The toxicity of repeated and high dose of CNPs treatment was assessed by histological and hematological analyses. Briefly, Cy5.5-CNPs (10, 22.5 or 90 mg/kg) were intravenously injected into BALB/c mice with single- or multi-dosage (three times). On day 7 after treatments, major organs (liver, lung, spleen, kidney, brain and heart) were collected from mice, and structural abnormalities in organ tissues were assessed by staining with H&E. In the case of hematological analyses, blood samples were collected from the mice on day 7 and centrifuged at 2200 rpm to obtain plasma. The following factors in blood samples were measured; alanine aminotransferase (ALT), blood urea nitrogen (BUN), alkaline phosphatase (ALP), aspartate Aminotransferase (AST), creatine kinase (CK) and troponin I. The cardiotoxicity by Cy5.5-CNPs was further analyzed after multiple-dosage. The heart tissues were collected from mice after treatment with 10, 22.5 or 90 mg/kg of Cy5.5-CNPs three times. The accumulation of Cy5.5-CNPs in heart tissues was observed using a Leica TCS SP8 confocal laser-scanning microscope. Collagen fiber in heart tissues were stained with Masson's trichrome. Briefly, heart tissues were incubated in Bouin's fixative for 30 min at 56 °C, and the nuclei were co-stained with Weigert's iron hematoxylin. Then, cytoplasm was stained with Biebrich scarlet-acid fuchsin, and then differentiated in phosphomolybdic–phosphotungstic acid. The collagen matrix in heart tissues was stained with aniline blue solution. The collagen in heart tissues were quantitatively analyzed using an Image Pro software, and collagen contents were presented in proportion to the total area of heart tissues.
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