Studies on the effect of calcium in interactions between heparin and heparin cofactor II using surface plasmon resonance

Heparin is biocompatible and can induce differentiation of human dental pulp cells

AIM

To investigate the biocompatibility, osteogenic bioactivity and mRNA expression of the osteo/odontogenic markers bone morphogenetic protein 2 (BMP-2), osteocalcin (OC) and alkaline phosphatase (ALP), induced by heparin in human dental pulp cells (hDPCs).

METHODOLOGY

hDPCs were exposed to the heparin, and cell viability was assessed by 3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide (MTT), and cell death was evaluated by flow cytometry. Osteogenic bioactivity was evaluated by the alkaline phosphatase (ALP) assay, and the detection of calcium deposits by alizarin red staining (ARS). The gene expression of BMP-2, OC and ALP was quantified with real-time PCR. Statistical analysis was performed with ANOVA and Bonferroni or Tukey post-test and t-test (α = 0.05).

RESULTS

Heparin had no cytotoxic effect and did not induce apoptosis. After 3 days, heparin had significantly higher ALP activity in comparison with the control (P < 0.05). Heparin had a significant (P < 0.05) stimulatory effect on the formation of mineralized nodules. BMP-2 and OC mRNA expressions were significantly higher in cells exposed to heparin than control group after 1 day (P < 0.05).

CONCLUSIONS

Heparin was biocompatible in hDPCs, induced osteogenic bioactivity and enhanced mRNA expression of osteo/odontogenic markers BMP-2 and OC. These results suggest that heparin has potential to induce osteo/odontogenic cell differentiation of hDPCs.

Serpin-glycosaminoglycan interactions

Serpins (serine protease inhibitors) have traditionally been grouped together based on structural homology. They share common structural features of primary sequence, but not all serpins require binding to cofactors in order to achieve maximal protease inhibition. In order to obtain physiologically relevant rates of inhibition of target proteases, some serpins utilize the unbranched sulfated polysaccharide chains known as glycosaminoglycans (GAGs) to enhance inhibition. These GAG-binding serpins include antithrombin (AT), heparin cofactor II (HCII), and protein C inhibitor (PCI). The GAGs heparin and heparan sulfate have been shown to bind AT, HCII, and PCI, while HCII is also able to utilize dermatan sulfate as a cofactor. Other serpins such as PAI-1, kallistatin, and α(1)-antitrypsin also interact with GAGs with different endpoints, some accelerating protease inhibition while others inhibit it. There are many serpins that bind or carry ligands that are unrelated to GAGs, which are described elsewhere in this work. For most GAG-binding serpins, binding of the GAG occurs in a conserved region of the serpin near or involving helix D, with the exception of PCI, which utilizes helix H. The binding of GAG to serpin can lead to a conformational change within the serpin, which can lead to increased or tighter binding to the protease, and can accelerate the rates of inhibition up to 10,000-fold compared to the unbound native serpin. In this chapter, we will discuss three major GAG-binding serpins with known physiological roles in modulating coagulation: AT (SERPINC1), HCII (SERPIND1), and PCI (SERPINA5). We will review methodologies implemented to study the structure of these serpins and those used to study their interactions with GAG's. We discuss novel techniques to examine the serpin-GAG interaction and finally we review the biological roles of these serpins by describing the mouse models used to study them.

Binding between the integrin alphaXbeta2 (CD11c/CD18) and heparin

The interactions between cell surface receptors and sulfated glucosamineglycans serve ubiquitous roles in cell adhesion and receptor signaling. Heparin, a highly sulfated polymer of uronic acids and glucosamine, binds strongly to the integrin receptor alphaXbeta2 (p150,95, CD11c/CD18). Here, we analyze the structural motifs within heparin that constitute high affinity binding sites for the I domain of integrin alphaXbeta2. Heparin oligomers with chain lengths of 10 saccharide residues or higher provide strong inhibition of the binding by the alphaX I domain to the complement fragment iC3b. By contrast, smaller oligomers or the synthetic heparinoid fondaparinux were not able to block the binding. Semipurified heparin oligomers with 12 saccharide residues identified the fully sulfated species as the most potent antagonist of iC3b, with a 1.3 microM affinity for the alphaX I domain. In studies of direct binding by the alphaX I domain to immobilized heparin, we found that the interaction is conformationally regulated and requires Mg2+. Furthermore, the fully sulfated heparin fragment induced conformational change in the ectodomain of the alphaXbeta2 receptor, also demonstrating allosteric linkage between heparin binding and integrin conformation.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.