Changes in HNK-1 epitope and collagen type IX in the aqueous humour of patients with pseudoexfoliation syndrome

Emerging roles of oxidative stress in the pathogenesis of pseudoexfoliation syndrome (Review)

Pseudoexfoliation syndrome (PEXS) is a systemic disease caused by defects in the extracellular matrix (ECM) remodelling process leading to the chronic deposition of extracellular, fibrillary, white flaky pseudoexfoliation material (PEXM) throughout the body. Specifically, PEXM deposits on the lens capsule cause open-angle glaucoma, cataracts and blindness in patients with PEXS. Several gene single nucleotide polymorphisms are linked to the development of PEXS in humans, including lysyl oxidase-like 1 gene, clusterin and fibulin-5. The exact reason for the PEXM generation and its resulting pathogenesis is not well understood. However, defective ECM remodelling and oxidative stress (OS) have been hypothesized as significant events leading to the PEXM. Specifically, the link between OS and PEXS has been well studied, although the investigation is still ongoing. The present review explored recent advances in various aspects of PEXS and the involvement of OS in the eye for PEXS development.

Pseudoexfoliation syndrome: The critical role of the extracellular matrix in pathogenesis and treatment

Pseudoexfoliation syndrome (PEXS) is an age-related condition manifesting mainly in ocular tissues. PEXS is manifested through excess aggregation of fibrillary extracellular material at the anterior part of the eye that consists of a plethora of biomolecules, such as different proteoglycans (PGs) and glycosaminoglycans. PEXS is often linked to increased intraocular pressure, and can also lead to pseudoexfoliation glaucoma with very poor prognosis. Various stimuli are known to affect PEXS, including oxidation stress (OS), UV radiation and osmotic pressure. OS, is prominently involved on the progression of the syndrome as it promotes fibrogenesis, possibly via the induction of transforming growth factor-β (TGF-β) and other biomolecular effectors. In addition, PEXS initiation is tightly connected with the dysregulation of extracellular matrix (ECM) homeostasis since aberrant expression of ECM molecules is linked to both the accumulation and low degradation of pseudoexfoliation material. This article aims at uncovering the crucial role of various ECM effectors such as lysyl oxidase-like proteins, matrix metalloproteinases, and TGF-β1, as well as the biochemical pathways involved in the development and the progression of the PEXS.

FACE analysis as a fast and reliable methodology to monitor the sulfation and total amount of chondroitin sulfate in biological samples of clinical importance

Glycosaminoglycans (GAGs) due to their hydrophilic character and high anionic charge densities play important roles in various (patho)physiological processes. The identification and quantification of GAGs in biological samples and tissues could be useful prognostic and diagnostic tools in pathological conditions. Despite the noteworthy progress in the development of sensitive and accurate methodologies for the determination of GAGs, there is a significant lack in methodologies regarding sample preparation and reliable fast analysis methods enabling the simultaneous analysis of several biological samples. In this report, developed protocols for the isolation of GAGs in biological samples were applied to analyze various sulfated chondroitin sulfate- and hyaluronan-derived disaccharides using fluorophore-assisted carbohydrate electrophoresis (FACE). Applications to biologic samples of clinical importance include blood serum, lens capsule tissue and urine. The sample preparation protocol followed by FACE analysis allows quantification with an optimal linearity over the concentration range 1.0–220.0 µg/mL, affording a limit of quantitation of 50 ng of disaccharides. Validation of FACE results was performed by capillary electrophoresis and high performance liquid chromatography techniques.

Evidence for oxidative stress in lens epithelial cells in pseudoexfoliation syndrome

PURPOSE

To investigate the oxidative status in lens epithelial cells of patients with pseudoexfoliation (PEX) syndrome.

METHODS

Lens capsule samples obtained during cataract surgery of patients with PEX syndrome and normal age-matched control subjects were examined for changes in the levels of glutathione (GSH), glutathione disulphide (GSSG), protein concentration, and lipid peroxidation. Concentrations of GSH, GSSG, lipid peroxidation, and protein concentration were determined by specific fluorescent assays.

RESULTS

This study shows a 2.2- and 2.0-fold decrease in GSH and GSSG levels, respectively, in PEX lens epithelial lens compared with non-PEX lens epithelial cells, as well as a 2.5-fold increase in lipid peroxidation product malondialdehyde (MDA) levels.

CONCLUSION

The increased MDA and decreased GSH levels indicate high oxidative stress. On the other hand, GSSG usually increases in cases of high-oxidative stress, but this is not always the case, as it may not always accumulate in cells. Our findings suggest a role for oxidative stress in the pathogenesis and the progression of PEX syndrome.

Pseudoexfoliation syndrome and its antioxidative protection deficiency as risk factors for age-related cataract

PURPOSE

Pseudoexfoliation syndrome (PES) seems to be a systemic condition. However, to an ophthalmologist it represents a continual challenge, due to unclear etiology and patho-genesis, and because of a potential for development of an aggressive glaucoma, and cataract surgery complications. According to some findings, PES could be a factor of hastened aging, which means that it could be considered as a secondary aging factor.

METHODS

Frequencies of secondary aging diseases (non-insulin dependent diabetes mellitus, atherosclerotic myocardiopathy, chronic obstructive lung diseases, arterial hypertension, and PES) were investigated in 162 patients with age-related cataract and 55 age- and sex-matched control subjects, and analyzed by a logistic regression. The authors also determined elements of antioxidative protection in a group of sera from patients with cataract and PES, and compared them to those obtained from patients with cataract without PES (activity of catalase and peroxidase, glutathione, vitamins C and E), and total antioxidative protection (%iMDA). Antioxidant defense of aqueous humors, expressed as a rate of induced malondialdehyde (%iMDA), and total thiol groups in the lens corticonuclear blocks (TSH) were estimated in samples of 17 patients with PES and cataract and 55 patients with cataract only.

RESULTS

Logistic regression showed the highest odds ratio for PES (OR=4.516; p<0.05). Catalytic activity of serum catalase had significantly lower values in patients with PES (p<0.05). Anti oxidative defense of aqueous humor and lens had lower values in patients with PES.

CONCLUSIONS

The results indicate that PES might be a significant factor for cataractogenesis. At least a part of pathogenesis alterations in an eye with PES could be the result of higher intensity of oxidative stress.

Oral glycine administration attenuates diabetic complications in streptozotocin-induced diabetic rats

Diabetes mellitus is a disease characterized by impaired glucose metabolism that leads to retinopathy, brain micro-infarcts and other complications. We have previously shown that oral glycine administration to diabetic rats inhibits non-enzymatic glycation of hemoglobin and diminishes renal damage. In this work, we evaluated the capacity of the amino acid glycine (1% w/v, 130 mM) to attenuate diabetic complications in streptozotocin (STZ)-induced diabetic Wistar rats and compared them with non-treated or taurine-treated (0.5% w/v, 40 mM) diabetic rats. Glycine-treated diabetic rats showed an important diminution in the percentage of animals with opacity in lens and microaneurysms in the eyes. Interestingly, there was a diminished expression of O-acetyl sialic acid in brain vessels compared with untreated diabetic rats (P<0.05). Additionally, peripheral blood mononuclear cells isolated from glycine-treated diabetic rats showed a better proliferative response to PHA or ConA than those obtained from non-treated diabetic rats (P<0.05). Glycine-treated rats had a less intense corporal weight loss in comparison with non-treated animals. Our results suggest that administration of glycine attenuates the diabetic complications in the STZ-induced diabetic rat model, probably due to inhibition of the non-enzymatic glycation process.

Collagen type IX and HNK-1 epitope in tears of patients with pseudoexfoliation syndrome

Pseudoexfoliation syndrome (PEX) is an age-related condition, which may cause open-angle glaucoma and has increasing interest since it seems to affect additional human tissues, i.e., cardiovascular tissue, skin, and still lacks elucidated pathogenesis. Collagen type IX and HNK-1 epitope have been considered characteristic constituents of the aqueous humour of PEX patients, since their amounts were increased in PEX aqueous humour compared to normal eyes. Since it has been proposed that the initial manifestations of PEX syndrome occur in conjunctiva, the present study was undertaken to investigate the presence of the same antigens in tears of PEX patients and their possible use as the biochemical markers for early diagnosis. Tears of PEX patients and healthy individuals were subjected to western blotting analysis for various basement membrane components identified in aqueous humour. It was found that collagen type IX and HNK-1 epitope were present in tears, the amount of the former being increased 2.7 times compared to normal (P<0.05), surprisingly high as compared with total protein or lysozyme activity in tears, which were found to be increased in PEX patients about 25% with no statistical differences (P approximately 0.4). The results suggest the possible use of tears' collagen type IX for the diagnosis of PEX syndrome.