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Abstract
The population of overweight and obese people, including children and adults, has increased markedly during the past several decades. Obesity has been recognised as a prerequisite condition associated with increased risk of cancers such as colon and rectum, kidney, pancreas, thyroid, gallbladder, and possibly other cancer types. Population suffering from obesity have also a higher risk of coronary heart disease, stroke, high blood pressure, diabetes, and a number of other chronic diseases. A high intake of fruits, herbs and vegetables is associated with a reduction of cardiovascular incidences. Numerous studies have confirmed that phytochemicals within plant foods are proposed are responsible for much of their health-protective effects. An ethnobotanical approach, with a systematic evaluation of traditional uses of indigenous plant foods, represents an effective method of selecting candidates for research. Indigenous plants have long history of use and recently they are promoted to commercial production nationally and internationally. Native Australian plants provide a possible source of novel health-promoting phytochemicals due to an extensive history of the uses of locally available plants by the Australian Aboriginal population, the unique characteristics of the Australian environment and, finally, the recent scientific evidences of their biological activities.
The aim of the present research was to evaluate potential health-promoting properties of three selected commercially grown native Australian herbs: Tasmannia pepper leaf (Tasmannia lanceolata, Winteraceae), anise myrtle (Syzygium anisatum, Myrtaceae) and lemon myrtle (Backhousia citriodora, Myrtaceae) and two fruits: Davidson s plum (Davidsonia pruriens F. Muell., Cunoniaceae) and quandong (Santalum acuminatum, A.D.C., Santalaceae). Bay leaf (Laurus Nobilis, Lauraceae) as well as rabbit eye (Vaccinium ashei) and southern highbush (V.darrowii x V. corymbosum) blueberries were also included as reference samples.
Polyphenolic-rich extracts obtained from these plant sources were characterised with regards to their composition and antioxidant capacitates using an array of both, reagent-based and cellular-based assays. Total phenolics (TP), ferric ion reducing antioxidant power (FRAP) assay and oxygen radical absorbance capacity (ORAC) assay showed that Tasmannia pepper leaf extract had 3-times higher level of total phenolics (911.9 ± 58 mg GA E/gDW) and was followed by anise myrtle and lemon myrtle (2.3- and 2.0-times, respectively greater than that of bay leaf). Tasmannia pepper leaf extract exhibited an outstanding ORAC values (12789 ± 996 μMol Trolox E/gDW), and also displayed the greatest antioxidant activity in the cellular antioxidant activity (CAA) assay (154.6 ± 1.17 μmol Q E/gDW). Tasmannia pepper leaf extract contained the highest level of total flavonoids (255.9 ± 3.3 mg Cat E/gDW). Ellagic acid and derivatives were the dominant compounds of anise myrtle (67.0%) and lemon myrtle (46.2%) fractions, accompanied by flavonoids (catechin, myricetin, hesperetin, quercetin). Tasmannia pepper leaf extract comprised of chlorogenic acid (28.8%) coupled with quercetin (11.39%). Tasmannia pepper leaf extract, inhibited efficiently the activity of α-glucosidase (IC50: 0.83 mg/mL) and pancreatic lipase (IC50: 0.60 mg/mL). Anise myrtle and lemon myrtle extracts had a pronounced -glucosidase inhibitory activities (IC50: 0.30 and 0.13 mg/mL, respectively) and were less effective against lipase. Tasmannia pepper leaf applied at a concentration of 1.0 mg/mL inhibited the activity of angiotensin converting enzyme (ACE) in 29.6%, and was closely followed by anise myrtle extract (25.6%).
Davidson s plum extract contained predominantly ellagic acid and ellagitannins (18.1%) accompanied by flavonoids (myricetin, quercetin, rutin, and anthocyanins) and had the highest level of total phenolic (949 ± 239 mg GA E/gDW). Davidson s plum extract also exhibited superior antioxidant capacity (FRAP: 9258 ± 926 μmol Fe+2/gDWand ORAC: 8791.5 ± 370 μMol Trolox E/gDW) to quandong, rabbit eye and southern highbush blueberry. It had similar inhibitory activities against isolated -glucosidase enzyme (IC50 of 0.13 mg/mL) to rabbit eye and southern highbush blueberry (IC50 = 0.097 and 0.091 mg/mL, respectively) and was the most efficient inhibitor of angiotensin converting-enzyme (ACE 91.2% inhibition at extract concentration of 1 mg/mL). Quandong extract comprised hydroxycinnamic acids, quercetin and cyanidin 3-glucoside, and was the most effective against pancreatic lipase (IC50: 0.60 mg/mL). Various levels of correlation between the level of isolated digestive enzyme-inhibitory activities and total phenolics and antioxidant capacities were identified, indicating a specificity of individual phenolic compounds present in the isolated fractions to complex with proteins.
Purified polyphenolic-rich extracts obtained from herbs and fruits were further evaluated for potential chemopreventive effects using a wide range of assays to assess cytoprotective, anti-proliferative, pro-apoptotic and anti-inflammatory activities. The evaluation of cytoprotective and anti-proliferative activities was conducted using a variety of cancer (HT-29; colorectal adenocarcinoma, AGS: gastric adenocarcinoma, HepG2: hepatocellular carcinoma and BL-13; bladder) and equivalent normal (CCD-18Co; colon normal and Hs738.St/Int; mixed stomach and intestine normal) cell lines. All herb and fruit extracts reduced the proliferation of cancer cell, with anise myrtle exhibiting an outstanding anti-proliferative effect. No significant reduction of cell viability of non-transformed cells (CCD-18Co and Hs 738.St/Int) was observed. The suppression of the proliferation of cancer cells was due to induction of apoptosis, as identified based on flow cytometry analysis of acute promyelocytic leukaemia cancer (HL-60) cells. This was confirmed by identified induction of caspase-3 activity. The results of the CBMNCyt assay suggested no direct DNA damage in HT-29 cells as a result of treatment with all extracts, applied at final concentrations of 0.5 and 1.0 mg/mL. The results of this study revealed a number of potential health-promoting properties of phytochemicals obtained from native Australian herbs and fruits.
Finally, anti-inflammatory activity of polyphenolic-rich extracts has been assessed by measuring their effect on the production of nitric oxide (NO ) concentration and prostaglandins E2 (PGE2) in LPS activated hepatocellular carcinoma (HepG2) model. With the exception of lemon myrtle, all evaluated extracts inhibited production of nitric oxide (NO ). All extracts inhibited the release of prostaglandin E2 (PGE2). Tasmannia pepper leaf was the most effective in inhibiting nitric oxide (NO ) release at 400 μg/mL and Davidson s plum showed the greatest effect in inhibition of prostaglandin E2 (PGE2) production. These results suggested that herbs and fruits extracts down-regulated the key enzymes involved inflammatory process: inducible nitric synthase (iNOS) and cyclooxygenase (COX-2).
In summary, this is the first study which revealed valuable health attributes of the selected commercially grown native Australian herbs and fruits. Future studies should be conducted to confirm these results at in vivo levels. If confirmed, these results would suggest potential application of these plants as a novel source for nutraceutical/food industry.