Role of the foregut in the early improvement in glucose tolerance and insulin sensitivity following Roux-en-Y gastric bypass surgery

Effects of bariatric surgery on adipokine-induced inflammation and insulin resistance

Over a third of the US population is obese and at high risk for developing type 2 diabetes, insulin resistance, and other metabolic disorders. Obesity is considered a chronic low-grade inflammatory condition that is primarily attributed to expansion and inflammation of adipose tissues. Indeed, adipocytes produce and secrete numerous proinflammatory and anti-inflammatory cytokines known as adipokines. When the balance of these adipokines is shifted toward higher production of proinflammatory factors, local inflammation within adipose tissues and subsequently systemic inflammation occur. These adipokines including leptin, visfatin, resistin, apelin, vaspin, and retinol binding protein-4 can regulate inflammatory responses and contribute to the pathogenesis of diabetes. These effects are mediated by key inflammatory signaling molecules including activated serine kinases such as c-Jun N-terminal kinase and serine kinases inhibitor κB kinase and insulin signaling molecules including insulin receptor substrates, protein kinase B (PKB, also known as Akt), and nuclear factor kappa B. Bariatric surgery can decrease body weight and improve insulin resistance in morbidly obese subjects. However, despite reports suggesting reduced inflammation and weight-independent effects of bariatric surgery on glucose metabolism, mechanisms behind such improvements are not yet well understood. This review article focuses on some of these novel adipokines and discusses their changes after bariatric surgery and their relationship to insulin resistance, fat mass, inflammation, and glucose homeostasis.

Menin and GIP are inversely regulated by food intake and diet via PI3/AKT signaling in the proximal duodenum

Background and Aims:

Ingestion of food stimulates the secretion of incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 to ensure the proper absorption and storage of nutrients. Menin is the 67 kDa protein product of the MEN1 gene recently reported to have a role in metabolism. In this study, we will determine the regulation of menin in the proximal duodenum by food intake and diet in correlation with GIP levels in the proximal duodenum of mice after an 18 h fast followed by 4 and 7 h refeeding and 3 months of high-fat diet.

Methods:

A dual luciferase assay was used to determine GIP promoter activity and ELISA was used to measure the levels of GIP after inhibition of menin through small interfering RNA (siRNA) and exposure to MAPK and AKT inhibitors. Colocalization of menin and GIP were determined by immunofluorescence.

Results:

Menin and GIP expression are regulated by fasting, refeeding and diet in the proximal duodenum. Overexpression of menin in STC-1 cells significantly inhibited GIP mRNA and promoter activity, whereas menin siRNA upregulated GIP levels. Inhibition of GIP expression by the PI3/AKT inhibitor, LY294002, was abrogated in STC-1 cells with reduced menin levels, whereas the MAPK inhibitor, UO126, inhibited the expression of GIP independent of menin. Exposure of STC-1 cells to GIP reduced menin expression in a dose-dependent manner via PI3K-AKT signaling.

Conclusion:

Feeding and diet regulates the expression of menin, which inversely correlates with GIP levels in the proximal duodenum. In vitro assays indicate that menin is a negative regulator of GIP via inhibition of PI3K-AKT signaling. We show menin colocalizing with GIP in K cells of the proximal gut and hypothesize that downregulation of menin may serve as a mechanism by which GIP is regulated in response to food intake and diet.

GLP-1 response to a mixed meal: what happens 10 years after Roux-en-Y gastric bypass (RYGB)?

BACKGROUND

Oral meal consumption increases glucagon-like peptide 1 (GLP-1) release which maintains euglycemia by increasing insulin secretion. This effect is exaggerated during short-term follow-up of Roux-en-y gastric bypass (RYGB). We examined the durability of this effect in patient with type 2 diabetes (T2DM) >10 years after RYGB.

METHODS

GLP-1 response to a mixed meal in the 10-year post-RYGB group (n = 5) was compared to lean (n = 9), obese (n = 6), and type 2 diabetic (n = 10) controls using a cross-sectional study design. Analysis of variance (ANOVA) was used to evaluate GLP-1 response to mixed meal consumption from 0 to 300 min, 0-20 min, 20-60 min, and 60-300 min, respectively. Weight, insulin resistance, and T2DM were also assessed.

RESULTS

GLP-1 response 0-300 min in the 10-year post-RYGB showed a statistically significant overall difference (p =  0.01) compared to controls. Furthermore, GLP-1 response 0-20 min in the 10-year post-RYGB group showed a very rapid statistically significant rise (p = 0.035) to a peak of 40 pM. GLP-1 response between 20 and 60 min showed a rapid statistically significant (p = 0.041) decline in GLP-1 response from ~40 pM to 10 pM. GLP-1 response in the 10-year post-RYGB group from 60 to 300 min showed no statistically significant difference from controls. BMI, HOMA, and fasting serum glucose before and >10 years after RYGB changed from 59.9 → 40.4, 8.7 → 0.88, and 155.2 → 87.6 mg/dl, respectively, and were statistically significant (p < 0.05).

CONCLUSIONS

An exaggerated GLP-1 response was noted 10 years after RYGB, strongly suggesting a durability of this effect. This phenomenon may play a key role in maintaining type 2 diabetes remission and weight loss after RYGB.

Comparable early changes in gastrointestinal hormones after sleeve gastrectomy and Roux-En-Y gastric bypass surgery for morbidly obese type 2 diabetic subjects

BACKGROUND

Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGBP) are associated with similar type 2 diabetes mellitus (T2DM) resolution rates for morbidly obese subjects. However, the mechanisms underlying the resolution of T2DM after SG have not been clarified to date. This study aimed to compare the early changes in gastrointestinal hormones involved in insulin and glucagon secretion in morbidly obese T2DM subjects undergoing SG or RYGBP.

METHODS

This prospective study investigated 12 subjects with T2DM who had undergone SG (n = 6) or RYGBP (n = 6). Five body mass index (BMI)-matched obese non-diabetic subjects and five BMI-matched obese diabetic subjects served as control subjects. Glucose, insulin, glucagon, glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and GLP-2 were determined after a standardized mixed liquid meal before surgery and 6 weeks afterward.

RESULTS

After 6 weeks, five of the six subjects in each surgical group presented with T2DM remission, although the area under the curve (AUC)0–120 of glucose was greater than that of the non-diabetic control subjects (P < 0.01). Postsurgically, the indices of insulin and glucagon secretion were comparable between the two surgical groups. The AUC0–120 of GLP-1 (P < 0.05) and GLP-2 (P < 0.05) was significantly and comparably enlarged after SG and RYGB. The postsurgical GIP response was significantly associated with the glucagon response throughout the meal test (ρ = 0.747; P < 0.01).

CONCLUSIONS

The data show that in a cohort of morbidly obese T2DM subjects, SG and RYGBP are associated with an early improvement in glucose tolerance, similar changes in insulin and glucagon secretion, and a similar GLP-1, GIP, and GLP-2 response to a standardized mixed liquid meal.

Non-systemic drugs: a critical review

Non-systemic drugs act within the intestinal lumen without reaching the systemic circulation. The first generation included polymeric resins that sequester phosphate ions, potassium ions, or bile acids for the treatment of electrolyte imbalances or hypercholesteremia. The field has evolved towards non-absorbable small molecules or peptides targeting luminal enzymes or transporters for the treatment of mineral metabolism disorders, diabetes, gastrointestinal (GI) disorders, and enteric infections. From a drug design and development perspective, non-systemic agents offer novel opportunities to address unmet medical needs while minimizing toxicity risks, but also present new challenges, including developing a better understanding and control of non-transcellular leakage pathways into the systemic circulation. The pharmacokinetic-pharmacodynamic relationship of drugs acting in the GI tract can be complex due to the variability of intestinal transit, interaction with chyme, and the complex environment of the surface epithelia. We review the main classes of nonabsorbable agents at various stages of development, and their therapeutic potential and limitations. The rapid progress in the identification of intestinal receptors and transporters, their functional characterization and role in metabolic and inflammatory disorders, will undoubtedly renew interest in the development of novel, safe, non-systemic therapeutics.

Ileal interposition with sleeve gastrectomy for treatment of type 2 diabetes mellitus

AIM

Combination of laparoscopic ileal interposition (II) with sleeve gastrectomy (SG) is an upcoming procedure, which offers good metabolic improvement and weight reduction without causing significant malabsorption. The objective of this study was to evaluate the results of this novel procedure for control of type 2 diabetes, obesity, hypertension, and related metabolic abnormalities.

MATERIALS AND METHODS

The II and SG was performed in 43 patients (M:F = 25:18) from February 2008. Participants had a mean age of 47.2 ± 8.2 years (range 29-66 years), mean duration of diabetes of 10.1 ± 9.2 years (range 1-32 years), and mean preoperative body mass index (BMI) of 33.2 ± 7.8 kg/m2. All patients had poorly controlled type 2 diabetes mellitus (DM) [mean glycated hemoglobin (HbA1C) 9.6 ± 2.1%] despite use of oral hypoglycemic agents (OHAs) and/or insulin. Thirty (70%) patients had hypertension, 20 (46%) had dyslipidemia, and 18 (42%) had significant microalbuminuria. The primary outcome was remission of diabetes (HbA1C < 6.5% without OHAs/insulin) and the secondary outcomes were reduction in antidiabetic agent requirement and components of metabolic syndrome.

RESULTS

Mean follow-up was for 20.2 ± 8.6 months (range 4-40 months). Postoperatively, glycemic parameters (fasting and post-lunch blood sugar, HbA1C improved in all patients (P < 0.05) at all intervals. Twenty (47%) patients had remission in diabetes and the remaining patients showed significantly decreased OHA requirement. All patients had weight loss between 15 and 30% (P < 0.05). Twenty-seven (90%) patients had remission in hypertension. At 3 years, the mean fall in HbA1C (34%) was more than reduction in BMI (25%). There was a declining trend in lipids and microalbuminuria postoperatively, though it was significant for microalbuminuria only.

CONCLUSIONS

The laparoscopic II with SG seems to be a promising procedure for control of type 2 DM, hypertension, weight reduction, and associated metabolic abnormalities. A multicenter study with larger number of patients and a longer follow-up period is needed to substantiate our preliminary findings.

Laparoscopic ileal interposition with diverted sleeve gastrectomy for treatment of type 2 diabetes

OBJECTIVE

The objective of the present study was to prospectively evaluate the results of laparoscopic ileal interposition (II) with diverted sleeve gastrectomy (DSG) for control of T2DM and related metabolic abnormalities.

METHODS

All patients underwent II +DSG. They had T2DM≥5 years with poor glycemic control despite adequate dosage of oral hypoglycemic agents (OHAs) and/or insulin. The primary outcome was remission of diabetes (HbA1C<6.5% without OHAs/insulin), and secondary outcomes were reduction in antidiabetic agent requirement and components of metabolic syndrome.

RESULTS

We report the preliminary postoperative follow-up data of 9.1±5.3 months (range: 3-21 months). There were 17 patients (male:female=12:5) with mean age of 50.7±8.1 (range, 34-66 years), duration of diabetes of 15.1±5.8 years (range, 5-30 years), and preoperative body mass index of 29.2±7.5 kg/m(2)(range, 22.4-37.5 kg/m(2)). Eight patients (45%) had hypertension, while dyslipidemia and microalbuminuria was present in 7 patients (39%) each. Twelve patients (70.5%) had diabetes remission. Seven/eight (87.5%) patients had remission in hypertension. All participants had weight loss ranging between 15% and 30%. Postoperatively statistically significant decline was observed in the glycemic and lipid parameters, microalbuminuria at all intervals (p<0.05). Two patients had vitamin B12 deficiency 1 year after surgery.

CONCLUSION

Ileal interposition combined with DSG addresses both foregut and hindgut theories and brings about remissions in T2DM patients with reasonable safety. Our preliminary observations demonstrated the feasibility and efficacy of this novel surgical procedure as a promising option in T2DM.

Mechanisms of improved glycaemic control after Roux-en-Y gastric bypass

Roux-en-Y gastric bypass (RYGB) greatly improves glycaemic control in morbidly obese patients with type 2 diabetes, in many even before significant weight loss. Understanding the responsible mechanisms may contribute to our knowledge of the pathophysiology of type 2 diabetes and help identify new drug targets or improve surgical techniques. This review summarises the present knowledge based on pathophysiological studies published during the last decade. Taken together, two main mechanisms seem to be responsible for the early improvement in glycaemic control after RYGB: (1) an increase in hepatic insulin sensitivity induced, at least in part, by energy restriction and (2) improved beta cell function associated with an exaggerated postprandial glucagon-like peptide 1 secretion owing to the altered transit of nutrients. Later a weight loss induced improvement in peripheral insulin sensitivity follows.

Current evidence for a role of GLP-1 in Roux-en-Y gastric bypass-induced remission of type 2 diabetes

Weight-reducing surgical procedures such as Roux-en-Y gastric bypass (RYGB) have proven efficient as means of decreasing excess body weight. Furthermore, some studies report that up to 80% of patients with type 2 diabetes mellitus (T2DM) undergoing RYGB experience complete remission of their T2DM. Interestingly, the majority of remissions occur almost immediately following the operation and long before significant weight loss has taken place. Following RYGB, dramatic increases in postprandial plasma concentrations of the incretin hormone glucagon-like peptide-1 (GLP-1) have been recorded, and the known antidiabetic effects of GLP-1 are thought to be key mediators in RYGB-induced remission of T2DM. However, the published studies on the impact of RYGB on GLP-1 secretion are few, small and often not controlled properly. Furthermore, mechanistic studies delineating the role of endogenous GLP-1 secretion in RYGB-induced remission of T2DM are lacking. This article critically evaluates the current evidence for a role of GLP-1 in RYGB-induced remission of T2DM.

Insulin resistance and bariatric surgery

The objective of this article is to systematically review the changes in insulin resistance after various types of bariatric surgical procedures. A Pubmed and EMBASE search for studies measuring insulin resistance before and after bariatric surgery was done and all original research articles from 1980 to present (2011) were included. Only the currently widely performed bariatric procedures were included. A meta-analysis of change in HOMA-IR was conducted, grouping studies with similar duration of follow-up. The percentage decrease in HOMA-IR at <=2 weeks, 1 month, 3 months, 6 months, 12 months and >16-18 months was found to be (mean ± standard error) -33.48 ± 5.78, -46.43 ± 6.99, -38.79 ± 9.64, -58.62 ± 7.38, -44.91 ± 7.98 and -67.04 ± 10.78%, respectively. RYGB (gastric bypass) and BPD (biliopancreatic diversion) produced a significant decrease in insulin resistance at 2 weeks after surgery, while LSG (sleeve gastrectomy) was strongly trending. LSG produced an earlier decrease in insulin resistance when compared to LAGB (gastric banding). RYGB, BPD and LSG produce an early decrease in insulin resistance through yet unknown mechanisms.

Leucine signaling in the pathogenesis of type 2 diabetes and obesity

Epidemiological evidence points to increased dairy and meat consumption, staples of the Western diet, as major risk factors for the development of type 2 diabetes (T2D). This paper presents a new concept and comprehensive review of leucine-mediated cell signaling explaining the pathogenesis of T2D and obesity by leucine-induced over-stimulation of mammalian target of rapamycin complex 1 (mTORC1). mTORC1, a pivotal nutrient-sensitive kinase, promotes growth and cell proliferation in response to glucose, energy, growth factors and amino acids. Dairy proteins and meat stimulate insulin/insulin-like growth factor 1 signaling and provide high amounts of leucine, a primary and independent stimulator for mTORC1 activation. The downstream target of mTORC1, the kinase S6K1, induces insulin resistance by phosphorylation of insulin receptor substrate-1, thereby increasing the metabolic burden of β-cells. Moreover, leucine-mediated mTORC1-S6K1-signaling plays an important role in adipogenesis, thus increasing the risk of obesity-mediated insulin resistance. High consumption of leucine-rich proteins explains exaggerated mTORC1-dependent insulin secretion, increased β-cell growth and β-cell proliferation promoting an early onset of replicative β-cell senescence with subsequent β-cell apoptosis. Disturbances of β-cell mass regulation with increased β-cell proliferation and apoptosis as well as insulin resistance are hallmarks of T2D, which are all associated with hyperactivation of mTORC1. In contrast, the anti-diabetic drug metformin antagonizes leucine-mediated mTORC1 signaling. Plant-derived polyphenols and flavonoids are identified as natural inhibitors of mTORC1 and exert anti-diabetic and anti-obesity effects. Furthermore, bariatric surgery in obesity reduces increased plasma levels of leucine and other branched-chain amino acids. Attenuation of leucine-mediated mTORC1 signaling by defining appropriate upper limits of the daily intake of leucine-rich animal and dairy proteins may offer a great chance for the prevention of T2D and obesity, as well as other epidemic diseases of civilization with increased mTORC1 signaling, especially cancer and neurodegenerative diseases, which are frequently associated with T2D.