The Fatty Kidney and Beyond: A Silent Epidemic

Genetic studies on metabolic disorder associated kidney diseases

Diabetic kidney disease (DKD) and obesity-related kidney diseases are the representative chronic kidney diseases related to metabolic disorders. Genome-wide association studies (GWAS) have been extensively performed, and a substantial number of confirmed loci have been identified to be associated with many common diseases or quantitative traits, including type 2 diabetes, obesity, and chronic kidney diseases. By contrast, GWAS for DKD have identified limited number of susceptible loci, and the robust replication of these loci in independent studies has not yet been accomplished. As of 2024, no GWAS have been reported on obesity-related kidney diseases. Therefore, the genetic studies on DKD or obesity-related kidney diseases have not provided satisfiable results. However, by genetic correlation studies and Mendelian Randomization studies, that were performed using multi-traits GWAS data suggested that DKD, obesity-related kidney diseases, and obesity share common genetic mechanisms. Since obesity or overweight is a reversible condition, the effective interventions to reduce body weights might contribute to the prevention of the development of not only obesity-related kidney diseases, but also DKD or other types of chronic kidney diseases. Further genetic studies are necessary to understand the genetic architecture of DKD and obesity-related kidney diseases, and should be expanded.

Comparative Analysis of Renal Function Outcomes Following Sleeve Gastrectomy and Roux-en-Y Gastric Bypass: A Systematic Review and Meta-analysis

BACKGROUND

Obesity is a significant risk factor for chronic kidney disease (CKD), with metabolic bariatric surgery offering potential renal benefits. However, there is limited comparative data on the impact of Roux-en-Y gastric bypass (RYGB) versus laparoscopic sleeve gastrectomy (LSG) on renal function in individuals with obesity without end-stage renal disease (ESRD). The objective of this study was to compare renal function outcomes following RYGB and LSG in patients with obesity, focusing on estimated glomerular filtration rate (eGFR), serum creatinine, albumin-creatinine ratio (ACR), and serum cystatin C.

METHODS

A systematic review and meta-analysis were conducted following Cochrane and PRISMA guidelines. Data from 17 observational studies (n = 3339) were analyzed. Primary outcomes included changes in eGFR, ACR, serum creatinine, and cystatin C. Secondary outcomes included excess weight loss (%EWL) and total weight loss (%TWL). Statistical analysis involved fixed and random-effects models based on heterogeneity levels.

RESULTS

RYGB demonstrated significant improvements in eGFR (SMD =  - 0.71; 95% CI - 0.89 to - 0.52, p < 0.00001) and serum cystatin C (MD =  - 0.10; 95% CI - 0.17 to - 0.03, p = 0.004) compared to LSG. No significant differences were found for serum creatinine (MD =  - 1.06; 95% CI - 4.42 to 2.30, p = 0.54) or ACR (MD = 1.95; 95% CI - 0.39 to 4.29, p = 0.10). RYGB also showed greater long-term weight loss, particularly at 5 years (%EWL: MD = 22.00; 95% CI 6.56 to 37.44, p = 0.005).

CONCLUSIONS

RYGB offers similar renal improvements with superior weight loss compared to LSG in individuals with obesity without ESRD. These findings emphasize the need for personalized treatment approaches and further research to validate these outcomes.

From Adipose to Ailing Kidneys: The Role of Lipid Metabolism in Obesity-Related Chronic Kidney Disease

Obesity has emerged as a significant public health crisis, closely linked to the pathogenesis and progression of chronic kidney disease (CKD). This review explores the intricate relationship between obesity-induced lipid metabolism disorders and renal health. We discuss how excessive free fatty acids (FFAs) lead to lipid accumulation in renal tissues, resulting in cellular lipotoxicity, oxidative stress, and inflammation, ultimately contributing to renal injury. Key molecular mechanisms, including the roles of transcriptional regulators like PPARs and SREBP-1, are examined for their implications in lipid metabolism dysregulation. The review also highlights the impact of glomerular and tubular lipid overload on kidney pathology, emphasizing the roles of podocytes and tubular cells in maintaining kidney function. Various therapeutic strategies targeting lipid metabolism, including pharmacological agents such as statins and SGLT2 inhibitors, as well as lifestyle modifications, are discussed for their potential to mitigate CKD progression in obese individuals. Future research directions are suggested to better understand the mechanisms linking lipid metabolism to kidney disease and to develop personalized therapeutic approaches. Ultimately, addressing obesity-related lipid metabolism disorders may enhance kidney health and improve outcomes for individuals suffering from CKD.

Renal sinus adipose tissue: exploratory study of metabolic features and transcriptome compared with omental and subcutaneous adipose tissue

OBJECTIVE

The objective was to study metabolic characteristics and transcriptome of renal sinus adipose tissue (RSAT) located around renal arteries and veins.

METHODS

Adipose tissue biopsies from RSAT, omental (OAT), and subcutaneous (SAT) depots were obtained from healthy kidney donors (20 female, 20 male). Adipocyte glucose uptake rate and cell size were measured, and gene expression analyses using transcriptomics were performed.

RESULTS

RSAT adipocytes were significantly smaller, with a higher basal glucose uptake rate, than adipocytes from SAT and OAT. Transcriptomic analyses revealed 29 differentially expressed genes between RSAT and OAT (RSAT: 23 lower, 6 higher) and 1214 differentially expressed genes between RSAT and SAT (RSAT: 859 lower, 355 higher). RSAT demonstrated molecular resemblance to OAT, both exhibiting lower metabolic gene expression and higher expression of immune-related pathways, including IL-17, TNFα, and NF-κB signaling than SAT. Weighted gene coexpression network analysis associated RSAT with immune response and nucleic acid transport processes. Despite its location near the renal hilum, RSAT closely resembled OAT and there was a lack of expression in the classical brown adipose tissue genes. Gene enrichment analyses suggest an inflammatory environment in RSAT compared with SAT and, to some extent, OAT.

CONCLUSIONS

The findings suggest specific RSAT functions that could impact renal function and, possibly, the development of renal and cardiometabolic disorders.

Renoprotective effects of empagliflozin in high-fat diet-induced obesity-related glomerulopathy by regulation of gut-kidney axis

The increasing prevalence of obesity-related glomerulopathy (ORG) poses a significant threat to public health. Sodium-glucose cotransporter-2 (SGLT2) inhibitors effectively reduce body weight and total fat mass in individuals with obesity and halt the progression of ORG. However, the underlying mechanisms of their reno-protective effects in ORG remain unclear. We established a high-fat diet-induced ORG model using C57BL/6J mice, which were divided into three groups: normal chow diet (NCD group), high-fat diet (HFD) mice treated with placebo (ORG group), and HFD mice treated with empagliflozin (EMPA group). We conducted 16S ribosomal RNA gene sequencing of feces and analyzed metabolites from kidney, feces, liver, and serum samples. ORG mice showed increased urinary albumin creatinine ratio, cholesterol, triglyceride levels, and glomerular diameter compared with NCD mice (all P < 0.05). EMPA treatment significantly alleviated these parameters (all P < 0.05). Multitissue metabolomics analysis revealed lipid metabolic reprogramming in ORG mice, which was significantly altered by EMPA treatment. MetOrigin analysis showed a close association between EMPA-related lipid metabolic pathways and gut microbiota alterations, characterized by reduced abundances of Firmicutes and Desulfovibrio and increased abundance of Akkermansia (all P < 0.05). The metabolic homeostasis of ORG mice, especially in lipid metabolism, was disrupted and closely associated with gut microbiota alterations, contributing to the progression of ORG. EMPA treatment improved kidney function and morphology by regulating lipid metabolism through the gut-kidney axis, highlighting a novel therapeutic approach for ORG. NEW & NOTEWORTHY Our study uncovered that empagliflozin (EMPA) potentially protects renal function and morphology in obesity-related glomerulopathy (ORG) mice by regulating the gut-kidney axis. EMPA's reno-protective effects in ORG mice are associated with the lipid metabolism, especially in glycerophospholipid metabolism and the pantothenate/CoA synthesis pathways. EMPA's modulation of gut microbiota appears to be pivotal in suppressing glycerol 3-phosphate and CoA synthesis. The insights into gut microbiota-host metabolic interactions offer a novel therapeutic approach for ORG.

Association between the lipid accumulation product and chronic kidney disease among adults in the United States

The objective of this research was to explore the potential association between lipid accumulation product (LAP) and chronic kidney disease (CKD) among adult population of United States (US). Using cross-sectional data from the 2013 to 2018 National Health and Nutrition Examination Survey (NHANES), we explored the association of LAP with CKD, low estimated glomerular filtration rate (eGFR), and albuminuria. This analysis encompassed multivariate logistic regression analyses, smoothed curve fitting, subgroup analyses, and interaction tests. We found a significant positive association between higher ln-transformed LAP (LAP was transformed using a natural logarithm) and the prevalence of CKD, low-eGFR and albuminuria. Notably, this association of ln-transformed LAP with CKD and albuminuria was significantly influenced by diabetes status and sex (P for interaction < 0.05), while no significant interaction was observed regarding the association with low-eGFR (P for interaction > 0.05). Additionally, in model 3 (adjusted for all included covariates except eGFR and urinary albumin-creatinine ratio (UACR)), a nonlinear relationship was identified between ln-transformed LAP and the presence of both CKD and albuminuria, with inflection points of 4.57 and 4.49, respectively. This indicates that this correlation is more pronounced on the right of the inflection point. In conclusion, the findings indicate a significant association between LAP and the prevalence of CKD in US adults.

Cardiometabolic comorbidities and complications of obesity and chronic kidney disease (CKD)

Obesity and chronic kidney disease are two ongoing progressive clinical pandemics of major public health and clinical care significance. Because of their growing prevalence, chronic indolent course and consequent complications both these conditions place significant burden on the health care delivery system especially in developed countries like the United States. Beyond the chance coexistence of both of these conditions in the same patient based on high prevalence it is now apparent that obesity is associated with and likely has a direct causal role in the onset, progression and severity of chronic kidney disease. The causes and underlying pathophysiology of this are myriad, complicated and multi-faceted. In this review, continuing the theme of this special edition of the journal on " The Cross roads between Endocrinology and Nephrology" we review the epidemiology of obesity related chronic kidney disease (ORCKD), and its various underlying causes and pathophysiology. In addition, we delve into the consequent comorbidities and complications associated with ORCKD with particular emphasis on the cardio metabolic consequences and then review the current body of evidence for available strategies for chronic kidney disease modulation in ORCKD as well as the potential unique role of weight reduction and management strategies in its improvement and risk reduction.

Are we ready for an adipocentric approach in people living with type 2 diabetes and chronic kidney disease?

We are entering a new era in the management of adiposity-based chronic disease (ABCD) with type 2 diabetes (T2D) and related chronic kidney disease (CKD). ABCD, T2D and CKD can affect almost every major organ system and have a particularly strong impact on the incidence of cardiovascular disease (CVD) and heart failure. ABCD and the associated insulin resistance are at the root of many cardiovascular, renal and metabolic (CKM) disorders, thus an integrated therapeutic framework using weight loss (WL) as a disease-modifying intervention could simplify the therapeutic approach at different stages across the lifespan. The breakthrough of highly effective WL drugs makes achieving a WL of >10% possible, which is required for a potential T2D disease remission as well as for prevention of microvascular disease, CKD, CVD events and overall mortality. The aim of this review is to discuss the link between adiposity and CKM conditions as well as placing weight management at the centre of the holistic CKM syndrome approach with a focus on CKD. We propose the clinical translation of the available evidence into a transformative Dysfunctional Adipose Tissue Approach (DATA) for people living with ABCD, T2D and CKD. This model is based on the interplay of four essential elements (i.e. adipocentric approach and target organ protection, dysfunctional adiposity, glucose homeostasis, and lifestyle intervention and de-prescription) together with a multidisciplinary person-centred care. DATA could facilitate decision-making for all clinicians involved in the management of these individuals, and if we do this in a multidisciplinary way, we are prepared to meet the adipocentric challenge.

Role of perirenal adiposity in renal dysfunction among CKD individuals with or without diabetes: a Japanese cross-sectional study

INTRODUCTION

It remains unclear whether increased perirenal fat (PRF) accumulation is equally related to renal involvement in patients with and without diabetes mellitus (DM). We evaluated the association between PRF volume (PRFV) and low glomerular filtration rate (GFR) and proteinuria in people with or without type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

We performed a cross-sectional analysis of 473 individuals without T2DM (non-DM, n=202) and with T2DM (DM, n=271). PRFV (cm3), obtained from non-contrast CT, was indexed as PRF index (PRFV/body surface area, cm3/m2). Multivariate-adjusted models were used to determine the ORs of PRFV and PRFV index for detecting estimated GFR (eGFR) decrease of <60 mL/min/1.73 m2 proteinuria onset, or both.

RESULTS

Although body mass index (BMI), visceral fat area, and waist circumference were comparable between the non-DM and DM groups, kidney volume, PRFV, and PRFV index were higher in individuals with T2DM than in those without T2DM. In the multivariate analysis, after adjusting for age, sex, BMI, hypertension, smoking history, and visceral fat area ≥100 cm2, the cut-off values of PRFV index were associated with an eGFR<60 in individuals with DM (OR 6.01, 95% CI 2.20 to 16.4, p<0.001) but not in those without DM.

CONCLUSIONS

PRFV is associated with low eGFR in patients with T2DM but not in those without T2DM. This suggests that PRF accumulation is more closely related to the onset and progression of diabetic kidney disease (DKD) than non-DKD. Clarifying the mechanisms through which PRF influences DKD development could pave the way for novel prevention and treatment strategies.