Inhibitory Effect Of Low Density Lipoprotein Research Articles

Effective compounds in the fruit of Muntingia calabura Linn. cultivated in Taiwan evaluated with scavenging free radicals and suppressing LDL oxidation.

Scavenging effect of 2,2-diphenyl -2-picrylhydrazyl hydrate (DPPH) radicals, inhibitory effect of low-density lipoprotein (LDL) oxidation, Trolox equivalent antioxidant capacity (TEAC), and phenolic contents were used for the activity-guided separation to identify the effective compounds of Muntingia calabura Linn. fruit. Its ethanol extract with higher phenolic content and antioxidant activities was subjected to silica gel column chromatographic separation, which was sequentially eluted with n-hexane, 10-90% ethyl acetate (EA) in n-hexane, EA, EA/acetone (50/50, v/v), acetone, acetone/methanol (MeOH) (50/50, v/v), and MeOH; fifteen fractions (Fr. 1-15) were obtained. Fractions 13 and 14 with better antioxidant effects were mixed followed by purification of the effective compounds using HPLC. Two major compounds were isolated and identified as gallic acid and 1,2-benzenedicarboxylic acid diisooctyl ester through high performance liquid chromatography-mass spectrometry (HPLC-MS) and nuclear magnetic resonance (NMR) measurements. Their amounts in the fruit were 3.76 and 4.62 mg g-1. This study is the first report to clarify the effective antioxidant compounds of M. calabura Linn. fruit.

The intervention study of atorvastatin on the effect of proliferation and differentiation and the expression of low density lipoprotein receptor-related protein 5, dickkopf-1 mRNA of osteoblasts caused by low density lipoprotein

Objective The aim of this study was to explore the effect of low density lipoprotein(LDL) on the proliferation and differentiation of MC3T3-E1 osteoblasts, as well as the expression of low density lipoprotein receptor-related protein 5(LRP5) and dickkopf-1(DKK1) mRNA of MC3T3-E1 osteoblasts. The possible mechanisms of the treatment of atorvastatin on LDL expression in MC3T3-E1 osteoblasts were also investigated. Methods Proliferation, osteocalcin expression, LRP5, and expression of DKK1 mRNA of MC3T3-E1 with interaction of LDL at 0.05, 0.10, 0.20 mg/ml levels after 24 h, 48 h, 72 h were detected by CCK8, ELISA, and fluorescence quantitative PCR. Furthermore, proliferation, osteocalcin expression, LRP5 and DKK1 mRNA of MC3T3-E1 after the treatment of atorvastatin of 10-6mol/L and 10-5mol/L were also be studied, respectively. Results The effect of LDL on proliferation, expression of osteocalcin and expression of LRP5 and DKK1 mRNA in MC3T3-E1 osteoblasts was the most obvious under LDL with 0.20 mg/ml level. Under that level, atorvastatin(10-6 mol/L or 10-5 mol/L) was able to make the proliferation of MC3T3-E1 osteoblasts in 48 h and 72 h be decreased, while significantly caused upregulation of osteocalcin, LRP5 mRNA expression; and down regulated DKK1 mRNA expression(all P<0.05). Conclusions Atorvastatin can reduce the inhibitory effect of LDL on the proliferation and differentiation of osteoblasts. The mechanisms of atorvastatin on osteoblasts are possibly related to the osteoblast proliferation and expression of LRP5 mRNA and DKK1 mRNA of osteoblasts of wnt signal pathway. (Chin J Endocrinol Metab, 2015, 31: 707-711) Key words: Low density lipoprotein; Atorvastatin; Osteoblast; Low density lipoprotein receptor-related protein 5; Dickkopf-1

Low- and High-Density Lipoproteins Modulate Function, Apoptosis, and Proliferation of Primary Human and Murine Pancreatic β-Cells

A low high-density lipoprotein (HDL) plasma concentration and the abundance of small dense low-density lipoproteins (LDL) are risk factors for developing type 2 diabetes. We therefore investigated whether HDL and LDL play a role in the regulation of pancreatic islet cell apoptosis, proliferation, and secretory function. Isolated mouse and human islets were exposed to plasma lipoproteins of healthy human donors. In murine and human beta-cells, LDL decreased both proliferation and maximal glucose-stimulated insulin secretion. The comparative analysis of beta-cells from wild-type and LDL receptor-deficient mice revealed that the inhibitory effect of LDL on insulin secretion but not proliferation requires the LDL receptor. HDL was found to modulate the survival of both human and murine islets by decreasing basal as well as IL-1beta and glucose-induced apoptosis. IL-1beta-induced beta-cell apoptosis was also inhibited in the presence of either the delipidated protein or the deproteinated lipid moieties of HDL, apolipoprotein A1 (the main protein component of HDL), or sphingosine-1-phosphate (a bioactive sphingolipid mostly carried by HDL). In murine beta-cells, the protective effect of HDL against IL-1beta-induced apoptosis was also observed in the absence of the HDL receptor scavenger receptor class B type 1. Our data show that both LDL and HDL affect function or survival of beta-cells and raise the question whether dyslipidemia contributes to beta-cell failure and hence the manifestation and progression of type 2 diabetes mellitus.

Role of lipoprotein-associated lysophospholipids in migratory activity of coronary artery smooth muscle cells

The migration of vascular smooth muscle cells (SMCs) is a hallmark of the pathogenesis of atherosclerosis and restenosis after angioplasty. Plasma low-density lipoprotein (LDL), but not high-density lipoprotein (HDL), induced the migration of human coronary artery SMCs (CASMCs). Among bioactive lipids postulated to be present in LDL, lysophosphatidic acid (LPA) appreciably mimicked the LDL action. In fact, the LDL-induced migration was markedly inhibited by pertussis toxin, an LPA receptor antagonist Ki-16425, and a small interfering RNA (siRNA) targeted for LPA(1) receptors. Moreover, LDL contains a higher amount of LPA than HDL does. HDL markedly inhibited LPA- and platelet-derived growth factor (PDGF)-induced migration, and sphingosine 1-phosphate (S1P), the content of which is about fourfold higher in HDL than in LDL, mimicked the HDL action. The inhibitory actions of HDL and S1P were suppressed by S1P(2) receptor-specific siRNA. On the other hand, the degradation of the LPA component of LDL by monoglyceride lipase or the antagonism of LPA receptors by Ki-16425 allowed LDL to inhibit the PDGF-induced migration. The inhibitory effect of LDL was again suppressed by S1P(2) receptor-specific siRNA. In conclusion, LPA/LPA(1) receptors and S1P/S1P(2) receptors mediate the stimulatory and inhibitory migration response to LDL and HDL, respectively. The balance of not only the content of LPA and S1P in lipoproteins but also the signaling activity between LPA(1) and S1P(2) receptors in the cells may be critical in determining whether the lipoprotein is a positive or negative regulator of CASMC migration.

Effects of low density lipoprotein and oxidized low density lipoprotein on the cytotoxic activity of Asp-hemolysin to murine macrophages

We examined the effects of human low density lipoprotein (LDL) and oxidized LDL (Ox-LDL) on the cytotoxic activity of Asp-hemolysin from Aspergillus fumigatus Fresenius-Muramatsu strain to mouse peritoneal macrophages (M phi). The inhibitory effects of LDL and Ox-LDL on the cytotoxic activity of Asp-hemolysin to M phi increased in a dose-dependent manner, and the effect of Ox-LDL was greater than the inhibitory effect of LDL. Furthermore, the binding of Asp-hemolysin to LDL or Ox-LDL was observed by western blot analysis of the culture medium. These results suggest that the inhibition by LDL or Ox-LDL on the cytotoxic activity of Asp-hemolysin to M phi was due to the binding of LDL or Ox-LDL to Asp-hemolysin in the culture medium.

Effects of native and oxidized low-density lipoproteins on macrophage chemiluminescence

Effects of low-density lipoproteins (LDL) obtained from healthy donors and patients with hypercholesterolemia on spontaneous luminol-dependent and zymosan-induced chemiluminescence of rat macrophages were studied. Unlike LDL from healthy donors, native LDL from patients with hypercholesterolemia inhibited spontaneous chemiluminescence of macrophages. Simultaneous incubation with endotheliocytes from the umbilical vein led to the appearance of inhibitory effect of LDL from healthy donors (incubation for 24 h) and potentiated this effect of LDL from patients with hypercholesterolemia (incubation for 6 and 24 h). The inhibitory effect was more pronounced in LDL incubated with umbilical endotheliocytes under ischemic conditions then after aerobic incubations. This corresponded to higher oxidation of LDL confirmed by accumulation of thiobarbituric acid-reactive substances, increased fluorescence, and high electrophoretic mobility in agarose gel. These data suggest that the model system of spontaneous and zymosan-induced chemiluminescence of macrophages can be used for evaluating the degree of oxidation and potential atherogenicity of LDL.

Low density lipoprotein (LDL) inhibits histamine release from human mast cells

We examined the effect of low density lipoprotein (LDL) on histamine release from purified human lung mast cells. LDL inhibited anti-IgE- induced histamine release in a dose-dependent manner, with 100μg/ml LDL-protein inhibiting histamine release by 83±8% (mean±SEM); half-maximal inhibition occurred at 40–80 μg/ml. LDL also inhibited calcium ionophore A23187-induced histamine release in a dose-dependent manner, with 1 mg/ml of LDL inhibiting histamine release by 83 ± 9%; half maximal inhibition occurred at 220–280 μ/ml. Inhibition by LDL was time-dependent: half-maximal inhibition of anti-IgE- induced histamine release by LDL occurred at 30–50 minutes of incubation. The inhibitory effect of LDL was independent of buffer calcium concentrations (0–5 mM) or temperature (0–37°C). These data are consistent with a newly defined immunoregulatory role for LDL.

Oxidized low density lipoprotein can reduce the pinocytic activity in cultured human endothelial cells as measured by cellular uptake of [ 14C]sucrose

The effect of low density lipoprotein (LDL) on the pinocytic activity in human endothelial cells in culture, as measured by the uptake of [ 14C]sucrose, was studied. The cells were preincubated for 48 h with a low concentration of LDL (25 μg protein/ml) or a high concentration of LDL (150 μg protein/ml) in the presence of lipoprotein deficient serum. Then the pinocytic activity of the cells was measured in a subsequent incubation by measuring the uptake of [ 14C]sucrose. The higher LDL concentration resulted in a reduced cellular uptake of [ 14C]sucrose compared to the lower concentration of LDL When the additional LDL (the lower concentration subtracted from the higher) was replaced by high density lipoprotein, albumin or gamma globulin, no reduction of the uptake of [ 14C]sucrose was observed. The inhibitory effect of LDL on the uptake of [ 14C]sucrose was seen in endothelial cell cultures of different age and cell density. When the endothelial cell proliferation was arrested by gamma irradiation, the reducing effect of LDL on the pinocytic activity was unchanged as compared to nonirradiated controls. LDL prepared in the presence of EDTA and glutathione did not have the same reducing effect on the uptake of [ 14C]sucrose as control LDL prepared in the absence of antioxidants. Thus, oxidized LDL reduced the pinocytic activity in cultured endothelial cells. The inhibitory effect of LDL on the rate of pinocytosis was present before endothelial cell injury could be observed.

Action of low-density lipoprotein and compactin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, on the synthesis of dolichol-linked oligosaccharides and low-density-lipoprotein receptor in human skin fibroblasts.

To explore whether there is an inter-relationship between the rate of low-density (LD) lipoprotein binding to its receptor and the formation of dolichol-linked oligosaccharides, experiments were performed with human fibroblasts where the synthesis of lipoprotein receptor and dolichyl saccharides was under control of LD lipoprotein and compactin. Pretreatment of the cells with nonlabelled LD lipoprotein resulted in a suppression of both the binding of 125I-labelled LD lipoprotein to the receptor and the synthesis of dolichyl saccharides from [14C]acetate and [3H]mannose, but not from [3H]mevalonolactone. Compactin, in contrast, inhibited only the formation of dolichol-linked oligosaccharides. Mevalonolactone (1 microM) abolished the inhibitory effect of LD lipoprotein on dolichyl saccharide formation, but was not able to restore the receptor-binding capacity, thus suggesting that the synthesis of lipoprotein receptor is not coupled to the formation of dolichyl saccharides.

Lipoproteins and the inhibitory effect of human endothelial cells on platelet function.

We investigated the effect of plasma low density lipoproteins (LDL), very low density lipoproteins (VLDL), and high density lipoproteins (HDL) on the platelet inhibitory effect of primary cultures of human endothelial cell monolayers (ECM). ECM incubated with lipoprotein-deficient plasma (LDP) for 2 hours at 37 degrees C had an inhibitory effect on ADP- and collagen-induced platelet aggregation and prostaglandin production in platelet-rich plasma similar to that observed when ECM were preincubated with growth medium or plasma. Concentrations of LDL in LDP up to protein concentration of 1600 microgram/ml had an inhibitory effect on the endothelial cells' ability to modulate these platelet reactions. VLDL at the highest concentration (1600 microgram/ml) had a slightly inhibitory effect, whereas HDL showed no such effect. The inhibitory effect of LDL was not observed during the first hour of incubation. When HDL in concentrations similar to or higher than LDL were combined with LDL, the inhibitory effect of LDL was partially reduced. VLDL combined with LDL or HDL did not interfere with the effects of the later fractions. The inhibitory effect of LDL was significantly reduced when LDL were diluted in whole plasma. Prostacyclin which is synthesized and released from the endothelial cells and contributes to the inhibitory effect upon platelets did not change its effect on platelet reactivity by preincubation with the various lipoprotein fractions. The current studies may indicate that LDL have a direct effect on the endothelial cells and that this effect may be partially counteracted by HDL. This effect of LDL on the endothelial cells reduces the endothelium's ability to inhibit platelet aggregation and thus could favor the tendency to thrombus formation.