Adults with autoimmune diabetes: vascular risk, emerging complications and novel disease pathways

Background. The population of adults with autoimmune diabetes has grown worldwide. This is largely the result of better care and increased longevity of people with young-onset type 1 diabetes (T1D), but also of the increased number of latent autoimmune diabetes of the adult (LADA) diagnoses. Adults with autoimmune diabetes differ from those with type 2 diabetes (T2D), with challenges and uncertainties about the impact of aging in people with autoimmune diabetes. In the immediate future, we will have to face complications of autoimmune diabetes in the context of aging and long exposure to the disease, but a paucity of data is available in this regard. Therefore, studies elucidating the pathophysiology, epidemiology and clinical features of autoimmune diabetes in adults and elderly people, both those with T1D and LADA, are needed. Hypothesis. We hypothesized that clinical features and risk of diabetic chronic complications may differ in adults with different forms of diabetes. Therefore, we also hypothesize that the study of vascular and bone disorders in adults with autoimmune diabetes may unveil novel risk factors and pathways of chronic complications. Aims and methods. The overall aim of this project was to investigate the pathophysiology and clinical features of autoimmune diabetes and its complications during the adulthood and the senescence. More specifically we aimed to: 1. Evaluate whether rates and risk factors for vascular complications differ between LADA and T2D. To this aim data from the UK Prospective Diabetes Study (UKPDS) have been retrieved and analyzed. Diabetes autoantibodies (AAb) were measured in 5,062 UKPDS participants. The incidence of major adverse CV events (MACE), defined as CV death, nonfatal myocardial infarction or nonfatal stroke, was compared in those with LADA (>/- 1 AAb test positive) with those without LADA (AAb negative). 2. Evaluate bone health and its relationship with vascular complications in adults and aging people with autoimmune diabetes. To this aim adults with T1D followed in the centers of the IMDIAB group and elderly people enrolled in the 50-Years Joslin Medalist Study were fully characterized in terms of history of metabolic control, chronic complications and bone fractures. Bone mineral density was measured by DEXA in a subgroup of these subjects. Risk factors for impaired bone health and the relationship between bone fragility and vascular complications were investigated in both young adults and elderly with long standing type 1 diabetes. 3. To investigate circulating osteoprogenitors as a new mechanism of vascular complication in type 1 diabetes Osteocalcin (OCN) + monocytes were studied in a unique population with ≥ 50 years of T1D, the 50-Year Joslin Medalists. CD45 bright/CD14+/OCN+ cells in the circulating mononuclear blood cell fraction were quantified by flow cytometry in and reported as percentage of CD45 bright cells. Mechanisms were studied by inducing OCN expression in human monocytes in vitro. Results. Specific aim 1. There were 567 participants with LADA (11.2%). Compared with T2D, they were younger, with higher mean HbA1c and HDL-cholesterol values but lower body mass index, total cholesterol and systolic blood pressure values (all p <0.01). After median (25th – 75th percentile) 17.3 (12.6-20.7) years follow-up, MACE occurred in 157 (17.4 per 1000 person-years) LADA and 1544 (23.5 per 1000 person-years) T2D participants respectively (HR 0.73, 95% Confidence Interval [CI] 0.62–0.86, p<0.001). However, after adjustment for confounders, this difference was no longer significant (HRadj 0.90, 95% CI 0.76–1.07, p = 0.22). Specific aim 2. Among 600 adult subjects with T1D (age: 41.9±12.8 years, disease duration: 19.9 ± 12.0 years; BMI: 24.4 ± 3.7 kg/m2; 5-year average HbA1c: 7.6 ± 1.0%), 18.5% experienced at least one fragility fracture (73.8% had only one and 26.2% had more than one fracture). In this population, increased risk for >/-2 fractures was found in subjects in the highest tertile of HbA1c (>/-7.9%) compared with the lowest tertile (/-26 years versus <14 years) (RRR 7.59 [1.60-35.98], p = 0.01). The presence of neuropathy increased the risk of single fracture (RRR adj: 2.57 [95%CI: 1.21-5.46]), and multiple fractures (p-value for the difference of the effect on outcomes: 0.99). Differently, in a selected population of elderly T1D subjects (age: 66.0 ± 7.6 years) with an extreme disease duration (>50 years) we found a lower prevalence of fragility fractures (1.12%). Because of the low prevalence of chronic complications in this population (cardiovascular disease: 39.9%; retinopathy: 46.4%; nephropathy: 12.5%), we hypothesized an association between vascular complications and bone health. This was confirmed by a significant association found between history of cardiovascular disease and low bone mass at the femoral neck (RR: 4.6 [1.2–18.1], p = 0.03). Specific aim 3. Subjects without history of CVD (n = 16) showed lower levels of OCN+ monocytes than subjects with CVD (n = 14) (13.1 ± 8.4% vs 19.9 ±6.4%, p = 0.02). OCN+ monocytes level was inversely related to total high-density lipoprotein (HDL) cholesterol levels (r = -0.424, p = 0.02), large (r = -0.413, p = 0.02) and intermediate (r = -0.445, p = 0.01) HDL sub-fractions, but not to small HDL. In vitro, incubation with oxidized low-density lipoprotein (OxLDL) significantly increased the number of OCN+ monocytes (p <0.01). This action of OxLDL was significantly reduced by the addition of HDL in a concentration dependent manner (p <0.001). Inhibition of the scavenger receptor B1 (SR-B1) reduced the effects of both OxLDL and HDL (p <0.05). Conclusions. This project evaluated in depth the risk of cardiovascular disease, bone fragility and their intimate relationship in adult and elderly subjects with autoimmune diabetes. Our data show that the healthier cardiometabolic profile of subjects with LADA compared with T2D translates in a lower incidence of major cardiovascular events, which is mostly explained by traditional cardiovascular risk factors, including age, lipids and blood pressure. This highlights the importance of aggressively tackling these cardiovascular risk factors in autoimmune diabetes to keep the lower risk of CVD. On the other hand, we are showing an alarming increased risk of bone fractures in adults with T1D. As bone fragility fractures are among the most important causes of reduced life expectancy in elderly and because of the ageing of T1D population, our data claim for immediate action to tackle this emerging complication. Of note, we are showing a close relationship between bone fragility and chronic complications of diabetes, which has been confirmed also in a special population of elderly subjects with T1D protected from vascular complications. This might suggest that strategies to prevent vascular complications may also aid in preventing fragility fractures in T1D. Furthermore, this led to the hypothesis that common mechanisms of disease are shared between bone and vascular complications. This was explored by looking at the role of circulating osteoprogenitors in CVD, which were found lower in T1D subjects protected from CVD. Results regarding the regulation of OCN expression on monocytes by OxLDL and HDL through SR-B1 and its relationship with CVD provide new information on vascular pathophysiology specifically in T1D. Indeed, these findings may provide new insights on the mechanism of HDL-mediated cardiovascular protection in autoimmune diabetes and promote advances in therapeutic strategies in this population