Phospholipid alterations elicited by hexachlorobenzene in rat brain are strain-dependent and porphyria-independent.

Hexachlorobenzene (HCB) alters phospholipid and heme metabolisms in the liver and Harderian gland. The effects of HCB on phospholipid metabolism, in an organ considered to be non-responsive to its porphyrinogenic effects, remain to be studied. Therefore, as the brain is an organ with this feature, this paper analyzes the effects of HCB on brain phospholipid composition in order to investigate if there is any relationship between HCB-induced porphyrin metabolism disruption and phospholipid alterations. For this purpose, a time-course study of HCB effects on brain phospholipids was performed in two strains of rats differing in their susceptibility to acquire hepatic porphyria: Chbb THOM (low); and Wistar (high). This paper shows for the first time that rat brain phospholipids are affected by HCB exposure. Comparative studies show that HCB-induced disturbances in brain phospholipid patterns are time and strain-dependent. Thus, whereas major phospholipids, phosphatidylcholine and phosphatidylethanolamine were more altered in Wistar rats, minor phospholipids, phosphatidylinositol and phosphatidylserine were more affected in Chbb THOM rats. HCB intoxication led to a sphingomyelin/phosphatidylcholine molar ratio lower than the normal, in both strains. As was expected, brain porphyrin content was not altered by HCB intoxication in either strain. It can be concluded that HCB is able to alter brain phospholipid metabolism in a strain-dependent fashion, and in the absence of alterations in brain heme metabolism. In addition, HCB-induced disturbances in brain phospholipids were not related to the degree of hepatic porphyria achieved by the rats.

Hexachlorobenzene-induced alterations on neutral and acidic sphingomyelinases and serine palmitoyltransferase activities. A time course study in two strains of rats.

Hexachlorobenzene (HCB) induces porphyria both in humans and rodents, and hepatocarcinoma in rodents. In a previous work we observed that HCB produces a continuous decrease in hepatic sphingomyelin (SM) content in Wistar rats. A distinguishing characteristic of sphingolipids breakdown products is their participation in anti-proliferative and apoptotic processes and in the suppression of oncogenesis. As a first step to elucidate the role of SM decrease in the hepatotoxicity induced by HCB, the present study evaluates the metabolic causes of the continuous decrease in hepatic SM content observed in Wistar rats with HCB intoxication, and its relation with porphyria development. For this purpose, the time-course (3, 7, 15, 21 and 28 days) of the effects of HCB on hepatic SM levels and on some of the enzymes of SM synthesis (serine palmitoyltransferase, SPT) and catabolism (sphingomyelinases, SMases) was followed, using two strains of rats differing in their susceptibility to acquire porphyria: Chbb THOM (low) and Wistar (high). HCB (1 g kg(-1) b.w. per day) was administered by gastric intubation as an aqueous suspension. After 5 days of HCB treatment, animals were allowed a 2-day recovery period without HCB administration. Two phases in the HCB-induced damages to sphingolipid metabolism were observed. The first stage (7 days of treatment), common to both strains of rats, was characterized by a decrease in hepatic SM levels (17-25%) and in SPT activity (50-43%), while strain differences were found for the later stage. In Chbb THOM rats, hepatic SM content was restored to normal values concomitantly with an increase in SPT activity (44%, at day 28), and without any increase in SM catabolism. In addition, the level of the other phospholipids was not altered. In Wistar rats, hepatic SM levels decreased continuously throughout the experiment, accompanied by increases in SPT, acidic sphingomyelinase (A-SMase) and neutral sphingomyelinase (N-SMase) activities (86, 28.5 and 78% increase, respectively). A role for glutathione (GSH) in the interstrain differences or a direct effect of HCB on SM metabolism was not found. The present study: (a) demonstrates that N-SMase, A-SMase, and SPT are some of the enzymes that play a role in the HCB-induced decrease of hepatic SM content; (b) finds that HCB-induced alterations of SM metabolism do not correlate with HCB-induced accumulation of hepatic porphyrins; and (c) proposes a link between HCB-induced alterations in phospholipid pattern and in SM metabolism. The increased SM hydrolysis produced as a consequence of SMases induction could be regarded as a cellular response to liver injury elicited by HCB, perhaps acting through the activation of SM signal transduction pathway delaying the proliferative processes observed after long-term treatment with HCB in some rodent species. However, such protective mechanism appears to be strain-dependent.

Heme metabolism and lipid peroxidation in rat kidney hexachlorobenzene-induced porphyria: A compartmentalized study of biochemical pathogenic mechanisms.

In the present study, the effects of hexachlorobenzene (HCB) on lipid peroxidation and heme metabolism in the different constitutive suborgans of the kidney were determined. For this purpose, conjugated diene and malondialdehyde levels, as lipid peroxidation parameters, and porphyrin accumulation, uroporphyrinogen decarboxylase activity, and its inhibitor formation, as measures of heme metabolism, were determined in renal cortex, medulla, and papilla. Adult Wistar rats were treated with HCB during 1, 2, 3, or 4 weeks. A significant increase in cortical conjugated dienes was observed from the 1st week of treatment. The malondialdehyde levels rose by 47, 34, and 28% after 2, 3, and 4 weeks of intoxication, respectively. The porphyrin content showed a tenfold increase after 4 weeks of treatment, and the uroporphyrinogen decarboxylase activity was reduced by 26 and 58% with respect to control values after 3 and 4 weeks of treatment, respectively. The results demonstrate a direct correlation between the oxidative environment and the effect elicited by the drug on heme metabolism in the renal cortex. In contrast, in papilla and medulla, where the antioxidant systems were higher, HCB showed no porphyrinogenic effect.

Effects of hexachlorobenzene on phospholipid and porphyrin metabolism in Harderian glands: a time-course study in two strains of rats.

Hexachlorobenzene, one of the most persistent environmental pollutants, induces uroporphyria and phospholipid alterations in rat liver. Harderian glands produce a secretion that is rich in lipids and accumulate large amounts of protoporphyrin. The aim of the present study was to determine if hexachlorobenzene administration to rats affects phospholipid and porphyrin metabolisms in Harderian glands and if these effects are strain dependent. For this purpose, a time-course study (2, 3 and 4 weeks of hexachlorobenzene treatment) of phospholipid pattern and porphyrin content was performed comparatively in two strains of rats (Wistar and Chbb THOM) which differ in their susceptibility to develop HCB-induced porphyria. Hexachlorobenzene produced decreases in several phospholipid contents, but no changes in phosphatidylcholine levels. While the sphingomyelin/phosphatidylcholine molar ratio remained essentially constant until the third week in Chbb THOM rats, it showed a constant drop in Wistar rats, suggesting a more pronounced alteration of membrane fluidity in the later strain. In regard to porphyrin metabolism, Wistar rats showed an increase in the porphyrin content of the gland, while Chbb THOM animals showed a decrease. The study revealed that not only are the normal parameters of phospholipid and porphyrin metabolism in rat Harderian glands strain dependent, but the response to hexachlorobenzene is also.

Studies on the active centre(s) of rat liver porphyrinogen carboxy-lyase. In vivo effect of hexachlorobenzene on decarboxylation site(s) of porphyrinogens.

1. The role of histidine on the decarboxylation of porphyrinogens of 7-, 6-, and 5-COOH III brought about by porphyrinogen carboxy-lyase (PCL) was studied. 2. For this purpose hepatic PCL from normal and hexachlorobenzene (HCB) treated rats were modified with diethylpyrocarbonate. 3. The results indicated that the enzyme from both normal and porphytic animals had histidine at the binding sites of all the porphyrinogens assayed. 4. Comparative studies between the enzyme from normal and porphyric rats suggested that in vivo HCB treatment affected the active site for the decarboxylation of 7-, 6- and 5-COOH porphyrinogens III at histidine residues. 5. On the other hand arginine modification by 2,3-butanedione treatment altered 5-COOH porphyrinogen III decarboxylation for both enzymes. However this amino acid was not involved at the binding site of this substrate.

Influence of the strain of rats on the induction of hexachlorobenzene induced porphyria.

1. The present work undertakes a comparative study on the hexachlorobenzene (HCB) porphyria induction in female rats of Wistar and CHBBTHOM strains. The purpose was to characterize the CHBBTHOM strain with respect to the haem metabolic pathway, its regulatory mechanisms and its response to foreign drugs. 2. After 7 weeks of treatment it was observed that the hepatic porphyrins increased 140 times, ALA-synthase 4 times and PCL was 73% inhibited in the Wistar strain. 3. On the other hand the animals of CHBBTHOM strain showed lesser alteration on these parameters; hepatic porphyrins increased only 3-fold, ALA-synthase 1.7-fold and PLC was only 22% inhibited. 4. Total iron liver content was nearly equal in both strains of rats. 5. The results obtained would indicate that the lower susceptibility of the CHBBTHOM strain to acquire porphyria does not seem to be due to either: (1) congenital alterations of any parameters of the haem metabolic pathway, since the behaviour of normal animals from both strains was similar; or (2) a lower hepatic iron content in such animals. 6. These findings would suggest that the differential response to HCB to this strain would be looked for in another metabolic pathway, such as that involved in the metabolization process of the toxic.