Ocular Disorders Secondary to Systemic Disease and the Potential Role of Carnitines
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Ocular Disorders Secondary to Systemic Disease and the Potential Role of Carnitines Nicola Pescosolido, Barbara Imperatrice and Panagiotis Karavitis Ophthalmic Neuroscience Program, Department of Ophthalmology, University of Rome, Sapienza, Rome, Italy
Abstract
L-carnitine has a wide-ranging role in several physiological processes, but perhaps most significantly in long-chain fatty acid oxidation in the mitochondrial matrix. Osmolytic (or osmoprotective) properties have also been suggested for the compound. Importantly, the ability of L-carnitine to improve insulin sensitivity in insulin-resistant diabetic patients may, together with the agent’s antioxidant and antiapoptotic activity, provide some degree of protection against the progression of diabetic retinopathy. L-carnitine may also protect against the deleterious effects of ocular ischaemic syndrome, and, indeed, acetyl-L-carnitine has been shown to significantly improve retinal damage and visual acuity in patients with monolateral or bilateral retinal artery occlusion. The antioxidant, antiapoptotic and osmolytic properties of L-carnitine also suggest that this agent may have valuable clinical utility in neurotrophic keratopathy and bullous keratopathy. Thus, further detailed investigation of the important clinical potential of L-carnitine in various ocular conditions (e.g. diabetic retinopathy, ocular ischaemic syndrome, neurotrophic keratopathy and bullous keratopathy) that occur secondary to systemic diseases is now clearly warranted.
The pathophysiologies of various ocular disorders occurring secondary to systemic diseases have yet to be fully elucidated. However, it is generally accepted that most ocular pathologies result from functional deterioration of intraocular tissues. Many such pathologies are therefore age-related, or occur in individuals with a specific susceptibility, and can be appropriately managed with pharmacotherapy. Carnitine (β-hydroxy-γ-trimethylammonium butyrate) is an amine synthesized in the body from lysine and methionine.[1] The compound has a ubiquitous distribution, even though >95% of total body carnitine is found in the myocardium and skeletal muscle.[2,3] Carnitine has also been identified in ocular tissues, particularly in the lens.[3]
L-carnitine has a versatile role in various physiological reactions, including the following: the aerobic metabolism of glucose (Krebs cycle); increased oxidative phosphorylation velocity; the excretion of some organic acids and, perhaps most importantly, in long-chain fatty acid oxidation in the mitochondrial matrix.[2,3] More recently, osmolytic (or osmoprotective) properties have been suggested for L-carnitine. Indeed, high concentrations of L-carnitine are present in the lens relative to other ocular tissues,[3] and such concentrations may counter osmotic stress, lead to reduced protein aggregation and preserve ocular lens transparency.[4,5] This potential osmoprotectant activity of L-carnitine appears unrelated to
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