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Changes in Serum Ghrelin Concentration following Biliopancreatic Diversion for Obesity Gian Franco Adami,* Renzo Cordera,† Gabriella Andraghetti,† Giovanni B. Camerini,* Giuseppe M. Marinari,* and Nicola Scopinaro*

Abstract ADAMI, GIAN FRANCO, RENZO CORDERA, GABRIELLA ANDRAGHETTI, GIOVANNI B. CAMERINI, GIUSEPPE M. MARINARI, AND NICOLA SCOPINARO. Changes in serum ghrelin concentration following biliopancreatic diversion for obesity. Obes Res. 2004;12:684 – 687. Objective: Ghrelin is a recently discovered hormone that is produced mainly by the stomach and that increases food intake in rodents and humans. It has been postulated that the weight loss after gastric bypass surgery for obesity might be related to changes in serum ghrelin concentration. Research Methods and Procedures: Serum leptin and ghrelin concentrations were measured in a group of obese patients before biliopancreatic diversion (BPD) and 2 and 12 months postoperatively. Insulin sensitivity was determined from serum glucose and insulin levels according to the homeostatic model of assessment for insulin resistance (HOMA IR). Results: A sharp drop was observed in body weight, in BMI values, in HOMA IR data, and in serum leptin concentration at 2 and 12 months after BPD, whereas a significant increase of serum ghrelin level was observed at 12 months, when food intake had returned to preoperative levels. A negative correlation between the postoperative changes of serum ghrelin concentration and those of HOMA IR values was observed at 2 and 12 months after BPD. Discussion: No evidence upholding a relationship between serum ghrelin concentration and food intake after BPD was seen; the postoperative changes likely reflected the achievement of a new state of energy balance. The negative rela-

Received for review September 16, 2003. Accepted in final form February 11, 2004. The costs of publication of this article were defrayed, in part, by the payment of page charges. This article must, therefore, be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. *Dipartimento di Discipline Chirurgiche and †Dipartimento di Scienze Endocrine e Metaboliche, Universita` di Genova, Genova, Italy. Address correspondence to Gian Franco Adami, Dipartimento di Discipline Chirurgiche, Universita` di Genova, Largo Rosanna Benzi 8, 16132 Genova, Italy. E-mail: [email protected] Copyright © 2004 NAASO

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tionship observed between post-BPD changes in HOMA IR values and changes in serum ghrelin concentration supported the role of insulin in the modulation of ghrelin production. Key words: obesity surgery, ghrelin, leptin, homeostatic model of assessment for insulin resistance

Introduction Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor produced by the gastric mucosa, is thought to play a key role as an orexigenic agent in regulating food intake (1,2). The plasma ghrelin concentration increases on fasting and returns to baseline after refeeding (3,4). Ghrelin levels are lower in obese patients than in healthy controls and negatively correlated with BMI values, thus prompting the suggestion that obese patients might be resistant to ghrelin (5,6). Recently, a great deal of attention has focused on the effect of gastrointestinal surgery for obesity on circulating ghrelin levels, and studies have been carried out to elucidate the hormone’s involvement in the mechanisms of weight loss in operated patients. Subjects with body weight (BW)1 reduced by gastric bypass showed markedly lower serum ghrelin concentrations than obese patients, thus giving rise to the hypothesis that this decrease might account for the reduction of food intake and, consequently, for the weight loss observed after the operation (4,7). However, a longitudinal investigation has yielded contrasting results: A sharp increase of serum ghrelin level after gastric bypass for obesity was observed, and similar serum ghrelin levels were found in two groups of operated and nonoperated women with matched BMI values (8). The aim of this study was to investigate the effects of biliopancreatic diversion (BPD) (9) on the serum ghrelin levels of severely obese patients. Because preliminary data

1 Nonstandard abbreviations: BW, body weight; BPD, biliopancreatic diversion; HOMA IR, homeostatic model of assessment for insulin resistance.

Ghrelin following BPD, Adami et al.

Table 1. Patient characteristics before and 2 and 12 months following biliopancreatic diversion for obesity and percentage changes (⌬) in the variables at 2 and 12 months compared with preoperative levels

BW (kg) BMI (kg/m2) HOMA IR Leptin (ng L⫺1) Ghrelin (pmol/l)

Prior to BPD

2 Months after BPD

12 Months after BPD

⌬2 months

⌬12 months

135.9 ⫾ 6.26 48 ⫾ 4.02 8.2 ⫾ 2.02 41.3 ⫾ 4.08 241.4 ⫾ 21.6

117.4 ⫾ 5.71* 41.6 ⫾ 1.52* 2.2 ⫾ 0.54* 15.6 ⫾ 2.47* 209.0 ⫾ 34.8

89.9 ⫾ 4.5*‡ 31.5 ⫾ 1.09*‡ 1.0 ⫾ 0.16*‡ 7.5 ⫾ 0.9*‡ 310.8 ⫾ 47.7†

⫺14.0 ⫺14.0 ⫺47.0 ⫺10.3 ⫺10.3

⫺39.6 ⫺33.6 ⫺70.7 ⫺79.4 ⫹27.9

Mean values and SE are given. * p ⬍ 0.0001 vs. preoperative. † p ⬍ 0.05 vs. preoperative. ‡ p ⬍ 0.001 vs. 2 months.

demonstrated a close interaction between insulin action and plasma ghrelin and leptin concentrations, in this study, serum ghrelin concentrations were related to leptin levels and to the degree of insulin resistance evaluated by the homeostatic model of assessment for insulin resistance (HOMA IR): High HOMA IR values reveal an impaired insulin action, whereas a drop in HOMA IR index indicates an improvement in insulin sensitivity (10).

Research Methods and Procedures The study was carried out in 24 obese nondiabetic patients (nine men) eligible for BPD, with a mean initial BW of 135.8 kg (103 to 185) and mean initial BMI values of 47.8 kg/m2 (40.1 to 50.6). All patients gave their written informed consent before the operation. The patients were evaluated preoperatively and at 2 and 12 months after BPD. Before the operation, BW and stature were measured to the nearest 0.1 kg and 0.1 cm, respectively. Blood was drawn at 8.00 AM after an overnight fasting; after separation, samples were stored at ⫺70 °C until analysis. At the 2- and 12-month regular follow-up visit, blood was taken after the same procedures. Furthermore, the current food intake was evaluated by an accurate alimentary interview and compared with the preoperative one. Mean BW and BMI values at 2 and 12 months after BPD are reported in Table 1. Sera were analyzed for levels of ghrelin, glucose, insulin, and leptin. Plasma ghrelin levels were measured in duplicate by a commercial radioimmunoassay (Phoenix Pharmaceuticals, Belmont, CA) that uses 125I-labeled bioactive ghrelin as a tracer and a rabbit polyclonal antibody raised against full-length octanoylated human ghrelin that recognizes both acylated and desacylated ghrelin. To reduce sources of variation, all measurements were made in the same batch. Serum glucose concentration was measured by an enzymatic method on an automatic analyzer, serum insulin concentration by a standard sandwich enzyme immunoassay,

and serum leptin by immunoreactivity using a commercially available radioimmunoassay kit. Insulin sensitivity was estimated according to the HOMA IR. Mean percentage changes (⌬) of preoperative findings at 2 and 12 months were calculated for BW and BMI values, for HOMA IR data, and for the blood test variables. Given the small number of cases and the sample variance, nonparametric statistics were used: The differences were assessed by the Wilcoxon signed rank test for longitudinal comparisons and the relationships between data by the Kendall correlation coefficient.

Results Table 1 summarizes the results of this study. A marked reduction of BW and BMI values was observed at 2 months after BPD; this fall became even sharper at 12 months after the operation. Furthermore, a drop of HOMA IR values and serum leptin concentration was seen at the 2nd postoperative month, with a further reduction evident at 12 months; the changes in BW, BMI, HOMA IR values, and serum leptin concentration between 2 and 12 months after BPD were all statistically significant. In contrast, at 2 months after BPD, mean serum ghrelin concentration was in essence similar to that observed before the operation, and at 12 months, a slight but significant increase was found. At 2 months, the mean food intake assessed by alimentary interview was reduced by 30% compared with the initial finding, whereas at 1 year after BPD, all the operated subjects reported food consumption substantially similar to or greater than preoperative habits. The results of the analyses on the relationships between variables and between their percentage changes at 2 and 12 months after BPD are reported in Tables 2 and 3 (only statistically significant data are reported). BMI values were uncorrelated with serum ghrelin level, positively associated with HOMA IR data at every time-point, and positively OBESITY RESEARCH Vol. 12 No. 4 April 2004

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Table 2. Association (Kendall z values) of BMI vs. serum leptin and ghrelin concentrations and HOMA IR values at 2 and 12 months after BPD Variables BMI vs. Ghrelin Leptin HOMA IR

Prior to BPD

1.936*

2 Months after BPD

2.07† 3.06§

12 Months after BPD

2.48‡ 1.95*

Only statistically significant data are reported. * p ⬍ 0.05. † p ⬍ 0.03. ‡ p ⬍ 0.01. § p ⬍ 0.002.

related to serum leptin concentration only at 2 and 12 months after BPD (Table 2). The postoperative changes in serum ghrelin concentration were negatively correlated to the postoperative changes in HOMA IR data at 2 and 12 months and positively related to postoperative changes in serum leptin concentration only at 12 months after BPD.

Discussion As expected, BPD was followed by a marked decrease of BW and BMI values. This drop in body mass is accompanied by a progressive reduction of serum leptin concentration and by a gradual improvement toward normalization of insulin sensitivity, as revealed by HOMA IR data. These results are in full agreement with the literature and are the outcome of both the decrease of body mass and adipose tissue size and the new anatomo-functional conditions of the upper gastrointestinal tract resulting from the operation (11–14). In contrast, a slow increase of serum ghrelin concentration was observed: Values at 2 months after BPD were substantially similar to those measured preoperatively, whereas at 12 months, they were significantly higher than initial readings. The values observed after BPD were similar to those observed by Holdstock et al. after gastric bypass surgery (8). It has been postulated that a decrease in serum ghrelin concentration, putatively curbing appetite and thereby leading to a reduction of food intake, might contribute to the weight loss after gastric bypass for obesity (7). However, longitudinal data have demonstrated a marked increase of serum ghrelin concentration after gastric bypass (8), thus challenging this hypothesis. Serum ghrelin level rises sharply in response to a reduction of food intake and to a negative energy balance (3,4); therefore, it could be specu686


Table 3. Association (Kendall z values) of percentage changes (⌬) in serum ghrelin concentration vs. percentage changes (⌬) in serum leptin concentration and in HOMA IR values at 2 and 12 months following BPD

⌬ Ghrelin vs. ⌬ Leptin ⌬ HOMA IR

2 Months after BPD

12 Months after BPD

⫺2.55‡

1.89* ⫺2.13§

Only statistically significant data are reported. * p ⬍ 0.05. § p ⬍ 0.03. ‡ p ⬍ 0.01.

lated that the postoperative increase in ghrelin levels simply reflects the diminished food consumption due to gastric bypass. However, this assumption is contradicted by the findings obtained in this study after BDP: in the 1-year post-BPD subjects, a rise of serum ghrelin concentration corresponded to a maintained or even increased food intake. Therefore, these results point to the absence of any clear relationship between food intake and serum ghrelin concentration after gastrointestinal surgery for obesity. The findings of this study do support an interaction between ghrelin and insulin action. In fact, although absolute serum ghrelin concentration and HOMA IR values were negatively correlated only at 12 months after BPD, the postoperative changes occurring in serum ghrelin concentration were negatively related to the postoperative changes in HOMA IR values at 2 and 12 months. These findings are in line with the results obtained in obese subjects (5,6), in anorectic patients (15), and in postgastric bypass patients (8) and support the close physiological relationship between ghrelin and insulin. A recent study in humans showed that insulin infusion causes a decrease in serum ghrelin level, prompting the suggestion that insulin might dynamically modulate ghrelin production (16). Therefore, it can be hypothesized that the postoperative increase of serum ghrelin levels could be accounted for by the marked improvement in insulin sensitivity, with the corresponding reduction of insulin secretion occurring after BPD (9,10,14). The statistically significant association between postBPD changes in serum ghrelin concentration, and the changes in the serum leptin observed at 12 months after the operation parallels the postoperative correlations seen in gastric bypass patients (8). This finding lends additional support to the hypothesis that ghrelin may contribute, with insulin and leptin, to a still poorly understood adipose tissue regulatory system, which may be impaired in obesity.


In conclusion, the results of this study provide no evidence of a relationship between food intake and ghrelin levels after gastrointestinal surgery for obesity. In contrast, it is possible that the gradual postoperative increase in serum ghrelin concentration merely reflects changes in BW and in body fat mass and, therefore, corresponds to the achievement of a new state of energy balance. The changes occurring after BPD in the system of adipose tissue regulatory peptides could represent a metabolic resetting, which ultimately may lead to a reduction of the risk of diabetes and cardiovascular disease associated with obesity.

Acknowledgments No outside funding/support was provided for this study.

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