# Cellular Antioxidant Effects and Bioavailability of Food Supplements Rich in Hydroxyrosol
## 4 Discussion  
Our study explores the antioxidant potential of two food supplements derived from olive vegetation water, mainly characterized by a high content of hydroxyytrosol. The antioxidant activity was determined by measuring the cellular antioxidant activity, the catalase and SOD activities in the HepG2 cell line, as well as the inhibition of lipid peroxidation and glycosylation in the HaCat cell line. The tests carried out have shown that both olive-derived products have a strong positive influence on cells; this influence is complex and not one-dimensional. This reflects the complex nature of the sample materials and suggests a powerful synergy of hydroxyytrosol with other olive phenols, which is further potentiated in the presence of the grape phytocomplex. In particular, both supplements are able to reduce oxidative parameters in vitro.  
On one hand, P-1, containing 94% olive water concentrate, showed a good capacity in the CAA and SOD assays, but a better performance in preventing isoprostanes formation in vitro when compared to P-2 (Table 6). On the other hand, P-2, containing olive and grape concentrates, showed a greater antioxidant potential for scavenging reactive species, as indicated by its greater potential in removing the hydroxyl radicals and by its higher SOD and catalase activities. Regarding the prevention of AGEs accumulation, both products showed an excellent capacity in vitro. The overall better antioxidant performance of P-2 in vitro could be explained by the higher concentration of olive-derived polyphenols, as well as the presence of grape-derived antioxidants, which include, among others, the trans-resveratrol, anthocyanins and proanthocyanidin monomers.  
Table 6 describes the cellular effects measured, and their links to the attributed in vivo effects.  
The mechanism of this positive influence needs to be better understood and has led us to further investigations on the mechanisms and dynamics of the effects of food supplements derived from olive vegetation water on human cells. However, understanding the absorption and bioavailability of these key molecules after oral administration remains a prerequisite before any potential health effect can be derived. In this sense, the pilot trial shows that the hydroxyytrosol supplied with a hydrophilic matrix combining olive fruit concentrate and lemon or grape juices is effectively absorbed, and then urinarily excreted as hydroxyytrosol in its free form.  
In subsequent studies, the exact excreted fraction will be determined, and further focus will be placed on the metabolites to obtain a broader picture of the entire ADME properties.  
Overall, preliminary data obtained in vitro indicate that the aqueous extracts of olives can actually improve the cellular redox status and related markers, and that their main active ingredient is bioavailable to the human body. Aqueous olive concentrates, with or without grape concentrate, are valid candidates for the prevention of cellular oxidative damage, and thus merit further attention.  
Conceptualization, investigation, writing--original draft preparation, methodology, formal analysis: C.B.; writing--review and editing, formal analysis: S.S.; visualization, methodology: P.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the German Federal Ministry for Economy and Energy under the program ZIM (Zentrales Innovationsprogramm Mittelstand), grant numbers 16 KN038023 and ZF4226901 SK6.  
Ethical review and approval were waived for this study, as only urine was taken, there was no medical intervention and there was no danger to the health of the test persons.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The authors declare no conflict of interest.