Background: Weight loss surgery is the most effective treatment for obesity, and it reduces cardiovascular and cancer risk through poorly understood mechanisms. MicroRNAs (miRNAs) are short RNA molecules that regulate the stability and translation of many mRNAs. We hypothesized that levels of specific circulating miRNAs are altered following surgery and may contribute to lower cancer risk.

Objectives: To investigate the change of miRNA following surgery.

Methods: All patients underwent gastric “sleeve operation”. RNA was isolated from sera of 21 patients (14 men, 7 women) before and 3 months after surgery. Sera were combined into two pools, which served for cDNA library construction followed by miSeq sequencing. The levels of candidate miRNAs were validated in the individual samples by QRT-PCR.

Results: Serum miR-122 was significantly up-regulated 3 months post-bariatric surgery in sera of patients, whose endothelial function had greatly improved. In addition, serum miR-122 levels correlated positively with endothelial function as measured by FMD. The changes in miR-122 levels from pre-surgery to 3 months post-surgery also tended to correlate with the respective changes in FMD.

Conclusions: The serum miR-122/miR-451 ratio may serve as a marker for endothelial function in obese patients. miR-122 is the dominant miRNA in the liver and a known tumor suppressor. Our findings suggest a role for circulating miR-122 in the maintenance of vascular endothelial cells (VECs) and in the prevention of cancer. Further studies are required to elucidate the mechanism of its secretion into circulation and its absorption by VECs, as well as its relevant cellular targets.