systems namely pathway specific induction and carbon catabolite repression. Under derepressing conditions in the wild type only alpha-L-arabinofuranosidase B could be detected by Western blotting analysis. This indicates that alpha-L-arabinofuranosidase B is of importance in the initiation of specific induction of the various arabinose activities in A. niger grown on arabinose containing structural polysaccharides.

Arabinofuranosyluracil↗
PubMed1993

Induction of glucose oxidase, catalase, and lactonase in Aspergillus niger.

The induction of glucose oxidase, catalase, and lactonase activities was studied both in wild-type and in glucose oxidase regulatory and structural mutants of Aspergillus niger. The structural gene for glucose oxidase was isolated and used for Northern analysis and in transformation experiments using various gox mutations. Wild-type phenotype could be restored in the glucose oxidase-negative mutant (goxC) by transformation with the structural gene. We conclude, therefore, that the goxC marker which is located on chromosome 2 represents the structural gene of glucose oxidase. Glucose and a high oxygen level are necessary for the induction of all three enzyme activities in the wild-type strain and it was shown that both glucose and oxygen effects reflect regulation at the transcriptional level. The goxB mutation results in constitutive expression of all three activities although modulated to some extent by the carbon source. The goxE mutation only has an effect on lactonase and glucose oxidase expression and does not relieve the necessity for a high oxygen level. Catalase and lactonase could not be induced in the glucose oxidase-negative strain (goxC). Addition of H2O2 resulted in the induction of all three enzymes in the wild-type without glucose being present. The H2O2 induction is probably mediated by the goxB product. Besides the H2O2 induction there is still an effect of the carbon source on the induction. A model for induction of glucose oxidase, catalase, and lactonase in A. niger is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspergillus↗
PubMed1975

Influence of double infections on the induction of thymidine kinase by UV-irradiated herpes simplex virus types 1 and 2 and pseudorabies virus.

Simultaneous infection of primary rabbit kidney cells with HSV type 1 TK+ and a TK- strain results in a mutual influence of both viruses on the induction of thymidine kinase (TK). TK+ virus has an enhancing and TK- virus a depressing effect on TK induction by a superinfecting TK+ virus. The enzyme induction depends on the ratio of multiplicities of both viruses. The mutual influence on TK induction depends further on the time of addition of the superinfecting virus: the effect of the second virus can still be observed when given 6 hours after primary infection. Identical phenomena can be observed using combinations with HSV type 2 or Pseudorabies viruses. The ability of HSV to induce TK is progressively inactivated with increasing the time of UV-irradiation. The depressing effect of a TK- strain and the stimulating effect of a TK+ strain on superinfecting TK+ strains is UV-sensitive: after 6 minutes of UV-irradiation neither inhibition nor stimulation of TK induction by a superinfecting TK+ strain can be observed. Infection by long-term (20 minutes) UV-irradiated TK+ strains results in a depression of TK induction by a superinfecting TK+ virus. Long-term irradiation of the TK- virus does not show this effect. Cytosine-arabinoside has no effect on the mutual influence of TK induction by TK+ and TK-strains; the phenomenon of mutual depression therefore has to be considered an early process.

Cell-Free System↗
PubMed1998

Role of axillary lymph node dissection after tumor downstaging with induction chemotherapy for locally advanced breast cancer.

BACKGROUND: Induction chemotherapy has become the standard of care for patients with locally advanced breast cancer (LABC) and currently is being evaluated in prospective clinical trials in patients with earlier-stage disease. To better gauge the role of axillary lymph node dissection in patients with LABC this study was performed to assess initial axillary status on physical and ultrasound examination, axillary tumor downstaging following induction chemotherapy, and the accuracy of physical examination compared with axillary sonography in predicting which patients will have axillary lymph node metastases found on pathologic examination. METHODS: Between 1992 and 1996, 147 consecutive patients with LABC were registered in a prospective trial of induction chemotherapy using 5-fluorouracil, doxorubicin, and cyclophosphamide. Physical and ultrasound examinations of the axilla were performed at diagnosis and after induction chemotherapy. Segmental resection with axillary lymph node dissection or modified radical mastectomy was performed, followed by postoperative chemotherapy and irradiation of the breast or chest wall and regional lymphatics. RESULTS: Following induction chemotherapy, 43 (32%) of the 133 patients with clinically positive lymph nodes on initial examination had axillary tumor downstaging as assessed by physical and ultrasound examination. The sensitivity of axillary sonography in identifying axillary metastases was significantly higher than that of physical examination (62% vs. 45%, P=.012). The specificity of physical examination (84%) was higher than that of sonography (70%), but the difference did not reach statistical significance. Among the 55 patients in whom the findings of both physical and ultrasound examination of the axilla were negative following induction chemotherapy, 29 patients (53%) were found to have axillary lymph node metastases on pathologic examination of the axillary contents. However, 28 (97%) of these patients had either 1 to 3 positive lymph nodes or only micrometastases 2 to 5 mm in diameter. CONCLUSIONS: Preoperative clinical assessment of the axilla by physical examination combined with ultrasound examination is not completely accurate in predicting metastases in patients with LABC following tumor downstaging. However, patients with negative findings on both physical and ultrasound examinations of the axilla may be potential candidates for omission of axillary dissection if the axilla will be irradiated because minimal axillary disease remains. Patients who have positive findings on preoperative physical or ultrasound examinations should receive axillary dissection to ensure local control. A prospective randomized trial of axillary dissection versus axillary radiotherapy in patients with a clinically negative axilla following induction chemotherapy is currently underway.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2002

Differential induction of CYP1A1 in duodenum, liver and kidney of rats after oral intake of soil containing polycyclic aromatic hydrocarbons.

We have analyzed the induction of the cytochrome P450 enzyme CYP1A1 as a biomarker of effect in duodenum, liver and kidney of rats after oral intake of contaminated soil particles. The soil samples originated from industrial sites and were contaminated with polycyclic aromatic hydrocarbons (PAH) to variable extents, ranging from 60 to 4700 mg PAH/kg soil. Soil samples were administered for one week as a mixture with commercial rodent diets. After exposure, microsomes of several organs were prepared and analyzed for CYP1A1, enzymatically and by Western blots. All contaminated soils led to induction of CYP1A1 in duodenal mucosa cells, regardless of their extent of contamination, showing that relevant doses were mobilized in the gastrointestinal tract and adsorbed. Subsequent distribution of non-metabolized compounds is indicated by induction of CYP1A1 in the liver. However, some samples did not lead to a response in the liver, due to their quantitative and qualitative contaminant composition. In accordance with previous results, there is a sigmoidal dose-response relationship between induction of hepatic CYP1A1 levels and the soil contamination with higher condensates of PAH. In contrast, the response in the duodenum appeared to be hyperbolic and correlated well with the amounts of total PAH. Highly contaminated soil, being nearly devoid of higher condensates of PAH, led to pronounced induction in the duodenum but failed to induce CYP1A1 in the liver. Successful passage of contaminants through the intestinal barrier and the liver compartment is shown by increased CYP1A1 expression in the kidney. Compared with enzyme levels induced in the liver, those of the kidney are much lower and amount to only about 1/20 of the liver values for soils with high induction potential. Hence, oral PAH intake leads to differential induction patterns of CYP1A1 in duodenum, liver and kidney of rats. The observations raise questions concerning the role of the primary duodenal PAH metabolism in preventing contaminant-dependent hazardous effects, and of the significance of differential CYP1A1 expressions for carcinogenic processes in several tissues.

Animals↗
PubMed2002

Isomaltose formed by alpha-glucosidases triggers amylase induction in Aspergillus nidulans.

Among various alpha-glucobioses examined, isomaltose was the most effective inducer for amylase synthesis in Aspergillus nidulans. Amylase induction by maltose was completely inhibited by addition of castanospermine or cycloheximide, while induction by isomaltose was not affected by the inhibitors, suggesting that amylase induction by maltose requires inducible alpha-glucosidases. Disruption of the alpha-glucosidase A gene ( agdA), the alpha-glucosidase B gene ( agdB), or both genes did not abolish maltose-dependent induction, although amylase production induced by maltose decreased about 2-fold in the agdA/ agdB double disruptant, compared with that in the agdB disruptant at all concentrations tested. Upon induction by isomaltose, amylase synthesis was enhanced considerably in the agdB and agdA/ agdB disruptants. Even at 3 nM, isomaltose induced amylase production in the double disruptant, supporting the suggestion that isomaltose is a physiological inducer for amylase. Therefore, maltose must be converted to isomaltose by alpha-glucosidases prior to triggering amylase synthesis, but no specific alpha-glucosidase is required for amylase induction by maltose. Probably any alpha-glucosidases having isomaltose-forming activity, including AgdA and AgdB, may participate in amylase induction by maltose.

Aspergillus nidulans↗
PubMed2003

Nucleosome transactions on the Hypocrea jecorina (Trichoderma reesei) cellulase promoter cbh2 associated with cellulase induction.

The 5' regulatory region of the cbh2 gene of Hypocrea jecorina contains the cbh2 activating element (CAE) which is essential for induction of cbh2 gene expression by sophorose and cellulose. The CAE consists of two motifs, a CCAAT box on the template strand and a GTAATA box on the coding strand, which cooperate during induction. Northern analyses of cbh2 gene expression has revealed an absolute dependence on induction, but no direct effect of Cre1-mediated carbon catabolite repression. Investigation of the chromatin structure in the wild-type strain showed that, under repressing conditions, there is a nucleosome free region (nfr) around the CAE, which is flanked by strictly positioned nucleosomes. Induction results in a loss of positioning of nucleosomes -1 and -2 downstream of the CAE, thus making the TATA box accessible. Simultaneous mutation of both motifs of the CAE, or of the CCAAT-box alone, also leads to shifting of nucleosome -1, which normally covers the TATA-box under repressing conditions, whereas mutation of the GTAATA element results in a narrowing of the nfr, indicating that the proteins that bind to both motifs in the CAE interact with chromatin, although in different ways. A cellulase-negative mutant strain, which has previously been shown to be altered in protein binding to the CAE, still displayed the induction-specific changes in nucleosome structure, indicating that none of the proteins that directly interact with CAE are affected, and that nucleosome rearrangement and induction of cbh2 expression are uncoupled. Interestingly, the carbon catabolite repressor Cre1 is essential for strict nucleosome positioning in the 5' regulatory sequences of cbh2 under all of the conditions tested, and induction can occur in a promoter that lacks positioned nucleosomes. These data suggest that Cre1, the Hap2/3/5 complex and the GTAATA-binding protein are all involved in nucleosome assembly on the cbh2 promoter, and that the latter two respond to inducing conditions by repositioning nucleosome -1.

Base Sequence↗
PubMed1995

Accelerated induction therapy and resection for poor prognosis stage III non-small cell lung cancer.

BACKGROUND: Induction therapy and resection may improve the survival of patients with poor prognosis stage III non-small cell lung cancer, at the cost of significant treatment prolongation. The purpose of this study was to assess toxicity, response, and survival of an accelerated induction regimen and resection in poor prognosis stage III non-small cell lung cancer. METHODS: Forty-two surgically staged patients with poor prognosis stage III non-small cell lung cancer received 11 days of induction treatment consisting of 96 hours of continuous chemotherapy infusions of cisplatin (20 mg.m-2.day-2), 5 fluorouracil (1,000 mg.m-2.day-2), and etoposide (75 mg.m-2.day-2) concurrent with accelerated fractionation radiation therapy (1.5 Gy twice a day, to a dose of 27 Gy). Induction was followed in 4 weeks by resection. Postoperatively, a second course of continuous chemotherapy and concurrent accelerated fractionation radiation therapy (postoperative dose 13 to 36 Gy) was given. RESULTS: Despite some degree of induction toxicity in all patients there was only one induction death (2.4%). A clinical partial response was seen in 24 patients (57%). Thirty-six patients (86%) underwent thoracotomy, and resection was possible in 33 (79%). Pathologic downstaging was seen in 17 patients (40%), and 2 patients (5%) had no residual carcinoma at operation. There were 11 postoperative complications (31%) and 4 postoperative deaths (11%). Thirteen patients (31%) are alive and disease-free, 24 (57%) have persistent disease or have recurred (15 distant, 5 locoregional, 4 both), and 9 patients are alive with disease. The median survival is 21 months and the 2-year Kaplan-Meier survival is 43%, with no differences identified between stages IIIA and IIIB patients (p = 0.63). CONCLUSIONS: We conclude that accelerated induction therapy and resection in poor prognosis stage III non-small cell lung cancer (1) is toxic, with a 12% treatment mortality; (2) is effective with a 79% resection rate and 40% pathologic downstaging rate; (3) provides excellent local control; (4) may prolong survival; and (5) is of value in stage IIIB as well as stage IIIA patients.

Adult↗
PubMed1987

Inhibition of cyclic AMP-dependent induction of ornithine aminotransferase by simple carbohydrates in cultured hepatocytes.

Glucose administration inhibits the induction of ornithine aminotransferase (OAT) in both the whole animal and cultured hepatocytes. We have examined the ability of several hexoses and related molecules to inhibit the cAMP-dependent induction of OAT in primary cultures of adult rat hepatocytes. The hexoses (D-glucose, fructose, sorbitol, sorbose, and mannose) that were effective as inhibitors of OAT induction also resulted in accumulation of lactate in the culture medium, although lactate itself was not effective as an inhibitor. The hexoses and related 6-carbon structures (galactose, L-glucose, 2-deoxyglucose, 3-O-methylglucose, rhamnose, mannitol, and inositol) that were not effective as inhibitors of OAT induction did not result in accumulation of lactate in the culture medium. These results suggest that the carbohydrate repression of hepatic OAT requires metabolism of the carbohydrate by the liver cell. Upon addition to the culture medium of several compounds related to carbohydrate metabolism, many (ribose, xylitol, dihydroxyacetone, and glycerol) exhibited an inhibitory effect, with glycerol exhibiting the greatest effect. Fructose and glycerol inhibit OAT induction in the presence of 2-deoxyglucose, suggesting that the inhibitory effect of nonglucose carbohydrates is not occurring through conversion to glucose. The carbon sources observed to be most effective as inhibitors of OAT induction (glycerol, fructose, sorbitol, and sorbose result in more than 90% inhibition at 25 mM) all enter the glycolytic pathway at the triosephosphate level. The mechanism of the inhibitory effect of simple carbohydrates on OAT induction is not known but may involve an increase in certain glycolytic intermediates. Glucose and the related carbon sources exert their effect by inhibiting the cAMP-dependent increase in OAT synthesis. The cAMP-dependent increase in OAT mRNA was inhibited by fructose. These findings suggest that the carbohydrate inhibition of the cAMP-dependent increase in OAT synthesis occurs at a pretranslational level.

Animals↗
PubMed1990

Accelerated essential fatty acid deficiency by delta 9 desaturase induction: dissociation between the effects on liver and other tissues.

Essential fatty acid (EFA) deficiency is an important tool in probing the role of arachidonic acid (20:4(n-6] in pathophysiologic processes, but requires stringent and prolonged deprivation of (n-6) fatty acids. The present study investigated whether induction of the delta 9 desaturase, which is responsible for the synthesis of oleate, the precursor of 20:3(n-9) which uniquely accumulates in the deficiency state, might serve to accelerate the biochemical and biological effects of EFA deficiency. By alternately fasting and feeding animals a fat-free diet, it was possible to induce markedly the delta 9 desaturase selectively in liver. This dietary manipulation in consequence led to dramatic and rapid changes in hepatic phospholipid fatty acid composition. Within 2 weeks, 20:3(n-9) to 20:4(n-6) ratios in liver phospholipids were several fold greater than those seen in animals fed a fat-free diet alone. These changes, however, contrasted with those seen in the serum and other tissues. The mol% of 20:3(n-9) in serum was not increased by delta 9 desaturase induction and the 20:3(n-9) to 20:4(n-6) ratio was only modestly increased. The effects of delta 9 desaturase induction were even more attenuated in tissues other than the liver. Desaturase induction led to a doubling in the 20:3(n-9) to 20:4(n-6) ratio in phosphatidylcholine in renal cortex and heart, although the ratio in the other phospholipids was unaffected. The 20:3(n-9) to 20:4(n-6) ratio in peritoneal macrophage phospholipids was unaffected by desaturase induction. Thus, delta 9 desaturase induction greatly augments the synthesis of (n-9) fatty acids within the liver and leads to the rapid and substantial accumulation of the abnormal fatty acid, 20:3(n-9). This markedly augmented synthesis of hepatic 20:3(n-9), however, is not reflected in increased plasma levels of 20:3(n-9), and thus the effects of delta 9 desaturase induction are attenuated in tissues other than the liver. These data underscore the notable ability of the liver to maintain polyunsaturated fatty acid homeostasis.

Animals↗
PubMed1986

Diacylglycerol amplifies the induction in vivo of tyrosine aminotransferase and ornithine decarboxylase by glucocorticoid.

In adrenalectomized rats, diacylglycerol, a potent activator of protein kinase C, specifically enhanced the induction of tyrosine aminotransferase and ornithine decarboxylase by even maximally effective doses of dexamethasone phosphate, but itself had no effect on these enzyme inductions in the absence of glucocorticoid. The amplifications of enzyme induction by diacylglycerol was dose-dependent and the time courses of the amplified inductions were similar to those of the inductions by dexamethasone phosphate alone. Since diacylglycerol did not affect the induction of these enzymes by glucagon and insulin, its amplifying effect seemed to be specific for induction by glucocorticoids.

Adrenalectomy↗
PubMed1989

Quantitative assessment of enzyme induction by peroxisome proliferators and application to determination of effects on triglyceride biosynthesis in primary cultures of rat hepatocytes.

Potencies for the induction of peroxisomal fatty acyl-CoA oxidase (FACO) and microsomal laurate hydroxylase (LH) were determined for clofibric acid (CPIB), ciprofibrate (Cipro) and gemfibrozil (Gem) in primary cultures of rat hepatocytes based on complete concentration-response analysis and determination of theoretical maximum inductive responses for Cipro. CPIB and Cipro each induced FACO and LH in a concentration-dependent manner. Scatchard analysis of the data allowed calculation of EC50 values (mM) of 0.82 and 0.028 (for FACO) and 0.22 and 0.0081 (for LH) for CPIB and Cipro respectively. The EC50 ratios (CPIB/Cipro) were identical (29-fold) for induction of FACO and LH, supporting the concept that these enzymes are induced by CPIB and Cipro through a common mechanism. By comparison, Gem was relatively ineffective as an inducer of FACO and LH. Furthermore, Gem did not antagonize Cipro-mediated enzyme inductions, suggesting that Gem is a peroxisome proliferator of low potency rather than a partial agonist. Based on the potency and time-course profiles observed for induction of FACO and LH, the effects of CPIB, Cipro and Gem on triglyceride (TG) biosynthesis were determined in the cultured rat hepatocytes. Conditions of maximal FACO and LH induction by the drugs did not result in inhibition of TG biosynthesis in the cells. These results support the in vivo evidence which indicates that FACO and LH induction are not causally linked to the hypotriglyceridemic actions of peroxisome proliferating drugs.

Acyl-CoA Oxidase↗