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.

Prospects for an anti-ghrelin vaccine to treat obesity

In the battle to treat the pandemic of obesity, one therapeutic strategy is to block endogenous signals that stimulate appetite and control body weight. One such molecule is ghrelin, a gut peptide that is the only known orexigenic hormone and is a likely contributor to mealtime hunger. The relative importance of ghrelin in long-term body-weight regulation (and thus its promise as an anti-obesity target) is uncertain, however, because genetic and pharmacologic blockade of ghrelin signaling have yielded variable results to date. Using a novel approach of vaccinating rats against their own ghrelin, Zorilla et al. report that animals with high ghrelin-specific antibody titers displayed restricted body weight, without evidence of non-specific inflammation following the vaccine. These results favor a meaningful role for ghrelin in energy homeostasis, hinting at a possible new anti-obesity approach. More broadly, the work of Zorilla et al. supports the feasibility of vaccinations directed against specific autologous targets--immunopharmacotherapy that could potentially be developed to target a wide array of medical conditions.

Gastrointestinal regulation of food intake

Despite substantial fluctuations in daily food intake, animals maintain a remarkably stable body weight, because overall caloric ingestion and expenditure are exquisitely matched over long periods of time, through the process of energy homeostasis. The brain receives hormonal, neural, and metabolic signals pertaining to body-energy status and, in response to these inputs, coordinates adaptive alterations of energy intake and expenditure. To regulate food consumption, the brain must modulate appetite, and the core of appetite regulation lies in the gut-brain axis. This Review summarizes current knowledge regarding the neuroendocrine regulation of food intake by the gastrointestinal system, focusing on gastric distention, intestinal and pancreatic satiation peptides, and the orexigenic gastric hormone ghrelin. We highlight mechanisms governing nutrient sensing and peptide secretion by enteroendocrine cells, including novel taste-like pathways. The increasingly nuanced understanding of the mechanisms mediating gut-peptide regulation and action provides promising targets for new strategies to combat obesity and diabetes.

Reduction of Cr(VI) under acidic conditions by the facultative Fe(lll)-reducing bacterium Acidiphilium cryptum

The potential for biological reduction of Cr(VI) under acidic conditions was evaluated with the acidophilic, facultatively metal-reducing bacterium Acidiphilium cryptum strain JF-5 to explore the role of acidophilic microorganisms in the Cr cycle in low-pH environments. An anaerobic suspension of washed A. cryptum cells rapidly reduced 50 microM Cr(VI) at pH 3.2; biological reduction was detected from pH 1.7-4.7. The reduction product, confirmed by XANES analysis, was entirely Cr(III) that was associated predominantly with the cell biomass (70-80%) with the residual residing in the aqueous phase. Reduction of Cr(VI) showed a pH optimum similar to that for growth and was inhibited by 5 mM HgCl2, suggesting that the reaction was enzyme-mediated. Introduction of O2 into the reaction medium slowed the reduction rate only slightly, whereas soluble Fe(III) (as ferric sulfate) increased the rate dramatically, presumably by the shuttling of electrons from bioreduced Fe(II) to Cr(VI) in a coupled biotic-abiotic cycle. Starved cells could not reduce Cr(VI) when provided as sole electron acceptor, indicating that Cr(VI) reduction is not an energy-conserving process in A. cryptum. We speculate, rather, that Cr(VI) reduction is used here as a detoxification mechanism.

The mechanism of diabetes control after gastrointestinal bypass surgery reveals a role of the proximal small intestine in the pathophysiology of type 2 diabetes

SUMMARY BACKGROUND DATA

Most patients who undergo Roux-en-Y gastric bypass (RYGB) experience rapid resolution of type 2 diabetes. Prior studies indicate that this results from more than gastric restriction and weight loss, implicating the rearranged intestine as a primary mediator. It is unclear, however, if diabetes improves because of enhanced delivery of nutrients to the distal intestine and increased secretion of hindgut signals that improve glucose homeostasis, or because of altered signals from the excluded segment of proximal intestine. We sought to distinguish between these two mechanisms.

METHODS

Goto-Kakizaki (GK) type 2 diabetic rats underwent duodenal-jejunal bypass (DJB), a stomach-preserving RYGB that excludes the proximal intestine, or a gastrojejunostomy (GJ), which creates a shortcut for ingested nutrients without bypassing any intestine. Controls were pair-fed (PF) sham-operated and untreated GK rats. Rats that had undergone GJ were then reoperated to exclude the proximal intestine; and conversely, duodenal passage was restored in rats that had undergone DJB. Oral glucose tolerance (OGTT), food intake, body weight, and intestinal nutrient absorption were measured.

RESULTS

There were no differences in food intake, body weight, or nutrient absorption among surgical groups. DJB-treated rats had markedly better oral glucose tolerance compared with all control groups as shown by lower peak and area-under-the-curve glucose values (P < 0.001 for both). GJ did not affect glucose homeostasis, but exclusion of duodenal nutrient passage in reoperated GJ rats significantly improved glucose tolerance. Conversely, restoration of duodenal passage in DJB rats reestablished impaired glucose tolerance.

CONCLUSIONS

This study shows that bypassing a short segment of proximal intestine directly ameliorates type 2 diabetes, independently of effects on food intake, body weight, malabsorption, or nutrient delivery to the hindgut. These findings suggest that a proximal intestinal bypass could be considered for diabetes treatment and that potentially undiscovered factors from the proximal bowel might contribute to the pathophysiology of type 2 diabetes.

Emerging therapeutic strategies for obesity

The rising tide of obesity is one of the most pressing health issues of our time, yet existing medicines to combat the problem are disappointingly limited in number and effectiveness. Fortunately, a recent burgeoning of mechanistic insights into the neuroendocrine regulation of body weight provides an expanding list of molecular targets for novel, rationally designed antiobesity pharmaceuticals. In this review, we articulate a set of conceptual principles that we feel could help prioritize among these molecules in the development of obesity therapeutics, based on an understanding of energy homeostasis. We focus primarily on central targets, highlighting selected strategies to stimulate endogenous catabolic signals or inhibit anabolic signals. Examples of the former approach include methods to enhance central leptin signaling through intranasal leptin delivery, use of superpotent leptin-receptor agonists, and mechanisms to increase leptin sensitivity by manipulating SOCS-3, PTP-1B, ciliary neurotrophic factor, or simply by first losing weight with traditional interventions. Techniques to augment signaling by neurochemical mediators of leptin action that lie downstream of at least some levels of obesity-associated leptin resistance include activation of melanocortin receptors or 5-HT2C and 5-HT1B receptors. We also describe strategies to inhibit anabolic molecules, such as neuropeptide Y, melanin-concentrating hormone, ghrelin, and endocannabinoids. Modulation of gastrointestinal satiation and hunger signals is discussed as well. As scientists continue to provide fundamental insights into the mechanisms governing body weight, the future looks bright for development of new and better antiobesity medications to be used with diet and exercise to facilitate substantial weight loss.

Overfeeding-induced weight gain suppresses plasma ghrelin levels in rats

The elevation of plasma ghrelin associated with weight loss has been taken as evidence of a role for ghrelin in the adaptive response to body weight change. However, there has been no clear experimental evidence that circulating ghrelin is suppressed by weight gain. We investigate this issue using a model of involuntary (intra-gastric gavage) overfeeding-induced obesity. Rats were first maintained at normal body weight with 4 daily tube-feedings of liquid diet (2.11 kcal/ml), each delivered at a volume of 9 ml. Gavage volume was then increased to 13 ml/feeding for 2 weeks, during which rats gained 25% of their initial body weight. Fasting plasma ghrelin levels and the response to 9- and 13-ml intra-gastric load sizes were measured during the weight-stable and overfed conditions. We found that: 1) weight gain decreased circulating ghrelin levels; 2) this response could not be attributed to additional food in the gastrointestinal tract; 3) the ghrelin response to nutrient loads was diminished in the obese vs normal-weight conditions. Having discounted diet composition and differences in gastric contents at the time of blood sampling, the decrease in ghrelin levels with overfeeding can be unambiguously attributed to physiological correlates of weight gain.

Central nervous system control of food intake and body weight

The capacity to adjust food intake in response to changing energy requirements is essential for survival. Recent progress has provided an insight into the molecular, cellular and behavioural mechanisms that link changes of body fat stores to adaptive adjustments of feeding behaviour. The physiological importance of this homeostatic control system is highlighted by the severe obesity that results from dysfunction of any of several of its key components. This new information provides a biological context within which to consider the global obesity epidemic and identifies numerous potential avenues for therapeutic intervention and future research.

Role of metabolically active hormones in the insulin resistance associated with short-term glucocorticoid treatment

BACKGROUND

The mechanisms by which glucocorticoid therapy promotes obesity and insulin resistance are incompletely characterized. Modulations of the metabolically active hormones, tumour necrosis factor alpha (TNF alpha), ghrelin, leptin and adiponectin are all implicated in the development of these cardiovascular risk factors. Little is known about the effects of short-term glucocorticoid treatment on levels of these hormones.

RESEARCH METHODS AND PROCEDURES

Using a blinded, placebo-controlled approach, we randomised 25 healthy men (mean (SD) age: 24.2 (5.4) years) to 5 days of treatment with either placebo or oral dexamethasone 3 mg twice daily. Fasting plasma TNFalpha, ghrelin, leptin and adiponectin were measured before and after treatment.

RESULTS

Mean changes in all hormones were no different between treatment arms, despite dexamethasone-related increases in body weight, blood pressure, HDL cholesterol and insulin. Changes in calculated indices of insulin sensitivity (HOMA-S, insulin sensitivity index) were strongly related to dexamethasone treatment (p < 0.001).

DISCUSSION

Our data do not support a role for TNF alpha, ghrelin, leptin or adiponectin in the insulin resistance associated with short-term glucocorticoid treatment.

Ghrelin levels in young children with Prader-Willi syndrome

OBJECTIVE

To explore the hypothesis that high ghrelin levels contribute to obesity in Prader-Willi syndrome (PWS), we assessed whether the increased levels observed in older persons with PWS exist in very young children, before the onset of hyperphagia.

STUDY DESIGN

We measured ghrelin levels in nine children with PWS (17-60 months of age) and eight healthy control subjects of equivalent body mass index (BMI), age, and sex.

RESULTS

PWS and control groups had equivalent BMI (16.8 +/- 1.4 vs 16.1 +/- 0.9 kg/m(2), respectively; P = .24), age (37.8 +/- 15.4 vs 50.3 +/- 17.7 months; P = .14), and sex. PWS and control groups also had equivalent fasting levels of total ghrelin (787 +/- 242 vs 716 +/- 135 pg/mL, respectively; P = .24), bioactive ghrelin (102 +/- 35 vs 91 +/- 23 pg/mL; P = .45), insulin, and glucose. Ghrelin correlated negatively with BMI among controls (r = -0.760, P = .029) but not PWS (r = 0.015, P = .97).

CONCLUSIONS

Children <5 years of age with PWS, who had not yet developed hyperphagia or excessive obesity, had normal ghrelin levels, in contrast with the hyperghrelinemia of older, hyperphagic people with PWS. It is possible that ghrelin levels increase suddenly before hyperphagia develops.

Ghrelin and the short- and long-term regulation of appetite and body weight

Ghrelin, an acylated upper gastrointestinal peptide, is the only known orexigenic hormone. Considerable evidence implicates ghrelin in mealtime hunger and meal initiation. Circulating levels decrease with feeding and increase before meals, achieving concentrations sufficient to stimulate hunger and food intake. Preprandial ghrelin surges occur before every meal on various fixed feeding schedules and also among individuals initiating meals voluntarily without time- or food-related cues. Ghrelin injections stimulate food intake rapidly and transiently, primarily by increasing appetitive feeding behaviors and the number of meals. Preprandial ghrelin surges are probably triggered by sympathetic nervous output. Postprandial suppression is not mediated by nutrients in the stomach or duodenum, where most ghrelin is produced. Rather, it results from post-ingestive increases in lower intestinal osmolarity (information probably relayed to the foregut via enteric nervous signaling), as well as from insulin surges. Consequently, ingested lipids suppress ghrelin poorly compared with other macronutrients. Beyond a probable role in meal initiation, ghrelin also fulfills established criteria for an adiposity-related hormone involved in long-term body-weight regulation. Ghrelin levels circulate in relation to energy stores and manifest compensatory changes in response to body-weight alterations. Ghrelin crosses the blood-brain barrier and stimulates food intake by acting on several classical body-weight regulatory centers, including the hypothalamus, hindbrain, and mesolimbic reward system. Chronic ghrelin administration increases body weight via diverse, concerted actions on food intake, energy expenditure, and fuel utilization. Congenital ablation of the ghrelin or ghrelin-receptor gene causes resistance to diet-induced obesity, and pharmacologic ghrelin blockade reduces food intake and body weight. Ghrelin levels are high in Prader-Willi syndrome and low after gastric bypass surgery, possibly contributing to body-weight alterations in these settings. Extant evidence favors roles for ghrelin in both short-term meal initiation and long-term energy homeostasis, making it an attractive target for drugs to treat obesity and/or wasting disorders.

Direct stimulation of ghrelin secretion by sympathetic nerves

The hormone ghrelin is secreted mainly from the gut, rises in peripheral plasma before meals, and is implicated in stimulating hunger, initiating meals, and developing obesity. We hypothesize that activation of the sympathetic nervous system contributes to preprandial ghrelin surges. The present studies in isoflurane-anesthetized Wistar rats were designed to determine whether sympathetic nerves and neurohormones are capable of stimulating ghrelin secretion. We activated gut sympathetic nerves by two methods: electrical sympathetic nerve stimulation (SNS) and chemical sympathetic nerve activation with iv tyramine (TYR) administration. Portal venous blood was sampled before and during a 10-min sympathetic stimulation. Successful activation of gut sympathetic nerves was verified by increments in portal venous norepinephrine. SNS increased portal ghrelin by 206 +/- 50%. In contrast, simply isolating gut sympathetic nerves without applying current had a minimal effect on ghrelin levels. TYR also increased portal ghrelin [change (Delta), +52 +/- 11%], whereas saline infusion had little effect. We next determined whether the neural stimulation of ghrelin secretion was mediated indirectly via the suppression of insulin secretion during SNS and TYR. Streptozotocin-induced diabetes prevented a fall in insulin during TYR, yet the portal ghrelin response (Delta = +47 +/- 18%) was similar to that in nondiabetic rats. Lastly, to test for humoral stimulation of ghrelin, we infused the sympathetic neurohormone, epinephrine, to achieve levels found during severe stress. Epinephrine failed to stimulate ghrelin secretion (Delta = +4 +/- 35%). We conclude that the neural, but not the neurohumoral, branch of the sympathetic nervous system can directly stimulate ghrelin secretion.

Effect of Aging on the Response of Ghrelin to Acute Weight Loss

OBJECTIVES

To determine whether the failure of the orexigenic hormone ghrelin to increase as it normally does with weight loss contributes to impaired weight recovery in older persons.

DESIGN

Prospective diet intervention study.

SETTING

University of Washington Medical Center from 2001 through 2005.

PARTICIPANTS

Twenty-one younger (18-35) and 18 older (> or =70) men and women.

INTERVENTION

Two weeks of a weight-maintaining diet were followed in sequence by 2 weeks of 30% calorie restriction, then 4 weeks of ad libitum food intake.

MEASUREMENTS

Twenty-four-hour plasma ghrelin levels, dual x-ray absorptiometry scan for body composition, resting energy expenditure, and calorie intakes were measured.

RESULTS

Both younger and older subjects lost weight with calorie restriction and failed to fully regain their baseline weight. The older adults trended toward increasing their calorie intake above their baseline level during the ad libitum period (111+/-66 kcal, P=.11), whereas the younger individuals did not (-236+/-95 kcal, P=.02). There was no statistically significant difference between the two cohorts in 24-hour ghrelin levels before or after calorie restriction. Ghrelin levels in the two cohorts increased equivalently after calorie restriction and decreased after ad libitum food consumption resumed.

CONCLUSION

Ghrelin levels in healthy older individuals respond appropriately in a compensatory manner to changes in body weight and calorie intake.

Administration of Lispro insulin with meals improves glycemic control, increases circulating leptin, and suppresses ghrelin, compared with regular/NPH insulin in female patients with type 1 diabetes

CONTEXT

Overweight and obesity are overrepresented in adolescents with type 1 diabetes mellitus (T1DM). Exogenous insulin administration often poorly reproduces normal insulin patterns and may less effectively regulate leptin and ghrelin, two hormones involved in the control of appetite and adiposity.

OBJECTIVE

The objective of the study was to determine whether insulin regimens that better replicate normal insulin patterns and augment postprandial nutrient disposal may help normalize leptin and ghrelin and improve body weight regulation.

DESIGN, SETTING, AND PARTICIPANTS

Ten young women with T1DM were studied in this 2-wk prospective, balanced crossover-design study at the University of California, Davis.

INTERVENTION

Participants received either a single injection of regular + NPH insulin (R+N) or two mealtime injections of Lispro insulin in randomized order on 2 separate days. Meal composition and total insulin administered were the same on both treatment days.

MAIN OUTCOME MEASURES

Plasma glucose, insulin, leptin, and ghrelin concentrations were monitored over the 10-h study period.

RESULTS

Lispro produced two distinct mealtime peaks of insulin, compared with one prolonged rise with R+N. Lispro reduced postprandial hyperglycemia and total glucose area under the curve. Leptin increased more on the Lispro (2.7 +/- 0.7 vs. 0.7 +/- 0.5 ng/ml, P = 0.02). Ghrelin was more suppressed after lunch with Lispro (P = 0.004).

CONCLUSIONS

Injection of Lispro insulin with meals produces more physiological insulin patterns, better glucose control, and improved leptin and ghrelin regulation than R+N. More closely mimicking normal insulin, leptin, and ghrelin responses to meals with fast-acting insulin may have implications for body weight regulation in T1DM.

Ghrelin induces feeding in the mesolimbic reward pathway between the ventral tegmental area and the nucleus accumbens

Ghrelin, a powerful orexigenic peptide released from the gut, stimulates feeding when injected centrally and has thus far been implicated in regulation of metabolic, rather than hedonic, feeding behavior. Although ghrelin's effects are partially mediated at the hypothalamic arcuate nucleus, via activation of neurons that co-express neuropeptide Y and agouti-related protein (NPY/Agrp neurons), the ghrelin receptor is expressed also in other brain sites. One of these is the ventral tegmental area (VTA), a primary node of the mesolimbic reward pathway, which sends dopaminergic projections to the nucleus accumbens (Acb), among other sites. We injected saline or three doses of ghrelin (0, 0.003, 0.03, or 0.3 nmol) into the VTA or Acb of rats. We found a robust feeding response with VTA injection of ghrelin, and a more moderate response with Acb injection. Because opioids modulate feeding in the VTA and Acb, we hypothesized that ghrelin's effects in one site were dependent on opioid signaling in the opposite site. The general opioid antagonist, naltrexone (NTX), injected into the Acb did not affect feeding elicited by ghrelin injection into the VTA, and NTX in the VTA did not affect feeding elicited by ghrelin injected into the Acb. These results suggest interaction of a metabolic factor with the reward system in feeding behavior, indicating that hedonic responses can be modulated by homeostatic factors.

Neuroendocrine profiles associated with energy intake, sleep, and stress in the night eating syndrome

CONTEXT

Night eating syndrome (NES) is characterized by evening hyperphagia and frequent awakenings with ingestion of food. It is associated with obesity and depressed mood. Greater understanding of hormonal influences on NES is desirable.

OBJECTIVE

Our objective was to evaluate 25-h profiles of hormones involved in energy balance, sleep, and stress in NES.

DESIGN

Blood assays for glucose, insulin, ghrelin, leptin, melatonin, cortisol, TSH, and prolactin were sampled repeatedly among NES and control subjects. Food intake and depressive symptoms were assessed.

SETTING AND PARTICIPANTS

Fifteen NES and 14 matched control participants stayed three nights in a General Clinical Research Center.

MAIN OUTCOME MEASURES

We assessed differences between NES and control participants in the 25-h profiles of eight hormones.

RESULTS

Nocturnal food intake was higher among NES participants, although their daily calorie intake was similar to that of controls. Reflecting their increased nocturnal intake, insulin (P < 0.001) and glucose levels (P = 0.07) among NES participants were higher than those of controls. Ghrelin levels were significantly lower in NES participants than in controls from 0100-0900 h (P = 0.003). Levels of plasma cortisol, melatonin, leptin, and prolactin did not differ between groups, but there was a trend for TSH levels (P = 0.07) to be higher during the 25 h in NES. NES participants had greater depressive symptoms than controls (P < 0.001). The differences in the levels of glucose, insulin, and ghrelin between NES and controls are closely associated with nocturnal food intake.

Hormonal and metabolic defects in a prader-willi syndrome mouse model with neonatal failure to thrive

Prader-Willi syndrome (PWS) has a biphasic clinical phenotype with failure to thrive in the neonatal period followed by hyperphagia and severe obesity commencing in childhood among other endocrinological and neurobehavioral abnormalities. The syndrome results from loss of function of several clustered, paternally expressed genes in chromosome 15q11-q13. PWS is assumed to result from a hypothalamic defect, but the pathophysiological basis of the disorder is unknown. We hypothesize that a fetal developmental abnormality in PWS leads to the neonatal phenotype, whereas the adult phenotype results from a failure in compensatory mechanisms. To address this hypothesis and better characterize the neonatal failure to thrive phenotype during postnatal life, we studied a transgenic deletion PWS (TgPWS) mouse model that shares similarities with the first stage of the human syndrome. TgPWS mice have fetal and neonatal growth retardation associated with profoundly reduced insulin and glucagon levels. Consistent with growth retardation, TgPWS mice have deregulated liver expression of IGF system components, as revealed by quantitative gene expression studies. Lethality in TgPWS mice appears to result from severe hypoglycemia after postnatal d 2 after depletion of liver glycogen stores. Consistent with hypoglycemia, TgPWS mice appear to have increased fat oxidation. Ghrelin levels increase in TgPWS reciprocally with the falling glucose levels, suggesting that the rise in ghrelin reported in PWS patients may be secondary to a perceived energy deficiency. Together, the data reveal defects in endocrine pancreatic function as well as glucose and hepatic energy metabolism that may underlie the neonatal phenotype of PWS.

Ghrelin plasma levels during psychopharmacological treatment

The mechanisms underlying weight gain induced by psychopharmacological agents are poorly understood. Because the recently discovered enteric hormone, ghrelin, stimulates food intake, we hypothesized that increases in circulating ghrelin levels might mediate the weight gain caused by certain antidepressants and atypical antipsychotic drugs. Fifty-two patients receiving psychopharmacological treatments were included in the study: 16 patients received antidepressants that are not known to induce weight gain, and 13 patients received mirtazapine or trimipramine, which are antidepressants known to lead to weight gain; 6 patients received clozapine and olanzapine, which have the highest liability among the antipsychotics to cause weight gain, and 17 patients received other antipsychotics. Fasting venous blood samples for the measurement of ghrelin were drawn in the morning between 06:00 and 08:00 a.m. in the second week of treatment. Although psychopharmacological treatment induced significant weight changes in the expected directions (most prominent in the clozapine or olanzapine treatment group), ghrelin levels did not differ significantly between groups. Psychotropic drugs with different propensities to induce body weight gain are associated with similar concentrations of plasma ghrelin in psychiatric patients after a short period of treatment.

Regulation of Ghrelin in Physiologic and Pathophysiologic States

Ghrelin, a ligand for the growth hormone secretagogue receptor, is an orexigenic hormone produced in the gastrointestinal tract. In humans and other animals, circulating ghrelin levels fluctuate over the course of the day in relation to food intake. If circulating ghrelin plays a role in determining food intake from meal to meal, it will be important to understand the factors that regulate plasma ghrelin levels in relation to feeding. Circulating ghrelin levels also appear to reflect body weight changes over the longer term, raising the possibility that ghrelin functions as an adiposity signal. This review discusses some of the factors known to affect ghrelin levels, including nutrient stimulation of the gastrointestinal tract, diet composition, and weight loss. We also consider potential hormonal and neural mediators of the effects of nutrients and weight change on ghrelin levels.

Ghrelin and energy balance: focus on current controversies

Ghrelin is an enteric peptide that is the only known circulating appetite stimulant. This feature of the hormone has garnered widespread attention, as reflected by more than 1000 scientific papers featuring ghrelin that have been published since the first reports of its orexigenic actions, approximately four years ago. In this review, we discuss data that support roles for ghrelin in the short-term regulation of pre-meal hunger and meal initiation, functioning as a unique orexigenic counterpart to short-acting gastrointestinal satiation factors, such as cholecystokinin (CCK). We also highlight evidence indicating that ghrelin satisfies recognized criteria to be viewed as a participant in long-term body-weight regulation--a potential anabolic counterpart to the traditional adiposity hormones, leptin and insulin. We then discuss the following controversial questions in ghrelin research and offer our opinions regarding these debates. (1) Is ghrelin synthesized within the brain? (2) How does ghrelin increase food intake? (3) Does des-acyl ghrelin have a physiologic function? (4) Are there receptors for ghrelin other than GHS-R1a? (5) Does ghrelin regulate insulin secretion? (6) Does ghrelin regulate gastrointestinal motility? (7) Can ghrelin or ghrelin-receptor agonists be used to treat wasting conditions? Finally, we offer a speculative model of ghrelin as a thrifty gene product that evolved to help animals consume and store fat well, thereby increasing their chances of survival during times of famine. We suggest that ghrelin is a "saginary" hormone, from the Latin, saginare, which means, "to fatten".

Ghrelin Is Suppressed by Glucagon and Does Not Mediate Glucagon-Related Growth Hormone Release

BACKGROUND

Glucagon stimulation is routinely used as a provocative test to assess growth hormone (GH) sufficiency in pediatrics. Ghrelin also markedly stimulates GH secretion. Because glucagon stimulates the promoter of the ghrelin gene in vitro as well as ghrelin secretion by the perfused rat stomach, we sought to determine whether ghrelin mediates glucagon-induced GH secretion.

METHODS

We compared ghrelin, GH, insulin and glucose responses following administration of 0.03 mg/kg intravenously (iv; max. 1 mg) and 0.1 mg/kg intramuscularly (im; max. 2 mg) of glucagon in two groups (n = 10-11/group) of GH-sufficient children. We also measured ghrelin before and 6 min after iv administration of 1 mg glucagon in 21 adult subjects.

RESULTS

In children, glucagon caused a 26% decrease in ghrelin and a 72% increase in glucose concentrations that were independent of the dose or administration route of glucagon. In contrast, the insulin response was 2-3 times higher following administration of 0.1 mg/kg im compared to 0.03 mg/kg of glucagon iv. There was a significant correlation between the maximum decrease in ghrelin and increases in glucose (p = 0.03) but not in insulin. There was a significant correlation between ghrelin and GH area under the curve after controlling for the dose of glucagon (p = 0.03) but not for the maximum increase in glucose.In normal adults, glucagon administration caused a 7% decrease in ghrelin concentrations after 6 min (p = 0.0002).

CONCLUSION

Ghrelin does not play a causal role in the GH response to pharmacological glucagon administration, which suppresses ghrelin levels starting a few minutes after injection.

Deletion of the RIIβ-Subunit of Protein Kinase A Decreases Body Weight and Increases Energy Expenditure in the Obese, Leptin-Deficient ob/ob Mouse

Disruption of the RIIbeta regulatory subunit of protein kinase A (PKA) results in mice with a lean phenotype, nocturnal hyperactivity, and increased resting metabolic rate. In this report, we have examined whether deletion of RIIbeta would lead to increased metabolism and rescue the obese phenotype of the leptin-deficient ob/ob (ob) mouse. Body weight gain and food consumption were decreased, whereas basal oxygen consumption and nocturnal locomotor activity were increased in the double mutant animals compared with ob mice. The ob mice are unable to maintain body temperature when placed in a cold environment due to a loss of brown adipose tissue activation, and this cold sensitivity was partially rescued by concomitant disruption of RIIbeta. These findings indicate that PKA modifies the phenotype of the leptin-deficient mouse, leading to increases in both thermogenesis and energy expenditure.

Molecular characterization of a dechlorinating community resulting from in situ biostimulation in a trichloroethene-contaminated deep, fractured basalt aquifer and comparison to a derivative laboratory culture

Sodium lactate additions to a trichloroethene (TCE) residual source area in deep, fractured basalt at a U.S. Department of Energy site have resulted in the enrichment of the indigenous microbial community, the complete dechlorination of nearly all aqueous-phase TCE to ethene, and the continued depletion of the residual source since 1999. The bacterial and archaeal consortia in groundwater obtained from the residual source were assessed by using PCR-amplified 16S rRNA genes. A clone library of bacterial amplicons was predominated by those from members of the class Clostridia (57 of 93 clones), of which a phylotype most similar to that of the homoacetogen Acetobacterium sp. strain HAAP-1 was most abundant (32 of 93 clones). The remaining Bacteria consisted of phylotypes affiliated with Sphingobacteria, Bacteroides, Spirochaetes, Mollicutes, and Proteobacteria and candidate divisions OP11 and OP3. The two proteobacterial phylotypes were most similar to those of the known dechlorinators Trichlorobacter thiogenes and Sulfurospirillum multivorans. Although not represented by the bacterial clones generated with broad-specificity bacterial primers, a Dehalococcoides-like phylotype was identified with genus-specific primers. Only four distinct phylotypes were detected in the groundwater archaeal library, including predominantly a clone affiliated with the strictly acetoclastic methanogen Methanosaeta concilii (24 of 43 clones). A mixed culture that completely dechlorinates TCE to ethene was enriched from this groundwater, and both communities were characterized by terminal restriction fragment length polymorphism (T-RFLP). According to T-RFLP, the laboratory enrichment community was less diverse overall than the groundwater community, with 22 unique phylotypes as opposed to 43 and a higher percentage of Clostridia, including the Acetobacterium population. Bioreactor archaeal structure was very similar to that of the groundwater community, suggesting that methane is generated primarily via the acetoclastic pathway, using acetate generated by lactate fermentation and acetogenesis in both systems.