Diabetes is associated with significantly accelerated rates of atherosclerotic and hypertensive cardiovascular diseases. The cellular and molecular mechanisms are still not fully understood, mainly due to the lack of animal models that mirror the changes in human beings. Atherosclerosis involves several cell types including monocytes, vascular smooth muscle cells and endothelial cells [1]. Increased oxidant stress in these cell types has been suggested to be one key factor in atherosclerosis [2].We have recently shown that pig vascular smooth muscle cells (VSMC) cultured under high glucose (HG, 25 mmol/l) conditions to mimic the diabetic Diabetologia (2002) 45: 125±133 Role of 12-lipoxygenase and oxidant stress in hyperglycaemiainduced acceleration of atherosclerosis in a diabetic pig model Abstract Aims/hypothesis. We previously showed that vascular smooth muscle cells and endothelial cells cultured under high glucose conditions produced more 12(S)-hydroxyeicosatetraenoic acid (12-HETE), the 12-lipoxygenase (12-LO) product of arachidonate metabolism, relative to normal glucose. Because the lipoxygenase (LO) pathway has been associated with oxidant stress and the pathogenesis of atherosclerosis, we now examined 12-LO activation in vivo in a pig model of diabetes-induced accelerated atherosclerosis which displays human characteristics.Methods. The animal model was developed in pigs who were fed a normal or high fat diet and given streptozotocin injections to produce normolipemicnormoglycaemic (NLNG), normolipemic-hyperglycaemic (NLHG), hyperlipemic-normoglycaemic (HLNG) and hyperlipemic-hyperglycaemic (HLHG) pigs. Tissue samples were obtained from key arterial beds to examine 12-LO expression at 20 weeks after the pigs began their diet.Results. All HG pigs maintained threefold higher serum glucose concentrations. The HL groups developed atherosclerosis but diabetic HLHG pigs showed markedly accelerated atherosclerosis (twofold) relative to non-diabetic HLNG pigs. Immunostaining showed progressive increases in 12-LO in arteries in the order NLNG, NLHG, HLNG and HLHG. Leukocyte-type 12-LO protein (immuno-blotting) as well as mRNA expression (by competitive PCR) in abdominal and coronary arteries were significantly greater in HLHG pigs than in all the other three groups. Furthermore, increased oxidant stress was observed in monocytes from NLHG and HLNG pigs, and greatly potentiated in HLHG pigs. Conclusions/interpretation. These results are consistent with the hypothesis that 12-LO activation plays a key role in accelerated atherosclerosis due to diabetes and hyperlipemia. [Diabetologia (2002) 45: 125±133]