Evaluation of pro-inflammatory and anti-inflammatory cytokines in type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterized as multifactorial disorders attributable to T cell-mediated destruction of the pancreatic β cells caused by interaction between inherited and ecological factors (Al-Terehi et al. 2016). It accounts for 80–90% in diabetic children and adolescents (Dabelea et al. 2014). The incidence of DM was 387 million in 2014, and a raise of approximately 205 million new cases is expected to occur by 2035 (International Diabetes Federation 2015). Some of the diabetic patients are asymptomatic particularly in children with absolute insulin insufficiency who may undergo polyphagia, polydipsia, polyuria, blurred vision, and weight loss. Uncontrolled diabetic individuals may cause stupor, coma, and ketoacidosis or non-ketotic hyperosmolar syndrome that may lead to death (Galtier 2010).

Cytokines are extracellular proteins of low molecular weight that act as immune response mediators. They perform in highly complex pathways that regulate the inflammatory process, and they are essential to conduct response to the lesion site. Low-grade chronic inflammation and stimulation of the innate immune system are identified to be strongly linked to the pathogenesis of DM (Navarro-González and Mora-Fernández 2008). Pro and anti-inflammatory cytokines have been suggested to be implicated in the events of diabetes (Banerjee and Saxena 2014). Previous reports revealed that definite pro and/or anti-inflammatory cytokines are able to interfere with insulin responsive glucose uptake and stimulate insulin resistance (M and DR 2014).

Pro-inflammatory cytokines, interleukin-1alpha (IL-1α), and interleukin-1beta (IL-1β) are strong inflammatory inducers that could significantly relate to the pathogenesis of DM (Buraczynska et al. 2007). IL-1 is expressed early in the insulate infiltrate and may be regarded as a circulating biomarker of T1DM risk. The major IL-1 activities are performed by IL-1β, which is released from producing cells through pathways as yet unclear, and IL-1α that is either anchored in the plasma membrane or transported into the nucleus as a transcriptional coregulator (Dinarello et al. 2012). Interleukin-10 (IL-10) is an anti-inflammatory and immunosuppressive substance created inside the body and acting as a regulator of immune response (Moore et al. 2001). The release of IL-10 produces an efficient autocrine mechanism for controlling pro-inflammatory cytokine production when its expression was delayed (Kolla et al. 2009).

In the present study, we have tried to illustrate the relationship between pro-inflammatory and anti-inflammatory cytokines such as IL-1α, IL-1β, and IL-10 which are simultaneously responsible for of T1D pathogenesis in children and adolescents below 25 years with varying duration of diabetes.

Type 1 diabetes mellitus is a systemic disease causing abnormal fat, carbohydrate, and protein metabolism owing to insulin insufficiency (Poplawska-Kita et al. 2014). Insulin is one of the islet autoantigens responsible for the stimulation of T-lymphocyte functions, production of inflammatory cytokines, and T1DM progression (Tchorzewski et al. 2001). In T1DM, cells enhancing native and adaptive immunity infiltrate pancreatic islets, thus producing an abnormal inflammatory process known as insulitis recognized by autoreactive T cells and pathological autoantibody production (Bailey-Bucktrout et al. 2013). In cooperation within filtrating innate immune cells that release elevated concentrations of IL-1α and IL-1β, effectors T cells generate β-cells damage (Baumann et al. 2012). The pro-inflammatory cytokines serve in disease strength, while anti-inflammatory cytokines act to delay inflammation and support healing (Dinarello 2007).

In the present study, our data revealed that serum cytokine IL-1α level was significantly higher in T1DM patients than control subjects. This result is in agreement with previous investigators who demonstrated an elevated activity of inflammation in T1D patients because of hyperglycemia and advanced glycation end products construction. Furthermore, Ozer et al. 2003 indicated that the pro-inflammatory cytokines IL-1α and TNF-α could act essential roles alone or in combination in T1D pathogenesis (Glowinska and Urban 2003; Wasmuth et al. 2004; Dandona et al. 2004).

The pro-inflammatory cytokine IL-1β showed higher serum level in T1D patients compared to controls. This result is in the same line with Sesterheim et al. (2007) who observed that this cytokine serve in an autoimmune damage of pancreatic β-cells which favor the process of autoimmune and inflammatory response typical of T1D. Furthermore, our results are in accordance with results obtained by Dogan et al. (2006) who detected high concentrations of inflammatory markers in recently diagnosed T1D patients, what suggests that systemic inflammation is contributed to the onset of the disease. However, the level of this marker is known to stay high during DM progression, and it can probably relate to the development of complications.

Our findings showed that there was a significant increase of serum IL-10 level in diabetic patients as compared to controls. These results are consistent with a study performed by Reis et al. (2012), and He et al. (2014) demonstrated that the elevated levels of IL-10 in T1DM patients may be due to the production from a compensatory mechanism to the rise of pro-inflammatory cytokines. Regarding this purpose, the cytokines implicated in the pathogenesis of T1DM are essential for the progress of the disease, acting both in the positive control (pro-inflammatory cytokines) and in the negative control (anti-inflammatory cytokines) of the inflammation, and they can act in a cascade or alone. Also, Urcelay et al. (2004) demonstrated that IL-10 is an anti-inflammatory cytokine that appears to act trying to prevent DM development.

In our study, cytokine levels did not present correlations with each other. A probable reason for this fact is that the high levels of these inflammatory mediators appear primarily at the local level, through the advance of DM complication showing a systemic slight raise in blood flow in diabetic patients (Cardoso et al. 2017). On the other hand, a correlation was observed between the pro-inflammatory cytokines (IL-1α and IL-1β) that is important in the pathogenesis of insulin-dependent diabetes mellitus (Alexandraki et al. 2008). So, El-Mohamady et al. (2009) confirmed the principle that IL-1 antagonism has therapeutic potential in the management of DM, but they recommended that autoimmune constituent of T1DM might require therapeutic combination (e.g., with anti-CD3 antibodies). Additionally, He et al. (2014) noticed that the levels of cytokines (IL-1 and IL-10) were accomplished and they noticed the higher levels of cytokines in diabetic children as compared to controls.

Our data revealed that insulin was positively associated with IL-1β.Similar outcomes were achieved by previous study of Pérez-Marín et al. (2015) who detect elevated concentration of IL-1β in early diagnosed children with diabetes. So, Molloul et al. (2010) proposed that suppression of cytokine induced β-cells destruction may be a possible current approach for β-cell protection. Regarding age, our study reported a positive correlation with both of BMI and IL-1β which are in consistent with other investigations who stated that age-related decay of immune function owing to obesity, redox discrepancy, social stress, and chronic infections by pathogens are some of the aspects which prompt permanent irregulation and stimulation of the pro-inflammatory response (Vasto et al. 2007; Chung et al. 2009; Freund et al. 2010; Shaw et al. 2011; Danese and BS 2012; Li 2013). Such as, low-grade, chronic inflammation is induced by greater concentrations of pro-inflammatory proteins owing to an age-associated redox discrepancy that induces several pro-inflammatory signaling pathways (Chung et al. 2009; Xu et al. 2010).

In order to predict if the inflammatory cytokines (IL-1α, IL-1β, and IL-10) were beneficial as biomarkers in early screening for T1DM and in monitoring immunological treatment, diagnostic reliability was determined to select the best cut-off value within the patient group (calculated from the control group). Our data revealed that IL10 was the best to discriminate T1DM with cut-off value of 5.95 pg/ml and, at this value, the sensitivity was 96% and specificity was 90%. The next most useful test was IL-1α and its cut-off value of 0.615 pg/ml at which the sensitivity was 87% and specificity was 80%. Finally, the last one was IL-1β with cut-off value of 0.545 pg/ml, which had the lowest sensitivity and specificity (70% and 67%, respectively).

We conclude that circulating levels of IL-1α, IL-1β, and IL-10 were highly significant in type 1 diabetic patients compared to healthy controls but their levels are not related to disease duration and body mass index. This is highly expressive of the convenience of these cytokines alone, or in combination to support in further investigative type 1 diabetes pathophysiology and monitoring pharmacological interventions to interpose with the progress and evolution of diabetes.

Our study had some limitations; first of all, it was a retrospective study. Secondly, the patients, in whom autoimmune diseases (e.g., rheumatoid arthritis); steroid therapy and macrovascular complications (e.g., myocardial infarction); any diabetic complications such as nephropathy, neuropathy, or retinopathy; and acute or chronic diseases were excluded, which mean that there was a potential bias in the selection of the study subjects.

Future larger scale prospective studies are required to confirm the correlations and predict the value of more pro-inflammatory and anti-inflammatory serum levels within patients with T1DM.