466 JOURNAL OF COSMETIC SCIENCE
Figure 11. (A) Percentage of collagen gel contraction shown as MEAN ± SEM of the mean of eight
independent experiments. Statistical significance: ***p 0.001, calculated using an unpaired student’s
t-test. (B) Representative images showing collagen gel contraction after tetrapeptide-1 treatment and after
microcurrent stimulation (1000 µA, 70 mv/mm, 1 hour).
Figure 12. Relative gene expression in HDFa cocultured with HEKa treated at different concentrations of S
rebaudiana extract for 24 hours. Data shown as MEAN ± SEM of the mean of six independent experiments
performed in duplicates. Statistical significance: *p 0.05, calculated using an unpaired student’s t test.

467 DELIVERING SUSTAINABLE SOLUTIONS TO IMPROVE WELLBEING
Figure 13. Relative gene expression in HDFa cocultured with HEKa treated at different concentrations of S
rebaudiana extract for 24 hours. Data shown as MEAN ± SEM of the mean of six independent experiments
performed in duplicates. Statistical significance: *p 0.05, calculated using an unpaired student’s t test.
Figure 14. (A) Percentage of type I collagen synthesis and elastin in HDFa and HEKa cocultures treated
with S rebaudiana extract for 48 hours (for collagen) or 72 hours (for elastin) respect to control. Data shown
as MEAN ± SEM of the mean of four to five independent experiments performed in triplicates. Statistical
significance: **p 0.01, calculated using an unpaired Student’s t test. B) %MMPs synthesis in HDFa
and HEKa cocultures treated with stevia rebaudiana extract for 24 hours respect to control. Data shown as
MEAN ± SEM of the mean of 4 independent experiments performed in triplicates. Statistical significance:
**p 0.01, ****p 0.0001, calculated using an unpaired student’s t test.