Defective superoxide-dismutase molecules accumulate with age in human lenses.
ABSTRACT The specific activity of superoxide dismutase (SOD) in human transparent lenses declines as a function of age. Immunotitration using monospecific antibodies showed that, with increasing age, lenses exhibit an accumulation of catalytically inactive, but antigenically reactive, enzyme molecules. Antiserum produced against denatured enzyme removed the inactive molecules from the lens homogenates without affecting the enzyme activity. These aberrant molecules are at least partially denatured and are totally devoid of catalytic activity.
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ABSTRACT: The aging eye appears to be at considerable risk from oxidative stress. Lipid peroxidation (LPO) is one of the mechanisms of cataractogenesis, initiated by enhanced promotion of oxygen free radicals in the eye fluids and tissues and impaired enzymatic and non-enzymatic antioxidant defenses of the crystalline lens. The present study proposes that mitochondria are one of the major sources of reactive oxygen species (ROS) in mammalian and human lens epithelial cells and that therapies that protect mitochondria in lens epithelial cells from damage and reduce damaging ROS generation may potentially ameliorate the effects of free radical-induced oxidation that occur in aging ocular tissues and in human cataract diseases. It has been found that rather than complete removal of oxidants by the high levels of protective enzyme activities such as superoxide dismutase (SOD), catalase, lipid peroxidases in transparent lenses, the lens conversely, possess a balance between peroxidants and antioxidants in a way that normal lens tends to generate oxidants diffusing from lenticular tissues, shifting the redox status of the lens to become more oxidizing during both morphogenesis and aging. Release of the oxidants (O(2)(-)·, H(2)O(2) , OH·, and lipid hydroperoxides) by the intact lenses in the absence of respiratory inhibitors indicates that these metabolites are normal physiological products inversely related to the lens life-span potential (maturity of cataract) generated through the metal-ion catalyzed redox-coupled pro-oxidant activation of the lens reductants (ascorbic acid, glutathione). The membrane-bound phospholipid (PL) hydroperoxides escape detoxification by the lens enzymatic reduction. The lens cells containing these species would be vulnerable to peroxidative attack which trigger the PL hydroperoxide-dependent chain propagation of LPO and other damages in membrane (lipid and protein alterations). The increased concentrations of primary LPO products (diene conjugates, lipid hydroperoxides) and end fluorescent LPO products were detected in the lipid moiety of the aqueous humor samples obtained from patients with cataract as compared to normal donors. Since LPO is clinically important in many of the pathological effects and aging, new therapeutic modalities, such as patented N-acetylcarnosine prodrug lubricant eye drops, should treat the incessant infliction of damage to the lens cells and biomolecules by reactive lipid peroxides and oxygen species and "refashion" the affected lens membranes in the lack of important metabolic detoxification of PL peroxides. Combined in ophthalmic formulations with N-acetylcarnosine, mitochondria-targeted antioxidants are promising to become investigated as a potential tool for treating a number of ROS-related ocular diseases, including human cataracts.Cell Biochemistry and Function 03/2011; 29(3):183-206. · 1.85 Impact Factor
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ABSTRACT: Background: As the lens is constantly exposed to light and oxygen which generate harmful reactive oxygen species (ROS), we wanted to explore if the intracellular antioxidant enzyme copper-zinc superoxide dismutase (SOD1) is important for the protection against age-related cataract development. Methods: The development of lens opacities and the lens oxidative status were studied in different age-groups of mice lacking SOD1 and in wild-type mice. The lens opacities were quantified from lens photographs using digital image analysis. Thereafter, the lenses were homogenized and analysed regarding their contents of reduced glutathione (GSH) and protein carbonyls, suggestive of protein oxidation. Results: The 18-week-old mice of both genotypes had clear lenses. At 1 year of age the SOD1 null mice had developed cortical lens opacities whereas the wild-type mice did not show equivalent changes until 2 years of age. The lens contents of GSH decreased only in the 2-year-old wild-type mice whereas the carbonyls increased over time without any differences between the two genotypes. Conclusions: This study indicates that the lack of SOD1 may accelerate age-related lens opacity development and that intracellular superoxide-derived oxidative stress may be damaging to the lens during ageing. We thus suggest that the antioxidant enzyme SOD1 participates in the protection against age-related cataract. © 2012 The Authors. Clinical and Experimental Ophthalmology © 2012 Royal Australian and New Zealand College of Ophthalmologists.Clinical and Experimental Ophthalmology 03/2012; · 1.96 Impact Factor
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ABSTRACT: A common modification of human long-lived proteins is spontaneous isomerisation of aspartate residues, and its biological importance can be inferred from the ubiquitous presence of protein isoaspartate methyl transferase (PIMT), that repairs this damage. Cyclisation of L-Asp residues yields four isomers: L-Asp, L-isoAsp, D-Asp and D-isoAsp, however little is known about their rate of formation or interconversion. This is important because PIMT is inactive towards D-isoAsp. Peptides containing the four Asp isoforms corresponding to a susceptible site (Asp 151) in the chaperone, αA-crystallin, were examined for their interconversion at pH 7. D-Asp formed from L-Asp readily, whereas L-isoAsp was not detected until significantly later. D-isoAsp formed very slowly, with just 1% present after 8 days at 60(0)C. These findings can be used to rationalise the substrate specificity of PIMT. In addition, both the D-isoAsp and L-isoAsp peptides were found to be remarkably stable, showing little conversion to other isomers, even after weeks of incubation. Therefore L-isoAsp and D-isoAsp appear to represent "terminal" stages of L-Asp modification. If PIMT is present, L-isoAsp may be reverted to L-Asp, however there appears to be no prospect of reversing D-isoAsp formation in aged proteins. Interestingly, Asp 151 in recombinant αA crystallin isomerised more rapidly than the L-Asp peptide.Mechanisms of ageing and development 02/2013; · 4.18 Impact Factor