Xanthommatin is Behind the Antioxidant Activity of the Skin of Dosidicus gigas

Abstract

Marine bioactive compounds have been found in very different sources and exert a very vast array of activities. Squid skin, normally considered a discard, is a source of bioactive compounds such as pigments. Recovering these compounds is a potential means of valorizing seafood byproducts. Until now, the structure and molecular properties of the bioactive pigments in jumbo squid skin (JSS) have not been established. In this study, methanol–HCl (1%) pigment extracts from JSS were fractionated by open column chromatography and grouped by thin-layer chromatography in order to isolate antioxidant pigments. Antioxidant activity was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH●) and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS●+) radical scavenging assays and ferric reducing power (FRAP) assay. Fractions 11–34 were separated and grouped according to flow rate values (F1–F8). Fractions F1, F3, and F7 had the lowest IC50 against ABTS●+ per milligram, and fractions F3 and F7 showed the lowest IC50 in the FRAP assay. Finally, fraction F7 had the highest DPPH● scavenging activity. The chemical structure of the F7 fraction was characterized by infrared spectroscopy, 1H nuclear magnetic resonance, and electrospray ionization–mass spectrometry. One of the compounds identified in the fraction was xanthommatin (11-(3-amino-3-carboxypropanoyl)-1-hydroxy-5-oxo-5H-pyrido[3,2-a]phenoxazine-3-carboxylic acid) and their derivatives (hydro- and dihydroxanthommatin). The results show that JSS pigments contain ommochrome molecules like xanthommatin, to which the antioxidant activity can be attributed.

Chemical structure and antioxidant activity of cephalopod skin ommochrome pigment extracts

“…with antioxidants were obtained from squid skin using acidified ethanol (Aubourg et al, 2016) and acidified methanol (Chan-Higuera et al, 2019a, c). Moreover, the main ommochromes identified in squid skin pigmented extracts are xanthommatin and dihydroxhantommatin (Chan-Higuera et al, 2019c).…”

“…1 H-NMR spectroscopy analysis was employed to provide information regarding the chemical composition and conformation of the obtained pigments (Figure 2). In a recent study, using 1 H-NMR spectra Chan-Higuera et al (2019c) revealed the presence of xanthommatin (11-(3-amino-3-carboxypropanoyl)-1-hydroxy-5-oxo-5H-pyrido[3,2 a]phenoxazine-3-carboxylic acid) and its derivatives (hydro-and dihydroxanthommatin) in antioxidant pigments from the squid skin. These pigments are considered to be tryptophan-derived metabolites that come from the kynurenine pathway (Daniels & Reed, 2012).…”

In Vitro Antiplasmodium and Chloroquine Resistance Reversal Effects of Andrographolide

“…(2) Reducing Power Assay. Reducing power of each test compound was tested according to Oyaizu [21,22], where 1 ml of different concentrations of each of andrographolide (1 nM-1 mM) prepared in ethanol were mixed with 5 ml of a solution containing equal volumes of potassium ferricyanide [K 3 Fe(CN) 6 ] and PBS (200 mM and pH 6.5). e mixture was incubated for 20 min at room temperature, and then 2.5 ml of 10% TCA (w/v) was added to the mixture, and the mixture was centrifuged at 3000 rpm for 10 min.…”

“…e extent of the absorbance augmentation is directly proportional to the reducing power of the compound. Results are expressed as % of absorbance augmentation [21,22].…”

Characterization of the Jumbo Squid (Dosidicus gigas) Skin By-Product by Shotgun Proteomics and Protein-Based Bioinformatics

“…Peptides derived from a tryptic hydrolysate of jumbo squid skin exhibited strong inhibition of lipid peroxidation that was much higher than the natural antioxidant α-tocopherol [15]. Skin molecules as xanthommatin also showed in vitro antioxidant effects [16]. Additionally, cytotoxic, antimicrobial, anti-biofilm, angiotensin converting enzyme (ACE)-inhibitory peptides, and anti-tumoral properties have been demonstrated for skin ink and the hydrolyzed skin of different squid species [14,17,18].…”