High-Mobility Group Box-1 Modulates the Expression of Inflammatory and Angiogenic Signaling Pathways in Diabetic Retina

The chemokine landscape: one system multiple shades

Leukocyte trafficking is mainly governed by chemokines, chemotactic cytokines, which can be concomitantly produced in tissues during homeostatic conditions or inflammation. After the discovery and characterization of the individual chemokines, we and others have shown that they present additional properties. The first discoveries demonstrated that some chemokines act as natural antagonists on chemokine receptors, and prevent infiltration of leukocyte subsets in tissues. Later on it was shown that they can exert a repulsive effect on selective cell types, or synergize with other chemokines and inflammatory mediators to enhance chemokine receptors activities. The relevance of the fine-tuning modulation has been demonstrated in vivo in a multitude of processes, spanning from chronic inflammation to tissue regeneration, while its role in the tumor microenvironment needs further investigation. Moreover, naturally occurring autoantibodies targeting chemokines were found in tumors and autoimmune diseases. More recently in SARS-CoV-2 infection, the presence of several autoantibodies neutralizing chemokine activities distinguished disease severity, and they were shown to be beneficial, protecting from long-term sequelae. Here, we review the additional properties of chemokines that influence cell recruitment and activities. We believe these features need to be taken into account when designing novel therapeutic strategies targeting immunological disorders.

A simple but novel glycymicelle ophthalmic solution based on two approved drugs empagliflozin and glycyrrhizin: in vitro/in vivo experimental evaluation for the treatment of corneal alkali burns

A simple but novel ophthalmic solution based on two approved drugs was developed to reposition existing drugs to treat new diseases. This nanoformulation was developed using the phytochemical drug glycyrrhizin as an amphiphilic nanocarrier to micellarly solubilize empagliflozin (EMP), an oral drug that is widely used to control high blood glucose but has poor water solubility. This novel nanoformulation, which we designated the EMP@glycymicelle ophthalmic solution, was obtained using a simple preparation process. The resulting solution was a clear solution with an EMP encapsulation efficiency of 97.91 ± 0.50%, a small glycymicelle size of 6.659 ± 0.196 nm, and a narrow polydispersity index of 0.226 ± 0.059. The optimized formulation demonstrated that EMP was soluble in water up to 18 mg ml^-1 because of its encapsulation within glycymicelles. The EMP@glycymicelle ophthalmic solution exhibited excellent characteristics, including good storage stability, fast in vitro release profiles, improved in vitro antioxidant activity, and no ocular irritation. Ocular permeation evaluation showed that the EMP@glycymicelle ophthalmic solution had strong ocular permeation of EMP, and it reached the posterior segment of mouse eyes after ocular topical administration. The treatment efficacy evaluation showed that the EMP@glycymicelle ophthalmic solution had a significant effect against corneal alkali burns in mice, prompting corneal wound healing, recovering corneal sensitivity, reducing corneal haze, and relieving corneal NV invasion. The mechanism of inhibiting HMGB1 signaling was involved in this strong treatment effect. These results indicated that the EMP@glycymicelle ophthalmic solution provided a new concept of drug repurposing and a promising ocular system for the nano-delivery of EMP with significantly improved in vivo profiles.

Involvement of High Mobility Group Box 1 Protein in Optic Nerve Damage in Diabetes

Introduction

Diabetic patients routinely have high levels of high mobility group box 1 (HMGB1) protein in their plasma, vitreous and ocular membranes, which is strongly correlated with subclinical chronic inflammation in the eye. Our previous work has suggested that high HMGB1 in diabetes plays a role in retinal inflammation and angiogenesis, but its role in the optic nerve damage is unclear. Therefore, our goal is to examine the role of HMGB1 in optic nerve damage in diabetes.

Methods

Gene expression of HMGB1 was quantified in the optic nerve from streptozotocin-induced diabetic mice by qRT-PCR, and their protein expressions by Western blot analysis and immunofluorescence staining. Using immunohistochemical technique, expression of reactive astrogliosis (indicator of neuroinflammation) and nerve demyelination/damage were determined by quantifying glial fibrillary acid protein (GFAP) and myelin basic protein (MBP), respectively. The role of HMGB1 in the optic nerve damage and alteration visual pathways was confirmed in mice receiving glycyrrhizin, a HMGB1 inhibitor. Similar parameters were measured in the optic nerve from human donors with diabetes.

Results

Compared to normal mice, diabetic mice exhibited increased levels of HMGB1, higher GFAP expression, and decreased MBP in the optic nerve. Double immunofluorescence microscopy revealed that diabetes induced increased HMGB1 immunoreactivities were significantly colocalized with GFAP in the optic nerve. Glycyrrhizin supplementation effectively reduced HMGB1 and maintained normal axonal myelination and visual conduction. Results from mice optic nerve confirmed the results obtained from human donors with diabetes.

Discussions

Thus, diabetes-induced HMGB1 upregulation promotes optic nerve demyelination and inflammation. The regulation of HMGB1 activation has potential to protect optic nerve damage and the abnormalities of visual pathways in diabetic patients.

Glycyrrhiza glabra alcoholic root extract ameliorates hyperglycemia, hyperlipidemia, and glycation-induced free iron-mediated oxidative reactions

Hyperglycemia-associated oxidative stress leads to various pathophysiological complications in diabetes mellitus. Here, the effects of Glycyrrhiza glabra (G. glabra) root extract of streptozotocin (STZ)-induced diabetic changes and the associated free iron-mediated oxidative reactions were investigated. The animals were divided into five group, Group 1: Control (NC received buffer); Group 2: STZ-induced (DC); Group 3: Control treated with G. glabra root extract (NT, 60 mg/Kg b.w daily for 1 month); Group 4: Diabetic treated with the extract (60 mg/Kg b.w daily for 1 month); Group 5: Diabetic treated with glibenclamide (DTG, 8.6 mg/Kg b.w for 1 month). STZ (i) induced hyperglycemia, abnormal intraperitoneal glucose tolerance test (IPGTT), increased HbA_1c and decreased plasma insulin levels (ii) hyperlipidemia (iii) lowered antioxidant enzyme activities (iv) diminished RBC membrane fluidity (v) enhanced hemoglobin glycation-induced iron release and associated free radical reactions. Treatment with the extract resulted in significant reversal of hyperglycemia (DC: 205.0 ± 7.0 mg/dl vs. DT: 87.5 ± 4.5 mg/dl, p < .05); HbA_1c (DC: 11.5 ± 2.0 vs. DT: 7.5 ± 0.8 vs. DT: 7.5 ± 0.8, p < .05); insulin (DC: 0.3 ± 0.06 vs. DT: 1.25 ± 0.15 μgm/L, p < .05); free iron (DC: 150.4 ± 7.07 vs. DT: 98.8 ± 7.7 μgm/gm of Hb, p < .05); TBARS (DC + H₂ O₂ : 24.62 ± 11.30 vs. DC + H₂ O₂ : 9.82 ± 2.56 mmoles/h, p < .05); carbonyl (DC: 40.40 ± 1.57 vs. DT: 25.50 ± 1.12 mmoles/g of Hb, p < .05) levels and β-cell count/pancreatic islet (DC: 85 ± 15 vs. DT: 125 ± 20, p < .05). Thus, G. glabra extract is quite effective against hyperglycemia and the associated free iron-mediated oxidative stress. PRACTICAL APPLICATIONS: Chronic use of oral hypoglycemic synthetic drugs may produce side effects and drug resistance. Recently, various plant extracts are being researched to explore their antihyperglycemic potential. Here, the effects of this alcoholic powdered root extract on STZ-induced diabetic changes and associated oxidative stress, including hemoglobin-induced free iron-mediated oxidative reactions were examined. The STZ-induced diabetic changes and hemoglobin-glycation-induced free iron-mediated oxidative reactions were alleviated in the Wistar rats after 1-month of treatment with the extract. We have also reported previously that glycyrrhizin, a bioactive constituent of Glycyrrhiza glabra root inhibits peroxidase, esterase activities of hemoglobin and hemoglobin-mediated oxidative damage without affecting oxygen-binding capacity of the protein. This preclinical work further substantiates the potential therapeutic use of the G. glabra whole root extract in the treatment of diabetes mellitus.

Overview of key molecular and pharmacological targets for diabetes and associated diseases

Diabetes epidemiological quantities are demonstrating one of the most important communities' health worries. The essential diabetic difficulties are including cardiomyopathy, nephropathy, inflammation, and retinopathy. Despite developments in glucose decreasing treatments and drugs, these diabetic complications are still ineffectively reversed or prohibited. Several signaling and molecular pathways are vital targets in the new therapies of diabetes. This review assesses the newest researches about the key molecules and signaling pathways as targets of molecular pharmacology in diabetes and diseases related to it for better treatment based on molecular sciences. The disease is not cured by current pharmacological strategies for type 2 diabetes. While several drug combinations are accessible that can efficiently modulate glycemia and mitigate long-term complications, these agents do not reverse pathogenesis, and in practice, they are not established to modify the patient's specific molecular profiling. Therapeutic companies have benefited from human genetics. Genome exploration, which is agnostic to the information that exists, has revealed tens of loci that impact glycemic modulation. The physiological report has begun to examine subtypes of diseases, illustrate heterogeneity and propose biochemical therapeutic pathways.

The Potential Application of Pentacyclic Triterpenoids in the Prevention and Treatment of Retinal Diseases

Retinal diseases are a leading cause of impaired vision and blindness but some lack effective treatments. New therapies are required urgently to better manage retinal diseases. Natural pentacyclic triterpenoids and their derivatives have a wide range of activities, including antioxidative, anti-inflammatory, cytoprotective, neuroprotective, and antiangiogenic properties. Pentacyclic triterpenoids have great potential in preventing and/or treating retinal pathologies. The pharmacological effects of pentacyclic triterpenoids are often mediated through the modulation of signalling pathways, including nuclear factor erythroid-2 related factor 2, high-mobility group box protein 1, 11β-hydroxysteroid dehydrogenase type 1, and Src homology region 2 domain-containing phosphatase-1. This review summarizes recent in vitro and in vivo evidence for the pharmacological potential of pentacyclic triterpenoids in the prevention and treatment of retinal diseases. The present literature supports the further development of pentacyclic triterpenoids. Future research should now attempt to improve the efficacy and pharmacokinetic behaviour of the agents, possibly by the use of medicinal chemistry and targeted drug delivery strategies.

The anti-diabetic activity of licorice, a widely used Chinese herb

ETHNOPHARMACOLOGICAL RELEVANCE

A great deal of valuable experience has been accumulated in the traditional Chinese medicine (TCM) system for the treatment of "Xiaoke" disease which is known as diabetes mellitus now. As the most-commonly used Chinese herb, licorice has been used in TCM for more than two thousand years. It is often used in combination with other herbs to treat metabolic disorders, especially diabetes mellitus.

AIM OF THE STUDY

To summarize the characteristics, mechanisms, and clinical use of licorice and its active components for treating diabetes mellitus.

METHODS

PubMed, Web of Science, Research Gate, Science Direct, Google Scholar, and Academic Journals were used as information sources by the inclusion of the search terms 'diabetes', 'licorice', 'licorice extracts', 'flavonoids', 'triterpenoids', and their combinations, mainly from 2005 to 2019.

RESULTS

Licorice extracts, five flavonoids and three triterpenoids isolated from licorice possess great antidiabetic activities in vivo and in vitro. This was done by several mechanisms such as increasing the appetency and sensitivity of insulin receptor site to insulin, enhancing the use of glucose in different tissues and organs, clearing away the free radicals and resist peroxidation, correcting the metabolic disorder of lipid and protein, and improving microcirculation in the body. Multiple signaling pathways, including the PI3K/Akt, AMPK, AGE-RAGE, MAPK, NF-кB, and NLRP3 signaling pathways, are targets of the licorice compounds.

CONCLUSION

Licorice and its metabolites have a great therapeutic potential for the treatment of diabetes mellitus. However, a better understanding of their pharmacological mechanisms is needed for evaluating its efficacy and safety.

The Complex Relationship between Diabetic Retinopathy and High-Mobility Group Box: A Review of Molecular Pathways and Therapeutic Strategies

High-mobility group box 1 (HMGB1) is a protein that is part of a larger family of non-histone nuclear proteins. HMGB1 is a ubiquitary protein with different isoforms, linked to numerous physiological and pathological pathways. HMGB1 is involved in cytokine and chemokine release, leukocyte activation and migration, tumorigenesis, neoangiogenesis, and the activation of several inflammatory pathways. HMGB1 is, in fact, responsible for the trigger, among others, of nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), toll-like receptor-4 (TLR-4), and vascular endothelial growth factor (VEGF) pathways. Diabetic retinopathy (DR) is a common complication of diabetes mellitus (DM) that is rapidly growing in number. DR is an inflammatory disease caused by hyperglycemia, which determines the accumulation of oxidative stress and cell damage, which ultimately leads to hypoxia and neovascularization. Recent evidence has shown that hyperglycemia is responsible for the hyperexpression of HMGB1. This protein activates numerous pathways that cause the development of DR, and HMGB1 levels are constantly increased in diabetic retinas in both proliferative and non-proliferative stages of the disease. Several molecules, such as glycyrrhizin (GA), have proven effective in reducing diabetic damage to the retina through the inhibition of HMGB1. The main focus of this review is the growing amount of evidence linking HMGB1 and DR as well as the new therapeutic strategies involving this protein.

Loss of High-Mobility Group Box 1 (HMGB1) Protein in Rods Accelerates Rod Photoreceptor Degeneration After Retinal Detachment

Purpose

Retinal detachment (RD) disrupts the nutritional support and oxygen delivery to photoreceptors (PRs), ultimately causing cell death. High-mobility group box 1 (HMGB1) can serve as an extracellular alarmin when released from stressed cells. PRs release HMGB1 after RD. The purpose of this study was to investigate the relationship between HMGB1 and PR survival after RD.

Methods

Acute RD was created by injection of hyaluronic acid (1%) into the subretinal space in C57BL/6 mice and mice with a rhodopsin-Cre-mediated conditional knockout (cKO) of HMGB1 in rods (HMGB1ΔRod). Immunofluorescence (IF) in retinal sections was used to localize HMGB1, rhodopsin, and Iba-1 proteins. Optical coherence tomography and electroretinography were used to quantify retinal thickness and function, respectively. The morphology of the retina was assessed by hematoxylin and eosin.

Results

HMGB1 protein was localized to the nuclei of all retinal neurons, including PRs, with cones staining more intensely than rods. HMGB1 protein was also found in the inner and outer segments of cones but not rods. Creation of RD caused a dramatic increase of HMGB1 protein IF in rods. cKO of HMGB1 in rods did not affect retinal structure or function. However, after RD, loss of rods and reduction in the thickness of the outer nuclear layer were significantly increased in the HMGB1ΔRod retinas as compared to the control. Interestingly, depletion of HMGB1 in rods did not affect the activation and mobilization of microglia/macrophages normally seen after RD.

Conclusions

Increased HMGB1 expression in stressed rods may represent an intrinsic mechanism regulating their survival after RD.

Cross-Talk between Sirtuin 1 and the Proinflammatory Mediator High-Mobility Group Box-1 in the Regulation of Blood-Retinal Barrier Breakdown in Diabetic Retinopathy

Purpose: High-mobility group box-1 (HMGB1) mediates inflammation and breakdown of blood-retinal barrier (BRB) in diabetic retina. Sirtuin-1 (SIRT1) has protective effects against inflammation and oxidative stress. The aim of this study was to investigate the interaction between HMGB1 and SIRT1 in regulating BRB breakdown in diabetic retina. Methods: BRB breakdown was assessed in vivo with fluorescein isothiocyanate-conjugated dextran. Vitreous samples from 47 proliferative diabetic retinopathy (PDR) and 19 nondiabetic patients, and epiretinal membranes from 13 patients with PDR were studied by enzyme-linked immunosorbent assay and immunohistochemistry. Retinas from 4-week diabetic rats and from normal rats intravitreally injected with HMGB1 were studied by spectrophotometric assay, Western blot analysis, and RT-PCR. We also studied the effect of the HMGB1 inhibitor glycyrrhizin and the SIRT1 activator resveratrol on diabetes-induced biochemical changes in the retina. Results: HMGB1 levels in vitreous samples from PDR patients were significantly higher than in nondiabetic controls, whereas SIRT1 levels were significantly lower in vitreous samples from patients with inactive PDR than those in patients with active PDR and nondiabetic controls. In epiretinal membranes, SIRT1 was expressed in vascular endothelial cells and stromal cells. Diabetes and intravitreal injection of HMGB1 in normal rats downregulated SIRT1expression, whereas glycyrrhizin and resveratrol normalized diabetes-induced downregulation of SIRT1. Resveratrol significantly attenuated diabetes-induced downregulation of occludin and upregulation of HMGB1 and receptor for advanced glycation end products in the retina and breakdown of BRB. Conclusions: Our findings suggest that a functional link between SIRT1 and HMGB1 is involved in regulating of BRB breakdown in diabetic retina.

Activation of GABAB Receptor Suppresses Diabetic Neuropathic Pain through Toll-Like Receptor 4 Signaling Pathway in the Spinal Dorsal Horn

Diabetic neuropathic pain (DNP) is a prevalent complication in diabetes patients. Neuronal inflammation and activation of Toll-like receptor 4 (TLR4) are involved in the occurrence of DNP. However, the underlying mechanisms remain unclear. Downregulation of gamma-aminobutyric acid B (GABA_B) receptor contributes to the DNP. GABA_B receptor interacts with NF-κB, a downstream signaling factor of TLR4, in a neuropathic pain induced by chemotherapy. In this study, we determined the role of TLR4/Myd88/NF-κB signaling pathways coupled to GABA_B receptors in the generation of DNP. Intrathecal injection of baclofen (GABA_B receptor agonist), LPS-RS ultrapure (TLR4 antagonist), MIP (MyD88 antagonist), or SN50 (NF-κB inhibitor) significantly increased paw withdrawal threshold (PWT) and paw withdrawal thermal latency (PWTL) in DNP rats, while intrathecal injection of saclofen (GABA_B receptor blocker) decreased PWT and PWTL in DNP rats. The expression of TLR4, Myd88, NF-κBp65, and their downstream components IL-1 and TNF-α was significantly higher in the spinal cord tissue in DNP rats compared to control rats. Following inhibition of TLR4, Myd88, and NF-κB, the expression of IL-1 and TNF-α decreased. Activation of GABA_B receptors downregulated the expression of TLR4, Myd88, NF-κBp65, IL-1, and TNF-α. Blockade of GABA_B receptors significantly upregulated expression of TLR4, Myd88, NF-κBp65, IL-1, and TNF-α. These data suggest that activation of the TLR4/Myd88/NF-κB signaling pathway is involved in the occurrence of DNP in rats. Activation of GABA_B receptor in the spinal cord may suppress the TLR4/Myd88/NF-κB signaling pathway and alleviate the DNP.

Suppression of HMGB1 Released in the Glioblastoma Tumor Microenvironment Reduces Tumoral Edema

HMGB1 is a ubiquitously expressed intracellular protein that binds DNA and transcription factors and regulates chromosomal structure and function. Under conditions of cell death or stress, it is actively or passively released by cells into the extracellular environment, where it functions as damage-associated molecular pattern (DAMP) that orchestrates pro-inflammatory cytokine release and inflammation. Our results demonstrate that HMGB1 is secreted in the tumor microenvironment after oncolytic HSV (oHSV) infection in vitro and in vivo. The impact of secreted HMGB1 on tumor growth and response to oncolytic viral therapy was evaluated by using HMGB1-blocking antibodies in vitro and in mice bearing intracranial tumors. IVIS and MRI imaging was utilized to visualize in real time virus spread, tumor growth, and changes in edema in mice. Our data showed that HMGB1 released in tumor microenvironment orchestrated increased vascular leakiness and edema. Further HMGB1 blocking antibodies rescued vascular leakiness and enhanced survival of intracranial glioma-bearing mice treated with oHSV.

HMBG1 as a Driver of Inflammatory and Immune Processes in the Pathogenesis of Ocular Diseases

High-mobility group box 1 (HMGB1) is a nuclear protein that can also act as an extracellular trigger of inflammation, proliferation, and migration in eye diseases. It induces signaling pathways by binding to the receptor for advanced glycation end products (RAGE) and Toll-like receptors (TLRs) 2, 4, and 9. This proinflammatory activity is considered to be important in the pathogenesis of a wide range of ocular diseases resulting from hemodynamic changes, presence of neovascular endothelial cells, secretion of intraocular immune factors or inflammation, and apoptosis of retinal cell layers. Further work is needed to elucidate in detail how HMGB1 contributes to ocular disease and how its damaging activity can be modulated. In this review, we summarize current knowledge on HMGB1 as a ligand that can evoke inflammation and immune responses in ocular diseases.

Pathological roles of the homeostatic chemokine CXCL12

CXCL12 is a CXC chemokine that traditionally has been classified as a homeostatic chemokine. It contributes to physiological processes such as embryogenesis, hematopoiesis and angiogenesis. In contrast to these homeostatic functions, increased expression of CXCL12 in general, or of a specific CXCL12 splicing variant has been demonstrated in various pathologies. In addition to this increased or differential transcription of CXCL12, also upregulation of its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) contributes to the onset or progression of diseases. Moreover, posttranslational modification of CXCL12 during disease progression, through interaction with locally produced molecules or enzymes, also affects CXCL12 activity, adding further complexity. As CXCL12, CXCR4 and ACKR3 are broadly expressed, the number of pathologies wherein CXCL12 is involved is growing. In this review, the role of the CXCL12/CXCR4/ACKR3 axis will be discussed for the most prevalent pathologies. Administration of CXCL12-neutralizing antibodies or small-molecule antagonists of CXCR4 or ACKR3 delays disease onset or prevents disease progression in cancer, viral infections, inflammatory bowel diseases, rheumatoid arthritis and osteoarthritis, asthma and acute lung injury, amyotrophic lateral sclerosis and WHIM syndrome. On the other hand, CXCL12 has protective properties in Alzheimer's disease and multiple sclerosis, has a beneficial role in wound healing and has crucial homeostatic properties in general.

HMGB1 inhibits insulin signalling through TLR4 and RAGE in human retinal endothelial cells

In the past decade, the role of inflammation has been shown in diabetes and its complications. Little is available on high mobility group box 1 (HMGB1) actions on the proteins involved in insulin signal transduction, which may be altered to result in insulin resistance in the retina. Retinal endothelial cells (REC) were grown in normal or high glucose and treated with recombinant human HMGB1, an Epac1 agonist, or both. Additional cells were treated with advanced glycation end-products (RAGE) or toll-like receptor 4 (TLR4) siRNA prior to rhHMGB1. Proteins lysates were processed for Western blotting for TLR4, RAGE, insulin receptor, Akt, and IRS-1 phosphorylation. We found that rhHMGB1 blocked insulin and Akt phosphorylation through either RAGE or TLR4 actions. Epac1 overcame both endogenous and exogenous HMGB1 to maintain normal insulin signalling. Taken together, these data offer upstream targets to maintain proper insulin signal transduction in the retinal vasculature.

Cysteine mediated disulfide bond formation in RAGE V domain facilitates its functionally relevant dimerization

Receptor for Advanced Glycation End product (RAGE) is a multiligand receptor implicated in diverse pathological conditions such as diabetes, atherosclerosis, cancer and neural diseases. Extracellular, RAGE consists of V, C1 and C2 domains. Here, we show RAGE exists as a monomer in equilibrium with a fraction of a covalently linked dimer of monomers via its V domain through cysteine. In order to understand the functional implication of this dimer, we examined the binding capacity and functional potential of RAGE dimer via advanced glycation end products (AGEs) which shows enhanced binding capacity towards V domain, ERK phosphorylation, cytokine release and actin polymerization ability of the dimeric form for AGEs compared with the reduced monomeric form. Our data, suggests that the dimeric state of RAGE controls its function and ligand mediated signaling which may play important role in RAGE mediated various diseases.

Role of Inflammation in Diabetic Retinopathy

Diabetic retinopathy is a common complication of diabetes and remains the leading cause of blindness among the working-age population. For decades, diabetic retinopathy was considered only a microvascular complication, but the retinal microvasculature is intimately associated with and governed by neurons and glia, which are affected even prior to clinically detectable vascular lesions. While progress has been made to improve the vascular alterations, there is still no treatment to counteract the early neuro-glial perturbations in diabetic retinopathy. Diabetes is a complex metabolic disorder, characterized by chronic hyperglycemia along with dyslipidemia, hypoinsulinemia and hypertension. Increasing evidence points to inflammation as one key player in diabetes-associated retinal perturbations, however, the exact underlying molecular mechanisms are not yet fully understood. Interlinked molecular pathways, such as oxidative stress, formation of advanced glycation end-products and increased expression of vascular endothelial growth factor have received a lot of attention as they all contribute to the inflammatory response. In the current review, we focus on the involvement of inflammation in the pathophysiology of diabetic retinopathy with special emphasis on the functional relationships between glial cells and neurons. Finally, we summarize recent advances using novel targets to inhibit inflammation in diabetic retinopathy.

High mobility group B1 up-regulates angiogenic and fibrogenic factors in human retinal pigment epithelial ARPE-19 cells

Hypoxia-induced retinal neovascularization plays a central role in the pathogenesis of diabetic retinopathy. This study aimed to investigate whether hypoxia leads to the release of nuclear high mobility group box 1 (HMGB1) peptides from cultured retinal pigment epithelial ARPE-19 cells, to determine the effect of HMGB1 on angiogenic cytokine production and elucidate the involved signaling pathways. A chemical hypoxia mimetic agent, cobalt chloride, induced SIRT1 downregulation, HMGB1 nucleocytoplasmic relocation and extracellular release from ARPE-19 cells, implicating its autocrine function. Resveratrol treatment significantly reduced secretion of HMGB1 from ARPE-19 cells exposed to hypoxia. Cell proliferation and cell cycle analyses demonstrated that exogenous HMGB1 caused significant growth suppression and G1 cell cycle arrest in ARPE-19 cells. Morphological observations showed that HMGB1 enhanced adhesion, but suppressed migration of ARPE-19 cells. More intriguingly, HMGB1 up-regulated expression of angiofibrogenic factors in ARPE-19 cells, including VEGF, bFGF, TGF-β2, and CTGF. Signal profiling characterization indicated that HMGB1 triggered hyperphosphorylation of Akt, p38 MAPK, and NF-κB, but not that of ERK, JNK, and Smad2, whereas inhibition of PI3K, MAPK, or NF-κB significantly attenuated the HMGB1-driven cytokine overproduction in ARPE-19 cells. Functional neutralization with anti-TLR4 and -RAGE antibodies confirmed that both receptors were involved in the cytokine overproduction. In conclusion, chemically-mimicked hypoxia induced nucleocytoplasmic relocation and release of HMGB1 peptides, which in turn up-regulated the production of angiofibrogenic factors in RPE cells, thereby contributing to the pathogenesis of hypoxia-associated diabetic retinopathies. Conversely, blockades of intraocular HMGB1 bioavailability or signal activation may prevent angiofibrogenesis in development of diabetic retinopathy.

Opening eyes to nanomedicine: Where we are, challenges and expectations on nanotherapy for diabetic retinopathy

People affected with ocular diseases will significantly increase over the next decades, and, consequently, a substantial increase in health costs is expected. Diabetic retinopathy is the most common chronic complication of diabetes. The treatment of eye diseases affecting the posterior segment, such as diabetic retinopathy, is quite challenging due to the anatomy, physiology and biochemistry of the eye. Therefore, the development of new therapeutics for posterior eye diseases has been a major focus of pharmaceutical research in the area of vision sciences. Several nanosystems already offer efficient solutions for ophthalmological conditions, targeting internal eye tissues, as the retina, and many novel products are expected to appear hereafter. This review provides an insight on nanoparticle-based solutions for therapies directed to posterior segment of the eye diseases, particularly diabetic retinopathy, the present scenario, and the demands and expectations for the future.

HMGB1 siRNA can reduce damage to retinal cells induced by high glucose in vitro and in vivo

BACKGROUND

Diabetic retinopathy (DR), one of the most common complications of late-phase diabetes, is associated with many risk factors, among which continuous low-grade inflammation is one of the principal ones. As such, lowering inflammation levels and maintain the viability of human retinal endothelial cells (HRECs) are critical for DR therapy. HMGB1 is a well-known proinflammatory cytokine. However, whether HMGB1 small interfering RNA (siRNA) can protect retina cells under a high-glucose environment from morphological changes and functional abnormalities remain undetermined. We aimed to investigate the effect of HMGB1 siRNA on retinal cells in DR.

MATERIALS AND METHODS

A total of 80 adult Wistar rats were randomly divided into four groups (n=20 each): normal control, diabetes mellitus (DM), scrambled (Scr) siRNA, and HMGB1 siRNA. Rats in the DM, Scr siRNA, and siRNA groups were established by intraperitoneal injection of streptozotocin. At 16 weeks after injection, rats in the siRNA and Scr-siRNA groups were intravitreally injected with 2 μL HMGB1 siRNA and 2 μL Scr-siRNA, while rats in the control and DM groups were intravitreally injected with the same dose of sterile saline. At 1 week after injections, we performed the following experiments. Immunohistochemical staining and real-time quantitative polymerase chain reaction were performed to test HMGB1 protein and messenger RNA expression in retinas. We performed TUNEL assays to detect retinal cell apoptosis and electroretinography to detect retinal function. In HRECs treated with high glucose, proliferation, morphology, apoptosis, super-oxide dismutase (SOD), and reactive oxygen species production were detected. Western blot was applied to determine the expressions of HMGB1 and its related protein and apoptosis protein.

RESULTS

Intravitreal injection of HMGB1 siRNA reduced protein and messenger RNA expression of HMGB1 (both P<0.05). Intravitreal injection of HMGB1 siRNA reduced apoptosis of retinal cells (P<0.05), protected morphological changes in the retina, and improved the function of the retina (P<0.05). In HRECs treated with high glucose, HMGB1 siRNA pretreatment increased cell viability, reduced cell apoptosis, and reduced oxidative damage to cells (all P<0.05). Western blot detection found that HMGB1 siRNA pretreatment can inhibit the expression of cleaved caspase 3 and improve the expression of BCL2 (P<0.05). HMGB1 and NFκB expression increased in a time-dependent manner in the high-glucose environment and IKKβ and NFκB protein expression decreased significantly after HMGB1 silencing.

CONCLUSION

As a therapeutic target, HMGB1 siRNA can reduce retinal cell damage induced by high glucose in vitro and in vivo and delay DR progress through the HMGB1-IKKβ-NFκB signaling pathway.

High Mobility Group Box-1: A Missing Link between Diabetes and Its Complications

High mobility group box-1 (HMGB-1), a damage-associated molecular pattern, can be actively or passively released from various cells under different conditions and plays a pivotal role in the pathogenesis of inflammation and angiogenesis-dependent diseases. More and more evidence suggests that inflammation, in addition to its role in progression of diabetes, also promotes initiation and development of diabetic complications. In this review, we focus on the role of HMGB-1 in diabetes-related complications and the therapeutic strategies targeting HMGB-1 in diabetic complications.

Current concepts regarding developmental mechanisms in diabetic retinopathy in Taiwan

Diabetic retinopathy (DR) is one of the most feared complications of diabetes and is a leading cause of acquired blindness in working adults. The prevalence of undiagnosed diabetes in Taiwan is about 4%, and the annual incidence of T2D (Type 2 Diabetes) in Taiwan is 1.8% following the 1985 WHO criteria. Multiple mechanisms have been shown in T2DR with some signaling pathways, including the polyol pathway, PKC pathway, AGEs pathway, and MAPK pathway. However, the cause of vision loss in diabetic retinopathy is complex and remains incompletely understood. Herein, we try to fully understand the new concepts regarding hyperglycemia-induced biochemical pathways contributing to DR pathophysiology. Our work may be able to provide new strategies for the prevention and treatment of diabetic vascular complications.

Depressed basal hypothalamic neuronal activity in type-1 diabetic mice is correlated with proinflammatory secretion of HMBG1

We recently found indicators of hypothalamic inflammation and neurodegeneration linked to the loss of neuroprotective factors including insulin-like growth factor (IGF-1) and IGF binding protein-2 (IGFBP-3) in mice made diabetic using streptozotocin (STZ). In the current work, a genetic model of type-1 diabetes (Ins2(Akita) mouse) was used to evaluate changes in neuronal activity and concomitant changes in the proinflammatory mediator high-mobility group box-1 (HMBG1). We found basal hypothalamic neuronal activity as indicated by manganese-enhanced magnetic resonance imaging (MEMRI) was significantly decreased in 8 months old, but not 2 months old Ins2(Akita) diabetic mice compared to controls. In tissue from the same animals we evaluated the expression of HMBG1 using immunohistochemistry and confocal microscopy. We found decreased HMBG1 nuclear localization in the paraventricular nucleus of the hypothalamus (PVN) in 8 months old, but not 2 months old diabetic animals indicating nuclear release of the protein consistent with an inflammatory state. Adjacent thalamic regions showed little change in HMBG1 nuclear localization and neuronal activity as a result of diabetes. This work extends our previous findings demonstrating changes consistent with hypothalamic neuroinflammation in STZ treated animals, and shows active inflammatory processes are correlated with changes in basal hypothalamic neuronal activity in Ins2(Akita) mice.

Neuroinflammatory responses in diabetic retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes and has been recognized as a vascular dysfunction leading to blindness in working-age adults. It becomes increasingly clear that neural cells in retina play an important role in the pathogenesis of DR. Neural retina located at the back of the eye is part of the brain and a representative of the central nervous system. The neurosensory deficits seen in DR are related to inflammation and occur prior to the clinically identifiable vascular complications. The neural deficits are associated with abnormal reactions of retina glial cells and neurons in response to hyperglycemia. Improper activation of the innate immune system may also be an important contributor to the pathophysiology of DR. Therefore, DR manifests characteristics of both vasculopathy and chronic neuroinflammatory diseases. In this article, we attempt to provide an overview of the current understanding of inflammation in neural retina abnormalities in diabetes. Inhibition of neuroinflammation may represent a novel therapeutic strategy to the prevention of the progression of DR.