-Dr. Sandeep Kumar Singh, Research Scientist
flavonoids belong to one of the large group of plant polyphenol found largely in the leaves, bark, seeds and flowers of plants. On the basis of their structure, flavonoids are basically divided into six groups, including flavonols, flavones, flavan-3-ols, flavanones, isoflavones, and the anthocyanins. Flavonoids have two benzene rings on either side of a 3-carbon ring. They basically differ in the arrangements of methoxy, hydroxyl, and glycosidic side groups as well as in the conjugation between the A- and B- rings. The flavonoids basically includes; flavonols, flavones, flavan-3-ols, flavanones, isoflavones, and the anthocyanins. Among these, the flavones are the most common and abundant within the families and genera of the higher plants. The structural difference among the flavonoid family results from the difference in the number of hydroxyl groups’ substitution pattern and the degree of glycosylation of these groups.
Flavonoids possess several biochemical properties, but the most important biological role of flavonoids has been reported to have antioxidant and hydrogen-donating capacity. The antioxidant activity of ﬂavonoids mainly depends upon the functional groups arrangement in their structure. Moreover, the powerful direct scavenger action, flavones exert an important indirect antioxidant activity contributing to the homeostasis of metal chelation, calcium, enzymatic activity modulation and stabilization of membranes through anti-lipid peroxidation. The B ring hydroxyl configuration is the most important factor of scavenging of ROS and RNS because it donates hydrogen and an electron to hydroxyl, peroxynitrite radicals and peroxyl, stabilizing them and results into a relatively stable ﬂavonoids radical.
Antioxidant mechanism of the flavonoids by which injury can be prevented against free radical includes (1) activation of antioxidant enzymes; 2) Direct scavenging of reactive oxygen species (ROS); 3) reduction of α-tocopheryl radicals; 4) metal chelating activity; 5) increase in antioxidant properties of low molecular antioxidants; 6) mitigation of oxidative stress caused by nitric oxide; 7) increase in uric acid levels; 8) inhibition of oxidases.
Oxidative stress which usually produces because of the imbalance between antioxidants and reactive oxygen species (ROS) is one of the important events in any neurodegenerative disorders. This oxidative stress has been linked to various other diseases too apart from neurodegenerative disease including ischemic injury, cancer, atherosclerosis and inflammation. Flavonoids play an important role in preventing the adverse effect of ROS by protecting the neurons against oxidative stress and hence suppress neuronal damage and improve cognitive function. Various flavonoids derivatives has been reported to have potential antioxidant and neuroprotective activity in-vtro and in-vivo. Several recent studies suggested that flavonoids have greater importance specially in neuroprotection in Alzheimer’s and Parkinson’s diseasesi) by affecting gene expression ii) by the modulation of intracellular signaling cascades which control neuronal survival, death and differentiation; and iii) by interacting with mitochondria.