Strawberry polyphenols attenuate ethanol-induced gastric lesions in rats by activation of antioxidant enzymes and attenuation of MDA increase

Abstract

Background and aim: Free radicals are implicated in the aetiology of gastrointestinal disorders such as gastric ulcer, colorectal cancer and inflammatory bowel disease. Strawberries are common and important fruit due to their high content of essential nutrient and beneficial phytochemicals which seem to have relevant biological activity on human health. In the present study we investigated the antioxidant and protective effects of three strawberry extracts against ethanol-induced gastric mucosa damage in an experimental in vivo model and to test whether strawberry extracts affect antioxidant enzyme activities in gastric mucosa.

Methods/principal findings: Strawberry extracts were obtained from Adria, Sveva and Alba cultivars. Total antioxidant capacity and radical scavenging capacity were performed by TEAC, ORAC and electron paramagnetic resonance assays. Identification and quantification of anthocyanins was carried out by HPLC-DAD-MS analyses. Different groups of animals received 40 mg/day/kg body weight of strawberry crude extracts for 10 days. Gastric damage was induced by ethanol. The ulcer index was calculated together with the determination of catalase and SOD activities and MDA contents. Strawberry extracts are rich in anthocyanins and present important antioxidant capacity. Ethanol caused severe gastric damage and strawberry consumption protected against its deleterious role. Antioxidant enzyme activities increased significantly after strawberry extract intake and a concomitantly decrease in gastric lipid peroxidation was found. A significant correlation between total anthocyanin content and percent of inhibition of ulcer index was also found.

Conclusions: Strawberry extracts prevented exogenous ethanol-induced damage to rats' gastric mucosa. These effects seem to be associated with the antioxidant activity and phenolic content in the extract as well as with the capacity of promoting the action of antioxidant enzymes. A diet rich in strawberries might exert a beneficial effect in the prevention of gastric diseases related to generation of reactive oxygen species.

Figure 1. Hydroxyl radical scavenging activities of strawberry extracts.

Positive control (DMPO, H₂O₂ and FeSO₄) signal amplitude was compared to those of the DMPO-OH adducts recorded in the presence of strawberry extracts. The decrease in the signal amplitude in the samples correlates with their radical scavenging activity. (A) Typical EPR spectrum of the OH^• radical trapped with DMPO from the Fenton reaction (positive control), (B) typical EPR spectra obtained after the strawberry extract was added.

Figure 2. Representative HPLC-DAD chromatograms recorded at 520 nm showing the anthocyanin profiles of the strawberry samples.

Adria, Alba and Sveva cultivars. Peaks: 1, (Epi)afzelechin-(4→8)Pg 3-glucoside; 2, Cy-3-glucoside; 3, Pg 3,5-diglucoside; 4, Pg 3-glucoside; 5, Pg 3-rutinoside; 6, Cy 3-malonylglucoside; 7, Pg 3-malonylglucoside; 8, Pg 3-acetylglucoside; 9, Pg 3-succinylglucoside or Pg 3-methylmalonylglucoside.

Figure 3. Protective effect of strawberry extracts on gastric injury in rats.

Representative rat stomachs exposed to absolute ethanol for one hour: (A) non-pretreated rats, (B) rats pretreated with 100 mg/kg of Quercetin. Rats pretreated with 40 mg/kg of strawberry crude extracts once per day for 10 days: (C) Adria extract, (D) Alba extract and (E) Sveva extract. The last administration of strawberry extract was 2 h before absolute ethanol administration that induced gastric lesions.

Figure 4. Effect of intragastric pretreatment with the different strawberry extract and quercetin on the ulcer index induced by ethanol.

^* Significant inhibition as compared to the value in the ethanol group (p<0.05).

Figure 5. Effect of intragastric pretreatment with the different strawberry extract and 100 mg/kg of quercetin on the malondialdehyde concentration (nmol/mg prot.) in gastric mucosa.

^* Statistical significance (p<0.05) of difference in MDA concentrations in non-pretreated rats exposed to absolute ethanol (Ethanol) as compared to the control animals (control). ^** Statistical significance (p<0.05) of difference in MDA concentrations in pretreated rats as compared to the non-pretreated rats exposed to ethanol (Ethanol).

Figure 6. Effect of intragastric pretreatment with the different strawberry extract and quercetin on the superoxide dismutase activity (U/mg prot.) in gastric mucosa.

^* Statistical significance (p<0.05) of difference in SOD activity in non-pretreated rats exposed to ethanol (Ethanol) as compared to the control animals (Control). ^** Statistical significance (p<0.05) of difference in SOD activity in pretreated rats as compared to the non-pretreated rats exposed to absolute ethanol (Ethanol) group. ^## Significant difference in relation to the Sveva cultivar (p<0.05).

Figure 7. Effect of intragastric pretreatment with the different strawberry extract and 100 mg/kg of quercetin on the Cat activity (U/mg prot.) in gastric mucosa.

^* Statistical significance (p<0.05) of difference in Cat activity in non-pretreated rats exposed to ethanol (Ethanol) as compared to the control animals (Control). ^** Statistical significance (p<0.05) of difference in Cat activity in pretreated rats compared to the non-pretreated rats exposed to ethanol (Ethanol) group.