Clinical utility of chitotriosidase enzyme activity in nephropathic cystinosis

Abstract

Contains fulltext : 138675.pdf (publisher's version ) (Open Access)BackgroundNephropathic cystinosis is an inherited autosomal recessive lysosomal storage disorder characterized by the pathological accumulation and crystallization of cystine inside different cell types. WBC cystine determination forms the basis for the diagnosis and therapeutic monitoring with the cystine depleting drug (cysteamine). The chitotriosidase enzyme is a human chitinase, produced by activated macrophages. Its elevation is documented in several lysosomal storage disorders. Although, about 6% of Caucasians have enzyme deficiency due to homozygosity of 24-bp duplication mutation in the chitotriosidase gene, it is currently established as a screening marker and therapeutic monitor for Gaucher inverted question marks disease.MethodsPlasma chitotriosidase activity was measured in 45 cystinotic patients, and compared with 87 healthy controls and 54 renal disease patients with different degrees of renal failure (CKD1-5). Chitotriosidase levels were also correlated with WBC cystine in 32 treated patients. Furthermore, we incubated control human macrophages in-vitro with different concentrations of cystine crystals and monitored the response of tumor necrosis factor-alpha (TNF- inverted question mark) and chitotriosidase activity. We also compared plasma chitotriosidase activity in cystinotic knocked-out (n inverted question mark= inverted question mark10) versus wild-type mice (n inverted question mark= inverted question mark10).ResultsPlasma chitotriosidase activity in cystinotic patients (0 inverted question mark3880, median 163 nmol/ml/h) was significantly elevated compared to healthy controls (0 inverted question mark90, median 18 nmol/ml/h) and to CKD patients (0 inverted question mark321, median 52 nmol/ml/h), P inverted question mark< inverted question mark0.001 for both groups. Controls with decreased renal function had mild to moderate chitotriosidase elevations; however, their levels were significantly lower than in cystinotic patients with comparable degree of renal insufficiency. Chitotriosidase activity positively correlated with WBC cystine content for patients on cysteamine therapy (r inverted question mark= inverted question mark0.8), P inverted question mark< inverted question mark0.001. In culture, human control macrophages engulfed cystine crystals and released TNF- inverted question mark into culture supernatant in a crystal concentration dependent manner. Chitotriosidase activity was also significantly increased in macrophage supernatant and cell-lysate. Furthermore, chitotriosidase activity was significantly higher in cystinotic knocked-out than in the wild-type mice, P inverted question mark= inverted question mark0.003.ConclusionsThis study indicates that cystine crystals are potent activators of human macrophages and that chitotriosidase activity is a useful marker for this activation and a promising clinical biomarker and therapeutic monitor for nephropathic cystinosis