Trapping of uridine phosphates by D-galactose in ethanol-treated liver

In vivo study of brain metabolism in galactosemia by 1H and 31P magnetic resonance spectroscopy

In order to further evaluate different hypotheses concerning brain metabolism in galactosemia, six adult patients aged 18-29 years with classical galactosemia under dietary treatment underwent localized 1H and 31P magnetic resonance spectroscopy (MRS) in addition to conventional T1- and T2-weighted MRI. Galactose-1-phosphate levels in erythrocytes were 1.1-3.7 mg/dl, plasma concentrations of galactitol ranged from 8.4-14.2 mumol/l. Imaging revealed abnormal peripheral myelination in five and enlargement of lateral ventricles in two patients. Brain galactitol in parieto-occipital white matter was below detectability of 1H MRS leading to the assumption that brain concentrations of the free metabolite was well below 1 mmol/kg. Signal intensities of free myo-inositol, which was postulated to be indicative of changes in the second messenger pathway, were within the normal range. MRS data revealed a normal energy status of the brain. In summary 1H and 31P MRS indicated normal metabolite concentrations as compared to healthy controls.

2-Deoxy-2-fluoro-D-galactose protein N-glycosylation

2-Deoxy-2-fluoro-D-galactose (dGalF), added to the medium of primary cultured rat hepatocytes, inhibited N-glycosylation of membrane (gp 120) and secretory glycoproteins (alpha 1-macroglobulin) in a concentration-dependent manner. Complete inhibition of N-glycosylation was achieved at concentrations of 1 mM and above. At identical concentrations, 2-deoxy-2-fluoro-D-glucose (dGlcF) caused only incomplete inhibition of N-glycosylation. dGalF reduced incorporation of D-[2,6-3H]mannose into lipid-linked oligosaccharides indicating interference with their assembly in the dolichol cycle.

Enhanced galactose metabolism in isolated perfused livers of folate-treated suckling rats

Folic acid (1 mg/day) was administered intraperitoneally to seven-day-old suckling rats for a period of seven days. Livers of folate-treated animals took up galactose rapidly during the first 35 minutes of perfusion, whereas uptake was delayed in the controls (sham-injected and untreated). More glucose was released by all groups when galactose was perfused than when other substrates were used. With each hexose tested, livers of the folate group consistently released less glucose but more lactate than the controls. The specific activity of galactose-1-phosphate uridyltransferase was elevated in livers of the folate group compared to the controls perfused with either galactose or glucose. A similar finding was made for ATP levels in perfused livers of this group. The differences in transferase and ATP levels in perfused livers of folate-treated over the control groups may explain the enhanced galactose uptake pattern.

Kinetics of ethanol inhibition of galactose elimination in perfused pig liver

The effect of ethanol (5--25 mM) on the galactose elimination kinetics in the intact liver was studied in the isolated perfused pig liver, using the steady-state infusion technique. Ethanol reduced galactose-Vmax on average to 0.07 mmol/min kg liver in six experiments from 0.43 mmol/min kg obtained in control experiments without ethanol. Also Km was significantly reduced from 0.23 mmol/l plasma water to 0.03 mmol/l. Ethanol increased UDP-galactose ten-fold simultaneous with a rise in hepatic outflow ratio of lactate to pyruvate to about 300 from 10; this indicates that ethanol inhibits epimerase. In experiments with increasing galactose elimination rates, the concentration of galactose-1-P increased much less than the concentration of galactose, and the phosphorylation of galactose therefore seems to be rate-limiting. In vitro galactokinase is inhibited by galactose-1-P. In the present study ethanol increased galactose-1-P five to ten times, and the reduction of Vmax and Km by ethanol could be explained by uncompetitive inhibition by galactose-1-P with Ki about 0.1 mmol/l. Ethanol decreased UDP-glucose to about 40% and UTP to less than 5%, probably due to trapping as UDP-galactose. This may depress the forward transferase reaction, and therefore the other co-substrate galactose-1-P rises--and inhibits galactokinase.

Increased serum urate in galactosemia patients after a galactose load: a possible role of nucleotide deficiency in galactosemic liver injury

Five galactosemic and 5 normal children received an oral load of galactose under standardized conditions. The maximal blood galactose level after 1.5 hours was 12.6 +/- 2.0 (S.D.) mmol/l in individuals with a deficiency of uridylyl transferase (EC2.7.7.12) as compared to 5.8 +/- 1.2 (S.D.) mmol/l in the controls. The concentration of serum urate in galactosemics increased to 155% of the fasting level (P less than 0.005); no rise was detectable in the controls. The elimination of urate with the urine was augmented by the same amount in both groups. Our studies provide evidence for an increased catabolism of hepatic nucleotides. This may lead to a deficiency of nucleotides which is proposed as a cause of galactosemic liver injury.