AAQ the chemical which restore vision in mice; holds promise to treat human blindness by Amina Shakrullah
A team of scientists discovered a chemical which has a temporary ability to bring back the vision of blind mice. The scientists are working to improve the chemical with a hope that this compound will also help to restore the vision of people suffering from degenerative blindness. The team has scientists from the University of California Berkeley and researchers from the University of Washington and Munich. This approach holds promise for the patients who are suffering from blindness disorders like; retinitis pigmentosa, the most common form of inherited blindness and muscular degeneration related to age which is a common cause of acquired blindness in the developed countries. The rods and cones, the light sensitive cells in the retina are dead in both diseases. In the absence of light sensitive cells the eye will not have functional photo-receptors.
The name of the chemical compound which restores vision in blind mice is AAQ (acrylamide-azobenzene-quaternary ammonium). According to a leading researcher Richard Karmer, professor of molecular and cell biology, AAQ acts on remaining normally blind cells in the retina and make them sensitive to light. The AAQ compound is a photoswitch. It binds with the protein ion channels which are present on the surface of retinal cells. The AAQ which is switched on by light alters the flow of ions through the protein channels and activates the neurons. AAQ activates the neurons in a much similar way the rods and cones, light sensitive cells, get activated.
Shining light into one end of a dark tube caused blind mice injected with AAQ to retreat to the dark end. (Image: Neuron)
Karmer claimed that we discovered a unique light sensitive molecule which has the ability to turn on and off the neural activity. The use of AAQ chemical is a safer alternative as compared to other approaches like gene or stem cell therapies. The use of chemical to restore sight is safer because the chemical will eventually deteriorate while in case of stem cell and gene therapy retina will be changed permanently. It is a matter of fact that the use of chemical is also less intrusive instead of implanting light sensitive electronic chips in the eye.
Karmer also said that an important feature of the technique is that it simply uses a chemical and dose of the chemical is adjustable. The chemical can also be used in a combination with other therapies. The therapy using AAQ chemical can be discontinued if desired results are not obtained. When an improved chemical will be available in the market one can replace the older one. But you will lose all these options if you genetically modify a gene or implant a chip in the eye.
Dr.Russell Van Gelder, an opthamologist, said that the discovery of chemical to restore blindness is a major advancement. The findings of the scientists and researchers team are due to be published uptill 26th july in the Neuron journal. Scientists used genetically mutated blind mice in the experiment. The mutations caused death of light sensitive cells rods and cones and inactivation of the photopigments in the eye within a few months of birth. Then a small amount of AAQ was injected into the eyes of blind mice. Scientists confirmed that the mice have restored light sensitivity. They observed contraction of mice’s pupils in bright light and mice also showed light avoidance, which is a typical behavior of rodents.
According to Van Gelger, the approach to use photoswitch provides a real hope to the patients suffering from retinal degeneration. He said we still need to prove with evidences that the compound is as effective and safe for human as it is in mice. But the experimental results which come across show that the compound work better at restoring light sensitive retina blindness which are due to genetic disease.
The technologies which are currently being evaluated to restore sight to people, whose rods and cones had died, include regeneration of rods and cones by injecting stem cells; gene therapy to make blind neurons sensitive to light by inserting a photoreceptor gene also known as “optogenetics”, and installation of small light sensitive retinal chips having electrodes attached to them that will help to trigger the blind neurons. Karmer said that already a lot of people have retinal implants and had restore low vision.
About eight years ago, a group of scientists including Karmer, Trauner and their colleagues developed an optogenetic technique. The technique chemically alters the potassium ion channels in the blind neurons which were also having photoswitch latch on them. Normally the open potassium ion channels are helpful in turning off a cell. But because of attached photoswitch cells will help to activate and deactivate neurons as they will be opened in the presence of ultraviolet light and closed in the presence of green light.
Afterward, Trauner artificially synthesized AAQ which is a photoswitch which attaches to potassium channel without genetically modifying the channels. According to Karmer, New modified AAQ which are being tested are better, as they activate neurons for a few days instead of hours. To activate neurons they use blue green light of moderate intensity and the photoswitches automatically deactivates in darkness means there is no need of a second color of light to deactivate these photoswitches. That’s why scientists are very excited about them.
-Amina
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