The effect of C-cigarette smoke or E-cigarette vapor exposure on the retina
In medium-term C-cigarette smoke exposure subgroup, the level of pro-inflammatory cytokines TNF-α (Fig. 2c) was reduced in retina. The level of anti-angiogenic cytokines PEDF (Fig. 2e) slightly increased, and the Ratio of VEGF vs. PEDF (Fig. 2f) decreased by about 40% compared to control mice. However, after long-term exposure, only the level of IL-1β (Fig. 2a) is higher in C-cigarette smoke exposure mice than control mice (about 1.8 folds).
In short-term E-cigarette vapor exposure groups, the expression of iNOS (Fig. 2h) in nicotine-free subgroup was increased, while the levels of TNF-α (Fig. 2i) and Ratio of VEGF vs. PEDF (Fig. 2l) decreased significantly. Results from nicotine-containing E-cigarette subgroup showed a decresed level of TNF-α (Fig. 2i) and down-regulated VEGF over PEDF (Fig. 2l) in vapor exposure mice than the control mice.
In medium-term exposure groups, the level of iNOS (Fig. 2h,) and Ratio of VEGF vs. PEDF (Fig. 2l) are increased significantly in nicotine-free E-cigarette subgroup. In contrast, the data from nicotine-containing subgroup indicated that the expression of IL-1β (Fig. 2g) decreased, but TNF-α (Fig. 2i) increased significantly. There is no significant difference between nicotine-containing subgroup and control mice for the Ratio of VEGF vs. PEDF, though with a higher level of PEDF in vapor exposure subgroup.
Interestingly, long-term nicotine-containing E-cigarette vapor exposure reduced the expression of TNF-α (Fig. 2i) in retina, and down-regulated the Ratio of VEGF vs. PEDF (Fig. 2l) as well.
Comparing the effect of C-cigarette smoke with E-cigarette vapor (nicotine-free or nicotine-containing) on retinal tissue
In medium-term exposure groups, the expression of pro-inflammatory mediator TNF-α (Fig. 3c) proteins in retinal tissues from mice exposed to C-cigarette smoke was decreased by 27%, along with a decreased ratio of VEGF vs. PEDF (Fig. 3f) by 38%. Surprisingly, most of the investigated factors in the nicotine free E-cigarette subgroup changed in an opposite trend with C-cigarette subgroup, except of TNF-α (Fig. 3c). In the nicotine-containing E-cigarette subgroup, the expression level of IL-1β (Fig. 3a) decreased by 44% after exposure, while TNF-α (Fig. 3c) increased by 103%. Besides, the regulation trends of iNOS, VEGF and PEDF are similar to the C-cigarette subgroup.
In long-term exposure group, the changes trend in C-cigarette exposure subgroup are similar to the medium-term group. The most significant change is the upregulated IL-1β protein by 81% (Fig. 3a), while the change of the Ratio of VEGF vs. PEDF (Fig. 3f) is less. In nicotine-containing E-cigarette group, IL-1β and TNF-α were both down-regulated by 10% and 30% respectively, while the iNOS was up-regulated by 17%. In addition, the expression levels of VEGF (Fig. 4d) and PEDF (Fig. 3e) were increased simultaneously, giving the decreased Ratio of VEGF vs. PEDF (Fig. 3f) by 17%.
Comparing the different effects of medium- and long-term exposure of E-cigarette vapor on RPE and choroid.
In RPE, after medium-term nicotine-free E-cigarette vapor exposure, the protein levels of IL-1β (Fig. 4a), iNOS (Fig. 4b), and VEGF (Fig. 4d) were up-regulated, and the Ratio of VEGF vs. PEDF (Fig. 4f) increased significantly as well. Simultaneously, the data from nicotine-containing subgroup indicated that the levels of IL-1β, TNF-α (Fig. 4c) increased significantly. The increasement of the Ratio of VEGF vs. PEDF is more significant than nicotine-free subgroup. In long-term nicotine-containing exposure subgroup, the changes of protein levels of pro-inflammation mediators are similar but less significant than that from medium-term exposure subgroup, and the Ratio of VEGF vs. PEDF was not significant anymore.
In choroid, after medium-term nicotine-free E-cigarette vapor exposure, the levels of IL-1β (Fig. 4a), TNF-α (Fig. 4c), and VEGF (Fig. 4d) all increased significantly. The data from nicotine-containing subgroup showed a slightly increase of IL-1β, and a significantly decreased Ratio of VEGF vs. PEDF (Fig. 4f). In addition, long-term exposure of nicotine-containing E-cigarette vapor resulted in higher levels of IL-1β, iNOS and Ratio of VEGF vs. PEDF in choroid.
The comprehensive effects of long-term exposure of E-cigarette (nicotine-free vs nicotine-containing) vapor on retina, RPE and choroid.
Mice that were exposed to nicotine-free E-cigarette for medium-term, only the expression of iNOS (Fig. 5b) increased obviously in retina. In RPE tissue, the Ratio of VEGF vs. PEDF (Fig. 5f) increased by 219% surprisingly. However, the regulation trends of mediators in choroidal tissue are different from retina and RPE, in which, the levels of IL-1β (Fig. 5a) and TNF-α (Fig. 5c) were increased by 298% and 398% dramatically.
In nicotine-containing E-cigarette subgroup of medium-term exposure, the level of TNF-α (Fig. 5c) increased by 103% in retina. In RPE tissue, the levels of IL-β (Fig. 5a) and TNF-α (Fig. 5c) dramatically increased by 421% and 113% respectively. Besides, the Ratio of VEGF vs. PEDF (Fig. 5f) significantly increased by 445%. However, the change of cytokines levels in choroid was not as obvious, wherein, only IL-β (Fig. 5a) was upregulated by 130%.
In long-term nicotine containing E-cigarette vapor exposure subgroups, the change of cytokines levels was not significant in both retina and RPE. However, in choroid, the level of VEGF (Fig. 5j) was up-regulated by 128%, accompanied with the down-regulated level of PEDF (Fig. 5k) by 29%, resulting in a dramatically increased Ratio of VEGF vs. PEDF (Fig. 5l) by 221%.