Intrahepatic Amino Acid and Glucose Metabolism in A D–Galactosamine-Induced Rat Liver Failure Model

Abstract

A better understanding of the hepatic metabolic pathways affected by fulminant hepatic failure (FHF) would help develop nutritional support and other nonsurgical medical therapies for FHF. We used an isolated perfused liver system in combination with a mass-balance model of hepatic intermediary metabolism to generate a comprehensive map of metabolic alterations in the liver in FHF. To induce FHF, rats were fasted for 36 hours, during which they received 2 D-galactosamine injections. The livers were then perfused for 60 minutes via the portal vein with amino acid-supplemented Eagle minimal essential medium containing 3% wt/ vol bovine serum albumin and oxygenated with 95% O 2 /5% CO 2 . Control rats were fasted for 36 hours with no other treatment before perfusion. FHF rat livers exhibited reduced amino acid uptake, a switch from gluconeogenesis to glycolysis, and a decrease in urea synthesis, but no change in ammonia consumption compared with normal fasted rat livers. Mass-balance analysis showed that hepatic glucose synthesis was inhibited as a result of a reduction in amino acid entry into the tricarboxylic acid cycle by anaplerosis. Furthermore, FHF inhibited intrahepatic aspartate synthesis, which resulted in a 50% reduction in urea cycle flux. Urea synthesis by conversion of exogenous arginine to ornithine was unchanged. Ammonia removal was quantitatively maintained by glutamine synthesis from glutamate and a decrease in the conversion of glutamate to ␣-ketoglutarate. Mass-balance analysis of hepatic metabolism will be useful in characterizing changes during FHF, and in elucidating the effects of nutritional supplements and other treatments on hepatic function. (HEPATOLOGY 2001;34:360-371.)Since the late 1980s, orthotopic liver transplantation has become the only widely accepted treatment for fulminant hepatic failure (FHF). [1][2][3][4] Because of the severe shortage in donor organs, various alternatives aimed at providing a "substitute" liver, such as xenogeneic whole liver perfusion 5 and extracorporeal bioartificial liver devices, 6,7 are being developed. Such systems, which can be used as a bridge to transplantation or provide temporary relief during the most acute phase of hepatic failure, are promising, although technically complex and expensive. It has been hypothesized that hepatic encephalopathy may result from the elevation of circulating levels of putative toxins such as ammonia, mercaptans, short-chain fatty acids, [8][9][10] and an abnormal amino acid profile. [11][12][13] In FHF patients, alterations in amino acid concentrations in systemic plasma have been characterized by several investigators, 14,15 which led to the use of solutions rich in branchedchain amino acids (BCAA) for the treatment of hepatic encephalopathy. 16,17 These approaches, which were largely unsuccessful, aimed at counteracting the observed shifts in metabolite levels in the systemic circulation; however, systemic changes in metabolite levels do not solely reflect alterations in liver function, but also changes in whole-b...

Mitochondrial energetic metabolism: A simplified model of TCA cycle with ATP production

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“…Because the system of linear equations is overdetermined (more equations than unknown fluxes), fluxes are determined by linear regression (18,19). The vector r calc represents the best global fit to the linear system given by Equation 4, but individual vector elements may not exactly satisfy local constraints, i.e.…”

“…The vector r calc represents the best global fit to the linear system given by Equation 4, but individual vector elements may not exactly satisfy local constraints, i.e. a flux balance around a particular metabolite may not close completely, similar to the way individual points may not lie on the linearly regressed line found by minimizing the sum of the least square distances between all of the points and the line (19). All the matrix operations were performed by using MATLAB (Mathworks Inc., Natick, MA) and routinely took a few minutes for each measurement set on a DELL Inspiron laptop computer with an Intel Pentium M processor.…”