Studies on the biochemical effects of the aldose reductase inhibitor 2,7-difluorospirofluorene-9,5′-imidazolidine-2′,4′-dione (Al 1576, HOE 843): Detection of d-glucaric and d-glucuronic acid excretion by high resolution 1H and 13C NMR spectroscopy

Abstract The effects of two aldose reductase inhibitors on the biochemical composition of rat urine were investigated using high resolution 1 H and 13 C NMR spectroscopy. We report the elevated excretion of d -glucaric acid (DGA) and d -glucuronic acid (GCA) following treatment with 2,7-difluorospirofluorene-9,5′-imidazolidine-2′,4′-dione (Imirestat, IM. Al 1576. HOE 843) at 50 mg/kg/day for 1 month, but not with 3-4-bromo-2-nuorobenzyl-4-oxo-3-phthalazine-1-ylacetic acid (Ponalrestat, Statil), dosed at 50 mg/kg/day for 2 weeks. Sugar aciduria was also detected following treatment with the cytochrome P450 inducer phenobarbitone (PB) at 45 mg/kg/day for 1 month, although the qualitative and quantitative pattern of excretion of sugar acids differed greatly between the IM and PB treatment groups. The levels of GCA excreted are elevated 11-fold by IM treatment from 19.0 to 210.0 μmol/ 24 hr, but only 2.5-fold by PB, from 9.7 to 23.9 smol/24 hr. DGA was not detectable in control urine, although levels did increase by 30% during the study from 7.5 to 10.9 μmol/24 hr, between day 8 and day 29, with IM treatment, and by 60% from 1.7 to 4.9 μmol/24 hr following PB administration for the same time period. This predominant elevation of DGA and GCA caused by IM treatment far exceeds previous records. In contrast, PB treatment resulted in an increase in intensity of a number of partially resolved sugar resonances, but at a much lower level than resulted from IM treatment. A raised level of DGA and GCA is usually associated with hepatic P450 induction; however, we report here profound DGA and GCA uria as a result of the inhibition of the aldehyde reductase, hexonate dehydrogenase (EC 1.1.1.19, EC 1.1.1.20). This mechanism is not closely linked to P450 induction, corroborating the current view that elevated excretion of DGA is not a reliable indicator of hepatic enzyme induction. This study further demonstrates the use of high resolution NMR spectroscopy in the detection of a novel biochemical effect which may go unnoticed during routine clinical chemistry tests.