Role of hepatocellular regeneration in chlordecone potentiated hepatotoxicity of carbon tetrachloride.

Previous histomorphometric studies led us to hypothesize that suppression of hepatocellular regeneration and the repair of the hepatolobular architecture was involved besides bioactivation phenomenon in the progressive and irreversible phase of toxicity resulting from CD + CCl4 interaction. We have recently observed significant protection from CD potentiated CCl4 toxicity in animals which are stimulated for active hepatocellular regeneration. The present work is an extension of our earlier histomorphometric investigation, taking 3H-thymidine (3H-T) incorporation as a biochemical parameter to assess hepatocellular regeneration followed by autoradiographic analysis of liver sections in normal (N) or chlordecone (CD) treated (10 ppm in diet for 15 days) male rats undergoing sham (SH) or partial hepatectomies (PH). Initial experiments established that in normal (N) rats, greatest 3H-T incorporation into hepatocellular nuclear DNA occurs at 2 days post-PH which returns to basal levels by 7 days. CD treatment alone did not change this phenomenon. 3H-T incorporation into nuclear DNA and the percentage of labelled cells as evidenced by autoradiography of liver sections were significantly elevated in N rats at 1-2 h after CCl4 (100 microliters/kg) administration and returned to basal level by 6 h. Serum enzymes (AST and ALT) in N rats undergoing SH and PH were not altered, but were significantly elevated in CD rats following CCl4 (100 microliters/kg) administration. CCl4-induced serum enzyme elevations were significantly lower in 2 days post-PH (PH2) rats when compared to SH rats or 7 days post-PH (PH7) rats maintained on CD diet, indicating that CD potentiated CCl4 hepatotoxicity is significantly reduced in livers stimulated for regenerative activity by PH.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of chlordecone-potentiated carbon tetrachloride hepatotoxicity and lethality by partial hepatectomy.

Chlordecone (CD) pretreatment is known to markedly potentiate CCl4 hepatotoxicity. Previous studies have shown that prior exposure to CD obtunds the increased hepatocellular regeneration and repair observed in non-treated rats challenged with a single, low dose of CCl4. These observations allowed us to hypothesize that suppression of hepatic regeneration and tissue repair by CD + CCl4 combination treatment might be involved in this interaction. To test this hypothesis, CCl4 hepatotoxicity was evaluated in actively regenerating livers using CD-treated (10 ppm in the diet for 15 days), surgically partially hepatectomized (PH) male Sprague-Dawley rats. Rats undergoing no surgical manipulation (CTRL) and sham operation (SH) were included as appropriate controls. Surgical manipulations were conducted on day 15 of the dietary protocol. Based on liver-to-body weight ratios (LW/BW), mitotic indices, hepatic cytochrome P-450 content, and hepatic glutathione (GSH and GSSG) levels, PH-induced hepatocellular regeneration was not affected by pretreatment with CD. Thus, the PH model was considered valid for assessing the effects of CD + CCl4 combination treatment. CCl4 (100 microliter/kg; i.p.) was administered 1, 2, 4 or 7 days after the surgical manipulations. Hepatotoxicity was assessed 24 h later by measuring LW/BW and serum enzymes (SGPT, SGOT and ICD) in all four groups. Hepatic histopathological, histomorphometric and lethal effects were assessed in animals receiving CCl4 1 or 7 days after the surgical manipulations. CCl4-induced increases in LW/BW were observed in CD + PH rats receiving CCl4 4 or 7 days post-PH, but not in the 1 or 2 day post-PH groups in which the hepatocellular regeneration was maximal. CCl4-induced serum enzyme elevations were significantly less in the CD + PH rats as compared to CD + SH. This decrease in the serum enzyme elevations was most prominent in the 1 day post-PH group, where the hepatocellular mitotic activity was most pronounced. CCl4 lethality, assessed in the 1 day post-surgical manipulation group, was also decreased in the CD + PH rats in comparison to CD + SH rats. Such a protection was not observed in rats receiving CCl4 7 days post-PH. These data are consistent with and are supportive of the hypothesis that a suppression of otherwise normally stimulated hepatocellular regeneration following low-dose CCl4 administration is involved in the marked amplification of CCl4 toxicity by CD.

Comparative changes in hepatic DNA, RNA, protein, lipid, and glycogen induced by a subtoxic dose of CCl4 in chlordecone, mirex, and phenobarbital pretreated rats.

Male Sprague-Dawley rats (200-250 g) were maintained on a normal powdered diet or on a similar diet containing 10 ppm chlordecone (CD), 10 ppm mirex (M) or 225 ppm phenobarbital (PB) for 15 days. On day 15, the animals received a single i.p. administration of CCl4 (100 microliters/kg). Hepatic DNA, RNA, protein, lipid and glycogen were determined 1, 4, 6, 12, 24 and 36 h after CCl4 administration. A significant decrease (18%) in hepatic protein was observed 24 h after CCl4 challenge in the CD-pretreated rats; significant changes were not observed in the other treatment groups. Hepatic RNA was decreased (37%) in CD-pretreated rats at 36 h; no changes were observed in the DNA content. Hepatic RNA and DNA were increased (20% and 16%, respectively) 6 h after exposure to CCl4 alone. Lipid content was increased at all time points starting at 4 h in response to CCl4 challenge in the CD-pretreated rats. In the M- and PB-pretreated rats increases in hepatic lipid (22 and 28%, respectively) were observed only at the 6-h time point. Only a transient increase occurred after CCl4 alone at 4 h. While depletion of hepatic glycogen was manifested in all groups at all time points following CCl4, that in the CD + CCl4 group was the greatest. A recovery of glycogen beginning at 12 h was observed in the rats receiving CCl4 alone and in the M and PB pretreated animals. No such recovery was evident in CD + CCl4 group. These studies indicate that biochemical changes compatible with cellular death are more pronounced in the CD-pretreated rats than in those receiving CCl4 alone, suggesting that the metabolic and supportive biochemical mechanisms for hepatocellular repair are suppressed in rats receiving CD + CCl4.

The effect of dietary exposure to a mirex plus chlordecone combination on CCl4 hepatotoxicity.

The purpose of these studies was to investigate the effect of a mirex plus chlordecone combination on CCl4-induced hepatotoxicity. Male Sprague-Dawley rats were maintained on control diet or on diets containing 10 ppm chlordecone (CD), 10 ppm mirex (M), or M plus CD (10 ppm each; MCD) for 15 days. On Day 15 the rats received a single ip injection of CCl4 (100 microliters/kg) and hepatotoxicity was assessed 24 hr later. Animals in the control group receiving CCl4 alone were unaffected. Significant increases in liver-to-body weight ratios were observed in all three pretreatment groups following CCl4 challenge. Increases in serum enzymes (SGPT, SGOT, and ICD) occurred in all three pretreatment groups with CD = MCD greater than M greater than control. While MCD and CD pretreatment led to significant cholestasis and decreases in PG excretion, no such effect was observed with M. Light microscopic examination of tissues revealed swollen hepatocytes (balloon cells), hepatocellular necrosis, and lipid accumulation in the MCD, CD, and M groups following CCl4 challenge. In summary, as assessed by serum enzyme elevation, biliary flow and hepatic excretory function, M pretreatment led to only a slight increase in CCl4 hepatotoxicity. The MCD combination pretreatment did not potentiate hepatotoxicity above that seen with CD alone. These results provide additional evidence that CD pretreatment results in a rather specific sensitization of animals to CCl4 toxicity in ways independent of the actions of M.