In this study, serum irisin, preptin, and adropin in obese patients before and after bariatric surgery were compared with values in healthy normal-weight control participants. Serum irisin at baseline was significantly lower in obese patients than in control participants, but the difference was no longer significant 6 months after bariatric surgery. At 6 months, both serum irisin and adropin had significantly increased. Preptin also increased, but the difference from baseline was of borderline significance. The changes from before to after surgery were bidirectional. For each of the three peptides, the baseline value before surgery was significantly associated with the subsequent increase or decrease in serum level after surgery. The study results are in line with those reported by Lee et al. who reported bidirectional changes 1 month after Roux-en-Y gastric bypass surgery, with elevations of serum irisin at 9 months, but not at 1 month, associated with lower preoperative levels. Preptin and adropin were not studied [
16]. Our results and those of Lee et al. indicate that preoperative serum levels of peptides like irisin influence the increase that occurs in response to the postoperative reduction in body mass. In this study, the preoperative HbA1c percentages in patients with increased and decreased postoperative serum irisin were different. Preoperative HbA1c was significantly higher in patients with high preoperative serum irisin that decreased following surgery, indicating that impaired glucose metabolism may be related to irisin production and its change after reduction in body mass. A study by Shoukry et al. reported an association of irisin production and type 2 diabetes mellitus (T2DM), with a decrease in serum irisin in obese patients with T2DM but not in healthy controls and higher serum irisin in obese than in lean controls [
12]. A systematic review and meta-analysis of 23 studies reported that circulating irisin concentrations were significantly lower in T2DM patients than in controls without T2DM [
21]. If relatively low serum irisin has unfavorable effects on glucose and lipid metabolism, then the study results indicate that a history of T2DM may inhibit desirable effects of postoperative body mass reduction on irisin production. Preoperative serum irisin was lower in obese patients than in control participants, but at 6 months after surgery, the difference was no longer significant. Preoperative EBW, HbA1c, total cholesterol, LDL cholesterol, and triglycerides levels were all significantly associated with serum irisin before surgery. The result is consistent with a role of irisin in lipid and glucose metabolism as discussed above; however, EBW was the only anthropometric variable that was associated with irisin level. The postoperative analysis found no significant associations of patient variables and irisin level. Several previous studies have investigated changes in serum irisin after body mass reduction. Fukushima et al. found no significant changes in serum irisin after body mass reduction resulting from diet, exercise therapy, and cognitive behavioral therapy [
13]. However, the reduction in BMI of 2.4 kg/m
2 was less than 9.96 ± 4.3 kg/m
2 in our study. Demirpence et al. found no change in serum irisin after sleeve gastrectomy, but the follow-up was at 3 months, which was shorter than the 6 months in our study [
11]. Majorczyk et al. reported stable irisin levels at 6 and 12 months after LSG or laparoscopic Roux-en-Y gastric bypass [
15]. Lee at al. found that preoperative serum irisin concentration was significantly correlated with the percentage of body weight lost in 1 year, suggesting that preoperative irisin might be at least in part associated with weight loss following bariatric surgery in morbidly obese patients [
16]. We conclude that bariatric surgery might restore impaired irisin production but the effect depends on glucose and lipid metabolism. In some patients, irisin levels decreased despite successful body mass reduction.
Baseline serum adropin concentrations in the bariatric surgery patients and control participants were similar, but the concentration increased had significantly increased at 6 months in patients compared with controls. The changes of adropin serum levels after surgery were bidirectional, but unlike irisin and preptin, an increase was observed in 87% of the patients. The results suggest that obesity may not impair adropin production and that body mass reduction may increase production, enhancing the effect of surgery. The results is in line with a previous report of increased serum adropin after body mass reduction with 8 weeks of exercise training in obese elderly people [
22] and 3 months after Roux-en-Y gastric bypass in overweight and obese adults [
19]. Patients with an increase in serum adropin after surgery were younger than those with a decrease, but serum adropin was not significantly correlated with age as reported by Butler et al. who reported a negative correlation of adropin serum levels and age [
19]. The relationship of age and serum adropin requires additional study.
The changes in serum preptin were similar to those of adropin. Although comparable to controls before surgery, preptin increased in the 6 months after surgery, but with borderline significance. Like irisin and adropin, change in preptin level after surgery was bidirectional. Multiple regression analysis found that EBW and BMI at 6 months were independently associated with serum preptin level, but the association as not significant when all patient characteristics were evaluated together. To the best of our knowledge, there are no other studies on the changes in preptin production after body mass reduction. Postoperative changes in preptin need further investigation in a larger sample size over a longer period of observation.
The changes of serum irisin, preptin, and adropin were not related to the type of bariatric surgery; the baseline and follow-up results in patients with LABG and LSG before and after surgery were similar. Irisin, adropin, and preptin levels were higher 6 months after bariatric surgery than at baseline. The changes in each of the three peptides were bidirectional. We conclude that in some patients, body mass reduction may restore impaired production of energy regulating peptides that may add to the benefits of the bariatric procedure. Studies are ongoing to assess the changes at 12 and 24 months after surgery to determine whether the changes associated with the reduction of body mass are transient or permanent.