plasma leptin concentrations and esophageal hypomotility in obese patients

1Department of Gastroenterology and 2Endocrinology, Centre Hospitalier de l’Université de Montréal (CHUM); 3Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec Correspondence: Dr Mickael Bouin, Gastroenterology Department, CHUM, St-Luc, 1058 St-Denis, Montreal, Quebec H2X 3J4. Telephone 514-890-8000, e-mail mickael.bouin@umontreal.ca Received for publication July 18, 2014. Accepted November 7, 2014 Obesity is asociated with several metabolic, cardiovascular, respiratory and locomotor disorders (1). Regarding the digestive system, obesity is recognized as a risk factor for cholelithiasis, nonalcoholic steatohepatitis, colorectal cancer and gastroesophageal reflux disease. Esophageal motor disorders were documented in more than one-half of obese subjects evaluated in a previous report by our group (2), as well as in other reports in the literature (3,4), in which esophageal body hypomotility was the most prevalent abnormality, regardless of upper gastrointestinal symptoms, comorbidities or medications. The cause of this phenomenon remains unknown. An association between leptin and gastrointestinal motility disorders may explain this phenomenon. Leptin, a hormone largely derived from adipose tissue, increases satiety and modulates energy balance (5). Basal leptin concentrations vary according to sex, weight and the time of day (6). Elevated leptin levels have been demonstrated in the obese population (7). It is known that leptin receptors at the blood-brain barrier are saturated and that the response of hypothalamic cells to leptin is decreased in obese patients. As a result, leptin in these patients cannot regulate satiety and modulate energy balance. In animal studies, leptin decreased gastric emptying and small intestinal motility (8-10). Leptin receptors located at the afferent and efferent vagus nerve endings are a possible explanation. A positive feedback has been proposed between leptin and the hormone cholecystokinin, which is known to inhibit pyloric relaxation and decrease gastric emptying (11). Jorge et al (12) reported that high levels of leptin were related to an increase in wave amplitude in the middle and distal esophagus in diabetic patients. In the present study, we tested the hypothesis that obese patients with esophageal dysmotilities have higher serum leptin concentrations than obese patients with a normal motility profile. ORiginal aRTicle

that leptin receptors at the blood-brain barrier are saturated and that the response of hypothalamic cells to leptin is decreased in obese patients.As a result, leptin in these patients cannot regulate satiety and modulate energy balance.
In animal studies, leptin decreased gastric emptying and small intestinal motility (8)(9)(10).Leptin receptors located at the afferent and efferent vagus nerve endings are a possible explanation.A positive feedback has been proposed between leptin and the hormone cholecystokinin, which is known to inhibit pyloric relaxation and decrease gastric emptying (11).Jorge et al (12) reported that high levels of leptin were related to an increase in wave amplitude in the middle and distal esophagus in diabetic patients.
In the present study, we tested the hypothesis that obese patients with esophageal dysmotilities have higher serum leptin concentrations than obese patients with a normal motility profile.

METHODS
The present analysis was a prospective study conducted at the University of Montreal Hospital Centre (Montreal, Quebec), from September 2011 to December 2012.The present study adhered to the Helsinki declaration and was approved by the Ethics Committee of University of Montreal Hospital Centre.

Patients
All patients undergoing preoperative evaluation for bariatric surgery were referred for inclusion in a study protocol investigating preoperative esophageal motility.The inclusion criteria were: body mass index (BMI) ≥30 kg/m 2 ; between 18 and 70 years of age; and without risk for pregnancy.Exclusion criteria were inability to provide free and informed consent, or refusal to participate.

Esophageal manometry
High-resolution manometry (InSIGHT g3, Sandhill Scientific, USA) was performed by a single technician and the results interpreted by one gastroenterologist specialized in digestive motility disorders.Esophageal manometry was performed according to a standardized protocol.
Manometric measurements were made after 10 swallows of 5 mL of saline water while supine.The following measurements were recorded: upper esophageal sphincter -upper esophageal sphincter pressure (mmHg) and coordination of sphincter (%); esophageal body -presence of effective contractions (%), peristaltic waves (%), duration of contractions(s), proximal and distal wave of contraction's amplitude (mmHg) and type of contraction waves (primary, secondary or tertiary); and lower esophageal sphincter (LES) -location of the sphincter (cm), LES pressure (mmHg), residual pressure of the LES (mmHg) and relaxation percentage (%).Normal values corresponded with recognized international standards (13).

Questionnaires
Two standardized questionnaires were administered to patients after manometry was performed.Data regarding upper gastrointestinal symptoms, epidemiology, comorbidities and medication were collected.A review of the medical record was performed to complete the research data.

Leptin
The measurement of plasma leptin levels was performed using a standardized protocol.The patient fasted ≥8 h before esophageal manometry and a blood sample was drawn.Blood samples were centrifuged and stored at −80°C.Plasma leptin levels were measured using radioimmunoassay (Human Leptin RIA kit, Millipore, USA).
Fasting plasma levels of leptin are variable in the general population, with sex and BMI the most recognized factors for this variation.The normal distribution of basal plasma leptin is usually obtained according to the following formulas ( 6 To take into account these variables and eliminate possible anthropomorphic bias (ie, sex and BMI), a corrected leptin score for each patient was obtained as a ratio of the raw leptin value for the patient divided by the normal predicted value according to sex and BMI.
Using the Wilcoxon test, plasma leptin levels and leptin corrected scores in patient groups with esophageal dysmotility were compared with patients with a normal motility profile.

RESULTS
Seventeen patients (13 female) were included.The mean (± SD) age was 40±10 years and the mean BMI was 46±7 kg/m 2 .Esophageal manometry detected dysmotility in 47% (n=8) of the patients; esophageal body hypomotility was found in 63% (n=5) of these patients.Following these results, groups with and without esophageal dysmotility were compared.Epidemiological data, medication(s) and comorbidities showed no statistically significant differences (Table 1).
Mean basal leptin levels were higher in the group with dysmotility (45.39 ng/mL) than in the group without dysmotility (40.78 ng/mL) (Figure 1) but failed to reach statistical significance (P=0.88).
Corrected leptin scores, taking into account the known factors of plasma leptin variations, were higher in the group with esophageal dysmotility than in the group without dysmotility (99% versus 66% of the predicted value [P≤0.05])(Figure 2).

DISCUSSION
Leptin concentrations were higher in obese patients with esophageal dysmotility than in those without esophageal dysmotility.This is in agreement with our starting hypothesis and supports a possible role for leptin in the etiology of esophageal hypomotility in obese patients.Raw leptin values were higher in the eosophageal dysmotility group but were not statistically significant.This statistical result is not surprising given that plasma leptin levels vary according to sex and BMI.However, the corrected leptin scores (raw leptin value/predicted leptin value), which eliminate potential biases, revealed a clear statistical increase in plasma leptin in obese patients with esophageal dysmotility.
Two patients had previously undergone bariatric surgery.Because leptin is derived from adipose tissue and not gastric mucosa, we do not believe that leptin values in obese patients, even if they have undergone previous bariatric surgery, would be altered.
Esophageal dysmotility was reported in approximately 50% of obese patients in our previous study (2).The majority (85%) of these patients had esophageal body hypomotility.In the current study, we found a similar prevalence of esophageal dysmotility (47%) and the majority had esophageal body hypomotility.The clinical relevance of these motor disturbances was discussed in our previous report (2).
The rationale linking increased plasma leptin levels with decreased esophageal motility is based on the fact that endogenous leptin is now known to be increased in the plasma of obese patients with esophageal dysmotility, and that exogenous leptin administration decreased gastrointestinal motility in animal models testing this hypothesis (10).We believe that leptin may belong to a digestive physiology feedback in the context of esophageal motility.We know that leptin is produced by adipose tissue in a linear fashion, and that leptin receptors are located at the afferent and efferent vagus nerve endings.Thus, an increase in leptin level could lead to earlier satiety and esophageal dysmotility to modulate energy balance.We are not aware of any studies investigating the biological effect of leptin on esophageal or digestive motility in human subjects.Further research is needed to confirm the contribution of leptin to esophageal dysmotility in obese patients.

DISCLOSURES:
The authors have no financial disclosures or conflicts of interest to declare.

CONCLUSION
Esophageal hypomotility is prevalent in obese patients; however, its cause remains unknown.Leptin has been shown to decrease gastric emptying and intestinal motility in animal models.The present study showed higher leptin concentrations in obese patients with esophageal dysmotility than in those without esophageal dysmotility.Results of the present study support a possible role for leptin in the etiology of esophageal hypomotility in obese patients.

Figure 1 )
Figure 1) Basal plasma leptin values in obese patients with and without esophageal dysmotility.P Not significant

Figure 2 )
Figure 2) Corrected leptin scores (raw value/predicted value) in obese patients with and without esophageal dysmotility.P≤0.05