Aims/hypothesis The aim of this study was to determine the potential role of sphingosine kinase 1 (SPHK1), a key sphingolipid metabolic enzyme, in glucose metabolism and homeostasis. Methods SMMC-7721 hepatoma cells and C2C12 myotube cells were used to explore the role of SPHK1 in glucose uptake in vitro. KK/Ay type 2 diabetic mice, which were transfected with adenovirus harbouring the human SPHK1 gene by i.v. injection, were used to investigate the glucoselowering effects of SPHK1 in vivo.Results The basal glucose uptake and the insulin-stimulated glucose uptake in both 7721 cells and C2C12 cells were markedly enhanced when SPHK1 was overexpressed by adenovirus-mediated gene transfer, whereas they were substantially reduced when the expression of SPHK1 was inhibited or the activity of SPHK1 was blocked. Insulin could activate SPHK1 of both cell lines in a dosedependent manner. SPHK1 gene delivery significantly reduced the blood glucose level of KK/Ay diabetic mice, but had no effect on that of normal animals. It also attenuated elevated levels of plasma insulin, NEFA, triacylglycerol, cholesterol and LDL, significantly ameliorated hyperglycaemia-induced injury of liver, heart and kidney, and enhanced phosphorylation of insulin-signalling kinases such as Akt and glycogen synthase kinase 3β in livers of the diabetic animals. Conclusions/interpretation SPHK1 is involved in insulin signalling and plays an important role in the regulation of glucose and fat metabolism; adenovirus-mediated SPHK1 gene transfer might provide a novel strategy in the treatment of type 2 diabetes mellitus.

This study was made to test the validity of a simple biopsy technique for assessing the metabolic capacity of skeletal muscle. The biopsy is stimulated under mineral oil without attachment, i.e., without load or tension, then freeze-clamped and assayed for ATP, phosphocreatine, glucose 6-phosphate, and lactate. The mineral oil creates a closed anaerobic system. Background studies demonstrated in the absence of a load, metabolic changes with stimulation were little affected by cutting the fibers to obtain the biopsy; and high-energy phosphate (approximately P) consumption during a brief tetanus was not much lower than that for an isometric tetanus. Individual fast-twitch oxidative-glycolytic (IIA) and fast-twitch glycolytic (IIB) fibers obtained from the freeze-clamped biopsy showed distinct differences in approximately P consumption and metabolic changes. The results indicate that this technique could be useful for studies of normal and pathological human muscle.