Background: Previous studies showed that heparinâ��s anti-allergic activity is molecular weight dependent and\r\nresides in oligosaccharide fractions of <2500 daltons.\r\nObjective: To investigate the structural sequence of heparinâ��s anti-allergic domain, we used nitrous acid\r\ndepolymerization of porcine heparin to prepare an oligosaccharide, and then fractionated it into disaccharide,\r\ntetrasaccharide, hexasaccharide, and octasaccharide fractions. The anti-allergic activity of each oligosaccharide\r\nfraction was tested in allergic sheep.\r\nMethods: Allergic sheep without (acute responder) and with late airway responses (LAR; dual responder) were\r\nchallenged with Ascaris suum antigen with and without inhaled oligosaccharide pretreatment and the effects on\r\nspecific lung resistance and airway hyperresponsiveness (AHR) to carbachol determined. Additional inflammatory\r\ncell recruitment studies were performed in immunized ovalbumin-challenged BALB/C mice with and without\r\ntreatment.\r\nResults: The inhaled tetrasaccharide fraction was the minimal effective chain length to show anti-allergic activity.\r\nThis fraction showed activity in both groups of sheep; it was also effective in inhibiting LAR and AHR, when\r\nadministered after the antigen challenge. Tetrasaccharide failed to modify the bronchoconstrictor responses to\r\nairway smooth muscle agonists (histamine, carbachol and LTD4), and had no effect on antigen-induced histamine\r\nrelease in bronchoalveolar lavage fluid in sheep. In mice, inhaled tetrasaccharide also attenuated the ovalbumininduced\r\nperibronchial inflammatory response and eosinophil influx in the bronchoalveolar lavage fluid. Chemical\r\nanalysis identified the active structure to be a pentasulfated tetrasaccharide ([IdoU2S (1�®4)GlcNS6S (1�®4) IdoU2S\r\n(1�®4) AMan-6S]) which lacked anti-coagulant activity.\r\nConclusions: These results demonstrate that heparin tetrasaccharide possesses potent anti-allergic and antiinflammatory\r\nproperties, and that the domains responsible for anti-allergic and anti-coagulant activity are distinctly\r\ndifferent.
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