IgA nephropathy is associated with elevated urinary mitochondrial DNA copy numbers

Dapagliflozin Reduces Urinary Kidney Injury Biomarkers in Chronic Kidney Disease Irrespective of Albuminuria Level

The beneficial effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors in patients with chronic kidney disease (CKD) with low albuminuria levels have not been established. This study aimed to compare the effects of dapagliflozin on kidney injury biomarkers in patients with CKD stratified by albuminuria level. We prospectively enrolled healthy volunteers (HVs; n = 20) and patients with CKD (n = 54) with and without diabetes mellitus. Patients with CKD were divided into two age-matched and sex-matched subgroups according to urinary albumin-creatinine ratio (uACR) levels (<300 mg/g and ≥300 mg/g). The CKD group received dapagliflozin (10 mg/day). Urine samples were collected before treatment and after 3 and 6 months of dapagliflozin. Urinary kidney injury molecule-1 (KIM-1), interleukin-1β (IL-1β), and mitochondrial DNA nicotinamide adenine dinucleotide dehydrogenase subunit-1 (mtND1) copy number were measured. The estimated glomerular filtration rate (eGFR) of patients with CKD was lower than that of HVs (P < 0.001). During the study period, eGFR decreased and uACR did not change in the CKD group. Kidney injury markers were significantly elevated in patients with CKD compared with those in HVs. Dapagliflozin reduced urinary KIM-1, IL-1β, and mtDNA copy number in patients with CKD after 6 months of treatment. In further, the levels of urinary KIM-1 and IL-1β, patients with CKD decreased after 6 months of dapagliflozin treatment regardless of albuminuria level. Dapagliflozin reduced urinary kidney injury biomarkers in patients with CKD, regardless of albuminuria level. These findings suggest that SGLT2 inhibitors may also attenuate the progression of low albuminuric CKD.

The Effects of Coenzyme Q10 on Contrast-Induced Acute Kidney Injury in Type 2 Diabetes: A Randomized Clinical Trial

Contrast-induced acute kidney injury (CI-AKI) is a frequent challenge following the injection of contrast media and its subsequent oxidative stress. The aim of the present study was to evaluate the preventive effects of coenzyme Q10 (Q10), as a mitochondrial-targeted antioxidant in CI-AKI in diabetic patients, who account for a large proportion of angiographic cases. A total of 118 diabetic patients were randomly assigned to receive 120 mg of oral coenzyme Q10 (Q10 group) or placebo (Placebo group) for four days, starting 24 hours before contrast media injection. Blood urea nitrogen (BUN), serum and urinary creatinine, estimated glomerular filtration rate (eGFR), urinary malondialdehyde (UMDA), urinary total antioxidant capacity (UTAC), and urinary mitochondrial to nuclearDNA ratios (mtDNA/nDNA ratio) were evaluated before and after the treatment period. Urine sediments were also evaluated to report the urine microscopy score (UMS).The levels of BUN, serum and urine creatinine, and UMS were similar in the Q10 and placebo groups. EGFR was lower in the Q10 group before the treatment (p=0.013) but not after. The urinary mtDNA/nDNA ratio was 3.05±1.68 and 3.69±2.58 in placebo and Q10 groups, but UTAC was found to be lower in Q10 both before (p=0.006) and after the treatment (p<0.001). The incidence of CI-AKI was 14.40% and the mtDNA/nNDA ratio was similar between CI-AKI and non-CI-AKI patients. In conclusion, Q10 treatment shows no favorable effect on prevention of CI-AKI or a urinary mtDNA/nDNA ratio among diabetic patients.

Mitochondrial DNA copy number in peripheral blood of IgA nephropathy: a cross-sectional study

Mitochondrial DNA (mtDNA) copy number (CN) is a biomarker of mitochondrial function and has been reported associated with kidney disease. However, its association with IgA nephropathy (IgAN), the most common cause of glomerulonephritis (GN), has not been evaluated. We included 664 patients with biopsy-proven IgAN and measured mtDNA-CN in peripheral blood by multiplexed real-time quantitative polymerase chain reaction (RT-qPCR). We examined the associations between mtDNA-CN and clinical variables and found that patients with higher mtDNA-CN had higher estimated glomerular filtration rate (eGFR) (r = 0.1009, p = .0092) and lower serum creatinine (SCr), blood urea nitrogen (BUN), and uric acid (UA) (r=-0.1101, -0.1023, -0.07806, respectively, all p values <.05). In terms of pathological injury, mtDNA-CN was higher in patients with less mesangial hypercellularity (p = .0385, M0 vs. M1 score by Oxford classification). Multivariable logistic regression analyses also showed that mtDNA-CN was lower for patients with moderate to severe renal impairment (defined as eGFR < 60 mL/min/1.73 m²) vs. mild renal impairment, with the odds ratio of 0.757 (95% confidence interval: 0.579-0.990, p = .042). In conclusion, mtDNA-CN was correlated with better renal function and less pathological injury in patients with IgAN, proposing that systemic mitochondrial dysfunction may be involved in or reflect the development of IgAN.

Proteomic profiling of IgA nephropathy reveals distinct molecular prognostic subtypes

IgA nephropathy (IgAN) is a heterogeneous disease, which poses a series of challenges to accurate diagnosis and personalized therapy. Herein, we constructed a systematic quantitative proteome atlas from 59 IgAN and 19 normal control donors. Consensus sub-clustering of proteomic profiles divided IgAN into three subtypes (IgAN-C1, C2, and C3). IgAN-C2 had similar proteome expression patterns with normal control, while IgAN-C1/C3 exhibited higher level of complement activation, more severe mitochondrial injury, and significant extracellular matrix accumulation. Interestingly, the complement mitochondrial extracellular matrix (CME) pathway enrichment score achieved a high diagnostic power to distinguish IgAN-C2 from IgAN-C1/C3 (AUC>0.9). In addition, the proteins related to mesangial cells, endothelial cells, and tubular interstitial fibrosis were highly expressed in IgAN-C1/C3. Most critically, IgAN-C1/C3 had a worse prognosis compared to IgAN-C2 (30% eGFR decline, p = 0.02). Altogether, we proposed a molecular subtyping and prognostic system which could help to understand IgAN heterogeneity and improve the treatment in the clinic.

Natural products for kidney disease treatment: Focus on targeting mitochondrial dysfunction

The patients with kidney diseases are increasing rapidly all over the world. With the rich abundance of mitochondria, kidney is an organ with a high consumption of energy. Hence, renal failure is highly correlated with the breakup of mitochondrial homeostasis. However, the potential drugs targeting mitochondrial dysfunction are still in mystery. The natural products have the superiorities to explore the potential drugs regulating energy metabolism. However, their roles in targeting mitochondrial dysfunction in kidney diseases have not been extensively reviewed. Herein, we reviewed a series of natural products targeting mitochondrial oxidative stress, mitochondrial biogenesis, mitophagy, and mitochondrial dynamics. We found lots of them with great medicinal values in kidney disease. Our review provides a wide prospect for seeking the effective drugs targeting kidney diseases.

Roles of Mitochondrial DNA Damage in Kidney Diseases: A New Biomarker

The kidney is a mitochondria-rich organ, and kidney diseases are recognized as mitochondria-related pathologies. Intact mitochondrial DNA (mtDNA) maintains normal mitochondrial function. Mitochondrial dysfunction caused by mtDNA damage, including impaired mtDNA replication, mtDNA mutation, mtDNA leakage, and mtDNA methylation, is involved in the progression of kidney diseases. Herein, we review the roles of mtDNA damage in different setting of kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD). In a variety of kidney diseases, mtDNA damage is closely associated with loss of kidney function. The level of mtDNA in peripheral serum and urine also reflects the status of kidney injury. Alleviating mtDNA damage can promote the recovery of mitochondrial function by exogenous drug treatment and thus reduce kidney injury. In short, we conclude that mtDNA damage may serve as a novel biomarker for assessing kidney injury in different causes of renal dysfunction, which provides a new theoretical basis for mtDNA-targeted intervention as a therapeutic option for kidney diseases.

Empagliflozin suppresses urinary mitochondrial DNA copy numbers and interleukin-1β in type 2 diabetes patients

Sodium-glucose co-transporter 2 (SGLT2) inhibitors improve cardiovascular and renal outcomes in type 2 diabetes mellitus (T2DM) patients. However, the mechanisms by which SGLT2 inhibitors improve the clinical outcomes remain elusive. We evaluated whether empagliflozin, an SGLT2 inhibitor, ameliorates mitochondrial dysfunction and inflammatory milieu of the kidneys in T2DM patients. We prospectively measured copy numbers of urinary and serum mitochondrial DNA (mtDNA) nicotinamide adenine dinucleotide dehydrogenase subunit-1 (mtND-1) and cytochrome-c oxidase 3 (mtCOX-3) and urinary interleukin-1β (IL-1β) in healthy volunteers (n = 22), in SGLT2 inhibitor-naïve T2DM patients (n = 21) at baseline, and in T2DM patients after 3 months of treatment with empagliflozin (10 mg, n = 17 or 25 mg, n = 4). Both urinary mtDNA copy numbers and IL-1β levels were higher in the T2DM group than in healthy volunteers. Baseline copy numbers of serum mtCOX-3 in the T2DM group were lower than those in healthy volunteers. Empagliflozin induced marked reduction in both urinary and serum mtND-1 and mtCOX-3 copy numbers, as well as in urinary IL-1β. Empagliflozin could attenuate mitochondrial damage and inhibit inflammatory response in T2DM patients. This would explain the beneficial effects of SGLT2 inhibitors on cardiovascular and renal outcomes.

Renal mitochondrial injury in the pathogenesis of CKD: mtDNA and mitomiRs

Chronic kidney disease (CKD) is a public health concern that affects over 200 million people worldwide and is associated with a tremendous economic burden. Therefore, deciphering the mechanisms underpinning CKD is crucial to decelerate its progression towards end-stage renal disease (ESRD). Renal tubular cells are populated with a high number of mitochondria, which produce cellular energy and modulate several important cellular processes, including generation of reactive oxygen species (ROS), calcium homeostasis, proliferation, and apoptosis. Over the past few years, increasing evidence has implicated renal mitochondrial damage in the pathogenesis of common etiologies of CKD, such as diabetes, hypertension, metabolic syndrome (MetS), chronic renal ischemia, and polycystic kidney disease (PKD). However, most compelling evidence is based on preclinical studies because renal biopsies are not routinely performed in many patients with CKD. Previous studies have shown that urinary mitochondrial DNA (mtDNA) copy numbers may serve as non-invasive biomarkers of renal mitochondrial dysfunction. Emerging data also suggest that CKD is associated with altered expression of mitochondria-related microRNAs (mitomiRs), which localize in mitochondria and regulate the expression of mtDNA and nucleus-encoded mitochondrial genes. This review summarizes relevant evidence regarding the involvement of renal mitochondrial injury and dysfunction in frequent forms of CKD. We further provide an overview of non-invasive biomarkers and potential mechanisms of renal mitochondrial damage, especially focusing on mtDNA and mitomiRs.

Mitochondrial Oxidative Stress and Cell Death in Podocytopathies

Podocytopathies are kidney diseases that are driven by podocyte injury with proteinuria and proteinuria-related symptoms as the main clinical presentations. Albeit podocytopathies are the major contributors to end-stage kidney disease, the underlying molecular mechanisms of podocyte injury remain to be elucidated. Mitochondrial oxidative stress is associated with kidney diseases, and increasing evidence suggests that oxidative stress plays a vital role in the pathogenesis of podocytopathies. Accumulating evidence has placed mitochondrial oxidative stress in the focus of cell death research. Excessive generated reactive oxygen species over antioxidant defense under pathological conditions lead to oxidative damage to cellular components and regulate cell death in the podocyte. Conversely, exogenous antioxidants can protect podocyte from cell death. This review provides an overview of the role of mitochondrial oxidative stress in podocytopathies and discusses its role in the cell death of the podocyte, aiming to identify the novel targets to improve the treatment of patients with podocytopathies.

Urinary C5b-9 as a Prognostic Marker in IgA Nephropathy

C5b-9 plays an important role in the pathogenesis of immunoglobin A nephropathy (IgAN). We evaluated C5b-9 as a prognostic marker for IgAN. We prospectively enrolled 33 patients with biopsy-proven IgAN. We analyzed the correlation between baseline urinary C5b-9 levels, posttreatment changes in their levels, and clinical outcomes, including changes in proteinuria, estimated glomerular filtration rate (eGFR), and treatment response. Baseline urinary C5b-9 levels were positively correlated with proteinuria (r = 0.548, p = 0.001) at the time of diagnosis. Changes in urinary C5b-9 levels were positively correlated with changes in proteinuria (r = 0.644, p < 0.001) and inversely correlated with changes in eGFR (r = −0.410, p = 0.018) at 6 months after treatment. Changes in urinary C5b-9 levels were positively correlated with time-averaged proteinuria during the follow-up period (r= 0.461, p = 0.007) but were not correlated with the mean annual rate of eGFR decline (r = −0.282, p = 0.112). Baseline urinary C5b-9 levels were not a significant independent factor that could predict the treatment response in logistic regression analyses (odds ratio 0.997; 95% confidence interval, 0.993 to 1.000; p = 0.078). Currently, urinary C5b-9 is not a promising prognostic biomarker for IgAN, and further studies are needed.

Minimal Change Disease Is Associated with Mitochondrial Injury and STING Pathway Activation

We hypothesized that minimal change disease (MCD) pathogenesis may be associated with mitochondrial injury, and that the degree of mitochondrial injury at the time of diagnosis may serve as a valuable prognostic marker. We compared urinary mitochondrial DNA (mtDNA) at the time of diagnosis in patients with MCD and age- and sex-matched healthy controls (MHC) (n = 10 each). We analyzed the site and signal intensity of immunohistochemical (IHC) staining of stimulator of interferon genes (STING) using kidney tissues at the time of diagnosis in patients with MCD. Patients with MCD were divided into high (n = 6) and low-intensity (n = 14) subgroups according to the signal intensity. Urinary mtDNA levels were elevated in the MCD groups more than in the MHC group (p < 0.001). Time-averaged proteinuria and frequency of relapses during the follow-up period were higher in the high-intensity than in the low-intensity subgroup (1.18 ± 0.54 vs. 0.57 ± 0.45 g/day, p = 0.022; and 0.72 ± 0.60 vs. 0.09 ± 0.22 episodes/year, p = 0.022, respectively). Mitochondrial injury may be associated with MCD pathogenesis, and the signal intensity of STING IHC staining at the time of diagnosis could be used as a valuable prognostic marker in MCD.

Importance of urinary mitochondrial DNA in diagnosis and prognosis of kidney diseases

Mitochondrial injury plays an important role in the occurrence and development of kidney diseases. However, the existing assays to determine mitochondrial function restrict our ability to understand the relationship between mitochondrial dysfunction and kidney damage. These limitations may be overcome by recent findings on urinary mitochondrial DNA (UmtDNA). Elevated UmtDNA level may serve as a surrogate biomarker of mitochondrial dysfunction, kidney damage, and progression and prognosis of kidney diseases. Herein, we review the recent research progress on UmtDNA in kidney diseases diagnosis and highlight the research areas that should be expanded in future as well as discuss the future perspectives.

Donor-Derived Cell-Free DNA in Kidney Transplantation: Origins, Present and a Look to the Future

Since its first detection in 1948, donor-derived cell-free DNA (dd-cfDNA) has been employed for a myriad of indications in various medical specialties. It has had a far-reaching impact in solid organ transplantation, with the most widespread utilization in kidney transplantation for the surveillance and detection of allograft rejection. The purpose of this review is to track the arc of this revolutionary test—from origins to current use—along with examining challenges and future prospects though the lens of transplant nephrology.

Donor-derived Cell-free DNA: Advancing a Novel Assay to New Heights in Renal Transplantation

Despite advances in transplant immunosuppression, long-term renal allograft outcomes remain suboptimal because of the occurrence of rejection, recurrent disease, and interstitial fibrosis with tubular atrophy. This is largely due to limitations in our understanding of allogeneic processes coupled with inadequate surveillance strategies. The concept of donor-derived cell-free DNA as a signal of allograft stress has therefore rapidly been adopted as a noninvasive monitoring tool. Refining it for effective clinical use, however, remains an ongoing effort. Furthermore, its potential to unravel new insights in alloimmunity through novel molecular techniques is yet to be realized. This review herein summarizes current knowledge and active endeavors to optimize cell-free DNA-based diagnostic techniques for clinical use in kidney transplantation. In addition, the integration of DNA methylation and microRNA may unveil new epigenetic signatures of allograft health and is also explored in this report. Directing research initiatives toward these aspirations will not only improve diagnostic precision but may foster new paradigms in transplant immunobiology.

Mitochondrial dysfunction in kidney injury, inflammation, and disease: Potential therapeutic approaches

Mitochondria are energy-producing organelles that not only satisfy the high metabolic demands of the kidney but sense and respond to kidney injury-induced oxidative stress and inflammation. Kidneys are rich in mitochondria. Mitochondrial dysfunction plays a critical role in the progression of acute kidney injury and chronic kidney disease. Mitochondrial responses to specific stimuli are highly regulated and synergistically modulated by tightly interconnected processes, including mitochondrial dynamics (fission, fusion) and mitophagy. The counterbalance between these processes is essential in maintaining a healthy network of mitochondria. Recent literature suggests that alterations in mitochondrial dynamics are implicated in kidney injury and the progression of kidney diseases. A decrease in mitochondrial fusion promotes fission-induced mitochondrial fragmentation, but a reduction in mitochondrial fission produces excessive mitochondrial elongation. The removal of dysfunctional mitochondria by mitophagy is crucial for their quality control. Defective mitochondrial function disrupts cellular redox potential and can cause cell death. Mitochondrial DNA derived from damaged cells also act as damage-associated molecular patterns to recruit immune cells and the inflammatory response can further exaggerate kidney injury. This review provides a comprehensive overview of the role of mitochondrial dysfunction in acute kidney injury and chronic kidney disease. We discuss the processes that control mitochondrial stress responses to kidney injury and review recent advances in understanding the role of mitochondrial dysfunction in inflammation and tissue damage through the use of different experimental models of kidney disease. We also describe potential mitochondria-targeted therapeutic approaches.

Minor Glomerular Abnormalities are Associated with Deterioration of Long-Term Kidney Function and Mitochondrial Injury

Minor glomerular abnormalities (MGAs) are unclassified glomerular lesions indicated by the presence of minor structural abnormalities that are insufficient for a specific pathological diagnosis. The long-term clinical outcomes and pathogenesis have not been examined. We hypothesized that MGAs would be associated with the deterioration of long-term kidney function and increased urinary mitochondrial DNA (mtDNA) copy numbers. We retrospectively enrolled patients with MGAs, age-/sex-/estimated glomerular filtration rate (eGFR)-matched patients with immunoglobulin A nephropathy (IgAN), and similarly matched healthy controls (MHCs; n = 49 each). We analyzed the time × group interaction effects of the eGFR and compared mean annual eGFR decline rates between the groups. We prospectively enrolled patients with MGAs, age- and sex-matched patients with IgAN, and MHCs (n = 15 each) and compared their urinary mtDNA copy numbers. Compared to the MHC group, the MGA and IgAN groups displayed differences in the time × group effects of eGFR, higher mean annual rates of eGFR decline, and higher urinary mtDNA copy numbers; however, these groups did not significantly differ from each other. The results indicate that MGAs are associated with deteriorating long-term kidney function, and mitochondrial injury, despite few additional pathological changes. We suggest that clinicians conduct close long-term follow-up of patients with MGAs.