Biomedical subjects

M C Ríos de Molina

Publications and source records attributed to M C Ríos de Molina.

15 recordsLinked to original sources

PubMed2002

The decrease in uroporphyrinogen decarboxylase activity induced by ethanol predisposes rats to the development of porphyria and accelerates xenobiotic-triggered porphyria, regardless of hepatic damage.

We evaluated the porphyrinogenic ability of ethanol (20% in drinking water) per se, its effect on the development of sporadic porphyria cutanea tarda induced by hexachlorobenzene in female Wistar rats (170-190 g, N = 8/group), and the relationship with hepatic damage. Twenty-five percent of the animals receiving ethanol increased up to 14-, 25-, and 4.5-fold the urinary excretion of delta-aminolevulinate, porphobilinogen, and porphyrins, respectively. Ethanol exacerbated the precursor excretions elicited by hexachlorobenzene. Hepatic porphyrin levels increased by hexachlorobenzene treatment, while this parameter only increased (up to 90-fold) in some of the animals that received ethanol alone. Ethanol reduced the activities of uroporphyrinogen decarboxylase, delta-aminolevulinate dehydrase and ferrochelatase. In the ethanol group, many of the animals showed a 30% decrease in uroporphyrinogen activity; in the ethanol + hexachlorobenzene group, this decrease occurred before the one caused by hexachlorobenzene alone. Ethanol exacerbated the effects of hexachlorobenzene, among others, on the rate-limiting enzyme delta-aminolevulinate synthetase. The plasma activities of enzymes that are markers of hepatic damage were similar in all drug-treated groups. These results indicate that 1) ethanol exacerbates the biochemical manifestation of sporadic hexachlorobenzene-induced porphyria cutanea tarda; 2) ethanol per se affects several enzymatic and excretion parameters of the heme metabolic pathway; 3) since not all the animals were affected to the same extent, ethanol seems to be a porphyrinogenic agent only when there is a predisposition, and 4) hepatic damage showed no correlation with the development of porphyria cutanea tarda.

Animals↗

PubMed2001

How does hexachlorobenzene treatment affect liver uroporphyrinogen decarboxylase?

The aims of the present work were: (1) to investigate whether the strong decrease of liver uroporphyrinogen decarboxylase (UroD) activity observed in experimental porphyria cutanea tarda is due to alteration of the enzymatic protein and (2) to improve the knowledge about the normal liver enzyme. With these purposes, several physicochemical studies for enzymatic characterization were carried out comparatively on the 12-fold purified liver enzyme of both normal and hexachlorobenzene porphyric rat. The study shows that the enzyme from porphyric rats has a higher activation energy, lower reactivity index and lower optimum pH than the normal one. In addition, it did not reach the Vmax at any of the substrate concentrations assayed (up to 28 microM uroporphyrinogen III), while the normal enzyme reached the plateau around 14 microM. The porphyric enzyme appears to be more protected than the normal against the inhibitory action of several metals, particularly Cu2+ and Pb2+, and against thermal inactivation. Zn2+ did not affect enzymatic activity, whereas Cu2+, Hg2+, Fe2+, Pb2+, and Cd2+ lowered the activities of both normal and porphyric enzyme in a dose-related way. It was also observed that the larger the atomic radius in its hydrated state, the lower the effect of the metal. Neither glutathione nor dithiothreitol significantly altered enzymatic activity in the range of concentrations assayed. beta-Mercaptoethanol had diverse effects, as regards both the concentration assayed and the enzymatic sample used. Assays with cystine showed a dual behaviour of both normal and porphyric enzymatic activity. Western blots for both preparations revealed a single band (65 kDa) with a similar intensity. This study show that hexachlorobenzene treatment modifies the physicochemical properties of liver UroD leading to a sharp decrease of its activity, without affecting its antigenic reactivity probably as a consequence of changes at the conformational level promoted by the binding of its reported inhibitor.

Animals↗

PubMed1999

Effect of alpha lipoic acid amide on hexachlorobenzene porphyria.

The aim of this work is to study the effect of thioctamide--the commercial form of alpha lipoic acid amide--on the porphyrinogenic action of hexachlorobenzene (HCB). For this purpose, porphyria was induced in rats by chronic HCB treatment, with or without simultaneous thioctamide administration. Two different groups of rats were used as reference: one treated with vehicle (control) and the other treated with thioctamide (TO). Urine delta aminolevulic acid, porphobilinogen, and porphyrin excretions were lower in the HCB + TO treated group than in the HCB group, and the same happened with liver uroporphyrin accumulation. On the other hand, the second stage of uroporphyrinogen-decarboxylase activity was significantly higher in the HCB + TO group than in the HCB group. delta aminolevulic acid synthase activity was higher in the HCB group. Hepatic thiobarbituric acid reactive substances were lower in HCB + TO group than in HCB group. Thus, we might suggest that TO would decrease HCB effects by means of its free radical scavenging ability, and by having a direct effect on uroporphyrinogen-decarboxylase activity.

Animals↗

PubMed1998

[Effect of the thioctamide in relation to the hexachlorobenzene action].

Chronic administration of Hexachlorobenzene, with or without the simultaneous administration of Tioctamide was assayed. Hexachlorobenzene alone produced the characteristic porphyria, detected through an increase of the urinary excretion and the hepatic accumulation of porphyrins, as well as by a decrease of the Uroporphyrinogen decarboxylase activity. The content of hepatic conjugated dienes did not change while those of malondialdehyde increased, although without reaching levels of statistical significance. These results would indicate the occurrence of an light lipid peroxidation process. The Thioctamide (25 mg/kg body weight) produced more noxious effects than protective ones, which were detected by a high level of Glutamate piruvate transaminase activity and a decrease of the hepatic Uroporphyrinogen decarboxylase activity, at its first step of decarboxylation. These results might indicate that: 1) high doses of Thioctamide decreases Uroporphyrinogen decarboxylase activity, masking its possible protective effect from Hexachlorobenzene's action through free radicals production and, 2) Uroporphyrinogen decarboxylase is a more sensitive parameter than conjugated dienes or malondialdehyde levels to assay the free radicals in vivo Hexachlorobenzene production. In any case, the Thioctamide assayed in lower and non toxic doses, perhaps might protect against Hexachlorobenzene's action through its free radical scavenger ability.

5-Aminolevulinate Synthetase↗

PubMed1996

Precancerous pathology evoked by hexachlorobenzene treatment.

The porphyrinogenic and carcinogenic ability of hexachlorobenzene (HCB) was assayed in male and female gold hamsters, and histological examinations of tissue alterations were performed. So it was studied, in liver: a) porphyrin content which was significantly increased at five months of HCB treatment, specially in males, and the pattern of accumulated porphyrins which was altered independent of the sex, b) haem pathway enzymes:delta aminolaevulinic acid synthase, ferrochelatase and porphyrinogen carboxylyase (PCL); among which only PCL appeared to be altered just at ten months of HCB feeding. While thyroid gland and kidney remained unaltered along the treatment time, liver and spleen exhibited a noticeable size variation and morphological alterations. In fact the spleen in treated animals was hypotrophic showing a red pulp less developed with respect to the Malpighian corpuscles and many macrophages with iron deposits. Respect to the liver, enlargement in size of hepatocytes, high content of iron deposits, no PAS positive structures in the cytoplasm, several small lipid droplets, microsteatosis although no cytonecrosis, polymorphic nuclei, and proliferations of nucleoli were observed. Therefore HCB is able to cause precancerous pathology and to induce porphyria in hamsters, but not hyperthyroidism, upon this experimental conditions. By the way, males were found to be a good experimental model, better than females, to study the earliest relations between porphyria and cancer.

Animals↗

PubMed1996

Porphyrinogen carboxylyase. Studies on the existence of isoenzymes.

Porphyrinogen carboxylyase from normal rat liver was subjected to purification methods. Two different purification protocols were used. In both cases, the initial steps consisted in obtaining a liver homogenate, followed by centrifugation, salt precipitation and phosphate gel absorption. Scheme I consisted in then submitted the preparation to DEAE-cellulose, followed by Sephacryl S-200 and Phenyl-sepharose sequential column chromatographies. Scheme II involved an affinity column followed by a Sephadex G-75 gel filtration column. In both cases, the enzyme was stored at -20 degrees C until its assay. The addition of 2mM dithiotreytol to the incubation media or to the enzyme extract before storage, did not help improve the activity nor the stability of the enzyme. Those fractions containing the maximal enzyme activity, detected using Uroporphyrinogen III or Pentacarboxy-porphyrinogen III as substrate, were not always present in the same tubes for the different columns employed. In addition, the degree of purification obtained in some steps was different according to the substrate employed. The results suggest the existence of at least two isoenzymes for rat liver porphyrinogen carboxy-lyase.

Animals↗

PubMed1991

Liver ferrochelatase from normal and hexachlorobenzene porphyric rats. Mechanism of drug action.

1. The action of hexachlorobenzene (HCB) on hepatic ferrochelatase was investigated. 2. A direct action of HCB, pentachlorophenol, porphyrins and haem on this enzyme activity was discarded. 3. In HCB porphyric liver there is probably an activator tightly bound to the enzyme. 4. Pyridoxal phosphate (PPL) may be a cofactor of ferrochelatase from both normal and porphyric rats. 5. The PPL would be involved in the binding site of Fe2+ or at least in the approaching of Fe2+ to the active site of the enzyme. 6. The differences found between normal and porphyric preparations could be attributed to conformational changes elicited by the HCB.

Animals↗

PubMed1991

Studies on the active centre of rat liver porphyrinogen carboxylase in vivo effect of hexachlorobenzene.

1. Porphyrinogen carboxylase from the liver of normal and hexachlorobenzene porphyric rats was subjected to chemical modification using photo-oxidation with methylene blue, diethylpyrocarbonate, butane-2,3-dione, and phenylglyoxal. 2. All of these chemicals inactivated the enzyme from both sources. 3. Reversion of the diethylpyrocarbonate reaction with hydroxylamine as well as protection of the enzymes with uroporphyrinogen III indicated that histidine is involved at least in the first decarboxylation active site of the porphyrinogen carboxylyase, and perhaps in one or more sites where the removal of the other carboxyl groups take place. 4. Arginine seems not to be at the active site of the enzyme but at its environment since two diketones alter the enzyme activity, however the substrate did not protect the enzyme from the butane-2,3-dione modification. 5. Comparative studies between the enzyme from normal and porphyric animals suggest that the low enzyme activity from intoxicated animals could be due to alterations of its active centre environment produced by hexachlorobenzene treatment. This treatment seems to partially protect the active site of the porphyrinogen carboxylase from the modification reactions.

Animals↗

PubMed1987

Liver porphyrinogen carboxylase in hexachlorobenzene porphyric rats. Studies with intermediate porphyrinogens of series III and with uroporphyrinogen I.

The present work studies the action of hexachlorobenzene (HCB) on the decarboxylation of uroporphyrinogen (Urogen) I and III and also on the decarboxylation of intermediate porphyrinogens of series III under different conditions using liver of normal and porphyric rats as enzyme source. The same enzyme is involved in the Urogen decarboxylation of both isomeric series I and III and catalyses the four steps in both cases. HCB affects all of them. HCB blocks the four steps of Urogen III decarboxylation to the same degree, as a function of intoxication time. HCB leads, in general, to an increase in the efficiency (Km/Vmax) of the porphyric system. These data can be interpreted as a reaction of the organism to overcome the enzymatic blockade.

Animals↗

PubMed1985

The role of iron in the hexachlorobenzene induced porphyria. I. Studies on different types of iron and its relation with porphyrinogen carboxy-lyase decrease.

Studies were carried out to elucidate if in the hexachlorobenzene (HCB) porphyria, total, nonhaem and haem iron contents in liver are altered and if any relation exists between these alterations and the hepatic porphyrinogen carboxy-lyase (PCL) decrease in rats treated with the drug. It was observed that in porphyric livers total and non-haem iron levels increased significantly as a consequence of HCB intoxication while this treatment produced a non significant decrease in the haem iron content. Enzymic preparations of porphyric livers filtered through Sephadex G-25 columns which separate the free iron and that has a content of iron-protein greater than those in normals, exhibited a strong inhibition of PCL. Chelating agents, alpha' alpha' bipyridyl and 8-hydroxyquinoline do not revert such inhibition. The effect in vitro of ferritin, haemin and inorganic iron at different concentrations on normal PCL activity was also assayed. So, it could be observed that inorganic iron and haemin produce slight inhibition of PCL when added in concentrations higher than those corresponding to a porphyric liver (0.08 mM and 10(-6) M, respectively, as mean in the incubation media). So, they have not physiological significance. Ferritin does not modify the decarboxylation process. From these results it arises that iron does not play a direct role in the decrease of PCL activity in the experimental porphyria by HCB, not being the inhibitor made evident by heating assays. Iron could perhaps stimulate the metabolization of HCB, giving rise to active metabolite.

Animals↗

PubMed1984

Mechanism of hexachlorobenzene-induced porphyria in rats. Effect of phenobarbitone pretreatment.

The effect of a pretreatment with phenobarbitone (PB) on the porphyrinogenic action exerted by hexachlorobenzene (HCB) was examined in female rats. Kinetic studies of enzyme function after HCB poisoning showed that porphyrinogen carboxy-lyase was the only enzyme of haem biosynthesis that markedly lowered its activity. Both stages of uroporphyrinogen (UPG) III decarboxylation were decreased. This enzyme, together with UPG I synthase (increased levels) were the first enzymes altered. Subsequently, an increase in delta-aminolaevulinate (AmLev) synthase and ferrochelatase was detected; AmLev dehydratase was the last to increase. On long-term exposure, PB alone did not modify the basal values of haem intermediates; only the content of cytochrome P-450 increased. All the enzyme activities studied showed no significant changes, except ferrochelatase, which increased. With both drugs the metabolic impairment promoted by HCB was accelerated and enhanced by prior PB treatment leading to the onset of an earlier and stronger porphyria. A more noticeable accumulation and excretion of higher carboxylated porphyrins and precursors was more promptly observed as a consequence of the early porphyrinogen carboxy-lyase blockade and the concomitant induction of AmLev synthase. Although the enzymic activities of both AmLev dehydratase and ferrochelatase were enhanced, this response differed in time. For UPG I synthase this pretreatment elicited lower values than those found in the HCB group. Cytochrome P-450 contents were immediately and slightly enhanced by all the drugs, but the values for the combined treatment were the lowest. Of the several hypotheses that could explain the action of HCB on the haem pathway, our results would suggest that the porphyrinogenic action of HCB is mediated by some of its metabolic products.

5-Aminolevulinate Synthetase↗

PubMed1984

[Experimental porphyria induced by chlorinated hydrocarbons. Studies of porphyrinogen carboxy-lyase in the experimental model of human cutaneous delayed porphyria].

The present work tries to elucidate if the strong decrease of porphyrinogen carboxy-lyase (PCL) observed in the experimental porphyria caused by hexachlorobenzene (HCB) is due to the presence of an inhibitor or to a modification of the protein structure of the enzyme. For this purpose: a) cross-assays and heating ones were performed in order to look for the existence of a compound, that present in porphyric animals, would be responsible for the decrease of PCL activity found in them; b) the effect in vitro of HCB, HCB metabolites and other related compounds was studied to find the inhibitor of PCL activity and to look for a relation structure-inhibitory effect; c) hepatic PCL from porphyric and normal rats was purified, and enzyme properties were comparatively studied looking for structural differences between the enzymes obtained from both animal lots. The results indicate that: a) the heat deproteinized porphyric liver preparation produces an inhibition on the normal preparation, but it is smaller than the decrease produced in vivo by the HCB on this enzyme activity, thus other reasons may explain this behavior of PCL in intoxicated animals; b) the HCB had no effect on PCL activity, the phenolic compounds exhibited inhibitions of variable extent that were increased by the presence of electrophilic substituents on the benzenic ring. Pentachlorophenol, the main HCB metabolite, produced inhibition in the in vitro assays, but at doses that were not physiologically significant; thus, it seems not to be the inhibitor found in the heating assays; c) purification of 110 times for the hepatic PCL of both porphyric and normal rats was obtained. Incubation conditions, the effect of salts and chelating agents, the chromatographic behavior in DEAE-cellulose and Sephadex G-100 columns, were comparatively studied with both enzymatic preparations. The effect of sodium diethyldithiocarbamate, sodium pyrophosphate, dithiothreitol, temperature, pH and O2, as well as the chromatographic behavior, would suggest that structural differences in the PCL of porphyric animals may exist; the presence of a thermostable inhibitor could also contribute to the decrease of PCL activity due to HCB.

Animals↗

PubMed1980

Erythrocyte porphyrinogen carboxy-lyase activity in porphyria cutanea tarda and certain other human porphyrias.

Red cell porphyrinogen carboxy-lyase activity was measured using uroporphyrinogen III as substrate in 18 normal persons, 7 male patients with porphyria cutanea tarda, 3 female patients with erythropoietic protoporphyria and 2 female patients with variegate porphyria. The mean values obtained in normal subjects were 0.151 nmol of uroporphyrinogen disappeared in 30 min per mg of protein, and 0.038 nmol of coproporphyrinogen formed in 30 min per mg of protein. We have not been able to detect significant differences between males and females. In porphyria cutanea tarda the enzyme activity was the same as in normal subjects considering either substrate disappearance or end product formation. The differences were not significant at the p less than 0.05 level. Patients with variegata porphyria also exhibited normal erythrocyte porphyrinogen carboxy-lyase activity. The enzyme activity of erythrocytes from patients with erythropoietic protoporphyria was higher than in normals; mean values for specific activities being 0.204 nmol of uroporphyrinogen disappeared, and 0.071 nmol of coproporphyrinogen formed. The significance of the results with respect to the chemical picture of different porphyrias is discussed.

Carboxy-Lyases↗

PubMed1976

Studies on porphyrin biosynthesis in lead-intoxicated rabbits.

The present report deals with studies on porphyrins and porphyrinogen carboxy-lyase of red cells and urinary porphyrins from lead-intoxicated rabbits. It was shown that the free erythrocyte porphyrins are mixture of protoporphyrin 9, the main component, and minor proportions of Coproporphyrin, Uroporphyrin III and Phyriaporphyrin. Analysis of the urinary porphyrins deomonstrates the presence of Coproporphyrins III as the major component, together with 15-20% of other porphyrins: 10-14% 5-COOH, 1-2% 6-COOH, 2-3% 7-COOH porphyrin and 1-2% Uroporphyrin III. We have not been able to detect an increase of Uroporphyrin I. Assays of porphyrinogen carboxy-lyase activity in hemolysate supernatant using Uroporphyrinogen III and Phyriaporphyrinogen (Phyria'gen) III as substrates, showed the existence of a slight decrease of both decarboxylase activities, being more affected during the second stage, the Phyria'gen decarboxylation. A possible regulation mechanism responsible for the porphyrin picture is discussed.

Animals↗

PubMedDate not supplied

Rat urinary chemiluminescence: effect of ethanol and/or hexachlorobenzene uptake.

Hexachlorobenzene (HCB) administration to rats induces porphyria cutanea tarda, characterized by high levels of urinary porphyrins (> 40 micrograms/day) and accumulation of highly carboxylated porphyrins in liver (> 15 micrograms/g of tissue). Ethanol administration, under the conditions employed, was not porphyrinogenic and was able to diminish some of the responses elicited by HCB. Furthermore, ethanol and/or HCB administration leads to organ disturbances that involve oxidative stress. We have measured the changes in urinary chemiluminescence (CL) levels, as part of a systematic evaluation of the metabolic alterations in rats chronically treated with ethanol and/or HCB. The results, that constitute the first set of urinary CL data obtained from an animal model system, indicate that the measurement of the spontaneous urinary CL can constitute a fast, simple and sensitive method to evaluate disturbances associated with oxidative stress.

Animals↗