Diabetes-induced microvascular complications at the level of the spinal cord: a contributing factor in diabetic neuropathic pain

Neuroprotective Effects of a Hydrogen Sulfide Donor in Streptozotocin-Induced Diabetic Rats

Diabetic neuropathy is an important long-term complication of diabetes. This study explored the hypothesis that hydrogen sulfide (H2S) ameliorates neuropathic pain by controlling antiapoptotic and pro-apoptotic processes. The effects of a slow-releasing H2S donor, GYY4137, on the expression of antiapoptotic and pro-apoptotic genes and proteins, such as B-cell lymphoma 2 (Bcl2) and Bcl-2-like protein 4 (Bax), as well as caspases, cyclooxygenase (COX)-1 and COX-2, monocytes/macrophages, and endothelial cells, in the spinal cord of male Sprague-Dawley rats with streptozotocin-induced peripheral diabetic neuropathy, were investigated using reverse transcription-PCR, western blot and immunohistochemistry. The antihypoalgesic activities of GYY4137 on diabetic rats were evaluated using the tail flick test. Treatment of diabetic rats with GYY4137 attenuated thermal hypoalgesia and prevented both the diabetes-induced increase in Bax mRNA expression (p = 0.0032) and the diabetes-induced decrease in Bcl2 mRNA expression (p = 0.028). The GYY4137-treated diabetic group had increased COX-1 (p = 0.015), decreased COX-2 (p = 0.002), reduced caspase-7 and caspase-9 protein expression (p < 0.05), and lower numbers of endothelial and monocyte/macrophage cells (p < 0.05) compared to the non-treated diabetic group. In summary, the current study demonstrated the protective properties of H2S, which prevented the development of neuropathy related behavior, and suppressed apoptosis activation pathways and inflammation in the spinal cord. H2S-releasing drugs could be considered as possible treatment options of diabetic peripheral neuropathy.

Spinal cord vascular degeneration impairs duloxetine penetration

Introduction

Chronic pain is a prevalent physically debilitating health-related morbidity. Frontline analgesics are inadequate, providing only partial pain relief in only a proportion of the patient cohort. Here, we explore whether alterations in spinal cord vascular perfusion are a factor in reducing the analgesic capability of the noradrenaline reuptake inhibitor, duloxetine.

Method

An established rodent model of spinal cord vascular degeneration was used. Endothelial-specific vascular endothelial growth factor receptor 2 knockout mouse was induced via hydroxytamoxifen administered via intrathecal injection. Duloxetine was administered via intraperitoneal injection, and nociceptive behavioural testing was performed in both WT and VEGFR2KO mice. LC-MS/MS was performed to explore the accumulation of duloxetine in the spinal cord in WT and VEGFR2KO mice.

Results

Spinal cord vascular degeneration leads to heat hypersensitivity and a decline in capillary perfusion. The integrity of noradrenergic projections (dopa - hydroxylase labelled) in the dorsal horn remained unaltered in WT and VEGFR2KO mice. There was an association between dorsal horn blood flow with the abundance of accumulated duloxetine in the spinal cord and analgesic capacity. In VEGFR2KO mice, the abundance of duloxetine in the lumbar spinal cord was reduced and was correlated with reduced anti-nociceptive capability of duloxetine.

Discussion

Here, we show that an impaired vascular network in the spinal cord impairs the anti-nociceptive action of duloxetine. This highlights that the spinal cord vascular network is crucial to maintaining the efficacy of analgesics to provide pain relief.

Catecholaminergic and Cholinergic Systems Mediate Beneficial Effect of Vortioxetine on Diabetes-Induced Neuropathic Pain

The therapeutic potential of vortioxetine on mechanical hyperalgesia/allodynia was investigated in rats with streptozotocin-induced diabetes, and its possible mechanism of action was elucidated in this study. The obtained findings demonstrated that subacute vortioxetine treatment (5 and 10 mg/kg for 2 weeks) increased the reduced paw-withdrawal thresholds of diabetic rats both in the Randall-Selitto and Dynamic plantar tests. Moreover, the falling latencies of animals did not change in the Rota-rod assessments. These results suggest that vortioxetine administration significantly improved diabetes-induced hyperalgesia and allodynia responses in the rats without affecting their motor coordination. The vortioxetine (5 mg/kg)-induced antihyperalgesic and antiallodynic effects were reversed by AMPT, yohimbine, ICI 118,551, sulpiride and atropine pre-treatments, suggesting the involvement of the catecholaminergic system, α₂- and β₂-adrenoceptors, D_2/3 dopaminergic receptors and cholinergic muscarinic receptors in the exhibited pharmacological activity, respectively. Moreover, the data from the immunohistochemical studies indicated that the inhibition of c-Fos overexpression in dorsal horn neurons also mediates the beneficial effect of this drug. Vortioxetine induced no difference in plasma glucose levels in diabetic rats. If clinical studies confirm these findings, the concomitant beneficial effect of vortioxetine on mood disorders and its neutral activity profile on glycemic control may make it an alternative drug for the treatment of neuropathic pain.

Does Diabetes Affect the Surgical Outcomes in Cases With Cervical Ossification of the Posterior Longitudinal Ligament? A Multicenter Study From Asia Pacific Spine Study Group

STUDY DESIGN

Retrospective multicenter study.

OBJECTIVES

To evaluate the surgical outcomes of cervical ossification of the posterior longitudinal ligament (OPLL) in diabetes mellitus (DM) patients.

METHODS

Approximately 253 cervical OPLL patients who underwent surgical decompression with or without fixation were registered at 4 institutions in 3 Asian countries. They were followed up for at least 2 years. Demographics, imaging, and surgical information were collected, and cervical Japanese Orthopaedic Association (JOA) scores and the visual analog scale (VAS) for the neck were used for evaluation.

RESULTS

Forty-seven patients had DM, showing higher hypertension and cardiovascular disease prevalence. Although they presented worse preoperative JOA scores than non-DM patients (10.5 ± 3.1 vs. 11.8 ± 3.2; P = 0.01), the former showed comparable neurologic recovery at the final follow-up (13.9 ± 2.9 vs. 14.2 ± 2.6; P = 0.41). No correlation was noted between the hemoglobin A1c level in the DM group and the pre- and postoperative JOA scores. No significant difference was noted in VAS scores between the groups at pre- and postsurgery. Regarding perioperative complications, DM patients presented a higher C5 palsy frequency (14.9% vs. 5.8%; P = 0.04). A similar trend was observed when surgical procedure was limited to laminoplasty.

CONCLUSIONS

This is the first multicenter Asian study to evaluate the impact of DM on cervical OPLL patients. Surgical results were favorable even in DM cases, regardless of preoperative hemoglobin A1c levels or operative procedures. However, caution is warranted for the occurrence of C5 palsy after surgery.

Mechanism of gene network in the treatment of intracerebral hemorrhage by natural plant drugs in Lutong granules

PURPOSE

To study the effects of Lu-tong Granules (LTG) in ICH etermine the underlying mechanism of molecular network.

METHODS

Modern bioinformatics and network pharmacology methods were used to predict molecular network mechanisms between ICH and LTG. Animal experiments were carried out to verify the effect of LTG for the treatment of ICH, combined with behavior test and morphologic detection.

RESULTS

Forty-three active components in LTG and involved 192 gene targets were identified successfully. Moreoner, they were intersected with 1132 genes of ICH,88 intersection targets were obtained. subsequently, Cytoscape was used to screen Hub genes, in which,6 core molecules, including AKT1, IL6, VEGFA, CASP3, JUN and MMP9 were recognized. Furthermore, we constructed Six core compounds by " disease-drug-active ingredient-target-KEGG " (D-D-A-T-K) network, showed including quercetin, luteolin, β sitosterol, stigmasterol, kaempferol and formononetin, and PPI protein network interaction showed that AKT1:OS3 and CNA2:DKN1A had the highest correlation. Whereas the enrichment of GO and KEGG indicated that LTG was most likely to play a therapeutic role in ICH through AGE-RAGE signaling pathway in diabetic complications. Integrated analysis also showed that the first 10 pathways of KEGG are integrated into 59 genes, among which 6 core genes are closely involved. Lastly, molecular docking showed that there was a good binding activity between the core components and the core genes, and animal experiments confirmed effect of LTG in the treatment of ICH, by using TTC staining and behavior test.

CONCLUSION

LTG are effective for the treatment of ICH, the underlying mechanism could be involved in gene network including anti-inflammatory response, nerve repair, analgesia, anti-epilepsy and other aspects.

Targeting Vascular endothelial growth factor A with soluble vascular endothelial growth factor receptor 1 ameliorates nerve injury-induced neuropathic pain

Neuropathic pain is a distressing medical condition with few effective treatments. The role of Vascular endothelial growth factor A (VEGFA) in inflammation pain has been confirmed in many researches. However, the mechanism of VEGFA affects neuropathic pain remains unclear. In this study, we demonstrated that VEGFA plays an important role in spare nerve injury (SNI)-induced neuropathic pain, which is mediated by enhanced expression and colocalized of VEGFA, p-AKT and TRPV1 in SNI-induced neuropathic pain model. Soluble VEGFR1 (sFlt1) not only relieved mechanical hyperalgesia and the expression of inflammatory markers, but ameliorated the expression of VEGFA, VEGFR2, p-AKT, and TRPV1 in spinal cord. However, these effects of sFlt1 can be blocked by rpVEGFA and by 740 Y-P. Therefore, our study indication that targeting VEGFA with sFlt1 reduces neuropathic pain development via the AKT/TRPV1 pathway in SNI-induced nerve injury. This study elucidates a new therapeutic target for neuropathic pain.

Predictors of reoperation after surgery for spinal epidural abscess

BACKGROUND CONTEXT

Spinal epidural abscess is a rare but severe condition with high rates of postoperative adverse events.

PURPOSE

The objective of the study was to identify independent prognostic factors for reoperation using two datasets: an institutional and national database.

STUDY DESIGN/SETTING

Retrospective Review.

PATIENT SAMPLE

Database 1: Review of five medical centers from 1993 to 2016. Database 2: The National Surgical Quality Improvement Program (NSQIP) was queried between 2012 and 2016.

OUTCOME MEASURES

Thirty-day and ninety-day reoperation rate.

METHODS

Two independent datasets were reviewed to identify patients with spinal epidural abscesses undergoing spinal surgery. Multivariate analyses were used to determine independent prognostic factors for reoperation while including factors identified in bivariate analyses.

RESULTS

Overall, 642 patients underwent surgery for a spinal epidural abscess in the institutional cohort, with a 90-day unplanned reoperation rate of 19.9%. In the NSQIP database, 951 patients were identified with a 30-day unplanned reoperation rate of 12.3%. On multivariate analysis in the NSQIP database, cervical spine abscess was the only factor that reached significance for 30-day reoperation (OR=1.71, 95% CI=1.11-2.63, p=.02, Area under the curve (AUC)=0.61). On multivariate analysis in the institutional cohort, independent prognostic factors for 30-day reoperation were: preoperative urinary incontinence, ventral location of abscess relative to thecal sac, cervical abscess, preoperative wound infection, and leukocytosis (AUC=0.65). Ninety-day reoperation rate also found hypoalbuminemia as a significant predictor (AUC=0.66).

CONCLUSION

Six novel independent prognostic factors were identified for 90-day reoperation after surgery for a spinal epidural abscess. The multivariable analysis fairly predicts reoperation, indicating that there may be additional factors that need to be uncovered in future studies. The risk factors delineated in this study through the use of two large cohorts of spinal epidural abscess patients can be used to improve preoperative risk stratification and patient management.

Hypoxia-induced carbonic anhydrase mediated dorsal horn neuron activation and induction of neuropathic pain

ABSTRACT

Neuropathic pain, such as that seen in diabetes mellitus, results in part from central sensitisation in the dorsal horn. However, the mechanisms responsible for such sensitisation remain unclear. There is evidence that disturbances in the integrity of the spinal vascular network can be causative factors in the development of neuropathic pain. Here we show that reduced blood flow and vascularity of the dorsal horn leads to the onset of neuropathic pain. Using rodent models (type 1 diabetes and an inducible endothelial-specific vascular endothelial growth factor receptor 2 knockout mouse) that result in degeneration of the endothelium in the dorsal horn, we show that spinal cord vasculopathy results in nociceptive behavioural hypersensitivity. This also results in increased hypoxia in dorsal horn neurons, depicted by increased expression of hypoxia markers such as hypoxia inducible factor 1α, glucose transporter 3, and carbonic anhydrase 7. Furthermore, inducing hypoxia through intrathecal delivery of dimethyloxalylglycine leads to the activation of dorsal horn neurons as well as mechanical and thermal hypersensitivity. This shows that hypoxic signalling induced by reduced vascularity results in increased hypersensitivity and pain. Inhibition of carbonic anhydrase activity, through intraperitoneal injection of acetazolamide, inhibited hypoxia-induced pain behaviours. This investigation demonstrates that induction of a hypoxic microenvironment in the dorsal horn, as occurs in diabetes, is an integral process by which neurons are activated to initiate neuropathic pain states. This leads to the conjecture that reversing hypoxia by improving spinal cord microvascular blood flow could reverse or prevent neuropathic pain.

The Effect of Yiqi Huoxue Tongluo Decoction on Spinal Cord Microglia Activation and ASK1-MKK3-p38 Signal Pathway in Rats with Diabetic Neuropathic Pain

Diabetic neuropathic pain (DNP) is one of the most common chronic peripheral neuropathies in diabetes mellitus (DM). Objective. To observe the underlying mechanism of the effects of Yiqi Huoxue Tongluo Decoction (YQHX) on DNP rats. Methods. SD rats were intraperitoneally injected with 35 mg/kg streptozotocin (STZ) to prepare DNP models and were treated with YQHX for 8 weeks. Results. Studies have shown that the drug restores some levels of MWT, TWL, and MNCV, downregulates the levels of inflammatory factors IL-6, IL-1β, and TNF-α, downregulates the levels of ASK1-MKK3-p38, and weakens the level of OX42 activation. Conclusion. Yiqi Huoxue Tongluo Decoction can relieve DNP by affecting the activity of spinal cord microglia and the ASK1-MKK3-p38 signaling pathway, thereby reducing the central sensitization caused by the inflammatory response of DNP rats.

The consequence of endothelial remodelling on the blood spinal cord barrier and nociception

Nociception is a fundamental acute protective mechanism that prevents harm to an organism. Understanding the integral processes that control nociceptive processing are fundamental to our appreciation of which cellular and molecular features underlie this process. There is an extensive understanding of how sensory neurons interpret differing sensory modalities and intensities. However, it is widely appreciated that the sensory neurons do not act alone. These work in harmony with inflammatory and vascular systems to modulate pain perception. The spinal cord has an extensive interaction with the capillary network in the form of a blood spinal cord barrier to ensure homeostatic control of the spinal cord neuron milieu. However, there is an extensive appreciation that disturbances in the blood spinal cord barrier contribute to the onset of chronic pain. Enhanced vascular permeability and impaired blood perfusion have both been highlighted as contributors to chronic pain manifestation. Here, we discuss the evidence that demonstrates alterations in the blood spinal cord barrier influences nociceptive processing and perception of pain.

Spinal cord-wide structural disruption in type 2 diabetes rescued by exenatide "a glucagon-like peptide-1 analogue" via down-regulating inflammatory, oxidative stress and apoptotic signaling pathways

The mechanisms of spinal cord-wide structural and functional disruption in diabetic patients remain elusive. This study evaluated histopathological alterations of the spinal cord cytoarchitecture in T2DM model of rats and assessed the potential ameliorating effect of exenatide "a potent GLP-1 analogue". Thirty male rats were allocated into three groups; I (control), II (Diabetic): T2DM was induced by high fat diet for 8 weeks followed by a single I.P injection of STZ (25 mg/kg BW) and III (Diabetic/Exenatide): T2DM rats injected with exenatide (10 μg/Kg, S.C. twice daily for 2 weeks). Neurobehavioral sensory and motor tests were carried out and glycemic control biomarkers and indices of insulin resistance and sensitivity were measured. In addition, the spinal cord was processed for histological and immunohistochemical studies besides assessing its tissue homogenate levels of pro-inflammatory/anti-inflamatory cytokines and oxidant/antioxidant biomarkers. Moreover, RT-qPCR was performed to measure the expression of proapoptotic/antiapoptotic and neurotrophic genes. The diabetic rats exhibited thermal hyperalgesia, mechanical allodynia and decreased locomotor activity along with increased serum glucose, insulin, HbA1c, HOMA-IR while, quantitative insulin sensitivity check index (QUICKI) was decreased. Also, IL-1β NF-kB, MDA increased while IL-10, SOD activity and β-endorphin decreased in the spinal tissue. Up regulation of caspase-3 and down regulation of Bcl-2, nerve growth factor (NGF) and glial cell-derived neurotrophic (GDNF) in diabetic rats. Also, they exhibited histopathological changes and increased CD68 positive microglia and Bax immunoreactivity in the spinal cord. Subsequent to exenatide treatment, most biomolecular, structural and functional impairments of the spinal cord were restored in the diabetic rats. In conclusion, the neuro-modulating effect of exenatide against diabetic-induced spinal cord affection warrants the concern about its therapeutic relevance in confronting the devastating diabetic neuropathic complications.

Noninvasive Measurement of Retinal Microvascular Permeability During Loss of Endothelial Quiescence

In the retina EC dysfunction and angiogenesis are driven by an altered microenvironment e.g., diabetes, leading to hypoxia and inflammation in the retinal layers, resulting in excessive vascular leakage and growth. The gold standard for measuring blood-retinal barrier permeability in response to disease and or therapy has been the gold standard Evans blue (EB) assay. However, this technique has limitations in vivo, including nonspecific tissue binding and toxicity. Here we describe a novel imaging methodology combining sodium fluorescein fundus angiography (FFA) with mathematical quantification allowing retinal permeability to be noninvasively and accurately measured at multiple time points in the same animal, minimizing animal use in line with the 3Rs framework. In addition, this technique is a nontoxic, high throughput, sensitive, and cost-effective alternative technique to the Evans blue assay. Moreover, this technique can be translated to other species.

Quantifying Vascular Remodeling in the Mouse Spinal Cord

The spinal cord, a compartment of the central nervous system, is made up of a number of architecturally distinct neural centers that influence an array of neurophysiological systems. The primary role of the spinal cord is the modulation of sensory and motor function by acting as a relay station between the periphery and the brain. Inherently these are considered as neural networks, however the functional dynamics of these tissues consist of a heterogenic population of cell types, all working in harmony to maintain physiological function. Part of this cellular diversity comprises of the vascular network that delivers essential nutrients and oxygen to the spinal cord tissue, whilst also protecting it from potentially tissue damaging substances such as foreign entities including toxic pharmacological agents or pathogens. The viability of the spinal cord is dependent upon the harmonious balance between opposing angiogenic processes; vascular remodeling and vascular regression, tipping the balance to either side contributes to neurodegeneration. Exploring vascular remodeling in the central nervous system requires consideration of the anatomical landscape of the spinal cord and the dynamic nature of the microvasculature. Utilizing immunofluorescent staining and 3D image rendering analysis of the endothelium and mural cell population allows for investigation of cellular as well as molecular mediation of vascular remodeling in the spinal cord. This method can be utilized in a range of rodent models (utilizing pharmacological, disease models, transgenic and/or viral approaches) offering extensive appreciation of the blood-spinal cord barrier.

Painful diabetic peripheral neuropathy: Role of oxidative stress and central sensitisation

AIMS

Diabetic peripheral neuropathy (DPN) occurs in about half of people with diabetes, of whom a quarter may develop chronic pain. Pain may remain for years yet be difficult to treat because the underlying mechanisms remain unclear. There is consensus that processing excessive glucose leads to oxidative stress, interfering with normal metabolism. In this narrative review, we argue that oxidative stress may also contribute to pain.

METHODS

We reviewed literature in PubMed published between January 2005 and August 2021.

RESULTS AND CONCLUSIONS

In diabetes, hyperglycaemia and associated production of reactive species can directly increase pain signalling and activate sensory neurons; or the effects can be indirect, mediated by mitochondrial damage and enhanced inflammation. Furthermore, pain processing in the central nervous system is compromised in painful DPN. This is implicated in central sensitisation and dysfunctional pain modulation. However, central pain modulatory function is understudied in diabetes. Future research is required to clarify whether central sensitisation and/or disturbances in central pain modulation contribute to painful DPN. Positive results would facilitate early detection and future treatment.

Redefining distal symmetrical polyneuropathy features in type 1 diabetes: a systematic review

Diabetic neuropathy is among the most frequent complications of both type 1 (T1DM) and type 2 diabetes (T2DM) and commonly manifests as a distal symmetrical polyneuropathy (DSPN). Despite evidence that T1DM- and T2DM-related DSPN are separate entities, most of our knowledge on diabetic DSPN derives from studies focused on type 2 diabetes. This systematic review provides an overview of current evidence on DSPN in T1DM, including its epidemiological, pathophysiological and clinical features, along with principal diagnostic tests findings. This review included 182 clinical and preclinical studies. The results indicate that DSPN is a less frequent complication in T1DM compared with T2DM and that distinctive pathophysiological mechanisms underlie T1DM-related DSPN development, with hyperglycemia as a major determinant. T1DM-related DSPN more frequently manifests with non-painful than painful symptoms, with lower neuropathic pain prevalence compared with T2DM-associated DSPN. The overt clinical picture seems characterized by a higher prevalence of large fiber-related clinical signs (e.g., ankle reflexes reduction and vibration hypoesthesia) and to a lesser extent small fiber damage (e.g., thermal or pinprick hypoesthesia). These findings as a whole suggest that large fibers impairment plays a dominant role in the clinical picture of symptomatic T1DM-related DSPN. Nevertheless, small fiber diagnostic testing shows high diagnostic accuracy in detecting early nerve damage and may be an appropriate diagnostic tool for disease monitoring and screening.

VEGF-A/VEGFR-1 signalling and chemotherapy-induced neuropathic pain: therapeutic potential of a novel anti-VEGFR-1 monoclonal antibody

BACKGROUND

Neuropathic pain is a clinically relevant adverse effect of several anticancer drugs that markedly impairs patients' quality of life and frequently leads to dose reduction or therapy discontinuation. The poor knowledge about the mechanisms involved in neuropathy development and pain chronicization, and the lack of effective therapies, make treatment of chemotherapy-induced neuropathic pain an unmet medical need. In this context, the vascular endothelial growth factor A (VEGF-A) has emerged as a candidate neuropathy hallmark and its decrease has been related to pain relief. In the present study, we have investigated the role of VEGF-A and its receptors, VEGFR-1 and VEGFR-2, in pain signalling and in chemotherapy-induced neuropathy establishment as well as the therapeutic potential of receptor blockade in the management of pain.

METHODS

Behavioural and electrophysiological analyses were performed in an in vivo murine model, by using selective receptor agonists, blocking monoclonal antibodies or siRNA-mediated silencing of VEGF-A and VEGFRs. Expression of VEGF-A and VEGFR-1 in astrocytes and neurons was detected by immunofluorescence staining and confocal microscopy analysis.

RESULTS

In mice, the intrathecal infusion of VEGF-A (VEGF165 isoforms) induced a dose-dependent noxious hypersensitivity and this effect was mediated by VEGFR-1. Consistently, electrophysiological studies indicated that VEGF-A strongly stimulated the spinal nociceptive neurons activity through VEGFR-1. In the dorsal horn of the spinal cord of animals affected by oxaliplatin-induced neuropathy, VEGF-A expression was increased in astrocytes while VEGFR-1 was mainly detected in neurons, suggesting a VEGF-A/VEGFR-1-mediated astrocyte-neuron cross-talk in neuropathic pain pathophysiology. Accordingly, the selective knockdown of astrocytic VEGF-A by intraspinal injection of shRNAmir blocked the development of oxaliplatin-induced neuropathic hyperalgesia and allodynia. Interestingly, both intrathecal and systemic administration of the novel anti-VEGFR-1 monoclonal antibody D16F7, endowed with anti-angiogenic and antitumor properties, reverted oxaliplatin-induced neuropathic pain. Besides, D16F7 effectively relieved hypersensitivity induced by other neurotoxic chemotherapeutic agents, such as paclitaxel and vincristine.

CONCLUSIONS

These data strongly support the role of the VEGF-A/VEGFR-1 system in mediating chemotherapy-induced neuropathic pain at the central nervous system level. Thus, treatment with the anti-VEGFR-1 mAb D16F7, besides exerting antitumor activity, might result in the additional advantage of attenuating neuropathic pain when combined with neurotoxic anticancer agents.

Blocking endothelial apoptosis revascularizes the retina in a model of ischemic retinopathy

Aberrant, neovascular retinal blood vessel growth is a vision-threatening complication in ischemic retinal diseases. It is driven by retinal hypoxia frequently caused by capillary nonperfusion and endothelial cell (EC) loss. We investigated the role of EC apoptosis in this process using a mouse model of ischemic retinopathy, in which vessel closure and EC apoptosis cause capillary regression and retinal ischemia followed by neovascularization. Protecting ECs from apoptosis in this model did not prevent capillary closure or retinal ischemia. Nonetheless, it prevented the clearance of ECs from closed capillaries, delaying vessel regression and allowing ECs to persist in clusters throughout the ischemic zone. In response to hypoxia, these preserved ECs underwent a vessel sprouting response and rapidly reassembled into a functional vascular network. This alleviated retinal hypoxia, preventing subsequent pathogenic neovascularization. Vessel reassembly was not limited by VEGFA neutralization, suggesting it was not dependent on the excess VEGFA produced by the ischemic retina. Neutralization of ANG2 did not prevent vessel reassembly, but did impair subsequent angiogenic expansion of the reassembled vessels. Blockade of EC apoptosis may promote ischemic tissue revascularization by preserving ECs within ischemic tissue that retain the capacity to reassemble a functional network and rapidly restore blood supply.

Non-invasive measurement of retinal permeability in a diabetic rat model

OBJECTIVE

The gold standard for measuring blood-retinal barrier permeability is the Evans blue assay. However, this technique has limitations in vivo, including non-specific tissue binding and toxicity. This study describes a non-toxic, high-throughput, and cost-effective alternative technique that minimizes animal usage.

METHODS

Sodium fluorescein fundus angiography was performed in non-diabetic and diabetic Brown Norway rats on days 0, 7, 14, 21, and 28. Sodium fluorescein intensity in the retinal interstitium and a main retinal vessel were measured over time. The intensity gradients were used to quantify retinal vascular permeability. Post-study eyes were fixed, dissected, and stained (isolectin B4) to measure required parameters for permeability quantification including total vessel length per retinal volume, radius, and thickness.

RESULTS

In the non-diabetic cohort retinal permeability remained constant over the 28-day study period. However, in the diabetic cohort there was a significant and progressive increase in retinal permeability from days 14-28 (P < .01, P < .001, P < .0001).

CONCLUSIONS

This novel imaging methodology in combination with mathematical quantification allows retinal permeability to be non-invasively and accurately measured at multiple time points in the same animal. In addition, this technique is a non-toxic, rapid, sensitive, and cost-effective alternative to the Evans blue assay.