effect of infection of the filarial parasite brugia malayi - Pondicherry ...

4.1.3 DISCUSSION
4.1 3.1.1 Toxic oxygen radicals
The last few decades have seen great advances in understanding the parasite induced
host physiology in t m of host defense mechanism especially the role of oxidants (free
radicals) and antioxidant enzymes (Callahan et al., 1988). A free radical is any species
capable of independent existence that contains one or more unpaired electrons. They are
highly reactive and unstable and can injure some biological targets such as proteins, lipids,
carbohydrates and key molecules in membrane and nucleic acids. Moreover, free radicals
initiate autocatalytic reaction whereby, molecules with which they react are themselves
converted into free radical and thus propagate the chain of damage (Halliwell and
Guneridge, 1989).
The free radicals may be initiated within cells during the normal cellular metabolic
processes (Klebanoff, 1974; 1980), by ionizing radiation and certain anti-parasitic drugs
(Docampo and Moreno, 1984) and the host response is also a potent source of oxidants.
Molecular oxygen is a buadical and a relatively unreactive compound. It undergoes a four-
electron reduction to form water. However, it can be metabolized inviw to form highly
reactive derivative oxidants. A series of sequential one-electron transfer yields three reactive
intermediates superoxide anions, hydrogen peroxide and hydroxyl mhcal. When two free
radicals meet, they can join their unpaired electrons to form a covalent bond. When radicals
react with non-radicals. new radicals are generated invivo, which is likely to set off free
radical chain reaction (Halliwell et al., 1995; Thomas, 1995) (Fig. 53). The best studied
biologically relevant fra radical chain reaction is lipid peroxidation.
4.13.1.2 Lipid peroddation
Lipid peroxidation is an important consequence of oxidative cellular damage
(Plea and Witschi, 1976) involved in a variety of diseases and stress (Slater, 1984;
Halliwcll and Guttnidge, 1989). LPO involves the direct reaction of oxygen and ply
unsaturated fatty acid (PUFA) to form fm radicals and semistable -ides (Tappel,