Heparin and related molecules possess a variety of activities that are anti-inflammatory and could potentially be useful in the treatment of a range of inflammatory diseases. Previously, we have reported that low molecular weight fractions of heparin, of 4, 6 or 14 saccharides in length, inhibit the release of elastase from human neutrophils in a manner dependent upon the number of saccharides per heparin molecule (14 > 6 or 4 saccharides), suggesting that an optimum molecular weight may exist for this activity (Lever et al., 2003). In the present study, in order to examine this further, we have studied the effect of an alternative range (8–20 saccharides) of low molecular weight heparins, on elastase release from human neutrophils.

H eparin fractions were prepared from unfractionated heparin (UH) by heparinase digestion, yielding homogenously sized heparin populations of eight, ten, twelve or twenty saccharides in length (8sH, 10sH, 12sH and 20sH, respectively). These molecules (0.1–100 µg ml^-1) were compared for their effects on neutrophil elastase release in response to f-met-leu-phe (fMLP), both with and without prior priming with tumour necrosis factor- (TNF- ) Neutrophils, isolated from the venous blood of healthy donors (n=6) were stimulated with fMLP (10^-7 M), with or without pre-treatment with TNF- (30 minutes; 100 U ml^-1), in the absence and presence of test compounds and elastase release was quantified colorimetrically after 45 minutes. Data were analysed by ANOVA, followed by Dunnett’s test and were considered significant if P < 0.05.

The maximum inhibition seen with UH (100 µg ml^-1), in control experiments carried out in parallel, was 49±6% (fMLP alone) and 63±9% (TNF- + fMLP), respectively. By contrast, all of the low molecular weight fractions were more efficacious in inhibiting (P<0.05) fMLP-induced elastase release without (max. inhibition at 100 µg.ml^-1 : 8sH, 56±8%; 10sH, 68±6%; 12sH, 73±6%; 20sH, 88±3%) or with (8sH, 63±9%; 10sH, 84±5%; 12sH, 95±3%; 20sH, 95±3%) TNF- priming. Both the degree of inhibition and the potency of heparin fractions increased with the number of saccharides per molecule.

These data further suggest that an optimum molecular size exists for the inhibitory effect of heparin on neutrophil degranulation. Further experiments are required, however, to investigate the mechanism(s) of action underlying this effect.