Inflammatory markers and diabetic retinopathy in type 1 diabetes

Interleukins and redox impairment in type 2 diabetes mellitus: mini-review and pilot study

BACKGROUND

Type 2 diabetes mellitus (T2DM) represents a leading cause of morbidity and premature mortality, low-grade inflammation being acknowledged as a key contributor to its development and progression. A tailored therapeutic approach, based on sensitive and specific biomarkers, could allow a more accurate analysis of disease susceptibility/prognostic and of the response to treatment.

OBJECTIVES

This mini-review and pilot study had two main goals: (1) reviewing the most recent literature encompassing the use of interleukins as inflammatory markers influenced by the redox imbalances in T2DM and (2) assessing parameters that conjunctly evaluate the redox impairment and inflammatory burden of T2DM patients, taking into consideration smoking status, as such group-specific biomarkers are scarcely reported in literature.

METHODS

Firstly, PubMed database was surveyed to select and review the relevant studies employing interleukins as T2DM biomarkers and to assess if studies using combined inflammatory-redox indices were reported. Then, routine biochemical parameters were assessed in a pilot study -T2DM patients with 3 subgroups: non-smokers, smokers and ex-smokers, were compared to a control group of non-diabetic, apparently healthy non-smokers. Protein (AOPPs, AGEs), lipid/HDL (Amplex Red-based method) oxidative damage and inflammatory status (CRP, IL-1β, IL-6, IL-10) biomarkers were assessed. Cytokine ratios and 2 oxidative-inflammatory status indices were developed (IH1 and IH2) and evaluated.

RESULTS

We observed significant differences in terms of serum redox and inflammatory status (AOPPs, AGEs, CRP, CRP/HDL, CRP/IL-6, IL-10/IL-6, IH1) between T2DM patients compared to control and, moreover, between the subgroups formed considering smoking status (CRP, CRP/HDL, IH1). Glycemic control strongly influenced inflammatory status biomarkers: glycemia was positively correlated with the inflammatory parameters (CRP/IL-10) and inversely with the anti-inflammatory ones (IL-10, IL-10/IL-1β ratio).

CONCLUSIONS

Several of the assessed parameters may possess prognostic value for diabetics, especially when comparing subgroups with a different smoking history and could prove useful in clinical practice for assessing disease progress and therapeutic efficacy.

Cytokine Levels in Human Vitreous in Proliferative Diabetic Retinopathy

In this study, we compare the vitreous cytokine profile in patients with proliferative diabetic retinopathy (PDR) to that of patients without PDR. The identification of novel cytokines involved in the pathogenesis of PDR provides candidate therapeutic targets that may stand alone or work synergistically with current therapies in the management of diabetic retinopathy. Undiluted vitreous humor specimens were collected from 74 patients undergoing vitrectomy for various vitreoretinal disorders. Quantitative immunoassay was performed for a panel of 36 neuroinflammatory cytokines in each specimen and assessed to identify differences between PDR (n = 35) and non-PDR (n = 39) patients. Levels of interleukin-8 (IL-8), IL-15, IL-16, vascular endothelial growth factor (VEGF), VEGF-D, c-reactive protein (CRP), serum amyloid-A (SAA), and intracellular adhesion molecule-1 (ICAM1) were significantly increased in the vitreous of PDR patients compared to non-PDR patients (p < 0.05). We report novel increases in IL-15 and IL-16, in addition to the expected VEGF, in the human vitreous humor of patients with PDR. Additionally, we confirm the elevation of ICAM-1, VCAM-1, SAA, IL-8 and CRP in the vitreous of patients with PDR, which has previously been described.

Relationship between Proliferative Diabetic Retinopathy and Inflammatory Markers in Patients with Type 1 Diabetes in Brazil: A Nested Case Control Study

INTRODUCTION

This study examined the relationship between proliferative diabetic retinopathy (PDR) and serum levels of C-reactive protein, VEGF, TNF-α, and IL-6 inflammatory biomarkers, related to the pathophysiology of diabetic retinopathy.

METHODS

This cross-sectional, case control study comprised 240 patients with type 1 diabetes (80 cases with PDR and 160 controls without diabetic retinopathy) who were matched for gender and duration of diabetes.

RESULTS

C-reactive protein was the only inflammatory biomarker that was positively related to PDR (OR 1.96; 95% CI 1.01-3.78, p = 0.0045). We also noted an association between high glycated hemoglobin levels, the use of angiotensin-converting enzyme inhibitor, low glomerular filtration rate, and PDR.

CONCLUSION

Patients with higher levels of C-reactive protein are more likely to present with PDR. We did not find a link between serum levels of VEGF, TNF-α, or IL-6 and PDR. The function of inflammatory biomarkers in PDR must be addressed in further studies.

The association between the red cell distribution width and diabetic nephropathy in patients with type-2 diabetes mellitus

BACKGROUND

Red cell distribution width (RDW) has been reported to be involved in metabolic syndrome and cardiovascular events. Patients with diabetic nephropathy (DN) are often found to be with high level of RDW. The aim of this study was to explore whether RDW was associated with DN severity and progression in patients with type-2 diabetes mellitus (T2DM).

METHODS

A total of 175 T2DM patients with biopsy-proven DN were enrolled. The baseline clinical and pathologic data of these patients was extracted from the medical records. The patients then were divided into two groups based on the median (13.6%) of RDW level; group 1: <13.6% and group 2: ≥13.6%. The effect of RDW level on the renal outcomes was evaluated by using cox regression analysis.

RESULTS

Compared with the patients with lower RDW level, the patients with higher level of RDW had higher proportions of female, longer DM duration, lower levels of eGFR, albumin and hemoglobin, and more serious glomerular damage. Moreover, the RDW levels were negatively corrected with eGFR (r = -0.283, p < 0.001), but positively related with proteinuria (r = 0.227, p = 0.003). In the follow-up period, 81(46.3%) patients had reached ESRD from baseline. Importantly, the Cox regression analyses showed that the levels of RDM had a significant effect on the risk of progression to ESRD (HR = 1.92, p < 0.01), albeit not emerged as an independent predictor.

CONCLUSIONS

These data indicated that the levels of RDW were significantly associated with increased risk of progression to ESRD in patients with DN, despite did not an independent predictor.

Changes in Inflammatory and Bone Turnover Markers After Periodontal Disease Treatment in Patients With Diabetes

BACKGROUND

The underlying mechanisms for increased osteopenia and fracture rates in patients with diabetes are not well understood, but may relate to chronic systemic inflammation. We assessed the effect of treating periodontal disease (POD), a cause of chronic inflammation, on inflammatory and bone turnover markers in patients with diabetes.

MATERIALS AND METHODS

Using an investigator-administered questionnaire, we screened a cross-section of patients presenting for routine outpatient diabetes care. We recruited 22 subjects with POD. Inflammatory and bone turnover markers were measured at baseline and 3 months following POD treatment (scaling, root planing and subantimicrobial dose doxycycline).

RESULTS

There were nonsignificant reductions in high-sensitivity C-reactive protein (6.34-5.52mg/L, P = 0.626) and tumor necrosis factor-alpha (10.37-10.01pg/mL, P = 0.617). There were nonsignificant increases in urinary C-terminal telopeptide (85.50-90.23pg/mL, P = 0.684) and bone-specific alkaline phosphatase (7.45-8.79pg/mL, P = 0.074). Patients with >90% adherence with doxycycline were 6.4 times more likely to experience reduction in tumor necrosis factor-alpha (P = 0.021) and 2.8 times more likely to experience reductions in high-sensitivity C-reactive protein (P = 0.133).

CONCLUSIONS

Treatment of POD in patients with diabetes resulted in nonsignificant lowering of inflammatory markers and nonsignificant increase in bone turnover markers. However, adherence to doxycycline therapy resulted in better treatment effects.

C-reactive protein and diabetic retinopathy in Chinese patients with type 2 diabetes mellitus

AIM

To investigate the relationship between C-reactive protein (CRP) and diabetic retinopathy (DR) in a cohort of Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

Community-based observational cohort study. There were 1131 participants recruited from November 2009 to September 2011 in Desheng community in urban Beijing. Patients diagnosed T2DM were recruited and underwent a standardized evaluation consisting of a questionnaire, ocular and anthropometric examinations and laboratory investigation. The presence and severity of DR were assessed by seven fields 30° color fundus photographs. Subjects were then classified into groups with no DR, any DR, or vision-threatening DR. CRP was analyzed from serum of study subjects.

RESULTS

A total of 1007 patients with T2DM were included for analysis, including 408 (40.5%) men and 599 (59.5%) women. The median CRP level was 1.5 mg/L for women and 1.1 mg/L for men (P=0.004, OR 0.37, 95% CI 0.18-0.74). After adjusting for possible covariates, higher levels of CRP were associated with lower prevalence of any DR (P=0.02, OR 0.55, 95% CI 0.35-0.89), but not associated with vision-threatening DR (P=0.62, OR 0.78, 95% CI 0.28-2.14). After stratification by sex, the inverse association between CRP and DR was found to be statistically significant in men (P=0.006, OR 0.35, 95% CI 0.16-0.73), but not in women (P=0.58, OR 0.88, 95% CI 0.29-1.16).

CONCLUSION

The data drawn from a Chinese population with T2DM suggest that increasing CRP levels may be inversely associated with development of DR.

Relationship between C-Reactive Protein Level and Diabetic Retinopathy: A Systematic Review and Meta-Analysis

Objectives

To date, the relationship between C-reactive protein (CRP) level and diabetic retinopathy (DR) remains controversial. Therefore, a systematic review and meta-analysis was used to reveal the potential relationship between CRP level and DR.

Methods

A systematic search of PubMed, Embase.com, and Web of Science was performed to identify all comparative studies that compared the CRP level of two groups (case group and control group). We defined that diabetic patients without retinopathy and /or matched healthy persons constituted the control group, and patients with DR were the case group.

Results

Two cross sectional studies and twenty case control studies including a total of 3679 participants were identified. After pooling the data from all 22 studies, obvious heterogeneity existed between the studies, so a subgroup analysis and sensitivity analysis were performed. Removing the sensitivity studies, the blood CRP levels in the case group were observed to be higher than those in the control group [SMD = 0.22, 95% confidence interval (CI), 0.11–0.34], and the blood CRP levels in the proliferative diabetic retinopathy (PDR) group were also higher than those in the non-proliferative diabetic retinopathy (NPDR) group [SMD = 0.50, 95% CI, 0.30–0.70].

Conclusions

The results from this current meta-analysis indicate that the CRP level might be used as a biomarker to determine the severity of DR.

How apoptotic β-cells direct immune response to tolerance or to autoimmune diabetes: a review

Type 1 diabetes (T1D) is a metabolic disease that results from the autoimmune attack against insulin-producing β-cells in the pancreatic islets of Langerhans. Currently, there is no treatment to restore endogenous insulin secretion in patients with autoimmune diabetes. In the last years, the development of new therapies to induce long-term tolerance has been an important medical health challenge. Apoptosis is a physiological mechanism that contributes to the maintenance of immune tolerance. Apoptotic cells are a source of autoantigens that induce tolerance after their removal by antigen presenting cells (APCs) through a process called efferocytosis. Efferocytosis will not cause maturation in dendritic cells, one of the most powerful APCs, and this process could induce tolerance rather than autoimmunity. However, failure of this mechanism due to an increase in the rate of β-cells apoptosis and/or defects in efferocytosis results in activation of APCs, contributing to inflammation and to the loss of tolerance to self. In fact, T1D and other autoimmune diseases are associated to enhanced apoptosis of target cells and defective apoptotic cell clearance. Although further research is needed, the clinical relevance of immunotherapies based on apoptosis could prove to be very important, as it has translational potential in situations that require the reestablishment of immunological tolerance, such as autoimmune diseases. This review summarizes the effects of apoptosis of β-cells towards autoimmunity or tolerance and its application in the field of emerging immunotherapies.

Impact of periodontal disease on outcomes in diabetes

INTRODUCTION

The prevalence of periodontal disease (POD) among adults aged 30years and older in the United States is reported to be more than 47%, with higher prevalence seen among patients with diabetes mellitus (DM). POD has been associated with systemic inflammation, a known risk factor for cardiovascular and bone disease, both of which are more common in patients with DM. However, there is mixed evidence that treatment of POD reduces inflammation, improves DM control, and reduces DM complications. Our study objectives are to assess factors associated with POD in patients with DM and determine the impact of POD treatment on inflammation and bone turnover biomarkers associated with complications of DM.

METHODS

In this pilot study, we will first recruit 200 patients with DM to complete a 48-item investigator-administered questionnaire designed to assess socio-economic status, oral health status, adequacy of oral care, glycemic control and presence of DM complications. Responses will be verified by individual chart review. Then, using a crossover design, a subgroup of 24 subjects with responses suggestive of POD will be assigned to undergo POD treatment for three months followed by three months of routine dental care (group 1) or be followed for three months during routine dental care then receive POD treatment for three months (group 2). Outcome measures will be collected before and after POD treatment and include glycemic control and inflammatory and bone turnover biomarkers.

RESULTS

We hypothesize that the prevalence of POD among DM patients will be associated with inadequate glycemic control and greater DM complications.

Diabetic retinopathy risk factors: plasma erythropoietin as a risk factor for proliferative diabetic retinopathy

Purpose

The purpose of this study was to evaluate whether any stage of diabetic retinopathy (DR) is associated with levels of plasma erythropoietin and other plasma parameters.

Methods

It was examined a representative sample of 180 type 2 diabetes patients aged 40 to 79 years. Ophthalmic examination including a funduscopic examination, performed by an experienced ophthalmologist and the retinal finding were classified according to the grading system for diabetic retinopathy of ETDRS (Early Treatment Diabetic Retinopathy Study). It was measured the levels of plasma erythropoietin, cholesterol, triglyceride, apolipoproteins A and B, C-reactive protein, fasting blood glucose and hemoglobin A1C (HbA1C) in 88 DR patients and 92 controls without DR. Risk factors correlated with DR were compared between groups.

Results

The study group of 180 patients included 72 males and 108 females. The mean age of the patients with and without DR was 57.36 ± 8.87 years and 55.33 ± 8.28 years, respectively. Of the 88 patients with DR, only 9 (10%) had proliferative DR and the rest suffered from non-proliferative DR. The mean plasma levels of erythropoietin in proliferative DR group showed a significant difference in comparison to other groups. The mean plasma levels of cholesterol, triglyceride, apolipoproteins A and B, C-reactive protein, and fasting blood glucose were not significantly different in the three groups except for HbA1C. The absolute relative risk (ARR) also showed that erythropoietin was an increasing risk for proliferative DR (ARR, 1.17; 95% confidence interval, 1.060 to 1.420; odds ratio,1.060).

Conclusions

Of the factors studied, erythropoietin level showed significant increase in proliferative DR group. The stepwise raised in mean plasma erythropoietin level which demonstrates significant correlation with proliferative DR versus remaining two groups, will be an indication of its role in proliferative DR.

Epigallocatechin-3-gallate attenuates lipopolysaccharide-induced inflammation in human retinal endothelial cells

AIM

To investigate the mechanism underlying the anti-inflammatory effects of epigallocatechin-3-gallate (EGCG) in lipopolysaccharide (LPS)-stimulated human retinal endothelial cells (HRECs).

METHODS

HRECs pre-treated with EGCG (0-100 µmol/L) were stimulated with LPS (250 ng/mL). Levels of tumor necrosis factor alpha (TNF-α), vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1) and nitric oxide (NO) in the supernatants were determined by enzyme-linked immunosorbent assay (ELISA) and Griess assay. The protein expression of phosphorylated extracellular signal-regulated kinase (ERK) 1/2 and p38 mitogen-activated protein kinases (p38) were determined by Western blot analysis.

RESULTS

EGCG pre-treatment significantly inhibited the secretion of TNF-α, VEGF, MCP-1 and NO in LPS-stimulated HRECs. Moreover, EGCG effectively attenuated LPS-induced activation and phosphorylation of ERK1/2 and p38 in HRECs in a dose-dependent manner.

CONCLUSION

EGCG exhibited inhibitory effects on LPS-induced pro-inflammatory cytokines production by modulating ERK1/2 and p38 pathways in HRECs, suggesting EGCG as a potential candidate for anti-inflammatory intervention.

Neural inflammation and the microglial response in diabetic retinopathy

This chapter reviews the function of microglia and their potential roles in neural inflammation and pathological changes during diabetic retinopathy.

Association between red blood cell distribution width and macrovascular and microvascular complications in diabetes

AIMS/HYPOTHESIS

Red blood cell distribution width (RDW) has been reported to be a risk marker of morbidity and mortality for cardiovascular disease in various study populations. However, no studies have investigated the relationship between RDW and diabetes complications. We therefore evaluated RDW as a marker of macrovascular and microvascular complications in a nationally representative sample of the adult diabetes population in the USA.

METHODS

A cross-sectional study was performed using the nationwide 1988 to 1994 data set from the Third National Health and Nutrition Examination Survey. The association between RDW quartiles and macrovascular and microvascular complications was evaluated in 2,497 non-pregnant adults aged 20 years and older and affected by diabetes. Logistic regression modelling was used to adjust for potential confounding.

RESULTS

Compared with the lowest RDW quartile, higher RDW values (3rd and 4th quartiles) were associated with increased adjusted odds of any vascular complication (OR 4th quartile 2.06 [95% CI 1.11, 3.83]), myocardial infarction (OR 4th quartile 2.45 [95% CI 1.13, 5.28]), heart failure (OR 4th quartile 4.40 [95% CI 1.99, 9.72]), stroke (OR 4th quartile 2.56 [95% CI 1.21, 5.42]) and nephropathy (OR 4th quartile 2.33 [95% CI 1.42, 3.82]). The odds of developing diabetic retinopathy were not significantly increased across RDW quartiles.

CONCLUSIONS/INTERPRETATION

Higher RDW values are associated with increased odds of developing cardiovascular disease and nephropathy in a nationally representative sample of USA adults with diabetes. RDW may be an important clinical marker of vascular complications in diabetes and one that is independent of traditional risk factors and disease duration.

cAMP activates the generation of reactive oxygen species and inhibits the secretion of IL-6 in peripheral blood mononuclear cells from type 2 diabetic patients

Peripheral blood mononuclear cells (PBMNC) from patients with type 2 diabetes (DM2) have generated higher levels of reactive oxygen species (ROS) that were higher than those in cells from healthy individuals. In the presence of a cAMP-elevating agent, ROS production was significantly activated in PBMNC from DM2 patients but it was inhibited in cells from healthy subjects. Higher levels of IL-6 has been detected in the supernatant of PBMNC cultures from DM2 patients in comparison with healthy controls. When cells were cultured in the presence of a cAMP-elevating agent, the level of IL-6 decreased has by 46% in the supernatant of PBMNC from DM2 patients but it remained unaltered in controls. No correlations between ROS and IL-6 levels in PBMNC from DM2 patients or controls have been observed. Secretions of IL-4 or IFNgamma by PBMNC from patients or controls have not been affected by the elevation of cAMP. cAMP elevating agents have activated the production of harmful reactive oxidant down modulated IL-6 secretion by these cells from DM2 patients, suggesting an alteration in the metabolic response possibly due to hyperglicemia. The results suggest that cAMP may play an important role in the pathogenesis of diabetes.

Inflammatory, hemostatic, and other novel biomarkers for diabetic retinopathy: the multi-ethnic study of atherosclerosis

OBJECTIVE

There are conflicting data regarding relationships of systemic biomarkers of inflammation, hemostasis, and homocysteine with diabetic retinopathy. We examined these relationships in the Multi-Ethnic Study of Atherosclerosis.

RESEARCH DESIGN AND METHODS

A total of 921 participants with diabetes were included. Diabetic retinopathy was graded from retinal photographs. We defined two outcomes: any diabetic retinopathy and vision-threatening diabetic retinopathy (severe nonproliferative diabetic retinopathy or worse). Systemic markers analyzed were C-reactive protein, homocysteine, fibrinogen, plasmin-alpha(2)-antiplasmin complex (PAP), interleukin-6, d-dimer, factor VIII, serum creatinine, and urinary albumin-to-creatinine (UAC) ratio.

RESULTS

Prevalence of diabetic retinopathy was 33.2% and vision-threatening diabetic retinopathy 7.1%. After adjusting for established risk factors (diabetes duration, A1C, systolic blood pressure, waist-to-hip ratio, and use of diabetes medications), fibrinogen (odds ratio 1.14 [95% CI 1.01-1.32], P = 0.05) and PAP (1.25 [1.05-1.50], P = 0.01) were associated with any diabetic retinopathy, while PAP (1.54 [1.13-2.11], P = 0.007) and homocysteine (1.57 [1.16-2.11], P = 0.003) were associated with vision-threatening diabetic retinopathy. Only PAP remained significant after additional adjustment for serum creatinine and UAC ratio. Area under receiver-operator characteristic curve (AUROC) for diabetic retinopathy was constructed for established and novel risk factors. Established risk factors accounted for a 39.2% increase of the AUROC, whereas novel markers (fibrinogen, PAP, homocysteine, serum creatinine, and UAC ratio) only accounted for an additional 2.2%.

CONCLUSIONS

There were few associations of novel markers of inflammation, hemostasis, and homocysteine with diabetic retinopathy after controlling for established risk factors. These data suggest that there is limited clinical use of these biomarkers for prediction of diabetic retinopathy.

The role of inflammatory cytokines in diabetes and its complications

The prevalence of diabetes worldwide is increasing rapidly in association with the increase in obesity. Complications are a major fear of patients with diabetes. Complications of diabetes affect many tissues and organs, causing retinopathy, nephropathy, neuropathy, cardiovascular diseases, peripheral vascular diseases, stroke, and periodontal pathologies. Immunologic abnormalities are associated with type 1 and type 2 diabetes and diabetic complications. T cell abnormalities are believed to be the major cause of autoimmune disease in type 1 diabetes, leading to the destruction of pancreatic islets. In type 2 diabetes, inflammation and activation of monocytes are postulated to be important for enhancing insulin resistance and may contribute to the loss of insulin secretory function by islet cells. Many factors can enhance insulin resistance, including genetics, a sedentary lifestyle, obesity, and other conditions, such as chronic inflammation or infection. Increases in inflammation, such as activation of monocytes and increased levels of inflammatory markers, e.g., C-reactive protein, plasminogen activator inhibitor-1, and other cytokines, were reported in insulin-resistant states without diabetes. One possible mechanism is that abnormal levels of metabolites, such as lipids, fatty acids, and various cytokines from the adipose tissue, activate monocytes and increase the secretion of inflammatory cytokines, enhancing insulin resistance. According to this model, obesity activates monocytes and enhances insulin resistance, increasing the risk for type 2 diabetes. Abnormalities in innate immunity might also participate in the development of diabetic complications. In general, hyperglycemia is the main initiator of diabetic retinopathy, nephropathy, and neuropathy, and it participates in the development of diabetic cardiovascular diseases. Although the precise role of inflammation in the development of diabetic microvascular diseases is still unclear, it is likely that inflammation induced by diabetes and insulin resistance can accelerate atherosclerosis in patients with diabetes. Also, it was shown that conditions with an inflammatory basis, such as obesity and type 2 diabetes, can contribute to periodontal disease, suggesting that periodontal abnormalities may be partly influenced by inflammatory changes. Further research is required to confirm the role of inflammation and the onset of diabetes, microvascular diseases, and periodontal pathologies.