High Glucose Induces Biomolecular Dysregulation in Primary Human Corneal Epithelial Cells: Potential Biomarkers of Hyperglycemia-Driven Corneal Impairment.

Corneal hyperglycemia is associated with epithelial dysfunction characterized by impaired inflammation, oxidative stress, neuropathy and innate immune mechanisms, as observed in diabetic corneal keratopathy. Therefore, the aim of the study was to investigate at cellular level the effects of moderate to severe acute and chronic challenges of glucose on human primary cultures of corneal epithelial cells (CECs). Human CECs (Innoprot, Spain) were exposed to single or repeated 15 mM or 30 mM High Glucose (HG)-supplemented media (CEC Medium containing plain 5 mM glucose), every 2 days from first stimulations and harvested at day 1 (single/acute challenge) or at days 3 and 5 (repeated/chronic challenge). Mannitol was used as osmotic control and cell sustainability were monitored by trypan blue exclusion test and MTT. Conditioned media were subjected to protein analysis while monolayers were processed for relative real-time RT-PCR. Few selected mediators belonging to the inflammatory, complement, innate receptor, oxidative, DNA enzymes and neurotrophic pathways were tested, and protein levels were assayed on selected mediators (IL-6, IL-8, CFH and C5b-9; ELISA). HG exposure induced a time- and concentration-dependent decrease in CEC metabolic activity, without a comparable reduction in cell number. Acute HG exposure promoted an inflammatory response characterized by increased p65NF-κB, IL-1β, IL-6 and IL-8 transcripts, together with an early modulation of complement components and increased expression of CD55 and CD59 (regulators). Chronic HG exposure induced a marked shift toward complement activation, with increased C3aR1, C5aR1, C3, C5 and C9 transcripts and reduced CD55 and CD59 expression, with a progressive accumulation of CFH and C5b-9 proteins in a positive relationship. Chronic HG also increased IL-6 and IL-8 protein release and induced a coordinated upregulation of C5, C5aR1 and TLR-2, particularly at 30 mM HG. Antioxidant, DNA enzymes and neurotrophic pathways were differentially modulated over time, with an early Nrf-2 response followed by chronic Keap-1 upregulation and Nrf-2 reduction, progressive DNMT3a/HDAC1 expression, and a biphasic β-NGF/BDNF transcriptional profile. Overall, these findings support a proposed biphasic model of the CEC response to hyperglycemia, characterized by an initial adaptive molecular response followed by progressive dysregulation under prolonged exposure. This early molecular profile might represent an adaptive response to acute metabolic stress, although further studies are required to confirm this functional protective significance.