Experimental oral carcinogenesis in rats: histomorphometric study and global gene expression

Abstract

Oral tumorigenesis involves a field cancerization process that proceeds in a multifocal fashion through multiple events. The study design consisted of 4-nitroquinoline-N-oxide (4NQO)-induced oral carcinogenesis in rats. Drinking water was laced with 0.001% 4NQO. Rats were killed at 7, 14, 22, 28, 33, and 36 weeks. The tongues were bisected through longitudinal midline incision. Half was processed for routine histopathologic examination, whereas the other half was stored in liquid nitrogen and used for RNA extraction. An examination of hematoxylin and eosin-stained sections revealed progression from hyperkeratosis to varying degrees of dysplasia and ultimately to invasive squamous cell carcinoma of the tongue mucosa. Histomorphometry of the lingual salivary glands revealed a decrease in the volume fraction of the serous acini and almost no morphologic changes in the mucous glands. The excretory ducts of the serous glands exhibited various degrees of dysplasia. To study the global gene expression during 4NQO-induced tongue carcinogenesis, RNA samples from tongues at different times were analyzed by using Affymetrix rat oligonucleotide microarrays (Affymetrix, Inc., Santa Clara, Calif). A comparison of gene expression profiles in the treated animals at various time points revealed changes in genes involved in proliferation, apoptosis, adhesion, migration, DNA repair, and stress response. Of particular interest was the increase in the expression of genes associated with salivary glands, namely the common salivary protein 1, rat praline-rich salivary protein, neonatal submandibular gland proacinar cell protein precursor, rat pancreatic amylase, and lingual lipase. The results of the present study may hint at the role of salivary glands in the process of oral carcinogenesis.