Impact of bariatric surgery-induced weight loss on circulating PCSK9 levels in obese patients

Background and aims: To investigate the effect of obesity and bariatric-induced weight loss on circulating levels of proprotein convertase subtilisin/kexin 9 (PCSK9) in severely obese patients. Methods and results: In this non-randomized interventional study, we enrolled 36 severely obese patients (BMI 43.7 ± 5.6 kg/m2), of which 20 underwent bariatric surgery, and 12 nonobese healthy controls. An oral glucose tolerance test (75-g OGTT) was performed in 31 of these obese patients at baseline (T0) and in 14 patients at 6 months after bariatric surgery (T6) to assess plasma glucose, insulin and PCSK9 levels. Plasma PCSK9 levels were also measured in 18 of these obese patients at T0 during a 2-h hyperinsulinemic-euglycemic clamp (HEC). At T0, PCSK9 levels were higher in obese patients than in controls (274.6 ± 76.7 ng/mL vs. 201.4 ± 53.3 ng/mL) and dropped after bariatric surgery (T6; 205.5 ± 51.7 ng/mL) along with BMI (from 44.1 ± 5.9 kg/m2 to 33.1 ± 5.6 kg/m2). At T6, there was also a decrease in plasma glucose (T0 vs. T6: 6.0 ± 1.8 vs. 5.0 ± 0.5 mmol/L) and insulin (15.7 ± 8.3 vs. 5.4 ± 2.1 mU/L) levels. At T0, plasma PCSK9 levels decreased during OGTT in obese patients, reaching a nadir of 262.0 ± 61.4 ng/mL at 120 min with a hyperinsulinemic peak of 75.1 ± 40.0 mU/L, at 60 min. Similarly, at T0 insulin infusion during 2-h HEC acutely reduced plasma PCSK9 levels in obese patients. The aforementioned OGTT-induced changes in plasma PCSK9 levels were not observed neither in nonobese healthy controls nor in obese patients after bariatric-surgery weight loss. Conclusions: These results suggest a pivotal role of adipose tissue and insulin resistance on PCSK9 homeostasis in severely obese patients.