Apolipoprotein A-IV, a putative satiety/antiatherogenic factor, rises after gastric bypass

Multiomics Picture of Obesity in Young Adults

Obesity is a socially significant disease that is characterized by a disproportionate accumulation of fat. It is also associated with chronic inflammation, cancer, diabetes, and other comorbidities. Investigating biomarkers and pathological processes linked to obesity is especially vital for young individuals, given their increased potential for lifestyle modifications. By comparing the genetic, proteomic, and metabolomic profiles of individuals categorized as underweight, normal, overweight, and obese, we aimed to determine which omics layer most accurately reflects the phenotypic changes in an organism that result from obesity. We profiled blood plasma samples by employing three omics methodologies. The untargeted GC×GC-MS metabolomics approach identified 313 metabolites. To augment the metabolomic dataset, we integrated a label-free HPLC-MS/MS proteomics method, leading to the identification of 708 proteins. The genomic layer encompassed the genotyping of 647,250 SNPs. Utilizing omics data, we trained sparse Partial Least Squares models to predict body mass index. Molecular features exhibiting frequently non-zero coefficients were selected as potential biomarkers, and we further explored enriched biological pathways. Proteomics was the most effective in single-omics analyses, with a median absolute error (MAE) of 5.44 ± 0.31 kg/m2, incorporating an average of 24 proteins per model. Metabolomics showed slightly lower performance (MAE = 6.06 ± 0.33 kg/m2), followed by genomics (MAE = 6.20 ± 0.34 kg/m2). As expected, multiomic models demonstrated better accuracy, particularly the combination of proteomics and metabolomics (MAE = 4.77 ± 0.33 kg/m2), while including genomics data did not enhance the results. This manuscript is the first multiomics study of obesity in a gender-balanced cohort of young adults profiled by genomic, proteomic, and metabolomic methods. The comprehensive approach provides novel insights into the molecular mechanisms of obesity, opening avenues for more targeted interventions.

Using trials of caloric restriction and bariatric surgery to explore the effects of body mass index on the circulating proteome

Thousands of proteins circulate in the bloodstream; identifying those which associate with weight and intervention-induced weight loss may help explain mechanisms of diseases associated with adiposity. We aimed to identify consistent protein signatures of weight loss across independent studies capturing changes in body mass index (BMI). We analysed proteomic data from studies implementing caloric restriction (Diabetes Remission Clinical trial) and bariatric surgery (By-Band-Sleeve), using SomaLogic and Olink Explore1536 technologies, respectively. Linear mixed models were used to estimate the effect of the interventions on circulating proteins. Twenty-three proteins were altered in a consistent direction after both bariatric surgery and caloric restriction, suggesting that these proteins are modulated by weight change, independent of intervention type. We also integrated Mendelian randomisation (MR) estimates of the effect of BMI on proteins measured by SomaLogic from a UK blood donor cohort as a third line of causal evidence. These MR estimates provided further corroborative evidence for a role of BMI in regulating the levels of six proteins including alcohol dehydrogenase-4, nogo receptor and interleukin-1 receptor antagonist protein. These results indicate the importance of triangulation in interrogating causal relationships; further study into the role of proteins modulated by weight in disease is now warranted.

Systematic review of type 1 diabetes biomarkers reveals regulation in circulating proteins related to complement, lipid metabolism, and immune response

BACKGROUND

Type 1 diabetes (T1D) results from an autoimmune attack of the pancreatic β cells that progresses to dysglycemia and symptomatic hyperglycemia. Current biomarkers to track this evolution are limited, with development of islet autoantibodies marking the onset of autoimmunity and metabolic tests used to detect dysglycemia. Therefore, additional biomarkers are needed to better track disease initiation and progression. Multiple clinical studies have used proteomics to identify biomarker candidates. However, most of the studies were limited to the initial candidate identification, which needs to be further validated and have assays developed for clinical use. Here we curate these studies to help prioritize biomarker candidates for validation studies and to obtain a broader view of processes regulated during disease development.

METHODS

This systematic review was registered with Open Science Framework ( https://doi.org/10.17605/OSF.IO/N8TSA ). Using PRISMA guidelines, we conducted a systematic search of proteomics studies of T1D in the PubMed to identify putative protein biomarkers of the disease. Studies that performed mass spectrometry-based untargeted/targeted proteomic analysis of human serum/plasma of control, pre-seroconversion, post-seroconversion, and/or T1D-diagnosed subjects were included. For unbiased screening, 3 reviewers screened all the articles independently using the pre-determined criteria.

RESULTS

A total of 13 studies met our inclusion criteria, resulting in the identification of 266 unique proteins, with 31 (11.6%) being identified across 3 or more studies. The circulating protein biomarkers were found to be enriched in complement, lipid metabolism, and immune response pathways, all of which are found to be dysregulated in different phases of T1D development. We found 2 subsets: 17 proteins (C3, C1R, C8G, C4B, IBP2, IBP3, ITIH1, ITIH2, BTD, APOE, TETN, C1S, C6A3, SAA4, ALS, SEPP1 and PI16) and 3 proteins (C3, CLUS and C4A) have consistent regulation in at least 2 independent studies at post-seroconversion and post-diagnosis compared to controls, respectively, making them strong candidates for clinical assay development.

CONCLUSIONS

Biomarkers analyzed in this systematic review highlight alterations in specific biological processes in T1D, including complement, lipid metabolism, and immune response pathways, and may have potential for further use in the clinic as prognostic or diagnostic assays.

Systematic review of type 1 diabetes biomarkers reveals regulation in circulating proteins related to complement, lipid metabolism, and immune response

Aims

Type 1 diabetes (T1D) results from an autoimmune attack of the pancreatic β cells that progresses to dysglycemia and symptomatic hyperglycemia. Current biomarkers to track this evolution are limited, with development of islet autoantibodies marking the onset of autoimmunity and metabolic tests used to detect dysglycemia. Therefore, additional biomarkers are needed to better track disease initiation and progression. Multiple clinical studies have used proteomics to identify biomarker candidates. However, most of the studies were limited to the initial candidate identification, which needs to be further validated and have assays developed for clinical use. Here we curate these studies to help prioritize biomarker candidates for validation studies and to obtain a broader view of processes regulated during disease development.

Methods

This systematic review was registered with Open Science Framework (DOI 10.17605/OSF.IO/N8TSA). Using PRISMA guidelines, we conducted a systematic search of proteomics studies of T1D in the PubMed to identify putative protein biomarkers of the disease. Studies that performed mass spectrometry-based untargeted/targeted proteomic analysis of human serum/plasma of control, pre-seroconversion, post-seroconversion, and/or T1D-diagnosed subjects were included. For unbiased screening, 3 reviewers screened all the articles independently using the pre-determined criteria.

Results

A total of 13 studies met our inclusion criteria, resulting in the identification of 251 unique proteins, with 27 (11%) being identified across 3 or more studies. The circulating protein biomarkers were found to be enriched in complement, lipid metabolism, and immune response pathways, all of which are found to be dysregulated in different phases of T1D development. We found a subset of 3 proteins (C3, KNG1 & CFAH), 6 proteins (C3, C4A, APOA4, C4B, A2AP & BTD) and 7 proteins (C3, CLUS, APOA4, C6, A2AP, C1R & CFAI) have consistent regulation between multiple studies in samples from individuals at pre-seroconversion, post-seroconversion and post-diagnosis compared to controls, respectively, making them strong candidates for clinical assay development.

Conclusions

Biomarkers analyzed in this systematic review highlight alterations in specific biological processes in T1D, including complement, lipid metabolism, and immune response pathways, and may have potential for further use in the clinic as prognostic or diagnostic assays.

Changes in the Proteome Profile of People Achieving Remission of Type 2 Diabetes after Bariatric Surgery

Bariatric surgery (BS) results in metabolic pathway recalibration. We have identified potential biomarkers in plasma of people achieving type 2 diabetes mellitus (T2DM) remission after BS. Longitudinal analysis was performed on plasma from 10 individuals following Roux-en-Y gastric bypass (n = 7) or sleeve gastrectomy (n = 3). Sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) was done on samples taken at 4 months before (baseline) and 6 and 12 months after BS. Four hundred sixty-seven proteins were quantified by SWATH-MS. Principal component analysis resolved samples from distinct time points after selection of key discriminatory proteins: 25 proteins were differentially expressed between baseline and 6 months post-surgery; 39 proteins between baseline and 12 months. Eight proteins (SHBG, TF, PRG4, APOA4, LRG1, HSPA4, EPHX2 and PGLYRP) were significantly different to baseline at both 6 and 12 months post-surgery. The panel of proteins identified as consistently different included peptides related to insulin sensitivity (SHBG increase), systemic inflammation (TF and HSPA4-both decreased) and lipid metabolism (APOA4 decreased). We found significant changes in the proteome for eight proteins at 6- and 12-months post-BS, and several of these are key components in metabolic and inflammatory pathways. These may represent potential biomarkers of remission of T2DM.

Low-density lipoprotein receptor-related protein 1 (LRP1) is a novel receptor for apolipoprotein A4 (APOA4) in adipose tissue

Apolipoprotein A4 (APOA4) is one of the most abundant and versatile apolipoproteins facilitating lipid transport and metabolism. APOA4 is synthesized in the small intestine, packaged onto chylomicrons, secreted into intestinal lymph and transported via circulation to several tissues, including adipose. Since its discovery nearly 4 decades ago, to date, only platelet integrin αIIbβ3 has been identified as APOA4 receptor in the plasma. Using co-immunoprecipitation coupled with mass spectrometry, we probed the APOA4 interactome in mouse gonadal fat tissue, where ApoA4 gene is not transcribed but APOA4 protein is abundant. We demonstrate that lipoprotein receptor-related protein 1 (LRP1) is the cognate receptor for APOA4 in adipose tissue. LRP1 colocalized with APOA4 in adipocytes; it interacted with APOA4 under fasting condition and their interaction was enhanced during lipid feeding concomitant with increased APOA4 levels in plasma. In 3T3-L1 mature adipocytes, APOA4 promoted glucose uptake both in absence and presence of insulin in a dose-dependent manner. Knockdown of LRP1 abrogated APOA4-induced glucose uptake as well as activation of phosphatidylinositol 3 kinase (PI3K)-mediated protein kinase B (AKT). Taken together, we identified LRP1 as a novel receptor for APOA4 in promoting glucose uptake. Considering both APOA4 and LRP1 are multifunctional players in lipid and glucose metabolism, our finding opens up a door to better understand the molecular mechanisms along APOA4-LRP1 axis, whose dysregulation leads to obesity, cardiovascular disease, and diabetes.

Adiponectin/SIRT1 Axis Induces White Adipose Browning After Vertical Sleeve Gastrectomy of Obese Rats with Type 2 Diabetes

PURPOSE

White adipose tissue (WAT) browning plays a crucial role in energy metabolism. However, it remains unclear whether WAT browning is involved in the adipose reduction following sleeve gastrectomy (SG). Adiponectin is upregulated after Roux-en-Y gastric bypass surgery. The role of adiponectin in SG was further investigated in the current study.

MATERIALS AND METHODS

Diabetic Sprague Dawley rats were randomly divided into control, sham + libitum, sham + food restriction, and sleeve groups. Browning markers, including uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor (PPAR) γ, and PPARγ coactivator-1 alpha (PGC-1α), were examined 4 weeks after the operation.

RESULTS

UCP1, PPARγ, and PGC-1α expression were significantly higher in the sleeve group compared to the other study groups. The adipose tissue of the sleeve group exhibited tissue weight loss and additional morphological browning features. In addition, adiponectin expression in the sleeve group was significantly increased. Adiponectin upregulated the expression of the browning genes and sirtuin 1 (SIRT1) in 3T3-L1 adipocytes. SIRT1 could increase the WAT browning levels, revealing that adiponectin induced the browning process via the upregulation of SIRT1. Furthermore, SIRT1 represented a positive regulatory feedback loop for adiponectin. SIRT1 activated adenosine monophosphate-activated protein kinase (AMPK), which can mediate WAT browning. Inhibition of the AMPK signaling pathway by dorsomorphin decreased UCP1, PPARγ, and PGC-1α expression. However, additional studies are needed to understand the relationship between adiponectin and glucose homeostasis.

CONCLUSIONS

Sleeve gastrectomy increased adiponectin levels, which in turn upregulated SIRT1. Thus, SIRT1 may function as an endocrine signal to mediate WAT browning.

Changes in serum levels of Apo AIV in patients with newly diagnosed hyperthyroidism and hypothyroidism: a preliminary study

OBJECTIVES

Apolipoprotein AIV has a role in chylomicrons and lipid secretion and catabolism. Also, Apo-AIV plays a role in the regulation of appetite and satiety. Previous studies on rats have shown that hyperthyroidism and hypothyroidism are associated with significant changes in Apo-AIV serum levels. There has been no research on serum Apo-AIV changes in hyper and hypothyroidism in humans.

METHODS

This case-control study was performed on new patients with hyper and hypothyroidism. Eighteen patients with hyperthyroidism and 18 patients with hypothyroidism enrolled in the study. After 12 weeks treatment blood samples were recruited. If euthyroidism was achieved, serum Apo-AIV level was measured. Eighteen euthyroid healthy individuals without thyroid disease were chosen as the control group from general population.

RESULTS

Serum levels of Apo-AIV before treatment in hypothyroidism, hyperthyroidism and in the control group were 85.61, 110.66 and 33.51 mg/dL respectively (p<0.001), which was significantly higher in hyperthyroid patients than hypothyroidism and control group. In patients with hyperthyroidism there was a significant decrease in serum levels of Apo-AIV after treatment (p=0.044). However in hypothyroidism a non-significant elevation in serum levels of Apo-AIV was observed (p=0.403). Furthermore, serum levels of Apo-AIV after treatment were significantly higher in both hyperthyroidism and hypothyroidism in comparison to control group (p<0.001).

CONCLUSIONS

The results of this study for the first time showed that the serum level of Apo-AIV is increased in patients with hyperthyroidism and is decreased in patients with hypothyroidism, and after treatment, there was a significant difference with the control group.

Metabolic and cardiovascular outcomes of bariatric surgery

PURPOSE OF REVIEW

Bariatric surgery is an effective therapy for morbid obesity that also improves weight-related metabolic parameters and reduces morbidity and mortality. The purpose of this review is to consolidate our current understanding of metabolic, macrovascular and microvascular benefits of bariatric surgery and to provide an update.

RECENT FINDINGS

Early resolution of insulin resistance and type 2 diabetes mellitus (T2DM) varies by type of bariatric surgery and appears to be mediated by changes in secretion of gut hormones, metabolism of bile acids, expression of glucose transporters and the gut microbiome. Dyslipidaemia, atherosclerosis, microvascular complications of obesity and diabetes, systemic and tissue-level inflammation show evidence of regression and hypertension improves significantly after bariatric surgery.

SUMMARY

Bariatric surgery leads to improvements in obesity-related metabolic comorbidities such as dyslipidaemia, HDL functionality, hypertension, T2DM, insulin resistance and inflammation. It slows the atherosclerotic process and reduces cardiovascular and all-cause mortality. Recent data have demonstrated regression of the microvascular complications of obesity and diabetes including the regeneration of small nerve fibres. The magnitude of change in short-term metabolic effects depends on the surgical procedure whilst longer term effects are related to the amount of sustained excess weight loss.

Biomarkers of appetite: is there a potential role for metabolomics?

Knowing the biological signals associated with appetite control is crucial for understanding the regulation of food intake. Biomarkers of appetite have been defined as physiological measures that relate to subjective appetite ratings, measured food intake, or both. Several metabolites including amino acids, lipids and glucose were proposed as key molecules associated with appetite control over 60 years ago, and along with bile acids are all among possible appetite biomarker candidates. Additional metabolites that have been associated with appetite include endocannabinoids, lactate, cortisol and β-hydroxybutyrate. However, although appetite is a complex integrative process, studies often investigated a limited number of markers in isolation. Metabolomics involves the study of small molecules or metabolites present in biological samples such as urine or blood, and may present a powerful approach to further the understanding of appetite control. Using multiple analytical techniques allows the characterisation of molecules, such as carbohydrates, lipids, amino acids, bile acids and fatty acids. Metabolomics has proven successful in identifying markers of consumption of certain foods and biomarkers implicated in several diseases. However, it has been underexploited in appetite control or obesity. The aim of the present narrative review is to: (1) provide an overview of existing metabolites that have been identified in human biofluids and associated with appetite control; and (2) discuss the potential of metabolomics to deepen understanding of appetite control in humans.

Serum proteome changes and accelerated reduction of fat mass after laparoscopic gastric plication in morbidly obese patients

Laparoscopic Gastric Plication (LGP) is a relatively new bariatric surgical procedure which no part of the stomach is removed. It is not clearly understood how LGP leads to fatty tissue reduction. We aimed to investigate the impact of LGP on serum proteome and understand molecular mechanisms of LGP-induced weight loss post-surgery. A Prospective observational study of 16 obese individuals who underwent LGP was performed. A Label-free quantitative shotgun proteomics approach was used to compare serum proteome of subjects before surgery with serum of the same individuals 1 to 2 months post-surgery (T1) and 4 to 5 months post-surgery (T2). The proteome analysis revealed that 48 proteins were differentially regulated between pre-surgery and T1, and seven proteins between pre-surgery and T2 of which six proteins were shared between the two timepoints. Among differentially regulated proteins, four proteins (SRGN, FETUB, LCP1 and CFP) have not previously been described in the context of BMI/weight loss. Despite few differences following LGP, most regulated serum proteins are in accordance with alternative weight loss procedures. Pathway analysis revealed changes to lipid- and inflammatory pathways, including PPARα/RXRα, LXR/RXR and FXR/RXR activation, especially at T1. At T2, the pathways related to inflammation and immune system are most affected. SIGNIFICANCE: Among the available clinical therapies for morbid obesity, bariatric surgery is considered as the most effective approach to achieve long-term weight loss, alongside a significant improvement in metabolic syndrome. However, very little is known about the underlying mechanism associated with significant weight loss post-surgery. Understanding such mechanisms could lead to development of safer non-surgical weight loss approaches. We here present the first analysis of the impact of LGP on the serum proteome, to bring new insights into the underlying molecular mechanism. Our findings indicate that LGP has a comprehensive systemic effect based on the blood serum proteome profile which might account for accelerated reduction of fat mass after surgery, thus, food restriction is not the only reason for weight loss following this unique surgical approach. As secretory regions of the stomach are preserved in LGP and it is associated with minimal physiological and anatomical changes, the findings are of high importance in the field of bariatric surgery and weight loss.

Proteomic Analysis of Human Plasma during Intermittent Fasting

Intermittent fasting (IF) increases lifespan and decreases metabolic disease phenotypes and cancer risk in model organisms, but the health benefits of IF in humans are less clear. Human plasma derived from clinical trials is one of the most difficult sample sets to analyze using mass spectrometry-based proteomics due to the extensive sample preparation required and the need to process many samples to achieve statistical significance. Here, we describe an optimized and accessible device (Spin96) to accommodate up to 96 StageTips, a widely used sample preparation medium enabling efficient and consistent processing of samples prior to LC-MS/MS. We have applied this device to the analysis of human plasma from a clinical trial of IF. In this longitudinal study employing 8-weeks IF, we identified significant abundance differences induced by the IF intervention, including increased apolipoprotein A4 (APOA4) and decreased apolipoprotein C2 (APOC2) and C3 (APOC3). These changes correlated with a significant decrease in plasma triglycerides after the IF intervention. Given that these proteins have a role in regulating apolipoprotein particle metabolism, we propose that IF had a positive effect on lipid metabolism through modulation of HDL particle size and function. In addition, we applied a novel human protein variant database to detect common protein variants across the participants. We show that consistent detection of clinically relevant peptides derived from both alleles of many proteins is possible, including some that are associated with human metabolic phenotypes. Together, these findings illustrate the power of accessible workflows for proteomics analysis of clinical samples to yield significant biological insight.

Analysis of the plasma proteome using iTRAQ and TMT-based Isobaric labeling

Over the past decade, chemical labeling with isobaric tandem mass tags, such as isobaric tags for relative and absolute quantification reagents (iTRAQ) and tandem mass tag (TMT) reagents, has been employed in a wide range of different clinically orientated serum and plasma proteomics studies. In this review the scope of these works is presented with attention to the areas of research, methods employed and performance limitations. These applications have covered a wide range of diseases, disorders and infections, and have implemented a variety of different preparative and mass spectrometric approaches. In contrast to earlier works, which struggled to quantify more than a few hundred proteins, increasingly these studies have provided deeper insight into the plasma proteome extending the numbers of quantified proteins to over a thousand.

Biliopancreatic Diversion Decreases Postprandial Apolipoprotein A-IV Levels in Mildly Obese Individuals with Type 2 Diabetes Mellitus: a Prospective Study

BACKGROUND

Bariatric surgery usually leads to improvement on the general lipid profile, but its role in the levels of apolipoprotein A-IV (Apo-AIV) is not completely understood. Apo-AIV is a gut-released lipoprotein which is enrolled in satiety regulation and presents anti-inflammatory, anti-atherogenic, and anti-oxidative properties. The objective of this study was to determine the influence of biliopancreatic diversion (BPD) in the levels of Apo-AIV.

METHODS

This is a prospective exploratory study which evaluated eight obese individuals with type 2 diabetes mellitus (T2DM) who underwent BPD (Scopinaro operation) and were followed-up for 12 months. Apo-AIV levels were determined by means of serial dosages through a standard meal tolerance test (MTT) in the immediate preoperative period and then 12 months later.

RESULTS

There was a significant change in the Apo-AIV curve following MTT before and after surgery. At 0 and 45 min, the Apo-AIV levels did not significantly differ before and after surgery; at 120 and 180 min, Apo-AIV levels were significantly lower following BPD.

CONCLUSIONS

We observed a decrease of postprandial levels of Apo-AIV following MTT in mildly obese individuals with T2DM. This finding appears to be related to the suppression in the Apo-AIV response that obese individuals tend to present. Weight reduction itself, endotoxemia, and the large segments of bypassed intestine may be enrolled in this impaired response.

The impact of triglycerides on glucose tolerance: Lipotoxicity revisited

Elevated plasma triglycerides (TGs) are early key features of conditions associated with a dysregulation in glucose metabolism and may predict the development of type 2 diabetes (T2D) over time. Although the acute ingestion of lipid, either mixed with or shortly before the meal, is neutral or slightly beneficial on glucose tolerance, a short-term increase in plasma TGs induced by either an i.v. lipid infusion or a high-fat diet produces a deterioration of glucose control. Accordingly, chronic lowering of plasma TGs by fibrates improves glucose homeostasis and may also prevent T2D. The chronic effects of the elevation of dietary lipid intake are less clear, particularly in humans, being the quality of fat probably more important than total fat intake. Although on the bases of the available experimental and clinical evidence it cannot be easily disentangled, with respect to elevated non-esterified fatty acids (NEFA) the relative contribution of elevated TGs to glucose homeostasis disregulation seems to be greater and also more plausible. In conclusion, although the association between elevated plasma TGs and impaired glucose tolerance is commonly considered not causative or merely a consequence of NEFA-mediated lipotoxicity, the available data suggest that TGs per se may directly contribute to disorders of glucose metabolism.

Does gastric bypass surgery change body weight set point?

The relatively stable body weight during adulthood is attributed to a homeostatic regulatory mechanism residing in the brain which uses feedback from the body to control energy intake and expenditure. This mechanism guarantees that if perturbed up or down by design, body weight will return to pre-perturbation levels, defined as the defended level or set point. The fact that weight re-gain is common after dieting suggests that obese subjects defend a higher level of body weight. Thus, the set point for body weight is flexible and likely determined by the complex interaction of genetic, epigenetic and environmental factors. Unlike dieting, bariatric surgery does a much better job in producing sustained suppression of food intake and body weight, and an intensive search for the underlying mechanisms has started. Although one explanation for this lasting effect of particularly Roux-en-Y gastric bypass surgery (RYGB) is simple physical restriction due to the invasive surgery, a more exciting explanation is that the surgery physiologically reprograms the body weight defense mechanism. In this non-systematic review, we present behavioral evidence from our own and other studies that defended body weight is lowered after RYGB and sleeve gastrectomy. After these surgeries, rodents return to their preferred lower body weight if over- or underfed for a period of time, and the ability to drastically increase food intake during the anabolic phase strongly argues against the physical restriction hypothesis. However, the underlying mechanisms remain obscure. Although the mechanism involves central leptin and melanocortin signaling pathways, other peripheral signals such as gut hormones and their neural effector pathways likely contribute. Future research using both targeted and non-targeted 'omics' techniques in both humans and rodents as well as modern, genetically targeted, neuronal manipulation techniques in rodents will be necessary.

Circulating Apolipoprotein A-IV presurgical levels are associated with improvement in insulin sensitivity after Roux-en-Y gastric bypass surgery

BACKGROUND

Apolipoprotein A-IV (ApoA-IV) has been shown to be involved in obesity and diabetes pathogenesis in animal studies, but its role in humans is uncertain.

OBJECTIVES

The objective of this study was to determine the relation of ApoA-IV with changes in glucose metabolism and weight after bariatric surgery.

SETTING

University Hospital.

METHODS

The patients (n = 49) included lean controls (n = 8) and patients before and after a mean of 7 months after laparoscopic adjustable gastric banding (LAGB, n = 12), laparoscopic Roux-en-Y gastric bypass (RYGB, n = 22), or laparoscopic sleeve gastrectomy (SG, n = 11). ApoA-IV and other hormone assays were performed in the fasting and the postprandial state. Pearson's correlation analyses controlled for baseline BMI and percent excess weight loss (EWL) were used to determine relationships between ApoA-IV levels and insulin resistance (HOMA-IR).

RESULTS

With all bariatric procedures combined, the change in ApoA-IV [533 versus 518 microg/L, P = .813] or ApoA-IV area under the curve (AUC - 1072 versus 1042, P = .939) was not significant. None of the surgeries individually affected levels of fasting or ApoA-IV AUC. Bariatric surgery resulted in a decrease in HOMA-IR (5.3 versus 2.0, P<.001). In the RYGB group, higher baseline ApoA-IV levels correlated with decrease in HOMA-IR [r = -.6, P = .008]. This relationship was independent of EWL and was not observed in the LAGB or SG group. There was no association of ApoA-IV levels with EWL, insulin secretion, Peptide-YY, or leptin levels.

CONCLUSION

Preoperative ApoA-IV levels, rather than changes in levels, positively correlate with improvements in insulin sensitivity independent of weight loss after RYGB.

Evaluation of 9-cis retinoic acid and mitotane as antitumoral agents in an adrenocortical xenograft model

The available drug treatment options for adrenocortical carcinoma (ACC) are limited. In our previous studies, the in vitro activity of 9-cis retinoic acid (9-cisRA) on adrenocortical NCI-H295R cells was shown along with its antitumoral effects in a small pilot xenograft study. Our aim was to dissect the antitumoral effects of 9-cisRA on ACC in a large-scale xenograft study involving mitotane, 9-cisRA and their combination. 43 male SCID mice inoculated with NCI-H295R cells were treated in four groups (i. control, ii. 9-cisRA, iii. mitotane, iv. 9-cisRA + mitotane) for 28 days. Tumor size follow-up, histological and immunohistochemical (Ki-67) analysis, tissue gene expression microarray, quantitative real-time-PCR for the validation of microarray results and to detect circulating microRNAs were performed. Protein expression was studied by proteomics and Western-blot validation. Only mitotane alone and the combination of 9-cisRA and mitotane resulted in significant tumor size reduction. The Ki-67 index was significantly reduced in both 9-cisRA and 9-cisRA+mitotane groups. Only modest changes at the mRNA level were found: the 9-cisRA-induced overexpression of apolipoprotein A4 and down-regulation of phosphodiesterase 4A was validated. The expression of circulating hsa-miR-483-5p was significantly reduced in the combined treatment group. The SET protein was validated as being significantly down-regulated in the combined mitotane+9-cisRA group. 9-cisRA might be a helpful additive agent in the treatment of ACC in combination with mitotane. Circulating hsa-miR-483-5p could be utilized for monitoring the treatment efficacy in ACC patients, and the treatment-induced reduction in protein SET expression might raise its relevance in ACC biology.

Altered gut and adipose tissue hormones in overweight and obese individuals: cause or consequence?

The aim of this article is to review the research into the main peripheral appetite signals altered in human obesity, together with their modifications after body weight loss with diet and exercise and after bariatric surgery, which may be relevant to strategies for obesity treatment. Body weight homeostasis involves the gut–brain axis, a complex and highly coordinated system of peripheral appetite hormones and centrally mediated neuronal regulation. The list of peripheral anorexigenic and orexigenic physiological factors in both animals and humans is intimidating and expanding, but anorexigenic glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), peptide YY (PYY) and orexigenic ghrelin from the gastrointestinal tract, pancreatic polypeptide (PP) from the pancreas and anorexigenic leptin from adiposites remain the most widely studied hormones. Homeostatic control of food intake occurs in humans, although its relative importance for eating behaviour is uncertain, compared with social and environmental influences. There are perturbations in the gut–brain axis in obese compared with lean individuals, as well as in weight-reduced obese individuals. Fasting and postprandial levels of gut hormones change when obese individuals lose weight, either with surgical or with dietary and/or exercise interventions. Diet-induced weight loss results in long-term changes in appetite gut hormones, postulated to favour increased appetite and weight regain while exercise programmes modify responses in a direction expected to enhance satiety and permit weight loss and/or maintenance. Sustained weight loss achieved by bariatric surgery may in part be mediated via favourable changes to gut hormones. Future work will be necessary to fully elucidate the role of each element of the axis, and whether modifying these signals can reduce the risk of obesity.

The role of apolipoprotein A-IV in regulating glucagon-like peptide-1 secretion

Both glucagon-like peptide-1 (GLP-1) and apolipoprotein A-IV (apoA-IV) are produced from the gut and enhance postprandial insulin secretion. This study investigated whether apoA-IV regulates nutrient-induced GLP-1 secretion and whether apoA-IV knockout causes compensatory GLP-1 release. Using lymph-fistula-mice, we first determined lymphatic GLP-1 secretion by administering apoA-IV before an intraduodenal Ensure infusion. apoA-IV changed neither basal nor Ensure-induced GLP-1 secretion relative to saline administration. We then assessed GLP-1 in apoA-IV-/- and wild-type (WT) mice administered intraduodenal Ensure. apoA-IV-/- mice had comparable lymph flow, lymphatic triglyceride, glucose, and protein outputs as WT mice. Intriguingly, apoA-IV-/- mice had higher lymphatic GLP-1 concentration and output than WT mice 30 min after Ensure administration. Increased GLP-1 was also observed in plasma of apoA-IV-/- mice at 30 min. apoA-IV-/- mice had comparable total gut GLP-1 content relative to WT mice under fasting, but a lower GLP-1 content 30 min after Ensure administration, suggesting that more GLP-1 was secreted. Moreover, an injection of apoA-IV protein did not reverse the increased GLP-1 secretion in apoA-IV-/- mice. Finally, we assessed gene expression of GLUT-2 and the lipid receptors, including G protein-coupled receptor (GPR) 40, GPR119, and GPR120 in intestinal segments. GLUT-2, GPR40 and GPR120 mRNAs were unaltered by apoA-IV knockout. However, ileal GPR119 mRNA was significantly increased in apoA-IV-/- mice. GPR119 colocalizes with GLP-1 in ileum and stimulates GLP-1 secretion by sensing OEA, lysophosphatidylcholine, and 2-monoacylglycerols. We suggest that increased ileal GPR119 is a potential mechanism by which GLP-1 secretion is enhanced in apoA-IV-/- mice.

The pathophysiology of intestinal lipoprotein production

Intestinal lipoprotein production is a multistep process, essential for the absorption of dietary fats and fat-soluble vitamins. Chylomicron assembly begins in the endoplasmic reticulum with the formation of primordial, phospholipids-rich particles that are then transported to the Golgi for secretion. Several classes of transporters play a role in the selective uptake and/or export of lipids through the villus enterocytes. Once secreted in the lymph stream, triglyceride-rich lipoproteins (TRLs) are metabolized by Lipoprotein lipase (LPL), which catalyzes the hydrolysis of triacylglycerols of very low density lipoproteins (VLDLs) and chylomicrons, thereby delivering free fatty acids to various tissues. Genetic mutations in the genes codifying for these proteins are responsible of different inherited disorders affecting chylomicron metabolism. This review focuses on the molecular pathways that modulate the uptake and the transport of lipoproteins of intestinal origin and it will highlight recent findings on TRLs assembly.

ApoA-IV: current and emerging roles in intestinal lipid metabolism, glucose homeostasis, and satiety

Apolipoprotein A-IV (apoA-IV) is secreted by the small intestine on chylomicrons into intestinal lymph in response to fat absorption. Many physiological functions have been ascribed to apoA-IV, including a role in chylomicron assembly and lipid metabolism, a mediator of reverse-cholesterol transport, an acute satiety factor, a regulator of gastric function, and, finally, a modulator of blood glucose homeostasis. The purpose of this review is to update our current view of intestinal apoA-IV synthesis and secretion and the physiological roles of apoA-IV in lipid metabolism and energy homeostasis, and to underscore the potential for intestinal apoA-IV to serve as a therapeutic target for the treatment of diabetes and obesity-related disease.

Apolipoprotein A-IV: a protein intimately involved in metabolism

The purpose of this review is to summarize our current understanding of the physiological roles of apoA-IV in metabolism, and to underscore the potential for apoA-IV to be a focus for new therapies aimed at the treatment of diabetes and obesity-related disorders. ApoA-IV is primarily synthesized by the small intestine, attached to chylomicrons by enterocytes, and secreted into intestinal lymph during fat absorption. In circulation, apoA-IV is associated with HDL and chylomicron remnants, but a large portion is lipoprotein free. Due to its anti-oxidative and anti-inflammatory properties, and because it can mediate reverse-cholesterol transport, proposed functions of circulating apoA-IV have been related to protection from cardiovascular disease. This review, however, focuses primarily on several properties of apoA-IV that impact other metabolic functions related to food intake, obesity, and diabetes. In addition to participating in triglyceride absorption, apoA-IV can act as an acute satiation factor through both peripheral and central routes of action. It also modulates glucose homeostasis through incretin-like effects on insulin secretion, and by moderating hepatic glucose production. While apoA-IV receptors remain to be conclusively identified, the latter modes of action suggest that this protein holds therapeutic promise for treating metabolic disease.

Vertical sleeve gastrectomy restores glucose homeostasis in apolipoprotein A-IV KO mice

Bariatric surgery is the most successful strategy for treating obesity, yet the mechanisms for this success are not clearly understood. Clinical literature suggests that plasma levels of apolipoprotein A-IV (apoA-IV) rise with Roux-en-Y gastric bypass (RYGB). apoA-IV is secreted from the intestine postprandially and has demonstrated benefits for both glucose and lipid homeostasis. Because of the parallels in the metabolic improvements seen with surgery and the rise in apoA-IV levels, we hypothesized that apoA-IV was necessary for obtaining the metabolic benefits of bariatric surgery. To test this hypothesis, we performed vertical sleeve gastrectomy (VSG), a surgery with clinical efficacy very similar to that for RYGB, in whole-body apoA-IV knockout (KO) mice. We found that VSG reduced body mass and improved both glucose and lipid homeostasis similarly in wild-type mice compared with apoA-IV KO mice. In fact, VSG normalized the impairment in glucose tolerance and caused a significantly greater improvement in hepatic triglyceride storage in the apoA-IV KO mice. Last, independent of surgery, apoA-IV KO mice had a significantly reduced preference for a high-fat diet. Altogether, these data suggest that apoA-IV is not necessary for the metabolic improvements shown with VSG, but also suggest an interesting role for apoA-IV in regulating macronutrient preference and hepatic triglyceride levels. Future studies are necessary to determine whether this is the case for RYGB as well.

Proteomic analysis in type 2 diabetes patients before and after a very low calorie diet reveals potential disease state and intervention specific biomarkers

Very low calorie diets (VLCD) with and without exercise programs lead to major metabolic improvements in obese type 2 diabetes patients. The mechanisms underlying these improvements have so far not been elucidated fully. To further investigate the mechanisms of a VLCD with or without exercise and to uncover possible biomarkers associated with these interventions, blood samples were collected from 27 obese type 2 diabetes patients before and after a 16-week VLCD (Modifast ∼450 kcal/day). Thirteen of these patients followed an exercise program in addition to the VCLD. Plasma was obtained from 27 lean and 27 obese controls as well. Proteomic analysis was performed using mass spectrometry (MS) and targeted multiple reaction monitoring (MRM) and a large scale isobaric tags for relative and absolute quantitation (iTRAQ) approach. After the 16-week VLCD, there was a significant decrease in body weight and HbA1c in all patients, without differences between the two intervention groups. Targeted MRM analysis revealed differences in several proteins, which could be divided in diabetes-associated (fibrinogen, transthyretin), obesity-associated (complement C3), and diet-associated markers (apolipoproteins, especially apolipoprotein A-IV). To further investigate the effects of exercise, large scale iTRAQ analysis was performed. However, no proteins were found showing an exercise effect. Thus, in this study, specific proteins were found to be differentially expressed in type 2 diabetes patients versus controls and before and after a VLCD. These proteins are potential disease state and intervention specific biomarkers.

Trial Registration

Controlled-Trials.com ISRCTN76920690

Integration of satiety signals by the central nervous system

Individual meals are products of a complex interaction of signals related to both short-term and long-term availability of energy stores. In addition to maintaining the metabolic demands of the individual in the short term, levels of energy intake must also maintain and defend body weight over longer periods. To accomplish this, satiety pathways are regulated by a sophisticated network of endocrine and neuroendocrine pathways. Higher brain centers modulate meal size through descending inputs to caudal brainstem regions responsible for the motor pattern generators associated with ingestion. Gastric and intestinal signals interact with central nervous system pathways to terminate food intake. These inputs can be modified as a function of internal metabolic signals, external environmental influences, and learning to regulate meal size.

Small-angle X-ray scattering of apolipoprotein A-IV reveals the importance of its termini for structural stability

ApoA-IV is an amphipathic protein that can emulsify lipids and has been linked to protective roles against cardiovascular disease and obesity. We previously reported an x-ray crystal structure of apoA-IV that was truncated at its N and C termini. Here, we have extended this work by demonstrating that self-associated states of apoA-IV are stable and can be structurally studied using small-angle x-ray scattering. Both the full-length monomeric and dimeric forms of apoA-IV were examined, with the dimer showing an elongated rod core with two nodes at opposing ends. The monomer is roughly half the length of the dimer with a single node. Small-angle x-ray scattering visualization of several deletion mutants revealed that removal of both termini can have substantial conformational effects throughout the molecule. Additionally, the F334A point mutation, which we previously showed increases apoA-IV lipid binding, also exhibited large conformational effects on the entire dimer. Merging this study's low-resolution structural information with the crystal structure provides insight on the conformation of apoA-IV as a monomer and as a dimer and further defines that a clasp mechanism may control lipid binding and, ultimately, protein function.

Apolipoprotein A-IV as a novel gene associated with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine-metabolic disorder, affecting 6-10% of women of reproductive age. The etiology remains poorly understood. To investigate the differentially expressed proteins from PCOS patients versus healthy women, the protein expression in follicular fluid was analyzed using two-dimensional electrophoresis (2-DE). Since follicular fluid contains a number of secretory proteins required for oocyte fertilization and follicle maturation, it is possible that follicular fluid can be used as a provisional source for identifying pivotal proteins associated with PCOS. In this study, six overexpressed proteins [kininogen 1, cytokeratin 9, antithrombin, fibrinogen γ-chain, apolipoprotein A-IV (apoA-IV) precursor and α-1-B-glycoprotein (A1BG)] in follicular fluids from PCOS patients were identified with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) and nano LC-MS/MS. Western blot analysis confirmed that the protein expression levels of apoA-IV precursor and A1BG were increased in follicular fluid from PCOS patients compared with those from normal controls. The analysis of protein expression for other proteins revealed individual variation. These results facilitate the understanding of the molecular mechanisms of PCOS and provide candidate biomarkers for the development of diagnostic and therapeutic tools.

Reduced cardiovascular risk after bariatric surgery is linked to plasma ceramides, apolipoprotein-B100, and ApoB100/A1 ratio

BACKGROUND

Obesity-associated hyperlipidemia and hyperlipoproteinemia are risk factors for cardiovascular disease (CVD). Recently, ceramide-derived sphingolipids were identified as a novel independent CVD risk factor. We hypothesized that the beneficial effect of Roux-en-Y gastric bypass (RYGB) on CVD risk is related to ceramide-mediated improvement in lipoprotein profile.

METHODS

A prospective study of patients undergoing RYGB was conducted. The patients' clinical data and biochemical markers related to cardiovascular risk were documented. Plasma ceramide subspecies (C14:0, C16:0, C18:0, C18:1, C20:0, C24:0, and C24:1), apolipoprotein (Apo)B100 and ApoA1 were quantified preoperatively and 3 and 6 months after RYGB, as was the Framingham risk score. Brachial artery reactivity testing was performed before and 6 months after RYGB.

RESULTS

Ten patients (9 women; age 48.6 ± 9.6 yr; body mass index, 48.5 ± 5.8 kg/m(2)) were included in the present study. At 6 months postoperatively, the mean body mass index had decreased to 35.7 ± 5.0 kg/m(2), corresponding to 51.3% ± 10.0% excess weight loss. The fasting total cholesterol, triglycerides, low-density lipoprotein, free fatty acids, ApoB100, ApoB100/ApoA1 ratio and insulin resistance estimated from Homeostasis Model of Assessment of Insulin Resistance were significantly reduced compared with the preoperative values. The ApoB100/ApoA1 ratio correlated with a reduction in ceramide subspecies (C18:0, C18:1, C20:0, C24:0, and C24:1; P < .05). ApoB100 and the ApoB100/ApoA1 ratio also correlated positively with the reduction in triglycerides, low-density lipoprotein, and Homeostasis Model of Assessment of Insulin Resistance (P < .05). Brachial artery reactivity testing correlated inversely with ApoB100 and total ceramide (P = .05). Furthermore, the change in brachial artery reactivity testing correlated with the decrease in C16:0 (P < .03).

CONCLUSION

Our data suggest that improvements in lipid profiles and CVD risk factors after gastric bypass surgery could be linked to changes in ceramide lipids. Mechanistic studies are needed to determine whether this link is causative or purely correlative.

Roux-en-Y gastric bypass surgery increases number but not density of CCK-, GLP-1-, 5-HT-, and neurotensin-expressing enteroendocrine cells in rats

BACKGROUND

Roux-en-Y gastric bypass (RYGB) surgery is very effective in reducing excess body weight and improving glucose homeostasis in obese subjects. Changes in the pattern of gut hormone secretion are thought to play a major role, but the mechanisms leading to both changed hormone secretion and beneficial effects remain unclear. Specifically, it is not clear whether changes in the number of hormone-secreting enteroendocrine cells, or changes in the releasing stimuli, or both, are important.

METHODS

We estimated numbers of enteroendocrine cells after immunohistochemical staining in fixed tissue samples from rats at 10-11 months after RYGB.

KEY RESULTS

Numbers of glucagon-like peptide-1 (GLP-1) (L-cells, co-expressing peptide YY (PYY)), cholecystokinin (CCK), neurotensin, and 5-HT-immunoreactive cells were significantly increased in the Roux and common limbs, but not the biliopancreatic limb in RYGB rats compared with sham-operated, obese rats fed high-fat diet, and chow-fed controls. This increase was mostly accounted for by general hyperplasia of all intestinal wall layers of the nutrient-perfused Roux and common limbs, and less to increased density of expression. The number of ghrelin cells in the bypassed stomach was not different among the three groups.

CONCLUSIONS & INFERENCES

The findings suggest that the number of enteroendocrine cells increases passively as the gut adapts, and that the increased total number of L- and I-cells is likely to contribute to the higher circulating levels of GLP-1, PYY, and CCK, potentially leading to suppression of food intake and stimulation of insulin secretion. Whether changes in releasing stimuli also contribute to altered circulating levels will have to be determined in future studies.

Gastrointestinal weight-loss surgery: glimpses at the molecular level

Pharmacotherapy for obesity remains a key challenge, and gastrointestinal weight-loss surgery remains a preferred option to help reduce excess body weight along with resolution of several comorbidities associated with obesity. This offers a unique opportunity to study the underlying mechanisms of gastro-intestinal weight-loss surgery to develop effective and less invasive long-term therapeutic interventions potentially mimicking the benefits of gastrointestinal weight-loss surgery. Here, we present an integrative analysis of currently available human transcriptomics data sets pre- and post-surgery and propose a computational biology strategy for selecting putative drug targets. We anticipate that approaches similar to the one that we outline here, would help elucidate underlying mechanisms that result in metabolic improvements and provide guidance on pharmaceutical targets to develop effective and less invasive therapies for obesity and related comorbidities.

The oral microflora in obesity and type-2 diabetes

Background

Type 2 diabetes mellitus (T2DM) is prevalent in people with obesity. It has been proposed that these conditions are related to specific features of the microflora of the mouth and lower gastrointestinal (GI) tract. Hyperglycemia often resolves quickly after Roux-en-Y gastric bypass (RYGB) but the role of the GI microflora cannot be examined easily because of reduced intestinal mobility. We propose that the study of microorganisms present in the mouth of patients undergoing RYGB will contribute to our understanding of the role of bacteria in the pathogenesis of T2DM.

Objective

To conduct a feasibility study to examine differences in oral microbes in obese patients with and without T2DM and to determine whether it is feasible to measure changes after gastric bypass surgery.

Methods

Individuals with morbid obesity (n=29), of whom 13 had T2DM, were studied. Oral rinses, stool samples, and blood samples were obtained before RYGB, and oral rinses and blood samples were obtained at 2 and 12 weeks postsurgery.

Results

Prior to surgery, participants with T2DM had slightly higher total levels of oral bacteria than those without diabetes. Those with HbA1c > 6.5% had rather lower levels of Bifidobacteria in the mouth and stool. At 2 weeks post-RYGB, patients with T2DM were able to reduce or discontinue their hypoglycemic medications. Stool samples could not be obtained but oral rinses were readily available. The levels of oral Bifidobacteria had increased tenfold and levels of circulating endotoxin and tumor necrosis factor-alpha had decreased.

Conclusions

The study of oral bacteria before and after RYGB is feasible and should be tested in larger patient populations to increase our understanding of the role of microorganisms in the pathogenesis of obesity and T2DM.

Apolipoprotein A-IV improves glucose homeostasis by enhancing insulin secretion

Apolipoprotein A-IV (apoA-IV) is secreted by the small intestine in response to fat absorption. Here we demonstrate a potential role for apoA-IV in regulating glucose homeostasis. ApoA-IV-treated isolated pancreatic islets had enhanced insulin secretion under conditions of high glucose but not of low glucose, suggesting a direct effect of apoA-IV to enhance glucose-stimulated insulin release. This enhancement involves cAMP at a level distal to Ca(2+) influx into the β cells. Knockout of apoA-IV results in compromised insulin secretion and impaired glucose tolerance compared with WT mice. Challenging apoA-IV(-/-) mice with a high-fat diet led to fasting hyperglycemia and more severe glucose intolerance associated with defective insulin secretion than occurred in WT mice. Administration of exogenous apoA-IV to apoA-IV(-/-) mice improved glucose tolerance by enhancing insulin secretion in mice fed either chow or a high-fat diet. Finally, we demonstrate that exogenous apoA-IV injection decreases blood glucose levels and stimulates a transient increase in insulin secretion in KKAy diabetic mice. These results suggest that apoA-IV may provide a therapeutic target for the regulation of glucose-stimulated insulin secretion and treatment of diabetes.

Vagal innervation of the hepatic portal vein and liver is not necessary for Roux-en-Y gastric bypass surgery-induced hypophagia, weight loss, and hypermetabolism

OBJECTIVE

To determine the role of the common hepatic branch of the abdominal vagus on the beneficial effects of Roux-en-Y gastric bypass (RYGB) on weight loss, food intake, food choice, and energy expenditure in a rat model.

BACKGROUND

Although changes in gut hormone patterns are the leading candidates in RYGB's effects on appetite, weight loss, and reversal of diabetes, a potential role for afferent signaling through the vagal hepatic branch potentially sensing glucose levels in the hepatic portal vein has recently been suggested in a mouse model of RYGB.

METHODS

Male Sprague-Dawley rats underwent either RYGB alone (RYGB; n = 7), RYGB + common hepatic branch vagotomy (RYGB + HV; n = 6), or sham procedure (sham; n = 9). Body weight, body composition, meal patterns, food choice, energy expenditure, and fecal energy loss were monitored up to 3 months after intervention.

RESULTS

Both RYGB and RYGB + HV significantly reduced body weight, adiposity, meal size, and fat preference, and increased satiety, energy expenditure, and respiratory exchange rate compared with sham procedure, and there were no significant differences in these effects between RYGB and RYGB + HV rats.

CONCLUSIONS

Integrity of vagal nerve supply to the liver, hepatic portal vein, and the proximal duodenum provided by the common hepatic branch is not necessary for RYGB to reduce food intake and body weight or increase energy expenditure. Specifically, it is unlikely that a hepatic portal vein glucose sensor signaling RYGB-induced increased intestinal gluconeogenesis to the brain depends on vagal afferent fibers.

Obesity surgery and gut-brain communication

The prevalence of obesity, and the cluster of serious metabolic diseases it is associated with, continues to rise globally, and hopes for effective treatment with drugs have been considerably set back. Thus, success with bariatric surgeries to induce sustained body weight loss and effectively cure most of the associated co-morbidities appears almost "miraculous" and systematic investigation of the mechanisms at work has gained momentum. Here, we will discuss the basic organization of gut-brain communication and review clinical and pre-clinical investigations on the potential mechanisms by which gastric bypass surgery leads to its beneficial effects on energy balance and glucose homeostasis. Although a lot has been learned regarding changes in energy intake and expenditure, secretion of gut hormones, and improvement in glucose homeostasis, there has not yet been the "breakthrough observation" of identifying a key signaling component common to the beneficial effects of the surgery. However, given the complexity and redundancy of gut-brain signaling and gut signaling to other relevant organs, it is perhaps more realistic to expect a number of key signaling changes that act in concert to bring about the "miracle".

Mechanisms responsible for excess weight loss after bariatric surgery

Obesity has increased alarmingly in the United States and is increasing in many countries of the world. Because obesity is an important risk factor for type 2 diabetes and other chronic diseases, it is important to develop approaches to counter the rapid increase in adiposity. One approach is bariatric surgery, the most successful clinical intervention known for treating obesity. Surgery can result in impressive weight loss and improvement of obesity-related comorbidities. Yet the mechanisms responsible for this remarkable effect of surgery remain controversial. It is now clear that caloric restriction, per se, does not explain all the reduction in stored fat mass after surgery. A number of gastrointestinal hormones, including glucagon-like peptide (GLP)-1, peptide YY, oxyntomodulin, GLP-2, glucose-dependent insulinotropic polypeptide, ghrelin, and others, can play roles in energy homeostasis and could be involved in bariatric-surgery-related weight loss and weight loss maintenance. Vagal innervation may play a role. In addition, there may be other yet-uncharacterized factors that could participate. This review discusses the possible roles of these hormonal mechanisms in various types of bariatric surgery to help elucidate some of the potential mechanisms at play in short-term and long-term post-bariatric surgery weight loss. Understanding such mechanisms could lead to new and efficacious means to control or even reduce the epidemic of obesity.

Differential expression of serine-threonine kinase receptor-associated protein in patients with systemic lupus erythematosus

The serine-threonine kinase receptor-associated protein (STRAP), a 39 kDa protein localized predominantly in cytoplasm, is an important inhibitor of transforming growth factor beta (TGF-ß) signaling and a regulator of cell proliferation. To investigate the application of STRAP as a novel biomarker in evaluating the pathological condition of systemic lupus erythematosus (SLE), and to determine the possible involvement of STRAP in SLE pathogenesis, the expression levels of STRAP in peripheral blood mononuclear cells (PBMC) of SLE patients were analyzed. PBMC were collected from six patients with active SLE, six with stable SLE and six healthy controls; after protein extraction and concentration determination, the samples were labeled with reagents for isobaric tagging for relative and absolute protein quantification (iTRAQ) and detected by tandem mass spectrometry. The initial proteomic analysis identified and quantified hundreds of proteins. Of these, STRAP was found to decrease more than three-fold in active SLE patients compared with healthy controls (the relative ratio was 0.291). The under-expression of STRAP in active SLE was further verified by western blot in larger independent sample sets. Clinical data analyses revealed that the levels of STRAP in SLE inversely correlated to the SLE disease activity index (SLEDAI) (r = -0.607, p < 0.05). These results indicate that the under-expression of STRAP may be a negative factor in the pathogenic process of SLE; as a result, this may also be of clinical significance as a potential condition-specific indicator of active SLE.

Deletion of a subgroup of ribosome-related genes minimizes hypoxia-induced changes and confers hypoxia tolerance

Hypoxia is a widely occurring condition experienced by diverse organisms under numerous physiological and disease conditions. To probe the molecular mechanisms underlying hypoxia responses and tolerance, we performed a genome-wide screen to identify mutants with enhanced hypoxia tolerance in the model eukaryote, the yeast Saccharomyces cerevisiae. Yeast provides an excellent model for genomic and proteomic studies of hypoxia. We identified five genes whose deletion significantly enhanced hypoxia tolerance. They are RAI1, NSR1, BUD21, RPL20A, and RSM22, all of which encode functions involved in ribosome biogenesis. Further analysis of the deletion mutants showed that they minimized hypoxia-induced changes in polyribosome profiles and protein synthesis. Strikingly, proteomic analysis by using the iTRAQ profiling technology showed that a substantially fewer number of proteins were changed in response to hypoxia in the deletion mutants, compared with the parent strain. Computational analysis of the iTRAQ data indicated that the activities of a group of regulators were regulated by hypoxia in the wild-type parent cells, but such regulation appeared to be diminished in the deletion strains. These results show that the deletion of one of the genes involved in ribosome biogenesis leads to the reversal of hypoxia-induced changes in gene expression and related regulators. They suggest that modifying ribosomal function is an effective mechanism to minimize hypoxia-induced specific protein changes and to confer hypoxia tolerance. These results may have broad implications in understanding hypoxia responses and tolerance in diverse eukaryotes ranging from yeast to humans.

Recurrent hypoglycemia exacerbates cerebral ischemic damage in streptozotocin-induced diabetic rats

BACKGROUND AND PURPOSE

Stroke and heart disease are the most serious complications of diabetes accounting for >65% of mortality among diabetics. Although intensive insulin therapy has significantly improved the prognosis of diabetes and its complications, it is associated with an elevated risk of recurrent hypoglycemia (RH). We tested the hypothesis that RH exacerbates cerebral ischemic damage in a rodent model of diabetes.

METHOD

We determined the extent of neuronal death in CA1 hippocampus after global cerebral ischemia in control and streptozotocin-induced diabetic rats. Diabetic animals included an insulin-treated streptozotocin-diabetic (ITD) group and a group of ITD rats exposed also to 10 episodes of hypoglycemia (ITD+recurrent hypoglycemia: RH). Hypoglycemia (55 to 65 mg/dL blood glucose) was induced twice daily for 5 consecutive days.

RESULTS

As expected, uncontrolled diabetes (streptozotocin-diabetes, untreated animals) resulted in a 70% increase in ischemic damage as compared with the control group. Insulin treatment was able to lower ischemic damage by 64% as compared with the diabetic group. However, ITD+RH rats had 44% more damage when compared with the ITD group. We also observed that free radical release from mitochondria is increased in ITD+RH rats.

CONCLUSIONS

This is the first report on the impact of RH in exacerbating cerebral ischemic damage in diabetic animals. Our results suggest that increased free radical release from mitochondria may be responsible for observed increased ischemic damage in ITD+RH rats. RH thus may be an unexplored but important factor responsible for increased ischemic damage in diabetes.

Proteomic profiling of human plasma by iTRAQ reveals down-regulation of ITI-HC3 and VDBP by cigarette smoking

Biomarkers in noninvasive fluids indicative of cigarette smoke's effects are urgently needed. In this pilot study, we utilized the proteomic approach, isobaric Tags for Relative and Absolute Quantitation (iTRAQ), to identify differentially expressed plasma proteins in healthy cigarette smokers compared to healthy nonsmokers; select proteins were further confirmed by immunoblot analysis. Significant, differentially expressed proteins identified in the plasma separated subjects based on their condition as smokers or nonsmokers. Several of the proteins identified in this study are associated with immunity and inflammatory responses and have been shown to be associated with tobacco-related diseases, including chronic obstructive pulmonary disease (COPD) and lung cancer. Proteins up-regulated in smokers included complement component 8 polypeptide chains α, β, and γ, and mannose-binding protein C, and proteins down-regulated included inter-α-trypsin inhibitor heavy chain H3 (ITI-HC3) and vitamin D-binding protein (VDBP). In addition, gelsolin and vitronectin, known tissue leakage proteins, were up- and down-regulated, respectively. Our results demonstrate for the first time that chronic cigarette smoking can influence the expression profile of the human plasma proteome. Proteins identified in this pilot study may serve as candidate biomarkers of diseases resulting from exposure to cigarette smoke in future molecular epidemiological studies.

Association between the APOA2 promoter polymorphism and body weight in Mediterranean and Asian populations: replication of a gene-saturated fat interaction

OBJECTIVE

The APOA2 gene has been associated with obesity and insulin resistance (IR) in animal and human studies with controversial results. We have reported an APOA2-saturated fat interaction determining body mass index (BMI) and obesity in American populations. This work aims to extend our findings to European and Asian populations.

METHODS

Cross-sectional study in 4602 subjects from two independent populations: a high-cardiovascular risk Mediterranean population (n = 907 men and women; aged 67 ± 6 years) and a multiethnic Asian population (n = 2506 Chinese, n = 605 Malays and n = 494 Asian Indians; aged 39 ± 12 years) participating in a Singapore National Health Survey. Anthropometric, clinical, biochemical, lifestyle and dietary variables were determined. Homeostasis model assessment of insulin resistance was used in Asians. We analyzed gene-diet interactions between the APOA2 -265T>C polymorphism and saturated fat intake (<or ≥ 22 g per day) on anthropometric measures and IR.

RESULTS

Frequency of CC (homozygous for the minor allele) subjects differed among populations (1-15%). We confirmed a recessive effect of the APOA2 polymorphism and replicated the APOA2-saturated fat interaction on body weight. In Mediterranean individuals, the CC genotype was associated with a 6.8% greater BMI in those consuming a high (P = 0.018), but not a low (P = 0.316) saturated fat diet. Likewise, the CC genotype was significantly associated with higher obesity prevalence in Chinese and Asian Indians only, with a high-saturated fat intake (P = 0.036). We also found a significant APOA2-saturated fat interaction in determining IR in Chinese and Asian Indians (P = 0.026).

CONCLUSION

The influence of the APOA2 -265T>C polymorphism on body-weight-related measures was modulated by saturated fat in Mediterranean and Asian populations.

Gastric bypass surgery alters behavioral and neural taste functions for sweet taste in obese rats

Roux-en-Y gastric bypass surgery (GBS) is the most effective treatment for morbid obesity. GBS is a restrictive malabsorptive procedure, but many patients also report altered taste preferences. This study investigated the effects of GBS or a sham operation (SH) on body weight, glucose tolerance, and behavioral and neuronal taste functions in the obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats lacking CCK-1 receptors and lean controls (LETO). OLETF-GBS rats lost body weight (-26%) and demonstrated improved glucose tolerance. They also expressed a reduction in 24-h two-bottle preference for sucrose (0.3 and 1.0 M) and decreased 10-s lick responses for sucrose (0.3 through 1.5 M) compared with OLETF-SH or LETO-GBS. A similar effect was noted for other sweet compounds but not for salty, sour, or bitter tastants. In lean rats, GBS did not alter responses to any stimulus tested. Extracellular recordings from 170 taste-responsive neurons of the pontine parabrachial nucleus revealed a rightward shift in concentration responses to oral sucrose in obese compared with lean rats (OLETF-SH vs. LETO-SH): overall increased response magnitudes (above 0.9 M), and maximum responses occurring at higher concentrations (+0.46 M). These effects were reversed by GBS, and neural responses in OLETF-GBS were statistically not different from those in any LETO groups. These findings confirm obesity-related alterations in taste functions and demonstrate the ability of GBS to alleviate these impairments. Furthermore, the beneficial effects of GBS appear to be independent of CCK-1 receptor signaling. An understanding of the underlying mechanisms for reduced preferences for sweet taste could help in developing less invasive treatments for obesity.