Abstract. The successful treatment of severe bacterial keratitis continues to be a challenge in animals and humans. In the present study the aim was to assess gaseous therapy using gaseous nitric oxide (gNO) in a murine model of Pseudomonas aeruginosa keratitis. The cornea of anesthetized mice was mechanically scratched and covered with a bacterial suspension of P. aeruginosa. One day later, the infected eyes were exposed to 200 ppm NO for 30 min. Three to seven days later the mice were sacrificed and the bulbi were obtained and processed for light microscopy. The read out parameter was the maximal corneal thickness and the severity of the hypopyon. The therapy with NO did not result in either a reduction of inflammation concerning the maximal corneal thickness or the severity of the hypopyon. The bacterial load was not investigated due to technical limitations. Thus, exposure to gNO did not reduce the local inflammation in P. aeruginosa induced murine keratitis at the investigated time-points. This does not exclude effects of NO on the bacterial load, and in experimental and human keratitis.
IntroductionBacterial keratitis is a major cause of blindness worldwide with a high incidence (1). This is due to low hygiene standards and water quality with a greater risk of infection in poor countries. In addition, the widespread use of contact lenses and associated complications in wealthier countries contributes to severe keratitis (2,3). Staphylococcus aureus and Pseudomonas aeruginosa are two predominant gram-positive and gram-negative bacterial strains responsible for causing this disease (1,4,5). The resistance of bacteria to antibiotics is reducing the efficacy of bacterial keratitis treatment. Therefore, research into the development of novel therapeutic approaches is essential. In this regard photodynamic inactivation has been in experimental and clinical use throughout the last decade (6-8). Research on cystic fibrosis established an antimicrobial effect of gaseous nitric oxide (gNO) in infections with P. aeruginosa using a rat model (9). Furthermore, a study in white rabbits demonstrated that a treatment using 200 ppm gNO significantly reduced the bacterial load in wounds of the dorsal skin surface (10). Thus, in view of the possibility of a surface treatment for keratitis, this therapeutic strategy demonstrated a feasible approach.The aim of the current study was to evaluate gNO application as a potential treatment of experimental keratitis in vivo for the first time. However, this series of experiments did not serve as proof of the anti-inflammatory effect of gNO.
Materials and methodsAnimals and anaesthesia. Young (age, 9-10.5 weeks) female C57BL/6 mice [n=19; standard housing conditions (3-5 animals per cage) with 12-h light/dark cycle, minimum 70% humidity and chow/water were provided ad libitum; Janvier Labs, Saint-Berthevin Cedex, France] were used in the present study. All animal care and experimental procedures were approved by the local governmental animal care committee (permit no. 58/2013) and wer...