Cholestane-3β, 5α, 6β-triol: Further insights into the performance of this oxysterol in diagnosis of Niemann-Pick disease type C

In recent years the oxysterol species cholestane-3β, 5α, 6β-triol (C-triol) has found application as a diagnostic biomarker for Niemann-Pick disease type C. Other studies have described increased C-triol in patients with Niemann-Pick disease type A/B and milder increases in lysosomal acid lipase deficiency (LALD), whereas they note normal C-triol levels in Smith-Lemli-Opitz syndrome (SLOS) and familial hypercholesterolaemia (FH) patients. Herein, we review data collected in our laboratory during method evaluation along with 5 years of routine analysis and present findings which differ from those reported by other groups with respect to LALD, SLOS and FH in particular, whilst providing further evidence regarding the clinical sensitivity and specificity of this biomarker, which are difficult to accurately assess. All of our Wolman disease (severe LALD) patients have demonstrated gross elevations of C-triol at diagnosis, with reduction to normal levels after induction of enzyme replacement therapy. In diagnostic specimens from SLOS patients we observed very low or undetectable C-triol levels whereas in post-therapeutic SLOS patients demonstrated normalised levels; we also describe a homozygous FH patient in which C-triol is significantly elevated. Upon investigation, we found that C-triol was formed artefactually from cholesterol during our sample preparation, i.e. this is a false positive of analytical origin; at present it is unclear whether similar effects occur during sample preparation in other laboratories. Our data demonstrates clinical sensitivity of 100% during routine application to diagnostic specimens; this is in keeping with other estimates, yet in a small proportion of patients diagnosed prior to C-triol measurement, either by Filipin staining of fibroblasts or molecular genetics, we have observed normal C-triol concentrations. Clinical specificity of C-triol alone is 93.4% and 95.3% when performed in conjunction with lysosomal enzymology. These performance statistics are very similar to those achieved with Filipin staining of cultured fibroblasts in the 5 years preceding introduction of C-triol to routine use in our laboratory. It is increasingly apparent to us that although this analyte is a very useful addition to the diagnostic tools available for NPC, with considerable advantages over more invasive and time-consuming methods, the interpretation of results is complex and should be undertaken only in light of clinical details and results of other analyses including enzymology for lysosomal acid lipase and acid sphingomyelinase.

The impact of biomarkers analysis in the diagnosis of Niemann-Pick C disease and acid sphingomyelinase deficiency

BACKGROUND

Although representing two distinct disease entities, Niemann-Pick disease type C (NP-C) disease and acid sphingomyelinase deficiency (ASMD) share several phenotypic features. The lack of biomarkers was responsible in the past of diagnostic delay. Recently, plasma oxysterols, cholestan-3β,5α,6β-triol (Triol) and 7-ketocholesterol (7-KC) and lysosphingolipids, Lyso-sphingomyelin (Lyso-SM) and Lysosphingomyelin-509 (Lyso-SM-509), have been proposed as diagnostic biomarkers. We aimed to assess the diagnostic power of the two biomarkers categories and to evaluate possible correlations with patients' age and clinical phenotypes.

PATIENTS AND METHODS

We analyzed plasma oxysterols and lysosphingolipids in patients affected by NP-C and ASMD, and compared with healthy controls.

RESULTS

Oxysterols were always increased in both NP-C and ASMD. In NP-C, Lyso-SM and Lyso-SM-509 were increased in 70%, and 100% of patients, respectively. Biomarkers negatively correlated with patients' age, with highest levels in early-infantile, intermediate in the late-infantile and lowest in the juvenile phenotype. In ASMD, lysosphingolipids were both increased, with a greater order of magnitude than in NP-C, with highest levels in chronic-neurovisceral vs visceral phenotype.

CONCLUSIONS

Lysosphingolipids are useful biomarkers for a rapid and precise diagnosis, allowing clear distinction between NP-C and ASMD. They are more reliable biomarkers than oxysterols and correlate with patients' age and clinical phenotype.

Anti-apoptotic phenotypes of cholestan-3β,5α,6β-triol-resistant human cholangiocytes: characteristics contributing to the genesis of cholangiocarcinoma

The oxysterols cholestan-3β,5α,6β-triol (Triol) and 3-keto-cholest-4-ene (3K4) are increased in Opisthorchis viverrini-associated hamster cholangiocarcinoma and induce DNA damage and apoptosis via a mitochondria-dependent mechanism in MMNK-1 human cholangiocytes. Based on these observations, we hypothesized that chronic exposure of cholangiocytes to these pathogenic oxysterols may allow a growth advantage to a subset of these cells through selection for resistance to apoptosis, thereby contributing to cholangiocarcinogenesis. To test this hypothesis, we cultured MMNK-1 cells long-term in the presence of Triol. Alteration in survival and apoptotic factors of Triol-exposed cells were examined. Cells cultured long-term in the presence of Triol were resistant to H2O2-induced apoptosis, and demonstrated an increase in the phosphorylation of p38-α, CREB, ERK1/2 and c-Jun. Elevations in the ratio of Bcl-2/Bax and in the protein levels of anti-apoptotic factors including cIAP2, clusterin, and survivin were detected. These results show that long-term exposure of MNNK-1 cells to low doses of Triol selects for kinase-signaling molecules which regulate resistance to apoptosis and thereby enhance cell survival. Clonal expansion of such apoptosis-resistant cells may contribute to the genesis of cholangiocarcinoma.