LDL oxidative modifications in well- or moderately controlled type 2 diabetes

Metabolomics study of fibroblasts damaged by UVB and BaP

We have recently shown that both UVB and BaP can induce the production of ROS, apoptosis and even cancer. However, the differences in the metabolic profiles of skin damaged by UVB, BaP or UVB combined with BaP have not been studied. Therefore, we examined the metabolic changes in the human foreskin fibroblast injured by UVB or BaP or the combination of the two, using ultra performance liquid chromatography (UPLC) coupled with quadrupole time-of-flight mass spectrometry (qTOF-MS). 24 metabolites were altered in the UVB damage group, 25 in the BaP damage group, and 33 in the UVB combined with BaP group. These alterations indicated that the metabolic mechanisms of HFF-1 cells treated with UVB or BaP are related to multiple main metabolites including glycerophosphocholine (PC), lactosylceramide (LacCer), guanidinosuccinic acid (GSA), glutathione(GSH), and lysophosphatidylcholine (LysoPC) and the main mechanisms involved glycerophospholipid and glutathione metabolism. Thus, our report provided useful insight into the underlying mechanisms of UVB and BaP damage to skin cells.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

LDL oxidative modification and carotid atherosclerosis: results of a multicenter study

OBJECTIVE

Serum LDL conjugated diene concentration is a marker of oxidative modification of LDL. We investigated the relationship between LDL conjugated dienes and cross-sectional subclinical atherosclerosis assessed by carotid IMT in high-risk subjects of a multicenter study.

METHODS

Serum LDL conjugated dienes and ultrasonographically assessed carotid intima-media thickness (IMT(mean), IMT(max) and IMT(mean-max)) were available for 553 subjects from Finland, France, Italy, the Netherlands, and Sweden.

RESULTS

In multivariate regression analysis, gender (p < 0.001), age (p < 0.001), systolic blood pressure (IMT(mean), p = 0.01; IMT(mean-max), p = 0.05) and serum LDL conjugated dienes (p = 0.02 for both IMT(mean) and IMT(mean-max)) were the strongest determinants of IMT variation, adjusted for study center, ultrasound videotape reader and serum LDL cholesterol. Pack-years of smoking, added into the regression model, did not destroy the significant association between increased serum LDL conjugated dienes and IMT. Ratio of LDL conjugated dienes to LDL particle cholesterol was higher in subjects of Northern recruiting centers than of Southern centers (r = 0.39, p < 0.0001).

CONCLUSIONS

There was a cross-sectional association between in vivo increased LDL oxidative modification and subclinical atherosclerosis after adjustment for traditional risk factors. The subjects in Northern countries of Europe had more oxidatively modified lipids per cholesterol in LDL particle than subjects in Southern countries.

Effects of oxidized low-density lipoproteins on the hepatic microvasculature

Oxidized low-density lipoproteins (oxLDLs) are involved in proinflammatory and cytotoxic events in different microcirculatory systems. The liver is an important scavenger organ for circulating oxLDLs. However, the interaction of oxLDL with the hepatic microcirculation has been poorly investigated. The present study was conducted to examine the effects of differently modified oxLDLs on the hepatic microvasculature. C57Bl/6J mice were injected intravenously with low-density lipoprotein (LDL), or LDL oxidized for 3 h (oxLDL(3)) or 24 h (oxLDL(24)), at doses resembling oxLDL plasma levels in cardiovascular disease patients. Radioiodinated ligands were used to measure blood decay and organ distribution, and nonlabeled ligands to evaluate microcirculatory responses, examined by in vivo microscopy 30-60 min after ligand injection, immunohistochemistry, and scanning and transmission electron microscopy. Mildly oxLDL (oxLDL(3)) was cleared from blood at a markedly slower rate than heavily oxLDL (oxLDL(24)), but significantly faster than LDL (P < 0.01). Injected oxLDLs distributed to liver. OxLDL effects were most pronounced in central areas of the liver lobules where oxLDL(3) elicited a significant (P < 0.05) reduction in perfused sinusoids, and both oxLDL(3) and oxLDL(24) significantly increased the numbers of swollen endothelial cells and adherent leukocytes compared with LDL (P < 0.05). OxLDL-treated livers also exhibited increased intercellular adhesion molecule (ICAM)-1 centrilobular staining. Electron microscopy showed a 30% increased thickness of the liver sinusoidal endothelium in the oxLDL(3) group (P < 0.05) and a reduced sinusoidal fenestration in centrilobular areas with increased oxidation of LDL (P for linear trend <0.05). In conclusion, OxLDL induced several acute changes in the liver microvasculature, which may lead to sinusoidal endothelial dysfunction.

Low density lipoprotein from patients with Type 2 diabetes increases expression of monocyte matrix metalloproteinase and ADAM metalloproteinase genes

Aims

Type 2 diabetes is characterised by increased plasma concentrations of pro-inflammatory cytokines [such as tumour necrosis factor – alpha; TNF-α] and soluble forms of adhesion molecules involved in leukocyte – endothelial interactions. These molecules are synthesised as transmembrane proteins and the plasma soluble forms are generated by ectodomain cleavage from the cell surface by members of the ADAM [adisintegrin and metalloproteinase] proteinase family. We hypothesised that plasma low density lipoprotein [LDL] from subjects with Type 2 diabetes would influence in vitro monocytic ADAM and matrix metalloproteinase [MMP] gene expression differently compared to control LDL.

Methods

We examined relative mRNA expression by real time PCR in a monocytic cell line [THP-1] cultured for 4, 8 and 24 hrs with human plasma LDL derived from subjects with [n = 5] or without [n = 4] Type 2 diabetes. Gene expression for MMP-1 and 9, and ADAM – 8, 15, 17 and 28 was studied.

Results

Type 2 diabetes LDL significantly increased gene expression of MMP – 1 [p < 0.01] MMP – 9 [p < 0.001], and ADAM 17 [p < 0.05], – 28 [p < 0.01] and – 15 [p < 0.01] compared to control LDL. Type 2 diabetes LDL had disparate effects on inhibitors of MMP.

Conclusion

These data suggest that Type 2 diabetes LDL could lead to increased adhesion molecule and TNF alpha cell surface shedding, and vascular plaque instability, by promoting increased expression of ADAM and MMP genes.

The Role of Consumption of Alpha-Linolenic, Eicosapentaenoic and Docosahexaenoic Acids in Human Metabolic Syndrome and Type 2 Diabetes- A Mini-Review

The human metabolic syndrome and its frequent sequela, type 2 diabetes are epidemic around the world. Alpha-linolenic acid (ALA, 18:3 n-3), eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) consumption ameliorates some of these epidemics' features thus leading one to question if consumption of EPA and DHA, and their metabolic precursor ALA reduce the conversion of metabolic syndrome to type 2 diabetes and reduce the major cause of death in the metabolic syndrome and type 2 diabetes-myocardial infarction. Contributing to myocardial infarction are metabolic syndrome's features of dyslipidemia (including elevated total cholesterol and LDL-c), oxidation, inflammation, hypertension, glucose intolerance, overweight and obesity. Inflammation, glucose and lipid levels are variously influenced by disturbances in various adipocytokines which are in turn positively impacted by n-3 polyunsaturated fatty acid consumption. Type 2 diabetes has all these features though elevated total cholesterol and LDL-c are rarer. It is concluded that EPA and DHA consumption significantly benefits metabolic syndrome and type 2 diabetes primarily in terms of dyslipidemia (particularly hypertriglyceridemia) and platelet aggregation with their impact on blood pressure, glucose control, inflammation and oxidation being less established. There is some evidence that EPA and/or DHA consumption, but no published evidence that ALA reduces conversion of metabolic syndrome to type 2 diabetes and reduces death rates due to metabolic syndrome and type 2 diabetes. ALA's only published significance appears to be platelet aggregation reduction in type 2 diabetes.

Electronegative low-density lipoprotein subfraction from type 2 diabetic subjects is proatherogenic and unrelated to glycemic control

BACKGROUND

The physicochemical and biological characteristics of electronegative low-density lipoprotein (LDL) (LDL(-)) from type 2 diabetic patients (DM2), before and after insulin therapy, were studied.

METHODS

Total LDL was subfractionated in LDL(+) (native LDL) and LDL(-) by anion-exchange chromatography.

RESULTS

The proportion of LDL(-) was increased in plasma from DM2 patients compared to control subjects (13.8 +/- 4.6% versus 6.1 +/- 2.5, P < 0.05) and was not modified after glycemic optimization (14.0 +/- 5.9%). LDL(-) from DM2 patients presented similar differential characteristics versus LDL(+) than LDL(-) from controls; that is, decreased apoB and oxidizability, and increased triglyceride, nonesterified fatty acids (NEFA), apoE, apoC-III, platelet-activating factor (PAF) acetylhydrolase activity and aggregability. No difference in particle size, antioxidants, malondialdehyde (MDA), fructosamine or glycated low-density lipoprotein (gLDL) was observed between LDL subfractions. Concerning differences between LDL subfractions isolated from DM2 and from control subjects, the former showed increased MDA, fructosamine and gLDL proportion and decreased LDL size and antioxidant content. The only effect of glycemic optimization was a decrease in fructosamine and gLDL in LDL(+) from DM2 subjects. LDL(-) from DM2 patients presented low binding affinity to the low-density lipoprotein receptor (LDLr) in cultured fibroblasts compared to LDL(+) and two- to threefold increased ability to release interleukin-8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) in endothelial cells.

CONCLUSION

These results suggest that, although nonenzymatic glycosylation and oxidation are increased in type 2 diabetes, these features would not be directly involved in the generation of LDL(-). Moreover, LDL(-) properties suggest that the high proportion observed in plasma could promote accelerated atherosclerosis in DM2 patients through increased residence time in plasma and induction of inflammatory responses in artery wall cells.

The inflammatory properties of electronegative low-density lipoprotein from type 1 diabetic patients are related to increased platelet-activating factor acetylhydrolase activity

AIMS/HYPOTHESIS

Chemical and biological characteristics of LDL(-) from type 1 diabetic subjects were analysed. The diabetic patients were studied during poor and optimised glycaemic control.

MATERIALS AND METHODS

Total LDL was subfractionated into electropositive LDL(+) and electronegative LDL(-) by anion exchange chromatography and the lipid and protein composition of the two determined.

RESULTS

LDL(-) differed from LDL(+) in that it had higher triglyceride, non-esterified fatty acids, apoE, apoC-III and platelet-activating factor acetylhydrolase (PAF-AH), as well as lower apoB relative content. No evidence of increased oxidation was observed in LDL(-). LDL(-) increased two-fold the release of interleukin 8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) in endothelial cells, suggesting an inflammatory role. Optimisation of glycaemic control after insulin therapy decreased the proportion of LDL(-), but did not modify the composition of LDL subfractions, except for a decrease in PAF-AH activity in LDL(-). The possibility that LDL(-) could be generated by non-enzymatic glycosylation was studied. Fructosamine and glycated LDL content in LDL subfractions from type 1 diabetic patients was greater than in LDL subfractions isolated from normoglycaemic subjects, and decreased after glycaemic optimisation in both subfractions. However, no difference was observed between LDL(+) and LDL(-) before and after insulin therapy.

CONCLUSIONS/INTERPRETATION

These results provide evidence that LDL(-) is not produced by glycosylation. Nevertheless, LDL(-) from diabetic patients displays inflammatory potential reflected by the induction of chemokine release in endothelial cells. This proatherogenic effect could be related to the high PAF-AH activity in LDL(-).

D-4F Induces Heme Oxygenase-1 and Extracellular Superoxide Dismutase, Decreases Endothelial Cell Sloughing, and Improves Vascular Reactivity in Rat Model of Diabetes

Background— Apolipoprotein A1 mimetic peptide, synthesized from D-amino acid (D-4F), enhances the ability of HDL to protect LDL against oxidation in atherosclerotic animals.

Methods and Results— We investigated the mechanisms by which D-4F provides antioxidant effects in a diabetic model. Sprague-Dawley rats developed diabetes with administration of streptozotocin (STZ). We examined the effects of daily D-4F (100 μg/100 g of body weight, intraperitoneal injection) on superoxide (O 2 − ), extracellular superoxide dismutase (EC-SOD), vascular heme oxygenase (HO-1 and HO-2) levels, and circulating endothelial cells in diabetic rats. In response to D-4F, both the quantity and activity of HO-1 were increased. O 2 − levels were elevated in diabetic rats (74.8±8×10 3 cpm/10 mg protein) compared with controls (38.1±8×10 3 cpm/10 mg protein; P <0.01). D-4F decreased O 2 − levels to 13.23±1×10 3 ( P <0.05 compared with untreated diabetics). The average number of circulating endothelial cells was higher in diabetics (50±6 cells/mL) than in controls (5±1 cells/mL) and was significantly decreased in diabetics treated with D-4F (20±3 cells/mL; P <0.005). D-4F also decreased endothelial cell fragmentation in diabetic rats. The impaired relaxation typical of blood vessels in diabetic rats was prevented by administration of D-4F (85.0±2.0% relaxation). Western blot analysis showed decreased EC-SOD in the diabetic rats, whereas D-4F restored the EC-SOD level.

Conclusions— We conclude that an increase in circulating endothelial cell sloughing, superoxide anion, and vasoconstriction in diabetic rats can be prevented by administration of D-4F, which is associated with an increase in 2 antioxidant proteins, HO-1 and EC-SOD.

Clinical significance of the physicochemical properties of LDL in type 2 diabetes

Atherosclerosis is the leading cause of death in type 2 diabetes. LDL cholesterol and atherosclerosis are related, both in healthy people and those with diabetes; however, people with diabetes are more prone to atheroma, even though their LDL cholesterol levels are similar to those in their non-diabetic peers. This is because LDL particles are modified in the presence of diabetes to become more atherogenic. These modifications include glycation in response to high plasma glucose levels; oxidative reactions mediated by increased oxidative stress; and transfer of cholesterol ester, which makes the particles smaller and denser. The latter modification is strongly associated with hypertriglyceridaemia. Oxidatively and non-oxidatively modified LDL is involved in plaque formation, and may thus contribute to the accelerated atherosclerosis. This review discusses the techniques currently used to determine the physicochemical properties of LDL, and examines the evidence that modification of these properties plays a role in the accelerated atherosclerosis associated with type 2 diabetes.