Role of 12-lipoxygenase and oxidant stress in hyperglycaemia-induced acceleration of atherosclerosis in a diabetic pig model

Abstract

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]

Simvastatin Modulates Angiotensin II Signaling Pathway by Preventing Rac1-Mediated Upregulation of p27

“…When NADPH oxidase activity was inhibited by DPI, the Ang II increase in H 2 O 2 production was eliminated. Thus, our results confirm previous observations regarding the involvement of ROS in Ang II-mediated signaling in MC (24,46,47). This study, however, provides new insights by establishing a sequential link between Ang II-induced Rac1 activity and an increase in intracellular H 2 O 2 production as dominant-negative Rac1 transfected MC failed to increase H 2 O 2 production.…”

Lipoxygenase Products Regulate Nitric Oxide and Inducible Nitric Oxide Synthase Production in Interleukin-1.BETA. Stimulated Vascular Smooth Muscle Cells.

“…On the other hand, the sPLA2 and LOX enzymes also can be induced by inflammatory cytokines. In particular, 12-LOX is known to be expressed in atherosclerotic lesions (18) and to play a key role in the pathogenesis of accelerated vascular disease. A pharmacological LOX inhibitor or specific molecular LOX inhibitor, such as the 12-LOX ribozyme, could significantly reduce the extent of neointimal thickening in balloon-injured rat carotid arteries (30,31).…”

“…In addition, LOX enzymes have been shown to be expressed in macrophage-rich areas of atherosclerotic lesions (17). A recent study has indicated that 12-LOX is expressed in the vascular tissue of diabetic atherosclerosis (18). Furthermore, targeted disruption of the 12-LOX gene diminishes atherosclerosis in apo E-gene deficient mice (19).…”

Increased 12/15-Lipoxygenase Enhances Cell Growth, Fibronectin Deposition, and Neointimal Formation in Response to Carotid Injury

“…9,10 12/15LO and its products are increased in the vascular wall of animal models of atherosclerosis and injury-induced restenosis. 11 Compared with uninjured carotids, 12/15LO expression is significantly increased in rat carotids on day 12 after injury. 12 Moreover, pharmacological or ribozyme-mediated inhibition of the 12/ 15LO gene in vascular injury models results in attenuated NIF 12,13 ; yet, the effects of baseline elevations in 12/15LO on injury-induced NIF and the factors downstream of 12/15LO that mediate these effects in vivo are incompletely understood.…”

“…15 Furthermore, 12/15LO expression is increased in the vascular wall in a porcine model of diabetes. 11 Endothelial cells isolated from db/db diabetic mice have increased 12/ 15LO expression, whereas the db/db mice also have increased levels of 12S-and 15S-HETE in vivo. 16 The obese Zucker rat model of metabolic syndrome also displays increased carotid 12/15LO expression and NIF after balloon angioplasty relative to lean Zucker rats.…”