Spontaneous hibernomas in Sprague-Dawley rats.
Hibernomas are rare neoplasms originating in brown adipose tissue of humans and other animal species, including laboratory animals. Background incidence values for these tumors in all common strains of laboratory rats are generally accepted as being <0.1%. Between April 2000 and April 2007, however, sixty-two hibernomas (an overall prevalence of 3.52%) were observed in a total of 1760 Sprague-Dawley rats assigned to three carcinogenesis bioassays at two separate research laboratories. All rats were obtained from Charles River's breeding facilities in either Portage, Michigan, or Raleigh, North Carolina. Tumors (twenty-nine benign and thirty-three malignant) were randomly distributed among test article-treated and control groups and were considered to be spontaneous. Most tumors originated in the thoracic cavity, and they were usually described as soft, mottled to tan masses with nodular to lobulated profiles. Immunohistochemical procedures for uncoupling protein 1 (UCP1) confirmed brown adipose tissue as the site of origin rather than white fat. The marked increase in hibernomas in our studies suggests that greater numbers of spontaneous hibernomas may be sporadically encountered in future carcinogenesis studies with Sprague-Dawley rats. The increased potential for hibernomas to arise as spontaneous neoplasms has important implications in studies involving peroxisome proliferators-activated receptor (PPAR) drugs, lipophilic environmental chemicals (e.g., polychlorinated biphenyls), and other molecules or physiologic processes (e.g., beta-adrenergic stimulation) that may target brown fat adipocytes.
Bruner
Richard H
RH
Biotechnics, LLC, Hillsborough, North Carolina 27278, USA. rbruner@biotechnicsinc.com
Novilla
Meliton N
MN
Picut
Catherine A
CA
Kirkpatrick
Jeannie B
JB
O'Neill
Thomas P
TP
Scully
Kathryn L
KL
Lawrence
Wade B
WB
Goodman
Dawn G
DG
Saladino
Brett H
BH
Peters
David G
DG
Parker
George A
GA
D002001:Adipose Tissue, Brown / Q000473:pathology; D000818:Animals; D015197:Carcinogenicity Tests; D005260:Female; D007150:Immunohistochemistry; D007473:Ion Channels / Q000378:metabolism; D008067:Lipoma / Q000453:epidemiology / Q000473:pathology / Q000662:veterinary*; D008297:Male; D024101:Mitochondrial Proteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012376:Rodent Diseases / Q000453:epidemiology / Q000473:pathology; D000071256:Uncoupling Protein 1
D007473:Ion Channels; D024101:Mitochondrial Proteins; C000604371:UCP1 protein, human; C000604373:Ucp1 protein, rat; D000071256:Uncoupling Protein 1