New role for heparan sulfate: Regulator of leukotriene generation in mouse E-mast cells

In this work, bovine heparan sulfate, pig mucosa heparin and squid chondroitin sulfate-E glycosaminoglycans (GAGs) were compared as to their affect on the synthesis of leukotrienes C₄ (LTC₄) and B₄ (LTB₄) as well as on the production of prostaglandin D₂ (PGD₂) in cultured mouse E-mast cells (E-MC). The maximum percent increase in LTC₄ generation in cells treated with 0.2 μg heparan sulfate was 52 ± 3% (mean ± S.E., n = 5). Whereas 0.5 μg of the GAG increased the production of LTB₄ by 50% Ten micrograms of heparin slightly increased the LTC₄ production (33%) whereas lower doses were found to be ineffective. No significant increase in LTC₄ production was demonstrated when the IgE sensitized E-MC were treated with chondroitin sulfate-E GAG prior to the antigen challenge. Neither one of the three GAGs, at the various doses used, affected the antigen induced exocytosis of β-hexosaminidase from the IgE sensitized E-MC. After 15 min preincubation with heparan sulfate, antigen induced release of PGD₂ from 1 × 10⁶ sensitized cells was inhibited from 5.4 ng ± 0.1 ng into 3.5 ng ± 0.1 ng at 0.5 μg/m1 GAG. All of the three types of GAGs used were uneffective when the E-MC were activated by calcium ionopore A23187. Upon stimulation by IgE-antigen or calcium ionophore A23187, cultured mouse E-MC release preformed mediators and produce oxidative metabolites of arachidonic acid predominantly through the 5-lipoxygenase pathway (1,2,3). Leukotriene C₄ (LTC₄) and B₄ (LTB₄) are two of the major components of the 5-lipoxygenase pathway within the mouse E-MC (1,4). The mechanisms for regulating leukotriene synthesis are not fully understood. This study focused on the role of heparan sulfate and heparin GAGs in the regulation of leukotriene synthesis in cultured mouse E-MC. Heparan sulfate is closely related to heparin GAG. It is characterized by a higher content of N-acetyl groups than is heparin while the content of N-sulfate groups are lower (5). Its predominant uronic acid is glucoronic acid, as opposed to iduronic acid in heparin. The degree of 0-sulfation is lower and corresponds to that of the iduronic acid and N-sulfate content (5). From a biological viewpoint, heparin is characteristically stored in the granule of mast cells, from which it can be released in response to certain stimuli. Heparan sulfate proteoglycan, on the other hand, is an ubiquitous component of cell surfaces of many or all cell types (5). This study demonstrates that heparan and heparin GAG effectively regulate the leukotrienes synthesis after IgE-antigen stimulation of mouse E-MC. However, they were uneffective when the cells were activated by calcium ionopore A23187.