Antioxidant and cytotoxic activities of three species of tropical seaweeds

Abstract

Background: Three species of seaweeds (Padina tetrastromatica, Caulerpa racemosa and Turbinaria ornata) are widely consumed by Asians as nutraceutical food due to their antioxidant properties. Studies have shown that these seaweeds exhibit bioactivities which include antimicrobial, antiviral, anti-hypertensive and anticoagulant activities. However, investigations into the mechanisms of action pertaining to the cytotoxic activity of the seaweeds are limited. The aim of this study was to determine the antioxidant and cytotoxic activities of whole extracts of P. tetrastromatica, C. racemosa and T. ornata, including the cellular events leading to the apoptotic cell death of the extract treated-MCF-7 cells. Bioassay guided fractionation was carried out and the compounds identified.

Methods: Powdered samples were sequentially extracted for 24 h. Their antioxidant activities were assessed by the DPPH radical, superoxide, nitric oxide and hydroxyl radical scavenging assays. The cytotoxic activity of the extract-treated MCF-7cells was assessed using the MTT assay. The most potent fraction was subjected to bioassay guided fractionation with column chromatography. All the fractions were tested for cytotoxic activity, caspase activity and effect on DNA fragmentation.

Results: All three seaweeds showed potent radical scavenging activities in the various assays. The activity of the cellular antioxidant enzymes, superoxide dismutase, catalase and glutathione reductase, in MCF-7 cells, decreased in a time-dependent manner. The partially purified fractions exhibited higher cytotoxic activity, as assessed by the MTT assay, than the whole extracts in the breast adenocarcinoma cell line, MCF-7. LC-MS analysis revealed the presence of bioactive alkaloids such as camptothecin, lycodine and pesudopelletierine.

Conclusion: Based on the results obtained, all three seaweeds are rich sources of enzymatic and non-enzymatic antioxidants which could contribute to their reported medicinal benefits.

Fig. 1

Antioxidant enzyme activities of methanolic extracts of P. tetrastromatica, C. racemosa and T. ornate for 8, 16 and 24 h. Untreated MCF-7 cells were used as the control and set as 100 %. Each value is expressed as mean ± SD (n = 3). a superoxide dismutase (SOD), b catalase (CAT), c glutathione reductase (GR). Note the enzyme activity decreasing upon treatment

Fig. 2

MS spectra of protonated and deprotonated molecules. a Camptothecin at [M + H] + of m/z 371; lycodine at [M-H]- of m/z 277; camptothecin at [M + H] + of m/z 371; pseudopelletierine at [M + H] + of m/z 171; Camptothecin at [M + H] + of m/z 371; Pseudopelletierine at [M + H] + of m/z 171; Camptothecin at [M + H] + of m/z 371. b Compounds with pharmacological activity isolated and identified in P. tetrastromatica, C. racemosa and T. ornata fractions

Fig. 3

Caspase activities of MCF-7 cells treated with seaweed fractions. a Caspase-8, b Caspase-9 and c Caspase-3 activities of MCF-7 cells treated with 12 μg/mL of partially purified P. tetrastromatica column chromatographic fraction, 18 μg/mL of partially purified C. racemosa column chromatographic fraction and 12 μg/mL of partially purified T. ornata column chromatographic fraction. Mitomycin-c was used as a positive control for caspase-8 and 9 activities while positive control for caspase-3 was colchicine (*p < 0.05; **p < 0.01). Note caspase activity induction upon cell treatment

Fig. 4

DNA fragmentation in MCF-7 cells treated with seaweed fractions. Lane M: 1000 bp DNA marker, Lane 1 : Untreated MCF-7 cells (negative control), Lanes 2 and 3: MCF-7 cells treated with 12 μg/mL of P. tetrastromatica for 24 and 48 h, respectively, Lanes 4 and 5: MCF-7 cells treated with 18 μg/mL of C. racemosa for 24 and 48 h, respectively, Lanes 6 and 7: MCF-7 cells treated with 12 μg/mL of T. ornata for 24 and 48 h, respectively