SAT-LB95 Low Density Lipoprotein Receptor and Proprotein Convertase Subtilisin/Kexin Type 9 Kinetics Using Heavy Water (2H2O) Labeling and Mass Spectrometry

Abnormally high blood cholesterol levels in low density lipoprotein (LDL) increases the risk of heart disease. Cell surface receptors such as LDL-receptors (LDLr) regulate the clearance of LDL from blood circulation. As cholesterol levels decrease, cells promote cholesterol synthesis and cholesterol uptake by increasing LDLr expression. Another regulatory protein of plasma cholesterol clearance is proprotein convertase subtilisin/kexin type 9 (PCSK9). It is secreted from the liver into circulation where it can bind to and target LDLr to the lysosome for subsequent degradation. The current model of cholesterol regulation describes how increased cholesterol content down-regulates the number of LDLr promoted by PCSK9 mediated degradation, however minimal knowledge is not known about LDLr and PCSK9 kinetics using heavy water labeling, and how cholesterol enriched diet affects LDLr and PCSK9 kinetics in vivo. Therefore, our objective(s) were to establish a method 1) to measure the kinetics of LDLr and PCSK9 via stable isotopic metabolic labeling with heavy water (2H2O) in vivo 2) to further test established models of cholesterol metabolic regulation on LDLr and PCSK9 turnover after feeding mice a cholesterol enriched diet. We hypothesize that a cholesterol enriched diet will decrease both LDLr and PCSK9 synthesis rates. In order to test this, mice were fed a cholesterol enrich diet for 1 week and metabolically labeled with heavy water (2H2O) up to 36 hours. LDLr and PCSK9 were immunoprecipitated from liver and deuterium incorporation into LDLr and PCSK9 were measured via mass spectrometry. Our results revealed high cholesterol feeding down-regulated cholesterol synthesis and LDLr fractional synthesis rate decreased from 10.0% to 6% per hour. PCSK9 concentration also decreased from 1 to 0.2 (ng/ml / total mg protein), but the synthesis rate increased from 9.0%/day in control mice to 19.5%/day in high cholesterol diet. These results suggest high cholesterol feeding increases PCSK9 synthesis that potentially depletes the intracellular pool to target LDLr to the lysosome thus decreasing LDLr turnover. This research provides a flux-based approach to measure the kinetics of LDLr and PCSK9 for a molecular based kinetic insight of their functions in physiology, disease and therapy.

A REVIEW: AZADIRACHTA INDICA AS ANTIHYPERLIPIDEMIC ACTIVITY

Antihyperlipidemic agents having various pharmacological actions are being tested clinically3. Elevated lipid levels result from increased absorption through the gut or enhanced endogenous synthesis and therefore two ways are feasible to reduce hyperlipidemia; to block endogenous synthesis or to decrease absorption. Whole plant of Azadirachta indica gives the Antihyperlipidemic activity. Several genetic conditions are known to responsible for primary Hyperlipidemia, such as lipoprotein lipase deficiency, apolipoprotein C-II deficiency etc. In our study we choose cholesterol diet which contains the common ingredients in our daily food. Cholesterol feeding has been often used to elevate serum or tissue cholesterol levels to assess the hypercholesterolemia- related metabolic disturbances in animals. Cholesterol feeding alone however does not affect the serum TG level. Keywords: Azadirachta indica, antihyperlipidemic, antiatherosclerotic activities, Maceration.

Regression of Atherosclerotic Plaques of Cholesterol-Fed Rabbits by Combined Chemotherapy With Paclitaxel and Methotrexate Carried in Lipid Core Nanoparticles

In previous studies, it was demonstrated that lipid core nanoparticles (LDE) resemble the low-density lipoprotein structure and carrying the antiproliferative agent paclitaxel (PTX) strongly reduced atherosclerosis lesions induced in rabbits by cholesterol feeding. Currently, the aim was to verify whether combining LDE-PTX treatment with methotrexate (MTX) associated with LDE (LDE-MTX) could accelerate the atherosclerosis regression attained with single LDE-PTX treatment, after withdrawing the cholesterol feeding. Thirty-eight rabbits were fed 1% cholesterol chow for 8 weeks. Six of these rabbits were then euthanized for analyses of the aorta (controls). In the remaining rabbits, cholesterol feeding was withdrawn, and those 32 animals were allocated to 3 groups submitted to different 8-week intravenous treatments, all once/week: LDE-PTX (n = 10; 4 mg/kg), LDE-PTX + LDE-MTX (n = 11; 4 mg/kg), and LDE-alone (n = 11). Rabbits were then euthanized and aortas were excised for morphometric, immunohistochemical, and gene expression analyses. After cholesterol feeding withdrawal, in comparison with LDE-alone group, both LDE-PTX and LDE-PTX + LDE-MTX treatments had the ability to increase the regression of plaque areas: −49% in LDE-PTX and −59% for LDE-PTX + LDE-MTX. However, only LDE-PTX + LDE-MTX treatment elicited reduction in the intima area, estimated in −57%. Macrophage presence in aortic lesions was reduced 48% by LDE-PTX and 43% by LDE-PTX + LDE-MTX treatment. Matrix metalloproteinase 9 was reduced by either LDE-PTX (74%) or LDE-PTX + LDE-MTX (78%). Tumor necrosis factor α gene expression was reduced 65% by LDE-PTX and 79% by LDE-PTX + LDE-MTX. In conclusion, treatment with LDE-PTX indeed accelerated plaque reduction after cholesterol feeding; LDE-PTX + LDE-MTX further increased this effect, without any observed toxicity. These results pave the way for the use of combined chemotherapy to achieve stronger effects on aggravated, highly inflamed atherosclerotic lesions.

Low-Dose Fluvastatin Prevents the Functional Alterations of Endothelium Induced by Short-Term Cholesterol Feeding in Rabbit Carotid Artery

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, commonly known as statins, are the medical treatment of choice for hypercholesterolemia. In addition to lowering serum-cholesterol levels, statins appear to promote pleiotropic effects that are independent of changes in serum cholesterol. In this study, we investigated the effects of low-dose fluvastatin on antioxidant enzyme activities (superoxide dismutase, SOD; catalase), total nitrite/nitrate levels, and vascular reactivity in 2% cholesterol-fed rabbits. This diet did not generate any fatty streak lesions on carotid artery wall. However, SOD activity significantly increased with cholesterol feeding whereas the catalase activities decreased. The levels of nitrite/nitrate, stable products of NO degradation, diminished. Moreover, dietary cholesterol reduced vascular responses to acetylcholine, but contractions to serotonin were augmented. Fluvastatin treatment abrogated the cholesterol-induced increase in SOD, increased the levels of nitric oxide metabolites in tissue, and restored both the impaired vascular responses to acetylcholine and the augmented contractile responses to serotonin without affecting plasma-cholesterol levels. Phenylephrine contractions and nitroglycerine vasodilatations did not change in all groups. This study indicated that fluvastatin treatment performed early enough to improve impaired vascular responses may delay cardiovascular complications associated with several cardiovascular diseases.