Phenol-Rich Feijoa sellowiana (Pineapple Guava) Extracts Protect Human Red Blood Cells from Mercury-Induced Cellular Toxicity

Abstract

Plant polyphenols, with broadly known antioxidant properties, represent very effective agents against environmental oxidative stressors, including mercury. This heavy metal irreversibly binds thiol groups, sequestering endogenous antioxidants, such as glutathione. Increased incidence of food-derived mercury is cause for concern, given the many severe downstream effects, ranging from kidney to cardiovascular diseases. Therefore, the possible beneficial properties of Feijoa sellowiana against mercury toxicity were tested using intact human red blood cells (RBC) incubated in the presence of HgCl₂. Here, we show that phenol-rich (10-200 µg/mL) extracts from the Feijoa sellowiana fruit potently protect against mercury-induced toxicity and oxidative stress. Peel and pulp extracts are both able to counteract the oxidative stress and thiol decrease induced in RBC by mercury treatment. Nonetheless, the peel extract had a greater protective effect compared to the pulp, although to a different extent for the different markers analyzed, which is at least partially due to the greater proportion and diversity of polyphenols in the peel. Furthermore, Fejioa sellowiana extracts also prevent mercury-induced morphological changes, which are known to enhance the pro-coagulant activity of these cells. These novel findings provide biochemical bases for the pharmacological use of Fejioa sellowiana-based functional foods in preventing and combating mercury-related illnesses.

Keywords: feijoa extracts; functional food; glutathione; mercury; oxidative stress; red blood cells; thiol groups.

Figure 1

Feijoa peel acetonic extract reduces Hg-induced hemolysis. Cells were treated with 40 μM HgCl₂ for 24 h with increasing acetonic extract concentrations. Data are the means ± standard errors of the mean (SEM) (n = 9). Statistical significance was calculated by one-way ANOVA followed by Tukey’s test. ** (p < 0.05) indicates a significant difference from cells lacking HgCl₂ treatment. # (p < 0.05) and ## (p < 0.01) indicate significant differences from cells lacking Feijoa extract treatment.

Figure 2

Feijoa pulp extract reduces Hg-induced hemolysis. Cells were treated with 40 μM HgCl₂ for 24 h in the presence of increasing concentrations of extract. Data are the means ± SEM (n = 9). Statistical significance was calculated with one-way ANOVA followed by Tukey’s test. ** (p < 0.05) indicates a significant difference from cells lacking HgCl₂ treatment. # (p < 0.05) and ## (p < 0.01) indicate significant differences from cells lacking Feijoa extract treatment.

Figure 3

Feijoa peel extract protects against Hg-induced reactive oxygen species (ROS) production in red blood cells (RBC). Cells were treated with 40 μM HgCl₂ for 4 h in the presence of increasing concentrations of extract. ROS production was determined by fluorescence unit means of the dichlofluorescein (DCF) probe. Data are the means ± SEM (n = 9). Statistical significance was calculated with one-way ANOVA followed by Tukey’s test. ** (p < 0.05) indicates a significant difference from cells lacking HgCl₂ treatment. # (p < 0.05) and ## (p < 0.01) indicate significant differences from cells lacking Feijoa extract treatment.

Figure 4

Feijoa pulp extract protects against Hg-induced ROS production in RBC. Cells were treated with 40 μM HgCl₂ for 4 h in the presence of increasing concentrations of extract. ROS production was determined by fluorescence unit means of the DCF probe. Data are the means ± SEM (n = 9). Statistical significance was calculated with one-way ANOVA followed by Tukey’s test. ** (p < 0.05) indicates a significant difference from cells lacking HgCl₂ treatment. # (p < 0.05) and ## (p < 0.01) indicate significant differences from cells lacking Feijoa extract treatment.

Figure 5

Feijoa peel and pulp extracts protect against Hg-induced glutathione (GSH) decrease in RBC. Cells were treated with 40 μM HgCl₂ for 4 h in the presence of increasing concentrations of Feijoa peel or pulp. Data are the means ± SEM (n = 9). Statistical significance was calculated with one-way ANOVA followed by Tukey’s test. * (p < 0.05) and ** (p < 0.01) indicate significant differences from cells lacking Feijoa extract treatment.

Figure 6

Feijoa peel and pulp extracts protect against Hg-induced membrane thiol depletion in RBC. Cells were treated with 40 μM HgCl₂ for 4 h in the presence of increasing concentrations of Feijoa peel or pulp. Data are the means ± SEM (n = 9). Statistical significance was calculated with one-way ANOVA followed by Tukey’s test. * (p < 0.05) and ** (p < 0.01) indicate significant differences from cells lacking Feijoa extract treatment.

Figure 7

Peel and pulp extracts of Feijoa reduce microvesicles (MV) released from RBC. Untreated cells are shown in (A). Cells were treated with 40 μM HgCl₂ for 4 h (B) and concurrently treated with 20 or 80 µg/mL of Feijoa peel (C and D, respectively) and pulp (E and F, respectively) extracts. RBC were stained with Annexin V-FITC.