Pathogenesis of hepatic steatosis during total parenteral nutrition

The hepatic toxicity of TPN that is seen clinically appears to be multifactorial in origin. Most patients develop a combination of hepatic steatosis with evidence of cholestasis and abnormalities in liver function. The model that we have studied is one of pure hepatic steatosis since, on repeated study, these rats do not develop any liver function abnormalities. It is unclear whether this is related to the fact that these are short-term experiments, that rat livers respond differently from humans, or that rats do not have gallbladders. It has not been possible to carry these experiments out beyond 3 weeks since the rats develop bacterial colonization of the central lines as well as evidence of line sepsis. thus confounding the issue of hepatic toxicity being due to the TPN or to sepsis. One hypothesis is that hepatic steatosis is an early marker of liver toxicity and that prevention or reversal of hepatic steatosis may protect the liver from further abnormality. Insulin and glucagon seem to play a critical role in the development of TPN-associated hepatic steatosis. Specifically, an elevated portal venous insulin-glucagon molar ratio appears to be the primary stimulus and any treatment that lowers this ratio should diminish hepatic steatosis. The use of glucagon as a treatment modality is new. We have found no evident side effects of low dose glucagon in rats when it is added to the TPN solution. Glutamine has received much attention recently as a nutritional pharmacological agent in ameliorating some of the intestinal complications of parenteral nutrition and is well tolerated when administered appropriately. Intravenous lipid administration is an important nonprotein calorie source, especially when a high dextrose base cannot be used, and plays a role as well in preventing the development of hepatic steatosis. Thus, it is suggested that the clinical treatment of hepatic steatosis during TPN can be safely performed using any one, or a combination, of these modalities and without having to discontinue the TPN infusions. Since we observed no deterioration of liver function in rats receiving TPN for up to 2 weeks, we cannot completely relate these findings and recommendations to the hepatic dysfunction seen clinically with the use of TPN. Additional study will be required before this can be conclusively determined.