Effect of a novel free radical scavenger, edaravone, on puromycin aminonucleoside induced nephrosis in rats

Minimal change nephrotic syndrome and prohibitin-2 gene polymorphism

BACKGROUND

Patients with minimal change nephrotic syndrome (MCNS) often also have allergic diseases. Abnormalities of Th2-derived cytokines and T-cell functions contribute to development of these diseases. On the other hand, imbalances between reactive oxygen species (ROS) and antioxidants have been implicated in MCNS and progression of atopic dermatitis. ROS, produced mainly within mitochondria, subject cells to oxidative stress, while prohibitin 2 protects mitochondria by increasing tolerance to ROS. Additionally, podocin, a member of the slit diaphragm protein complex, contains PHB-like domain that serves as a signaling platform regulating podocyte function through associated transmembrane proteins.

PATIENTS AND METHOD

Then, we performed exome sequencing analysis in five patients with frequently relapsing their MCNS associated with allergic disease and serum IgE concentrations of 2000 IU/L or higher.

RESULTS

We detected a heterozygous prohibitin 2 polymorphism, c.873-3_873-2 delCA (rs111523336), in 1 patient. This mutation in exon 9 caused frameshifts in regions connected to splicing sites, where they could disrupt transcription of prohibitin 2. Frequency of this polymorphism in exon 9 is 7.3% among Japanese. Increase in peripheral blood ROS even MCNS remission state suggests the heterozygous prohibitin 2 variant may contribute to give more susceptibility towards the recurrence of MCNS as well as atopic skin disease. This increase may have progression of atopic dermatitis, which sometimes heralded.

CONCLUSION

The prohibitin-2 polymorphism may reduce ROS tolerance in glomerular epithelium and led to high local exposure to ROS, increasing permeability of the glomerular basement membrane to result in proteinuria. Imbalance between ROS and antioxidants together with failure of signal transduction in the glomerular slit membrane caused by prohibitin 2 abnormality could have contributed to nephrotic syndrome in our patients. Prohibitin 2 analysis is needed in additional MCNS patients with concomitant allergic disease.

Sialic acid supplementation ameliorates puromycin aminonucleoside nephrosis in rats

Defects in sialylation are known to have serious consequences on podocyte function leading to collapse of the glomerular filtration barrier and the development of proteinuria. However, the cellular processes underlying aberrant sialylation in renal disease are inadequately defined. We have shown in cultured human podocytes that puromycin aminonucleoside (PAN) downregulates enzymes involved in sialic acid metabolism and redox homeostasis and these can be rescued by co-treatment with free sialic acid. The aim of the current study was to ascertain whether sialic acid supplementation could improve renal function and attenuate desialylation in an in vivo model of proteinuria (PAN nephrosis) and to delineate the possible mechanisms involved. PAN nephrotic rats were supplemented with free sialic acid, its precursor N-acetyl mannosamine or the NADPH oxidase inhibitor apocynin. Glomeruli, urine, and sera were examined for evidence of kidney injury and therapeutic efficacy. Of the three treatment regimens, sialic acid had the broadest efficacy in attenuating PAN-induced injury. Proteinuria and urinary nephrin loss were reduced. Transmission electron microscopy revealed that podocyte ultrastructure, exhibited less severe foot process effacement. PAN-induced oxidative stress was ameliorated as evidenced by a reduction in glomerular NOX4 expression and a downregulation of urine xanthine oxidase levels. Sialylation dysfunction was improved as indicated by reduced urinary concentrations of free sialic acid, restored electrophoretic mobility of podocalyxin, and improved expression of a sialyltransferase. These data indicate that PAN induces alterations in the expression of enzymes involved in redox control and sialoglycoprotein metabolism, which can be ameliorated by sialic acid supplementation possibly via its properties as both an antioxidant and a substrate for sialylation.

NADPH oxidase-mediated upregulation of connexin43 contributes to podocyte injury

The gap junction protein connexin43 (Cx43) was markedly increased in podocytes in a rat model of nephrosis induced by puromycin. However, the mechanisms and roles of the altered Cx43 in podocytes are still unclear. Given that oxidative stress mediates podocyte injury under a variety of pathological situations, we examined the possible involvement of an oxidative stress-related mechanism in the regulation of Cx43. Incubation of podocytes with puromycin led to a time- and concentration-dependent loss of cell viability, which was preceded by an elevation in Cx43 levels. Concomitantly, puromycin also induced NOX4 expression and promoted superoxide (O(2)(·-)) generation. Inhibition of NADPH oxidase with apocynin and diphenyleneiodonium chloride or addition of the superoxide dismutase mimetic tempol completely abrogated, whereas the O(2)(·-) donors menadione and 2,3-dimethoxy-1,4-naphthoquinone reproduced, the effects of puromycin on Cx43 expression and cell injury. Further analysis demonstrated that treatment of podocytes with several structurally different gap-junction inhibitors significantly attenuated the cytotoxicity of puromycin. Our results thus indicate that NADPH oxidase-mediated upregulation of Cx43 contributes to podocyte injury.

Ezetimibe alone or in combination with pitavastatin prevents kidney dysfunction in 5/6 nephrectomized rats fed high-cholesterol

We attempted to elucidate the relationship between cholesterol absorption and kidney damage by investigating the renoprotective effect of ezetimibe, a cholesterol absorption inhibitor, in 5/6 nephrectomized rats (Nx). The Nx or sham-operated rats (Sham) were fed 1% high-cholesterol diet (HC) containing ezetimibe (10 mg/[kg d]), pitavastatin (3 mg/[kg d]), or both for 8 weeks. Pathological changes, endothelial nitric oxide synthase (eNOS) messenger RNA (mRNA), and oxidative stress were assessed in the kidney. The Sham fed HC exhibited hypercholesterolemia and glomerulosclerosis with macrophage infiltration in the kidney, and ezetimibe attenuated these changes. The Nx exhibited hypercholesterolemia, increased urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), glomerulosclerosis with macrophage infiltration and interstitial fibrosis, and downregulation of eNOS mRNA. The HC increased cholesterol further and worsened the kidney damage with increased 8-OHdG. Ezetimibe attenuated the hypercholesterolemia, kidney dysfunction, and pathological changes. The beneficial effects of ezetimibe were significantly associated with reduced 8-OHdG (P < .01). Pitavastatin did not reduce cholesterol or 8-OHdG, but it did significantly suppress the kidney damage with upregulated eNOS mRNA by 2.5-fold (P < .02). The combination of ezetimibe and pitavastatin synergistically ameliorated the kidney damage. The kidney dysfunction and pathological changes were significantly associated with cholesterol, markers of cholesterol absorption (campesterol and cholestanol), and 8-OHdG (P < .001-.05). Multiple regression analysis revealed that the markers of cholesterol absorption were independently associated with the kidney damage. Ezetimibe confers renoprotective effects by inhibiting cholesterol absorption, which in turn reduces oxidative stress; and pitavastatin additively ameliorates kidney damage by increasing NO production via mechanisms independent of cholesterol reduction.

Angiotensin II type 2 receptor-interacting protein prevents vascular senescence

Angiotensin II type 2 (AT(2)) receptor-interacting protein (ATIP), which interacts with the C-terminal tail of the AT(2) receptor, regulates the functions of the AT(2) receptor. We have reported that AT(2) receptor stimulation attenuated vascular senescence. Therefore, we examined the possible negative role of ATIP in regulating vascular senescence. We generated ATIP-transgenic (Tg) mice, and cultured vascular smooth muscle cells (VSMCs). Persistent angiotensin II stimulation induced increases in SA-β-gal-positive cells and the level of a DNA damage marker, 8-OHdG in VSMC, whereas these effects of angiotensin II were attenuated in VSMC prepared from ATIP-Tg mice. Angiotensin II treatment also upregulated the expression of methyl methanesulfonate-sensitive 2 (MMS2), a DNA repair factor, and Src homology 2 domain-containing protein-tyrosine phosphatase 1 (SHP-1) activity, whereas these effects of angiotensin II were further enhanced in ATIP-Tg VSMC. In vivo, x-ray irradiation to mice caused increases in SA-β-gal-positive area and 8-OHdG level in the thoracic aorta; however, these effects were reduced in ATIP-Tg mice, with a significant increase in MMS2 expression. These results suggest that ATIP could inhibit VSMC senescence, involving MMS2 expression and SHP-1 activity. ATIP might be a new therapeutic molecule to treat vascular aging and age-related vascular diseases.

Beyond free radical scavenging: Beneficial effects of edaravone (Radicut) in various diseases (Review)

Free radicals play an important role in the pathogenesis of a variety of diseases; thus, they are an attractive target for therapeutic intervention in these diseases. Compounds capable of scavenging free radicals have been developed for this purpose and some, developed for the treatment of cerebral ischemic stroke, have progressed to clinical trials. One such scavenger, edaravone, is used to treat patients within 24 h of stroke. Edaravone, which can diffuse into many disease-affected organs, also shows protective effects in the heart, lung, intestine, liver, pancreas, kidney, bladder and testis. As well as scavenging free radicals, edaravone has anti-apoptotic, anti-necrotic and anti-cytokine effects in various diseases. Here, we critically review the literature on its clinical efficacy and examine whether edaravone should be considered a candidate for worldwide development, focusing on its effects on diseases other than cerebral infarction. Edaravone has been safely used as a free radical scavenger for more than 10 years; we propose that edaravone may offer a novel treatment option for several diseases.

Numb protects renal proximal tubular cells from puromycin aminonucleoside-induced apoptosis through inhibiting Notch signaling pathway

Numb was originally discovered as an intrinsic cell fate determinant in Drosophila by antagonizing Notch signaling. The present study is to characterize the role of Numb in oxidative stress-induced apoptosis of renal proximal tubular cells. Exposure of NRK52E cells to puromycin aminonucleoside (PA) resulted in caspase 3-dependent apoptosis. Numb expression was downregulated by PA in a time- and dose-dependent manner. Knocking down endogenous Numb by siRNA sensitized NRK52E cells to PA-induced apoptosis, whereas overexpressing Numb protected NRK52E cells from PA-induced apoptosis. Moreover, PA activated Notch signaling in a time- and dose-dependent manner as indicated by increased expression of the intracellular domain of Notch and Hes-1. Notch signaling inhibitor DAPT significantly attenuated Numb siRNA-augmented apoptosis. On the other hand, overexpression of intracellular domain of Notch1 could reverse the protective effect of Numb on PA-induced apoptosis. Taken together, our data demonstrated that, in renal proximal tubular cells, Numb functions as a protective molecule on PA-induced apoptosis through antagonizing Notch signaling activity.

Effects of mineralocorticoid and angiotensin II receptor blockers on proteinuria and glomerular podocyte protein expression in a model of minimal change nephrotic syndrome

AIM

Several proteins constituting the slit diaphragm are considered important for maintaining capillary wall permselectivity. Early intervention with blockers of angiotensin II receptors (AR) and mineralocorticoid receptors (MR) is effective against proteinuria in models of chronic hypertensive and protein-induced renal damage. However, the effects of AR and/or MR blockers in a model of acute nephrotic syndrome remain unknown. The effects of AR and MR blockers were examined in puromycin aminonucleoside (PAN)-treated rats.

METHODS

Six week old male Sprague-Dawley (SD) rats were injected with PAN or vehicle and assigned to groups as follows: vehicle (group C); PAN (group P); PAN followed 3 days later by administration of the MR blocker, eplerenone (group MR), and by the AR blocker, losartan (group AR). Blood pressure and urinary protein excretion were measured and all rats were killed for immunohistochemical investigation on day 14 after PAN administration.

RESULTS

Blood pressure did not change throughout the study period. Proteinuria was decreased in groups MR and AR compared with group P (on day 14 after PAN administration, respectively; group P vs AR, P < 0.01; group P vs MR, P < 0.05). Nephrin, podocin and podocalyxin staining was preserved in the glomeruli of groups MR and AR compared with group P.

CONCLUSION

The MR and AR blockers decreased proteinuria in the acute model of nephrotic syndrome with preserved expression of glomerular podocyte protein independently of blood pressure.

Increased nitric oxide production by T- and B-cells in idiopathic nephrotic syndrome

The pathogenesis of idiopathic nephrotic syndrome (INS) remains unclear. To study the role of nitric oxide (NO) in INS, we measured intracellular NO produced by T- and B-cells using a novel fluorescent indicator. Twelve children with INS (mean age 7.3 years; group A-1: in relapse, group A-2: in remission) were enrolled in the study together with 16 children with other renal diseases (9.5 years; group B) and 42 healthy control children (7.7 years; group C). The amount of NO produced by CD3+ cells (T-cells) and CD19+ cells (B-cells) and of plasma NO(x) was measured by flow cytometry and colorimetry, respectively. The average amount of NO produced by CD3+ and CD19+ cells in group A-1 subjects was significantly higher than that produced by these cells in group A-2 and B patients and the healthy controls (group C), respectively (P < 0.01), and it decreased after the patients achieved remission (P < 0.01). Plasma NO(x) levels in group A-1 patients was also highest among the different groups (P < 0.01). There were no significant differences in intracellular NO and plasma NO(x) among group A-2, B, and C subjects (P > 0.05). A significant correlation between plasma NO(x) and urinary protein excretion was found only in group A patients and not in group B patients. We conclude that an aberrant immune system may exist not only in T-cells but also in B-cells, and NO may play some role in INS.