Numerous studies have reported the anti-inflammatory properties of COS. In a study conducted by Yoon
et al. to investigate the effect of COS on LPS-stimulated RAW 264.7 cells, the researchers discovered that COS exposure led to a dose-dependent attenuation of LPS-induced secretion of TNF-α and IL-6 in the incubation medium [
33]. Moreover, a corresponding decrease in TNF-alpha and IL-6 at the mRNA level indicated that COS exposure downregulated the expression of these cytokines at the transcription level. COS exposure was also found to decrease the lipopolysaccharide (LPS)-induced secretion of nitric oxide (NO) in the medium. Interestingly, the addition of external TNF-α to the medium reversed the COS-mediated decrease in IL-6 and NO levels thereby indicating that the anti-inflammatory effect of COS was by modulation of TNF-α pathway Yoon
et al. have also investigated the protective effects of COS against glycerol-induced acute renal failure (a model of renal oxidative stress) [
34] and their data indicate that COS mitigates the glycerol-induced inflammatory response, improves renal function, and has antioxidant effects in kidney. Fernandes
et al. have demonstrated that the anti-inflammatory activity of COS in carrageenan-induced paw edema method was not only dose-dependent but also molecular weight-dependent at higher doses [
35]. Quia
et al. reported on the protective effect of COS in LPS-induced sepsis [
36]. They found that treatment by COS not only attenuated organ dysfunction but also improved survival rate after LPS injection. To further dissect the mechanism, they examined several pro-inflammatory markers, including neutrophil infiltration in organs and TNF-α and IL-1β in serum, and found levels of these cytokines were significantly reduced in COS-treated animals. The redox imbalance in LPS-induced sepsis resulting from depletion of glutathione (GSH) and catalase (CAT) levels and increase in malondialdehyde (MDA) levels was also found to have been reversed by COS exposure. Furthermore, signal pathways activated by LPS, such as c-Jun NH(2)-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), were also found to have been attenuated by COS treatment. These data demonstrate that the protection afforded by COS against LPS challenge in the mouse model could be by virtue of its anti-inflammatory as well as antioxidant properties.
Pangestuti
et al. have described the effects of COS in four different molecular weight ranges (<1, 1–3, 3–5, and 5–10 kDa) for their ability to modulate inflammatory mediators in LPS-stimulated BV2 microglial cells [
37]. At a concentration of 500 μg/mL, COS was found to attenuate the production of NO and prostaglandin E
2 (PGE
2) by inhibiting iNOS and COX-2 expression. Furthermore, the expression levels and release of inflammatory cytokines, including TNF-α, IL-6 andIL-1β, were also attenuated by COS. Notably, the inhibitory activity of COS was found to be dependent on its molecular weight, and lower molecular weight COS showed higher activity. In addition, this study confirmed the suppressive effects of COS on phosphorylation of JNK and p38 MAPK. Chung
et al. have investigated the effects of COS against allergic reaction and allergy-induced asthma
in vivo and
in vitro [
38]. COS, consisting of glucosamine (GlcN)(
n),
n = 3–5, was shown to be capable of inhibiting antigen-stimulated degranulation and cytokine generation in rat basophilic leukemia RBL-2H3 cells. This study also examined a protective effect of COS against ovalbumin (OVA)-induced lung inflammation in mouse model of asthma. The researchers discovered that animals receiving a daily oral administration of COS (16 mg/kg body weight/day) had a significant reduction in the mRNA expression and protein levels of IL-4, IL-5, IL-13, and TNF-α in their lung tissue and bronchoalveolar lavage fluid (BALF); protein levels of IL-4, IL-13, and TNF-α in BALF were decreased by 5.8-fold, 3.0-fold, and 9.9-fold, respectively, in comparison with the OVA-sensitized/challenged asthma control group. Choi
et al. have demonstrated the effect of COS on body weight gain, adipocyte size, adipokine level, lipid profile, and adipose tissue gene expression profile in high-fat (HF) diet-induced obese mice [
39]. Compared with the HF diet mice, mice fed HF diet supplemented with 3% COS had gained 15% less weight but did not display any change in food and energy intake. COS supplementation was also observed to have markedly improved the serum and hepatic lipid profiles. Microarray analysis revealed that dietary COS supplementation modulated adipogenesis-related genes such as matrix metallopeptidases 3, 12, 13, and 14, tissue inhibitor of metalloproteinase 1, and cathepsin K in the adipose tissues. Twenty-five percent of the COS-responsive genes identified are also involved in immune response, including inflammatory response and cytokine production. In a study conducted by Wei
et al., it was discovered that pretreatment with COS at 50–200 µg/mL could substantially abrogate NO production through the reduction of iNOS expression in LPS-activated L9 microglial cells [
40]. In addition, COS was found to markedly decrease LPS-induced phosphorylation of p38 MAPK and extracellular signal-related protein kinase ½ and could also inhibit activation of NF-κB and activator protein-1 (AP-1) In a rat model of autoimmune anterior uveitis, Fang
et al. discovered that COS treatment markedly attenuated the clinical scores and infiltration of leukocytes in the iris/ciliary body (ICB) in a dose-dependent manner [
41]. The expression of inflammatory mediators such as TNF-α, iNOS, MCP-1 (Monocyte Chemotactic Protein-1), RANTES (CCL-5; regulated on activation normal T cell expressed and secreted), fractalkine, and intercellular adhesion molecule (ICAM)-1 was also substantially decreased in animals treated with COS. Moreover, in the ICB, COS decreased the degradation of IKB and levels of p65 thereby resulting in inhibition of DNA-binding by NF-KB. Under
in vitro conditions, sensitized lymphocytes derived from the spleens of COS-treated animals had a reduced chemotactic mobility towards the aqueous humor and the levels of the previously mentioned inflammatory mediators in culture media was found to be reduced.
Li
et al. have reported a mechanism by which COS attenuates inflammation in endothelial cells [
42]. Regardless of the endothelial cell type, COS was found to be instrumental in suppressing the LPS-induced nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB)-dependent inflammatory gene expression, and this was associated with reduced nuclear translocation of NF-κB. LPS enhances O-GlcNAc modification of NF-κB/p65 and activates NF-κB pathway, and this could be prevented either by siRNA knockdown of O-GlcNAc transferase (OGT) or pretreatment with COS. Inhibition of MAPK or superoxide generation is also known to abolish LPS-induced NF-κB O-GlcNAcylation. Consistent with these observations, aortic tissue from LPS-treated mice showed enhanced NF-κB/p65 O-GlcNAcylation, and this was absent in tissues from mice that were pretreated with COS. Hence, COS-mediated attenuation of inflammatory response in vascular endothelial cells is most likely through decreased OGT-dependent O-GlcNAcylation of NF-κB. In a separate report, Li
et al. stated that in porcine iliac artery endothelial cells (PIECs) treated with COS, the LPS-induced mRNA expression of E-selectin and ICAM-1 was reduced through the inhibition of p38 MAPK/ERK1/2 and NF-κB signal cascade. Inhibition of p38 MAPK and ERK1/2, also resulted in suppression of LPS-induced nuclear translocation of NF-κB p65. Both these effects were dose-dependent and ultimately inhibited adhesion of U973 cells to PIECs. Based on these results, it can be concluded that inhibition of MAPK phosphorylation and NF-κB activation in LPS-treated PIECs by COS results in decrease in expression of E-selectin and ICAM-1.
Table 3 is a summary of the literature on these studies.