Free radical scavenging potential of L-proline: evidence from in vitro assays

Abstract

An assessment of the potential of proline to scavenge free radicals was made in a couple of in vitro assay systems, namely graft co-polymerization and autooxidation of pyrogallol. Both these assays are essentially dependent upon free radical mechanisms. Graft co-polymerization involved a ceric (Ce(4+)) ion- or gamma-radiation-induced grafting of methyl acrylate (MA) onto a cellulose backbone. The degree of grafting, measured gravimetrically, was taken as a measure of free radical generation. The gamma-radiation-dependent grafting was far greater than that due to Ce(4+) ions. Inclusion of proline in the assay, irrespective of the initiator used, led to suppression of grafting in a concentration-dependent manner indicating the ability of proline to scavenge free radicals. The gamma-radiation-dependent grafting was also suppressed by hydroquinone and glutathione but not by ascorbate, glycine and spermine. In contrast to graft co-polymerization, proline did not inhibit the autooxidation of pyrogallol, a reaction involving superoxide radical generation. A subset of data constitutes an evidence for the ability of proline to scavenge free radicals in vitro. It is implied by extension that free proline, known to accumulate in plant tissues during abiotic stresses, would contribute to scavenging of surplus free radicals produced under a variety of abiotic stresses.

Proline modulates the intracellular redox environment and protects mammalian cells against oxidative stress

“…Interestingly, we found that proline was ineffective at protecting cells against superoxide generators such as menadione. Recently, it was reported that proline does not interact with superoxide in vitro [53]. Our cellular studies concur with this finding and suggest that proline exhibits specificity toward H 2 O 2 -induced stress.…”

Experimental Resistance to Drug Combinations in Leishmania donovani: Metabolic and Phenotypic Adaptations

“…High levels of hypoxanthine were also found in the resistant lines of our study (IMP and AMP were not detected). Although the precise role of proline remains unclear, our findings and the above-mentioned reports all point toward proline as a general stress-response metabolite, and it has been demonstrated that proline can act as a free radical scavenger in vitro (56). Hence, in drug-resistant L. donovani lines, increased levels of proline might protect against oxidative stress caused by drug pressure.…”

Role of proline under changing environments

“…The activities of APX (ascorbate peroxidase), MDHAR (monohydro ascorbate reductase) and DHAR (dihydro ascorbate reductase) enzymes, which are the components of ASC-GSH cycle, were significantly enhanced by exogenous proline application in tobacco cultures exposed to salinity stress (Hoque et al 2007). Kaul et al 97 using in vitro studies, showed that exogenously applied l-proline proved to be a potent free radical (particularly ROS) scavenger. Hong et al 91 concluded that the role of proline as a free radical scavenger is more important in alleviating stress than its role as a simple osmolyte.…”