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Iok-Hou Pang

Publications and source records attributed to Iok-Hou Pang.

15 recordsLinked to original sources
PubMed2006

TGFbeta2-induced changes in human trabecular meshwork: implications for intraocular pressure.

PURPOSE: Transforming growth factor (TGF)-beta2 levels are elevated in glaucomatous human aqueous humor. TGFbeta is a cytokine that alters extracellular matrix (ECM) metabolism, and excess ECM has been proposed to increase aqueous outflow resistance in the trabecular meshwork (TM) of glaucomatous eyes. This study was undertaken to investigate effects of TGFbeta2 on secretion of fibronectin and the protease inhibitor plasminogen activator inhibitor (PAI)-1 from human TM cell cultures and perfused human ocular anterior segments. METHODS: Total RNA was isolated from pooled human TM cell monolayers and used for a gene microarray expression analysis. Supernatants from treated human TM cells were analyzed by ELISA for fibronectin or PAI-1 content. TGFbeta2 effects on intraocular pressure (IOP) were evaluated in a perfused organ culture model using human anterior segments, and eluates were analyzed for fibronectin and PAI-1 content. RESULTS: Overnight treatment of TM cells with TGFbeta2 upregulated multiple ECM-related genes, such as PAI-1. TGFbeta2 also increased secretion of both fibronectin and PAI-1 from TM cells. TGFbeta2 effects on TM cells were blocked by inhibitors of the TGFbeta type I receptor. In perfused human anterior segments, TGFbeta2 treatment elevated IOP and increased eluate fibronectin and PAI-1 content. CONCLUSIONS: TGFbeta2 effects on IOP may be transduced by TGFbeta type-I receptor-mediated changes in TM secretion of ECM-related factors such as fibronectin and PAI-1. Modulation of TGFbeta2-induced changes in the ECM may provide a novel and viable approach to the management of glaucoma.

Aged↗
PubMed2006

Semiquantitative optic nerve grading scheme for determining axonal loss in experimental optic neuropathy.

PURPOSE: To describe and evaluate a semiquantitative optic nerve grading scheme for assessing axonal loss in endothelin (ET)-1-induced chronic optic neuropathy. METHODS: Optic nerve cross-sections from both eyes of 39 Brown Norway rats unilaterally treated with various concentrations of ET-1 or physiological saline solution via a surgically implanted osmotic minipump were processed for light and transmission electron microscopy (TEM). The optic nerve damage grade, between 0 (no damage) and 10 (total damage), was based on the number of zones of approximately equal damage and the mean percentage of damage within each zone. Grading was performed under light microscopy by three observers and compared with axonal survival determined with TEM using two quantification methods: the sampling method, in which approximately 10% of the section was counted, and the full-count method, in which the whole section was counted (n = 12). Axonal survival was expressed as a ratio of axon counts in the experimental to control eye. Before these comparisons, the inter- and intraobserver agreement rates were determined in another group of 85 and 12 ET-1-treated animals, respectively. RESULTS: The interobserver kappa was 0.66 (95% confidence interval [CI]: 0.58-0.74) for all eyes and 0.55 (95% CI: 0.43-0.67) for the experimental eyes only. The intraobserver kappa was 0.80, 0.81, and 0.80 for all 24 eyes and 0.60, 0.64, and 0.71 for experimental eyes only. The correlation between damage grade in the experimental eye and axonal survival using the TEM sampling method (Spearman's rho = -0.677 for all animals and -0.827 for the subset of animals with full counts only) was lower than that with the full-count method (Spearman's rho = -0.926). When axonal survival was less than 0.7, the sampling method always underestimated the extent of damage. CONCLUSIONS: The grading scheme had good inter- and intraobserver agreement, and high correlation with the TEM methods. It is a practical and time-saving method, requiring less than 1 minute per nerve and is an alternative to sampling methods that can yield significant errors.

Animals↗
PubMed2005

Dexamethasone alters F-actin architecture and promotes cross-linked actin network formation in human trabecular meshwork tissue.

Elevated intraocular pressure is an important risk factor for the development of glaucoma, a leading cause of irreversible blindness. This ocular hypertension is due to increased hydrodynamic resistance to the drainage of aqueous humor through specialized outflow tissues, including the trabecular meshwork (TM) and the endothelial lining of Schlemm's canal. We know that glucocorticoid therapy can cause increased outflow resistance and glaucoma in susceptible individuals, that the cytoskeleton helps regulate aqueous outflow resistance, and that glucocorticoid treatment alters the actin cytoskeleton of cultured TM cells. Our purpose was to characterize the actin cytoskeleton of cells in outflow pathway tissues in situ, to characterize changes in the cytoskeleton due to dexamethasone treatment in situ, and to compare these with changes observed in cell culture. Human ocular anterior segments were perfused with or without 10(-7) M dexamethasone, and F-actin architecture was investigated by confocal laser scanning microscopy. We found that outflow pathway cells contained stress fibers, peripheral actin staining, and occasional actin "tangles." Dexamethasone treatment caused elevated IOP in several eyes and increased overall actin staining, with more actin tangles and the formation of cross-linked actin networks (CLANs). The actin architecture in TM tissues was remarkably similar to that seen in cultured TM cells. Although CLANs have been reported previously in cultured cells, this is the first report of CLANs in tissue. These cytoskeletal changes may be associated with increased aqueous humor outflow resistance after ocular glucocorticoid treatment.

Actin Cytoskeleton↗
PubMed2005

Acute effects of glaucoma medications on rat intraocular pressure.

The rat has been used increasingly in glaucoma research, but many aspects regarding the regulation of its intraocular pressure (IOP) are still unknown. For example, it is not clear whether glaucoma medications can lower IOP in the rat similarly to human. This information will be valuable in evaluating this animal model for its usefulness in predicting drug effects in patients. Hence, we tested the acute IOP effects of selected glaucoma drugs topical administered onto the rat eye. In these studies, IOP was measured using the Tono-Pen XL tonometer. After a correlation between the IOP reported by the Tono-Pen and actual IOP was established, IOP measurements were obtained in slightly sedated adult rats. Effects of glaucoma medications were tested in two groups of animals. One group (12 h/L) was housed in a 12-h/12-h light/dark cycle. The other (24 h/L) was housed under constant light. Exposure of the animals to constant light increased their basal IOP from 20.5+/-0.6 mmHg (mean+/-S.E.M., n=12) to 32.0+/-0.5 mmHg. At 3 h after topical administration, Betoptic S lowered IOP by 4.3+/-1.7 mmHg (n=6) and 3.7+/-0.3 mmHg (n=6) in the 12 and 24h/L rats, respectively. Pilocarpine did not affect rat IOP. Xalatan produced a biphasic response in the rat. At 3h after topical administration, it increased IOP by 7.9+/-1.4 and 7.0+/-1.0 mmHg in the 12 and 24 h/L rats, respectively. By the next day, it decreased IOP by 3.0+/-1.0 and 6.0+/-0.8 mmHg in the 12 and 24 h/L rats, respectively. The IOP-enhancing effect of Xalatan was dose-dependent. The present study indicates that IOP responses of the rat to different pharmacological agents are not identical to those of the human. In the rat, Betoptic S, but not pilocarpine, lowered IOP. Xalatan initially increased then decreased IOP.

Animals↗
PubMed2005

Evaluation of inducible nitric oxide synthase in glaucomatous optic neuropathy and pressure-induced optic nerve damage.

PURPOSE: To determine whether inducible nitric oxide synthase (NOS-2) is involved in glaucomatous optic neuropathy. METHODS: Chronic elevation of rat intraocular pressure (IOP) leading to optic nerve damage was induced by episcleral injection of hypertonic saline, which caused sclerosis and blockade of aqueous humor outflow pathways. Expression of NOS-2 in the retina and optic nerve head (ONH) was evaluated by immunohistochemistry, gene array analysis, and quantitative PCR (Q-PCR). Immunohistochemistry was also used to assess the NOS-2 level in the ONH from primary open-angle glaucoma (POAG) and nonglaucomatous human eyes. Finally, an NOS-2 inhibitor, aminoguanidine, administered orally in the drinking water, was tested for its effect on optic nerve injury in rats with ocular hypertension. RESULTS: Chronically elevated IOP in the rat produced optic nerve damage that correlated with pressure change (r(2) = 0.77), but did not increase NOS-2 immunoreactivity in the optic nerve, ONH, or ganglion cell layer. Retinal and ONH NOS-2 mRNA levels did not correlate with either IOP level or severity of optic nerve injury. Similarly, there was no difference in NOS-2 immunoreactivity in the optic nerve or ONH between POAG and nonglaucomatous eyes. Furthermore, aminoguanidine treatment did not affect the development of pressure-induced optic neuropathy in the rat. CONCLUSIONS: As demonstrated by several independent methods, glaucomatous optic neuropathy was not associated with a significant change in the expression of NOS-2 in the retina, ONH, or optic nerve.

Aged↗
PubMed2005

Noninvasive measurement of rodent intraocular pressure with a rebound tonometer.

PURPOSE: The present study evaluated the applicability of a rebound tonometer in measuring intraocular pressure (IOP) in rats and mice. METHODS: The accuracy of the TonoLab rebound tonometer was determined in cannulated mouse and rat eyes. IOP was manipulated by changing reservoir height, and tonometer pressure readings were recorded by an independent observer. IOP values were recorded in conscious Wistar rats and in four different strains of mice. The effects of anesthesia on IOP were evaluated in two different strains of mice. RESULTS: The IOP readings generated by the rebound tonometer correlated very well with the actual pressure in the eye. In rats, this linear correlation had a slope of 0.96 +/- 0.05 (mean +/- SEM, n = 4) and a Y-intercept of -2.1 +/- 1.2. In mice, the slope was 0.99 +/- 0.05 (n = 3), and the Y-intercept was 0.8 +/- 1.4. Using this method, the resting IOP of conscious male Wistar rats was observed to be 18.4 +/- 0.1 mm Hg (n = 132). In mice, strain differences in IOP were detected. Baseline IOP values in Balb/c, C57-BL/6, CBA, and 11- to 12-month-old DBA/2J mice were 10.6 +/- 0.6, 13.3 +/- 0.3, 16.4 +/- 0.3, and 19.3 +/- 0.4 mm Hg (n = 12), respectively. In separated studies, anesthesia lowered IOP from 14.3 +/- 0.9 to 9.2 +/- 0.5 mm Hg (n = 8) in C57-BL/6 mice, and from 16.6 +/- 0.4 to 9.4 +/- 0.6 mm Hg (n = 10) in CBA mice. CONCLUSIONS: The rebound tonometer was easy to use and accurately measured IOP in rats and mice. This technique, together with advances in genetic and other biological studies in rodents, will be valuable in the further understanding of the etiology and pathology of glaucoma.

Anesthesia, Local↗
PubMed2003

Expression of matrix metalloproteinases and their inhibitors in human trabecular meshwork cells.

PURPOSE: Matrix metalloproteinases (MMPs) are involved in trabecular meshwork (TM) extracellular matrix metabolism and have been shown to increase aqueous outflow facility. The purpose of this study was to characterize effects of cytokines, a phorbol ester, and prostanoids on the expression of MMP-1, -2, -3, and -9 and tissue inhibitors of metalloproteinases (TIMP)-1 and -2 in cultured human TM cells. METHODS: Five human TM cell strains were treated with selected compounds. Levels of proMMPs and TIMPs in cell media were quantified by ELISA. MMP-3 activity was assayed by casein zymography. RESULTS: All human TM cell strains produced detectable basal amounts of proMMPs and TIMPs. 12-O-tetradecanoyl-phorbol-13-acetate was effective in increasing the levels of proMMP-1, -3, and -9 and TIMP-1. Its effect on proMMP-1 was concentration-dependent with an EC(50) of 2 to 3 nM. Interleukin (IL)-1alpha did not affect levels of proMMP-1 and -2 or the TIMPs, but was most efficacious in increasing proMMP-3 production with an EC(50) of 0.5 ng/mL. The IL-1alpha-induced upregulation of proMMP-3 correlated with an increase in MMP-3 activity. Tumor necrosis factor-alpha activated proMMP-3 production in some but not all cell strains. Platelet-derived growth factor-BB was generally ineffective in modulating MMP and TIMP levels. Prostaglandins E(2) and F(2alpha) at 10 micro M did not affect levels of proMMP-1 or -3. CONCLUSIONS: The expression of the different MMPs and TIMPs in human TM cells was independently regulated. Production of MMP-3 was maximally activated by IL-1alpha. The IL-1alpha-stimulated expression of MMP-3 provides a probable mechanism for IL-1alpha-enhanced aqueous outflow.

Adolescent↗
PubMed2003

Involvement of AP-1 in interleukin-1alpha-stimulated MMP-3 expression in human trabecular meshwork cells.

PURPOSE: Stromelysin-1 (MMP-3) degrades extracellular matrix and increases aqueous outflow. In the trabecular meshwork (TM), interleukin (IL)-1alpha is a potent inducer of MMP-3 expression. In different cells, IL-1alpha activates different signaling pathways, such as nuclear factor (NF)-kappaB-mediated protein expression, the phospholipase A(2) (PLA(2))-activated arachidonate cascade, and activator protein (AP)-1-associated transcription. In the present study, pharmacological tools were used to delineate the signaling mechanism involved in the effect of IL-1alpha on MMP-3 production in human TM cells compared with other ocular cells. METHODS: Human TM and three other ocular cells (ciliary muscle, corneoscleral fibroblast, and lamina cribrosa) were cultured in 24-well plates in the presence or absence of IL-1alpha, with or without specific inhibitors of selected signaling pathways. Secreted proMMP-3 was quantified by ELISA, and MMP-3 activity was assayed by casein zymography. RESULTS: IL-1alpha (5 ng/mL) increased proMMP-3 levels in human TM cells to 10- to 38-fold of control (P < 0.001). The effect of IL-1alpha was blocked by Gö6976, a protein kinase C micro (PKC micro ) inhibitor; PD98059, a mitogen-activated protein kinase kinase (MEK) inhibitor; SB202190, a p38 inhibitor; and SR11302, an AP-1 inhibitor; but not by inhibitors of casein kinase II, NFkappaB, PLA(2), phospholipase D (PLD), cyclooxygenases, lipoxygenase, or sphingomyelinase. SR11302 did not inhibit the effect of IL-1alpha on MMP-3 production in the other ocular cells tested. CONCLUSIONS: Based on the pharmacological effects of the inhibitors, the data indicate that activation of PKC micro, MEK, and p38 leading to the activation of AP-1 is critical to the IL-1alpha-stimulated upregulation of MMP-3 in human TM cells. Therefore, it is likely that compounds that activate the AP-1 pathway would upregulate the production of MMP-3 and improve aqueous outflow.

Adolescent↗
PubMed2003

Aqueous outflow-enhancing effect of tert-butylhydroquinone: involvement of AP-1 activation and MMP-3 expression.

PURPOSE: To test the effect of stimulators of activator protein (AP)-1, on expression of stromelysin (MMP-3) in human TM cells and on aqueous outflow in perfused human anterior segments. METHODS: Change in MMP-3 expression was determined by immunoassay of proMMP-3 levels in the media of cultured human TM cells. Anterior segments of human donor eyes with or without glaucoma were perfused with vehicle or the AP-1 stimulator tert-butylhydroquinone (tBHQ). The outflow rates or intraocular pressure (IOP), and proMMP-3 levels in the perfusate were monitored. RESULTS: AP-1 stimulators, such as beta-naphthoflavone, 3-methylcholanthrene, and tBHQ, significantly upregulated (2-4-fold) TM cell expression of MMP-3. The stimulatory effect of tBHQ was concentration dependent, with an EC(50) of approximately 3 micro M, and was blocked by concomitant treatment with 100 nM SR11302, which sequesters AP-1. When nonglaucomatous human eyes were perfused with tBHQ (10 micro M), both outflow rates and perfusate proMMP-3 level increased significantly within the first 24 hours. The outflow effect of tBHQ was suppressed when SR11302 (100 nM) was added in the perfusate. tBHQ also lowered the IOP by more than 40% in perfused glaucomatous eyes. CONCLUSIONS: An AP-1 activator, tBHQ, upregulated expression of MMP-3 in cultured human TM cells and perfused human eyes and enhanced outflow ex vivo. These effects were blocked by sequestering AP-1, suggesting that activation of AP-1 can lead to increased MMP-3 production in the TM, which in turn improves outflow facility. This unique mechanism may provide a novel therapy for glaucoma.

Anterior Eye Segment↗
PubMed2002

A new method and device to induce transient retinal ischemia in the rat.

PURPOSE: To describe and characterize a novel, non-invasive method to induce retinal ischemia in the rat. METHODS: Retinal ischemia was produced by applying a compression force with a suture thread anchored about 2mm behind the limbus of the eye in order to increase intraocular pressure and reduce ocular blood flow. Both ends of the suture thread were connected to weights via a pulley system. The effect of various weights (20, 25, or 35 g) on retinal damage was tested in animals of different body weights (350 and 574 g). Scotopic ERG measurements and histological sections of retinal tissue were used to evaluate possible functional and morphological changes to the retina as a consequence of ischemia followed by reperfusion. RESULTS: Retinal ischemia was achieved by this method with good reproducibility. The degree of retinal damage, as quantified by ERG measurement, correlated with the amount of weight connected to the suture thread. Seven days after 60 minutes of retinal ischemia, the amplitudes of A- and B-waves of eyes compressed with a 20 g weight were 84 +/- 11% and 86 +/- 16% (mean +/- SEM, n = 4, amplitudes before ischemia defined 100%), respectively. The A- and B-wave amplitudes of eyes compressed with 25 g were 69 +/- 7% and 76 +/- 6% (n = 11), respectively. A 35 g treatment produced A- and B-wave amplitudes of 55 +/- 3.9% and 52 +/- 4% (n = 35), respectively. There was no significant difference in the level of ischemic damage in the two groups of animals with different body weights evaluated in this study. At two weeks after 60-minute retinal ischemia, there was a significant decrease (by 31.1%) in the cell density in the retinal ganglion cell layer. CONCLUSIONS: The pulley method is an easy, non-invasive, and highly reproducible technique for inducing retinal ischemia in rats. This procedure may provide a useful animal model of ischemic retinopathy.

Animals↗
PubMed2002

Advances in glaucoma therapeutics.

Glaucoma is a major cause of irreversible blindness in the world. The prevalence of glaucomatous loss in vision will continue to grow as our populations age. Ocular hypertension is a major risk factor for the development of glaucoma and current glaucoma therapy is directed at lowering intraocular pressure. Several new ocular hypotensive agents have been introduced in the past several years providing a variety of treatment options. In addition, various classes of neuroprotective agents demonstrating activity in a wide variety of animal models have been proposed as potential new glaucoma therapeutics. Although these approaches will slow the progression of vision loss, they do not directly intervene in the disease process(es). Advances have been made attempting to understand the pathogenic pathways involved in glaucomatous damage to the eye and in methods to clinically measure glaucoma damage. An increased understanding of the pathophysiology of glaucoma will lead to the development of new therapeutic agents that intervene and perhaps even reverse glaucomatous damage to the eye. There also is a need to develop new methods to clinically measure glaucoma damage because, currently, considerable damage occurs before glaucoma is diagnosed and glaucoma remains underdiagnosed in the general population.

Journal Article↗
PubMedDate not supplied

Inherited glaucoma in DBA/2J mice: pertinent disease features for studying the neurodegeneration.

The glaucomas are neurodegenerative diseases involving death of retinal ganglion cells and optic nerve head excavation. A major risk factor for this neurodegeneration is a harmfully elevated intraocular pressure (IOP). Human glaucomas are typically complex, progressive diseases that are prevalent in the elderly. Family history and genetic factors are clearly important in human glaucoma. Mouse studies have proven helpful for investigating the genetic and mechanistic basis of complex diseases. We previously reported inherited, age-related progressive glaucoma in DBA/2J mice. Here, we report our updated findings from studying the disease in a large number of DBA/2J mice. The period when mice have elevated IOP extends from 6 months to 16 months, with 8-9 months representing an important transition to high IOP for many mice. Optic nerve degeneration follows IOP elevation, with the majority of optic nerves being severely damaged by 12 months of age. This information should help with the design of experiments, and we present the data in a manner that will be useful for future studies of retinal ganglion cell degeneration and optic neuropathy.

Animals↗