Heparin Oligosaccharides as Vasoactive Intestinal Peptide Inhibitors via their Binding Process Characterization

BACKGROUND

It has been proven that vasoactive intestinal peptide (VIP) was involved in the pathogenesis of prostate cancer. Cardin et al. found that by an alanine scan, the heparin-binding site on VIP was exactly the same sequence in VIP and its receptor. Therefore, heparin could competitively block the binding of VIP and its receptor. However, the structure-activity relationship between heparin and VIP has not been reported, especially in terms of the sequence and sulfation patterns of heparin oligosaccharides upon binding to VIP.

OBJECTIVE

The binding process between heparin oligosaccharides and VIPA variety of experiments was designed to study the structure-activity relationship between heparin oligosaccharides and VIP.

METHODS

Heparin was enzymatically digested and purified to produce heparin oligosaccharides, and the structures were characterized by NMR. The binding capacity between heparin oligosaccharides and VIP was analyzed by GMSA and ITC experiments. The binding between heparin oligosaccharides and VIP was simulated using a molecular docking program to show the complex. ELISA assay was used to investigate the effect of non-anticoagulant heparin oligosaccharides on the VIP-mediated cAMP/PKA signaling pathway in vitro.

RESULTS

The results indicated that both the length and the sulfation pattern of heparin oligosaccharides affected its binding to VIP. VIP could induce the expression of cAMP at a higher level in PC3 cells, which could be regulated by the interaction of heparin oligosaccharides and VIP.

CONCLUSION

The binding between heparin oligosaccharides and VIP could block the binding between VIP and its receptor on tumor cells. Downloading the regulation of the expression level of cAMP could possibly further affect the subsequent activation of PKA. These non-anticoagulant heparin oligosaccharides may block the VIP-mediated cAMP/PKA signaling pathway and thus exert their antitumor activity.

Uncovering the detailed mode of cleavage of heparinase I toward structurally defined heparin oligosaccharides

For a more insightful investigation into the specificity of bacterial heparinase I, a series of structurally well-defined heparin oligosaccharides was synthesized using a highly efficient chemoenzymatic strategy. Apart from the primary cleavage site, five glycosidic linkages of oligosaccharides with varying modifications to obtain secondary cleavage sites were degraded by a high concentration of heparinase I. The reactivity of linkages toward heparinase I was not entirely dependent on the 2-O-sulfated iduronic acid being cleaved or the neighboring 6-O-sulfated glucosamine residues, but it was dependent on higher degrees of sulfation of oligosaccharides and indispensable N-substituted glucosamine adjacent to the cleavable linkage. Moreover, the enzyme demonstrated less preferential cleavage toward glycosidic linkages containing glucuronic acid than those containing iduronic acid of the counterpart oligosaccharides. Biolayer interferometry revealed differences in reactivity that are not completely consistent with different affinities of substrates to enzyme. Our study presented accurate information on the cleavage promiscuity of heparinase I that is crucial for heparin depolymerization.

Re-visiting the structure of heparin

The sulfated polysaccharide heparin has been used as a life-saving anticoagulant in clinics well before its detailed structure was known. This mini-review is a survey of the evolution in the discovery of the primary and secondary structure of heparin. Highlights in this history include elucidation and synthesis of the specific sequence that binds to antithrombin, the development of low-molecular-weight heparins currently used as antithrombotic drugs, and the most promising start of chemo-enzymatic synthesis. Special emphasis is given to peculiar conformational properties contributing to interaction with proteins that modulate different biological properties.

Heparin-derived supersulfated disaccharide inhibits allergic airway responses in sheep

The tetrasaccharide sequence of heparin oligosaccharides is the minimum chain length possessing anti-allergic activity, as the disaccharide fraction is inactive. Since sulfation pattern can modify the biological actions of heparin, we hypothesized that "supersulfation" of the inactive heparin disaccharide could confer anti-allergic activity to this molecule. To test this, we produced a supersulfated heparin disaccharide (Hep-SSD) and evaluated its anti-allergic activity in sheep with documented antigen-induced early and late airway responses (EAR and LAR) and airway hyperresponsiveness (AHR). Porcine intestinal heparin was depolymerized with nitrous acid, the disaccharide fraction separated by size exclusion chromatography, and then treated with pyridine-sulfur trioxide complex to yield Hep-SSD. Its chemical structure [IdoU2',3',4'S (1→4) AMan1,3,6S] was confirmed by HPLC, Mass Spectrometry and NMR analysis. Inhaled doses of 5 mg, 10 mg and 20 mg Hep-SSD produced inhibition of EAR (8%, 35% and 35%), LAR (50%, 80%, and 77%) and AHR (67%, 100% and 75%), respectively. A single oral dose of 2 mg/kg Hep-SSD given 90 min before challenge significantly inhibited EAR, LAR and AHR, but 1 mg/kg was ineffective. Multi dose oral treatment with Hep-SSD had a cumulative effect, as a once daily dose of 2 mg/kg for 3 days (last dose, 16 h before antigen) inhibited EAR, LAR and AHR by 30%, 75% and 74%, respectively. Finally, the oral activity of Hep-SSD could be enhanced 4 fold by formulating it with Carbopol(®)934P, in an enteric coated capsule. These data demonstrate that "supersulfation" can confer biological activity to the inactive heparin disaccharide. Both inhaled and oral Hep-SSD demonstrate significant anti-allergic activity and, therefore, may have therapeutic potential.