2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Nitrosyl-iron Complexes as Potent Smart Nitric Oxide Biosenors: MRI imaging Techniques in Progress

R. Sharma and S. Kwon
Florida State University, US

Keywords:
nitric oxide, MRI, NO-iron complex

Abstract:
Nitric oxide is a gaseous, free radical which plays a role as a diffusible intracellular second messenger. It is emerging as biosensor for monitoring myocardial ischemia and the effect of HMG-CoA reductase inhibitor statins. Presently, nitric oxide synthase (e-NOS) expression and fluorescent indicators are sole choice of in vivo bioimaging of NO and accurate measurement still remains a problem. The fluorescent indicators for NO imaging remain choice in living cells. We propose different NO indicators as potent imaging contrast agents using bioimaging techniques of MRI, EPR and fluorescent imaging with their limitations and quantitative limits. Our focus in this paper is on different characteristics of nitrosyl-iron complexes as MRI signal intensity enhancers and NO visualization by magnetic resonance imaging (MRI) technique. The paramagnetic NO-Fe-DTC metal complex used as contrast agents in MRI, enhances the relaxation of neighboring protons that visualize the NO generated in living animals. Other natural contrast effect is imparted by NO exposure to hemoglobin during MRI signal recording and it serves as source of in vitro MRI and in vivo functional MRI. The functional MRI signal intensity of venous blood in T1-,T2-, and T2*-weighted images proportionately changes with NO. Different approaches of blood hemoglobin and NO interaction appear to monitor fMRI signal. Mainly, metHb and NO-Hb enhanced the signal intensity, while ascorbate decreased the NO dependent fMRI signal intensity. These observations suggest a blood flow-independent effect. Other approaches are emerging in employing MRI techniques such as increased cerebral blood volume after NO precursor L-arginine or NO donor administered or tumor blood flow and partial oxygen pressure changes. These new approaches open a perspective on the bioimaging of NO and the in vivo elucidation of NO effects by magnetic resonance techniques.

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