Steatosis is involved in the progression of kidney disease in a high-fat-diet-induced non-alcoholic steatohepatitis mouse model

Impact of High-Fat Diet-induced Metabolic Dysfunction-associated Steatotic Liver Disease on Heart, Kidney, and Skeletal Muscle Metabolomes in Wild-Type Mice

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) can be recapitulated in mice fed a high-fat diet. The development of MASLD and the diet per se can both perturb metabolism in key extrahepatic tissues such as the heart, kidney, and skeletal muscle. To date, these alterations have not been well described in this animal model of diet-induced MASLD. Methodology: Male C57BL/6J mice were fed either standard (SC, n = 12) or high-fat chow (HF, n = 11) for 18 weeks. Metabolites were extracted from the heart, kidney, and skeletal muscle and analyzed by 1H nuclear magnetic resonance (NMR) spectroscopy, along with multivariate and univariate statistical analyses. Results: Kidney metabolite profiles exhibited the largest differences between HF and SC diets, followed by those of skeletal muscle and then the heart. Some alterations were common across all tissues, namely decreased trimethylamine and elevated levels of linoleic acid and polyunsaturated fatty acids in HF compared to SC (p < 0.05 for all three metabolites). Overall, the metabolite variations were consistent with shifts in carbohydrate and lipid substrate selection for oxidation, increased tissue stress in the heart and kidneys, and altered choline metabolism. These findings may serve as additional important descriptors of MASLD onset and progression.

Selective peroxisome proliferator-activated receptor-α modulator improves hypertriglyceridemia and muscle quality in patients with chronic kidney disease: A retrospective observational study

BACKGROUND & AIMS

Patients with chronic kidney disease (CKD) often have additional health problems, including sarcopenia and sarcopenic obesity. These conditions involve ectopic fat accumulation within muscles. This ectopic fat deposition reduces muscle quality, leading to weaker muscle strength and poorer physical performance. Persistent hypertriglyceridemia contributes to ectopic fat accumulation. Metabolic abnormalities, including dyslipidemia, are major factors in CKD development. Triglycerides (TG) and muscle quality are thus important factors in CKD management. Recently developed selective peroxisome proliferator-activated receptor α modulator (SPPARMα) hold promises for improving hypertriglyceridemia. However, their effectiveness and impact on muscle quality in CKD patients remain unclear. This study aimed to evaluate the effect of SPPARMα on muscle quality and its efficacy in CKD patients.

METHODS

This retrospective observational study involved CKD patients with dyslipidemia. We included patients who initiated medications for hypertriglyceridemia. We compared changes in lipid profiles, renal function, and muscle quality, assessed by phase angle, over six months between two groups: those receiving this type of medication and those receiving conventional treatment.

RESULTS

Among 245 patients diagnosed with CKD and hypertriglyceridemia, 52 started medications for hypertriglyceridemia. Of these, 26 received SPPARMα, and 26 received conventional lipid-lowering medications (statins, ezetimibe, eicosapentaenoic acid, and fibrates). SPPARMα significantly reduced TG (from 296.8 ± 106.1 to 153.0 ± 86.1, p < 0.001) without affecting glomerular filtration rate or urinary protein levels. Conventional treatment also improved TG (from 261.6 ± 89.5 to 173.6 ± 81.3, p < 0.001). Only patients treated with SPPARMα showed significant improvement in muscle quality. Their phase angle increased from 5.41 ± 0.6 to 5.55 ± 0.6 after six months of treatment (p < 0.05).

CONCLUSIONS

Our study demonstrates that the newly developed SPPARMα significantly lowers TG levels in CKD patients without harming their kidneys. Additionally, only patients treated with SPPARMα showed improvement in muscle quality. These findings suggest that SPPARMα may be a valuable treatment option for CKD patients with dyslipidemia, particularly those with low muscle quality.

Dyslipidemia-induced renal fibrosis related to ferroptosis and endoplasmic reticulum stress

Dyslipidemia may induce chronic kidney disease and trigger both ferroptosis and endoplasmic reticulum (ER) stress, but the instigating factors are incompletely understood. We tested the hypothesis that different models of dyslipidemia engage distinct kidney injury mechanisms. Wild-type (WT) or proprotein-convertase subtilisin/kexin type-9 (PCSK9)-gain-of-function (GOF) Ossabaw pigs were fed with a 6-month normal diet (ND) or high-fat diet (HFD) (n = 5-6 each). Renal function and fat deposition were studied in vivo using CT, and blood and kidney tissue studied ex-vivo for lipid profile, systemic and renal vein FFAs levels, and renal injury mechanisms including lipid peroxidation, ferroptosis, and ER stress. Compared with WT-ND pigs, both HFD and PCSK9-GOF elevated triglyceride levels, which were highest in WT-HFD, whereas total and LDL cholesterol levels rose only in PCSK9-GOF pigs, particularly in PCSK9-GOF/HFD. The HFD groups had worse kidney function than the ND groups. The WT-HFD kidneys retained more FFA than other groups, but all kidneys developed fibrosis. Furthermore, HFD-induced ferroptosis in WT-HFD indicated by increased free iron, lipid peroxidation, and decreased glutathione peroxidase-4 mRNA expression, while PCSK9-GOF induced ER stress with upregulated GRP94 and CHOP protein expression. In vitro, pig kidney epithelial cells treated with palmitic acid and oxidized LDL to mimic HFD and PCSK9-GOF showed similar trends to those observed in vivo. Taken together, HFD-induced hypertriglyceridemia promotes renal FFA retention and ferroptosis, whereas PCSK9-GOF-induced hypercholesterolemia elicits ER stress, both resulting in renal fibrosis. These observations suggest different targets for preventing and treating renal fibrosis in subjects with specific types of dyslipidemia.

Association of NAFLD/NASH, and MAFLD/MASLD with chronic kidney disease: an updated narrative review

Chronic kidney disease (CKD) and nonalcoholic fatty liver disease (NAFLD), metabolic dysfunction-associated fatty liver disease (MAFLD) and metabolic dysfunction-associated steatotic liver disease (MASLD) account for substantial financial burden worldwide. These alarming features call for enhanced efforts to prevent and manage the development and progression of CKD. Accumulating evidence supporting a causal role of NAFLD/MAFLD/MASLD-in CKD opens new horizons to achieve this aim. Recent epidemiological studies and meta-analyses exploring the association of NAFLD/MAFLD/MASLD with CKD and the characteristics of NAFLD/MAFLD/MASLD associated with the odds of incident CKD are discussed. The involved pathomechanisms, including the common soil hypothesis, genetics, gut dysbiosis, and portal hypertension, are examined in detail. Finally, lifestyle changes (diet and physical exercise), direct manipulation of gut microbiota, and drug approaches involving statins, renin-angiotensin-aldosterone system inhibitors, GLP-1 Receptor Agonists, Sodium-glucose cotransporter-2, pemafibrate, and vonafexor are examined within the context of prevention and management of CKD among those with NAFLD/MAFLD/MASLD. The evolving NAFLD/MAFLD/MASLD nomenclature may generate confusion among practicing clinicians and investigators. However, comparative studies investigating the pros and contra of different nomenclatures may identify the most useful definitions among NAFLD/MAFLD/MASLD and strategies to identify, prevent, and halt the onset and progression of CKD.

Neutrophils and NADPH Oxidases Are Major Contributors to Mild but Not Severe Ischemic Acute Kidney Injury in Mice

Upregulation of free radical-generating NADPH oxidases (NOX), xanthine oxidoreductase (XOR), and neutrophil infiltration-induced, NOX2-mediated respiratory burst contribute to renal ischemia-reperfusion injury (IRI), but their roles may depend on the severity of IRI. We investigated the role of NOX, XOR, and neutrophils in developing IRI of various severities. C57BL/6 and Mcl-1ΔMyelo neutrophil-deficient mice were used. Oxidases were silenced by RNA interference (RNAi) or pharmacologically inhibited. Kidney function, morphology, immunohistochemistry and mRNA expression were assessed. After reperfusion, the expression of NOX enzymes and XOR increased until 6 h and from 15 h, respectively, while neutrophil infiltration was prominent from 3 h. NOX4 and XOR silencing or pharmacological XOR inhibition did not protect the kidney from IRI. Attenuation of NOX enzyme-induced oxidative stress by apocynin and neutrophil deficiency improved kidney function and ameliorated morphological damage after mild but not moderate/severe IRI. The IR-induced postischemic renal functional impairment (BUN, Lcn-2), tubular necrosis score, inflammation (TNF-α, F4/80), and decreases in the antioxidant enzyme (GPx3) mRNA expression were attenuated by both apocynin and neutrophil deficiency. Inhibition of NOX enzyme-induced oxidative stress or the lack of infiltration by NOX2-expressing neutrophils can attenuate reperfusion injury after mild but not moderate/severe renal IR.

Vascular endothelial cell-specific overexpression of CNP did not improve liver fibrosis in HFFCD-induced NASH, but did improve renal lesions

Mice with endothelial-cell-specific overexpression of C-type natriuretic peptide (E-CNP Tg mice) were shown to be protected against hepatic fibrosis and inflammation induced by high fat diet (HFD) feeding, with improved insulin sensitivity and attenuated weight gain. A recently developed high-fat, high-fructose, high-cholesterol diet (HFFCD) is considered to be a superior model to HFD, owing to the resemblance to human non-alcoholic steatohepatitis (NASH). In this study, we therefore aimed to reveal whether these previous findings with E-CNP Tg mice on HFD can be observed in a newly developed NASH model.　Patients with NASH have been suggested to be at higher risk of developing chronic kidney disease, so we also assessed the kidney histology of these mice. After 8 months of HFFCD feeding, the livers of E-CNP Tg mice and controls showed progressive fibrosis, which resembled the features of human NASH. However, no significant differences were observed in NAFLD activity scores between E-CNP Tg mice and controls, although there was a tendency for improvement in E-CNP Tg mice. The reduced levels of GCB, a receptor for CNP, may have weakened the action of CNP in the current model. In the kidneys, HFFCD showed glomerular hypertrophy and tubular atrophy in the cortical region, which were suppressed in E-CNP Tg mice. The present study did not prove the therapeutic effect of CNP on NASH in the HFFCD model, but provided evidence of its potential beneficial effects on NASH-associated renal damage.

Effect of (poly)phenol-rich 'Daux Belan' apple supplementation on diet-induced obesity and glucose intolerance in C57BL/6NCrl mice

Obesity is a state of metabolic dysfunction that can lead to dyslipidemia and impaired glucose homeostasis. Apple polyphenols have been shown to ameliorate dyslipidemia/metabolic dysfunction in humans. The influence of apple (poly)phenols on energy metabolism in high-fat (HF) diet-induced obese mice remains controversial. This study examined the effect of dietary supplementation of (poly)phenol-rich 'Daux Belan' apple (DB; 6.2 mg gallic acid equivalence (GAE)/mouse/day; 0.15% (poly)phenol) in the form of freeze-dried powder on glucose and lipid metabolism in male HF-fed C57BL/6NCrl mice, in comparison to low-(poly)phenol-containing 'Zestar' apple (Z; 0.4 mg GAE/mouse/day). Obesity, glucose intolerance, hypertriglyceridemia, and hepatic lipid vacuolation were induced by HF feeding while circulating cholesterol levels remained unchanged. DB apple supplementation did not protect against HF-induced body weight gain, hyperglycemia, hepatic triglyceride level elevation, and hepatic lipid vacuolation at the tested dosage. Future studies should be conducted with increased DB dosage and employ apple (poly)phenols supplemented in the form of extracts or sugar-free powder.

Assessment of the impact of glyphosate and 2,4-D herbicides on the kidney injury and transcriptome changes in obese mice fed a Western diet

The development of chronic kidney disease has been associated with comorbidities resulting from the consumption of Westernized dietary (WD) patterns, including obesity and other metabolic dysfunctions. Kidneys also have a crucial role in the metabolism and excretion of xenobiotics, including herbicides. There is limited knowledge regarding the simultaneous exposure to WD and glyphosate (glypho) and 2,4-D, the most used herbicides globally. Thus, this study examined whether exposure to glypho and/or 2,4-D, either individually or in mixed, could impact the early effects of WD intake on kidney histology and gene expression in a rodent model. Male C57BL6J mice were fed a WD containing 20% lard, 0.2% cholesterol, 20% sucrose, and high sugar solution with 23.1 and 18.9 g/L of D-fructose and D-glucose for six months. During this period, the mice also received glypho (0.05 or 5 mg/kg/day), 2,4-D (0.02 or 2 mg/kg/day), or a mixture of both (0.05 +0.02, 5 +2 mg/kg/day) via intragastric administration five times per week. The doses were within or below the established regulatory limits. While single or mixed exposures did not alter WD-induced obesity, tubular lipid vacuolation, or increased serum creatinine levels; the exposure to higher doses of the mixture (5 +2) reduced the mesangial matrix area and tubular cell proliferation, while increasing the density of F4/80 macrophages in the renal interstitium. In terms of transcriptomic analysis, the herbicide mixture altered the expression of 415 genes in the kidney, which were found to be associated with immune response processes, particularly those related to phagocyte activity. While discrete, findings indicate that herbicide mixtures, rather than single exposures, might induce minor deleterious effects on the kidneys of obese mice under WD intake.

Five-Aminolevulinic Acid (5-ALA) Induces Heme Oxygenase-1 and Ameliorates Palmitic Acid-Induced Endoplasmic Reticulum Stress in Renal Tubules

Steatosis, or ectopic lipid deposition, is the fundamental pathophysiology of non-alcoholic steatohepatitis and chronic kidney disease. Steatosis in the renal tubule causes endoplasmic reticulum (ER) stress, leading to kidney injury. Thus, ER stress could be a therapeutic target in steatonephropathy. Five-aminolevulinic acid (5-ALA) is a natural product that induces heme oxygenase (HO)-1, which acts as an antioxidant. This study aimed to investigate the therapeutic potential of 5-ALA in lipotoxicity-induced ER stress in human primary renal proximal tubule epithelial cells. Cells were stimulated with palmitic acid (PA) to induce ER stress. Cellular apoptotic signals and expression of genes involved in the ER stress cascade and heme biosynthesis pathway were analyzed. The expression of glucose-regulated protein 78 (GRP78), a master regulator of ER stress, increased significantly, followed by increased cellular apoptosis. Administration of 5-ALA induced a remarkable increase in HO-1 expression, thus ameliorating PA-induced GRP78 expression and apoptotic signals. BTB and CNC homology 1 (BACH1), a transcriptional repressor of HO-1, was significantly downregulated by 5-ALA treatment. HO-1 induction attenuates PA-induced renal tubular injury by suppressing ER stress. This study demonstrates the therapeutic potential of 5-ALA against lipotoxicity through redox pathway.

Identifying disease progression in chronic kidney disease using proton magnetic resonance spectroscopy

Chronic kidney disease (CKD) affects approximately 10% of the world population, higher still in some developing countries, and can cause irreversible kidney damage eventually leading to kidney failure requiring dialysis or kidney transplantation. However, not all patients with CKD will progress to this stage, and it is difficult to distinguish between progressors and non-progressors at the time of diagnosis. Current clinical practice involves monitoring estimated glomerular filtration rate and proteinuria to assess CKD trajectory over time; however, there remains a need for novel, validated methods that differentiate CKD progressors and non-progressors. Nuclear magnetic resonance techniques, including magnetic resonance spectroscopy and magnetic resonance imaging, have the potential to improve our understanding of CKD progression. Herein, we review the application of magnetic resonance spectroscopy both in preclinical and clinical settings to improve the diagnosis and surveillance of patients with CKD.

Uromodulin Regulates Murine Aquaporin-2 Activity via Thick Ascending Limb-Collecting Duct Cross-Talk during Water Deprivation

Uromodulin, a urinary protein synthesized and secreted from the thick ascending limb (TAL) of the loop of Henle, is associated with hypertension through the activation of sodium reabsorption in the TAL. Uromodulin is a potential target for hypertension treatment via natriuresis. However, its biological function in epithelial cells of the distal nephron segment, particularly the collecting duct, remains unknown. Herein, we examined the regulation of uromodulin production during water deprivation in vivo as well as the effect of uromodulin on the activity of the water channel aquaporin−2 (AQP2) in vitro and in vivo using transgenic mice. Water deprivation upregulated uromodulin production; immunofluorescence experiments revealed uromodulin adhesion on the apical surface of the collecting duct. Furthermore, the activation of AQP2 was attenuated in mice lacking uromodulin. Uromodulin enhanced the phosphorylation and apical trafficking of AQP2 in mouse collecting duct cells treated with the vasopressin analog dDAVP. The uromodulin-induced apical trafficking of AQP2 was attenuated via endocytosis inhibitor treatment, suggesting that uromodulin activates AQP2 through the suppression of endocytosis. This study provides novel insights into the cross−talk between TAL and the collecting duct, and indicates that the modulation of uromodulin is a promising approach for diuresis and hypertension treatment.

The protective effects of curcumin on metabolic syndrome and its components: In-silico analysis for genes, transcription factors, and microRNAs involved

BACKGROUND

We aimed to identify the molecular mechanisms behind curcumin's therapeutic benefits for metabolic syndrome (MetS) and its components.

METHODS

The Comparative Toxicogenomics Database, MIENTURNET, Metascape, GeneMania, and Cytoscape software were critical analytic tools.

RESULTS

Curcumin may have therapeutic effects on MetS and its components via the following genes: NOS3, IL6, INS, and ADIPOQ, particularly PPARG. Curcumin has higher docking scores than other genes with INS and PPARG (docking scores: -8.3 and -5.8, respectively). Physical interactions (56%) were found to be the most prevalent for dyslipidemia, co-expression for hypertension, obesity, T2DM, and MetS. "Galanin receptor pathway", "lipid particles composition", "IL-18 signaling pathway", "response to extracellular stimulus", and "insulin resistance" were listed in the first of the key pathways for MetS, dyslipidemia, hypertension, obesity, and diabetes, respectively. The protein-protein interaction enrichment analysis study also identified "vitamin B12 metabolism," "folate metabolism," and "selenium micronutrient network" as three major molecular pathways linked to MetS targeted by curcumin. PPARG was the key transcription factor that regulated practically all curcumin-targeted genes linked to MetS and its components. Curcumin targeted hsa-miR-155-5p, which has been linked to T2DM, hypertension, and MetS, as well as hsa-miR-130b-3p and hsa-miR-22-3p, which have been linked to dyslipidemia and obesity, respectively. In silico, sponges that regulated hsa-miR-155-5p were developed and evaluated. Curcumin, MetS, and its components have been found to target adipocytes, cardiac myocytes, smooth muscle, the liver, and pancreas. Curcumin's physicochemical properties and pharmacokinetics are closely connected with its therapeutic advantages in MetS and its components due to its high gastrointestinal absorption, drug-likeness, water solubility, and lipophilic nature. Curcumin is a CYP1A9 and CYP3A4 inhibitor. Although curcumin has a low bioavailability, it can be synthesized and administered to increase its pharmacokinetic features.

CONCLUSIONS

Curcumin needs to undergo therapeutic optimization and further study into its pharmacological structure before it can be used to treat MetS and its components.