Pathogenesis of retinopathy of prematurity

Platelet-Derived Growth Factor Subunit A Strengthens the Neurovascular Unit and Inhibits Retinal Vascular Regression Under Hyperoxic Conditions

Retinopathy of prematurity (ROP) is primarily caused by the exposure of preterm infants with underdeveloped blood vessels to high oxygen concentrations. This damages the astrocytes that promote normal vascular development, leading to avascularity, pathological neovascularization, and retinal detachment, and even blindness as the disease progresses. In this study, the aim was to investigate the differences in the characteristics of astrocytes and blood vessels between wild-type (WT) and genetically modified mice overexpressing platelet-derived growth factor subunit A (PDGF-A) in the retina immediately after high oxygen exposure, a protocol in the oxygen-induced retinopathy (OIR) model of ROP. Our results showed that PDGF-A mice exhibited an increased population of astrocytes and higher vascular density than WT mice and that PDGF-A strengthened the resistance to hyperoxic conditions. In the OIR model, PDGF-A mice had reduced avascular zone areas following hyperoxia exposure. Furthermore, immunostaining for NG2 and CD31 showed that pericytes tended to regress earlier than endothelial cells, particularly at the vessel edges in both WT and transgenic mice, indicating relatively higher susceptibility to hyperoxia-induced damage. These findings suggest that PDGF-A plays a crucial role in stabilizing retinal vessels and may serve as a novel therapeutic target for ROP, highlighting the potential significance of PDGF-A in the pathological mechanisms of retinal diseases.

Angiogenic signaling pathways and anti-angiogenic therapy for cancer

Angiogenesis, the formation of new blood vessels, is a complex and dynamic process regulated by various pro- and anti-angiogenic molecules, which plays a crucial role in tumor growth, invasion, and metastasis. With the advances in molecular and cellular biology, various biomolecules such as growth factors, chemokines, and adhesion factors involved in tumor angiogenesis has gradually been elucidated. Targeted therapeutic research based on these molecules has driven anti-angiogenic treatment to become a promising strategy in anti-tumor therapy. The most widely used anti-angiogenic agents include monoclonal antibodies and tyrosine kinase inhibitors (TKIs) targeting vascular endothelial growth factor (VEGF) pathway. However, the clinical benefit of this modality has still been limited due to several defects such as adverse events, acquired drug resistance, tumor recurrence, and lack of validated biomarkers, which impel further research on mechanisms of tumor angiogenesis, the development of multiple drugs and the combination therapy to figure out how to improve the therapeutic efficacy. Here, we broadly summarize various signaling pathways in tumor angiogenesis and discuss the development and current challenges of anti-angiogenic therapy. We also propose several new promising approaches to improve anti-angiogenic efficacy and provide a perspective for the development and research of anti-angiogenic therapy.

Lowly expressed LNC01136 fails to aid HIF-1α to induce BTG2 expression resulting in increased proliferation of retinal microvascular endothelial cells

BACKGROUND

Retinal neovascularization (RN), a major cause of blindness occurring in multiple types of ophthalmic diseases, is closely associated with hypoxic conditions. However, the underlying pathological mechanisms of RN have not been fully elucidated. BTG2 is anti-proliferative factor. The up-stream of BTG2 gene within 3000 bp expresses a long non-coding RNA, LNC01136.

METHODS

we initially compared the expression of BTG2 and LNC01136 in human retinal microvascular endothelial cells (hRMECs) with other eye-associated cells, including Muller cells, ARPE19 cells and RGC-5, in response to a hypoxia mimetic agent (CoCl₂). FISH and PCR tests were performed to determine the enrichment of LNC01136 in different cellular components. LNC01136 were overexpressed or knockdown to determine the effect on BTG2 expression. Finally, ChIP, RIP and Co-IP assays were performed to determine the interaction among BTG2, HIF-1α, LNC01136 and CNOT7.

RESULTS

After the treatment with CoCl₂, expression levels of BTG2 and LNC01136 were strongly induced in Muller cells, ARPE19 cells and RGC-5, but weakly in hRMECs. LNC01136 is prominently located in cell nucleus and aids HIF-1α to enhance transcription of BTG2, which consequently inhibits cell growth. The anti-proliferative effect of BTG2 is probably associated to the interaction with CNOT7 and the regulation of multiple cell cycle-related proteins.

CONCLUSIONS

This study revealed that LNC01136 is a cell growth suppressor by recruiting HIF-1α to induce BTG2 expression. However the low expression of LNC01136 in hRMECs compared to other eye-associated cells promoted hRMECs' proliferation, which is probably a cause of RN under hypoxia.

Low-dose ranibizumab administration in retinopathy of prematurity

PURPOSE

To evaluate the efficiency of low-dose intravitreal ranibizumab therapy in the treatment of aggressive retinopathy of prematurity (A-ROP).

METHODS

A total of 124 eyes of 62 patients who underwent intravitreal ranibizumab after an A-ROP diagnosis between January 2015 and January 2021 were evaluated retrospectively. After receiving family-approved informed consent, low-dose intravitreal ranibizumab was administered, and regular follow-ups were performed.

RESULTS

Patients included in the study had a mean birth week of 26.6 (23-33 weeks), a mean birth weight of 905 (450-1970) grams, and an average injection postnatal time of 9.1 (4-19) weeks. The mean follow-up period was 63 (24-250) weeks. In all eyes, ROP regressed in the first week after injection, and no asymmetrical response was observed in the eyes of any baby. A total of 58 eyes recovered with a single dose of intravitreal injection therapy, and peripheral retinal vascularization was completed. A second injection was required in 38 eyes. Rescue treatment was applied in addition to intravitreal ranibizumab treatment in 22 eyes of 11 babies. None of the patients had any ocular or systemic side effects.

CONCLUSION

Low-dose intravitreal ranibizumab injection with close follow-up and appropriate timing is an effective treatment modality in A-ROP. Even among patients undergoing rescue laser treatment, the treatment can be completed with a wide visual field.

Newly Identified Peptide, Peptide Lv, Promotes Pathological Angiogenesis

Background We recently discovered a small endogenous peptide, peptide Lv, with the ability to activate vascular endothelial growth factor receptor 2 and its downstream signaling. As vascular endothelial growth factor through vascular endothelial growth factor receptor 2 contributes to normal development, vasodilation, angiogenesis, and pathogenesis of various diseases, we investigated the role of peptide Lv in vasodilation and developmental and pathological angiogenesis in this study. Methods and Results The endothelial cell proliferation, migration, and 3-dimensional sprouting assays were used to test the abilities of peptide Lv in angiogenesis in vitro. The chick chorioallantoic membranes and early postnatal mice were used to examine its impact on developmental angiogenesis. The oxygen-induced retinopathy and laser-induced choroidal neovascularization mouse models were used for in vivo pathological angiogenesis. The isolated porcine retinal and coronary arterioles were used for vasodilation assays. Peptide Lv elicited angiogenesis in vitro and in vivo. Peptide Lv and vascular endothelial growth factor acted synergistically in promoting endothelial cell proliferation. Peptide Lv-elicited vasodilation was not completely dependent on nitric oxide, indicating that peptide Lv had vascular endothelial growth factor receptor 2/nitric oxide-independent targets. An antibody against peptide Lv, anti-Lv, dampened vascular endothelial growth factor-elicited endothelial proliferation and laser-induced vascular leakage and choroidal neovascularization. While the pathological angiogenesis in mouse eyes with oxygen-induced retinopathy was enhanced by exogenous peptide Lv, anti-Lv dampened this process. Furthermore, deletion of peptide Lv in mice significantly decreased pathological neovascularization compared with their wild-type littermates. Conclusions These results demonstrate that peptide Lv plays a significant role in pathological angiogenesis but may be less critical during development. Peptide Lv is involved in pathological angiogenesis through vascular endothelial growth factor receptor 2-dependent and -independent pathways. As anti-Lv dampened the pathological angiogenesis in the eye, anti-Lv may have a therapeutic potential to treat pathological angiogenesis.

Systemic Rho-kinase inhibition using fasudil in mice with oxygen-induced retinopathy

PURPOSE

To investigate the influence of the selective Rho-kinase (ROCK) inhibitor, fasudil, on the mRNA level of proinflammatory factors and the retinal vascular development in mice with oxygen-induced retinopathy (OIR).

METHODS

C57BL/6J mice underwent standard protocol for OIR induction from postnatal days 7 to 12. Subsequently, they received a daily intraperitoneal injection of fasudil or sodium chloride from P12 to P16. Analyses were performed using vascular staining on retinal flat mounts, RNA expression by qPCR, and immunohistochemistry on paraffin sections.

RESULTS

On retinal flat mounts, the proportion of avascular area and tuft formation did not differ between the fasudil and NaCl group. Immunohistochemical staining revealed a less intense staining with inflammatory markers after fasudil. Nevertheless, there were no differences on RNA level between the two groups.

CONCLUSIONS

In conclusion, our findings support that daily systemic application of fasudil does not decrease retinal neovascularization in rodents with oxygen-induced retinopathy. The results of our study together with the controversial results on the effects of different ROCK inhibitors from the literature makes it apparent that effects of ROCK inhibition are more complex, and further studies are necessary to analyze its potential therapeutic effects.

The Role of Melanin to Dissociate Oxygen from Water to Treat Retinopathy of Prematurity

BACKGROUND

Retinopathy of Prematurity (ROP) is a potentially blinding disorder that commonly afflicts premature infants who are born prior to 31weeks of gestation or with a body weight less than 1250 grams (about 2.75 pounds). Another risk factor is excessive oxygen in incubators, which can lead to blindness. A compounding factor is that survival rates for premature infants are rising with concomitantly more cases of ROP. We have reported an unsuspected intrinsic property of melanin to dissociate water. This capability can be considered an alternative treatment option for adult and neonatal diseases. It is known that exogenous surfactant administration suppresses bronchopulmonary dysplasia and consequent death, randomized, controlled trials with various respiratory interventions did not show any significant reductions in morbidity and mortality rates. During a descriptive study about the three leading causes of blindness in the world, the ability of melanin to transform light energy into chemical energy through the dissociation of water molecule was unraveled. Initially, during 2 or 3 years; we tried to link together our findings with the widely accepted metabolic pathways already described in molecular pathway databases, which have been developed to collect and organize the current knowledge on metabolism scattered across a multitude of scientific evidence.

OBSERVATIONS

The current report demonstrates the main problems that afflict premature babies with an emphasis on the growth of abnormal vessels in the retina, the explanation for which is unknown until date. We also reported a case of a baby who suffered digestive and respiratory problems with a brain haemorrhage that was successfully treated by laser photocoagulation. We hypothesise that most likely this effect was due to the melanin level and melanin itself produces oxygen via dissociating with water molecules.

CONCLUSION

We postulate that the intrinsic effect of melanin may easily convert visible and invisible light into chemical energy via a water dissociation reaction similar to the one in plant's chlorophyll, and markedly elevated with diagnosis and treatment of the complications related to premature babies.

Metabolomics Applicable to Retinal Vascular Diseases

Metabolomics refers to the systematic identification and quantification of the small molecule metabolites (the metabolome) of a biological system in a given space (cell, tissue, organ, biological fluid, or organism) and time. Global metabolic profiling provides broad range of coverage for most of the analytes present in any tissue. Human retina is metabolically highly active, and retinal vascular diseases such as age-related macular degeneration (AMD), diabetic retinopathy (DR), retinal vein occlusion (RVO), central retinal artery occlusion, and retinopathy of prematurity (ROP) are often associated with the disruptions in metabolic activities. A systematic study of total retinal metabolites from human diseased retina is a major challenge owing to the nonavailability of tissue specimens. Therefore, vitreous humor being very proximal to retina could be used as surrogate for retinal metabolomic analysis. As the extraction method adopted for such analysis determines the type of metabolites, two different types of solvent (methanol and chloroform)-based extraction methods could be used for retinal vascular patient samples (vitreous humor). Metabolites obtained from both the extraction methods are then subjected to LC-MS/MS for detection and identification.

Low-dose ranibizumab as primary treatment of posterior type I retinopathy of prematurity

OBJECTIVE

The aim of this study was to evaluate the visual and structural outcomes of eyes that received ranibizumab as treatment for retinopathy of prematurity (ROP).

METHODS

This was a retrospective case series of infants who received a 0.2 mg (0.02 mL) intravitreal injection of ranibizumab as the primary treatment for type 1 ROP. Outcome measures included regression or recurrence of ROP, complications of treatment, and assessment of visual acuity and refractive error.

RESULTS

Forty-two eyes of 21 infants (13 male) were included. Mean gestational age and birth weight were 24.6 ± 1.3 weeks and 613 ± 91 g, respectively. Mean age at injection was 37.4 ± 2.2 weeks postmenstrual age, and mean follow-up period was 10.1 ± 7 months. Active neovascularization regressed rapidly, and anatomical outcomes were favourable in all eyes. Twelve eyes of 6 infants received supplemental laser photocoagulation at a mean post-menstrual age (PMA) of 72.0 ± 27.3 weeks when vascularization had not advanced beyond zone II. Visual acuity was measurable in 28 of 42 eyes. Mean visual acuity was 0.94 ± 0.36 logMAR. Mean spherical equivalent was +1.00. There were no ocular or systemic complications in these patients and no cicatricial complications were observed with no progression to stage 4 or 5 disease.

CONCLUSIONS

A single intravitreal dose of 0.2 mg (0.02 mL) ranibizumab showed favourable anatomical and functional outcomes in eyes with type 1 ROP.

Omega-3 fatty acids in prevention of diabetic retinopathy

OBJECTIVES

To review the competence of Omega-3 fatty acids in restricting the progression, thereby leading to prevention of diabetic retinopathy.

KEY FINDINGS

Owing to their anti-inflammatory and anti-angiogenic properties, Omega-3 fatty acids alleviate major aetiological agents. These fatty acids are renowned for their beneficial effects in various cardiovascular and other disorders; however, their potential to prevent the progression of diabetic retinopathy remains least explored.

SUMMARY

Utilizing this potential, we may develop effective prophylactic agents which markedly inhibit the advent of retinal angiogenesis and prevent the apoptosis of retinal endothelial and neuronal cells, thereby averting retinal degeneration, hence safeguarding diabetic patients from this sight-threatening complication.

Intravitreal anti-VEGF treatment for retinopathy of prematurity in infants with active adenoviral keratoconjunctivitis

PURPOSE

To evaluate the results of intravitreal anti-vascular endothelial growth factor (anti-VEGF) treatment for retinopathy of prematurity (ROP) in infants with active adenoviral keratoconjunctivitis (AKC).

MATERIAL AND METHODS

A retrospective analysis was performed using the medical records of all infants treated with intravitreal injections of anti-VEGF agents during an AKC outbreak previously reported in the literature at a tertiary center for treatment of ROP. The infants were divided into two groups. Group 1 included nine infants (18 eyes) with AKC, while Group 2 included 13 infants (26 eyes) without AKC.

RESULTS

During the AKC outbreak, 22 infants were treated with anti-VEGF agents for treatment-requiring ROP. In all patients in both groups, the ROP and plus disease displayed a significant regression within 2 days after the intravitreal injections. Moreover, no serious complications such as endophthalmitis, retinal detachment, cataract or intravitreal hemorrhage were observed after the treatment and there were no statistically significant differences between the groups in terms of postoperative complications.

CONCLUSION

Immediate and appropriate intervention is very important in cases of treatment-requiring ROP otherwise it can result in blindness. However, laser treatment for ROP is technically difficult in infants with active AKC. The results of this study showed that favorable outcomes without serious ocular complications could be obtained via intravitreal injections of anti-VEGF agents in infants with active AKC.

7,8-DHF Treatment Induces Cyr61 Expression to Suppress Hypoxia Induced ER Stress in HK-2 Cells

Acute kidney injury (AKI) is a common syndrome which is strongly linked to high morbidity and mortality. Hypoxia is the leading cause of AKI and the proximal renal tubular cells are the most damaged part in the kidney during this period. It has been observed that 7,8-dihydroxyflavone (7,8-DHF) plays a protective role by acting on antiapoptosis and antioxidative stress. In this study we explored functions of 7,8-DHF in protecting human proximal tubular cell line HK-2 from hypoxia insults. We observed that treatment of 7,8-DHF could improve the viability of ischemic cell. Mechanistically, we found that 7,8-DHF could elevate the expression of cysteine-rich protein 61 (Cyr61), a protective immediate early gene in AKI. In addition, treatment of 7,8-DHF decreased CCAAT/enhancer-binding protein homologous protein (CHOP) expression, which is a marker protein during endoplasmic reticulum (ER) stress activation. Intriguingly, overexpression of Cyr61 significantly reduced CHOP expression. Taken together, our results provide novel insights into the possible protective role of 7,8-DHF by activating Cyr61 signaling and suppressing ER stress in hypoxic HK-2 cells which have potential clinical implications for the treatment of AKI.

IGF-1 in retinopathy of prematurity, a CNS neurovascular disease

The retina is part of the central nervous system and both the retina as well as the brain can suffer from severe damage after very preterm birth. Retinopathy of prematurity is one of the major causes of blindness in these children and brain neuronal impairments including cognitive defects, cerebral palsy and intraventricular hemorrhage (IVH) are also complications of very preterm birth. Insulin-like growth factor 1 (IGF-1) acts to promote proliferation, maturation, growth and survival of neural cells. Low levels of circulating IGF-1 are associated with ROP and defects in the IGF-1 gene are associated with CNS disorders including learning deficits and brain growth restriction. Treatment of preterm infants with recombinant IGF-1 may potentially prevent ROP and CNS disorders. This review compares the role of IGF-1 in ROP and CNS disorders. A recent phase 2 study showed a positive effect of IGF-1 on the severity of IVH but no effect on ROP. A phase 3 trial is planned.

Efficacy of intravitreal bevacizumab for zone-II retinopathy of prematurity

PURPOSE

To assess the effect of intravitreal bevacizumab for Type 1 retinopathy of prematurity (ROP) in zone II ROP.

METHODS

We conducted a randomized clinical trial. Preterm infants with a gestational age less than 34 weeks or birthweight less than 2000 g were examined at 4 weeks chronological age or 31 weeks postmenstrual age (whichever was later). Preterm infants with Zone-II/Stage 2 or 3 and plus disease were included. Eligible infants were randomized to receive either conventional indirect laser therapy or intravitreal bevacizumab injections (0.625 mg/0.025 ml). The primary outcome was defined as treatment failure: ROP persistence or recurrence by 90 weeks postmenstrual age.

RESULTS

Our study population comprised 79 infants (158 eyes) with Zone-II ROP. Randomly, 43 infants (86 eyes) were assigned to receive intravitreal bevacizumab and 36 infants (72 eyes) to receive conventional indirect laser therapy. All the infants were followed up at least until 90 weeks postmenstrual age. Stage-3 ROP recurred in nine eyes (10.5%) in the bevacizumab group and one eye (1.4%) in the laser group (p value = 0.018). In recurrent cases after the second treatment, ROP in eight of the nine eyes (88.8%) in the bevacizumab group and the eye in the laser group regressed.

CONCLUSION

Recurrence of neovascularization with bevacizumab monotherapy seems to be higher than that with conventional laser therapy among infants with Type 1 ROP in zone II ROP but reinjection of bevacizumab causes regression in most recurrent cases.

Retinopathy of prematurity: the need for prevention

More than 450,000 babies are born prematurely in the USA every year. The improved survival of even the most vulnerable low body weight preterm infants has, despite improving health outcomes, led to the resurgence in preterm complications including one of the major causes for blindness in children, retinopathy of prematurity (ROP). The current mainstay in ROP therapy is laser photocoagulation and the injection of vascular endothelial growth factor (VEGF) antibodies in the late stages of the disease after the onset of neovascularization. Both are proven options for ophthalmologists to treat the severe forms of late ROP. However, laser photocoagulation destroys major parts of the retina, and the injection of VEGF antibodies, although rather simple to administer, may cause a systemic suppression of normal vascularization, which has not been studied in sufficient depth. However, the use of neither VEGF antibody nor laser treatment prevents ROP, which should be the long-term goal. It should be possible to prevent ROP by more closely mimicking the intrauterine environment after preterm birth. Such preventive measures include preventing the toxic postbirth influences (eg, oxygen excess) as well as providing the missing intrauterine factors (eg, insulin growth factor 1) and are likely to also reduce other complications of premature birth as well as ROP. This review is meant to summarize the current knowledge on the prevention of ROP with a particular emphasize on the use of insulin growth factor 1 supplementation.

Slit-miR-218-Robo axis regulates retinal neovascularization

miR-218 is an important intronic microRNA (miRNA or miR) which is known to regulate angiogenesis in tumors. The present study aimed to investigate the effects of miR-218, as well as its host genes, Slit2 and Slit3, on oxygen-induced retinal neovascularization (RNV) and to explore the associated mechanisms of action. For this purpose, a mouse model of oxygen-induced retinopathy (OIR) was established. The expression levels of miR-218-1 and miR-218-2, as well as those of their host genes, Slit2 and Slit3, were determined by RT-qPCR. Fluorescein angiography was performed on the retinas of the mice with OIR, and RNV was quantified by H&E staining in order to evaluate the effect of pCDH-CMV-miR-218 intravitreal injection on RNV in the mouse model of OIR. Roundabout, axon guidance receptor, homolog 1 (Robo1) expression was detected in mouse retinal vascular endothelial cells expressing high or low levels of miR-218 and in retinal tissues from mice with OIR by western blot analysis. Cell migration was evaluated by a scratch wound assay. We noted that in the mice with OIR, the expression level of miR-218 was significantly downregulated. We also noted that Robo1 expression was suppressed by miR-218. Furthermore, in the mice with OIR, the expression level of miR-218 was significantly downregulated, and that of miR-218-1 and its host gene, Slit2, was concomitantly downregulated as well. The restoration of miR-218 inhibited retinal angiogenesis by targeting Robo1. Taken together, our findings suggest that the Slit2-miR-218-Robo1 axis contributes to the inhibition of retinal angiogenesis and that miR-218 may be a new therapeutic target for preventing RNV.

Intravitreal ranibizumab as a primary or a combined treatment for severe retinopathy of prematurity

PURPOSE

The aim of the study was to assess the outcomes of severe retinopathy of prematurity (ROP) in zone I or posterior zone II treated with intravitreal ranibizumab (IVR) as monotherapy or combined treatment with laser photocoagulation.

METHODS

This is a retrospective study analyzing clinical records of the included patients. Patients were divided into two groups: group 1 included patients who received only IVR treatment; and group 2 was subdivided into group 2A - including patients with IVR as initial treatment and complementary laser photocoagulation if retinal neovascularization or plus disease did not regress, and group 2B - including patients with initial laser photocoagulation and IVR as rescue therapy. Favorable outcomes were regression of the retinal neovascularization and plus disease, meaning control of the disease. Unfavorable outcomes were progression to stages 4 and 5 of ROP.

RESULTS

Fifty-seven eyes were included in the study. Mean birth weight and gestational age were 1,281±254 g and 29.5±2.1 weeks, respectively. Group 1 comprised of 16 eyes, with favorable outcomes in 14 eyes (87.5%). Group 2 comprised of 41 eyes, with favorable outcomes in 29 eyes (70.7%), in a mean follow-up period of 12.8 months.

CONCLUSION

IVR was effective to treat severe cases of ROP as a primary or a combined treatment. Forty-three of the 57 treated eyes (75.4%) achieved regression of ROP and favorable outcomes.

CCN1/Cyr61-PI3K/AKT signaling promotes retinal neovascularization in oxygen-induced retinopathy

Retinal neovascularization (RNV) is a characteristic pathological finding of retinopathy of prematurity (ROP). Cysteine-rich 61 [Cyr61, also known as CCN family member 1 (CCN1)] has been reported to mediate angiogenesis. The aim of the present study was to investigate the mechanisms of CCN1/Cyr61-phosphoinositide 3-kinase (PI3K)/AKT signaling in ROP. The contribution of CCN1 to human umbilical vein endothelial cell (HUVEC) proliferation and apoptosis under hypoxic conditions was determined using a cell counting kit-8 (CCK-8) and Annexin V/propidium iodide (PI) staining, respectively, as well as using siRNA targeting CCN1 (CCN1 siRNA). The cells exposed to hypoxia were also treated with the PI3K/AKT inhibitor, LY294002. In addition, mouse pups with oxygen-induced retinopathy (OIR) were administered an intravitreal injection of CCN1 siRNA. RNV was assessed by magnesium-activated adenosine diphosphatease (ADPase) staining. RT-qPCR, western blot analysis, immunofluorescence staining and immunohistochemistry were used to detect the distribution and expression of CCN1, PI3K and AKT. Exposure to hypoxia increased the neovascularization clock hour scores (from 1.23±0.49 to 5.60±0.73, P<0.05) and the number of preretinal neovascular cells, as well as the mRNA and protein expression levels of CCN1, PI3K and AKT (all P<0.05). The injection of CCN1 siRNA decreased the neovascularization clock hour scores and the number of preretinal neovascular cells (1.53±0.72 vs. 4.76±1.04; 12.0±2.8 vs. 31.4±2.6, respectively, both P<0.05), as well as the mRNA and protein expression levels of CCN1, PI3K and AKT (protein, −45.3, −22.5 and −28.4%; mRNA, −43.7, −58.7 and −42.9%, respectively, all P<0.05) compared to the administration of scrambled siRNA under hypoxic conditions. Treatment with LY294002 decreased the mRNA and protein expression levels of CCN1 in the cells exposed to hypoxia (both P<0.05). The administration of CCN1 siRNA resulted in less severe neovascularization in the eyes of the the mouse pups with OIR. Thus, out data suggest that CCN1 plays an important role in RNV in ROP, and may thus be a potential target for the prevention and treatment of ROP.

Polymorphisms of Vascular Endothelial Growth Factor and Retinopathy of Prematurity

PURPOSE

Retinopathy of prematurity (ROP) is a major problem among preterm survivors of neonatal intensive care. Neovascularization of the retina is prominent in the proliferative stages of ROP and is under the control of factors such as vascular endothelial growth factor (VEGF). The authors investigated the association of ROP with VEGF genetic polymorphisms and clinical (maternal, perinatal, neonatal) risk factors among preterm infants admitted to the neonatal intensive care unit.

METHODS

The frequencies of VEGF 634 C/G and VEGF 936 C/T polymorphisms were determined in DNA from 102 preterm infants by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique.

RESULTS

The frequency of the VEGF 634 CG genotype was significantly higher, whereas the frequency of the VEGF 634 CC genotype was significantly lower among neonates with ROP. The frequencies of the VEGF 634 GG, VEGF 936 CC, and VEGF 936 CT genotypes were similar in both groups. The distribution of VEGF 634 G allele was significantly different between the two groups. By logistic regression analysis, low birth weight, presence of maternal disease, respiratory distress syndrome, hypotension, and VEGF 634 CG genotype remained significant risk factors for the development of ROP.

CONCLUSIONS

The results support the hypothesis that the carrier state of VEGF 634 C/G polymorphism has an impact on the risk of ROP in infants. A broader study may suggest that this marker could be used as an indicator in the screening for ROP.

Hypoxia-induced retinal neovascularization in zebrafish embryos: a potential model of retinopathy of prematurity

Retinopathy of prematurity, formerly known as a retrolental fibroplasia, is a leading cause of infantile blindness worldwide. Retinopathy of prematurity is caused by the failure of central retinal vessels to reach the retinal periphery, creating a nonperfused peripheral retina, resulting in retinal hypoxia, neovascularization, vitreous hemorrhage, vitreoretinal fibrosis, and loss of vision. We established a potential retinopathy of prematurity model by using a green fluorescent vascular endothelium zebrafish transgenic line treated with cobalt chloride (a hypoxia-inducing agent), followed by GS4012 (a vascular endothelial growth factor inducer) at 24 hours postfertilization, and observed that the number of vascular branches and sprouts significantly increased in the central retinal vascular trunks 2-4 days after treatment. We created an angiography method by using tetramethylrhodamine dextran, which exhibited severe vascular leakage through the vessel wall into the surrounding retinal tissues. The quantification of mRNA extracted from the heads of the larvae by using real-time quantitative polymerase chain reaction revealed a twofold increase in vegfaa and vegfr2 expression compared with the control group, indicating increased vascular endothelial growth factor signaling in the hypoxic condition. In addition, we demonstrated that the hypoxic insult could be effectively rescued by several antivascular endothelial growth factor agents such as SU5416, bevacizumab, and ranibizumab. In conclusion, we provide a simple, highly reproducible, and clinically relevant retinopathy of prematurity model based on zebrafish embryos; this model may serve as a useful platform for clarifying the mechanisms of human retinopathy of prematurity and its progression.

Evaluation of anti-HIF and anti-angiogenic properties of honokiol for the treatment of ocular neovascular diseases

Pathological activation of the hypoxia-inducible-factor (HIF) pathway leading to expression of pro-angiogenic genes, such as vascular endothelial growth factor (VEGF), is the fundamental cause of neovascularization in ocular ischemic diseases and cancers. We have shown that pure honokiol inhibits the HIF pathway and hypoxia-mediated expression of pro-angiogenic genes in a number of cancer and retinal pigment epithelial (RPE) cell lines. The crude extracts, containing honokiol, from Magnolia plants have been used for thousands of years in the traditional oriental medicine for a number of health benefits. We have recently demonstrated that daily intraperitoneal injection of honokiol starting at postnatal day (P) 12 in an oxygen induced retinopathy mouse model significantly reduced retinal neovascularization at P17. Here, we evaluate the mechanism of HIF inhibition by honokiol in RPE cells. Using chromatin immunoprecipitation experiments, we demonstrate that honokiol inhibits binding of HIF to hypoxia-response elements present on VEGF promoter. We further show using a number of in vitro angiogenesis assays that, in addition to anti-HIF effect, honokiol manifests potent anti-angiogenic effect on human retinal micro vascular endothelial cells. Our results suggest that honokiol possesses potent anti-HIF and anti-angiogenic properties. These properties of honokiol make it an ideal therapeutic agent for the treatment of ocular neovascular diseases and solid tumors.

Natural product inhibitors of ocular angiogenesis

Natural products are characterized by high chemical diversity and biochemical specificity; therefore, they are appealing as lead compounds for drug discovery. Given the importance of angiogenesis to many pathologies, numerous natural products have been explored as potential anti-angiogenic drugs. Ocular angiogenesis underlies blinding eye diseases such as retinopathy of prematurity (ROP) in children, proliferative diabetic retinopathy (DR) in adults of working age, and age-related macular degeneration (AMD) in the elderly. Despite the presence of effective therapy in many cases, these diseases are still a significant health burden. Anti-VEGF biologics are the standard of care, but may cause ocular or systemic side effects after intraocular administration and patients may be refractory. Many anti-angiogenic compounds inhibit tumor growth and metastasis alone or in combination therapy, but a more select subset of them has been tested in the context of ocular neovascular diseases. Here, we review the promise of natural products as anti-angiogenic agents, with a specific focus on retinal and choroidal neovascularization. The multifunctional curcumin and the chalcone isoliquiritigenin have demonstrated promising anti-angiogenic effects in mouse models of DR and choroidal neovascularization (CNV) respectively. The homoisoflavanone cremastranone and the flavonoid deguelin have been shown to inhibit ocular neovascularization in more than one disease model. The isoflavone genistein and the flavone apigenin on the other hand are showing potential in the prevention of retinal and choroidal angiogenesis with long-term administration. Many other products with anti-angiogenic potential in vitro such as the lactone withaferin A, the flavonol quercetin, and the stilbenoid combretastatin A4 are awaiting investigation in different ocular disease-relevant animal models. These natural products may serve as lead compounds for the design of more specific, efficacious, and affordable drugs with minimal side effects.

Activation of the endothelin system mediates pathological angiogenesis during ischemic retinopathy

Retinopathy of prematurity adversely affects premature infants because of oxygen-induced damage of the immature retinal vasculature, resulting in pathological neovascularization (NV). Our pilot studies using the mouse model of oxygen-induced retinopathy (OIR) showed marked increases in angiogenic mediators, including endothelins and endothelin receptor (EDNR) A. We hypothesized that activation of the endothelin system via EDNRA plays a causal role in pathological angiogenesis and up-regulation of angiogenic mediators, including vascular endothelial growth factor A (VEGFA) in OIR. Mice were exposed to 75% oxygen from post-natal day P7 to P12, treated with either vehicle or EDNRA antagonist BQ-123 or EDNRB antagonist BQ-788 on P12, and kept at room air from P12 to P17 (ischemic phase). RT-PCR analysis revealed increased levels of EDN2 and EDNRA mRNA, and Western blot analysis revealed increased EDN2 expression during the ischemic phase. EDNRA inhibition significantly increased vessel sprouting, resulting in enhanced physiological angiogenesis and decreased pathological NV, whereas EDNRB inhibition modestly improved vascular repair. OIR triggered significant increases in VEGFA protein and mRNA for delta-like ligand 4, apelin, angiopoietin-2, and monocyte chemoattractant protein-1. BQ-123 treatment significantly reduced these alterations. EDN2 expression was localized to retinal glia and pathological NV tufts of the OIR retinas. EDN2 also induced VEGFA protein expression in cultured astrocytes. In conclusion, inhibition of the EDNRA during OIR suppresses pathological NV and promotes physiological angiogenesis.

Sildenafil attenuates vaso-obliteration and neovascularization in a mouse model of retinopathy of prematurity

PURPOSE

We sought to determine the effect of sildenafil on retinal vascular changes in a mouse model of oxygen-induced retinopathy (OIR).

METHODS

Vascular defects in OIR mice were quantified by measuring vaso-obliteration at postnatal days 12 and 17 (P12 and P17) and neovascularization at P17 to compare sildenafil-treated to dextrose-treated OIR mice. Retinal HIF1α protein expression was quantified by Western blotting and normalized to that of β-actin. Right ventricular hypertrophy was measured by Fulton's index as a surrogate for hyperoxia-induced pulmonary hypertension.

RESULTS

At P12, OIR mice treated with sildenafil demonstrated a 24% reduction in vaso-obliteration (P < 0.05), whereas at P17, treated animals showed a 50% reduction in neovascularization (P < 0.05) compared to dextrose-treated controls. Sildenafil-treated OIR mice had stabilization of retinal HIF1α at P12, immediately after hyperoxia. At P17, sildenafil-treated OIR mice had decreased HIF1α relative to untreated mice. OIR mice developed right ventricle hypertrophy that was significant compared to that in room air controls, which was abrogated by sildenafil.

CONCLUSIONS

Sildenafil treatment significantly decreased retinal vaso-obliteration and neovascularization in a mouse OIR model. These effects are likely due to sildenafil-induced HIF1α stabilization during hyperoxia exposure. Furthermore, we confirm disease overlap by showing that OIR mice also develop hyperoxia-induced right ventricular hypertrophy, which is prevented by sildenafil. This study is a first step toward delineating a potential therapeutic role for sildenafil in OIR and further suggests that there may be common pathophysiologic mechanisms underlying hyperoxia-induced retinal and pulmonary vascular disease.

Oxygen-induced retinopathy induces short-term glial stress and long-term impairment of photoentrainment in mice

BACKGROUND

Retinopathy of prematurity is a serious potentially blinding disease of pre-term infants. There is extensive vascular remodeling and tissue stress, but data concerning alterations in retinal neurons and glia, and long-term functional sequelae are still incomplete.

METHODS

ROP was induced using the oxygen-induced retinopathy (OIR) mouse model. Postnatal day 7 (P7) 129SVE mice were exposed to hyperoxia (75 ± 0.5 % oxygen) for 5 days, and then returned to normoxia to induce OIR. Exposed animals were euthanized at 5 (P17-OIR) and 14 days (P26-OIR) after return to normal air, together with corresponding age-matched control mice (P17-C and P26-C respectively) raised only in room air. Their retinas were examined by immunohistochemistry using a battery of antibodies against key glial and neuronal proteins. A further group of OIR mice and controls were examined at 10 weeks of age for their ability to re-entrain to changing 12 h light/12 h dark cycles, assayed by wheel-running actimetry. In this protocol, animals were subjected to three successive conditions of 300 lux, 15 lux and 1 lux ambient light intensity coupled with 6 hours of jetlag. Animals were euthanized at 4 months of age and used in immunoblotting for rhodopsin.

RESULTS

Compared to P17-C, immunohistochemical staining of P17-OIR sections showed up-regulation of stress-related and glutamate-regulatory proteins in astrocytes and Müller glial cells. In contrast, glial phenotypic expression in P26-OIR retinas largely resembled that in P26-C. There was no loss in total retinal ganglion cells (RGC) at either P17-OIR or P26-OIR compared to corresponding controls, whereas intrinsically photosensitive RGC showed significant decreases, with 375 ± 13/field in P26-OIR compared to 443 ± 30/field in P26-C (p < 0.05). Wheel actimetry performed on control and OIR-treated mice at 4 months demonstrated that animals raised in hyperoxic conditions had impaired photoentrainment at low illuminance of 1 lux, as well as significantly reduced levels of rhodopsin compared to age-matched controls.

CONCLUSIONS

OIR leads to transient up-regulation of retinal glial proteins involved in metabolism, and partial degeneration of intrinsically photosensitive RGC and rod photoreceptors. OIR affects circadian photo-entrainment at low illuminance values, possibly by affecting the rod pathway and/or intrinsically photosensitive RGC input to the circadian clock. This study hence shows that retinopathy of prematurity affects light-regulated circadian behavior in an animal model, and may induce similar problems in humans.

Inhibition of oxygen-induced ischemic retinal neovascularization with adenoviral 15-lipoxygenase-1 gene transfer via up-regulation of PPAR-γ and down-regulation of VEGFR-2 expression

15-lipoxygenase-1 (15-LOX-1) plays an important role in angiogenesis, but how it works still remains a controversial subject. The aims of our study are focused on determining whether or not 15-LOX-1 inhibiting oxygen-induced ischemic retinal neovascularization (RNV) and the underlying regulatory mechanism involving of 15-LOX-1, peroxisome proliferator-activated receptor γ (PPAR-γ) and vascular endothelial growth factor receptor 2 (VEGFR-2) in oxygen-induced retinopathy (OIR). Recombinant adenoviral vectors that expressing the 15-LOX-1 gene (Ad-15-LOX-1-GFP) or the green fluorescence protein gene (Ad-GFP) were intravitreous injected into the OIR mice at postnatal day 12 (P12), the mice were sacrificed 5 days later (P17). Retinal 15-LOX-1 expression was significantly increased at both mRNA and protein levels after 15-LOX-1 gene transfer. Immunofluorescence staining of retinal sections revealed 15-LOX-1 expression was primarily in the outer plexiform layer (OPL), inner nuclear layer (INL) and ganglion cell layer (GCL) retina. Meanwhile, RNV was significantly inhibited indicated by fluorescein retinal angiography and quantification of the pre-retinal neovascular cells. The expression levels of PPAR-γ were significantly up-regulated while VEGFR-2 were significantly down-regulated both in mRNA and protein levels. Our results suggested 15-LOX-1 gene transfer inhibited RNV in OIR mouse model via up-regulation of PPAR-γ and further down-regulation of VEGFR-2 expression. This could be a potentially important regulatory mechanism involving 15-LOX-1, PPAR-γ and VEGFR-2 during RNV in OIR. In conclusion, 15-LOX-1 may be a new therapeutic target for treating neovascularization diseases.

Temporal quantification of oxygen saturation ranges: an effort to reduce hyperoxia in the neonatal intensive care unit

OBJECTIVE

To reduce exposure to hyperoxia and its associated morbidities in preterm neonates.

STUDY DESIGN

A multidisciplinary group was established to evaluate oxygen exposure in our neonatal intensive care unit. Infants were assigned target saturation ranges and signal extraction technology implemented to temporally quantify achievement of these ranges. The outcomes bronchopulmonary dysplasia/death, retinopathy of prematurity (ROP)/death, severe ROP and ROP requiring surgery were compared in a pre- versus post-intervention evaluation using multivariate analyses.

RESULT

A total of 304 very low birth weight pre-initiative infants were compared with 396 post-initiative infants. Multivariate analyses revealed decreased odds of severe ROP (adjusted odds ratio (OR): 0.41; 95% confidence interval (CI): 0.24-0.72) and ROP requiring surgery (adjusted OR 0.31; 95% CI: 0.17-0.59) post-initiative. No differences in death were observed.

CONCLUSION

Significant reductions in severe ROP and ROP requiring surgery were observed after staff education and implementation of new technology to quantify success in achieving targeted saturations and reinforce principles and practices.

Antiangiogenic and antineuroinflammatory effects of kallistatin through interactions with the canonical Wnt pathway

Kallistatin is a member of the serine proteinase inhibitor superfamily. Kallistatin levels have been shown to be decreased in the vitreous while increased in the circulation of patients with diabetic retinopathy (DR). Overactivation of the Wnt pathway is known to play pathogenic roles in DR. To investigate the role of kallistatin in DR and in Wnt pathway activation, we generated kallistatin transgenic (kallistatin-TG) mice overexpressing kallistatin in multiple tissues including the retina. In the oxygen-induced retinopathy (OIR) model, kallistatin overexpression attenuated ischemia-induced retinal neovascularization. In diabetic kallistatin-TG mice, kallistatin overexpression ameliorated retinal vascular leakage, leukostasis, and overexpression of vascular endothelial growth factor and intracellular adhesion molecule. Furthermore, kallistatin overexpression also suppressed Wnt pathway activation in the retinas of the OIR and diabetic models. In diabetic Wnt reporter (BAT-gal) mice, kallistatin overexpression suppressed retinal Wnt reporter activity. In cultured retinal cells, kallistatin blocked Wnt pathway activation induced by high glucose and by Wnt ligand. Coprecipitation and ligand-binding assays both showed that kallistatin binds to a Wnt coreceptor LRP6 with high affinity (Kd = 4.5 nmol/L). These observations suggest that kallistatin is an endogenous antagonist of LRP6 and inhibitor of Wnt signaling. The blockade of Wnt signaling may represent a mechanism for its antiangiogenic and antineuroinflammatory effects.

Retinopathy of Prematurity: A Study of Incidence and Risk Factors in NICU of Al-Minya University Hospital in Egypt

Background:

Retinopathy of prematurity (ROP) is a serious complication of prematurity treatment and can lead to blindness unless recognized and treated early.

Objective:

To estimate the incidence of ROP in preterm infants in our NICU, to identify the risk factors which predispose to ROP, and to assess the outcome of these cases.

Materials and Methods:

ROP prospective screening survey was performed enrolling all prematures admitted to the NICU from January 2009 to December 2010, with a gestational age of 32 weeks or less at birth and a birth weight of 1500 g or less. Infants whom gestational age was >32 weeks or birth weight was >1500 g were included if they exposed to oxygen therapy for more than 7 days. Also infants who were born between 32 and 34 weeks gestational age were examined if they had a course of instability (like sepsis, asphyxia or ventilation). A total of 172 infants (88 females) had retinal evaluation by indirect ophthalmoscopy from the 4^th postnatal week and followed up periodically. Perinatal risk factors for ROP were assessed using univariate and multivariate analysis. Infants who progressed to stage 3 ROP with plus disease were given laser therapy.

Results:

Out of the studied 172 infants, 33 infants (19.2%) developed ROP in one or both eyes; 18 (54.5%) cases stage 1, 9 (27.3%) cases stage 2 and 6 (18.2%) cases stage 3 with plus disease. None of the studied neonates presented ROP at stages 4 or 5. The six cases diagnosed as ROP stage 3 with plus disease underwent laser ablative therapy. Laser was effective in treatment and decreasing the progression of ROP. Univariate analysis showed that there was a significant relationship between the occurrence of ROP and gestational age (P=0.000), sepsis (P=0.004), oxygen therapy (P=0.018), and frequency of blood transfusions (P=0.030). However, nonsignificant relationship was found between the occurrence of ROP and sex, mode of delivery, birth weight, respiratory distress syndrome, patent ductus arteriosus, intraventricular hemorrhage, hypotension, phototherapy, duration of oxygen therapy, mechanical ventilation, and CPAP (all P>0.05). Gestational age, sepsis, oxygen therapy and frequency of blood transfusions remained significant variables after logistic regression analysis.

Conclusion:

The incidence of ROP in this study was 19.2%; low gestational age, sepsis, oxygen therapy and frequent blood transfusions were significant risk factors for ROP. Laser was effective in treatment and decreasing the progression of ROP. As this is a unit-based study, a comprehensive countrywide survey on ROP in Egypt is recommended to determine any regional differences in disease incidence.

AMD-associated genes encoding stress-activated MAPK pathway constituents are identified by interval-based enrichment analysis

Purpose

To determine whether common DNA sequence variants within groups of genes encoding elements of stress-activated mitogen-activated protein kinase (MAPK) signaling pathways are, in aggregate, associated with advanced AMD (AAMD).

Methods

We used meta-regression and exact testing methods to identify AAMD-associated SNPs in 1177 people with AAMD and 1024 AMD-free elderly peers from 3 large-scale genotyping projects on the molecular genetics of AMD. SNPs spanning independent AAMD-associated genomic intervals were examined with a multi-locus-testing method (INRICH) for enrichment within five sets of genes encoding constituents of stress-activated MAPK signaling cascades.

Results

Four-of-five pathway gene sets showed enrichment with AAMD-associated SNPs; findings persisted after adjustment for multiple testing in two. Strongest enrichment signals (P = 0.006) existed in a c-Jun N-terminal kinase (JNK)/MAPK cascade (Science Signaling, STKE CMP_10827). In this pathway, seven independent AAMD-associated regions were resident in 6 of 25 genes examined. These included sequence variants in: 1) three MAP kinase kinase kinases (MAP3K4, MAP3K5, MAP3K9) that phosphorylate and activate the MAP kinase kinases MAP2K4 and MAP2K7 (molecules that phosphorylate threonine and tyrosine residues within the activation loop of JNK); 2) a target of MAP2K7 (JNK3A1) that activates complexes involved in transcriptional regulation of stress related genes influencing cell proliferation, apoptosis, motility, metabolism and DNA repair; and 3) NR2C2, a transcription factor activated by JNK1A1 (a drugable molecule influencing retinal cell viability in model systems). We also observed AAMD-related sequence variants resident in genes encoding PPP3CA (a drugable molecule that inactivates MAP3K5), and two genes (TGFB2, TGFBR2) encoding factors involved in MAPK sensing of growth factors/cytokines.

Conclusions

Linkage disequilibrium (LD)-independent genomic enrichment analysis yielded associations of AAMD with aggregates of functionally related genes encoding constituents of the JNK MAPK signaling pathway. FDA-approved drugs now exist to target constituents of stress-activated MAPK pathways and may offer reasonable approaches to preventing or treating AAMD.

Genetic polymorphisms of vascular endothelial growth factor and risk for retinopathy of prematurity in South of Iran

Retinopathy of prematurity (ROP) is a multifactorial disease, that cause visual impairment in premature children. The exact pathogenesis and etiology of ROP is unknown and genetic susceptibility is considered as risk factor. Vascular endothelial growth factor (VEGF) plays a major role in retinal neovascularization and subsequently retinal detachment. VEGF polymorphism is associated with proliferative ROP in some studies. We examined the possible association of the VEGF gene polymorphisms with ROP in preterm infants in south of Iran. A total of 111 preterm infants were examined by ophthalmologist and after that were genotyped. Genotyping of the VEGF +405 (rs2010963) and VEGF +936 (rs3025039) was done by the polymerase chain reaction and restriction fragment length polymorphism methods. The frequency of VEGF alleles, genotypes and haplotype distribution were compared between groups. The patients were divided in three groups: 66 to the normal group (normal fundoscopy), and 45 to the ROP group; 30 infants were not treated with Lasertherapy (Regressive group) and 15 treated with Lasertherapy. The frequency of VEGF +405 and VEGF +936 G/C genotypes as well as allele frequencies was not different between groups. No significant difference was found between ROP with treatment and ROP without lasertherapy. Our report indicate that there is no association between the carrier states of gene polymorphisms VEGF +405, VEGF +936 and progression or spontaneous regression of ROP in preterm infants in Iranian population. However, it should be considered that angiogenesis is a complex process and genetic factors in addition to environmental factors are contributed in this pathway.

Retinopathy of prematurity: a study of prevalence and risk factors

Background:

Retinopathy of prematurity (ROP) is a serious complication of prematurity treatment and can lead to blindness unless recognized and treated early.

Objective:

The objective was to estimate the prevalence of ROP in preterm infants in the Neonatal Intensive Care Unit (NICU), to identify the risk factors which predispose to ROP, and to assess the outcome of these cases.

Materials and Methods:

A ROP prospective screening survey was performed enrolling all prematures admitted to the NICU from January 2009 to December 2010, with a gestational age of 32 weeks or less at birth and a birth weight of 1500 g or less. Infants whose gestational age was >32 weeks or birth weight was >1500 g were included if they were exposed to oxygen therapy for more than 7 days. A total of 172 infants (84 males and 88 females) had retinal evaluation by indirect ophthalmoscopy from the fourth postnatal week and followed up periodically. Perinatal risk factors for ROP were assessed using univariate and multivariate analysis. Infants who progressed to stage 3 ROP were given laser therapy.

Results:

Out of the studied 172 infants, 33 infants (19.2%) developed ROP in one or both eyes; 18 (54.5%) cases stage 1, 9 (27.3%) cases stage 2, and 6 (18.2%) cases stage 3. None of the studied neonates presented ROP at stages 4 or 5. The six cases diagnosed as ROP stage 3 underwent laser ablative therapy. Univariate analysis showed that there was a significant relationship between the occurrence of ROP and gestational age (P = 0.000), sepsis (P = 0.004), oxygen therapy (P = 0.018), and frequency of blood transfusions (P = 0.030). However, an insignificant relationship was found between the occurrence of ROP and sex, mode of delivery, birth weight, respiratory distress syndrome, patent ductus arteriosus, intraventricular hemorrhage, hypotension, phototherapy, duration of oxygen therapy, mechanical ventilation, and CPAP (all P > 0.05). Gestational age, sepsis, oxygen therapy, and frequency of blood transfusions remained significant variables after logistic regression analysis.

Conclusion:

The prevalence of ROP in this study was 19.2%; low gestational age, sepsis, oxygen therapy, and frequent blood transfusions were significant risk factors for ROP. Laser was effective in treatment and decreasing the progression of ROP. As this is a unit-based study, a comprehensive countrywide survey on ROP in Egypt is recommended to determine any regional differences in disease prevalence.

Overexpression of pigment epithelium-derived factor inhibits retinal inflammation and neovascularization

Pigment epithelium-derived factor (PEDF) is a serine proteinase inhibitor with antiangiogenic activities. To investigate whether PEDF overexpression has an impact on ocular neovascularization in vivo, we generated PEDF transgenic (PEDF-Tg) mice that ubiquitously express human PEDF driven by the β-actin promoter. The PEDF-Tg mice under normal conditions did not show any abnormalities in retinal histologic findings or visual function. In contrast, PEDF-Tg animals with oxygen-induced retinopathy (OIR) developed significantly less severe retinal neovascularization compared with wild-type (Wt) mice with OIR. In addition, PEDF-Tg mice with OIR had significantly lower vascular leakage in the retina but higher occludin levels than the Wt mice with OIR, suggesting a protective effect on the blood-retinal barrier. Furthermore, retinal levels of proinflammatory factors were significantly lower in PEDF-Tg mice with OIR than in the Wt mice with OIR. In the laser-induced choroidal neovascularization (CNV) model, the CNV area was significantly smaller in the PEDF-Tg mice than in the Wt mice. Also, the laser burn-induced overexpression of proangiogenic and inflammatory factors was observed in the retina and retinal pigment epithelium of Wt mice but not in PEDF-Tg mice. Taken together, these results suggest that overexpression of PEDF inhibits retinal inflammation and neovascularization in both the OIR and laser-induced CNV models. The PEDF-Tg mice provide a useful model for studying the roles of angiogenic inhibitors in neovascular disorders such as diabetic retinopathy.

Lack of association of genetic polymorphisms of angiotensin-converting enzyme gene I/D and glutathione-S-transferase enzyme T1 and M1 with retinopathy of prematures

One of the most frequently observed causes of blindness in infancy is the pathogenesis known as retinopathy of prematurity (ROP). Angiotensin-converting enzyme (ACE) is a vital enzyme in the renin-angiotensin-aldosterone system; it is involved in the development of cardiovascular system diseases linked to I/D polymorphism of the ACE gene. Glutathione-S-transferase enzyme (GST) is one of the most important regulating components of the antioxidant system; there are indications that certain polymorphisms of GST genes (GSTT1, GSTM1), especially the null genotypes, increase the tendency for oxidative stress diseases. We investigated a possible correlation between ACE gene I/D and GSTT1 and GSTM1 gene polymorphisms in 56 prematures suffering from ROP and a control group composed of 48 prematures without ROP in a hospital in Turkey. PCR was used to detect the ACE I/D, GSTT1 and GSTM1 gene polymorphisms. Genotype was determined based on bands formed on agarose gel electrophoresis. We found no significant differences in genotype frequency of the ACE I/D, GSTT1 and GSTM1 genes between normal subjects and patients with ROP. Our results do not support an association of ACE I/D, GSTT1 and GSTM1 gene polymorphisms with risk for ROP.

The mouse retina as an angiogenesis model

The mouse retina has been used extensively over the past decades to study both physiologic and pathologic angiogenesis. Over time, various mouse retina models have evolved into well-characterized and robust tools for in vivo angiogenesis research. This article is a review of the angiogenic development of the mouse retina and a discussion of some of the most widely used vascular disease models. From the multitude of studies performed in the mouse retina, a selection of representative works is discussed in more detail regarding their role in advancing the understanding of both the ocular and general mechanisms of angiogenesis.

Animal models of choroidal and retinal neovascularization

There have been numerous types of animal models of choroidal neovascularization (CNV) and retinal neovascularization (RNV). Understanding the pathobiology of CNV and RNV is important when evaluating and utilizing these models. Both CNV and RNV are dynamic processes. A break or defect in Bruchs' membrane is necessary for CNV to develop. This may be induced with a laser, mechanically via surgery, or in the setting of transgenic mice. Some of the transgenic mouse models spontaneously develop RNV and/or retinal angiomatous proliferation (RAP)-like lesions. The pathogenesis of RNV is well-known and is generally related to ischemic retinopathy. Models of oxygen-induced retinopathy (OIR) closely resemble retinopathy of prematurity (ROP). The streptozotocin (STZ) rat model develops features similar to diabetic retinopathy. This review summarizes general categories and specific examples of animal models of CNV and RNV. There are no perfect models of CNV or RNV and individual investigators are encouraged to choose the model that best suits their needs.

Non-invasive stem cell therapy in a rat model for retinal degeneration and vascular pathology

BACKGROUND

Retinitis pigmentosa (RP) is characterized by progressive night blindness, visual field loss, altered vascular permeability and loss of central vision. Currently there is no effective treatment available except gene replacement therapy has shown promise in a few patients with specific gene defects. There is an urgent need to develop therapies that offer generic neuro-and vascular-protective effects with non-invasive intervention. Here we explored the potential of systemic administration of pluripotent bone marrow-derived mesenchymal stem cells (MSCs) to rescue vision and associated vascular pathology in the Royal College Surgeons (RCS) rat, a well-established animal model for RP.

METHODOLOGY/PRINCIPAL FINDINGS

Animals received syngeneic MSCs (1x10(6) cells) by tail vein at an age before major photoreceptor loss.

PRINCIPAL RESULTS

both rod and cone photoreceptors were preserved (5-6 cells thick) at the time when control animal has a single layer of photoreceptors remained; Visual function was significantly preserved compared with controls as determined by visual acuity and luminance threshold recording from the superior colliculus; The number of pathological vascular complexes (abnormal vessels associated with migrating pigment epithelium cells) and area of vascular leakage that would ordinarily develop were dramatically reduced; Semi-quantitative RT-PCR analysis indicated there was upregulation of growth factors and immunohistochemistry revealed that there was an increase in neurotrophic factors within eyes of animals that received MSCs.

CONCLUSIONS/SIGNIFICANCE

These results underscore the potential application of MSCs in treating retinal degeneration. The advantages of this non-invasive cell-based therapy are: cells are easily isolated and can be expanded in large quantity for autologous graft; hypoimmunogenic nature as allogeneic donors; less controversial in nature than other stem cells; can be readministered with minor discomfort. Therefore, MSCs may prove to be the ideal cell source for auto-cell therapy for retinal degeneration and other ocular vascular diseases.

Maintaining retinal astrocytes normalizes revascularization and prevents vascular pathology associated with oxygen-induced retinopathy

Astrocytes are well known modulators of normal developmental retinal vascularization. However, relatively little is known about the role of glial cells during pathological retinal neovascularization (NV), a leading contributor to vision loss in industrialized nations. We demonstrate that the loss of astrocytes and microglia directly correlates with the development of pathological NV in a mouse model of oxygen-induced retinopathy (OIR). These two distinct glial cell populations were found to have cooperative survival effects in vitro and in vivo. The intravitreal injection of myeloid progenitor cells, astrocytes, or astrocyte-conditioned media rescued endogenous astrocytes from degeneration that normally occurs within the hypoxic, vaso-obliterated retina following return to normoxia. Protection of the retinal astrocytes and microglia was directly correlated with accelerated revascularization of the normal retinal plexuses and reduction of pathological intravitreal NV normally associated with OIR. Using astrocyte-conditioned media, several factors were identified that may contribute to the observed astrocytic protection and subsequent normalization of the retinal vasculature, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Injection of VEGF or bFGF at specific doses rescued the retinas from developing OIR-associated pathology, an effect that was also preceded by protection of endogenous glia from hypoxia-induced degeneration. Together, these data suggest that vascular-associated glia are also required for normalized revascularization of the hypoxic retina. Methods developed to target and protect glial cells may provide a novel strategy by which normalized revascularization can be promoted and the consequences of abnormal NV in retinal vascular diseases can be prevented.

Retinopathy of prematurity

This article briefly reviews the history of ROP followed by a discussion of the pathogenesis of this complex disorder. We describe the International Classification System for ROP and identify risk factors and screening recommendations. Finally, we discuss some of the measures that have been used in an attempt to both prevent and treat ROP.

Retinopathy of prematurity: an eye toward better outcomes

Retinopathy of prematurity (ROP) results from the abnormal growth of blood vessels in the vascular bed supporting the developing retina. Estimated to cause up to 500 new cases of blindness in the U.S. each year, ROP affects primarily infants born at less than 1,500 g. Although its etiology is not well understood, ROP is thought to occur as a result of a complex interaction between oxygen and vascular growth factors. This article briefly reviews the history of ROP, discusses its pathophysiology, and addresses the risk factors and strategies for prevention.

The Relationship of Retinal VEGF and Retinal IGF-1 mRNA with Neovascularization in an Acidosis-Induced Model of Retinopathy of Prematurity

PURPOSE

Acidosis-induced retinopathy (AIR) in the neonatal rat provides an alternative model for retinopathy of prematurity (ROP). We studied the relationship of vascular endothelial growth factor (VEGF) retinal mRNA and insulin-like growth factor-1 (IGF-1) retinal mRNA expression with the emergence of neovascularization (NV) in AIR.

METHODS

Two hundred seventy-five newborn Sprague-Dawley rats were raised in 11 expanded litters of 25. Using our established AIR model, acidosis was induced by twice-daily gavage with NH4Cl from day 2 to day 8 of life (n=175). Rats were sacrificed at days 5, 8, and 10. Nongavaged rats were used as age-matched controls (n=100). Retinae from left eyes were dissected, flatmounts were ADPase-stained, and the presence and severity of NV was scored in a masked manner. Individual right retinae were processed for analysis of retinal VEGF and IGF-1 mRNA using quantitative real-time reverse-transcriptase PCR (qRT-PCR).

RESULTS

Retinal VEGF mRNA was increased 1.4-fold at day 10 in AIR, when compared with age-matched controls (p=0.03). This correlated with maximal NV at day 10 in AIR. Retinal IGF-1 mRNA was decreased to 82% of its normal expression on day 8 (p=0.006), prior to maximal NV, before returning to normal expression at day 10, when compared with nonacidotic controls.

CONCLUSIONS

In AIR, preretinal neovascularization is associated with decreased retinal IGF-1 mRNA prior to maximal NV and increased retinal VEGF mRNA at the time of maximal NV. These growth factor changes in AIR are similar to those seen with hypercarbic oxygen-induced retinopathy. The retinal IGF-1 pathway may provide an alternative target for therapeutic intervention in abnormal retinal angiogenesis.

The photographic screening for retinopathy of prematurity study (photo-ROP). Primary outcomes

PURPOSE

To evaluate the utility of remote digital fundus imaging as compared to indirect ophthalmoscopy to screen for retinopathy of prematurity (ROP).

METHODS

This was a prospective, multicenter, masked clinical trial. Infants <31 weeks gestational age and <1000 g at birth were eligible for enrollment. Eligible enrolled infants were screened for ROP employing serial fundus imaging followed by indirect ophthalmoscopy. The main outcome measures were diagnostic sensitivity, specificity, positive and negative predictive values, and accuracy of image interpretation compared to ophthalmoscopy.

RESULTS

Fifty-one infants (102 eyes) meeting eligibility criteria were enrolled between February 2001 and February 2002. Mean weekly examinations per infant (+/-SD) were 5.73 +/- 3.22 (median 7; range 2-10). For the purposes of this study, the reading center established a definition of ROP seen on digital fundus images deemed sufficiently severe (termed clinically significant ROP, or CSROP) to warrant on-site examination by an ophthalmologist experienced in ROP. CSROP developed in 59 of 102 eyes (57.8%; 31 right eyes and 28 left eyes). Of the eyes with CSROP, 22% (13/59; 7 right eyes and 6 left eyes) progressed to ROP severe enough to require treatment according to the criteria of the Early Treatment for ROP Randomized Trial. Using onsite indirect ophthalmoscopic diagnosis as the reference standard, CSROP was identified by digital images with a sensitivity of 92% (94% right eyes and 89% left eyes) and specificity of 37.21% (40% right eyes and 35% left eyes), and Early Treatment for Retinopathy of Prematurity (ETROP) prethreshold Type I with a sensitivity of 92% (86% right eyes and 100% left eyes) and specificity of 67.39% (67% right eyes and 68% left eyes).

CONCLUSIONS

Remote interpretation of digital fundus images is a useful adjunct to conventional bedside ROP screening by indirect ophthalmoscopy. Diagnostic sensitivity in this study was excellent. It was highly unlikely that severe ROP would be missed when image quality was high. Differences between the two screening approaches in timing of diagnosis of CSROP and ETROP were not statistically significant. Remote digital fundus imaging as deployed in this study is unlikely to supplant bedside ophthalmoscopic examination due to limitations in diagnostic sensitivity, specificity, and accuracy when image quality is poor.