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Background and Hypothesis: Measurement of glomerular filtration rate (GFR) is subject to inaccurate urine collection. Clearances of d-serine and d-asparagine, rare enantiomers of amino acids, are the measures of GFR since they are almost free of tubular secretion and reabsorption. We hypothesize that d-serine and d-asparagine can accurately determine urine volume and GFR., Methods: This cross-sectional observational study included 209 living kidney transplant donors and recipients for whom GFR was measured using the clearance of inulin. Assuming that urine excretions of d-serine and d-asparagine are constant and using urine levels of d-serine and d-asparagine from each urine collection, an equation for estimated urine volume (eUV) was established. Based on the eUV, the abnormal urine volume was replaced with an estimate with which the GFR was re-evaluated., Result: Clearances of d-serine and d-asparagine were minor in proportional biases when compared with that of creatinine. Using 627 urine collection, the equation for eUV (mL/min) was established as 21.88/urine d-Ser (0.40 + 0.20 × log10(urine d-Asn)). Using eUV, we identified 20 instances where urine collection volumes varied significantly from the estimated values. After replacement with eUV, measured GFR (mGFR) was corrected to adjusted mGFR, which was within approximately 20 mL/min/1.73m2 of the mGFR., Conclusion: d-Serine and d-asparagine are nearly completely excreted in urine after glomerular filtration, enabling the estimation of urine volume and correct mGFR. Besides reflecting GFR, d-serine and d-asparagine can be used to estimate urine volume. By applying the eUV method, mGFR determined using clearance methods becomes more accurate., (© The Author(s) 2024. Published by Oxford University Press on behalf of the ERA.)

Background: Hypomagnesemia (Hypo-Mg) predicts mortality and chronic kidney disease (CKD) progression. However, in CKD, its prevalence, kidney-intrinsic risk factors, and the effectiveness of oral magnesium (Mg) therapy on serum Mg levels is uncertain., Methods: In a cross-sectional study enrolling pre-dialysis outpatients with CKD, the prevalence of electrolyte abnormalities (Mg, sodium, potassium, calcium and phosphorus) was compared. In an open-label randomized controlled trial (RCT), we randomly assigned CKD patients to either the magnesium oxide (MgO) or control arm. The outcome was serum Mg levels at 1 year., Results: In 5126 patients, Hypo-Mg was the most common electrolyte abnormality (14.7%) with similar prevalence across stages of CKD. Positive proteinuria was a risk factor of Hypo-Mg (odds ratio 2.2; 95% confidence interval 1.2-4.0). However, stratifying the analyses by diabetes mellitus (DM), it was not significant in DM (Pinteraction = 0.04). We enrolled 114 patients in the RCT. Baseline analyses showed that higher proteinuria was associated with higher fractional excretion of Mg. This relationship between proteinuria and renal Mg wasting was mediated by urinary tubular markers in mediation analyses. In the MgO arm, higher proteinuria or tubular markers predicted a significantly lower 1-year increase in serum Mg. In patients with a urinary protein-to-creatinine ratio (uPCR) <0.3 g/gCre, serum Mg at 1 year was 2.4 and 2.0 mg/dL in the MgO and control arms, respectively (P < 0.001), with no significant between-group difference in patients whose uPCR was ≥0.3 g/gCre (Pinteraction=0.001)., Conclusions: Proteinuria leads to renal Mg wasting through tubular injuries, which explains the high prevalence of Hypo-Mg in CKD., (© The Author(s) 2018. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.)

Background: Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays., Methods: Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR., Results: We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C., Conclusions: A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced., (© 2014 The American Association for Clinical Chemistry.)

Background: Recent post hoc analysis proved the efficacy and tolerability of risedronate in osteoporotic patients with renal impairment, but the combination of active vitamin D in chronic kidney disease (CKD) patients taking glucocorticoids remains unknown., Methods: We conducted a prospective study enrolling 114 CKD patients (creatinine clearance > or =30 ml/min/1.73 m(2)) receiving glucocorticoid therapy for > or =6 months. Eighty-eight subjects who had received active vitamin D (aVD) were randomly assigned to either a group treated with aVD only (group A), or to a group also receiving risedronate 2.5 mg/day (group B). The remaining patients (group C) received risedronate only., Results: After 1 year 100 subjects were analysed. Risedronate was effective on the lumbar spine, but not on the femoral neck. The lumbar bone mineral density (BMD) significantly increased by 2.8 and 2.5% in groups B and C, respectively, but decreased by 1.0% in group A. Serum N-terminal telopeptides of type I collagen (S-NTX) and bone alkaline phosphatase (ALP) fell significantly in groups B and C at 3 and 6 months, respectively, while in group A S-NTX remained unchanged and bone ALP significantly increased. There was no significant difference between groups B and C regarding BMD and bone markers. The reduction rate of S-NTX (bone ALP) at 6 months predicted the increase in lumbar BMD at 1 year with a sensitivity of 73% (34%) and a specificity of 46.2% (100%)., Conclusions: Risedronate is effective in increasing BMD with or without aVD in CKD patients receiving long-term glucocorticoid therapy. Bone markers are of some use in predicting the response to anti-resorptive therapy.

Background: In mammals, the renal medulla is in a hypertonic environment related to the renal concentrating mechanism. Renal cells accumulate osmolytes such as betaine to protect cells from the perturbing effect of high concentration of electrolytes. Hypertonicity-induced cell death and the effect of betaine were investigated in Madin Darby canine kidney (MDCK) cells., Methods: Cell viability was detected by 3-(4,5-dimethylthiazo-2-yl)-2,5-diphenyl tetrazolium bromide assay. DNA fragmentation was determined by FACS analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) staining and agarose gel electrophoresis. Activities of caspase-1, -3, -8, and -9 were measured., Result: When the cells were exposed to 700 mOsm medium for 24 h, 40% of the cells were detached. TUNEL staining showed that about 20% of detached cells were apoptotic, indicating that both necrosis and apoptosis contributed to the hypertonicity-induced cell death in MDCK cells. DNA laddering was demonstrated in hypertonic cells. Caspase-3, -8, and -9 activities of the adherent cells exposed to 700 mOsm for 24 h increased approximately 20-, 3-, and 4-fold the value of isotonic cells, respectively. However, there was no significant change in caspase-1 activity. Addition of 1 mM betaine into the medium protected the cells against the hypertonicity-induced cytotoxicity and apoptosis. Betaine prevented the induction of caspase-3, -8, and -9 activities after hypertonic exposure to about 50%., Conclusions: The present study demonstrates that (i) apoptosis is involved in the hypertonicity-induced cell death in MDCK cells; (ii) caspase-3, -8, and -9 may contribute to the apoptosis; and (iii) betaine has protective effect on the hypertonicity-induced apoptosis.

Background: With progressive renal disease, structural derangement increasingly encompasses the tubulointerstitial compartment. Tubulointerstitial injury is a critical determinant of renal functional reserve and prognosis in renal disease. Interstitial cells acquiring characteristic of myofibroblasts are an important contributor to interstitial fibrosis. Caldesmon, a calmodulin or actin binding protein, is a molecular marker of differentiation in smooth muscle cells and has recently been shown by us to be a good marker of mesangial cell activation in IgA nephropathy patients. METHODS. We studied whether the expression of caldesmon in interstitium of the kidney was enhanced in the process of glomerular disease and whether it would be a marker of interstitial activation in specific disease states. We performed immunohistochemical staining with anti-caldesmon antibodies in 38 biopsy specimens from IgA nephropathy patients and analysed them quantitatively with a computer-aided manipulator. Interstitial caldesmon expression were compared with histological changes and clinical parameters., Results: Caldesmon expression was enhanced where interstitial cell infiltration and fibrosis were found. Immunoelectron microscopy revealed that caldesmon staining in the renal interstitium was cytoplasmic, and in the processes of myofibroblast-like cells. Caldesmon expression was more prominent in the intense CD68 infiltrated group than in the low positive cells infiltrated group. Patients showing high intensity of interstitial caldesmon expression had significantly higher urinary protein excretion than those showing low intensity of caldesmon expression. Next, 15 patients were treated with glucocorticoid and heparin for 4-8 weeks and re-biopsies were performed. Caldesmon expression was reduced in concomitant with decreased interstitial cell infiltration. Follow-up of these patients (average 24 months) revealed a significant suppression of urinary protein excretion and significant improvement of creatinine clearance., Conclusion: These results suggest that the interstitial caldesmon expression is associated with the progression of IgA nephropathy, and glucocorticoid--heparin therapy may reverse the phenotypic change of interstitial cells during the disease process of glomerulonephritis.

Background: During peritoneal dialysis, the peritoneal mesothelium is exposed continually to hypertonic dialysates. The purpose of this study is to see if rat mesothelial cells have an osmoregulatory mechanism to adapt to hypertonic environment., Methods: The intracellular content of organic osmolytes was measured by HPLC methods. Myo-inositol transport activity was measured by Na+-dependent uptake of [3H]myo-inositol. mRNA abundance for the Na+/myo-inositol co-transporter (SMIT) was examined by Northern and slot-blot analyses., Results: In isotonic mesothelial cells, only myo-inositol could be detected. After switching to hypertonic medium made by addition of NaCl, myo-inositol content gradually increased and peaked at 48 h after the switch. The myo-inositol content in hypertonic cells increased > 7-fold over the value in isotonic cells. The contents of betaine and glycerophosphorylcholine (GPC) also increased but were less than that of myo-inositol. Sorbitol was not accumulated in this condition. When glucose was used to increase medium osmolality, all of the four osmolytes were increased by hypertonicity (myo-inositol > sorbitol > GPC > betaine). Thus, myo-inositol is the most abundant osmolyte in the mesothelial cells. Na+-dependent myo-inositol uptake in hypertonic cells was approximately 7-fold the uptake in isotonic cells, reaching a maximum 16 h after switching to a hypertonic medium. The uptake rate increased as medium osmolality increased from 300 to 500 mosm/kg. SMIT mRNA rapidly increased after increasing medium osmolality, reaching a maximum 8 h after the switch. The relative increase in the mRNA abundance was approximately 11 times isotonic levels., Conclusions: Mesothelial cells respond to extracellular hypertonicity by increasing SMIT mRNA abundance, myo-inositol transport activity and accumulating myo-inositol into the cells.

Background: Activation and consequent phenotypic modulation of mesangial cells is considered to play a crucial role in the process of glomerular disease progression. Caldesmon, a calmodulin and actin-binding protein, is a molecular marker of the phenotypic change in smooth-muscle cells., Subjects and Methods: We studied whether the expression of caldesmon in mesangial cells was enhanced in the process of IgA nephropathy and whether it would be a marker of mesangial activation indicating prognostic significance in specific disease states. We performed immunohistochemical staining with anticaldesmon and alpha-smooth-muscle actin (alpha-SMA) antibodies in 32 biopsy specimens from IgA nephropathy patients and analysed them quantitatively with a computer-aided manipulator., Results: The glomerular expression of caldesmon was enhanced in IgA nephropathy patients. We compared caldesmon expression with composite histological scores (cell score and matrix score), clinical parameters and expressions of alpha-SMA. There was a statistically significant correlation between the caldesmon score and the histological scores (cell score and matrix score, P<0.0001, P<0.01 respectively). Patients showing a high intensity of caldesmon expression (defined as caldesmon score > or = 35; H-group) had significantly higher urinary protein excretion than those showing a low intensity of caldesmon expression (defined as caldesmon score < 35; L-group) (1.2 +/- 1.2 g/24 h vs 0.41 +/- 0.53 g/24 h, P<0.05). Caldesmon and alpha-SMA expression had a statistically significant correlation (P<0.000). Next, 13 patients were treated with glucocorticoid-heparin for 4-8 weeks and re-biopsies were performed. After the therapy, the caldesmon and alpha-SMA scores were significantly lower than those before the therapy (P<0.01)., Discussion: These results suggest that the expression of caldesmon in glomeruli is associated with the progression of IgA nephropathy, and that glucocorticoid heparin therapy may reverse the phenotype of mesangial cells during the disease process of glomerulonephritis.