Development and Evaluation of Europium-Based Quantitative Lateral Flow Immunoassay for the Chronic Kidney Disease Marker Cystatin-C

This study aimed to establish a Europium label time-resolved fluorescence immunoassay (TRFIA) to detect the chronic kidney disease (CKD) biomarker Cystatin-C. An Europium based Time resolved fluorescence immunoassay was developed to detect the concentration of Cystatin-C in a urine sample to increase the sensitivity with captured anti-Cystatin-C antibodies immobilized on nitrocellulose membrane and then bonded with detection anti-Cystatin-C labelled with CM-EU, followed by fluorescence measurement using time-resolved fluorometry in 15 min. The performance of this TRFIA was evaluated using the clinical urine serum and compared with the ELISA assays. The linear calibration range was 0.015-32 µg/ml, and the limit of detection (LOD) quantified was 0.0001 µg/ml. This current work has improved the LOD of our previous work from 0.013 µg/ml to 0.001 µg/ml. These results indicated that the CM-EU nanoparticle-based LFIA is rapid, more sensitive, reliable, and reproducible for point-of-care testing of Cys-C concentrations in urine.

Functional characterization of Cystatin C in orange-spotted grouper, Epinephelus coioides

Cystatin C is an endogenous inhibitor of cysteine proteases and widely exist in organisms. Several studies in mammals have showed that Cystatin C plays critical role in the immune defense against microorganisms. It is also well known that some fish Cystatin C have important immune regulation functions in inflammatory responses. However, the function of fish Cystatin C in virus infection as well as its underlying molecular mechanisms remain to be elucidated. In the present study, a Cystatin C gene termed Ec-CysC was identified from orange-spotted grouper, Epinephelus coioides. The full-length of Ec-CysC cDNA was 817 bp with a 387 bp open reading frame (ORF) that encoded a 129-amino acid (aa) protein, including 18-aa signal peptide and 111-aa mature polypeptide. The deduced amino acid of Ec-CysC shared three conserved domains containing Glycine at the N-terminus region, QVVAG motif in the middle and PW motif near the C-terminus region. Transcription analysis of the Ec-CysC gene showed its expression in all twelve examined tissues including liver, spleen, kidney, brain, intestine, heart, skin, muscle, fin, stomach, gill and head kidney. Its expression following stimulation with Singapore grouper iridovirus (SGIV) was further tested in spleen, the relative expression of Ec-CysC was significantly up-regulated at 12 h post-infection. The subcellular localization experiment revealed that Ec-CysC was mainly distributed in the cytoplasm in Grouper Spleen (GS) cells. In vitro, Overexpression of Ec-CysC in GS cells significantly reduced the expression of viral genes, namely, ORF162, ORF049 and ORF072. Meanwhile, we found that overexpression of Ec-CysC resulted in upward trend of expression of inflammatory cytokines TNF-a, IL-1β and IL8 during SGIV infection. Further, SGIV-inducible apoptosis and Caspase-3 activity were also weakened by overexpression Ec-CysC in fathead minnow (FHM) cells. These results indicated that Ec-CysC might have a deeper involvement in fish immune defense, and played important roles in inflammation and apoptosis induced by SGIV.

Molecular characterization, expression and functional analysis of cystatin C in Japanese flounder (Paralichthys olivaceus)

Cystatins are natural tight-binding reversible inhibitors of cysteine proteases found in a wide arrange of organisms. Studies have shown that cystatins play important roles under both physiological and pathological conditions in mammals. However, much less is known about fish cystatins. In this study, we described the identification and analysis of the gene encoding cystatin C in Japanese flounder (Paralichthys olivaceus). This gene had a high homology with the sequence of cystatin C in many fish species and had a signal peptide and three conserved functional sites. The results of qRT-PCR showed that the gene was highly expressed in the liver. Lipopolysaccharide, peptidoglycan and polyinosinic-polycytidylic acid all increased its expression after stimulation. Functional analysis showed that the recombinant P. olivaceus cystatin C purified from Escherichia coli had cysteine protease inhibitory activity and could inhibit bacterial growth by binding to bacteria. Meanwhile, rPocystatin C could up-regulate the expression of cytokines tumor necrosis factor α and interleukin 10. These results indicated that cystatin C of P. olivaceus might be considered to have the similar immunomodulatory function to mammalian cystatin.

[Preparation of monoclonal antibody against cystatin C and establishment of its immunoassay system]

OBJECTIVE

To prepare human cystatin C( CysC) recombinant protein and produce monoclonal antibodies with high affinity and specificity. Develop a competitive ELISA detection system to detect of CysC in human serum.

METHODS

The CysC gene sequence was found on NCBI. The optimized gene fragments were synthesized and the recombinant CysC protein was expressed in Escherichia coli then used to immunize Balb/c mice. The positive hybridoma cell lines were obtained by hybridoma cell fusion techniques and ascites monoclonal antibody was prepared and purified. Affinity of the antibody was measured by indirect ELISA. Then competitive ELISA detection system was established, and 52 cases of human serum samples were detected by the detection system.

RESULTS

Four stable cell lines secreting CysC monoclonal antibodies were obtained. Antibody Ab3 was used as a detection antibody and HRP labeling was performed. Its affinity constant was 4. 26 × 10~6L/mol. The linear range of detection was 0. 011-1. 924 μg/mL. The detection limit was 4. 598 ng/mL and IC_(50) was 0. 145 μg/mL. The established competitiveELISA serum detection system could accurately detect those 52 serum samples.

CONCLUSION

The monoclonal antibody against CysC with high affinity and specificity has been successfully obtained. A reliable competitive ELISA serum detection system is established. The method provides a basis for the development of CysC rapid immunoassay kit.

Application of amide hydrogen/deuterium exchange mass spectrometry for epitope mapping in human cystatin C

Human cystatin C (hCC) is a small cysteine protease inhibitor whose oligomerization by propagated domain swapping is linked to certain neurological disorders. One of the ways to prevent hCC dimerization and fibrillogenesis is to enable its interaction with a proper antibody. Herein, the sites of interaction of hCC with dimer-preventing mouse monoclonal anti-hCC antibodies Cyst28 are studied and compared with the binding sites found for mAb Cyst10 that has almost no effect on hCC dimerization. In addition, hCC epitopes in complexes with native polyclonal antibodies extracted from human serum were studied. The results obtained with hydrogen-deuterium exchange mass spectrometry (HDX MS) were compared with the previous findings made using the excision/extraction MS approach. The main results from the two complementary MS-based approaches are found to be in agreement with each other, with some differences being attributed to the specificity of each method. The findings of the current studies may be important for future design of hCC dimerization inhibitors.

Isolation and characterization of autoantibodies against human cystatin C

Hereditary cystatin C amyloid angiopathy (HCCAA) is a severe neurodegenerative disorder related to the point mutation in cystatin C gene resulting in human cystatin C (hCC) L68Q variant. One of the potential immunotherapeutic approaches to HCCAA treatment is based on naturally occurring antibodies against cystatin C. A recent growing interest in autoantibodies, especially in the context of neurodegenerative diseases, emerges from their potential use as valuable diagnostic markers and for controlling protein aggregation. In this work, we present characteristics of natural anti-hCC antibodies isolated from the IgG fraction of human serum by affinity chromatography. The electrophoresis (1-D and 2-D) results demonstrated that the isolated NAbs are a polyclonal mixture, but their electrophoretic properties did not allow to classify the new autoantibodies to any particular type of IgG. The Fc-glycan status of the studied autoantibodies was assessed using mass spectrometry analysis. For the isolated NAbs, the epitopic fragments in hCC sequence were identified by MS-assisted proteolytic excision of the immune complex and compared with the ones predicted theoretically. The knowledge of hCC fragments binding to NAbs and other ligands may contribute to the search for new diagnostic methods for amyloidosis of different types and the search for their treatment.

Expression of cystatin C in human esophageal cancer

AIMS AND BACKGROUND

Cystatin C is a member of the cysteine protease inhibitors and its function is to decrease protease activity. A recent study showed that it was aberrantly expressed in many malignant tumors in association with tumor invasion and metastasis. We attempted to detect its expression in esophageal cancer tissues and adjacent reparative normal tissues.

METHODS AND DESIGN

Samples of cancers and non-cancerous esophageal tissues were obtained as matched pairs from 30 surgery patients with esophageal cancer and paraffin embedded. The expression of cystatin C in tissues was investigated by immunohistochemistry. Fisher's exact test was used to analyze the relationship between esophageal cancer tissues and adjacent normal tissues. Furthermore, mRNA was extracted, and reverse transcriptase polymerase chain reaction was performed.

RESULTS

The intensity of cystatin C immunostaining in tumor tissues was increased compared to that of adjacent normal tissues. mRNA expression of the cystatin C gene was greater in esophageal cancer than in normal tissues (P <0.05).

CONCLUSIONS

Our results indicate that cystatin C may play an important role in the pathogenesis and metastasis of esophageal cancer.

Expression of cystatin C in human esophageal cancer

AIMS AND BACKGROUND

Cystatin C is a member of the cysteine protease inhibitors and its function is to decrease protease activity. A recent study showed that it was aberrantly expressed in many malignant tumors in association with tumor invasion and metastasis. We attempted to detect its expression in esophageal cancer tissues and adjacent reparative normal tissues.

METHODS AND DESIGN

Samples of cancers and non-cancerous esophageal tissues were obtained as matched pairs from 30 surgery patients with esophageal cancer and paraffin embedded. The expression of cystatin C in tissues was investigated by immunohistochemistry. Fisher's exact test was used to analyze the relationship between esophageal cancer tissues and adjacent normal tissues. Furthermore, mRNA was extracted, and reverse transcriptase polymerase chain reaction was performed.

RESULTS

The intensity of cystatin C immunostaining in tumor tissues was increased compared to that of adjacent normal tissues. mRNA expression of the cystatin C gene was greater in esophageal cancer than in normal tissues (P <0.05).

CONCLUSIONS

Our results indicate that cystatin C may play an important role in the pathogenesis and metastasis of esophageal cancer.

Cystatin C is a reliable marker for estimation of glomerular filtration rate in renal transplantation: validation of a new turbidimetric assay using monospecific sheep antibodies

BACKGROUND

The potential use of cystatin C was recently assessed in kidney transplantation. A new particle-enhanced turbidimetric immunoassay (PETIA) that uses sheep antibodies (Binding Site human cystatin C immunoassay) has been developed. Analytical performance of this new assay was evaluated. Clinical relevance was determined by comparison with a reference method in a cohort of kidney transplant patients.

METHODS

First, the analytical performance of the Binding Site cystatin C kit was tested on SPA(PLUS)® and Hitachi® analyzers. Second, a comparison study was performed using SPA(PLUS)® analyzer against two other cystatin C methods (the Siemens-PENIA method on BNII® and the Dako-PETIA application on Olympus AU640®). Third, the glomerular filtration rate (GFR) was estimated using several predictive cystatin C- and creatinine-based equations and compared to GFR measured by an isotopic method (⁹⁹(m)Tc-DTPA). These predictive algorithms were analyzed with respect to bias, precision and accuracy.

RESULTS

Total intra-assay and inter-assay coefficients of variation were below 5%. Values obtained with the SPA(PLUS)® correlated with the Siemens-PENIA and the Dako-PETIA methods. The creatinine and cystatin C-based equation allowed reliable assessment of GFR in our population of renal transplantation.

CONCLUSIONS

The use of algorithms based on cystatin C and creatinine could provide a reliable estimate of GFR in kidney transplantation.