Urinary sodium excretion after gastric bypass surgery

Urinary Metabolomic Changes Accompanying Albuminuria Remission following Gastric Bypass Surgery for Type 2 Diabetic Kidney Disease

In the Microvascular Outcomes after Metabolic Surgery randomised clinical trial (MOMS RCT, NCT01821508), combined metabolic surgery (gastric bypass) plus medical therapy (CSM) was superior to medical therapy alone (MTA) as a means of achieving albuminuria remission at 2-year follow-up in patients with obesity and early diabetic kidney disease (DKD). In the present study, we assessed the urinary ¹H-NMR metabolome in a subgroup of patients from both arms of the MOMS RCT at baseline and 6-month follow-up. Whilst CSM and MTA both reduced the urinary excretion of sugars, CSM generated a distinctive urinary metabolomic profile characterised by increases in host–microbial co-metabolites (N-phenylacetylglycine, trimethylamine N-oxide, and 4-aminobutyrate (GABA)) and amino acids (arginine and glutamine). Furthermore, reductions in aromatic amino acids (phenylalanine and tyrosine), as well as branched-chain amino acids (BCAAs) and related catabolites (valine, leucine, 3-hydroxyisobutyrate, 3-hydroxyisovalerate, and 3-methyl-2-oxovalerate), were observed following CSM but not MTA. Improvements in BMI did not correlate with improvements in metabolic and renal indices following CSM. Conversely, urinary metabolites changed by CSM at 6 months were moderately to strongly correlated with improvements in blood pressure, glycaemia, triglycerides, and albuminuria up to 24 months following treatment initiation, highlighting the potential involvement of these shifts in the urinary metabolomic profile in the metabolic and renoprotective effects of CSM.

Role of the Autonomic Nervous System in Mechanism of Energy and Glucose Regulation Post Bariatric Surgery

Even though lifestyle changes are the mainstay approach to address obesity, Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) are the most effective and durable treatments facing this pandemic and its associated metabolic conditions. The traditional classifications of bariatric surgeries labeled them as “restrictive,” “malabsorptive,” or “mixed” types of procedures depending on the anatomical rearrangement of each one of them. This conventional categorization of bariatric surgeries assumed that the “restrictive” procedures induce their weight loss and metabolic effects by reducing gastric content and therefore having a smaller reservoir. Similarly, the “malabsorptive” procedures were thought to induce their main energy homeostatic effects from fecal calorie loss due to intestinal malabsorption. Observational data from human subjects and several studies from rodent models of bariatric surgery showed that neither of those concepts is completely true, at least in explaining the multiple metabolic changes and the alteration in energy balance that those two surgeries induce. Rather, neuro-hormonal mechanisms have been postulated to underly the physiologic effects of those two most performed bariatric procedures. In this review, we go over the role the autonomic nervous system plays- through its parasympathetic and sympathetic branches- in regulating weight balance and glucose homeostasis after SG and RYGB.

Inquiry into the short- and long-term effects of Roux-en-Y gastric bypass on the glomerular filtration rate

Bariatric surgery is known to attenuate glomerular hyperfiltration over the long term and thereby protect the kidney from mechanical damage. Whether this effect is directly related to weight loss or is independent of weight as are some of its other beneficial metabolic effects is not known. We explored this question in a preliminary study that directly measured glomerular filtration rate (GFR) before, immediately after, and again many months after Roux-en-Y gastric bypass after large weight loss had occurred. We simultaneously measured stimulated circulating glucagon-like peptide-1, which is upregulated after Roux-en-Y gastric bypass and is a putative mediator of GFR after bariatric surgery. We found no weight-independent effect of Roux-en-Y gastric bypass on GFR nor an association between circulating GLP-1 levels and GFR. These findings, if confirmed in larger studies, will help steer future enquiries in this area.

Which Patients with Obesity Are at Risk for Renal Disease?

Obesity-related glomerulopathy (ORG) is an increasingly recognized cause of end-stage kidney disease. The most common clinical presentation is a slowly increasing nonnephrotic proteinuria that is followed by a progressive decline of kidney function. Key histological findings are glomerulomegaly and lesions of focal and segmental glomerulosclerosis. A central pathogenic mechanism is the increased sodium reabsorption by proximal tubules that typically accompanies obesity. This causes a decrease in the offer of sodium to the macula densa in the distal nephron, which results in a vasodilation of afferent glomerular arterioles and glomerular hyperfiltration. From a clinical point of view, it is essential to differentiate focal segmental glomerulosclerosis secondary to obesity from primary glomerular processes, which requires a careful differential diagnosis. Diet-induced weight loss, bariatric surgery, and renin-angiotensin blockers are the fundamental therapeutic measures in ORG. The recently developed sodium-glucose cotransporter 2 inhibitors and glucagon-like peptide 1 agonist represent a significant advance in renal protection and will probably improve clinical kidney outcomes in ORG.

Impact of Metabolic Surgery on Renal Injury in Pre-Clinical Models of Diabetic Kidney Disease

BACKGROUND

Surgical approaches to the treatment of obesity and type 2 diabetes, most notably the Roux-en-Y gastric bypass (RYGB) procedure, have been shown to be renoprotective, reducing the incidence of albuminuria and end-stage kidney disease over 15- to 20-year follow-up in patients with obesity. The tissue level effects of metabolic surgery on the diabetic kidney are not easily interrogated in clinical samples. However, elucidation of the cellular and molecular basis for the renoprotective effects of metabolic surgery is now emerging from a body of pre-clinical work in rodent models of diabetic kidney disease (DKD).

SUMMARY

Experimental metabolic surgery (RYGB, sleeve gastrectomy [SG], Roux-en-Y oesophagojejunostomy, and duodenojejunal bypass) exerts a pronounced albuminuria-lowering effect in rat models of DKD. Following RYGB in the Zucker diabetic fatty rat, glomerular histology is improved as demonstrated by reductions in podocyte stress, glomerulomegaly, and glomerulosclerosis. Glomerular ultrastructure improves after RYGB and after SG, manifested by quantifiable reductions in podocyte foot process effacement. The transcriptional programme underpinning these structural improvements has been characterized at the pathway level using RNA sequencing and is associated with a significant reduction in the activation of inflammatory and fibrotic responses. Key Messages: Experimental metabolic surgery reduces biochemical, histological, and molecular indices of DKD. These pre-clinical data support a growing interest in the potential utility of metabolic surgery as a therapeutic approach to slow renal functional decline in patients with obesity and DKD.

Low serum sodium concentrations in patients with obesity normalizes with weight loss

BACKGROUND & AIMS

Obesity is associated with higher extracellular fluid (ECF) compared to intracellular fluid (ICF) volume and this dysregulation is associated with hypertension and abdominal obesity, associated with metabolic syndrome. As sodium is predominantly an extracellular cation, a higher ECF/ICF ratio will lower serum sodium concentration. The aim of the study was to see whether weight loss, due to dieting and bariatric surgery, had any impact on serum sodium concentrations in patients with severe obesity.

METHODS

Patients with a BMI ≥35 kg/m² admitted for bariatric surgery at Innlandet Hospital Trust, Norway during 2012-14 were included in the study (n = 119). Clinical data and blood samples were recorded at inclusion, after mean six months of dieting, as well as six and 12 months after bariatric surgery.

RESULTS

At inclusion, mean serum sodium was in the lower normal range, 138.3 (SD 2.4) mmol/L, but increased to 141.8 (SD 1.9) mmol/L after weight loss. The increase was significantly correlated to total weight loss (rho: 0.29, p = 0.007). Twelve months after surgery, serum sodium was significantly higher in patients with a normal BMI (<25 kg/m²) compared to patients with overweight.

CONCLUSION

Obesity and hypertension are associated with body fluid dysregulation affecting serum sodium concentrations. As mild hyponatremia, even within the normal sodium range, is associated with increased total mortality and major cardiovascular disease events, serum sodium might be a potential risk marker in patients with obesity.

Characterization of the renal cortical transcriptome following Roux-en-Y gastric bypass surgery in experimental diabetic kidney disease

INTRODUCTION

Roux-en-Y gastric bypass surgery (RYGB) reduces albuminuria and the long-term incidence of end-stage renal disease in patients with obesity and diabetes. Preclinical modeling in experimental diabetic kidney disease demonstrates that improvements in glomerular structure likely underpin these findings.

RESEARCH DESIGN AND METHODS

In adult male Zucker diabetic fatty (ZDF) rats, we profiled the effect of RYGB on weight and metabolic control as well biochemical, structural and ultrastructural indices of diabetic renal injury. Furthermore, we sequenced the renal cortical transcriptome in these rats and used bioinformatic pathway analyses to characterize the transcriptional alterations governing the renal reparative response to RYGB.

RESULTS

In parallel with improvements in weight and metabolic control, RYGB reduced albuminuria, glomerulomegaly, podocyte stress and podocyte foot process effacement. Pathway analysis of RYGB-induced transcriptomic changes in the renal cortex highlighted correction of disease-associated alterations in fibrosis, inflammation and biological oxidation pathways. RYGB reversed disease-associated changes in the expression of transforming growth factor (TGF)-β superfamily genes that strongly correlated with improvements in structural measures of glomerulopathy.

CONCLUSIONS

Improved glomerular structure in ZDF rats following RYGB is underpinned by pathway level changes, including interruption of the TGF-β-driven early profibrotic programme. Our data provide an important layer of experimental support for clinical evidence demonstrating that RYGB arrests renal damage in patients with obesity and type 2 diabetes.

Obesity, Hypertension, and Bariatric Surgery

PURPOSE OF REVIEW

Obesity increases the risk of hypertension. However, blood pressure decreases before any significant loss of body weight after bariatric surgery. We review the mechanisms of the temporal dissociation between blood pressure and body weight after bariatric surgery.

RECENT FINDINGS

Restrictive and bypass bariatric surgery lower blood pressure and plasma leptin levels within days of the procedure in both hypertensive and normotensive morbidly obese patients. Rapidly decreasing plasma leptin levels and minimal loss of body weight point to reduced sympathetic nervous system activity as the underlying mechanism of rapid blood pressure decline after bariatric surgery. After the early rapid decline, blood pressure does not decrease further in patients who, while still obese, experience a steady loss of body weight for the subsequent 12 months. The divergent effects of bariatric surgery on blood pressure and body weight query the role of excess body weight in the pathobiology of the obesity phenotype of hypertension. The decrease in blood pressure after bariatric surgery is moderate and independent of body weight. The lack of temporal relationship between blood pressure reduction and loss of body weight for 12 months after sleeve gastrectomy questions the nature of the mechanisms underlying obesity-associated hypertension.

Cardiac natriuretic peptides

Investigations into the mixed muscle-secretory phenotype of cardiomyocytes from the atrial appendages of the heart led to the discovery that these cells produce, in a regulated manner, two polypeptide hormones - the natriuretic peptides - referred to as atrial natriuretic factor or atrial natriuretic peptide (ANP) and brain or B-type natriuretic peptide (BNP), thereby demonstrating an endocrine function for the heart. Studies on the gene encoding ANP (NPPA) initiated the field of modern research into gene regulation in the cardiovascular system. Additionally, ANP and BNP were found to be the natural ligands for cell membrane-bound guanylyl cyclase receptors that mediate the effects of natriuretic peptides through the generation of intracellular cGMP, which interacts with specific enzymes and ion channels. Natriuretic peptides have many physiological actions and participate in numerous pathophysiological processes. Important clinical entities associated with natriuretic peptide research include heart failure, obesity and systemic hypertension. Plasma levels of natriuretic peptides have proven to be powerful diagnostic and prognostic biomarkers of heart disease. Development of pharmacological agents that are based on natriuretic peptides is an area of active research, with vast potential benefits for the treatment of cardiovascular disease.

Metabolic Surgery to Treat Obesity in Diabetic Kidney Disease, Chronic Kidney Disease, and End-Stage Kidney Disease; What Are the Unanswered Questions?

Obesity is a major factor in contemporary clinical practice in nephrology. Obesity accelerates the progression of both diabetic and non-diabetic chronic kidney disease and, in renal transplantation, both recipient and donor obesity increase the risk of allograft complications. Obesity is thus a major driver of renal disease progression and a barrier to deceased and living donor kidney transplantation. Large observational studies have highlighted that metabolic surgery reduces the incidence of albuminuria, slows chronic kidney disease progression, and reduces the incidence of end-stage kidney disease over extended follow-up in people with and without type 2 diabetes. The surgical treatment of obesity and its metabolic sequelae has therefore the potential to improve management of diabetic and non-diabetic chronic kidney disease and aid in the slowing of renal decline toward end-stage kidney disease. In the context of patients with end-stage kidney disease, although complications of metabolic surgery are higher, absolute event rates are low and it remains a safe intervention in this population. Pre-transplant metabolic surgery increases access to kidney transplantation in people with obesity and end-stage kidney disease. Metabolic surgery also improves management of metabolic complications post-kidney transplantation, including new-onset diabetes. Procedure selection may be critical to mitigate the risks of oxalate nephropathy and disruption to immunosuppressant pharmacokinetics. Metabolic surgery may also have a role in the treatment of donor obesity, which could increase the living kidney donor pool with potential downstream impact on kidney paired exchange programmes. The present paper provides a comprehensive coverage of the literature concerning renal outcomes in clinical studies of metabolic surgery and integrates findings from relevant mechanistic pre-clinical studies. In so doing the key unanswered questions for the field are brought to the fore for discussion.

Improving obesity and blood pressure

Obesity-associated hypertension is a serious public health concern. Sympathetic nervous system (SNS) overactivity, especially in the kidneys, is an important mechanism linking obesity to hypertension. Some adipokines play important roles in elevating blood pressure (BP). Hyperinsulinemia caused by insulin resistance stimulates sodium reabsorption, enhances sodium retention, and increases circulating plasma volume. Hyperinsulinemia also stimulates both the renin-angiotensin-aldosterone system (RAAS) and the SNS, resulting in the acceleration of atherosclerosis through the hypertrophy of vascular smooth muscle cells, which contributes to increased peripheral vascular resistance. Obesity is associated with increased RAAS activity despite volume overload, as the tissue RAASs are stimulated in obese hypertensive individuals. Mineralocorticoid receptor-associated hypertension must also be considered in obese patients with resistant hypertension. Obstructive sleep apnea syndrome (OSAS) is the most common cause of secondary hypertension. Some components of the gut microbiota contribute to BP control; therefore, gut dysbiosis caused by obesity might lead to increased BP. The ratio of visceral fat to subcutaneous fat is higher in Japanese patients than in Caucasian patients, which may explain why Japanese patients are more susceptible to metabolic disorders even though they are less obese than Caucasian individuals. Obesity-associated kidney dysfunction directly increases BP, leading to further deterioration of kidney function. A bodyweight reduction of more than 3% or 5 kg significantly lowers BP. Gastrointestinal bypass surgery is an effective treatment for morbid obesity and its related metabolic disorders, including hypertension. Because both obesity and hypertension are representative lifestyle-related disorders, lifestyle modification, especially to improve obesity, should be performed first as a treatment for hypertension.

Hypertension as a Metabolic Disorder and the Novel Role of the Gut

Purpose of Review

Hypertension is related to impaired metabolic homeostasis and can be regarded as a metabolic disorder. This review presents possible mechanisms by which metabolic disorders increase blood pressure (BP) and discusses the importance of the gut as a novel modulator of BP.

Recent Findings

Obesity and high salt intake are major risk factors for hypertension. There is a hypothesis of “salt-induced obesity”; i.e., high salt intake may tie to obesity. Heightened sympathetic nervous system (SNS) activity, especially in the kidney and brain, increases BP in obese patients. Adipokines, including adiponectin and leptin, and renin-angiotensin-aldosterone system (RAAS) contribute to hypertension. Adiponectin induced by a high-salt diet may decrease sodium/glucose cotransporter (SGLT) 2 expression in the kidney, which results in reducing BP. High salt can change secretions of adipokines and RAAS-related components. Evidence has been accumulating linking the gastrointestinal tract to BP. Glucagon-like peptide-1 (GLP-1) and ghrelin decrease BP in both rodents and humans. The sweet taste receptor in enteroendocrine cells increases SGLT1 expression and stimulates sodium/glucose absorption. Roux-en-Y gastric bypass improves glycemic and BP control due to reducing the activity of SGLT1. Na/H exchanger isoform 3 (NHE3) increases BP by stimulating the intestinal absorption of sodium. Gastrin functions as an intestinal sodium taste sensor and inhibits NHE3 activity. Intestinal mineralocorticoid receptors also regulate sodium absorption and BP due to changing ENaC activity. Gastric sensing of sodium induces natriuresis, and gastric distension increases BP. Changes in the composition and function of gut microbiota contribute to hypertension. A high-salt/fat diet may disrupt the gut barrier, which results in systemic inflammation, insulin resistance, and increased BP. Gut microbiota regulates BP by secreting vasoactive hormones and short-chain fatty acids. BP-lowering effects of probiotics and antibiotics have been reported. Bariatric surgery improves metabolic disorders and hypertension due to increasing GLP-1 secretion, decreasing leptin secretion and SNS activity, and changing gut microbiome composition. Strategies targeting the gastrointestinal system may be therapeutic options for improving metabolic abnormalities and reducing BP in humans.

Summary

SNS, brain, adipocytes, RAAS, the kidney, the gastrointestinal tract, and microbiota play important roles in regulating BP. Most notably, the gut could be a novel target for treatment of hypertension as a metabolic disorder.

Impact of bariatric surgery on cardiovascular and renal complications of diabetes: a focus on clinical outcomes and putative mechanisms

INTRODUCTION

Cardiovascular and renal disease accounts for a substantial proportion of the morbidity and mortality associated with obesity and type 2 diabetes mellitus (T2DM). Bariatric surgery is associated with improved long-term cardiovascular and renal outcomes.

AREAS COVERED

All major case-control, cohort, and randomized controlled trial studies of bariatric surgery in adults with T2DM were screened and data on prespecified cardiovascular and renal outcomes collated. Bariatric surgery reduces all-cause mortality and risk of cardiovascular disease, albuminuria and progressive chronic kidney disease. Patients with poorer glycemic control and established microvascular disease preoperatively may stand to benefit the most from the surgical approach. Reduced sympathetic drive, remission of glomerular hypertension, enhanced natriuresis, gut microbiota shifts, reduced systemic and renal inflammation, improved lipoprotein profiles, and reductions in chronic cardiac remodeling may all be implicated.

EXPERT COMMENTARY

Ongoing RCTs of bariatric surgery selectively recruiting patients with class 1 obesity and established microvascular complications of diabetes will help to better characterize which subgroups of patients benefit most from this effective therapy.

Metabolic Effects of Bariatric Surgery

BACKGROUND

Obesity can be defined as a chronic subcortical brain disease, as there is an important neurophysiological component to its etiology based on changes in the functioning of those areas of the brain controlling food intake and reward. Extensive metabolic changes accompany bariatric surgery-based treatment of obesity. Consequently, the term “metabolic” surgery is being increasingly adopted in relation to the beneficial effects these procedures have on chronic diseases like type 2 diabetes.

CONTENT

In the present review, we focus on the key biochemical and physiological changes induced by metabolic surgery and highlight the beneficial effects accrued systemically with the use of an organ-based approach. Understanding the impact on and interactions between the gut, brain, adipose tissue, liver, muscle, pancreas, and kidney is key to understanding the sum of the metabolic effects of these operations.

SUMMARY

Further mechanistic studies are essential to assess the true potential of metabolic surgery to treat metabolic comorbidities of obesity beyond type 2 diabetes. Approaches that may mitigate the metabolic side effects of surgery also require attention. Understanding the positive impact of metabolic surgery on metabolic health may result in a wider acceptance of this intervention as treatment for metabolic, comorbid conditions.