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Abstract
Using sensitive high performance liquid chromatography (HPLC), we measured free amino acid concentrations in the undiluted vitreous samples of patients who underwent pars plana vitrectomy for treatment of idiopathic preretinal macular fibrosis (PMF, n = 8), proliferative diabetic retinopathy (PDR, n = 12), or proliferative vitreoretinopathy (PVR, n = 15) to investigate the effect of vitreoretinal diseases on the concentrations of free amino acids in human vitreous. The most abundant amino acid was glutamine in all of three groups. Other major amino acids commonly found in the human vitreous samples were serine, alanine, arginine, valine, and lysine. Patients with PDR and PVR showed significantly lower concentrations of glutamine in vitreous (PDR: 655 ± 230 nmoles/ml, PVR: 683 ± 302 nmoles/ml) than those with PMF (PMF: 975 ± 247 nmoles/ml; significance level, PDR: p < 0.01, PVR: p < 0.05). In addition, patients with grade D PVR showed significantly lower concentration of glutamine (357 ± 117 nmoles/ml) than those with grade C PVR (802 ± 256 nmoles/ml, p < 0.005), or PMF (p < 0.005). These results suggest two possible mechanisms for the alteration of intravitreal glutamine in the pathologic conditions. The first possibility is a reduced amount of supply of glutamine that is normally transported or released from surrounding tissues into vitreous humor. The second possibility is an increased amount of uptake and utilization of glutamine by cells within vitreous and pathologic tissues.