Jagadeesan Madhavan

Lysyl Oxidase Activity in the Ocular Tissues and the Role of LOX in Proliferative Diabetic Retinopathy and Rhegmatogenous Retinal Detachment

PURPOSE Lysyl oxidase (LOX) cross-links the side chain of collagen and elastin and thereby contributes to extracellular matrix (ECM) integrity. ECM remodeling is seen in various ocular diseases. Until now, there have been no reports on the LOX enzymes activity in ocular tissues. The purpose of this study was to estimate LOX activity and expression in human donor ocular tissues and to measure the specific activity of LOX in the vitreous of proliferative diabetic retinopathy (PDR) and rhegmatogenous retinal detachment (RRD). METHOD Human donor eyeballs obtained from an eye bank were used to study tissue distribution of LOX. Human vitreous specimens were obtained during vitreoretinal surgery from PDR (n = 16) and RRD (n = 10). LOX activity was estimated by N-acetyl-3,7-dihydroxyphenoxazine assay, immunohistochemistry, and real-time polymerase chain reaction (RT-PCR). Matrix metalloprotease (MMP)-2 and -9 were quantified in the vitreous by sandwich enzyme-linked immunosorbent assay (ELISA). RESULTS The specific activity of LOX in ocular tissues was on the order of vitreous, iris ciliary body, lens, choroid RPE, and retina, which were comparable by mRNA expression and immunolocalization. The vitreous level of LOX activity decreased significantly in PDR and RRD, with an increase in total MMP-2 and -9 levels compared with normal donor vitreous. CONCLUSIONS LOX activity showed a statistically significant decrease in the vitreous of PDR and RRD relative to control specimens. This effect can contribute to the inadequate collagen cross-linking that causes the ECM changes that occur in these diseases.

The relationship between tumor cell differentiation and age at diagnosis in retinoblastoma

PURPOSE To determine the relationship between tumor cell differentiation and age at diagnosis in retinoblastoma. METHODS Medical records of 170 patients with retinoblastoma treated by enucleation were reviewed retrospectively. Age at diagnosis and histopathological features were analyzed. RESULTS Well-differentiated tumors presented earlier than poorly differentiated tumors. The frequency of presentation was highest in the first year of age for well-differentiated tumors and in the third year of age for poorly differentiated tumors (P < .0001). Bilateral well-differentiated tumors presented earlier than bilateral poorly differentiated tumors. Similarly, unilateral well-differentiated tumors presented earlier than unilateral poorly differentiated tumors. CONCLUSIONS Differentiated tumors present earlier than poorly differentiated tumors, irrespective of laterality in retinoblastoma.

Retinoblastoma: from disease to discovery.

Retinoblastoma has contributed much to the understanding of cancer. It provided the classic ‘two-hit model’ for oncogenesis and helped to identify the first tumor suppressor gene RB1. Thirty years since then, the search for additional events underlying disease progression continues. Phenotypic variations in retinoblastoma offer numerous clues to disease pathogenesis. Understanding their molecular biological basis will provide insight into mechanisms underlying tumor progression. These not fully understood genetic and stochastic events play a major role in uncontrolled retinal precursor cell proliferation. Comparative genomic hybridization and gene expression studies have facilitated probing of genes controlling basic events in cellular development, i.e. proliferation, differentiation and apoptosis. Research to determine the cell of origin that underlies the evolution of retinoblastoma can lead to understanding of the stochastic events underlying the genesis of this cancer, which currently remains unclear. In this review, we discuss the recent developments in retinoblastoma and describe how they are beginning to shape a new and revised picture of retinoblastoma pathogenesis and progression.

High Glucose Induced Differential Expression of Lysyl Oxidase and Its Isoform in ARPE-19 Cells

Purpose: Lysyl oxidase (LOX) stabilizes the extracellular matrix (ECM) by cross-linking collagen and elastin molecules. In proliferative diabetic retinopathy (PDR), there is ECM remodeling with neovascularization and basement membrane changes. While protease activities are well reported, the role of LOX in the pathogenesis of diabetic retinopathy is less studied. This study was done to see the effect of high glucose on the activity and expression of LOX and its isoforms in ARPE-19 cells. Materials and methods: ARPE-19 cells were exposed to high glucose up to 48 h, and LOX activity was determined by N-acetyl-3,7-dihydroxyphenoxazine assay. The mRNA expression of LOX and its isoforms was done by real-time PCR and the protein expression by ELISA. Immunohistochemistry for LOX was done in epiretinal membrane from PDR. Results: With an increase in glucose concentration LOX activity and protein was reduced significantly at 30 mM glucose at 48 h. mRNA expression of LOX, LOXL1, and LOXL2 varied with time and concentration of glucose. Vascular endothelial growth factor (VEGF) increased the LOX activity as well as the mRNA expression. Pigment epithelium-derived factor (PEDF) downregulated the mRNA expression of LOX, LOXL1, and LOXL2. The matrix metalloprotease (MMP) activity increased significantly with the increase in glucose concentration. The diabetic neovascular membrane showed increased immunostaining of LOX. Conclusions: This study suggests that although the LOX activity, which is composite of all the isoforms, was reduced under high glucose conditions, there was a differential mRNA expression with increased LOX and LOXL1 and decreased LOXL2 expression.

Severity of familial isolated retinitis pigmentosa across different inheritance patterns among an Asian Indian cohort.

PURPOSE To predict the progression to legal blindness in patients with isolated inherited retinitis pigmentosa. METHODS This retrospective study evaluated patients with isolated inherited retinitis pigmentosa for age at onset, duration of the disease, and best-corrected visual acuity in an Asian Indian cohort. The Mann–Whitney U test was used to analyze the variables. RESULTS Of 134 patients evaluated, 72% were autosomal recessive, 17% were autosomal dominant, and 11% were X-linked recessive pedigrees. Median age at onset was 8 years for X-linked recessive, 11 years for autosomal recessive, and 21 years for autosomal dominant disease, which was statistically significant. The refractive error due to axial myopia was significantly high in X-linked recessive (−3.50 diopter sphere) compared to autosomal recessive (−1 diopter sphere) and autosomal dominant (0.00 diopter sphere) cases (P < .000). Legal blindness occurred in 50% of X-linked recessive and autosomal recessive cases but in only 32% of autosomal dominant cases. CONCLUSION Identifying the gene defects involved in this cohort will help understand the phenotype variability.