In this study, the physicochemical, antioxidant, antibacterial properties, and the toxicity of propolis particles produced by stingless bee Heterotrigona itama found in Brunei Darussalam were investigated. Propolis particles of different sizes were extracted from raw propolis using various volume fractions of ethanol in water. Spectroscopic analyses were utilized to characterize the chemical structures, functional groups, as well as absorbance and fluorescence properties. The total antioxidant capacity of propolis particles, which was assessed using DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, was found to increase with volume fraction of ethanol. The maximum antioxidant capacity was as high as 317.65 mg ascorbic acid equivalent per gram of propolis particles. All of the propolis particles showed antibacterial activity against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The diameters of the inhibition zone were either significantly higher or equivalent to those of two standard antibiotics (rifampicin and streptomycin), suggesting strong antibacterial activity. The toxicity studies of propolis particles against Caenorhabditis elegans revealed that they are non-toxic after 24 h exposure. Overall findings suggest that H. itama propolis particles are not only an important source of natural antioxidants that could be beneficial for human health, but they have potentials as antimicrobial against bacteria.
The present study focused on the evaluation of phytochemical properties, essential mineral elements, and heavy metals contained in raw propolis produced by stingless bees Geniotrigona thoracica , Heterotrigona itama , and Tetrigona binghami found in the same ecological conditions and environment in Brunei Darussalam. The results indicated that propolis of the three stingless bee species mainly consisted of lipids (45.60–47.86%) and very low carbohydrate (0.17–0.48%) and protein contents (0.18–1.18%). The propolis was rich in mineral elements, thus good sources of minerals, while they contained low concentrations of all heavy metals. Propolis of the different bee species could be distinguished based on their mineral compositions. The vibrational and absorption spectra suggested that propolis contains π-conjugated aliphatic and aromatic compounds as well as aromatic acids having amine, ester, carbonyl, alkyl, and hydroxyl functional groups which might be attributed to the presence of phenolic and flavonoid compounds. The antioxidant capacity of the propolis, based on radical scavenging activity of their ethanol extract, was in line with their total phenolic content. The ethanol extract of the propolis also showed antimicrobial activities against four bacterial strains ( Bacillus subtilis, Staphylococcus aureus, Escherichia coli , and Pseudomonas aeruginosa ). The propolis showed slightly higher antibacterial activity against Gram-positive ( B. subtilis and S. aureus ) bacteria, indicating that the antimicrobial active compounds could be associated with flavonoids, which were quantified to be approximately comparable in all the propolis.
Chitosan is a natural polysaccharide that has ideal properties as a polymer nanoparticle for drug delivery applications because it is easy to synthesize, inexpensive, biocompatible, biodegradable, non-immunogenic, and non-toxic. In this study, chitosan nanoparticles were fabricated in an acidic solution in the presence of potassium persulfate using a microwave technique. The effects of the reaction time, temperature, and weight ratio of potassium persulfate/chitosan on the yield and particle size were evaluated. It was found that the yield increased non-linearly, whereas the size of chitosan nanoparticles was 3 nm in the absence of potassium persulfate, which tended to increase with an increase in the potassium persulfate concentration. The chitosan nanoparticles were also treated with samarium for fluorescence detection. The fluorescence intensity at 590 nm of samarium-treated chitosan nanoparticles increased by a factor of more than 20 when compared with the samarium ion itself and was significantly higher than that of the untreated chitosan nanoparticles. It is indicated that chitosan nanoparticles are not only useful for drug carriers, where the drug delivery can be traced by monitoring fluorescence emission, but with the photoemissive properties of chitosan nanoparticles treated with samarium, they could also be applicable as environmentally friendly photocatalysts for the photodegradation of discharged pollutants as well as efficient photosensitizers that participate in energy transfer.
Purpose Contact lenses have direct contact with the corneal surface and can induce sight‐threatening infection of the cornea known as Acanthamoeba keratitis. The objective of this study was to evaluate the dysprosium‐based nanoparticles (Dy‐based NPs), namely Fe3O4‐PEG‐Dy2O3 nanocomposites and Dy(OH)3 nanorods, as an active component against Acanthamoeba sp., as well as the possibility of their loading onto contact lenses as the drug administering vehicle to treat Acanthamoeba keratitis (AK). Methods The Dy‐based NPs were synthesized, and they were loaded onto commercial contact lenses. The loading content of the NPs and their release kinetics was determined based on the absorbance of their colloidal solution before and after soaking the contact lenses. The cytotoxicity of the NPs was evaluated, and the IC50 values of their antiamoebic activity against Acanthamoeba sp. were determined by MTT colorimetric assay, followed by observation on the morphological changes by using light microscopy. The mechanism of action of the Dy‐based NPs against Acanthamoeba sp. was evaluated by DNA laddering assays. Results The loading efficiencies of the Dy‐based NPs onto the contact lens were in the range of 30.6–36.1% with respect to their initial concentration (0.5 mg ml–1). The Dy NPs were released with the flux approximately 5.5–11 μg cm–2 hr–1, and the release was completed within 10 hr. The emission of the NPs consistently showed a peak at 575 nm due to Dy3+ ion, offering the possible monitoring and tracking of the NPs. The SEM images indicated the NPs are aggregated on the surface of the contact lenses. The DNA ladder assay suggested that the cells underwent DNA fragmentation, and the cell death was due most probably to necrosis, rather than apoptosis. The cytotoxicity assay of Acanthamoeba sp. suggested that Fe3O4‐PEG, Fe3O4‐PEG‐Dy2O3, Dy(NO3)3.6H2O and Dy(OH)3 NPs have an antiamoebic activity with the IC50 value being 4.5, 5.0, 9.5 and 22.5 μg ml–1, respectively. Conclusions Overall findings in this study suggested that the Dy‐based NPs can be considered as active antiamoebic agents and possess the potential as drugs against Acanthamoeba sp. The NPs could be loaded onto the contact lenses; thus, they can be potentially utilized to treat Acanthamoeba keratitis (AK).
In the present study, the antibacterial activities of ethanolic and water extracts of propolis produced by stingless bees Tetrigona binghami, Heterotrigona itama, and Geniotrigona thoracica found in Brunei against four different bacterial strains were quantified. Additionally, spectroscopic and colorimetric methods, including Fourier transform infrared, absorption, fluorescence, aluminum chloride, and Folin-Ciocalteu analyses were used to characterize the propolis extracts. Flavonoid, phenolic, and aromatic acid compounds in the propolis extracts were also quantified, as these compounds are responsible for their antioxidant capacity. The antibacterial activity was determined based on bacterial growth inhibition zones using the disc diffusion, and it was further confirmed by the minimum inhibitory and bactericidal concentrations, which were evaluated using the broth macrodilution method. The propolis extracts exhibited antibacterial activities but were lower compared to streptomycin, which was used as a standard antibiotic. The MIC values of the water extracts were 2500 μg/mL, and those of the ethanolic extracts were in the range of 2500‒10000 μg/mL, much higher than other reported propolis from different countries. Their MBC test further suggested that the propolis extracts were bacteriostatic. The overall findings evidenced the quantities of the antibacterial and antioxidant properties of the propolis extracts, although the results suggested low antibacterial activities of the propolis extracts from Brunei stingless bees.
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