Longitudinal assessment of renal function in native kidney after bariatric surgery

Relationships Between Changes in Serum Ketone Body Levels and Metabolic Effects in Patients with Severe Obesity Who Underwent Laparoscopic Sleeve Gastrectomy

BACKGROUND

Serum ketone bodies increase due to dynamic changes in the lipid metabolisms of patients undergoing bariatric surgery. However, there have been few studies on the role of ketone bodies after bariatric surgery. We aimed to clarify the role of and relationship between the changes in serum ketone bodies and weight loss, as well as between those changes and the metabolic effects after laparoscopic sleeve gastrectomy (LSG).

METHODS

We recruited 52 patients with severe obesity who underwent LSG. We measured acetoacetic acid (AcAc) and β-hydroxybutyric acid (β-OHB) at the baseline, 1 month, and 6 months after LSG. Subsequently, we compared the changes in the serum ketone bodies with weight-loss effects and various metabolic parameters.

RESULTS

At 1 month after LSG, β-OHB significantly increased (p = 0.009), then significantly decreased 6 months after LSG (p = 0.002). In addition, β-OHB in patients without Type 2 diabetes (T2D) and metabolic dysfunction-associated steatohepatitis (MASH) was notably higher than in patients with T2D at 1 month after LSG (p < 0.001). In the early phase, both AcAc and β-OHB mainly had strong positive correlations with changes in T2D- and MASH-related parameters. In the middle term after LSG, changes in both AcAc and β-OHB were positively correlated with changes in lipid parameters and chronic kidney disease-related parameters.

CONCLUSION

We demonstrated that the postoperative surge of ketone bodies plays a crucial function in controlling metabolic effects after LSG. These findings suggest the cause- and consequence-related roles of ketone bodies in the metabolic benefits of bariatric surgery.

Impact of Bariatric Surgery in the Short and Long Term: A Need for Time-Dependent Dosing of Drugs

Sparse information is available on pharmacokinetic changes of drugs over time after bariatric surgery. By reviewing the literature on the short- and long-term pharmacokinetic changes of drugs, several patterns were identified for 39 drugs. No relevant pharmacokinetic changes were identified for roughly a third of the drugs. Of the remaining drugs, levels were variable and partly unpredictable shortly after the surgery. In the long term, most of the drug levels remain altered, but in some cases they returned to preoperative values. Based on the changes and the efficacy-safety balance of each drug, clinicians may need to perform additional clinical monitoring for specific drugs, including measuring drug levels. This review provides suggestions for clinicians and pharmacists for specific time-dependent drug dosing advice.

The Impact and Effectiveness of Weight Loss on Kidney Transplant Outcomes: A Narrative Review

Obesity is a worldwide epidemic that leads to several non-communicable illnesses, including chronic kidney disease (CKD). Diet and lifestyle modifications have shown a limited impact in the treatment of obesity. Because the group of end-stage renal disease (ESRD) patients examined in this study had limited access to kidney transplantation (KT), patients with obesity were thought to be at an increased risk of intraoperative and postoperative KT complications. Although bariatric surgery (BS) is now recognized as the gold standard treatment for morbid obesity, its role in ESRD or kidney transplant patients remains unknown. It is critical to know the correlation between weight loss and complications before and after KT, the impact of the overall graft, and patients' survival. Hence, this narrative review aims to present updated reports addressing when to perform surgery (before or after a KT), which surgical procedure to perform, and again, if strategies to avoid weight regain must be specific for these patients. It also analyzes the metabolic alterations produced by BS and studies its cost-effectiveness pre- and post-transplantation. Due to the better outcomes found in KT recipients, the authors consider it more convenient to perform BS before KT. However, more multicenter trials are required to provide a solid foundation for these recommendations in ERSD patients with obesity.

Glomerular hyperfiltration

Circulating blood is filtered across the glomerular barrier to form an ultrafiltrate of plasma in the Bowman's space. The volume of glomerular filtration adjusted by time is defined as the glomerular filtration rate (GFR), and the total GFR is the sum of all single-nephron GFRs. Thus, when the single-nephron GFR is increased in the context of a normal number of functioning nephrons, single glomerular hyperfiltration results in 'absolute' hyperfiltration in the kidney. 'Absolute' hyperfiltration can occur in healthy people after high protein intake, during pregnancy and in patients with diabetes, obesity or autosomal-dominant polycystic kidney disease. When the number of functioning nephrons is reduced, single-nephron glomerular hyperfiltration can result in a GFR that is within or below the normal range. This 'relative' hyperfiltration can occur in patients with a congenitally reduced nephron number or with an acquired reduction in nephron mass consequent to surgery or kidney disease. Improved understanding of the mechanisms that underlie 'absolute' and 'relative' glomerular hyperfiltration in different clinical settings, and of whether and how the single-nephron haemodynamic and related biomechanical forces that underlie glomerular hyperfiltration promote glomerular injury, will pave the way toward the development of novel therapeutic interventions that attenuate glomerular hyperfiltration and potentially prevent or limit consequent progressive kidney injury and loss of function.

Changes in Kidney Fat upon Dietary-Induced Weight Loss

As the metabolic role of kidney fat remains unclear, we investigated the effects of dietary weight loss on kidney fat content (KFC) and its connection to kidney function and metabolism. Overweight or obese participants (n = 137) of a dietary intervention trial were classified into quartiles of weight loss in a post hoc manner. Kidney sinus (KSF) and cortex fat (KCF) were measured by magnetic resonance imaging at baseline, week 12 and week 50. Weight loss effects on KFC were evaluated by linear mixed models. Repeated measures correlations between KFC, other body fat measures and metabolic biomarkers were obtained. KSF, but not KCF, decreased significantly across weight loss quartiles at week 12 (quartile 4: -21.3%; p = 0.02) and 50 (-22.0%, p = 0.001), which remained significant after adjusting for VAT. There were smaller improvements regarding creatinine (-2.5%, p = 0.02) at week 12, but not week 50. KSF, but not KCF, correlated with visceral (r_rm = 0.38) and subcutaneous fat volumes (r_rm = 0.31) and liver fat content (r_rm = 0.32), as well as diastolic blood pressure and biomarkers of lipid, glucose and liver metabolism. Dietary weight loss is associated with decreases in KSF, but not KCF, which suggests that KSF may be the metabolically relevant ectopic fat depot of the kidney. KSF may be targeted for obesity-related disease prevention.

Improvement of Renal Function After Bariatric Surgery: a Systematic Review and Meta-analysis

BACKGROUND/OBJECTIVE

The effect of bariatric surgery in renal function varies and the postoperative benefit time point remains unclear. We aim to assess the changes of renal function after bariatric surgery (BS) in different postoperative periods and subgroups.

METHODS

We searched the databases of PubMed and Cochrane from inception to December 14, 2020. Articles included in the study were drawn from all recipients of BS that provided assessments of renal function pre and post-surgery. Meta-analysis was performed to compare glomerular filtration rate (GFR), serum creatinine, albumin-to-creatinine ratio (ACR), and albuminuria before and after BS.

RESULTS

The study included 49 articles involving 8515 patients. Compared with pre-operative renal function, the overall analysis showed that bariatric surgery significantly reduced serum creatinine levels, ACR, and albuminuria. There was significant increase of GFR in the CKD subgroup, yet a noticeable decrease in the hyperfiltration subgroup. The most significant improvement in GFR was seen 6-12 months after BS, while ACR dropped most dramatically 12-24 months after BS.

CONCLUSIONS

Bariatric surgery can improve renal function in obese patients with kidney dysfunction, especially 1 year after surgery.

Extracellular fluid volume: A suitable indexation variable to assess impact of bariatric surgery on glomerular filtration rate in patients with chronic kidney disease

BACKGROUND

Bariatric surgery (BS) might be a nephroprotective treatment in obese patients with chronic kidney disease (CKD), and the non-linear relation between body surface area (BSA) and extracellular fluid volume (ECFV) in obese people raises the question of the most relevant way to scale glomerular filtration rate (GFR) for assessing renal function changes after BS.

METHODS

We screened 1774 BS candidates and analysed 10 consecutive participants with CKD stage 3. True GFR (mGFR), measured by the renal clearance of 51Cr-ethylenediaminetetraacetic acid (EDTA), was scaled either to BSA (mGFRBSA) or to ECFV measured by 51Cr-EDTA distribution volume (mGFRECFV) before and one year after BS.

RESULTS

The 10 candidates for BS had a mean body mass index of 43.3 ± 3.6 kg/m2 and a mean GFR of 48 ± 8 mL/min/1.73 m2. Six participants had a sleeve gastrectomy and four had a Roux-en-Y gastric bypass. One year after BS, ECFV decreased (23.2 ± 6.2 to 17.9 ± 4.3 L, p = 0.001), absolute mGFR was not significantly modified (74 ± 23 versus 68 ±19 mL/min), mGFRBSA did not change significantly (53 ± 18 versus 56 ± 17 mL/min/1.73 m2) whereas mGFRECFV significantly increased (42 ± 13 versus 50 ± 14 mL/min/12.9 L, p = 0.037). The relation between mGFRECFV and mGFRBSA was different from the identity line before (p = 0.014) but not after BS (p = 0.09).

CONCLUSION

There is a difference between mGFRBSA and mGFRECFV following BS and the latter might better reflect the adequacy between renal function and corpulence.

The Relationship Between Preoperative Kidney Function and Weight Loss After Bariatric Surgery in Patients with Estimated Glomerular Filtration Rate ≥ 30 mL/min: Tehran Obesity Treatment Study

INTRODUCTION

Severe obesity can lead to progressive kidney injury and chronic kidney disease (CKD). The current study aimed at determining whether preoperative kidney function level in patients with estimated glomerular filtration rate (eGFR) ≥30 mL/min affects weight loss after bariatric surgery.

METHODS

A total of 1958 bariatric patients underwent laparoscopic sleeve gastrectomy and gastric bypass from March 2013 to March 2017. The patients were categorized according to preoperative eGFR (30-59, 60-89, 90-124, and ≥ 125 mL/min). Changes in body mass index (BMI), percentage of total weight loss (TWL%), and percentage of excess weight loss (EWL%) were compared across the eGFR categories. Moreover, multivariable logistic regression analysis was used to evaluate the relationship between eGFR and insufficient weight loss (defined as not achieving 50% EWL at 12 months after surgery).

RESULTS

Preoperative eGFR was positively associated with unadjusted ΔBMI (P trend < 0.001), TWL% (P trend < 0.001), and EWL% (P trend = 0.007) after 12 months of surgery. However, these associations were no longer significant after multivariable adjustment. Further, univariate analysis demonstrated a positive relationship between preoperative eGFR and insufficient weight loss (odds ratio [OR] 1.38; 95% confidence interval [CI] 1.11-1.71; P = 0.004). By contrast, preoperative eGFR was not a predictor of insufficient weight loss in multivariable logistic regression analysis (OR 0.98; 95% CI 0.46-1.24; P = 0.886).

CONCLUSION

Although patients with lower preoperative eGFR experience less weight loss after bariatric surgery, preoperative kidney function does not appear to have an independent impact on postoperative weight loss in patients with eGFR ≥ 30 mL/min.

Effect of weight loss on the estimated glomerular filtration rates of obese patients at risk of chronic kidney disease: the RIGOR-TMU study

BACKGROUND

Weight-reduction therapies, including bariatric surgery (BS), are standard treatments for severely obese patients with type 2 diabetes; however, the outcomes of these therapies are inconclusive for obese patients with chronic kidney disease (CKD). This study aimed to investigate the effects of BS or non-surgical interventions on the estimated glomerular filtration rate (eGFR) and to determine whether BS can be recommended for renal function preservation based on body mass index (BMI) and eGFR changes in obese patients with CKD.

METHODS

This study used data from the weight Reduction Intervention on GFR in Obese Patients with Renal Impairment-Taipei Medical University (TMU) study, which was a large, long-term, propensity score-matched cohort study based on clinical data from patients who registered at weight-reduction centres at TMU and its affiliated hospitals from 2008 to 2016. The patients were stratified according to whether they had undergone BS and into the mild, moderate, and high CKD risk groups using the Kidney Disease: Improving Global Outcomes guidelines. The primary outcome was the eGFR calculated using the Taiwan Chronic Kidney Disease-Epidemiology Collaboration equation. Cox regression models were used to determine hazard ratios (HRs) for eGFR decreases ≥25%.

RESULTS

A total of 4332 obese patients were enrolled in this study. After propensity score matching, 1620 patients, including 60.2% women, with a mean age of 36.5 (9.9) years were divided into BS or non-surgery groups (n = 810 per group). The overall mean eGFRs increased by 4.4 (14) mL/min·1.73 m² and decreased by 6.4 (16.0) mL/min·1.73 m² in the BS and non-surgery groups, respectively. The decrease in BMI in the BS and non-surgery groups were 2.5 and 1.3 kg/m² , respectively. In the moderate/high CKD risk BS group, a significant correlation was evident between an increased eGFR and a reduced BMI (Spearman's correlation -0.229, P < 0.001). The Cox regression analysis showed that the BS group had a significantly lower risk of an eGFR decline ≥25% at 12 months [adjusted HR (aHR) 0.47, P = 0.03). After BS, obese patients with hypertension or albuminuria had significantly lower risks of eGFR declines ≥25% (aHR 0.37, P = 0.02 and aHR 0.13, P = 0.0018, respectively).

CONCLUSIONS

Bariatric surgery was associated with eGFR preservation in all obese patients and, particularly, in those with moderate-to-high CKD risks. A longer term outcome study is warranted to determine the benefits of BS for CKD patients.

Obesity and bariatric intervention in patients with chronic renal disease

Obesity is associated with chronic metabolic conditions that directly and indirectly cause kidney parenchymal damage. A review of the literature was conducted to explore existing evidence of the relationship between obesity and chronic kidney disease as well as the role of bariatric surgery in improving access to kidney transplantation for patients with a high body mass index. The review showed no definitive evidence to support the use of a transplant eligibility cut-off parameter based solely on the body mass index. Moreover, in the pre-transplant scenario, the obesity paradox is associated with better patient survival among obese than non-obese patients, although promising results of bariatric surgery are emerging. However, until more information regarding improvement in outcomes for obese kidney transplant candidates is available, clinicians should focus on screening of the overall frailty condition of transplant candidates to ensure their eligibility and addition to the wait list.

Nutritional Management for Chronic Kidney Disease Patients who Undergo Bariatric Surgery: A Narrative Review

Bariatric surgery (BS) may be effective for chronic kidney disease (CKD) patients by reducing microalbuminuria and proteinuria, and by facilitating their meeting inclusion criteria for kidney transplantation. However, nutritional management for this population is complex and specific guidelines are scarce. A literature search was performed to create dietetic practice for these patients based on the most recent evidence. For the purposes of nutritional recommendations, we divided the patients into 2 subgroups: 1) patients with CKD and dialysis, and 2) patients after kidney transplantation. Before surgery, nutritional care includes nutritional status evaluation and adjusting doses of supplements to treat deficiencies and daily nutrient intake according to the dietary restrictions derived from kidney disease, including quantities of fluids, protein, phosphorus, potassium, and vitamins. After BS, these patients are at major risk for lean body mass loss, malnutrition and dehydration because of fluid restriction and diuretics. Postoperative nutritional recommendations should be carefully tailored according to CKD nutritional limitations and include specific considerations regarding protein, fluids, and supplementation, in particular calcium, vitamin A, and vitamin D. Nutritional management of CKD and kidney transplant patients undergoing BS is challenging and future studies are required to establish uniform high-level evidence-based guidelines.