Rationale for an experimental treatment of retinitis pigmentosa: 140-month test of hypothesis with one patient.

BACKGROUND

Numerous mutations in over 100 rod genes are the well-established cause of apoptotic death of these cells and development of night blindness in retinitis pigmentosa (RP). Cone death is either concomitant or follows rod death with resultant loss of critical peripheral and central day vision. As cones are generally not encumbered by genetic mutations, the causes of their death and its prevention are the central problems of RP research. Currently no FDA-approved medications are available for retarding RP progression.

HYPOTHESIS

It is proposed that cones, which are outnumbered 20:1 by rods, undergo apoptosis as a consequence of neurotrophic factor deficiencies and oxidative stresses accompanying massive rod death: increased retinal oxygen tension; leakage of lipid-peroxidation catalysts from disrupted membranes; reactive oxygen species from active/hyperactive microglia ingesting rod-apoptotic bodies. Accordingly we developed and tested a treatment regimen with a range of antioxidants in combination with the off-label use of deprenyl (1 mg/day), a safe antiapoptotic agent, which also upregulates eight neurotrophic factors. Since deprenyl inhibits only one of four mitochondrial apoptotic pathways, we added the antibiotic minocycline (100 mg/day) to our protocol at month 76. Minocycline complements deprenyl's therapeutic properties: it inhibits all four apoptotic pathways; inhibits apoptosis-initiating proteins; as phenol exerts powerful antioxidant properties; upregulates three antioxidant enzymes; downregulates oxidative/inflammatory microglia activities. Its safe long-term use for acne and rheumatoid arthritis received FDA approval; it passes the blood/brain and blood/retinal barriers readily; and because of its rapid and complete absorption causes no intestinal disturbances. The National Eye Institute has initiated in 2010 and 2011 clinical trials with minocycline (200 mg/day) for diabetic macular edema and retinal branch vein occlusion.

TESTING OF HYPOTHESIS

The hypothesis was tested for 140 months with one RP patient monitored by Humphrey Perimetry, which was quantitated by two parameters: (a) sum of decibel units, (b) number of detected light sources (visual field). Although no decline was observed in these parameters during the first 50 months of treatment, they declined by 10-28% during months 50-65. These declines reversed upon introduction of minocycline: over the total 140-month treatment, the right eye visual field showed 0% decline and left eye 13.3% decline. Rate constants for logarithmic decline of visual field measured prior to treatment indicate that visual fields would have decreased by 64% and 70%, respectively by month 140 in the absence of treatment.