Hepatocellular Regenerative Proliferation
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Directness||Weight of Evidence||Quantitative Understanding|
|Chronic Cyp2E1 Activation Leading to Liver Cancer||directly leads to||Strong||Not Specified|
Life Stage Applicability
How Does This Key Event Relationship Work
Hepatocytes are typically quiescent, with only about 1-2% turnover. However, following surgical resection or chemically induced injury, the liver is able to activate cell division and regenerate itself. On a cellular level, the liver has two modes of regeneration: (1) cellular hypertrophy and division of existing cells; (2) dedifferentiation, redifferentiation, and proliferation of a population of facultative stem cells that is located at the Canals of Hering (Stanger 2015).
On a molecular level, how liver regeneration occurs is less completely understood. Molecular signals that are released from dying cells trigger regenerative proliferation of existing cells. Important players include the transcription factors AP-1 (particularly the c-Jun monomer) and NF-kappaB, both of which are not normally expressed in adult liver, but are up-regulated following partial hepatectomy and are required for hepatic regeneration.
Weight of Evidence
Strong. The liver is well known to regenerate itself following chemical or surgical injury. It is widely accepted that significant cytotoxicity to the liver leads to regenerative proliferation (Forbes and Newsome 2016).
Empirical Support for Linkage
Strong. That hepatotoxicity leads to regenerative proliferation has been widely reported for a number of liver toxicants (as well as surgical resection of the liver). This is a very data-rich field. Below we summarize a few examples of the empirical data supporting this relationship.
Furan is a rodent hepatocarcinogenic chemical that is proposed to operate through a mode of action involving cytotoxicity followed by regenerative proliferation (Fransson-Steen, et al. 1997, Moser, et al. 2009). In support of the relationship between hepatotoxicity and regenerative proliferation, mice and rats exposed to dose ranges of furan present with cytotoxicity at lower doses than the doses at which they present regenerative proliferation. Mice exposed to a dose range of 0, 0.5, 1, 2, 4, 8 mkd had significant levels of liver cytotoxicity (measured by serum ALT) beginning at 1 mkd, and significant levels of cellular proliferation (measured by BrdU incorporation) at 8 mkd (Moser, et al. 2009). F344 rats exposed to 0-16 mkd furan showed significant increases in cell death starting at 2-4 mkd, and proliferation at 8-16 mkd (Ding, et al. 2012). Cytotoxicity also begins at earlier time points than regenerative proliferation. Cell death and proliferation were also measured in male Sprague-Dawley rats exposed to 30 mkd furan over a three month time course. Apoptosis was detected after one day, whereas proliferation began to occur after three days (Hickling, et al. 2010).
Male Wistar rats treated with a single, necrogenic dose of thioacetamide had serum AST levels of approximately: 500, 2250, 1900 and 500 at 12, 24 (peak), 48 and 72 hours post-exposure; levels were restored to normal after 96 hours. Levels of regenerative cellular proliferation followed closely after, and peaked at 48 hours; thereby demonstrating a temporal concordance between cytotoxicity and regenerative proliferation (Bautista, et al. 2010). Rats exposed to thioacetamide presented with hepatotoxicity (increased ALT) beginning at 24 hours post-exposure followed by increased regenerative proliferation at 36 hours post-exposure (samples were taken over the following time-course: 6, 12, 24, 36, 48, 72 and 96 hours); thereby demonstrating a temporal concordance between cytotoxicity and regenerative proliferation (Mangipudy, et al. 1995).
B6C3F1 mice were exposed to 0, 34, 90, 138, or 277 mg/kg/day of chloroform for 4 days or for 5 days/week for 3 weeks. Hepatic necrosis was observed to be elevated above control in all dose groups at both time points. Cellular proliferation (by labelling index, BrdU incorporation) in the liver increased in a dose-dependent manner at both time points (4 days and 3 weeks), but were first significantly increased above control levels at 34 mg/kg bw (4 day group) or 138 mg/kg bw (3 week group). These data demonstrate the temporal concordance between cytotoxicity and regenerative proliferation of hepatocytes; the trend is particularly clear at the 3 week time-point (Larson, et al. 1994).
The temporal concordance between cytotoxicity and cellular proliferation (regeneration) has also been well documented following exposure to carbon tetrachloride (Benson and Springer 1999, Doolittle, et al. 1987, Eschenbrenner and Miller 1946, Lee, et al. 1998, Nakata, et al. 1985).
Uncertainties or Inconsistencies
We are not aware of any instance in which significant amounts of hepatotoxicity (in genetically normal livers) would not lead to regenerative cellular proliferation.
Quantitative Understanding of the Linkage
Unable to determine.
Evidence Supporting Taxonomic Applicability
Bautista, M., Andres, D., Cascales, M., Morales-Gonzalez, J.A., Sanchez-Reus, M.I., 2010. Effect of gadolinium chloride on liver regeneration following thioacetamide-induced necrosis in rats. Int. J. Mol. Sci. 11, 4426-4440.
Benson, J., Springer, D., 1999. Improved risk estimates for carbon tetrachloride. Final Report. Project No., 54940. DE-FC04-96AL76406.
Ding, W., Petibone, D.M., Latendresse, J.R., Pearce, M.G., Muskhelishvili, L., White, G.A., Chang, C.-., Mittelstaedt, R.A., Shaddock, J.G., McDaniel, L.P., Doerge, D.R., Morris, S.M., Bishop, M.E., Manjanatha, M.G., Aidoo, A., Heflich, R.H., 2012. In vivo genotoxicity of furan in F344 rats at cancer bioassay doses. Toxicol. Appl. Pharmacol. 261, 164-171.
Doolittle, D.J., Muller, G., Scribner, H.E., 1987. Relationship between hepatotoxicity and induction of replicative DNA synthesis following single or multiple doses of carbon tetrachloride. J. Toxicol. Environ. Health 22, 63-78.
Eschenbrenner, A.B., Miller, E., 1946. Liver necrosis and the induction of carbon tetrachloride hepatomas in strain A mice. J. Natl. Cancer Inst. 6, 325-341.
Forbes, S.J., Newsome, P.N., 2016. Liver regeneration - mechanisms and models to clinical application. Nat. Rev. Gastroenterol. Hepatol. 13, 473-485.
Fransson-Steen, R., Goldsworthy, T.L., Kedderis, G.L., Maronpot, R.R., 1997. Furan-induced liver cell proliferation and apoptosis in female B6C3F1 mice. Toxicology 118, 195-204.
Hickling, K.C., Hitchcock, J.M., Oreffo, V., Mally, A., Hammond, T.G., Evans, J.G., Chipman, J.K., 2010. Evidence of oxidative stress and associated DNA damage, increased proliferative drive, and altered gene expression in rat liver produced by the cholangiocarcinogenic agent Furan. Toxicol. Pathol. 38, 230-243.
Larson, J.L., Wolf, D.C., Butterworth, B.E., 1994. Induced cytolethality and regenerative cell proliferation in the livers and kidneys of male B6C3F1 mice given chloroform by gavage. Fundamental and applied toxicology : official journal of the Society of Toxicology 23, 537-43.
Lee, V.M., Cameron, R.G., Archer, M.C., 1998. Zonal location of compensatory hepatocyte proliferation following chemically induced hepatotoxicity in rats and humans. Toxicol. Pathol. 26, 621-627.
Mangipudy, R.S., Chanda, S., Mehendale, H.M., 1995. Tissue repair response as a function of dose in thioacetamide hepatotoxicity. Environ. Health Perspect. 103, 260-267.
Moser, G.J., Foley, J., Burnett, M., Goldsworthy, T.L., Maronpot, R., 2009. Furan-induced dose–response relationships for liver cytotoxicity, cell proliferation, and tumorigenicity (furan-induced liver tumorigenicity). Experimental and Toxicologic Pathology 61, 101-111.
Nakata, R., Tsukamoto, I., Miyoshi, M., Kojo, S., 1985. Liver regeneration after carbon tetrachloride intoxication in the rat. Biochem. Pharmacol. 34, 586-588.
Stanger, B.Z., 2015. Cellular homeostasis and repair in the mammalian liver. Annu. Rev. Physiol. 77, 179-200.