Increased cyclooxygenase 2 expression in association with oral lichen planus severity

Abstract

Background/purpose: Although some studies have shown induction of cyclooxygenase 2 (COX-2) in oral lichen planus (OLP), an association between COX-2 upregulation and OLP clinical severity has not been investigated. Therefore, we aimed to compare COX-2 expression in OLP with that in normal oral tissues, and to determine correlations between COX-2 expression and both clinical criteria and visual analog scale (VAS) scores.

Materials and methods: COX-2 expression was studied in 25 OLP and 13 normal oral tissues by immunohistochemistry. Both clinical criteria and VAS scores were used to evaluate the clinical severity of OLP. The differences in COX-2 expression between OLP and normal tissues, and the correlations between COX-2 expression and clinical severity were determined by the nonparametric statistical tests.

Results: COX-2 expression was significantly increased in OLP epithelium when compared with normal epithelium (P < 0.001), and intense COX-2 staining in inflammatory infiltrates was observed in the OLP lamina propria. COX-2 expression in OLP epithelium and inflammatory infiltrates was significantly correlated with the clinical criteria score (r = 0.428, P = 0.007, and r = 0.681, P < 0.001, respectively), whereas a significant correlation with the VAS score was observed only in OLP inflammatory infiltrates (r = 0.605, P < 0.001).

Conclusion: Enhanced COX-2 expression in both OLP epithelium and inflammatory infiltrates correlates well with the clinical severity. An association between VAS score and COX-2 expression in OLP inflammatory infiltrates suggests an important role of additional COX-2 expression from inflammation in causing pain in OLP patients.

Keywords: cyclooxygenase 2; immunohistochemistry; oral lichen planus; visual analog pain scale.

Figure 1

Increased COX-2 expression in OLP. COX-2 expression (brown staining in the cytoplasm) in OLP epithelium was greater than that in normal epithelium. Note intense COX-2 staining in OLP inflammatory infiltrates in the lamina propria. The OLP section, in which the primary antibody against COX-2 was omitted, showed no staining as a negative control. As a positive control for COX-2 expression, the OSCC specimen showed intense brown staining in the cancer cells and stromal inflammatory cells. Original magnification, 200×. COX-2 = cyclooxygenase 2; OLP = oral lichen planus; OSCC = oral squamous cell carcinoma.

Figure 2

Significant increase in COX-2 expression, as evaluated by the IHC staining score in both (A) OLP epithelium and (B) inflammatory infiltrates. The box-plot graphs demonstrated a significantly higher COX-2 expression in OLP epithelium and inflammatory infiltrates than in normal oral mucosa. The horizontal lines in each box plot represent the 25^th percentile, 50^th percentile, and 75^th percentile of COX-2 expression. *P < 0.001. COX-2 = cyclooxygenase 2; IHC = immunohistochemical; OLP = oral lichen planus.

Figure 3

Various degrees of COX-2 expression in different clinical criteria scores. The representative section from each clinical criteria score (0–5) is shown for COX-2 staining. Note the most intense COX-2 staining in OLP epithelial cells and inflammatory infiltrates for the clinical criteria score 5. Original magnification, 200×. COX-2 = cyclooxygenase 2; OLP = oral lichen planus.

Figure 4

Correlation data between COX-2 expression in (A and C) OLP epithelium and (B and D) inflammatory infiltrates, as assessed by the IHC staining score on the y-axis, and (A and B) the clinical criteria score and (C and D) the VAS score on the x-axis. Note the significant and positive correlations found between (A and B) COX-2 expression in OLP epithelium and inflammatory infiltrates and the clinical criteria score, and between COX-2 expression in OLP inflammatory infiltrates and the VAS score (the regression line in D). COX-2 = cyclooxygenase 2; IHC = immunohistochemical; OLP = oral lichen planus; VAS = visual analog scale.