## 3 Results and Discussion
### Anti-inflammatory Activity  
The relationship between anti-inflammatory activity and the enzymes COX-1 (cyclooxygenase-1) and COX-2 (cyclooxygenase-2) is closely tied to the inflammatory response and the production of prostaglandandins [103]. COX-1 and COX-2 are enzymes involved in synthesizing prostaglandandins from arachidonic acid, a fatty acid found in cell membranes. COX1 is constitutively expressed in many tissues and maintains normal physiological functions, such as protecting the stomach lining and regulating blood platelets. COX-1 produces prostaglandandins that are involved in these housekeeping functions [103]. Meanwhile, COX2 is typically produced during inflammation and is responsible for producing the prostaglandandins that contribute to the inflammatory response. COX-2 is often upregulated in response to various stimuli, including injury or infection [103]. Non-steroidal anti-inflammatory drugs (NSAIDs), including indomethacin and celecoxib, exert their anti-inflammatory effects by suppressing the activity of both COX-1 and COX-2 enzymes [104]. Nevertheless, there is considerable interest in natural extracts or compounds with anti-inflammatory properties that may act as inhibitors of COX-1 and COX-2 [105; 106; 107]. One of these groups may be polyphenols, more precisely, flavonoids [108]. Figure 5: Antimicrobial activities of the polyphenol-rich extracts (GF-CE and GF-PE) determined by the disc diffusion assay. Values represent the mean \(\pm\) standard deviation. Different letters mean significant differences between the polyphenol-rich extracts (\(p<0.05\)). Figure 6 shows the anti-inflammatory effects of the GF peel polyphenol-rich extracts (GF-CE and GF-PE) and GF-EO against the biomarkers COX1 and COX2. The GF-EO, GF-CE, and GF-PE exhibited activities as COX1 and COX2 inhibitors, with IC\({}_{50}\) values of 0.97 \(\pm\) 0.1, 25 \(\pm\) 0.1, and 0.67 \(\pm\) 0.058 ug/mL for COX1 and 3.9 \(\pm\) 0.1, 0.28 \(\pm\) 0.0006, and 0.7 \(\pm\) 0.1 ug/mL for COX2, compared to the reference standards celexoxib and indomethacin, with values of 97.5 \(\pm\) 0.1 and 6.25 \(\pm\) 0.002, and 0.31 \(\pm\) 0.01 and 0.52 \(\pm\) 0.01, respectively. It was noticed from the results that EO has a weak activity as a COX2 inhibitor and good activity as an inhibitor of COX1, while the GF-CE has selective activity as a COX2 inhibitor and mild inhibitor of COX1, but the GF-PE has a weak activity as a COX2 inhibitor compared to the extract obtained from the crude GF peels and good activity as a COX1 inhibitor. The bioactive extracts obtained from GF peels showed a significantly better activity (\(p\) < 0.05) than synthetic drugs. Our results are consistent with recent studies, which demonstrate the inhibitory effect of grapefruit peel extracts on the production of inflammatory mediators, including prostaglandin E2 and nitric oxide (NO), in LPS-activated RAW 264.7 cells. Flavanone glycosides have been identified as significant contributors to the anti-inflammatory activity of citrus peels due to their higher abundance compared to polymethoxyflavones [109]. Furthermore, in vivo investigations have indicated that the EO extracted from grapefruit peels exhibits anti-inflammatory properties compared to the negative control group over the entire 5 h post-induction assessment period [110]. The correlation between inhibiting COX-1 and COX-2 and anti-inflammatory activity is rooted in the role of these enzymes in the inflammatory process. Inflammation involves the production of prostaglandandins, which COX-1 and COX-2 synthesize. By inhibiting these enzymes, the production of prostaglandandins is reduced, leading to a decreased inflammatory response. The GF-PE had a higher content of valuable phytochemicals, such as naringenin, narirutin, hesperidin, ferulic acid, and chlorogenic acid.