The Effects of Vitamin D on Microvascular Endothelial Function in Bariatric Surgery Patients

Introduction: Obesity is associated with microvascular dysfunction, reduced bioavailability of nitric oxide (NO) and vitamin D deficiency. The effects of vitamin D and surgical weight loss on microvascular function is inconclusive. Methods: Fifteen adults undergoing bariatric surgery were recruited (BMI: 47.1 + 6.3 kg/m2) for participation. On the day of surgery, abdominal subcutaneous and visceral adipose tissue biopsies were obtained. Three months after surgery (n = 8, BMI: 40.7 + 5.6 kg/m2), gluteal subcutaneous adipose fat pad biopsies were obtained. Isolated resistance arteries (RAs) were cannulated for vascular reactivity measurements to acetylcholine (ACh; 10-9-10-4 M), pressure gradients (Δ10-Δ100 cmH2O), and with and without the eNOS inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME), H2O2 scavenger, polyethyleneglycol catalase (PEG-CAT) and 1,25 hydroxyvitamin D (1-25(OH)2D) as well as combinations of the aforementioned agents. Vascular wall NO production was measured by fluorescence microscopy and a NO detection kit. Results: On average, subjects’ BMI decreased as well (post: 40.7 ± 5.6 kg/m2 vs. pre: 47.1 ± 6.3 kg/m2, p < 0.01). On average, subjects lost 13.3 kg of the body weight. Vitamin D improved FID, AChID and NO production compared to baseline in RAs from both VAT and SAT obtained on the day of surgery (Figure 1, n = 15 p < 0.01 (VAT), p < 0.05 (SAT)). These enhancements were reduced with L-NAME (p < 0.05), but not with PEG-CAT. RAs from the post-surgery SAT sample demonstrated improved FID, AChID and NO production at baseline and an enhanced effect of the eNOS inhibitor, L-NAME, compared to those collected on the day of surgery (p < 0.05) and a reduced effect with PEG-CAT was observed (p < 0.05). Conclusion: Vitamin D improved FID, AChID and NO production in resistance arteries from subcutaneous and visceral adipose tissue and these effects were abolished via eNOS inhibitor, L-NAME, but not by the H2O2 scavenger, PEG-CAT. Moreover, patients’ FID, AChID and NO production improved after surgical weight loss.