Free radicals are an atom or group
of atoms that has at least one unpaired electron and is therefore unstable and
highly reactive. The propagation of free radicals can bring about many adverse
reactions leading to extensive tissue damage (Cotran et al., 1999; Yu et al.,
1992). Antioxidants may offer resistance against oxidative stress by scavenging
the free radicals. Antioxidants are compounds that can reduce or inhibits the
oxidation of lipids or other molecules by inhibiting the initiation or
propagation of oxidative chain reactions. The antioxidant activity of the
compounds is mainly due to their redox properties in absorbing and neutralizing
free radicals, quenching singlet and triplet oxygen or decomposing peroxides (Stahl and Sies, 2005).
In the present study, the free radical scavenging and antioxidant
potential of Mosinone-A was assessed by subjecting the radicals and
oxidants namely DPPH, ABTS+, H2O2, NO-
and OH•. The Mosinone-A exhibited strong radical scavenging activity
against DPPH+, ABTS+, H2O2-,
OH• and Fe2+ assay.
Many studies have been reported on the use of medicinal plants as radical
scavengers (Pham et al., 2011).
Mosinone-A exhibited strong reducing power and free radical scavenging
effect on free radical, hydroxyl, superoxide and hydrogen peroxide radicals.
Ascorbic acid is a very good reducing agent and free radical
scavenger. It is also reported to prevent the damage to RBC membrane by
interacting with superoxide and hydroxyl radical (Beyer, 1994). DPPH is a
relatively stable free radical and usually used as a substrate to evaluate the
antioxidant assay. This assay determines
the ability of Mosinone-A to reduce DPPH radical to the corresponding hydrazine
by converting the unpaired electrons to paired ones (Sreejayam and Rao, 1996).
Antioxidants and other radical scavenger can act by converting the unpaired
electrons to paired ones. The maximum concentration (50?M) of Mosinone-A
exhibited the highest percentage of inhibition which indicates that Mosinone-A
causes reduction of DPPH radical in a strohometric manner.
ABTS assay is based on the
inhibition of the absorbance of the radical cation ABTS+, which has
a characteristic long wavelength absorption spectrum (Sanchez-Moreno, 2002).
ABTS, a protonated radical has characteristic absorbance maximum at 734nm which
decreases with the scavenging of proton radicals (Mathew and Abraham, 2004).
The results obtained imply the activity of the Mosinone-A either by inhibiting
or scavenging the ABTS+ radicals. Superoxide anion is produced from
molecular oxygen due to oxidative enzymes (Sainani et al., 1997) of body by non
enzymatic reaction such as auto-oxidation by catecholamines (Hemmani and
Parihar, 1998). Superoxide anion
radical is one of the strongest reactive oxygen species among the free radicals
could be generated and it also has the ability to change to other harmful
reactive oxygen species and free radicals within the living cells (Yen, 1995).
The probable mechanism of scavenging the superoxide anions may be due to
inhibitory effect of the Mosinone-A towards generation of superoxides in the in
vitro reaction mixture.
The hydroxyl radical
(OH-) thus produced may attack the sugar of DNA bases causing sugar
fragmentation, base loss and DNA strand breakage (Halliwell, 1994). This
radical has the capacity to induce carcinogenesis, mutagenesis and which
rapidly initiates lipid peroxidation (Rajesh et al., 2008). From the present results, it is inferred that the
Mosinone-A have better hydroxyl radical scavenging activity as reflected in
terms of percentage inhibition. Nitric oxide (NO) is a reactive free radical
produced by phagocytes and endothelial cells, to yield more reactive species
such as peroxy nitrite which can be decomposed to OH radical. Excess concentration of NO is
associated with several diseases (Ialenti et
al., 1993). Oxygen reacts with the excess nitric oxide to generate nitrite
and peroxynitrite anions which acts as free radicals. The level of nitric oxide was significantly
reduced in this study by the effect of Mosinone-A indicating the free radicals
scavenging properties in a concentration dependent manner.
In the reducing power
assay, the presence of antioxidants in the sample results in the reduction of
Fe3+ to Fe 2+ by donating an electron. The amount of Fe2+
can then be monitored by measuring the formation of perl’s blue at 700
nm. Increasing absorbance indicates an
increase in reductive ability by the Mosinone-A. From the above results,
it can be concluded that Mosinone-A showed the most potent in vitro antioxidant
activity with high percentage inhibition. This may be attributed to the
presence of acetogenein and tetra hydro furan portion in the molecules which
probably play a role as an effective free radical scavenger and have an
effective anticancer agent.