Evaluating the mechanisms of improved glucose homeostasis after bariatric surgery in Ossabaw miniature swine

BACKGROUND

Roux-en-Y gastric bypass (RYGB) is the most common bariatric operation; however, the mechanism underlying the profound weight-independent effects on glucose homeostasis remains unclear. Large animal models of naturally occurring insulin resistance (IR), which have been lacking, would provide opportunities to elucidate such mechanisms. Ossabaw miniature swine naturally exhibit many features that may be useful in evaluating the anti diabetic effects of bariatric surgery.

METHODS

Glucose homeostasis was studied in 53 Ossabaw swine. Thirty-two received an obesogenic diet and were randomized to RYGB, gastrojejunostomy (GJ), gastrojejunostomy with duodenal exclusion (GJD), or Sham operations. Intravenous glucose tolerance tests and standardized meal tolerance tests were performed prior to, 1, 2, and 8 weeks after surgery and at a single time-point for regular diet control pigs.

RESULTS

High-calorie-fed Ossabaws weighed more and had greater IR than regular diet controls, though only 70% developed IR. All operations caused weight-loss-independent improvement in IR, though only in pigs with high baseline IR. Only RYGB induced weight loss and decreased IR in the majority of pigs, as well as increasing AUCinsulin/AUCglucose.

CONCLUSIONS

Similar to humans, Ossabaw swine exhibit both obesity-dependent and obesity-independent IR. RYGB promoted weight loss, IR improvement, and increased AUCinsulin/AUCglucose, compared to the smaller changes following GJ and GJD, suggesting a combination of upper and lower gut mechanisms in improving glucose homeostasis.

Ghrelin increases the motivation to eat, but does not alter food palatability

Homeostatic eating cannot explain overconsumption of food and pathological weight gain. A more likely factor promoting excessive eating is food reward and its representation in the central nervous system (CNS). The anorectic hormones leptin and insulin reduce food reward and inhibit related CNS reward pathways. Conversely, the orexigenic gastrointestinal hormone ghrelin activates both homeostatic and reward-related neurocircuits. The current studies were conducted to identify in rats the effects of intracerebroventricular ghrelin infusions on two distinct aspects of food reward: hedonic valuation (i.e., "liking") and the motivation to self-administer (i.e., "wanting") food. To assess hedonic valuation of liquid food, lick motor patterns were recorded using lickometry. Although ghrelin administration increased energy intake, it did not alter the avidity of licking (initial lick rates or lick-cluster size). Several positive-control conditions ruled out lick-rate ceiling effects. Similarly, when the liquid diet was hedonically devalued with quinine supplementation, ghrelin failed to reverse the quinine-associated reduction of energy intake and avidity of licking. The effects of ghrelin on rats' motivation to eat were assessed using lever pressing to self-administer food in a progressive-ratio paradigm. Ghrelin markedly increased motivation to eat, to levels comparable to or greater than those seen following 24 h of food deprivation. Pretreatment with the dopamine D1 receptor antagonist SCH-23390 eliminated ghrelin-induced increases in lever pressing, without compromising generalized licking motor control, indicating a role for D1 signaling in ghrelin's motivational feeding effects. These results indicate that ghrelin increases the motivation to eat via D1 receptor-dependent mechanisms, without affecting perceived food palatability.

Effects of gastric bypass surgery in patients with type 2 diabetes and only mild obesity

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) ameliorates type 2 diabetes in severely obese patients through mechanisms beyond just weight loss, and it may benefit less obese diabetic patients. We determined the long-term impact of RYGB on patients with diabetes and only class I obesity.

RESEARCH DESIGN AND METHODS

Sixty-six consecutively selected diabetic patients with BMI 30-35 kg/m(2) underwent RYGB in a tertiary-care hospital and were prospectively studied for up to 6 years (median 5 years [range 1-6]), with 100% follow-up. Main outcome measures were safety and the percentage of patients experiencing diabetes remission (HbA(1c) <6.5% without diabetes medication).

RESULTS

Participants had severe, longstanding diabetes, with disease duration 12.5 ± 7.4 years and HbA(1c) 9.7 ± 1.5%, despite insulin and/or oral diabetes medication usage in everyone. For up to 6 years following RYGB, durable diabetes remission occurred in 88% of cases, with glycemic improvement in 11%. Mean HbA(1c) fell from 9.7 ± 1.5 to 5.9 ± 0.1% (P < 0.001), despite diabetes medication cessation in the majority. Weight loss failed to correlate with several measures of improved glucose homeostasis, consistent with weight-independent antidiabetes mechanisms of RYGB. C-peptide responses to glucose increased substantially, suggesting improved β-cell function. There was no mortality, major surgical morbidity, or excessive weight loss. Hypertension and dyslipidemia also improved, yielding 50-84% reductions in predicted 10-year cardiovascular disease risks of fatal and nonfatal coronary heart disease and stroke.

CONCLUSIONS

This is the largest, longest-term study examining RYGB for diabetic patients without severe obesity. RYGB safely and effectively ameliorated diabetes and associated comorbidities, reducing cardiovascular risk, in patients with a BMI of only 30-35 kg/m(2).

Broad dissemination of plasmid-mediated quinolone resistance genes in sediments of two urban coastal wetlands

Contamination of soil and water with antibiotic-resistant bacteria may create reservoirs of antibiotic resistance genes that have the potential to negatively impact future public health through horizontal gene transfer. The plasmid-mediated quinolone resistance genes qnrA, qnrB, qnrS, qepA, and aac(6')-Ib-cr were detected by PCR amplification of metagenomic DNA from surface sediments of the Tijuana River Estuary, a sewage-impacted coastal wetland along the U.S.-Mexico border; sediments of Famosa Slough, a nearby urban wetland that is largely unaffected by sewage, contained only qnrB, qnrS, and qepA. The number of PCR-positive sites and replicates increased in both wetlands after rainfall. Real-time quantitative PCR revealed a significant increase (p < 0.0005) in qnrA abundance (copies per gram sediment or per 16S rDNA copy) in Tijuana River Estuary sediments immediately following rainfall, but no significant change was measured at Famosa Slough (p > 0.1). Nucleotide sequences of cloned qnrA amplicons were all affiliated with qnrA genes found on plasmids of clinical isolates with one exception that was most similar to the chromosomal qnrA gene found in Shewanella algae. Our results suggest that urban wetlands may become reservoirs of antibiotic resistance genes, particularly where wastewater is improperly managed.

Ghrelin suppresses glucose-stimulated insulin secretion and deteriorates glucose tolerance in healthy humans

OBJECTIVE

The orexigenic gut hormone ghrelin and its receptor are present in pancreatic islets. Although ghrelin reduces insulin secretion in rodents, its effect on insulin secretion in humans has not been established. The goal of this study was to test the hypothesis that circulating ghrelin suppresses glucose-stimulated insulin secretion in healthy subjects.

RESEARCH DESIGN AND METHODS

Ghrelin (0.3, 0.9 and 1.5 nmol/kg/h) or saline was infused for more than 65 min in 12 healthy patients (8 male/4 female) on 4 separate occasions in a counterbalanced fashion. An intravenous glucose tolerance test was performed during steady state plasma ghrelin levels. The acute insulin response to intravenous glucose (AIRg) was calculated from plasma insulin concentrations between 2 and 10 min after the glucose bolus. Intravenous glucose tolerance was measured as the glucose disappearance constant (Kg) from 10 to 30 min.

RESULTS

The three ghrelin infusions raised plasma total ghrelin concentrations to 4-, 15-, and 23-fold above the fasting level, respectively. Ghrelin infusion did not alter fasting plasma insulin or glucose, but compared with saline, the 0.3, 0.9, and 1.5 nmol/kg/h doses decreased AIRg (2,152 +/- 448 vs. 1,478 +/- 2,889, 1,419 +/- 275, and 1,120 +/- 174 pmol/l) and Kg (0.3 and 1.5 nmol/kg/h doses only) significantly (P < 0.05 for all). Ghrelin infusion raised plasma growth hormone and serum cortisol concentrations significantly (P < 0.001 for both), but had no effect on glucagon, epinephrine, or norepinephrine levels (P = 0.44, 0.74, and 0.48, respectively).

CONCLUSIONS

This is a robust proof-of-concept study showing that exogenous ghrelin reduces glucose-stimulated insulin secretion and glucose disappearance in healthy humans. Our findings raise the possibility that endogenous ghrelin has a role in physiologic insulin secretion, and that ghrelin antagonists could improve beta-cell function.

Metabolic surgery to treat type 2 diabetes: clinical outcomes and mechanisms of action

Several gastrointestinal (GI) operations that were designed to promote weight loss can powerfully ameliorate type 2 diabetes mellitus (T2DM). Although T2DM is traditionally viewed as a chronic, relentless disease in which delay of end-organ complications is the major treatment goal, GI surgery offers a novel endpoint: complete disease remission. Ample data confirm the excellent safety and efficacy of conventional bariatric operations-especially Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding-to treat T2DM in severely obese patients. Use of experimental procedures as well as conventional bariatric operations is increasingly being explored in less obese diabetic patients, with generally favorable results, although further assessment of risk:benefit profiles is needed. Mounting evidence indicates that certain operations involving intestinal diversions improve glucose homeostasis through varied mechanisms beyond reduced food intake and body weight, for example by modulating gut hormones. Research to elucidate such mechanisms should facilitate the design of novel pharmacotherapeutics and dedicated antidiabetes GI manipulations. Here we review evidence regarding the use and study of GI surgery to treat T2DM, focusing on available published reports as well as results from the Diabetes Surgery Summit (DSS) in Rome and the World Congress on Interventional Therapies for T2DM in New York City.

Comparison of competitive radioimmunoassays and two-site sandwich assays for the measurement and interpretation of plasma ghrelin levels

CONTEXT

Ghrelin, an endogenous ligand for the GH secretagogue receptor, is an orexigenic peptide hormone produced primarily by the stomach. Recent studies suggest significant differences in the specificity of currently available ghrelin assays.

OBJECTIVE

The aim of the study was to compare four ghrelin assays (two commercially available and two developed by our group) of differing specificity, each used on the same set of more than 800 plasma samples from a human study.

DESIGN

Thirteen volunteers were sampled every 20 min for 6 h after consumption of one of three isocaloric drinks consisting of either 80% fat, 80% carbohydrate, or 80% protein. The samples were assayed by RIA for total and active ghrelin, as well as by sandwich assays for acyl and des-acyl ghrelin. The ghrelin profiles for each individual were smoothed using a statistical algorithm to lessen the effects of pulsatility and noise.

RESULTS

The sandwich assays for acyl and des-acyl ghrelin yielded ghrelin values that were lower than those from the corresponding RIAs. The ghrelin profiles after nutrient ingestion were similar, yet key differences among the four assays were apparent; in particular, percentage changes were significantly greater in the sandwich assays.

CONCLUSIONS

The lower levels and greater relative changes in ghrelin values reported by the sandwich assays are consistent with greater assay specificity. When applied to the nutrient study, the sandwich assays were better able to distinguish the different responses to different nutrients than were the RIAs.

Endocrine mechanisms mediating remission of diabetes after gastric bypass surgery

Bariatric surgery is currently the most effective method to promote major, sustained weight loss. Roux-en-Y gastric bypass (RYGB), the most commonly performed bariatric operation, ameliorates virtually all obesity-related comorbid conditions, the most impressive being a dramatic resolution of type 2 diabetes mellitus (T2DM). After RYGB, 84% of patients with T2DM experience complete remission of this disease, and virtually all have improved glycemic control. Increasing evidence indicates that the impact of RYGB on T2DM cannot be explained by the effects of weight loss and reduced energy intake alone. Weight-independent antidiabetic actions of RYGB are apparent because of the very rapid resolution of T2DM (before weight loss occurs), the greater improvement of glucose homeostasis after RYGB than after an equivalent weight loss from other means, and the occasional development of very late-onset, pancreatic beta-cell hyperfunction. Several mechanisms probably mediate the direct antidiabetic impact of RYGB, including enhanced nutrient stimulation of L-cell peptides (for example, GLP-1) from the lower intestine, intriguing but still uncharacterized phenomena related to exclusion of the upper intestine from contact with ingested nutrients, compromised ghrelin secretion, and very probably other effects that have yet to be discovered. Research designed to prioritize these mechanisms and identify potential additional mechanisms promises to help optimize surgical design and might also reveal novel pharmaceutical targets for diabetes treatment.

Diabetes remission and reduced cardiovascular risk after gastric bypass in Asian Indians with body mass index <35 kg/m(2)

BACKGROUND

Roux-en-Y gastric bypass (RYGB) benefits patients with type 2 diabetes mellitus (T2DM) and a body mass index (BMI) >35 kg/m(2); however, its effectiveness in patients with T2DM and a BMI <35 kg/m(2) is unclear. Asian Indians have a high risk of T2DM and cardiovascular disease at relatively low BMI levels. We examined the safety and efficacy of RYGB in Asian Indian patients with T2DM and a BMI of 22-35 kg/m(2) in a tertiary care medical center.

METHODS

A total of 15 consecutive patients with T2DM and a BMI of 22-35 kg/m(2) underwent RYGB. The data were prospectively collected before surgery and at 1, 3, 6, and 9 months postoperatively.

RESULTS

Of the 15 patients, 8 were men and 7 were women (age 45.6 +/- 12 years). Their preoperative characteristics were BMI 28.9 +/- 4.0 kg/m(2), body weight 78.7 +/- 12.5 kg, waist circumference 100.2 +/- 6.8 cm, and duration of T2DM 8.7 +/- 5.3 years. At baseline, 80% of subjects required insulin, and 20% controlled their T2DM with oral hypoglycemic medication. The BMI decreased postoperatively by 20%, from 28.9 +/- 4.0 kg/m(2) to 23.0 +/- 3.6 kg/m(2) (P <.001). All antidiabetic medications were discontinued by 1 month after surgery in 80% of the subjects. At 3 months and thereafter, 100% were euglycemic and no longer required diabetes medication. The fasting blood glucose level decreased from 233 +/- 87 mg/dL to 89 +/- 12 mg/dL (P <.001), and the hemoglobin A1c decreased from 10.1% +/- 2.0% to 6.1% +/- 0.6% (P <.001). Their waist circumference, presence of dyslipidemia, and hypertension improved significantly. The predicted 10-year cardiovascular disease risk (calculated using the United Kingdom Prospective Diabetes Study equations) decreased substantially for fatal and nonfatal coronary heart disease and stroke. No mortality, major surgical morbidity, or excessive weight loss occurred.

CONCLUSION

RYGB safely and effectively eliminated T2DM in Asian Indians with a BMI <35 kg/m(2). Larger, longer term studies are needed to confirm this benefit.

Minireview: Hormonal and metabolic mechanisms of diabetes remission after gastrointestinal surgery

Bariatric surgery is the most effective available treatment for obesity. The most frequently performed operation, Roux-en-Y gastric bypass (RYGB), causes profound weight loss and ameliorates obesity-related comorbid conditions, especially type 2 diabetes mellitus (T2DM). Approximately 84% of diabetic patients experience complete remission of T2DM after undergoing RYGB, often before significant weight reduction. The rapid time course and disproportional degree of T2DM improvement after RYGB compared with equivalent weight loss from other interventions suggest surgery-specific, weight-independent effects on glucose homeostasis. Potential mechanisms underlying the direct antidiabetic impact of RYGB include enhanced nutrient stimulation of lower intestinal hormones (e.g. glucagon-like peptide-1), altered physiology from excluding ingested nutrients from the upper intestine, compromised ghrelin secretion, modulations of intestinal nutrient sensing and regulation of insulin sensitivity, and other changes yet to be fully characterized. Research aimed at determining the relative importance of these effects and identifying additional mechanisms promises not only to improve surgical design but also to identify novel targets for diabetes medications.

Circadian rhythm profiles in women with night eating syndrome

Night eating syndrome (NES) is characterized by evening hyperphagia and frequent awakenings accompanied by food intake. Patients with NES display a delayed circadian pattern of food intake but retain a normal sleep-wake cycle. These characteristics initiated the current study, in which the phase and amplitude of behavioral and neuroendocrine circadian rhythms in patients with NES were evaluated. Fifteen women with NES (mean age +/- SD, 40.8 +/- 8.7 y) and 14 control subjects (38.6 +/- 9.5 y) were studied in the laboratory for 3 nights, with food intake measured daily. Blood also was collected for 25 h (every 2 h from 0800 to 2000 h, and then hourly from 2100 to 0900 h) and assayed for glucose and 7 hormones (insulin, ghrelin, leptin, melatonin, cortisol, thyroid-stimulating hormone [TSH] and prolactin). Statistical analyses utilized linear mixed-effects cosinor analysis. Control subjects displayed normal phases and amplitudes for all circadian rhythms. In contrast, patients with NES showed a phase delay in the timing of meals, and delayed circadian rhythms for total caloric, fat, and carbohydrate intake. In addition, phase delays of 1.0 to 2.8 h were found in 2 food-regulatory rhythms-leptin and insulin-and in the circadian melatonin rhythm (with a trend for a delay in the circadian cortisol rhythm). In contrast, circulating levels of ghrelin, the primary hormone that stimulates food intake, were phase advanced by 5.2 h. The glucose rhythm showed an inverted circadian pattern. Patients with NES also showed reduced amplitudes in the circadian rhythms of food intake, cortisol, ghrelin, and insulin, but increased TSH amplitude. Thus, patients with NES demonstrated significant changes in the timing and amplitude of various behavioral and physiological circadian markers involved in appetite and neuroendocrine regulation. As such, NES may result from dissociations between central (suprachiasmatic nucleus) timing mechanisms and putative oscillators elsewhere in the central nervous system or periphery, such as the stomach or liver. Considering these results, chronobiologic treatments for NES such as bright light therapy may be useful. Indeed, bright light therapy has shown efficacy in reducing night eating in case studies and should be evaluated in controlled clinical trials.

Energy balance in congenital generalized lipodystrophy type I

Congenital generalized lipodystrophy type 1 (CGL-1) is characterized by an absence of adipose tissue and decreased serum leptin levels. Low leptin levels in CGL-1 support the claim that subjects are hypermetabolic and hyperphagic. The present study examines this claim. We determined 24-hour energy expenditure (24-h EE) (kilocalories) (n = 2) and resting metabolic rate (RMR) per kilogram of lean body mass (LBM) (n = 3) in CGL-1 and in 18 healthy control subjects. The 24-h EEs of control and subjects with CGL were compared with respect to kilocalories required per day relative to kilograms of LBM and with respect to RMR relative to kilograms of LBM. Fasting leptin, adiponectin, and 24-hour ghrelin levels were also measured in subjects with CGL-1. The 24-h EE per kilogram of LBM for the subjects with CGL-1 falls on the same regression line observed for this relationship in the controls. The RMR per kilogram of LBM in subjects with CGL-1 also was similar to that in controls. Both 24-h EE and RMR were quite increased when reported per kilogram of total body weight. Subjects with CGL-1 also have decreased fasting leptin and adiponectin hormone levels and no premeal ghrelin rise. People with CGL-1 have similar RMR and daily caloric requirements as healthy controls when these parameters are expressed as a function of LBM. Appetite-regulating hormone levels in CGL-1 suggest that multiple factors act to control appetite in these individuals.

Acyl and total ghrelin are suppressed strongly by ingested proteins, weakly by lipids, and biphasically by carbohydrates

CONTEXT

Ghrelin is an orexigenic hormone that can increase body weight. Its circulating levels increase before meals and are suppressed after food ingestion. Understanding the effects of specific types of ingested macronutrients on ghrelin regulation could facilitate the design of weight-reducing diets.

OBJECTIVE

We sought to understand how ingestion of carbohydrates, proteins, or lipids affect acyl (bioactive) and total ghrelin levels among human subjects, hypothesizing that lipids might suppress ghrelin levels less effectively than do either carbohydrates or proteins.

DESIGN

This was a randomized, within-subjects cross-over study.

SETTING

The study was conducted at a University Clinical Research Center.

PARTICIPANTS

There were 16 healthy human subjects included in the study.

INTERVENTIONS

Isocaloric, isovolemic beverages composed primarily of carbohydrates, proteins, or lipids were provided.

MAIN OUTCOME MEASURES

The magnitude of postprandial suppression of total and acyl ghrelin levels (measured with a novel acyl-selective, two-site ELISA) was determined.

RESULTS

All beverages suppressed plasma acyl and total ghrelin levels. A significant effect of macronutrient class on decremental area under the curve for both acyl and total ghrelin was observed; the rank order for magnitude of suppression was protein more than carbohydrate more than lipid. Total ghrelin nadir levels were significantly lower after both carbohydrate and protein, compared with lipid beverages. In the first 3 postprandial hours, the rank order for acyl and total ghrelin suppression was carbohydrate more than protein more than lipid. In the subsequent 3 h, there was a marked rebound above preprandial values of acyl and total ghrelin after carbohydrate ingestion alone.

CONCLUSIONS

These findings suggest possible mechanisms contributing to the effects of high-protein/low-carbohydrate diets to promote weight loss, and high-fat diets to promote weight gain.

Development of a porcine Roux-en-Y gastric bypass survival model for the study of post-surgical physiology

BACKGROUND

Rodents have been used to examine physiologic changes after bariatric surgery, but differences in gastric/vagal anatomy may limit their utility. Swine may be a more appropriate animal model because of anatomic and physiologic similarities to humans. The aim of this study was to establish a survival model of Roux-en-Y gastric bypass (RYGBP) in swine and to evaluate its potential in studies of physiology.

METHODS

13 miniature swine, 5 Yucatan [26.4 +/- 1.6 kg], 4 Hanford [28.3 +/- 0.6 kg] and 4 other breed [54.9 +/- 6.2 kg] underwent open RYGBP, and were kept alive to 30 (n=4), 60 (n=1) or 90 (n=2) postoperative days.

RESULTS

4 early animals had staple-line leakage within 7 days from surgery and 1 animal experienced unmanageable pain at 42 days after surgery. One animal experienced immediate cardiopulmonary collapse. 58% of animals survived to their projected endpoint. Necropsy of 1 animal at its 90-day endpoint revealed a gastro-gastric fistula. Anatomic features in swine that differ from humans, such as thick perigastric membranes, required adjustment to the standard RYGBP technique used in humans to achieve satisfactory results. Caloric intake decreased in some but not all animals, and was linked to feeding regimen. By postoperative day 30, animals weighed 5.7-29.1% less than their projected, non-operative weight. Serum assays of ghrelin and PYY were conducted, with results consistent with the procedure.

CONCLUSIONS

The use of swine as a model for bariatric surgery has promise, but also has associated pitfalls that must be addressed for this to be an effective model.

Mineralogy influences structure and diversity of bacterial communities associated with geological substrata in a pristine aquifer

Our understanding of mineralogical influences on subsurface microbial community structure and diversity has been difficult to assess due to difficulties in isolating this variable from others in the subsurface environment. In this study, biofilm coupons were used to isolate specific geological substrata from the surrounding geological matrix during colonization by microorganisms suspended in the surrounding groundwater for an 8-week period. Upon retrieval, the structure and diversity of the microbial community associated with each type of substratum was evaluated using 16S rDNA-based terminal-restriction fragment length polymorphism (T-RFLP). Phylogenetic affiliations of the populations associated with each type of substratum were established based on sequence analysis of near full-length 16S rDNA obtained through construction of a clone library. Hematite, quartz, and saprolite each harbored a community dominated by members of the division Proteobacteria (>67% of community). However, the different substrata selected for different subdivisions of bacteria within the Proteobacteria. After accounting for the influence exerted by substratum type on recovery of DNA from the attached populations, both phylogenetic data and Jaccard and Bray-Curtis similarity indices derived from terminal-restriction fragment (T-RF) profiles suggested a strong mineralogical influence on the structure and composition of the solid phase-associated community. The results suggest that mineralogical heterogeneity influences microbial community structure and diversity in pristine aquifers.