Roivainen, A. | Search bioRxiv

bioRxiv2020

Seasonal variation in brain mu-opioid receptor availability

Seasonal rhythms influence mood and sociability. The brain -opioid receptor (MOR) system modulates a multitude of seasonally varying socioemotional functions, but its seasonal variation remains elusive with no previously reported in vivo evidence. Here, we studied the seasonal effects on brain MOR availability via analysing a dataset (n=204) of [11C]carfentanil positron emission tomography (PET) scans of healthy volunteers. We found that seasonally varying daylength had an inverted U-shaped functional relationship with brain MOR availability. Brain regions sensitive to daylength spanned the socio-emotional brain circuits, where MOR availability formed a spring-like peak. Causal effect of daylength on brain MOR availability was further verified by a post hoc experiment with repeated PET imaging of rats (n=9) under seasonal photoperiodic simulation. Therefore, the in vivo brain MOR availability in normal humans shows significant seasonal variation, which aligns with expected seasonal variation in mood and suicidality.

neuroscience↗

bioRxiv2020

Radiosynthesis and Preclinical Evaluation of Ga-NOTA-Folate for PET Imaging of Folate Receptor β Positive Macrophages

Folate receptor {beta} (FR-{beta}) is one of the markers expressed on macrophages and a promising target for imaging of inflammation. Here, we report the radiosynthesis and preclinical evaluation of [68Ga]Ga-NOTA-folate (68Ga-FOL). First, we determined the affinity of 68Ga-FOL using human FR-{beta} expressing cells. Then, we studied atherosclerotic mice with 68Ga-FOL and 18F-FDG PET/CT. After sacrifice, the tissues excised were measured with a {gamma}-counter for ex vivo biodistribution. Further, the tracer distribution and co-localization with macrophages in aorta cryosections were studied using autoradiography, hematoxylin-eosin staining and immunostaining with anti-Mac-3 antibody. Specificity of 68Ga-FOL was assessed in a blocking study with excess of folate glucosamine. As a last step, human radiation doses were extrapolated from rat PET data. We were able to produce 68Ga-FOL at high radioactivity concentration, with high molar activity and radiochemical purity. The cell binding studies showed high (5.1 {+/-} 1.1 nM) affinity of 68Ga-FOL to FR-{beta}. The myocardial uptake of 68Ga-FOL (SUV 0.43 {+/-} 0.06) was 20-folds lower compared to 18F-FDG (SUV 10.6 {+/-} 1.8, P = 0.001). The autoradiography and immunohistochemistry of aorta revealed that 68Ga-FOL radioactivity co-localized with Mac-3-positive macrophage-rich atherosclerotic plaques. The plaque-to-healthy vessel wall ratio of 68Ga-FOL (2.44 {+/-} 0.15) was significantly higher than that of 18F-FDG (1.93 {+/-} 0.22, P = 0.005). Blocking studies verified 68Ga-FOL specificity to FR. As estimated from rat data the human effective dose was 0.0105 mSv/MBq. The organ with highest absorbed dose was kidney (0.1420 mSv/MBq). In conclusion, 68Ga-FOL is a promising new FR-{beta}-targeted tracer for imaging macrophage-associated inflammation. TABLE OF CONTENT/ABSTRACT GRAPHIC O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

biochemistry↗