**1. Introduction**

With increasing awareness of functional properties of products from marine organisms, their attractiveness, both as a source of nutritious food items and stockpot of novel, biologically-active compounds, continuously expand [1]. The characteristic color of spines and armors of sea urchins are attributed to calcium salts of polyhydroxynaphthoquinone pigments derivatives—spinochromes and echinochromes—exhibiting a vast range of pharmacological activities. One of the most popular pigments is the echinochrome A (6-ethyl-2,3,5,7,8-pentahydroxy-1,4-naphthoquinone), which is known to be a biologically-active compound with antimicrobial, antialgal, and antioxidant activities [2]. Most of all, it has been ascertained that a treatment with echinochrome protected the mitochondrial functions in cardiomyocytes, against the acardiotoxic drugs (*tert*-Butyl hydroperoxide, sodium nitroprusside) [3]. There are controversial data in the literature, in terms of Ech's capacity to activate an immune response, some data suggest that Ech has an ability to activate inflammation, whereas others suggest that it can suppress inflammation [4,5]. Pharmacological studies in vitro and in vivo demonstrated that naphthoquinone pigments have a wide therapeutic latitude and are nontoxic, at therapeutic doses [6].

In Russia, echinochrome is produced from the sand dollar *Scaphechinus mirabilis*. It is the active substance in the cardioprotective and antioxidant drug Histochrome® (C (Ech) = 0.2 mg mL−1) and is available in ampoules, permitted for subconjunctival, parabulbar, or intravenous administration [7,8]. One of the main setbacks to the wide use of Ech, is its insolubility in aqueous solutions and high susceptibility to oxidative destruction. Improvement of therapeutic efficacy of drugs can be achieved by modifying the formulation technique, for instance, by means of polymeric systems. Marine natural edible polymers have been widely used in hydrogels, drug encapsulation, and drug delivery because of their benefits, comprising such advantages as biocompatibility, biodegradability, and adhesiveness [9,10].

In order to provide a stable and biocompatible environment to the Ech, polymeric matrix systems, based on polysaccharides from red algae, have been proposed to be suitable candidates for oral delivery [11]. Polysaccharides of red algae, carrageenans (CRGs) are a class of linear galactans with alternating 1,3- and 1,4-linked galactose residues (D- and G-units). Several types of these polysaccharides were identified, based on the structure of their disaccharide repeating units, the pattern of sulfation, and the presence of 3,6-anhydrogalactose (DA-unit), as a 4-linked residue [12]. The three most industrially-exploited types, in the order of increasing sulfation degrees and decreasing gelation capabilities, respectively, are the κ-, ι- and λ- CRGs. Natural CRGs are often hybrids of more than one of these units and are composed of several carrabiose moieties, the proportions and structures of which vary with species, the life stages of seaweeds, and the ecophysiological and developmental conditions [13–15]. CRGs are widely utilized due to their excellent physical properties, such as thickening, gelling, and stabilizing effects in the food industry [16,17]. CRGs have successfully become appealing tools in immunotherapy and drug delivery, due to their immuno-active features and valuable physical properties as gelling [18,19].

Recently we have established that Ech is incorporated into the CRG supramolecular structure, which results in formation of complexes with altered Ech properties, such as decreased oxidative degradation and improved solubility. Along with the suitable physico-chemical properties, an Ech complex with CRG, in mice, revealed a high gastroprotective activity, surpassing the effect of either of the components used alone [11].

Unravelling the influence of CRGs–Ech complexes on some immunological parameters (ROS formation in phagocytic cells, the cytokine production in human whole blood model) and on human epithelial cell monolayers, will provide essential information for the rational design of CRG-based matrices for Ech delivery, for oral administration. It would also inspire the design of new approaches in assessing the modification of biological properties of biomaterials, used in delivery systems. The aim of this work was to investigate the biological properties of Ech that was included in a CRG matrix.
