Single-cell bioluminescence imaging of deep tissue in freely moving animals.

Bioluminescence is a natural light source based on luciferase catalysis of its substrate luciferin. We performed directed evolution on firefly luciferase using a red-shifted and highly deliverable luciferin analog to establish AkaBLI, an all-engineered bioluminescence in vivo imaging system. AkaBLI produced emissions in vivo that were brighter by a factor of 100 to 1000 than conventional systems, allowing noninvasive visualization of single cells deep inside freely moving animals. Single tumorigenic cells trapped in the mouse lung vasculature could be visualized. In the mouse brain, genetic labeling with neural activity sensors allowed tracking of small clusters of hippocampal neurons activated by novel environments. In a marmoset, we recorded video-rate bioluminescence from neurons in the striatum, a deep brain area, for more than 1 year. AkaBLI is therefore a bioengineered light source to spur unprecedented scientific, medical, and industrial applications.

A luciferin analogue generating near-infrared bioluminescence achieves highly sensitive deep-tissue imaging.

In preclinical cancer research, bioluminescence imaging with firefly luciferase and D-luciferin has become a standard to monitor biological processes both in vitro and in vivo. However, the emission maximum (λmax) of bioluminescence produced by D-luciferin is 562 nm where light is not highly penetrable in biological tissues. This emphasizes a need for developing a red-shifted bioluminescence imaging system to improve detection sensitivity of targets in deep tissue. Here we characterize the bioluminescent properties of the newly synthesized luciferin analogue, AkaLumine-HCl. The bioluminescence produced by AkaLumine-HCl in reactions with native firefly luciferase is in the near-infrared wavelength ranges (λmax=677 nm), and yields significantly increased target-detection sensitivity from deep tissues with maximal signals attained at very low concentrations, as compared with D-luciferin and emerging synthetic luciferin CycLuc1. These characteristics offer a more sensitive and accurate method for non-invasive bioluminescence imaging with native firefly luciferase in various animal models.

Multicolor Bioluminescence Obtained Using Firefly Luciferin.

Firefly bioluminescence is widely used in life science research as a useful analysis tool. For example, the adenosine-5`-triphosphate (ATP)-dependent enzymatic firefly bioluminescence reaction has long been utilized as a microbial monitoring tool. Rapid and sensitive firefly luciferin-luciferase combinations are used not only to measure cell viability but also for reporter-gene assays. Recently, bioluminescence was utilized as a noninvasive, real-time imaging tool for living subjects to monitor cells and biological events. However, the number of commercialized luciferase genes is limited and tissue-permeable near-infrared (NIR) region emitting light is required for in vivo imaging. In this review, recent studies describing synthetic luciferin analogues predicted to have red-shifted bioluminescence are summarized. Luciferase substrates emitting red, green, and blue light that were designed and developed in our laboratory are presented. The longest emission wavelength of the synthesized luciferin analogues was recorded at 675 nm, which is within the NIR region. This compound is now commercially available as "Aka Lumine®".

Clinical features of hepatocellular carcinoma seronegative for both HBsAg and anti-HCV antibody but positive for anti-HBc antibody in Japan.

OBJECTIVE: We determined the prevalence of patients with hepatocellular carcinoma (HCC) who were positive for only anti-hepatitis B core (anti-HBc) antibody among 284 Japanese patients and compared their clinical features to those who were hepatitis B surface antigen positive [HBsAg(+)]. METHODS: Serum HBsAg and anti-hepatitis C virus (anti-HCV) antibody were examined for all HCC patients. Testing for anti-HBc antibody was performed in the HBsAg(-)/anti-HCV(-) patients. The clinical factors and the survival rate were compared between the HBsAg(+) patients (HCC-B) and those positive for anti-HBc alone (HCC-PB). RESULTS: There were 19 (6.7%) HBsAg(+), 236 (83.1%) anti-HCV(+), seven (2.5%) HBsAg(+)/anti-HCV(+), and 22 (7.7%) HBsAg(-)/anti-HCV(-) among the 284 patients tested. Sixteen (72.7%) of the 22 HBsAg(-)/anti-HCV(-) patients were assigned to the HCC-PB group. The prevalence of positivity for anti-HBc alone among all 284 HCC patients was 5.6%. Significant differences between the HCC-PB and HCC-B groups were that age at diagnosis was higher in the HCC-PB group (72.1 yr) than in the HCC-B group (56.2 yr) (p < 0.001), the serum alpha-fetoprotein concentrations were lower in the HCC-PB group (8.2 ng/ml) than in the HCC-B group (43 ng/ml) (p = 0.0488), and a higher familial history of liver disease was observed in the HCC-B group (p = 0.0373). However, there was no significant difference in the cumulative survival rate. CONCLUSIONS: Positivity for anti-HBc alone is not rare compared to HBsAg(+), and the clinical features of positivity for anti-HBc alone are similar to those of HBsAg(+). Some differences in the clinical features between the two groups may be explained by differences in the time of first exposure to hepatitis B virus. Therefore, the natural course of acute hepatitis B may be reconsidered.