P0062GLUCOSYLCERAMIDE SYNTHASE INHIBITION WITH VENGLUSTAT IN CLASSIC FABRY DISEASE PATIENTS LEADS TO PROGRESSIVE REDUCTION OF ENDOTHELIAL CELL GLOBOTRIAOSYLCERAMIDE INCLUSION VOLUME

Abstract

Abstract Background and Aims Fabry disease (FD) is a rare, X-linked, genetic disorder caused by mutations in the gene for the lysosomal enzyme alpha-galactosidase A (αGal-A). The progressive accumulation of glycosphingolipids, most notably globotriaosylceramide (GL-3), in lysosomes of a variety of organs and cell types leads, over decades, to renal, cardiovascular, and other clinical manifestations. In a phase 2 study, glucosylceramide synthase inhibition with venglustat led to a progressive reduction in plasma GL-3 to low-normal levels. Scoring by light microscopy showed a reduction in lysosomal GL-3 inclusions in skin capillary endothelial cells (EC) after 3 years of therapy, although not after 6 months. To further characterize the effect of venglustat using more precise methods, we applied unbiased stereological methods to quantitate GL-3 inclusions in skin ECs. Methods Skin biopsies were obtained from classic male Fabry disease patients (N = 11) at baseline and during daily treatment with venglustat in a phase 2 study (NCT02228460, NCT02489344). Images from at least 50 superficial skin capillaries were obtained using transmission electron microscopy at 7,500 X magnification. The fraction of the volume (Vv) of cytoplasm occupied by GL-3 inclusions [Vv(Inc/Endo)] in all ECs in these capillaries was estimated using point counting by a masked reader. Two-sided paired t tests were used to evaluate differences between baseline and post-treatment values at each time point. Results Venglustat therapy led to a significant reduction from baseline in Vv(Inc/Endo) of 21.1% after 6 months and 38.7% after 3 years of treatment (Figure). Conclusions Treatment with venglustat led to a reduction in GL-3 inclusion fractional volume in skin capillary ECs which was detectable after 6 months using precise quantitative methods. This was followed by further reduction over the next 2 1/2 years. We posit that, in the absence of αGal-A activity, inhibition of GL-3 production with venglustat allowed other enzymatic or non-enzymatic mechanisms to progressively reduce EC lysosomal GL-3 content, and that long-term venglustat therapy may therefore prevent or reverse progressive tissue injury in Fabry disease.