Role of connexin 32 in acetaminophen toxicity in a knockout mice model

Abstract

Gap junctional intercellular communication (GJIC), by which glutathione (GSH) and inorganic ions are transmitted to neighboring cells, is recognized as being largely involved in toxic processes of chemicals. We examined acetaminophen (APAP)-induced hepatotoxicity clinicopathologically using male wild-type mice and mice lacking the gene for connexin32, a major gap junction protein in the liver [knockout (Cx32KO) mice]. When APAP was intraperitoneally administered at doses of 100, 200, or 300mg/kg, hepatic centrilobular necrosis with elevated plasma aminotransferase activities was observed in wild-type mice receiving 300mg/kg, and in Cx32KO mice given 100mg/kg or more. At 200mg/kg or more, hepatic GSH and GSSG contents decreased significantly and the effect was more severe in wild-type mice than in Cx32KO mice. On the other hand, markedly decreased GSH staining was observed in the hepatic centrilobular zones of Cx32KO mice compared to that of wild-type mice. These results demonstrate that Cx32KO mice are more susceptible to APAP hepatotoxicity than wild-type mice, and indicate that the distribution of GSH of the centrilobular zones in the hepatic lobules, rather than GSH and GSSG contents in the liver, is important in APAP hepatotoxicity. In conclusion, Cx32 protects against APAP-induced hepatic centrilobular necrosis in mice, which may be through the GSH transmission to neighboring hepatocytes by GJIC.

Connexin32: a mediator of acetaminophen-induced liver injury?

“…At 100 and 200 mg/kg APAP injected intraperitoneally, increased ALT quantities and more pronounced necrotic cell death were observed in Cx32 −/− animals. These effects were, however, not seen at 300 kg/mg APAP (Igarashi et al 2014), a commonly used dose for experimental testing purposes (Harril et al 2009; McGill et al 2012; Mossanen and Tacke 2015), which is in line with the findings of our study. With the exception of a lower hepatic amount of IL-1β after 0 and 6 hours and rather fortuitous variations in IL-10 and IFNγ amounts at a single time point, we also failed to detect modifications in serum and liver pro-inflammatory and anti-inflammatory cytokine levels in Cx32-deficient mice.…”

“…Several signaling cascades are known to underlie APAP-induced liver toxicity, yet little is known about the involvement of GJIC. A limited number of reports have described a role for Cx32-based gap junctions in APAP-triggered hepatotoxicity using genetically modified animals, albeit with contradicting outcome (Igarashi et al 2014; Naiki-Ito et al 2010). In this respect, Naiki-Ito and colleagues administered up 1000 mg/kg APAP intragastrically to rats carrying a mutated Cx32 gene and noticed decreased ALT serum levels and lowered histopathological damage after 24 hours (Naiki-Ito et al 2010).…”

“…In contrast, another report described increased serum aminotransferase values and more pronounced liver insults in Cx32 −/− C57BL/6 mice after administration of APAP, indicating a cytoprotective function for hepatic Cx32 in APAP-induced injury (Igarashi et al 2014). There are substantial differences in the set-up of these studies, especially those using APAP, and with some exceptions (Igarashi et al 2014), they have mainly focused on the measurement of parameters of cell death, which indeed is the most typical read-out of liver toxicity. However, like for most other hepatotoxicants, this ultimate outcome of APAP poisoning is preceded by a number of key events in which Cx32 signaling could also play a role.…”

Tetramethylpyrazine Suppresses Transient Oxygen-Glucose Deprivation-Induced Connexin32 Expression and Cell Apoptosis via the ERK1/2 and p38 MAPK Pathway in Cultured Hippocampal Neurons

“…On the one hand, Mathieu et al previously investigated Cx32 hemichannels facilitate the apoptotic-to-necrotic transition, which typically occurs in the final stage of hepatocellular apoptosis [37]. On the other hand, Isao et al demonstrated that Cx32 protects against acetaminophen-induced hepatic centrilobular necrosis in mice [38]. Although seemingly paradoxical, these results may all be correct depending on the cells examined and the type of stimulation.…”

Connexin hemichannel inhibition reduces acetaminophen-induced liver injury in mice

“…In fact, although being critical mediators of liver homeostasis (Maes et al, 2015a), connexins and their channels are also frequently involved in liver toxicity (Maes et al, 2015b). A number of studies have shown a role for Cx32-based gap junctions in APAP-triggered hepatotoxicity using genetically modified animals, albeit with contradicting outcomes (Igarashi et al, 2014; Maes et al, 2016b; Naiki-Ito et al, 2010; Park et al, 2013). In a recent study, our group questioned the suitability of genetically deficient rodents for investigating the involvement of Cx32 in APAP-induced hepatotoxicity (Maes et al, 2016b).…”