Lynne Johnson

Positron Emission Tomography Imaging May Provide a Novel Biomarker and Understanding of Right Ventricular Dysfunction in Patients with Idiopathic Pulmonary Arterial Hypertension

Background— The clinical course in pulmonary arterial hypertension (PAH) is variable, and there is limited information on the determinants and progression of right ventricular (RV) dysfunction. The objective is to develop PET metabolic imaging of the RV as a noninvasive tool in patients with PAH. Methods and Results— We performed PET scanning in 16 patients with idiopathic PAH (age, 41±14 years, 82% women) using 13N-NH3 for perfusion imaging and 18F-fluorodeoxyglucose for metabolic imaging. The myocardium was divided into 6 regions of interest (3 left ventricular [LV], 3 RV), and time-activity curves were generated. A 2- compartment model was used to calculate myocardial blood flow (MBF), and Patlak analysis was used to calculate the rate of myocardial glucose uptake (MGU). All patients underwent cardiac catheterization, cardiac MRI, and cardiopulmonary exercise testing with gas exchange. MBF, MGU, and the ratio of RV/LV MGU were correlated to clinical parameters. Pulmonary artery (PA) pressure was 79±19/30±8 mm Hg (mean, 48±10 mm Hg). MBF was 0.84±0.33 mL/g per minute for the LV and 0.45±0.14 mL/g per minute for the RV. Mean MGU was 136±72 nmol/g per minute for the LV and 96±69 nmol/g per minute for the RV. The ratio of RV/LV MGU correlated significantly with PA systolic (r=0.75, P=0.0085) and mean (r=0.87, P=0.001) pressure and marginally with maximum oxygen consumption (r=−0.59, P=0.05). RV free wall MGU also correlated well with mean PA pressure (r=0.66, P=0.03). Conclusions— PET scanning with 13N-NH3 and 18F-fluorodeoxyglucose is a feasible modality for quantifying RV blood flow and metabolism in patients with idiopathic PAH.

Morphological Changes and Immunohistochemical Expression of RAGE and its Ligands in the Sciatic Nerve of Hyperglycemic Pig (Sus Scrofa)

The aim of our project was to study the effect of streptozotocin (STZ)–-induced hyperglycemia on sciatic nerve morphology, blood plasma markers and immunohistochemical expression of RAGE (the Receptor for Advanced Glycation End-products), and its ligands–-S100B and Carboxymethyl Lysine (CML)-advanced glycation endproduct (AGE) in the laboratory pig. Six months after STZ–-injections, blood plasma measurements, morphometric analysis of sciatic nerve fiber density, immunofluorescent distribution of potential molecular neuropathy contributors, ELISA measurement of plasma AGE level and HPLC analysis of sciatic nerve levels of one of the pre-AGE and the glycolysis intermediate products–-methylglyoxal (MG) were performed. The results of our study revealed that STZ–-injected animals displayed elevated levels of plasma glucose, gamma glutamyl transferase (GGT) and triglycerides. The sciatic nerve of STZ-injected pigs revealed significantly lower numbers of small-diameter myelinated fibers, higher immunoreactivity for RAGE and S100B and increased levels of MG as compared to control animals. Our results correspond to clinical findings in human patients with hyperglycemia/diabetes-evoked peripheral neuropathy and suggest that the domestic pig may be a suitable large animal model for the study of mechanisms underlying hyperglycemia-induced neurological complications in the peripheral nerve and may serve as a relevant model for the pre-clinical assessment of candidate drugs in neuropathy.

Targeting very small model lesions pretargeted with bispecific antibody with 99mTc-labeled high-specific radioactivity polymers.

BackgroundTwo-step targeting with bispecific antibody and 99mTc-labeled high-specific radioactivity polymers was used for molecular imaging of two very small model lesions in rats. Methods and resultsSprague–Dawley rats (group I) were injected with surrogate antigen-coated beads (SA beads) in the right hind leg or unmodified beads in the contralateral hind leg. In group II, femoral artery de-endothelialization was induced in the left hind leg and sham operation was performed in the contralateral hind leg. Bispecific antibody Z2D3 F(ab′)2-anti-DTPA F(ab′)2 was injected intravenously 24 h after SAB injection or 1 week after endothelial denudation. 99mTc-labeled polymers were injected intravenously 24 h later and &ggr;-images obtained at 2 and 24 h in group I or approximately 2.5 h in group II. Lesions were visualized by 2 h. In group I, SA beads-specific uptake in muscles was significantly greater than with unmodified beads (P<0.015). In group II, lesions were visualized by 2.5 h after radiopolymer injection with uptake activity 2.1±0.6 times greater than in the contralateral side from in-vivo images (P<0.004) and 1.8±0.7 times by &ggr;-scintillation counting (P<0.04). ConclusionPretargeting with Z2D3 bispecific antibody for the localization of radiolabeled polymers enabled successful in-vivo &ggr;-imaging of very small lesions in two rat models of extravascular and intravascular targets. Biodistribution data confirmed that pretargeting with bispecific antibody enabled targeted visualization of two different very small model lesions by in-vivo &ggr;-imaging.

A Novel Monoclonal Antibody for RAGE-Directed Imaging Identifies Accelerated Atherosclerosis in Diabetes

Receptor for advanced glycation end products (RAGE) binds advanced glycation end products and other inflammatory ligands and is expressed in atherosclerotic plaques in diabetic and nondiabetic subjects. The higher expression in diabetes mellitus corresponds to the accelerated course of the atherosclerosis. This study was designed to test the hypothesis that the level of RAGE expression in atherosclerosis can be detected by quantitative in vivo SPECT and that counts in the target will correlate with the strength of the biologic signal. Methods: A monoclonal murine antibody was developed against the V-domain of RAGE, fragmented into F(ab′)2 and labeled with 99mTc, and injected at a dose of 15.14 ± 1.23 MBq into 24-wk-old male apolipoprotein E null (ApoE−/−) mice (n = 22), including mice with streptozotocin-induced diabetes mellitus (n = 8), nondiabetic mice (n = 8), and control ApoE−/−/RAGE−/− double-knock-out mice (n = 6). Four hours later (allowing for blood-pool clearance), the mice were imaged and sacrificed, and the proximal aorta was removed and counted to calculate the percentage injected dose of RAGE per gram of tissue, followed by histologic and immunohistochemical characterization. Results: Radiotracer uptake in the aortic lesions was clearly visualized noninvasively by SPECT. RAGE uptake as percentage injected dose in diabetic ApoE−/− mice (1.39 ± 0.16 × 10−2) was significantly higher than that in nondiabetic ApoE−/− mice (0.48 ± 0.27 × 10−2) (P < 0.0001). The radiotracer uptake was highly correlated with RAGE expression by quantitative immunohistomorphometry (r = 0.82, P = 0.002) and with percentage of macrophages (r = 0.86, P < 0.0001). Conclusion: In this study, 99mTc-labeled anti-RAGE F(ab′)2 SPECT successfully identified early accelerated disease in diabetes mellitus for age-matched ApoE−/− mice and quantified RAGE expression over a range of lesion severities.

Beneficial Effect of Glucose Control on Atherosclerosis Progression in Diabetic ApoE−/− Mice: Shown by Rage Directed Imaging

Objective. Receptor for advanced glycated endproducts (RAGE) plays an important role in atherogenesis in diabetes. We imaged RAGE to investigate the effect of glucose control to suppress RAGE and reduce atherosclerosis in apolipoprotein E null (apoE−/−) diabetic mice. Methods and Results. Thirty-three apoE−/− mice received streptozotocin and 6 weeks later 15 began treatment with insulin implants. Blood glucose measurements during study averaged: 140 ± 23 mg/dL (treated) and 354 ± 14 mg/dL (untreated). After 15 wk 30 mice were injected with 99mTc-anti-RAGE F(ab′)2, 3 with 99mTc-nonimmune IgG F(ab′)2, and all with CT contrast agent and underwent SPECT/CT imaging. At necropsy, the proximal aorta was weighed, counted, and sectioned and the % injected dose per gram (%ID/g) was calculated. From the merged SPECT/CT scans, tracer uptake localized to arteries was lower in the treated mice: 3.15 ± 1.82 × 10−3 versus 8.69 ± 4.58 × 10−3%ID (P = 0.001). Percent cross-sectional lesion area was smaller in the treated (14.3 ± 7.8% versus 29.5 ± 10.9%) (P = 0.03). RAGE uptake on scans (%ID) correlated with quantitative RAGE staining in the atheroma and with %ID/g (R = 0.6887; P = 0.01). Lesion size as percent cross-sectional area was smaller in the treated (14.3 ± 7.8% versus 29.5 ± 10.9%) (P = 0.03). RAGE uptake on scans (%ID) correlated with quantitative RAGE staining in the atheroma and with %ID/g (R = 0.6887; P = 0.01). Conclusions. These results support the importance of suppressing RAGE to reduce atherosclerotic complications of diabetes and value of molecular imaging to assess treatment effect.