Combination therapy with losartan and L-carnitine protects against endothelial dysfunction of streptozotocin-induced diabetic rats

Endothelial dysfunction is a critical factor during the initiation of diabetic cardiovascular complications and angiotensin II appears to play a pivotal role in this setting. The present study aimed to investigate whether the combination therapy with losartan and the nutritional supplement, L-carnitine can provide an additional protection against diabetes-associated endothelial dysfunction and elucidate the possible mechanism(s) underlying this effect. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ) (60 mg/kg) in rat. Effects of losartan (20 mg/kg, orally, 3 months) and L-carnitine (200 mg/kg, orally, 3 months) on tumor necrosis factor (TNF)-α, oxidative stress parameters, endothelial nitric oxide synthase expression (eNOS), and vascular function were evaluated. Our results showed a marked increase in aortic superoxide anion (O2(-)) production and serum malondialdehyde (MDA) level alongside attenuating antioxidant enzyme capacities in diabetic rats. This was associated with a significant increase in anigiotensin II type 1 receptor gene expression and TNF-α serum level of diabetic rats alongside reducing aortic eNOS gene expression and nitric oxide (NO) bioavailability. The single or combined administration of losartan and L-carnitine significantly inhibited these changes. Additionally, the vascular endothelium-dependent relaxation with acetylcholine (ACh) in aortic diabetic rat was significantly ameliorated by the single and combined administration of losartan or L-carnitine. Noteworthy, the combination therapy exhibited a more profound response over the monotherapy. Collectively, our results demonstrate that the combined therapy of losartan and L-carnitine affords additive beneficial effects against diabetes-associated endothelial dysfunction, possibly via normalizing the dysregulated eNOS and reducing the inflammation and oxidative stress in diabetic rats.