Oral Administration of Tetrahydrobiopterin Prevents Endothelial Dysfunction and Vascular Oxidative Stress in the Aortas of Insulin-Resistant Rats

Abstract

We have reported that a deficiency of tetrahydrobiopterin (BH(4)), an active cofactor of endothelial NO synthase (eNOS), contributes to the endothelial dysfunction through reduced eNOS activity and increased superoxide anion (O(2)(-)) generation in the insulin-resistant state. To further confirm this hypothesis, we investigated the effects of dietary treatment with BH(4) on endothelium-dependent arterial relaxation and vascular oxidative stress in the aortas of insulin-resistant rats. Oral supplementation of BH(4) (10 mg. kg(-1). d(-1)) for 8 weeks significantly increased the BH(4) content in cardiovascular tissues of rats fed high levels of fructose (fructose-fed rats). Impairment of endothelium-dependent arterial relaxation in the aortic strips of the fructose-fed rats was reversed with BH(4) treatment. The BH(4) treatment was associated with a 2-fold increase in eNOS activity as well as a 70% reduction in endothelial O(2)(-) production compared with those in fructose-fed rats. The BH(4) treatment also partially improved the insulin sensitivity and blood pressure, as well as the serum triglyceride concentration, in the fructose-fed rats. Moreover, BH(4) treatment of the fructose-fed rats markedly reduced the lipid peroxide content of both aortic and cardiac tissues and inhibited the activation of 2 redox-sensitive transcription factors, nuclear factor-kappaB and activating protein-1, which were increased in fructose-fed rats. The BH(4) treatment of control rats did not have any significant effects on these parameters. These results indicate that BH(4) augmentation is essential for the restoration of eNOS function and the reduction of vascular oxidative stress in insulin-resistant rats.

Increased expression of CCAAT/enhancer binding protein-β and -δ and monocyte chemoattractant protein-1 genes in aortas from hyperinsulinaemic rats

“…It has been reported that several transcription factors, including nuclear factor-κB, have a role in the regulation of Ccl2 expression [27,28]. Using an electrophoretic gel retardation assay, we have previously shown increased binding activity of NF-κB in the aorta and in the heart of fructose-feeding-induced hyperinsulinaemic rats using an electrophoretic gel retardation assay [21]. In addition to the effect on Ccl2 gene, C/EBP-β, and C/EBP-δ regulate the transcription of a number of genes involved in the inflammatory response [8,29].…”

“…To examine the effects of insulin on Cebpb, Cebpd and Ccl2 expression in cardiovascular tissues, we studied rats fed on a fructose diet, which show insulin resistance and hyperinsulinaemia [21,22]. As shown in Table 1, the body weight gains of the rats fed on the control diet and the rats fed on the fructose diet were similar over the study period.…”

C-reactive protein decreases endothelial nitric oxide synthase activity via uncoupling

“…Endothelial dysfunction has been linked to reduced BH4 availability and uncoupling of eNOS [15,36,37]. Various clinical studies have also demonstrated that administration of BH4 improves endothelial dysfunction in conditions characterized by reduced availability of NO and increased production of reactive oxygen species, such as hypercholesterolemia [38], coronary artery disease [24] and smoking [39].…”

Insulin-Induced Generation of Reactive Oxygen Species and Uncoupling of Nitric Oxide Synthase Underlie the Cerebrovascular Insulin Resistance in Obese Rats

“…Reduced BH 4 levels due to oxidative degradation of BH 4 to BH 2 has been reported in diabetes (Shinozaki et al, 2000). Furthermore, BH 2 competes for binding to NOS at the BH 4 site, thus promoting NOS uncoupling and loss of NO production (Katusic et al, 2009).…”