Inhibition of gluconeogenesis in vitro by a metabolite of hypoglycin

High-resolution (1)H NMR and magic angle spinning NMR spectroscopic investigation of the biochemical effects of 2-bromoethanamine in intact renal and hepatic tissue

The metabolic consequences of xenobiotic-induced toxicity were investigated using high-resolution magic angle spinning (MAS) NMR spectroscopy of intact tissue. Renal papillary necrosis (RPN) was induced in Sprague-Dawley rats (n = 12) via a single i.p. dose of 250 mg/kg 2-bromoethanamine (BEA) hydrobromide. At 2, 4, 6, and 24 h after treatment with BEA, three animals were killed and tissue samples were obtained from liver, renal cortex, and renal medulla. Tissue samples were also removed at 2 and 24 h from matched controls (n = 6). (1)H MAS NMR spectroscopic techniques were used to analyze samples of intact tissue ( approximately 10 mg). Decreased levels of nonperturbing renal osmolytes (glycerophosphocholine, betaine, and myo-inositol) were observed in the renal papilla of BEA-treated animals at 6 and 24 h postdose (p.d.), concomitant with a relative increase in the tissue concentration of creatine. Increased levels of glutaric acid were found in all tissues studied in BEA-treated animals at 4 and 6 h p.d., indicating the inhibition of mitochondrial fatty acyl CoA dehydrogenases and mitochondrial dysfunction. Increased levels of trimethylamine-N-oxide occurred in the renal cortex at 6 h p.d. Changes in the metabolite profile of liver included an increase in the relative concentrations of triglycerides, lysine, and leucine. The novel application of (1)H MAS NMR to the biochemical analysis of intact tissues following a toxic insult highlights the potential of this technique as a toxicological probe in providing a direct link between urinary biomarkers of toxicity and histopathological evaluation of toxicological lesions.

1H and 2H NMR spectroscopic studies on the metabolism and biochemical effects of 2-bromoethanamine in the rat

Male Fischer 344 rats were dosed with 2-bromoethanamine hydrobromide (BEA, N = 6) or [1,2,2,-2H4]-bromoethanamine hydrobromide (BEA-d4, N = 6) at 150 mg/kg i.p. and urine was collected -24 to 0 hr pre-dose and at 0-2 hr, 2-4 hr, 4-8 hr and 8-12 hr post-dose (p.d.). Urine samples were analysed directly using 500 and 600 MHz 1H NMR and 92.1 MHz 2H NMR spectroscopy. The major observed effect of BEA treatment was the induction of transient elevations in urinary glutaric acid (GTA) and adipic acid (ADA) excretion lasting up to 24 hr p.d. Most of the GTA was excreted in the 0-8 hr p.d. with maximal rates of 100-120 microM/hr for each rat occurring between 4 and 8 hr p.d. in animals treated with BEA or BEA-d4. GTA and ADA were shown to be of endogenous origin as there was no detectable incorporation of the 2H label into either compound following treatment of rats with BEA-d4. Following BEA-treatment there was an initial decrease in the levels of urinary citrate, succinate, 2-oxoglutarate and trimethylamine-N-oxide. A subsequent recovery of citrate and succinate was noted following the onset of medullary nephropathy. The abnormal urinary metabolite profiles were similar to that observed in the urine of humans with glutaric aciduria type II (an inborn error of metabolism) caused by a lack of mitochondrial fatty acyl coenzyme A dehydrogenases indicating that BEA or its metabolites have similar metabolic consequences. The BEA metabolite aziridine was detected by 1H and 2H NMR spectroscopy of the urine 8 hr p.d. together with BEA itself and two novel metabolites 2-oxazolidone (OX) and 5-hydroxy-2-oxazolidone (HOX). The formation of OX requires the reaction of BEA with endogenous bicarbonate followed by a cyclisation reaction eliminating HBr. Dosing rats with authentic OX resulted in the excretion of HOX but did not cause glutaric or adipic aciduria indicating that either aziridine or BEA itself was responsible for the presumed defect in mitochondrial metabolism.

The effects of hypoglycin on glucose metabolism in the rat. A kinetic study in vivo and [U-14C,2-3H]glucose

1. The kinetics of glucose metabolism were evaluated in rats deprived of food 15-21 h after the administration of hypoglycaemic doses of hypoglycin (100 mg/kg body wt.) by following changes in the specific radioactivities of 14C and 3H in blood glucose after an intravenous dose of [U-14C,2-3H]glucose [Katz, Rostami & Dunn (1974) Biochem. J. 142, 161-170]. 2. During this time, recycling of glucose through the Cori cycle was virtually abolished, the rate of irreversible disposal of glucose and its total body mass were both decreased by about 70%, whereas there was little effect on the mean transit time for glucose. 3. It was concluded that hypoglycaemia is due to inhibition of gluconeogenesis.