Inflammation is a normal body response toward any pathogens, injured tissue and toxins. Undesired adverse reactions are coupled with long term consumption of the available anti-inflammatory medications. Therefore, finding safe and more efficient alternative is currently mandatory. Carrageenan-induced acute inflammatory response (edematous state) in experimental animals is used to examine the efficiency of the novel anti-inflammatory molecules. Here, the potential anti-edematous role of PCA (25 and 50 mg/kg) was investigated following carrageenan injection in mice. Carrageenan injection enhances excessive release of different pro-inflammatory mediators and potentiated vasodilatation, resulting in the development of paw and the increase in its size which is recorded after 8 hours. Additionally, microscopic examination revealed alterations in paw tissue architecture and the accumulation of infiltrating inflammatory cells and increased inter-fiber space were observed, these findings are in agreement with previous report (Zhang et al. 2020). Interestingly, PCA administration decreased significantly the volume of the developed paw edema after carrageenan injection and decreased the infiltrated immune cells at the site of injury; this effect may be attributed to its antioxidative characteristics.
Oxidative stress is a fundamental mechanism implicated in the pathogenesis of paw edema following carrageenan application. In the current study, a disturbance in the redox status was recorded as characterized by the elevated MDA and the declined GSH, SOD and CAT activities. Previous reports demonstrated the overproduction of ROS following carrageenan administration. These active molecules affect the plasma membrane integrity and enhance its lipoperoxidation (Zhang et al. 2020), which may explain the increased MDA (lipid peroxidation marker) in the present study. GSH, SOD and CAT are among the main quenching cellular antioxidants, their depletion indicate the development of oxidative stress and cellular impairments. It has been suggested that blocking lipoperoxidation and the enhancement of cellular antioxidants capacity may alleviate the oxidative challenge associated with the development of paw edema. Interestingly, PCA administration was able to suppress oxidative insults following carrageenan application through inhibiting lipoperoxidation and enhancing the depleted antioxidant proteins. The antioxidative activity of PCA was reported in earlier studies. Bhattacharjee et al. (Bhattacharjee et al. 2017) showed that PCA inhibited ROS production, lipoperoxidation, and protein carbonylation, and increased GSH along with antioxidant enzymes (SOD, CAT, GR, GPx) in the myocardial tissue of diabetic rats. PCA was also found to protect hepatic tissue against oxidative damage by decreasing MDA level and enhancing level of GSH and SOD in response to cisplatin exposure (Habib et al. 2021). Moreover, Al Olayan et al. (Al Olayan et al. 2020) stated that PCA provided neuroprotection against cadmium intoxication through enhancing cellular antioxidants gene expression and decreasing lipid peroxidation. Authors attributed these effects to its ability to upregulate nuclear-related factor 2 mRNA expression.
Carrageenan injection triggered excessive release of different inflammatory mediators in the paw skin as characterized by the increased COX-II activity and its product (PGE2) accompanied by upregulation of iNOS mRNA expression and its product (NO). The secretion of pro-inflammatory cytokines and the release of various inflammatory mediators such as COX-II and PGE2 are major events implicated during acute inflammatory responses. The elevated PGE2 reflects the overactivation of COX-II resulting in the progression of inflammation symptoms including redness, fever, swelling and pain [38]. iNOS is upregulated in response to overproduction of pro-inflammatory cytokines and its upregulation is coupled with NO formation which further interact with superoxide anions and produce highly reactive peroxynitrite radicals resulting in oxidative and inflammatory responses (Alsharif et al. 2020). NO is also known to inflammatory responses such as vasodilation, increased vascular permeability, exudate formation, and prostaglandin synthase activation [39]. PCA administration was found to decrease levels and mRNA expression of the increased COX-II, PGE2, iNOS and NO in the inflamed tissue. The anti-inflammatory property of PCA has been discussed previously in different experimental models. Min et al. (Min et al. 2010) observed that PCA downregulated COX-II and iNOS, and diminished their products (PGE2 and NO) in RAW 264.7 cells treated with lipopolysaccharide. In addition, PCA showed anti-inflammatory activity following doxorubicin through downregulation of COX-II and iNOS in the renal tissue (Molehin et al. 2019).
Excessive amounts of inflammatory mediators including TNF-α, IL-1β, IL-6 and IL-8 along with elevated level of NF-ĸB were recorded following carrageenan injection. These results are in line with previous studies (Haddadi &Rashtiani 2020). Cross-talk between oxidative stress and inflammatory response has been confirmed in inflammatory conditions. Overproduction of ROS is strongly related to the development of inflammation upon carrageenan injection through activating immune cells and secretion of pro-inflammatory mediators. Additionally, higher lipid peroxidation product has been linked with oversecretion of pro-inflammatory cytokines (Ou et al. 2019). Macrophages and lymphocytes accumulate at the inflammation site and enhance releasing pro-inflammatory cytokines. The increased TNF-α and IL-1β during inflammatory response cause hyperalgesia and inflammatory pain (Kadetoff et al. 2012). It has been reported that crosslink between the inflammatory mediators is demonstrated following carrageenan application. Carrageenan enhances phosphorylation of ERK1/2, JNK and p38 which trigger the secretion of TNF-α. Consequently, TNF-α enhance secretion of IL-1β, IL-6, COX-II and PGE2 in addition to upregulation of iNOS expression (Ou et al. 2019). NF-κB is transcriptional inflammatory mediator that regulates the activity and differentiation of immune cells in addition to the production of production of different inflammatory markers, which may explain the elevation in the examined inflammatory mediators following carrageenan injection (Almeer et al. 2019).
Therefore, agents that are able to deactivate NF-κB may be applied as anti-inflammatory drugs. Interestingly, PCA administration following carrageenan suppressed markedly the development of inflammation and its associated events. Former studies revealed the anti-inflammatory characteristics of PCA in different experimental protocols. PCA also was found to decrease the overproduced pro-inflammatory cytokines in the cortical tissue upon cadmium exposure (Al Olayan et al. 2020). Moreover, PCA suppressed the secreted TNF-α, IL-6 and IL-1β. Authors attributed this effect to the deactivation of and NF-κB signaling following LPS-mediated acute lung injury (Wei et al. 2012). Additionally, Crespo and collaborators (Crespo et al. 2017) demonstrated that PCA inhibited inflammatory response associated with colitis partially through decreasing pro-inflammatory cytokines and suppressing NF-κB activity. PCA administration blockades the activities of COX-II, iNOS and NF-κB in mouse epidermis following the exposure to 12-O-tetradecanoylphorbol-13-acetate (Cichocki et al. 2010). In another report, PCA downregulated the expression of COX-II and iNOS in the kidney tissue after the treatment with doxorubicin (Molehin et al. 2019). PCA was reported to attenuate production and expressions of TNF-α, IL-1β, and iNOS, COX-II and PGE2 via the regulation of NF-kB and MAPK activation in LPS- treated RAW 264.7 {Min, 2010 #2651}.
In the current study, carrageenan injection increased significantly MPO activity and MCP-1 level in the skin paw tissue. These results reflect the migration and infiltration of neutrophils and the degree of tissue damage at the inflamed tissue. These results are in agreement with previous reports (Abdel-Lateff et al. 2020, Almeer et al. 2019). Among other treatments (Zhang &de Mejia 2020), PCA was found to decrease the production of pro-inflammatory cytokines and MCP-1 level. This effect has been attributed to the attenuation of NF-κB and JNK/MAPK-mediated inflammatory responses in adipocytes treated by LPS. Additionally, PCA protected against methotrexate-induced hepatorenal tissues through suppressing inflammatory mediators including MPO, NO, TNF-α and IL-1β (Owumi et al. 2019). Moreover, PCA deactivated MPO and decreased the increased NO, TNF-α and IL-1β in the hypothalamic, testicular and epididymal tissues following furan exposure.