Massimo Boemi

Oscillating glucose is more deleterious to endothelial function and oxidative stress than mean glucose in normal and type 2 diabetic patients

OBJECTIVE—To explore the possibility that oscillating glucose may outweigh A1C levels in determining the risk for cardiovascular diabetes complications. RESEARCH DESIGN AND METHODS—A euinsulinemic hyperglycemic clamp at 5, 10, and 15 mmol/l glucose was given in increasing steps as a single “spike” or oscillating between basal and high levels over 24 h in normal subjects and type 2 diabetic patients. Flow-mediated dilatation, a marker of endothelial function, and plasma 3-nitrotyrosine and 24-h urinary excretion rates of free 8-iso PGF2α, two markers of oxidative stress, were measured over 48 h postclamp. RESULTS—Glucose at two different levels (10 and 15 mmol/l) resulted in a concentration-dependent fasting blood glucose–independent induction of both endothelial dysfunction and oxidative stress in both normal and type 2 diabetic patients. Oscillating glucose between 5 and 15 mmol/l every 6 h for 24 h resulted in further significant increases in endothelial dysfunction and oxidative stress compared with either continuous 10 or 15 mmol/l glucose. CONCLUSIONS—These data suggest that oscillating glucose can have more deleterious effects than constant high glucose on endothelial function and oxidative stress, two key players in favoring cardiovascular complications in diabetes. Concomitant vitamin C infusion can reverse this impairment.

Serum paraoxonase is reduced in type 1 diabetic patients compared to non-diabetic, first degree relatives; influence on the ability of HDL to protect LDL from oxidation

Paraoxonase is a serum enzyme with an anti-oxidant function, protecting low density lipoproteins (LDL) from oxidative modifications. Diabetic patients are suggested to be at greater risk of oxidative stress, which may contribute to the significantly higher incidence of vascular disease in this population. Less efficient protection mechanisms may be one feature of the greater susceptibility to oxidation in diabetes. In this context, the present study examined the hypothesis that serum paraoxonase is reduced in type 1 (insulin-dependent) diabetic patients and that the reduction can affect the anti-oxidant capacity of HDL. Serum paraoxonase concentrations and activities were compared in type 1 patients and first degree, non-diabetic relatives with particular attention paid to the confounding effects of paraoxonase gene polymorphisms. In addition, the ability of HDL-paraoxonase to protect low density lipoproteins from oxidation was analysed in an in vitro system. Serum concentrations and enzyme activities of paraoxonase were significantly lower in type 1 patients compared to non-diabetic, first degree relatives. The differences were independent of promoter and coding region polymorphisms, which influence serum concentrations and activities of the enzyme. Overall, paraoxonase concentrations were a mean 13.3+/-4.5% lower (P<0.02) in type 1 patients. Specific activities did not differ between diabetic and non-diabetic groups. The concentration ratios of LDL cholesterol:paraoxonase (1.37+/-0.51 vs. 1.18+/-0.37, P=0.003) and apolipoprotein B:paraoxonase (0.84+/-0.33 vs. 0.71+/-0.40; P=0.012) were significantly higher in diabetic patients, consistent with a reduced capacity to protect LDL from oxidation. In vitro oxidation studies showed that a significantly higher level of lipid hydroperoxides was generated in LDL in the presence of HDL, containing paraoxonase levels equivalent to those of type 1 patients, compared to HDL containing paraoxonase levels equivalent to those of control subjects (mean difference 8.1%, P<0.05). The study demonstrates that serum concentrations of the antioxidant enzyme paraoxonase are significantly lower in type 1 (insulin-dependent) diabetic patients compared to non-diabetic, first-degree relatives, independently of known gene polymorphisms. Concentrations are reduced to an extent that can affect its anti-oxidant capacity. The results are consistent with the contention that modifications to serum paraoxonase in type 1 patients can increase risk of lipoprotein oxidation and, consequently, risk of vascular disease.

Mitochondrial DNA backgrounds might modulate diabetes complications rather than T2DM as a whole.

Mitochondrial dysfunction has been implicated in rare and common forms of type 2 diabetes (T2DM). Additionally, rare mitochondrial DNA (mtDNA) mutations have been shown to be causal for T2DM pathogenesis. So far, many studies have investigated the possibility that mtDNA variation might affect the risk of T2DM, however, when found, haplogroup association has been rarely replicated, even in related populations, possibly due to an inadequate level of haplogroup resolution. Effects of mtDNA variation on diabetes complications have also been proposed. However, additional studies evaluating the mitochondrial role on both T2DM and related complications are badly needed. To test the hypothesis of a mitochondrial genome effect on diabetes and its complications, we genotyped the mtDNAs of 466 T2DM patients and 438 controls from a regional population of central Italy (Marche). Based on the most updated mtDNA phylogeny, all 904 samples were classified into 57 different mitochondrial sub-haplogroups, thus reaching an unprecedented level of resolution. We then evaluated whether the susceptibility of developing T2DM or its complications differed among the identified haplogroups, considering also the potential effects of phenotypical and clinical variables. MtDNA backgrounds, even when based on a refined haplogroup classification, do not appear to play a role in developing T2DM despite a possible protective effect for the common European haplogroup H1, which harbors the G3010A transition in the MTRNR2 gene. In contrast, our data indicate that different mitochondrial haplogroups are significantly associated with an increased risk of specific diabetes complications: H (the most frequent European haplogroup) with retinopathy, H3 with neuropathy, U3 with nephropathy, and V with renal failure.

Underexpression of the apolipoprotein E4 isoform in an Italian population.

Apolipoprotein (apo) E polymorphism was examined in a population of Italian blood donors. A significantly reduced frequency of the epsilon 4 allele was observed in comparison to a combined Caucasian population. Apo E polymorphism was also associated with significant differences in plasma lipid and lipoprotein levels. Notably, total and low-density lipoprotein cholesterol as well as triglycerides were increased, whereas high-density lipoprotein cholesterol was decreased in carriers of the E4 isoform. This is the first report of a significantly lower frequency of the apo E4 isoform in a European population. The reduced occurrence of an apo E isoform, which is associated with a more atherogenic lipid/lipoprotein profile, may be a contributory factor to the relatively lower incidence of cardiovascular disease in the Italian population.

Zinc-Dependent Low Thymic Hormone Level in Type I Diabetes

Zinc is required for optimal functioning of the immune system. It was recently reported that one of the best-known thymic hormones responsible for the maturation and differentiation of the thymus-derived T-lymphocyte line, i.e., serum thymic factor (STF), is biologically active only when bound to zinc ions; in this form it has been called thymulin (Zn-STF). Because low serum and tissue zinc values have been reported to occur in diabetic conditions, and because defects of T-lymphocyte–dependent functions are also present in diabetic patients, even metabolically well-controlled diabetic patients, we investigated the serum level of zinc and the plasma level of both active Zn-STF and inactive STF thymic hormones in 15 young patients suffering from type I (insulin-dependent) diabetes. Serum zinc levels were significantly reduced in diabetic conditions and did not correlate with the degree of metabolic compensation measured by glycosylated hemoglobin. In diabetes, the active form of thymulin is strongly reduced, whereas the inactive form is abnormally elevated. In vitro zinc addition to diabetic plasma samples also induces zinc saturation of inactive thymic hormone molecules: the total thymic hormone measured in these experimental conditions shows values in diabetic patients comparable with those observed in healthy age-matched individuals, suggesting that low thymulin levels recorded in diabetic conditions are due not to a thymic failure in synthesizing and secreting thymic hormone but to a peripheral defect in zinc saturation of the hormone molecules. The zinc-dependent failure of thymic hormone, present even in fairly compensated diabetic conditions, might account for the apparent insulin-independent immunological abnormalities associated with type I diabetes.

N-Glycomic Changes in Serum Proteins in Type 2 Diabetes Mellitus Correlate with Complications and with Metabolic Syndrome Parameters

Background Glycosylation, i.e the enzymatic addition of oligosaccharides (or glycans) to proteins and lipids, known as glycosylation, is one of the most common co-/posttranslational modifications of proteins. Many important biological roles of glycoproteins are modulated by N-linked oligosaccharides. As glucose levels can affect the pathways leading to glycosylation of proteins, we investigated whether metabolic syndrome (MS) and type 2 diabetes mellitus (T2DM), pathological conditions characterized by altered glucose levels, are associated with specific modifications in serum N-glycome. Methods We enrolled in the study 562 patients with Type 2 Diabetes Mellitus (T2DM) (mean age 65.6±8.2 years) and 599 healthy control subjects (CTRs) (mean age, 58.5±12.4 years). N-glycome was evaluated in serum glycoproteins. Results We found significant changes in N-glycan composition in the sera of T2DM patients. In particular, α(1,6)-linked arm monogalactosylated, core-fucosylated diantennary N-glycans (NG1(6)A2F) were significantly reduced in T2DM compared with CTR subjects. Importantly, they were equally reduced in diabetic patients with and without complications (P<0.001) compared with CTRs. Macro vascular-complications were found to be related with decreased levels of NG1(6)A2F. In addition, NG1(6)A2F and NG1(3)A2F, identifying, respectively, monogalactosylated N-glycans with α(1,6)- and α(1,3)-antennary galactosylation, resulted strongly correlated with most MS parameters. The plasmatic levels of these two glycans were lower in T2DM as compared to healthy controls, and even lower in patients with complications and MS, that is the extreme “unhealthy” phenotype (T2DM+ with MS). Conclusions Imbalance of glycosyltransferases, glycosidases and sugar nucleotide donor levels is able to cause the structural changes evidenced by our findings. Serum N-glycan profiles are thus sensitive to the presence of diabetes and MS. Serum N-glycan levels could therefore provide a non-invasive alternative marker for T2DM and MS.

Paraoxonase 1: genetics and activities during aging.

The increasing longevity of the population, one of the most important issues throughout the planet, is a very complex phenomenon (trait), likely resulting from a variety of environmental determinants interacting with and modulated by genetic mechanisms, mostly devoted to maintenance and repair. In fact, the genes involved in longevity impact upon basic processes such as inflammation, glucose and energy utilization, and oxidative stress. Based on the free radical theory of aging, in the past few years we have focused our attention on an enzyme that protects lipids from peroxidative damage-paraoxonase 1 (PON1). PON1 has been widely investigated, especially for its involvement in atherosclerosis and age-related diseases. In this review, we summarize data on the role played by PON1 on aging and its possible involvement in human longevity, focusing on the relationship between genetic polymorphisms and enzyme activity and its capability to counteract oxidative stress.

MiR-21-5p and miR-126a-3p levels in plasma and circulating angiogenic cells: relationship with type 2 diabetes complications

Innovative biomarkers are required to manage type 2 diabetic patients (T2DM). We focused our study on miR-126-3p and miR-21-5p levels, as biomarkers of endothelial function and inflammation. MiRNAs levels were measured in plasma from 107 healthy subjects (CTR) and 193 diabetic patients (T2DM), 76 without (T2DM NC) and 117 with (T2DM C) complications. When diabetic complication were analysed as a whole, miR-126-3p and miR-21-5p levels declined significantly from CTR to T2DM NC and T2DM C patients. When miRNAs levels were related to specific complications, significantly higher miR-21-5p levels (0.46 ± 0.44 vs. 0.26±0.33, p < 0.001) and significant lower miR-126-3p levels (0.21±0.21 vs. 0.28±0.22, p = 0.032) were found in T2DM with previous major cardiovascular events (MACE) vs. all the others T2DM patients. To confirm these results we focused on circulating angiogenic cells (CACs) from a subgroup of 10 CTR, 15 T2DM NC and 15 T2DM patients with MACE. CACs from T2DM patients expressed higher miR-21-5p and lower miR-126-3p levels than CACs from CTR. Furthermore, CACs from T2DM + MACE showed the highest levels of miR-21-5p. Circulating miR-21-5p and miR-126-3p emerge as dynamic biomarkers of systemic inflammatory/angiogenic status. Their expression levels in CACs from T2DM with MACE suggest a shift from a proangiogenic to a proinflammatory profile.

Diabetes mellitus and chronic heart failure.

Cardiovascular disease has a high prevalence in diabetic patients. Diabetes mellitus is an important risk factor for atherosclerosis and coronary disease mainly through obesity, hyperlipidemia, insulin-resistance, hyperinsulinemia, hyperglycemia and altered homeostasis. The correlation between diabetes and chronic heart failure is not widely documented in the literature. According to the Framingham study, the incidence of cardiovascular morbidity per year is 39.1% in diabetic males and 17.2% in diabetic females; chronic heart failure afflicts 7.6% of diabetic males and 11.4% of diabetic females. Actual knowledge about pathophysiology suggests that cardiac involvement in diabetes is not only related to macrovascular injury but also to other factors, such as alterations of autonomic nervous system, that can contribute to diabetic cardiopathy. The present study evaluated the prevalence of chronic heart failure in an Italian diabetic population in order to discuss the rationale of the therapeutic strategies.

Neuronal semaphorins regulate a primary immune response.

Semaphorins are involved in a wide range of biological processes, including axon guidance, neuronal migration, angiogenesis, cardio- and osteo-genesis. Recently they have also been found to be important for immune response. Sema3A reduces the activation of T cells through its cell-surface receptors, including members of the neuropilin and plexin families. By contrast, Sema4D (CD100), which is expressed on the surface of T, B and dendritic cells, increases B cell and dendritic cell function using either plexin B1 or CD72 as receptors. The transmembrane protein Sema4A is involved in the activation of immune cells through interactions with Tim-2. Emerging evidence also indicates that additional semaphorins and related molecules seem to function in the reciprocal stimulation of T cells and antigen-presenting cells (APCs). This paper discusses the functions of these semaphorins in the immune system, focusing on their roles in T cell-APC interactions.