Role of Glycation in Human Lens Protein Structure Change

Quantification of protein glycation using vibrational spectroscopy

FTIR-ATR and Raman spectroscopy can distinguish between glycated and non-glycated proteins.

Cataract Preventive Role of Isolated Phytoconstituents: Findings from a Decade of Research

Cataract is an eye disease with clouding of the eye lens leading to disrupted vision, which often develops slowly and causes blurriness of the eyesight. Although the restoration of the vision in people with cataract is conducted through surgery, the costs and risks remain an issue. Botanical drugs have been evaluated for their potential efficacies in reducing cataract formation decades ago and major active phytoconstituents were isolated from the plant extracts. The aim of this review is to find effective phytoconstituents in cataract treatments in vitro, ex vivo, and in vivo. A literature search was synthesized from the databases of Pubmed, Science Direct, Google Scholar, Web of Science, and Scopus using different combinations of keywords. Selection of all manuscripts were based on inclusion and exclusion criteria together with analysis of publication year, plant species, isolated phytoconstituents, and evaluated cataract activities. Scientists have focused their attention not only for anti-cataract activity in vitro, but also in ex vivo and in vivo from the review of active phytoconstituents in medicinal plants. In our present review, we identified 58 active phytoconstituents with strong anti-cataract effects at in vitro and ex vivo with lack of in vivo studies. Considering the benefits of anti-cataract activities require critical evaluation, more in vivo and clinical trials need to be conducted to increase our understanding on the possible mechanisms of action and the therapeutic effects.

Advanced glycation end products and diabetic complications

During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.

Molecular pathology and age estimation

Over the course of our lifetime a stochastic process leads to gradual alterations of biomolecules on the molecular level, a process that is called ageing. Important changes are observed on the DNA-level as well as on the protein level and are the cause and/or consequence of our 'molecular clock', influenced by genetic as well as environmental parameters. These alterations on the molecular level may aid in forensic medicine to estimate the age of a living person, a dead body or even skeletal remains for identification purposes. Four such important alterations have become the focus of molecular age estimation in the forensic community over the last two decades. The age-dependent accumulation of the 4977bp deletion of mitochondrial DNA and the attrition of telomeres along with ageing are two important processes at the DNA-level. Among a variety of protein alterations, the racemisation of aspartic acid and advanced glycation endproducs have already been tested for forensic applications. At the moment the racemisation of aspartic acid represents the pinnacle of molecular age estimation for three reasons: an excellent standardization of sampling and methods, an evaluation of different variables in many published studies and highest accuracy of results. The three other mentioned alterations often lack standardized procedures, published data are sparse and often have the character of pilot studies. Nevertheless it is important to evaluate molecular methods for their suitability in forensic age estimation, because supplementary methods will help to extend and refine accuracy and reliability of such estimates.

Fluorescence from the Maillard Reaction and its Potential Applications in Food Science

The chemistry of the Maillard reaction involves a complex set of steps, and its interpretation represents a challenge in basic and applied aspects of Food Science. Fluorescent compounds have been recognized as important early markers of the reaction in food products since 1942. However, the recent advances in the characterization of fluorophores' development were observed in biological and biomedical areas. The in vivo non-enzymatic glycosylation of proteins produces biological effects, promoting health deterioration. The characteristic fluorescence of advanced glycosylation end products (AGEs) is similar to that of Maillard food products and represents an indicator of the level of AGE-modified proteins, but the structure of the fluorescent groups is, typically, unknown. Application of fluorescence measurement is considered a potential tool for addressing key problems of food deterioration as an early marker or index of the damage of biomolecules. Fluorophores may be precursors of the brown pigments and/or end products. A general scheme of the Maillard reaction is proposed in this article, incorporating the pool concept. A correct interpretation of the effect of environmental and compositional conditions and their influences on the reaction kinetics may help to define the meaning of fluorescence development for each particular system.

Diabetes, oxidative stress, and antioxidants: a review

Increasing evidence in both experimental and clinical studies suggests that oxidative stress plays a major role in the pathogenesis of both types of diabetes mellitus. Free radicals are formed disproportionately in diabetes by glucose oxidation, nonenzymatic glycation of proteins, and the subsequent oxidative degradation of glycated proteins. Abnormally high levels of free radicals and the simultaneous decline of antioxidant defense mechanisms can lead to damage of cellular organelles and enzymes, increased lipid peroxidation, and development of insulin resistance. These consequences of oxidative stress can promote the development of complications of diabetes mellitus. Changes in oxidative stress biomarkers, including superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, glutathione levels, vitamins, lipid peroxidation, nitrite concentration, nonenzymatic glycosylated proteins, and hyperglycemia in diabetes, and their consequences, are discussed in this review. In vivo studies of the effects of various conventional and alternative drugs on these biomarkers are surveyed. There is a need to continue to explore the relationship between free radicals, diabetes, and its complications, and to elucidate the mechanisms by which increased oxidative stress accelerates the development of diabetic complications, in an effort to expand treatment options.

Cataract surgery on diabetic patients. A prospective evaluation of risk factors and complications

PURPOSE

This study presents an evaluation of cataract surgery on diabetic patients. One experienced surgeon carried out phaco emulsification on all subjects and the same surface-coated one-piece PMMA-lens-type was implanted. The lens fluorescence and the blood-aqueous barrier (BAB) were then evaluated as experimental preoperative risk indicators.

RESULTS

During follow-up, 10 out of 39 diabetic patients progressed unilaterally in diabetic retinopathy or developed macular oedema, a significant relative risk. Neither lens fluorescence, BAB, HbA1c, level of retinopathy, type/duration of diabetes, diabetes treatment or antihypertensive treatment differed significantly between the group of patients with postoperative progression of retinopathy/macular oedema and those without. Results indicated NIDDM (non-insulin-dependent diabetes mellitus/type 2 diabetes) patients might have increased risk of a postoperative macular oedema.

CONCLUSION

When diabetic retinopathy (DR) is not in a proliferative phase it should not be regarded as a contraindication to modern cataract surgery. Neither lens fluorescence nor BAB is valuable as a risk indicator for postoperative progression of DR.

Research on aging in Portugal

This review presents an analysis of the current state of gerontological and geriatric research in Portugal, and highlights the need for a national consensus and funding for age-related research projects. Such efforts must be multidisciplinary, since the process of aging encompasses biological, psychological, social, economic and cultural aspects. Demographic studies reveal a growing population of elderly in Portugal as a result of a healthier population in general. This increased life expectancy, however, is accompanied by a parallel increase in degenerative pathologies and care costs among the elderly. Preventive medicine is an important tool to reduce health care costs and avoid or abbreviate suffering from age-related syndromes, but such projects on a national basis neither exists, nor does gerontology or geriatrics receive funding to perform needed research. Consequently, research on aging depends on the initiative of individual investigators who, without funding or cohesive programs, can do little to improve the low scientific output in this area. The implementation of a national program, that can establish health care policy and priorities as well as fund the necessary research, will permit organized cooperation among the different scientific disciplines related to aging. This is a crucial step toward improving present knowledge, ensuring application of experimental and statistical results to the clinical care of the aging population, and attract young investigators to this field.

Relative importance of aldose reductase versus nonenzymatic glycosylation on sugar cataract formation in diabetic rats

The relative importance of sorbitol formation versus nonenzymatic glycosylation and advanced glycosylation end products (AGEs) on sugar cataract formation was examined in diabetic rats. Diabetes was experimentally induced in young, 50 g rats with streptozotocin, and aldose reductase inhibitors were administered in the diet for up to 8 weeks at concentrations of 0.06% for tolrestat or ponalrestat and 0.0125% for AL-1576. Cataract formation was monitored by hand-held slit lamp for up to 11 weeks. Lens polyol levels were monitored by GLC, glycosylated protein levels were spectrophotometrically determined, and AGE products were estimated by fluorescence measurements and ELISA. Sugar cataract formation was observed in all untreated diabetic rats while cataract formation was inhibited in all diabetic rats treated with the AR inhibitors. Lens sorbitol levels were reduced in all ARI-treated rats. Glycosylated lens protein levels were elevated in the diabetic rats, and these levels were not significantly lower in the non-cataractous lenses from ARI-treated diabetic rats. Fluorescence measurements of the lens proteins revealed increased lens AGE levels in all diabetic rats, and these were slightly reduced in the aldose reductase inhibitor treated diabetics. With ELISA, immunoreactive AGEs were only detected in cataractous lenses from the untreated diabetic rats. Immunoreactive AGEs were not detected in the clear lenses of the aldose reductase inhibitor treated diabetics or in the non-diabetic controls. These results support the concept that sugar cataract formation is initiated by the aldose reductase catalyzed intracellular accumulation of polyols and that these sugar cataracts can be prevented through inhibition of aldose reductase.