Doxazosin increases low density lipoprotein receptor activity

The effect of the alpha 1 adrenoreceptor antagonist doxazosin on low density lipoprotein (LDL) receptor activity, has been studied in cultured skin fibroblasts. Doxazosin at a concentration of 10(-5) M significantly increased the LDL receptor activity. The possible clinical implications of this observation are discussed.     

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.     

The effect of pravastatin in relation to low density lipoprotein receptor activity

Pravastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, suppresses new synthesis of cholesterol via HMG-CoA in hepatocytes. As a result, low density lipoprotein (LDL) receptor activity in the liver is enhanced, which leads to lowering of plasma cholesterol. Inhibitors are shown to be effective in heterozygous familial hypercholesterolaemia (FH). Although FH heterozygotes are defined genetically as possessing half the normal LDL receptor activity, some heterogeneity of LDL receptor activity is observed in these patients. To see whether the effect of an inhibitor is related to LDL receptor activity in each patient, pravastatin was administered to 7 FH heterozygotes for 3 months at a daily dose of 10 mg; their mean LDL receptor activities measured before the therapy were 45.0 +/- 9.9% of the normal control. After medication, mean serum total cholesterol decreased from 349.0 to 279.7 mg/dl (p less than 0.05), and LDL-cholesterol decreased from 272.6 to 207.7 mg/dl (p less than 0.05). A significant correlation between the initial LDL receptor activity and the effect of pravastatin was not proved. However, the pre-treatment level of LDL-cholesterol was positively correlated (r = 0.795) with the absolute decrement of LDL-cholesterol after 3 months (p less than 0.05). This implies that the more LDL-cholesterol was elevated, the more pravastatin was effective.     

Activation of lipoprotein lipase increases serum high density lipoprotein 2 cholesterol and enlarges high density lipoprotein 2 particles in rats

It is known that postheparin plasma lipoprotein lipase (LPL) activity correlates with serum high density lipoprotein cholesterol (HDL-C) levels in humans and animals. Furthermore, LPL has been reported to cause enlargement of HDL particle size in vitro. However, these effects have not yet been experimentally proven. The aim of this study was to determine whether LPL has a role in increase in HDL-C and enlargement of HDL particle by activating the LPL function with NO-1886, the LPL promoting agent. NO-1886 administration increased postheparin plasma LPL activity without influencing hepatic triglyceride lipase activity. NO-1886 increased serum HDL(2)-cholesterol (HDL(2)-C) concentration and enlarged HDL(2) particle size, but did not increase serum HDL(3)-cholesterol concentration or enlarge HDL(3) particle size. Also, serum HDL(2)-C concentrations were positively correlated with HDL(2) particle size (r=0.910). Our study demonstrates that the LPL activation induced with NO-1886 may cause production of HDL(2)-C by catabolism of triglyceride-rich lipoproteins and enlarges HDL(2) particle size in rats.     

SKP-450 inhibits migration and DNA synthesis stimulated by oxidized low density lipoprotein in smooth muscle cells

This study was carried out to examine the inhibitory effects of SKP-450 (2-[2"(1", 3"-dioxolone)-2-methyl]-4-(2'-oxo-1'-pyrrolidinyl)-6-nitro-2H-1-be nzo pyran), a potassium channel opener, on the proliferation and migration stimulated by oxidized low density lipoprotein (LDL) of cultured smooth muscle cells of Wistar Kyoto rat aorta. SKP-450 (10(-7) and 10(-6) M) as well as probucol (10(-7)-10(-5) M) reduced the production of thiobarbituric acid reactive substances from LDL submitted to CuSO(4) (10 microM). The increased [3H]thymidine incorporation and migration (chemotactic and wound-edge) of the cultured smooth muscle cells in association with increased production of platelet-derived growth factor (PDGF)-BB-like immunoreactivity stimulated by oxidized LDL were significantly reduced by SKP-450 (10(-7)-10(-6) M). Inhibition by SKP-450 of the oxidized LDL-stimulated [3H]thymidine incorporation was antagonized by iberiotoxin (10(-7) M), but not by glibenclamide (10(-6) M), suggestive of mediation of Ca(2+)-activated K(+) channel opening in the action of SKP-450. Taken together, SKP-450 inhibited the proliferation and migration of the smooth muscle cells as well as PDGF production stimulated by oxidized LDL, accompanying with its antiperoxidative action.     

Treatment of diet-resistant polygenic hypercholesterolaemic patients with a new nicotinate derivative; in vivo and in vitro low density lipoprotein metabolic studies

Six patients (four women and two men) with mild to moderate hypercholesterolemia, but with no clinical evidence of the disease being monogenic familial hypercholesterolaemia and who, over the previous 3 months on a rigidly controlled hypolipidaemic diet therapy, showed no reduction in plasma cholesterol levels, were recruited into a study to assess the metabolic effects of Pirozadil, a new nicotinic acid derivative. After a 3 month treatment period, a significant reduction in plasma cholesterol from 299.8 +/- 31.2 mg/dl (mean +/- SD) to 256.8 +/- 18.1 mg/dl (P less than 0.02) and Low Density Lipoprotein (LDL) cholesterol from 211.7 +/- 44.9 mg/dl to 168.8 +/- 19.0 mg/dl (P less than 0.05) was observed. Although there was a trend toward decreased plasma and Very Low Density Lipoprotein (VLDL) triglyceride, the differences did not reach statistical significant. High Density Lipoprotein (HDL) cholesterol was unchanged. The drug was well tolerated with no side effects noted. To assess the mode of action, autologous125I-labelled LDL was injected and apoprotein B (apo B) kinetic parameters were measured; production rate (PR) and fractional catabolic rate (FCR). An in vitro measurement of the in vivo catabolism (LDL-apo B receptor activity in freshly isolated lymphocytes) was also measured pre- and post-treatment. The pharmacological intervention resulted in a significant decrease of 19.9% in PR from 10.5 +/- 1.81 mg/kg/d to 8.41 +/- 1.13 mg/kg/d (P less than 0.05) while the FCR remained relatively unchanged (0.260 +/- 0.042 vs 0.248 +/- 0.040 pools/d) as did the LDL receptor activity (78.2 +/- 20.9 vs 69.3 +/- 21.4 ng LDL/mg cell protein/hr).(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulation of low density lipoprotein receptor activity in liver membrane of guggulsterone treated rats

Chronic feeding of guggulsterone to rats showed hypolipidaemic activity in blood serum and liver membrane lipids. The decrease in serum cholesterol is associated with enhanced uptake of LDL by the liver through receptor mediated endocytosis, located on the surface of the cell membrane. In the present communication it has been shown that membranes prepared from liver of guggulsterone treated rats exhibit up to 87% increase in binding sites for human 125I-LDL. Significant decrease in lipid levels of serum as well as of membrane were observed. Lipid lowering activity of the drug in relation to LDL catabolism and other possible mechanisms have been explained.     

Lipolytic activity of cis-beta-carboxyacrylamidine: studies in vivo and in vitro.

cis-β-Carboxyacrylamidine, a product isolated from the fermentation broth of the actinomycete, Streptomyces fur longus var.fur longus nov. sp., stimulated lipolysis in rat adipose tissue and isolated fat cells. Lipid-mobilizing activity in vivo was indicated by the increase in plasma FFA concentrations that occurred after the compound was administered orally. Daily doses reduced body weight gain but after approximately 5 days the rats became resistant to this effect of the compound. Resistant animals still responded to the lipid-mobilizing activity of the agent with an increase in plasma FFA levels. cis-β-Carboxyacrylamidine did not increase cyclic AMP concentrations in incubated adipose tissue. Also it neither stimulated adenylate cyclase or cyclic AMP-dependent protein kinase nor inhibited cyclic AMP phosphodiesterase or phosphoprotein phosphatase. The lipolytic mechanism was found to differ from the mechanism of N-ethylmaleimide. Also cis-β-carboxyacrylamidine inhibited soluble hormone-sensitive lipase, suggesting that soluble hormone sensitive lipase may not be the lipase mainly responsible for the response of adipose tissue and isolated fat cells to lipolytic hormones.     

地拉卓对人类单核细胞株源性巨噬细胞摄取乙酰化低密度脂蛋白的影响

目的 观察地拉卓(血管扩张及抗血小板药)对人类单核细胞株(THP-1)源性巨噬细胞摄取乙酰化低密度脂蛋白(Ac-LDL)的影响.方法 以不加入地拉卓为对照组,以分别加入50、100μmol·L-1地拉卓为实验组;用细胞摄取Ac-LDL及Northern印迹方法,观察地拉卓对THP-1源性巨噬细胞受体摄取Ac-LDL以及对巨噬细胞清道夫受体-A mRNA表达的影响.结果 与对照组比较,巨噬细胞对Ac-LDL结合量和降解量随地拉卓浓度的增加而被明显抑制(均P<0.01);巨噬细胞ScR-A mRNA表达随地拉卓浓度的增加而减弱.结论 地拉卓抑制THP-1源性巨噬细胞对Ac-LDL结合和降解的作用是通过抑制ScR-A mRNA的表达来实现,其对动脉粥样硬化形成早期可能具有抑制作用.     

Effects of in vitro addition of captopril on copper-induced low density lipoprotein oxidation.

Low density lipoprotein (LDL) was incubated with 20 microM of the angiotensin converting enzyme (ACE) inhibitors captopril, fosinopril and quinapril or ethanol. Oxidation of LDL was initiated by addition of CuSO4 and monitored for production of conjugated dienes, thiobarbituric acid reactive substances (TBARS) and lipid peroxides. The inhibition of production of conjugated dienes was expressed as the lag phase in minutes. The lag phase for control samples was 55.2 +/- 6.1 (mean +/- s.e. mean) min and for captopril 86.4 +/- 7.0 min (P = 0.0058). Quinapril had a small but nonsignificant effect, fosinopril and ethanol had no effect. LDL incubated with captopril showed only 13.8% of TBARS and 22.7% of lipid peroxides produced by control (100%) after 1 h. Increasing concentrations of captopril showed a linear increase in the lag phase. We conclude that captopril increases the resistance of LDL to copper-induced oxidation.     

Methylamine irisolidone,a novel compound,increases total ATPase activity and inhibits apoptosis in vivo and in vitro

We propose to further research the protective effect of MMI on myocardium ischemic rat model and H9c2 cells that underwent cell apoptosis induced by hypoxia. We established the myocardium ischemic rat model via the cardiac surgical procedures in vivo and treated the model rats with different concentration of MMI. In vitro, with the pretreatment of MMI for 12 h in the model of Na₂S₂O₄-induced hypoxia injury, the H9c2 cells viability was determined by MTT assay. We found that MMI had significantly improved cardiac function of the myocardial ischemia, and significantly decreased the reactive oxygen species level. The expression of P53, Bcl-2, Bax, and caspase-9 was also induced by MMI. In vitro study revealed a concentration-dependent increase in cell viability associated with MMI pretreatment. Annexin V-FITC and PI staining results showed that MMI had a preventive effect on hypoxia-induced apoptosis in H9c2 cells. MMI also inhibited the mitochondrial membrane potential decrease and increased total ATPase activity during hypoxia in H9c2 cells. In conclusion, MMI can enhance the cardiac function in myocardial ischemic rat and increase cell viability and attenuate the apoptosis in H9c2 cells induced by hypoxia, which was associated with inhibiting MMP decreasion and increasing total ATPase activity.     

Activation of membrane outward currents by human low density lipoprotein in mouse peritoneal macrophages

Summary The aim of the present study was to search for electrophysiological effects of human lipoproteins on membrane currents in mouse peritoneal macrophages which had been cultured for 5 to 20 days. Whole-cell currents were recorded by using a voltage-clamp technique.Low density lipoprotein (LDL, 100 g/ml) increased a slowly activating nonspecific cation current (i_so) in the positive potential range to 244 ± 23% of the reference (test potential + 55 mV, n = 13, P < 0.005). Augmentation of current resulted out of a negative shift of the activation curve along the voltage axis (–22 mV) and an increase of maximally available current.Furthermore, LDL increased a rapidly activating outward current (i_fo) at test potentials positive to the potassium equilibrium potential. At +55 mV i_fo-amplitude increasedto 165 ± 14% ofreference (n = 16, P < 0.005). LDL-induced effects on i_fo-current could be mimicked by application of the calcium ionophore A 23187 (1 mol/l) which led to an increase of i_fo-current to 161 ± 25% of the reference (test potential + 55 mV, n = 11, P < 0.005).Acetylated-LDL (100 g/ml, 5–15 min) produced no significant effect on the membrane currents under investigation. Correspondence to U. Borchard at the above address     

Calcium antagonists as inhibitors of in vitro low density lipoprotein oxidation and glycation

The peroxidation step in lipid transformation is considered to be essential in the pathogenesis of atherosclerosis. Calcium antagonists (CA) appear to have antioxidant effects in addition to their potent vasorelaxant properties. In the present study, we compared the antioxidative efficacy of CA (amlodipine, lacidipine, nifedipine, isradipine, diltiazem, and semotiadil) in the copper-catalysed oxidation of low-density lipoprotein (LDL) with that of glycated(g)/glycoxidated(go) LDL. This issue is of great importance when considering the potential therapeutic use of antioxidant drugs in diabetes-associated vasculopathy. Oxidation of native LDL was inhibited most efficiently (>90%) by lacidipine and semotiadil in the concentration range 10(-4)-10(-3) M. We found, however, a dramatic decrease in antioxidant activity towards g/goLDL as compared to native LDL in all the CA tested. Only lacidipine significantly inhibited copper-mediated oxidation of g/goLDL in the whole concentration range tested (10(-5) M-10(-3) M). This probably resulted from the increased auto-oxidative potential introduced by early and advanced glycation end products (AGE) into the g/goLDL. We noted that coincubation of LDL with 10(-3) M CA and 0.5 M glucose under oxidative/non-oxidative conditions partially or fully restored the antioxidant capacity of the different CA to inhibit the subsequent copper-catalysed oxidation of the modified LDL. This is a clear indication that CA inhibit glycative or glycoxidative LDL changes during the preceding long-term glycation period. The notion that both oxidative changes and long-term glycation effects were reduced by CA was corroborated by fluorescence analysis, AGE-ELISA, quantitation of lipid peroxidation, and thiobarbituric acid reactive substance (TBARS) measurement of long-term g/goLDL. The strongest antioxidative effects during long-term glycation of LDL were seen with isradipine, lacidipine, nifedipine, and semotiadil. Diltiazem was the only CA that could not prevent TBARS formation in LDL during the long-term glycation period. In contrast, Amadori product formation, as measured by the generation of fructosamines, was not significantly reduced by any CA tested. Thus CA, like other antioxidants, significantly retard AGE formation, while initial glycation reactions, such as Amadori product formation, are only weakly inhibited.     

Protection of low density lipoprotein oxidation at chemical and cellular level by the antioxidant drug dipyridamole.

1. The oxidative modification of low density lipoprotein (LDL) is thought to be an important factor in the initiation and development of atherosclerosis. Natural and synthetic antioxidants have been shown to protect LDL from oxidation and to inhibit atherosclerosis development in animals. Synthetic antioxidants are currently being tested, by they are not necessarily safe for human use. 2. We have previously reported that dipyridamole, currently used in clinical practice, is a potent scavenger of free radicals. Thus, we tested whether dipyridamole could affect LDL oxidation at chemical and cellular level. 3. Chemically induced LDL oxidation was made by Cu(II), Cu(II) plus hydrogen peroxide or peroxyl radicals generated by thermolysis of 2,2'-azo-bis(2-amidino propane). Dipyridamole, (1-10 microM), inhibited LDL oxidation as monitored by diene formation, evolution of hydroperoxides and thiobarbituric acid reactive substances, apoprotein modification and by the fluorescence of cis-parinaric acid. 4. The physiological relevance of the antioxidant activity was validated by experiments at the cellular level where dipyridamole inhibited endothelial cell-mediated LDL oxidation, their degradation by monocytes, and cytotoxicity. 5. In comparison with ascorbic acid, alpha-tocopherol and probucol, dipyridamole was the more efficient antioxidant with the following order of activity: dipyridamole > probucol > ascorbic acid > alpha-tocopherol. The present study shows that dipyridamole inhibits oxidation of LDL at pharmacologically relevant concentrations. The inhibition of LDL oxidation is unequivocally confirmed by use of three different methods of chemical oxidation, by several methods of oxidation monitoring, and the pharmacological relevance is demonstrated by the superiority of dipyridamole over the naturally occurring antioxidants, ascorbic acid and alpha-tocopherol and the synthetic antioxidant probucol.     

Mulberry leaf extract inhibits the oxidative modification of rabbit and human low density lipoprotein

In a previous study, we demonstrated that the intake of mulberry leaves or their 1-butanol extract (MLBE) reduced the concentration of serum lipids and atheromatous thickening of arterial intima in hypercholesterolemic rabbits. In the present study, we investigated the antioxidative activity of MLBE and isoquercitrin, the main component of MLBE. First, we determined the effect on a stable radical agent, finding that quercetin, isoquercitrin and MLBE scavenged the DPPH radical. We then determined the copper-induced oxidative modification of rabbit and human low-density lipoprotein (LDL). Oxidation of LDL was spectrophotometrically monitored by changes in absorbance at 234 nm accompanied by the formation of conjugated dienes, and measured the formation of thiobarbituric acid reacting substances (TBARS). Quercetin, an aglycone of isoquercitrin, inhibited the formation of conjugated dienes and TBARS by copper-induced oxidative modification of rabbit and human LDLs. MLBE and isoquercitrin also inhibited the oxidation of LDL. These results indicate that mulberry leaves inhibit the oxidative modification of LDL and suggest that mulberry leaves may had prevent atherosclerosis.     

Antioxidant protection of low density lipoprotein by procyanidins: structure/activity relationships

The antioxidant activity of catechins and oligomeric procyanidins against low density lipoproteins peroxidation was studied by means of three distinct methods: cis-parinaric acid fluorescence decay, conjugated-dienes detection, and oxygen consumption. A relationship between the radical trapping efficiency of procyanidins and their structure was investigated. The results indicated that: (i) interflavan linkage type (C4[bond]C6 or C4[bond]C8) exerts a significant effect upon radical-trapping antioxidant activity of procyanidins. It is suggested that the conformation adopted by each procyanidin in aqueous solution influence their hydrophilic character, hence affecting their interaction with the peroxyl radicals present in aqueous phase and those in LDL particle (lipidic nature); (ii) antioxidant activity increase with the degree of polymerization for the compounds with (-)-epicatechin (epi) as structural unit (epi, dimer B2 (epi-epi) and trimer C1 (epi-epi-epi)); (iii) galloylation increases antioxidant activity of procyanidins, specially in the case of B2-3"-O-gallate dimer, which revealed the maximal trapping efficiency.     

Atorvastatin affects low density lipoprotein and non-high density lipoprotein cholesterol relations with apolipoprotein B in type 2 diabetes mellitus: modification by triglycerides and cholesteryl ester transfer protein

Objectives: Non-HDL-cholesterol (non-HDL-C) and apolipoprotein (apo) B are proposed as treatment targets. The extent to which statin therapy affects relationships of LDL-C and non-HDL-C with apoB was examined in type 2 diabetes. Methods: Analyses were performed in 217 hypertriglyceridaemic type 2 diabetic patients (Diabetes Atorvastatin Lipid Intervention (DALI) cohort). 61 patients randomized to placebo, 70 to 10 mg atorvastatin daily and 65 – 80 mg atorvastin daily completed follow-up. Results: Baseline fasting LDL-C of 2.42 mmol/l and non-HDL-C of 3.69 mmol/l corresponded to the apoB guideline target of 0.90 g/l. During atorvastatin (10 and 80 mg daily), the LDL-C target was achieved most frequently, and lower LDL-C (2.38 and 2.29 mmol/l) and non-HDL-C (3.24 and 3.19 mmol/l) concentrations corresponded to this apoB goal. Decreases in LDL-C during atorvastatin treatment were negatively related (p < 0.001), but decreases in non-HDL-C were positively related to changes in triglycerides (p < 0.001), independently from decreases in apoB (p < 0.001 for all). Decreases in LDL-C and non-HDL-C were positively associated with decreases in cholesteryl ester transfer protein mass (p < 0.001). Conclusions: During atorvastatin lower LDL-C and non-HDL-C levels correspond to the apoB guideline target, which would favour its use as treatment target.     

Doxazosin treatment and peroxidation of low-density lipoprotein among male hypertensive subjects: in vitro and ex vivo studies.

Doxazosin is an antihypertensive drug that gives rise to 6- and 7-hydroxydoxazosin during hepatic metabolism. The structures of the hydroxymetabolites suggest that they may possess antioxidative properties. The aim of the present study was to examine whether doxazosin and 6- and 7-hydroxydoxazosin were able to scavenge free radicals and whether these compounds might protect low-density lipoprotein (LDL) against in vitro and ex vivo oxidation. Both 6- and 7-hydroxydoxazosin showed radical scavenging capacity as assessed by measuring scavenging of 1,1-diphenyl-2-picrylhydrazyl radicals. In vitro incubation with 10 microM 6- and 7-hydroxydoxazosin significantly reduced human mononuclear cell-mediated oxidation of LDL, measured as the formation of lipid peroxides and the relative electrophoretic mobility of LDL (to 10 and 6% of the control, respectively). Furthermore, formation of conjugated dienes in LDL during Cu2+-induced oxidation was significantly reduced in the presence of 5 microM 6- and 7-hydroxydoxazosin (to 28% of tmax [time to maximum] of control). However, treatment of hypertensive patients with increasing doses of doxazosin (from 1 to 8 mg/day) for 8 weeks altered neither Cu2+-catalyzed, 2,2'azobis-(2-amidinopropane hydrochloride)-initiated, nor cell-mediated oxidation of patient LDL ex vivo. Furthermore, the total antioxidative capacity of plasma was unaffected by treatment. In conclusion, the present study shows that 6- and 7-hydroxydoxazosin have radical scavenging properties and protect LDL against in vitro oxidation. However, treatment of hypertensive male subjects with increasing doses of doxazosin for 8 weeks did not affect ex vivo oxidation of LDL.     

Bufalin inhibits CYP3A4 activity in vitro and in vivo

Aim： To investigate the inhibitory interactions of bufalin and CYP3A4. Methods： Recombinant human CYP3A4 was incubated with bufalin in vitro. Bufalin was administered ig and iv to Wistar rats to further estimate its impact on CYP3A4, and midazolam was given to index the activity of CYP3A4. Results： The IC50 of bufalin was 14.52 μmol/L. Bufalin affected CYP3A4 activity with increases in AUC0-t and t1/2, and decreases in CL and the formation of 1-hydroxy-midazolam after ig or iv administration of midazolam （P〈0.05）. An increase in Cmax after ig bufalin administration （P〈0.05） was observed. Conclusion： Bufalin showed a modest but significant inhibition of CYP3A4 both in vitro and in vivo. The likelihood of an interaction between bufalin and the CYP3A4-metabolized drugs in human might not be negated.