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ObjectiveTo find biological functions such as antibacterial and antioxidant activities in several tropical plants and to investigate the possibility of antibiotic substitute agents to prevent and treat diseases caused by pathogenic bacteria.MethodsPlants such as Poncirus trifoliata fruit (Makrut), Zingiber officinale Rosc (Khing), Areca catechu L. (Mak), Solanum melongena L. I (Makkhuayao), and Solanum melongena L. II (Makhurapro) were extracted by methanol, n-hexane, chloroform, ethyl acetate, butanol and water. The free radical scavenging activities were measured using 2-diphenyl-2-picryl hydrazyl photometric assay. Antibacterial activities with a minimum inhibitory concentration (MIC) were observed by agar diffusion assay against pathogenic strains of Escherichia coli, Burkholderia sp., Haemopilus somnus, Haemopilus parasuis, Clostridium perfringens, and Pantoea agglomerans.ResultsPoncirus trifoliata fruit methanol extract showed antibacterial activities against gram-negative and gram-positive pathogens. Additionally, this showed the strongest antibacterial activity against Burkholderia sp. and Haemopilus somnus with MIC 131 μg/mL, respectively. Areca catechu L. water extract showed antibacterial activities against Burkholderia sp., Haemopilus somnus, and Haemopilus parasuis. The MIC value for Haemopilus parasuis was 105 μg/mL in this. Antioxidant activity of Zingiber officinale Rosc n-hexane extract showed 2.23 mg/mL effective concentration 50% (EC50) value was the highest activity among tropical plants extracts. Total polyphenol content in Zingiber officinale Rosc methanol extract was 48.4 μg/mL and flavonoid content was 22.1 μg/mL showed the highest values among tested plants extracts.ConclusionTaken together, these results suggest that tropical plants used in this study may have a potential benefit as an alternative antibiotics agent through their antibacterial and antioxidant activities.

To examine the neuroprotective effects of black galingale, its protection was tested against glutamate-induced neurotoxicity in primary cortical cultured neurons. It was found that an aqueous extract of this medicinal plant exhibited significant protection against glutamate-induced toxicity in primary cultured rat cortical cells. In order to clarify the neuroprotective mechanism(s) of this observed effect, isolation was performed to seek and identify active fractions and components. By such fractionation, bioactive methoxyflavone derivatives were isolated from the methanol extracts from the air-dried rhizomes of black galingale. 5-Hydroxy-3,7,3',4'-tetramethoxyflavone exhibited significant neuroprotective activities against glutamate-induced toxicity, exhibiting cell viability of about 60-70%, at concentrations ranging from 0.1 μm to 10 μm. Therefore, the neuroprotective effect of black galingale might be due to the inhibition of glutamate-induced toxicity by the methoxyflavone derivatives it contains.

The roots of black galingale (Kaempferia parviflora) were chloroform-extracted and the isolated two sesquiterpene and immunotoxicity effects were studied. The structures and stereochemistry of these compounds were established on the basis of analysis of spectra including UV, MS, (1)H-NMR, and (13)C-NMR as follows: 1 (4α-acetoxycadina-2,9-diene-1,8-dione), 2 (1α,3α,4β-trihydroxy-9-cadinen-8-one). Compound 2 had a significant toxic effect against early fourth-stage larvae of Aedes aegypti L. with an LC(50) value of 0.7 μM and an LC(90) value of 3.8 μM. The results could be useful in search for newer, safer, and more effective natural immunotoxicity agents against A. aegypti.