(405) Mechanisms Underlying Increased Susceptibility and Severity of Bacterial Keratitis in Diabetic Mice

Introduction/Rationale: Diabetic patients have a higher incidence of infections, with increased severity and a higher prevalence of multidrug resistance. This study was to investigate the role of programmed cell death (PCD) pathways as an underlying mechanism for increased susceptibility and severity of bacterial keratitis in diabetic C57BL/6 mice.

Methods: Streptozotocin-induced diabetic (DM) C57BL/6 mice were inoculated with Pseudomonas aeruginosa (Pa), and the PCD pathways in the control, normoglycemic mice and STZ-treated mice were determined by immunohistochemistry using antibodies that detect the active forms of Caspase-8 (intrinsic apoptosis) and RIPK3 (necroptosis). The role of PCD pathways was determined by Casp8 and RIPK3 inhibitors. The therapeutic effects of targeting necroptosis were assessed using RIPK3 and HMGB1 inhibitors as adjunctive treatments, concomitantly applied with antibiotics to eliminate the invading bacterial pathogen.

Results: At 1-day post-infection (dpi), hyperglycemia increased neutrophil but suppressed macrophage infiltration. While in the control corneas, cleaved casp8 was stained strongly in NL, phosphor-RIPK3 was mostly detected in DM epithelial layer and stromal infiltrates. Inhibition of caspase activity worsens the outcome of keratitis, whereas blocking RIOPK3 prevents Pa infection in NL and greatly reduces the severity of keratitis in DM corneas. At 16 h post-infection, concomitant application of RIPK3 inhibitor or cell impermeable inhibitor HMGB1, a prototype of alarmin released from lytic PCD pathways, reduced lingering inflammation in Pa-infected corneas at 3 dpi.

Conclusion: Hyperglycemia skews apoptosis towards necroptosis, leading to exacerbated bacterial keratitis in B6 mice. Preventing or reversing this PCD shift may serve as an adjunct therapy for treating microbial keratitis in diabetic patients.