Nonuniform Cardiac Denervation Observed by 11C-meta-Hydroxyephedrine PET in 6-OHDA-Treated Monkeys

Parkinson's disease presents nonmotor complications such as autonomic dysfunction that do not respond to traditional anti-parkinsonian therapies. The lack of established preclinical monkey models of Parkinson's disease with cardiac dysfunction hampers development and testing of new treatments to alleviate or prevent this feature. This study aimed to assess the feasibility of developing a model of cardiac dysautonomia in nonhuman primates and preclinical evaluations tools. Five rhesus monkeys received intravenous injections of 6-hydroxydopamine (total dose: 50 mg/kg). The animals were evaluated before and after with a battery of tests, including positron emission tomography with the norepinephrine analog 11C-meta-hydroxyephedrine. Imaging 1 week after neurotoxin treatment revealed nearly complete loss of specific radioligand uptake. Partial progressive recovery of cardiac uptake found between 1 and 10 weeks remained stable between 10 and 14 weeks. In all five animals, examination of the pattern of uptake (using Logan plot analysis to create distribution volume maps) revealed a persistent region-specific significant loss in the inferior wall of the left ventricle at 10 (P<0.001) and 14 weeks (P<0.01) relative to the anterior wall. Blood levels of dopamine, norepinephrine (P<0.05), epinephrine, and 3,4-dihydroxyphenylacetic acid (P<0.01) were notably decreased after 6-hydroxydopamine at all time points. These results demonstrate that systemic injection of 6-hydroxydopamine in nonhuman primates creates a nonuniform but reproducible pattern of cardiac denervation as well as a persistent loss of circulating catecholamines, supporting the use of this method to further develop a monkey model of cardiac dysautonomia

A High Separation Factor for ¹⁶⁵Er from Ho for Targeted Radionuclide Therapy

Background: Radionuclides emitting Auger electrons (AEs) with low (0.02–50 keV) energy, short (0.0007–40 µm) range, and high (1–10 keV/µm) linear energy transfer may have an important role in the targeted radionuclide therapy of metastatic and disseminated disease. Erbium-165 is a pure AE-emitting radionuclide that is chemically matched to clinical therapeutic radionuclide 177Lu, making it a useful tool for fundamental studies on the biological effects of AEs. This work develops new biomedical cyclotron irradiation and radiochemical isolation methods to produce 165Er suitable for targeted radionuclide therapeutic studies and characterizes a new such agent targeting prostate-specific membrane antigen. Methods: Biomedical cyclotrons proton-irradiated spot-welded Ho(m) targets to produce 165Er, which was isolated via cation exchange chromatography (AG 50W-X8, 200–400 mesh, 20 mL) using alpha-hydroxyisobutyrate (70 mM, pH 4.7) followed by LN2 (20–50 µm, 1.3 mL) and bDGA (50–100 µm, 0.2 mL) extraction chromatography. The purified 165Er was radiolabeled with standard radiometal chelators and used to produce and characterize a new AE-emitting radiopharmaceutical, [165Er]PSMA-617. Results: Irradiation of 80–180 mg natHo targets with 40 µA of 11–12.5 MeV protons produced 165Er at 20–30 MBq·µA−1·h−1. The 4.9 ± 0.7 h radiochemical isolation yielded 165Er in 0.01 M HCl (400 µL) with decay-corrected (DC) yield of 64 ± 2% and a Ho/165Er separation factor of (2.8 ± 1.1) · 105. Radiolabeling experiments synthesized [165Er]PSMA-617 at DC molar activities of 37–130 GBq·µmol−1. Conclusions: A 2 h biomedical cyclotron irradiation and 5 h radiochemical separation produced GBq-scale 165Er suitable for producing radiopharmaceuticals at molar activities satisfactory for investigations of targeted radionuclide therapeutics. This will enable fundamental radiation biology experiments of pure AE-emitting therapeutic radiopharmaceuticals such as [165Er]PSMA-617, which will be used to understand the impact of AEs in PSMA-targeted radionuclide therapy of prostate cancer

Fetal dopamine receptor characteristics assessed in utero

Any tracer in fetal tissue comes from maternal arterial blood. Provided steady state is achieved and intermediate compartments are reversible, the Logan graphical methods should be applicable to the assessment of binding parameters in the fetal brain. Two pregnant rhesus macaques were studied with fallypride and the Logan method was used to assess dopamine receptor distribution volume ratios (DVRs) in both maternal and fetal striatum. The agreement between fetal striatal DVRs using maternal arterial blood and maternal and fetal cerebellum as input functions strongly supports our hypothesis that the conditions necessary for graphical analysis have been met

Echocardiogram measurements at baseline, 10 and 14 weeks after 6-OHDA for each animal.

<p>FS is calculated as [(LVD_d – LVD_s)/LVD_d]×100. Three animals experienced large decreases in FS compared to baseline, but there was no significant change in left ventricle diameter or in anterior and posterior wall thickness. This suggests that the increased luminal dimensions of the left ventricle were not due to the loss of cardiac muscle. AWd, anterior wall thickness in diastole. AWs, anterior wall thickness in systole. PWd, posterior wall thickness in diastole. PWs, posterior wall thickness in systole. LVD_d, left ventricle diameter in diastole. LVD_s, left ventricle diameter in systole. FS, fractional shortening.</p

Systolic and diastolic blood pressure measurements during 6-OHDA administration.

<p>Blood pressure results from a representative animal (RH2318). A, Both pressures increase immediately after each 6-OHDA dosing (arrows). B, Change in systolic and diastolic blood pressure from peak of pressure following 6-OHDA until levels normalized at which time the next injection of 6-OHDA was administered. The amount of time to normalize paralleled the change in blood pressure. At the accumulated dose of 2.0 mg/kg, this animal required 61 minutes to regulate blood pressure. bp, blood pressure.</p

Circulating plasma catecholamine levels (pg/mL) at baseline (0) and at 1, 4, 10, and 14 weeks after 6-OHDA in three animals.

<p>The values in parentheses are the natural logarithms of the concentration values and used to graph correlations in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035371#pone-0035371-g005" target="_blank">Figure 5</a>. For statistical analysis, non-detectable levels (nd) levels were considered as the lowest detection level with 1.5 pg/mL for norepinephrine and 3.0 pg/mL for epinephrine. Post hoc analysis with Bonferroni multiple comparisons detected significance at all timepoints compared to baseline for norepinephrine and DOPAC (*<i>P</i><0.05, ** <i>P</i><0.01).</p

Distribution volume maps before and after systemic 6-OHDA dosing.

<p>Maps express regional capacity of the tissue for MHED uptake relative to whole blood, thus providing a measure of the density of nerve terminals. Each individual map consists of 8 sectors and 7 rings (apex of the heart at the center, base of the LV at the edge), totaling to 56 blocks of data per timepoint. MHED uptake significantly decreased at each timepoint after 6-OHDA compared to baseline (<i>P</i><0.001). Scales (mL whole blood/g tissue) are similar between animals and identical across time points for each individual. The compass rose indicates regions: A, anterior; S, septal; I, inferior; L, lateral.</p

Experimental timeline.

<p>All procedures were performed in 5 adult rhesus monkeys following a within-subject experimental design. MHED PET scans, plasma catecholamines, troponin I and ECGs (*) were performed at baseline and 1, 4, 10 and 14 weeks after 6-OHDA. Echocardiograms (Echo) were obtained at baseline and 10 and 14 weeks after 6-OHDA. Clinical rating (CR) was performed at baseline and 4, 10 and 14 weeks following toxin administration. Food consumption and feces were monitored daily and body weight was measured weekly throughout the course of the study (shading). Animals were euthanized 14 weeks following 6-OHDA administration.</p