Sialic acid-binding immunoglubulin-like lectin 9 (Siglec-9) is a ligand of vascular adhesion protein 1 (VAP-1). A gallium 68-labeled peptide of Siglec-9, 68 Ga-DOTA-Siglec-9, holds promise as a novel PET tracer for imaging of inflammation. This first-inhuman study investigated the safety, tolerability, biodistribution, and radiation dosimetry of this radiopharmaceutical. Methods: Six healthy males underwent dynamic whole-body PET/CT. Serial venous blood samples were drawn from 1-240 min after intravenous injection of 162 ± 4 MBq of 68 Ga-DOTA-Siglec-9. In addition to gamma counting, the plasma samples were analyzed by high-performance liquid chromatography to detect intact tracer and radioactive metabolites. Radiation doses were calculated using the OLINDA/EXM 2.2 software. In addition, a patient with early rheumatoid arthritis was studied with both 68 Ga-DOTA-Siglec-9 and 18 F-FDG PET/CT to determine the ability of the new tracer to detect arthritis. Results: 68 Ga-DOTA-Siglec-9 was well tolerated by all subjects. 68 Ga-DOTA-Siglec-9 was rapidly cleared from blood circulation and several radioactive metabolites were detected. The organs with the highest absorbed doses were the urinary bladder wall (0.38 mSv/MBq) and kidneys (0.054 mSv/MBq). The mean effective dose was 0.022 mSv/MBq (range 0.020-0.024 mSv/MBq). Most importantly, however, 68 Ga-DOTA-Siglec-9 was able to detect arthritis comparable to 18 F-FDG. Conclusion: Intravenous injection of 68 Ga-DOTA-Siglec-9 was safe and biodistribution is favorable for testing of the tracer in larger group of patients with rheumatoid arthritis planned in the next phase of clinical trials. The effective radiation dose of 68 Ga-DOTA-Siglec-9 was within the same range as those of other 68 Ga-labeled tracers. Injection of 150 MBq of 68 Ga-DOTA-Siglec-9 would expose a subject to 3.3 mSv. These findings support the possible repeated clinical use of 68 Ga-DOTA-Siglec-9, e.g., in trials aiming to elucidate the treatment efficacy of novel drug candidates.

Cryptochrome 2 (Cry2) is a core clock gene important for circadian regulation. It has also been associated with anxiety and depressive‐like behaviors in mice, but the previous findings have been conflicting in terms of the direction of the effect. To begin to elucidate the molecular mechanisms of this association, we carried out behavioral testing, PET imaging, and gene expression analysis of Cry2−/− and Cry2+/+ mice. Compared to Cry2+/+ mice, we found that Cry2−/− mice spent less time immobile in the forced swim test, suggesting reduced despair‐like behavior. Moreover, Cry2−/− mice had lower saccharin preference, indicative of increased anhedonia. In contrast, we observed no group differences in anxiety‐like behavior. The behavioral changes were accompanied by lower metabolic activity of the ventro‐medial hypothalamus, suprachiasmatic nuclei, ventral tegmental area, anterior and medial striatum, substantia nigra, and habenula after cold stress as measured by PET imaging with a glucose analog. Although the expression of many depression‐associated and metabolic genes was upregulated or downregulated by cold stress, we observed no differences between Cry2−/− and Cry2+/+ mice. These findings are consistent with other studies showing that Cry2 is required for normal emotional behavior. Our findings confirm previous roles of Cry2 in behavior and extend them by showing that the effects on behavior may be mediated by changes in brain metabolism.

Hydroxysteroid 17-beta dehydrogenase 12 (HSD17B12) is suggested to be involved in the elongation of very long chain fatty acids. Previously, we have shown a pivotal role for the enzyme during mouse development. In the present study we generated a conditional Hsd17b12 knockout (HSD17B12cKO) mouse model by breeding mice homozygous for a floxed Hsd17b12 allele with mice expressing the tamoxifen-inducible Cre recombinase at the ROSA26 locus. Gene inactivation was induced by administering tamoxifen to adult mice. The gene inactivation led to a 20% loss of body weight within six days, associated with drastic reduction in both white (83% males, 75% females) and brown (65% males, 60% females) fat, likely due to markedly reduced food and water intake. Furthermore, the knockout mice showed sickness behavior and signs of liver toxicity, specifically microvesicular hepatic steatosis and increased serum alanine aminotransferase (4.6-fold in males, 7.7-fold in females). The hepatic changes were more pronounced in females than males. Pro-inflammatory cytokines, such as interleukin 6 (IL-6), IL-17 and granulocyte-colony stimulating factor were increased in the HSD17B12cKO mice indicating inflammatory response. Serum lipidomics study showed an increase in the amount of dihydroceramides, despite the dramatic overall loss of lipids. In line with the proposed role for HSD17B12 in the fatty acid elongation, we observed accumulation of ceramides, dihydroceramides, hexosylceramides and lactosylceramides with shorter than 18-carbon fatty acid side chains in the serum. The results indicate that HSD17B12 is essential for proper lipid homeostasis, and HSD17B12 deficiency rapidly results in fatal systemic inflammation and lipolysis in adult mice.