There is evidence that increased fruit and vegetable consumption can improve human health. Epidemiological and clinical studies have established an inverse correlation between fruit and vegetable consumption, and the incidence of diseases such as some specific cancers, cardiovascular disease and obesity. Within plants, molecules known as phytochemicals are believed to contribute to the health protective and disease preventive properties of some fruits and vegetables.
Mangoes are tropical fruits that are widely consumed in both developed and developing countries and are a rich and diverse source of phytochemicals. The mango is one of the most consumed fruits in Asia, with annual production only exceeded by that of citrus, apples and grapes. Current studies have focussed on the biological significance of phytochemicals and extracts mainly found in temperate climate fruits such as plums and apples, with very few studies assessing the effects of phytochemical extracts from tropical fruits. There is also very little known about cultivar and within fruit differences regarding potential health benefits.
In the work described in this PhD thesis, flesh and peel extracts from three phylogenetically diverse mango (Mangifera indica L.) cultivars, Nam Doc Mai (NDM), Irwin (IW) and Kensington Pride (KP) were assessed for their bioactivity in disease models associated with breast cancer and obesity. Biological activities associated with mango fruit extracts and/or fractions were assessed in cell-based assays in both breast cancer and adipocyte cell lines. In these studies high throughput screening technologies were utilised to detect bioactive components in different mango varieties.
In human breast cancer MCF-7 cells, peel and flesh extracts from the Irwin, Nam Doc Mai and Kensington Pride cultivars were assessed for their anti-proliferative effects. We also assessed two signalling pathways implicated in cellular proliferation; extracellular signal-regulated kinase activity and increases in intracellular free Ca2+ ([Ca2+]I). Our results demonstrated that mango cultivar peel and flesh extracts did not significantly alter ERK phosphorylation compared to controls. The peel and flesh of some extracts were shown to reduce relative maximal peak [Ca2+]I post adenosine triphosphate (ATP) stimulation. NDM peel extract had the greatest effect among the extracts. Additionally, [Ca2+]I recovery was prolonged by NDM and IW peel extracts. KP extracts however did not affect [Ca2+]I recovery post adenosine triphosphate stimulation.
Mango peel and flesh extracts were also assessed for their effects on the 3T3-L1 pre-adipocyte cell line, a model for adipogenesis. Mango flesh extracts from the three cultivars did not affect adipogenesis. Peel extracts however, from the Irwin and Nam Doc Mai cultivars inhibited adipogenesis, with most potent effects observed for the Nam Doc Mai peel extract. In contrast, Kensington Pride peel extract promoted adipogenesis. Inhibition of adipogenesis from the peel extracts was also associated with increases in the average nuclear area per cell. Similar effects were also observed when cells were treated with resveratrol, and suggest that Irwin and Nam Doc Mai extracts may act via pathways similar to resveratrol.
To further understand the differences between mango peel extract effects on adipogenesis, preparative HPLC fractions of methanol peel extracts from Irwin, Nam Doc Mai and Kensington Pride were studied. Peel extracts from the three cultivars were separated into four fractions and were evaluated for their effects on lipid accumulation, nuclei count and nuclear area in differentiating 3T3-L1 cells. From the three mango cultivars, the more polar peel fractions (1-3) inhibited lipid accumulation with greater potency than fraction 4. In the IW cultivar, the fraction containing the more lipophilic components (fraction 4) enhanced lipid accumulation, and in KP and NDM cultivars, fraction 4 promoted lipid accumulation greater than fractions 1-3. Mass spectrometry was used to evaluate the levels and types of compounds in all fractions. Within fraction 4, five long chain free fatty acids (palmitoleic, palmitic, linolenic, linoleic and oleic acid) as well as bis-fatty acid glycosides were detected. These compounds were not present in any other peel fractions. Free fatty acids have previously been reported to promote lipid accumulation during differentiation. In this study, lipophilic components appear to be responsible for the lipid accumulation promoting effects of some mango extracts and are the likely cause of the diversity of effects of peel extracts from different mango cultivars on lipid accumulation.
In summary, the results from this thesis demonstrate bioactive diversity across mango cultivars, as well as within parts of the fruit such as the peel and flesh. This work also highlights the unique phytochemical compositions between cultivars. These differences appear to greatly impact adipogenesis in 3T3-L1 cells, and chemopreventive activity in MCF-7 cells. Our work also demonstrates the applicability of high throughput techniques to nutritional bioactive research. Such an approach may accelerate our understanding of the nutritional benefits of tropical fruits such as mangoes, which have not been extensively studied.