Influence of harvest time on citrus pectin and its in vitro inhibition of fibroblast growth factor signal transduction
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Seasonal changes in pectin content and chemical composition were studied in three anatomical layers of 'Rio Red' grapefruit (Citrus paradisi Macf), a currently popular cultivar in the Rio Grande Valley in Texas, USA. Fruits were harvested at intervals between August 1998 and May 1999. Pectin content in flavedo decreased throughout the season, while in albedo and segment membrane the pectin content was lowest in mid-season (November and January). In all three layers the anhydrogalacturonic acid (AGA) content of pectin was highest in mid-season. While the methoxyl content (MC) of pectin increased, the total neutral sugar (TNS) content of pectin decreased in all three layers throughout the season. The in vitro effect of grapefruit pectin on fibroblast growth factor (FGF)-FGF receptor (FGFR) interaction was also investigated. The strong interdependence of heparin on factor-receptor interaction provides means for identifying new antagonists of growth factor activity and thus for treatment of various diseases. Our results showed that grapefruit pectin significantly inhibited the binding of FGF-1 to FGFR1 in the presence of 0.1 g ml-1 heparin. Pectin of albedo from grapefruits harvested in January was the most potent inhibitor. The in vitro inhibitory activity was significantly correlated with the percentage of rhamnose. Kinetic studies revealed a competitive nature of pectin on FGF signal transduction with heparin. The observation that the biological activity of heparin can be antagonised by citrus pectin suggests that pectins should be investigated further as anti-growth factor agents for potential health benefits. 2002 Society of Chemical Industry.
