Biochemistry and Clinical Role of Human Cystatin C

Cystatin C is associated with risk of venous thromboembolism in subjects with normal kidney function--the Tromsø study

BACKGROUND

Previous studies have shown an association between impaired kidney function, assessed by cystatin C-based estimated glomerular filtration rate, and venous thromboembolism. The aim of this study was to investigate whether serum cystatin C was associated with a risk of venous thromboembolism among subjects with normal kidney function in a prospective population-based study.

DESIGN AND METHODS

Cystatin C was measured in serum from 3251 men and women with normal kidney function, aged 25-84 years, who participated in the Tromsø study in 1994-1995. Normal kidney function was defined as a creatinine-based estimated glomerular filtration rate greater than 90 mL/min/1.73 m(2) and absence of microalbuminuria. Incident venous thromboembolism was registered from the date of inclusion through to the end of follow-up, September 1, 2007. Cox-regression models were used to calculate hazard ratios with 95% confidence intervals for venous thromboembolism.

RESULTS

There were 83 incident venous thromboembolic events, of which 53 (63.9 %) were provoked, during a median of 12.3 years of follow-up. A one standard deviation (0.11 mg/L) increase in serum cystatin C levels was associated with a 43% (hazard ratio 1.43; 95% confidence interval 1.17-1.72) increased risk of total venous thromboembolism. Subjects with cystatin C levels in the top quartile (≥ 0.87 mg/L) had a 2.5-fold (hazard ratio 2.51; 95% confidence interval 1.27-4.96) increased risk of venous thromboembolism compared to those with levels in the bottom quartile (≤ 0.72 mg/L) in adjusted analysis. The risk estimates were even higher for provoked venous thromboembolism (hazard ratio 3.11; 95% confidence interval 1.23-7.86).

CONCLUSIONS

Serum cystatin C levels were associated with the risk of venous thromboembolism in subjects with normal kidney function. Our findings suggest that elevated serum cystatin C levels may promote venous thrombosis beyond reflecting impaired kidney function.

Comparing cystatin C and creatinine in the diagnosis of pediatric acute renal allograft dysfunction

BACKGROUND

Allograft function following renal transplantation is commonly monitored using serum creatinine. Multiple cross-sectional studies have shown that serum cystatin C is superior to creatinine for detection of mild to moderate chronic kidney dysfunction. Recent data in adults indicate that cystatin C might also be a more sensitive marker of acute renal dysfunction. This study aims to compare cystatin C and creatinine for detection of acute allograft dysfunction in children using pediatric RIFLE (risk of renal dysfunction, injury to the kidney, failure or loss of kidney function, end stage renal disease) criteria for acute kidney injury.

METHODS

Retrospective chart review of post-transplant period in 24 patients in whom creatinine and cystatin C were measured every day. Allograft dysfunction was defined as a sustained rise in marker concentration above the mean of the three preceding measurements.

RESULTS

In total, there were 13 episodes of allograft dysfunction. Maximum RIFLE stages with creatinine were 'R' in 7, 'I' in 4, and 'F' in 2, with cystatin C 'R' in 6, 'I' in 4 and 'F' in 3, respectively. In 9/13 cases, both markers rose simultaneously, in three, the rise in creatinine preceded cystatin C by 1-5 days (median 4). In one case, the rise in cystatin C preceded creatinine by 1 day. The time lag was not statistically different. The maximum relative rise of creatinine was significantly higher than cystatin C. By multiple linear regression analysis, the maximum rise of cystatin C was related to the maximum rise of creatinine, but independent of patient age, gender, steroid dose, and anthropometric data.

CONCLUSIONS

In this pediatric population, cystatin C was not superior to creatinine for the detection of acute allograft dysfunction.

The impact of interlaboratory differences in cystatin C assay measurement on glomerular filtration rate estimation

BACKGROUND AND OBJECTIVES

Cystatin C (CysC) is a promising marker of GFR. Several equations have been derived to estimate GFR from its serum concentration. Heterogeneity in the performance of these equations exists in validation studies even when the same CysC assay from the same manufacturer is utilized. This study was designed to examine the differences in CysC and GFR estimation (eGFR) using Siemens' nephelometric immunoassay and the Mayo Clinic equation. The ability of the eGFRs to predict measured GFR was also examined.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Ninety-seven split samples were sent to laboratories at Children's Hospital of Eastern Ontario (CHEO) in Ottawa, Canada, and at the Mayo Clinic in Rochester, Minnesota.

RESULTS

The mean CHEO CysC was 0.17 mg/L (10%) lower than the mean Mayo Clinic CysC. Using the Mayo Clinic equation, the mean eGFR difference was 7.2 ml/min per 1.73 m(2) (15%). Approximately 36% of the results agreed within 10%, while 13% were discordant by greater than 30%. Larger absolute differences in mean eGFR between the two laboratories were found in the subgroup with CysC less than 1.41 mg/L as compared with the subgroup greater than 1.41 mg/L (9.5 versus 5.0 ml/min per 1.73 m(2)). Correction of CHEO values to the Mayo Clinic did not improve GFR estimation.

CONCLUSIONS

Significant differences in CysC measurement exist between laboratories using the same assay by the same manufacturer and these lead to clinically relevant differences in GFR estimation. This interlaboratory variability needs to be recognized when interpreting and comparing CysC and eGFR results.

Targeted quantitative mass spectrometric immunoassay for human protein variants

BACKGROUND

Post-translational modifications and genetic variations give rise to protein variants that significantly increase the complexity of the human proteome. Modified proteins also play an important role in biological processes. While sandwich immunoassays are routinely used to determine protein concentrations, they are oblivious to protein variants that may serve as biomarkers with better sensitivity and specificity than their wild-type proteins. Mass spectrometry, coupled to immunoaffinity separations, can provide an efficient mean for simultaneous detection and quantification of protein variants.

RESULTS

Presented here is a mass spectrometric immunoassay method for targeted quantitative proteomics analysis of protein modifications. Cystatin C, a cysteine proteinase inhibitor and a potential marker for several pathological processes, was used as a target analyte. An internal reference standard was incorporated into the assay, serving as a normalization point for cystatin C quantification. The precision, linearity, and recovery characteristics of the assay were established. The new assay was also benchmarked against existing cystatin C ELISA. In application, the assay was utilized to determine the individual concentration of several cystatin C variants across a cohort of samples, demonstrating the ability to fully quantify individual forms of post-translationally modified proteins.

CONCLUSIONS

The mass spectrometric immunoassays can find use in quantifying specific protein modifications, either as a part of a specific protein biomarker discovery/rediscovery effort to delineate the role of these variants in the onset of the disease, progression, and response to therapy, or in a more systematic study to delineate and understand human protein diversity.

Urinary cystatin C as a biomarker for acute kidney injury and its immunohistochemical localization in kidney in the CDDP-treated rats

Cystatin C, a cysteine protease inhibitor, is a novel biomarker of renal damage. In the present study, we examined the urinary and plasma levels of cystatin C and how useful they are for the early detection of acute kidney injury (AKI) in CDDP-treated rats in comparison with other biomarkers (β2-microglobulin, calbindin, clusterin, EGF, GST-α, GST-μ, KIM-1, NGAL, osteopontin, TIMP-1, and VEGF). The urinary levels of cystatin C, GST-α, KIM-1, and EGF changed prior to proximal tubule damage and increases in plasma urea nitrogen and creatinine levels, suggesting their usefulness for predicting AKI. On the other hand, the plasma cystatin C level hardly changed. We also investigated the localization of cystatin C in the kidney according to the progression of renal damage. Cystatin C was predominantly localized in the proximal tubule of the cortex, and its immunohistochemical expression was not affected by CDDP treatment. In addition, cystatin C was observed in the lumen of the renal tubule in the cortex, cortico-medullary junction, and medulla during the progression of renal damage, although its immunoreactive area ratio was very low. In conclusion, urinary cystatin C measurements can detect CDDP-induced AKI as early as KIM-1, GST-α, and EGF in rats, although the change ratio of the cystatin C was smaller than others. Immunohistochemical cystatin C expression in the proximal tubule of the kidney was hardly changed by the CDDP treatment, but it was newly observed in the renal tubule lumen after CDDP treatment.

Longitudinal study of Cystatin C in healthy term newborns

OBJECTIVE

The purpose of this study was to determine the levels of Cystatin C in healthy term newborns in the first month of life.

INTRODUCTION

Cystatin C may be a suitable marker for determining the glomerular filtration rate because it is not affected by maternal renal function.

METHODS

Cohort study. Inclusion: term newborns with appropriate weight; mother without renal failure or drugs that could affect fetal glomerular filtration rate. Exclusion: malformations; hypertension or any condition that could affect glomerular filtration rate. Cystatin C (mg/L)and creatinine (rng/dl) were determined in the mother (Mo) and in the newborn at birth (Day-0), 3rd (Day-3), 7th(Day-7) and 28t>h(Day-28) days.

STATISTICS

one way ANOVA and Pearson's correlation tests. Sample size of 20 subjects for a = 5% and a power test = 80% (p<0.05).

RESULTS

Data from 21 newborns were obtained (mean + standard deviation): MoCystatin C=1.00 ± 0.20; Day-0 Cystatin C 1.70 ± 0.26; Day-3 Cystatin C = 1.51 ± 0.20; Day-7 Cystatin C = 1.54 ± 0.10; Day-28 Cystatin C = 1.51 ± 0.10. MoCystatin C was smaller than Day-0 Cystatin C (p < 0.001), while MoCreatinine was not different from Day-0 Creatinine. Cystatin C only decreased from Day-0 to Day-3 (p = 0.004) but newborns Creatinine decreased along the time. Correlations were obtained between MoCystatin C and MoCreatinine (p = 0.012), as well as Day-3 (p = 0.047) and Day-28 (p = 0.022) Cystatin C and Creatinine values.

CONCLUSION

Neonatal Cystatin C values were not affected by MoCystatin C and became stable from the 3rd day of life.

Cystatin C, a novel urinary biomarker for sensitive detection of acute kidney injury during haemorrhagic fever with renal syndrome

To explore the value of cystatin C for evaluating acute kidney injury (AKI) in haemorrhagic fever with renal syndrome (HFRS), the concentrations of cystatin C in serum and urine samples from HFRS patients were determined. The serum and urinary cystatin C concentrations significantly increased in HFRS patients compared with normal controls (p < 0.001). In the acute phase of HFRS, urinary cystatin C increased to higher levels than serum creatinine, especially in severe or critical cases in the oliguric stage. Furthermore, higher levels of urinary cystatin C in the acute phase positively correlated with increased severity of the subsequent kidney injury. In conclusion, urinary cystatin C is a more sensitive clinical marker for AKI in HFRS, which may enable us to initiate treatment measures as early as possible.

A panel of urinary biomarkers to monitor reversibility of renal injury and a serum marker with improved potential to assess renal function

The Predictive Safety Testing Consortium's first regulatory submission to qualify kidney safety biomarkers revealed two deficiencies. To address the need for biomarkers that monitor recovery from agent-induced renal damage, we scored changes in the levels of urinary biomarkers in rats during recovery from renal injury induced by exposure to carbapenem A or gentamicin. All biomarkers responded to histologic tubular toxicities to varied degrees and with different kinetics. After a recovery period, all biomarkers returned to levels approaching those observed in uninjured animals. We next addressed the need for a serum biomarker that reflects general kidney function regardless of the exact site of renal injury. Our assay for serum cystatin C is more sensitive and specific than serum creatinine (SCr) or blood urea nitrogen (BUN) in monitoring generalized renal function after exposure of rats to eight nephrotoxicants and two hepatotoxicants. This sensitive serum biomarker will enable testing of renal function in animal studies that do not involve urine collection.

Urinary clusterin, cystatin C, beta2-microglobulin and total protein as markers to detect drug-induced kidney injury

Earlier and more reliable detection of drug-induced kidney injury would improve clinical care and help to streamline drug-development. As the current standards to monitor renal function, such as blood urea nitrogen (BUN) or serum creatinine (SCr), are late indicators of kidney injury, we conducted ten nonclinical studies to rigorously assess the potential of four previously described nephrotoxicity markers to detect drug-induced kidney and liver injury. Whereas urinary clusterin outperformed BUN and SCr for detecting proximal tubular injury, urinary total protein, cystatin C and beta2-microglobulin showed a better diagnostic performance than BUN and SCr for detecting glomerular injury. Gene and protein expression analysis, in-situ hybridization and immunohistochemistry provide mechanistic evidence to support the use of these four markers for detecting kidney injury to guide regulatory decision making in drug development. The recognition of the qualification of these biomarkers by the EMEA and FDA will significantly enhance renal safety monitoring.

Can serum cystatin C reflect the glomerular filtration rate accurately in pediatric patients under chemotherapeutic treatment? A comparative study with Tc-99m DTPA two-plasma sample method

OBJECTIVE

It was assessed whether cystatin C (cysC) could be used as a marker of glomerular filtration rate (GFR) by considering the technetium-99m diethylenetriamine penta-acetate (Tc-99m DTPA)-two blood sample method (GFRTc-99m DTPA) as the reference in pediatric patients under chemotherapeutic treatment.

METHODS

The chemotherapy group (CG) consisted of 31 patients (21 females, 10 males median age: 8.2 years; range: 2-16 years) who had been planned to receive allogenic hematopoietic stem cell transplantation. All patients in the CG received conditioning regimen (includes chemotherapy protocol) before hematopoietic stem cell transplantation. In addition, 21 patients (14 females, seven males median age: 9.5 years; range: 4-16 years) without any chemotherapy (nonchemotherapy group: nCG) were also prospectively investigated. Serum cysC, serum creatinine, GFRTc-99m DTPA, and GFR with a cysC-based formula (GFRcysC) were analyzed. Tubular function was also assessed.

RESULTS

Although we found good correlation between GFRTc-99m DTPA and cysC (r = -0.78), GFRTc-99m DTPA and GFRcysC (r = 0.91), cysC and creatinine (r = 0.91) in nCG, the same correlations were poor in CG (r = -0.42, r = 0.43, r = 0.46, respectively). Tubular function was impaired after chemotherapy. Bias+/-1.96 SD values were -6+/-15.7 and -3+/-54.8 ml/min/1.73 m in nCG and CG, respectively. Precision was also better in nCG (10 ml/min/1.73 m) than in CG (27.6 ml/min/1.73 m).

CONCLUSION

Serum cysC and GFRcysC cannot reflect GFR accurately in pediatric patients under chemotherapeutic treatment. Tubular cell damage induced by chemotherapeutics could be a responsible factor through the impairment of tubular absorption and metabolism of cysC.

Elevated level of serum cystatin-C concentration is a useful predictor for myelosuppression induced by methotrexate for treatment of rheumatoid arthritis

Methotrexate (MTX) is indispensable for the treatment of rheumatoid arthritis (RA). However, a small number of patients treated with MTX occasionally encounter some life-threatening events, including myelosuppression. Renal insufficiency, one of risk factors for these events, is difficult to assess because the serum creatinine concentration level and estimated glomerular filtration rate are sometimes inaccurately determined in aged RA patients. As a better indicator to evaluate this pathology, we measured the serum cystatin-C (Cys-C) level in 78 RA patients ≥ 50 years who were treated with MTX and observed for a year. The measurement achieved successful screening of two patients with leukocytopenia, one with interstitial lung disease (ILD), and two with liver dysfunction. An additional four referral inpatients with MTX-induced adverse events (three with pancytopenia, one with ILD) were enrolled for analysis, amounting to 82 patients. The logistic regression analysis showed that a correlation was observed between myelotoxicity and serum Cys-C level (elevation per 0.1 mg/dl; odds ratio 2.34, 95% confidence interval 1.08-5.09, p = 0.03). In conclusion, elderly RA patients potentially have subclinical renal insufficiency detected by the serum Cys-C concentration level. The elevated level of serum Cys-C is a more sensitive indicator to predict MTX-induced myelotoxicity than that of serum creatinine.

Serum immunoglobulin free light chain measurements and heavy chain isotype usage provide insight into disease biology in patients with POEMS syndrome

POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, skin changes) syndrome is a rare paraneoplastic syndrome in which nearly all patients have a monoclonal lambda restricted plasma cell disorder. We investigated whether patients with POEMS have abnormal serum immunoglobulin free light chain (FLC) ratios. Fifty patients with newly diagnosed POEMS syndrome were assessed. Cystatin C levels were measured to discern whether subclinical renal insufficiency could account for FLC elevations in the presence of a normal FLC ratio. Forty-five patients (90%) had elevated lambda FLC; however, only nine (18%) had abnormal FLC ratios. The rise in serum FLC of POEMS patients appeared to be multifactorial-both a function of subclinical renal insufficiency and polyclonal activation of medullary and extramedullary plasma cells. Those patients expressing a clonal IgA were more likely to have clonal plasmacytosis observed on iliac crest biopsy than those with IgG. In summary, serum immunoglobulin profiles are unique in POEMS syndrome as compared with other plasma cell disorders.

Cystatin C increases in cardiac injury: a role in extracellular matrix protein modulation

AIMS

Numerous lines of evidence suggest a role of oxidative stress in initiation and progression of heart failure. We identify novel pathways of oxidative stress in cardiomyocytes using proteomic technology.

METHODS AND RESULTS

Cardiomyocytes and cardiac fibroblasts isolated from rat hearts were treated with sublethal doses of H(2)O(2) for detection of secreted protein factors in the conditioned media by mass spectrometry-based proteomics. Comparison between the two cell types leads to the finding that H(2)O(2) caused an elevated cystatin C protein in the conditioned medium from cardiomyocytes. When cardiomyopathy was induced in mice by chronic administration of doxorubicin, elevated cystatin C protein was detected in the plasma. Myocardial ischaemia by left anterior descending coronary artery occlusion causes an increase in the level of cystatin C protein in the plasma. In myocardial tissue from the ischaemic area, an increase in cystatin C correlates with the inhibition of cathepsin B activity and accumulation of fibronectin and collagen I/III. Overexpressing cystatin C gene or exposing fibroblasts to cystatin C protein results in an inhibition of cathepsin B and accumulation of fibronectin and collagen I/III.

CONCLUSION

Oxidants induce elevated cystatin C production from CMCs. Cystatin C plays a role in cardiac extracellular matrix remodelling.

Application of cystatin C reduction ratio to high-flux hemodialysis as an alternative indicator of the clearance of middle molecules

BACKGROUND/AIMS

Although high-flux (HF) dialyzers with enhanced membrane permeability are widely used in current hemodialysis (HD) practice, urea kinetic modeling is still being applied to indicate the adequacy of both low-flux (LF) and HF HD. In comparison with urea (molecular weight, 60 Da) and beta(2)-microglobulin (beta(2)MG, 12 kDa), cystatin C (CyC, 13 kDa) is a larger molecule that has attractive features as a marker for assessing solute clearance. We postulated that CyC might be an alternative for indicating the clearance of middle molecules (MMs), especially with HF HD.

METHODS

Eighty-nine patients were divided into LF and HF groups. Using single pool urea kinetic modeling, the urea reduction ratio (URR) and equilibrated Kt/V(urea) (eKt/V(urea)) were calculated. The serum CyC concentrations were measured using particle-enhanced immunonephelometry. As indices of the middle molecular clearance, the reduction ratios of beta(2)MG and CyC were calculated.

RESULTS

The beta(2)MG reduction ratio (beta(2)MGRR) and CyC reduction ratio (CyCRR) were higher in the HF group compared to the LF group. However, the URR and eKt/Vurea did not differ between the two groups. The CyCRR was significantly correlated with the eKt/V(urea) and beta(2)MGRR (r = 0.47 and 0.69, respectively, both p < 0.0001).

CONCLUSIONS

Compared to the LF dialyzer, the HF dialyzer removed CyC and beta(2)MG more efficiently. Unlike the beta(2)MGRR, the CyCRR was correlated with the eKt/V(urea) and beta(2)MGRR. This study suggests a role for the CyCRR as an alternative indicator of the removal of MMs.

Impact of biomarker development on drug safety assessment

Drug safety has always been a key aspect of drug development. Recently, the Vioxx case and several cases of serious adverse events being linked to high-profile products have increased the importance of drug safety, especially in the eyes of drug development companies and global regulatory agencies. Safety biomarkers are increasingly being seen as helping to provide the clarity, predictability, and certainty needed to gain confidence in decision making: early-stage projects can be stopped quicker, late-stage projects become less risky. Public and private organizations are investing heavily in terms of time, money and manpower on safety biomarker development. An illustrative and "door opening" safety biomarker success story is the recent recognition of kidney safety biomarkers for pre-clinical and limited translational contexts by FDA and EMEA. This milestone achieved for kidney biomarkers and the "know how" acquired is being transferred to other organ toxicities, namely liver, heart, vascular system. New technologies and molecular-based approaches, i.e., molecular pathology as a complement to the classical toolbox, allow promising discoveries in the safety biomarker field. This review will focus on the utility and use of safety biomarkers all along drug development, highlighting the present gaps and opportunities identified in organ toxicity monitoring. A last part will be dedicated to safety biomarker development in general, from identification to diagnostic tests, using the kidney safety biomarkers success as an illustrative example.

Decreased cystatin C immunoreactivity in spinal motor neurons and astrocytes in amyotrophic lateral sclerosis

Cystatin C (CC), a cysteine protease inhibitor involved in protein degradation, is a marker of Bunina bodies in lower motor neurons in amyotrophic lateral sclerosis (ALS). TAR-DNA binding protein-43 (TDP-43)-immunoreactive inclusions are also histological hallmarks of ALS but whether CC is found in motor neurons with or without TDP-43-positive inclusions in ALS is not known. To determine whether inclusion body formation affects cytoplasmic CC immunoreactivity, we examined spinal cords from 9 ALS patients and 12 control subjects by immunohistochemistry. Most anterior horn cells (AHCs) showed moderate to intense immunoreactivity in controls, whereas CC immunoreactivity was markedly decreased in AHCs in ALS cases. The proportion of CC-immunolabeled AHCs was reduced regardless of whether they contained Bunina bodies. In contrast, the proportion of CC-immunolabeled AHCs was significantly reduced in those with TDP-43 inclusions. Cystatin C immunoreactivity of astrocytes in the spinal gray matter and white matter in ALS was significantly decreased compared with controls. These findings suggest that the formation of TDP-43 inclusions, but not of Bunina bodies, may be linked to the content of CC in spinal motor neurons and that perturbations in endogenous levels of CC in neuronal and glial cells may be part of the neurodegenerative processes in ALS.

Renal dysfunction in cystic fibrosis: is there cause for concern?

Most people associate cystic fibrosis (CF) with lung disease. Although this is the major cause of morbidity and mortality, CF is in fact a multi-organ disease. Patients with CF are living longer. Accompanying their increased life expectancy are complications not previously encountered. One of the less obvious concerns is that of renal dysfunction associated with long-term exposure to aminoglycosides as well as renally toxic immunosuppressants in lung transplant recipients. This article reviews what is known about the extent of the problem, summarizes what the current practices of measuring and monitoring renal function in patients with CF, and makes suggestions for alternative approaches. In particular, the potential role of cystatin C will be discussed.

Early detection of microalbuminuria and hypertension in children of very low birthweight

OBJECTIVE

We retrospectively investigated a cohort of very low birthweight infants (VLBWI) by comparing two methods for assessment of albuminuria: nephelometry (standard) and high performance liquid chromatography (HPLC), measuring urinary immunoreactive and non-immunoreactive albumin to evaluate if the latter is more sensitive in identifying childhood onset of albuminuria and hypertension in VLBWI individuals.

METHODS

Spot urine samples of a total of 109 subjects (5.3 +/- 2.2 years old) who were VLBWI were investigated by HPLC and nephelometry. Twenty-eight subjects were small for gestational age (SGA) and 81 were appropriate for gestational age (AGA). Blood Pressure (BP) was also recorded.

RESULTS

Twelve children (11%) with albuminuria 20 mg/g Cr by nephelometry versus 48 (44.5%) by HPLC (p < 0.001) were identified. The mean +/- SD of values in the range of normoalbuminuria was 2.9 +/- 5.81 by nephelometry versus 22.6 +/- 14 for HPLC (p < 0.001). The values were not statistically different in the two birthweight categories (<1000, 1000-1499 g), in AGA versus SGA and in high BP (>90th percentile) versus normal BP children.

CONCLUSIONS

Microalbuminuria by HPLC was more marked in VLBWI than in adults and the difference between values using the two methods was significative.

Serum cystatin C and the risk of Alzheimer disease in elderly men

BACKGROUND

Multiple lines of research suggest that increased cystatin C activity in the brain protects against the development of Alzheimer disease (AD).

METHODS

Serum cystatin C levels were analyzed at two examinations of the Uppsala Longitudinal Study of Adult Men, a longitudinal, community-based study of elderly men (age 70 years, n = 1,153 and age 77 years, n = 761, a subset of the age 70 examination). Cox regressions were used to examine associations between serum cystatin C and incident AD. AD cases were identified by cognitive screening and comprehensive medical chart review in all subjects.

RESULTS

On follow-up (median 11.3 years), 82 subjects developed AD. At age 70 years, lower cystatin C was associated with higher risk of AD independently of age, APOE4 genotype, glomerular filtration rate, diabetes, hypertension, stroke, cholesterol, body mass index, smoking, education level, and plasma amyloid-beta protein 40 and 42 levels (hazard ratio [HR] for lowest [<1.12 micromol/L] vs highest [>1.30 micromol/L] tertile = 2.67, 95% CI 1.22-5.83, p < 0.02). The results were similar at age 77 years (43 participants developed AD during follow-up). Furthermore, a 0.1-mumol/L decrease of cystatin C between ages 70 and 77 years was associated with a 29% higher risk of incident AD (HR 1.29, 95% CI 1.03-1.63, p < 0.03).

CONCLUSIONS

Low levels of serum cystatin C precede clinically manifest Alzheimer disease (AD) in elderly men free of dementia at baseline and may be a marker of future risk of AD. These findings strengthen the evidence for a role for cystatin C in the development of clinical AD.

The identification of disease-induced biomarkers in the urine of BSE infected cattle

Background

The bovine spongiform encephalopathy (BSE) epidemic and the emergence of a new human variant of Creutzfeldt-Jakob Disease (vCJD) have led to profound changes in the production and trade of agricultural goods. The rapid tests currently approved for BSE monitoring in slaughtered cattle are all based on the detection of the disease related isoform of the prion protein, PrP^d, in brain tissue and consequently are only suitable for post-mortem diagnosis. Objectives: In instances such as assessing the health of breeding stock for export purposes where post-mortem testing is not an option, there is a demand for an ante-mortem test based on a matrix or body fluid that would permit easy access and repeated sampling. Urine and urine based analyses would meet these requirements.

Results

Two dimensional differential gel eletrophoresis (2D-DIGE) and mass spectrometry analyses were used to identify proteins exhibiting differential abundance in the urine of BSE infected cattle and age matched controls over the course of the disease. Multivariate analyses of protein expression data identified a single protein able to discriminate, with 100% accuracy, control from infected samples. In addition, a subset of proteins were able to predict with 85% ± 13.2 accuracy the time post infection that the samples were collected.

Conclusion

These results suggest that in principle it is possible to identify biomarkers in urine useful in the diagnosis, prognosis and monitoring of disease progression of transmissible spongiform encephalopathy diseases (TSEs).

Glomerular filtration rate estimates decrease during high altitude expedition but increase with Lake Louise acute mountain sickness scores

AIM

Acute mountain sickness (AMS) can result in pulmonary and cerebral oedema with overperfusion of microvascular beds, elevated hydrostatic capillary pressure, capillary leakage and consequent oedema as pathogenetic mechanisms. Data on changes in glomerular filtration rate (GFR) at altitudes above 5000 m are very limited.

METHODS

Thirty-four healthy mountaineers, who were randomized to two acclimatization protocols, undertook an expedition on Muztagh Ata Mountain (7549 m) in China. Tests were performed at five altitudes: Zurich pre-expedition (PE, 450 m), base camp (BC, 4497 m), Camp 1 (C1, 5533 m), Camp 2 (C2, 6265 m) and Camp 3 (C3, 6865 m). Cystatin C- and creatinine-based (Mayo Clinic quadratic equation) GFR estimates (eGFR) were assessed together with Lake Louise AMS score and other tests.

RESULTS

eGFR significantly decreased from PE to BC (P < 0.01). However, when analysing at changes between BC and C3, only cystatin C-based estimates indicated a significant decrease in GFR (P = 0.02). There was a linear decrease in eGFR from PE to C3, with a decrease of approx. 3.1 mL min(-1) 1.73 m(-2) per 1000 m increase in altitude. No differences between eGFR of the two groups with different acclimatization protocols could be observed. There was a significant association between eGFR and haematocrit (P = 0.01), whereas no significant association between eGFR and aldosterone, renin and brain natriuretic peptide could be observed. Finally, higher AMS scores were significantly associated with higher eGFR (P = 0.01).

CONCLUSIONS

Renal function declines when ascending from low to high altitude. Cystatin C-based eGFR decreases during ascent in high altitude expedition but increases with AMS scores. For individuals with eGFR <40 mL min(-1) 1.73 m(-2), caution may be necessary when planning trips to high altitude above 4500 m above sea level.

Serum and urine cystatin C levels in children with post-pyelonephritic renal scarring: a pilot study

AIM

We aimed to investigate in children with a history of acute pyelonephritis the influence of unilateral post-pyelonephritic renal scarring detected by DMSA scan on serum (S(CysC)) and urine cystatin C (U(CysC)) as well as upon other traditional markers of renal damage.

METHODS

Children with DMSA proven pyelonephritis (n = 28) were grouped as either scar [+] (n = 19, unilateral renal scarring) or scar [-] (no scarring, n = 9). The scar [+] group was further divided into scar-1 (differential DMSA uptake, Delta(DMSA) </= 10%; n = 8) and scar-2 (Delta(DMSA) > 10%, n = 11) subgroups. S(CysC), serum creatinine, urine NAG, microalbumin, protein, fractional sodium excretion (FE(Na)), tubular phosphate reabsorption (TPR), and U(CysC/Cr) were evaluated in all patients.

RESULTS

Neither S(CysC) nor U(CysC) were affected by age, height, and weight. scar [+] versus scar [-] groups and scar-1 versus scar-2 subgroups were not different with regard to all studied parameters. S(CysC) did not increase in children with post-pyelonephritic unilateral renal scarring. However, 11 children with slightly increased (>0.95 mg/l) S(CysC) levels in scar [+] group tended to have higher Delta(DMSA), albeit not significantly. Furthermore, U(CysC/Cr) correlated well with urine microalbumin, NAG, and FE(Na) in all children and the scar [+] group (P < 0.05).

CONCLUSION

S(CysC) and U(CysC) did not differ among pediatric patients with and without unilateral post-pyelonephritic renal scarring. However, Delta(DMSA) uptake between the two kidneys tended to be raised in children with S(CysC) levels higher than the reference ranges. Additionally, U(CysC/Cr) exhibits parallelism with tubular functions.

Chronic kidney disease (CKD) in the elderly -- a geriatrician's perspective

Chronic kidney disease (CKD) is becoming increasingly prevalent among many different populations all over the world, including the US and Europe. Its multitude of complications with devastating outcomes leads to a significantly higher risk for cardio-vascular and all-cause mortality in an individual. However, it is clear now that early detection of CKD might not only delay some of the complications but also prevent them. Therefore, various important public health organizations all over the world have turned their focus and attention to CKD and its risk factors, early detection and early intervention. Nevertheless, the general goals in preventing the increase in CKD and its complications are far from being completely achieved. Why is this so? What is the magnitude and complexity of the problem? How is it affecting the population - are there differences in its affection by age, gender or frail elderly versus the robust? Are we modifying the risk factors appropriately and aggressively? Are there subtle differences in managing the risk factors in those on dialysis versus the non-dialysis CKD patients? Is it important to treat anaemia of CKD aggressively, will it make a difference in the disease progression, its complications or to quality of life? What do these unfortunate individuals commonly succumb to? What do we advise patients who refuse dialysis or those who desire dialysis or transplant? Are there useful non-dialytic treatment recommendations for those who refuse dialysis? What is the role of the physicians caring for the elderly with CKD? When should the primary care givers refer a CKD patient to a nephrologist? The key to eventually controlling incident and prevalent CKD and improve quality of life of affected individuals, lies in not only knowing these and many other vital aspects, but also in applying such knowledge compulsively in day-to-day practice by each and every one us. As CKD is increasingly a disease of the elderly with men being affected more, this review details fairly comprehensively the vital aspects of CKD, especially from a primary care geriatrician's practical standpoint.

Genotype and plasma concentration of cystatin C in patients with late-onset Alzheimer disease

BACKGROUND

A polymorphism locating at position 73 of cystatin C (CST3) exon 1 was suggested to be associated with Alzheimer disease (AD), but with contradictory results. The relationship between the CST3 genotype and the cystatin C plasma level in AD remains unknown.

OBJECTIVE

We aim to determine the association between CST3 polymorphism and the plasma levels of cystatin C in AD and nondemented control individuals.

METHOD

The polymorphisms of the CST3 genotype were determined using PCR followed by restriction fragment length polymorphism analysis, and the plasma cystatin C concentrations were quantified by sandwich ELISA in 175 AD and 461 control subjects.

RESULTS

Although the CST3A allele frequencies were similar between the two groups, the CST3A/A homozygote was significantly associated with late-onset AD. As expected, the established AD genetic risk factor APOE epsilon4 allele was overrepresented in the AD cohort. The plasma cystatin C levels were lower in the AD patients than in the control group. Furthermore, plasma cystatin C levels were associated positively with age and negatively with CST3A allele in the control group.

CONCLUSION

The homozygous CST3A/A genotype confers a risk for AD in Taiwan Chinese. Such an association may be due to the reduced level of cystatin C in the peripheral circulation.

Can cystatin C replace creatinine to estimate glomerular filtration rate? A literature review

BACKGROUND

With the increasing knowledge that estimation of glomerular filtration rate (GFR) from serum creatinine (Scr) has limited value, researchers have developed new equations based on serum cystatin C (Cys C).

AIM

To compare the performance of serum Cys C and Cys C-based GFR equations to Scr and Scr-based GFR equations.

METHODS

A Medline literature search for studies in English.

RESULTS

Fourteen studies in kidney transplant patients and 29 in patients with native kidney disease were identified. 70% of studies on transplants favored Cys C over Scr while 60% favored serum Cys C over Scr in patients with native kidney disease. Three studies in transplant patients and 6 in patients with native kidney disease compared the performances of Cys C- and Scr-based equations. 70% of the studies performed on transplantation favored Cys C, while 85% the studies performed in native kidney diseases showed superiority of Cys C-based equations.

CONCLUSION

A large number of studies favor Cys C over Scr for the estimation of GFR. Still, many reports show no superiority of Cys C over Scr. Consistent with this, more studies are needed to study the performance of Cys C-based GFR equations.

Cystatin C and Estimates of Renal Function: Searching for a Better Measure of Kidney Function in Diabetic Patients

Background: Early identification of impairment in renal function is crucial in diabetic patients. Serum cystatin C may be the most sensitive indicator of glomerular filtration rate (GFR) in the clinical setting.

Methods: We compared cystatin C with creatinine, the Cockcroft-Gault (C-G) formula, and the Modification of Diet in Renal Disease (MDRD) study equation for the assessment of early decreased renal function in 288 diabetic patients (125 type 1, 163 type 2) with renal impairment [GFR: 4–222 mL · min−1 · (1.73 m2)−1]. Relationships of cystatin C, creatinine, and iohexol clearance were linearized by plotting their reciprocals in a simple regression model. Diagnostic efficiency was calculated from ROC curves.

Results: In this study population, cystatin C (P = 0.0013) was better correlated with GFR (r = 0.857) than were creatinine (r = 0.772), C-G (r = 0.750), and MDRD (r = 0.806), a result replicated in patients with normal renal function (P = 0.023, type 1; P = 0.011, type 2), but not in those with decreased GFR. Mean cystatin C concentrations showed step-by-step statistically significant increases as GFR decreased, allowing very early detection of reduction in renal function. At 90 mL · min−1 · (1.73 m2)−1 and 75 mL · min−1 · (1.73 m2)−1 cut-points, diagnostic efficiencies of cystatin C (89% and 92%) were better than those of the other variables (79%–82% and 85%–86%, respectively; P = 0.01).

Conclusions: All data supported the value of serum cystatin C compared with conventional estimates based on serum creatinine measurement for detecting very early reduction of renal function. Use of cystatin C to measure renal function will optimize early detection, prevention, and treatment strategies for diabetic nephropathy.

Glomerular filtration rate as measured by serum cystatin C is an important determinant of plasma homocysteine and serum methylmalonic acid in the elderly

OBJECTIVES

To explore the dependence of glomerular filtration rate (GFR) on plasma total homocysteine (tHcy) and serum methylmalonic acid (MMA), as well as the consequences for the diagnosis of cobalamin and/or folic acid deficiency in an elderly community-dwelling population.

DESIGN AND SETTING

Population-based study of 209 community-dwelling subjects, mean age 76 years.

INTERVENTIONS

Four months' treatment study with oral vitamin B(12), folic acid and B(6) or placebo.

MAIN OUTCOME MEASURES

Determinants of tHcy and MMA: cystatin C as a marker of GFR and serum/plasma concentrations of vitamin B(12) and folate, age and sex.

RESULTS

Elevated cystatin C (>1.55 mg L(-1)) was found in 31.3% (men) and 13.0% (women). Elevated tHcy (> or = 16 micromol L(-1)) occurred in 53% and elevated MMA (> or = 0.34 micromol L(-1)) in 11% of all subjects. When GFR was taken into consideration, the proportion of elevated tHcy was reduced to 10% (20/209), whilst the proportion of elevated MMA was unchanged. Cystatin C was correlated with tHcy (r = 0.45, P < 0.001) and with MMA (r =0.28, P < 0.001), independently of vitamin B(12)- and folate status. According to multiple regression, independent predictors for tHcy were plasma folate (15%), cystatin C (11%) and vitamin B(12) (4%), and for MMA, cystatin C (8%) and vitamin B(12) (2%).

CONCLUSIONS

The prevalence of elevated tHcy may be overestimated in elderly populations unless GFR is taken into account. Nomograms for evaluation of tHcy and MMA in relation to both cystatin C and serum creatinine are presented.

Kidney function and markers of inflammation in elderly persons without chronic kidney disease: the health, aging, and body composition study

Inflammatory markers are elevated in persons with estimated glomerular filtration rates less than 60 ml/min/1.73 m2. As cystatin C may detect small changes in kidney function not detected by estimated glomerular filtration rate, we evaluated the association between cystatin C and serum markers of inflammation in older adults with estimated glomerular filtration rate >or=60. This is an analysis using measures from the Health, Aging, and Body Composition Study, a cohort of well-functioning adults aged 70-79 years. Cystatin C correlated with all five inflammatory biomarkers: C-reactive protein (r=0.08), interleukin-6 (r=0.19), tumor necrosis factor alpha (TNF-alpha) (r=0.41), soluble TNF receptor 1 (STNF-R1) (r=0.61), and soluble TNF receptor 2 (STNF-R2) (r=0.54); P<0.0005 for all. In adjusted analyses, cystatin C concentrations appeared to have stronger associations with each biomarker compared with estimated glomerular filtration rate or serum creatinine. Participants with a cystatin C>or=1.0 mg/l had significantly higher levels of all five biomarkers compared to those with a cystatin C<1.0 (mean differences ranging 16-29%, all P<0.05). Cystatin C has a linear association with inflammatory biomarkers in an ambulatory elderly cohort with estimated glomerular filtration rates >or=60; associations are particularly strong with TNF-alpha and the STNF-R.

Cystatin C as a reliable marker of renal function following heart valve replacement surgery with cardiopulmonary bypass

BACKGROUND

Little is known about serum cystatin C as a marker of renal function in cardiac surgery patients. The aim of this study was to assess its utility post cardiopulmonary bypass (CPB).

METHODS

60 heart valve replacement patients were enrolled, and 26 of them had low-dose corticosteroid treatment on the first 3 days postoperatively. Serum creatinine, serum cystatin C and 24-h creatinine clearance rate (CCR) adjusted by body surface area were determined preoperation, days 1, 2, 3, 7 post operation.

RESULTS

Serum creatinine increased and peaked at day 3 postoperatively, while cystatin C peaked at day 2, and the adjusted CCR also reached a minimum at day 2. The inverse of cystatin C correlated better with CCR than that of creatinine (r=0.751 vs. 0.629). Using adjusted CCR as "golden standard", cystatin C was superior to creatinine in diagnosing renal dysfunction (area under the curve [AUC] for cystatin C 0.876, 95% confidence interval 81.8-93.4; AUC for creatinine 0.801, 95% confidence interval 72.5-87.7; p=0.045). Low-dose corticosteroid treatment has no significant effect on cystatin C.

CONCLUSION

In agreement with many other investigators, the present findings support cystatin C is a reliable marker of renal function. It is superior to creatinine in patients post CPB.

Alteration of cystatin C in the cerebrospinal fluid of multiple sclerosis

The protein profiles in the cerebrospinal fluid of 10 patients with multiple sclerosis (MS), 10 patients with neuromyelitis optica (NMO), 8 inflammatory disease control patients, and 4 noninflammatory disease control patients were screened by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. Peaks of 12.5 kDa were significantly lower in multiple sclerosis, NMO, and inflammatory disease control patients than in noninflammatory disease control patients, and 13.4 kDa peaks were higher in NMO than in inflammatory disease control patients. Further analyses demonstrated that both peaks were cystatin C. Enzyme-linked immunosorbent assay showed that the cystatin C levels tended to be lower in multiple sclerosis and NMO. Alterations of cystatin C may relate to the pathogeneses of demyelinating diseases.

Cystatin C reference values and aging

OBJECTIVES

The aim of this study was to determine the reference values for serum cystatin C (CysC) with a particular focus on the effect of aging.

DESIGN AND METHODS

The study was performed on a consecutive series of subjects (258 men and 396 women). Laboratory parameters and a detailed personal and family medical history were collected.

RESULTS

CysC showed a significant correlation with age in both sexes, which was confirmed with multivariate linear regression after adjustment for SCr (serum creatinine). Age-related reference intervals were established for cystatin C (<45 years, <0.95 mg/L and >45 years, <1.20 mg/L).

CONCLUSIONS

The use of CysC reference values adjusted for age should be carefully taken into consideration.

Long-term intake of North American ginseng has no effect on 24-hour blood pressure and renal function

Ginseng is consumed by 10% to 20% of adults in Asia and by up to 5% in Western countries. Despite observational evidence suggesting a link between its intake and the development of hypertension, there remains no long-term scrutiny for its effect on blood pressure (BP). We therefore undertook a randomized, placebo-controlled, double-blinded, crossover trial in 52 hypertensive individuals to determine the effect of 12-week North American ginseng intake on 24-hour BP; we also measured serum cystatin C as a marker of renal function. After a 4-week placebo run-in, we randomly assigned 52 participants to 3 g/day of ginseng or placebo for 12 weeks. This was followed by an 8-week washout and a subsequent 12-week period in which the opposite treatment was administered. At run-in and at weeks 0 and 12 of each treatment period, participants were fitted with an ambulatory BP monitor to assess 24-hour BP. The primary outcome was the treatment difference at week 12 in mean 24-hour systolic BP. Secondary outcomes were treatment differences at week 12 in other ambulatory BP parameters and serum cystatin C. Forty participants (77%) completed the trial, with 3 removed from main analysis (n=2, antihypertensive drug changes; n=1, incomplete ambulatory monitoring). In the remaining 37, 12-week ginseng treatment was associated with a neutral effect on all ambulatory BP parameters compared with placebo; an intention-to-treat analysis supported this. Ginseng did not affect serum cystatin C level. Overall, long-term ginseng use had no effect on 24-hour BP and renal function in hypertensive individuals.

Cystatin C can be affected by nonrenal factors: A preliminary study on leukemia

OBJECTIVE

The aim of this study was to evaluate the influence of malignancy and the impact of nephrotoxic drugs used in bone marrow transplantation (BMT) on the circulating levels of cystatin C in leukemia.

METHODS

We studied nineteen patients (eleven men and eight women; mean age 30.1 +/- 11.2, 27.9 +/- 7.1 years) with acute lymphoblastic leukemia, acute myeloid leukemia and chronic myeloid leukemia. Cystatin C, urea, creatinine and creatinine clearance (CrCl) were measured 24 h before BMT, 1 week after BMT, 2 weeks after BMT and 3 weeks after BMT. The control group consisted of twenty healthy adults, and the mean age was 29.1 +/- 8.9.

RESULTS

At the pretransplantation period, values of cystatin C were significantly higher than in the control group (P < 0.05). Urea, creatinine and CrCl values were not statistically different from the controls. One week after BMT, the level of cystatin C was significantly low as compared to the levels measured 24 h before BMT, but was still significantly higher than the controls (P < 0.05), whereas the levels of urea, creatinine and CrCl were in accordance with the levels of the controls. Two and three weeks after BMT, cystatin C values maintained the significant increase (P < 0.05), whereas the values of urea, creatinine and CrCl still corresponded with those of the controls in both group.

CONCLUSIONS

Our preliminary data expose that cystatin C is not a reliable GFR marker in patients during leukemia or for monitoring nephrotoxic drugs used in BMT, but we can not reach definitive conclusion due to no gold standard for comparing the diagnostic accuracy of cystatin C. Further study is needed to elucidate the precise mechanism underlying this observation.