A multi-institutional group lead by the Indian Institute of Technology Jodhpur has created a fluorescent molecular probe that can be used to diagnose Alzheimer’s disease. The research was conducted in partnership with the Indian Institute of Technology Kharagpur and the Council of Scientific & Industrial Research – Indian Institute of Chemical Biology, Kolkata.
Dr. Surajit Ghosh, Professor, Department of Bioscience & Bioengineering, IIT Jodhpur, along with his research scholars Mr. Rathnam Mallesh, Ms. Juhee Khan, and Mr. Rajsekhar Roy, and Prof. Nihar Ranjan Jana, Head of the Department of Biosciences, IIT Kharagpur, Dr. Parasuraman Jaisankar, Head of the Organic & Medicinal Chemistry Division, CSIR
According to the Alzheimer’s and Related Disorders Society of India’s (ARDSI) Dementia India Report 2010, there would be around 7.6 million Indians with Alzheimer’s and other dementia conditions by 2030. It is believed that the aberrant accumulation of plaques in and around brain cells causes Alzheimer’s disease. Amyloid-beta (A) is a type of tiny protein (peptide) that accumulates to form plaques.
Alzheimer’s disease is diagnosed through evaluation of cognitive capabilities, observation of brain size and structure using SPECT, PET, and MRI scans, and identification of amyloid plaques. In order to detect amyloid plaques, cerebrospinal fluid (CSF) is extracted using a spinal tap or PET scans are performed. Although both techniques are effective, they are intrusive and costly.
Dr. Surajit Ghosh, Professor, Department of Bioscience & Bioengineering, and Dean of Research and Development at IIT Jodhpur, stated, “Optical imaging systems that use fluorescent or color-based chemicals to target tissues and molecules of interest are considered superior diagnostic techniques in the biomedical field,” in describing his research. In the absence of radioactive chemicals or pricey equipment, he explained, fluorescence probes can facilitate speedy and secure analytical sensing.
Fluorescent probe diagnosis is injecting a fluorescence substance that binds selectively to the amyloid plaque and measuring the change in fluorescent properties using a suitable detector. In addition to being able to connect specifically and selectively to A aggregates, the fluorescent chemical must also be able to pass the blood-brain barrier and reach the brain. When it connects to A aggregates, its fluorescent characteristics (colour and intensity) must likewise change. In addition, for easy detection, the fluorescence must occur in the visible light spectrum. The commercially available fluorescent probe ThT has little ability to permeate the blood-brain barrier and only a 2.5-fold increase in fluorescence intensity.
“Using molecular docking experiments, we examined the binding modalities of RM-28 with A aggregates and found that this probe binds to the entry site, inner clefts, and surface of the A aggregates. Dr. Ghosh stated that RM-28 might potentially replace ThT in the detection of A aggregates in both in vitro and in vivo diagnostic procedures and could also act as a template molecular scaffold for developing unique or new fluorescence probes.
The scientists have successfully designed and manufactured a variety of fluorescent compounds based on benzothiazole that selectively bind to A aggregates. All of these compounds were seen to emit fluorescence in a single colour when unbound, and the emission colour changed toward red in the visible light (rainbow – violet indigo blue green yellow orange red) spectrum as the fluorescence intensity increased. A molecule termed RM28, for instance, was yellow while free and orange when bound to A aggregates, with a 7.5-fold increase in fluorescence intensity after binding. RM28 was evaluated using brain tissues from AD mice.
This chemical was stable in biological fluids and was able to cross the blood-brain barrier without difficulty. Even in the presence of competing biomolecules, it was selective for A aggregates. Therefore, the probe discovered by the study team will give a non-invasive, cost-effective, and trustworthy alternative to spinal taps and PET scans for diagnosing Alzheimer’s.