Kensuke Asaba

Suppressing renal NADPH oxidase to treat diabetic nephropathy

Renal nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase is an important source of oxidative stress and its expression is enhanced in the glomerulus and distal tubules of diabetic nephropathy. High glucose-induced protein kinase C signalling or renal angiotensin II signalling increases the membrane translocation of cytosolic component p47phox. NADPH oxidase-derived reactive oxygen species (ROS) in the podocytes damage the glomerular basement membrane and the slit diaphragm causing proteinuria, and mesangial and glomerular endothelial NADPH oxidase increase TGF-β and cause collagen and fibronectin accumulation. Tubular NADPH oxidase stimulated by angiotensin II or aldosterone contributes to sodium retention and to tubulointerstitial damage. Thus, inhibition of the renal renin–angiotensin II–aldosterone system with angiotensin-converting enzyme inhibitor, angiotensin II type 1 receptor blocker or selective aldosterone inhibitor indirectly suppresses NADPH oxidase reducing renal ROS, proteinuria and glomerulosclerosis. Statins are also effective in blocking the membrane translocation of Rac, especially in diabetes with hypercholesterolemia where ROS is produced by the intrinsic NADPH oxidase and by the activated macrophages. A medical herb, picrorhiza, inhibits the membrane translocation of p47phox, is a specific inhibitor of NADPH oxidase and, more so than superoxide dismutase mimetics, may be a promising strategy for the treatment of diabetic nephropathy.

Double-edged action of SOD mimetic in diabetic nephropathy.

Oxidative stress plays an important role in the pathogenesis of diabetic complications, and we investigated the effect of superoxide dismutase (SOD) mimetic, tempol, in diabetic nephropathy. Streptozotocin-induced diabetic rats were treated with tempol from 2 weeks until 8 weeks. The expression of NADPH oxidase, catalase, and myeloperoxidase (MPO), superoxide dismutase activity, and production of peroxide and hypochlorite were evaluated. Tempol treatment prevented the increase in NADPH oxidase and peroxide production in the glomeruli of diabetic rat. Catalase was decreased without change in SOD activity, and MPO was enhanced in the kidney of diabetic rats. Tempol treatment stimulated SOD activity and increased the conversion of superoxide to hydrogen peroxide, and hydrogen peroxide on its hand was converted to hypochlorite by the increased MPO. The reduction of peroxide by tempol was followed by the decrease in TGF-β and mesangial matrix expansion. However, tempol did not reduce hypochlorite or urinary protein excretion. In conclusion, tempol inhibited glomerular matrix expansion via suppression of peroxide production and TGF-β, but it failed to reduce proteinuria, probably due to the increased hypochlorite production in diabetic nephropathy.

The Resistive Index Is a Marker of Renal Function, Pathology, Prognosis, and Responsiveness to Steroid Therapy in Chronic Kidney Disease Patients

To evaluate the significance of the renal resistive index (RI) as a noninvasive marker of renal histological damage and a prognostic indicator, we examined RI by Doppler ultrasonography in 202 chronic kidney disease (CKD) patients who underwent renal biopsy. RI increased as the CKD stage progressed and correlated with age, systolic blood pressure, estimated glomerular filtration rate (eGFR), and renal histological changes, including glomerulosclerosis, arteriolosclerosis, and tubulointerstitial damage. Prognostic evaluation with a median follow-up period of 38.5 months revealed that patients with RI ≥ 0.7 (high RI group, n = 39) had significantly poorer renal survival than those with RI < 0.65 (normal RI group, n = 120) and 0.65 ≤ RI < 0.7 (high-normal RI group, n = 43). The patients in the high-normal RI group showed good response to steroids. However, in the high RI group, steroid therapy did not significantly improve renal survival. Of the clinical indices studied, RI ≥ 0.7, hypertension, proteinuria, and low eGFR at diagnosis were independent risk factors for worsening renal dysfunction. In conclusion, RI in CKD patients was considered as a marker of renal function, histological damage, and renal prognosis, and a possible determinant of indication for steroids.

Nitric oxide generated by nNOS in the macula densa regulates the afferent arteriolar diameter in rat kidney

Nitric oxide (NO) derived from neuronal NO synthase (nNOS) in the macula densa is a modulator of tubuloglomerular feedback. However, little is known about the regulation of the afferent arteriolar diameter by NO from the macula densa in salt-sensitive hypertension. We investigated the relationship between nNOS in the macula densa and the afferent arteriolar diameter in deoxycorticosterone acetate (DOCA)-salt hypertensive rats treated with angiotensin converting enzyme (ACE) inhibitor or thiazide for 5 weeks. DOCA rats had reduced nNOS expression in the macula densa compared to controls and reduction of NO production evaluated with 4,5-diaminofluorescein diacetate in the juxtaglomerular apparatus (JGA). Treatment with ACE inhibitor and thiazide increased nNOS and NO production in the JGA. The diameter of the afferent arteriole observed by SEM using microvascular casts was smaller in DOCA rats compared to control rats, and ACE inhibitor or thiazide dilated the afferent arteriole with a positive correlation to nNOS immunoreactivity in the macula densa. In conclusion, the afferent arteriolar diameter might be regulated by NO derived from nNOS in the macula densa in DOCA-salt hypertensive rats.

Detection of myeloperoxidase in membranous nephropathy-like deposits in patients with anti-neutrophil cytoplasmic antibody–associated glomerulonephritis☆

Anti-neutrophil cytoplasmic antibody-associated glomerulonephritis is usually classified as a pauci-immune type. However, it sometimes shows immune complex deposition of unknown origin. We examined the glomerular localization of myeloperoxidase by double immunofluorescence and immunoelectron microscopy in cases of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis with membranous nephropathy-like immunoglobulin G deposition to investigate the immune complex antigens in these cases. Six (35%) of the biopsy samples from 17 cases with anti-neutrophil cytoplasmic antibody-associated glomerulonephritis showed granular deposition of immunoglobulin G along the glomerular capillary walls. Light microscopy revealed necrotizing crescentic glomerulonephritis with segmental thickening of the glomerular basement membrane. Electron microscopy showed electron-dense deposits in intramembranous and mesangial areas. However, the size and distribution of the deposits were irregular and segmental in the examined cases, unlike typical global and subepithelial lesions of membranous nephropathy. Double immunofluorescence using Alexa Fluor 594-labeled anti-myeloperoxidase antibody and fluorescein isothiocyanate-labeled anti-immunoglobulin G antibody, as well as immunoelectron microscopy using anti-myeloperoxidase antibody labeled with 25-nm gold particles revealed partial colocalization of myeloperoxidase and immunoglobulin G within the glomerular basement membrane and mesangium. In some cases of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis, myeloperoxidase may form immune complexes and develop membranous nephropathy-like lesions.

Fibrillary glomerulonephritis associated with essential thrombocytosis.

A 68-year-old man with a 30-year history of essential thrombocytosis developed nephrotic syndrome. Renal biopsy showed massive deposits of Congo red-negative periodic acid Schiff (PAS)-positive substance in the mesangium and capillary wall that was positive for IgG. Electron microscopic examination revealed 10- to 20-nm fibrils in the deposits, and there was no other organ involvement; thus, we diagnosed fibrillary glomerulonephritis. This is the first report of a case of fibrillary glomerulonephritis associated with essential thrombocytosis.

Primary amyloidosis with multiple pulmonary nodular lesions and IgA nephropathy-like renal involvement.

A 66-year-old woman demonstrated multiple nodular lesions in the lungs without symptoms, and laboratory tests and transbronchial lung biopsy (TBLB) had been negative for malignancy, tuberculosis and sarcoidosis 15 years ago. She developed proteinuria and hematuria 10 years later. Renal biopsy revealed focal segmental mesangial proliferation with predominant IgA deposition in the paramesangium, suggesting IgA nephropathy. However, electron-microscopic observation revealed 8-12 nm fibril deposits in the interstitium and few in the mesangium that were positively stained with amyloid P protein and negative for amyloid A protein. Re-evaluation of previous TBLB samples showed apple-green birefringence with Congo-red staining that was resistant to potassium permanganate reaction. Electron-microscopic observation with high magnification and immunostaining for amyloid components led to a diagnosis of AL amyloidosis in this patient with predominant mesangial IgA deposition and slowly progressive nodular lesions in the lungs.

Spironolactone with ACE inhibitor is effective in gross hematuria caused by nephroptosis

Abstract  Gross hematuria caused by nephroptosis is difficult to treat and sometimes requires surgical treatment. We experienced a case of a 64‐year‐old woman with gross hematuria due to nephroptosis and glomerular thin basement membrane that showed remission of hematuria with the blockade of the renin‐angiotensin‐aldosterone system with an angiotensin‐converting enzyme inhibitor and spironolactone.

The reduced expression of proximal tubular transporters in acquired Fanconi syndrome with κ light chain deposition

In a case of acquired Fanconi syndrome associated with smoldering myeloma, we confirmed the deposition of protease-resistant κ light chain proteins in a proximal tubular injury and found the decreased expression of apical tubular transporters including sodium glucose co-transporter, sodium phosphate co-transporter, uric acid transporter 1, and a decrease of Na+/K+-ATPase in the basolateral membrane. The protease-resistant kappa light chain has a pathological role in the expression of tubular transporters in the proximal tubule and causes Fanconi syndrome associated with smoldering myeloma.