Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To develop a prediction model for postoperative prognosis in patients with cholangiocarcinoma(CCA)based on the expression of silence information regulator 2(SIRT2).Methods:The differential expression of SIRT2 between CCA and normal tissues was analyzed using TCGA and GEO databases.Gene set enrichment analysis(GSEA)was used to explore potential mechanisms of SIRT2 in CCA.The expression of SIRT2 protein in CCA tissues and normal tissues(including 44 pairs of specimens)was also detected by immunohistochemistry(IHC)in 89 resectable CCA patients who underwent surgical treatment in the First Affiliated Hospital of Bengbu Medical College between January 2016 and December 2021.The relationship between SIRT2 expression and clinicopathological characteristics and prognosis of CCA patients was analyzed.A survival prediction model for patients with resectable CCA was constructed with COX regression results,the calibration curve and the time-dependent receiver operating characteristic curve(ROC)were used to evaluate the performance of the constructed model,and the predictive power between this model and the American Joint Committee on Cancer(AJCC)/TNM staging system(8th edition)was compared.Results:SIRT2 mRNA was overexpressed in CCA tissues as shown in TCGA and GEO databases.IHC staining showed that SIRT2 protein expression in CCA tissues was significantly higher than that in adjacent non-tumor tissues.GSEA results showed that elevated SIRT2 expression may be involved in multiple metabolism-related signaling pathway,such as fatty acid metabolism,oxidative phosphorylation and amino acid metabolism.SIRT2 expression was related to serum triglycerides level,tumor size and lymph node metastasis(all P<0.05).The survival analysis results showed that patients with higher SIRT2 expression had a significantly lower overall survival(OS)than patients with lower SIRT2 expression(P<0.05).Univariate COX regression analysis suggested that pathological differentiation,clinical stage,postoperative treatment and SIRT2 expression level were associated with the prognosis of CCA patients(all P<0.05).Multivariate regression analysis confirmed that clinical stage and SIRT2 expression level were independent predictors of OS in postoperative CCA patients(both P<0.05).A nomogram based on SIRT2 for prediction of survival in postoperative CCA patients was constructed.The C-index of the model was 0.675,and the area under the time-dependent ROC curve(AUC)for predicting survival in the first,second,and third years was 0.879,0.778,and 0.953,respectively,which were superior to those of AJCC/TNM staging system(8th Edition).Conclusions:SIRT2 is highly expressed in CCA tissues,which is associated with poor prognosis in patients with resectable CCA.The nomogram developed based on SIRT2 may have better predictive power than the AJCC/TNM staging system(8th edition)in prediction of survival of postoperative CCA patients.

Objective:To determine the optimal irradiation energy and frequency for the establishment of melasma mouse model using simple ultraviolet irradiation, and to provide guidance on animal strains and irradiation protocols for the successful establishment of melasma model.Methods:Animal models of melasma were established using BALB/c female mice and C57BL/6JNifdc female mice. BALB/c female mice were divided into 4 groups using a simple randomization method: A, B, C and G, with 5 mice in each group. C57BL/6JNifdc female mice were divided into 4 groups: D, E, F and H, with 5 mice in each group. All mice were irradiated with 8.428 mW/cm 2 of ultraviolet light. The irradiation time was 15 s (single irradiation energy of 0.13 J/cm 2) in groups A and D, 15 min (single irradiation energy of 7.59 J/cm 2) in groups B and E, and 30 min (single irradiation energy of 15.17 J/cm 2) in groups C and F. Each cycle consisted of 5 consecutive days of irradiation followed by 2 days of cessation, totaling 4 cycles of irradiation. Groups G and H were not irradiated. At the end of irradiation, all mice were kept under normal conditions. One week later, 3 mice from each group were selected for HE, Masson-Fontana, Masson, and immunohistochemical staining. Quantitative analysis was performed to measure the thickness of the acanthocyte layer, melanin granules, collagen percentage, and interleukin-1 (IL-1) levels. The remaining mice were kept for an additional week, depilated and photographed to observe the changes in coloration. Data were analyzed using SPSS 27.0 software, measurement data that did not conform to normal distribution were represented by M( Q1, Q3) and comparisons between groups were made using the Kruskal-Wallis rank sum test. Results:During the entire irradiation process, no visible discoloration was observed in the BALB/c female mice in all groups. In contrast, varying sizes of discoloration appeared in the C57BL/6JNifdc female mice in groups D, E, and F after irradiation in the second week. However, by the third week, the discoloration in group D gradually disappeared, while the discoloration in group E was more obvious than before. At the same time, group F exhibited significant discoloration, with some mice exhibited signs of skin peeling, burning and breakage on their backs. After the 4th week of irradiation, no new discoloration was formed in group D. The discoloration was more obvious in group E, and most mice in group F showed skin burn breakage. Two weeks after the completion of irradiation, there was no obvious discoloration on the dorsal skin of BALB/c female mice in all groups. In C57BL/6JNifdc female mice, group D showed no obvious discoloration, group E exhibited lighter discoloration compared to the 4th week post-irradiation, and group F had crusted skin at the burn sites with lighter discoloration than before. However, the discoloration in groups E and F was still obviously visible to the naked eye. HE staining showed that the difference in the thickness of the echinocyte layer was not statistically significant in groups A, B, C, and G ( H=1.08, P=0.782); whereas the difference was statistically significant in groups D, E, F and H ( H=12.85, P=0.005). The thickness of the echinocyte layer decreased gradually with the extension of the irradiation time. Additionally, there was a disruption in the arrangement of epidermal spindles in group F, and this situation was not observed in groups D and E. Masson-Fontana staining revealed no significant pigmentation in any of the BALB/c female mice. The difference in melanin granule counts between groups A, B, C, and G was not statistically significant ( H=7.77, P=0.051). In contrast, C57BL/6JNifdc female mice exhibited more noticeable pigmentation in the epidermis and dermis in groups E and F. The difference in melanin particle counts among groups D, E, F and H was statistically significant ( H=17.61, P<0.001), with melanin deposition increasing gradually with the duration of irradiation. Masson staining showed that the difference in collagen percentage between groups A, B, C, and G was not statistically significant ( H=7.26, P=0.064). However, significant disorganization of fibers and a loose structure were observed in groups E and F. The difference in collagen percentage between groups D, E, F, and H was statistically significant ( H=8.65, P=0.034). Immunohistochemical results showed that the difference in IL-1 expression levels between groups A, B, C, and G was statistically significant ( H=17.86, P<0.001); also between groups D, E, F, and H was statistically significant ( H=14.19, P=0.003), suggesting that ultraviolet irradiation stimulated an inflammatory response in the skin of mice. Conclusion:BALB/c female mice are not suitable for melasma models under the frequency and duration of irradiation in this experiment. C57BL/6JNifdc female mice are irradiated with a single irradiation energy dose of 7.59 J/cm 2 five days a week for 4 weeks, which can establish stable animal models of melasma with a specific level of pigmentation that persisted for at least 2 weeks.

Objective:To determine the optimal irradiation energy and frequency for the establishment of melasma mouse model using simple ultraviolet irradiation, and to provide guidance on animal strains and irradiation protocols for the successful establishment of melasma model.Methods:Animal models of melasma were established using BALB/c female mice and C57BL/6JNifdc female mice. BALB/c female mice were divided into 4 groups using a simple randomization method: A, B, C and G, with 5 mice in each group. C57BL/6JNifdc female mice were divided into 4 groups: D, E, F and H, with 5 mice in each group. All mice were irradiated with 8.428 mW/cm 2 of ultraviolet light. The irradiation time was 15 s (single irradiation energy of 0.13 J/cm 2) in groups A and D, 15 min (single irradiation energy of 7.59 J/cm 2) in groups B and E, and 30 min (single irradiation energy of 15.17 J/cm 2) in groups C and F. Each cycle consisted of 5 consecutive days of irradiation followed by 2 days of cessation, totaling 4 cycles of irradiation. Groups G and H were not irradiated. At the end of irradiation, all mice were kept under normal conditions. One week later, 3 mice from each group were selected for HE, Masson-Fontana, Masson, and immunohistochemical staining. Quantitative analysis was performed to measure the thickness of the acanthocyte layer, melanin granules, collagen percentage, and interleukin-1 (IL-1) levels. The remaining mice were kept for an additional week, depilated and photographed to observe the changes in coloration. Data were analyzed using SPSS 27.0 software, measurement data that did not conform to normal distribution were represented by M( Q1, Q3) and comparisons between groups were made using the Kruskal-Wallis rank sum test. Results:During the entire irradiation process, no visible discoloration was observed in the BALB/c female mice in all groups. In contrast, varying sizes of discoloration appeared in the C57BL/6JNifdc female mice in groups D, E, and F after irradiation in the second week. However, by the third week, the discoloration in group D gradually disappeared, while the discoloration in group E was more obvious than before. At the same time, group F exhibited significant discoloration, with some mice exhibited signs of skin peeling, burning and breakage on their backs. After the 4th week of irradiation, no new discoloration was formed in group D. The discoloration was more obvious in group E, and most mice in group F showed skin burn breakage. Two weeks after the completion of irradiation, there was no obvious discoloration on the dorsal skin of BALB/c female mice in all groups. In C57BL/6JNifdc female mice, group D showed no obvious discoloration, group E exhibited lighter discoloration compared to the 4th week post-irradiation, and group F had crusted skin at the burn sites with lighter discoloration than before. However, the discoloration in groups E and F was still obviously visible to the naked eye. HE staining showed that the difference in the thickness of the echinocyte layer was not statistically significant in groups A, B, C, and G ( H=1.08, P=0.782); whereas the difference was statistically significant in groups D, E, F and H ( H=12.85, P=0.005). The thickness of the echinocyte layer decreased gradually with the extension of the irradiation time. Additionally, there was a disruption in the arrangement of epidermal spindles in group F, and this situation was not observed in groups D and E. Masson-Fontana staining revealed no significant pigmentation in any of the BALB/c female mice. The difference in melanin granule counts between groups A, B, C, and G was not statistically significant ( H=7.77, P=0.051). In contrast, C57BL/6JNifdc female mice exhibited more noticeable pigmentation in the epidermis and dermis in groups E and F. The difference in melanin particle counts among groups D, E, F and H was statistically significant ( H=17.61, P<0.001), with melanin deposition increasing gradually with the duration of irradiation. Masson staining showed that the difference in collagen percentage between groups A, B, C, and G was not statistically significant ( H=7.26, P=0.064). However, significant disorganization of fibers and a loose structure were observed in groups E and F. The difference in collagen percentage between groups D, E, F, and H was statistically significant ( H=8.65, P=0.034). Immunohistochemical results showed that the difference in IL-1 expression levels between groups A, B, C, and G was statistically significant ( H=17.86, P<0.001); also between groups D, E, F, and H was statistically significant ( H=14.19, P=0.003), suggesting that ultraviolet irradiation stimulated an inflammatory response in the skin of mice. Conclusion:BALB/c female mice are not suitable for melasma models under the frequency and duration of irradiation in this experiment. C57BL/6JNifdc female mice are irradiated with a single irradiation energy dose of 7.59 J/cm 2 five days a week for 4 weeks, which can establish stable animal models of melasma with a specific level of pigmentation that persisted for at least 2 weeks.