Nitrosyl-iron complexes as potent smart nitric oxide biosensors: MRI imaging techniques in progress

Presently, EPR and fluorescent biosensors are sole choice of in vivo bioimaging of NO and accurate measurement still remains a problem. We propose different NO biosensors as potent imaging contrast agents using multimodal bioimaging techniques of MRI, EPR and fluorescent imaging with their limitations and quantitative limits. Our focus in this paper is on different characteristics of known biosensors and 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. These observations suggest a blood flow-independent effect. Other approaches are emerging to get biosensors for multimodal imaging. These new approaches open a perspective on the bioimaging of NO and the in vivo elucidation of NO effects by magnetic resonance techniques.