A cholesterol-enriched diet induces ultrastructural changes in retinal and macroglial rabbit cells

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration

Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Rabbit

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the laboratory rabbit used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Changes in Retinal Structure and Ultrastructure in the Aged Mice Correlate With Differences in the Expression of Selected Retinal miRNAs

Age and gender are two important factors that may influence the function and structure of the retina and its susceptibility to retinal diseases. The aim of this study was to delineate the influence that biological sex and age exert on the retinal structural and ultrastructural changes in mice and to identify the age-related miRNA dysregulation profiles in the retina by gender. Experiments were undertaken on male and female Balb/c aged 24 months (approximately 75–85 years in humans) compared to the control (3 months). The retinas were analyzed by histology, transmission electron microscopy, and age-related miRNA expression profile analysis. Retinas of both sexes showed a steady decline in retinal thickness as follows: photoreceptor (PS) and outer layers (p < 0.01 for the aged male vs. control; p < 0.05 for the aged female vs. control); the inner retinal layers were significantly affected by the aging process in the males (p < 0.01) but not in the aged females. Electron microscopy revealed more abnormalities which involve the retinal pigment epithelium (RPE) and Bruch’s membrane, outer and inner layers, vascular changes, deposits of amorphous materials, and accumulation of lipids or lipofuscins. Age-related miRNAs, miR-27a-3p (p < 0.01), miR-27b-3p (p < 0.05), and miR-20a-5p (p < 0.05) were significantly up-regulated in aged male mice compared to the controls, whereas miR-20b-5p was significantly down-regulated in aged male (p < 0.05) and female mice (p < 0.05) compared to the respective controls. miR-27a-3p (5.00 fold; p < 0.01) and miR-27b (7.58 fold; p < 0.01) were significantly up-regulated in aged male mice vs. aged female mice, whereas miR-20b-5p (−2.10 fold; p < 0.05) was significantly down-regulated in aged male mice vs. aged female mice. Interestingly, miR-27a-3p, miR-27b-3p, miR-20a-5p, and miR-20b-5p expressions significantly correlated with the thickness of the retinal PS layer (p < 0.01), retinal outer layers (p < 0.01), and Bruch’s membrane (p < 0.01). Our results showed that biological sex can influence the structure and function of the retina upon aging, suggesting that this difference may be underlined by the dysregulation of age-related mi-RNAs.

Racial differences and determinants of macular thickness profiles in multiethnic Asian population: the Singapore Epidemiology of Eye Diseases Study

Aim

To evaluate racial differences, and ocular and systemic determinants of macular thickness (MT), measured by spectral-domain optical coherence tomography (SD-OCT) in a normal multiethnic Asian population.

Method

MT was measured from a 6×6 mm2 central macular area using the Cirrus high-definition OCT (HD-OCT) (Carl Zeiss Meditec, Dublin, CA). The associations between ocular and systemic factors with MT were evaluated using linear regression analyses with generalised estimating equation models to account for intereye correlation.

Results

7447 healthy eyes (2577 Chinese, 2072 Malays and 2798 Indians) of 4510 subjects were included. Multivariable analysis showed that older age (per decade, β=−4.39), female gender (β=−5.74), diabetes (β=−1.10), chronic kidney disease (CKD) (β=−3.21), longer axial length (per mm, β=−2.34), flatter corneal curvature (per mm, β=−1.79) and presence of cataract (β=−0.94) were associated with thinner overall average MT (OMT) (all p≤0.026); higher total cholesterol (β=0.44; p=0.010) was associated with thicker OMT. All these factors were also associated with thinner central subfield MT (CSMT) (all p≤0.001), except for cataract, total cholesterol and CKD. Meanwhile, longer axial length (β=2.51; p<0.001) was associated with thicker CSMT. OMT (mean±SD) was thickest in Chinese (279.9±12.5 µm), followed by Malays (276.5±13.7 µm) and Indians (272.4±13.1 µm), with p≤0.003 for all interethnic comparisons. Similar trend was observed for CSMT.

Conclusion

There are interethnic differences in MT profile among Asians, particularly between Chinese and Indians. Ocular and systemic factors affect MT measurements as well. This Asian-specific information may be incorporated into existing clinical interpretation of macular OCT scans to aid in improving the diagnostic and monitoring accuracy of macular diseases among Asians.

The role of patient's systemic characteristics and plateletcrit in developing toxic anterior segment syndrome after uneventful phaco surgery: A case-control study

PURPOSE

To compare the systemic and ocular characteristics and laboratory findings of patients developing toxic anterior segment syndrome (TASS) after uneventful phaco surgery with unaffected subjects undergoing the same surgery in the same session.

DESIGN

A retrospective case-control study.

METHODS

The study group consisted of 26 eyes of 26 patients who underwent uneventful phaco surgery and who went on to develop TASS, while the control group included 39 subjects who had routine phaco surgery in the same session by the same surgeon. The sterilization stages of reusable instruments, disposable instruments, and compositions were recorded. The preoperative systemic diseases, complete blood count parameters, glycosylated hemoglobin (HbA1c), biochemical parameters, thyroid hormone profiles, and the surgical features were compared between the two groups.

RESULTS

Type 2 diabetes mellitus (DM), systemic hypertension (HT), hyperlipidemia, chronic ischaemic heart disease, and chronic renal failure were significantly more common in the TASS group (p < 0.05). Proliferative diabetic retinopathy was also more frequent in the TASS group (p = 0.003). Mean HbA1c% values, white blood cell count, neutrophil/lymphocyte ratio, platelet counts, platelet distribution width, and plateletcrit parameters were significantly higher in the TASS group (p < 0.05). Multivariate logistic regression analysis revealed that a high plateletcrit level (p = 0.001, odds ratio [95% CI]; 22.27 [3.36-147.76]) and systemic HT (p = 0.044, odds ratio [95% CI]; 7.13 [1.05-48.12]) are independently associated with the development of TASS.

CONCLUSION

Although TASS may arise as a result of insufficient sterilization of instruments or intraocular solutions, patient factors may also contribute to its development. Systemic vascular disorders such as uncontrolled type 2 DM, systemic hypertension, and hyperlipidemia may increase the risk of TASS after uneventful phaco surgery. Abnormal parameters associated with systemic inflammation, such as higher plateletcrit level, may facilitate the development of TASS. These findings may be a predicting factor of TASS development for uneventful cataract surgeries.

Cholesterol regulates polymodal sensory transduction in Müller glia

Over- and underexposure to cholesterol activates glia in neurodegenerative brain and retinal diseases but the molecular targets of cholesterol in glial cells are not known. Here, we report that disruption of unesterified membrane cholesterol content modulates the transduction of chemical, mechanical and temperature stimuli in mouse Müller cells. Activation of TRPV4 (transient receptor potential vanilloid type 4), a nonselective polymodal cation channel was studied following the removal or supplementation of cholesterol using the methyl-beta cyclodextrin (MβCD) delivery vehicle. Cholesterol extraction disrupted lipid rafts and caveolae without affecting TRPV4 trafficking or membrane localization protein. However, MβCD suppressed agonist (GSK1016790A)- and temperature-evoked elevations in [Ca²⁺ ]_i , and suppressed transcellular propagation of Ca²⁺ waves. Lowering the free membrane cholesterol content markedly prolonged the time-course of the glial swelling response, whereas MβCD:cholesterol supplementation enhanced agonist- and temperature-induced Ca²⁺ signals and shortened the swelling response. Taken together, these data show that membrane cholesterol modulates polymodal transduction of agonists, swelling and temperature stimuli in retinal radial glia and suggest that dyslipidemic retinas might be associated with abnormal glial transduction of ambient sensory inputs.

Epiretinal Membrane: Prevalence and Risk Factors from the Korea National Health and Nutrition Examination Survey, 2008 through 2012

PURPOSE

To investigate the prevalence and risk factors for an epiretinal membrane (ERM) in Korean population.

METHODS

Using the database of the Korea National Health and Nutrition Examination Survey from 2008 through 2012, 14,772 participants 40 years of age or older with gradable fundus photographs were included. The presence of ERM was determined by using fundus photographs. The prevalence of ERM was estimated and possible risk factors including systemic factors, nutritional status, and blood tests were analyzed via multiple logistic regression analyses.

RESULTS

The prevalence of ERM was 2.9% (95% confidence interval [CI], 2.6% to 3.3%). On multiple logistic regression analysis, the prevalence of ERM was affected by age. The odds ratios (ORs) against the forties were 2.70, 5.48, and 5.69 in the fifties, sixties, and seventies, respectively. ERM was also significantly affected by cataract surgery (OR, 2.82; 95% CI, 2.08 to 3.81) and by the increase in intake of 100-mg calcium (OR, 1.05; 95% CI, 1.00 to 1.11). ERM had negative associations with red blood cell count (OR, 0.66; 95% CI, 0.45 to 0.95).

CONCLUSIONS

The estimated nation-wide prevalence of ERM in Korea is 2.9%. The presence of ERM in the general population is associated with age, cataract surgery, increased dietary calcium, and a low red blood cell count.

Retinal Macroglial Responses in Health and Disease

Due to their permanent and close proximity to neurons, glial cells perform essential tasks for the normal physiology of the retina. Astrocytes and Müller cells (retinal macroglia) provide physical support to neurons and supplement them with several metabolites and growth factors. Macroglia are involved in maintaining the homeostasis of extracellular ions and neurotransmitters, are essential for information processing in neural circuits, participate in retinal glucose metabolism and in removing metabolic waste products, regulate local blood flow, induce the blood-retinal barrier (BRB), play fundamental roles in local immune response, and protect neurons from oxidative damage. In response to polyetiological insults, glia cells react with a process called reactive gliosis, seeking to maintain retinal homeostasis. When malfunctioning, macroglial cells can become primary pathogenic elements. A reactive gliosis has been described in different retinal pathologies, including age-related macular degeneration (AMD), diabetes, glaucoma, retinal detachment, or retinitis pigmentosa. A better understanding of the dual, neuroprotective, or cytotoxic effect of macroglial involvement in retinal pathologies would help in treating the physiopathology of these diseases. The extensive participation of the macroglia in retinal diseases points to these cells as innovative targets for new drug therapies.

Neuroprotective Effects of Low-Dose Statins in the Retinal Ultrastructure of Hypercholesterolemic Rabbits

To evaluate the pleiotropic effects to statins, we analyze the qualitative and quantitative retinal changes in hypercholesterolemic rabbits after a low-dosage statin treatment. For this purpose, New Zealand rabbits were split into three groups: control (G0; n = 10), fed a standard diet; hypercholesterolemic (G1; n = 8), fed a 0.5% cholesterol-enriched diet for 8 months; and statins (G2; n = 8), fed a 0.5% cholesterol-enriched diet for 8 months, together with the administration of statin (pravastatin or fluvastatin sodium) at a dose of 2 mg / kg / day each diet. The retinas were analyzed by transmission electron microscopy and immunohistochemistry (glial fibrillary acidic protein). The retinal thickness of nuclear and plexiform layers were quantified in semi-thin sections. The results revealed that the low-statin-treated rabbits in comparison with the hypercholesterolemic group showed: i) a more preserved structure in all retinal layers; ii) a significant reduction in retinal thickness; iii) a decrease in cell death in the nuclear-and ganglion-cell layers; iv) a reduction of hydropic degeneration in the plexiform and nerve-fiber layers; v) a preservation of astrocytes and of the retinal area occupied by them; and vi) a better-preserved retinal vascular structure. Our findings indicate that low doses of statins can prevent retinal degeneration, acting on retinal macroglia, neurons and retinal vessels, despite that hypercholesterolemia remained unchanged. Thus, the pleiotropic effects of the statins may help safeguard the retinal ultrastructure.

Prenatal nicotine exposure enhances Cx43 and Panx1 unopposed channel activity in brain cells of adult offspring mice fed a high-fat/cholesterol diet

Nicotine, the most important neuroteratogen of tobacco smoke, can reproduce brain and cognitive disturbances per se when administered prenatally. However, it is still unknown if paracrine signaling among brain cells participates in prenatal nicotine-induced brain impairment of adult offspring. Paracrine signaling is partly mediated by unopposed channels formed by connexins hemichannels (HCs) and pannexins serving as aqueous pores permeable to ions and small signaling molecules, allowing exchange between the intra- and extracellular milieus. Our aim was to address whether prenatal nicotine exposure changes the activity of those channels in adult mice offspring under control conditions or subjected to a second challenge during young ages: high-fat/cholesterol (HFC) diet. To induce prenatal exposure to nicotine, osmotic minipumps were implanted in CF1 pregnant mice at gestational day 5 to deliver nicotine bitartrate or saline (control) solutions. After weaning, offspring of nicotine-treated or untreated pregnant mice were fed ad libitum with chow or HFC diets for 8 weeks. The functional state of connexin 43 (Cx43) and pannexin 1 (Panx1) unopposed channels was evaluated by dye uptake experiments in hippocampal slices from 11-week-old mice. We found that prenatal nicotine increased the opening of Cx43 HCs in astrocytes, and Panx1 channels in microglia and neurons only if offspring mice were fed with HFC diet. Blockade of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX₂) and prostaglandin E receptor 1 (EP₁), ionotropic ATP receptor type 7 (P2X₇) and NMDA receptors, showed differential inhibition of prenatal nicotine-induced channel opening in glial cells and neurons. Importantly, inhibition of the above mentioned enzymes and receptors, or blockade of Cx43 and Panx1 unopposed channels greatly reduced adenosine triphosphate (ATP) and glutamate release from hippocampal slices of prenatally nicotine-exposed offspring. We propose that unregulated gliotransmitter release through Cx43 and Panx1 unopposed channels may participate in brain alterations observed in offspring of mothers exposed to tobacco smoke during pregnancy.

Defects in the retina of Niemann-pick type C 1 mutant mice

Background

Niemann-Pick type C1 (NPC1) disease is an inherited lysosomal storage disease caused by mutation of the Npc1 gene, resulting in a progressive accumulation of unesterified cholesterol and glycolipids in lysosomes of multiple tissues and leading to neurodegeneration and other disease. In Npc1 mutant mice, retinal degeneration including impaired visual function, lipofuscin accumulation in the pigment epithelium and ganglion cells as well as photoreceptor defects has been found. However, the pathologies of other individual cell types of the retina in Npc1 mutant mice are still not fully clear. We hypothesized that horizontal cells, amacrine cells, bipolar cells and glial cells are also affected in the retina of Npc1 mutant mice.

Results

Immunohistochemistry and electron microscopy were used to investigate pathologies of ganglion cells, horizontal cells, amacrine cells, bipolar cells, and optic nerves as well as altered activity of glial cells in Npc1 mutant mice.

Electron microscopy reveals that electron-dense inclusions are generally accumulated in ganglion cells, bipolar cells, Müller cells, and in the optic nerve. Furthermore, abnormal arborisation and ectopic processes of horizontal and amacrine cells as well as defective bipolar cells are observed by immunohistochemistry for specific cellular markers. Furthermore, hyperactivity of glial cells, including astrocytes, microglial cells, and Müller cells, is also revealed.

Conclusions

Our data extend previous findings to show multiple defects in the retina of Npc1 mutant mice, suggesting an important role of Npc1 protein in the normal function of the retina.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-014-0126-2) contains supplementary material, which is available to authorized users.

Improved visual function with dietary intervention in a child with lipemia retinalis

We present a 4.8-year-old female with grade 3 lipemia retinalis due to lipoprotein lipase deficiency, an abnormal electroretinogram, and bilateral decreased visual acuity. Strict dietary intervention resulted in reversal of lipemia retinalis, normalization of her electroretinogram, and improved visual acuity in both eyes.

Differential effects of the estrogen receptor agonist estradiol on toxicity induced by enzymatically-derived or autoxidation-derived oxysterols in human ARPE-19 cells

PURPOSE/AIM OF THE STUDY

Disturbances in cholesterol metabolism and increased levels of cholesterol oxidation products (oxysterols) in retina may contribute to age-related macular degeneration (AMD). The role of oxysterols or of their target receptors liver X receptors (LXRs) and estrogen receptors (ERs) in the pathogenesis of MD is ill-known. The purpose of this study is to determine the extent to which the oxysterols 27-hydroxycholesterol (27-OHC), 25-hydroxycholesterol (25-OHC) and 7-ketocholesterol (7-KC) affect the transcriptional activity of LXR and ER.

MATERIALS AND METHODS

ARPE-19 cells, untreated or incubated with 27-OHC, 25-OHC or 7-KC for 24 h were harvested. We used Western blot analyses for detecting ERs and LXRs expression, dual luciferase assays for measuring LXRs and ERs transcriptional activity, cytotox-ONE homogeneous membrane integrity assay for measuring cytotoxicity, JC-1 method for measuring mitochondrial membrane potential changes and ELISA for measuring cytokine levels.

RESULTS

Both LXRs and ERs are expressed and are transcriptionally active in ARPE-19 cells. 27-OHC, 25-OHC and 7-KC inhibited ER-mediated transcriptional activity, whereas 27-OHC and 25-OHC increased LXR-mediated transcription. E2 reduced 25-OHC and 27-OHC-induced cytotoxicity, mitochondrial permeability potential decline, and cytokine secretion. The LXR agonist GW3965 or the LXR antagonist 5α-6α-epoxycholesterol-3-sulfate (ECHS) did not offer protection against either 27-OHC and 25-OHC or 7-KC.

CONCLUSIONS

Increased levels of oxysterols can decrease ER and increase LXR signaling. ER agonists can offer protection against cytotoxic effects of 27-OHC and 25-OHC, two oxysterols derived by enzymatic reactions. Although they exert similar toxicity, the cellular mechanisms involved in the toxic effects of oxysterols whether derived by enzymatic or autoxidation reactions appear to be different.

Antiatherosclerotic Effect of Canarium odontophyllum Miq. Fruit Parts in Rabbits Fed High Cholesterol Diet

The effect of C. odontophyllum (CO) fruit parts was investigated in hypercholesterolemic rabbits. Forty-nine rabbits, which were randomly divided into seven groups of seven animals (n = 7), received a diet containing different parts of CO fruit parts for 8 weeks. The groups were as follows: (1) normal diet: NC group and (2) hypercholesterolemic diet: PC, HS (10 mg/kg/day simvastatin), HPO (20 g kg(-1) oil extracted from the pulp of CO), HKO (20 g kg(-1) oil extracted from the kernel of CO), HF (50 g kg(-1) fullfat pulp of CO), and HD (50 g kg(-1) defatted pulp of CO). Among these groups, rabbits receiving defatted pulp of CO showed the greatest cholesterol lowering effect as it had reduced plasma LDL-C, TC, and thiobarbiturate reactive substance (TBARS) levels as well as atherosclerotic plaques. The presence of high dietary fiber and antioxidants activity are potential factors contributing to the cholesterol lowering effect. Consequently, these results indicate the potential use of CO defatted pulp as a cholesterol lowering and antioxidant agent.

Low-dosage statins reduce choroidal damage in hypercholesterolemic rabbits

PURPOSE

To describe the ultrastructural changes in the choroid of long-term hypercholesterolemic rabbits after a low-dosage statin treatment and to evaluate some pleiotropic effects of these drugs on the morphology of endothelial cells (EC) and vascular smooth-muscle cells (VSMC).

METHODS

New Zealand rabbits were divided into three groups: G0, fed a standard diet; G1, fed a 0.5% cholesterol-enriched diet for 8 months and G2, fed a 0.5% cholesterol-enriched diet for 8 months plus administration of fluvastatin sodium or pravastatin sodium at a dose of 2 mg/Kg/day each. Eyes were processed for transmission-electron microscopy.

RESULTS

G1 had a lipid build-up at the suprachoroidea that compressed the vascular layers with the lumens of the vessels to the point of collapse in some instances. By contrast, G2 underwent a substantial decrease in suprachoroidal foam cells and of lipids in the vascular layers while the vascular lumens were normal. The preservation of cytoplasmic organelles, caveolar system and other ultrastructural features of EC and VSMC in G2 contrasted with the numerous signs of necrosis observed in G1. Bruch's membrane (BM) in G2 contained fewer lipids and more collagen than in G1.

CONCLUSION

Treatment with a low dosage of fluvastatin sodium or pravastatin sodium reduced the lipid build-up as well as the macrophages in the choroid and restored the vascular lumens of choroidal vessels independently of the cholesterol effect. The normal ultrastructural features of choroidal EC and VSMC in statin-treated animals suggest that the endothelial function is preserved and the ischaemia reduced.

Cholesterol-enriched diet causes age-related macular degeneration-like pathology in rabbit retina

BACKGROUND

Alzheimer's disease (AD) and age-related macular degeneration (AMD) share several pathological hallmarks including β-amyloid (Aβ) accumulation, oxidative stress, and apoptotic cell death. The causes of AD and AMD are likely multi-factorial with several factors such as diet, environment, and genetic susceptibility participating in the pathogenesis of these diseases. Epidemiological studies correlated high plasma cholesterol levels with high incidence of AD, and feeding rabbits with a diet rich in cholesterol has been shown to induce AD-like pathology in rabbit brain. High intake of cholesterol and saturated fat were also long been suspected to increase the risk for AMD. However, the extent to which cholesterol-enriched diet may also cause AMD-like features in rabbit retinas is not well known.

METHODS

Male New Zealand white rabbits were fed normal chow or a 2% cholesterol-enriched diet for 12 weeks. At necropsy, animals were perfused with Dulbecco's phosphate-buffered saline and the eyes were promptly removed. One eye of each animal was used for immunohistochemistry and retina dissected from the other eye was used for Western blot, ELISA assays, spectrophotometry and mass spectrometry analyses.

RESULTS

Increased levels of Aβ, decreased levels of the anti-apoptotic protein Bcl-2, increased levels of the pro-apoptotic Bax and gadd153 proteins, emergence of TUNEL-positive cells, and increased generation of reactive oxygen species were found in retinas from cholesterol-fed compared to normal chow-fed rabbits. Additionally, astrogliosis, drusen-like debris and cholesterol accumulations in retinas from cholesterol-fed rabbits were observed. As several lines of evidence suggest that oxidized cholesterol metabolites (oxysterols) may be the link by which cholesterol contributes to the pathogenesis of AMD, we determined levels of oxysterols and found a dramatic increase in levels of oxysterols in retinas from cholesterol-fed rabbits.

CONCLUSIONS

Our results suggest that cholesterol-enriched diets cause retinal degeneration that is relevant to AMD. Furthermore, our data suggests high cholesterol levels and subsequent increase in the cholesterol metabolites as potential culprits to AMD.

Protective effects of Morus alba leaves extract on ocular functions of pups from diabetic and hypercholesterolemic mother rats

Phytotherapy is frequently considered to be less toxic and free from side effects than synthetic drugs. Hence, the present study was designed to investigate the protective use of crude water extract of Morus alba leaves on ocular functions including cataractogenesis, biochemical diabetic and hypercholesterolemic markers, retinal neurotransmitters and retinopathy of rat pups maternally subjected to either diabetes and/or hypercholesterolemia. Application of crude water extract of Morus alba resulted in amelioration of the alterations of maternal serum glucose, LDL, HDL, total cholesterol and creatine phosphokinase activity as well as retinal neurotransmitters including acetylcholine (ACE), adrenaline (AD), nor-adrenaline (NAD), serotonin (5-HT), histamine (HS), dopamine (DA) and gamma amino butyric acid (GABA). The retina of pups of either diabetic and/or hypercholesterolemia mothers exhibited massive alterations of retinal neurotransmitters. The alterations of retinal neurotransmitters were correlated with the observed pathological alterations of retinal pigmented epithelium, photoreceptor inner segment and ganglion cells and increased incidence of DNA fragmentation and apoptosis cell death. However, protection with Morus alba extract led to amelioration of the pathological alterations of retinal neurons and estimated neurotransmitters. Furthermore, a striking incidence of cataract was detected in pups of either diabetic and/or hypercholesterolemic mothers. Highest cataractogenesis was observed in pups of combined -treated groups. Our data indicate that experimental maternal diabetes alone or in combination with hypercholesterolemia led to alteration in the ocular structures of their pups, with an increasing incidence of cataract and retinopathy, and the effects of the extract might be attributed to the hypoglycaemic, antihypercholesterolemic and anti-oxidative potential of flavonoids, the major components of the plant extract.

CD36 plays an important role in the clearance of oxLDL and associated age-dependent sub-retinal deposits

Age-related macular degeneration (AMD) represents the major cause of vision loss in industrialized nations. Laminar deposits in Bruch's membrane (BM) are among the first prominent histopathologic features, along with drusen formation, and have been found to contain oxidized lipids. Increases in concentrations of oxidized LDL (oxLDL) in plasma are observed with age and high fat high (HFHC) cholesterol diet. CD36 is the principal receptor implicated in uptake of oxLDL, and is expressed in the retinal pigment epithelium (RPE). We determined if CD36 participates in oxLDL uptake in RPE and correspondingly in clearance of sub-retinal deposits. Uptake of oxLDL by RPE in vitro and in vivo was CD36-dependent. CD36 deficiency in mice resulted in age-associated accumulation of oxLDL and sub-retinal BM thickening, despite fed a regular diet. Conversely, treatment of HFHC-fed ApoE null mice with a CD36 agonist, EP80317 (300 μg/kg/day), markedly diminished thickening of BM, and partially preserved (in part) photoreceptor function. In conclusion, our data uncover a new role for CD36 in the clearance of oxidized lipids from BM and in the prevention of age-dependent sub-retinal laminar deposits.

The oxysterol 27-hydroxycholesterol increases β-amyloid and oxidative stress in retinal pigment epithelial cells

Background

Alzheimer's disease (AD) and age-related macular degeneration (AMD) share several pathological features including β-amyloid (Aβ) peptide accumulation, oxidative damage, and cell death. The causes of AD and AMD are not known but several studies suggest disturbances in cholesterol metabolism as a culprit of these diseases. We have recently shown that the cholesterol oxidation metabolite 27-hydroxycholesterol (27-OHC) causes AD-like pathology in human neuroblastoma SH-SY5Y cells and in organotypic hippocampal slices. However, the extent to which and the mechanisms by which 27-OHC may also cause pathological hallmarks related to AMD are ill-defined. In this study, the effects of 27-OHC on AMD-related pathology were determined in ARPE-19 cells. These cells have structural and functional properties relevant to retinal pigmented epithelial cells, a target in the course of AMD.

Methods

ARPE-19 cells were treated with 0, 10 or 25 μM 27-OHC for 24 hours. Levels of Aβ peptide, mitochondrial and endoplasmic reticulum (ER) stress markers, Ca²⁺ homeostasis, glutathione depletion, reactive oxygen species (ROS) generation, inflammation and cell death were assessed using ELISA, Western blot, immunocytochemistry, and specific assays.

Results

27-OHC dose-dependently increased Aβ peptide production, increased levels of ER stress specific markers caspase 12 and gadd153 (also called CHOP), reduced mitochondrial membrane potential, triggered Ca²⁺ dyshomeostasis, increased levels of the nuclear factor κB (NFκB) and heme-oxygenase 1 (HO-1), two proteins activated by oxidative stress. Additionally, 27-OHC caused glutathione depletion, ROS generation, inflammation and apoptotic-mediated cell death.

Conclusions

The cholesterol metabolite 27-OHC is toxic to RPE cells. The deleterious effects of this oxysterol ranged from Aβ accumulation to oxidative cell damage. Our results suggest that high levels of 27-OHC may represent a common pathogenic factor for both AMD and AD.

Sclerochorioretinal abnormalities in hypercholesterolemic rabbits treated with rosiglitazone

BACKGROUND AND OBJECTIVE

To evaluate early retinal, choroidal, and scleral abnormalities induced by a hypercholesterolemic diet and the prevention of these abnormalities after oral administration of rosiglitazone in rabbits.

MATERIALS AND METHODS

Fifty-four New Zealand rabbits were divided into four study groups: control group, normal diet; group 1, hypercholesterolemic diet; group 2, hypercholesterolemic diet associated with daily administration of 3 mg of rosiglitazone from day 14 after beginning the diet; and group 3, hypercholesterolemic diet associated with daily administration of 3 mg of rosiglitazone since the beginning of the experiment. Sclera and choroid underwent histologic and histomorphometric analyses. Retina underwent immunohistochemical analysis with anti-calretinin and anti-glial fibrillary acidic protein (GFAP) antibodies.

RESULTS

No abnormalities were observed in the control group. Group 1 had significant increases in scleral and choroidal thicknesses compared with the control group (P < .01) and group 3 (P < .05). Group 1 presented significant increases in immunoreactivity (P < .001) to the anti-calretinin antibody compared with the other groups. Groups 2 and 3 had significant (P < .002) increases in calretinin immunoreactivity compared with the control group. GFAP was negative in all groups.

CONCLUSION

The hypercholesterolemic diet induced early retinal, choroidal, and scleral abnormalities. Rosiglitazone preserved the structural anatomy.

Serum low-density lipoprotein cholesterol level is strong risk factor for acquired color vision impairment in young to middle-aged Japanese men: the Okubo Color Study Report 2

OBJECTIVE

To investigate associations between blood low-density lipoprotein cholesterol (LDL-C) levels and the prevalence of acquired color vision impairment (ACVI) in middle-aged Japanese men.

METHODS

Participants in this cross-sectional study underwent color vision testing, ophthalmic examination, a standardized interview and examination of venous blood samples. Ishihara plates, a Lanthony 15-hue desaturated panel, and Standard pseudoisochromatic Plates part 2 were used to examine color vision ability. The Farnsworth-Munsell 100-hue test was performed to define ACVI. Smoking status and alcohol intake were recorded during the interview. We performed logistic regression analysis adjusted for age, LDL-C level, systemic hypertension, diabetes, cataract, glaucoma, overweight, smoking status, and alcohol intake. Adjusted odds ratios for four LDL-C levels were calculated.

RESULTS

A total of 1042 men were enrolled, 872 participants were eligible for the study, and 31 subjects were diagnosed with ACVI. As compared to the lowest LDL-C category level (<100 mg/dl), the crude OR of ACVI was 3.85 (95% confidence interval [CI], 1.24-11.00) for the 2nd highest category (130-159 mg/dl), and 4.84 (95% CI, 1.42-16.43) for the highest level (>or=160 mg/dl). The multiple-adjusted ORs were 2.91 (95% CI, 0.87-9.70) for the 2nd highest category and 3.81 (95% CI, 1.03-14.05) for the highest level. Tests for trend were significant (P<0.05) in both analyses.

CONCLUSIONS

These findings suggested that the prevalence of ACVI is higher among middle-aged Japanese men with elevated LDL-C levels. These changes might be related to deteriorated neurologic function associated with lipid metabolite abnormalities.

Aging, age-related macular degeneration, and the response-to-retention of apolipoprotein B-containing lipoproteins

The largest risk factor for age-related macular degeneration (ARMD) is advanced age. A prominent age-related change in the human retina is the accumulation of histochemically detectable neutral lipid in normal Bruch's membrane (BrM) throughout adulthood. This change has the potential to have a major impact on physiology of the retinal pigment epithelium (RPE). It occurs in the same compartment as drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD. Here we present evidence from light microscopic histochemistry, ultrastructure, lipid profiling of tissues and isolated lipoproteins, and gene expression analysis that this deposition can be accounted for by esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles constitutively produced by the RPE. This work collectively allows ARMD lesion formation and its aftermath to be conceptualized as a response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (CAD) (Tabas et al., 2007). This approach provides a wide knowledge base and sophisticated clinical armamentarium that can be readily exploited for the development of new model systems and the future benefit of ARMD patients.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Alterations in the choroid in hypercholesterolemic rabbits: reversibility after normalization of cholesterol levels

Endothelial damage in atherosclerosis is characterized by abnormal vascular functionality. Hyperlipidemic patients show alterations in ocular vascularization. However, it is not known whether these alterations are reversible after the lipid profile returns to normal. This study evaluates a rabbit model of hypercholesterolemia, examining the ultrastructural changes in the choroid, and the changes in it after a period of normal blood-cholesterol values induced by a standard diet. Rabbits were divided into three groups: G0, fed a standard diet; G1A, fed a 0.5% cholesterol-enriched diet for 8 months; and G1B, fed a 0.5% cholesterol-enriched diet for 8 months followed by a standard diet for a further 6 months. Eyes were processed for transmission electron microscopy. G1A had a buildup of lipids at the suprachoroidea that compressed the vascular layers, and hypertrophy of endothelial and vascular smooth muscle cells. In G1B there was less lipid accumulation than in G1A, but this was not followed by reversal of the choroidal damage. The suprachoroidea thickness of G1B was still greater than in G0 due to abundant collagen fibers. The intervascular spaces of the choroid had fewer lipids than G1A but more collagen fibers than G0. The large- and medium-sized vessel layers and choriocapillaris were less compressed than in G1A but exhibited basal membrane and endothelial changes similar to those in G1A. Normalization of serum cholesterol levels is not enough to reverse cholesterol-induced vascular damage to the choroid. These choroidal changes could be compatible with a chronic ischemia that could produce retinal degeneration.

Macroglial and retinal changes in hypercholesterolemic rabbits after normalization of cholesterol levels

This study evaluates hypercholesterolemic rabbits, examining the retinal changes in Müller cells and astrocytes as well as their variations after a period of normal blood-cholesterol values induced by a standard diet. New Zealand rabbits were divided into three groups: G0, fed a standard diet; G1A, fed a 0.5% cholesterol-enriched diet for 8 months; and G1B, fed as G1A followed by standard diet for 6 months. Eyes were processed for transmission electron microscopy and immunohistochemistry (GFAP). While G1B resembled G0 more than did G1A, they shared alterations with G1A: a) as in G1A, Müller cells were GFAP+, filled spaces left by axonal degeneration, formed glial scars and their nuclei were displaced to the nerve-fibre layer. The area occupied by the astrocytes associated with the nerve-fibre bundles (AANFB) and by perivascular astrocytes (PVA) in G1A and G1B was significantly lower than in controls. However, no significant differences in PVA were found between G1A and G1B. In G1B, type I PVA was absent and replaced by hypertrophic type II cells; b) Bruch's membrane (BM) was thinner in G1B than in G1A; c) the retinal pigment epithelium (RPE) cytoplasm contained fewer lipids in G1B than in G1A; d) in G1A and G1B choriocapillaris and retinal vessel showed alterations with respect to G0; e) cell death and axonal degeneration in the retina were similar in G1A and G1B. The substitution of a hyperlipemic diet by a standard one normalizes blood-lipid levels. However, the persistence of damage at retinal vessels and BM-RPE could trigger chronic ischemia.