TY - JOUR
T1 - Apples increase nitric oxide production by human saliva at the acidic pH of the stomach
T2 - A new biological function for polyphenols with a catechol group?
AU - Peri, Laura
AU - Pietraforte, Donatella
AU - Scorza, Giuseppe
AU - Napolitano, Aurora
AU - Fogliano, Vincenzo
AU - Minetti, Maurizio
PY - 2005/9/1
Y1 - 2005/9/1
N2 - Dietary inorganic nitrate is secreted in saliva and reduced to nitrite by bacterial flora. At the acidic pH of the stomach nitrite is present as nitrous acid in equilibrium with nitric oxide (.NO), and other nitrogen oxides with nitrating and nitrosating activity. .NO in the stomach exerts several beneficial effects, but nitrosating/nitrating species have been implicated as a possible cause of epithelial neoplasia at the gastroesophageal junction. We investigated the effects of apple extracts on .NO release by human saliva at pH 2. A water extract obtained from apple homogenate increased .NO release caused by acidification of saliva. Data show that polyphenols were responsible for this activity, with chlorogenic acid and (+)-catechin the most active and concentrated species. However, ferulic acid, a hydroxycinnamic acid with only one aromatic hydroxyl group, did not increase .NO release. Fructose, the most representative sugar in apples, was also inactive. Interestingly, ascorbic acid in saliva induced a SCN --enhanced burst of .NO but, unlike apple, the release was transient. The simultaneous addition of ascorbic acid and apple extract caused a burst of .NO followed by the increased steady-state level characteristic of saliva containing apple extract. Chlorogenic acid and (+)-catechin, but not ferulic acid, formed o-semiquinone radicals and nitrated polyphenols, suggesting the scavenging of .NO2 by o-semiquinones. Our results propose that some apple polyphenols not only inhibit nitrosation/nitration but also promote .NO bioavailabilty at the gastric level, a previously unappreciated function.
AB - Dietary inorganic nitrate is secreted in saliva and reduced to nitrite by bacterial flora. At the acidic pH of the stomach nitrite is present as nitrous acid in equilibrium with nitric oxide (.NO), and other nitrogen oxides with nitrating and nitrosating activity. .NO in the stomach exerts several beneficial effects, but nitrosating/nitrating species have been implicated as a possible cause of epithelial neoplasia at the gastroesophageal junction. We investigated the effects of apple extracts on .NO release by human saliva at pH 2. A water extract obtained from apple homogenate increased .NO release caused by acidification of saliva. Data show that polyphenols were responsible for this activity, with chlorogenic acid and (+)-catechin the most active and concentrated species. However, ferulic acid, a hydroxycinnamic acid with only one aromatic hydroxyl group, did not increase .NO release. Fructose, the most representative sugar in apples, was also inactive. Interestingly, ascorbic acid in saliva induced a SCN --enhanced burst of .NO but, unlike apple, the release was transient. The simultaneous addition of ascorbic acid and apple extract caused a burst of .NO followed by the increased steady-state level characteristic of saliva containing apple extract. Chlorogenic acid and (+)-catechin, but not ferulic acid, formed o-semiquinone radicals and nitrated polyphenols, suggesting the scavenging of .NO2 by o-semiquinones. Our results propose that some apple polyphenols not only inhibit nitrosation/nitration but also promote .NO bioavailabilty at the gastric level, a previously unappreciated function.
KW - Antioxidants
KW - Apple polyphenols
KW - Chlorogenic acid
KW - Gastric juice
KW - Nitration
KW - Nitric oxide
KW - Nitrite
KW - Nitrogen dioxide
KW - Nitrosation
KW - Saliva
U2 - 10.1016/j.freeradbiomed.2005.04.021
DO - 10.1016/j.freeradbiomed.2005.04.021
M3 - Article
C2 - 16085185
AN - SCOPUS:23444436373
SN - 0891-5849
VL - 39
SP - 668
EP - 681
JO - Free Radical Biology and Medicine
JF - Free Radical Biology and Medicine
IS - 5
ER -