Effect Of Probiotics On Lipopolysaccharide-induced Hepatic Pro-inflammatory Cytokine Expression And Liver Damage In Mice

Background:Lipopolysaccharide (LPS) has essential role in the pathogenesis of D-galactosamine-sensitized animal models and alcoholic liver diseases of animals and humans, by stimulating release of pro-inflammatory mediators that cause hepatic damage and intestinal barrier impairment. Probiotics are the living micro-organisms that can confer a health benefit to the host should they be ingested in adequate amounts. There have raised a wealth of interests in the immunomodulatory functions of probiotics in recent years, including modulation of gut microbial homeostasis, maintenance of the gastrointestinal barrier function, antagonizing pathogens to colonize, and regulation of local and systemic immune responses. Oral pretreatment of probiotics have been shown to attenuate the hepatic injury and intestinal barrier dysfunction in D-galactosamine-sensitized and alcoholic liver disease models. The improvement in hepatic function in these models is usually attributive to their direct precautionary action against the impairment of intestinal barrier, thus reducing transfer of intestine-derived LPS to the liver and aggravating hepatic damage. On the other hand, given the close vascular and lymphatic link between the liver and gut as well as the fact that orally administered probiotics have capability to influence local and systemic immunity in experimental animals and humans, we hypothesized that oral pretreatment of probiotics might also enable the liver to directly attenuate the pro-inflammatory responses and liver damage induced by subsequent LPS stimulation. To this end, we sought to construct a liver injury model induced by LPS,in which intestine-derived microbial components (such as LPS) might play little role in mediating hepatic damage and pro-inflammatory responses, and then selected several probiotic strains to examine their potential preventive effect in the model.Methods:C57BL/6mice with or without their intestinal commensal bacteria deleted were treated (IP) with LPS with different dosage or its vehicle PBS, and samples were harvested at different time post LPS treatment to determine hepatic TNF-a and serum ALT levels as well as bacterial count in the liver. Mice were given (IG) supplements of diverse probiotic strains or its vehicle PBS daily for10consecutive days, and then injected with LPS or PBS. Serum ALT levels, hepatic and serum TNF-a expression, and hepatic histological changes were assessed at different time post LPS treatment. Other mechanism-associated parameters were also studied by in vivo experiments.Results:In a mouse model of LPS-induced hepatic injury, the levels of hepatic tumor necrosis factor-alpha (TNF-a) and serum alanine aminotransferase (ALT) of mice with depleted intestinal commensal bacteria were not significantly different from that of the control models. Pre-feeding mice for10days with Lactobacillus fermentum ZYL0401(LF41), significantly alleviated LPS-induced hepatic TNF-a expression and liver damage. After LF41pretreatment, mice had dramatically more L.fermentum-specific DNA in the ileum, significantly higher levels of ileal cyclooxygenase (COX)-2and interleukin10(IL-10) and hepatic prostaglandin E2(PGE2). However, hepatic COX-1, COX-2, and IL-10protein levels were not changed after the pretreatment. There were also higher hepatic IL-10protein levels after LPS challenge in LF41-pretreaed mice than in the control mice. Attenuation of hepatic TNF-a was mediated via the PGE2/E prostanoid4(EP4) pathway, and serum ALT levels were attenuated in an IL-10-dependent manner. A COX-2blockade abolished the increase in hepatic PGE2and IL-10associated with LF41. In LF41-pretreated mice, a blockade of IL-10caused COX-2-dependent promotion of hepatic PGE2, without affecting hepatic COX-2levels. In LF41-pretreated mice, COX2prevented enhancing TNF-a expression in both hepatic mononuclear cells and the ileum, and averted TNF-a-mediated increase in intestinal permeability. Together, we demonstrated that LF41pre-feeding enabled the liver to alleviate LPS-induced hepatic TNF-a expression and injury via a PGE2-EP4-and IL-10-dependent mechanism. Conclusion:We constructed a liver injury model by administering intraperitoneally low-dose LPS to mice, thus bypassing gut as a source of LPS as well as other bacterial components in the intestine. Using this model, we demonstrated that pretreatment of mice with H-LF41for10days endued the liver with the capacity to alleviate LPS-induced hepatic TNF-a expression and liver injury. The preventive effect was associated with increase in hepatic PGE2and LPS-induced hepatic IL-10levels after10days of H-LF41pretreatment, and was mediated via a PGE2-EP4-and IL-10-dependent mechanism. This protective role by H-LF41in LPS-induced liver damage, which is different from probiotic-mediated protection of liver function that is indirectly resulted from ameliorating disturbance in microbial composition and intestinal barrier dysfunction, is a new supplement to the already known protective effect of probiotics on hepatic injury.