Relationship between elastin-derived peptides and the development of microvascular complications: a longitudinal study in children with Type 1 (insulin-dependent) diabetes mellitus

Hyperglycemia with or without insulin resistance triggers different structural changes in brain microcirculation and perivascular matrix

Both type-1 and type-2 DM are related to an increased risk of cognitive impairment, neurovascular complications, and dementia. The primary triggers for complications are hyperglycemia and concomitant insulin resistance in type-2 DM. However, the diverse mechanisms in the pathogenesis of diabetes-related neurovascular complications and extracellular matrix (ECM) remodeling in type-1 and 2 have not been elucidated yet. Here, we investigated the high fat-high sucrose (HFHS) feeding model and streptozotocin-induced type-1 DM model to study the early effects of hyperglycemia with or without insulin resistance to demonstrate the brain microcirculatory changes, perivascular ECM alterations in histological sections and 3D-reconstructed cleared brain tissues. One of the main findings of this study was robust rarefaction in brain microvessels in both models. Interestingly, the HFHS model leads to widespread non-functional angiogenesis, but the type-1 DM model predominantly in the rostral brain. Rarefaction was accompanied by basement membrane thickening and perivascular collagen accumulation in type-1 DM; more severe blood-brain barrier leakage, and disruption of perivascular ECM organization, mainly of elastin and collagen fibers' structural integrity in the HFHS model. Our results point out that the downstream mechanisms of the long-term vascular complications of hyperglycemia models are structurally distinctive and may have implications for appropriate treatment options.

The role of elastin-derived peptides in human physiology and diseases

Once considered as inert, the extracellular matrix recently revealed to be biologically active. Elastin is one of the most important components of the extracellular matrix. Many vital organs including arteries, lungs and skin contain high amounts of elastin to assure their correct function. Physiologically, the organism contains a determined quantity of elastin from the early development which may remain physiologically constant due to its very long half-life and very low turnover. Taking into consideration the continuously ongoing challenges during life, there is a physiological degradation of elastin into elastin-derived peptides which is accentuated in several disease states such as obstructive pulmonary diseases, atherosclerosis and aortic aneurysm. These elastin-derived peptides have been shown to have various biological effects mediated through their interaction with their cognate receptor called elastin receptor complex eliciting several signal transduction pathways. In this review, we will describe the production and the biological effects of elastin-derived peptides in physiology and pathology.

Soluble elastin peptides in cardiovascular homeostasis: Foe or ally

Elastin peptides, also known as elastin-derived peptides or elastokines, are soluble polypeptides in blood and tissue. The blood levels of elastin peptides are usually low but can increase during cardiovascular diseases, such as atherosclerosis, aortic aneurysm and diabetes with vascular complications. Generally, elastin peptides are derived from the degradation of insoluble elastic polymers. The biological activities of elastin peptides are bidirectional, e.g., a pro-inflammatory effect on monocyte migration induction vs. a protective effect on vasodilation promotion. However, recent in vivo studies have demonstrated that elastin peptides promote the formation of atherosclerotic plaques in hypercholesterolemic mice and induce hyperglycemia and elevations in plasma lipid levels in fasted mice. More important, the detrimental effects induced by elastin peptides can be largely inhibited by genetic or pharmacological blockade of the elastin receptor complex or by neutralization of an antibody against elastin peptides. These studies indicate new therapeutic strategies for the treatment of cardiovascular diseases by targeting elastin peptide metabolism. Therefore, the goal of this review is to summarize current knowledge about elastin peptides relevant to cardiovascular pathologies to further delineate their potential application in cardiovascular disease.

High-glucose levels and elastin degradation products accelerate osteogenesis in vascular smooth muscle cells

Diabetes mellitus (DM) is a chronic disease in which the body either does not use or produce the glucose metabolising hormone insulin efficiently. Calcification of elastin in the arteries of diabetics is a major predictor of cardiovascular diseases. It has been previously shown that elastin degradation products work synergistically with transforming growth factor-beta 1 (TGF-β1) to induce osteogenesis in vascular smooth muscle cells. In this study, we tested the hypothesis that high concentration of glucose coupled with elastin degradation products and TGF-β1 (a cytokine commonly associated with diabetes) will cause a greater degree of osteogenesis compared to normal vascular cells. Thus, the goal of this study was to analyse the effects of high concentration of glucose, elastin peptides and TGF-β1 on bone-specific markers like alkaline phosphatase (ALP), osteocalcin (OCN) and runt-related transcription factor 2 (RUNX2). We demonstrated using relative gene expression and specific protein assays that elastin degradation products in the presence of high glucose cause the increase in expression of the specific elastin-laminin receptor-1 (ELR-1) and activin receptor-like kinase-5 (ALK-5) present on the surface of the vascular cells, in turn leading to overexpression of typical osteogenic markers like ALP, OCN and RUNX2. Conversely, blocking of ELR-1 and ALK-5 strongly suppressed the expression of the osteogenic proteins. In conclusion, our results indicate that glucose plays an important role in amplifying the osteogenesis induced by elastin peptides and TGF-β1, possibly by activating the ELR-1 and ALK-5 signalling pathways.

Antibodies to elastin peptides in sera of Belgian Draught horses with chronic progressive lymphoedema

REASONS FOR PERFORMING STUDY

Chronic progressive lymphoedema (CPL) is a recently recognised disease of the lymphatic system characterised by lesions in the skin of the lower legs in several draught horse breeds, including the Belgian Draught hourse. Clinical signs slowly progress and result in severe disfigurement of the limbs. Ideally, supportive treatment should be started early in the disease process. However early diagnosis and monitoring progression of CPL is still a challenge.

HYPOTHESIS

Elastin changes, characterised by morphological alterations as well as increased desmosine levels, in the skin of the distal limbs of horses affected with CPL are probably associated with a marked release of elastin degradation products, which elicit production of circulating anti-elastin antibodies (AEAbs) in the serum. An enzyme-linked immunosorbent assay (ELISA) for detection of serum AEAbs may document elastin breakdown.

METHODS

An ELISA technique was used to evaluate levels of AEAbs in sera of 97 affected Belgian Draught horses that were clinically healthy except for possible skin lesions, associated with CPL in their distal limbs. The horses were divided into 5 groups according to the severity of these skin lesions: normal horses (Group 1, n = 36), horses with mild lesions (Group 2, n = 43), horses with moderate lesions (Group 3, n = 8), horses with severe lesions (Group 4, n = 10) and, as a control, healthy Warmblood horses, unaffected by the disease (Group 5, n = 83).

RESULTS

Horses with clinical signs of CPL had significantly higher AEAb levels compared to clinically normal Belgian Draught horses and to healthy Warmblood horses. These levels correlated with severity of lesions.

CONCLUSIONS

CPL in draught horses is associated with an increase of serum AEAbs.

POTENTIAL RELEVANCE

Evaluation of serum levels of AEAbs by ELISA might be a useful diagnostic aid for CPL. Pathological degradation of elastic fibres, resulting in deficient support of the distal lymphatics, is proposed as a contributing factor for CPL in Belgian Draught horses.

Antibodies to elastin peptides in sera of Warmblood horses at different ages

REASONS FOR PERFORMING STUDY

Early diagnosis and monitoring progression of chronic diseases in elastin-rich tissues, such as chronic progressive lymphoedema in draught horses and chronic obstructive pulmonary disease (COPD) is still a real challenge in the horse. Use of an enzyme-linked immunosorbent assay (ELISA) to detect anti-elastin antibody (AEAb) levels might be useful to assess the status of such diseases. Baseline levels, representing physiological breakdown of elastin in normal horses, are not available at present.

HYPOTHESIS

Levels of AEAb in healthy horses are generally low and follow the same age-related pattern as found in man. Therefore, elevation of AEAb levels in serum can be used to evaluate pathological elastin breakdown in elastin-rich tissues.

METHODS

Sera of 84 clinically healthy Warmblood horses were evaluated for the presence of AEAbs by means of a modified version of an ELISA technique used in man. The horses were divided in 5 age groups: A) < 4 months; B) 4-23 months; C) 2-3 years; D) 4-10 years; and E) > 11 years.

RESULTS

Antibodies to elastin were found in all equine serum samples tested. Their levels were lowest in Group A, low in Groups B and E and highest in animals age 2-10 years.

CONCLUSIONS

Measuring AEAbs in serum of horses by an ELISA technique proved to be possible and levels were stable during well-defined life stages.

POTENTIAL RELEVANCE

Changes in AEAb levels are expected to be useful for early diagnosis and for monitoring progression of diseases that affect elastin-rich tissues, such as chronic progressive lymphoedema and COPD.

Detection of elastin derived peptides in cerebrospinal fluid of patients with first ever ischaemic stroke

OBJECTIVE

We have previously reported the optimized methods for the detection of elastin derived peptides (EDP) in the serum, synovial fluid, and bronchoalveolar lavage. The aim of the present study was to investigate whether EDP are detectable in cerebrospinal fluid (CSF) of patients with acute brain ischaemia.

PATIENTS AND METHODS

Twenty-seven first ever ischaemic stroke patients (mean age 61.5+/-10.8 years; age range 47-70 years; 12 women) were studied in acute phase (1-15 days after the onset) with clinical evaluations, radiological assessments, and the analysis of serum and CSF based on Western blot and ELISA for the detection and quantification of EDP.

RESULTS

None of the serum EDP concentrations are significantly higher in stroke patients compared with 25 healthy control individuals. However, EDP levels in CSF are strongly (p<0.0001) elevated compared with healthy subjects. They correlated with total cholesterol (r=0.53; p=0.02), triglycerides (r=0.67; p=0.004) and retinopathy (r=0.24; p=0.03), and with the interval between the stroke onset and the time of lumbar puncture (r=0.35; p=0.02).

CONCLUSION

EDPs are detectable in CSF of healthy subjects and patients with ischaemic stroke. Acute brain infarction is followed by increased levels of EDP in CSF.

Serum AGE-elastin derived peptides among diabetic children

The purpose of the study was to measure advanced glycated end products (AGE) of elastin in human serum. In the present study, we adapted an ELISA technique for the determination of AGE-elastin-derived peptides (AGE-EDP) in human sera of healthy and diabetic subjects. This test makes use of human aortic elastin hydrolyzed by a chemical procedure (alpha-elastin) and AGE-Hemocyanin. Polyclonal sera from rabbit against AGE-Hemocyanin and from sheep against alpha-elastin were obtained and their specificity was tested via direct and competitive ELISA. Sera of 60 Type 1 (insulin-dependent) diabetic children and 28 healthy subjects were tested. The patients with vascular complications showed significant higher levels of age, diabetes duration, systolic blood pressure (SBP), diastolic blood pressure (DBP), dose, EDP and AGE-EDP than those without vascular complications. AGE-EDP concentrations of all diabetics correlated with triglycerides (r=0.19; p=0.04). The correlation was found between AGE-EDP and DBP in the subgroup of patients with microalbuminuria+retinopathy (r=0.94; p=0.0006). The subgroup of patients with microalbuminuria (n=19) showed correlation with age (r=0.24; p=0.008), AGE-EDP (r=0.65; p=0.0001), EDP (r=0.51; p=0.0001) and SBP (r=0.33; p=0.0003). Further studies are necessary to elucidate the relationship between the serum level of AGE-elastin degradation products and diabetic vascular complications. The measurement of non-invasive markers of elastin synthesis and degradation may be useful in monitoring development and therapeutic intervention in diabetic vascular complications.

Detection of Free Antielastin Antibodies among Diabetic Children

Antibodies to elastin breakdown products are found in the serum of all human subjects and correlate with their respective serum peptide levels. The presence of these antielastin antibodies (AEAbs) and the corresponding antigens in circulation leads to the formation of circulating immune complexes (CICs). The aim of this study was to determine if the serum levels of free AEAbs (not bound in CICs) correlate with the development of vascular complications in diabetic children. To this end, we used a method for detecting immune complexes (complement inhibition factor [CIF]-enzyme-linked immunosorbent assay [ELISA]) in combination with an ELISA for detection of AEAbs. The levels of free immunoglobulin G (IgG) AEAbs were studied in the sera of 54 diabetic children (mean age 12.3+/-4 years; diabetes duration 5.2+/-3.7 years). Thirty-two of the children had vascular complications (group 1), and 22 were without vascular complications (group 2). Twenty healthy children (mean age 13.6+/-4.2 years) were used as controls. The diabetics showed statistically significant higher levels of free AEAbs (0.490 E492+/-0.244 E492 vs 0.307 E492+/-0.081 E492; p = .02) compared with the control group. In group 1, free AEAbs showed statistically significant higher levels than controls (0.523+/-0.269 vs 0.307+/-0.081; p = .016). Eighteen of 54 (33%) patients were positive for free AEAbs (13 of 32 [41%] in group 1 and 5 of 22 [22%] in group 2). Free AEAb levels in all diabetics showed a correlation with systolic blood pressure (r = .44; p = .01), diastolic blood pressure (r = .46; p = .009), total cholesterol (r = .33; p = .05), triglycerides (r= .38; p = .03), high-density lipoprotein (r= -.46; p = .009), serum fructose (r= .43; p = .001), and microalbuminuria (r= .41; p = .002). Patients who had vascular pathology showed a correlation of free AEAbs with microalbuminuria (r= .434; p= .026), serum fructose (r= .63; p = .0004), hemoglobin A1c (r= .392; p = .043), and triglycerides (r= .456; p = .025). These findings suggest that elevated levels of free IgG AEAbs are associated with the development of diabetic vascular complications in children.

Antibodies to advanced glycation end products in children with diabetes mellitus

The tissue accumulation of advanced glycation end products (AGE) alters the structure and function of long-lived proteins. A number of studies have shown that tissue accumulation of AGE correlates with the severity of diabetic complications. Proteins containing AGE are highly immunogenic and anti-AGE antibodies were found in sera of diabetic rats and human. Considering the potential use of anti-AGE antibodies as a marker of AGE deposition during diabetes, we have investigated, by competitive ELISA, the presence of anti-AGE antibodies in sera of 58 children with Type 1 diabetes mellitus. The patients were studied for the period of 5 years. Positive for anti-AGE antibodies were 19 children with diabetes. Fourteen of them showed initial data for vascular complications. Anti-AGE antibodies were related to age (r = .25, P = .024), duration of diabetes (r = .41, P = .0001), HbA1c (r = .27, P = .016), microalbuminuria (r = .41, P = .0001), retinopathy (r = .35, P = .001), triglycerides (r = .27, P = .016), and total cholesterol (r = .19, P = .05). In conclusion, our study showed that the investigation of the levels and dynamics of anti-AGE antibodies might give the possibility for early diagnosis and prognosis of the severity of diabetic late complications.

Serum antibodies to collagen type IV and development of diabetic vascular complications in children with type 1 (insulin-dependent) diabetes mellitus. A longitudinal study

Thickening of basement membrane in capillaries and small vessels is a well-known finding and important in the progression of diabetic microangiopathy. To monitor the metabolism of the basement membrane protein collagen type IV (CIV) in diabetes mellitus, serum levels of IgG, IgM and IgA to CIV were measured using an ELISA method in 28 children with Type 1 diabetes mellitus over a period of 6 years. These values were compared to serum antibodies to CIV in 24 age- and sex-matched controls. At the end of the study, 11 children had diabetic microangiopathy. IgG to CIV was associated with age (r = .33, P = .026), diabetes duration (r = .32, P = .021), HbA1c (r = .31, P = .019), microalbuminuria (r = .32, P = .022) and anti-AGE antibodies (r = .47, P = .0007). IgM to CIV correlated with age (r = .46, P = .001), diabetes duration (r = .45, P = .001), HbA1c (r = .26, P = .038) and anti-AGE antibodies (r = .26, P = .038) and IgA to CIV with triglycerides (r = .29, P = .038) and anti-AGE antibodies (r = .44, P = .0025). We suggest that serum levels of IgG to CIV can be used as a marker for the development of diabetic microalbuminuria.