Relationship between tissue selectivity and lipophilicity for inhibitors of HMG-CoA reductase

Design and synthesis of atorvastatin derivatives with enhanced water solubility, hepatoselectivity and stability

Statins are effective 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R) inhibitors, which are successfully used for cardiovascular disease treatment. Statins' side effects are generally attributed to poor bioavailability and hepatoselectivity, which are closely related to their high lipophilicity. Targeted delivery of statins to the liver is considered as a way to reduce unwanted side effects. Herein we report on synthesis and evaluation of atorvastatin conjugates targeting the galactose-specific hepatic asialoglycoprotein receptor (ASGPR). The prepared conjugates showed greater water solubility compared to unmodified atorvastatin. The synthesised compounds demonstrated potent binding to the ASGPR with submicromolar K D values. The conjugates with an amide bond connecting atorvastatin and the targeting moiety displayed the optimal stability under model conditions, as they underwent hydrolysis only when incubated with the intracellular protease. The hydrolysis products effectively inhibited HMG-R activity. The results suggest that the designed amide-based compounds have the potential to be further developed as orally administered prodrugs of atorvastatin.

Statin Use is Associated With Insulin Resistance in Participants of the Canadian Multicentre Osteoporosis Study

Context

Statins have been linked to the development of diabetes and atherosclerotic plaque calcification in patients with cardiac disease.

Objective

To determine the association between statin use and statin characteristics and insulin resistance and abdominal aortic calcification (AAC) in participants of the Canadian Multicentre Osteoporosis Study (CaMos).

Design

Observational study.

Setting

General community.

Participants

Nondiabetic participants of the Kingston CaMos site.

Intervention

Insulin resistance and AAC in statin users and nonstatin users were compared with and without the inclusion of a propensity score (PS) to be on a statin. The covariates of hypertension, sex, body mass index, smoking, kidney stones, and age that were included in the PS were selected based on clinical judgment confirmed by the statistical analysis of a difference between statin users and nonstatin users.

Main Outcome Measures

Insulin resistance measured by the homeostasis model assessment (HOMA-IR) and AAC assessed on lateral spine radiographs using the Framingham methodology.

Results

Using a general linear model, statin use was associated with higher levels of HOMA-IR after stratified PS adjustment (β = 1.52, [1.18-1.95], P < 0.01). Hydrophilic statin users (n = 9) and lipophilic statins users (n = 30) had higher HOMA-IR compared to nonstatin users (n = 125) ([β = 2.29, (1.43-3.68), P < 0.001] and [β = 1.36, (1.04-1.78), P < 0.05]), respectively, in general linear models after stratified PS adjustment. Statin use was associated with AAC without stratifying by PS in the Wilcoxon test, but was no longer significant when stratified by PS.

Conclusions

Statins, widely prescribed drugs to lower cholesterol, may have unintended consequences related to glucose homeostasis that could be relevant in healthy aging.

Probable Statin-Induced Testicular Pain

Objective:

To describe a case of a patient experiencing testicular pain on 3 occasions after taking 3 different statins.

Case Summary:

A 54-year-old man with hyperlipidemia was started on lovastatin therapy. His other medications included aspirin, levothyroxine, buspirone, and atenolol. Seven months after starting lovastatin, the patient experienced testicular discomfort that resolved upon discontinuation of the drug. Afterward, he started simvastatin and again experienced testicular discomfort. The simvastatin was changed to atorvastatin, and the pain resolved. However, 3 months after starting atorvastatin, the patient developed testicular pain, which resolved after the drug was stopped. During each of the episodes, the patient's pain increased when he was sitting, driving, or wearing tight clothing. The Naranjo probability scale indicates that statins probably caused the patient's pain.

Discussion:

Testicular pain is rarely caused by medications. Product labeling for statins does not list urinary adverse events as common. However, labeling for atorvastatin and pravastatin lists rare urologic adverse effects. A literature search did not reveal any previously reported cases of testicular adverse effects from statins. However, statins have been shown to inhibit cholesterol synthesis in the testis. Some data indicate that statins reduce serum testosterone concentrations, but other data indicate that statins have no effect on sex hormones or spermatogenesis. Data are also available indicating that aspirin might affect testosterone concentrations and testicular function. It is difficult to know whether either of the above hormonal mechanisms was associated with our patient's testicular discomfort, but the time course and challenge/rechallenge aspects of the case suggest that the statins were the cause.

Conclusions:

Urologic adverse effects of statins rarely occur but should not be overlooked by medical providers.

Synthesis and biological activity of 4,5-polymethylenepyrazole-derived HMG-COA reductase inhibitors

New HMG-CoA reductase inhibitors, in which 3-substituted 4,5-polymethylenepyrazoles are employed as a hydrophobic anchor connected to tetrahydro-4-hydroxy-2H-pyran-2-one by a two-carbon bridge, were designed and synthesized to exhibit significant inhibitory activity comparable to mevinolin. The most potent enzyme inhibitor (11cc, IC(50)=0.01 muM) is 4-fold more potent than lovastatin.

Substituted pyrazoles as hepatoselective HMG-CoA reductase inhibitors: discovery of (3R,5R)-7-[2-(4-fluoro-phenyl)-4-isopropyl-5-(4-methyl-benzylcarbamoyl)-2H-pyrazol-3-yl]-3,5-dihydroxyheptanoic acid (PF-3052334) as a candidate for the treatment of hypercholesterolemia

In light of accumulating evidence that aggressive LDL-lowering therapy may offer increased protection against coronary heart disease, we undertook the design and synthesis of a novel series of HMG-CoA reductase inhibitors based upon a substituted pyrazole template. Optimizing this series using both structure-based design and molecular property considerations afforded a class of highly efficacious and hepatoselective inhibitors resulting in the identification of (3 R,5 R)-7-[2-(4-fluoro-phenyl)-4-isopropyl-5-(4-methyl-benzylcarbamoyl)-2 H-pyrazol-3-yl]-3,5-dihydroxy-heptanoic (PF-3052334) as a candidate for the treatment of hypercholesterolemia.

Modulation of metoprolol pharmacokinetics and hemodynamics by diphenhydramine coadministration during exercise testing in healthy premenopausal women

Premenopausal women may be most vulnerable to acute coronary syndromes at a point in their menstrual cycle when their plasma estrogen levels are the lowest during and immediately after menstruation. Metoprolol is a first-line drug in the management of patients with acute coronary syndrome; however, when metoprolol was marketed in 1982, women were largely excluded from clinical trials. Furthermore, the over-the-counter antihistamine diphenhydramine inhibited the metabolism of the CYP2D6 substrate metoprolol in healthy, young men with pharmacokinetic and pharmacodynamic consequences. The pharmacokinetics and pharmacodynamics of metoprolol and its interaction with diphenhydramine were investigated in a randomized, double-blind, crossover, placebo-controlled manner in healthy, premenopausal extensive (EM; n = 16) and poor metabolizer (PM; n = 4) women immediately after menstruation. During the placebo phase, EMs had between 5.2- and 8.4-fold higher total clearance (CL/F) of R- and S-metoprolol compared with PMs, whereas the latter had a 35% greater area under the effect curve (AUEC) and 60% greater EC(50) value for heart rate reduction than EMs (all P < 0.05). Diphenhydramine coadmininstration caused a 2.2- to 3.2-fold decrease in CL/F of metoprolol enantiomers with a resulting 21% increase in AUEC and 29% increase in EC(50) value for heart rate reduction in EMs (all P < 0.05). This is the first study to report an in-depth elucidation of metoprolol's pharmacokinetics and hemodynamics in premenopausal EM and PM women at a point in their menstrual cycle when vulnerability for acute coronary events may be greatest. Caution is warranted when the over-the-counter antihistamine diphenhydramine is part of a chronic therapeutic regimen.

Guinea pigs as models to study the hypocholesterolemic effects of drugs

Guinea pigs are useful models to investigate the mechanisms of the hypocholesterolemic effects of drugs. Like humans, guinea pigs are one of the few species that carry the majority of cholesterol in LDL. This animal model has also been shown to develop atherosclerosis when challenged with hypercholesterolemic diets. In addition, plasma lipid profiles in males, females and ovariectomized guinea pigs, a model for menopause, follow similar patterns to those observed in humans. In this report, drugs aimed at lowering plasma cholesterol and triglycerides in hyperlipidemic individuals are reviewed. Studies analyzing the hypolipidemic effect of HMG-CoA reductase inhibitors, acyl CoA cholesterol acyltransferase inhibitors, fibrates, bile acid resins, apical sodium bile acid transporter inhibitors, and others show that guinea pigs and humans have comparable responses to drug therapy. In addition, results from the limited clinical reports addressing specific effects of drugs on LDL catabolism or VLDL synthesis are in agreement with observations in guinea pigs. From the review of these studies, it is apparent that the guinea pig is a useful animal model to further explore the mechanisms of action of lipid lowering drugs including effects on specific receptors and regulatory enzymes involved in cholesterol metabolism and on early atherosclerosis development.

ABBREVIATIONS

ACAT, acyl-CoA:cholesterol acyltransferase; ASBT, apical sodium co-dependent bile acid transporter; ApoB, apolipoprotein B; CHD, coronary heart disease; CYP7, cholesterol 7alpha-hydroxylase; HDL, high density lipoprotein; HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A; FCR, free catabolic rate; LDL, low density lipoprotein; PPAR, peroxisome proliferators-activated receptor; TC, total cholesterol; TG, triglycerides; VLDL, very low density lipoprotein.

Synthesis, characterization and anticonvulsant activity of enaminones. Part 6: Synthesis of substituted vinylic benzamides as potential anticonvulsants

A comparison of enaminones from various unsubstituted and p-substituted benzamides to the analogous benzylamines has been undertaken with the aim of elucidating the essential structural parameters necessary for anticonvulsant activity. Initial studies on methyl 4-N-(benzylamino)-6-methyl-2-oxocyclohex-3-en-1-oate, 3a, 3-N-(benzylamino)cyclohex-2-en-1-one, 3p, and 5,5-dimethyl-3-N-(benzylamino)-cyclohex-2-en-1-one, 3r indicated that benzylamines possessed significant anti-maximal electroshock seizure (MES) activity. Evaluation of the analogous benzamides revealed significant differences in anticonvulsant activity, these differences were most probably related to the differences in their three-dimensional structures.

The magnitude of decrease in hepatic very low density lipoprotein apolipoprotein B secretion is determined by the extent of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition in miniature pigs

It has been postulated that the rate of hepatic very low density lipoprotein (VLDL) apolipoprotein (apo) B secretion is dependent upon the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. To test this hypothesis in vivo, apoB kinetic studies were carried out in miniature pigs before and after 21 days treatment with high-dose (10 mg/kg/day), atorvastatin (A) or simvastatin (S) (n = 5). Pigs were fed a diet containing fat (34% of calories) and cholesterol (400 mg/day; 0.1%). Statin treatment decreased plasma total cholesterol [31 (A) vs. 20% (S)] and low density lipoprotein (LDL) cholesterol concentrations [42 (A) vs. 24% (S)]. Significant reductions in plasma total triglyceride (46%) and VLDL triglyceride (50%) concentrations were only observed with (A). Autologous [131I]VLDL, [125I]LDL, and [3H]leucine were injected simultaneously, and apoB kinetic parameters were determined by triple-isotope multicompartmental analysis using SAAM II. Statin treatment decreased the VLDL apoB pool size [49 (A) vs. 24% (S)] and the hepatic VLDL apoB secretion rate [50 (A) vs. 33% (S)], with no change in the fractional catabolic rate (FCR). LDL apoB pool size decreased [39 (A) vs. 26% (S)], due to reductions in both the total LDL apoB production rate [30 (A) vs. 21% (S)] and LDL direct synthesis [32 (A) vs. 23% (S)]. A significant increase in the LDL apoB FCR (15%) was only seen with (A). Neither plasma VLDL nor LDL lipoprotein compositions were significantly altered. Hepatic HMG-CoA reductase was inhibited to a greater extent with (A), when compared with (S), as evidenced by 1) a greater induction in hepatic mRNA abundances for HMG-CoA reductase (105%) and the LDL receptor (40%) (both P < 0.05); and 2) a greater decrease in hepatic free (9%) and esterified cholesterol (25%) (both P < 0.05). We conclude that both (A) and (S) decrease hepatic VLDL apoB secretion, in vivo, but that the magnitude is determined by the extent of HMG-CoA reductase inhibition.

Hypocholesterolemic effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in the guinea pig: atorvastatin versus simvastatin

Male Hartley guinea pigs were fed a hypercholesterolemic diet rich in lauric and myristic acids with 0, 10, or 20 mg/kg of simvastatin or atorvastatin for 21 days. Atorvastatin and simvastatin resulted in a lowering of plasma low-density lipoprotein (LDL) cholesterol in a dose-dependent manner by an average of 48 and 61% with 10 and 20 mg/kg, respectively. Both statins were equally effective in lowering plasma LDL cholesterol and apolipoprotein B (apo-B) levels. Atorvastatin and simvastatin treatments yielded LDL particles that differed in composition from the control. Due to the relevance of LDL oxidation and cholesteryl ester transfer in plasma to the progression of atherosclerosis, these parameters were analyzed after statin treatment. Atorvastatin and simvastatin treatment decreased the susceptibility of LDL particles to oxidation by 95% as determined by the formation of thiobarbituric acid reactive substances. An 80% decrease in the transfer of cholesteryl ester between high-density lipoprotein (HDL) and the apo-B-containing lipoproteins was observed after simvastatin and atorvastatin treatment. In addition, statin effects on plasma LDL transport were studied. Simvastatin- and atorvastatin-treated guinea pigs exhibited 125 and 175% faster LDL fractional catabolic rates, respectively, compared with control animals. No change in LDL apo-B flux was induced by either treatment; however, LDL apo-B pool size was reduced after statin treatment. Hepatic microsomal free cholesterol was lower in the atorvastatin and simvastatin groups. However, only atorvastatin treatment resulted in an 80% decrease of acyl-CoA:cholesterol acyltransferase activity (P < 0.001). In summary, atorvastatin and simvastatin had similar LDL cholesterol lowering properties, but these drugs modified LDL transport and hepatic cholesterol metabolism differently.

The HMG-CoA reductase inhibitor atorvastatin increases the fractional clearance rate of postprandial triglyceride-rich lipoproteins in miniature pigs

We have previously shown in vivo that the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin decreases hepatic apolipoprotein B (apoB) secretion into plasma. To test the hypothesis that atorvastatin modulates exogenous triglyceride-rich lipoprotein (TRL) metabolism in vivo, an oral fat load (2 g fat/kg body wt) containing retinol (50 000 IU) was given to 6 control miniature pigs and to 6 animals after 28 days of treatment with atorvastatin 3 mg. kg-1. d-1. A multicompartmental model was developed by use of SAAM II and kinetic analysis performed on the plasma retinyl palmitate (RP) data. Peak TRL (d<1.006 g/mL; Sf>20) triglyceride concentrations were decreased 29% by atorvastatin, and the time to achieve this peak was delayed (5.2 versus 2.3 hours; P<0.01). The TRL triglyceride 0- to 12-hour area under the curve was decreased by 24%. In contrast, atorvastatin treatment had no effect on peak TRL RP concentrations, time to peak, or its rate of appearance into plasma; however, the TRL RP 0- to 12-hour area under the curve was decreased by 20%. Analysis of the RP kinetic parameters revealed that the TRL fractional clearance rate was increased significantly, 1.4-fold (3.093 versus 2.276 pools/h; P=0.012), with atorvastatin treatment. The percent conversion of TRL RP from the rapid-turnover to the slow-turnover compartment was decreased by 47% with atorvastatin treatment. The TRL RP fractional clearance rate was negatively correlated with very low density lipoprotein apoB production rate measured in the fasting state (r=-0.49). Thus, although atorvastatin had no effect on intestinal TRL assembly and secretion, plasma TRL clearance was significantly increased, an effect that may relate to a decreased competition for removal processes by hepatic very low density lipoprotein.

Inhibition of HMG-CoA reductase by atorvastatin decreases both VLDL and LDL apolipoprotein B production in miniature pigs

In the present studies, the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor atorvastatin was used to test the hypothesis that inhibition of cholesterol biosynthesis in vivo with a consequent reduction in the availability of hepatic cholesterol for lipoprotein synthesis, would (1) reduce very low density lipoprotein (VLDL) apolipoprotein B (apoB) secretion into the plasma, (2) reduce the conversion of VLDL apoB to LDL apoB, and (3) reduce LDL apoB direct synthesis. ApoB kinetic studies were carried out in six control miniature pigs and in six animals after 21 days of administration of atorvastatin (3 mg/kg per day). Pigs were fed a fat- (34% of calories; polyunsaturated to monounsaturated to saturated ratio, 1:1:1) and cholesterol- (400 mg/d cholesterol; 0.1%; 0.2 mg/kcal) containing pig chow-based diet. Atorvastatin treatment significantly reduced plasma total cholesterol, LDL cholesterol, total triglyceride, and VLDL triglyceride concentrations by 16%, 31%, 19%, and 28%, respectively (P < .01). Autologous 131I-VLDL, 125I-LDL, and [3H]leucine were injected simultaneously into each pig, and apoB kinetic data were analyzed using multicompartmental analysis (SAAM II). The VLDL apoB pool size decreased by 29% (0.46 versus 0.65 mg/kg; P = .002), which was entirely due to a 34% reduction in the VLDL apoB production rate (PR) (1.43 versus 2.19 mg/kg per hour; P = .027). The fractional catabolic rate (FCR) was unchanged. The LDL apoB pool size decreased by 30% (4.74 versus 6.75 mg/kg; P = .0004), which was due to a 22% reduction in the LDL apoB PR (0.236 versus 0.301 mg/kg per hour; P = .004), since the FCR was unchanged. The reduction in LDL apoB PR was primarily due to a 34% decrease in conversion of VLDL apoB to LDL apoB; however, this reduction was not statistically significant (P = .114). Hepatic apoB mRNA abundance quantitated by RNase protection assay was decreased by 13% in the atorvastatin-treated animals (P = .003). Hepatic and intestinal LDL receptor mRNA abundances were not affected. We conclude that inhibition of hepatic HMG-CoA reductase by atorvastatin reduces both VLDL and LDL apoB concentrations, primarily by decreasing apoB secretion into the plasma and not by an increase in hepatic LDL receptor expression. This decrease in apoB secretion may, in part, be due to a reduction in apoB mRNA abundance.

Synthesis and biological activity of methanesulfonamide pyrimidine- and N-methanesulfonyl pyrrole-substituted 3,5-dihydroxy-6-heptenoates, a novel series of HMG-CoA reductase inhibitors

A novel series of methanesulfonamide pyrimidine- and N-methanesulfonyl pyrrole-substituted 3,5-dihydroxy-6-heptenoates were synthesized and evaluated for their ability to inhibit the enzyme HMG-CoA reductase in vitro. Monocalcium bis(+)-7-[4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N- methanesulfonylaminopyrimidin)-5-yl]-(3R,5S)-dihydroxy-(E)-6-he ptenoate (3a, S-4522) was selected as a candidate for further evaluation. Compound 3a was approximately four times more potent than lovastatin sodium salt (in inhibiting HMG-CoA reductase in vitro (IC50 = 11 nM). Compound 3a was shown to be the most potent cholesterol biosynthesis inhibitor in this series (IC50 = 1.12 nM) in rat isolated hepatocytes; its inhibitory activity was approximately 100 times more potent than pravastatin.

Effects of propionic acid and pravastatin on HMG-CoA reductase activity in relation to forestomach lesions in the rat

Administration of 4% propionic acid in powdered diet to rats for 12 weeks induces severe hyperplastic lesions in the forestomach mucosa. The mechanisms underlying this damage are not yet clear. Several lipophilic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors such as lovastatin and simvastatin produce forestomach lesions similar to propionic acid after oral administration and the degree of alterations is correlated with their in vitro inhibitory potency (Kloss et al. 1991). Therefore it is possible, that sustained inhibition of HMG-CoA reductase and induction of hyperplasias may be somehow connected. For that reason we investigated, whether or not propionic acid has any influence on HMG-CoA reductase activity in vitro and in vivo, because propionic acid has been suggested to suppress liver cholesterol synthesis, and also whether or not pravastatin, a more polar HMG-CoA reductase inhibitor than lovastatin displays similar effects on forestomach mucosa. In untreated forestomach microsomes in vitro, propionic acid at a concentration of 51 mM (pH 5.7) inhibited HMG-CoA reductase activity by 51 + or - 10%, but at pH 7.2 no inhibition of the enzyme could be detected. Furthermore 4% propionic acid-treatment did not lower serum cholesterol. In contrast to lovastatin (Kloss et al. 1991), oral administration of pravastatin (up to 25% in the diet) did not produce any forestomach lesions in the rat. On the other hand, pretreatment with pravastatin revealed that HMG-CoA reductase activity in microsomes exceeded the activity of control forestomach and liver microsomes by 4.9 fold and 6.7 fold respectively, whereas no induction of this enzyme (neither liver nor forestomach) could be observed by pretreatment with 4% propionic acid for 12 weeks. Despite increased hepatic HMG-CoA reductase activity, pravastatin-treatment significantly lowered serum cholesterol levels of rats. These results show that sustained inhibition of HMG-CoA reductase activity in forestomach microsomes is not strongly connected with hyperplasia development.

Cholesterol and cataracts

Inherited defects in enzymes of cholesterol metabolism and use of drugs which inhibit lens cholesterol biosynthesis can be associated with cataracts in animals and man. The basis of this relationship apparently lies in the need of the lens to satisfy its sustained requirement for cholesterol by on-site synthesis, and impairing this synthesis can lead to alteration of lens membrane structure. Lens membrane contains the highest cholesterol content of any known membrane. The Smith-Lemli-Opitz syndrome, mevalonic aciduria, and cerebrotendinous xanthomatosis all involve mutations in enzymes of cholesterol metabolism, and affected patients can develop cataracts. Two established models of rodent cataracts are based on treatment with inhibitors of cholesterol biosynthesis. The long-term ocular safety of the very widely used vastatin class of hypocholesterolemic drugs is controversial. Some vastatins are potent inhibitors of cholesterol biosynthesis by animal lenses, can block cholesterol accumulation by these lenses and can produce cataracts in dogs. Whether these drugs inhibit cholesterol biosynthesis in human lenses at therapeutic doses is unknown. Results of clinical trials of 1-5 years duration in older patient populations indicate high ocular safety. However, considering the slow life-long growth of the lens and its continuing need for cholesterol, longterm safety of the vastatins should perhaps be viewed in units of 10 or 20 years, particularly with younger patients.

Antiatherosclerotic activity of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase in cholesterol-fed rabbits: a biochemical and morphological evaluation

Atherosclerotic lesion development was assessed in the thoracic aorta and chronically denuded iliac-femoral artery of hypercholesterolemic New Zealand White rabbits using inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase which have previously been shown to possess varying degrees of hepatoselectivity in rats. Atorvastatin, previously known as CI-981 (2.5 mg/kg), PD135022 (1.0 mg/kg), simvastatin (2.5 mg/kg), lovastatin (2.5 mg/kg), PD134965 (1.0 mg/kg), pravastatin (2.5 mg/kg) and BMY22089 (2.5 mg/kg) were added to a 0.5% cholesterol, 3% peanut, 3% coconut oil diet and fed for 8 weeks. Although reductions in plasma total cholesterol of 27% to 60%, VLDL-cholesterol of 31% to 71% and plasma total cholesterol exposure of 37% to 43% were obtained, no correlation between these parameters and vascular lipid content, lesion size or monocyte-macrophage content was noted. Iliac-femoral lipid content was unchanged; however, atorvastatin and simvastatin significantly reduced the cholesterol content of the thoracic aorta by 45%-62%. Atorvastatin and PD135022 reduced the size of the iliac-femoral lesion by 67% and monocyte-macrophage content by 72%. Simvastatin, lovastatin and PD134965 decreased the monocyte-macrophage content; however, lesion size was unchanged. Pravastatin and BMY22089 had no effect on lesion size or content. No compound significantly reduced the extent of thoracic aortic lesions. We concluded that changes in plasma lipids and lipoproteins noted with the various HMG-CoA reductase inhibitors did not account for the beneficial effect on atherosclerotic lesion development. The antiatherosclerotic potential of the HMG-CoA reductase inhibitors was compound-specific and clearly not a class effect.

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)

New approaches to atherosclerosis: an overview

The mechanisms of action and selected agents for a variety of approaches to the treatment of atherosclerosis have been reviewed. In Table I, each approach is listed according to its primary physiological effect. This is a simplification, of course, and some agents, such as ACAT inhibitors, may have primary effects in all of these categories. As one goes from left to right, the benefit of each physiological effect becomes more speculative. There is no question of the benefit of LDL reduction, but less evidence exists for the clinical benefits of HDL elevation. With regard to direct anti-atherosclerotic effects, most approaches have yet to gather clinical data of any type. Perhaps as a result, the degree of medicinal chemistry effort in each area to date declines as one goes from left to right. This situation is changing rapidly, however. As evidence supporting the HDL hypothesis accumulates and knowledge of how to elevate HDL levels grows, very exciting opportunities for medical advances present themselves. Likewise, the knowledge base for nonlipid intervention is growing and very rapid advances are being achieved with the plaque-imaging techniques needed for evaluating such agents in man. Such results can only lead to greater opportunities for pharmacological intervention. Thus, in the future, much greater research effort will likely be dedicated to HDL elevation and nonlipid approaches. Through these efforts, physicians of the future should be armed with several complementary agents that can reduce the risk of cardiovascular disease in all patient populations.

Biliary excretion of chenodeoxycholyllysylrhodamine in Wistar rats: a possible role of a bile acid as a carrier for drugs

The effect on biliary excretion of rhodamine after its conjugation to give chenodeoxycholyl-lysyl-rhodamine (cheno-lys-R) was studied in male Wistar rats. Following its intravenous injection via the jugular vein of animals cheno-lys-R was efficiently excreted into bile with a peak biliary excretion of 31.6 +/- 1.2% dose 5 min-1 and a cumulative biliary excretion of 96.4 +/- 2.0% in 30 min of the total dose administered. Unlike cheno-lys-R, rhodamine had a poor biliary excretion of 1.0 +/- 0.1% dose 5 min-1 and a cumulative biliary excretion of 3.3 +/- 0.6% in 30 min. Cheno-lys-R had a short plasma half-life (t1/2 alpha) of 4.0 +/- 0.5 min, whereas free rhodamine had a longer half life (t1/2 alpha) of 82.1 +/- 1.4 min. The plasma clearances of cheno-lys-R and rhodamine were 41.2 +/- 6.5 and 9.0 +/- 1.2 ml/min per kg, respectively. The data indicate that the cationic fluorescent xenobiotic, rhodamine, when conjugated to the bile salt analogue, greatly increased the biliary excretion of rhodamine and that cheno-lys acted as a carrier for hepatic uptake of rhodamine. Thus, an appropriate bile salt derivative may be used to target a drug to the liver.

Hepatic and nonhepatic sterol synthesis and tissue distribution following administration of a liver selective HMG-CoA reductase inhibitor, CI-981: comparison with selected HMG-CoA reductase inhibitors

Since cholesterol biosynthesis is an integral part of cellular metabolism, several HMG-CoA reductase inhibitors were systematically analyzed in in vitro, ex vivo and in vivo sterol synthesis assays using [14C]acetate incorporation into digitonin precipitable sterols as a marker of cholesterol synthesis. Tissue distribution of radiolabeled CI-981 and lovastatin was also performed. In vitro, CI-981 and PD134967-15 were equipotent in liver, spleen, testis and adrenal, lovastatin was more potent in extrahepatic tissues than liver and BMY21950, pravastatin and PD135023-15 were more potent in liver than peripheral tissues. In ex vivo assays, all inhibitors except lovastatin preferentially inhibited liver sterol synthesis; however, pravastatin and BMY22089 were strikingly less potent in the liver. CI-981 inhibited sterol synthesis in vivo in the liver, spleen and adrenal while not affecting the testis, kidney, muscle and brain. Lovastatin inhibited sterol synthesis to a greater extent than CI-981 in the spleen, adrenal and kidney while pravastatin and BMY22089 primarily affected liver and kidney. The tissue distribution of radiolabeled CI-981 and lovastatin support the changes observed in tissue sterol synthesis. Thus, we conclude that a spectrum of liver selective HMG-CoA reductase inhibitors exist and that categorizing agents as liver selective is highly dependent upon method of analysis.