Hepatocellular Cytoplasmic Inclusions in a Cynomolgus Monkey

Abstract

Spontaneous hepatocellular intracytoplasmic inclusions were observed in a 4-year old male cynomolgus monkey used in a toxicity study. Histopathological findings of the inclusions revealed an eosinophilic ground glass appearance. The inclusions were positive for periodic acid Schiff and colloidal iron under diastase or hyaluronidase treatment, and they included microvacuoles which stained positive in oil red O. Ultrastructurally, the inclusions consisted of many lipid droplets with granular substances and disintegration of organelles, but there were had no limiting membrane around the inclusions. Any abnormal findings such as necrosis, inflammation or virus particles were not detected. Our case was considered to be a kind of a disease categorized under metabolic diseases with unknown mechanisms, and it might provide information as a historical control in the assessment of monkey toxicity studies.