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H A Sancovich

Publications and source records attributed to H A Sancovich.

At least 19 recordsLinked to original sources
PubMed2002

Ontogeny of 5-aminolevulinic dehydratase and porphobilinogen deaminase activities in the yolk sac membrane and liver of chick embryos.

1. Chick embryos of 7, 9, 11, 12, 13, 14, 15, 17 and 19 d of embryonic development were examined to determine the activities of 5-aminolevulinic dehydratase (ALA-D, EC 4.2.1.24) and porphobilinogen deaminase (PBG-D, EC 4.3.1.8). 2. Liver and yolk sac membrane ALA-D specific activities showed a maximum between 12 and 13 d of embryonic development, yolk sac membrane PBG-ase activity a maximum at 9 d and at 7 d in liver. Total activities of ALA-D and PBG-D were not constant during the course of embryonic development but probably related to the changes of intensity of haem synthesis. 3. ALA-D and PBG-ase activities were higher in yolk sac membrane than in liver, showing the importance of the yolk sac membrane as erythropoietic tissue. PBG-D catalysed the rate-limiting reaction of the cytosolic steps in the biosynthetic pathway in both tissues.

Age Factors↗
PubMed1999

Hexachlorobenzene, a dioxin-type compound, increases malic enzyme gene transcription through a mechanism involving the thyroid hormone response element.

Hexachlorobenzene (HCB) is a dioxin-type chemical that acts mainly through the aryl hydrocarbon receptor. Chronic exposure of rats to HCB increases the activity of malic enzyme (ME). In this report, we show that this increase is correlated with an induction of ME messenger RNA (mRNA) levels, with the maximal HCB effect achieved after 9 days of intoxication. This effect is specific for ME, as other liver enzymes, such as glyceraldehyde-3-phosphate dehydrogenase, phosphoenol pyruvate carboxykinase, and mitochondrial alpha-glycerol-3-phosphate dehydrogenase, are not affected by HCB. The induction of ME mRNA levels is accompanied by an increase in ME promoter activity, as demonstrated by transient transfection experiments performed in rat hepatoma H35 cells. In an attempt to identify the cis-regulatory elements responsible for the HCB effect, different promoter deletions and mutations were used. The results obtained localize the responsive region between positions -315 and -177. This region does not contain either consensus xenobiotic response or activating protein-1 elements, the two main mediators of dioxin compounds described to date. In contrast, a thyroid hormone response element (TRE) is located between -281 to -261. Deletions and mutations of the TRE element do not respond to HCB, demonstrating that this element mediates the response of this dioxin-type compound. As ME gene expression is regulated mainly by thyroid hormones, we next investigated the role of T3 receptor (T3R) in the ME gene transcriptional induction mediated by HCB. Using Scatchard analysis, we show that neither T3R binding features for its ligand nor alpha1 or beta1T3R mRNA levels are changed with the toxic. In gel shift assays, however, we observed that protein/DNA complexes formed on TRE from the ME promoter were induced by HCB. Using an oligonucleotide with a mutation that eliminates the TRE function, we demonstrate a loss of the induced protein/DNA complexes. Together, these data suggest that the dioxin-type compound HCB increases ME gene transcription by modulating the levels of still unidentified nuclear proteins that bind to the TRE element of the ME promoter.

Animals↗
PubMed1998

Hexachlorobenzene-induced alterations of rat hepatic microsomal membrane function.

The time and dose-dependent effects of the in vivo administration of hexachlorobenzene (HCB), on hepatic microsomal membrane functions, were studied in female Wistar rats. Administration of HCB (100 mg/100 g b.w.) resulted in time-dependent decreases in the activity of two membrane-bound enzymes: 5'nucleotidase and Na+/K+ ATPase. HCB was found to cause a significant rise in protein tyrosine kinase (PTK) activity during the early stages of intoxication (day 2), followed by a significant decrease at 10 days, returning to control levels after 20 days of treatment. A stimulatory effect of HCB on in vitro endogenous microsomal protein phosphorylation was observed from 2 days of intoxication up to 30 days of treatment, with an important stimulation of phosphorylation at 5 days. Administration of HCB (100 mg/100 g b.w.) for 10 days caused a 50% reduction in epidermal growth factor receptor (EGF-R) ligand binding. The effects of known specific inhibitors of protein phosphatases on endogenous protein phosphorylation were studied. HCB affected the labelling of several bands, as well as the 5'nucleotidase and PTK activities, in a dose-dependent manner. In conclusion, this study indicated that the in vivo administration of HCB results in a significant alteration of membrane function.

5'-Nucleotidase↗
PubMed1998

[Effect of thyroid hormones on the modulation of genetic expression of liver cytosolic malic enzyme, in rats poisoned with hexachlorobenzene].

Hexachlorobenzene (HCB) is a widespread environmental pollutant. Chronic exposure of laboratory animals to HCB triggers porphyria, induction of liver microsomal enzymes, low levels of T4 reproductive dysfunction's, liver and thyroid tumors. Previous findings from our laboratory have shown that HCB increased the activity of the liver thyroid-responsive enzymes: malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PD) without any change in the mytochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD). In this study we have demonstrated that HCB treatment increased ME mRNA. We also have investigated if HCB affected: a) the thyroid hormone receptor (TR) concentration and binding affinity for its ligands, b) specifically the ME gene expression, or other thyroid hormone responsive enzymes were affected as well, c) Protein/DNA complex formed on the thyroid responsive element (TRE). Livers from female Wistar rats intoxicated with HCB (100 mg/100 g b.w.), for 9 and 15 days, were analyzed. Northern blot hybridization analysis, have demonstrated that ME mRNA levels increased 4 times and 2 times after 9 and 15 days intoxication respectively, without any alterations in the mRNA levels of other thyroid hormone responsive enzymes such as glyceraldheyde 3- phosphate dehydrogenase, phosphoenolpyruvatecarboxikinase and alpha-GPD. These results suggest that HCB affects specifically, ME gene expression. Hepatic T3 and T4 levels evaluated by RIA were not affected by HCB. Scatchard analyses showed that TR affinity and number of sites were not altered after 9 and 15 days of HCB treatment (control, Ka: 1.9 nM, Bmax 3.9 f/mol 100 micrograms DNA: HCD 9 days Ka: 2.1 nM, Bmax 4.5 fmol/100 micrograms DNA: HCB 15 days Ka 1.9 nM. Bmax 5.1 fmol/100 micrograms DNA intoxication, neither at 9 nor at 15 days. Electrophoresis mobility shift assay showed that HCB did not modify nuclear protein extract affinity for the TREs sequence. Our results suggest that TR itself was not directly involved in the induction of ME gene expression by HCB. Nevertheless TR could interact with other transcription factors in the overexpression of ME gene.

Animals↗
PubMed1995

Hepatic indices of thyroid status in rats treated with hexachlorobenzene.

The functional thyroid status of hexachlorobenzene (HCB)-treated rats was studied. HCB caused a depletion of serum thyroxine (T4), but did not change L-3,5,3'-triiodothyronine (T3) levels in serum of rats. The activities of the thyroid regulated mitochondrial enzyme L-glycerolphosphate dehydrogenase (LGPD) and cytosolic enzymes, malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) were assayed in livers of normal and HCB (100 mg/100 g bw) treated Wistar rats. Mitochondrial LGPD activity did not change significantly, however ME, 6GPD and G6PD were induced by HCB only in non-thyroidectomized animals. The absence of cytosolic enzymes induction in thyroidectomized rats treated with HCB indicates that HCB is not intrinsically thyromimetic. The induction of hepatic ME, G6PD and 6PGD activities in HCB thyroidectomized rats was dependent on the presence of thyroid hormone. The unchanged activity of mitochondrial LGPD in contrast to the increased activities of the cytosolic enzymes ME, G6PD and 6PGD is not consistent with a shift in functional thyroid status following HCB treatment.

Animals↗
PubMed1994

Effect of thyroidectomy and thyroxine on hexachlorobenzene induced porphyria.

The role of thyroid status in hexachlorobenzene (HBC) induced porphyria was studied in normal, thyroidectomized and thyroxine (T4) treated rats. Female Wistar rats were treated with HCB for different periods of time. Serum T4 levels were depressed after 8 days of HCB administration whereas levels of triiodothyronine (T3) were not altered. T4 administered simultaneously with HCB resulted in hyperthyroxinemia. The time course of porphyrinogen carboxy-lyase (PCL) activity in the three HBC treated groups was studied. A rapid and significant decrease of PCL activity was found after 8 days of HCB treatment in T4 treated rats with respect to untreated animals. In contrast, HCB treatment of normal and thyroidectomized rats elicited a significant decrease of PCL activity after 21 and 30 days, respectively. This study shows that thyroid hormone plays an important role in the early establishment of HCB induced porphyria.

Animals↗
PubMed1991

Studies on the decrease of liver cytochrome P-450 content by triiodothyronine.

In the rat liver, the microsomal content of cytochrome P-450 decreased by 50% after triiodothyronine (T3) administration. The molecular basis for the decreased cytochrome P-450 levels was investigated. The activities of the enzymes involved in heme synthesis or degradation were not altered by thyroid hormone administration. The incorporation of 3H-delta-aminolaevulinate into the liver microsomal heme was markedly reduced in T3-treated rats. The latter appeared not to reflect a lowered binding affinity of the apoprotein moiety of cytochrome P-450 for heme. The sodium dodecyl sulfate gel electrophoresis of the microsomal preparation showed a decrease in apocytochrome P-450. It is suggested that the amount of the apocytochrome may be the primary event affected in the formation of cytochrome P-450, by triiodothyronine treatment of thyroidectomized rats.

5-Aminolevulinate Synthetase↗
PubMed1990

Further evidence for an essential histidyl residue at the active site of pig liver 5-aminolevulinic acid dehydratase.

Photoxidation with methylene blue and rose bengal and chemical modification by diethylpryrocarbonate of pig liver 5-aminolevulinic acid dehydratase produced strong inactivation of the enzyme which was concentration dependent. Loss of enzyme activity by both photoxidation and ethoxyformylation was pH and time-dependent and protected by the presence of the substate and competitive inhibitors. The rate of inactivation was directly related to the state of protonation of histidyl groups, the unprotonated from being modified at a much faster rate than the protonated form. Plots of the pseudo-first order rate constants for 5-aminolevulinic acid dehydratase inactivation against pH resulted in typical titration curves showing inflection points at about pH 6.4 for methylene blue and rose bengal and 6.8 for diethylprocarbonate providing further and unequivocal evidence for the existence of critical histidyl groups at the active centre of the enzyme.

Animals↗
PubMed1989

Enhanced thyroxine metabolism in hexachlorobenzene-intoxicated rats.

The effect of hexachlorobenzene (HCB) (1 g/kg bw) administration for 4 weeks, on thyroxine (T4) and triiodothyronine (T3) metabolism was studied in Wistar rats. The effect on serum binding of T4 has also been studied. Animals were injected with a tracer dose of either labeled hormone and by examining serum L-125I-T4 and L-125-I-T3, kinetics of radiolabeled hormones metabolism were calculated. The T4 metabolic clearance (MCI) as well as the distribution space, were increased by 6 fold. Decreased serum T4 levels result from an increase both in deiodinative and fecal disposal in HCB-treated rats. 125I-T3 metabolism was slightly affected. The enhanced peripheral disposition of thyroxine appears to lead to increased thyroid function, as measured by augmented TSH serum levels and 125I-thyroidal uptake. Serum binding of T4 was not affected.

Animals↗
PubMed1988

The isolation and identification of indigoid pigments from urine.

A purple pigment, phyriaviolin, and a blue pigment, phyriaazulin, have been found in relatively large amounts in the urine of patients suffering from two diverse pathological conditions, porphyria cutanea tarda and Crohn's disease. The two pigments have been characterised by chemical, spectroscopic, and chromatographic studies and identified to be indirubin and indigo (indigotin). Possible reasons for their formation are discussed.

Chromatography, Thin Layer↗
PubMed1988

Effect of triiodothyronine in the regulation of haem biosynthetic pathway.

Triiodothyronine administration to thyroidectomized animals, decreased cytochrome P-450 content by 50%. Haem oxygenase was not modified by triiodothyronine treatment, either alone or with a suboptimal dose of CoCl2. Under the same conditions hepatic delta-amino-laevulinic acid synthase activity was not affected. Triiodothyronine caused a two fold increase in tryptophan pyrrolase activity. Both the hole and total enzyme were increased to the same degree. Porphobilinogen deaminase-Uroporphyrinogen III Co-synthase activity was induced by 67% over thyroidectomized values, in triiodothyronine treated rats, and only 32% above the sham operated controls. Our results suggest that under triiodothyronine stimulation, the decrease in cytochrome P-450 content is not due to an enhanced rate of degradation of the haem moiety, but it rather dissociates to increase the cellular haem pool, and saturates in part the newly synthesized apotryptophan pyrrolase.

5-Aminolevulinate Synthetase↗
PubMed1985

Progesterone, its A/B cis reduction and delta aminolevulinic acid synthetase in the developing hen.

In steroidogenic tissues of the developing hen, specially in the right ovary, 5 beta reductase (Rase) increases after hatching. delta aminolevulinic acid synthetase (ALAs) in these tissues is more active than hepatic ALAs during most embryonic stages. But after hatching, only hepatic and adrenal ALAs increase sharply; ALAs increases only moderately in the left ovary and descends to very low values in the right one. A relationship between ALAs and Rase curves during embryonic development of the left ovary and the adrenal suggests that 5 beta pregnanedione is a natural inducer of ALAs in these functional endocrine glands, at least during their embryonic stages.

3-Hydroxysteroid Dehydrogenases↗
PubMed1976

Macrocyclic intermediates in the biosynthesis of porphyrins.

The hepta-, hexa- and penta-carboxylic porphyrins found in the faeces of rats poisoned with hexachlorobenzene have been separated by high-pressure liquid chromatography and characterized largely by spectroscopie methods. Their structures were confirmed by total synthesis, as part of a programme in which eleven of the fourteen hepta-, hexa- and penta-carboxylic porphyrins derived from uroporphyrin III have now been synthesized as their methyl esters. The four isomeric heptacarboxylic and three of the pentacarboxylic porphyrinogens have been incubated with haemolysates of chicken erythrocytes, and they are all converted into protoporphyrin IX but at different rates. On the basis of this and other evidence we conclude that the decarboxylation of uroporphyrinogen III to coproporphyrinogen III is a stepwise process taking place by a preferred pathway (both in normal and abnormal metabolism); the acetic acid groups are decarboxylated in a sequential clockwise fashion starting with that on the D ring and followed by those on the A, B and C rings. In the poisoned rats the uroporphyrinogen decarboxylase enzyme (or group of enzymes) is probably partially inhibited and the pentacarboxylic porphyrinogen with an acetic acid group on ring C accumulates. The latter is then transformed by a side pathway into dehydroisocoproporphyrinogen and thence into dehydroisocoproporphyrin and its congeners.

Animals↗
PubMed1976

Hepta- and hexa-carboxylic porphyrinogen intermediates in haem biosynthesis.

In the course of our studies on intermediates in normal and abnormal metabolism of porphyrins we have synthesised a number of porphyrins related to uroporphyrin-III and compared them with materials isolated from natural sources. In the present paper we show that the corresponding porphyrinogens are all metabolised to protoporphyrin-IX by haemolysates of chicken erythrocytes, but at different rates. The results are discussed in relation to our conclusions concerning the preferred pathway of degradation of uro'gen-III to coproporphyrinogen-III, which indicate a clockwise sequence of decarboxylation reactions.

Animals↗