An NMR study on the effect of glucose availability on carbohydrate metabolism in Dipetalonema viteae and Brugia pahangi

Abstract

Adult Brugia pahangi and Dipetalonema viteae utilise a percentage of absorbed glucose (ca. 15%) in the formation of the disaccharide trehalose [8]. This paper reports an investigation, employing 13C-NMR techniques, of the utilisation of trehalose by these nematodes and also the effect of glucose availability on metabolic product composition. The metabolism of [1- 13C]trehalose in D. viteae differed dramatically from that of [1- 13C]glucose under normal experimental conditions. A succinate/lactate ratio of 0.73 was obtained from the metabolism of [1- 13C]trehalose compared with 0.05 from [1- 13C]glucose at an initial concentration of ca. 5 mM. Similar, but less consistent, results were obtained from B. pahangi adults. Macrofilariae of D. viteae were fed variable, low levels of glucose at hourly intervals for 8 h, and a significant relationship ( P < 0.001) between the glucose addition rate and the ratio of succinate to lactate production was obtained. The lower the amount of glucose added each hour, the higher was the observed succinate to lactate ratio. The percentage yield of succinate increased greatly as the amount of added glucose was diminished. Parallel experiments performed on B. pahangi macrofilariac indicated that B. pahangi did not increase their succinate output so greatly with reduced glucose availability. It is clear that in the absence of available external glucose, B. pahangi and D. viteae draw on their internal trehalose reserves as a source of carbohydrate for energy generation. It is further apparent, particularly in the case of D. viteae, that when glucose availability is reduced, there is a significant switch from homolactate fermentation of exogenous glucose, to the utilisation of a partial tricarboxylic acid cycle, either in the forward or the reverse direction.