Table_1_Histamine-Induced Conjunctivitis and Breakdown of Blood–Tear Barrier in Dogs: A Model for Ocular Pharmacology and Therapeutics.pdf

Conjunctival inflammation disturbs the blood–tear barrier and thus affects the tear film stability and composition. We aimed to develop a non-invasive and reliable method to induce conjunctivitis in dogs, a large animal model for translational work on ocular surface disease in humans. Six beagle dogs underwent a randomized, vehicle-controlled, balanced crossover trial—on six separate days, one eye received topical artificial tears (vehicle), while the other eye received one of six concentrations of histamine solution (0.005–500 mg/ml). At sequential times after eyedrop administration, a conjunctivitis score was given to each eye based on the degree of palpebral and bulbar conjunctival hyperemia and chemosis, ocular pruritus, and discharge. Total protein content (TPC) and serum albumin were quantified in tear fluid at baseline and 20 min. Additionally, 13 dogs presenting for various ophthalmic diseases with associated conjunctivitis were examined. Experimentally induced conjunctivitis developed rapidly (<1 min) following topical histamine administration and lasted for 1–3 h (four lowest doses) to 6–8 h (two highest doses). The severity of conjunctivitis was dose-dependent. Histamine was overall well tolerated, although transient blepharitis, aqueous flare, and ocular hypertension occurred in a few dogs receiving histamine ≥375 mg/ml. TPC and serum albumin levels increased in tears of eyes receiving histamine ≥1.0 mg/ml, being significantly higher than vehicle and baseline in eyes receiving histamine ≥375 mg/ml. Lacrimal albumin levels were also increased in 13 dogs with naturally acquired conjunctivitis, up 2.7–14.9 fold compared to contralateral healthy eyes. Histamine-induced conjunctivitis represents a robust model for translational work on the ocular surface given the low cost, non-invasiveness, self-resolving nature, ability to adjust the duration and severity of the disease, and shared features with naturally occurring ocular diseases. Histamine solutions of 1, 10, and 375 mg/ml induce mild, moderate, and severe conjunctivitis in dogs, respectively. Leakage of serum albumin in tear fluid of eyes with conjunctivitis suggests a breakdown of the blood–tear barrier.</p

Box and whisker plot of mucosal IDO-1 H-score in the duodenum of dogs with protein-losing enteropathy (PLE), chronic enteropathy (CE) and healthy Beagle dogs.

Dogs with PLE– 6 dogs, median– 77.66, interquartile range- 40.18. Dogs with CE– 18 dogs, median– 58.69, interquartile range- 26.82, healthy Beagle control dogs- 8 dogs, median– 45.26, interquartile range- 31.68.</p

RNA <i>in situ</i> hybridization of IDO-1 mRNA in the duodenal mucosa of a dog with protein-losing enteropathy.

RNA in situ hybridization of IDO-1 mRNA in the duodenal mucosa of a dog with protein-losing enteropathy.</p

<i>Post hoc</i> analysis of IDO-1 mRNA expression in the duodenal mucosa of dogs with protein-losing enteropathy (PLE), chronic enteropathy (CE), and healthy Beagle control dogs using RNA <i>in situ</i> hybridization.

P-values obtained from Tukey's HSD (Honestly Significant Difference) post-hoc analysis after one-way analysis of variance testing of percentage mucosal IDO-1 positive mRNA and IDO-1 H-score in the duodenal mucosa of dogs with PLE (n = 6), dogs with CE (n = 18) and healthy Beagle control dogs (n = 8).</p

Box and whisker plot of percentage mucosal IDO-1 positive mRNA in the duodenum of dogs with protein-losing enteropathy (PLE), chronic enteropathy (CE) and healthy Beagle dogs.

Dogs with PLE– 6 dogs, median– 32.18, interquartile range- 11.19. Dogs with CE– 18 dogs, median– 25.28, interquartile range- 9.56, healthy Beagle control dogs- 8 dogs, median– 19.65, interquartile range- 11.44.</p

Scatter plot of serum tryptophan concentrations and duodenal mucosal IDO-1 H-score in dogs with protein-losing enteropathy.

Scatter plot of serum tryptophan concentrations (nmol/ml) and duodenal mucosal IDO-1 H-score of 6 dogs with protein-losing enteropathy (PLE). Serum tryptophan concentrations were significantly negatively correlated with mucosal IDO-1 H-score in dogs with PLE (Spearman’s rank correlation co-efficient: -0.94, P = 0.0048).</p

RNA <i>in situ</i> hybridization of IDO-1 mRNA in the duodenal mucosa of a healthy Beagle control dog.

RNA in situ hybridization of IDO-1 mRNA in the duodenal mucosa of a healthy Beagle control dog.</p

Group comparison of average (±sd) CCECAI and CIBDAI over time.

Group comparison of average (±sd) CCECAI and CIBDAI over time.</p

This file contains all clinical raw data fort he trial.

(PDF)</p

Study design.

A total of thirty-five dogs were enrolled and fifteen dogs were excluded. Each box represents the period when the dogs were on Purina HA diet (grey), Treatment 1 with GAG (black), and Treatment 2 with placebo (upward diagonal).</p