I never thought a simple teaspoon of turmeric in my food could alter the way I perceive things around me. Literally! No pun intended! A recent study published in 2013 states the beneficial effects that curcumin, the main component of turmeric, has on rescuing retinal degenerations or more simply put, vision loss.
Retinal degenerations are the deterioration of the retina resulting in irreversible blindness. There are two common forms of this degenerative disease. The first one is known as Age-related muscular degeneration (AMD) and usually affects older adults and results in a loss of vision in the center of the visual field, known as the macula because of damage to the retina. The second one is known as Retinitis Pigmentosa (RP), which is the main focus of this paper. RP is an inherited degenerative eye disease, in which genetic defects cause cell death of the rod and cone photoreceptors, predominantly the rod photoreceptors.
Rods are photoreceptor cells concentrated at the outer edges of the retina and function in less intense light and are used for peripheral vision. Cones are responsible for color vision and function best in bright light. Some of the symptoms for RP include decreased vision at night or in low light, loss of peripheral vision also known as “tunnel vision,” and loss of central vision in more advanced stages of the disease (Figure 1).
RP is commonly caused by mutations in Rhodopsin. Rhodopsin is a biological pigment in photoreceptor cells in the retina that is responsible for the first events in the perception of light. This pigment is a G-protein coupled receptor and is the most abundant protein in rod photoreceptor cells. Rhodopsin consists of a protein moiety called opsin and a covalently bound co-factor 11-cis retinal. Mutations in Rhodopsin have been classified into three different groups however this paper only focuses on the Class III mutants. Class III mutants are expressed at very low levels and remain in localized in the Endoplasmic Reticulum (ER). These mutants form the Rhodopsin chromophore poorly and cause abnormal trafficking of the protein resulting in formation of aggregates retained near the ER.
The genetic link between the P23H mutant in rhodopsin and RP has been established however the mechanism underlying photoreceptor degeneration due to this mutation is yet to be understood. Studies suggest that the negative effect exerted by the P23H mutation leads to aggregation and mislocalization of rhodopsin thereby leading to photoreceptor cell death in RP. Therefore, researchers are evaluating synthetic and natural compounds to check for their therapeutic effects in helping treat these protein aggregates. In this study researchers wanted to test whether curcumin exerts anti-protein aggregating activity in the retina and rescue photoreceptors from degeneration due to misfolded rhodopsin.
In this study the researchers wanted to test to check whether curcumin does in fact exhibit protein-aggregating properties. In order to test this they had cells expressing wild type (WT), P23H mutant rhodopsin and P23H mutant rhodopsin treated with curcumin. (Figure 2). Tags were also used to help visualize the area in which these proteins aggregate. The first image depicts the area in which Rhodopsin is localized, as shown by the green marker. In the second image the cells have been co-labeled with an ER-maker, therefore the red marks the location of the ER in this image. Lastly, the third image shows an overlay of the first two images. The green marker shows that in the WT the rhodopsin is localized to the plasma membrane. The white arrow in the P23H rhodopsin mutant marks the formation of protein aggregates localized in the ER region. The red arrow shows that the mutant aggregates were disrupted upon treatment with curcumin and resembled the WT. Thus this experiment helped conclude that curcumin helps disrupt protein aggregates as well as the distribution pattern of the mutant.
Next the researchers wanted to test whether curcumin improved retinal morphology, so they used P23H rhodopsin mutant transgenic rats for evaluation (Figure 3).
The untreated transgenic rats, as expected, developed severe retinal degeneration. The photoreceptor outer nuclear layer (ONL) and inner nuclear layer (INL) segments were shorter and the ONL region was found to be very thin, only containing 2-3 nuclei. Whereas the transgenic rats that were treated with curcumin showed an overall improvement in retinal morphology. The photoreceptor ONL and INL were longer and ONL preserved 6-7 rows of photoreceptor nuclei. A wild-type normal rat retina was also used in this case, which served as a control and the curcumin treated rats and this control were very similar in morphology.
The ONL and INL regions of the photoreceptor cells were also tested to see how thick these layers were. Again it was found that in the curcumin treated rats these regions were significantly thicker than the rats not treated with curcumin. These regions play an important role, as the ONL contains the light detecting portion of the eye and contains nuclear bodies such as rods and cones and the INL contains numbers of closely packed cells which help send electrical signals to our brains when light is detected. Since the ONL region was found to be significantly thicker in the curcumin treated mutants the numbers of photoreceptor cells, rods and cones, also showed a great increase. Thus, these results were able to show that curcumin does in fact have an impact on improving the retinal morphology of P23H rhodopsin mutants. This study is able to provide evidence to support the therapeutic potential of curcumin. In future studies, administration of curcumin in combination with other therapies may be more effective in treating diseases at a faster rate!
Unlike other synthetic compounds, which provide an instant fix, natural compounds like Turmeric need to be taken consistently over long periods of time to be most effective. I never would have imagined that adding just a pinch of this compound would truly help spice up my life as well as provide a myriad of other benefits at the same time. However folks! Don’t be too generous with the Turmeric; add a pinch not a dash, for it makes all the difference in making sure you don’t turn yellow!