Fabry Cardiomyopathy: Myocardial Fibrosis, Inflammation and Down-Regulation of Mannose6Phosphate Receptors cause Low accessibility to Enzyme Replacement Therapy

Background Clinical impact of enzyme replacement therapy (ERT) on advanced Fabry disease cardiomyopathy (FDCM) appears limited. The pathologic mechanisms involved are still unclear. Methods Ten male patients with advanced FDCM (echocardiographic maximal wall thickness 19.3 ± 2.1 mm) underwent left ventricular endomyocardial biopsy before and 4 hours after beta-agalsidase infusion (1 mg/Kg). Comparative studies between pre and post infusion samples included: histology and electron microscopy; assessment of myocardial alpha-galactosidase A activity; immunohistochemistry for alpha-galactosidase A and semiquantitative evaluation (from 0 to 3) of its cardiomyocyte content; Ultrastructural immunogold analysis with anti-alpha-galactosidase A ab. Western Blot (WB) quantification of mannose-6-phosphate receptors (M6Pr). Controls were surgical left ventricular biopsies from patients with mitral stenosis. Results Histologic and Ultrastructural evaluation showed no removal of storage material while myocardial fibrosis was 9.8 ± 6.8 vs 3.8 ± 2.0 of controls and virus-negative lymphocytic inflammation was observed in 7 out of 10 patients. At Ultrastructural immunogold analysis, Myocardial alpha-galactosidase A activity increased in post infusion samples by overall 1.89-fold. Alpha-galactosidase A immunostaining in cardiomyocytes was absent at baseline in all patients and did not significantly improve in post-infusion samples. Immunogold particles increased by 1.33 - fold ( 17.6 ± 3.6 pre infusion vs 21.5 ± 5.9 post ) remaining far from normal controls (86.9 ± 6.6). Protein analysis showed M6Pr in advanced FDCM to be 81% lower than in normal heart. Conclusions Our study shows a low accessibility to ERT of cardiomyocytes affected by advanced FDCM. It is sustained by myocardial fibrosis, inflammation and severe down-regulation of M6Pr. ### Competing Interest Statement The authors have declared no competing interest. * EMB : Endomyocardial Biopsy ERT : Enzyme Replacement Therapy FD : Fabry Disease. FDCM : Fabry Disease Cardiomyopathy GB3 : Globotriacylceramide. M6Pr : Mannose-6-phosphate Receptor TEM : Transmission Electron Microscopy AB : Antibody