In vivo and in vitro³¹P magnetic resonance spectroscopic studies of the hepatic response of healthy rats and rats with acute hepatic damage to fructose loading

Abstract

The hepatic response to a fructose challenge for control rats, and rats subjected to an acute sublethal dose of carbon tetrachloride (CCl4) or bromobenzene (BB), was compared using dynamic in vivo 31P MRS. Fructose loading conditions were used in which control rats showed only a modest increase in hepatic phosphomonoester (PME), and a small decrease in ATP, Pi, and intracellular pH after fructose administration. Both CCl4 and BB-treated rats showed a much greater fructose-induced accumulation of PME than did controls. Trolox C, a free radical scavenger, prevented most of this PME increase. BB-treated rats, given sufficient time to recover from the hepatotoxic insult, responded to the fructose load similarly to controls. Liver aldolase activities of control, toxicant-treated rats, and toxicant plus Trolox C-treated rats correlated inversely with PME accumulation after fructose loading (correlation coefficient: -0.834, P < 0.05). Perchloric acid extracts of rat livers studied by in vitro 31P MRS confirmed that the PME accumulation after fructose loading is mainly due to an increase in fructose 1-phosphate. These studies are consistent with the aldolase-catalyzed cleavage of fructose 1-phosphate being rate-limiting in hepatic fructose metabolism, and that the CCl4 and BB treatment modify and inactivate the aldolase enzyme.

Hepatic 31P magnetic resonance spectroscopy: a hepatologist's user guide

“…Mann et al (43) through relief of biliary obstruction and Leij‐Halfwerk et al (44) through infusion of intravenous ATP). Finally, some investigators have used the infusion of intravenous fructose (or d ‐tagatose, a stereoisomer of d ‐fructose (38)) to further study hepatic energy metabolism (39, 40). Since intravenous fructose uniformly depletes hepatic ATP, some research suggests that the measurement of ATP recovery can serve as a dynamic ‘hepatic energy stress test’ (Table 2, fructose studies), with impaired livers demonstrating slower recovery.…”

“…Various studies with disparate aims also seem to yield a consistent conclusion about ATP levels: (38)) to further study hepatic energy metabolism (39,40). Since intravenous fructose uniformly depletes hepatic ATP, some research suggests that the measurement of ATP recovery can serve as a dynamic 'hepatic energy stress test' ( Table 2, fructose studies), with impaired livers demonstrating slower recovery.…”

“…Intracellular pH can be calculated from the relative chemical shift of Pi from a reference (often the α‐ATP signal, as this is thought to be relatively pH insensitive) (22). The Henderson–Hasselbach equation can be used: pH=6.75+log[(δ−0.75)/(3.35−δ)] where δ is the chemical shift in ppm for the Pi resonance (23). However, the equation requires very precise measurement of δ, as even small changes result in large variance of the pH.…”

Influence of preculture on the prefreeze and postthaw characteristics of hepatocytes

“…Spectra acquired using a 10-s relaxation delay indicated that the phosphorous metabolites were fully relaxed using a 5-s delay, and that nuclear Overhauser enhancement of the phosphorus resonances were minimal. Chemical shifts were referenced to glycerolphosphocholine at −0.13 ppm (Merchant et al, 1999), and the tentative peak assignments were made based on previously published reports (Bell et al, 1993;Changani et al, 1999;Changani et al, 1996;Harvey et al, 1999;Lu et al, 1994;Gillham and Brindle, 1996;Williams et al, 1998). Metabolite peak areas were computed using the instrument software.…”

“…The complicated monoester region of the spectrum is expanded in Figure 5. Metabolites were identified based on chemical shift values taken from previous literature reports (Bell et al, 1993;Changani et al, 1999;Changani et al, 1996;Gillham and Brindle, 1996;Harvey et al, 1999;Lu et al, 1994;Williams et al, 1998). Metabolites quantified for this investigation are 6-phosphogluconate (6PG), 4.92 ppm; glucose-6-phosphate (G6P), 4.51 ppm; glycerol-3-phosphate (G3P), 4.44 ppm; phosphoglycerate (PG), 4.10 ppm; fructose-6-phosphate ( ppm.…”