## 3 Results and Discussion
### The Restoration of Mitochondrial Cytochrome II Activities in UVb-Irradiated Human Fibroblasts  
Further evidence of the protective effect of AF on mitochondria damaged by UVb light is shown in Figure 6, where mitochondrial cytochrome II activities are compared in UVb-irradiated skin fibroblasts because succinate dehydrogenase (SDH) is an enzyme complex that is bound to the inner mitochondrial membrane in respiratory complex II and is considered to prevent ROS generation [11; 48]. A more recent study also revealed a strong correlation between age and a significant decrease in complex II activity that was specific to senescent skin cells but not with a decrease in complex IV activity [49]. Therefore, the results of Figure 6 suggest that the ability of the AF to protect against mitochondrial dysfunction due to exogenous stress prevents the skin aging process.  
The protective effect on mitochondria was measured as the ratio of SDH activities in UVb-irradiated human skin fibroblasts treated with various concentrations of the samples up to 25 mU/mg to the SDH activities in the control cells (not treated with UVb light) (data not shown). In Figure 6, all three samples, quercetin, the AE, and the AF, clearly restored SDH activity in UVb-irradiated skin cells up to 89.30 \(\pm\) 1.14% of the control after treatment with 0.5% of the AF, the highest concentration, and similar results were obtained from cells treated with 0.3% of the AF. Specifically, 10 ug/mL quercetin maintained SDH activity at 69.55 \(\pm\) 6.33% in the mitochondria of UVb-irradiated human fibroblasts, while SDH activities were substantially reduced to 39.06 \(\pm\) 3.68% in cells that were only exposed to  
Figure 6: Comparison of succinate dehydrogenase activities, a component of mitochondrial complex II, in UVb-irradiated human skin fibroblasts treated with 10 ug/mL quercetin or various concentrations of the two aloe extract samples. AW: Hot water extraction of _Aloe vera leaf_ skin at 100 \({}^{\circ}\)C for 24 h. AF: _L. plantarum_ fermentation of _Aloe vera leaf_ skin at 37 \({}^{\circ}\)C for 3 days and extraction with an ultrasonicator at 40 kHz for 1 h at room temperature. The mean values \(\pm\) SD for separate triplicate experiments are shown, and error bars represent the SD. The significance of the difference was set to **_p_ < 0.01 and ***_p_ < 0.001 compared with the control (UV–) group.  
UVb light without treatment with the samples. This result was also supported by the recent work that flavonoids have their cytoprotective effects on mitochondrial pathways [10]; especially, quercetin showed the inhibition of oxidative stress by directly scavenging ROS [50]. However, in cells treated with 0.3% AW and the AF, SDH enzyme activities were not substantially reduced, and the values were only 68.15 \(\pm\) 2.88% and 92.30 \(\pm\) 4.61% of the control, respectively. Interestingly, a less than 20% decrease in SDH activity was observed in adding 0.3% of the AF, which were much better than those obtained with quercetin and AW. These results clearly proved that AF exerts a fairly strong effect on protecting against mitochondrial damage by restoring complex II activity in mitochondrial electron transport pathways since SDH is a key enzyme in the respiratory complex of mitochondria [44]. Therefore, the results of Figures 3, 5 and 6 imply that AF delays/inhibits the skin aging process because complex II was most closely correlated with skin cell aging [49]. However, a more detailed correlation with the activation of mitochondrial function should be explained by considering multi-functional mitochondrial protein such as voltage-dependent anion channel (VDAC) after treating the samples [10].