Giridhar R. Akkaraju

High-porosity poly(ε-caprolactone)/mesoporous silicon scaffolds: Calcium phosphate deposition and biological response to bone precursor cells

In this study, the fabrication and characterization of highly porous composites composed of poly(epsilon-caprolactone) and bioactive mesoporous silicon (BioSilicon) prepared using salt-leaching and microemulsion/freeze-drying methods are described. The role of silicon, along with porosity, in the scaffolds on calcium phosphate deposition was assessed using acellular in vitro calcification analyses. The presence of bioactive silicon in these scaffolds is essential for the deposition of calcium phosphate while the samples are immersed in simulated body fluid (SBF). Silicon-containing scaffolds produced using salt-leaching methods are more likely to calcify as a consequence of SBF exposure than those produced using microemulsion methods. In vitro proliferation and cell viability assays of these porous composites using human embryonic kidney fibroblast cells indicate that no cytotoxic effects are present in the scaffolds under the conditions used. Preliminary analyses of bone sialoprotein and alkaline phosphatase expression using orthopedically relevant mesenchymal cells derived from bone marrow suggest that such scaffolds are capable of mediating osteoblast differentiation. Overall, the results show that these porous silicon-containing polymer scaffolds enhance calcification, can be considered nontoxic to cells, and support the proliferation, viability, attachment, and differentiation of bone precursor cells.

Medicinal Surface Modification of Silicon Nanowires: Impact on Calcification and Stromal Cell Proliferation

Medicinal surface modification of silicon nanowires (SiNWs) with selected bisphosphonates, such as the known antiosteoporotic drug alendronate, is described. In terms of specific assays relevant to orthopedic applications, the impact of selected bisphosphonate attachment on acellular calcification in simulated plasma is reported. To further investigate biocompatibility, proliferation assays of these modified nanowires were carried out using an orthopedically relevant cell line: mesenchymal stem cells derived from mouse stroma. It is found that the identity of the bisphosphonate ligand strongly and sensitively impacts its resultant cytotoxicity.

Fe3O4-nanoparticles within porous silicon: Magnetic and cytotoxicity characterization

The magnetic properties of porous silicon/Fe3O4 composites are investigated with respect to the adjustability of the blocking temperature along with an evaluation of any size-dependent changes in cytocompatibility. Fe3O4-nanoparticles have been infiltrated within mesoporous silicon, resulting in a system with tunable magnetic properties due to the matrix-morphology, the loading of the nanoparticles, and their size. In order to provide basic information regarding its suitability as a therapeutic platform, the cytotoxicity of these composites have been investigated by a trypan blue exclusion assay with respect to human embryonic kidney 293 cells, and the results compared with cell-only and known cytotoxic controls.

In Vitro Gene Delivery with Large Porous Silicon Nanoparticles Fabricated Using Cost-Effective, Metal-Assisted Chemical Etching

The cytocompatibility, cell membrane affinity, and plasmid DNA delivery from surface oxidized, metal-assisted stain-etched mesoporous silicon nanoscale particles (pSiNPs) to human embryonic kidney (HEK293) cells is demonstrated, suggesting the possibility of using such material for targeted transfection and drug delivery.

Bimodal-hybrid heterocyclic amine targeting oxidative pathways and copper mis-regulation in Alzheimer's disease†

Oxidative stress resulting from metal-ion misregulation plays a role in the development of Alzheimers disease (AD). This process includes the production of tissue-damaging reactive oxygen species and amyloid aggregates. Herein we describe the synthesis, characterization and protective capacity of the small molecule, lipoic cyclen, which has been designed to target molecular features of AD. This construct utilizes the biologically compatible and naturally occurring lipoic acid as a foundation for engendering low cellular toxicity in multiple cell lines, radical scavenging capacity, tuning the metal affinity of the parent cyclen, and results in an unexpected affinity for amyloid without inducing aggregation. The hybrid construct thereby shows protection against cell death induced by amyloid aggregates and copper ions. These results provide evidence for the rational design methods used to produce this fused molecule as a potential strategy for the development of lead compounds for the treatment of neurodegenerative disorders.

Synthesis, Characterization, and Activity of a Triazine Bridged Antioxidant Small Molecule

Metal-ion misregulation and oxidative stress continue to be components of the continually evolving hypothesis describing the molecular origins of Alzheimers disease. Therefore, these features are viable targets for synthetic chemists to explore through hybridizations of metal-binding ligands and antioxidant units. To date, the metal-binding unit in potential therapeutic small molecules has largely been inspired by clioquinol with the exception of a handful of heterocyclic small molecules and open-chain systems. Heterocyclic small molecules such as cyclen (1,4,7,10-tetraazacyclododecane) have the advantage of straightforward N-based modifications, allowing the addition of functional groups. In this work, we report the synthesis of a triazine bridged system containing two cyclen metal-binding units and an antioxidant coumarin appendage inspired by nature. This new potential therapeutic molecule shows the ability to bind copper in a unique manner compared to other chelates proposed to treat Alzheimers disease. DPPH and TEAC assays exploring the activity of N-(2-((4,6-di(1,4,7,10-tetraazacyclododecan-1-yl)-1,3,5-triazin-2-yl)amino)ethyl)-2-oxo-2H-chromene-3-carboxamide (molecule 1) show that the molecule is antioxidant. Cellular studies of molecule 1 indicate a low toxicity (EC50 = 80 μM) and the ability to protect HT-22 neuronal cells from cell death induced by Aβ + copper(II), thus demonstrating the potential for molecule 1 to serve as a multimodal therapeutic for Alzheimers disease.

DNA site-specific N3-adenine methylation targeted to estrogen receptor-positive cells.

A compound that can target cells expressing the estrogen receptor (ER), and produce predominantly 3-MeA adducts in those cells has been designed and synthesized. This compound produces mainly the 3-MeA adduct upon reaction with calf thymus DNA, and binds to the ER with a relative binding affinity of 51% (estradiol = 100%). The compound is toxic to ER-expressing MCF-7 breast cancer cells, and pre-treatment with the ER antagonist fulvestrant abrogates the toxicity. Pre-treatment of MCF-7 cells with netropsin, which inhibits N3-adenine methylation by the compound, resulted in a threefold decrease in the toxicity. These results demonstrate the feasibility of this strategy for producing 3-MeA adducts in targeted cells.