Disarming Pore-Forming Toxins with Biomimetic Nanosponges in Intraocular Infections

Abstract

Intraocular infections are prevalent after traumatic injuries or after common ocular surgeries. Infections cause inflammation that can damage the retina and architecture of the eye, often resulting in poor visual outcomes. Severe cases may result in blindness or require enucleation of the eye. Treatments for intraocular infections include intravitreal antibiotics and corticosteroids or surgical vitrectomy in serious cases. The increase in multidrug-resistant infections calls for novel treatment options. In the present study, a biomimetic erythrocyte-derived nanosponge was tested for the ability to neutralize pore-forming toxins from the most frequent Gram-positive bacterial causes of intraocular infections (Staphylococcus aureus, Enterococcus faecalis, Streptococcus pneumoniae, and Bacillus cereus). Nanosponge pretreatment of supernatants reduced hemolytic activity in vitro. In a murine sterile endophthalmitis model, nanosponge pretreatment of injected supernatants resulted in greater retinal function and less ocular pathology compared to that in eyes injected with untreated supernatants from all pathogens except methicillin-resistant S. aureus. In a murine bacterial endophthalmitis model, treatment with gatifloxacin and gatifloxacin-nanosponges reduced intraocular bacterial burdens, except in the case of methicillin-sensitive S. aureus. For all pathogens, eyes in both treatment groups showed decreased ocular pathology and inflammation. Overall, reductions in retinal function loss afforded by gatifloxacin-nanosponge treatment were significant for E. faecalis, S. pneumoniae, and methicillin-resistant S. aureus but not for B. cereus and methicillin-sensitive S. aureus. These results suggest that clinical improvements in intraocular infections following nanosponge treatment were dependent on the complexity and types of toxins produced. Nanosponges might serve as an adjunctive therapy for the treatment of ocular infections. IMPORTANCE Endophthalmitis is a blinding consequence of bacterial invasion of the interior of the eye. Because of increases in the numbers of ocular surgeries and intraocular injections, the incidence of endophthalmitis is steadily increasing. Staphylococcus aureus, Enterococcus faecalis, Streptococcus pneumoniae, and Bacillus cereus are leading causes of infection following ocular procedures and trauma and are increasingly more difficult to treat due to multidrug resistance. Each of these pathogens produces pore-forming toxins that contribute to the pathogenesis of endophthalmitis. Treatment of these infections with antibiotics alone is insufficient to prevent damage to the retina and vision loss. Therefore, novel therapeutics are needed that include agents that neutralize bacterial pore-forming toxins. Here, we demonstrate that biomimetic nanosponges neutralize pore-forming toxins from these ocular pathogens and aid in preserving retinal function. Nanosponges may represent a new form of adjunct antitoxin therapy for serious potentially blinding intraocular infections.

An Eye on Staphylococcus aureus Toxins: Roles in Ocular Damage and Inflammation

“…These nanoparticles, termed nanosponges, neutralized α-toxin and reduced hemolytic activity in vitro, protected mice from developing staphylococcal α-toxin induced skin lesions, and decreased mortality after systemic injection of a lethal dose of α-toxin [91]. In a mouse model of S. aureus endophthalmitis, Coburn et al [92] reported that intraocular injection of nanosponges alone following infection did not result in improved retinal function compared to untreated mice. However, injection of nanosponges in conjunction with the fourth-generation fluoroquinolone gatifloxacin resulted in decreased inflammation, less damage to the retinal architecture, and significantly improved retinal function compared to untreated or gatifloxacin only treated mice following intraocular infection with an MRSA ocular isolate [92].…”

“…In a mouse model of S. aureus endophthalmitis, Coburn et al [92] reported that intraocular injection of nanosponges alone following infection did not result in improved retinal function compared to untreated mice. However, injection of nanosponges in conjunction with the fourth-generation fluoroquinolone gatifloxacin resulted in decreased inflammation, less damage to the retinal architecture, and significantly improved retinal function compared to untreated or gatifloxacin only treated mice following intraocular infection with an MRSA ocular isolate [92]. These studies suggested that nanosponges might be a viable adjunctive therapy for intraocular infections caused by S. aureus .…”

Immune Inhibitor A Metalloproteases Contribute to Virulence inBacillusEndophthalmitis

“…Our findings suggest that the InhAs may facilitate intraocular bacterial growth by producing an environment more conducive to persistence. Current therapeutics are relatively ineffective in treating Bacillus endophthalmitis [1,[9][10][11][59][60][61][62][63], and due to its rapidly blinding course, Bacillus endophthalmitis requires early and precise treatment [62,63]. Treatment strategies for Bacillus and other types of endophthalmitis should be based on knowledge of the virulence factors that contribute to disease pathogenesis.…”

“…Every 2 hours, 20-μL aliquots were track diluted in PBS and plated onto BHI agar plates, and counted after 24 hours [2,6,21,23,26,65,[65][66][67]. Values are expressed in percent hemolysis relative to a 100% lysis control, as previously described [16,19,26,61,68].Values represent the means ± SD of two independent experiments.…”

Innate Immune Interference Attenuates Inflammation InBacillusEndophthalmitis

“…From a treatment standpoint, Bacillus endophthalmitis cases are difficult and are often associated with worse patient outcomes than infections caused by other pathogenic species. 6,[8][9][10][11] The pathogenicity of Bacillus endophthalmitis is linked to the inflammogenic potential of the bacterial cell wall and the secretion of toxins and enzymes. [12][13][14][15][16][17][18] The severe nature of Bacillus endophthalmitis requires prompt and rapid therapy to halt disease progression.…”