Oxidative stress impact on barrier function of porcine angular aqueous plexus cell monolayers

Peroxynitrite-Scavenging Organosilica Nanomedicines for Light-Controllable NO Release and Precision On-Demand Glaucoma Therapy

Nitric oxide (NO) is a promising approach for treating ocular hypertension and glaucoma. However, its clinical application is limited by its uncontrollable release and the unwanted overproduction of peroxynitrite. Herein, a denitrifying hollow mesoporous organosilica nanoparticle (HMMN) with framework cohybridization is first constructed to encapsulate S-nitroso-N-acetyl-d,l-penicillamine (SNAP) to produce SNAP@HMMN with dual capacities of selective peroxynitrite removal and controllable NO release. Featuring a large corneal permeability, the well-designed SNAP@HMMN can achieve trans-corneal delivery to reach the target trabecular meshwork (TM)/Schlemm's canal (SC) site. Upon light irradiation, the intraocular pressure (IOP) is appropriately lowered in an adjustable and long-lasting manner while the outflow tissues are protected from nitrative damage, which is expected to realize precision on-demand glaucoma therapy with little biosafety concern, promising significant clinical translational potential.

Effect of Prostaglandin E2 Agonist Omidenepag on the Expression of Matrix Metalloproteinase in Trabecular Meshwork Cells

Purpose

To investigate the effects of prostaglandin E2 agonist omidenepag (OMD) on the expression of matrix metalloproteinase (MMP) in human trabecular meshwork (TM) cells.

Methods

Primarily cultured human TM cells were exposed to 0, 1, 10, or 40 μmol/L OMD for 3 days. The permeability through the TM cell monolayer was assessed using carboxyfluorescein. Expressions of messenger ribonucleic acid and protein levels of MMP-1, MMP-3, and MMP-9 were measured by reverse transcription polymerase chain reaction and Western blotting, respectively. Also, the permeability, expression of messenger ribonucleic acid, and protein levels of MMPs were measured after exposure to 1 μmol/L latanoprost free acid (LAT).

Results

OMD and LAT did not affect the cellular survival (all p > 0.05). Each concentration of OMD and LAT did not affect the permeability of carboxyfluorescein significantly (all p > 0.05). LAT increased the level of MMP-1 protein but did not increase the levels of MMP-3 and MMP-9 proteins. Each concentration of OMD did not affect the levels of MMP-1, MMP-3, and MMP-9 proteins (all p > 0.05)

Conclusions

In TM cells, prostaglandin E2 agonist OMD did not increase the permeability through the TM cell monolayer, and the protein levels of MMPs. These suggest that the direct effect on the trabecular outflow by OMD may be limited.

The Application of Nitric Oxide for Ocular Hypertension Treatment

Despite of various therapeutic methods for treating ocular hypertension and glaucoma, it still remains the leading cause of irreversible blindness. Intraocular pressure (IOP) lowering is the most effective way to slow disease progression and prevent blindness. Among the ocular hypotensive drugs currently in use, only a couple act on the conventional outflow system, which is the main pathway for aqueous humor outflow and the major lesion site resulting in ocular hypertension. Nitric oxide (NO) is a commendable new class of glaucoma drugs that acts on the conventional outflow pathway. An increasing number of nitric oxide donors have been developed for glaucoma and ocular hypertension treatment. Here, we will review how NO lowers IOP and the types of nitric oxide donors that have been developed. And a brief analysis of the advantages and challenges associated with the application will be made. The literature used in this review is based on Pubmed database search using ‘nitric oxide’ and ‘glaucoma’ as key words.

Lifetime exposure of ambient PM2.5 elevates intraocular pressure in young mice

Epidemiological studies suggest that ambient particulate matter exposure may be a new risk factor of glaucoma, but it lacks solid experimental evidence to establish a causal relationship. In this study, young mice (4 weeks old) were exposed concentrated ambient PM2.5 (CAP) for 9 months, which is throughout most of the life span of a mouse under heavy pollution. CAP was introduced using a versatile aerosol concentration enrichment system which mimics natural PM2.5 exposure. CAP exposure caused a gradual elevation of intraocular pressure (IOP) and an increase in aqueous humor outflow resistance. In the conventional outflow tissues that regulates IOP, inducible nitric oxide synthase (iNOS) was up-regulated and 3-nitrotyrosine (3-NT) formation increased. At the cellular level, PM2.5 exposure increased the transendothelial electrical resistance of cells that control IOP (AAP cells). This is accompanied by increased reactive oxygen species (ROS), iNOS and 3-NT levels. Peroxynitrite scavenger MnTMPyP successfully treated the IOP elevation and restored it to normal levels by reducing 3-NT formation in outflow tissues. This study provides the novel evidence that in young mice, lifetime whole-body PM2.5 exposure has a direct toxic effect on intraocular tissues, which imposes a significant risk of IOP elevation and may initiate the development of ocular hypertension and glaucoma. This occurs as a result of protein nitration of conventional aqueous humor outflow tissues.

VIP Stabilizes the Cytoskeleton of Schlemm's Canal Endothelia via Reducing Caspase-3 Mediated ZO-1 Endolysosomal Degradation

Objectives

In glaucomatous eyes, the main aqueous humor (AH) outflow pathway is damaged by accumulated oxidative stress arising from the microenvironment, vascular dysregulation, and aging, which results in increased outflow resistance and ocular hypertension. Schlemm's canal (SC) serves as the final filtration barrier of the main AH outflow pathway. The present study is aimed at investigating the possible regulation of vasoactive intestinal peptide (VIP) on the cytoskeleton by stabilizing ZO-1 in SC.

Methods

Model of chronic ocular hypertension (COH) induced by episcleral venous cauterization was treated with topical VIP. The ultrastructure of junctions, ZO-1 levels, and permeability of the SC inner wall to FITC-dextran (70 kDa) were detected in the COH models. The F-actin distribution, F/G-actin ratio, and ZO-1 degradation pathway in human umbilical vein endothelial cells (HUVECs) and HEK 293 cells were investigated.

Results

ZO-1 in the outer wall of the SC was less than that in the inner wall. COH elicited junction disruption, ZO-1 reduction, and increased permeability of the SC inner wall to FITC-dextran in rats. ZO-1 plays an essential role in maintaining the F/G-actin ratio and F-actin distribution. VIP treatment attenuated the downregulation of ZO-1 associated with COH or H₂O₂-induced oxidative damage. In H₂O₂-stimulated HUVECs, the caspase-3 inhibitor prevents ZO-1 disruption. Caspase-3 activation promoted endolysosomal degradation of ZO-1. Furthermore, a decrease in caspase-3 activation and cytoskeleton redistribution was demonstrated in VIP + H₂O₂-treated cells. The knockdown of ZO-1 or the overexpression of caspase-3 blocked the effect of VIP on the cytoskeleton.

Conclusion

This study provides insights into the role of VIP in stabilizing the interaction between the actin cytoskeleton and cell junctions and may provide a promising targeted strategy for glaucoma treatment.

Endogenous dual stimuli-activated NO generation in the conventional outflow pathway for precision glaucoma therapy

High intraocular pressure (IOP) has been regarded as a predominant risk factor for glaucoma. Nitric oxide (NO) is shown to lower IOP, but the magnitude and duration of IOP reduction are not satisfying due to the poor cornea penetration of NO drugs and limited NO generation in the trabecular meshwork (TM)/Schlemm's canal (SC) area. Herein, we introduce deep cornea penetrating biodegradable hollow mesoporous organosilica (HOS) nanocapsules for the efficient co-delivery of hydrophobic JS-K (J_R) and hydrophilic l-Arginine (L_O). The resulting HOS-J_RL_O can be reduced and oxidized by the ascorbic acid (AA) and catalysis of endothelial nitric oxide synthase (eNOS) in the TM/SC microenvironment to release NO for inducing appreciable IOP reduction in various glaucoma mouse models. In addition to developing an endogenous stimuli-responsive NO nanotherapeutic, this study is also expected to establish a versatile, non-invasive, and efficacious treatment paradigm for precision glaucoma therapy.

Effect of Anti-vascular Endothelial Growth Factor on the Matrix Metalloproteinase Activity in Trabecular Meshwork Cells

Purpose: To investigate the effects of anti-vascular endothelial growth factor (anti-VEGF) on the activity of matrix metalloproteinase (MMP) in human trabecular meshwork cells (HTMC). Methods: Primary HTMC cultures were exposed to 0, 0.25, and 0.50 mg/mL anti-VEGF bevacizumab (BV) for 24 hours. The permeability through the trabecular meshwork cell monolayer was assessed using carboxyfluorescein and trans-epithelial endothelial electrical resistance (TEER). The levels of MMP-1/-2 were measured by Western blotting and the production of nitric oxide (NO) was assessed with the Griess assay. Results: Bevacizumab at 0.50 mg/mL decreased the permeability of carboxyfluorescein significantly (p = 0.017) and did not affect TEER (p = 0.308). Administration of 0.50 mg/mL BV decreased MMP-1 and MMP-2 activities (p = 0.014, p = 0.016, respectively) and inhibited NO production significantly (p = 0.023). Conclusions: Anti-VEGF decreased the permeability through the HTMC monolayer, which was accompanied by decreased MMP-1/-2 activity and limited NO production.

Effect of Minoxidil on Trabecular Outflow via the Paracellular Pathway

PURPOSE

To investigate the pathway and effects of minoxidil on trabecular outflow in cultured human trabecular meshwork (TM) cells.

METHODS

After exposing primarily cultured TM cells to 0, 10, 50, or 100 μM minoxidil sulfate (MS), trabecular outflow was assessed by measuring TM cell monolayer permeability to carboxyfluorescein and transepithelial electrical resistance. To assess the pathway of permeability changes, caveolin-1, occludin, and claudin-5 levels were measured via western blot. Generation of reactive oxygen species (ROS) was measured using the dichlorofluorescein diacetate assay. To assess the involvement of nitric oxide (NO) in minoxidil-induced permeability increase, the degrees of endothelial nitric oxide synthase mRNA expression and NO production were measured with reverse transcription polymerase chain reaction and Griess assays, respectively. Permeability was also measured with co-exposure to 50 μM N-acetyl cysteine.

RESULTS

MS significantly increased TM cell monolayer permeability (p < 0.05) and decreased transepithelial electrical resistance (p < 0.05). MS decreased the degree of endothelial nitric oxide synthase mRNA expression but did not affect NO production. MS decreased occludin and claudin-5 levels but did not affect caveolin-1 level. MS at 100 μM increased the generation of ROS, and MS-induced permeability increase was attenuated after co-exposure to 50 μM N-acetyl cysteine.

CONCLUSIONS

Minoxidil may preferentially increase trabecular permeability via a paracellular pathway by downregulation of tight junction proteins. This minoxidil-induced permeability through the TM may be mediated by generation of ROS.

Cell senescence altered the miRNA expression profile in porcine angular aqueous plexus cells

Purpose

This study investigates the impact of aging on the miRNA expression profile in porcine angular aqueous plexus (AAP) cells, which are the porcine equivalent of human Schlemm's canal endothelial cells.

Methods

AAP endothelial cells were isolated and cultured in physiologic (5% O₂) or hyperoxic condition (40% O₂) for 14 days to induce cell senescence. miRNA and protein expression profiles of control and senescent cells were analyzed with miRNA microarray and isobaric tags for relative and absolute quantification (iTRAQ), respectively.

Results

The miRNA microarray identified 33 differentially expressed miRNAs in senescent cells compared with controls (p<0.05), and quantitative real-time PCR (qRT-PCR) confirmed 12 of them (p<0.05). iTRAQ analysis identified 148 upregulated and 222 downregulated proteins (p<0.05, fold change>1.2). Bioinformatics analysis of miRNA microarray and proteomics data predicted that six out of seven miRNAs are associated with aqueous humor outflow by targeting integrin and the downstream pathways (Src/Rho kinase, focal adhesion kinase (FAK)/NO-cGMP), and one miRNA might influence gap junction by targeting the Inositol trisphosphate receptor (IP3R) /Protein kinase C (PKC) pathway.

Conclusions

This study identified miRNAs in senescent AAP cells that might regulate aqueous humor outflow by targeting proteins involved in focal adhesion, cytoskeleton, NO-cGMP signaling, and gap junction.

Effect and Mechanism of Phosphodiesterase Inhibitors on Trabecular Outflow

PURPOSE

Phosphodiesterase (PDE) inhibitors increase matrix metalloproteinase (MMP) production by inhibiting re-uptake of adenosine and may potentiate nitric oxide (NO) activity. This study was performed to investigate the effects and mechanisms of PDE inhibitors on trabecular outflow in cultured human trabecular meshwork cells (HTMCs).

METHODS

Primary HTMC cultures were exposed to 0, 20, and 50 μM dipyridamole (DPD) or theophylline (TPN). Permeability through the HTMC monolayer was assessed using carboxyfluorescein. The production of NO was assessed using the Griess assay and MMP-2 levels were measured via Western blotting.

RESULTS

DPD significantly increased permeability accompanied with increased nitrite concentration and MMP-2 levels (all p < 0.05). TPN increased nitrite but did not affect permeability or MMP-2 levels significantly (p > 0.05). When treated with DPD and TPN together, both permeability and nitrite production were increased; however, MMP-2 levels showed no difference compared to DPD exposure alone (p > 0.05).

CONCLUSIONS

DPD increased trabecular permeability accompanied with increased nitrite production and MMP-2 levels. PDE inhibitors may increase trabecular outflow by increasing MMP-2 levels and by potentiating NO activity through cyclic GMP in HTMC.

Association of serum uric acid levels with primary open-angle glaucoma: a 5-year case-control study

PURPOSE

It has been hypothesised that uric acid (UA) has a protective effect against oxidative damage in the central nervous system. Therefore, we investigated serum UA concentrations in patients with primary open-angle glaucoma (POAG) and explored the relationship between serum UA concentration and glaucoma severity.

METHODS

This prospective, cross-sectional, case-control study was conducted in 163 POAG patients and 103 normal controls. Clinical and demographic information was obtained from the medical data platform of the Eye & ENT Hospital of Fudan University, Shanghai, China. The POAG patients were categorised into mild [median deviation (MD) ≤ 6.00 dB], moderate (MD > 6 Db-≥12 dB) and severe (MD > 12 dB) subgroups, based on their visual field MD results.

RESULTS

The level of serum UA in the POAG group (0.321 ± 0.084 mmol/l) was approximately 12.77% lower (p < 0.001) than that of the control group (0.362 ± 0.053 mmol/l). The UA/creatinine (Cr) ratio was approximately 14.99% lower (p < 0.001) in patients with POAG (4.47 ± 1.15), compared with the control group (5.14 ± 1.05). The mean level of UA was lowest in the severe POAG group, followed by the moderate POAG group, and the mild POAG group (p < 0.001). A similar trend was observed when UA levels were compared between the POAG and control groups in males. Multivariate regression analyses showed a significant negative correlation between UA and vertical cup-disc ratio (B = -0.320, p = 0.034), and UA and MD (B = -0.441, p = 0.031) in males.

CONCLUSION

Primary open-angle glaucoma patients have lower UA levels; however, a negative association between UA levels and disease severity was evident in male patients.

Outflow enhancement by three different ab interno trabeculectomy procedures in a porcine anterior segment model

PURPOSE

To evaluate three different microincisional ab interno trabeculectomy procedures in a porcine eye perfusion model.

METHODS

In perfused porcine anterior segments, 90° of trabecular meshwork (TM) was ablated using the Trabectome (T; n = 8), Goniotome (G; n = 8), or Kahook device (K; n = 8). After 24 h, additional 90° of TM was removed. Intraocular pressure (IOP) and outflow facility were measured at 5 and 10 μl/min perfusion to simulate an elevated IOP. Structure and function were assessed with canalograms and histology.

RESULTS

At 5 μl/min infusion rate, T resulted in a greater IOP reduction than G or K from baseline (76.12% decrease versus 48.19% and 47.96%, P = 0.013). IOP reduction between G and K was similar (P = 0.420). Removing another 90° of TM caused an additional IOP reduction only in T and G but not in K. Similarly, T resulted in the largest increase in outflow facility at 5 μl/min compared with G and K (first ablation, 3.41 times increase versus 1.95 and 1.87; second ablation, 4.60 versus 2.50 and 1.74) with similar results at 10 μl/min (first ablation, 3.28 versus 2.29 and 1.90 (P = 0.001); second ablation, 4.10 versus 3.01 and 2.01 (P = 0.001)). Canalograms indicated circumferential flow beyond the ablation endpoints.

CONCLUSIONS

T, G, and K significantly increased the outflow facility. In this model, T had a larger effect than G and K.

22q11.2 microduplication syndrome and juvenile glaucoma

BACKGROUND

22q11.2 microduplication is a relatively recently recognized syndrome. Findings in affected individuals range from apparent normality to a wide variety of systemic and ocular conditions. We describe the association between 22q11.2 microduplication and juvenile glaucoma in two brothers.

MATERIALS AND METHODS

We reviewed ophthalmological, genetic, and hematological medical records of two patients and their unaffected mother.

RESULTS

A 2.07 Mb interstitial duplication in 22q11.21 and a smaller 182 kb duplication in 22q11.23 were identified in both subjects. Patient 1 showed an initial intraocular pressure (IOP) of 15 mmHg in right eye (RE) and 32 mmHg in left eye (LE) under maximum medical treatment. Deep sclerectomy surgery in LE was converted to trabeculectomy due to a macroperforation of the trabeculo-descemetic membrane. Postoperatively, the patient developed persistent hypotony with retinal folds, while IOP in RE increased to 28 mmHg. Trabeculectomy in RE was also complicated by persistent hypotony. Autologous blood injection was performed, resulting in an increase in both visual acuity and IOP. Patient 2 presented with an IOP of 29 mmHg in RE and 33 mmHg in LE. We planned an elective trabeculectomy and added orally administered acetazolamide. The patient developed bilinear cytopenia that contraindicated the surgical procedure. After hematologic normalization, the patient underwent trabeculectomy in LE, causing persistent hypotony. We performed deep sclerectomy surgery in RE, without any significant intra- or post-operative complications.

CONCLUSIONS

22q11.2 microduplication syndrome can be associated with juvenile glaucoma. Trabeculectomy may be complicated by persistent hypotony. Deep sclerectomy appears to be a better surgical option, although the presence of a thin sclera may result in conversion to trabeculectomy.

Age-Related Changes in Human Schlemm's Canal: An in Vivo Optical Coherence Tomography-Based Study

Purpose: To investigate age-related changes in human Schlemm’s canal (SC) using spectral-domain optical coherence tomography (SD-OCT).

Methods: A total of 125 normal eyes were imaged using SD-OCT nasally and temporally. The age-related variations of SC sagittal diameter and cross-sectional area (CSA) from four age groups [A (16–20 years), B (21–40 years), C (41–60 years), and D (61–80 years)] were analyzed with Spearman correlation.

Results: The positive detection rates of SC showed a significantly downward trend with age. The mean CSA was 13,296 ± 1,897 μm² nasally and 14,552 ± 2,589 μm² temporally. The mean CSA was significantly larger in the temporal than in the nasal region (P < 0.05). Nasal CSA values varied among the four age groups (P = 0.004).

Conclusion: Our study found for the first time that SC in vivo exhibits a morphological variant with age in healthy humans. Clinicians may need to consider this phenomenon when performing examinations targeting SC for glaucoma patients.

The association between serum uric acid and glaucoma severity in primary angle closure glaucoma: a retrospective case-control study

Uric acid (UA) is a major antioxidant molecule and has been hypothesized to have a protective effect on the central nervous system against oxidative damage. We prospectively investigated the serum concentration of UA in primary angle closure glaucoma (PACG), and explored the association between serum concentration of UA and the severity of PACG. Using a retrospective case-control study design, 886 PACG subjects and 994 control subjects who attended the Eye & ENT Hospital of Fudan University, were eligible for this study. Glaucoma severity was classified as mild (MD ≤ 6.00 dB), moderate (12 dB ≥ MD > 6 dB) and severe (MD > 12 dB) based on the MD (mean deviation). The levels of UA were significantly lower (p = 0.025) in PACG (0.286 ± 0.082 mmol/l) compared with control (0.295 ± 0.085 mmol/l). The mean serum UA levels were lowest in the severe group (0.281 ± 0.074 mmol/l) followed by moderate (0.282 ± 0.080 mmol/l) and mild (0.297 ± 0.090 mmol/l) with significant differences among the three groups (p = 0.032). In multivariate regression analysis, there was a significant negative correlation between UA level and vertical cup-disc ratio (B = −0.165, p = 0.035). Significantly lower serum UA concentration in PACG and its negative association with disease severity presented it as an important candidate in reaction to oxidative stress in glaucoma pathogenesis.

From DNA damage to functional changes of the trabecular meshwork in aging and glaucoma

Glaucoma is a degenerative disease of the eye. Both the anterior and posterior segments of the eye are affected, extensive damage being detectable in the trabecular meshwork and the inner retina-central visual pathway complex. Oxidative stress is claimed to be mainly responsible for molecular damage in the anterior chamber. Indeed, oxidation harms the trabecular meshwork, leading eventually to endothelial cell decay, tissue malfunction, subclinical inflammation, changes in the extracellular matrix and cytoskeleton, altered motility, reduced outflow facility and (ultimately) increased IOP. Moreover, free radicals are involved in aging and can be produced in the brain (as well as in the eye) as a result of ischemia, leading to oxidation of the surrounding neurons. Glaucoma-related cell death occurs by means of apoptosis, and apoptosis is triggered by oxidative stress via (a) mitochondrial damage, (b) inflammation, (c) endothelial dysregulation and dysfunction, and (d) hypoxia. The proteomics of the aqueous humor is significantly altered in glaucoma as a result of oxidation-induced trabecular damage. Those proteins whose aqueous humor levels are increased in glaucoma are biomarkers of trabecular meshwork impairment. Their diffusion from the anterior to the posterior segment of the eye may be relevant in the cascade of events triggering apoptosis in the inner retinal layers, including the ganglion cells.

The Outflow Pathway: A Tissue With Morphological and Functional Unity

The trabecular meshwork (TM) plays an important role in high-tension glaucomas. Indeed, the TM is a true organ, through which the aqueous humor flows from the anterior chamber to Schlemm's canal (SC). Until recently, the TM, which is constituted by endothelial-like cells, was described as a kind of passive filter. In reality, it is much more. The cells delineating the structures of the collagen framework of the TM are endowed with a cytoskeleton, and are thus able to change their shape. These cells also have the ability to secrete the extracellular matrix, which expresses proteins and cytokines, and are capable of phagocytosis and autophagy. The cytoskeleton is attached to the nuclear membrane and can, in millionths of a second, send signals to the nucleus in order to alter the expression of genes in an attempt to adapt to biomechanical insult. Oxidative stress, as happens in aging, has a deleterious effect on the TM, leading eventually to cell decay, tissue malfunction, subclinical inflammation, changes in the extracellular matrix and cytoskeleton, altered motility, reduced outflow facility, and (ultimately) increased IOP. TM failure is the most relevant factor in the cascade of events triggering apoptosis in the inner retinal layers, including ganglion cells. J. Cell. Physiol. 231: 1876-1893, 2016. © 2016 Wiley Periodicals, Inc.

Endothelial nitric oxide synthase-related mechanotransduction changes in aged porcine angular aqueous plexus cells

PURPOSE

To investigate effects of aging on endothelial nitric oxide synthase (eNOS) expression and signaling in angular aqueous plexus (AAP) (functional equivalent to human Schlemm's canal) cells subjected to shear stress.

METHODS

The AAP cells were isolated differentially from porcine outflow tissues using puromycin selection. Cell aging was induced by culturing cells in hyperoxia condition (40% oxygen and 5% carbon dioxide) for 14 days. The AAP cells grown in chamber slides were exposed to a shear stress of 8 dynes/cm(2) for 24 hours. Expression of eNOS, eNOS-phospho Thr495, eNOS-phospho Ser1177, and Akt-phospho was tested by Western blot analysis and immunofluorescence staining. Nitric oxide (NO) levels were measured using the Griess assay.

RESULTS

Compared with control, eNOS levels in aged cells were significantly reduced by 60% (P < 0.05; n = 6). Phosphorylation of eNOS at Ser1177 and Akt at Ser473 was 63% and 80% lower in aged cells, respectively, whereas phosphorylation of the eNOS inhibition site (Thr495) increased by 6.1-fold (P < 0.05; n = 6). Shear stress (8 dynes/cm(2) for 24 hours) increased eNOS abundance (total protein and at cell borders) and phosphorylation at Ser1177 by 1.7-fold and 1.8-fold, respectively (P < 0.05; n = 6), whereas aged cells were unresponsive. In control cells exposed to shear stress, the NO concentration was 1.8-fold higher than in the static group (P < 0.05; n = 4); however, aged cells were unresponsive to shear stress (mean ± SD, 4.3 ± 1.3 vs. 4.1 ± 1.4 μM).

CONCLUSIONS

Aged AAP cells appear compromised in their mechanotransduction machinery involving eNOS, the protein product of the gene, NOS3, polymorphisms of which impart a risk for the development of glaucoma.

Oxidative and pro-inflammatory impact of regular and denicotinized cigarettes on blood brain barrier endothelial cells: is smoking reduced or nicotine-free products really safe?

Background

Both active and passive tobacco smoke (TS) potentially impair the vascular endothelial function in a causative and dose-dependent manner, largely related to the content of reactive oxygen species (ROS), nicotine, and pro-inflammatory activity. Together these factors can compromise the restrictive properties of the blood–brain barrier (BBB) and trigger the pathogenesis/progression of several neurological disorders including silent cerebral infarction, stroke, multiple sclerosis and Alzheimer’s disease. Based on these premises, we analyzed and assessed the toxic impact of smoke extract from a range of tobacco products (with varying levels of nicotine) on brain microvascular endothelial cell line (hCMEC/D3), a well characterized human BBB model.

Results

Initial profiling of TS showed a significant release of reactive oxygen (ROS) and reactive nitrogen species (RNS) in full flavor, nicotine-free (NF, “reduced-exposure” brand) and ultralow nicotine products. This release correlated with increased oxidative cell damage. In parallel, membrane expression of endothelial tight junction proteins ZO-1 and occludin were significantly down-regulated suggesting the impairment of barrier function. Expression of VE-cadherin and claudin-5 were also increased by the ultralow or nicotine free tobacco smoke extract. TS extract from these cigarettes also induced an inflammatory response in BBB ECs as demonstrated by increased IL-6 and MMP-2 levels and up-regulation of vascular adhesion molecules, such as VCAM-1 and PECAM-1.

Conclusions

In summary, our results indicate that NF and ultralow nicotine cigarettes are potentially more harmful to the BBB endothelium than regular tobacco products. In addition, this study demonstrates that the TS-induced toxicity at BBB ECs is strongly correlated to the TAR and NO levels in the cigarettes rather than the nicotine content.

Cell senescence reduced the mechanotransduction sensitivity of porcine angular aqueous plexus cells to elevation of pressure

PURPOSE

To investigate the effect of pressure/flow on the barrier function and protein expression of normal and senescent porcine aqueous humor plexus (AAP) cells, which are the porcine equivalent of human Schlemm's canal endothelial cells.

METHODS

AAP cells were grown for 2 weeks in physiological (5% O2) or hyperoxic conditions (40% O2) to model cell senescence. Control and senescent AAP cells were subjected to control and elevated hydrostatic pressure gradient of 10 mm Hg for 72 hours. Hydraulic conductivity (HC) and transendothelial electric resistance (TEER) were measured. The expressions of senescence-associated β-galactosidase and DNA damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) were monitored, and the protein expression profile was analyzed by Western blot.

RESULTS

After 14 days of hyperoxia, AAP cells stained positive for 8-OHdG and β-galactosidase. Pressure elevation/flow resulted in significant increase of HC in control cells (from 1.37 ± 0.12 to 1.64 ± 0.18 μL/mm Hg/min/cm(2), P < 0.05), but not in senescent cells (1.15 ± 0.17 and 1.08 ± 0.10 μL μL/mm Hg/min/cm(2)). TEER changes were consistent with the HC results. Western blot analysis showed that the expression level of myosin light chain, claudin-5, and VE-cadherin significantly reduced under pressure elevation in control cells but not in senescent cells.

CONCLUSIONS

AAP cells are mechano-sensitive; however, cell senescence rendered the cells less responsive to mechanical stimulus, which may have pathological consequences.

Hyperoxia increases the elastic modulus of alveolar epithelial cells through Rho kinase

Patients with acute lung injury are administered high concentrations of oxygen during mechanical ventilation, and while both hyperoxia and mechanical ventilation are necessary, each can independently cause additional injury. However, the precise mechanisms that lead to injury are not well understood. We hypothesized that alveolar epithelial cells may be more susceptible to injury caused by mechanical ventilation because hyperoxia causes cells to be stiffer due to increased filamentous actin (f-actin) formation via the GTPase RhoA and its effecter Rho kinase (ROCK). We examined cytoskeletal structures in cultured murine lung alveolar epithelial cells (MLE-12) under normoxic and hyperoxic (48 h) conditions. We also measured cell elasticity (E) using an atomic force microscope in the indenter mode. Hyperoxia caused increased f-actin stress fibers and bundle formation, an increase in g- and f-actin, an increase in nuclear area and a decrease in nuclear height, and cells became stiffer (higher E). Treatment with an inhibitor (Y-27632) of ROCK significantly decreased E and prevented the cytoskeletal changes, while it did not influence the nuclear height and area. Pre-exposure of cells to hyperoxia promoted detachment when cells were subsequently stretched cyclically, but the ROCK inhibitor prevented this effect. Hyperoxia caused thickening of vinculin focal adhesion plaques, and inhibition of ROCK reduced the formation of distinct focal adhesion plaques. Phosphorylation of focal adhesion kinase was significantly reduced by both hyperoxia and treatment with Y-27632. Hyperoxia caused increased cell stiffness and promoted cell detachment during stretch. These effects were ameliorated by inhibition of ROCK.