Band keratopathy in MRL/l and MRL/n mice

Corneal Dystrophy in Dutch Belted Rabbits as a Possible Model of Thiel-Behnke Subtype of Epithelial-Stromal TGFβ-Induced Corneal Dystrophy

The International Committee for Classification of Corneal Dystrophies (IC3D) categorized corneal dystrophies in humans using anatomic, genotypic, and clinicopathologic phenotypic features. Relative to the IC3D classification, a review of the veterinary literature confirmed that corneal dystrophy is imprecisely applied to any corneal opacity and to multiple poorly characterized histologic abnormalities of the cornea in animals. True corneal dystrophy occurs in mice with targeted mutations and spontaneously in pet dogs and cats and in Dutch belted (DB) rabbits, but these instances lack complete phenotyping or genotyping. Corneal dystrophy in DB rabbits can be an important confounding finding in ocular toxicology studies but has only been described once. Therefore, the ophthalmology and pathology of corneal dystrophy in 13 DB rabbits were characterized to determine whether the findings were consistent with or a possible model of any corneal dystrophy subtypes in humans. Slit lamp and optical coherence tomography (OCT) imaging were used to characterize corneal dystrophy over 4 months in young DB rabbits. The hyperechoic OCT changes correlated with light microscopic findings in the anterior stroma, consisting of highly disordered collagen fibers and enlarged keratocytes. Histochemical stains did not reveal abnormal deposits. Small clusters of 8 to 16 nm diameter curly fibers identified by transmission electron microscopy were consistent with Thiel-Behnke (TBCD) subtype of epithelial-stromal transforming growth factor β-induced dystrophies. Sporadic corneal dystrophy in DB rabbits appears to be a potential animal model of TBCD, but genotypic characterization will be required to confirm this categorization.

Ketamine/Xylazine-Induced Corneal Damage in Mice

Purpose

We have observed that the commonly used ketamine/xylazine anesthesia mix can induce a focally severe and permanent corneal opacity. The purpose of this study was to establish the clinical and histological features of this deleterious side effect, its sensitivity with respect to age and anesthesia protocol, and approaches for avoiding it.

Methods

Young C57BL/6J, C57BLKS/J, and SJL/J mice were treated with permutations of anesthesia protocols and compared using slit-lamp exams, optical coherence tomography, histologic analyses, and telemetric measurements of body temperature.

Results

Ketamine/xylazine induces corneal damage in mice with a variable frequency. Among 12 experimental cohorts, corneal damage associated with ketamine/xylazine was observed in 9 of them. Despite various treatments to avoid corneal dehydration during anesthesia, the frequency of corneas experiencing damage among responding cohorts was 42% (26% inclusive of all cohorts), which is significantly greater than the natural prevalence (5%). The damage was consistent with band keratopathy. It appeared as a white or gray horizontal band located proximal to the pupil and was positive for subepithelial calcium deposition with von Kossa stain.

Conclusions

The sum of our clinical and histological observations is consistent with ketamine/xylazine-induced band keratopathy in mice. This finding is relevant for mouse studies involving the eye and/or vision-dependent behavioral assays, which would both be prone to artifact without appreciation of the damage caused by ketamine/xylazine anesthesia. Use of yohimbine is suggested as a practical means of avoiding this complication.

Ocular Toxicity Assessment From Systemically Administered Xenobiotics

The eye is a unique sensory structure, which must be evaluated for toxicity to determine the safety of drugs, industrial chemicals, and consumer products. Changes in the structure and/or function of ocular tissues following systemic administration of a potential new drug in preclinical animal models can result in significant delays in the development of a new therapeutic and in some cases lead to termination of the development. The ability to detect and characterize ocular toxicity in preclinical models and to predict risk in patients is critically dependent on the preclinical testing strategy, the availability and use of state-of-the-art ocular safety assessment tools, and the knowledge of drug mechanism of action and the current regulatory environment. This review describes the design and execution of toxicity studies with the incorporation of current methods for in vivo assessment of ocular toxicity, including methods for detecting early changes in the eye. In addition, anatomical differences among laboratory animals, preparation of globes for examination, and iatrogenic and spontaneous ocular findings are described that can affect interpretation of toxicological findings. Finally, the correlation between nonclinical outcomes and clinical evaluations is discussed in terms of expected therapeutic uses, indications, and regulatory consequences of ocular effects.

Animal models of Sjögren's syndrome

Sjögren's syndrome is an autoimmune, chronic inflammatory disease characterized by focal mononuclear cell infiltration of exocrine tissues, accompanied by loss of secretory function. The pathogenesis of autoimmune diseases is complex and, therefore, difficult to study in vitro. As of today, the role of initiating factors remains obscure, clinical symptoms develop late, and there are no tests for early diagnosis of SS. Hence, the disease is difficult to detect and treat. Animal models may provide insights into the identification of target antigens, narrowing the relevant pathological immune mechanisms, and to study the evolution of tissue pathology. This review summarizes current knowledge on murine strains, both spontaneous and induced models, used to study Sjögren's syndrome. Special attention is paid to the characteristics of different strains regarding their properties to mimic specific aspects or stages of the disease.

Lymphocytic infiltration and goblet cell marker alteration in the conjunctiva of the MRL/MpJ-Fas(lpr) mouse model of Sjögren's syndrome

Sjögren's syndrome is an autoimmune disorder characterized by a progressive, immune-mediated destruction of mucosal tissues such as the lacrimal and salivary glands, leading to ocular and oral dryness. The MRL/MpJ-Fas(lpr) mouse is one of the animal models used to study this disease. However, little is known about the potential alterations in the conjunctiva in this murine model. The purpose of this study was to determine: (1) whether the conjunctiva is infiltrated by T lymphocytes, (2) characterize the type, amount and temporal sequence of the inflammatory infiltrates, and (3) investigate whether the amount of conjunctival goblet cells is altered in this murine model of Sjögren's syndrome. Female 4-, 9-, 13-, 16-, and 18-/20-wk-old MRL/MpJ-Fas(lpr) (lpr, diseased) and congenic MRL/MpJ (+/+, control) mice were used. Right eyes were either fixed, frozen, cryosectioned, and studied by immunofluorescence microscopy or the conjunctiva was removed, homogenized and analyzed by electrophoresis and Western blot analysis. The following antibodies were used: anti-CD3 (specific T lymphocyte marker), anti-cytokeratin 7 (CK-7), anti-PKD (formerly known as PKCmu, both markers of goblet cell bodies), anti-PGP 9.5 (pan-neuronal marker), anti-VIP and TH (markers for parasympathetic and sympathetic nerves, respectively), anti-adrenergic (alpha(1) and beta(1-3)) and muscarinic (M(1)-M(3)) receptor subtypes (markers for neurotransmitter receptors of the sympathetic and parasympathetic pathways, respectively). Left eyes were fixed, embedded, sectioned, and stained. Hematoxylin/eosin, Giemsa, or alcian blue/periodic acid Schiff's reagent were used to study lymphocyte infiltration; to determine the presence of eosinophils, neutrophils, and mast cells; and to count the number of goblet cells, respectively. By immunofluorescence microscopy, lymphocytes were detected in the conjunctiva of 9-wk-old lpr, but not +/+, mice. The lymphocytic infiltration became more extensive as the animals aged, with 16- and 18-/20-wk lpr mice appearing to have a greater lymphocytic infiltration than +/+ mice at the same age. By Western blot analysis, the amount of CD3 was enhanced in lpr compared to +/+ mice by the 16th wk, but not by the 9th wk. No major differences in the presence of eosinophils, neutrophils and degranulated mast cells between lpr and +/+ mice were observed. By light microscopy, a significant increase in goblet cell number was found in lpr mice compared to +/+ mice at 16 wks on. By Western blotting, the amount of CK-7 was significantly increased at 9 wks on and the amount of PKD was significantly increased at 16 wks. By immunofluorescence microscopy, there were no major differences in distribution of sympathetic and parasympathetic nerves present in the lpr conjunctiva compared to that of +/+ mice at any ages, although slight differences were observed with increased age. Muscarinic receptor expression was decreased, as less M(3) receptor subtype-associated immunofluorescence was detected in older lpr mice compared to +/+ mice and confirmed by Western blot analysis. No differences in the localization or the amount of alpha(1)- or beta(1-3)-adrenergic receptor immunodetection were observed between lpr and +/+ mice. We conclude that the conjunctiva is a target tissue in Sjögren's syndrome-related inflammation in this murine model.

High expression of interleukin-1beta in the corneal epithelium of MRL/lpr mice is under the control of their genetic background

MRL/Mp mice bearing the Fas deletion mutant gene, lpr (MRL/lpr), spontaneously develop polyarthritis, sialoadenitis and dacryoadenitis, resembling rheumatoid arthritis (RA), and also corneal involvement such as keratopathy and scleritis, which is a major complication in RA patients. In this study, we found that the expression levels of IL-1beta and MMP-1 mRNAs in cornea were high in both MRL/lpr and MRL/Mp-+/+ strains of mice at an age younger than when they develop any inflammatory lesions. This was not true of other inbred strains, even those bearing the lpr gene, and also not of (NZB x NZW) F1 lupus mice. There was no significant difference in the expression of IL-1alpha and TGFbeta in cornea in these strains. Using crosses between MRL/lpr and C3H/HeJ-lpr/lpr (C3H/lpr) mice, at least the expression of IL-1beta was found to be under the control of the MRL genetic background, likely with a recessive mode of inheritance. Considering that IL-1beta in cornea was detected particularly in the epithelial layer, the high expression of IL-1beta in cornea is most likely involved in the genetic predisposition for corneal involvement and possibly also for arthritis in an MRL strain of mice.

Detection of anti-neutrophil cytoplasmic antibodies in MRL/Mp-lpr/lpr mice and analysis of their target antigens

Anti-neutrophil cytoplasmic antibodies (ANCA) have been widely studied and recognized to be clinically very important for some human diseases including systemic rheumatic diseases. We analyzed ANCA response and their target antigens in MRL/Mp-lpr/lpr (MRL-lpr) mice, an animal model of systemic rheumatic disease. P-ANCA was detected in 57% of the mice. Antibodies to the known P-ANCA target antigens at the same age were examined. Among these, antibodies to high mobility group (HMG) proteins HMG1 and HMG2 were detected in 57% of the mice, 75% of which were also positive for P-ANCA. These anti-HMG1/HMG2 activities were absorbed by preincubation with a mixture of HMG1 and HMG2. In contrast, antibodies to myeloperoxidase and cathepsin G were detected in 14% and 7%, respectively, but these activities were not inhibited by preincubation with corresponding antigens. In addition, the titers of P-ANCA and anti-HMG1/HMG2 antibodies in MRL-lpr mice were significantly correlated with each other. Thus, HMG1 and HMG2 were considered to be significant target antigens of P-ANCA in MRL-lpr mice.

Presence of Langerhans cells in the central cornea linked to the development of ocular herpes in mice

Recurrences of herpetic stromal keratitis are believed to be initiated by reactivation of herpes simplex virus infection, probably in the trigeminal ganglion. Genetic features of the virus and the host as well as the immune status of the host influence the outcome of infection. Following infection on the snout with HSV-1, mice with normal corneas usually develop mild anterior segment disease. We studied the induction of herpetic infection in mice that had abnormal corneas, containing center due to trauma or a spontaneous dystrophy. The corneal abnormality led to more frequent herpetic stromal keratitis and more severe anterior chamber reaction. In addition, we found that snout-infected mice with dystrophic corneas had an increased risk of dying from viral infection. Our data suggest that not only the strain of virus and the genetic background of the mouse, but also the state of the cornea itself, can contribute to susceptibility to ocular herpes infection.

Androgen control of autoimmune expression in lacrimal glands of MRL/Mp-lpr/lpr mice

The purpose of the present study was to determine, by utilizing an animal model of Sjögren's syndrome, whether androgen therapy might ameliorate autoimmune sequelae in the lacrimal gland. Age-matched female MRL/Mp-lpr/lpr mice were administered subcutaneous implants of placebo- or testosterone-containing pellets after the onset of disease. Lacrimal glands and, for comparison, submandibular glands were collected from sacrificed mice immediately prior to androgen administration and following 17 and 34 days of maintained hormone exposure. Tissues were processed for light microscopy and examined with a computer-assisted image analysis system. Results demonstrated that testosterone exposure dramatically reduced lymphocyte infiltration in lacrimal tissue: following 34 days of treatment, the percentage infiltrate had undergone a 12-fold decrease. This hormone action, which was time dependent, involved significant abrogations in both infiltrate size and number. Testosterone administration also induced a significant 2- to 3-fold rise in lacrimal gland weight and acinar area and a 2-fold reduction in acinar density/field, compared to values in placebo-treated controls. In addition, androgen administration significantly decreased the magnitude of lymphocyte infiltration in submandibular glands. Overall, our findings demonstrate that androgen therapy may reverse autoimmune sequelae in lacrimal, as well as submandibular, glands in a mouse model of Sjögren's syndrome.

Polyarthritis in MRL lpr/lpr mice

Mice of the inbred strain MRL/MpJ-lpr/lpr are affected by a systemic autoimmune disease and a spontaneously occurring polyarthritis. To characterize the arthritis a histopathological study was performed on the joints of the four limbs and of the spinal column of 7, 16, 22 and 28-week-old animals of both sexes. Polyarthritis, the severity of which increased with age was detected in all mice. Proliferation of the synovial lining cells, already evident in 7-week-old animals, was the initial lesion. In the majority of cases infiltrates containing lymphocytes with a few plasmocytes, histiocytes, polymorphonuclear neutrophils and eosinophils were detected later on. The most pronounced changes were observed in the hind-paws, the fore-paws, the knee and hip joints, paired articulations being symmetrically involved. A pannus was seen at the most in 10% of the joints leading to limited and superficial destruction of the cartilage. Rheumatoid nodules were not seen. From 16 weeks of age deposits of unknown nature, often surrounded by phagocytosing macrophages and/or neutrophils, were observed in the articular and/or extra-articular connective tissue and in the vessels. There was a positive correlation between their presence and the intensity of the arthritis. The articular lesions in our study differ from those in rheumatoid arthritis because they lacked the specific and characteristic histological features of the human disease.

Sjögren's syndrome in MRL/l and MRL/n mice

Six autoimmune murine models (MRL/l, MRL/n, NZB, NZB/NZW, PN, C57BL/6J-lpr/lpr) were compared with normal control C57BL/6J and DBA/2 mice to determine if spontaneous autoimmune disease was associated with evidence of Sjögren's syndrome. Schirmer tests documented dry eyes in NZB/NZW and PN mice; other autoimmune strains and controls had normal tear formation. All autoimmune mice had conjunctivitis, but this abnormality was most severe in the PN strain. Ninety-eight percent of MRL/l and MRL/n mice had mononuclear cell infiltrates in lacrimal glands, and salivary glands were involved to a lesser degree. New Zealand mice and PN mice had smaller gland lesions. The extensive gland destruction in MRL/l and MRL/n mice suggested that these substrains merit further studies as animal models of Sjögren's syndrome.