A primary pathological defect in the heritable
eye disorder Stargardt disease is excessive accumulation of cytotoxic
lipofuscin bisretinoids in the retina. Age-dependent accumulation of
lipofuscin in the retinal pigment epithelium (RPE) matches the age-dependent increase in the incidence of the atrophic (dry) form of
age-related macular degeneration (AMD) and therefore may be one of several pathogenic factors contributing to AMD progression.
Lipofuscin bisretinoid synthesis in the retina depends on the influx of serum
retinol from the circulation into the RPE. Formation of the tertiary
retinol-binding protein 4 (RBP4)-transthyretin-retinol complex in the serum is required for this influx. Herein, we report the pharmacological effects of the non-
retinoid RBP4 antagonist,
BPN-14136.
BPN-14136 dosing in the Abca4-/- mouse model of increased lipofuscinogenesis significantly reduced serum RBP4 levels and inhibited bisretinoid synthesis, and this inhibition correlated with a partial reduction in visual cycle
retinoids such as retinaldehydes serving as bisretinoid precursors.
BPN-14136 administration at doses inducing maximal serum RBP4 reduction did not produce changes in the rate of the visual cycle, consistent with minimal changes in dark adaptation. Abca4-/- mice exhibited dysregulation of the
complement system in the retina, and
BPN-14136 administration normalized the
retinal levels of proinflammatory
complement cascade components such as
complement factors D and H,
C-reactive protein, and C3. We conclude that
BPN-14136 has several beneficial characteristics, combining inhibition of bisretinoid synthesis and reduction in retinaldehydes with normalization of the
retinal complement system.
BPN-14136, or a similar compound, may be a promising
drug candidate to manage
Stargardt disease and dry AMD.