Determination of bioactive properties of food grade extracts from Icelandic edible brown seaweed sugar kelp (Saccharina latissima) with in vitro human cell cultures (THP-1)

Abstract

Background: Sugar kelp (Saccharina latissima, formerly known as Laminaria saccharina) is a brown seaweed which naturally occurs in the North Atlantic. Seaweeds may be one of the last natural food resources abundantly available. They are known to contain many compounds which may have additional functional benefits. This edible seaweed is characterized by high content of nutrients including carbohydrates and polyphenols, which are recognized antioxidants. Because their natural environment is a 3% saline solution, they are very resistant to mild extraction methods. However, extracts from solvent extractions usually contain residual solvents, making them unacceptable for high quality functional foods and high end cosmetics. The objective of this study was to test the biological properties of three extracts from sugar kelp (Saccharina latissima).

Methods: Cold water, hot water, and ethanol: water (70:30 v/v) extracts were prepared. Total Carbohydrate Content (TCC) was determined by the phenol - sulphuric acid method and values were expressed as mg of fucose/g of dry extract. Total Polyphenol Content (TPC) was determined and expressed as mg of Gallic Acid Equivalent (GAE)/100g of dry extract. Oxygen Radical Absorbance Capacity (ORAC) assay was performed for all extracts and values were expressed as mu M of Trolox (R) Equivalent/g of dry extract. Human leukemia monocytic cell line (THP-1) was used to investigate the bioactivity of Saccharina extracts. Extracts were applied to PMA differentiated THP-1 cells. Cytotoxicity of derived extracts was assessed by light microscopy followed by XTT proliferation assay. Enzyme-linked Immunosorbent assays (ELISA) were performed to determine secretion of interleukin - 10 (IL-10), tumor necrosis factor - alpha (TNF-alpha) and interleukin - 6 (IL-6).

Results: The cold water extract exhibited very toxic properties toward macrophages and was thereby excluded from the experimental proceedings with use of the macrophages. Among all the tested extracts, the hot water extract was richest in sugars (682 +/- 243 mg fucose/g dry extract) and polyphenols (96.5 +/- 5.6 mg GAE/g dry extract), which was correlated to the determined ORAC values (1686 +/- 99 mu M TE/g dry extract). The addition of hot water and ethanol extracts at concentrations 100 mu g/ml triggered secretion of pro-inflammatory cytokine TNF-alpha suggesting immunomodulatory properties of Saccharina extracts toward macrophages.

Conclusions: The present study suggests that carbohydrate enriched extracts from Icelandic edible seaweed Saccharina latissima have antioxidant and immunomodulatory properties towards human THP-1 derived macrophages. The carbohydrate and polyphenol correlated with ORAC values confirming antioxidant properties of the derived extracts. The hot water extract affected the pro-inflammatory (TNF-alpha) and anti-inflammatory (IL-10) cytokine secretion in macrophages, suggesting their bioactivity through immunomodulatory actions and can be considered for practical applications in functional foods and cosmetics.