Oral Peroxisome Proliferator-Activated Receptor-α Agonist Enhances Corneal Nerve Regeneration in Patients With Type 2 Diabetes

Abstract

Diabetic corneal neuropathy (DCN) is a common complication of diabetes. However, there are very limited therapeutic options. We investigated the effects of a peroxisome proliferator-activated receptor-α (PPAR-α) agonist, fenofibrate, on 30 patients (60 eyes) with type 2 diabetes. On in vivo confocal microscopy evaluation, there was significant stimulation of corneal nerve regeneration and a reduction in nerve edema after 30 days of oral fenofibrate treatment, as evidenced by significant improvement in corneal nerve fiber density (CNFD) and corneal nerve fiber width, respectively. Corneal epithelial cell morphology also significantly improved in cell circularity. Upon clinical examination, fenofibrate significantly improved patients' neuropathic ocular surface status by increasing tear breakup time along with a reduction of corneal and conjunctival punctate keratopathy. Tear substance P (SP) concentrations significantly increased after treatment, suggesting an amelioration of ocular surface neuroinflammation. The changes in tear SP concentrations was also significantly associated with improvement in CNFD. Quantitative proteomic analysis demonstrated that fenofibrate significantly upregulated and modulated the neurotrophin signaling pathway and linolenic acid, cholesterol, and fat metabolism. Complement cascades, neutrophil reactions, and platelet activation were also significantly suppressed. Our results showed that fenofibrate could potentially be a novel treatment for patients with DCN.

Trial registration: ClinicalTrials.gov NCT03869931.

Figure 1

Representative IVCM and slit-lamp images of the study patients before and after treatment. A: Images of corneal subbasal nerve plexus before (1 and 2) and after (3 and 4) fenofibrate treatment, demonstrating an increase in CNFD. IVCM images show beadings (2) with abrupt ending of nerve fibers before treatment and continuous nerve fibers (4) after treatment. B: IVCM images of corneal epithelial cells before (1 and 2) and after (3 and 4) fenofibrate treatment, demonstrating a morphological improvement and restoration of regular polygonal shape along with a reduction in cell size. C: Slit-lamp images of the ocular surface superficial punctate keratopathy, which was stained green with fluorescein dye under cobalt blue light before (1 and 2) and after (3 and 4) fenofibrate treatment, demonstrating a significant reduction in punctate keratopathy and a more stable tear film.

Figure 2

Bar charts showing the corneal nerve, epithelial cells, and ocular surface clinical parameters of patients with diabetes before and after treatment. CNFD (A), CNBD (B), CNFL (C), CTBD (D), CNFA (E), CNFW (F), CFracDim (G), epithelial cell density (H), average size of epithelial cells (I), circularity of epithelial cells (J), TBUT (K), ocular surface staining (Oxford score) (L), corneal staining (NEI score) (M), corneal sensitivity (N), and Schirmer I test (O). *P < 0.05, **P ≤ 0.01.

Figure 3

Box-and-whisker plots showing the representative tear proteins of the patients with diabetes and scatter plots showing the GSEA. A: Plots demonstrate a significantly upregulated APOA4, APOC1, and C1QA and a significantly downregulated SAA1 in patients with diabetes (before treatment) compared with control subjects. B: After fenofibrate treatment, there was a significantly upregulated ST6GAL1, TCC9A, RAB5A, and SMAD1 and a significantly downregulated COA6, and LMNB1. The y-axis represents the log₁₀ values of normalized protein peak intensity. The box ranges from the first quartile to the third quartile of the distribution of proteins, and the range represents the interquartile range. The median of the data set is indicated by a line across the box. Top whiskers represent values higher than the median, and bottom whiskers represent values lower than the median. The vertical line on the box plot extends from the minimum to the maximum of the data set. Scatter plots for GSEA results (ES and −log₁₀ [P value]) showing the enrichment pathways (P < 0.05) in patients with diabetes vs. control subjects (A) and patients with diabetes before and after treatment (B). Red dots represent the significantly upregulated pathways, and blue dots represent the significantly downregulated pathway.