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Histopathological Analysis of Rat Hepatotoxicity Based on Macrophage Functions: in Particular, an Analysis for
Jyoji Yamate1, Takeshi Izawa1, Mitsuru Kuwamura1
1Laboratory of Veterinary Pathology, Life and Environmental Sciences, Osaka Prefecture University, Rinkuu Ourai Kita 1-58, Izumisano, Osaka 598-8531, Japan.
Abstract:
Hepatic macrophages play an important role in homeostasis. The functional abnormalities of hepatic macrophages primarily or secondarily influence chemically induced hepatotoxicity. However, the evaluation system based on their functions has not yet been established. Recently, a new concept (M1-/M2-macrophage polarization) was proposed; M1-macropahges are induced by INF-γ, and show high phagocytosis/tissue damage, whereas M2-macropahges are induced by IL-4 and play roles in reparative fibrosis by releasing IL-10 and TGF-β1. In hepatogenesis, CD68-expressing M1-macrophages predominantly exist in embryos; in neonates, in contrast, CD163-/CD204-expressing M2-macrophages appear along the sinusoids and mature as Kupffer cells. Activated Kupffer cells by liposome decrease AST and ALT values, whereas AST and ALT values are increased under Kupffer cells depleted with clodronate treatment. Since Kupffer cells may be involved in clearance of liver enzymes, macrophage condition should be taken into consideration when hepatotoxicity is analyzed. In TAA-induced acute hepatic lesions, INF-γ, TNF-α and IL-6 for M1-factors and IL-4 for M2-factors are already increased before histopathological change; the appearance of CD68-expressing M1-macrophages and CD163-expressing M2-macrophages follows in injured centrilobular lesions, and TGF-β1 and IL-10 are increased for reparative fibrosis. CD68-expressing M1-macrophages co-express MHC class II and Iba-1, whereas CD163-expressing M2-macrophages also express CD204 and Galectin-3. Under macrophage depletion by clodoronate, TAA-treated rat livers show prolonged coagulation necrosis of hepatocytes, and then develop dystrophic calcification without reparative fibrosis. The depletion of hepatic macrophages influences hepatic lesion development. Collectively, a histopathological analysis method for hepatotoxicity according to M1-/M2-macrophage polarization would lead to the refinement of hazard characterization of chemicals in food and feed.
Insights
Hepatic macrophages, polarized into M1 (tissue damage) or M2 (repair), influence chemical-induced liver injury. Analyzing macrophage polarization offers a refined method for assessing chemical hepatotoxicity.
Area of Science:
- Hepatology
- Immunology
- Toxicology
Background:
- Hepatic macrophages are crucial for liver homeostasis and are implicated in chemically induced hepatotoxicity.
- Existing evaluation systems for hepatotoxicity do not fully incorporate hepatic macrophage functions.
- The M1/M2 macrophage polarization concept, driven by specific cytokines, offers a new framework for understanding macrophage roles.
Purpose of the Study:
- To investigate the role of M1/M2 macrophage polarization in the development of chemically induced hepatotoxicity.
- To explore the potential of macrophage polarization analysis as a refined method for hepatotoxicity hazard characterization.
Main Methods:
- Analysis of M1 (INF-γ induced, CD68+) and M2 (IL-4 induced, CD163+) macrophage markers in liver tissues.
- Assessment of cytokine profiles (INF-γ, TNF-α, IL-6, IL-4, TGF-β1, IL-10) during hepatotoxicity.
- Evaluation of liver injury and repair mechanisms in macrophage-depleted (clodronate) versus control animal models.
Main Results:
- M1 and M2 macrophage populations and associated cytokines are altered during chemically induced liver injury (TAA model).
- CD68+ M1 macrophages and CD163+ M2 macrophages appear sequentially in injured liver zones, correlating with damage and repair.
- Macrophage depletion exacerbates hepatotoxicity, leading to prolonged necrosis and impaired fibrosis, highlighting their protective/regulatory roles.
Conclusions:
- Hepatic macrophage polarization is a critical factor in the pathogenesis and resolution of chemically induced hepatotoxicity.
- The dynamic interplay between M1 and M2 macrophages influences the severity and outcome of liver injury.
- Histopathological analysis based on M1/M2 macrophage polarization can enhance the hazard characterization of chemicals.
