Background and Aims: Hepatic sinusoidal cells are known actors in the fibrogenic response to injury. Activated hepatic stellate cells (HSCs), liver sinusoidal endothelial cells, and Kupffer cells are responsible for sinusoidal capillarization and perisinusoidal matrix deposition, impairing vascular exchange and heightening the risk of advanced fibrosis. While the overall pathogenesis is well understood, functional relations between cellular transitions during fibrogenesis are only beginning to be resolved. At single‐cell resolution, we here explored the heterogeneity of individual cell types and dissected their transitions and crosstalk during fibrogenesis. Approach and Results: We applied single‐cell transcriptomics to map the heterogeneity of sinusoid‐associated cells in healthy and injured livers and reconstructed the single‐lineage HSC trajectory from pericyte to myofibroblast. Stratifying each sinusoidal cell population by activation state, we projected shifts in sinusoidal communication upon injury. Weighted gene correlation network analysis of the HSC trajectory led to the identification of core genes whose expression proved highly predictive of advanced fibrosis in patients with nonalcoholic steatohepatitis (NASH). Among the core members of the injury‐repressed gene module, we identified plasmalemma vesicle–associated protein (PLVAP) as a protein amply expressed by mouse and human HSCs. PLVAP expression was suppressed in activated HSCs upon injury and may hence define hitherto unknown roles for HSCs in the regulation of microcirculatory exchange and its breakdown in chronic liver disease. Conclusions: Our study offers a single‐cell resolved account of drug‐induced injury of the mammalian liver and identifies key genes that may serve important roles in sinusoidal integrity and as markers of advanced fibrosis in human NASH.

PET imaging at late time points after injection may allow tracer clearance from normal tissue and hence improve image contrast and detectability. ⁵⁵Co is a promising isotope with high positron yield and a long half-life suitable for imaging at delayed time points. Here, we compared the 3 radioconjugates [⁶⁸Ga]Ga-DOTATATE, [⁶⁴Cu]Cu-DOTATATE, and [⁵⁵Co]Co-DOTATATE by PET/CT imaging in NOD-SCID mice bearing subcutaneous somatostatin receptor–expressing AR42J tumors. Methods:⁵⁵Co and ⁶⁴Cu were produced by the ⁵⁴Fe(d,n)⁵⁵Co and ⁶⁴Ni(p,n)⁶⁴Cu nuclear reactions, whereas ⁶⁸Ga was obtained from a ⁶⁸Ge/⁶⁸Ga generator. ⁵⁵Co and ⁶⁴Cu were labeled with DOTATATE by heating in a sodium acetate buffer and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer, respectively. AR42J tumor–bearing mice were dynamically scanned 0–1 h after injection. For ⁶⁴Cu and ⁵⁵Co, additional imaging was also performed at late time points after 4 and 24 h. Dose calculations were based on a known biodistribution. The cumulated disintegrations in each organ were calculated by integration of a fitted exponential function to the biodistribution of each respective organ. Equivalent doses were calculated by OLINDA/EXM using the MIRD formalism. Results: Tumor uptake was rapid from 0 to 1 h after injection for all 3 radioconjugates. Normal-tissue ratios as represented by tumor-to-liver, tumor-to-kidney, and tumor-to-muscle ratios increased significantly over time, with [⁵⁵Co]Co-DOTATATE reaching the highest ratio of all radioconjugates. For [⁵⁵Co]Co-DOTATATE, the tumor-to-liver ratio increased to 65 ± 16 at 4 h and 50 ± 6 at 24 h, which were 15 (P < 0.001) and 30 (P < 0.001) times higher, respectively, than the corresponding ratios for [⁶⁴Cu]Cu-DOTATATE and 5 (P < 0.001) times higher than that of [⁶⁸Ga]Ga-DOTATATE at 1 h. Correspondingly, tumor-to-kidney and tumor-to-muscle ratios for [⁵⁵Co]Co-DOTATATE were 4 (P < 0.001) and 11 (P < 0.001) times higher than that of [⁶⁴Cu]Cu-DOTATATE at 24 h. An equivalent dose was calculated as 9.6E−02 mSv/MBq for [⁵⁵Co]Co-DOTATATE. Conclusion: [⁵⁵Co]Co-DOTATATE demonstrated superior image contrast compared with [⁶⁴Cu]Cu-DOTATATE and [⁶⁸Ga]Ga-DOTATATE for PET imaging of somatostatin receptor–expressing tumors, warranting translation into clinical trials. Dosimetry calculations found that effective doses for [⁵⁵Co]Co-DOTATATE were comparable to those for both [⁶⁴Cu]Cu-DOTATATE and [⁶⁸Ga]Ga-DOTATATE.

The issue of whether ^99mTc-DTPA can replace ⁵¹Cr-EDTA for measurement of plasma clearance as a surrogate for glomerular filtration rate (GFR) is of great relevance to daily clinical practice. Prompted by the shortage of ⁵¹Cr-EDTA we conducted a head-to-head comparison in patients attending our department for GFR determination. The two tracers (3.7 MBq of ⁵¹Cr-EDTA and 8 MBq of ^99mTc-DTPA) were administered intravenously immediately after each other, and the standard number of blood samples were drawn. Fifty-four patients were enrolled. In 51 of these, single-sample measurement was performed with the following results: GFR_EDTA was 84.6 ± 23.3 mL/min, GFR_DTPA was 84.2 ± 24.7 mL/min. The mean difference was 0.4 ± 2.8 mL/min, p = 0.32, and results based on the two tracers were highly correlated (r = 0.995). GFR_DTPA exceeded GFR_EDTA at high GFR values (difference < 0 at GFR_EDTA >91.4 mL/min) and vice versa (difference > 0 at GFR_EDTA < 91.4 mL/min). However, differences fell within few GFR units that most often will have no clinical consequence. We therefore conclude that ^99mTc-DTPA can replace ⁵¹Cr-EDTA for single-sample determination of GFR in a clinical setting.

Angiogenesis is crucial in tissue repair and prevents scar tissue formation following an ischemic event such as myocardial infarction. The ischemia induces formation of new capillaries, which have high expression of integrin α_vβ₃. [⁶⁸Ga]Ga-NODAGA-E[(cRGDyK)]₂ ([⁶⁸Ga]Ga-RGD) is a promising PET-radiotracer reflecting angiogenesis by binding to integrin α_vβ₃. A Göttingen mini-pig underwent transient catheter-induced left anterior descending artery (LAD) occlusion for 120 min, and after 8 weeks was imaged on a Siemens mMR 3T PET/MR system. A large antero-septal infarction was evident by late gadolinium enhancement (LGE) on the short axis and 2–4 chamber views. The infarcted area corresponded to the area with high [⁶⁸Ga]Ga-RGD uptake on the fused PET/MR images, with no uptake in the healthy myocardium. To support the hypothesis that [⁶⁸Ga]Ga-RGD uptake reflects angiogenesis, biopsies were sampled from the infarct border and healthy myocardium. Expression of α_vβ₃ was evaluated using immunohistochemistry. The staining showed higher α_vβ₃ expression in the capillaries of the infarct border compared to those in the healthy myocardium. These initial data confirm in vivo detection of angiogenesis using [⁶⁸Ga]Ga-RGD PET in a translational model, which overall support the method applicability when evaluating novel cardio-protective therapies.