*3.4. Anti-Inflammatory Activity of Lipids and Fatty Acids from Sea Cucumbers*

Lipids are best known for their integral role in biological membranes and as signaling molecules in the cytoplasm. Sea cucumbers are rich sources of lipids, phospholipids, and various fatty acids that exert a wide variety of biological activities. Eicosapentaenoic acid (EPA), isolated from *Cucumaria frondosa*, has a potent anti-obesity effect and modulates the peroxisome proliferator activated receptor γ (PPARγ) signaling in the inflammatory condition of insulin resistance, as well as type 2 diabetes [57,58]. Phosphatidylcholine (EPA-PC) (Figure 4: (**7**)) and phosphatidylethanolamine (EPA-PE) (Figure 4: (**8**)) from *Cucumaria frondosa* improve chronic inflammation and alter the interaction between macrophages and adipocytes [59,60]. Moreover, EPA-PC and EPA-PE diminish chronic inflammation by promoting the M2-dominant polarization of macrophages in white adipose tissue, as observed in 3T3L1 and RAW264.7 transwell coculture. EPA-PC and EPA-PE also inhibit the transactivation of NF-κB in RAW264.7 macrophages and upregulate PPARγ expression in 3T3-L1 adipocytes in the coculture, indicating that they may alleviate adipose tissue inflammation [59,60]. Both EPA-PC and EPA-PE reduced the serum TNFα, IL-6, and monocyte chemoattractant protein (MCP), increased the serum heme oxygenase-1 (HO-1) levels (one of the most abundant enzymes involved in oxidative stress and with antiinflammatory properties), and attenuated macrophage infiltration in the liver and adipose tissue of high-fat high-sucrose diet-induced inflammation in mice [61]. Moreover, EPA-PC inhibited amyloid β-protein-induced neurotoxicity by alleviating the NLR family pyrin

domain-containing 3 (NLRP3) inflammasome in an Alzheimer's disease rat model [62]. EPA phospholipids derived from *Cucumaria frondosa* mitigated obesity-induced inflammation by reducing TNFα and IL-6 in the serum of diet-induced obese mice [63]. A fatty acid-rich fraction (n-hexane phase) of *Apostichopus japonicus* has shown several immunomodulatory activities in an ovalbumin-induced allergic airway inflammation mouse model and in splenocytes [64]. This fraction reduced eosinophil infiltration and goblet cell hyperplasia and attenuated IL-4, IL-5, IL-13, and IL-17 in the spleen and bronchoalveolar lavage fluid of mice. It also increased the expression of anti-inflammatory cytokines (TGFβ and IL-10) in bronchoalveolar lavage fluid and a splenocyte culture medium [64]. FrondanolTM is a nutraceutical lipid extract (rich in 12-methyltetradecanoic acid (Figure 4: (**9**)) and myristoleic acid (Figure 4: (**10**))) of the intestines of the edible Atlantic sea cucumber *Cucumaria frondosa*. Frondanol has potent anti-inflammatory activity and has been shown to attenuate inflammation in an adjuvant arthritis rat model, as well as an ear edema mouse model [65]. It also potently inhibits lipoxygenase (LOX) pathways, reducing leukotriene production in human polymorphonuclear cells [65]. More recently, Subramanya et al. [16] demonstrated that chronic treatment with Frondanol decreased inflammation in a DSS-induced colitis mouse model. Frondanol markedly reduced proinflammatory cytokine mRNA expression in colon tissue and cytokine levels in the circulation, while inhibiting production of the proinflammatory mediator leukotriene B4 (LTB4) [16]. Sphingolipids isolated from *Cucumaria frondosa* decrease the serum proinflammatory cytokines, as well as mRNA expression in the adipose tissue of obese mice by the inhibition of phosphorylated JNK, IκB, and NF-κB nuclear translocation [66]. Furthermore, these sphingolipids attenuated renal fibrosis and inflammation via the inactivation of TGFβ/Smad signaling pathway in STZ-HFD-fed type 2 diabetic mice [67]. The cerebrosides and glucosylceramides extracted from *Cucumaria frondosa* reduced the expression of proinflammatory cytokines and thereby improved the insulin sensitivity in adipose tissues of high-fructose diet-fed rats [68].

**Figure 4.** Structures of anti-inflammatory fatty acid derivatives derived from sea cucumbers (structures (**7**) and (**8**) re-used from reference [59]).

#### *3.5. Anti-Inflammatory Activity of Miscellaneous Crude Extracts of Sea Cucumbers*

Several aqueous and organic solvent-extracted fractions of various sea cucumber species have shown marked anti-inflammatory activity in various in vivo and in vitro models. Frondanol A5 (isopropyl alcohol/water extract of epithelium from the sea cucumber *Cucumaria frondosa*) decreased the production of inflammatory cytokines, such as IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12, IL-17A, interferon gamma (IFNγ), and TNFα, in an

APCMin/+ mouse model [69]. Additionally, Frondanol A5 also suppressed the mRNA expression of inflammatory markers (5-LOX and 5-lipoxygenase activating protein (FLAP)) and an angiogenesis marker in intestinal tumors [69]. An ethyl-acetate fraction (which contains mostly phenolic compounds) of the sea cucumber *Holothuria scabra* attenuates inflammation in vitro by inhibiting the production of NO and proinflammatory cytokines via the NF-κB and JNK pathways [70]. The ethyl-acetate fraction from another sea cucumber species, *Stichopus japonicus*, markedly reduced inflammation by inhibiting the production of NO and PGE2 (via downregulating the iNOS and COX-2 gene expression). Moreover, the fraction was shown to suppress the transcription of proinflammatory cytokines in LPSstimulated murine macrophages through suppression of the phosphorylation of MAPK [71]. An aqueous fraction of *Stichopus japonicus* reduced production of the proinflammatory cytokines IL-6, and TNFα in LPS-stimulated macrophages and inhibited antigen-induced mast cell degranulation and IL-4 mRNA expression in antigen-stimulated RBL-2H3 rat basophil [72]. An aqueous extract of the sea cucumber *Stichopus chloronotus* demonstrated both anti-inflammatory and antioxidative activities by upregulating cartilage-specific markers such as collagen type II, aggrecan core protein, and SRY-Box transcription factor 9 (sox-9) expression and downregulating collagen type 1, IL-1, IL-6, IL-8, matrix metalloproteinases (MMP)-1, MMP-3, MMP-13, COX-2, iNOS, and protease-activated receptor 2 (PAR-2) expression [73]. An aqueous extract of *Holothuria polii* attenuated the levels of the inflammatory markers IL-6, NO, and MMP-9 in mouse mammary epithelial SCp2 cells and the levels of IL-1β produced in THP-1 human monocytes [74]. A methanol body wall extract of the sea cucumber *Holothuria atra* downregulated the proinflammatory cytokines TNFα, and IL-1β in a cecal ligation and puncture rat model [75]. The body wall preparation of *Isostichopus badionotus* suppressed the expression of proinflammatory genes, including TNFα, iNOS, COX-2, NF-κB, and IL-6, in a mouse ear inflammation model [76]. Ethanol extracts obtained from four species of sea cucumbers belonging to the family Holothuriidae (namely, Holothuriidae ni1, Holothuriidae ni2, Holothuriidae ni3, and Holothuriidae ni4) showed potent antioxidant and COX-2 inhibitory activities in vitro [77].


**Table 1.** Anti-inflammatory bioactive compounds and extracts derived from sea cucumbers.

## **Table 1.** *Cont.*



#### **Table 1.** *Cont.*

#### **4. Anti-Inflammatory Compounds from Sea Urchins**

Sea urchins are seafloor-dwelling invertebrates belonging to the phylum Echinodermata that have high nutritional and medicinal properties. They are rich in vitamins, minerals, proteins, fatty acids, and polysaccharides and possess anticancer, anticoagulant/antithrombotic, antimicrobial, anti-inflammatory, and antioxidant properties. The extracts and hydrolysates of sea urchins contain various bioactive compounds, especially glycosides, pigments, sphingolipids, glycolipids, sulphate, and phospholipids [78]. The anti-inflammatory properties of various active components isolated from sea urchins are summarized in Table 2.
