NAD+ Homeostasis in Diabetic Kidney Disease

SIRT3-Mediated Deacetylation of SDHA Rescues Mitochondrial Bioenergetics Contributing to Neuroprotection in Rotenone-Induced PD Models

Mitochondrial dysfunction is critically involved in the degeneration of dopamine (DA) neurons in the substantia nigra, a common pathological feature of Parkinson's disease (PD). Previous studies have demonstrated that the NAD+-dependent acetylase Sirtuin 3 (SIRT3) participates in maintaining mitochondrial function and is downregulated in aging-related neurodegenerative disorders. The exact mechanism of action of SIRT3 on mitochondrial bioenergetics in PD pathogenesis, however, has not been fully described. In this study, we investigated the regulatory role of SIRT3-mediated deacetylation of mitochondrial complex II (succinate dehydrogenase) subunit A (SDHA) and its effect on neuronal cell survival in rotenone (ROT)-induced rat and differentiated MN9D cell models. The results revealed that SIRT3 activity was suppressed in both in vivo and in vitro PD models. Accompanying this downregulation of SIRT3 was the hyperacetylation of SDHA, impaired activity of mitochondrial complex II, and decreased ATP production. It was found that the inhibition of SIRT3 activity was attributed to a reduction in the NAD+/NADH ratio caused by ROT-induced inhibition of mitochondrial complex I. Activation of SIRT3 by icariin and honokiol inhibited SDHA hyperacetylation and increased complex II activity, leading to increased ATP production and protection against ROT-induced neuronal damage. Furthermore, overexpression of SDHA also exerted potent protective benefits in cells treated with ROT. In addition, treatment of MN9D cells with the NAD+ precursor nicotinamide mononucleotide increased SIRT3 activity and complex II activity and promoted the survival of cells exposed to ROT. These findings unravel a regulatory SIRT3-SDHA axis, which may be closely related to PD pathology. Bioenergetic rescue through SIRT3 activation-dependent improvement of mitochondrial complex II activity may provide an effective strategy for protection from neurodegeneration.

Optimized protocol for quantification of extracellular nicotinamide adenine dinucleotide: evaluating clinical parameters and pre-analytical factors for translational research

Nicotinamide adenine dinucleotide (NAD+), a coenzyme for more than 500 enzymes, plays a central role in energy production, metabolism, cellular signaling, and DNA repair. Until recently, NAD+ was primarily considered to be an intracellular molecule (iNAD+), however, its extracellular species (eNAD+) has recently been discovered and has since been associated with a multitude of pathological conditions. Therefore, accurate quantification of eNAD+ in bodily fluids such as plasma is paramount to answer important research questions. In order to create a clinically meaningful and reliable quantitation method, we analyzed the relationship of cell lysis, routine clinical laboratory parameters, blood collection techniques, and pre-analytical processing steps with measured plasma eNAD+ concentrations. Initially, NAD+ levels were assessed both intracellularly and extracellularly. Intriguingly, the concentration of eNAD+ in plasma was found to be approximately 500 times lower than iNAD+ in peripheral blood mononuclear cells (0.253 ± 0.02 μM vs. 131.8 ± 27.4 μM, p = 0.007, respectively). This stark contrast suggests that cellular damage or cell lysis could potentially affect the levels of eNAD+ in plasma. However, systemic lactate dehydrogenase in patient plasma, a marker of cell damage, did not significantly correlate with eNAD+ (n = 33; r = -0.397; p = 0.102). Furthermore, eNAD+ was negatively correlated with increasing c-reactive protein (CRP, n = 33; r = -0.451; p = 0.020), while eNAD+ was positively correlated with increasing hemoglobin (n = 33; r = 0.482; p = 0.005). Next, variations in blood drawing, sample handling and pre-analytical processes were examined. Sample storage durations at 4°C (0-120 min), temperature (0° to 25°C), cannula sizes for blood collection and tourniquet times (0 - 120 s) had no statistically significant effect on eNAD+ (p > 0.05). On the other hand, prolonged centrifugation (> 5 min) and a faster braking mode of the centrifuge rotor (< 4 min) resulted in a significant decrease in eNAD+ levels (p < 0.05). Taken together, CRP and hemoglobin appeared to be mildly correlated with eNAD+ levels whereas cell damage was not correlated significantly to eNAD+ levels. The blood drawing trial did not show any influence on eNAD+, in contrast, the preanalytical steps need to be standardized for accurate eNAD+ measurement. This work paves the way towards robust eNAD+ measurements, for use in future clinical and translational research, and provides an optimized hands-on protocol for reliable eNAD+ quantification in plasma.

Pathomechanisms of Diabetic Kidney Disease

The worldwide occurrence of diabetic kidney disease (DKD) is swiftly rising, primarily attributed to the growing population of individuals affected by type 2 diabetes. This surge has been transformed into a substantial global concern, placing additional strain on healthcare systems already grappling with significant demands. The pathogenesis of DKD is intricate, originating with hyperglycemia, which triggers various mechanisms and pathways: metabolic, hemodynamic, inflammatory, and fibrotic which ultimately lead to renal damage. Within each pathway, several mediators contribute to the development of renal structural and functional changes. Some of these mediators, such as inflammatory cytokines, reactive oxygen species, and transforming growth factor β are shared among the different pathways, leading to significant overlap and interaction between them. While current treatment options for DKD have shown advancement over previous strategies, their effectiveness remains somewhat constrained as patients still experience residual risk of disease progression. Therefore, a comprehensive grasp of the molecular mechanisms underlying the onset and progression of DKD is imperative for the continued creation of novel and groundbreaking therapies for this condition. In this review, we discuss the current achievements in fundamental research, with a particular emphasis on individual factors and recent developments in DKD treatment.

CDCT-induced nephrotoxicity in rat by apoptosis via metabolic disturbance

Compound diclofenac sodium chlorphenamine maleate tablets (CDCT) are widely used for the cold in Asia. However, CDCT can cause hematuria symptoms in clinical, and the underlying mechanism is unknown. This study aims to investigate the CDCT-induced changes of morphology in kidney and metabolites and further explore the possible mechanisms of CDCT-induced nephrotoxicity. Sprague-Dawley rats were exposed to the CDCT at a clinical equivalent dose for 6 days. CDCT exposure can induce kidney injury and death. Pathological changes, including creatinine, urea nitrogen, and histopathology, were observed in rats. Furthermore, metabolomic-driven energy and glycerophospholipid metabolism pathway disorders, accompanied by remarkably changed key metabolites, such as succinate, leukotriene B4 (LTB4 ), and cardiolipin (CL), are observed in the CDCT-induced nephrotoxicity. Functionally, succinate accumulation leads to mitochondrial damage, as evidence by the imbalance of complex I and complex II and an increase in mitochondrial reactive oxygen species (mito SOX). Meanwhile, LTB4 activated the NF-κB signaling, as shown by increased protein of p65, phosphor-p65, and decreased protein of IκBα and phosphor-IκBα. Eventually, the apoptosis pathway was triggered in response to reduced CL, inflammation, and mito SOX, as demonstrated by the expression of cyt c, Bax, Bcl-2, caspase-3, and caspase-9. This study indicated that CDCT-induced metabolic disorders triggered nephrotoxicity and provided a comprehensive information to elucidate the mechanism of CDCT induced nephrotoxicity.

Renal-Protective Roles of Lipoic Acid in Kidney Disease

The kidney is a crucial organ that eliminates metabolic waste and reabsorbs nutritious elements. It also participates in the regulation of blood pressure, maintenance of electrolyte balance and blood pH homeostasis, as well as erythropoiesis and vitamin D maturation. Due to such a heavy workload, the kidney is an energy-demanding organ and is constantly exposed to endogenous and exogenous insults, leading to the development of either acute kidney injury (AKI) or chronic kidney disease (CKD). Nevertheless, there are no therapeutic managements to treat AKI or CKD effectively. Therefore, novel therapeutic approaches for fighting kidney injury are urgently needed. This review article discusses the role of α-lipoic acid (ALA) in preventing and treating kidney diseases. We focus on various animal models of kidney injury by which the underlying renoprotective mechanisms of ALA have been unraveled. The animal models covered include diabetic nephropathy, sepsis-induced kidney injury, renal ischemic injury, unilateral ureteral obstruction, and kidney injuries induced by folic acid and metals such as cisplatin, cadmium, and iron. We highlight the common mechanisms of ALA’s renal protective actions that include decreasing oxidative damage, increasing antioxidant capacities, counteracting inflammation, mitigating renal fibrosis, and attenuating nephron cell death. It is by these mechanisms that ALA achieves its biological function of alleviating kidney injury and improving kidney function. Nevertheless, we also point out that more comprehensive, preclinical, and clinical studies will be needed to make ALA a better therapeutic agent for targeting kidney disorders.

NAD+ precursor supplementation prevents mtRNA/RIG-I-dependent inflammation during kidney injury

Our understanding of how global changes in cellular metabolism contribute to human kidney disease remains incompletely understood. Here we show that nicotinamide adenine dinucleotide (NAD+) deficiency drives mitochondrial dysfunction causing inflammation and kidney disease development. Using unbiased global metabolomics in healthy and diseased human kidneys, we identify NAD+ deficiency as a disease signature. Furthermore using models of cisplatin- or ischaemia-reperfusion induced kidney injury in male mice we observed NAD+ depletion Supplemental nicotinamide riboside or nicotinamide mononucleotide restores NAD+ levels and improved kidney function. We find that cisplatin exposure causes cytosolic leakage of mitochondrial RNA (mtRNA) and activation of the cytosolic pattern recognition receptor retinoic acid-inducible gene I (RIG-I), both of which can be ameliorated by restoring NAD+. Male mice with RIG-I knock-out (KO) are protected from cisplatin-induced kidney disease. In summary, we demonstrate that the cytosolic release of mtRNA and RIG-I activation is an NAD+-sensitive mechanism contributing to kidney disease.

Mitochondrial and NAD+ metabolism predict recovery from acute kidney injury in a diverse mouse population

Acute kidney failure and chronic kidney disease are global health issues steadily rising in incidence and prevalence. Animal models on a single genetic background have so far failed to recapitulate the clinical presentation of human nephropathies. Here, we used a simple model of folic acid-induced kidney injury in 7 highly diverse mouse strains. We measured plasma and urine parameters, as well as renal histopathology and mRNA expression data, at 1, 2, and 6 weeks after injury, covering the early recovery and long-term remission. We observed an extensive strain-specific response ranging from complete resistance of the CAST/EiJ to high sensitivity of the C57BL/6J, DBA/2J, and PWK/PhJ strains. In susceptible strains, the severe early kidney injury was accompanied by the induction of mitochondrial stress response (MSR) genes and the attenuation of NAD+ synthesis pathways. This is associated with delayed healing and a prolonged inflammatory and adaptive immune response 6 weeks after insult, heralding a transition to chronic kidney disease. Through a thorough comparison of the transcriptomic response in mouse and human disease, we show that critical metabolic gene alterations were shared across species, and we highlight the PWK/PhJ strain as an emergent model of transition from acute kidney injury to chronic disease.

The Role of Oxidative Stress-Mediated Inflammation in the Development of T2DM-Induced Diabetic Nephropathy: Possible Preventive Action of Tannins and Other Oligomeric Polyphenols

Diabetic nephropathy is manifested in more than 10% of people with diabetes. It is a common cause of kidney failure and end-stage kidney disease. Understanding of mechanisms underlying the initiation and development of diabetes-induced kidney injuries will allow for the development of more effective methods of prevention and treatment of the disease. Diabetic nephropathy is a wide-ranging complication of diabetes, and it is necessary to discuss the "weight" of pro-inflammatory pathways and molecules in the progress of renal injuries during the development of the disease. A large spectrum of pro-inflammatory molecules and pathways participate in different stages of the pathophysiological progression of diabetic nephropathy, including pro-inflammatory cytokines, chemokines, their receptors, adhesion molecules, and transcription factors. On the other hand, it is known that one of the consequences of hyperglycemia-induced ROS generation is the up-regulation of pro-inflammatory cascades, which, in turn, activate the transcription of genes encoding cytokines-chemokines, growth factors, and extracellular matrix proteins. It is a proven fact that a variety of plant secondary metabolites, such as tannins, flavonoids, and other polyphenols, demonstrate significant anti-diabetic, redox-modulating properties and effectively modulate the inflammatory response. Thus, this review is discussing the possible role of plant phenols in the prevention and treatment of diabetic nephropathy.

SGLT2 inhibitors improve kidney function and morphology by regulating renal metabolic reprogramming in mice with diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. SGLT2 inhibitors are clinically effective in halting DKD progression. However, the underlying mechanisms remain unclear. The serum and kidneys of mice with DKD were analyzed using liquid chromatography with tandem mass spectrometry (LC–MS/MS)-based metabolomic and proteomic analyses. Three groups were established: placebo-treated littermate db/m mice, placebo-treated db/db mice and EMPA-treated db/db mice. Empagliflozin (EMPA) and placebo (10 mg/kg/d) were administered for 12 weeks. EMPA treatment decreased Cys-C and urinary albumin excretion compared with placebo by 78.60% and 57.12%, respectively (p < 0.001 in all cases). Renal glomerular area, interstitial fibrosis and glomerulosclerosis were decreased by 16.47%, 68.50% and 62.82%, respectively (p < 0.05 in all cases). Multi-omic analysis revealed that EMPA treatment altered the protein and metabolic profiles in the db/db group, including 32 renal proteins, 51 serum proteins, 94 renal metabolites and 37 serum metabolites. Five EMPA-related metabolic pathways were identified by integrating proteomic and metabolomic analyses, which are involved in renal purine metabolism; pyrimidine metabolism; tryptophan metabolism; nicotinate and nicotinamide metabolism, and glycine, serine and threonine metabolism in serum. In conclusion, this study demonstrated metabolic reprogramming in mice with DKD. EMPA treatment improved kidney function and morphology by regulating metabolic reprogramming, including regulation of renal reductive stress, alleviation of mitochondrial dysfunction and reduction in renal oxidative stress reaction.

Sirtuin Family and Diabetic Kidney Disease

Diabetes mellitus (DM) is gradually attacking the health and life of people all over the world. Diabetic kidney disease (DKD) is one of the most common chronic microvascular complications of DM, whose mechanism is complex and still lacks research. Sirtuin family is a class III histone deacetylase with highly conserved NAD⁺ binding domain and catalytic functional domain, while different N-terminal and C-terminal structures enable them to bind different deacetylated substrates to participate in the cellular NAD⁺ metabolism. The kidney is an organ rich in NAD⁺ and database exploration of literature shows that the Sirtuin family has different expression localization in renal, cellular, and subcellular structures. With the progress of modern technology, a variety of animal models and reagents for the Sirtuin family and DKD emerged. Machine learning in the literature shows that the Sirtuin family can regulate pathophysiological injury mainly in the glomerular filtration membrane, renal tubular absorption, and immune inflammation through various mechanisms such as epigenetics, multiple signaling pathways, and mitochondrial function. These mechanisms are the key nodes participating in DKD. Thus, it is of great significance for target therapy to study biological functions of the Sirtuin family and DKD regulation mechanism in-depth.