Pivotal Role of Hepatocellular Regeneration in the Ultimate Hepatotoxicity of CCl 4 in Chlordecone-, Mirex-, or Phenobarbital-Pretreated Rats
Authors: Kodavanti Prasada Rao S. , Kodavanti Urmila P. , Faroon Obaid M. , Mehendale Harihara M. 
Published: April 2009

Our earlier histomorphometric and biochemical studies suggested that the progressive phase of the interactive toxicity of chlordecone (CD) + CCl4involves suppression of hepatocellular regeneration. The objective of the present work was to correlate hepatocellular regeneration with CCl4(100 μl/kg)-induced hepatotoxicity in rats maintained for 15 days on a normal (N) diet, relative to the regenerative response in rats maintained on a diet containing either 10 ppm CD, 225 ppm phenobarbital (PB), or 10 ppm mirex (M). Hepatocellular regeneration was assessed by measuring DNA and3H-thymidine (3H-T) incorporation, followed by autoradiographic analysis of liver sections. Hepatotoxicity was assessed by measuring plasma transaminases (aspartate and alanine) followed by histopathological observations of liver sections for necrotic, swollen, and lipid-laden cells. Lethality studies were also carried out to assess the consequence of hepatotoxicity on animal survival. Dietary 10 ppm CD potentiated the hepatotoxicity of CCl4to a greater extent than PB or M, as evidenced by elevations in plasma enzymes. Although the serum enzymes were significantly elevated in PB rats in contrast to the slight elevations in N and M rats, they returned to normal levels by 96 hr. However, serum enzyme elevations in CD rats were progressive with time until death of the animals. Actual liver injury by CCl4was greater in PB- than in CD-pretreated rats, as evidenced by histopathological observations. A 100% mortality occurred in CD-pretreated rats at 60 hr after CCl4administration, whereas no mortality occurred in either N-, M-, or PB-pretreated rats, indicating recovery from liver injury. Hepatocellular nuclear DNA levels were significantly decreased starting at 6 hr after CCl4administration to CD-pretreated rats, but not in M- or PB-pretreated rats.3H-T incorporation into nuclear DNA as well as percentage of labeled cells showed a biphasic increase in N rats: 1 at 1-2 hr, and the other at 36-48 hr after CCl4administration. However, only 1 peak of3H-T incorporation at 36-48 hr was observed in the CD + CCl4combination, which was also significantly lower when compared to that observed after the M or PB + CCl4combination treatments. These findings suggest that there is recovery in N-, PB-, or M-pretreated rats from CCl4-induced injury by virtue of the stimulated hepatocellular regeneration and tissue repair. In CD-pretreated rats, CCl4toxicity is progressive because of mitigated hepatocellular regeneration (at 2-6 hr), supporting the concept that hepatocellular regeneration plays a critical role in determining whether hepatotoxicity becomes permissively progressive or actively regressive, owing to tissue repair mechanisms. In the absence of hepatocellular regeneration and tissue repair, progressive liver injury leads to sustained hepatic failure (24 hr), culminating in animal death. These findings underscore the importance of assessing additional parameters of hepatobiology indicative of the ultimate outcome of toxicity rather than relying solely on indices of liver injury, particularly during the inflictive phase of chemically-induced liver injury.