Cardiovascular complications of diabetes

CELF1 contributes to aberrant alternative splicing patterns in the type 1 diabetic heart

Dysregulated alternative splicing (AS) that contributes to diabetes pathogenesis has been identified, but little is known about the RNA binding proteins (RBPs) involved. We have previously found that the RBP CELF1 is upregulated in the diabetic heart; however, it is unclear if CELF1 contributes to diabetes-induced AS changes. Utilizing genome wide approaches, we identified extensive changes in AS patterns in Type 1 diabetic (T1D) mouse hearts. We discovered that many aberrantly spliced genes in T1D hearts have CELF1 binding sites. CELF1-regulated AS affects key genes within signaling pathways relevant to diabetes pathogenesis. Disruption of CELF1 binding sites impairs AS regulation by CELF1. In sum, our results indicate that CELF1 target RNAs are aberrantly spliced in the T1D heart leading to abnormal gene expression. These discoveries pave the way for targeting RBPs and their RNA networks as novel therapies for cardiac complications of diabetes.

Antidiabetic potential of polyoxotungstates: in vitro and in vivo studies

Diabetes mellitus is a chronic metabolic disorder continuously affecting people all over the world. A common way to treat diabetes mellitus is to limit the conversion of carbohydrates into glucose which is mediated by glucosidase enzymes. Diabetes mellitus is also famous for its life-threatening microvascular (retinopathy, neuropathy and nephropathy) and macrovascular (atherosclerosis) complications. Aldose reductases present in eye lens (ALR1) and kidney (ALR2) are responsible for microvascular complications. The production of advanced glycation end products (AGEs) is involved in the development of atherosclerosis. The present work was aimed at the synthesis and in vitro/in vivo evaluation of different polyoxotungstates against glucosidases (α- and β), aldose reductases (ALR1 and ALR2) and AGEs to discover a new treatment which may limit the complications associated with diabetes mellitus. The polyanion [P6W18O79](20-) was found to be the most potent inhibitor of α-glucosidase (IC50 = 1.33 ± 0.41 μM), ALR1 (IC50 = 0.4 ± 0.009 μM) and ALR2 (IC50 = 0.38 ± 0.02 μM). Animal studies showed that the polyanion [H2W12O40](6-) was very effective in reducing the blood glucose level to 84.25 ± 5.07 mg dL(-1) when compared with standard antidiabetic drug glibenclamide (150.62 ± 9.35 mg dL(-1)) measured after maximum 8 h of dose administration. The data obtained from in vitro and in vivo experiments confirm that [P6W18O79](20-) and [H2W12O40](6-) could be used as a new treatment of diabetes mellitus.

Neutrophil-lymphocyte ratio as a predictor of major adverse cardiac events among diabetic population: a 4-year follow-up study

The neutrophil-lymphocyte ratio (NLR) is an inflammatory marker of major adverse cardiac events (MACEs) in both acute coronary syndromes and stable coronary artery disease. The use of NLR as a predictive tool for MACEs among diabetic patients has not been elucidated. An observational study included 338 diabetic patients followed at our clinic between 2007 and 2011. Patients were arranged into equal tertiles according to the 2007 NLR. The MACEs included acute myocardial infarction, coronary revascularization, and mortality. The lowest NLR tertile (NLR < 1.6) had fewer MACEs compared with the highest NLR tertile (NLR > 2.36; MACEs were 6 of 113 patients vs 24 of 112 patients, respectively; P < .0001). In a multivariate model, the adjusted hazard ratio of third NLR tertile compared with first NLR tertile was 2.8 (95% confidence interval 1.12-6.98, P = .027). The NLR is a significant independent predictor of MACEs in diabetic patients. Further studies with larger numbers are needed.

The role of Cys-298 in aldose reductase function

Diabetic tissues are enriched in an "activated" form of human aldose reductase (hAR), a NADPH-dependent oxidoreductase involved in sugar metabolism. Activated hAR has reduced sensitivity to potential anti-diabetes drugs. The C298S mutant of hAR reproduces many characteristics of activated hAR, although it differs from wild-type hAR only by the replacement of a single sulfur atom with oxygen. Isothermal titration calorimetry measurements revealed that the binding constant of NADPH to the C298S mutant is decreased by a factor of two, whereas that of NADP(+) remains the same. Similarly, the heat capacity change for the binding of NADPH to the C298S mutant is twice increased; however, there is almost no difference in the heat capacity change for binding of the NADP(+) to the C298S. X-ray crystal structures of wild-type and C298S hAR reveal that the side chain of residue 298 forms a gate to the nicotinamide pocket and is more flexible for cysteine compared with serine. Unlike Cys-298, Ser-298 forms a hydrogen bond with Tyr-209 across the nicotinamide ring, which inhibits movements of the nicotinamide. We hypothesize that the increased polarity of the oxidized nicotinamide weakens the hydrogen bond potentially formed by Ser-298, thus, accounting for the relatively smaller effect of the mutation on NADP(+) binding. The effects of the mutant on catalytic rate constants and binding constants for various substrates are the same as for activated hAR. It is, thus, further substantiated that activated hAR arises from oxidative modification of Cys-298, a residue near the nicotinamide binding pocket.

Maternal diet high in fat reduces docosahexaenoic acid in liver lipids of newborn and sucking rat pups

The effect of a maternal diet high in fat, similar to Western foods, and of diabetes on liver essential fatty acid composition of the mother and the newborn and sucking pups was investigated. Female Sprague-Dawley rats were fed on either a low-fat (42 g/kg) or a high-fat (329 g/kg) diet for 10 d before mating, throughout pregnancy and post-partum. On the first day of pregnancy, diabetes was induced by intravenous administration of streptozotocin in half the animals from the two diet groups. Half the pups were killed at birth, and the remaining pups and mothers at days 15 and 16 respectively. At birth, there was a significant reduction in the proportions of docosahexaenoic acid (DHA) in the liver phosphoglycerols and neutral lipids of the pups of both high-fat control and diabetic mothers compared with those of low-fat control and diabetic mothers. Diabetes decreased arachidonic (AA) and linoleic acid values in both the low- and high-fat groups at birth. The sucking pups of both the high-fat control and diabetic mothers exhibited a significant reduction in DHA and a concomitant compensatory increase in AA and a lowering in DHA–AA balance. In the mothers, the high-fat diet significantly increased the proportions of DHA in ethanolamine phosphoglycerols but had no observable effect in choline phosphoglycerols and neutral lipids. In the fetus the DHA level (g/100 g total fatty acids) was disproportionately reduced by the maternal high-fat diet. The adverse effect of the high-fat diet on the level of DHA (g/100 g total fatty acids) was greater in the neonate (and by implication the fetus) than in the sucking pups or mothers. It is concluded that a distortion of the biochemistry is induced in the offspring through a maternal high-fat diet, without genetic predisposition.

Dimethylarginine dimethylaminohydrolase inhibition and asymmetric dimethylarginine accumulation contribute to endothelial dysfunction in rats exposed to glycosylated protein: Effects of aminoguanidine

OBJECTIVES

To determine whether alterations of endogenous asymmetric dimethylarginine (ADMA) concentration and dimethylarginine dimethylaminohydrolase (DDAH) activity are involved in endothelial dysfunction induced by glycosylated bovine serum albumin (GBSA) in rats and effects of aminoguanidine on them.

METHODS

Endothelium-dependent relaxation of aortic rings from Sprague-Dawley rats after treatment with GBSA in vitro and in vivo was tested. Serum concentrations of ADMA, nitrite/nitrate, and activities of aortic DDAH, nitric oxide synthase (NOS) and superoxide dismutase were measured in GBSA-treated rats. Moreover, serum contents of glycosylated serum protein, and malondialdehyde were also assayed.

RESULTS

Endothelium-dependent relaxation was significantly impaired either by incubation of aortic rings with GBSA (1.70mmol/l) in vitro for 60min or by injection of GBSA (35mg/kg/d, i.v.) to normal rats for 4 weeks, and serum ADMA levels were remarkably elevated in GBSA-treated rats, which was accompanied by decreases of nitrite/nitrate concentrations, NOS and DDAH activities. Furthermore, elevated glycosylated serum protein, malondialdehyde levels, and reduced superoxide dismutase activity were also observed in GBSA-treated rats. Treatment with aminoguanidine not only improved impairment of endothelium-dependent relaxation but also prevented elevation of endogenous ADMA, which were concomitant with increases of nitrite/nitrate concentration, NOS and DDAH activity. Serum levels of glycosylated serum protein, malondialdehyde, and vascular superoxide dismutase activity were also normalized after aminoguanidine treatment.

CONCLUSIONS

Decreased DDAH activity and elevated endogenous ADMA is implicated in endothelial dysfunction of rats exposed to GBSA. Aminoguanidine can protect endothelium of rat aorta against injury induced by GBSA both in vitro and in vivo.

Fibrates inhibit aldose reductase activity in the forward and reverse reactions

Fibrates such as bezafibrate, gemfibrozil, clofibric acid, ciprofibrate and fenofibrate, are ligands for peroxisome proliferator-activated receptor alpha (PPARalpha), and are used as therapeutic agents in the treatment of hyperlipidemia. Synthesis and accumulation of sorbitol in cells due to aldose reductase (AR) activity is implicated in secondary diabetic complications. In pursuit of finding a lead compound identification to design an effective AR inhibitor employing fragment-based design-like approach, we found that this class of compounds and their nearest neighbors could inhibit AR. Bezafibrate and gemfibrozil displayed a mixed non-competitive inhibition pattern in the glyceraldehyde reduction activity and pure non-competitive inhibition pattern in the benzyl alcohol oxidation activity of AR. Clofibric acid, ciprofibrate and fenofibrate showed pure non-competitive inhibition patterns in the forward reaction. In the reverse reaction, clofibric acid displayed a non-competitive inhibition pattern while ciprofibrate and fenofibrate displayed competitive inhibition patterns. This finding reveals for the first time a novel attribute of the fibrates in the regulation of AR activity and may be useful as lead compounds to control the function of AR in the progression and treatment of secondary diabetic complications in addition to other clinical conditions. Alternatively, these findings demonstrate that AR plays a significant role in the fibrate metabolism under various scenarios.

Cardiovascular effects of endomorphins in alloxan-induced diabetic rats

Endomorphins, the endogenous, potent and selective mu-opioid receptor agonists, have been shown to decrease systemic arterial pressure (SAP) in rats. In the present study, responses to endomorphins were investigated in systemic vascular bed of alloxan-induced diabetic rats and in non-diabetic rats. Diabetes was induced by alloxan (220 mg/kg, i.p.) in male Wistar rats. At 4-5 weeks after the onset of diabetes, intravenous injections of endomorphins (1-30 nmol/kg) led to an increase of SAP and heart rate (HR) consistently and dosed-dependently. SAP increased 7.68+/-3.73, 11.19+/-4.55, 21.19+/-2.94 and 27.48+/-6.21% from the baseline at the 1, 3, 10 and 30 nmol/kg dose, respectively, of endomorphin 1 (n=4; p<0.05), and similar changes were observed in response to endomorphin 2. The hypertension could be antagonized markedly by i.p. 2 mg/kg of naloxone. On the other hand, bilateral vagotomy would attenuate the effects of hypertension and diminished the changes of HR in response to endomorphins. With diabetic rats, 6-10 weeks after the induction of diabetes, intravenous injections of endomorphins produced non-dose-related various changes in SAP, such as a single decrease, or a single increase, or biphasic changes characterized by an initial decrease followed by a secondary increase, or no change at all. These results suggest that diabetes may lead to the dysfunction of the cardiovascular system in response to endomorphins. Furthermore, the diabetic rats of 4-5 weeks after alloxan-treatment, the increase in SAP and HR caused by i.v. endomorphins might be explained by a changed effect of vagus and by a naloxone-sensitive mechanism.

AGE-related cross-linking of collagen is associated with aortic wall matrix stiffness in the pathogenesis of drug-induced diabetes in rats

Diabetes mellitus is major risk factor for cardiovascular disease, and atherosclerosis accounts for most of the morbidity and mortality of diabetic patients. To examine the effects of diabetes on the vessel wall, we examined the association of collagen cross-linking in relation to matrix stiffness of the descending aorta in streptozotocin-induced diabetic rats. The matrix stiffness of the vessel was determined by measuring the tensile properties of the tissue. Seven weeks following the establishment of diabetes, both control and diabetic rats were killed and the descending aortas were excised and analyzed. The findings from biomechanical analysis indicated a significant increase in maximum load (26%), stress (22%), Young's modulus of elasticity (60%), and toughness (32%) in diabetic aortas compared to control. In contrast, the maximum strain of the diabetic rat aorta was significantly reduced by 20% compared to control rats, suggesting stiffening of the blood vessel. The results from biochemical analysis showed that the amount of total collagen increased by 21% in diabetic tissues compared to the control. The sequential extractions of collagen showed that the diabetic specimens yielded 34% more neutral salt-soluble collagen (NSC) than the control. The amount of pepsin-soluble collagen was 31% less in diabetic tissues than in the control group, whereas the amount of insoluble collagen (ISC) increased by 56%. A significant accumulation in advanced glycation end products (AGEs) were seen in pepsin- and collagenase-soluble collagen in diabetic vessel. Furthermore, the altered biomechanical properties of the vessel wall were strongly correlated with the biochemistry of collagen. Overall, these results provide evidence that the diabetic state is associated with the changes in collagen biochemistry and in the biomechanics of the blood vessel.

Disparity of autonomic control in type 2 diabetes mellitus

AIMS/HYPOTHESIS

Acute insulinaemia activates the sympathetic drive in a nonuniform manner. The extent and nature of such activation in type 2 diabetic patients who do not have neuropathy have not yet been addressed despite evidence relating sympathetic activation to cardiovascular risk. We planned to determine the magnitude and extent of the sympathetic drive and its reflex responses in patients with type 2 diabetes and fasting hyperinsulinaemia.

METHODS

We measured resting muscle sympathetic nerve activity (MSNA) as the mean frequency of multi-unit bursts and single unit muscle sympathetic nerve activity (s-MSNA) in 17 overweight patients with type 2 diabetes and two matched normal control groups comprising 17 overweight and 16 normal-weight subjects. We also tested the MSNA and s-MSNA responses to cold pressor and isometric hand-grip tests, along with the effect of sympatho-vagal balance on heart period variability.

RESULTS

Both MSNA and s-MSNA in the group with type 2 diabetes (66+/-3.5 bursts/100 beats and 78+/-4.5 impulses/100 beats) were greater (at least p<0.0001) than in the overweight control group (42+/-2.6 bursts/100 beats and 48+/-3.4 impulses/100 beats) and normal-weight control group (43+/-6.2 bursts/100 beats and 51+/-7.1 impulses/100 beats), though the three groups had similar reflex responses, baroreflex sensitivity and sympatho-vagal balance controlling the heart period.

CONCLUSIONS/INTERPRETATION

The patients with type 2 diabetes had no evidence of impaired reflex or autonomic control of heart period variability at a time when there was central sympathetic activation to the periphery. Furthermore, being overweight itself was not associated with sympathetic activation.

Impact of type 2 diabetes mellitus on sympathetic neural mechanisms in hypertension

BACKGROUND

Essential hypertension (EHT) is a major cardiovascular risk factor, and the additional presence of type 2 diabetes mellitus (DM2) increases this risk. However, although the sympathetic nerve hyperactivity of EHT is known to play a role in cardiovascular risk, the level of sympathetic nerve activity is known neither in DM2 nor in hypertensive type 2 diabetic patients (EHT+DM2). Therefore, we planned to quantify the vasoconstrictor sympathetic nerve activity in patients with EHT+DM2 and with DM2 relative to that in matched groups with EHT and normal blood pressure (NT).

METHODS AND RESULTS

In 68 closely matched subjects with EHT+DM2 (n=17), DM2 (n=17), EHT (n=17), and NT (n=17), we measured resting muscle sympathetic nerve activity as the mean frequency of multiunit bursts (MSNA) and of single units (s-MSNA) with defined vasoconstrictor properties. The s-MSNA in EHT+DM2 (97+/-3.8 impulses/100 beats) was greater (at least P<0.001) than in EHT (69+/-3.4 impulses/100 beats) and DM2 (78+/-4.1 impulses/100 beats), and all these were significantly greater (at least P<0.01) than in NT (53+/-3.3 impulses/100 beats) despite similar age and body mass index. The MSNA followed a similar trend. In addition, the level of insulin was also raised in EHT+DM2 (20.4+/-3.6 microU/mL) and DM2 (18.1+/-3.1 microU/mL; at least P<0.05) compared with HT or NT.

CONCLUSIONS

Patients with EHT+DM2, EHT, or DM2 had central sympathetic hyperactivity, although plasma insulin levels were raised only in EHT+DM2 and DM2. The combination of EHT and DM2 resulted in the greatest sympathetic hyperactivity and level of plasma insulin, and this hyperactivity could constitute a mechanism for the increased risks of this condition.

[Possible genetic causes for late complications of diabetes mellitus]

BACKGROUND

Hyperglycemia occurs in every patient with diabetes mellitus. It is the most important factor in the development of diabetic complications. However, the onset, intensity and the progression of complications show large interindividual variations. Manifestation in families and the lack of complications in some diabetics with poor metabolic control indicate a genetic predisposition to develop diabetic complications like nephropathy, neuropathy and angiopathy.

NEPHROPATHY

Diabetic nephropathy occurs only in 25 to 40% of the diabetic patients. Therefore a genetic risk factor for this complication is very likely. Various variations in genes like ACE-gene and angiotensinogen-gene have been described, which could be associated with the development of diabetic nephropathy.

NEUROPATHY

Peripheral diabetic neuropathy occurs in up to 66% of all diabetics. Therefore and because of the possible pathological mechanisms genetic risk factors like variations in the Na/K-ATPase-gene and in the aldose reductase-gene are discussed.

RETINOPATHY

An association between diabetic retinopathy and polymorphisms in the ACE-gene and the aldose reductase-gene seems very unlikely, because up to 75% of the diabetic patients suffer from retinopathy after 15 years of diabetes.

MACROANGIOPATHY

A large number of studies show an association between diabetic macroangiopathy and genetic variations in the ACE-gene (I/D-variant) and the paraoxonase-gene (2 isoforms).

CONCLUSION

Based on the current evidence for associations of genetic markers with diabetic complications, the generation of an individual risk profile based on genetic markers seems to be possible. In addition to near euglycemia genetic markers could direct therapeutic strategies and lead to new therapeutic approaches.

Diabetes complications and their potential prevention: aldose reductase inhibition and other approaches

Despite recent advances both in the chemistry and molecular pharmacology of antidiabetic drugs, diabetes still remains a life-threatening disease, which tends to spread all over the world. The clinical profile of diabetic subjects is often worsened by the presence of several long-term complications, namely neuropathy, nephropathy, retinopathy, and cataract. Several attempts have been made to prevent or at least to delay them. The most relevant are reported in this review, including the development of compounds acting as aldose reductase inhibitors, anti-advanced glycation end-product drugs, free radical scavengers, vasoactive agents, essential fatty acid supplementation, and neurotropic growth factors.