Cystatin C - More than a filtration marker?

Potential relationship between eGFRcystatin C /eGFRcreatinine -ratio and glomerular basement membrane thickness in diabetic kidney disease

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease and renal replacement therapy worldwide. A pathophysiological hallmark of DKD is glomerular basal membrane (GBM) thickening, whereas this feature is absent in minimal change disease (MCD). According to fundamental transport physiological principles, a thicker GBM will impede the diffusion of middle-molecules such as cystatin C, potentially leading to a lower estimated GFR (eGFR) from cystatin C compared to that of creatinine. Here we test the hypothesis that thickening of the glomerular filter leads to an increased diffusion length, and lower clearance, of cystatin C. Twenty-nine patients with a kidney biopsy diagnosis of either DKD (n = 17) or MCD (n = 12) were retrospectively included in the study. GBM thickness was measured at 20 separate locations in the biopsy specimen and plasma levels of cystatin C and creatinine were retrieved from health records. A modified two-pore model was used to simulate the effects of a thicker GBM on glomerular water and solute transport. The mean age of the patients was 52 years, and 38% were women. The mean eGFRcystatin C /eGFRcreatinine -ratio was 74% in DKD compared to 98% in MCD (p < 0.001). Average GBM thickness was strongly inversely correlated to the eGFRcystatin C /eGFRcreatinine -ratio (Pearson's r = -0.61, p < 0.01). Two-pore modeling predicted a eGFRcystatin C /eGFRcreatinine -ratio of 78% in DKD. We provide clinical and theoretical evidence suggesting that thickening of the glomerular filter, increasing the diffusion length of cystatin C, lowers the eGFRcystatin C /eGFRcreatinine -ratio in DKD.

Association of Cystatin C with Metabolic Syndrome and Its Prognostic Performance in Non-ST-Segment Elevation Acute Coronary Syndrome with Preserved Renal Function

OBJECTIVE

The underlying mechanisms by which cystatin C affects cardiovascular disease (CVD) are not very clear. Metabolic syndrome (MetS) is a cluster of risk factors that increase the risk of CVD. Here, we aimed to investigate the association of cystatin C with metabolic syndrome and cardiovascular outcomes in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) with preserved renal function.

METHODS

In total, 422 NSTE-ACS patients with preserved renal function were enrolled to examine the association of cystatin C with MetS. MetS was defined based on the NCEP-ATP-III guidelines. Major adverse cardiovascular events (MACEs) were also evaluated, which included cardiac death, nonfatal myocardial infarction (MI), target vessel revascularization (TVR), heart failure, and nonfatal stroke. All patients underwent a 12-month follow-up for MACEs after admission.

RESULTS

Cystatin C was significantly correlated with metabolic risk factors and inflammation markers. The prevalence of MetS and MACEs correlated with cystatin C levels. Cystatin C showed a strong diagnostic performance for cardiovascular risk factors and outcomes in ROC analysis. After adjustment for multiple risk factors, cystatin C level was independently associated with MetS (OR 2.299, 95% CI 1.251-4.225, and P = 0.007). During a 12-month follow-up, the patients with high cystatin C level and MetS had higher incidence of MACEs (Log-rank = 24.586, P < 0.001) and cardiac death (Log-rank = 9.890, P = 0.020) compared to the others. Multivariate Cox analysis indicated that cystatin C level was an independent predictor of MACEs (HR 2.609, 95% CI 1.295-5.257, and P = 0.007).

CONCLUSION

Cystatin C may be an independent predictor of metabolic syndrome and therefore valuable for management of NSTE-ACS patients. Further multicenter, large-scale studies are required to assess the implication of these results.

Cystatin C-Adiponectin Complex in Plasma Associates with Coronary Plaque Instability

Aim: Adiponectin (APN) is an adipocyte-derived bioactive molecule with antiatherogenic properties. We previously reported that cystatin C (CysC) abolished the anti-atherogenic effects of APN. We aimed to elucidate the clinical significance of CysC–APN complex in patients with coronary artery disease (CAD).

Methods: We enrolled 43 stable CAD male patients to examine the relationship between CysC–APN complex and coronary plaque characteristics. Serum was immunoprecipitated by the anti-APN antibody and immunoblotted by the anti-CysC antibody to demonstrate the presence of CysC–APN complexes in vivo. To confirm their binding in vitro, HEK293T cell lysates overexpressing myc-APN and FLAG-CysC were immunoprecipitated with an anti-myc or anti-FLAG antibody, followed by immunoblotting with an anti-APN or anti-CysC antibody.

Results: CysC was identified as a specific co-immunoprecipitant with APN by the anti-APN antibody in human serum. In vitro, FLAG-CysC was co-immunoprecipitated with myc-APN by the antimyc antibody and myc-APN was co-immunoprecipitated with FLAG-CysC by the anti-FLAG antibody. Among CAD patients, serum CysC–APN complex levels negatively correlated with fibrotic components of coronary plaques and positively correlated with either necrotic or lipidic plus necrotic components. Plaque burden negatively correlated with serum APN levels but not serum CysC–APN complex levels. Serum CysC levels had no association with plaque characteristics. In multivariate analysis, CysC–APN complex levels were identified as the strongest negative factor for fibrotic components and the strongest positive factor for both necrotic and lipidic plus necrotic components.

Conclusion: Measuring serum CysC–APN complex levels is helpful for evaluating coronary plaque instability in CAD patients.

The prognostic value of first-trimester cystatin C levels for gestational complications

AIMS

This study is designed to evaluate predictive value of first-trimester cystatin C levels for long-term pregnancy complications.

METHODS

The cross-sectional study population consisted of patients who admitted to outpatient clinic of a Maternity Hospital between September 2013 and December 2014. Among the 203 participants who accepted to participate in the study, 174 subjects who continued antenatal follow-up in the same clinic were included in the final analyses. Cystatin C, blood urea nitrogen, Creatinine levels and estimated glomerular filtration rates were evaluated in the first-trimester routine antenatal visit. Mode of delivery and gestational complications were noted.

RESULTS

First-trimester cystatin C levels were significantly higher in cases complicated with preterm delivery and premature rupture of membrane (PROM) compared to uncomplicated ones (0.58±0.07 vs. 0.55±0.07, P=0.041, and 0.58±0.07 vs. 0.55±0.07, P=0.036). With a cutoff value of 0.505 mg/L, sensitivity of cystatin C for preterm delivery and PROM was 91.9% and specificity was 27.7% with a negative predictive value of 92.3% and a positive predictive value of 26.6%.

CONCLUSION

Detection of cystatin C levels in the first trimester of pregnancy for the prediction of preterm/PROM seems as a promising preliminary data. The relatively higher first-trimester cystatin C levels in complicated pregnancies are conspicuous. The results imply that in pregnancy cystatin C might be more than a marker for renal function.

The cystatin C/creatinine ratio, a marker of glomerular filtration quality: associated factors, reference intervals, and prediction of morbidity and mortality in healthy seniors

The ratio of cystatin C (cysC) to creatinine (crea) is regarded as a marker of glomerular filtration quality associated with cardiovascular morbidities. We sought to determine reference intervals for serum cysC-crea ratio in seniors. Furthermore, we sought to determine whether other low-molecular weight molecules exhibit a similar behavior in individuals with altered glomerular filtration quality. Finally, we investigated associations with adverse outcomes. A total of 1382 subjectively healthy Swiss volunteers aged 60 years or older were enrolled in the study. Reference intervals were calculated according to Clinical & Laboratory Standards Institute (CLSI) guideline EP28-A3c. After a baseline exam, a 4-year follow-up survey recorded information about overall morbidity and mortality. The cysC-crea ratio (mean 0.0124 ± 0.0026 mg/μmol) was significantly higher in women and increased progressively with age. Other associated factors were hemoglobin A1c, mean arterial pressure, and C-reactive protein (P < 0.05 for all). Participants exhibiting shrunken pore syndrome had significantly higher ratios of 3.5-66.5 kDa molecules (brain natriuretic peptide, parathyroid hormone, β2-microglobulin, cystatin C, retinol-binding protein, thyroid-stimulating hormone, α1-acid glycoprotein, lipase, amylase, prealbumin, and albumin) and creatinine. There was no such difference in the ratios of very low-molecular weight molecules (urea, uric acid) to creatinine or in the ratios of molecules larger than 66.5 kDa (transferrin, haptoglobin) to creatinine. The cysC-crea ratio was significantly predictive of mortality and subjective overall morbidity at follow-up in logistic regression models adjusting for several factors. The cysC-crea ratio exhibits age- and sex-specific reference intervals in seniors. In conclusion, the cysC-crea ratio may indicate the relative retention of biologically active low-molecular weight compounds and can independently predict the risk for overall mortality and morbidity in the elderly.

Developmental regulation of synthesis and dimerization of the amyloidogenic protease inhibitor cystatin C in the hematopoietic system

The cysteine protease inhibitor cystatin C is thought to be secreted by most cells and eliminated in the kidneys, so its concentration in plasma is diagnostic of kidney function. Low extracellular cystatin C is linked to pathologic protease activity in cancer, arthritis, atherosclerosis, aortic aneurism, and emphysema. Cystatin C forms non-inhibitory dimers and aggregates by a mechanism known as domain swapping, a property that reportedly protects against Alzheimer disease but can also cause amyloid angiopathy. Despite these clinical associations, little is known about the regulation of cystatin C production, dimerization, and secretion. We show that hematopoietic cells are major contributors to extracellular cystatin C levels in healthy mice. Among these cells, macrophages and dendritic cells (DC) are the predominant producers of cystatin C. Both cell types synthesize monomeric and dimeric cystatin C in vivo, but only secrete monomer. Dimerization occurs co-translationally in the endoplasmic reticulum and is regulated by the levels of reactive oxygen species (ROS) derived from mitochondria. Drugs or stimuli that reduce the intracellular concentration of ROS inhibit cystatin C dimerization. The extracellular concentration of inhibitory cystatin C is thus partly dependent on the abundance of macrophages and DC, and the ROS levels. These results have implications for the diagnostic use of serum cystatin C as a marker of kidney function during inflammatory processes that induce changes in DC or macrophage abundance. They also suggest an important role for macrophages, DC, and ROS in diseases associated with the protease inhibitory activity or amyloidogenic properties of cystatin C.