- Title
- Brown algae as a source of bioactive compounds for pancreatic cancer treatment
- Creator
- Dang, Thanh Trung
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Marine macro-algae (seaweeds) are a rich source of bioactive compounds that have the potential to be used as functional constituents for human health applications. Bioactive compounds from brown algae include pigments, sulfated polysaccharides (fucoidans), phlorotannins (marine phenolics), terpenes and other secondary metabolites. These compounds have been reported to possess biological activity against a range of chronic diseases, including cancer. Pancreatic cancer has a high mortality rate and short survival timeline due to difficulties associated with achieving a correct diagnosis at an early stage of the disease, a predisposition to metastasise to other organs within the body, and a lack of progress in the development of new therapeutic strategies. For decades, gemcitabine has remained the single front-line chemotherapeutic agent for treating advanced adenocarcinoma of the pancreas. A low proportion of patients however see direct and meaningful benefit from gemcitabine, with current combinatorial chemo-radiation treatment regimens delivering only limited survival benefits. Brown algae Sargassum vestitum; Sargassum linearifolium; Phyllospora comosa; Padina sp.; Hormosira banksii and Sargassum podocanthum are species found in Eastern Coast of NSW, Australia. Despite their relative abundance, knowledge of the phytochemical properties of extracts from these species remains limited. Therefore, an assessment of the bioactive potential of compounds derived from these brown algae against pancreatic cancer is justified. The current study hypothesised that the physico-chemical profile and antioxidant activities of bioactive compounds derived from brown algae could be improved through optimisation of drying and extraction conditions, and that phytochemical fractions or individual compounds isolated from the algae display efficacy against pancreatic cancer cell lines. The overall aims were to: Optimise drying conditions for algae to preserve chemical activity and antioxidant power.; Optimise the extraction of phenolics from algae using irradiative technologies such as ultrasound and microwave. ; Isolate key components including fucoxanthin, phenolics and polysaccharides for assessment of their cytotoxic activity against a range of pancreatic cancer cell lines. Six drying methods were applied to H. banksii samples including de-humidification, vacuum and freeze drying, sun drying (in direct sunlight), as well as microwave and oven drying. The temperature of 50 °C was found to be optimal for both de-humiditification and vacuum oven drying, while sun drying produced the highest bioactive compound yield and was the most cost effective. Among the six algal extracts, H. banksii possessed the highest total phenolic content (TPC) with 158.82 mg GAE.g-1 followed by S. vestitum and Padina sp. (141.91 and 124.65 mg GAE.g-1, respectively). Total flavonoid content (TFC) was highest in H. banksii (29.31 mg CAE.g-1), while Padina sp. produced the highest tannin content (56.17 mg CAE.g-1). Fucoxanthin content was present in all six extracts, with four species - Padina sp.; S. linearifolium; S. vestitum and S. podocanthum possessing with high concentrations (1.97; 1.76; 1.65 and 1.46 mg fucoxanthin.g-1) respectively. Extraction of phenolics from H. banksii using aqueous ethanol (70%) and ultrasonic irradiation improved both total yield and antioxidant activity. Optimal extraction conditions were determined to be; temperature = 30 °C, extraction time = 60 min., irradiation power = 60% (150w). The highest values of TPC and antioxidant activity (ABTS, DPPH and FRAP)achieved were 23.12 mg GAE.g-1, 85.64 TE.g-1, 47.24 TE.g-1 and 12.56 TE.g-1, respectively. Microwave-assisted extraction was applied to extract phenolics from S. vestitum using aqueous ethanol 70% as a solvent. From the preliminary experiments and literature, acetone was proved to be the best solvent in relation to yields of phenolics and produced the highest antioxidant activity compared to methanol, water and ethyl acetate. However, ethanol was preferred on safety grounds for usage as well as minimal solvent residue in the sample. Therefore, ethanol 70% is suitable for extraction of phenolics from S. vestitum. The maximal values of TPC and antioxidant activities gained from this alga were 58.2 mg GAE.g-1, 149.84 mg TE.g-1, 116.54 mg TE.g-1 and 67.95 mg TE.g-1, respectively with the optimal conditions determined to be irradiation time of 75 seconds, ethanol percentage of 70% and power of 80% (1080w). Polysaccharides from H.banksii were extracted using water and separated by precipitation using pure ethanol and centrifugation. Sulfated polysaccharides (fucoidans) were observed in three fractions (CF50, CF70 and CFR). Antioxidant activities of the CF50 and CF70 fractions were low, while high activity was observed in the CFR fraction due to the presence of high concentrations of phenolics. Finally, from the H.banksii extract, fucoxanthin was isolated through solvent partitioning and column chromatography techniques, in high purity (92.3%; validated by HPLC). Phenolic compounds were separated in solvent fractions of differing polarity (hexane, dichloromethane, ethyl acetate and butanol fractions), with ethyl acetate possessing the highest TPC value and antioxidant activities. Sulfated polysaccharides (fucoidan) with higher sulfate content were found in the CF70 fraction. Fucoxanthin, phenolic and polysaccharide fractions were investigated for cytotoxic activity against a range of pancreatic cancer cell lines. With a range of concentrations (25 – 200 ng.mL-1), phenolic compounds possessing medium polarity (ethyl acetate fraction) showed excellent cancer cell growth inhibition properties (70-100%) against Mia PaCa-2, BxPC-3 and CFPAC-1 cell lines but was also toxic towards normal pancreas cells (HPDE). It was noted that polar phenolic compounds (butanol fraction) exhibited high cytotoxic activity against these cancer cells but low toxicity against non-tumorigenic cells. Fucoxanthin was also a potent agent against pancreatic cancer cell lines with high growth inhibition (inhibition of 30.91–92.81% at concentrations of 100–200 µg.mL-1). Polysaccharides fractions (CF50 and CF70)showed quite high activity (inhibition of 39.35 – 82.82% at the concentrations of 100–200 µg.mL-1) against these cancer cells with low toxicity towards normal cells (IC50 values were 526.32 µg.mL-1 (CF50) and 781.25 µg.mL-1 (CF70)). In summary, the hypothesis was supported and the aims were achieved in these studies. Three out of six drying methods were found to be effective for producing higher yields of phenolics and stronger antioxidant activities. The bioactive components extracted using ultrasound and microwave techniques were optimised for high efficacy of phenolics and antioxidant activities. In addition, purified fucoxanthin and polar phenolics obtained by partition and column chromatography showed strong potential against pancreatic cancer cell lines. Sulfated polysaccharide fractions (CF50 and CF70) exhibited high cytotoxic effects against pancreatic cancer cell lines with less toxicity to non-tumorigenic cells. These algal components have potential application in the functional food and pharmaceutical industries.
- Subject
- brown algae; phenolics; antioxidant activities; pancreatic cancer
- Identifier
- http://hdl.handle.net/1959.13/1412277
- Identifier
- uon:36453
- Rights
- Copyright 2018 Thanh Trung Dang
- Language
- eng
- Full Text
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