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This review article appraises the extraction methods, compositions, and bioactivities of the essential oils from the Citrus species (family: Rutaceae) endemic to Malaysia including C. aurantifolia, C. grandis, C. hystrix, and C. microcarpa. Generally, the fresh peels and leaves of the Citrus species were extracted using different methods such as steam and water distillation, Likens-Nikerson extraction, solvent extraction, and headspace solid-phase micro-extraction (HS-SPME). Most of the Citrus oils were found to be rich in monoterpene hydrocarbons with limonene (1) as the major component identified in the peels of C. aurantifolia (39.3%), C. grandis (81.6%–96.9%), and C. microcarpa (94.0%), while sabinene (19) was the major component in the peels of C. hystrix (36.4%–48.5%). In addition, citronellal (20) (61.7%–72.5%), linalool (18) (56.5%), and hedycaryol (23) (19.0%) were identified as the major components in the oil of C. hystrix leaves, C. grandis blossom and C. microcarpa leaves, respectively. The C. hystrix essential oil has been experimentally shown to have antimicrobial and antifeedant activities, while no bioactivity study has been reported on the essential oils of other Malaysian Citrus species.

Scurrula ferruginea (Jack) Danser is one of the mistletoe species belonging to Loranthaceae family, which grows on the branches of many deciduous trees in tropical countries. This study evaluated the antioxidant activities of S. ferruginea extracts. The cytotoxic activity of the selected extracts, which showed potent antioxidant activities, and high phenolic and flavonoid contents, were investigated in human breast cancer cell line (MDA-MB-231) and non-cancer human skin fibroblast cells (HSF-1184). The activities and characteristics varied depending on the different parts of S. ferruginea, solvent polarity, and concentrations of extracts. The stem methanol extract showed the highest amount of both phenolic (273.51 ± 4.84 mg gallic acid/g extract) and flavonoid contents (163.41 ± 4.62 mg catechin/g extract) and strong DPPH• radical scavenging (IC50 = 27.81 μg/mL) and metal chelation activity (IC50 = 80.20 μg/mL). The stem aqueous extract showed the highest ABTS•+ scavenging ability. The stem methanol and aqueous extracts exhibited dose-dependent cytotoxic activity against MDA-MB-231 cells with IC50 of 19.27 and 50.35 μg/mL, respectively. Furthermore, the extracts inhibited the migration and colony formation of MDA-MB-231 cells in a concentration-dependent manner. Morphological observations revealed hallmark properties of apoptosis in treated cells. The methanol extract induced an increase in ROS generation and mitochondrial depolarization in MDA-MB-231 cells, suggesting its potent apoptotic activity. The present study demonstrated that the S. ferruginea methanol extract mediated MDA-MB-231 cell growth inhibition via induction of apoptosis which was confirmed by Western blot analysis. It may be a potential anticancer agent; however, its in vivo anticancer activity needs to be investigated.

Discovery of new therapeutic agents from nature, especially plants is one of the promising approaches for treatment of various diseases. In traditional medicine Scurrula ferruginea is applied to treat some disorders. To the best of our knowledge, there are no investigations on antioxidant capacity and antimicrobial activities of S.ferruginea in Malaysia. The present study was conducted to determine total phenolic content, Fe2+ chelating activity, antioxidative and antimicrobial potential of flowers, leaves and stems of S.ferruginea extracts. Antioxidant capacity, and total phenolic content of extracts were evaluated using DPPH free radical scavenging and Folin-Ciocalteu assays. Antibacterial properties were evaluated by disc diffusion, minimum inhibitory concentration and minimum bactericidal concentration methods. Results indicated the highest total phenolic content for stem extract (309.069). All S. ferruginea extracts exhibited antioxidant activity in a dose dependent manner. Stem extract showed capacity to scavenge free radicals and it was also found to chelate Fe2+ better than others. All extracts presented moderate inhibition ability against selected bacteria. The most significant values of MIC and MBC were belonged to the stem extract. These findings suggest that acetone extracts of S. ferruginea, particularly stem extract, are potentially sources of antioxidant compounds.

Two new prenylated flavonoids, 4',5-dihydroxy-6,7-(2,2-dimethylpyrano)-2'-methoxy-8-γ,γ-dimethylallylflavone 1 and 3'-hydroxycycloartocarpin 2 along with six known flavonoids, 5,7-dihydroxy-4'-methoxy-8-prenylflavanone 3, isobavachalcone 4, pyranocycloartobiloxanthone A 5, artocarpin 6, chaplashin 7 and cycloartocarpin 8 were isolated for the first time from the leaves and the heartwoods of Artocarpus anisophyllus Miq. The structures of isolated flavonoids were elucidated spectroscopically using 1D and 2D NMR, FTIR, MS, UV and also by comparison with literature data. These flavonoids were screened for their antioxidant and tyrosinase inhibitory activities. The dichloromethane and ethyl acetate crude extracts together with 3'-hydroxycycloartocarpin 2, pyranocycloartobiloxanthone A 5 and artocarpin 6 showed DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity with SC 50 values of 80.2, 40.0, 152.9, 20.2 and 140.0 µg/mL in 30 min, respectively. Pyranocycloartobiloxanthone A 5 exhibited significant tyrosinase inhibitory activity against tyrosinase from mushroom with IC 50 values of 60.5 µg/mL.

Five prenylflavonoids and two prenylchalcones from Artocarpus lowii King, A. scortechinii King and A. teysmanii Miq., and acetylated derivatives of cycloheterophyllin and artonin E were investigated for their ability to inhibit arachidonic acid (AA), collagen and adenosine diphosphate (ADP)-induced platelet aggregation in human whole blood by using an electrical impedance method. Among the tested compounds, only cycloheterophyllin inhibited AA-induced platelet aggregation with an IC(50) value of 100.9 microM. It also showed strong inhibition against ADP-induced aggregation, with an IC(50) value of 57.1 microM. Isobavachalcone, 2',4'-dihydroxy-4-methoxy-3'-prenyldihydrochalcone, cycloartobiloxanthone, artonin E and artonin E triacetate showed selective inhibition against ADP-induced aggregation, with IC(50) values ranging from 55.3 to 192.0 microM, but did not show such effect against other inducers.

Justicia gendarussa methanolic leaf extracts from five different locations in the Southern region of Peninsular Malaysia and two flavonoids, kaempferol and naringenin, were tested for cytotoxic activity. Kaempferol and naringenin were two flavonoids detected in leaf extracts using gas chromatography-flame ionization detection (GC-FID). The results indicated that highest concentrations of kaempferol and naringenin were detected in leaves extracted from Mersing with 1591.80 mg/kg and 444.35 mg/kg, respectively. Positive correlations were observed between kaempferol and naringenin concentrations in all leaf extracts analysed with the Pearson method. The effects of kaempferol and naringenin from leaf extracts were examined on breast cancer cell lines (MDA-MB-231 and MDA-MB-468) using MTT assay. Leaf extract from Mersing showed high cytotoxicity against MDA-MB-468 and MDA-MB-231 with IC50 values of 23 μg/mL and 40 μg/mL, respectively, compared to other leaf extracts. Kaempferol possessed high cytotoxicity against MDA-MB-468 and MDA-MB-231 with IC50 values of 23 μg/mL and 34 μg/mL, respectively. These findings suggest that the presence of kaempferol in Mersing leaf extract contributed to high cytotoxicity of both MDA-MB-231 and MDA-MB-468 cancer cell lines.

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