Abstract
Phlorotannins are phloroglucinol-based phenolic compounds, occurring particularly in brown macroalgae, that have been recognized for their promising bioactive properties. In this study, the extraction of phlorotannins from Fucus vesiculosus was evaluated with particular emphasis on the influential parameters, including the solvent concentration, solvent-solid ratio, extraction temperature and extraction time, using a single-factor design followed by a Box-Behnken design. The maximum total phlorotannin content, determined using the 2,4-dimethoxybenzaldehyde (DMBA) method, corresponded to 2.92 ± 0.05 mg of phloroglucinol equivalents/g dry seaweed (mg PGE/g DS), and was achieved for extracts carried out with acetone 67% (v/v), a solvent-solid ratio of 70 mL/g and temperature at 25 °C. This crude extract, together with a semi-purified phlorotannin fraction, were further evaluated for their anti-enzymatic capacity against α-glucosidase, α-amylase and pancreatic lipase, both showing promising inhibitory effects, particularly against α-glucosidase for which a greater inhibitory effect was observed compared to the pharmaceutical drug acarbose (IC50 = 4.5 ± 0.8 and 0.82 ± 0.3 μg/mL, respectively, against 206.6 ± 25.1 μg/mL). Additionally, the ultra-high-pressure liquid chromatography coupled to mass spectrometry (UHPLC-MS) analysis carried out on the ethyl acetate fraction revealed the presence of fucols, fucophlorethols, fuhalols and several other phlorotannin derivatives. Moreover, possible new phlorotannin compounds, including fucofurodiphlorethol, fucofurotriphlorethol and fucofuropentaphlorethol, have been tentatively identified in this extract. Overall, this study provides evidence that F. vesiculosus phlorotannin-rich extracts hold potential for the management of the activity of α-glucosidase, α-amylase and pancreatic lipase, which are well known to be linked to metabolic disorders such as diabetes and obesity.
Highlights
Phlorotannins are phenolic compounds consisting of dehydro-oligomers or dehydro-polymers formed through the C–C and/or C–O–C oxidative coupling of phloroglucinol (1,3,5-trihydroxybenzene) monomeric units that is known to occur on brown macroalgae [1]
Phenolic compounds are soluble in solvents less polar than water, and the most common extractants used for these compounds are methanol, ethanol and acetone or aqueous mixtures of these
Differences in the extraction procedures and experimental protocols might be the explanation for the observation of such discrepancies, as well as other non-considered factors. These results suggest that phlorotannins from F. vesiculosus are important contributors to the antidiabetic and anti-obesity properties claimed for this species and that these compounds hold the potential to control blood glucose levels and overall energy intake through inhibition of α-glucosidase, α-amylase and pancreatic lipase
Summary
Phlorotannins are phenolic compounds consisting of dehydro-oligomers or dehydro-polymers formed through the C–C and/or C–O–C oxidative coupling of phloroglucinol (1,3,5-trihydroxybenzene) monomeric units that is known to occur on brown macroalgae [1] Species such Eisenia bicyclis, Ishige okamurae, Sargassum thunbergii, Sargassum fusiforme, Undaria pinnatifida and Ascophyllum nodosum, as well as algae belonging to the genera Cystophora, Ecklonia and Fucus, are examples of marine brown algae that have been reported as good sources of phlorotannins with promising health benefits including antioxidant, anti-inflammatory, antibacterial, anticancer, antidiabetic and anti-obesity properties [2]. Drugs 2019, 17, 162 have raised their interest in algae phenolics, triggering an exponential increase in the number of phlorotannins-related publications Among these algae, Fucus vesiculosus, commonly known as bladderwrack, appears as an interesting source of such compounds [3]. F. vesiculosus has long been harvested and used as a food source in far East Asian countries, and in some coastal countries in Western Europe and in Alaska [5], due to its remarkable therapeutic properties mainly for treating goiter and obesity [6], and cellulite, blood clot formations, rheumatoid arthritis, asthma, atherosclerosis, diabetes, psoriasis and skin diseases, cancer and other oxidative and inflammatory related conditions [7,8,9,10]
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