Phlorotannins Remarkably Suppress the Formation of Nε-(Carboxymethyl)lysine in a Collagen-Glyoxal Environment

N ε-(Carboxymethyl)lysine (CML), which is formed by the glycation of collagen, is a skin-accumulating advanced glycation end product and has been shown to be deeply involved in diabetic osteopenia and skin aging. In this study, we prepared the phlorotannins of marine algal polyphenols from Japanese Lessoniaceae ( Ecklonia cava, Ecklonia kurome, cultured E. kurome, Ecklonia stolonifera, Eisenia nipponica, and Eisenia bicyclis) and evaluated their inhibitory activities against CML formation in a collagen-glyoxal environment. The level of CML formed from the glycation of collagen by glyoxal was detected using an enzyme-linked immunosorbent assay. Except for E. stolonifera, the level of CML formation in the treatment with crude phlorotannins at 0.16 µg/mL was found to be comparable to that in the treatment with 0.40 mM aminoguanidine hydrochloride (AG) which is a typical antiglycation agent. In the test using phloroglucinol and isolated eckols (eckol, fucofuroeckol A, phlorofucofuroeckol A, dieckol, and 8,8’-bieckol) at a concentration of 0.80 µg/mL, the level of CML formed was lower for each compound, except for phlorofucofuroeckol A, than the data obtained with the addition of 2.0 mM AG. The mass concentration of 0.80 µg/mL was converted to 6.3 µM for phloroglucinol, 2.2 µM for eckol, 1.7 µM for fucofuroeckol A, 1.3 µM for phlorofucofuroeckol A, and 1.1 µM for dieckol and 8,8’-bieckol. From a comparison of the molar concentrations, it was found that phloroglucinol and the eckols inhibited the formation of CML resulting from glycation of collagen by glyoxal at concentrations of approximately 317 to 1818 times lower than AG.

The Quest for Phenolic Compounds from Macroalgae: A Review of Extraction and Identification Methodologies

The current interest of the scientific community for the exploitation of high-value compounds from macroalgae is related to the increasing knowledge of their biological activities and health benefits. Macroalgae phenolic compounds, particularly phlorotannins, have gained particular attention due to their specific bioactivities, including antioxidant, antiproliferative, or antidiabetic. Notwithstanding, the characterization of macroalgae phenolic compounds is a multi-step task, with high challenges associated with their isolation and characterization, due to the highly complex and polysaccharide-rich matrix of macroalgae. Therefore, this fraction is far from being fully explored. In fact, a critical revision of the extraction and characterization methodologies already used in the analysis of phenolic compounds from macroalgae is lacking in the literature, and it is of uttermost importance to compile validated methodologies and discourage misleading practices. The aim of this review is to discuss the state-of-the-art of phenolic compounds already identified in green, red, and brown macroalgae, reviewing their structural classification, as well as critically discussing extraction methodologies, chromatographic separation techniques, and the analytical strategies for their characterization, including information about structural identification techniques and key spectroscopic profiles. For the first time, mass spectrometry data of phlorotannins, a chemical family quite exclusive of macroalgae, is compiled and discussed.

Evaluation of Anti-glycation Activities of Phlorotannins in Human and Bovine Serum Albumin-glyceraldehyde Models

The anti-glycation activities of phlorotannins contained in the Japanese Lessoniaceae ( Ecklonia cava, Eck. kurome, Eck. stolonifera, Eisenia arborea, and Eis. bicyclis) were tested using serum albumin-glyceraldehyde (GA) models. In the human serum albumin (HSA)-GA model and the bovine serum albumin (BSA)-GA model, the concentrations of crude phlorotannins at 50% inhibition (IC50) of fluorescent advanced glycation end products (AGEs) formation was in the range of 0.48 to 0.70 mg/mL and 0.52 to 0.75 mg/mL, respectively. In tests using phloroglucinol and purified phlorotannins (eckol, fucofuroeckol A, phlorofucofuroeckol A, dieckol, and 8,8'-bieckol), dieckol had the highest inhibitory activity (IC50: 5.5 × 102 μM) against fluorescent AGEs formation in HSA-GA model and showed about 18 times inhibition compared with aminoguanidine hydrochloride of positive control. In the BSA albumin model, 8,8'-bieckol had about 27 times AGEs formation inhibitory activity (IC50: 6.2 × 102 μM) against aminoguanidine hydrochloride. In tests on GA scavenging activity, it was shown that compounds with phloroglucinol tetramer or higher had a scavenging rate of 70%, or more, with a reaction time of 120 minutes. These results suggest that among the phlorotannins, in particular the dimers of eckol (dieckol and 8,8'-bieckol), there are effective compounds for inhibiting the formation of AGEs derived from GA.

Evaluation of Anti-glycation Activities of Phlorotannins in Human and Bovine Serum Albumin-methylglyoxal Models

In this study, the anti-glycation activities of phlorotannins contained in the Japanese Lessoniaceae ( Ecklonia cava, Eck. kurome, Eck. stolonifera, Eisenia arborea, and Eis. bicyclis) were tested using serum albumin-methlglyoxal (MGO) models. In the human serum albumin (HSA)-MGO model and the bovine serum albumin (BSA)-MGO model, the concentrations of crude phlorotannins at 50% inhibition (IC50) of fluorescent advanced glycation end products (AGEs) formation was in the range of 0.45 to 0.53 mg/mL and 0.43 to 0.53 mg/mL, respectively. Among the purified phlorotannins, phlorofucofuroeckol A with the benzobisbenzofuran skeleton had the highest inhibitory activities (IC50: 4.8 × 102 μM in HSA-MGO model and 4.1 × 102 μM in BSA-MGO model) against fluorescent AGEs formation, and showed about 13 times the inhibition in the HSA-MGO model, and about 20 times the inhibition in the BSA-MGO model, with respect to aminoguanidine hydrochloride, which was used as a positive control. In the test on MGO-scavenging activity using HPLC analysis, it showed that eckol and its simple dimers (dieckol and 8,8′-bieckol) had higher scavenging rate than aminoguanidine hydrochloride. In addition, it was revealed by liquid chromatography-electrospray ionization-mass spectrometry that eckol reacted with MGO and formed two adducts with it. These results strongly suggest that phlorotannins are novel and effective anti-glycation substances derived from natural plants.

Extraction and Identification of Phlorotannins from the Brown Alga, Sargassum fusiforme (Harvey) Setchell

Phlorotannins are a group of complex polymers of phloroglucinol (1,3,5-trihydroxybenzene), which are unique compounds from marine brown algae. In our present study, a procedure for extraction and enrichment of phlorotannins from S. fusiforme with highly antioxidant potentials was established. After comparison of different extraction methods, the optimal extraction conditions were established as follows. The freeze-dried seaweed powder was extracted with 30% ethanol-water solvent with a solid/liquid ratio of 1:5 at temperature of 25 °C for 30 min. After extraction, the phlorotannins were fractioned by different solvents, among which the ethyl acetate fraction exhibited both the highest total phlorotannin content (88.48 ± 0.30 mg PGE/100 mg extract) and the highest antioxidant activities. The extracts obtained from these locations were further purified and characterized using a modified UHPLC-QQQ-MS method. Compounds with 42 different molecular weights were detected and tentatively identified, among which the fuhalol-type phlorotannins were the dominant compounds, followed by phlorethols and fucophlorethols with diverse degree of polymerization. Eckol-type phlorotannins including some newly discovered carmalol derivatives were detected in Sargassum species for the first time. Our study not only described the complex phlorotannins composition in S. fusiforme, but also highlighted the challenges involved in structural elucidation of these compounds.