Hyperuricemia and chronic kidney disease: to treat or not to treat

Hyperuricemia is common in chronic kidney disease (CKD) and may be present in 50% of patients presenting for dialysis. Hyperuricemia can be secondary to impaired glomerular filtration rate (GFR) that occurs in CKD. However, hyperuricemia can also precede the development of kidney disease and predict incident CKD. Experimental studies of hyperuricemic models have found that both soluble and crystalline uric acid can cause significant kidney damage, characterized by ischemia, tubulointerstitial fibrosis, and inflammation. However, most Mendelian randomization studies failed to demonstrate a causal relationship between uric acid and CKD, and clinical trials have had variable results. Here we suggest potential explanations for the negative clinical and genetic findings, including the role of crystalline uric acid, intracellular uric acid, and xanthine oxidase activity in uric acid-mediated kidney injury. We propose future clinical trials as well as an algorithm for treatment of hyperuricemia in patients with CKD

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Angiopoietin-like-4 and minimal change disease

<div><p>Background</p><p>Minimal Change Disease (MCD) is the most common type of nephrotic syndrome in children. Angiopoietin-like-4 (Angplt4) has been proposed as mediator of proteinuria in MCD. The aim of this study was to evaluate the role of Angptl4 as a biomarker in MCD.</p><p>Methods</p><p>Patients with biopsy-proven primary MCD, focal segmental glomerulosclerosis, membranous nephropathy (60, 52 and 52 respectively) and 18 control subjects had urinary and serum Angptl4 measured by Elisa. Frozen kidney tissue sections were stained for Angptl4.</p><p>Results</p><p>Angptl4 was not identified in glomeruli of MCD patients in relapse. Urinary Angptl4 levels were elevated in MCD in relapse as well as in patients with massive proteinuria due to other glomerular diseases.</p><p>Conclusion</p><p>Neither serum nor urine Angptl4 appear to be good biomarkers in MCD. Elevated urinary Angptl4 n glomerular disease appears to reflect the degree of proteinuria rather than any specific disease.</p></div

Urinary Angptl4 in MCD, FSGS, MN patients and control subjects.

<p>(A) Urinary Angptl4 in MCD, FSGS, MN patients and control subjects. (B) Urinary Angptl4 in FSGS and MN patients during relapse and remission. MCD minimal change disease, FSGS focal segmental glomerulosclerosis, MN membranous nephropathy, n refers to the number of patients, data expressed as mean±SD.</p

Demographic characteristics of patients and control subjects.

<p>Demographic characteristics of patients and control subjects.</p

Glomerular Angplt4 staining in patients with MCD and other glomerulopathies.

<p>Angptl4 angiopoietin-like-4, MCD minimal change disease, FSGS focal segmental glomerulosclerosis, LN lupus nephritis, MPGN membranoproliferative glomerulonephritis, n refers to the number of patients, Green, blue and red stains represent Angptl4, DAPI and synaptopodin respectively. Yellow lines represent scale bars. Magnification x200.</p

Serum Angptl4 in MCD, FSGS, MN during relapse and control subjects.

<p>Angptl4 angiopoietin-like-4, MCD minimal change disease, FSGS focal segmental glomerulosclerosis, MN membranous nephropathy, n refers to the number of patients, data expressed as mean±SD.</p

Nephrin is necessary for podocyte recovery following injury in an adult mature glomerulus

<div><p>Nephrin (<i>Nphs1</i>) is an adhesion protein that is expressed at the podocyte intercellular junction in the glomerulus. <i>Nphs1</i> mutations in humans or deletion in animal genetic models results in a developmental failure of foot process formation. A number of studies have shown decrease in expression of nephrin in various proteinuric kidney diseases as well as in animal models of glomerular disease. Decrease in nephrin expression has been suggested to precede podocyte loss and linked to the progression of kidney disease. Whether the decrease in expression of nephrin is related to loss of podocytes or lead to podocyte detachment is unclear. To answer this central question we generated an inducible model of nephrin deletion (<i>Nphs1</i>^Tam-Cre) in order to lower nephrin expression in healthy adult mice. Following tamoxifen-induction there was a 75% decrease in nephrin expression by 14 days. The <i>Nphs1</i>^Tam-Cre mice had normal foot process ultrastructure and intact filtration barriers up to 4–6 weeks post-induction. Despite the loss of nephrin expression, the podocyte number and density remained unchanged during the initial period. Unexpectedly, nephrin expression, albeit at low levels persisted at the slit diaphragm up to 16–20 weeks post-tamoxifen induction. The mice became progressively proteinuric with glomerular hypertrophy and scarring reminiscent of focal and segmental glomerulosclerosis at 20 weeks. Four week-old <i>Nphs1</i> knockout mice subjected to protamine sulfate model of podocyte injury demonstrated failure to recover from foot process effacement following heparin sulfate. Similarly, <i>Nphs1</i> knockout mice failed to recover following nephrotoxic serum (NTS) with persistence of proteinuria and foot process effacement. Our results suggest that as in development, nephrin is necessary for maintenance of a healthy glomerular filter. In contrast to the developmental phenotype, lowering nephrin expression in a mature glomerulus resulted in a slowly progressive disease that histologically resembles FSGS a disease linked closely with podocyte depletion. Podocytes with low levels of nephrin expression are both susceptible and unable to recover following perturbation. Our results suggest that decreased nephrin expression independent of podocyte loss occurring as an early event in proteinuric kidney diseases might play a role in disease progression.</p></div

Conditional deletion of nephrin in podocytes.

<p>(A) Schematic of the targeting vector containing a neomycin cassette, Frt sites and loxP sites were engineered to flank exon 5 of mouse nephrin. Successful recombination was verified using Southern blot with probes 1 and 2 flanking the nephrin gene. (B) Immunofluorescence images showing absence of nephrin in paraffin embedded mouse kidney section. Synaptopodin staining was used to identify podocytes. C) Coomassie blue stained SDS-PAGE gel showing severe albuminuria/proteinuria in the Nphs1^fl/fl,Cre+ animals at 2 weeks following birth. BSA standards (0.5–20 μg/dl). (D) Transmission and Scanning electron microscopy images showing podocyte foot process developmental abnormalities following nephrin deletion.</p

Residual nephrin at the membrane is associated with actin.

<p>(A) Isolated glomeruli from wild type and Nphs1^Tam-Cre mice kidneys were lysed in RIPA buffer containing 1% Triton X-100 at 4°C. Lysates were resolved with SDS-PAGE gel under reducing conditions and probed with nephrin and actin antibodies. Triton X1000 soluble fraction (S) and insoluble pellet (P) were separated by centrifugation. Nephrin is seen primarily in the insoluble fraction or pellet. (B) Glomerular lysates in RIPA buffer at 37°C showing no improvement in nephrin solubulity. (C) Glomerular lysates in RIPA buffer without 1.5 M MgCl₂ shows slight improvement in nephrin solubility with prominence of the high molecular weight band in the Nphs1^Tam-Cre mice. (D) Glomerular lysates in RIPA buffer containing 1M potassium iodide (KI) show dramatic improvement in nephrin solubility. IB: Immunoblot.</p