IN VITRO ANTIOXIDANT AND PRO-APOPTOTIC ACTIVITIES OF PULCHERRIMINIC ACID PRODUCED BY A MARINE-DERIVED BACTERIAL ISOLATE FROM THE GULF OF MANNAR, TAMIL NADU, INDIA

Abstract

Pulcherriminic acid, a cyclic dipeptide (diketopiperazine) pigment biosynthesized by marine bacteria, has recently attracted considerable scientific interest owing to its diverse biological activities. In the present study, Pulcherriminic acid was isolated from a marine bacterial strain recovered from coastal waters of the Gulf of Mannar, Tamil Nadu, India. The physicochemical parameters governing pigment production were systematically optimized using a one-factor-at-a-time (OFAT) strategy. A battery of in vitro antioxidant assays — including the Ferric Reducing Antioxidant Power (FRAP) assay, Oxygen Radical Absorbance Capacity (ORAC) assay was employed to comprehensively characterize the radical scavenging and cytoprotective properties of the purified compound. Furthermore, the pro-apoptotic potential of Pulcherriminic acid was evaluated in AGS gastric cancer cells by quantitative real-time PCR (qRT-PCR), examining the expression of Caspase-3 and BCL-2, two pivotal regulators of the intrinsic apoptotic pathway. The compound demonstrated moderate but consistent antioxidant activity across all assay platforms, with a FRAP activity of 55.3% at 100 µg/mL, and ORAC value of 40.2 µmol Trolox equivalents (TE) per gram, a measurable MDA concentration of 160.4 ± 1.9 nmol/ml. At the molecular level, treatment with Pulcherriminic acid at IC₅₀ concentration produced a dramatic 20.47-fold upregulation of Caspase-3 and a near-complete 0.028-fold downregulation of BCL-2, collectively confirming induction of the intrinsic mitochondrial apoptotic pathway. These findings position Pulcherriminic acid as a biologically meaningful marine-derived compound with dual antioxidant and pro-apoptotic activities that merit further investigation.