In a significant research that could impact thousands, a multi-institutional team led by Indian Institute of Technology Jodhpur has developed an efficient fluorescent molecular probe, enabling rapid and safe analytical sensing, for the diagnosis of Alzheimer’s disease. The illness is believed to be caused by the abnormal build-up of plaques in and around brain cells.
The diagnosis method of Alzheimer’s disease will provide an reliable alternative. Fluorescent probe diagnosis involves injecting a fluorescent chemical that specifically attaches itself to the amyloid plaque and assessing the change in fluorescent properties using an appropriate detector.
IIT Jodhpur carried out the research in collaboration with Indian Institute of Technology Kharagpur, and Council of Scientific & Industrial Research – Indian Institute of Chemical Biology, Kolkata. The research results have been recently published in ACS Chemical Neuroscience journal.
Dr Surajit Ghosh, the co-author of the paper, said, “Optical imaging systems that use fluorescent or colour-based chemicals to target tissues and molecules of interest are considered better diagnostic techniques in the biomedical area.” He added that fluorescence probes can enable rapid and safe analytical sensing due to the absence of radioactive chemicals or expensive equipment.
Ghosh is a Professor, Department of Bioscience & Bioengineering, IIT Jodhpur.
According to the Dementia India Report 2010 by the Alzheimer’s and Related Disorders Society of India (ARDSI), there will be around 7.6 million Indians with Alzheimer’s and other dementia conditions by 2030 in India. Plaques are aggregates of a type of small protein (peptide) called amyloid-beta (Aβ).
The diagnosis of Alzheimer’s disease involves assessment of cognitive functions, the observation of brain size and structure through SPECT, PET and MRI scans, and the detection of amyloid plaques. Amyloid plaques are detected by extracting the brain fluid (cerebro-spinal fluid) through a spinal tap, or by PET Scans. Although both methods are reliable, they are invasive and expensive.
Fluorescent Chemical
The fluorescent chemical, in addition to being able to specifically and selectively attach to Aβ aggregates, must also be able to cross the blood-brain barrier to reach the brain. There must also be a change in its fluorescent properties – colour and intensity – when it attaches to Aβ aggregates. Furthermore, the fluorescence must be in the visible light region for easy detection. The commercially available fluorescent probe ThT has poor blood-brain barrier crossing ability and exhibits only a 2.5-fold change in fluorescence intensity.
“We studied the binding modes of RM-28 with Aβ aggregates using molecular docking experiments and found that this probe binds to the entry site, inner clefts and surface of the Aβ aggregates. RM-28 can potentially replace ThT in the detection of Aβ aggregates in both in vitro and in vivo diagnostic techniques and could also serve as template molecular scaffold for designing novel or new fluorescent probes,” said Dr. Ghosh on the future implications of their discovery.
The researchers have successfully designed and developed a series of benzothiazole based fluorescent molecules that can selectively bind to Aβ aggregates.
All these molecules were seen to emit fluorescence in one colour when unbound, and the emission colour shifted towards red in the visible light (rainbow – violet indigo blue green yellow orange red) spectrum with a concomitant increase in fluorescence intensity. For example, a molecule they named RM28 was yellow when unbound and orange when it was bonded to the Aβ aggregates, and there was a 7.5-fold increase in fluorescence intensity after binding. They used AD mice brain samples to test RM28.
This molecule was stable in biological fluids and could easily traverse the blood-brain barrier. It was also selective to Aβ aggregates in the presence of competing biomolecules. Hence, the probe found by the research team will provide a non-invasive and inexpensive reliable alternative to a spinal tap or PET Scan methods Alzheimer’s diagnosis.
What is Alzheimer’s disease
A progressive neurologic disorder that causes the brain to shrink (atrophy) and brain cells to die, Alzheimer’s disease is the most common cause of dementia — a continuous decline in thinking, behavioral and social skills that affects a person’s ability to function independently.
The early signs of the disease include forgetting recent events or conversations. As the disease progresses, a person with Alzheimer’s disease will develop severe memory impairment and lose the ability to carry out everyday tasks.
Alzheimer’s in India is quickly becoming more and more common as the economy of India continues to grow along with the already massive population. More than 60% of people with dementia are from low and middle income countries like India. This number will rise to more than 70% by 2050.
