Taxifolin ameliorates iron overload-induced hepatocellular injury: Modulating PI3K/AKT and p38 MAPK signaling, inflammatory response, and hepatocellular regeneration

Although physiological levels of iron are essential for numerous biological processes, excess iron causes critical tissue injury. Under iron overload conditions, non-chelated iron generates reactive oxygen species that mediate iron-induced tissue injury with subsequent induction of apoptosis, necrosis, and inflammatory responses. Because liver is a central player in iron metabolism and storage, it is vulnerable to iron-induced tissue injury. Taxifolin is naturally occurring compound that has shown potent antioxidant and potential iron chelation competency. The aim of the current study was to investigate the potential protective effects of taxifolin against iron-induced hepatocellular injury and to elucidate the underlining mechanisms using rats as a mammalian model. The results of the current work indicated that taxifolin inhibited iron-induced apoptosis and enhanced hepatocellular survival as demonstrated by decreased activity of caspase-3 and activation of the pro-survival signaling PI3K/AKT, respectively. Western blotting analysis revealed that taxifolin enhanced liver regeneration as indicated by increased PCNA protein abundance. Taxifolin mitigated the iron-induced histopathological aberration and reduced serum activity of liver enzymes (ALT and AST), highlighting enhanced liver cell integrity. Mechanistically, taxifolin modulated the redox-sensitive MAPK signaling (p38/c-Fos) and improved redox status of the liver tissues as indicated by decreased lipid peroxidation and protein oxidation along with enhanced total antioxidant capacity. Interestingly, it decreased liver iron content and down-regulated the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β. Collectively, these data highlight, for the first time, the ameliorating effects of taxifolin against iron overload-induced hepatocellular injury that is potentially mediated through anti-inflammatory, antioxidant, and potential iron chelation activities.

Visualization of Hepatocellular Regeneration in Mice After Partial Hepatectomy

BACKGROUND

Although hepatocellular regeneration is the cornerstone of liver homeostasis, current techniques for assessing such regeneration are limited. A method for visualizing the regeneration process would provide a means for advanced studies. Therefore, we examined the possibility of using fluorescence ubiquination-based cell cycle indicator (Fucci) mice for direct visualization of hepatocellular regeneration.

MATERIALS AND METHODS

We performed a two-thirds partial hepatectomy in conventional and Fucci mice. Fucci animals have orange Cdt1 expressed in the G₁ phase and green Geminin expressed in S/G₂/M phases. Regenerating livers were procured daily for 7 d. Immunohistochemical staining was performed for proliferative Ki67 and mitotic pHH3 serine 10 (pHH3) markers on formalin-fixed, paraffin-embedded tissue sections from conventional mice. The orange Cdt1 and green Geminin fluorescence indicative of the G₁ and S/G₂/M phases, respectively, were assessed in liver tissues, in vivo and ex vivo, with two-photon laser scanning microscopy.

RESULTS

Immunostaining with Ki67 and pHH3 revealed a typical profile of hepatocellular regeneration after hepatectomy in conventional mice, although immunostaining required more than a week to process. In contrast, hepatocellular regeneration could be visualized with two-photon microscopy within a few hours in regenerating livers of the Fucci mice. Only orange G₁ hepatocytes were seen in the baseline liver specimens; however, multiple bright green and yellow hepatocytes were seen 48 h after hepatectomy, indicating active hepatocytes in the S/G₂/M phases of the cell cycle.

CONCLUSIONS

Hepatocellular regeneration is readily visualized in regenerating livers of Fucci mice. The Fucci model is an exciting tool for advanced studies of hepatocellular and liver regeneration.