An in vitro model of leukocyte mediated injury to the corneal epithelium

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Aprepitant Restores Corneal Sensitivity and Reduces Pain in DED

Purpose

This study aims to assess the efficacy of two aprepitant formulations (X1 and X2), in a preclinical model of dry eye disease (DED) induced by benzalkonium chloride (BAK).

Methods

Two aprepitant formulations were tested on 7 to 8-week-old male mice for their efficacy. In vivo corneal fluorescein staining assessed epithelial damage as the primary end point on days 0, 3, 5, 7, 9, 12, and 14 using slit-lamp microscopy. The DED model was induced with 0.2% BAK twice daily for the first week and once daily for the next week. Mice were randomly assigned to 5 treatment groups: Aprepitant X1 (n = 10) and X2 (n = 10) formulation, 2 mg/mL dexamethasone (n = 10), control vehicle X (n = 10), 0.2% hyaluronic acid (n = 10), or no treatment (n = 10). Eye wiping, phenol red, and Cochet Bonnet tests assessed ocular pain, tear fluid secretion, and nerve function. After 7 days, the mice were euthanized to quantify leukocyte infiltration and corneal nerve density.

Results

Topical aprepitant X1 reduced BAK-induced corneal damage and pain compared to gel vehicle X (P = 0.007) and dexamethasone (P = 0.021). Aprepitant X1 and X2 improved corneal sensitivity versus gel vehicle X and dexamethasone (P < 0.001). Aprepitant X1 reduced leukocyte infiltration (P < 0.05) and enhanced corneal nerve density (P < 0.001). Tear fluid secretion remained statistically unchanged in both the X1 and X2 groups.

Conclusions

Aprepitant formulation X1 reduced pain, improved corneal sensitivity and nerve density, ameliorated epitheliopathy, and reduced leukocyte infiltration in male mouse corneas.

Translational Relevance

Aprepitant emerges as a safe, promising therapeutic prospect for the amelioration of DED's associated symptoms.

The induction of anterior chamber inflammation by factors released from hydrogen peroxide-injured corneas: effect of dexamethasone and indomethacin

Studies from our laboratory have demonstrated the release of high levels of neutrophil chemotactic factors (NCF) from isolated rabbit corneas injured by hydrogen peroxide (H2O2). The purpose of the present study was to determine the biological activity of these factors and to test the hypothesis that the intracameral injection of these factors can induce inflammation of the anterior segment. Under sterile conditions, the epithelial surfaces of isolated rabbit corneas were incubated with a 300 ul mixture of glucose (G) (1mg/ml) and glucose oxidase (GO) (20 U/ml) at 37 degrees C for 6 hours. This supernatant solution was collected and a 100 ul sample containing NCF, but not H2O2, was injected into the anterior chamber of anesthetized rabbit eyes (n = 8). Anterior chamber inflammation, characterized by moderate corneal edema associated with a fibrinous anterior chamber reaction, was evident 2 and 4 hours after injection. Aqueous humor analysis revealed the presence of fibrin and a large number of neutrophils (32 +/- 5 x 10(4) cells/ml). Control eyes, on the other hand, showed normal morphology and low levels of neutrophils after the injection of 100 ul minimum essential medium (MEM) (n = 8) (1.2 +/- 0.14 x 10(4) cells/ml), G/GO mixture (n = 8) (5 +/- 0.86 x 10(4) cells/ml), or supernatant solutions collected from MEM-treated corneas (n = 8) (15 +/- 2 x 10(4) cells/ml). To determine whether the inflammatory reaction observed was due to a direct effect of the chemoattractants or mediated through stimulation of arachidonic acid (AA) metabolites, we pretreated rabbit eyes with a sterile solution of 0.1% dexamethasone (n = 8 eyes) or with a sterile solution of 3.4% indomethacin (n = 8 eyes) three times a day, for one day, prior to the injection of NCF supernatant solution. Examination 2 hours and 4 hours after injection revealed inflammation characterized by mild-to-moderate corneal edema associated with a fibrinous anterior chamber reaction was observed with or without prior treatment with AA metabolite inhibitors. No difference in the degree of inflammation was detected clinically. Results of these studies suggest that NCF released from H2O2-injured corneas can directly induce inflammation of the anterior segment, and that metabolites of AA are not mediating the observed in vivo response.

Cornea derived neutrophil chemotactic factors: intracellular synthesis and release

The present study was designed to test the hypothesis that the release of neutrophil chemotactic factors (NCF) from isolated corneas following hydrogen peroxide stimulation requires specific intracellular synthesis. For these studies, the epithelial surfaces of isolated rabbit corneas were preincubated with various inhibitors of protein synthesis (cycloheximide, 10 micrograms/ml, and puromycin, 50 micrograms/ml) and transcription (actinomycin D, 5 micrograms/ml) for 60 min prior to exposure of the corneas to glucose (G, 1 mg/ml) and glucose oxidase (GO, 20 U/ml) for 6 h at 37 degrees C. All three inhibitors decreased the levels of NCF recovered in the extracorneal fluids by 80-98%, suggesting that peroxide acts to upregulate NCF production at both the transcription and translation levels. When corneas were incubated with G/GO for 6 h at 12 degrees C or 4 degrees C instead of 37 degrees C, a reduction in the levels of NCF recovered in the supernatants was noted at 12 degrees C (46-91% inhibition) and at 4 degrees C (67-96% inhibition), suggesting that the synthesis of NCF at cold temperature was only reduced but not totally inhibited. To demonstrate that the observed reduction in chemotactic activity recovered from corneas incubated at 12 degrees C or 4 degrees C is not due to a temperature-dependent inhibition of NCF biosynthesis, but rather to a disruption of intracellular vesicular transport, temperature shift experiments were performed. Corneas were incubated with G/GO overnight at 12 degrees C or 4 degrees C prior to shifting to 37 degrees C for an additional 6 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of neutrophil chemotactic factors from gastric tissue. Initial biochemical characterization

This study was designed to characterize neutrophil chemotactic factors released by gastric tissue. Full-thickness rabbit stomach (organ culture) was prepared and incubated in Ringer's solution at 37 degrees C. Culture supernatants were collected at 1, 2, 3, and 4 hr and assayed for neutrophil chemotactic activity in modified Boyden chambers. High levels of chemotactic activity were seen at 3 hr of incubation. Antral and fundic tissue were equally capable of producing neutrophil chemotactic activity. In addition, high levels of activity were seen from both the serosal and mucosal surfaces. Initial biochemical characterization of these gastric-derived factors revealed that: (1) a majority of the activity (80-90%) exhibited molecular weight values of greater than 300 kDa, (2) the chemotactic activity was heat stable but was partially reduced by treatment with a protease, subtilisin (37% inhibition), and (3) 70-80% of the activity in the supernatants was extracted into organic solvent (ethyl acetate). These factors may prove to be important in recruitment of neutrophils to areas of gastric injury.

Inflammatory mediators in alkali-burned corneas: preliminary characterization

Leukocyte chemotactic factors (LCF) are important inflammatory mediators which activate and recruit leukocytes from the circulation into sites of tissue damage. These factors were recently detected in the tear fluid of inflamed eyes induced by alkali burn. It remains unclear, however, whether the detected LCF are released from injured corneal tissues or leaked from the circulation. Using a corneal cup model developed in our laboratory, we began examining the capability of corneal tissues to produce LCF in response to alkali injury. We also evaluated the influence of citric acid on the production of LCF from corneas preinjured by the alkali sodium hydroxide (NaOH). For these studies, the epithelial surfaces of corneas isolated from bovine and human eyes were exposed to 1N NaOH for 35 seconds at room temperature. The NaOH was then removed and the epithelial surfaces washed once with buffer and incubated with culture medium for 1, 2, 4, and 6 hours at 37 degrees C/5% CO2 atmosphere. Our results showed that (1) NaOH2 induced corneal epithelial cell injury ranging from cell discoloration and moderate damage of the upper half of the epithelium (1-4 hrs) to total destruction of the epithelium (6 hrs); (2) NaOH-injured corneas (2 hr incubation post injury) produced significant levels of chemotactic activity (via checkerboard analysis) specific for neutrophils (115% maximum chemotactic response [MCR]) and mononuclear cells (94% MCR); (3) preliminary characterization of these factors revealed that they are protease and heat sensitive, extractable by organic solvents, and possess molecular weight values greater than 100,000 daltons; and (4) incubation of NaOH-pretreated corneas with 0.01% citric acid for 2 hours markedly inhibited the production of LCF for both neutrophils (98% inhibition) and mononuclear cells (91% inhibition). Results of these studies indicate that alkali-burned bovine and human corneas generate leukocyte chemoattractants which differ in their biochemical characteristics from previously known low molecular weight chemotactic factors such as C5a, interleukin-1, or leukotriene B4.