Tissue-specific effects of bariatric surgery including mitochondrial function

Sleeve Gastrectomy Reduces Oxidative Stress and Reverses Mitochondrial Dysfunction Associated with Metabolic Syndrome

INTRODUCTION

Previous studies have detected mitochondrial alterations in tissues of individuals with obesity and type 2 diabetes mellitus (T2DM). Metabolic surgery could be an effective treatment to improve mitochondrial morphology and reduce oxidative stress (OS).

METHODS

An experimental study was carried out using 48 male Wistar rats, divided into 6 groups (n = 8): control (C), induced Metabolic Syndrome (MS); intervention with sleeve gastrectomy (SG), MS + SG with 6 weeks postoperatively (MS + SG6), MS + SG with 12 weeks postoperatively (MS + SG12), and MS + SG with 24 weeks postoperatively (MS + SG24). Biochemical markers indicative of MS (glycemia, cholesterol, and triglyceride levels) and oxidative stress markers (nitric oxide levels, Superoxide dismutase and Myeloperoxidase activity) were determined. To study mitochondrial morphology, tissue sections of the thoracic aorta, stomach, liver, heart, and kidney were observed by electron microscopy.

RESULTS

MS group exhibited elevated glycemic values and dyslipidemia. SG and MS + SG groups showed improvements in glycemia and lipid profiles compared to MS. OS biomarkers indicated reduced oxidative stress in SG and MS + SG groups compared to MS. Electron microscopy revealed mitochondrial alterations in MS. SG group showed no changes compared to the control. MS + SG6 and MS + SG12 groups showed a recovery of mitochondrial morphology until reaching images similar to the control in MS + SG24.

CONCLUSION

Metabolic surgery could improve mitochondrial function by restoring mitochondrial morphology and architecture and, consequently, reducing systemic oxidative stress and remitting associated metabolic alterations.

Effect of Bariatric Surgery on Plasma Cell-Free Mitochondrial DNA, Insulin Sensitivity and Metabolic Changes in Obese Patients

While improvement of mitochondrial function after bariatric surgery has been demonstrated, there is limited evidence about the effects of bariatric surgery on circulatory cell-free (cf) mitochondrial DNA (mtDNA) and intracellular mtDNA abundance. Plasma and peripheral blood mononuclear (PBM) cells were isolated from healthy controls (HC) and bariatric surgery patients before surgery and 2 weeks, 3 months, and 6 months after surgery. At baseline, the plasma level of short cf-mtDNA (ND6, ~100 bp) fragments was significantly higher in obese patients compared to HC. But there was no significant variation in mean ND6 values post-surgery. A significant positive correlation was observed between preop plasma ND6 levels and HgbA1c, ND6 and HOMA-IR 2 weeks post-surgery, and mtDNA content 6 months post-surgery. Interestingly, plasma from both HC and obese groups at all time points post-surgery contains long (~8 kb) cf-mtDNA fragments, suggesting the presence of near-intact and/or whole mitochondrial genomes. No significant variation was observed in mtDNA content post-surgery compared to baseline data in both PBM and skeletal muscle samples. Overall, bariatric surgery improved insulin sensitivity and other metabolic parameters without significant changes in plasma short cf-mtDNA levels or cellular mtDNA content. Our study provides novel insights about possible molecular mechanisms underlying the metabolic effects of bariatric surgery and suggests the development of new generalized approaches to characterize cf-mtDNA.

Preoperative Circulating Succinate Levels as a Biomarker for Diabetes Remission After Bariatric Surgery

OBJECTIVE

To determine the potential use of baseline circulating succinate to predict type 2 diabetes remission after bariatric surgery.

RESEARCH DESIGN AND METHODS

Forty-five obese patients with diabetes were randomly assigned to Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (SG), or laparoscopic greater curvature plication. Anthropometric parameters were evaluated, and a complete biochemical analysis including circulating serum succinate concentrations was performed at baseline and 1 year after surgery. The results were externally validated in a second cohort including 88 obese patients with diabetes assigned to RYGB or SG based on clinical criteria.

RESULTS

Succinate baseline concentrations were an independent predictor of diabetes remission after bariatric surgery. Patients achieving remission after 1 year had lower levels of baseline succinate (47.8 [37.6-64.6] µmol/L vs. 64.1 [52.5-82.9] µmol/L; P = 0.018). Moreover, succinate concentrations were significantly decreased 1 year after surgery (58.9 [46.4-82.4] µmol/L vs. 46.0 [35.8-65.3] µmol/L, P = 0.005). In multivariate analysis, the best logistic regression model showed that baseline succinate (odds ratio [OR] 11.3, P = 0.031) and the type of surgery (OR 26.4, P = 0.010) were independently associated with remission. The C-statistic for this model was 0.899 (95% CI 0.809-0.989) in the derivation cohort, which significantly improved the prediction of remission compared with current available scores, and 0.729 (95% CI 0.612-0.846) in the validation cohort. Interestingly, patients had a different response to the type of surgery according to baseline succinate, with significant differences in remission rates.

CONCLUSIONS

Circulating succinate is reduced after bariatric surgery. Baseline succinate levels have predictive value for diabetes remission independently of previously described presurgical factors and improve upon the current available scores to predict remission.

Bariatric Surgery Reduces Elevated Urinary Mitochondrial DNA Copy Number in Patients With Obesity

OBJECTIVE

Obesity is an independent risk factor for chronic kidney disease. Recently, urinary mitochondrial DNA (mtDNA) has been used as a surrogate marker of mitochondrial damage in various kidney diseases. However, there are no data regarding its use in patients with obesity or the change in urinary mtDNA copy number after surgery.

DESIGN

We prospectively recruited age- and sex-matched healthy volunteers and patients with obesity (n = 22 in each group: nine men and 13 women). The copy number of urinary and serum mtDNA nicotinamide adenine dinucleotide dehydrogenase subunit-1 (mtND-1) and cytochrome-c oxidase 3 (mtCOX-3) was measured using quantitative PCR. We measured urinary mtDNA and body weight and carried out laboratory tests, 6 months after surgery.

RESULTS

Urinary mtND-1 copy number was significantly higher in the obese group than in healthy volunteers. However, urinary mtCOX-3 and serum ND-1 copy numbers in the obese group did not differ from that in the healthy volunteers. When patients with obesity were divided into two groups, according to their baseline mtND-1 copy number, bariatric surgery reduced the mtND-1 copy number (P = 0.006) in the high baseline mtDNA copy-number group. The change in urinary mtND-1 copy number was correlated with a change in urinary albumin (r = 0.478, P = 0.025).

CONCLUSIONS

Obesity is associated with elevated urinary mtND-1 copy number. Bariatric surgery reduces the elevated urinary mtND-1 copy number in patients with obesity. This suggests that bariatric surgery could attenuate mitochondrial damage in the kidney cells of patients with obesity.

From Normal to Obesity and Back: The Associations between Mitochondrial DNA Copy Number, Gender, and Body Mass Index

Mitochondrial DNA (mtDNA) encodes core subunits of oxidative phosphorylation complexes and, as a result of intricate regulatory crosstalk between nuclear and mitochondrial genomes, the total number of mtDNA copies fits the requirements of each cell type. Deviations from the physiological number of mtDNA copies are expected to be deleterious and might cause some inherited diseases and normal ageing. We studied 46 obese patients with type 2 diabetes (T2DM) one year after a laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB). The results were compared with normal-weight patients without T2DM (control group 1) (body mass index (BMI) = 22.5 ± 3.01 kg/m²) and patients with obesity without T2DM (control group 2) (BMI = 36 ± 3.45 kg/m²). We detected an increase of mtDNA copy number in the cells of the buffy coat obtained from peripheral blood, sampled one year after bariatric surgery. We also found that average mtDNA copy number as well as its dynamics (before and after the surgery) are gender-specific. To the best of our knowledge, this is the first evidence for the restoration of mtDNA copy number in obese patients after LSG and RYGB.

Targeting White Adipose Tissue with Exercise or Bariatric Surgery as Therapeutic Strategies in Obesity

Adipose tissue is critical to whole-body energy metabolism and has become recognized as a bona fide endocrine organ rather than an inert lipid reservoir. As such, adipose tissue is dynamic in its ability to secrete cytokines, free fatty acids, lipokines, hormones and other factors in response to changes in environmental stimuli such as feeding, fasting and exercise. While excess adipose tissue, as in the case of obesity, is associated with metabolic complications, mass itself is not the only culprit in obesity-driven metabolic abnormalities, highlighting the importance of healthy and metabolically adaptable adipose tissue. In this review, we discuss the fundamental cellular processes of adipose tissue that become perturbed in obesity and the impact of exercise on these processes. While both endurance and resistance exercise can promote positive physiological adaptations in adipose tissue, endurance exercise has a more documented role in remodeling adipocytes, increasing adipokine secretion and fatty acid mobilization and oxidation during post-exercise compared with resistance exercise. Exercise is considered a viable therapeutic strategy for the treatment of obesity to optimize body composition, in particular as an adjuvant therapy to bariatric surgery; however, there is a gap in knowledge of the molecular underpinnings of these exercise-induced adaptations, which could provide more insight and opportunity for precision-based treatment strategies.

In-and-Out Molecular Changes Linked to the Type 2 Diabetes Remission after Bariatric Surgery: An Influence of Gut Microbes on Mitochondria Metabolism

Different kinds of gastrointestinal tract modulations known as “bariatric surgery” are actually the most effective treatment for obesity and associated co-morbidities, such as type 2 diabetes (T2DM). The potential causes of those effects have yet to be explained. In our study, we focused on molecular changes evoked by laparoscopic sleeve gastrectomy leading to T2DM remission. Two complementary metabolomics techniques, namely, liquid chromatography coupled with mass spectrometry (LC-MS) and gas chromatography mass spectrometry (GC-MS), were used to study those effects in a group of 20 obese patients with T2DM selected from a cohort of 372 obese individuals who underwent bariatric surgery and did not receive anti-diabetic treatment afterward. Modified levels of carnitines, lipids, amino acids (including BCAA) and α- and β-hydroxybutyric acids were detected. Presented alterations suggest a major role of mitochondria activity in T2DM remission process. Moreover, some of the observed metabolites suggest that changes in gut microbiota composition may also correlate with the tempo of diabetes recovery. Additional analyses confirmed a relationship between biochemical and clinical parameters and the aforementioned metabolites, thereby, highlighting a role of mitochondria and microbes. Our data suggests that there is a previously undescribed relationship between mitochondria and gut microbiota, which changes after the bariatric surgery. More investigations are needed to confirm and explore the observed findings.

Effects of Weight Reduction After Sleeve Gastrectomy on Metabolic Variables in Saudi Obese Subjects in Aseer Province of Kingdom of Saudi Arabia

OBJECTIVES

The objectives of this study were to investigate the occurrence of oxidative stress, status of protective antioxidants enzymes, inflammatory biomarkers, and some metabolic health variables in the blood and to compare the results between those of the normal controls and obese patients submitted to sleeve gastrectomy-induced weight loss over a 1-year follow-up period.

MATERIALS AND METHODS

A prospective study was conducted in Aseer Central Hospital and Abha Private Hospital in the Kingdom of Saudi Arabia from January 2012 to January 2013 on 50 normal (BMI = 22-25 kg/m²) control subjects and 50 obese (BMI = 45-50 kg/m²) patients. A subset of 20 men and 80 women patients, aged 20-45 years, was included. The systemic blood cell counts were determined by Beckman Coulter UniCel analyzer. The occurrence of oxidative stress, the status of antioxidant enzyme system in the blood, levels of serum hepatic enzymes, cardiovascular risk factors, and serum sodium, potassium, copper, and zinc levels were determined by spectrophotometric procedures. The concentration of TSH and T₄ were analyzed by Siemens Immunoassay System.

RESULTS

Group 1 (Obese: preoperative) This group compared with the normal controls exhibited significant (p < 0.05) increase in inflammatory biomarkers, a significant (p < 0.05) rise in hepatic enzymes, a significant (p < 0.05) decrease in serum total bilirubin. Concentration of serum total cholesterol (TC), triacylglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and fasting blood glucose(FBG) were significantly (p < 0.05) increased, but HDL cholesterol (HDL-C) was significantly depleted (p < 0.05). Serum urea and creatinine contents were significantly (p < 0.05) decreased. Serum copper and zinc levels were significantly (p < 0.05) increased. Group 2: Sleeve Gastrectomy Surgery (Obese: postoperative) This group compared with the obese group, preoperatively, demonstrated a profound reduction in body weight (-32%) as well as in BMI (-29%). Serum malondialdehyde, a stress index, was significantly (p < 0.001) inhibited and conversely, activities of antioxidant enzymes: superoxide dismutase(Cu-Zn SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST), glucose-6-phosphate dehydrogenase (G6PDH), and vitamin C, were remarkably (p < 0.001) increased. Furthermore, remarkable improvements in deranged metabolic variables approaching normality were discernible. Inflammatory biomarkers in the blood and hepatic enzymes in serum were significantly (p < 0.001) decreased. Levels of TC, TG, LDL-C, FBG, and HDL-C in serum exhibited significant (p < 0.05) reductions, a reversal toward normality. Serum albumin and total bilirubin concentrations were significantly increased (p < 0.001). Serum sodium, potassium, copper, zinc, and TSH levels were significantly (p < 0.001) decreased.

CONCLUSIONS

Obesity is a chronic disease of multifactorial origin and resulted in perturbations of whole body metabolism in this study. It is thus likely that this imbalance was associated with an inhibition in protective antioxidants and occurrence of oxidative stress. The staging concept of sleeve gastrectomy is a safe and effective approach with remarkable efficacy in sustaining weight loss and bringing back normal metabolism of variables in tissues over a 1-year follow-up period.

Roux-en-Y Gastric Bypass Acutely Decreases Protein Carbonylation and Increases Expression of Mitochondrial Biogenesis Genes in Subcutaneous Adipose Tissue

BACKGROUND

Mitochondrial dysfunction in adipose tissue has been implicated as a pathogenic step in the development of type 2 diabetes mellitus (T2DM). In adipose tissue, chronic nutrient overload results in mitochondria driven increased reactive oxygen species (ROS) leading to carbonylation of proteins that impair mitochondrial function and downregulation of key genes linked to mitochondrial biogenesis. In patients with T2DM, Roux-en-Y gastric bypass (RYGB) surgery leads to improvements in glycemic profile prior to significant weight loss. Consequently, we hypothesized that improved glycemia early after RYGB would be paralleled by decreased protein carbonylation and increased expression of genes related to mitochondrial biogenesis in adipose tissue.

METHODS

To evaluate this hypothesis, 16 obese individuals were studied before and 7-8 days following RYGB and adjustable gastric banding (AGB). Subcutaneous adipose tissue was obtained pre- and post-bariatric surgery as well as from eight healthy, non-obese individual controls.

RESULTS

Prior to surgery, adipose tissue expression of PGC1α, NRF1, Cyt C, and eNOS (but not Tfam) showed significantly lower expression in the obese bariatric surgery group when compared to lean controls (p < 0.05). Following RYGB, but not after AGB, patients showed significant decrease in HOMA-IR, reduction in adipose protein carbonylation, and increased expression of genes linked to mitochondrial biogenesis.

CONCLUSIONS

These results suggest that rapid reduction in protein carbonylation and increased mitochondrial biogenesis may explain postoperative metabolic improvements following RYGB.

Effects of ovariectomy and intrinsic aerobic capacity on tissue-specific insulin sensitivity

High-capacity running (HCR) rats are protected against the early (i.e., ∼ 11 wk postsurgery) development of ovariectomy (OVX)-induced insulin resistance (IR) compared with low-capacity running (LCR) rats. The purpose of this study was to utilize the hyperinsulinemic euglycemic clamp to determine whether 1) HCR rats remain protected from OVX-induced IR when the time following OVX is extended to 27 wk and 2) tissue-specific glucose uptake differences are responsible for the protection in HCR rats under sedentary conditions. Female HCR and LCR rats (n = 40; aged ∼ 22 wk) randomly received either OVX or sham (SHM) surgeries and then underwent the clamp 27 wk following surgeries. [3-(3)H]glucose was used to determine glucose clearance, whereas 2-[(14)C]deoxyglucose (2-DG) was used to assess glucose uptake in skeletal muscle, brown adipose tissue (BAT), subcutaneous white adipose tissue (WAT), and visceral WAT. OVX decreased the glucose infusion rate and glucose clearance in both lines, but HCR had better insulin sensitivity than LCR (P < 0.05). In both lines, OVX significantly reduced glucose uptake in soleus and gastrocnemius muscles; however, HCR showed ∼ 40% greater gastrocnemius glucose uptake compared with LCR (P < 0.05). HCR also exhibited greater glucose uptake in BAT and visceral WAT compared with LCR (P < 0.05), yet these tissues were not affected by OVX in either line. In conclusion, OVX impairs insulin sensitivity in both HCR and LCR rats, likely driven by impairments in insulin-mediated skeletal muscle glucose uptake. HCR rats have greater skeletal muscle, BAT, and WAT insulin-mediated glucose uptake, which may aid in protection against OVX-associated insulin resistance.

Exercise training enhances white adipose tissue metabolism in rats selectively bred for low- or high-endurance running capacity

Impaired visceral white adipose tissue (WAT) metabolism has been implicated in the pathogenesis of several lifestyle-related disease states, with diminished expression of several WAT mitochondrial genes reported in both insulin-resistant humans and rodents. We have used rat models selectively bred for low- (LCR) or high-intrinsic running capacity (HCR) that present simultaneously with divergent metabolic phenotypes to test the hypothesis that oxidative enzyme expression is reduced in epididymal WAT from LCR animals. Based on this assumption, we further hypothesized that short-term exercise training (6 wk of treadmill running) would ameliorate this deficit. Approximately 22-wk-old rats (generation 22) were studied. In untrained rats, the abundance of mitochondrial respiratory complexes I-V, citrate synthase (CS), and PGC-1 was similar for both phenotypes, although CS activity was greater than 50% in HCR (P = 0.09). Exercise training increased CS activity in both phenotypes but did not alter mitochondrial protein content. Training increased the expression and phosphorylation of proteins with roles in β-adrenergic signaling, including β3-adrenergic receptor (16% increase in LCR; P < 0.05), NOR1 (24% decrease in LCR, 21% decrease in HCR; P < 0.05), phospho-ATGL (25% increase in HCR; P < 0.05), perilipin (25% increase in HCR; P < 0.05), CGI-58 (15% increase in LCR; P < 0.05), and GLUT4 (16% increase in HCR; P < 0.0001). A training effect was also observed for phospho-p38 MAPK (12% decrease in LCR, 20% decrease in HCR; P < 0.05) and phospho-JNK (29% increase in LCR, 20% increase in HCR; P < 0.05). We conclude that in the LCR-HCR model system, mitochondrial protein expression in WAT is not affected by intrinsic running capacity or exercise training. However, training does induce alterations in the activity and expression of several proteins that are essential to the intracellular regulation of WAT metabolism.

Permanence of molecular features of obesity in subcutaneous adipose tissue of ex-obese subjects

OBJECTIVE

Bariatric surgery represents a powerful tool for morbid obesity treatment. However, after stabilization of weight loss that follows surgical interventions, ex-obese patients face the problem of residual tissues removal. Actually, it is unknown whether the characteristics of this residual subcutaneous adipose tissue (SAT) are 'restored' with regard to molecular and morphological features.

DESIGN

To clarify this issue, we compared the SAT gene expression profile of ex-obese patients (ExOB-SAT, mean body mass index (BMI): 27.2±1.3 kg m(-2)) with that of lean (normal weight, NW-SAT, mean BMI: 22.6±1.1 kg m(-2)), overweight (OW-SAT, BMI: 27.65±0.2 kg m(-2)) and obese patients, according to BMI classes (OB1-SAT: 30 > or = BMI < or = 34.9, OB2-SAT: 35 > or = BMI < or = 39.9, OB3-SAT: BMI > or = 40).

SUBJECTS AND METHODS

A total of 58 samples of SAT were collected during surgical interventions. Gene expression levels were assessed by microarrays and significant genes were validated by RT-qPCR. Adipocyte hypertrophy, inflammatory infiltration and fibrosis were assessed by morphological techniques.

RESULTS

Global gene expression in ExOB-SAT was closely related to gene expression of OB3-SAT by hierarchical clustering procedures, in spite of different BMI. Metallothioneins (MT1A and MT2A) were the key over-expressed genes in both groups. At morphologic level, adipocyte hypertrophy and inflammatory infiltration improved after weight loss in ExOB-SAT, despite a persistence of fibrosis.

CONCLUSIONS

Taken together, these results demonstrate that SAT gene expression is not fully restored, even after an extensive and stable weight loss. The persistence of 'obesity molecular features' in ExOB-SAT suggests that the molecular signature of adipose tissue is not solely dependent on weight loss and may need longer time period to completely disappear.