Safety profile of repeated infusion of platelet-like nanoparticles in healthy dogs.

OBJECTIVE: To assess the safety and efficacy of the platelet-like nanoparticle (PLN), and to assess its safety in repeated administration. ANIMALS: 6 purpose-bred dogs. PROCEDURES: The PLN was administered IV at 3 different doses using a randomized crossover design. Each dog received a full dose of 8 X 1010 particles/10 kg, half dose, and 10 times the dose, with a 14-day washout period between doses. Biochemical, prothrombin time, partial thromboplastin time, and fibrinogen analyses were performed at baseline and 96 hours postinfusion. A CBC, kaolin-activated thromboelastography, platelet function assay closure time, and buccal mucosal bleeding time were performed at baseline and 1, 6, 24, 48, 72, and 96 hours postinfusion. RESULTS: No significant changes were observed over time in the thromboelastography parameters, closure time, and buccal mucosal bleeding time. After the administration of the half dose, hematocrit levels decreased significantly at 1, 6, 24, 48, and 96 hours, with all values within the reference range. The platelet count was decreased significantly at hours 1, 6, 24, 48, and 72 after administration of the half dose, with values less than the reference range at all hours but hour 72. No significant changes in serum biochemistry, coagulation panel, and fibrinogen were observed for all doses. No adverse events were noted during the first infusion. Three dogs experienced transient sedation and nausea after repeat infusion. CLINICAL RELEVANCE: The PLN resulted in a dilution of hematocrit and platelets, and did not significantly alter hemostasis negatively. The safety of repeated doses should be investigated further in dogs.

Comparison of Three Methods to Quantify Repair Cartilage Collagen Orientation.

OBJECTIVE: The aim of this study was to determine if the noninvasive or minimally invasive and nondestructive imaging techniques of quantitative T2-mapping or multiphoton microscopy (MPM) respectively, could detect differences in cartilage collagen orientation similar to polarized light microscopy (PLM). It was hypothesized that MRI, MPM, and PLM would all detect quantitative differences between repair and normal cartilage tissue. METHODS: Osteochondral defects in the medial femoral condyle were created and repaired in 5 mature goats. Postmortem, MRI with T2-mapping and histology were performed. T2 maps were generated and a mean T2 value was calculated for each region of interest. Histologic slides were assessed using MPM with measurements of autocorrelation ellipticity, and by PLM with application of a validated scoring method. Collagen orientation using each of the 3 modalities (T2-mapping, MPM, and PLM) was measured in the center of the repair tissue and compared to remote, normal cartilage. RESULTS: MRI, MPM, and PLM were able to detect a significant difference between repair and normal cartilage (n = 5). The average T2 value was longer for repair tissue (41.43 ± 9.81 ms) compared with normal cartilage (27.12 ± 14.22 ms; P = 0.04); MPM autocorrelation ellipticity was higher in fibrous tissue (3.75 ± 1.17) compared with normal cartilage (2.24 ± 0.51; P = 0.01); the average PLM score for repair tissue was lower (1.6 ± 1.02) than the score for remote normal cartilage (4.4 ± 0.42; P = 0.002). The strongest correlation among the methods was between MRI and PLM (r = -0.76; P = 0.01), followed by MPM and PLM (r = -0.58; P = 0.08), with the weakest correlation shown between MRI and MPM (r = 0.35; P = 0.31). CONCLUSION: All 3 imaging methods quantitatively measured differences in collagen orientation between repair and normal cartilage, but at very different levels of resolution. PLM is destructive to tissue and requires euthanasia, but because MPM can be used arthroscopically, both T2-mapping and MPM can be performed in vivo, offering nondestructive means to assess collagen orientation that could be used to obtain longitudinal data in cartilage repair studies.