Arginine Supplementation Promotes Extracellular Matrix and Metabolic Changes in Keratoconus

Abstract

Keratoconus (KC) is a common corneal ectatic disease that affects 1:500–1:2000 people worldwide and is associated with a progressive thinning of the corneal stroma that may lead to severe astigmatism and visual deficits. Riboflavin-mediated collagen crosslinking currently remains the only approved treatment to halt progressive corneal thinning associated with KC by improving the biomechanical properties of the stroma. Treatments designed to increase collagen deposition by resident corneal stromal keratocytes remain elusive. In this study, we evaluated the effects of arginine supplementation on steady-state levels of arginine and arginine-related metabolites (e.g., ornithine, proline, hydroxyproline, spermidine, and putrescine) and collagen protein expression by primary human corneal fibroblasts isolated from KC and non-KC (healthy) corneas and cultured in an established 3D in vitro model. We identified lower cytoplasmic arginine and spermidine levels in KC-derived constructs compared to healthy controls, which corresponded with overall higher gene expression of arginase. Arginine supplementation led to a robust increase in cytoplasmic arginine, ornithine, and spermidine levels in controls only and a significant increase in collagen type I secretion in KC-derived constructs. Further studies evaluating safety and efficacy of arginine supplementation are required to elucidate the potential therapeutic applications of modulating collagen deposition in the context of KC.

Raman Spectroscopic Study of Amyloid Deposits in Gelatinous Drop-like Corneal Dystrophy

“…The peaks intensity of 886 cm −1 and 940 cm −1 , related to tryptophan [ 25 , 33 ] and proline/valine, respectively [ 28 ], were higher in GDCD when compared to the control cornea. Even if these biomolecules are normally present in the cornea [ 42 , 43 ], the increased intensity of both the above peaks in the Raman spectra could be related to polyglutamine aggregates, formed from monomers with different length, and present in amyloid fibrils [ 41 , 44 ].…”

FAK Inhibition Attenuates Corneal Fibroblast Differentiation In Vitro

“…One method is to supplement culture media with ascorbic acid (vitamin C), which normally promotes collagen secretion and deposition without promoting myofibroblast differentiation [ 5 , 16 , 33 , 34 , 47 , 81 , 82 ]. This hCF stroma-like 3D model and their self-assembled matrix, which mimics the corneal stroma during development [ 33 , 47 , 83 ], but also useful in investigating other pathologies affecting the corneal stroma, such as keratoconus [ 84 , 85 , 86 ], wound healing [ 33 , 87 ], and diabetes [ 88 , 89 , 90 ]. Collectively, these studies highlight that by increasing ECM dimensionality around hCFs, which can significantly influence cell proliferation and survival, mechano-responses, and their differentiation capacity [ 33 , 47 , 83 ].…”

Sex Hormones, Growth Hormone, and the Cornea

“…Given the mechanistic effects of arginine on GH secretion in vivo, the role of excess arginine in promoting wound healing may be related to the local effects of GH on cell proliferation and migration, in addition to localized effects of arginine on promoting collagen secretion. A recent study from our group showed that arginine supplementation promoted collagen type I secretion in vitro by primary corneal fibroblasts isolated from KC corneas, even though basal gene expression of arginase, the primary enzyme involved in arginine metabolism, was found to be elevated in these cells [ 108 ]. These studies suggest that exogenous application of key metabolites important in collagen monomer synthesis may serve to promote acute collagen deposition, which has implications in developing therapeutics to promote rapid tissue repair.…”