1H NMR Spectroscopy Characterization of Porcine Vitreous Humor in Physiological and Photoreceptor Degeneration Conditions

Purpose: Qualitative and quantitative analysis of vitreous humor (VH) is important to discriminate between physiological and pathological conditions and may be particularly helpful when using animal models for ophthalmologic research. The aim of the present study was to investigate the physiological qualitative/quantitative composition of the VH of the standard pig using a metabolomics approach based on 1H nuclear magnetic resonance (NMR) spectroscopy. A secondary aim was the characterization of the VH of the porcine model of photoreceptor degeneration induced with iodoacetic acid (IAA), widely used in the biomedical field, and comparison with the physiological one. Methods: VH samples were collected from 30 pigs (17 in the physiological condition and 13 treated with IAA) upon vitrectomy and analyzed by means of 1H NMR spectroscopy for characterization. Results: On all analyzed samples, 40 molecules could be identified and quantified, with lactate being the most abundant in both physiological and photoreceptor degeneration conditions. Upon comparison, only 17 molecules showed statistical differences: In the IAA group, glucose and glutamine increased, while lactate, 4-amynobutyrate, hypoxanthine, dicarboxylic acids (succinate and fumarate), amino acids with their derivatives (creatine, alanine, valine, lysine, leucine, glycine, taurine, and isoleucine), and choline with its precursor sn-glycero-3-phosphocholine decreased. Conclusions: The results validate the metabolic impairment determined by glycolysis inhibition upon systemic IAA administration. In conclusion, this work represents the first characterization of the porcine VH metabolome in physiological conditions and provides additional information for the characterization and refinement of the IAA-induced photoreceptor degeneration model.