Gastrectomy with Roux-en-Y reconstruction as a lean model of bariatric surgery

Abstract

BackgroundAltered enteroendocrine hormone responses are widely believed to underlie the beneficial effects of bariatric surgery in type 2 diabetes. While elevated postprandial glucagon-like peptide-1 (GLP-1) is considered one of the mediators, increased postprandial glucagon levels have recently been implicated.ObjectivesWe investigated hormonal responses in lean patients after prophylactic total gastrectomy (PTG), as a model of Roux-en-Y gastric bypass without the confounding effects of obesity or massive weight loss.SettingUniversity hospital, United Kingdom.MethodsTen participants after PTG and 9 healthy volunteers were recruited for oral glucose tolerance tests. Plasma glucose, insulin, GLP-1, peptide YY, glucose-dependent insulinotropic-polypeptide, glucagon, oxyntomodulin, glucagon(1-61), and glicentin levels were assessed using immunoassays and/or mass spectrometry.ResultsPTG participants exhibited accelerated plasma glucose appearance, followed, in 3 of 10 cases, by hypoglycemia (<3 mM glucose). Plasma GLP-1, peptide YY, glucose-dependent insulinotropic-polypeptide, glicentin, and oxyntomodulin responses were elevated, and glucagon appeared to rise in PTG participants when measured with a glucagon-specific enzyme-linked immunosorbent assay. We revisited the specificity of this assay, and demonstrated significant cross-reactivity with glicentin and oxyntomodulin at concentrations observed in PTG plasma. Reassessment of glucagon with the same assay using a modified protocol, and by liquid chromatography-mass spectrometry, demonstrated suppression of glucagon secretion after oral glucose tolerance tests in both PTG and control cohorts.ConclusionsCare should be taken when assessing glucagon levels in the presence of elevated plasma levels of other proglucagon products. Substantial elevation of GLP-1 and insulin responses after PTG likely contribute to the observed hypoglycemia, and mirror similar hormone levels and complications observed in bariatric weight loss patients.

Mass spectrometric characterisation of the circulating peptidome following oral glucose ingestion in control and gastrectomised patients

“…However, where immunoassay data were available, the LC-MS peak area ratios for post-OGTT gut hormone levels in the gastrectomy group correlated well with immunoassay-derived concentrations. This indicates that the developed method is inherently quantitative, and is therefore applicable for the further development of fully quantitative studies using peptide standards and stable isotope labelled internal standards 10 . Arguably, our results suggest that nano LC-MS approaches are well suited for monitoring multiple peptides in parallel in small plasma samples.…”

“…Experiments were performed on plasma samples from a published study, which have previously been analysed by immunoassay for a range of gut and pancreatic peptides 10 . The study was approved by the National Health Service Research Ethics Committee and conducted in accordance with the ethical standards of the Helsinki Declaration of 1975.…”

“…Immunoassays on these samples have been described previously 10 . In brief, total GLP-1, total GIP and total PYY were measured using Mesoscale Discovery (MesoScale Diagnostics, Rockville, USA) assays according to the manufacturer's instructions.…”

“…The potential for LC-MS based methods to quantify peptides has been demonstrated previously, for example for proglucagon-derived peptides either following immuno-affinity based enrichment 9 or after depletion of abundant plasma proteins through solvent precipitation followed by solid phase extraction (SPE) 10 . Whilst these approaches have demonstrated good sensitivity and good correlation with existing immunoassays, they used targeted approaches with triple quadrupole based detection systems, requiring prior knowledge of the analyte under investigation.…”

Mechanisms for the metabolic success of bariatric surgery

“…In the pancreas, predominant expression of proconvertase 2 leads to preproglucagon processing to produce glucagon. Although some studies have reported an increase in postprandial glucagon after RYGB, a later study suggested that this work was confounded by the fact that RYGB causes large increases glicentin, another preproglucagon peptide that has increasing cross‐reactivity with standard glucagon enzyme‐linked immunosorbent assays with increasing plasma concentrations . Thus, more research is needed from independent groups utilising sensitive and specific assays to determine whether glucagon is increased with surgery or not.…”