The study has indicated that compounds that bind with the sigma receptor in the eye may be good treatments for the top two causes of vision loss: diabetic retinopathy and glaucoma.
"The effects of this drug on retinal health are phenomenal," said Dr. Sylvia Smith, retinal cell biologist and co-director of the Vision Discovery Institute in the Medical College of Georgia School of Medicine.
For the study, she compared retinal images from a diabetic mouse model treated with (+)- pentazocine to one that wasn't. She claimed that the differences were quite dramatic even to the untrained eye.
While sigma receptors are omnipresent inside the body, their role and what naturally activates them is still unknown. According to recent research, sigma receptors help protect cells from stress by ensuring an adequate level of the properly folded proteins they need for normal function.
The researchers have now shown that sigma receptors are located within the endoplasmic reticulum of cells, which controls protein synthesis and regulates calcium levels. When needed, the receptors appear to chaperone these proteins to the cell powerhouse, or mitochondria.
Smith believes that sigma receptors may help manage this hotbed of cell stress. In fact, sigma receptor binding with pentazocine increases with cellular stress.
Such cell protection role could help explain the resilience of the retina, which receives light and transforms it to a neural impulse that goes to the brain. The retina can tolerate regular insults, such as the light or high blood sugar, and still function for years.
However, in case of diabetic retinopathy for example, nerve cell damage and death are gradual, eventually spurring new blood vessels in an apparent attempt to get more blood and oxygen to dying cells. Instead, blood vessel proliferation results in further vision loss.
Now researchers are working towards breeding mice without a sigma receptor to better understand the receptor's role and whether regular treatment with the drug has a similar dramatic impact on other animal models of retinal disease.
"We need to know if we just hit it lucky with the Akita mouse or do we have something that could be of widespread benefit," said Smith.
However, pentazocine's binding with sigma receptors didn't impact insulin levels.
"It does not solve that problem of diabetes; however our findings do suggest that just because you are hyperglycemic does not mean you will have diabetic retinopathy," said Smith.
The study is published in the latest issue of Investigative Ophthalmology and Visual Science.