Near-Infrared Luciferin Analogs for <em>In Vivo</em> Optical Imaging

The firefly bioluminescence reaction has been exploited for in vivo optical imaging in life sciences. To develop highly sensitive bioluminescence imaging technology, many researchers have synthesized luciferin analogs and luciferase mutants. This chapter first discusses synthetic luciferin analogs and their structure–activity relationships at the luminescence wavelength of the firefly bioluminescence reaction. We then discuss the development of luciferin analogs that produce near-infrared (NIR) light. Since NIR light is highly permeable for biological tissues, NIR luciferin analogs might sensitively detect signals from deep biological tissues such as the brain and lungs. Finally, we introduce two NIR luciferin analogs (TokeOni and seMpai) and a newly developed bioluminescence imaging system (AkaBLI). TokeOni can detect single-cell signals in mouse tissue and luminescence signals from marmoset brain, whereas seMpai can detect breast cancer micro-metastasis. Both reagents are valid for in vivo bioluminescence imaging with high sensitivity

Dynorphin induced magnetic ordering in lipid bilayers as studied by 31P NMR spectroscopy

AbstractLipid bilayers of dimyristoyl phosphatidylcholine (DMPC) containing opioid peptide dynorphin A(1–17) are found to be spontaneously aligned to the applied magnetic field near at the phase transition temperature between the gel and liquid crystalline states (Tm=24°C), as examined by 31P NMR spectroscopy. The specific interaction between the peptide and lipid bilayer leading to this property was also examined by optical microscopy, light scattering, and potassium ion-selective electrode, together with a comparative study on dynorphin A(1–13). A substantial change in the light scattering intensity was noted for DMPC containing dynorphin A(1–17) near at Tm but not for the system containing A(1–13). Besides, reversible change in morphology of bilayer, from small lipid particles to large vesicles, was observed by optical microscope at Tm. These results indicate that lysis and fusion of the lipid bilayers are induced by the presence of dynorphin A(1–17). It turned out that the bilayers are spontaneously aligned to the magnetic field above Tm in parallel with the bilayer surface, because a single 31P NMR signal appeared at the perpendicular position of the 31P chemical shift tensor. In contrast, no such magnetic ordering was noted for DMPC bilayers containing dynorphin A(1–13). It was proved that DMPC bilayer in the presence of dynorphin A(1–17) forms vesicles above Tm, because leakage of potassium ion from the lipid bilayers was observed by potassium ion-selective electrode after adding Triton X-100. It is concluded that DMPC bilayer consists of elongated vesicles with the long axis parallel to the magnetic field, together with the data of microscopic observation of cylindrical shape of the vesicles. Further, the long axis is found to be at least five times longer than the short axis of the elongated vesicles in view of simulated 31P NMR lineshape

Synthesis and Luminescence Properties of Near-Infrared N-Heterocyclic Luciferin Analogues for In Vivo Optical Imaging

As a means of achieving highly sensitive bioluminescence imaging of deep tissues utilizing the firefly luciferin-luciferase (L-L) reaction, we previously reported a luciferin analogue, AkaLumine, which exhibits high cell-permeability and emits near-infrared (NIR) light with high tissue-penetration by the L-L reaction. However, while AkaLumine enables us to observe targets in deep tissues, its poor solubility in aqueous media limits its utility for in vivo imaging. Herein, to address this issue, we have synthesized three AkaLumine derivatives with N-heterocyclic aromatic rings as new red luciferin analogues that have substantially higher solubility than that of AkaLumine in phosphate buffered saline solution. One of the derivatives (herein termed seMpai) exhibits an emission maximum at 675 nm upon L-L reaction with Photinus pyralis luciferase and presents an activity in mouse-tissue imaging similar to that of AkaLumine. It is hoped that seMpai will extend the application of high-sensitivity NIR bioluminescence imaging in a wide range of biomedical research fields

Pilot Study: Estimation of Stroke Volume and Cardiac Output from Pulse Wave Velocity.

Transesophageal echocardiography (TEE) is increasingly replacing thermodilution pulmonary artery catheters to assess hemodynamics in patients at high risk for cardiovascular morbidity. However, one of the drawbacks of TEE compared to pulmonary artery catheters is the inability to measure real time stroke volume (SV) and cardiac output (CO) continuously. The aim of the present proof of concept study was to validate a novel method of SV estimation, based on pulse wave velocity (PWV) in patients undergoing cardiac surgery.This is a retrospective observational study. We measured pulse transit time by superimposing the radial arterial waveform onto the continuous wave Doppler waveform of the left ventricular outflow tract, and calculated SV (SVPWV) using the transformed Bramwell-Hill equation. The SV measured by TEE (SVTEE) was used as a reference.A total of 190 paired SV were measured from 28 patients. A strong correlation was observed between SVPWV and SVTEE with the coefficient of determination (R2) of 0.71. A mean difference between the two (bias) was 3.70 ml with the limits of agreement ranging from -20.33 to 27.73 ml and a percentage error of 27.4% based on a Bland-Altman analysis. The concordance rate of two methods was 85.0% based on a four-quadrant plot. The angular concordance rate was 85.9% with radial limits of agreement (the radial sector that contained 95% of the data points) of ± 41.5 degrees based on a polar plot.PWV based SV estimation yields reasonable agreement with SV measured by TEE. Further studies are required to assess its utility in different clinical situations

The Effects of Hemodynamic Changes on Pulse Wave Velocity in Cardiothoracic Surgical Patients

The effect of blood pressure on pulse wave velocity (PWV) is well established. However, PWV variability with acute hemodynamic changes has not been examined in the clinical setting. The aim of the present study is to investigate the effect of hemodynamic changes on PWV in patients who undergo cardiothoracic surgery. Using data from 25 patients, we determined blood pressure (BP), heart rate (HR), and the left ventricular outflow tract (LVOT) velocity-time integral. By superimposing the radial arterial waveform on the continuous wave Doppler waveform of the LVOT, obtained by transesophageal echo, we were able to determine pulse transit time and to calculate PWV, stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR). Increases in BP, HR, and SVR were associated with higher values for PWV. In contrast increases in SV were associated with decreases in PWV. Changes in CO were not significantly associated with PWV

How to Select Firefly Luciferin Analogues for In Vivo Imaging

Bioluminescence reactions are widely applied in optical in vivo imaging in the life science and medical fields. Such reactions produce light upon the oxidation of a luciferin (substrate) catalyzed by a luciferase (enzyme), and this bioluminescence enables the quantification of tumor cells and gene expression in animal models. Many researchers have developed single-color or multicolor bioluminescence systems based on artificial luciferin analogues and/or luciferase mutants, for application in vivo bioluminescence imaging (BLI). In the current review, we focus on the characteristics of firefly BLI technology and discuss the development of luciferin analogues for high-resolution in vivo BLI. In addition, we discuss the novel luciferin analogues TokeOni and seMpai, which show potential as high-sensitivity in vivo BLI reagents