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    Neuroprotective treatment promising for macular telangiectasia

    CNTF found effective in slowing vision loss from photoreceptor cell death in animal models


    In one recent study conducted by Ferenc Sallo, MD, PhD, and Tunde Peto, MD, PhD, of Moorfields Eye Hospital, London, visual field defects assessed by microperimetry were closely associated with defects in the ellipsoid zone measured by OCT. This shows that there is a good correlation between vision loss and retinal pathology, most likely at the level of photoreceptor functional loss, Dr. Friedlander said.

    The current evidence has convinced Dr. Friedlander that photoreceptor cell loss is intrinsic to the disorder rather than directly resulting from blood vessel changes, although we know that there is extensive “crosstalk” between vessels, photoreceptors, and glia, he said.

    In animal models, a class of molecules known as neurotrophic factors has proved effective in reducing the rate of photoreceptor loss during retinal degeneration, Dr. Friedlander said.

    CNTF, which belongs to this class, has slowed vision loss from photoreceptor cell death in 12 animal models of outer retinal degeneration, including in rats, cats, and dogs.

    Treating the outer retina of mice with phenotypic macular telangiectasia type 2 characteristics has shown profound functional and anatomic photoreceptor cell rescue without correcting associated vascular abnormalities.

    One obstacle to the therapy is the blood-retinal barrier, which prevents the penetration of a variety of molecules to the neurosensory retina from plasma, much as the blood-brain barrier prevents most molecules from passing between the central nervous system and systemic circulation.

    Encapsulated cell technology (ECT) (Neurotech USA) can deliver controlled, sustained delivery of therapeutic agents directly into the vitreous humor, thereby providing direct access to the retina while limiting leakage of the growth factor outside the eye.

    ECT consists of cells encapsulated within a semi-permeable polymer membrane. The devices can be surgically retrieved, providing an added level of safety.

    The MacTel Project collaborated with Neurotech, which is sponsoring the current clinical trial, to assess the safety and efficacy of using ECTs to deliver CNTF to patients with macular telangiectasia type 2.

    The phase I trial has been ongoing for 4 years, and shows that the device and CNTF are well tolerated without any significant adverse events. A 2-year phase II study is under way, and has enrolled 68 participants with macular telangiectasia type 2.

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