Indications and considerations for kidney biopsy: an overview of clinical considerations for the non-specialist.

Around 3 million people in the UK have chronic kidney disease and 20% of hospital admissions are complicated by acute kidney injury. Decline in kidney function is not a diagnosis; it is essential to identify and treat underlying causes of acute and chronic kidney disease to either achieve recovery or slow the decline of kidney function. Thorough clinical assessment and simple investigations help determine the category of kidney injury (pre-renal, intrinsic or post-renal) and inform the need for kidney biopsy, which can provide significant information in the evaluation of suspected intrinsic kidney disease, supporting diagnosis, guiding prognosis and management, and identifying disease relapse. The procedure is invasive and not without risk, which although small has the potential to be both organ- and life-threatening. This review outlines roles of kidney biopsy for the non-specialist, with focus of its role in patients with diabetes, lupus, myeloma and in the older patient.

Long- and short-term outcomes in renal allografts with deceased donors: A large recipient and donor genome-wide association study.

Improvements in immunosuppression have modified short-term survival of deceased-donor allografts, but not their rate of long-term failure. Mismatches between donor and recipient HLA play an important role in the acute and chronic allogeneic immune response against the graft. Perfect matching at clinically relevant HLA loci does not obviate the need for immunosuppression, suggesting that additional genetic variation plays a critical role in both short- and long-term graft outcomes. By combining patient data and samples from supranational cohorts across the United Kingdom and European Union, we performed the first large-scale genome-wide association study analyzing both donor and recipient DNA in 2094 complete renal transplant-pairs with replication in 5866 complete pairs. We studied deceased-donor grafts allocated on the basis of preferential HLA matching, which provided some control for HLA genetic effects. No strong donor or recipient genetic effects contributing to long- or short-term allograft survival were found outside the HLA region. We discuss the implications for future research and clinical application.

Biochemical Screening for Nonadherence Is Associated With Blood Pressure Reduction and Improvement in Adherence.

We hypothesized that screening for nonadherence to antihypertensive treatment using liquid chromatography-tandem mass spectrometry-based biochemical analysis of urine/serum has therapeutic applications in nonadherent hypertensive patients. A retrospective analysis of hypertensive patients attending specialist tertiary care centers was conducted in 2 European countries (United Kingdom and Czech Republic). Nonadherence to antihypertensive treatment was diagnosed using biochemical analysis of urine (United Kingdom) or serum (Czech Republic). These results were subsequently discussed with each patient, and data on follow-up clinic blood pressure (BP) measurements were collected from clinical files. Of 238 UK patients who underwent biochemical urine analysis, 73 were nonadherent to antihypertensive treatment. Their initial urinary adherence ratio (the ratio of detected to prescribed antihypertensive medications) increased from 0.33 (0-0.67) to 1 (0.67-1) between the first and the last clinic appointments. The observed increase in the urinary adherence ratio in initially nonadherent UK patients was associated with the improved BP control; by the last clinic appointment, systolic and diastolic BPs were ≈19.5 and 7.5 mm Hg lower than at baseline (P=0.001 and 0.009, respectively). These findings were further corroborated in 93 nonadherent hypertensive patients from Czech Republic-their average systolic and diastolic BPs dropped by ≈32.6 and 17.4 mm Hg, respectively (P<0.001), on appointments after the biochemical analysis. Our data show that nonadherent hypertensive patients respond to liquid chromatography-tandem mass spectrometry-based biochemical analysis with improved adherence and significant BP drop. Such repeated biochemical analyses should be considered as a therapeutic approach in nonadherent hypertensive patients.

Multicentre randomized controlled trial of angiotensin-converting enzyme inhibitor/angiotensin receptor blocker withdrawal in advanced renal disease: the STOP-ACEi trial.

BACKGROUND: Blood pressure (BP) control and reduction of urinary protein excretion using agents that block the renin-angiotensin aldosterone system are the mainstay of therapy for chronic kidney disease (CKD). Research has confirmed the benefits in mild CKD, but data on angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) use in advanced CKD are lacking. In the STOP-ACEi trial, we aim to confirm preliminary findings which suggest that withdrawal of ACEi/ARB treatment can stabilize or even improve renal function in patients with advanced progressive CKD. METHODS: The STOP-ACEi trial (trial registration: current controlled trials, ISRCTN62869767) is an investigator-led multicentre open-label, randomized controlled clinical trial of 410 participants with advanced (Stage 4 or 5) progressive CKD receiving ACEi, ARBs or both. Patients will be randomized in a 1:1 ratio to either discontinue ACEi, ARB or combination of both (experimental arm) or continue ACEi, ARB or combination of both (control arm). Patients will be followed up at 3 monthly intervals for 3 years. The primary outcome measure is eGFR at 3 years. Secondary outcome measures include the number of renal events, participant quality of life and physical functioning, hospitalization rates, BP and laboratory measures, including serum cystatin-C. Safety will be assessed to ensure that withdrawal of these treatments does not cause excess harm or increase mortality or cardiovascular events such as heart failure, myocardial infarction or stroke. RESULTS: The rationale and trial design are presented here. The results of this trial will show whether discontinuation of ACEi/ARBs can improve or stabilize renal function in patients with advanced progressive CKD. It will show whether this simple intervention can improve laboratory and clinical outcomes, including progression to end-stage renal disease, without causing an increase in cardiovascular events.

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.

Sialic acid attenuates puromycin aminonucleoside-induced desialylation and oxidative stress in human podocytes.

Sialoglycoproteins make a significant contribution to the negative charge of the glomerular anionic glycocalyx-crucial for efficient functioning of the glomerular permselective barrier. Defects in sialylation have serious consequences on podocyte function leading to the development of proteinuria. The aim of the current study was to investigate potential mechanisms underlying puromycin aminonucleosisde (PAN)-induced desialylation and to ascertain whether they could be corrected by administration of free sialic acid. PAN treatment of podocytes resulted in a loss of sialic acid from podocyte proteins. This was accompanied by a reduction, in the expression of sialyltransferases and a decrease in the key enzyme of sialic acid biosynthesis N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE). PAN treatment also attenuated expression of the antioxidant enzyme superoxide dismutase (mSOD) and concomitantly increased the generation of superoxide anions. Sialic acid supplementation rescued podocyte protein sialylation and partially restored expression of sialyltransferases. Sialic acid also restored mSOD mRNA expression and quenched the oxidative burst. These data suggest that PAN-induced aberrant sialylation occurs as a result of modulation of enzymes involved sialic acid metabolism some of which are affected by oxidative stress. These data suggest that sialic acid therapy not only reinstates functionally important negative charge but also acts a source of antioxidant activity.

Monocyte- and endothelial-derived microparticles induce an inflammatory phenotype in human podocytes.

BACKGROUND/AIMS: Proteinuria is associated with cardiovascular and chronic kidney disease. Microparticles (MPs) are bioactive vesicles shed from activated cells and also linked to cardiovascular disease. MP-like structures have been identified in the glomerular basement membrane, urinary space and between the glomerular basement membrane and the podocyte. We hypothesised that circulating MPs may provide a link between vascular injury and kidney diseases by inducing podocyte phenotypic alterations, thus propagating glomerular dysfunction and proteinuria. METHODS: Human umbilical vein endothelial cells and U937 monocytes were stimulated with TNF-α to produce MPs. These MPs were confirmed by electron microscopy, and added to differentiated podocyte monolayers to determine effects on podocyte albumin endocytosis and the production of soluble mediators. RESULTS: Monocyte and endothelial MPs upregulated podocyte production of pro-inflammatory mediators monocyte chemoattractant protein-1 (p < 0.001) and interleukin-6 (p < 0.001). Only monocyte MPs upregulated podocyte secretion of VEGF (p < 0.001), known to regulate glomerular permeability. Endothelial MPs decreased podocyte albumin endocytosis by 13% compared to control cells (p < 0.01). CONCLUSION: MPs alter endocytic functions of podocytes and induce secretion of pro-inflammatory cytokines, potentially leading to glomerular inflammation in vivo and the development of proteinuria. This study identifies a potential pathophysiological role for circulating MPs in the kidney through effects on the podocyte.

Low-level C-reactive protein levels exert cytoprotective actions on human podocytes.

BACKGROUND: Albuminuria and elevated C-reactive protein (CRP) levels are common manifestations of many inflammatory diseases. Cardiovascular-based drugs, with secondary anti-inflammatory actions, such as angiotensin-converting enzyme-inhibitors are able to reduce both proteinuria and CRP levels, raising the question of whether CRP directly influences the processes that result in proteinuria. As proteinuria is thought to be induced as a result of podocyte dysfunction, we investigated whether there is a pathomechanistic link with CRP. METHODS: Podocytes were analysed for evidence of endogenous CRP production in response to inflammatory agents. In addition, they were incubated in the presence of various concentrations of exogenous CRP and analysed for evidence of a response to treatment. RESULTS: Our results demonstrated that inflammatory agents such as macrophage-conditioned medium and interleukin-1ß induced the expression of CRP messenger RNA in podocytes. However, they were unable to induce CRP protein. Stimulation of podocytes with exogenous CRP demonstrated that 10 µg/mL CRP induced a low but significant level of interleukin-6 secretion. Tumour necrosis factor α, however, was not detected. CRP did up-regulate the expression of the slit diaphragm proteins nephrin and CD2AP, as well as the structural proteins ezrin and podocalyxin-like protein-1, proteins known to be involved in signalling via the phosphotidylinositol-3 (PI-3) kinase pathway. CRP exposure reduced caspase-3 enzyme activity and up-regulated the expression of the anti-apoptotic protein Bcl-2. In the presence of the PI-3 kinase inhibitor LY294002, the ability of CRP to suppress caspase-3 activity was significantly reduced. CONCLUSIONS: Taken together, these data suggest that rather than inducing podocyte damage, CRP may be a survival factor for podocytes by maintaining their structural integrity and initiating a survival cascade, which may facilitate podocyte recovery from injury.

Urine proteomics: the present and future of measuring urinary protein components in disease.

For centuries, physicians have attempted to use the urine for noninvasive assessment of disease. Today, urinalysis, in particular the measurement of proteinuria, underpins the routine assessment of patients with renal disease. More sophisticated methods for assessing specific urinary protein losses have emerged; however, albumin is still the principal urinary protein measured. Changes in the pattern of urinary protein excretion are not necessarily restricted to nephrourological disease; for instance, the appearance of beta-human chorionic gonadotropin in the urine of pregnant women is the basis for all commercially available pregnancy kits. Similarly, microalbuminuria is a clinically important marker not only of early diabetic nephropathy but also of concomitant cardiovascular disease. With the emergence of newer technologies, in particular mass spectrometry, it has become possible to study urinary protein excretion in even more detail. A variety of techniques have been used both to characterize the normal complement of urinary proteins and also to identify proteins and peptides that may facilitate earlier detection of disease, improve assessment of prognosis and allow closer monitoring of response to therapy. Such proteomics-based approaches hold great promise as the basis for new diagnostic tests and as the means to better understand disease pathogenesis. In this review, we summarize the currently available methods for urinary protein analysis and describe the newer approaches being taken to identify urinary biomarkers.

Statin-sensitive endocytosis of albumin by glomerular podocytes.

Glomerular podocytes are critical regulators of glomerular permeability via the slit diaphragm and may play a role in cleaning the glomerular filter. Whether podocytes are able to endocytose proteins is uncertain. We studied protein endocytosis in conditionally immortalized mouse and human podocytes using FITC-albumin by direct quantitative assay and by fluorescence microscopy and electron microscopy in mouse podocytes. Furthermore, in vivo uptake was studied in human, rat, and mouse podocytes. Both mouse and human podocytes displayed specific one-site binding for FITC-albumin with K(d) of 0.91 or 0.44 mg/ml and B(max) of 3.15 or 0.81 microg/mg cell protein, respectively. In addition, they showed avid endocytosis of FITC-albumin with K(m) of 9.48 or 4.5 mg/ml and V(max) of 474.3 or 97.4 microg.mg cell protein(-1).h(-1), respectively. Immunoglobulin and transferrin were inefficient competitors of this process, indicating some specificity for albumin. Accumulation of endocytosed albumin could be demonstrated in intracellular vesicles by fluorescence confocal microscopy and electron microscopy. Endocytosis was sensitive to pretreatment with simvastatin. In vivo accumulation of albumin was found in all three species but was most pronounced in the rat. We conclude that podocytes are able to endocytose protein in a statin-sensitive manner. This function is likely to be highly significant in health and disease. In addition, protein endocytosis by podocytes may represent a useful, measurable phenotypic characteristic against which potentially injurious or beneficial interventions can be assessed.

Podocyte biology in human disease.

The podocyte is a highly specialized cell that plays a key role in regulating the glomerular filtration barrier. A number of advances have been made in recent years, linked to the discovery of single-gene defects in hereditary glomerular disease, which highlight the role of this cell in preventing proteinuria. This article reviews the molecular biology of the podocyte, focusing on known genetic abnormalities.

The value of urine screening in a young adult population.

BACKGROUND: GPs in England and Wales are required to perform screening urinalysis on all newly registered patients. The value of this practice, however, is unclear. OBJECTIVE: The purpose of this study was to identify the prevalence of persistent urine abnormalities and to establish the added value of screening for both haematuria and proteinuria in a large cohort of young adults in the UK. METHODS: Urine screening was carried out in a cohort of young adults in a student health centre and a university hospital nephrology unit in a large British city. University students enrolling for health screening in a university health centre over a 2-year period were tested for haematuria and/or proteinuria by dipstick urinalysis. Subjects with persistent urine abnormalities were evaluated for the presence of significant renal tract pathology. RESULTS: Of 3808 students screened, 3570 provided an initial urine sample; 220 were abnormal. Of these, 38 (1% of original cohort) had persistent abnormalities (haematuria, 14; proteinuria, 16; both, eight). Subjects with isolated haematuria or proteinuria did not have significant pathology. In contrast, all the students with both haematuria and proteinuria had identifiable renal disease. CONCLUSIONS: Our findings do not support the value of routine screening for proteinuria or haematuria in young adults. However, the combination of haematuria and proteinuria is a powerful predictor for parenchymal renal disease. Thus, if proteinuria is detected, further testing for haematuria should be performed.