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Biomedical subjects

Jayakrishna Ambati

Publications and source records attributed to Jayakrishna Ambati.

At least 19 recordsLinked to original sources
PubMed2007

Role of amniotic membrane graft for ocular chemical and thermal injuries.

PURPOSE: To evaluate the results of amniotic membrane transplantation (AMT) for ocular surface reconstruction in chemical and thermal injuries. METHODS: Retrospective review of case records of patients who had undergone AMT for chemical injuries (January 1998 to May 2001). RESULTS: Seventy two eyes of 69 patients were studied of which 24 were acute cases (median-2 days, range, 1-20 days) and 48 were chronic cases (median-12.4 months, range, 1.02-95.8 months). Mean age was 22.4 years (SD +/- 13.34 years) and average follow up duration was 7.8 months (SD +/- 7.1). Main clinical findings were symblephara (52.8%), corneal vascularization (51.3%), conjunctivalization (45.8%), Limbal ischemia (45.8%), Limbal stem cell deficiency (55.5%) and epithelial defect (48.6%). 18 cases were due to acid injuries (5 acute, 13 chronic), 52 were due to alkali (18 acute and 34 chronic) and 2 cases were due to thermal burns (1 each acute and chronic). Overall success rate was 87.5% in acute cases and 72.9% in chronic cases. Indication-wise success rates were 94.3% for epithelial defect healing, 88.2% for symptomatic relief, 59.7% for ocular surface reconstruction, and 55% for improving limbal stem cell function. Success was not achieved in any outcome measure in 1/24 (4.2%) in acute group and 6/48 (12.5%) in chronic group. CONCLUSION: AMT helps in ocular surface reconstruction, promotes rapid epithelial healing and partially restores limbal stem cell function. It can be considered as an effective modality for the ocular surface restoration in chemical and thermal injuries in selected cases. Success rates in acute and chronic cases are comparable.

Acute Disease↗
PubMed2006

Corneal avascularity is due to soluble VEGF receptor-1.

Corneal avascularity-the absence of blood vessels in the cornea-is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders. But the molecular underpinnings of the avascular phenotype have until now remained obscure and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice and Pax6+/- patients with aniridia are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.

Animals↗
PubMed2006

CCR2 mediates increases in glial activation caused by exposure to HIV-1 Tat and opiates.

To assess the role of CCL2/MCP-1 in opiate drug abuse and HIV-1 comorbidity, the effects of systemic morphine and intrastriatal HIV-1 Tat on macrophage/microglial and astroglial activation were assessed in wild type and CCR2 null mice. Tat and/or morphine additively increased the proportion of CCL2 immunoreactive astroglia. The effects of morphine were prevented by naltrexone. Glial activation was significantly reduced in CCR2-/- versus wild-type mice following Tat or morphine plus Tat exposure. Thus, CCR2 contributes to local glial activation caused by Tat alone or in the presence of opiates, implicating CCR2 signaling in HIV-1 neuropathogenesis in drug abusers and non-abusers.

AIDS Dementia Complex↗
PubMed2006

Drusen complement components C3a and C5a promote choroidal neovascularization.

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in industrialized nations, affecting 30-50 million people worldwide. The earliest clinical hallmark of AMD is the presence of drusen, extracellular deposits that accumulate beneath the retinal pigmented epithelium. Although drusen nearly always precede and increase the risk of choroidal neovascularization (CNV), the late vision-threatening stage of AMD, it is unknown whether drusen contribute to the development of CNV. Both in patients with AMD and in a recently described mouse model of AMD, early subretinal pigmented epithelium deposition of complement components C3 and C5 occurs, suggesting a contributing role for these inflammatory proteins in the development of AMD. Here we provide evidence that bioactive fragments of these complement components (C3a and C5a) are present in drusen of patients with AMD, and that C3a and C5a induce VEGF expression in vitro and in vivo. Further, we demonstrate that C3a and C5a are generated early in the course of laser-induced CNV, an accelerated model of neovascular AMD driven by VEGF and recruitment of leukocytes into the choroid. We also show that genetic ablation of receptors for C3a or C5a reduces VEGF expression, leukocyte recruitment, and CNV formation after laser injury, and that antibody-mediated neutralization of C3a or C5a or pharmacological blockade of their receptors also reduces CNV. Collectively, these findings establish a mechanistic basis for the clinical observation that drusen predispose to CNV, revealing a role for immunological phenomena in angiogenesis and providing therapeutic targets for AMD.

Aged, 80 and over↗
PubMed2006

HIV-1 Tat and opiate-induced changes in astrocytes promote chemotaxis of microglia through the expression of MCP-1 and alternative chemokines.

Opiates exacerbate human immunodeficiency virus type 1 (HIV-1) Tat(1-72)-induced release of key proinflammatory cytokines by astrocytes, which may accelerate HIV neuropathogenesis in opiate abusers. The release of monocyte chemoattractant protein-1 (MCP-1, also known as CCL2), in particular, is potentiated by opiate-HIV Tat interactions in vitro. Although MCP-1 draws monocytes/macrophages to sites of CNS infection, and activated monocytes/microglia release factors that can damage bystander neurons, the role of MCP-1 in neuro-acquired immunodeficiency syndrome (neuroAIDS) progression in opiate abusers, or nonabusers, is uncertain. Using a chemotaxis assay, N9 microglial cell migration was found to be significantly greater in conditioned medium from mouse striatal astrocytes exposed to morphine and/or Tat(1-72) than in vehicle-, mu-opioid receptor (MOR) antagonist-, or inactive, mutant Tat(delta31-61)-treated controls. Conditioned medium from astrocytes treated with morphine and Tat caused the greatest increase in motility. The response was attenuated using conditioned medium immunoneutralized with MCP-1 antibodies, or medium from MCP-1(-/-) astrocytes. In the presence of morphine (time-release, subcutaneous implant), intrastriatal Tat increased the proportion of neural cells that were astroglia and F4/80+ macrophages at 7 days post-injection. This was not seen after treatment with Tat alone, or with morphine plus inactive Tat(delta31-61) or naltrexone. Glia displayed increased MOR and MCP-1 immunoreactivity after morphine and/or Tat exposure. The findings indicate that MCP-1 underlies most of the response of microglia, suggesting that one way in which opiates exacerbate neuroAIDS is by increasing astroglial-derived proinflammatory chemokines at focal sites of CNS infection and promoting macrophage entry and local microglial activation. Importantly, increased glial expression of MOR can trigger an opiate-driven amplification/positive feedback of MCP-1 production and inflammation.

Animals↗
PubMed2006

Loss of SPARC-mediated VEGFR-1 suppression after injury reveals a novel antiangiogenic activity of VEGF-A.

VEGF-A promotes angiogenesis in many tissues. Here we report that choroidal neovascularization (CNV) incited by injury was increased by excess VEGF-A before injury but was suppressed by VEGF-A after injury. This unorthodox antiangiogenic effect was mediated via VEGFR-1 activation and VEGFR-2 deactivation, the latter via Src homology domain 2-containing (SH2-containing) tyrosine phosphatase-1 (SHP-1). The VEGFR-1-specific ligand placental growth factor-1 (PlGF-1), but not VEGF-E, which selectively binds VEGFR-2, mimicked these responses. Excess VEGF-A increased CNV before injury because VEGFR-1 activation was silenced by secreted protein, acidic and rich in cysteine (SPARC). The transient decline of SPARC after injury revealed a temporal window in which VEGF-A signaling was routed principally through VEGFR-1. These observations indicate that therapeutic design of VEGF-A inhibition should include consideration of the level and activity of SPARC.

Angiogenesis Inhibitors↗
PubMed2005

Systemic soluble Tie2 expression inhibits and regresses corneal neovascularization.

This study was designed to determine if soluble Tie2 (sTie2) expression inhibits and regresses corneal neovascularization, and if VEGF contributes to its effect. The corneas of BALB/c mice were scraped and the mice were injected with either an adenovirus expressing soluble Tie2 (Ad.sTie2) or an empty adenoviral vector. When injected at the inhibition timepoint (one day prior to corneal injury), the mean percentage of neovascularized corneal area two weeks later in Ad.sTie2-treated mice vs. controls was 56.37+/-9.15% vs. 85.79+/-3.55% (p=0.04). At the regression timepoint (4 weeks after corneal scrape), the mean area of corneal neovascularization in Ad.sTie2-treated mice was 42.89+/-4.74% vs. 75.01+/-3.22% in the control group (p=0.007). VEGF expression was significantly higher in Ad.sTie2-treated mice at the inhibition timepoint and there was no significant difference at the regression timepoint. These findings suggest that sTie2 inhibits and regresses corneal neovascularization in a VEGF-independent manner.

Adenoviridae↗
PubMed2005

Eyelid disease.

Explore the source record for details and available documents.

Corneal Diseases↗
PubMed2005

Flt-1 intraceptors inhibit hypoxia-induced VEGF expression in vitro and corneal neovascularization in vivo.

PURPOSE: To determine whether subunits of VEGF receptor-1 coupled with an endoplasmic reticulum retention signal can block hypoxia-induced upregulation of VEGF secretion in corneal epithelial cells and block murine corneal angiogenesis induced by corneal injury. METHODS: Human corneal epithelial cells, transfected with plasmids encoding Flt23K or Flt24K (the VEGF-binding domains of the Flt-1 receptor coupled with the endoplasmic reticulum retention peptide KDEL), were subjected 2 days after transfection to 5% hypoxia for 24 hours. Supernatant was sampled at 24 hours and assayed for VEGF by ELISA. For in vivo models, mouse corneas underwent intrastromal injections of plasmids encoding Flt23K or Flt24K, and 2 days later, sustained injury induced by topical NaOH and mechanical scraping. Corneas were assessed 2 days later for VEGF ELISA and leukocyte counting or 1 week later for quantification of neovascularization. RESULTS: Hypoxia induced VEGF by human corneal epithelial cells was sequestered by both Flt23K and Flt24K; Flt-1 23K suppressed VEGF secretion as well. Intrastromal delivery of plasmid Flt23K suppressed VEGF by 40.4% (P = 0.009), leukocytes by 49.4% (P < 0.001), and neovascularization by 66.8% (P = 0.001). Flt24K suppressed VEGF expression by 30.8% (P = 0.042), leukocytes by 25.8% (P < 0.001), and neovascularization by 49.5% (P = 0.015). CONCLUSIONS: Flt-1 intraceptors, which are endoplasmic reticulum retention signal-coupled VEGF receptors, significantly suppress hypoxia-induced VEGF secretion by corneal epithelial cells in vitro. In vivo, delivery of naked plasmids expressing these intraceptors inhibits injury-induced upregulation of VEGF, leukocyte infiltration, and corneal neovascularization.

Animals↗
PubMed2004

Aquaporin-1 expression is decreased in human and mouse corneal endothelial dysfunction.

PURPOSE: To determine if aquaporin-1 expression is decreased in human and mouse corneal endothelial dysfunction. METHODS: Immunohistochemistry with anti-aquaporin 1 antibody and confocal microscopy were used to study a case series of human corneal specimens, and a mouse model of corneal endothelial injury was created with injection of sterile hot water into the anterior chamber with a 33 gauge needle. Western blotting of mouse and human corneas was used to provide confirmatory evidence. RESULTS: Aquaporin-1 was found to be expressed in normal human cornea and decreased in human corneas with endothelial disease but not in human corneas with non-endothelial corneal disease. Aquaporin-1 was also found to be reduced in mouse corneas subjected to corneal endothelial injury. Both results were confirmed by western blot analysis. CONCLUSIONS: Corneal endothelial injury is associated with decreased aquaporin-1 expression.

Animals↗
PubMed2003

An animal model of age-related macular degeneration in senescent Ccl-2- or Ccr-2-deficient mice.

The study and treatment of age-related macular degeneration (AMD), a leading cause of blindness, has been hampered by a lack of animal models. Here we report that mice deficient either in monocyte chemoattractant protein-1 (Ccl-2; also known as MCP-1) or its cognate C-C chemokine receptor-2 (Ccr-2) develop cardinal features of AMD, including accumulation of lipofuscin in and drusen beneath the retinal pigmented epithelium (RPE), photoreceptor atrophy and choroidal neovascularization (CNV). Complement and IgG deposition in RPE and choroid accompanies senescence in this model, as in human AMD. RPE or choroidal endothelial production of Ccl-2 induced by complement C5a and IgG may mediate choroidal macrophage infiltration into aged wild-type choroids. Wild-type choroidal macrophages degrade C5 and IgG in eye sections of Ccl2(-/-) or Ccr2(-/-) mice. Impaired macrophage recruitment may allow accumulation of C5a and IgG, which induces vascular endothelial growth factor (VEGF) production by RPE, possibly mediating development of CNV. These models implicate macrophage dysfunction in AMD pathogenesis and may be useful as a platform for validating therapies.

Aging↗
PubMed2003

VEGF164-mediated inflammation is required for pathological, but not physiological, ischemia-induced retinal neovascularization.

Hypoxia-induced VEGF governs both physiological retinal vascular development and pathological retinal neovascularization. In the current paper, the mechanisms of physiological and pathological neovascularization are compared and contrasted. During pathological neovascularization, both the absolute and relative expression levels for VEGF164 increased to a greater degree than during physiological neovascularization. Furthermore, extensive leukocyte adhesion was observed at the leading edge of pathological, but not physiological, neovascularization. When a VEGF164-specific neutralizing aptamer was administered, it potently suppressed the leukocyte adhesion and pathological neovascularization, whereas it had little or no effect on physiological neovascularization. In parallel experiments, genetically altered VEGF164-deficient (VEGF120/188) mice exhibited no difference in physiological neovascularization when compared with wild-type (VEGF+/+) controls. In contrast, administration of a VEGFR-1/Fc fusion protein, which blocks all VEGF isoforms, led to significant suppression of both pathological and physiological neovascularization. In addition, the targeted inactivation of monocyte lineage cells with clodronate-liposomes led to the suppression of pathological neovascularization. Conversely, the blockade of T lymphocyte-mediated immune responses with an anti-CD2 antibody exacerbated pathological neovascularization. These data highlight important molecular and cellular differences between physiological and pathological retinal neovascularization. During pathological neovascularization, VEGF164 selectively induces inflammation and cellular immunity. These processes provide positive and negative angiogenic regulation, respectively. Together, new therapeutic approaches for selectively targeting pathological, but not physiological, retinal neovascularization are outlined.

Animals↗
PubMed2003

Inhibition of corneal neovascularization by genetic ablation of CCR2.

PURPOSE: To determine if genetic ablation of the chemokine receptor CCR2 (involved in leukocyte and endothelial chemotaxis) inhibits the development of corneal neovascularization. METHODS: Wild-type C57BL/6J mice, as well as species-specific counterparts with targeted homozygous disruption of the CCR2, underwent chemical and mechanical denudation of corneal and limbal epithelium. Corneas were harvested 2 weeks after injury. Neovascularization was quantified by CD31 immunostaining. RESULTS: The mean percentages of neovascularized corneal area in control mice and CCR2-deficient mice 2 weeks after denudation were 58.3% and 38.8% (P = 0.047), respectively. CONCLUSIONS: Development of corneal neovascularization is inhibited in CCR2-deficient mice.

Animals↗
PubMed2003

Sustained inhibition of corneal neovascularization by genetic ablation of CCR5.

PURPOSE: To determine whether genetic ablation of the CC chemokine receptor CCR5 (involved in leukocyte and endothelial chemotaxis) inhibits the development of corneal neovascularization. METHODS: Wild-type C57BL/6J mice and species-specific counterparts with targeted homozygous disruption of the CCR5 gene underwent chemical and mechanical denudation of corneal and limbal epithelium. Corneas were harvested 2 and 4 weeks after injury. Neovascularization was quantified by CD31 immunostaining. Expression of VEGF protein was quantified by ELISA. RESULTS: The mean percentages of neovascularized corneal area in control mice and CCR5-deficient mice 2 weeks after denudation were 58.3% and 38.5% (P = 0.05), respectively. At 4 weeks after denudation, the corresponding percentages were 67.6% and 44.0% (P = 0.028). In CCR5-deficient mice, VEGF protein levels were reduced 51.1% at 2 weeks (P = 0.05) after injury and 37.3% at 4 weeks (P = 0.03). CONCLUSIONS: CCR5-deficient mice showed a persistent 34% to 35% inhibition of corneal neovascularization for up to 4 weeks. This inhibition correlates with reduced expression of VEGF. These data implicate CCR5 as one essential component in the development of corneal neovascularization.

Animals↗
PubMed2003

Targeted disruption of the CD18 or ICAM-1 gene inhibits choroidal neovascularization.

PURPOSE: To investigate the role of the leukocyte adhesion molecules CD18 and intercellular adhesion molecule (ICAM)-1 in the development of choroidal neovascularization (CNV). METHODS: Laser photocoagulation was used to induce CNV in wild-type C57BL/6J mice and species-specific counterparts with targeted homozygous disruption of the CD18 or ICAM-1 gene. Expression of CD18 and ICAM-1 after laser injury was assessed by immunostaining. CNV responses were compared on the basis of en masse volumetric measurements obtained by confocal microscopy 2 weeks after laser injury and by determination of fluorescein angiographic leakage at 1, 2, and 4 weeks after laser injury. RESULTS: The site of laser injury showed upregulation of ICAM-1 and invasion by CD18-positive leukocytes within 1 day of laser injury. Significantly fewer lesions exhibited fluorescein leakage defined to be pathologically significant in CD18-deficient mice at weeks 1, 2, and 4 weeks and in ICAM-1-deficient mice at 1 and 4 weeks, compared with the control. There were a significantly greater number of lesions without fluorescein leakage in CD18-deficient mice than in the other two groups at all time points. The volume of CNV in CD18- and ICAM-1-deficient mice was significantly less than in wild type. CONCLUSIONS: These data suggest a nonredundant role for leukocyte adhesion to vascular endothelium in the development of laser-induced choroidal neovascularization.

Animals↗
PubMed2003

Macrophage depletion inhibits experimental choroidal neovascularization.

OBJECTIVE: To investigate the role of macrophages in the development of laser-induced choroidal neovascularization (CNV) by selective depletion with liposomal clodronate (Cl(2)MDP-LIP). METHODS: Laser photocoagulation was used to induce CNV in wild-type C57BL/6J mice. Animals were treated with intravenous (IV) and/or subconjunctival (SC) Cl(2)MDP-LIP or PBS-LIP at the following time points: 2 days before, immediately after, 2 days before and immediately after, or 2 days after laser injury. CNV responses were compared on the basis of en masse volumetric measurements and fluorescein angiography after laser photocoagulation. Macrophages were identified by immunostaining for F4/80, and vascular endothelial growth factor (VEGF) expression was quantified by ELISA. RESULTS: Macrophages invaded the site of laser injury within 1 day of photocoagulation and peaked at 3 days. IV Cl(2)MDP-LIP significantly decreased the volume of CNV and angiographic leakage when administered 2 days before and/or immediately after laser injury, but not when administered 2 days after injury. SC Cl(2)MDP-LIP significantly decreased lesion volume when coadministered with IV PBS-LIP but not IV Cl(2)MDP-LIP. IV Cl(2)MDP-LIP was significantly more beneficial when administered 2 days before laser injury than immediately after, but combining SC Cl(2)MDP-LIP with IV treatment eliminated this difference. Reduction in CNV volume correlated with VEGF protein levels and number of infiltrating macrophages. CONCLUSIONS: Generalized macrophage depletion reduced the size and leakage of laser-induced CNV and was associated with decreased macrophage infiltration and VEGF protein. These findings define the role of the macrophage as a critical component in initiating the laser-induced CNV response.

Animals↗
PubMed2002

Angiostatin inhibits and regresses corneal neovascularization.

OBJECTIVE: To determine the ability of angiostatin and the angiostatin-producing low-metastatic (LM) clone of Lewis lung carcinoma (LLC) to inhibit and regress corneal neovascularization, as compared with the non-angiostatin-producing high-metastatic (HM) clone. METHODS: Three groups of C57BL6/J mice underwent chemical and mechanical denudation of corneal and limbal epithelium. One group remained tumor free while the other 2 were implanted with LLC cells (either the HM or LM clones) subcutaneously the day before, 2 weeks after, or 4 weeks after denudation. Corneas were harvested 2 weeks after tumor implantation (at 2, 4, and 6 weeks after denudation for tumor-free mice). Neovascularization was quantified by CD31 immunostaining. In a second experiment, recombinant angiostatin was delivered continuously for 2 weeks via an osmotic pump in mice with established corneal neovascularization. RESULTS: The mean percentages of neovascularized corneal area in mice 2 weeks after LM-LLC implantation were 4.6%, 3.7%, and 37.0%, at 2, 4, and 6 weeks after scraping, respectively. In contrast, in the mice implanted with HM-LLC, the corresponding values were 45.4% (P =.01), 90.1% (P =.03), and 80.3% (P =.005). For tumor-free mice, the corresponding values were 62.0% (P =.003), 68.9% (P =.03), and 59.3% (P =.06). Mice implanted with angiostatin pumps had a 37.7% neovascularized corneal area 2 weeks after implantation and 4 weeks after scraping while mice implanted with sham pumps had 60.5% (P =.007). CONCLUSION: Angiostatin inhibits and regresses corneal neovascularization induced by mechanical and alkali corneal injury. CLINICAL RELEVANCE: This appears to be the first evidence of biologically induced regression of corneal neovascularization, and the first direct demonstration of angiostatin-induced regression of neovascularization in any tissue.

Angiogenesis Inhibitors↗