Effect of multiple injections of small divided doses vs single injection of intravitreal bevacizumab on retinal neovascular model in rabbits

Nuclear factor kappa-B signaling is integral to ocular neovascularization in ischemia-independent microenvironment

Retinal ischemia promotes the upregulation of VEGF expression and accounts for most pathological features of retinal neovascularization (NV). Paradoxically, VEGF remains the pivotal stimulator of ocular NV, despite the absence of ischemia. Therefore, the central question arises as to how the various molecular mechanisms interplay in ischemia-independent NV. It's been suggested that NFκB plays a crucial role in the pathogenesis of diabetic vasculopathies. Here, we dissected the molecular mechanism of ocular NV in the rho/VEGF transgenic mouse model, which develops subretinal NV in ischemia-independent microenvironment. Furthermore, we examined whether intravitreal administration of YC-1, a HIF-1 inhibitor, can modulate the activation of NFκB and its downstream angiogenic signaling in the mouse retina. We demonstrated that YC-1 inhibited retinal NFκB/p65 DNA binding activity and downregulated NFκB/p65, FAK, α5β1, EPO, ET-1, and MMP-9 expression at the message and the protein levels. In addition, YC-1 significantly inhibited subretinal NV by reducing the number of neovascular lesions, the area of each lesion and the total area of NV per retina. We further investigated the influence of VEGF signaling pathway on HIF-1α transcriptional activity to substantiate that this mouse model develops subretinal NV in an ischemia-independent microenvironment. Our data demonstrated that VEGF overexpression didn't have any impact on HIF-1α transcriptional activity, whereas treatment with YC-1 significantly inhibited endogenous HIF-1 activity. Our study suggests that retinal NFκB transcriptional activity is pivotal to ischemia-independent mechanisms, which lead to the local activation of angiogenic cascades. Our data also indicate that the nexus between VEGF and NFκB is implicated in triggering the angiogenic cascade that promotes retinal NV. Hence, targeting the VEGF/NFκB axis may act in a negative feedback loop to suppress ocular NV. This study suggests that inhibition of NFκB activation may be a means of turning off a “master switch” responsible for initiating and perpetuating these ocular pathologies.

Pharmacokinetics, pharmacodynamics and pre-clinical characteristics of ophthalmic drugs that bind VEGF

Drugs that prevent the binding of VEGF to its trans-membrane cognate receptors have revolutionized the treatment of the most important chorioretinal vascular disorders: exudative age-related macular degeneration, diabetic macular edema, and retinal vein occlusions. Pegaptanib, which binds to VEGF165 and longer isoforms, ranibizumab and bevacizumab, which bind all VEGF-A isoforms, and aflibercept, which binds VEGF-A, VEGF-B, and placental growth factor, all bind VEGF165 with high affinity. The drugs have relatively long half-lives (7 to 10 days) after intravitreal depot injections and clinical durations of action that usually exceed 4 weeks. Plasma VEGF concentrations decrease after intravitreal injections of bevacizumab and aflibercept because their systemic half-lives are extended by their Fc fragments. Extensive in vitro and in vivo testing shows that the drugs prevent VEGF-mediated activation of endothelial cells while exhibiting little evidence of toxicity. Further anti-VEGF drug development is on-going.

Micro- and nano-fabricated implantable drug-delivery systems

Implantable drug-delivery systems provide new means for achieving therapeutic drug concentrations over entire treatment durations in order to optimize drug action. This article focuses on new drug administration modalities achieved using implantable drug-delivery systems that are enabled by micro- and nano-fabrication technologies, and microfluidics. Recent advances in drug administration technologies are discussed and remaining challenges are highlighted.

MEMS-enabled implantable drug infusion pumps for laboratory animal research, preclinical, and clinical applications

Innovation in implantable drug delivery devices is needed for novel pharmaceutical compounds such as certain biologics, gene therapy, and other small molecules that are not suitable for administration by oral, topical, or intravenous routes. This invasive dosing scheme seeks to directly bypass physiological barriers presented by the human body, release the appropriate drug amount at the site of treatment, and maintain the drug bioavailability for the required duration of administration to achieve drug efficacy. Advances in microtechnologies have led to novel MEMS-enabled implantable drug infusion pumps with unique performance and feature sets. In vivo demonstration of micropumps for laboratory animal research and preclinical studies include acute rapid radiolabeling, short-term delivery of nanomedicine for cancer treatment, and chronic ocular drug dosing. Investigation of MEMS actuators, valves, and other microstructures for on-demand dosing control may enable next generation implantable pumps with high performance within a miniaturized form factor for clinical applications.

Fluorescein angiography, optical coherence tomography, and histopathologic findings in a VEGF(165) animal model of retinal angiogenesis

BACKGROUND

To establish an animal model of retinal neovascularization using vascular endothelial growth factor (VEGF165) and analyze the model using optical coherence tomography (OCT), fluorescein angiography (FA), and histopathologic evaluation.

METHODS

Twelve rabbits were divided into groups as follows: group 1 (n = 3), sham intravitreous injections of 0.1 ml of balanced saline; group 2 (n = 6), one 10-μg intravitreal injection of VEGF165 on day 0; and group 3 (n = 3), two 10-μg intravitreal injections of VEGF165, one on day 0 and one on day 7. Follow-up evaluations (days 0, 3, 7, 14, 21, 28) included obtaining fundus color photographs and FA, OCT, and histopathologic examinations. Eyes were enucleated and stained with hematoxylin and eosin (H&E).

RESULTS

One injection of VEGF (group 2) was associated with dilatation and tortuosity of the retinal blood vessels that developed within 72 h. Retinal neovascularization was present by day 7 and regressed by day 14. However, even on day 28, the capillaries were still tortuous. Two VEGF injections (group 3) caused increased leakage and neovascularization up to day 14; severe capillary nonperfusion was seen during week 4. At the end of the follow-up period, OCT and histopathologic examination of group 3 showed peripapillary tractional retinal detachments. By day 7, the differences between the retinal thickness seen on OCT in groups 2 and 3 and the group 1 control group were significant (p < 0.001). The histologic findings showed increased vessel size in groups 2 and 3 by days 14 and 28 compared with the controls.

CONCLUSIONS

FA, OCT, and histopathologic findings showed that this retinal neovascularization model is efficient, sustainable, and reliable. One injection of VEGF165 created neovascularization that peaked after 1 week; two injections created more intense neovascularization that evolved to retinal detachments after 4 weeks.