374. Therapeutic Effect of Platelet Transfusions for Acute Neuronopathic Gaucher Disease

Abstract

Enzyme replacement therapy has led to resolution of most visceral manifestations in Gaucher disease (GD), but it is also limited by the instability of acid beta -glucosidase enzyme (GCase) in circulation, liver 1st bypass, and high cost. In addition, intravenous enzyme administration has not been effective for ameliorating central nervous system (CNS) deficits. Platelets are blood elements that contain cytoplasmic secretory vesicles. The involvement of platelet containing proteins in inflammation and angiogenesis has recently been indicated. We have recently shown that platelets/megakaryocytes could serve as efficient and protective depots for lysosomal enzyme generation and distribution. In this study the potential therapeutic benefits of platelet transfusion in treating neuronopathic GD (nGD) was evaluated using a murine model of acute nGD (4L;C). This model resembles the CNS phenotype and biochemistry of types 2 and 3 Gaucher disease, and premature death results from progressive CNS disease. Platelets containing significant amounts of wild type GCase (19 U/109 plt) were isolated from GFP mice and transfused weekly for four times into 4L;C mice beginning at 21 days of age. The average percentages of donor-derived platelets were at mean of 10% to 12.9% (ranging from 7.2 to 16.1%) as measured one hour after each transfusion by flow cytometry analysis with anti-CD41 staining for GFP-positive donor platelets. Clearance curves of transfused platelets were similar in 4L;C and wild-type recipients with comparable half-life of GFP+ platelets (t1/2=50 h), suggesting the lack of an immune-response against platelet-derived normal GCase in nGD mice. Importantly, the life-span of treated 4L;C mice was significantly extended from 46 days [untreated 4L;C (n=22)] to 54 days [treated, (n=7)]. Potential CNS benefits were assessed using hindlimb gait analysis that evaluated motor function. In comparison to normal controls, the untreated 4L;C mice exhibited abnormal splaying of their hindlimbs and progressive paresis. The platelet-treated 4L;C mice improved significantly toward normal behavior and had delays in the age of onset for CNS signs. Immunohistochemistry analysis showed that numbers of CD68+ cells were decreased in the cerebellum, brainstem and cortex of treated 4L;C mice, indicating the reduction of pro-inflammation by platelet transfusion. The clearance of GFP+ platelets by liver and spleen was shown by GFP signals detected in those organs of treated 4L;C mice. Quantification of the pathogenic lipids, glucosylceramide and glucosylsphingosine, is in progress to assess potential metabolic correction in various regions of brain and visceral organs in platelet-treated nGD mice. More studies are underway to further investigate possible mechanism(s) involved. In summary, our results demonstrate that repeated, moderate levels of platelet transfusion could extend the life span of nGD mice and improve CNS deficits. abbbb