[Effects of high-fat and low-carbohydrate diet combined with radiotherapy on tumor microenvironment of Lewis lung cancer bearing mice].

Objective: To investigate the effect of high-fat and low-carbohydrate diet combined with radiotherapy on the tumor microenvironment of mice with lung xenografts. Methods: C57BL/6J mice were selected to establish the Lewis lung cancer model, and they were divided into the normal diet group, the high-fat and low-carbohydrate diet group, the normal diet + radiotherapy group, and the high-fat and low-carbohydrate diet + radiotherapy group, with 18 mice in each group. The mice in the normal diet group and the normal diet + radiotherapy group were fed with the normal diet with 12.11% fat for energy supply, and the mice in the high-fat and low-carbohydrate diet group and the high-fat and low-carbohydrate diet + radiotherapy group were fed with high-fat and low-carbohydratediet with 45.00% fat for energy. On the 12th to 14th days, the tumor sites of the mice in the normal diet + radiotherapy group and the high-fat and low-carbohydrate diet + radiotherapy group were treated with radiotherapy, and the irradiation dose was 24 Gy/3f. The body weight, tumor volume, blood glucose and blood ketone level, liver and kidney function, and survival status of the mice were observed and monitored. Immunohistochemical staining was used to detect the tumor-associated microangiogenesis molecule (CD34) and lymphatic endothelial hyaluronan receptor 1 (LYVE-1), Sirius staining was used to detect collagen fibers, and multiplex immunofluorescence was used to detect CD8 and programmed death-1 (PD-1). Expression of immune cell phenotypes (CD3, CD4, CD8, and Treg) was detected by flow cytometry. Results: On the 27th day after inoculation, the body weigh of the common diet group was(24.78±2.22)g, which was significantly higher than that of the common diet + radiotherapy group [(22.15±0.48)g, P=0.030] and high-fat low-carbohydrate diet + radiotherapy group [(22.02±0.77)g, P=0.031)]. On the 15th day after inoculation, the tumor volume of the high-fat and low-carbohydrate diet + radiotherapy group was (220.88±130.05) mm3, which was significantly smaller than that of the normal diet group [(504.37±328.48) mm3, P=0.042)] and the high-fat, low-carbohydrate diet group [(534.26±230.42) mm3, P=0.016], but there was no statistically significant difference compared with the normal diet + radiotherapy group [(274.64±160.97) mm3]. In the 4th week, the blood glucose values of the mice in the high-fat and low-carbohydrate diet group were lower than those in the normal diet group, with the value being (8.00±0.36) mmol/L and (9.57±0.40) mmol/L, respectively, and the difference was statistically significant (P＜0.05). The blood ketone values of the mice in the high-fat and low-carbohydrate diet group were higher than those in the normal diet group, with the value being (1.00±0.20) mmol/L and (0.63±0.06) mmol/L, respectively, in the second week. In the third week, the blood ketone values of the two groups of mice were (0.90±0.17) mmol/L and (0.70±0.10) mmol/L, respectively, and the difference was statistically significant (P＜0.05). On the 30th day after inoculation, there were no significant differences in aspartate aminotransferase, alanine aminotransferase, creatinine, and urea between the normal diet group and the high-fat, low-carbohydrate diet group (all P＞0.05). The hearts, livers, spleens, lungs, and kidneys of the mice in each group had no obvious toxic changes and tumor metastasis. In the high-fat and low-carbohydrate diet + radiotherapy group, the expression of CD8 was up-regulated in the tumor tissues of mice, and the expressions of PD-1, CD34, LYVE-1, and collagen fibers were down-regulated. The proportion of CD8+ T cells in the paratumoral lymph nodes of the high-fat and low-carbohydrate diet + radiotherapy group was (25.13±0.97)%, higher than that of the normal diet group [(20.60±2.23)%, P＜0.050] and the normal diet + radiotherapy group [(19.26±3.07)%, P＜0.05], but there was no statistically significant difference with the high-fat and low-carbohydrate diet group [(22.03±1.75)%, P＞0.05]. The proportion, of CD4+ T cells in the lymph nodes adjacent to the tumor in the normal diet + radiotherapy group (31.33±5.16)% and the high-fat and low-carbohydrate diet + radiotherapy group (30.63±1.70)% were higher than that in the normal diet group [(20.27±2.15)%, P＜0.05] and the high-fat and low-carbohydrate diet group (23.70±2.62, P＜0.05). Treg cells accounted for the highest (16.58±5.10)% of T cells in the para-tumor lymph nodes of the normal diet + radiotherapy group, but compared with the normal diet group, the high-fat and low-carbohydrate diet group, and the high-fat and low-carbohydrate diet + radiotherapy group, there was no statistically significant difference (all P＞0.05). Conclusion: High-fat and low-carbohydrate diet plus radiotherapy can enhance the recruitment and function of immune effector cells in the tumor microenvironment, inhibit tumor microangiogenesis, and thus inhibit tumor growth.