Search for Natural Compounds - Based Therapeutic Approach against Alzheimer’s disease: Chitin and Chitosan – The Choice
© 2021 Mohammad Azizur Rahman, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Abstract
As the number of aged people is increasing globally, so is the case of neurodegenerative disease Alzheimer’s disease (AD). Though different treatment strategy have been applied against AD, success rate is meager. Thus, search for natural compounds capable of withstanding AD progression has received momentum. Present article evaluates the potentiality of chitin and chitosan, the natural bio-polymers, in ameliorating AD. Information presented here would be of immense importance to the AD patients, patients’ care givers, health care providers, researchers and policy makers round the world.
Introduction
Alzheimer’s disease (AD) is the most severe neurodegenerative disorder affecting memory and learning and behavior of the elderly. People over sixty years of old suffer from AD. AD patients become fully dependent on their family members and care-givers. They remain as burden to the family, society and affect the national economy negatively [1-3]. Currently, more than 45 million have been suffering from AD [4]. Unfortunately, no treatment stratagem has been found effective against AD. The available treatment strategies only ameliorate the symptoms associated with AD On the other hand, they cause some side effects that ultimately worsen the patients’ physical and mental state [1-3]. Thus, attempts have been made to discover natural, safe, easy to use, cost-effective treatment stratagem against AD [5]. Among different bio-polymers, chitin and chitosan seem promising as anti-AD agents. This article reviews the rationale in favor of chitin and chitosan as AD therapeutic agents.
Chitin and Chitosan
Chitin is a bio-polymer, formed by the repeated units of N-acetylD-glucosamine and chitosan is chitin’s deacetylated product [Fig. 1]. Chitin forms the exoskeletons of the lobsters, prawns, shrip, crustaceans, arthropods, mollusks and also the cell walls of the fungi [6-7]. Their extraction process is easy and both chemical and biological especially enzymatic processes have been applied worldwide. Their role as anti-oxidants, food preservatives, nanomaterials, drug delivery agents, water purifying chelates and as bio-fertilizers have been hailed [7-8]. As dietary fiber and cholesterol lowering agent, chitin and chitosan have also gained medicinal concern [9]. Their usage in some other aspects such as in ameliorating neurodegenerative diseases seems promising.
Figure 1: Structure of Chitin and Chitosan
Probable Role of Chitin and Chitosan in AD Amelioration
Among different etiological factors of AD are oxidative stress, excessive activity of acetyl choline esterase (ACE), proinflammatory cytokines, apoptosis, neurodegeneration. Formation of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFT) are the two hallmarks of AD [1, 10]. Fragmented product of chitin, named as chitosan oligosaccharides, have been found effective in down regulating the production of the pro-inflammatory cytokine tumor necrosis factor alpha (TNF α) and interleukin 6 (IL-6). It also lowers the production of inducible nitric oxide synthase (iNOs) activity [11]. Their inhibitory role against ACE activity, even at the case of Aβ25-35- induced ACE activity, have been noticed [12]. Chitosan oligosaccharide conjugated with caffeic acid have been found effective in inhibiting the activity of β-site amyloid precursor protein-cleaving enzyme (BACE), the regulatory enzyme of amyloid beta (Aβ) synthesis [13-14]. AD pathogenesis is aggravated through Aβ fibrillization [1, 10]. Chitosan oligosaccharides inhibit Aβ fibrillization as well as destabilize the already fibrilized aggregate and lowers neurotoxicity in hippocampal neurons [15]. Their roles in repairing of nerve injury and axonal outcome and sensory and motor function improvement have been recognized [16]. Thus, chitin, chitosan and their derivatives seem promising as AD ameliorating agents.
Conclusion
Alzhemier’s disease is posing threat to global health care and economic sectors highly. Natural compound-based medicinal approaches would benefit the AD patients, their care givers and health care providers immensely. In this regard, chitin and chitosan seem promising as anti-AD agents. Further studies including clinical trials are necessary to ascertain the therapeutic potentiality of these natural compounds against AD.
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