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

Retinal neurodegeneration in metabolic syndrome: a spectral optical coherence tomography study

AIM

To evaluate the effects of metabolic syndrome (MetS) on retinal neurodegeneration by optical coherence tomography (OCT).

METHODS

Patients diagnosed as MetS were compared with the age and sex-matched healthy control group (CG). Waist circumference measurements, fasting serological biochemical tests, and systemic blood pressures of all participants were evaluated. The MetS group was divided into 3 subgroups according to the number of MetS components: hypertension, diabetes mellitus, dyslipidemia (low-, high-density lipoprotein, hypertriglyceridemia), and visceral obesity findings; 3-component MetS3, 4-component MetS4, and all-component MetS5. All patients underwent complete eye examination and spectral OCT retinal imaging.

RESULTS

Totally 58 eyes of 58 patients were included in the MetS group and 63 eyes of 63 age and sex-matched healthy subjects were included in CG. MetS group was composed of 22 subjects in MetS3, 21 subjects in MetS4, and 15 subjects in the MetS5 subgroup. Mean foveal thickness (MetS, 218.7±23.1 µm vs CG, 228.8±21.9 µm, P=0.015), mean inferior (MetS, 283.4±17.0 µm vs CG, 288.7±38.4 µm, P=0.002), superior (MetS, 287.0±18.5 µm vs CG 297.3±17.1 µm, P=0.001), nasal (MetS 287.3±16.7 µm vs CG 297.9±13.9 µm, P=0.000) and temporal (274.5±17.6 µm vs CG 285.6±13.6 µm, P=0.000) thickness in the 3 mm Early Treatment of Diabetic Retinopathy Study (ETDRS) circle was significantly lower in the MetS group. There was no statistically significant difference in the mean inferior, superior, nasal, and temporal thickness of 6 mm ETDRS circle, total macular volume, peripapillary and macular retinal nerve fiber layer, macular ganglion cell layer with inner plexiform layer, and ganglion cell complex. No statistically significant difference was found in these values ​​between the MetS3, MetS4, and the MetS5 groups.

CONCLUSION

A significant reduction in central macular region thickness in MetS is detected and macular thickness is more susceptible to MetS induced neurodegeneration than peripapillary retinal nerve fiber layer.

Harnessing the Neuroprotective Behaviors of Müller Glia for Retinal Repair

Progressive and irreversible vision loss in mature and aging adults creates a health and economic burden, worldwide. Despite the advancements of many contemporary therapies to restore vision, few approaches have considered the innate benefits of gliosis, the endogenous processes of retinal repair that precede vision loss. Retinal gliosis is fundamentally driven by Müller glia (MG) and is characterized by three primary cellular mechanisms: hypertrophy, proliferation, and migration. In early stages of gliosis, these processes have neuroprotective potential to halt the progression of disease and encourage synaptic activity among neurons. Later stages, however, can lead to glial scarring, which is a hallmark of disease progression and blindness. As a result, the neuroprotective abilities of MG have remained incompletely explored and poorly integrated into current treatment regimens. Bioengineering studies of the intrinsic behaviors of MG hold promise to exploit glial reparative ability, while repressing neuro-disruptive MG responses. In particular, recent in vitro systems have become primary models to analyze individual gliotic processes and provide a stepping stone for in vivo strategies. This review highlights recent studies of MG gliosis seeking to harness MG neuroprotective ability for regeneration using contemporary biotechnologies. We emphasize the importance of studying gliosis as a reparative mechanism, rather than disregarding it as an unfortunate clinical prognosis in diseased retina.

The possible alleviating effect of garlic supplement on the neural retina in a rat model of hypercholesterolemia: a histological and immunohistochemical study

The purpose of this work was to prove that oxidative stress is the main mechanism responsible for retinal neurodegenerative changes, subsequent apoptosis, and inflammatory cytokine release in rats fed with a high cholesterol diet (HCD) and determine the role of garlic in alleviating these changes. Forty rats were equally divided into four groups: control, garlic-treated (positive control), HCD, and HCD + garlic-treated (HCD + G). By the end of the experiment (24 weeks) blood samples were collected for assessment of serum lipid profile, oxidative stress parameters, and plasma levels of IL-6 and TNF-α. Both eyes of the rats were enucleated; one was used for light microscopic examination and the other for electron microscopic examination. There was a significant increase in the levels of serum lipids, oxidative stress parameters, IL-6 and TNF-α, and area of expression of caspase-3 in the HCD group compared to both the control and HCD + G groups. Histological examination revealed degenerative changes in all layers of the neural retina in the HCD group. Garlic administration resulted in a significant improvement in the biochemical, immunohistochemical, and histological characteristics of hypercholesterolemic rats. These findings support the hypotheses that garlic has strong antioxidant, anti-apoptotic, and anti-inflammatory properties. Garlic ameliorates the neurodegenerative changes in the neural retina of hypercholesteremic rats.

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.

Fluvastatin protects neuronal cells from hydrogen peroxide-induced toxicity with decreasing oxidative damage and increasing PI3K/Akt/mTOR signalling

BACKGROUND

Statins, the most effective lipoprotein-cholesterol lowering drugs, are widely used for patients with cardiovascular disease. The pleiotropic effects of statins have been recently gained attention for their both beneficial and deleterious effects on neurons. We investigated the effects and molecular mechanisms of fluvastatin at clinically relevant concentrations on neuronal cells after induction of oxidative stress.

MATERIALS AND METHODS

Both SH-SY5Y, a representative cell line for in vitro neurone model, and human primary neuronal cells were applied. Cellular and biochemical assays were used to investigate the effects of fluvastatin in neurone cells.

RESULTS

Fluvastatin significantly restored H2O2-induced neuronal death in a dose-dependent manner (P < 0.05) and reversed H2O2-induced oxidative stress and damage via restoring mitochondrial function in neuronal cells (P < 0.05). Although fluvastatin inhibited prenylation in neuronal cells, the protective effects of fluvastatin against H2O2-induced neuronal cytotoxicity are not associated with prenylation inhibition or AMPK activation. In contrast, PI3K/Akt/mTOR activation mediated fluvastatin's neuroprotective activity (P < 0.05).

CONCLUSIONS

Our work demonstrates the beneficial effects of fluvastatin in neuronal cells under pathological conditions, and, furthermore, this is via prenylation-independent activation of PI3K/Akt/mTOR pathway. Our data highlights the functional significance of the PI3K/Akt/mTOR pathway in neuronal cells in response to oxidative stress.

Thinning of Macular Neuroretinal Layers Contributes to Sleep Disorder in Patients With Type 2 Diabetes Without Clinical Evidences of Neuropathy and Retinopathy

Aims: To investigate the impact of thinning at individual grids of macular neuroretinal layers, clinical factors, and inadequate light exposure on the specific components of sleep disorder in patients with type 2 diabetes. Methods: One hundred twenty-four patients with type 2 diabetes without clinical evidences of diabetic retinopathy and neuropathy (HbA1c: 8.3%, diabetes duration; 8.7 years) and 54 age- and sex-matched control subjects (HbA1c: 5.6%) underwent detailed clinical, neurological, and ophthalmological examinations. The sleep disorder was assessed by the Pittsburgh Sleep Quality Index Japanese Version (PSQI-J). The temporal structures of daily life were assessed by the Munich Chronotype Questionnaire Japanese Version. The thickness at nine grids defined by the Early Treatment Diabetic Retinopathy Study of nine macular neuroretinal layers was determined by swept-source optical coherence tomography and OCT-Explorer. The associations between the individual components of sleep disorders and the thickness at each grid of macular neuroretinal layers, clinical factors, or the temporal structures of daily life were examined. Results: The prevalence of the sleep disorder, global score, and four individual PSQI-J scores in patients with type 2 diabetes were higher than control subjects. The thickness of two and five grids of two inner retinal layers and four to seven grids of four outer retinal layers in patients with type 2 diabetes was thinner than those in control subjects. The thickness at one to eight grids of four outer retinal layers in type 2 diabetic patients was inversely associated with global score and five individual scores of sleep disorder. The thinning at one to two grids of the inner plexiform layer was related to three high individual scores of sleep disorder. The inappropriate light exposure was associated with the sleep disorder and altered macular neuroretinal layers. The high HbA1c and LDL-cholesterol levels were related to the high global score and two individual scores of sleep disorder, respectively. Conclusion: In patients with type 2 diabetes, the thinning at grids of the inner plexiform layer and outer retinal layers was associated with the high scores of specific components of the sleep disorder. The sleep disorder was also related to hyperglycemia, dyslipidemia, and inappropriate light exposure.

Retinal microvascular dysfunction in hypercholesterolemia

BACKGROUND

Hypercholesterolemia is one of the most important contributors to atherosclerosis. Whether hypercholesterolemia also affects the retinal microcirculation is unclear.

OBJECTIVE

The goal of our study was to assess the association of cholesterol levels with retinal microvascular function using dynamic and static retinal vessel analysis (RVA) in a primary prevention setting.

METHODS

This cross-sectional, observational study prospectively recruited 67 patients with hypercholesterolemia without known cardiovascular disease (mean age 64.4 ± 10.4 years; 45% female) and 78 healthy controls (mean age 61.8 ± 11.2 years; 45% female). The primary end point of the study was flicker-induced dilatation of retinal arterioles (FID_art) with secondary exploratory outcomes including venular FID (FID_ven), arteriovenous ratio, flow-mediated dilatation and arterial stiffness as measured with augmentation index and pulse wave velocity. Multiple regression analysis was performed to study the association of cholesterol levels with retinal microvascular function.

RESULTS

FID_art was significantly impaired in patients with hypercholesterolemia compared with healthy controls (mean FID_art 2.1 ± 1.8 vs 3.1 ± 1.8%, P = .001). This association remained when analysis was restricted to dyslipidemic patients without coexisting hypertension or lipid-lowering therapy. No significant differences remained for FID_ven, flow-mediated dilatation, arteriovenous ratio, or arterial stiffness between the groups. Low-density lipoprotein, but not high-density lipoprotein, cholesterol was a significant negative predictor of FID_art in multiple regression analysis.

CONCLUSION

Hypercholesterolemia is associated with significant retinal microvascular dysfunction as evidenced by a reduction in flicker-induced dilatation of retinal arterioles. Dynamic RVA may be a promising method for the study of retinal microvascular dysfunction in populations at elevated cardiovascular risk.

Retinal Cholesterol Content Is Reduced in Simvastatin-Treated Mice Due to Inhibited Local Biosynthesis Albeit Increased Uptake of Serum Cholesterol

Statins, a class of cholesterol-lowering drugs, are currently being investigated for treatment of age-related macular degeneration, a retinal disease. Herein, retinal and serum concentrations of four statins (atorvastatin, simvastatin, pravastatin, and rosuvastatin) were evaluated after mice were given a single drug dose of 60 mg/kg body weight. All statins, except rosuvastatin, were detected in the retina: atorvastatin and pravastatin at 1.6 pmol and simvastatin at 4.1 pmol. Serum statin concentrations (pmol/ml) were 223 (simvastatin), 1401 (atorvastatin), 2792 (pravastatin), and 9050 (rosuvastatin). Simvastatin was then administered to mice daily for 6 weeks at 60 mg/kg body weight. Simvastatin treatment reduced serum cholesterol levels by 18% and retinal content of cholesterol and lathosterol (but not desmosterol) by 24% and 21%, respectively. The relative contributions of retinal cholesterol biosynthesis and retinal uptake of serum cholesterol to total retinal cholesterol input were changed as well. These contributions were 79% and 21%, respectively, in vehicle-treated mice and 69% and 31%, respectively, in simvastatin-treated mice. Thus, simvastatin treatment lowered retinal cholesterol because a compensatory upregulation of retinal uptake of serum cholesterol was not sufficient to overcome the effect of inhibited retinal biosynthesis. Simultaneously, simvastatin-treated mice had a 2.9-fold increase in retinal expression of Cd36, the major receptor clearing oxidized low-density lipoproteins from Bruch's membrane. Notably, simvastatin treatment essentially did not affect brain cholesterol homeostasis. Our results reveal the statin effect on the retinal and brain cholesterol input and are of value for future clinical investigations of statins as potential therapeutics for age-related macular degeneration.

Dyslipidemia modulates Müller glial sensing and transduction of ambient information

Unesterified cholesterol controls the fluidity, permeability and electrical properties of eukaryotic cell membranes. Consequently, cholesterol levels in the retina and the brain are tightly regulated whereas depletion or oversupply caused by diet or heredity contribute to neurodegenerative diseases and vision loss. Astroglia play a central role in the biosynthesis, uptake and transport of cholesterol and also drive inflammatory signaling under hypercholesterolemic conditions associated with high-fat diet (diabetes) and neurodegenerative disease. A growing body of evidence shows that unesterified membrane cholesterol modulates the ability of glia to sense and transduce ambient information. Cholesterol-dependence of Müller glia - which function as retinal sentinels for metabolic, mechanical, osmotic and inflammatory signals - is mediated in part by transient receptor potential V4 (TRPV4) channels. Cholesterol supplementation facilitates, whereas depletion suppresses, TRPV4-mediated transduction of temperature and lipid agonists in Müller cells. Acute effects of cholesterol supplementation/depletion on plasma membrane ion channels and calcium homeostasis differ markedly from the effects of chronic dyslipidemia, possibly due to differential modulation of modality-dependent energy barriers associated with the functionality of polymodal channels embedded within lipid rafts. Understanding of cholesterol-dependence of TRP channels is thus providing insight into dyslipidemic pathologies associated with diabetic retinopathy, glaucoma and macular degeneration.