In vitro Properties of Methanol Extract and Sodium Alginate of Sargassum polycystum C. Agardh Brown Seaweed Collected from Malaysia.

The edible brown seaweed, Sargassum polycystum C. Agardh was harvested from the coastal region of Malaysia. In this study, analysis of the nutrition and metal content in the methanol extract showed positive for sodium, potassium, magnesium, vitamins A and E and arsenic contamination. The brine shrimp lethality assay (BSLA) revealed the extract to be non-toxic with LC50 value of 15.60 mg mL-1 (LC50 > 1). The antioxidant and antibacterial activities of the methanol extract were measured through various bioassays. The structural and physicochemical characterisation of the NaAlg, analysed through the 1H-NMR analysis revealed the M:G ratio of NaAlg at 0.733 with mannuronic (M) and guluronic (G) fractions at F M = 0.423 and F G = 0.577, respectively. The degraded NaAlg through methods of ultraviolet irradiation and sonication showed an increment in the in vivo antioxidant activities at intervals of 15 min, 30 min, 60 min, 90 min and 120 min. The Fourier transform infrared spectroscopy (FTIR) spectra of polysaccharides taken before and after UV irradiation showed breakage of covalent bonds and thus, increase in the intensity of both O-H and C-O stretching vibrations. Therefore, the increment in antioxidant activities observed in the treated samples were related to changes seen in their molecular structures.

Rumpai laut coklat yang boleh dimakan, Sargassum polycystum C. Agardh dituai dari kawasan pantai Malaysia. Dalam kajian ini, analisis kandungan nutrisi dan logam dalam ekstrak metanol menunjukkan ia positif untuk natrium, kalium, magnesium, vitamin A dan E dan pencemaran arsenik. Brine shrimp lethality assay (BSLA) mendedahkan ekstrak tersebut tidak bertoksik dengan nilai LC50 15.60 mg mL−1 (LC50 > 1). Aktiviti antioksidan dan antibakteria ekstrak metanol diukur melalui pelbagai bioassai. Pencirian struktur dan fizik NaAlg yang dianalisis melalui analisis 1H-NMR, mendedahkan nisbah M:G NaAlg pada 0.733 dengan pecahan manuronik (M) dan guluronik (G) masing-masing pada FM = 0.423 dan FG = 0.577. NaAlg yang dinyahgred melalui kaedah sinaran ultraviolet (UV) dan sonikasi menunjukkan peningkatan dalam aktiviti antioksidan in vivo pada selang masa 15 minit, 30 minit, 60 minit, 90 minit dan 120 minit. Spektra FTIR polisakarida yang diambil sebelum dan selepas sinaran UV menunjukkan kerosakan ikatan kovalen dan dengan itu, peningkatan dalam keamatan kedua-dua getaran regangan O­H dan C­O. Oleh itu, peningkatan dalam aktiviti antioksidan yang diperhatikan dalam sampel yang dirawat berkait dengan perubahan yang dilihat dalam struktur molekul.

Larvicidal activity, inhibition effect on development, histopathological alteration and morphological aberration induced by seaweed extracts in Aedes aegypti (Diptera: Culicidae).

OBJECTIVE: To investigate the larvicidal activity, inhibition effect on development, histopathological alteration and morphological aberration induced by the extracts derived from seaweeds Bryopsis pennata (B. pennata), Sargassum binderi (S. binderi) and Padina australis in Aedes aegypti (Ae. aegypti) larvae and to characterize the phytochemical components of the three seaweeds. METHODS: Larvicidal activity of the seaweeds towards the larvae of Ae. aegypti was determined according to WHO. The inhibition effect of seaweeds was assessed by determining the mortality, adult emergence rate, larval and pupa duration of the treated larvae. Histopathological effect on midgut epithelium of larvae and morphological aberration induced by the methanol extracts were examined. Phytochemical analysis was done to determine the presence of alkaloids, saponins, steroids and terpenoids in the seaweeds. RESULTS: Chloroform partition of B. pennata extract exhibited the strongest larvicidal activity (LC50 = 82.55 µg/mL), followed by methanol extract of B. pennata (LC50 = 160.07 µg/mL) and chloroform partition of S. binderi extract (LC50 = 192.43 µg/mL). The methanol extract of S. binderi exhibited the strongest effect on prolongation of larval period (1.5-fold longer as compared to control) and resulted in strongest inhibition effect in adult emergence (98.67%). The histopathological study showed that larvae treated with seaweed extracts had cytopathological alteration of the midgut epithelium. The morphological observation revealed that the anal papillae and terminal spiracles of larvae were the common sites of aberrations. CONCLUSIONS: The study provided information on various effects of seaweed extracts on Ae. aegypti. Further investigation on identifying the active compounds and their mechanisms of action is recommended.

Mosquitocidal and Oviposition Repellent Activities of the Extracts of Seaweed Bryopsis pennata on Aedes aegypti and Aedes albopictus.

The ever-increasing threat from infectious diseases and the development of insecticide resistance in mosquito populations drive the global search for new natural insecticides. The aims of this study were to evaluate the mosquitocidal activity of the extracts of seaweed Bryopsis pennata against dengue vectors Aedes aegypti and Aedes albopictus, and determine the seaweed's toxic effect on brine shrimp nauplii (as a non-target organism). In addition, the chemical compositions of the active larvicidal extract and fraction were analyzed by using liquid chromatography-mass spectrometry (LC-MS). Chloroform extract exhibited strong ovicidal activity (with LC50 values of 229.3 and 250.5 µg/mL) and larvicidal activity against Ae. aegypti and Ae. albopictus. The larvicidal potential of chloroform extract was further ascertained when its A7 fraction exhibited strong toxic effect against Ae. aegypti (LC50 = 4.7 µg/mL) and Ae. albopictus (LC50 = 5.3 µg/mL). LC-MS analysis of the chloroform extract gave a tentative identification of 13 compounds; Bis-(3-oxoundecyl) tetrasulfide was identified as the major compound in A7 fraction. Methanol extract showed strong repellent effect against female oviposition, along with weak adulticidal activity against mosquito and weak toxicity against brine shrimp nauplii. The mosquitocidal results of B. pennata suggest further investigation for the development of effective insecticide.

The major bioactive components of seaweeds and their mosquitocidal potential.

Seaweeds are one of the most widely studied natural resources for their biological activities. Novel seaweed compounds with unique chemical structures have been reported for their pharmacological properties. The urge to search for novel insecticidal compound with a new mode of action for development of botanical insecticides supports the relevant scientific research on discovering the bioactive compounds in seaweeds. The mosquitocidal potential of seaweed extracts and their isolated compounds are documented in this review paper, along with the discussion on bioactivities of the major components of seaweeds such as polysaccharides, phenolics, proteins, terpenes, lipids, and halogenated compounds. The effects of seaweed extracts and compounds toward different life stages of mosquito (egg, larva, pupa, and adult), its growth, development, and reproduction are elaborated. The structure-activity relationships of mosquitocidal compounds are discussed to extrapolate the possible chemical characteristics of seaweed compounds responsible for insecticidal properties. Furthermore, the possible target sites and mode of actions of the mosquitocidal seaweed compounds are included in this paper. The potential synergistic effects between seaweeds and commercial insecticides as well as the toxic effects of seaweed extracts and compounds toward other insects and non-target organisms in the same habitat are also described. On top of that, various factors that influence the mosquitocidal potential of seaweeds, such as abiotic and biotic variables, sample preparation, test procedures, and considerations for a precise experimental design are discussed. The potential of active seaweed extracts and compounds in the development of effective bioinsecticide are also discussed.