First PET Imaging Studies With 63Zn-Zinc Citrate in Healthy Human Participants and Patients With Alzheimer Disease

Abnormalities in zinc homeostasis are indicated in many human diseases, including Alzheimer disease (AD). 63Zn-zinc citrate was developed as a positron emission tomography (PET) imaging probe of zinc transport and used in a first-in-human study in 6 healthy elderly individuals and 6 patients with clinically confirmed AD. Dynamic PET imaging of the brain was performed for 30 minutes following intravenous administration of 63Zn-zinc citrate (∼330 MBq). Subsequently, body PET images were acquired. Urine and venous blood were analyzed to give information on urinary excretion and pharmacokinetics. Regional cerebral 63Zn clearances were compared with 11C-Pittsburgh Compound B (11C-PiB) and 18F-fluorodeoxyglucose (18F-FDG) imaging data. 63Zn-zinc citrate was well tolerated in human participants with no adverse events monitored. Tissues of highest uptake were liver, pancreas, and kidney, with moderate uptake being seen in intestines, prostate (in males), thyroid, spleen, stomach, pituitary, and salivary glands. Moderate brain uptake was observed, and regional dependencies were observed in 63Zn clearance kinetics in relationship with regions of high amyloid-β plaque burden (11C-PiB) and 18F-FDG hypometabolism. In conclusion, zinc transport was successfully imaged in human participants using the PET probe 63Zn-zinc citrate. Primary sites of uptake in the digestive system accent the role of zinc in gastrointestinal function. Preliminary information on zinc kinetics in patients with AD evidenced regional differences in clearance rates in correspondence with regional amyloid-β pathology, warranting further imaging studies of zinc homeostasis in patients with AD

The Global Diversity of Hemichordata

Phylum Hemichordata, composed of worm-like Enteropneusta and colonial Pterobranchia, has been reported to only contain about 100 species. However, recent studies of hemichordate phylogeny and taxonomy suggest the species number has been largely underestimated. One issue is that species must be described by experts, and historically few taxonomists have studied this group of marine invertebrates. Despite this previous lack of coverage, interest in hemichordates has piqued in the past couple of decades, as they are critical to understanding the evolution of chordates–as acorn worms likely resemble the deuterostome ancestor more closely than any other extant animal. This review provides an overview of our current knowledge of hemichordates, focusing specifically on their global biodiversity, geographic distribution, and taxonomy. Using information available in the World Register of Marine Species and published literature, we assembled a list of 130 described, extant species. The majority (83%) of these species are enteropneusts, and more taxonomic descriptions are forthcoming. Ptychoderidae contained the greatest number of species (41 species), closely followed by Harrimaniidae (40 species), of the recognized hemichordate families. Hemichordates are found throughout the world’s oceans, with the highest reported numbers by regions with marine labs and diligent taxonomic efforts (e.g. North Pacific and North Atlantic). Pterobranchs are abundant in Antarctica, but have also been found at lower latitudes. We consider this a baseline report and expect new species of Hemichordata will continue to be discovered and described as new marine habitats are characterized and explored