Aqueous levels of macrophage migration inhibitory factor and monocyte chemotactic protein-1 in patients with diabetic retinopathy

Diabetes, Diabetic Retinopathy, and Inflammatory Disorders

This review summarizes the impact of systemic and ocular inflammatory disorders on diabetes mellitus (DM) and diabetic retinopathy (DR). Local inflammation is a key pathology in diabetic retinopathy (DR) and is also an evolving target for clinical therapy. The legacy effects of local inflammation at the intracellular level make DR a persistent self-driven vicious process. Ocular inflammation is accompanied as well as incited by systemic inflammation due to diabetes mellitus (DM) itself. Over the years, a multitude of studies have evaluated the impact of systemic inflammatory disorders (SIDs, like rheumatoid arthritis, lupus, psoriasis, etc.) and anti-inflammatory drugs prescribed for managing them on manifestations of DM. Recent studies have indicated increased insulin resistance to be a result of chronic inflammation, and the anti-inflammatory drugs to have a protective effect towards DM. Very few studies have evaluated the impact of SIDs on DR. Furthermore, the evidence from these studies is conflicting, and while local anti-inflammatory therapy has shown a lot of clinical potential for use in DR, the results of systemic anti-inflammatory therapies have been inconsistent. The impact of local ocular inflammation due to uveitis on DR is a crucial aspect that has not been evaluated well at present. Initial pre-clinical studies and small-sized clinical reports have shown a strong and positive relationship between the presence of uveitis and the severity of DR as well as its progression, while larger cross-sectional patient surveys have refuted the same. The long term impact of ocular inflammation due to uveitis on DR needs to be studied while adjusting for confounders.

Changes in aqueous and vitreous inflammatory cytokine levels in nonproliferative diabetic retinopathy: systematic review and meta-analysis

OBJECTIVE

Diabetic retinopathy is a complication of diabetes mellitus with the potential for significant patient morbidity. Although changes to intraocular inflammatory cytokines are integral to disease pathogenesis, studies have been inconsistent about which exact cytokines are associated with diabetic retinopathy. We aimed to quantitatively summarize proangiogenic and proinflammatory cytokines in nonproliferative diabetic retinopathy (NPDR), given its frequency among those with diabetes mellitus.

METHODS

A systematic literature search without year limitation to February 21, 2022, identified 59 studies assessing vitreous or aqueous cytokine levels in NPDR, encompassing 1378 eyes with NPDR and 1288 eyes from nondiabetic controls. Effect sizes were generated as standardized mean differences (SMD) of cytokine concentrations between patients with NPDR and controls.

RESULTS

Concentrations (SMD, 95% confidence interval, and p value) of aqueous interleukin-6 (IL-6) (2.58, 1.17‒3.99; p = 0.0003), IL-8 (1.56, 0.39‒2.74; p = 0.009), IL-17 (13.55, 7.50‒19.59; p < 0.001), transforming growth factor beta (TGF-β) (2.44, 1.02‒3.85; p = 0.0007) and vascular endothelial growth factor (VEGF) (1.35, 0.76‒1.93; p < 0.00001), and vitreous VEGF (1.49, 0.60‒2.37; p = 0.001) were significantly higher in patients with NPDR when compared with those of healthy controls.

CONCLUSIONS

These cytokines may serve as disease markers of the biochemical alterations seen in NPDR and may guide interventions, as we move into an era of more targeted therapeutics.

Role of novel biomarker monocyte chemo-attractant protein-1 in early diagnosis & predicting progression of diabetic kidney disease: A comprehensive review

Diabetic kidney disease (DKD) is the most devastating complication of diabetes mellitus. Identification of patients at the early stages of progression may reduce the disease burden. The limitation of conventional markers such as serum creatinine and proteinuria intensify the need for novel biomarkers. The traditional paradigm of DKD pathogenesis has expanded to the activation of the immune system and inflammatory pathways. Monocyte chemo-attractant protein-1 (MCP-1) is extensively studied, as a key inflammatory mediator that modulates the development of DKD. Recent evidence supports the diagnostic role of MCP-1 in patients with or without proteinuria in DKD, as well as a significant role in the early prediction and risk stratification of DKD. In this review, we will summarize and update present evidence for MCP-1 for diagnostic ability and predicting the progression of DKD.

The roles of macrophage migration inhibitory factor in retinal diseases

Macrophage migration inhibitory factor (MIF), a multifunctional cytokine, is secreted by various cells and participates in inflammatory reactions, including innate and adaptive immunity. There are some evidences that MIF is involved in many vitreoretinal diseases. For example, MIF can exacerbate many types of uveitis; measurements of MIF levels can be used to monitor the effectiveness of uveitis treatment. MIF also alleviates trauma-induced and glaucoma-induced optic nerve damage. Furthermore, MIF is critical for retinal/choroidal neovascularization, especially complex neovascularization. MIF exacerbates retinal degeneration; thus, anti-MIF therapy may help to mitigate retinal degeneration. MIF protects uveal melanoma from attacks by natural killer cells. The mechanism underlying the effects of MIF in these diseases has been demonstrated: it binds to cluster of differentiation 74, inhibits the c-Jun N-terminal kinase pathway, and triggers mitogen-activated protein kinases, extracellular signal-regulated kinase-1/2, and the phosphoinositide-3-kinase/Akt pathway. MIF also upregulates Toll-like receptor 4 and activates the nuclear factor kappa-B signaling pathway. This review focuses on the structure and function of MIF and its receptors, including the effects of MIF on uveal inflammation, retinal degeneration, optic neuropathy, retinal/choroidal neovascularization, and uveal melanoma.

Role of Macrophage in Type 2 Diabetes Mellitus: Macrophage Polarization a New Paradigm for Treatment of Type 2 Diabetes Mellitus

Metabolic diseases such as type 2 diabetes mellitus are usually associated with meta-inflammation. β-cell failure is a marked feature observed in the pathogenesis of type 2 diabetes mellitus. Type 2 diabetes mellitus (T2DM) is a heterogeneous situation that is accompanied by not only defective insulin secretion but also peripheral insulin resistance. β-cells are the primary organ for insulin secretion; hence, it is crucial to maintain a significant β-cell mass in response to a variety of changes. Insulin resistance is a chief cause of T2DM, leading to increased free fatty acid (FFA) levels, which in turn elevates β-cell mass and insulin secretion as compensation for insulin insensitivity. It has recently been established that amplified numbers of innate immune cells, cytokines, and chemokines result in detrimental effects on islets in chronic conditions. Macrophage migration inhibitory factor (MIF) is the lymphokine that prevents arbitrary migration of macrophages and assembles macrophages at inflammatory loci. Inflammation is known to trigger monocytes to differentiate into macrophages. Progress of complications associated with type 2 diabetes mellitus, as indicated through recent findings, is also dependent on the buildup of macrophages in tissues vulnerable to diabetic injury. The present article scientifically evaluates the present knowledge concerning the mechanisms of monocyte and macrophage-mediated injury recruitment in complications associated with type 2 diabetes mellitus. It also describes some of the established and experimental therapies that might bring about a reduction in these inflammatory complications. Recent discoveries in the field of drug delivery have facilitated phenotype-specific targeting of macrophages. This review highlights the pathophysiology of type 2 diabetes mellitus, how macrophage induces type 2 diabetes mellitus and potential therapeutics for type 2 diabetes mellitus via macrophage-specific delivery.

Role of inflammatory cells in pathophysiology and management of diabetic retinopathy

Diabetic retinopathy (DR) is a sight-threatening complication of diabetes mellitus. Several inflammatory cells and proteins, including macrophages and microglia, cytokines, and vascular endothelial growth factors, are found to play a significant role in the development and progression of DR. Inflammatory cells play a significant role in the earliest changes seen in DR including the breakdown of the blood retinal barrier leading to leakage of blood into the retina. They also have an important role in the pathogenesis of more advanced stage of proliferative diabetic retinopathy, leading to neovascularization, vitreous hemorrhage, and tractional retinal detachment. In this review, we examine the function of numerous inflammatory cells involved in the pathogenesis, progression, and role as a potential therapeutic target in DR. Additionally, we explore the role of inflammation following treatment of DR.

Aqueous Humor Cytokines in Non-Proliferative Diabetic Retinopathy

Background and Objectives: Cytokines are cell-signaling proteins whose identification may serve as inflammatory markers or early indicators for progressive disease. The aim of our study was to quantify several cytokines in aqueous humor (AH) and their correlations with biochemical parameters in diabetic eyes with non-proliferative diabetic retinopathy (NPDR). Materials and Methods: A total of 62 eyes from 62 patients were included in the study: 37 eyes from nondiabetic patients (group 1), 13 diabetic eyes with no retinopathy changes (group 2) and 12 diabetic eyes with early and moderate NPDR (group 3). AH samples were collected during uneventful cataract surgery. The cytokines IL-1β, IL-6, IL-8, IL-10, IL-12, IP-10, MCP-1, TNF-α and VEGF were quantified using multiplex bead-based immunoassay. Due to unreliable results, IL-1β, TNF-α, IL-10 and IL-12 were excluded. Concentrations were compared between groups. Biochemical parameters (fasting blood sugar, glycated hemoglobin, C-reactive protein) and the duration of diabetes were recorded. Results: VEGF levels were significantly different between groups (p = 0.001), while levels of IL-6, IL-8, IP-10 and MCP-1 were comparable across all groups (p > 0.05). IL-6 concentration correlated with VEGF in group 1 (rho = 0.651, p = 0.003) and group 3 (rho = 0.857, p = 0.007); no correlation could be proved between IL-6, IL-8, IP-10, MCP-1 or VEGF and biochemical parameters. Duration of diabetes was not correlated with the cytokine levels in groups 2 and 3. The receiver operating characteristic (ROC) curve revealed that VEGF concentrations could discriminate early and moderate NPDR from diabetes, with an area under the curve (AUC) of 0.897 (p = 0.001, 95% CI = 0.74−1.0). Conclusions: Diabetes mellitus induces significant intraocular changes in the VEGF expression in diabetic patients vs. normal subjects, even before proliferative complications appear. VEGF was increasingly expressed once the diabetes progressed from no retinopathy to early or moderate retinopathy.

Changes in aqueous and vitreous inflammatory cytokine levels in proliferative diabetic retinopathy: a systematic review and meta-analysis

BACKGROUND

Diabetic retinopathy is a major complication of diabetes mellitus, where in its most advanced form ischemic changes lead to the development of retinal neovascularization, termed proliferative diabetic retinopathy (PDR). While the development of PDR is often associated with angiogenic and inflammatory cytokines, studies differ on which cytokines are implicated in disease pathogenesis and on the strength of these associations. We therefore conducted a systematic review and meta-analysis to quantitatively assess the existing body of data on intraocular cytokines as biomarkers in PDR.

METHODS

A comprehensive search of the literature without year limitation was conducted to January 18, 2021, which identified 341 studies assessing vitreous or aqueous cytokine levels in PDR, accounting for 10379 eyes with PDR and 6269 eyes from healthy controls. Effect sizes were calculated as standardized mean differences (SMD) of cytokine concentrations between PDR and control patients.

RESULTS

Concentrations (SMD, 95% confidence interval, and p-value) of aqueous IL-1β, IL-6, IL-8, MCP-1, TNF-α, and VEGF, and vitreous IL-2, IL-4, IL-6, IL-8, angiopoietin-2, eotaxin, erythropoietin, GM-CSF, GRO, HMGB-1, IFN-γ, IGF, IP-10, MCP-1, MIP-1, MMP-9, PDGF-AA, PlGF, sCD40L, SDF-1, sICAM-1, sVEGFR, TIMP, TNF-α, and VEGF were significantly higher in patients with PDR when compared to healthy nondiabetic controls. For all other cytokines no differences, failed sensitivity analyses or insufficient data were found.

CONCLUSIONS

This extensive list of cytokines speaks to the complexity of PDR pathogenesis, and informs future investigations into disease pathogenesis, prognosis, and management.

Inflammatory mediators in diabetic retinopathy: Deriving clinicopathological correlations for potential targeted therapy

The role of inflammation in diabetic retinopathy (DR) is well-established and dysregulation of a large number of inflammatory mediators is known. These include cytokines, chemokines, growth factors, mediators of proteogenesis, and pro-apoptotic molecules. This para-inflammation as a response is not directed to a particular pathogen or antigen but is rather directed toward the by-products of the diabetic milieu. The inflammatory mediators take part in cascades that result in cellular level responses like neurodegeneration, pericyte loss, leakage, capillary drop out, neovascularization, etc. There are multiple overlaps between the inflammatory pathways occurring within the diabetic retina due to a large number of mediators, their varied sources, and cross-interactions. This makes understanding the role of inflammation in clinical manifestations of DR difficult. Currently, mediator-based therapy for DR is being evaluated for interventions that target a specific step of the inflammatory cascade. We reviewed the role of inflammation in DR and derived a simplified clinicopathological correlation between the sources and stimuli of inflammation, the inflammatory mediators and pathways, and the clinical manifestations of DR. By doing so, we deliberate mediator-specific therapy for DR. The cross-interactions between inflammatory mediators and the molecular cycles influencing the inflammatory cascades are crucial challenges to such an approach. Future research should be directed to assess the feasibility of the pathology-based therapy for DR.

The role of inflammation in diabetic eye disease

Mounting evidence suggests that immunological mechanisms play a fundamental role in the pathogenesis of diabetic retinopathy (DR) and diabetic macular edema (DME). Upregulation of cytokines and other proinflammatory mediators leading to persistent low-grade inflammation is believed to actively contribute to the DR-associated damage to the retinal vasculature, inducing breakdown of the blood-retinal barrier, subsequent macular edema formation, and promotion of retinal neovascularization. This review summarizes the current knowledge of the biological processes providing an inflammatory basis for DR and DME. In addition, emerging therapeutic approaches targeting inflammation are discussed, including blockade of angiopoietin 2 and other molecular targets such as interleukin (IL)-6, IL-1β, plasma kallikrein, and integrins.

Monocyte chemoattractant protein-1 (MCP-1/CCL2) in diabetic retinopathy: latest evidence and clinical considerations

Diabetic retinopathy (DR) is considered as a diabetes-related complication that can render severe visual impairments and is also a risk factor for acquired blindness in both developed as well as developing countries. Through fibrovascular epiretinal membranes (ERMs), this condition can similarly lead to tractional retinal detachment. Laboratory efforts evaluating the DR pathogenesis can be provided by ocular vitreous fluid and ERMs resulting from vitrectomy. The clinical stages of DR are significantly associated with expression levels of certain chemokines, including monocyte chemotactic protein-1 (MCP-1) in the intraocular fluid. The MCP-1 is also a known potent chemotactic factor for monocytes and macrophages that can stimulate them to produce superoxide and other mediators. Following hyperglycemia, retinal pigmented epithelial (RPE) cells, endothelial cells, and Müller's glial cells are of utmost importance for MCP-1 production, and vitreous MCP-1 levels rise in patients with DR. Increased expression of the MCP-1 in the eyes can also play a significant role in the pathogenesis of DR. In this review, current clinical and laboratory progress achieved on the MCP-1 and the DR concerning neovascularization and inflammatory responses in vitreous and/or aqueous humor of DR patients was summarized. It was suggested that further exploration of the MCP-1/CCR2 axis association between clinical stages of DR and expression levels of inflammatory and angiogenic cytokines and chemokines, principally the MCP-1 might lead to potential therapies aiming at neutralizing antibodies and viral vectors.

Molecular and Pathophysiological Mechanisms of Diabetic Retinopathy in Relation to Adhesion Molecules

Diabetic Retinopathy (DR) is considered as a most common microvascular complication of diabetes affected by one in three people who are suffered for diabetes. Several pathophysiological mechanisms and adhesion molecules may play an etiologic role in the development of diabetes and its complications. The adhesion molecules located on both leucocytes and endothelial cells and considered as important molecules which can assessed the endothelial function. The functions of adhesion molecules involved in the cellular margination, slow rolling and transmigration of leukocytes. Hyperglycemia and its immediate biochemical sequelae or the low-grade inflammation directly alter endothelial function or influence endothelial cell functioning indirectly by induce oxidative stress and activates leukocytosis and leukocyte-endothelial cell interactions by the increased expression of adhesion molecules, growth factors, inflammatory factors, chemokines etc. and results DR. This review summarized the several pathophysiological mechanisms and role of adhesion molecules in disruption of homeostasis of vasculature by leukocytes in the development of diabetic retinopathy.

MIF Inhibitor ISO-1 Protects Photoreceptors and Reduces Gliosis in Experimental Retinal Detachment

Photoreceptor death and retinal gliosis underlie the majority of vision threatening retinal diseases including retinal detachment (RD). Although the underlying pathobiology of vision limiting processes in RD is not fully understood, inflammation is known to play a critical role. We conducted an iTRAQ proteomic screen of up- and down-regulated proteins in a murine model of RD to identify potential targetable candidates. Macrophage migration inhibitory factor (MIF) was identified and evaluated for neurotoxic and pro-gliotic effects during RD. Systemic administration of the MIF inhibitor ISO-1 significantly blocked photoreceptor apoptosis, outer nuclear layer (ONL) thinning, and retinal gliosis. ISO-1 and MIF knockout (MIFKO) had greater accumulation of Müller glia pERK expression in the detached retina, suggesting that Müller survival pathways might underlie the neuroprotective response. Our data show the feasibility of the MIF-inhibitor ISO-1 to block pathological damage responses in retinal detachment and provide a rationale to explore MIF inhibition as a potential therapeutic option for RD.

Diabetic macular oedema: clinical risk factors and emerging genetic influences

Diabetic macular oedema is the major cause of visual impairment in type 1 and type 2 diabetes. As type 2 diabetes becomes more prevalent worldwide, the prevalence of diabetic macular oedema is also expected to rise. Current management of diabetic macular oedema is challenging, expensive and not optimal in a subset of patients. Therefore, it is important to increase our understanding of the risk factors involved and develop preventative strategies. While clinical risk factors for diabetic macular oedema have been identified, few studies have addressed potential genetic risk factors. Epidemiology and family studies suggest genetic influences are of importance. In this review, we summarise known clinical risk factors, as well as discuss the small number of genetic studies that have been performed for diabetic macular oedema.

Elevated Activating Transcription Factor 4 and Glucose-Regulated 78 Kda Protein Levels Correlate with Inflammatory Cytokines in the Aqueous Humor and Vitreous of Proliferative Diabetic Retinopathy

PURPOSE

To determine concentrations of endoplasmic reticulum (ER) stress-related factors activating transcription factor 4 (ATF4) and glucose-regulated 78 kDa protein (GRP78) in vitreous and aqueous humor (AqH) of patients with proliferative diabetic retinopathy (PDR) and the correlation of ATF4, GRP78 and inflammatory cytokines interleukin-6(IL-6) and monocyte chemoattractant protein-1 (MCP-1).

MATERIALS AND METHODS

AqH and vitreous samples were collected from eyes of patients with PDR and idiopathic macular hole (IMH) which needed vitrectomy. Protein Levels of ATF4, GRP78, and IL-6, MCP-1 in samples were evaluated using enzyme-linked immunosorbent assay (ELISA).

RESULTS

ELISA analysis revealed significantly increased levels in both AqH and vitreous of ATF4 and GRP78 in eyes affected with PDR compared to the controls (all p < 0.001). The mean concentrations of IL-6, MCP-1 were also higher in both AqH and vitreous samples from patients with PDR compared to those of IMH (all p < 0.001). (Independent Student t-test, normality test followed with Skewness-Kurtosis Test). In addition, correlations of ATF4 and GRP78 with inflammatory factors IL-6 and MCP-1 in subjects of patients were analyzed. No significant correlation between the AqH concentrations of ATF4/IL-6 and ATF4/MCP-1 was detected in eyes of PDR patients (r = 0.346, p = 0.072 and r = 0.275, p = 0.157). Significant correlations were observed between AqH concentrations of GRP78/IL-6 (r = 0.724, p < 0.001), GRP78/MCP-1 (r = 0.654, p < 0.001) in PDR patients. Significant correlations were observed between vitreous concentrations of ATF4/IL-6 (r = 0.918, p < 0.001), ATF4/MCP-1 (r = 0.921, p < 0.001), GRP78/IL-6 (r = 0.978, p < 0.001), GRP78/MCP-1 (r = 0.979, p < 0.001) in PDR patients. No significant correlations was observed between AqH concentrations of ATF4/IL-6 (r = 0.187, p = 474), ATF4/MCP-1 (r = 0.240, p = 0.353), GRP78/IL-6 (r = 0.321, p = 0.209) and GRP78/MCP-1 (r = 0.169, p = 0.516) in eyes of IMH patients. And also no significant correlation was observed between vitreous concentrations of ATF4/IL-6 (r = 0.130, p = 0.563), ATF4/MCP-1(r = 0.029, p = 0.897), GRP78/IL-6 (r = 0.078, p = 0.717), GRP78/MCP-1 (r = 0.005, p = 0.982) in IMH patients. (Pearson correlation coefficient (two-tailed)).

CONCLUSIONS

Our results demonstrated that ATF4 and GRP78 may play an important role in the pathogenesis of PDR and work in concert with inflammatory cytokines IL-6 and MCP-1 in pathological process. ATF4 and GRP78 may be good diagnostic biomarkers and new therapeutic targets for PDR.

ABBREVIATIONS

ER stress, endoplasmic reticulum stress; ATF4, activating transcription factor 4; GRP78, glucose-regulated 78 kDa protein; AqH, aqueous humor; PDR, proliferative diabetic retinopathy; IL-6, interleukin-6; MCP-1, monocyte chemoattractant protein-1; IMH, idiopathic macular hole.

Absence of macrophage migration inhibitory factor reduces proliferative retinopathy in a mouse model

AIMS

Ischemia-induced neovascularization is the key feature of proliferative diabetic retinopathy. Macrophage migration inhibitory factor (MIF) is a pleiotropic proinflammatory and proangiogenic cytokine, and its levels are elevated in the vitreous of patients with proliferative diabetic retinopathy. In this study, we aimed at investigating the relative potential of MIF in the ischemia-induced retinal neovascularization.

METHODS

Both WT and MIF-knockout mice were subjected to the retinopathy of prematurity (ROP) model. Intraretinal vessel regrowth was assessed by whole-mount immunofluorescence, and preretinal neovascularization was analyzed in retinal vertical sections after periodic acid-Schiff staining in the hypoxic stage of the ROP model. Gene expression of selected proangiogenic and proinflammatory factors at postnatal day 13 (p13) was measured by real-time PCR. Vascular endothelial growth factor (VEGF) expression, recruitment of endothelial progenitor cells (EPCs) and microglial activation were analyzed with immunofluorescence.

RESULTS

MIF deficiency increased areas of vascular obliteration by 49%, reduced sprouting tips by 27% and inhibited preretinal angiogenesis by 35%. VEGF expression was reduced in Müller cells of MIF-knockout mice. MIF absence reduced gene expression of erythropoietin, tumor necrosis factor alpha and intercellular adhesion molecule-1 by 30, 70 and 50%, respectively, decreased the number of retinal EPCs by 37.5% and inhibited microglial activation in the hypoxic condition.

CONCLUSIONS

In conclusion, we found that MIF has proangiogenic and proinflammatory properties in retinal neovascularization. The proangiogenic role of MIF in ischemia-induced retinal neovascularization is associated with the expression of VEGF and erythropoietin, EPC recruitment and inflammation. Therefore, MIF has a potential role in the pathological angiogenesis of proliferative retinopathy.

Association of monocyte chemoattractant protein-1 gene 2518A/G polymorphism with diabetic retinopathy in type 2 diabetes mellitus: A meta-analysis

AIMS

The relationship between monocyte chemoattractant protein-1 (MCP-1) 2518 A/G polymorphism and diabetic retinopathy (DR) attracted intense interest recently, but the reported results are controversial. A meta-analysis was performed to assess the MCP-1 polymorphism associated with DR susceptibility in type 2 diabetes mellitus.

METHODS

Eligible studies were identified from PubMed, Embase, Web of science, Chinese Biomedical database, and references of retrieved articles. Pooled odds ratios (ORs) with their 95% confidence intervals (95%CI) were calculated by fixed or random-effects models.

RESULTS

Six studies involving 3415 patients without DR and 3468 with any DR were included in the final meta-analysis. Each 5 studies evaluated the associations of MCP-1 polymorphism and any DR and proliferative DR (PDR), respectively. Meta-analysis in fixed model demonstrated a significant association between MCP-1 polymorphism and any DR under the homozygous model (OR=1.36; 95%CI: 1.15-1.62, P<0.001), heterozygous model (OR=1.20; 95%CI: 1.02-1.42, P=0.031), dominant model (OR=1.28; 95%CI: 1.10-1.50, P=0.002), recessive model (OR=1.17; 95%CI: 1.05-1.31, P=0.004), and allelic model (OR=1.16; 95%CI: 1.07-1.25, P<0.001). Furthermore, a significant association of MCP-1 polymorphism and DR progression from non-proliferative DR to proliferative DR was identified under heterozygous model (OR=1.45; 95%CI: 1.04-2.02, P=0.030). Sensitivity analyses did not draw different findings.

CONCLUSIONS

Meta-analysis of existing data suggested that MCP-1 2518 A/G polymorphism affected the risk of presence and progression of DR in type 2 diabetes mellitus.

Tissue resident macrophages: Key players in the pathogenesis of type 2 diabetes and its complications

There is increasing evidence showing that chronic inflammation is an important pathogenic mediator of the development of type 2 diabetes (T2D). It is now generally accepted that tissue-resident macrophages play a major role in regulation of tissue inflammation. T2D-associated inflammation is characterized by an increased abundance of macrophages in different tissues along with production of inflammatory cytokines. The complexity of macrophage phenotypes has been reported from different human tissues. Macrophages exhibit a phenotypic range that is intermediate between two extremes, M1 (pro-inflammatory) and M2 (anti-inflammatory). Cytokines and chemokines produced by macrophages generate local and systemic inflammation and this condition leads to pancreatic β-cell dysfunction and insulin resistance in liver, adipose and skeletal muscle tissues. Data from human and animal studies also suggest that macrophages contribute to T2D complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases through cell-cell interactions and the release of pro-inflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. In this review we focus on the functions of macrophages and the importance of these cells in the pathogenesis of T2D. In addition, the contribution of macrophages to diabetes complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases is discussed.

Association of potential salivary biomarkers with diabetic retinopathy and its severity in type-2 diabetes mellitus: a proteomic analysis by mass spectrometry

AIM/HYPOTHESIS

The aim of our study was to characterize the human salivary proteome and determine the changes in protein expression in two different stages of diabetic retinopathy with type-2 diabetes mellitus: (1) with non-proliferative diabetic retinopathy (NPDR) and (2) with proliferative diabetic retinopathy (PDR). Type-2 diabetes mellitus without diabetic retinopathy (XDR) was designated as control.

METHOD

In this study, 45 saliva samples were collected (15 samples from XDR control group, 15 samples from NPDR disease group and 15 samples from PDR disease group). Salivary proteins were extracted, reduced, alkylated, trypsin digested and labeled with an isobaric tag for relative and absolute quantitation (iTRAQ) before being analyzed by an Orbitrap fusion tribrid mass spectrometer. Protein annotation, fold change calculation and statistical analysis were interrogated by Proteome Discoverer. Biological pathway analysis was performed by Ingenuity Pathway Analysis. Data are available via ProteomeXchange with identifiers PXD003723-PX003725.

RESULTS

A total of 315 proteins were identified from the salivary proteome and 119 proteins were found to be differentially expressed. The differentially expressed proteins from the NPDR disease group and the PDR disease group were assigned to respective canonical pathways indicating increased Liver X receptor/Retinoid X receptor (LXR/RXR) activation, Farnesoid X receptor/Retinoid X receptor (FXR/RXR) activation, acute phase response signaling, sucrose degradation V and regulation of actin-based motility by Rho in the PDR disease group compared to the NPDR disease group.

CONCLUSIONS/INTERPRETATION

Progression from non-proliferative to proliferative retinopathy in type-2 diabetic patients is a complex multi-mechanism and systemic process. Furthermore, saliva was shown to be a feasible alternative sample source for diabetic retinopathy biomarkers.

Inhibition of macrophage migration inhibitory factor reduces diabetic nephropathy in type II diabetes mice

Macrophage migration inhibitory factor (MIF) plays a critical role in inflammation and is elevated in diabetic kidney. However, whether MIF plays a causative role in diabetic nephropathy (DN) remains unclear. In the present study, we have demonstrated that after treatment of 8-week-old diabetic db/db and nondiabetic db/m mice with the MIF inhibitor ISO-1 (20 mg/kg) for 8 weeks, there was a significant decrease in blood glucose, albuminuria, extracellular matrix accumulation, epithelial-mesenchymal transition (EMT), and macrophage activation in the kidney of db/db mice. Incubation of macrophages with MIF induced the production of proinflammatory cytokines, including interleukin (IL) 6, IL-1β, tumor necrosis factor α (TNF-α). The conditioned media (CM) of MIF-activated macrophages and TNF-α induced by MIF caused podocyte damage. Moreover, CM from MIF-activated macrophages induced EMT of renal tubular cells, and this effect was blocked by ISO-1. Thus, MIF inhibition may be a potential therapeutic strategy for DN. This effect may be attributable to its inhibitory effect on macrophage activation in the diabetic kidney.

Expression of intraocular peroxisome proliferator-activated receptor gamma in patients with proliferative diabetic retinopathy

AIMS

To determine whether peroxisome proliferator-activated receptor gamma (PPARγ), which is recognized as a component of the exosomes circulating in plasma, is expressed intraocularly in patients with proliferative diabetic retinopathy (PDR).

METHODS

The concentrations of PPARγ and vascular endothelial growth factor (VEGF) in the aqueous humor and vitreous of 50 eyes with PDR and 38 control eyes were determined by ELISA. The levels of the mRNA and protein of PPARγ were determined in proliferative membranes from 12 PDR and 5 control eyes by quantitative RT-PCR and immunohistochemical analyses.

RESULTS

PPARγ was detected in the culture media of human umbilical vein endothelial cells indicating that PPARγ can be released into the extracellular fluid. The PPARγ concentrations in the aqueous humor and vitreous fluid were significantly higher in PDR patients than in controls (P<0.0005). There was a significant positive correlation between the PPARγ and VEGF concentrations (P<0.0005). The level of PPARγ increased as the clinical stage advanced. The expressions of the mRNA and protein of PPARγ were higher in the membranes of PDR than those of controls. Anti-VEGF therapy significantly reduced the VEGF concentration (P<0.0001) but not the PPARγ concentration.

CONCLUSIONS

PPARγ may play an important role in the pathogenesis of PDR.

Diabetic Retinopathy: Vascular and Inflammatory Disease

Diabetic retinopathy (DR) is the leading cause of visual impairment in the working-age population of the Western world. The pathogenesis of DR is complex and several vascular, inflammatory, and neuronal mechanisms are involved. Inflammation mediates structural and molecular alterations associated with DR. However, the molecular mechanisms underlying the inflammatory pathways associated with DR are not completely characterized. Previous studies indicate that tissue hypoxia and dysregulation of immune responses associated with diabetes mellitus can induce increased expression of numerous vitreous mediators responsible for DR development. Thus, analysis of vitreous humor obtained from diabetic patients has made it possible to identify some of the mediators (cytokines, chemokines, and other factors) responsible for DR pathogenesis. Further studies are needed to better understand the relationship between inflammation and DR. Herein the main vitreous-related factors triggering the occurrence of retinal complication in diabetes are highlighted.

Chemokine mediated monocyte trafficking into the retina: role of inflammation in alteration of the blood-retinal barrier in diabetic retinopathy

Inflammation in the diabetic retina is mediated by leukocyte adhesion to the retinal vasculature and alteration of the blood-retinal barrier (BRB). We investigated the role of chemokines in the alteration of the BRB in diabetes. Animals were made diabetic by streptozotocin injection and analyzed for gene expression and monocyte/macrophage infiltration. The expression of CCL2 (chemokine ligand 2) was significantly up-regulated in the retinas of rats with 4 and 8 weeks of diabetes and also in human retinal endothelial cells treated with high glucose and glucose flux. Additionally, diabetes or intraocular injection of recombinant CCL2 resulted in increased expression of the macrophage marker, F4/80. Cell culture impedance sensing studies showed that purified CCL2 was unable to alter the integrity of the human retinal endothelial cell barrier, whereas monocyte conditioned medium resulted in significant reduction in cell resistance, suggesting the relevance of CCL2 in early immune cell recruitment for subsequent barrier alterations. Further, using Cx3cr1-GFP mice, we found that intraocular injection of CCL2 increased retinal GFP⁺ monocyte/macrophage infiltration. When these mice were made diabetic, increased infiltration of monocytes/macrophages was also present in retinal tissues. Diabetes and CCL2 injection also induced activation of retinal microglia in these animals. Quantification by flow cytometry demonstrated a two-fold increase of CX3CR1⁺/CD11b⁺ (monocyte/macrophage and microglia) cells in retinas of wildtype diabetic animals in comparison to control non-diabetic ones. Using CCL2 knockout (Ccl2^−/−) mice, we show a significant reduction in retinal vascular leakage and monocyte infiltration following induction of diabetes indicating the importance of this chemokine in alteration of the BRB. Thus, CCL2 may be an important therapeutic target for the treatment of diabetic macular edema.

Levels of Selected Aqueous Humor Mediators (IL-10, IL-17, CCL2, VEGF, FasL) in Diabetic Cataract

PURPOSE

To compare levels of selected mediators in serums and aqueous humor (AH) of type 2 diabetes mellitus cataract patients with senile cataract patients, and to determine their association with postoperative corneal edema (CE).

METHODS

Patients (32 senile and 29 diabetic cataract) undergoing standardized phacoemulsification combined with intraocular lens implantation were recruited. CE was assessed using an ordinal scale (grade 0 to 3). IL-10, CCL2, IL-17, FasL, and VEGF were measured by ELISA.

RESULTS

Diabetic patients had higher AH levels of VEGF (p = .042) and IL-10 (p = .021), lower AH levels of FasL (p = .048), and higher serum levels of CCL2 (p = .002). AH levels of CCL2 were higher in diabetic patients with more severe CE at the first postoperative day (p = .012).

CONCLUSIONS

We found disturbed AH microenvironment in diabetic cataract, with significant changes for VEGF, IL-10, and FasL. Higher CCL2 was associated with the development of early postoperative CE in diabetic patients.

Association of monocyte chemoattractant protein-1 (MCP-1)2518A/G polymorphism with proliferative diabetic retinopathy in northern Chinese type 2 diabetes

BACKGROUND

The pathogenesis of proliferative diabetic retinopathy (PDR) remains poorly understood. Recent studies have implicated that monocyte chemoattractant protein-1 (MCP-1) is associated with diabetic microvascular or macrovascular complications. However, the relationship between single nucleotide polymorphism(SNP)c.2518A/G -rs1024611 in the MCP-1 gene with diabetic retinopathy remains controversial. In the present study, we evaluated the association of SNP in the MCP-1 gene with diabetic retinopathy (DR) and diabetic macular edema (DME) in a Chinese population from Northern China with type 2 diabetes.

METHODS

We conducted a case-control study, which enrolled 1,043 subjects with type 2 diabetes (528 with DR, including 277PDR; 515 without DR), and SNP genotyping of c.2518A/G in the MCP-1 gene was performed using the polymerase chain reaction. Genomic DNA was isolated from 3 ml samples of whole blood using a modified conventional DNA extraction method. The genotype and allele frequencies of 2518A/G were studied by using an automated DNA sequencer (ABI PRISM 3730 DNA Sequencer).

RESULTS

The demographic and clinical characteristics did not differ among genotype subgroups. The MCP-1(-2518) GG genotype was significantly associated with DR susceptibility with OR of 1.481 (95 % CI, 1.019-2.153) (P = 0.046). There were no significant differences in the MCP-1(-2518) G allele frequencies in DR compared to non-diabetic retinopathy (DNR) (P > 0.05, OR = 0.841, 95 % CI, 0.705-1.002). The MCP-1(-2518) GG genotype was significantly associated with high-risk PDR susceptibility with OR of 2.656 (95 % CI, 1.222-5.775) (P = 0.014). The MCP-1(-2518) G allele was significantly increased in high-risk PDR patients (P = 0.020, OR = 1.481, 95 % CI, 1.070-2.051) compared with A allele. Genotype and allele frequencies of various DME of the DR patients were compared, but there were no significant associations established (P > 0.05).

CONCLUSIONS

It is likely that the MCP-1 c.2518G/G genotype is a susceptibility gene for DR in Chinese type 2 diabetic patients, especially the high-risk PDR. There is no association with DME and c.2518G/G.

Molecular mechanisms involved in the bidirectional relationship between diabetes mellitus and periodontal disease

Both diabetes and periodontitis are chronic diseases. Diabetes has many adverse effects on the periodontium, and conversely periodontitis may have deleterious effects further aggravating the condition in diabetics. The potential common pathophysiologic pathways include those associated with inflammation, altered host responses, altered tissue homeostasis, and insulin resistance. This review examines the relationship that exists between periodontal diseases and diabetes mellitus with a focus on potential common pathophysiologic mechanisms.

670 nm LED ameliorates inflammation in the CFH(-/-) mouse neural retina

Para-inflammation in the neural retina is thought to contribute to the onset of some age-related retinal diseases. Continuous innate immune system activation, manifests in progressive chronic inflammation, macrophage invasion and cell loss, resulting in visual loss. We have previously shown that mitochondrial function is augmented following 670 nm LED exposure, leading to reduced retinal inflammation. Here, it was asked whether 670 nm LED regulates para-inflammation in an aged-related macular degeneration mouse model. Mutant CFH(-/-) mice were exposed to four 90 s exposures over 2 days for 1 week and 8 weeks. These regimes significantly reduced activated macrophage number, TNF-alpha and MIF protein expression levels. Immuno-reactivity to C3, C3b and calcitonin, all markers of inflammatory status were also altered. Finally, innate immune proteins, TLR 2 and 4, showed a marked decrease in protein expression. These findings support the notion that 670 nm LED regulates innate immunity, alleviating inflammation in the neural retina of an age-related macular degeneration mouse model.

Diabetic retinopathy and inflammation: novel therapeutic targets

Most anti-vascular endothelial growth factor (VEGF) therapies in diabetic macular edema are not as robust as in proliferative diabetic retinopathy. Although the VEGF appears to be a good target in diabetic macular edema, the anti-VEGF therapies appear to be of transient benefit as the edema recurs within a few weeks, and repeated injections are necessary. There is new evidence that indicates 'retinal inflammation' as an important player in the pathogenesis of diabetic retinopathy. There are common sets of inflammatory cytokines that are upregulated in both the serum and vitreous and aqueous samples, in subjects with diabetic retinopathy, and these cytokines can have multiple interactions to impact the pathogenesis of the disease. The key inflammatory events involved in the blood retinal barrier (BRB) alteration appear to be: (1) Increased expression of endothelial adhesion molecules such as ICAM1, VCAM1, PECAM-1, and P-selectin, (2) adhesion of leukocytes to the endothelium, (3) release of inflammatory chemokines, cytokines, and vascular permeability factors, (4) alteration of adherens and tight junctional proteins between the endothelial cells, and (5) infiltration of leukocytes into the neuro-retina, resulting in the alteration of the blood retinal barrier (diapedesis). VEGF inhibition itself may not achieve neutralization of other inflammatory molecules involved in the inflammatory cascade of the breakdown of the BRB. It is possible that the novel selective inhibitors of the inflammatory cascade (like angiopoietin-2, TNFα, and chemokines) may be useful therapeutic agents in the treatment of diabetic macular edema (DME), either alone or in combination with the anti-VEGF drugs.

Therapeutic interventions against inflammatory and angiogenic mediators in proliferative diabetic retinopathy

The global prevalence of diabetes is estimated to be 336 million people, with diabetic complications contributing to significant worldwide morbidity and mortality. Diabetic retinopathy results from cumulative microvascular damage to the retina and inflammation is recognized as a critical driver of this disease process. This paper outlines the pathophysiology leading to proliferative diabetic retinopathy and highlights many of the inflammatory, angiogenic, and cytokine mediators implicated in the development and progression of this disease. We focus a detailed discussion on the current targeted therapeutic interventions used to treat diabetic retinopathy.

Monocyte Chemoattractant Protein 1 (MCP-1) in obesity and diabetes

Monocyte Chemoattractant Protein-1 (MCP-1) is the first discovered and most extensively studied CC chemokine, and the amount of studies on its role in the etiologies of obesity- and diabetes-related diseases have increased exponentially during the past two decades. This review attempted to provide a panoramic perspective of the history, regulatory mechanisms, functions, and therapeutic strategies of this chemokine. The highlights of this review include the roles of MCP-1 in the development of obesity, diabetes, cardiovascular diseases, insulitis, diabetic nephropathy, and diabetic retinopathy. Therapies that specifically or non-specifically inhibit MCP-1 overproduction have been summarized.

Comparison of aqueous humor cytokine and chemokine levels in diabetic patients with and without retinopathy

Background

Major-histocompatibility-complex class I-related chain A (MICA) antigens are the ligands of NKG2D, which is an activating or coactivating receptor expressed on human NK cells and CD8⁺T cells. We sought to determine whether MICA expression in human corneal epithelium (HCE) could affect the cytotoxicity mediated by NK cells or CD8⁺T cells.

Methods

Cell cultures of HCE were harvested from human donor eyes. Flow cytometric analysis and ELISA was performed to determine the levels of MICA expression on HCE. Then, HCE was transfected with a lentivirus vector expressing MICA and GFP. Flow cytometric analysis, RT-PCR, western blot and ELISA were performed to check the levels of MICA expression. For cytotoxicity testing, allogeneic NK cells and CD8⁺T cells were isolated from peripheral blood mononuclear cells of healthy volunteers by magnetic cell sorting. The cytolytic activity of NK cells and CD8⁺T cells was assessed against MICA-transfected HCE (NK cells: E:T ratio = 3:1; CD8⁺T cells: E:T ratio = 10:1) using the nonradioactive cytotoxicity detection kit lactate deshydrogenase.

Results

Surface expression of MICA on corneal epithelium was identified at a low level. A cell line of stable human MICA-transfected corneal epithelium was successfully established. Heightened expression of MICA on HCE was found to promote the cytotoxicity mediated by NK cells or CD8⁺T cells, which could be blocked by an anti-MICA antibody.

Conclusion

MICA molecules may contribute to cytotoxic responses mediated by activated immune effector cells in corneal epithelium immunity.

Role of intravitreal inflammatory cytokines and angiogenic factors in proliferative diabetic retinopathy

OBJECTIVE

Inflammatory reaction has been shown to involve the progress of type 2 (non-insulin-dependent) diabetes. We, therefore, examined the effects of inflammatory cytokines and angiogenic factors in the pathogenesis of proliferative diabetic retinopathy (PDR) in type 2 diabetes.

PATIENTS AND METHODS

Vitreous fluid samples were obtained by vitrectomy from 62 eyes of PDR patients with type 2 diabetes and from 20 eyes of age-matched non-diabetic patients. The concentrations of interleukin 1 beta (IL1B), IL6, IL8, IL10, chemokine (C-C motif) ligand 2 (CCL2), endothelin 1 (EDN1), vascular endothelial growth factor (VEGF), and tumor necrosis factor (TNF) in the vitreous samples were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The concentrations of LI1B, IL6, IL8, CCL2, EDN1, VEGF, and TNF in the vitreous samples were considerably higher in PDR patients in comparison with the controls. However, the level of IL10 in PDR patients was similar to that obtained in the controls. Analysis of the correlations of the studied factors revealed the correlation of VEGF and IL6, VEGF and EDN1, IL8 and CCL2, and EDN1 and TNF in PDR patients. In addition, a significant positive correlation was observed between vitreous TNF as well as EDN1 and serum HbA(1)c levels in PDR patients.

CONCLUSIONS

The inflammatory cytokines and angiogenic factors IL1B, IL6, IL8, CCL2, EDN1, VEGF, and TNF are increased in the vitreous of PDR patients without an increase in IL-10. These results add support to the role of inflammatory cytokines and angiogenic factors in the genesis of PDR. Understanding the implication of these cytokines may provide diagnostic tools and therapeutic targets for treatment and prevention of PDR.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Inflammatory and angiogenic factors in the aqueous humor and the relationship to diabetic retinopathy

PURPOSE

To determine the relationship between the aqueous concentrations of inflammatory and angiogenic factors and the severity of diabetic retinopathy and diabetic macular edema.

METHODS

Aqueous samples were obtained from 50 eyes of diabetic patients and 28 eyes of nondiabetic subjects. The aqueous levels of inflammatory factors, including IL-1β, TNF-α, MCP-1, IP-10, IL-8, IL-6, and VEGF were measured with multiplex bead array assays. The aqueous levels of cytokines were investigated according to the severity of diabetic retinopathy and diabetic macular edema measured by optical coherence tomography.

RESULTS

The aqueous levels of MCP-1, IP-10, IL-8, and VEGF were higher in eyes of diabetic patients than in eyes of nondiabetic subjects. The aqueous levels of MCP-1 and IP-10 were elevated in eyes with severe NPDR and PDR compared to eyes with less severe DR and eyes of nondiabetic subjects. There was a trend toward elevated IL-8 levels in eyes with severe NPDR compared to eyes of nondiabetic subjects. The aqueous levels of VEGF were markedly elevated in eyes with PDR that had not received PRP compared to eyes with severe NPDR. Eyes with PDR that had received PRP treatment showed higher MCP-1 and IP-10 levels than eyes with PDR that had not received PRP treatment. The aqueous levels of IL-6 were positively correlated with TMV and CSMT in eyes with DR.

CONCLUSIONS

Elevation of MCP-1, IP-10, and IL-8 levels in eyes with severe NPDR suggests that inflammatory change precedes the development of neovascularization in PDR. The positive correlation between the aqueous levels of IL-6 and macular thickness indicates that IL-6 may play a central role in the development of diabetic macular edema.

Periodontitis and risk of diabetes mellitus

Diabetes mellitus (DM) is a complex disease with varying degrees of systemic and oral complications. The periodontium is also a target for diabetic damage. Diabetes is a pandemic in both developed and developing countries. In recent years, a link between periodontitis and diabetes mellitus has been postulated. The oral cavity serves as a continuous source of infectious agents that could further worsen the diabetic status of the patient and serve as an important risk factor deterioration of diabetes mellitus. The present review highlights the relationship between diabetes mellitus and periodontitis. The potential mechanisms involved in the deterioration of diabetic status and periodontal disease are also discussed.

The paradox of the neutrophil's role in tissue injury

The neutrophil is an essential component of the innate immune system, and its function is vital to human life. Its production increases in response to virtually all forms of inflammation, and subsequently, it can accumulate in blood and tissue to varying degrees. Although its participation in the inflammatory response is often salutary by nature of its normal interaction with vascular endothelium and its capability to enter tissues and respond to chemotactic gradients and to phagocytize and kill microrganisms, it can contribute to processes that impair vascular integrity and blood flow. The mechanisms that the neutrophil uses to kill microorganisms also have the potential to injure normal tissue under special circumstances. Its paradoxical role in the pathophysiology of disease is particularly, but not exclusively, notable in seven circumstances: 1) diabetic retinopathy, 2) sickle cell disease, 3) TRALI, 4) ARDS, 5) renal microvasculopathy, 6) stroke, and 7) acute coronary artery syndrome. The activated neutrophil's capability to become adhesive to endothelium, to generate highly ROS, and to secrete proteases gives it the potential to induce local vascular and tissue injury. In this review, we summarize the evidence for its role as a mediator of tissue injury in these seven conditions, making it or its products potential therapeutic targets.

Monocyte chemoattractant protein-1 (MCP-1) gene polymorphism as a potential risk factor for diabetic retinopathy in Japanese patients with type 2 diabetes

We examined the association between diabetic retinopathy and monocyte chemoattractant protein (MCP)-1 A-2518G polymorphism in 3802 Japanese type 2 diabetic subjects. The prevalence of diabetic retinopathy was higher as the number of G alleles increased, suggesting that the G allele of this polymorphism is a susceptibility allele for diabetic retinopathy.

The influence of diabetes mellitus on periodontal tissues: a pilot study

Purpose

The purpose of this study was to preliminarily evaluate the influence of diabetes mellitus (DM) on periodontal tissue without establishment of periodontitis.

Methods

Seven-week-old db/db mice were used for the diabetic experimental group and systematically healthy mice of the same age were used as controls. After 1 week of acclimatization, the animals were sacrificed for hard and soft tissue evaluation. The pattern of bone destruction was evaluated by stereomicroscope evaluation with alizarin red staining and radiographic evaluation by microscopic computerized tomography images. Histological evaluation was performed with hematoxylin and eosin stain for evaluation of soft tissue changes.

Results

In both stereomicroscope evaluation and radiograph image analysis, aggressive form of bone destruction was observed in diabetic animals when compared to the systematically healthy controls. In histological evaluation, apical migration of junctional epithelium with slight inflammatory cell infiltration was observed with disarrangement of connective tissue fibers.

Conclusions

Within the limits of this study, diabetic animals presented distortion in periodontal attachment and an aggressive bone loss pattern when compared to the healthy controls, suggesting that DM has an independent effect on periodontal tissue destruction irrespective of the presence or absence of periodontal disease.

Macrophage migration inhibitory factor: critical role in obesity, insulin resistance, and associated comorbidities

Obesity is associated with insulin resistance, disturbed glucose homeostasis, low grade inflammation, and comorbidities such as type 2 diabetes and cardiovascular disease. The cytokine macrophage migration inhibitory factor (MIF) is an ubiquitously expressed protein that plays a crucial role in many inflammatory and autoimmune disorders. Increasing evidence suggests that MIF also controls metabolic and inflammatory processes underlying the development of metabolic pathologies associated with obesity. This is a comprehensive summary of our current knowledge on the role of MIF in obesity and obesity-associated comorbidities, based on human clinical data as well as animal models of disease.

Systemic administration of HMG-CoA reductase inhibitor protects the blood-retinal barrier and ameliorates retinal inflammation in type 2 diabetes

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) are frequently used lipid-lowering drugs in type 2 diabetes. Recent emerging evidence suggests that statins protect cardiovascular function via lipid-independent mechanisms. However, the potential role of statins in diabetic retinopathy in type 2 diabetes is largely unclear. In the present study we have investigated the effect of lovastatin on blood-retinal barrier and inflammatory status in the retina of db/db mice and in cultured retinal cells. Male C57BL/KsJ db/db mice were randomly chosen to receive gastric gavage of lovastatin (10mg/kg/day) or vehicle control for 6 weeks. Retinal vascular permeability, the tight junction and inflammation were determined. The results showed that db/db mice at the age of 19 weeks exhibited significantly increased retinal vascular leakage and decreased tight junction protein level in the retina. Moreover, the expression of pro-inflammatory factors, e.g. ICAM-1 and TNF-alpha, was drastically up-regulated in diabetic retina. Lovastatin treatment normalized all of these changes. In cultured bovine retinal capillary endothelial cells (RCECs) and human ARPE-19 cells, lovastatin attenuated the decrease of tight junction protein (occludin) and adherens junction protein (VE-cadherin) expression-induced by TNF-alpha, a major pro-inflammatory cytokine in diabetic retinopathy. Lovastatin also attenuated TNF-alpha expression in RCEC. Towards the mechanism, we showed that lovastatin ameliorated ICAM-1 expression-induced by hypoxia and TNF-alpha in both RCECs and ARPE-19 cells, in part through inhibition of NF-kappaB activation. Taken together, these findings indicate that lovastatin protects blood-retinal barrier in diabetic retinopathy, which is likely via its anti-inflammatory effects.

The MIF receptor CD74 in diabetic podocyte injury

Although metabolic derangement plays a central role in diabetic nephropathy, a better understanding of secondary mediators of injury may lead to new therapeutic strategies. Expression of macrophage migration inhibitory factor (MIF) is increased in experimental diabetic nephropathy, and increased tubulointerstitial mRNA expression of its receptor, CD74, has been observed in human diabetic nephropathy. Whether CD74 transduces MIF signals in podocytes, however, is unknown. Here, we found glomerular and tubulointerstitial CD74 mRNA expression to be increased in Pima Indians with type 2 diabetes and diabetic nephropathy. Immunohistochemistry confirmed the increased glomerular and tubular expression of CD74 in clinical and experimental diabetic nephropathy and localized glomerular CD74 to podocytes. In cultured human podocytes, CD74 was expressed at the cell surface, was upregulated by high concentrations of glucose and TNF-alpha, and was activated by MIF, leading to phosphorylation of extracellular signal-regulated kinase 1/2 and p38. High glucose also induced CD74 expression in a human proximal tubule cell line (HK2). In addition, MIF induced the expression of the inflammatory mediators TRAIL and monocyte chemoattractant protein 1 in podocytes and HK2 cells in a p38-dependent manner. These data suggest that CD74 acts as a receptor for MIF in podocytes and may play a role in the pathogenesis of diabetic nephropathy.

Pigment epithelium-derived factor mitigates inflammation and oxidative stress in retinal pericytes exposed to oxidized low-density lipoprotein

Oxidized and/or glycated low-density lipoprotein (LDL) may mediate capillary injury in diabetic retinopathy. The mechanisms may involve pro-inflammatory and pro-oxidant effects on retinal capillary pericytes. In this study, these effects, and the protective effects of pigment epithelium-derived factor (PEDF), were defined in a primary human pericyte model. Human retinal pericytes were exposed to 100 microg/ml native LDL (N-LDL) or heavily oxidized glycated LDL (HOG-LDL) with or without PEDF at 10-160 nM for 24 h. To assess pro-inflammatory effects, monocyte chemoattractant protein-1 (MCP-1) secretion was measured by ELISA, and nuclear factor-kappaB (NF-kappaB) activation was detected by immunocytochemistry. Oxidative stress was determined by measuring intracellular reactive oxygen species (ROS), peroxynitrite (ONOO(-)) formation, inducible nitric oxide synthase (iNOS) expression, and nitric oxide (NO) production. The results showed that MCP-1 was significantly increased by HOG-LDL, and the effect was attenuated by PEDF in a dose-dependent manner. PEDF also attenuated the HOG-LDL-induced NF-kappaB activation, suggesting that the inhibitory effect of PEDF on MCP-1 was at least partially through the blockade of NF-kappaB activation. Further studies demonstrated that HOG-LDL, but not N-LDL, significantly increased ONOO(-) formation, NO production, and iNOS expression. These changes were also alleviated by PEDF. Moreover, PEDF significantly ameliorated HOG-LDL-induced ROS generation through up-regulation of superoxide dismutase 1 expression. Taken together, these results demonstrate pro-inflammatory and pro-oxidant effects of HOG-LDL on retinal pericytes, which were effectively ameliorated by PEDF. Suppressing MCP-1 production and thus inhibiting macrophage recruitment may represent a new mechanism for the salutary effect of PEDF in diabetic retinopathy and warrants more studies in future.

Anti-inflammatory effects of pigment epithelium-derived factor in diabetic nephropathy

Previously, we have reported that pigment epithelium-derived factor (PEDF) ameliorates albuminuria and inhibits matrix protein deposition in the kidney of streptozotocin (STZ)-induced diabetic rats, suggesting a renoprotective effect of PEDF in early stages of diabetic nephropathy. As inflammation is a major contributor to the development and progression of diabetic nephropathy, we examined in the present study whether PEDF inhibits renal inflammation in diabetic kidney. Diabetic rats received an intravenous injection of an adenovirus expressing PEDF (Ad-PEDF) or the same titer of a control virus. Three wk after the injection, diabetic rats treated with the control virus showed significantly elevated renal levels of proinflammatory factors such as ICAM-1, MCP-1, TNF-alpha, and VEGF compared with age-matched nondiabetic controls. Ad-PEDF effectively suppressed the overexpression of these proinflammatory factors in diabetic kidneys. In cultured primary human renal mesangial cells (HMC), the high-glucose medium-induced upregulation of VEGF and MCP-1 was largely blocked by PEDF. Furthermore, PEDF inhibited high glucose-induced activation of NF-kappaB, a key transcription factor mediating inflammatory responses, and hypoxia-inducible factor-1, a major activator of VEGF expression in HMC. These results suggest that the renoprotective effect of PEDF against diabetic nephropathy may be partially through its anti-inflammatory activity, likely by blocking the NF-kappaB and HIF-1 pathways.

ROLE OF MACROPHAGES IN COMPLICATIONS OF TYPE 2 DIABETES

1. Macrophage accumulation is a feature of Type 2 diabetes and is associated with the development of diabetic complications (nephropathy, atherosclerosis, neuropathy and retinopathy). The present article reviews the current evidence that macrophages contribute to the complications of Type 2 diabetes. 2. Macrophage-depletion studies in rodent models have demonstrated a causal role for macrophages in the development of diabetic complications. 3. Components of the diabetic milieu (high glucose, advanced glycation end-products and oxidized low-density lipoprotein) promote macrophage accumulation (via induction of chemokines and adhesion molecules) and macrophage activation within diabetic tissues. 4. Macrophages mediate diabetic injury through a variety of mechanisms, including production of reactive oxygen species, cytokines and proteases, which result in tissue damage leading to sclerosis. 5. A number of existing and experimental therapies can indirectly reduce macrophage-mediated injury in diabetic complications. The present article discusses the use of these therapies, given alone and in combination, in suppressing macrophage accumulation and activity. 6. In conclusion, current evidence supports a critical role for macrophages in the evolution of diabetic complications. Present therapies are limited in slowing the progression of macrophage-mediated injury. Novel strategies that are more specific at targeting macrophages may provide better protection against the development of Type 2 diabetic complications.

Gingival levels of monocyte chemoattractant protein-1 (MCP-1) in diabetes mellitus and periodontitis: an experimental study in rats

The objectives of this study were to investigate and compare the monocyte chemoattractant protein-1 (MCP-1) levels of gingival tissues in diabetes mellitus (DM) and periodontitis and to reveal the effects of MCP-1 on periodontal inflammation and destruction in these diseases. DM was created in 15 rats (group 1) by streptozotocin injection, and periodontitis was obtained by ligature induction in 15 rats (group 2). Fifteen systemically and periodontally healthy rats were used as control (group 3). Gingival MCP-1 levels were measured by enzyme-linked immunosorbent assay (ELISA). Periodontal inflammation was quantified by the inflammatory cell infiltration in the gingival samples, whereas periodontal destruction was assessed by the alveolar bone loss in the experimental regions. MCP-1 concentrations were higher in groups 1 and 2 than in group 3 (p < 0.001). Increased gingival inflammatory cell infiltration and alveolar bone loss were observed in groups 1 and 2 compared to group 3 (p < 0.001). There were positive correlations among the MCP-1 level, gingival inflammatory cell infiltration, and alveolar bone loss in groups 1 and 2 (p < 0.001). Our results suggest that (1) DM may lead to enhanced MCP-1 production in periodontal tissues likewise for periodontitis and (2) there may be a positive correlation between the MCP-1 concentration and diseased nature of periodontium in both diseases.

Ocular neovascularization: Implication of endogenous angiogenic inhibitors and potential therapy

Ocular neovascularization (NV) is the primary cause of blindness in a wide range of ocular diseases, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). The exact mechanism underlying the pathogenesis of ocular NV is not yet well understood, and as a consequence, there is no satisfactory therapy for ocular NV. In the last 10 years, a number of studies provided increasing evidence demonstrating that the imbalance between angiogenic stimulating factors and angiogenic inhibitors is a major contributor to the angiogenesis induced by various insults, such as hypoxia or ischemia, inflammation and tumor. The angiogenic inhibitors alone or in combination with other existing therapies are, therefore, believed to be promising in the treatment of ocular NV in the near future. This article reviews recent progress in studies on the mechanisms and treatment of ocular NV, focusing on the implication and therapeutic potential of endogenous angiogenic inhibitors in ocular NV.

Role of monocyte chemotactic protein-1 and nuclear factor kappa B in the pathogenesis of proliferative diabetic retinopathy

Intraocular concentrations of monocyte chemotactic protein-1 (MCP-1) are increased in proliferative diabetic retinopathy (PDR). Nuclear factor kappa B (NF-kappaB) is a transcription factor, and NF-kappaB binding site is located in gene promoter of MCP-1. This study was conducted to investigate the potential role of MCP-1 and NF-kappaB in the pathogenesis of PDR. Epiretinal membrane (ERM) samples were obtained during vitrectomy from 19 eyes with PDR and 16 eyes with idiopathic ERM. They were processed for RT-PCR analysis. Four PDR ERMs were processed for immunohistochemical analysis. In addition, cultured Müller glial cells were stimulated with glycated albumin or high glucose. After the stimulation, we examined nuclear localization of NF-kappaB p50, MCP-1 promoter activity, and MCP-1 concentration in culture media. MCP-1 mRNA expression was significantly higher in PDR (74%) than in idiopathic ERMs (38%) (P < 0.05). Immunohistochemical analysis revealed that MCP-1 protein is colocalized with active form of NF-kappaB p50. In vitro studies demonstrated that glycated albumin or high glucose induces NF-kappaB activation followed by up-regulation of MCP-1 promoter activity and protein production in glial cells. These results suggest that MCP-1, under the regulation of NF-kappaB, is involved in the pathogenesis of PDR.