Stephen G. Holt

Pathogenesis and treatment of renal dysfunction in rhabdomyolysis.

Rhabdomyolysis is a major cause of acute renal failure, and recent experimental data have provided a better understanding of the pathophysiology of the renal dysfunction. Renal failure is due to renal vasoconstriction, tubular damage caused by oxidant injury, and possibly tubular obstruction. Recent studies have provided greater insight into the rationale behind current therapy and potential treatment strategies. This review thus aims to summarise current understanding of the causes, pathogenesis and treatment of renal failure caused by rhabdomyolysis.

A chemiluminescense-based assay for S-nitrosoalbumin and other plasma S-nitrosothiols.

The lack of a simple assay for the quantification of S-nitrosothiols in complex biological matrices has hampered our understanding of their contribution to normal physiology and pathophysiological states. In this paper we describe an assay based upon the release of nitric oxide by reaction with a mixture consisting of Cu(I), iodine and iodide with subsequent quantification by chemiluminescense. With this method we can detect levels of S-nitrosothiols down to 5 nM in plasma. Following alkylation of free thiols with N-ethylmaleimide, and removal of nitrite with acidified sulfanilamide, we were able to measure known amounts of S-nitrosoalbumin added to plasma or whole blood, with an inter-assay variation for plasma S-nitrosothiols of ∼4%. Further studies showed that the mean concentration of circulating S-nitrosothiols in venous plasma of healthy human volunteers was 28 ± 7 nM.

Aortic Stiffness Is Independently Associated With Rate of Renal Function Decline in Chronic Kidney Disease Stages 3 and 4

Aortic stiffness and chronic kidney disease are closely linked by shared risk factors and associated increased cardiovascular mortality. At lower levels of renal function, aortic stiffness is independently associated with glomerular filtration rate. However, the longitudinal impact of aortic stiffness on renal function has not been reported previously. A cohort of 133 patients with chronic kidney disease stages 3 and 4 (estimated glomerular filtration rate: 15 to 59 mL/min per 1.73 m2) underwent prospective measurement of arterial stiffness parameters and monitoring of renal function. Aortic pulse wave velocity measurement was performed in 120 patients. The mean age was 69±12 years (mean±SD; 103 men, 30 women, and 23.3% diabetic). Mean systolic blood pressure was 155±21 mm Hg, and mean diastolic blood pressure was 83±11 mm Hg. The mean Modification of Diet in Renal Disease estimated glomerular filtration rate was 32±11 mL/min per 1.73 m2. Change in renal function was measured using reciprocal creatinine plots and the dichotomous combined end point of ≥25% decline in renal function or start of renal replacement therapy. After stepwise multivariate analysis, aortic pulse wave velocity was independently associated with gradient of reciprocal creatinine plot (r=0.46; P=0.014). In multivariate analysis of the end point of ≥25% decline in renal function or start of renal replacement therapy, independent predictors were aortic pulse wave velocity (r=0.48; P=0.002), systolic blood pressure (r=0.17; P=0.039), and urine protein:creatinine ratio (r=0.20; P=0.021). We, therefore, conclude that aortic stiffening is independently associated with rate of change in renal function in patients with chronic kidney disease stages 3 and 4.

Spectrum of chronic kidney disease in HIV-infected patients.

The aim of the study was to investigate the prevalence and aetiology of chronic kidney disease (CKD) and trends in estimated glomerular filtration rate (eGFR) in HIV‐infected patients.

Biological Variability of Plasma Intact and C-Terminal FGF23 Measurements

CONTEXT FGF23 measurement may have a role in the management of patients with chronic kidney disease (CKD). OBJECTIVE Our objective was to study the biological variability of plasma intact FGF23 (iFGF23) and C-terminal FGF23 (cFGF23) concentrations. DESIGN Plasma samples were taken from 12 healthy adults at multiple time points on 2 consecutive days to assess diurnal variability of FGF23 concentrations. Early-morning fasting and nonfasting samples were also taken over a 6-wk period to estimate components of biological variation. Samples from 170 volunteers were used to define reference intervals. FGF23 concentrations were measured by commercial ELISA. Western blotting was used to analyze FGF23 species from the plasma of healthy adults and patients with predialysis CKD and those undergoing dialysis. PARTICIPANTS AND SETTING A total of 180 healthy adults and 18 adults with stage 3-5D CKD participated in this study at a hospital research unit. MAIN OUTCOME MEASURE Estimates were made of the biological variability of plasma FGF23 concentrations. RESULTS iFGF23, but not cFGF23, showed significant diurnal variation. cFGF23 had a significantly lower intra-individual variation than iFGF23 (8.3 vs. 18.3%) but higher inter-individual variation than iFGF23 (28.9 vs. 19.2%). Fourteen samples would be needed to estimate an individuals homeostatic set point (within 10%) for iFGF23 compared with only three samples for cFGF23. Using Western blotting, C-terminal FGF23 fragments were detected in the plasma of individuals with normal renal function and at all stages of renal disease. The percent cFGF23 was significantly higher in those without renal impairment (P < 0.001) and was positively correlated with plasma phosphate concentration in those with normal renal function. CONCLUSIONS The high intra-individual biological variability of iFGF23 may limit its clinical use as a diagnostic or management tool. Risk-related thresholds may be more appropriate for clinical decision making based on cFGF23 measurements than conventional reference intervals. FGF23 cleavage pathways may be an important natural regulatory mechanism for phosphate control.

The impact of stopping inhibitors of the renin–angiotensin system in patients with advanced chronic kidney disease

Background. Inhibition of the renin-angiotensin-aldosterone system (RAAS) has shown to slow chronic kidney disease (CKD) progression. This is most notable at the earlier stages of diabetic and proteinuric nephropathies. Objective. Here, we observed the impact of discontinuation of angiotensin converting enzyme inhibitors (ACEi)/ angiotensin receptors blockers (ARB) in patients with advanced kidney disease. Methods. 52 patients (21 females and 31 males) with advanced CKD (stages 4 and 5), who attended our low clearance clinic (LCC) in preparation for renal replacement therapy (RRT). Mean age was 73.3 ± 1.8 years with an estimated glomerular filtration rate (eGFR) of 16.38 ± 1 ml/ min/1.73 m 2 . Baseline urine protein:creatinine ratio (PCR) was 77 ± 20 mg/mmol. 46% suffered from diabetes mellitus. Patients were followed for at least 12 months before and after ACEi/ARB were stopped. Results. 12 months after discontinuation of ACEi/ARB eGFR increased significantly to 26.6 ± 2.2 ml/min/ 1.73 m 2 (p = 0.0001). 61.5% of patients had more than a 25% increase in eGFR, whilst 36.5% had an increase exceeding 50%. There was a significant decline in the eGFR slope -0.39 ± 0.07 in the 12 months preceding discontinuation. The negative slope was reversed +0.48 ± 0.1 (p = 0.0001). Mean arterial blood pressure (MAP) increased from 90 ± 1.8 mmHg to 94 ± 1.3 mmHg (p = 0.02), however ≥50% of patients remained within target. Overall proteinuria was not affected (PCR before = 77 ± 20 and after = 121.6 ± 33.6 mg/mmol). Conclusion. Discontinuation of ACEi/ARB has undoubtedly delayed the onset of RRT in the majority of those studied. This observation may justify a rethink of our approach to the inhibition of the RAAS in patients with advanced CKD who are nearing the start of RRT.

Phosphorylated fetuin-A-containing calciprotein particles are associated with aortic stiffness and a procalcific milieu in patients with pre-dialysis CKD.

BACKGROUND Vascular stiffening occurs in normal ageing and is accelerated in chronic kidney disease (CKD). Vascular calcification contributes to this stiffening and to the high incidence of vascular morbidity and mortality in this population. A network of inhibitors work in concert to reduce mineralization risk in extra-osseous tissue. Fetuin-A is an important systemic inhibitor of ectopic calcification. A fraction of the total circulating fetuin-A interacts with mineral ions to form stable colloidal complexes, calciprotein particles (CPP), preventing deposition. We sought to assess whether CPP fetuin-A levels were associated with procalcific factors and aortic stiffness in a cohort of patients with Stages 3 and 4 CKD. METHODS We measured fetuin-A CPP levels, serum inflammatory markers [C-reactive protein (CRP), interleukin-6, tumour necrosis factor-α], oxidized low-density lipoprotein (oxLDL), bone morphogenetic protein-2 (BMP-2) and -7 (BMP-7) and aortic pulse wave velocity (APWV) in a cohort of 200 CKD patients. Serum measurements were also made in 78 healthy controls. CPP fetuin-A phosphorylation was characterized by phosphate-affinity gel chromatography. RESULTS Fetuin-A-containing CPPs were only detectable in the serum of CKD patients. Inflammatory markers, oxLDL and BMP-2 levels were all significantly higher in the CKD than control subjects. CPP fetuin-A levels were independently associated with serum phosphate, high-sensitivity C-reactive protein, oxLDL, BMP-2/7 ratio and inversely with estimated glomerular filtration rate (model R(2) = 0.51). After adjusting for confounders, CPP fetuin-A levels were independently associated with APWV. Only phosphorylated fetuin-A was present in serum CPP. CONCLUSION Increased CPP fetuin-A levels reflect an increasingly procalcific milieu and are associated with increased aortic stiffness in patients with pre-dialysis CKD.

Serum Calcification Propensity Predicts All-Cause Mortality in Predialysis CKD

Medial arterial calcification is accelerated in patients with CKD and strongly associated with increased arterial rigidity and cardiovascular mortality. Recently, a novel in vitro blood test that provides an overall measure of calcification propensity by monitoring the maturation time (T50) of calciprotein particles in serum was described. We used this test to measure serum T50 in a prospective cohort of 184 patients with stages 3 and 4 CKD, with a median of 5.3 years of follow-up. At baseline, the major determinants of serum calcification propensity included higher serum phosphate, ionized calcium, increased bone osteoclastic activity, and lower free fetuin-A, plasma pyrophosphate, and albumin concentrations, which accounted for 49% of the variation in this parameter. Increased serum calcification propensity at baseline independently associated with aortic pulse wave velocity in the complete cohort and progressive aortic stiffening over 30 months in a subgroup of 93 patients. After adjustment for demographic, renal, cardiovascular, and biochemical covariates, including serum phosphate, risk of death among patients in the lowest T50 tertile was more than two times the risk among patients in the highest T50 tertile (adjusted hazard ratio, 2.2; 95% confidence interval, 1.1 to 5.4; P=0.04). This effect was lost, however, after additional adjustment for aortic stiffness, suggesting a shared causal pathway. Longitudinally, serum calcification propensity measurements remained temporally stable (intraclass correlation=0.81). These results suggest that serum T50 may be helpful as a biomarker in designing methods to improve defenses against vascular calcification.

Predictors of Renal Outcome in HIV-Associated Nephropathy

BACKGROUND Human immunodeficiency virus (HIV)-associated nephropathy (HIVAN) is an important cause of end-stage renal disease among African American patients. This study was performed to study the epidemiology of HIVAN in a predominantly black African population and the impact of highly active antiretroviral therapy and other factors on the development of end-stage renal disease. METHODS We retrospectively identified all patients with HIVAN, defined by biopsy or strict clinical criteria, in 8 clinics in the United Kingdom. Baseline renal function, HIV parameters, renal pathological index of chronic damage, and responses to highly active antiretroviral therapy were analyzed, and factors associated with adverse renal outcome were identified. RESULTS From 1998 through 2004, we studied 16,834 patients, 61 of whom had HIVAN. HIVAN prevalence in black patients was 0.93%, and HIVAN incidence in those without renal disease at baseline was 0.61 per 1000 person-years. After a median of 4.2 years, 34 patients (56%) had developed end-stage renal disease. There were no significant differences in renal function and HIV parameters at baseline, time to initiation of highly active antiretroviral therapy, and rates of HIV RNA suppression between the 20 patients who developed end-stage renal disease >3 months after receiving the HIVAN diagnosis and the 23 patients who maintained stable renal function. However, the index of chronic damage score was significantly higher in those who developed end-stage renal disease (P < .001), and an index of chronic damage score >75 was associated with shorter renal survival (P < .001). CONCLUSIONS Whereas overall patient survival suggested an important benefit of highly active antiretroviral therapy, no additional renal benefit of early initiation of highly active antiretroviral therapy or viral suppression could be demonstrated in this large cohort of patients with established HIVAN. Severity of chronic kidney damage, as quantified by biopsy, was the strongest predictor of renal outcome.

Fetuin-A-Containing Calciprotein Particles Reduce Mineral Stress in the Macrophage

The formation of fetuin-A-containing calciprotein particles (CPP) may facilitate the clearance of calcium phosphate nanocrystals from the extracellular fluid. These crystals may otherwise seed extra-osseous mineralization. Fetuin-A is a partially phosphorylated glycoprotein that plays a critical role in stabilizing these particles, inhibiting crystal growth and aggregation. CPP removal is thought to be predominantly mediated by cells of the reticuloendothelial system via type I and type II class A scavenger receptor (SR-AI/II). Naked calcium phosphate crystals are known to stimulate macrophages and other cell types in vitro, but little is known of the effect of CPP on these cells. We report here, for the first time, that CPP induce expression and secretion of tumour necrosis factor (TNF)-α, interleukin (IL)-1β in murine RAW 264.7 macrophages. Importantly, however, CPP induced significantly lower cytokine secretion than hydroxyapatite (HAP) crystals of equivalent size and calcium content. Furthermore, CPP only had a modest effect on macrophage viability and apoptosis, even at very high levels, compared to HAP crystals, which were strongly pro-apoptotic at much lower levels. Fetuin-A phosphorylation was found to modulate the effect of CPP on cytokine secretion and apoptosis, but not uptake via SR-AI/II. Prolonged exposure of macrophages to CPP was found to result in up-regulated expression of SR-AI/II. CPP formation may help protect against some of the pro-inflammatory and harmful effects of calcium phosphate nanocrystals, perhaps representing a natural defense system for calcium mineral stress. However, in pathological states where production exceeds clearance capacity, these particles may still stimulate pro-inflammatory and pro-apoptotic cascades in macrophages, which may be important in the pathogenesis of vascular calcification.