Cholesterol Metabolism After Bariatric Surgery in Obesity

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Cholesterol Metabolism After Bariatric Surgery in Obesity

Abstract and Introduction

Abstract


Objective—Malabsorptive bariatric surgery (biliopancreatic diversion and biliointestinal bypass [BIBP]) reduces serum cholesterol levels more than restrictive surgery (adjustable gastric banding [AGB]), and this is thought to be due to greater weight loss. Our aim was to evaluate the changes of cholesterol metabolism induced by malabsorptive and restrictive surgery independent of weight loss.

Research design and methods—In a nonrandomized, self-selected, unblinded, active-comparator, bicenter, 6-month study, glucose metabolism (blood glucose and serum insulin levels and homeostasis model assessment of insulin resistance [HOMA-IR] index) and cholesterol metabolism (absorption: serum campesterol and sitosterol levels; synthesis: serum lathosterol levels; catabolism: rate of appearance and serum concentrations of serum 7-α- and serum 27-OH-cholesterol after infusions of deuterated 7-α- and 27-OH-cholesterol in sequence) were assessed in grade 3 obesity subjects undergoing BIBP (n = 10) and AGB (n = 10). Evaluations were performed before and 6 months after surgery.

Results—Subjects had similar values at baseline. Weight loss was similar in the two groups of subjects, and blood glucose, insulin levels, HOMA-IR, and triglycerides decreased in a similar way. In contrast, serum cholesterol, LDL cholesterol, non-HDL cholesterol, serum sitosterol, and campesterol levels decreased and lathosterol levels increased only in BIBP subjects, not in AGB subjects. A significant increase in 7-α-OH-cholesterol occurred only with BIBP; serum 27-OH-cholesterol decreased in both groups.

Conclusions—Malabsorptive surgery specifically affects cholesterol levels, independent of weight loss and independent of glucose metabolism and insulin resistance. Decreased sterol absorption leads to decreased cholesterol and LDL cholesterol levels, accompanied by enhanced cholesterol synthesis and enhanced cholesterol catabolism. Compared with AGB, BIBP provides greater cholesterol lowering.

Introduction


The epidemic of obesity has led to a dramatic increase of the number of bariatric procedures performed worldwide. Bariatric procedures are commonly divided into restrictive (adjustable gastric banding [AGB], vertical-banded gastroplasty, and sleeve gastrectomy), malabsorptive (biliopancreatic diversion [BPD] and biliointestinal bypass [BIBP]), and mixed procedures (gastric bypass and Roux-en-Y gastric bypass [RYGB]). Malabsorptive procedures are associated with a far greater weight loss than restrictive procedures and with quicker metabolic changes, namely drop of blood glucose levels.

Malabsorptive surgery also reduces serum cholesterol levels; in fact, it was originally intended for the treatment of hyperlipidemias and was highly effective even in patients without morbid obesity (the Program on Surgical Control of Hyperlipidemias study). Malabsorptive surgery is more effective than restrictive surgery in reducing cholesterol levels, and our group has shown that by 1 year after surgery, both BPD and BIBP reduce cholesterol levels more than AGB, and this effect is associated with greater weight loss. In addition, the cholesterol decrease correlates with loss of fat mass. Therefore, the main factor considered responsible for decreased cholesterol levels is weight loss.

However, up to 6 months, weight loss is similar with BIBP and AGB, and this led us to hypothesize that it was possible to study cholesterol absorption, as well as other aspects of cholesterol metabolism, independently of weight loss.

Therefore, we planned a study on the intestinal absorption of sterols, cholesterol synthesis, and cholesterol catabolism via synthesis of biliary acids in obese subjects before and 6 months after BIBP or AGB.

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