Defense Date

2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Pharmaceutical Sciences

First Advisor

Umesh Desai

Abstract

Current anticoagulants carry a serious risk of bleeding complications. In addition, narrow therapeutic index, drug interactions, immunological reactions, toxicity and high cost to benefit ratio limits the effective use of these drugs in patients with thrombotic conditions.Heparin is the most widely used anticoagulant. We hypothesized that one of the major drawback of heparins, its non-specific interaction with the plasma proteins arises as a result of negative charges. To reduce these non-specific interactions, our laboratory designed sulfated low molecular weight lignin (LMWL) like biomacromolecules, which were found to be direct inhibitors of thrombin and factor Xa, acting through a unique exosite-2 mediated process. To elucidate the structural basis of this mechanism, we studied unsulfated and size fractionated LMWLs. Detailed enzyme inhibition studies with sulfated and unsulfated LMWLs of ferulic and caffeic acid oligomers revealed that sulfation was not absolutely critical for dual inhibition property and smaller oligomers can yield a potent anticoagulant. Mechanistically, unsulfated LMWLs retained exosite-2 mediated inhibition mechanism. A major advantage expected of the unsulfated LMWLs is the possibility that orally bioavailable anticoagulants may become possible.To identify target specific structures within the heterogeneous population of sulfated LMWLs, we prepared sulfated β-O-4-linked oligomer using chemical synthesis. Enzyme inhibition studies revealed that the sulfated β-O-4 LMWL were highly selective direct inhibitors of thrombin. These results show for the first time that specific structural features on LMWL scaffold dictate inhibition specificity. Studies in plasma and blood display highly promising anticoagulant profile for further studies in animals. To further study the LMWL scaffold as macromolecular mimetic of heparin; we investigated their effect in preventing cellular infection by herpes simplex virus-1 (HSV-1). Based on previous findings on sulfated lignins a size-dependent study on unsulfated LMWLs was done. The unsulfated lignins were found to not only inhibit HSV-1 entry into mammalian cells, but were more potent than sulfated lignins. Interestingly, shorter chains were found to be as active as the longer ones, suggesting that structural features, in addition to carboxylate groups, may be important. It can be expected that unsulfated lignins also antagonize the entry of other enveloped viruses, like HIV-1 and HCV that utilize heparan sulfate to gain entry into cells. The results further present major opportunities for developing lignin-based antiviral formulations for topical use.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

5-11-2011

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