Lens cholesterol biosynthesis inhibition: A common mechanism of cataract formation in laboratory animals by pharmaceutical products

Identification and quantification of ionising radiation-induced oxysterol formation in membranes of lens fibre cells

Ionising radiation (IR) is a cause of lipid peroxidation, and epidemiological data have revealed a correlation between exposure to IR and the development of eye lens cataracts. Cataracts remain the leading cause of blindness around the world. The plasma membranes of lens fibre cells are one of the most cholesterolrich membranes in the human body, forming lipid rafts and contributing to the biophysical properties of lens fibre plasma membrane. Liquid chromatography followed by mass spectrometry was used to analyse bovine eye lens lipid membrane fractions after exposure to 5 and 50 Gy and eye lenses taken from wholebody 2 Gy-irradiated mice. Although cholesterol levels do not change significantly, IR dose-dependant formation of the oxysterols 7β-hydroxycholesterol, 7-ketocholesterol and 5, 6-epoxycholesterol in bovine lens nucleus membrane extracts was observed. Whole-body X-ray exposure (2 Gy) of 12-week old mice resulted in an increase in 7β-hydroxycholesterol and 7-ketocholesterol in their eye lenses. Their increase regressed over 24 h in the living lens cortex after IR exposure. This study also demonstrated that the IR-induced fold increase in oxysterols was greater in the mouse lens cortex than the nucleus. Further work is required to elucidate the mechanistic link(s) between oxysterols and IR-induced cataract, but these data evidence for the first time that IR exposure of mice results in oxysterol formation in their eye lenses.

Evaluation of lens opacity due to inhibition of cholesterol biosynthesis using rat lens explant cultures

Drug-induced lens opacity has the potential to cause blindness and is of concern in drug development. Inhibition of cholesterol biosynthesis is one of the causes of lens opacity. Lens opacity is only observed after chronic administration in in vivo nonclinical studies in drug development. Thus, to save resources (e.g., time and cost) and to reduce burden on animals, it is required to develop in vitro evaluation systems that can predict and avoid the risk of lens opacity earlier and easier. In this study, we investigated whether rat lens explant cultures could be useful for the evaluation of drug-induced lens opacity via inhibition of cholesterol biosynthesis. Nineteen drugs, including statins, allylamine, thiocarbamate, azole, and morpholine, which inhibit cholesterol biosynthesis, as well as a negative control (acetaminophen, rosiglitazone and troglitazone), were used. Rat lens explants were treated with drugs for 13 days at concentrations close to IC50 values or higher against cholesterol biosynthesis, and lens opacity (severity and region) was evaluated. In most cases, region-specific lens opacity limited in the equator to posterior pole, as observed in vivo was observed at IC50 values or higher concentrations. The severity of opacity was likely to be related to the inhibitory potency toward cholesterol biosynthesis, concentration of drugs distributed in the lens, or time of exposure. Furthermore, GSH levels were also involved in the deterioration of lens opacity. In conclusion, we demonstrated that rat lens explant cultures can be useful to assess the potential drug-induced lens opacity associated with inhibition of cholesterol biosynthesis and to elucidate the mechanisms of lens opacity.

The aging mouse lens transcriptome

Age is a major risk factor for cataract (ARC). However, the influence of aging on the lens transcriptome is under studied. Lens epithelial (LEC) and fiber cells (LFC) were isolated from young (3 month old) and aged (24 month old) C57BL/6J mice, and the transcriptome elucidated via RNAseq. EdgeR estimated differential gene expression in pairwise contrasts, and Advaita's Ipathway guide and custom R scripts were used to evaluate the potential biological significance of differentially expressed genes (DEGs). This analysis revealed age-dependent decreases in lens differentiation marker expression in both LECs and LFCs, with gamma crystallin transcripts downregulating nearly 50 fold in aged LFCs. The expression of the transcription factors Hsf4 and Maf, which are known to activate lens fiber cell preferred genes, are downregulated, while FoxE3, which represses gamma crystallin expression, is upregulated in aged fibers. Aged LECs upregulate genes controlling the immune response, complement pathways, and cellular stress responses, including glutathione peroxidase 3 (Gpx3). Aged LFCs exhibit broad changes in the expression of genes regulating cell communication, and upregulate genes involved in antigen processing/presentation and cholesterol metabolism, while changes in the expression of mitochondrial respiratory chain genes are consistent with mitochondrial stress, including upregulation of NDufa4l2, which encodes an alternate electron transport chain protein. However, age did not profoundly affect the response of LECs to injury as both young and aged LECs upregulate inflammatory gene signatures at 24 h post injury to similar extents. These RNAseq profiles provide a rich data set that can be mined to understand the genetic regulation of lens aging and how this impinges on the pathophysiology of age related cataract.

The Polymorphism rs2968 of LSS Gene Confers Susceptibility to Age-Related Cataract

Research showed that lanosterol can decrease protein aggregation in lens and reduce cataract formation. Lanosterol synthase (LSS) and 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) are the limiting enzymes in the process of synthesis of lanosterol. We demonstrate to investigate the association between functional single-nucleotide polymorphisms (SNPs) of LSS and HMGCR genes and age-related cataract (ARC) risks in Han Chinese population from Jiangsu Eye Study. This is a case-control study. We collected participants' venous blood for DNA genotyping and lens capsule samples for RNA. The SNPs of the genes were assayed with TaqMan RT-PCR genotyping. The quantitative RT-PCR was used to detect the LSS mRNA levels of lens epithelial cells (LECs) in individuals. The chi-square test was used to compare differences between ARC groups and controls of each SNP and to calculate the odds ratio (OR). We found that LSS-rs2968 of ARCs was different from controls (p = 0.018), but the significance was lost after Bonferroni correction (p = 0.072). We then further performed stratification analysis and found that LSS-rs2968 A allele was associated with nuclear type of ARC risk in Chinese population (p = 0.012, OR = 0.68). Consequently, we found that the mRNA expression of LSS was lower in LECs of all subtypes of ARC group than that of control group (p < 0.05). LSS-rs2968 A allele might play a role in the formation and development of nuclear type of ARC risk in Chinese population.