LDL particle subclasses in hypercholesterolemia: molecular determinants of reduced lipid hydroperoxide stability

Nrf2 deficiency deteriorates diabetic kidney disease in Akita model mice

Oxidative stress is an essential component in the progression of diabetic kidney disease (DKD), and the transcription factor NF-E2-related factor-2 (Nrf2) plays critical roles in protecting the body against oxidative stress. To clarify the roles of Nrf2 in protecting against DKD, in this study we prepared compound mutant mice with diabetes and loss of antioxidative defense. Specifically, we prepared compound Ins2^Akita/+ (Akita) and Nrf2 knockout (Akita::Nrf2^-/-) or Akita and Nrf2 induction (Akita::Keap1^FA/FA) mutant mice. Eighteen-week-old Akita::Nrf2^-/- mice showed more severe diabetic symptoms than Akita mice. In the Akita::Nrf2^-/- mouse kidneys, the glomeruli showed distended capillary loops, suggesting enhanced mesangiolysis. Distal tubules showed dilation and an increase in 8-hydroxydeoxyguanosine-positive staining. In the Akita::Nrf2^-/- mouse kidneys, the expression of glutathione (GSH) synthesis-related genes was decreased, and the actual GSH level was decreased in matrix-assisted laser desorption/ionization mass spectrometry imaging analysis. Akita::Nrf2^-/- mice exhibited severe inflammation and enhancement of infiltrated macrophages in the kidney. To further examine the progression of DKD, we compared forty-week-old Akita mouse kidney compounds with Nrf2-knockout or Nrf2 mildly induced (Akita::Keap1^FA/FA) mice. Nrf2-knockout Akita (Akita::Nrf2^-/-) mice displayed severe medullary cast formation, but the formation was ameliorated in Akita::Keap1^FA/FA mice. Moreover, in Akita::Keap1^FA/FA mice, tubule injury and inflammation-related gene expression were significantly suppressed, which was evident in Akita::Nrf2^-/- mouse kidneys. These results demonstrate that Nrf2 contributes to the protection of the kidneys against DKD by suppressing oxidative stress and inflammation.

The Lipoprotein Transport System in the Pathogenesis of Multiple Myeloma: Advances and Challenges

Multiple myeloma (MM) is an incurable neoplastic hematologic disorder characterized by malignant plasma cells, mainly in the bone marrow. MM is associated with multiple factors, such as lipid metabolism, obesity, and age-associated disease development. Although, the precise pathogenetic mechanisms remain unknown, abnormal lipid and lipoprotein levels have been reported in patients with MM. Interestingly, patients with higher APOA1 levels, the major apolipoprotein of high density lipoprotein (HDL), have better overall survival. The limited existing studies regarding serum lipoproteins in MM are inconclusive, and often contradictory. Nevertheless, it appears that deregulation of the lipoprotein transport system may facilitate the development of the disease. Here, we provide a critical review of the literature on the role of lipids and lipoproteins in MM pathophysiology. We also propose novel mechanisms, linking the development and progression of MM to the metabolism of blood lipoproteins. We anticipate that proteomic and lipidomic analyses of serum lipoproteins along with analyses of their functionality may improve our understanding and shed light on novel mechanistic aspects of MM pathophysiology.

Pharmacological Management of Dyslipidemia in Atherosclerosis: Limitations, Challenges, and New Therapeutic Opportunities

Clinical and epidemiological studies during the last 7 decades indicated that elevated low-density lipoprotein cholesterol (LDL-C) levels and reduced high-density lipoprotein cholesterol (HDL-C) levels correlate with the pathogenesis and progression of atherosclerotic lesions in the arterial wall. This observation led to the development of LDL-C-lowering drugs for the prevention and treatment of atherosclerosis, some with greater success than others. However, a body of recent clinical evidence shows that a substantial residual cardiovascular risk exists even at very low levels of LDL-C, suggesting that new therapeutic modalities are still needed for reduction of atherosclerosis morbidity and mortality. Unfortunately, HDL-C-raising drugs developed toward this goal had disappointing results thus far. Here, we critically review the literature presenting available evidence and challenges that need to be met and discuss possible new avenues for the development of novel lipid pharmacotherapeutics to reduce the burden of atherosclerosis.

Interdependence of oxysterols with cholesterol profiles in multiple sclerosis

PURPOSE

To investigate levels of oxysterols in healthy control (HC) and multiple sclerosis (MS) patients and their interdependence with demographic, clinical characteristics, and cholesterol biomarkers.

METHODS

This study included 550 subjects (203 HC, 221 relapsing-remitting MS (RR-MS), 126 progressive MS (P-MS)). A complete lipid profile including total cholesterol (TC); high-density lipoprotein-cholesterol (HDL-C); low-density lipoprotein-cholesterol (LDL-C); apolipoproteins (Apo) A1, A2, B, and E; C-reactive protein (CRP); 24-hydroxycholesterol (HC); 25-HC; 27-HC; 7α-HC; and 7-ketocholesterol (KC) was obtained. Lipoprotein particle sizing by proton nuclear magnetic resonance (H¹ NMR) was available for 432 subjects.

RESULTS

The levels of 24-HC, 27-HC, and 7α-HC (all p < 0.015) were lower in MS compared to HC, and 7-KC was higher in P-MS compared to RR-MS ( p < 0.001). TC, LDL-C, and ApoB were associated with higher levels of all oxysterols (all p < 0.05) in HC. In MS, LDL-C was associated with higher levels of 24-HC, 25-HC, 7-KC, and 7α-HC (all p < 0.05), while TC and ApoB were associated with increased levels of all oxysterols (all p < 0.005).

CONCLUSION

The findings of lower 24-HC, 27-HC, and 7α-HC in MS compared to HC and higher 7-KC in P-MS compared to RR-MS indicate that the oxysterol network is disrupted in MS.

Circulating oxidized low-density lipoprotein: a biomarker of atherosclerosis and cardiovascular risk?

Low-density lipoproteins (LDLs) are susceptible to structural modifications by oxidation, particularly the small dense LDL particles. The formation of lipid peroxidation derivates, such as thiobarbituric reactive substances, conjugated dienes, lipid hydroperoxides, and aldehydes, is associated with changes in apolipoprotein conformation and affects the functional properties of LDLs. Oxidized LDL (oxLDL) formation in the subendothelial space of the arterial wall is a key initiating step in atherosclerosis because it contributes to foam cell generation, endothelial dysfunction, and inflammatory processes. In the last decade, immunoassays were developed using monoclonal antibodies against oxidation-dependent epitopes of LDL which made it possible to directly measure oxLDL in the circulation. Increased circulating oxLDL concentrations have been related to cardiovascular disease in some studies, although not always independently after adjustment of classical lipid markers. The Asklepios Study, investigating 2524 healthy middle-aged subjects, showed that circulating oxLDL is affected by many biological and lifestyle factors, as well as (generalized) subclinical atherosclerosis.

Clin Chem Lab Med 2009;47:128–37.

Modified egg composition to reduce low-density lipoprotein oxidizability: high monounsaturated fatty acids and antioxidants versus regular high n-6 polyunsaturated fatty acids

Eggs high in n-6 PUFA, predominant in Western markets, were found to increase blood LDL oxidation, suggesting a new health concern beyond raising cholesterol. Protective composition was explored by increasing egg antioxidants and MUFA and reducing n-6 PUFA. Lag times to plasma LDL oxidation were significantly shortened with two eggs/day of high-PUFA compositions compared to a low-egg (2-4/week) regime, by 28.8% following "HPUFA-regular" ( p < 0.01) and by 27.2% following antioxidant-fortified "HPUFA-HAOX" ( p < 0.01). However, two "HMUFA-HAOX" eggs/day with reduced egg n-6 PUFA FA% (LA by 30.7%) and PUFA:MUFA ratio (LA:OA by 45.8%) plus increased antioxidants (vitamin E 500%, carotenoids 260%), resulting in increased plasma OA 33.3%, vitamin E 22.4%, and carotenoids 55.0% ( p < 0.01), were associated with lag-time only 6.6% shorter than low-egg (NS). Among health-oriented egg modifications, here for the first time they reduced associated LDL oxidization, consistent with anti-inflammation and antioxidant paradigms, warranting further research on functional advantages of antioxidative egg composition.

Rumenic Acid Significantly Reduces Plasma Levels of LDL and Small Dense LDL Cholesterol in Hamsters Fed a Cholesterol- and Lipid-Enriched Semi-Purified Diet

Conjugated linoleic acids (CLAs) consist of a series of positional and geometrical isomers of linoleic acid. CLA have been reported to beneficially affect cardiovascular risk factors in animal models. In order to assess the role of individual CLA isomers on lipoprotein cholesterol concentration, 30 hamsters were fed for 12 weeks an hyperlipidic diet containing pure cis-9,trans-11 CLA (c9,t11) or pure trans-10, cis-12 CLA (t10,c12) isomers given alone or as a mixture. Plasma total cholesterol, LDL and HDL cholesterol concentrations were significantly lower in the c9,t11 CLA isomer fed hamsters relative to the Control group, with the most substantially effect on LDL cholesterol (-56%; P < 0.05). Plasma triacylglycerol concentrations did not differ significantly regarding those two groups. Plasma cholesterol parameters showed a tendency to decrease in the t10,c12 CLA isomer and CLA mixture fed hamsters compared with the Control group, but differences were not significant. For the first time, the atherogenic fraction of small dense LDL was investigated. Plasma small dense LDL cholesterol concentration was lower in the c9,t11 CLA relative to Control, while the t10,c12 and CLA mixture groups showed only a non significant tendency to decrease. Taken together, these data indicate that feeding rumenic acid (c9,t11 CLA) may beneficially affect lipoprotein profile in hamster fed a cholesterol- and lipid-enriched semi-purified diet, when t10,c12 CLA isomer or CLA mixture would be less active.

Effect of dietary n−6 and n−3 polyunsaturated fatty acids on peroxidizability of lipoproteins in steers

The susceptibility of major plasma lipoproteins to lipoperoxidation was studied in relation to the FA composition of their neutral and polar lipids in steers given PUFA-rich diets. Two trials used, respectively, 18 ("sunflower" experiment, S) or 24 ("linseed" experiment, L) crossbred Salers x Charolais steers. Each involved three dietary treatments over a 70-d period: a control diet (CS or CL diets) consisting of hay and concentrate, or the same diet supplemented with oilseeds (4% diet dry matter) fed either as seeds (SS or LS diets) or continuously infused into the duodenum (ISO or ILO diets). Compared with control diets, ISO and ILO treatments tended to decrease the resistance time of LDL and HDL classes to peroxidation, mainly owing to the enrichment of their polar and neutral lipids with PUFA. With diets SS and LS, sensitivity of major lipoprotein classes (LDL, light and heavy HDL) was not affected because ruminal hydrogenation of dietary PUFA decreased their incorporation into lipoparticles. ISO and ILO treatments induced a more important production of conjugated dienes and hydroperoxides generated by peroxidation in the three lipoprotein classes due to the higher amounts of PUFA esterified in lipids of the core and the hydrophilic envelope of particles. The production of malondialdehyde (MDA) increased in steers fed linseed supplements, indicating that MDA production did not occur with linoleic acid provided by sunflower oil supplements. Thus, plasma peroxidation of PUFA generates toxic products in steers fed diets supplemented with PUFA and can be deleterious for the health of the animal during long-term treatment.

Statin therapy in acute coronary syndromes: mechanistic insight into clinical benefit

Randomized trials have established that statin treatment reduces coronary events in primary prevention and in patients with stable coronary artery disease. In unstable coronary artery disease, however, the pathophysiological background is distinct, and the potential benefits of statin therapy have not been evaluated until recently. Data from animal models and clinical studies indicate that statin treatment can influence a spectrum of molecular and cellular mechanisms that are intimately related to the pathogenesis of acute coronary syndromes; these include the reduction of circulating levels of atherogenic lipoproteins (very low density lipoprotein, very low density lipoprotein remnants, intermediate density lipoprotein, and low density lipoprotein) and thus of arterial lipid deposition and the attenuation of inflammation, modulation of thrombogenesis and thrombolysis, improvement of endothelial dysfunction, and reduction of ischemia/reperfusion injury. Indeed, findings from prospective and observational studies have demonstrated that statin treatment significantly improves clinical outcome after acute coronary syndromes. Therefore, early initiation of statin therapy after an acute coronary event not only enhances adherence to treatment but also preempts the occurrence of new events. In this review, we discuss recent important developments in our knowledge of the clinical evidence of the beneficial effects of early statin therapy in acute coronary syndromes and the biological mechanisms that underlie them.

Methods for measuring lipid metabolism in vivo

PURPOSE OF REVIEW

This review discusses diverse methods that have been used in several recent papers for the qualitative and quantitative analysis of lipids, studies of lipid oxidation, lipoprotein fractionation, and studies of lipid metabolism and metabolic kinetics using tracers. Papers for this review were selected on the basis of their timeliness, novelty, and/or their potential impact on diverse fields of lipid metabolism.

RECENT FINDINGS

Many methods used for studies of lipid metabolism employ advanced chromatographic and mass spectrometric techniques to characterize lipids. In particular, the use of stable isotopically labeled tracers has become increasingly important to study metabolic kinetics.

SUMMARY

Such developments in methodology will continue to advance studies of lipid metabolism in many areas of clinical interest, including heart disease, obesity, and diabetes.