Proline-rich proteins moderate the inhibitory effect of tea on iron absorption in rats

Tea inhibits iron absorption in studies in which tea is given with radiolabeled iron to humans as a single dose. Our objective was to test the hypothesis that proline-rich proteins (PRPs) may act as a defense against this effect by forming complexes with tannins, thereby preventing them from inhibiting iron absorption. Two studies were conducted. In study 1, rats were given test solutions containing (59)FeCl(3) in water, tea, or tea + gelatin (T/G). In study 2, the rats were divided into 3 groups and assigned to one of 3 nutritionally complete diets: control, tea (5 g tea tannin/kg diet), or T/G (5 g tea tannin + 60 g gelatin/kg diet). Rats were fed the respective diets for 5 d and then given a single (59)Fe-labeled meal of the diet. Iron absorption was measured by whole-body retention of the (59)Fe over a 2-wk period. Iron absorption in study 1 was lower in the tea group (24 +/- 9.6%, P < 0.05) than in the T/G (42 +/- 19.4%) or water groups (50 +/- 7.5%). In study 2, iron absorption did not differ among the groups. Rats fed the tea diet had dramatic hypertrophy of the parotid salivary glands. Adding gelatin as a proxy for salivary PRPs to the tea eliminated the inhibitory effect of tea on iron absorption. The results suggest that PRPs, whether from salivary glands or diet, can protect against the inhibition of iron absorption by tea.