Marked neointimal lipoprotein lipase increase in distinct models of proclivity to atherosclerosis: a feature independent of endothelial layer integrity

Lipoprotein lipase (LPL) in the arterial wall has been proposed to enhance the retention of apoB-containing lipoproteins, an early event in atherosclerosis. As the neointima is considered the primary site of lipid accumulation in atherogenesis, the arterial expression and location of LPL was investigated in distinct experimental models of neointimal formation in normolipidemic rabbits and rats. Neointima elicited by balloon aortic denudation or raised beneath an anatomically intact endothelial layer by placing a silastic collar around the common carotid artery, both showed a striking LPL immunostaining that mostly co-localized with neointimal smooth muscle cells. Besides, increased LPL protein and mRNA in deendothelialized aortas was demonstrated by Western and Northern blot analysis, respectively, suggesting an enhanced expression of LPL in injured arteries. It was concluded that LPL is increased in neointima developed in either denuded vessels or arteries with a preserved endothelium, a finding which suggests that LPL abundance may be an attribute of the neointima, whatever the stimulus that promotes its formation. On the basis of former evidence concerning the role of LPL in lipid retention, this study provides a possible explanation for the injury-induced vessel susceptibility to atherosclerosis, and the particular proneness of the neointimal layer to lipid accretion.

Effect of lercanidipine and its (R)-enantiomer on atherosclerotic lesions induced in hypercholesterolemic rabbits

The in vivo antiatherogenic activity of the calcium antagonist lercanidipine and its (R)-enantiomer was investigated in two different types of atherosclerotic lesions (hyperplastic and fatty-streak lesions) in rabbits. Lercanidipine (0.3, 1, and 3 mg kg(-1) week(-1)) as well as its (R)-enantiomer at 3 mg kg(-1) week(-1) were given by subcutaneous injection for 10 weeks to White New Zealand rabbits, with cholesterol feeding beginning at week 2. The hyperplastic lesion was obtained by positioning a hollow silastic collar around one carotid artery, while aortic fatty streak lesions were induced by cholesterol feeding. In untreated animals (n=5), 14 days after collar positioning an intimal hyperplasia was clearly detectable: the arteries without collar showed a intima/media (I/M) ratio of 0.03+/-0.02, whereas in carotids with a collar the ratio was 2+/-0.42. In lercanidipine-treated animals a significant and dose-dependent effect on intimal hyperplasia was observed. I/M ratios were 0.73+/-0.4, 0.42+/-0.1, 0.32+/-0.1 for 0.3, 1, and 3 mg kg(-1) week(-1), respectively (P<0.05). The lercanidipine enantiomer (3 mg kg(-1) week(-1)) was as effective as the racemate (0.41+/-0.11). Proliferation of smooth muscle cells, assessed by incorporation of BrdU into DNA, was reduced by about 50%, 70%, 85%, and 80% by lercanidipine (0.3, 1, and 3 mg kg(-1) week(-1)) and its (R)-enantiomer, respectively. The area of fatty-streaks in the aorta (n = 11-15) was significantly reduced by lercanidipine (3 mg kg(-1) week(-1), 16% vs 27%, P<0.05), a trend was observed also with lower doses. When different segments of the aorta were considered (arch, thoracic, abdominal) a significant and dose-dependent effect in the thoracic and abdominal aorta was observed also at lower doses. The (R)-enantiomer was as effective as lercanidipine. These results suggest a direct antiatherosclerotic effect of lercanidipine, independent of modulation of risk factors such as hypercholesterolemia and/or hypertension as demonstrated by the absence of stereoselectivity.

Dual effects of the antioxidant agents probucol and carvedilol on proliferative and fatty lesions in hypercholesterolemic rabbits

The in vivo direct antiatherogenic activity of the antioxidant probucol (200 mg/kg per day) or the beta-blocker with antioxidant properties carvedilol (10 and 20 mg/kg per day) was tested in the same animal in two different types of atherosclerotic lesion (proliferative and fatty lesions) induced in cholesterol-fed rabbits (1%). Drugs were given daily mixed with standard diet for 8 weeks; body weight and plasma lipid profile were not different among groups throughout the study. Aortic fatty lesions were induced by cholesterol feeding (n = 25 in each group) and their extent expressed as % of aorta inner surface covered by plaques was significantly reduced by both drugs (28.2+/-9.6%, P <0.05, 19.9+/-6.2%, P <0.01 for low- and high-dose carvedilol, respectively; 22.3+/-7.6%, P <0.01 for probucol, versus 41.6+/-10.7% in control rabbits). Proliferative lesions were obtained by positioning a hollow silastic collar around one carotid artery 6 weeks after dietary and drug treatments started (n = 5 in each group). The neointimal formation, mostly composed by myocytes, was determined by measuring cross-sectional thickness ratio of intimal (I) and medial (M) tissue of fixed arteries. In untreated animals, collared arteries resulted in a significant neointimal cell accumulation compared to the sham (1.10+/-0.14 versus 0.02+/-0.01) without change in medial thickness. I/M ratio was reduced by about 50% in animals treated with probucol (0.51+/-0.1) and carvedilol (0.66+/-0.21 and 0.52+/-0.1 in the low- and high-dose group, respectively). Total plasma TBARS were more than 50% lower in both probucol- and high-dose carvedilol-treated rabbits. Results show that pharmacological pretreatment with antioxidants directly inhibits early atherogenic processes, representing a potentially useful approach in the prevention of atherosclerosis.

The menopause and lipid metabolism: strategies for cardiovascular disease prevention

The menopause and its biology are as yet still incompletely understood. Very little is known about biological and molecular changes in cardiovascular target tissues and organs after menopause. Experimental and clinical evidence indicate that prevention of cardiovascular disease by estrogens is aimed both at the correction of risk factors and at the direct control of vessel structure and function. The effects of progestogens on these processes are still debated. Few other medical interventions have as great a potential for affecting morbidity and mortality as does hormone replacement therapy in postmenopausal women. Hormone replacement therapy has produced effects on health risk, some are reduced, some are raised, while some remain uncertain, suggesting that further testing through specific clinical trials are required before confident recommendations can be made about the full range of benefits and risks. Lipid lowering therapy may be an acceptable alternative for postmenopausal women at risk for cardiovascular disease.

Proapoptotic effect of atorvastatin on stimulated rabbit smooth muscle cells

The in vitro and in vivo activity of atorvastatin and other 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase inhibitors (fluvastatin, pravastatin and simvastatin) has been investigated. Atorvastatin, fluvastatin, pravastatin and simvastatin caused a significant and dose-dependent (0.1-50 microM) reduction in cell multiplication of vascular smooth muscle cells (SMC) in cultures associated with the retardation of cycling cells in the G1 and G2/M compartments at 24 h, a phenomenon leading to apoptosis (programmed cell death) in several experimental in vitro models. The effects on the cell cycle resulted in a strong inhibition of cell proliferation at 48 h, followed by apoptosis when incubation was prolonged to 72 h as assessed by nuclei morphology and cytofluorimetric analysis of DNA. The apoptotic effect observed for the statins is completely prevented by the addition of exogenous mevalonate at a 100 microm concentration. in vivo SMC proliferation was stimulated by applying a silastic collar to the outside surface of carotid arteries in normocholesterolemic rabbits in the presence of an anatomically intact endothelium. The positioning of the collar promoted apoptosis in control vessels as assessed by Terminal Deoxynucleotidyl Transferase-dUTP-Biotin Nick-End Labeling (TUNEL) assay. The pre-treatment with 5 mg kg-1 per day of atorvastatin before collar insertion strongly increased the number of TUNEL-positive cells, suggesting a pro-apoptotic effect of HMGCoA reductase inhibitors also in vivo, even though cell DNA rearrangement still needs to be excluded. No apoptotic signal was detectable in sham operated arteries with no collar in either control or atorvastatin-treated rabbits. These data indicate that HMGCoA reductase inhibitors effect on the arterial wall may involve the modulation of both cell proliferation and programmed cell deaths supporting a possible role of statins in the prevention of early lesion and restenosis.

Direct antiatherogenic activity of isradipine and lacidipine on neointimal lesions induced by perivascular manipulation in rabbits

The in vivo antiatherogenic activity of two calcium antagonists of the dihydropyridine class (isradipine and lacidipine) was investigated in a new experimental model. The proliferative lesion induced in the rabbit carotid artery was obtained by positioning a hollow silastic collar around the vessel. The neointimal formation was determined by measuring cross sectional thickness of intimal (I) and medial (M) tissue of fixed arteries obtained 14 days after collar placement. The effectiveness in inhibiting neointimal formation was assessed for isradipine (0.5, 1 and 4 mg kg-1 day-1) in normocholesterolemic (NC) animals and for lacidipine (1, 3, and 10 mg kg-1 day-1) in hypercholesterolemic (HC) rabbits. In NC control animals a neointimal formation was clearly detectable (I/M 0.53 +/- 0.18, n = 5). In isradipine-treated groups I/M ratios were significantly decreased (0.15 +/- 0.03, 0.12 +/- 0.02, 0.1 +/- 0.02 for the 0.5, 1 and 4 mg kg-1 day-1 doses respectively). In HC rabbits the administration of cholesterol 1% mixed with food and drug treatment started either 60 days before collar insertion (pretreated group, HC60) or on the same day (non pretreated group, HC15) of the collar placement. Only the pharmacological pretreatment was effective in reducing neointimal formation (0.47 +/- 0.02, 0.4 +/- 0.09, and 0.32 +/- 0.02 for dose 1, 3 and 10 mg kg-1 day-1 vs 1.1 +/- 0.14 in control animals). The inhibition of neointimal hyperplasia was much less evident in nonpretreated animals (0.7 +/- 0.15, 0.6 +/- 0.18 and 0.43 +/- 0.08 for dose 1, 3, and 10 mg kg-1 day-1 vs 0.72 +/- 0.2 in control animals). These results suggest a direct antiatherosclerotic effect of isradipine and lacidipine on neointimal hyperplasia induced in NC and HC pretreated rabbits independently of modulation of risk factors such as hypercholesterolemia and/or hypertension.

Effect of lacidipine on fatty and proliferative lesions induced in hypercholesterolaemic rabbits

1. The in vivo antiatherogenic activity of the calcium antagonist, lacidipine, was investigated in two different types of atherosclerotic lesions (proliferative and fatty lesions) induced in rabbits. 2. The proliferative lesion was obtained by positioning a hollow silastic collar around one carotid artery, while aortic fatty lesions were induced by cholesterol feeding. Cholesterol (1%) and lacidipine (1, 3, and 10 mg kg-1) were given daily mixed with standard diet for 8 weeks to White New Zealand rabbits. The intimal hyperplasia (proliferative lesion) was induced 6 weeks after dietary and drug treatment started. 3. The neointimal formation was determined by measuring cross sectional thickness of intimal (I) and medial (M) tissue of fixed arteries. In untreated animals (n = 5), 14 days after collar positioning an intimal hyperplasia was clearly detectable: the arteries with no collar (sham) showed an I/M tissue ratio of 0.03 +/- 0.02, whereas in the carotid with collar the ratio was 0.62 +/- 0.12. In lacidipine-treated animals a significant and dose-dependent effect on proliferative lesions at all three doses tested, was observed. I/M ratios were 0.47 +/- 0.02, 0.40 +/- 0.09, 0.32 +/- 0.02 for doses 1, 3, and 10 mg kg-1 day-1, respectively (P < 0.05). 4. The fatty lesion extent was significantly reduced by lacidipine at the 10 mg kg-1 day-1 dose, although a trend was also observed with lower dosage. 5. These results suggest a direct antiatherosclerotic effect of lacidipine, independent of modulation of risk factors such as hypercholesterolaemia and/or hypertension. Furthermore, the proliferative lesions are apparently more sensitive to lacidipine than are lipid-rich lesions.

Pathogenesis of atherosclerosis and the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors

Atherosclerosis is a complex multifactorial process resulting from an excessive inflammatory/fibroproliferative response to various forms of injurious stimuli to the arterial wall. The potential interactions of cells, cytokines, and growth-regulatory molecules among the different cells in the atherosclerotic lesion present numerous opportunities for modulating lesion formation and progression. Smooth muscle cell (SMC) migration and proliferation, together with lipid deposition, are now recognized as the major phenomena occurring within the arterial wall, and thus these phenomena serve as targets for pharmacologic intervention in the process of atherogenesis. Migration and proliferation of SMC are key events in atherosclerosis--and in restenosis after angioplasty. An understanding of the factors that induce such events is important for the prevention and treatment of these diseases. Mevalonate and other intermediates of cholesterol synthesis (isoprenoids) are essential for cell proliferation; hence drugs affecting this metabolic pathway are potential antiatherosclerotic agents. Recently, this group provided in vitro and in vivo evidence of decreases in SMC proliferation by fluvastatin and simvastatin, but not pravastatin, independent of their cholesterol-lowering properties. The in vitro inhibition of cell migration and proliferation induced by simvastatin and fluvastatin (70-90% decrease) was completely prevented by the addition of mevalonate, and partially prevented (70-80%) by farnesol or geranylgeraniol. This confirms the specific role of isoprenoid metabolites--most probably geranylgerylated protein(s)--in regulating cell migration and proliferation. The inhibitory effect of fluvastatin and simvastatin on cholesterol esterification induced by acetyl low density lipoprotein in macrophages was also prevented by the addition of geranylgeraniol.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant apolipoprotein A-IMilano dimer inhibits carotid intimal thickening induced by perivascular manipulation in rabbits

Apolipoprotein A-IMilano (apoA-IM), a natural variant of apolipoprotein A-I (apoA-I), confers to the carriers a significant protection against vascular disease. The antiatherogenic activity of a recombinant disulfide-linked apoA-IM dimer (rA-IM/A-IM) was analyzed in vivo by evaluating its effect on neointimal formation induced by periarterial manipulation in 1% cholesterol-fed rabbits. A flexible collar was applied around the carotid artery 21 days after the beginning of the dietary regimen, and animals were killed 10 days later. Rabbits were injected five times with reconstituted high-density lipoprotein containing egg phosphatidylcholine (EPC) and rA-IM/A-IM (119 mg EPC + 40 mg protein per dose) or with EPC liposomes (119 mg EPC per dose) beginning either 5 days before or at the day of collar positioning. Neither treatment affected plasma cholesterol levels. A significant intimal thickening was observed in control animals; the intima-to-media (I/M) ratio was 0.63 +/- 0.11 versus 0.03 +/- 0.05 for the sham-operated contralateral arteries. Neointimal formation was markedly inhibited in animals pretreated with rA-IM/A-IM before lesion induction (I/M, 0.26 +/- 0.19) but not in those in which treatment began the day of collar insertion (I/M, 0.74 +/- 0.14). EPC liposomes did not affect neointimal formation (I/M, 0.50 +/- 0.14 and 0.51 +/- 0.07 in the two treatment groups). Proliferation of smooth muscle cells, assessed by direct incorporation of bromo-2'-deoxyuridine (BrdU) into replicating DNA, was reduced by approximately 30% and 75% in the intimal and medial tissues of rA-IM/A-IM-pretreated rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo enhanced antitumor activity of carmustine [N,N'-bis(2-chloroethyl)-N-nitrosourea] by simvastatin

The effects of a combination of simvastatin, a cholesterol-lowering agent, and carmustine (BCNU; N,N'-bis(2-chloroethyl)-N-nitrosourea) on experimental C6 glioma were studied in vitro and in vivo. In vitro simvastatin and BCNU alone inhibited cell proliferation in a dose-dependent fashion. A subliminal concentration of simvastatin (0.1 microM) markedly and synergistically increased the BCNU toxicity to C6 glioma cells. The cytofluorimetric analysis of DNA from simvastatin-treated C6 glioma cells showed, besides the already described arrest in G1, an arrest/retardation in G2-M. Mitotic index from C6 cells incubated with simvastatin (10 microM) decreased by about 90%, indicating a specific C6 arrest/retardation in G2. The drug effects could be completely reversed by simvastatin withdrawal or mevalonate addition to the cultured cells. The combination of simvastatin and BCNU resulted predominantly from the profound retardation of cells in the G2-M compartment of the cell cycle. In vivo simvastatin (administered daily mixed with food) and BCNU (single i.p. injection), when given separately, caused a dose-dependent inhibition of labeling index in C6 glioma homografts (ID50, 61 mg/kg/day and 8.7 mg/kg, respectively). The combination of the lowest doses tested (simvastatin, 25 mg/kg/day and BCNU 0.3 mg/kg) resulted in a significant growth delay (compared to either drug alone) in C6 glioma (P < 0.05). There was no significant increase in toxicity as assessed by myelosuppression (WBC counts and bone marrow labeling index) and body weight. The results provide in vivo support for the combined use of simvastatin, a cholesterol-lowering agent, and BCNU in brain tumor treatment.

Experimental and clinical effects of isradipine relevant to atherosclerosis

A number of studies in experimental animal models have demonstrated the potential direct antiatherosclerotic effects of calcium antagonists. This class of compounds can influence several processes that are involved in the development of atherosclerotic lesions. This action is independent of either blood pressure reduction or hypercholesterolemia. A major problem encountered from the experimental data are the high doses used, which are several times higher than those used in the treatment of humans. One notable exception to this problem is the second-generation calcium antagonist isradipine, which exerts a direct antiatherosclerotic effect in rabbits at doses similar to those used in the clinic. Thus, this review is a summary of the effects and mechanisms of the antiatherosclerotic activity of isradipine.

PKC activity in rat C6 glioma cells: changes associated with cell cycle and simvastatin treatment

The parallel effects of simvastatin on cell cycle and PKC activity in rat C6 glioma cells were investigated. Simvastatin, 2.5 microM, for 24 h resulted in cell growth arrest in early G1 phase of the cell cycle and in a significant increase of total PKC activity (283 +/- 42 vs 470 +/- 61 pmoles/min/mg protein p = 0.002 for control cells and simvastatin-treated cells, respectively). The effect of simvastatin was fully prevented by mevalonate. A time dependent increase of PKC activity was observed in control exponentially free-growing C6 cells approaching confluency: a highly significant negative correlation (r = -0.91 p < 0.0001) between PKC activity and growth rate was calculated. PKC activity was high in cells arrested in G0 by serum starvation (0.4%). Following addition of complete medium (17.5% serum) the PKC activity progressively decreased and reached a minimum when cells traversed the G2/M phase, as determined by DNA analysis distribution. PKC activity dropped 30% in simvastatin-arrested early G1 cells; 44% in hydroxyurea-arrested cells at the G1/S boundary; and 73% in Colcemid mitosis-blocked cells. The results show that C6 glioma cell PKC activity is maximal in a G0 quiescent state and varies at different points of the cell cycle.

Effect of lacidipine on the carotid intimal hyperplasia induced by cuff injury

The in vivo antiatherogenic activity of the calcium antagonist lacidipine was investigated in arterial hyperplasia induced by perivascular manipulation of hypercholesterolemic carotid rabbits. This was accomplished by positioning a hollow silastic collar around one carotid, which within a few days induces an atherosclerotic lesion (proliferative lesion) showing biochemical and morphologic changes similar to those of early human atherosclerosis: the contralateral carotid, with no collar, served as control in the same animal. The effect of lacidipine was also investigated in aortic atherosclerotic lesions (fatty lesions) induced by hypercholesterolemia mixed with either cholesterol (1%) and lacidipine (3 mg/kg/day) or cholesterol (1%) alone for 8 weeks. Hypercholesterolemic New Zealand White rabbits were fed daily a standard diet. Intimal hyperplasia was mechanically induced in one carotid artery of each rabbit 6 weeks after dietary and drug treatment started. Neointimal formation was followed by measuring by light microscopy the cross-sectional thickness of intimal (I) and medial (M) tissue of fixed arteries. In positive control animals receiving dietary cholesterol only (n = 10), by 14 d after collar positioning the process of intimal hyperplasia was significantly pronounced. The control arteries showed an I:M tissue ratio of 0.03 +/- 0.02, whereas in the carotid with collar the ratio was 0.56 +/- 0.11. In the animals receiving lacidipine, neointimal formation was significantly lower [I:M tissue ratio 0.32 +/- 0.1 (n = 10), about 60% of positive controls]. Measurement of the percent area of the aortic intima covered by plaques did not show significant differences between control and lacidipine-treated animals. These results suggest a direct antiatherosclerotic effect of lacidipine on proliferative lesions.

Hormonal agents used in lowering lipoprotein(a)

Lipoprotein(a) (Lp(a)) plasma concentrations in Caucasian populations are classified as a quantitative genetic trait. Although the prevailing view has been that Lp(a) levels are affected by age and gender, recent data are beginning to indicate otherwise. Lp(a) levels change throughout life especially in females after menopause. Lp(a) levels decrease in women treated with anabolic steroids such as stanozolol and danazol. The Lp(a) plasma concentration is also profoundly affected by sex hormone variations during pregnancy. In men with prostatic cancer Lp(a) levels are reduced about 50% by estrogen therapy, and increased 20% by orchidectomy. We have evaluated the changes in Lp(a) and lipid levels in postmenopausal women following estrogen/progestogen replacement therapy. The mean level of Lp(a) in treated women was about 50% lower after 6 and 12 months of replacement therapy. A significant correlation between basal Lp(a) levels and the changes at either 6 or 12 months was observed, suggesting that therapy was particularly efficacious in those women with high basal Lp(a) levels. One year after therapy cessation, Lp(a) concentrations tended to return to pre-therapy values. In addition estrogen-progestogen treatment significantly lowered total-cholesterol (12%) and LDL-cholesterol (28%), and increased HDL-cholesterol (18%). From these studies it appears that sex hormones are actively involved in the modulation of plasma Lp(a) levels and that both female and male sex hormones possess a lowering effect. The results confirm a direct effect of sex hormones on Lp(a) metabolism and suggest that estrogen-progestogen treatment of postmenopausal women can improve the lipid profile not only by lowering total- and LDL-cholesterol and raising HDL cholesterol, but also by lowering plasma Lp(a).

The lowering of lipoprotein[a] induced by estrogen plus progesterone replacement therapy in postmenopausal women

OBJECTIVE

To evaluate whether estrogen plus progesterone replacement therapy influences the plasma lipoprotein[a] (Lp[a]) levels in postmenopausal women.

DESIGN

Fifty-five women who had been menopausal for at least 1 year were followed up for 12 months. Twenty-four subjects served as the control group and 31 subjects served as the therapy group. The therapy consisted of conjugated estrogen (1.25 mg/d) and medroxyprogesterone acetate (10 mg/d for 10 days a month). Blood samples were obtained before the start of therapy and at 6 months and 12 months after therapy. Nine subjects in the therapy group were followed up for an additional year after the treatment was suspended (washout group).

SETTINGS

All subjects were healthy women (mean age, 52 years) who had natural menopause at least 1 year before the beginning of recruitment. None of the women had received exogenous sex steroids or drugs known to influence lipid and lipoprotein metabolism in the previous 12 months.

MAIN RESULTS

In the control group, no change was noted in the plasma Lp[a] concentrations during the study. In the treatment group, the mean plasma Lp[a] concentrations decreased 50% after 6 months (P < .01) and remained at this level 12 months after treatment was started. In the washout group, mean plasma Lp[a] levels tended to return to pretherapy values. In addition, estrogen plus progesterone treatment significantly lowered total cholesterol levels by 15% and low-density lipoprotein cholesterol levels by 30%; it increased high-density lipoprotein cholesterol levels by 19%.

CONCLUSION

The results suggest that in estrogen plus progesterone-treated postmenopausal women, the lipid profile is improved not only by lowering low-density lipoprotein cholesterol levels and raising high-density lipoprotein levels, but also by lowering plasma Lp[a] concentrations.

Relationship between mevalonate pathway and arterial myocyte proliferation: in vitro studies with inhibitors of HMG-CoA reductase

The role of mevalonate and its products (isoprenoids) in the control of cellular proliferation was examined by investigating the effect of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (vastatins) on growth and on cholesterol biosynthesis of cultured arterial myocytes (SMC). Simvastatin (S) and fluvastatin (F), but not pravastatin (P), decreased the rate of growth of rat vascular SMC. The inhibition, evaluated as cell number, was dose-dependent with IC50 values of 2.8 and 2.2 microM for S and F, respectively; P (1-500 microM) was inactive. The inhibition of cell growth induced by 3.5 microM S (70% decrease) was prevented completely by the addition of 100 microM mevalonate, partially (70-85%) by the addition of 10 microM geraniol, 10 microM farnesol and 5 microM geranylgeraniol, but not by the addition of squalene, confirming the specific role of isoprenoid metabolites in regulating cell proliferation. All the tested vastatins inhibited the incorporation of [14C]acetate into cholesterol but P had 800 times lower potency than S and F. Similar results were obtained in SMC from human femoral artery. At least 80% inhibition of cholesterol synthesis was necessary to induce a decrease in SMC proliferation. To further investigate the relationship between cholesterol synthesis and cell growth, two enantiomers of F were investigated. The enantiomer more active on HMG-CoA reductase was 70- and 1.6-fold more potent on arterial myocyte proliferation than its antipode and the racemic mixture, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

HMG CoA reductase inhibitors. In vivo effects on carotid intimal thickening in normocholesterolemic rabbits

The in vivo activity of different 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (vastatins) on neointimal formation induced by insertion of a flexible collar around one carotid artery of normocholesterolemic rabbits was investigated. The contralateral carotid artery served as a sham control. Pravastatin, lovastatin, simvastatin, and fluvastatin were given mixed with food at daily doses of 20 mg/kg body wt for 2 weeks starting on the day of collar placement. The treatment with vastatins did not modify rabbit plasma cholesterol concentrations. The neointimal formation was assessed by measuring the cross-sectional thickness of intimal and medial tissues of fixed arteries with light microscopy. Fourteen days after collar placement, intimal hyperplasia (mostly cellular) was pronounced in treated carotid arteries. The intimal/medial (I/M) tissue ratio was 12-fold higher in treated arteries than in arteries without the collar (0.36 +/- 0.04 versus 0.03 +/- 0.02). Animals treated with lovastatin (n = 12), simvastatin (n = 12), and fluvastatin (n = 12) showed significantly less neointimal formation; I/M tissue ratios were 0.24 +/- 0.03, 0.20 +/- 0.03, and 0.17 +/- 0.03, respectively. The inhibition elicited by pravastatin (n = 12, 0.32 +/- 0.03) did not reach statistical significance. alpha-Actin antibody immunofluorescence analysis of serial sections revealed that cells present in the hyperplastic intima were mostly myocytes. Rates of intimal myocyte proliferation were also measured by incorporation of 5-bromo-2'-deoxyuridine, a thymidine analogue, into replicating DNA. Immunofluorescence analysis showed that 5-bromo-2'-deoxyuridine was actively incorporated into intimal myocytes after ++reinsertion of the collar, with a labeling index (percent of labeled myocytes) of 2.15 after 14 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lacidipine on experimental models of atherosclerosis

AIM

To evaluate the effect of lacidipine on the major processes of atherogenesis.

METHODS

Cell-culture methods were used to study the effect of lacidipine. Low-density lipoprotein (LDL) receptor expression and cholesterol esterification were evaluated in human skin fibroblasts and in mouse peritoneal macrophages, respectively. The effect of lacidipine on cellular proliferation was tested on aortic myocytes cultured from rat aorta.

RESULTS

Lacidipine did not affect LDL receptor expression, but it inhibited the ability of acetyl LDL to stimulate cholesterol esterification in macrophages by more than 95%. The drug inhibited cellular proliferation in a dose-dependent manner. This antiproliferative effect was confirmed in human femoral artery myocytes. In accord with the inhibitory effect on cellular growth, preliminary in vivo studies suggest that lacidipine may reduce neointimal formation induced by perivascular manipulation of the carotid artery in hypercholesterolemic rabbit.

CONCLUSIONS

Our results indicate that lacidipine may be antiatherosclerotic through an effect on the major processes involved in atheroma formation.

Cholesterol and mevalonic acid modulation in cell metabolism and multiplication

Cholesterol in animals is a major structural component of cell membranes. It may therefore play a functional role in the modulation of cell osmolarity, the process of pinocytosis and the activities of membrane-associated proteins such as ionic pumps, immune responses, etc. A major relationship exists between the cell-growth processes and the cholesterol biosynthetic pathway. The cholesterol needed for new membranes may be derived either from endogenous synthesis or from exogenous sources, principally plasma low-density-lipoproteins (LDL) which enter the cells by receptor-mediated endocytosis. Both these pathways are enhanced in rapidly growing cells. Conversely, if synthesis is inhibited and no exogenous cholesterol is available, cell growth is blocked. The 3-hydroxy-3-methylglutaryl CoA (HMGCoA) reductase (the rate-limiting reaction in cholesterol biosynthesis) is the enzyme which catalyzes the conversion of HMGCoA to mevalonic acid. It has been suggested that mevalonate may play an important role in cell proliferation. All cells need at least two products synthesized from mevalonate in order to proliferate, and the only one yet identified is cholesterol. Other melavonate-derived potential candidates as cell-cycle and cell-survival products include the dolichols ubiquinone side chains, isopentenyladenosine derivatives, etc. Furthermore, it has recently been shown that membrane association appears to be an important function in mevalonate-derive modifications of several important proteins such as cellular membrane G proteins, those coded for by oncogenes (ras proteins) and lamins (nuclear proteins). In recent years the development of cholesterol-synthesis-inhibiting drugs, for lowering plasma cholesterol levels has mainly been centred on the control of HMGCoA reductase activity (vastatins). However, because mevalonic acid is the precursor of numerous metabolites, any reduction of such activity may potentiate pleiotropic effects. Vastatins are now, therefore, receiving increased attention as potential pharmacological tools for the control of abnormal cell growth in pathological situations, i.e. tumours and vascular smooth muscle cell proliferation under atherogenic conditions. In our laboratories, we have demonstrated that simvastatin can prevent arterial myocyte proliferation both in vivo and in vitro. Simvastatin can also inhibit in vitro the rate of human glioma cell growth, since it shows a strong synergistic inhibitory effect on cell proliferation when used in association with anticancer agents such as Carmustine or beta-interferon. Both simvastatin-induced cell growth inhibition and the synergy observed with these drugs can be completely reversed by incubating cells with mevalonate. This shows that the effect of simvastatin of cell proliferation is due to its specific inhibitory activity on intracellular mevalonate synthesis.

Simvastatin, an inhibitor of cholesterol biosynthesis, shows a synergistic effect with N,N'-bis(2-chloroethyl)-N-nitrosourea and beta-interferon on human glioma cells

The effect of simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on human glioma cell growth was investigated. When incubated with simvastatin, cell proliferation decreased in a concentration-dependent fashion, as measured by cell number and [3H]-thymidine incorporation into DNA (concentration producing 50% inhibition, 60 nM). The effect was detectable 12 h after cells were exposed to the drug and persisted for 2 days. Addition of mevalonate to cells exposed effect of simvastatin in combination with beta-interferon and N,N'-bis(2-chloroethyl)-N-nitrosourea, both antitumoral drugs, was also evaluated by cell growth inhibition assay. The concentration producing 50% inhibition for each of these drugs was 650 units/ml and 50 nM, respectively. Subliminal concentrations of beta-interferon or N,N'-bis(2-chloroethyl)-N-nitrosourea were incubated together with 1 nM simvastatin. The data were analyzed with the aid of an isobologram using the concept of an envelope of additivity. Simultaneous cell exposure to simvastatin with either N,N'-bis(2-chloroethyl)-N-nitrosourea or beta-interferon produced a strong synergistic inhibitory effect on cell proliferation. These data provide in vitro support for the possibility that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, utilized as plasma cholesterol-lowering agents, could potentiate the effect of antiblastic drugs on tumor growth.

Triglyceride metabolism in 3T3-L1 cells. An in vivo 13C NMR study

13C nuclear magnetic resonance spectroscopy has been used to study triglyceride metabolism in 3T3-L1 cells incubated with [1-13/14C] acetate, myristate, palmitate, stearate, or oleate. Labeled cells embedded in agarose filaments were perfused in a specially fitted NMR tube within the spectrometer magnet. Incubation of 3T3-L1 cells with a specific fatty acid enriched the cellular triglycerides with that fatty acid; the NMR signal observed in the carbonyl region of the cell spectrum was due in large part to that fatty acid. NMR data demonstrated that cellular enzymes preferentially esterified saturated fatty acids at the glyceride sn-1,3 position and unsaturated fatty acids at the sn-2 position. cellular triglyceride hydrolysis by hormone-sensitive lipase was monitored by measuring the decrease in the integrated intensities of resonances arising from fatty acyl carbonyls esterified at glycerol carbons sn-1,3 and sn-2. Under basal conditions, the time courses were first-order, and the average rates were 0.14% of signal/min at both carbonyl positions. Under isoproterenol stimulated conditions, these rates were still first-order and increased 6.4-fold at the sn-1,3 position and 2.4-fold at the sn-2 position. The observation that the hydrolysis time courses were first-order suggested that only a small amount of cellular triglyceride was available to hormone-sensitive lipase, supporting the view that lipolytic enzymes operate at lipid surfaces where only small amounts of neutral lipid may be soluble. Attempts to correlate the measured rates with the rates of hydrolysis at the sn-1,3 and sn-2 positions were hindered by the fact that the chemical shifts of the carbonyl carbons of the diglyceride hydrolysis product did not overlie those of the triglyceride. Analysis of hydrolysis kinetics revealed that hormone-sensitive lipase exhibited little preference for a particular esterified fatty acid under basal conditions; however, under stimulated conditions, the enzyme exhibited a preference for certain triglyceride species.

Cholesterol metabolism in hypercholesterolemia-resistant rabbits

Normal rabbits typically respond to a diet high in cholesterol with a large increase in the concentration of plasma cholesterol. We have previously described the breeding and partial characterization of a variant rabbit which does not respond to a high cholesterol diet with changes in plasma cholesterol concentration. In the present report we have characterized three components involved in cholesterol homeostasis: the B/E (LDL) receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase activity (HMG-CoA reductase, EC 1.1.1.34) and acyl-coenzyme A: cholesterol acyltransferase activity (ACAT, EC 2.3.1.26) in the livers of the hypercholesterolemia-resistant rabbits. Using normal cholesterol-fed rabbit [125I] beta-VLDL as a ligand, liver membranes prepared from resistant rabbits fed a low-cholesterol diet had 70% higher binding capacity than membranes from normal rabbits fed the same diet. Similar experiments demonstrated that the resistant rabbits had a 240% higher B/E receptor binding capacity compared to normal animals when liver membranes were prepared from animals fed a 0.25% cholesterol-enriched diet. No difference in the binding affinity of [125I]beta-VLDL was detected in membranes prepared from normal or resistant animals. When fed a low-cholesterol diet, the resistant rabbits had approximately 2-fold higher hepatic HMG-CoA reductase activity (97.4 +/- 3.5 pmol product/mg/min in resistant animals compared to 45 +/- 1.1 pmol product/min/mg in normal animals). The difference was exaggerated in animals fed the 0.25% cholesterol-enriched diet, 73.3 +/- 5.5 vs 2.4 +/- 0.56 pmol product/min/mg for resistant and normal membranes respectively. The basal activity of ACAT in hepatic membranes was significantly lower in the resistant rabbits compared to normal rabbits (138 +/- 11 vs 268 +/- 19 pmol cholesteryl ester/min/mg in resistant and normal rabbits respectively); when fed a 0.25% cholesterol-enriched diet, the enzyme was induced 6-fold in normal animals but was increased only 2-fold in the resistant animal. These biochemical data suggested that the resistant rabbit maintained low intracellular cholesterol even when fed a cholesterol-enriched diet. Direct measurement of cellular cholesterol and cholesteryl esters demonstrated that the concentration of these lipids was significantly lower in the resistant animal than in normal animals with the largest differences found in the cytoplasmic rather than the membrane compartment. These studies demonstrate that the resistant rabbit manifests several quantitative differences in cholesterol metabolism and in the regulation of cholesterol metabolism; but these studies do not directly explain the underlying cause of the resistance to hypercholesterolemia in the resistant rabbit.

Effect of particle size and temperature on the conformation and physiological behavior of apolipoprotein E bound to model lipoprotein particles

The effect of particle size and structural order/disorder of the lipid domain on the conformation and physiological behavior of lipid-associated apolipoprotein E (apoE) was evaluated. Circular dichroic (CD) spectra of apoE bound to large (LME) and small (SME) microemulsion particles, composed of dimyristoylphosphatidylcholine (DMPC) and cholesteryl oleate (CO), and to DMPC disks revealed that at 4 degrees C, where all of the lipid constituents were in an ordered state, apoE bound to LME displayed approximately 60% alpha-helicity, while apoE bound to SME and DMPC disks displayed 73% and 95% helicity, respectively. Over the temperature range 4-50 degrees C, encompassing the lipid thermal transitions, only apoE bound to LME demonstrated an abrupt change in its CD spectrum (decrease in alpha-helicity) in response to temperature. To determine the source of the abrupt CD change, the constants for dissociation (Kd) of apoE from the surface of the large and small microemulsion particles were determined at 4, 25, and 37 degrees C. These results demonstrated that at 4 degrees C, the KdS for binding of apoE to the LME and SME were approximately equal; however, between 4 and 25 degrees C, there was a 5-fold increase in the Kd for binding of apoE to the LME, whereas the Kd for binding to the SME remained constant. The physiological effects of these differences in apoE secondary structure and equilibrium binding were examined by measuring the capacity of each apoE-containing particle to complete with LDL for binding to human fibroblasts, and by measuring the capacity of the apoE-microemulsion particles to suppress HMG-CoA reductase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol metabolism in fibroblasts from rabbits resistant to diet-induced hypercholesterolemia

We have previously described a colony of New Zealand White rabbits that are resistant to hypercholesterolemia when fed a cholesterol-enriched diet. The present studies used skin fibroblasts obtained from normal and hypercholesterolemia-resistant rabbits to investigate cholesterol metabolism and lipid composition in vitro. The lipid compositions of the two cell lines after incubation in either fetal calf serum or lipoprotein-deficient serum were similar. The conversion of radiolabeled acetate into sterol and phospholipids was higher in resistant fibroblasts than in normal fibroblasts. In contrast, incorporation of radiolabeled oleic acid into cholesteryl ester was significantly lower in resistant fibroblasts than in normal cells. In parallel experiments, the 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was higher and acyl-coenzyme A:cholesterol acyltransferase activity was lower in resistant cells compared to normal cells. Furthermore, binding, uptake, and degradation of normal rabbit 125I-labeled LDL (low density lipoproteins) were 30% higher in resistant than in normal fibroblasts. These observations are consistent with results from previous studies of cholesterol metabolism in the liver membranes of these rabbits. The results indicate that extrahepatic cells (such as fibroblasts) from the resistant rabbit exhibit the same altered cholesterol metabolism as that found in the hepatic tissues of these rabbits. These studies suggest that the resistant rabbit may provide an in vivo and in vitro system for studying the mechanisms by which some individuals of a species can minimize the effect of dietary cholesterol on the development of hypercholesterolemia and atherosclerosis.

Rapid modulation of rat adipocyte lipoprotein lipase: effect of calcium, A23187 ionophore, and thrombin

The effect of calcium ions on the lipoprotein lipase (LPL) activity in rat adipocytes has been investigated. Incubation of the cells in the absence of extracellular calcium produced a rapid decline of LPL activity in the cells. The enzyme, however, could be immediately reactivated in less than 3 min by the addition of calcium. The degree of reactivation was proportional to the concentration of extracellular calcium. alpha 1 agonists phenylephrine and methoxamine affected LPL activity only slightly, as did vasopressin and angiotensin II. In contrast, calcium ionophore A23187 elicited a quick and transient enzyme activation which reached its peak 4 min after the addition of the drug. Thrombin (0.1 U/ml) produced the most rapid and intense response. The effect of thrombin was already evident 10 s after its addition, and the enzyme activity almost doubled above the basal level. Extracellular calcium was necessary to achieve thrombin activation. Contrary to previous thought, these data support the conclusion that LPL may undergo rapid activation, and that calcium ions are critically involved in this activation process. Thrombin rapidly raises LPL activity and may be one of its physiological activators in vivo.

Development and partial metabolic characterization of a dietary cholesterol-resistant colony of rabbits

A colony of New Zealand white rabbits has been developed which, when fed a cholesterol-supplemented diet, exhibit unusual resistance to hypercholesterolemia and atherosclerosis, disorders usually observed in normal cholesterol-fed rabbits. When resistant rabbits (RT) were fed a normal low cholesterol diet (ND), their plasma lipoprotein patterns were significantly different from those of normal rabbits (NR) fed the same diet. The low density lipoprotein cholesterol (LDL-c)/high density lipoprotein cholesterol (HDL-c) ratio and LDL-c/very low density lipoprotein cholesterol (VLDL-c) ratio were lower in the resistant rabbits. The hydrated density of HDL of the normal-responsive rabbits was greater than that of the resistant rabbits. LDL from resistant rabbits contained a lower proportion of esterified cholesterol and protein than LDL from normal rabbits. Peripheral mononuclear cells from resistant rabbits bound about 30% more 125I-labeled rabbit LDL than mononuclear cells from normal rabbits. These results demonstrate that the plasma cholesterol levels of these animals is at least partly under genetic control and that compositional differences exist between the major plasma lipoprotein classes of normal and resistant rabbits even during the ingestion of low-cholesterol diet. The results indicate that at least a part of the difference in the cholesterolemic responses between the two rabbit groups is due to an enhanced LDL uptake by the mononuclear cells, and presumably by other somatic cells of the resistant group.