Expression of cyclooxygenase-1 and 2 in naturally-occurring canine cancer.

The purpose of this work was to determine cox-1 and cox-2 expression by immunohistochemistry in forms of naturally occurring canine cancer in order to identify animal systems for pre-clinical evaluation of cox inhibitors and cox-2 inhibitors in cancer. Canine lymphoma (LSA), prostatic carcinoma (PCA), osteosarcoma (OSA), oral melanoma (MEL), oral squamous cell carcinoma (SCC), oral fibrosarcoma (FSA), mammary carcinoma (MCA), and normal tissues were included. Cox-2 was expressed in epithelial tumors (17 of 26 SCC, 8 of 13 MCA, 5 of 9 PCA cases) and MEL (9 of 15 cases), but was generally absent in normal tissues. Cox-2 expression was minimal or absent in mesenchymal tumors and LSA. Cox-1 was expressed in normal epithelial tissues and in some osteoclast and osteoblast in bone, but was absent in normal lymph node. In conclusion, forms of canine cancer were identified for in vivo studies of the effects of cox inhibitors and selective cox-2 inhibitors on cancer.

Evaluation of the long-term pancreatic effects of constitutive nitric oxide synthase inhibition in dogs.

Constitutive and inducible isoforms of nitric oxide synthase (NOS) catalyze the synthesis of nitric oxide (NO) from L-arginine in various tissues and in different pathophysiologic states. Short-term treatment with NOS inhibitors has been associated with pancreatic enzyme elevations and pancreatic acinar cell degeneration; however, long-term pancreatic effects of NOS inhibition are not known. The purpose of this study was to evaluate the subchronic pancreatic effects of L-nitro-arginine (LNA), a compound that preferentially inhibits constitutive NOS isoforms. LNA was administered orally at doses of 10 and 30 mg/kg per day to 6 female dogs/group for 4 weeks. To differentiate whether the pancreatic effects of LNA may be related to its arginine structure, an additional group was given L-arginine (L-Arg) at plasma concentrations similar to the high dose of LNA (30 mg/kg per day). Pancreatic effects were monitored by changes in serum levels of pancreatic enzymes at regular intervals and by microscopic examinations at the end of the study. Both LNA and L-Arg were systematically available throughout the 4-week study period. LNA produced dose-related elevations (1.3-10-fold above concurrent control) in serum levels of pancreatic enzymes (amylase, lipase and trypsin-like immunoreactivity) during the 4-week treatment period with peak elevations occurring during the first week. Histologic assessments of the pancreas conducted at the end of the 4-week dosing period were unremarkable. Additionally, LNA treatment resulted in reduction in heart rate (40%), gastric distension and gastric mucosal erosion and ulceration. No pancreatic, cardiac, or gastric effects were seen with L-Arg, indicating that above effects were likely due to NOS inhibition. Results of this study confirmed previous observations of acute pancreatic alterations following the inhibition of constitutive NOS isoforms. However, these pancreatic alterations appear to be only transient effects as elevations in serum enzymes declined over time and no structural acinar cell damage was seen after continuous treatment with LNA for 4 weeks, suggesting an adaptation to NOS inhibition over time.

Cyclooxygenase-2 expression in the cornea of dogs with keratitis.

Cyclooxygenase-2 (COX-2) can be overexpressed at inflammatory sites, leading to the generation of proinflammatory prostanoids. Selective inhibitors of COX-2 have potential use in treating inflammatory conditions including ophthalmic diseases in veterinary medicine. Keratitis is considered the most common inflammatory eye disease in dogs. In this study we evaluated the expression of COX-2 in normal dog eyes and in dog eyes with keratitis by immunohistochemistry using isoform-specific antibodies. In the normal eye (n = 4), no COX-2 immunoreactivity was observed in the cornea. In keratitis, COX-2 (n = 12) expression was observed in all corneal layers (epithelium, stromal cells, and endothelium). COX-2 immunoreactivity was also noted in the stromal and epithelial cells of the iris and the stromal cells of the trabecular meshwork. These data indicate that COX-2 may play a pathophysiologic role in keratitis and suggest potential therapeutic implications of prostaglandin modulation in inflammatory eye diseases.