Scientific Report 2007

Molecular and Experimental Medicine

Division Of Biochemistry

Preserving Vision in Glaucoma, Diabetes, and Macular Degeneration

A. Hanneken, J. Johnson

The ability to maintain the health of aging nerve cells and restore the health of injured nerve cells has great potential for preserving and improving visual function in patients with numerous eye diseases. We are identifying compounds that protect nerves from the type of injury that leads to visual loss in macular degeneration, diabetes, and glaucoma, 3 of the leading causes of blindness.

Macular degeneration leads to the death of both retinal pigment epithelial (RPE) cells and photoreceptor cells. Diabetes and glaucoma lead to the death of retinal ganglion cells. We are screening multiple different compounds for their ability to protect these cell types from the type of injury that is thought to cause visual loss in these diseases. This injury is known as oxidative stress and is caused by an overproduction of reactive oxygen species (ROS), which are byproducts of oxygen metabolism. Although many cells can protect themselves from toxic byproducts of oxygen, high concentrations of these compounds can overwhelm the body's natural defense mechanisms. During the past several years, we have identified a group of compounds that protect RPE cells and retinal ganglion cells from cell death induced by oxidative stress. Shown in Figure 1 is the healthy appearance of RPE cells that have survived oxidative injury because of the protective effect of luteolin, a natural compound found in certain plants. Luteolin also prevents cell death induced by oxidative stress in retinal ganglion cells.

Fig. 1. Luteolin protects RPE cells from death induced by oxidative stress. A, Cells grown under normal conditions. B, Cells grown in the presence of luteolin alone. C, Cells dying after treatment with hydrogen peroxide. D, Cells surviving in the presence of luteolin and hydrogen peroxide. E, Cells dying after treatment with tert-butyl hydroperoxide. F, Cells surviving in the presence of luteolin and tert-butyl hydroperoxide.

Among the numerous risk factors associated with the development of macular degeneration are exposure to sunlight and high levels of lipofuscin (a byproduct of aging). To extend our initial studies into cellular models of macular degeneration, we have developed a light-based assay for identifying compounds that can protect RPE cells from the damage associated with light and aging pigments. In these experiments, RPE cells are grown in the presence of various components of lipofuscin and exposed to bright white or blue light. The levels of damaging ROS in the cells are measured after the light exposure. The cells containing various components of lipofuscin have high concentrations of ROS; the presence of protective compounds reduces these concentrations significantly. These effects are dose dependent. For example, Figure 2 shows the effect of various natural compounds on the reduction of ROS in RPE cells exposed to bright white light.

Fig. 2 Effect of various natural products on the accumulation of ROS in RPE cells exposed to light. RFU = relative fluorescence units.

The mechanisms through which these beneficial effects occur are under investigation. Some compounds enhance the production of glutathione, the cell's primary defense against oxidative injury. Other compounds neutralize the production of ROS, which cause cellular injury and death. Additionally, some compounds activate cells' antioxidant response element, which induces the expression of genes that increase the cells' resistance to oxidative injury.

We are validating and expanding these results. Our goal is to identify additional compounds and combinations that have greater potency and efficacy than the previously tested compounds and combinations. We are planning to move into preclinical models of macular degeneration, diabetes, and glaucoma to translate these research findings into new potential therapies for clinical care.

This research is the result of a partnership formed between the Scripps Mericos Eye Institute and Scripps Research aimed at bringing together the promise of biomedical research and the practice of medicine.

Publications

Hanneken, A., Lin, F.-F., Johnson, J., Maher, P. Flavonoids protect human retinal pigment epithelial cells from oxidative stress-induced cell death. Invest. Ophthal. Vis. Sci. 47:3164, 2006.