Why some patients respond poorly to statins and how this might be remedied

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1 European Heart Journal (22) 23, 2 26 doi:1.153/euhj , available online at on Review Article Why some patients respond poorly to statins and how this might be remedied G. R. Thompson, F. O Neill and M. Seed Departments of Investigative Science and Medicine, Imperial College School of Medicine, Hammersmith and Charing Cross Hospitals, London, U.K. Introduction The advent of the statins, competitive inhibitors of HMG CoA reductase and thus of cholesterol synthesis, has revolutionized the treatment and prevention of coronary heart disease. The reduction in coronary heart disease events in dyslipidaemic subjects largely reflects the extent to which these drugs lower LDL cholesterol, although additional mechanisms have been proposed in normolipidaemic individuals [1]. A meta-analysis of the five major statin trials showed an overall reduction in LDL cholesterol of 28%, which resulted in a 31% decrease in coronary heart disease events [2]. The latter value is 1% less than expected from the decrease in LDL cholesterol that occurred, judging from the Proportional Hazards analysis of the Lipid Research Clinics Coronary Primary Prevention Trial (CPPT) where cholestyramine was used to lower LDL [3]. This discrepancy may reflect differences in design and duration between the CPPT and statin trials but does not support the notion that statins reduce coronary heart disease events by actions ( pleiotropic effects ) which are additional to their LDL-lowering properties. Hence any factors which adversely affect the latter would be expected to diminish the benefits of statin therapy in the prevention of coronary heart disease, at least in hypercholesterolaemic subjects. Extrinsic factors The variations in response to statins between individuals that occur in a routine clinical setting are commonly due Key Words: Cholesterol, cholestanol, campesterol, hyperresponder, hypo-responder, statin. Revision submitted 2 November 21, and accepted 7 November 21. Correspondence: Emeritus Professor G. R. Thompson, Metabolic Medicine, Imperial College School of Medicine, Hammersmith Hospital, Du Cane Road, London W12 NN, U.K. g.thompson@ic.ac.uk X/2/32+7 $35./ to extraneous influences. First and foremost among these is poor compliance as manifested by erratic consumption or discontinuation of the drug regimen. Simons et al. [4] conducted a large survey in Australia which showed that 3% of patients discontinue taking statins within 6 7 months of starting them, despite the good tolerability and excellent safety profile of this class of drug, with one exception (see below). Even higher discontinuation rates were observed with lipidregulating drugs which had significant side effects, such as bile acid sequestrants and nicotinic acid. Background diet is also important in increasing the proportion of patients achieving the target levels of LDL cholesterol stipulated in current guidelines. An additive but not synergistic effect of a low fat, low cholesterol intake has been shown in patients treated with statins [5,6]. Time of administration is another factor, the optimal time for most statins being the evening, reflecting the diurnal rhythm of HMG CoA reductase activity; reductions in LDL cholesterol are significantly less when they are taken in the morning [7]. This does not apply to atorvastatin, which has a much longer duration of action than other statins [8]. Concomitant drug therapy is another possible cause of variability of response to statins which, apart from pravastatin, are metabolized via the cytochrome P45 3A4 or 2C9 pathways [9]. A reduced LDL cholesterollowering effect could be expected when statins are given concomitantly with cytochrome P45 inducers such as carbamazepine, phenytoin and rifampicin, which accelerate their metabolism via that pathway. In contrast, increased blood levels of statins occur when their metabolism is impaired by cytochrome P45 inhibitors such as amiodarone, cyclosporin and diltiazem, which can occasionally lead to rhabdomyolysis. Pharmacokinetic interaction may also explain the increased frequency of rhabdomyolysis observed when gemfibrozil is given together with a statin, especially cerivastatin. The latter compound has recently been withdrawn by the manufacturer following 31 fatal cases of rhabdomyolysis in the U.S.A, 12 of which were associated with 22 The European Society of Cardiology

2 Review 21 concomitant use of gemfibrozil [1]. Most of the remaining cases had been on a high dose of cerivastatin alone, which suggests that this particular compound is inherently more myotoxic than other statins. Intrinsic factors Intrinsic or genetically-determined factors are those responsible for the inter-individual variations in response seen under clinical trial conditions, where extrinsic influences such as variations in diet and compliance have been minimized. The extent of residual inter-individual variability in LDL cholesterol-lowering during statin therapy is considerable, and seems to be largely independent of the dose and drug used [11]. For example in a large trial of simvastatin 8 mg daily the mean reduction in LDL cholesterol was 46% [12]. However, decreases in the top 5% of responders ranged from 63 76% whereas in the bottom 5% changes ranged from 23% to +2%, the latter despite 6 months of treatment. Similarly, poor or diminishing responses over periods of up to 1 year have been observed in a minority of hypercholesterolaemic patients on simvastatin [13] and lovastatin [14]. The fact that this occurred also with pravastatin suggests that the waning of LDL-lowering efficacy in such individuals is not due to increased metabolism of these drugs via induction of the cytochrome P45 pathway but rather to a compensatory increase in HMG CoA reductase of sufficient magnitude to counteract their inhibitory effect on cholesterol synthesis [13]. It remains to be shown whether this phenomenon reflects genetic variation in HMG CoA reductase per se or in the sterol regulatory element-binding proteins (SREBPs), which regulate its expression. Inter-individual variability in response to statins occurs to a similar extent in patients with heterozygous familial hypercholesterolaemia as in those with non-familial hypercholesterolaemia [15], including a group of familial hypercholesterolaemia patients all having the same mutation [16] ; this suggests that differences in receptor-mediated LDL catabolism are not the explanation. Influence of interaction between the absorptive and synthetic cholesterol pathways The cholesterol circulating in plasma lipoproteins is derived both from the diet and endogenous synthesis. Dietary intake averages 2 6 mg daily on a Western diet and this mixes in the duodenum with up to twice that amount of cholesterol secreted in bile. Both sources of cholesterol must become incorporated into mixed micelles, as a result of the actions of pancreatic enzymes and bile salts, before undergoing absorption in the jejunum. Recent studies suggest that uptake by enterocytes is mediated by a saturable transport mechanism [17]. Plant sterols and stanols not only compete with cholesterol for micellar solubilization but probably also for this uptake pathway. In contrast with cholesterol, however, their further absorption is prevented by two or more ATP-binding cassette transporters. It has been proposed that these selectively mediate the efflux of plant sterols back into the intestinal lumen [18]. This proposal is based on the loss of this selectivity in phytosterolaemia, a rare disorder characterized by increased absorption of plant sterols and premature atherosclerosis, which has recently been shown to be due to mutations of ATP-binding cassette transporters G5 or G8 [19]. In the final stage of absorption cholesterol is incorporated into chylomicrons which are converted to remnant particles after their entry into plasma and exposure to lipoprotein lipase. These chylomicron remnants are subsequently taken up by receptors in the liver and the cholesterol which they contain acts to down-regulate the activity of HMG CoA reductase, thereby reducing the rate of endogenous cholesterol synthesis [2]. Conversely, reduced influx of cholesterol via the absorptive pathway results in up-regulation of HMG CoA reductase and increased synthesis. The role of genetic factors in determining interindividual differences in response to dietary cholesterol both in animals and man has been reviewed elsewhere [21]. Briefly, most people fed high intakes of cholesterol in the diet show a modest rise in plasma cholesterol while a minority shows either a marked rise or no change. Replicate studies suggest that these patterns of response to dietary cholesterol are reproducible, leading to the terms hypo- and hyper-responders. Further studies have shown that hyper-responders had low basal rates of cholesterol synthesis before being put onto the high cholesterol diet, whereas hypo-responders had higher basal rates of cholesterol synthesis. Furthermore, people whose plasma cholesterol on their normal diet was in the high range tended to be more efficient absorbers of cholesterol in percentage terms than those whose plasma cholesterol was at the low or normal end of the range. Hence, people with a high serum cholesterol, and those who show an exaggerated response to dietary cholesterol, tend to hyper-absorb dietary cholesterol and have a low rate of cholesterol synthesis, whereas people who absorb the least have a lower serum cholesterol despite having a higher rate of synthesis. Role of apolipoprotein E4 The most likely explanation for the above findings is that genetically-influenced differences in cholesterol absorption efficiency determine both the magnitude of the rise in plasma cholesterol and the extent to which the rate of cholesterol synthesis is down-regulated when the cholesterol content of the diet is raised. Probably the most frequently studied factor in this context is apolipoprotein E (apoe).

3 22 G. R. Thompson et al. The existence of apoe polymorphism in humans is well documented and three major alleles have been described, E2, 3 and 4. The normal apoe genotype, 3/3, is possessed by two-thirds of the population, whereas about 2% have the E3/4 genotype. A small minority, probably less than 5% have the E4/4 genotype, except in Finland where there is an increased prevalence of the E4 allele. Sarkinnen et al. [22] examined the effect of a low fat diet without and with the addition of 3 mg of cholesterol on the serum cholesterol of three groups of Finns, with apoe 3/3, 3/4 or 4/4 genotypes. All three groups showed a decrease in serum cholesterol on the low fat diet, with the greatest fall in the E4/4s and the least in the 3/3s, the 3/4s being intermediate. With the addition of 3 mg of cholesterol daily to the low fat diet, the subsequent rise in serum cholesterol in the E4/4s was greater than in 3/4s and 3/3s. This suggests that individuals homozygous for E4 show exaggerated responses to removal of cholesterol and saturated fat from the diet as well as to the addition of cholesterol alone, compared with people with other phenotypes. Another Finnish study provided an explanation for this phenomenon in that people with an E4 allele, who are often hypercholesterolaemic to start with, absorb cholesterol more efficiently and have lower synthetic rates than those with a normal phenotype [23]. Clinical consequences What are the clinical implications of these putative genetic influences? One of the many subgroup analyses conducted on the results of the Scandinavian Simvastatin Survival Study (4S) involved the Finnish cohort who were divided into quartiles according to their serum cholestanol:cholesterol ratio [24]. Cholestanol was used as an index of cholesterol absorption and correlated very closely with the serum level of campesterol, another marker of cholesterol absorption, as shown in Fig. 1. Those in the lowest quartile of the cholestanol to cholesterol ratio were regarded as hypoabsorbers, those in the highest quartile as hyperabsorbers. As in previous studies, an inverse correlation between cholesterol absorption and synthesis is evident, synthesis being indicated by the ratio of lathosterol to cholesterol. Values of serum cholesterol were similar in each quartile at baseline and remained so in those on placebo throughout the trial. However, when the subgroup treated with simvastatin was examined, it was found that the reduction in serum cholesterol in Q4, the high absorbers and low synthesizers, was less marked than in Q1, who absorbed less and synthesized more. The probable reason for this differential effect was that subjects in the fourth quartile showed a less marked decrease in their lathosterol:cholesterol ratio when on simvastatin than did those in the first quartile. Thus, people whose cholesterol synthesis rate was low to start with showed a lesser decrease in synthesis when treated with simvastatin than those people whose rate was initially high. Cholestanol (1 2 mmol.mol 1 ) Campesterol (1 2 mmol.mol 1 ) Lathosterol (1 2 mmol.mol 1 ) Quartile 1 n = n = n = n = Cholesterol (mmol.l 1 ) Figure 1 Baseline ratios of markers of cholesterol absorption (cholestanol and campesterol) and synthesis (lathosterol) according to quartiles of the cholestanol:cholesterol ratio in plasma of Finnish cohort of 4S [24]. Reproduced with permission [21]. Using mevalonic acid rather than lathosterol as an index of cholesterol synthesis, Naoumova et al. [25] also found that a poor response to statins was associated with a low basal rate of cholesterol synthesis. The possibility that this phenomenon was due to inheritance of the apoe4 allele, presumably via an associated increase in cholesterol absorption, is supported by data from four of the 11 studies [26,29,31,36] shown in Table 1. However, despite a definite trend towards a lessened response to statins in those with an E4 allele in most of the other studies, the differences were not statistically significant and further data are needed to substantiate or refute this explanation. Genetic variability in the expression of ATP-binding cassette transporters loci in the small intestine provides an alternative albeit hypothetical explanation for inter-individual differences in cholesterol absorption. In their subgroup analysis of 4S, Miettinen et al. [37] also examined the reduction in risk of coronary events according to quartiles of the cholestanol: cholesterol ratio. The relative risk of coronary heart disease was reduced by 38 25% in simvastatin-treated subjects in the first, second and third quartiles but it was not reduced in those in the fourth quartile. Therefore people with a high cholestanol to cholesterol ratio at the start of the trial, the high absorbers/low synthesizers, showed no reduction in coronary events when treated with simvastatin and had the same relative risk of recurrent coronary heart disease as placebo-treated subjects.

4 Review 23 Table 1 Effect of apoe phenotype on LDL response to statin therapy Authors (reference) ΔLDL-C on treatment according to apoe phenotype Comparison O Malley and Illingworth, 199 [27] ε2, 36%; ε3, 37%; ε4, 31% No differences De Knijff et al., 199 [28] ε2, 44%; ε3, 39%; ε4, 35% No differences Ojala et al., 1991 [29] E3/3, 28%; E3/4, 2% E3/4<E3/3, P= 4 Berglund et al., 1993 [3] Data not provided No differences Carmena et al., 1993 [31] ε2, 47%; ε3, 41%; ε4, 32% ε4<ε2 and3,p< 1 Leitersdorf et al., 1993 [32] E3/4 best but no data provided Non-contributory Karayan et al., 1994 [33] ε2, 29%; ε3, 34%; ε4, 33% No differences Ordovas et al., 1994 [34] ε2, 36%; ε3, 27%; ε4, 26% ε3 and4<ε2, P= 4 Leren and Hjermann, 1995 [35] ε4 absent 32%. ε4 present 21% Difference not significant Ballantyne et al., 2 [36] ε3, 29%; ε4, 23% ε4<ε3, P= 3 O Neill et al., 21 [26] ε2and3, 38%; ε4, 27% ε4<ε2 and3,p< 2 Therapeutic approaches to enhancing statin responsiveness As discussed above, evidence from both experimental animals and man strongly suggests that down-regulation of HMG CoA reductase resulting from increased absorption of intestinal cholesterol is associated with below average decreases in LDL cholesterol on statin therapy. The fact that this phenomenon has been observed under controlled trial conditions suggests that it is genetically determined rather than a reflection of a high intake of dietary cholesterol, although the latter may well be a contributory factor under free living conditions. The possible role of the apoe4 allele has already been mentioned but there are many other steps in cholesterol absorption at which genetic variation could influence absorptive efficiency [21]. For example in sitosterolaemia, mutations of ATP-binding cassette transporters result in increased absorption of cholesterol as well as of plant sterols [19], with a consequent down-regulation of HMG CoA reductase and lack of response to simvastatin [38]. The likelihood that hyper-absorption is the primary defect and that downregulation of HMG CoA reductase is a secondary phenomenon is further supported by the data of Miettinen et al. [24,37], already cited, which showed that hyper-absorbers in the Finnish cohort of 4S had less marked decreases in LDL cholesterol and cholesterol synthesis than subjects with lower rates of cholesterol absorption. We have recently made similar observations in hypercholesterolaemic subjects treated with atorvastatin 1 mg daily, in whom the ensuing decrease in LDL cholesterol was inversely proportional to the pre-treatment plasma campesterol:cholesterol ratio i.e. to cholesterol absorption [39]. Turning to treatment, it has long been known that pharmacological inhibitors of cholesterol absorption lower LDL cholesterol. For example, neomycin, a cationic antibiotic, precipitates polyanionic mixed micelles within the intestinal lumen and thereby inhibits cholesterol absorption. Complete blockade of cholesterol absorption by this means decreases LDL cholesterol by more than 3%, despite a compensatory increase in hepatic cholesterol synthesis, but side effects preclude the long-term use of neomycin for this purpose. A new and apparently safe cholesterol absorption inhibitor, ezetimibe, which acts on the mucosal rather than on the micellar phase of absorption, is currently undergoing clinical trials. Preliminary data show that a dose of 1 mg daily reduces LDL cholesterol by about 2% [4], as shown in Fig. 2. Non-pharmacological inhibitors of cholesterol absorption include plant sterols and stanols, as reviewed 2 years ago [41]. Plant sterols occur naturally in vegetable oils whereas plant stanols are found in tall oil, a side product of the manufacture of paper from conifers. The main plant sterols, sitosterol and campesterol, can be readily converted to their stanol counterparts, sitostanol and campestanol, by hydrogenation. All these compounds compete with cholesterol for incorporation into mixed micelles but the limited solubility of free sterols and stanols makes it difficult to dissolve them in fat spreads in high enough concentrations to be effective. This can be overcome by esterifying them with long chain fatty acids, which increase their lipid solubility and facilitate their incorporation into foods. The ester bond Mean percentage change from baseline (%) Baseline Time (weeks) Figure 2 Decrease in LDL cholesterol during administration of ezetimibe 25 1 mg daily. Reproduced with permission [48]. =Placebo; =ezetimibe 25 mg; =ezetimibe 1 mg; =ezetimibe 5 mg; =ezetimibe 1 mg.

5 24 G. R. Thompson et al. 1 2 mmol.l * * * * * Lathosterol Campesterol Sitosterol Figure 3 Changes in plasma plant sterol (campesterol and sitosterol):cholesterol ratios after sequential treatment with atorvastatin 1 mg ( ), atorvastatin 1 mg plus plant stanol ester 2 g ( ) and atorvastatin 2 mg ( ), each daily for 4 wks [39]. =Baseline. *P< 5. subsequently undergoes enzymatic hydrolysis within the intestinal lumen, releasing free sterol or stanol. Numerous studies have shown that plant stanol ester intakes in the region of 2 g/day (expressed as free stanol) achieve reductions in LDL cholesterol of 1 15%. Marketed (as Benecol) in various forms of food including margarine, cream cheese, yoghurt and cereal bars, stanol esters have been shown to be an effective and safe means of lowering LDL in several categories of subjects, including children and adults with familial hypercholesterolaemia, diabetics and post-menopausal women with coronary heart disease. Similar decreases in LDL cholesterol occur with margarine containing plant sterol esters (Flora Proactiv); the comparable LDLlowering ability of equivalent amounts of plant sterols and stanols reflects the fact that both of them induce similar decreases in cholesterol absorption and compensatory increases in cholesterol synthesis. A possible advantage of plant stanols is that they limit the increase in plasma plant sterols observed during statin therapy [24], as we recently confirmed (Fig. 3). Combined inhibition of the absorptive and synthetic cholesterol pathways Several studies have shown enhancement of the LDL lowering effects of statins when inhibitors of cholesterol absorption are given concomitantly. As shown in Table 2, four studies utilized plant stanol esters [42 45] and the fifth, ezetimibe [46]. The effects are additive, resulting in incremental decreases in LDL cholesterol ranging from 1 2% compared with statin therapy alone. A preliminary report based on the Finnish cohort of 4S suggests that the additive effect of stanol ester on LDL-lowering by simvastatin was most marked in those with highest basal levels of indices of cholesterol absorption, plasma cholestanol and campesterol, and the lowest level of lathosterol, an index of cholesterol synthesis, but this remains to be confirmed [47]. However, the data in Table 2 clearly show that inhibition of cholesterol absorption exerts a favourable effect at any given dose of statin, which in most instances is similar to or greater than that achieved by doubling the dose of the latter, as we also confirmed recently [39]. Hence the combined use of statins and plant stanol esters or ezetimibe should help overcome suboptimal decreases in LDL cholesterol as well as enable lower doses of statins to be used, thereby reducing the incidence of dose-related side effects such as myopathy. References [1] Ridker PM, Rifai N, Clearfield M et al., for the air Force/ Texas Coronary Atherosclerosis Prevention Study Investigators. Measurement of C-reactive protein for the targeting of statin therapy in the primary prevention of acute coronary events. N Engl J Med 21; 344: [2] LaRosa JC, He J, Vupputuri S. Effect of statins on risk of coronary disease: a meta-analysis of randomised controlled trials. JAMA 1999; 282: [3] Lipid Research Clinics Program. The Lipid Research Clinics Coronary Primary Prevention Trial results. II. The relationship of reduction in incidence of coronary heart disease to cholesterol lowering. JAMA 1984; 251: Table 2 Combined effects of cholesterol absorption inhibition and statin therapy Authors (reference) Design Subjects (n) Methods Results of combined therapy Gylling et al., 1996 [42] PC NIDDM (8) Pravastatin 4 mg+marge stan est 3 g, 7 weeks Gylling et al., 1997 [43] O, UC P-M and CHD (11) Simvastatin 1 2 mg+stan est marge 3 g, 12 wk Vuorio et al., 2 [44] O, UC FH (12) Simvastatin 2 4 mg+stan est marge 2 2g,6wk Blair et al., 2 [45] DB, PC, R HC (167) Statin and marge stan est 3 g, 8wk Kosoglu et al., 2 [46] DB, PC,, R HC (23) Simvastatin 1 mg EZE 1 mg, 2wk TC 31% vs pravastatin alone LDL-C 16% vs simvastatin alone TC and LDL-C 14% and 2% vs simvastatin alone TC and LDL-C 7% and 1% vs statin alone TC and LDL-C 9% and 17% vs simvastatin alone Design: O=open, UC=uncontrolled, R=randomized, DB=double blind, PC=placebo controlled, =parallel group Subjects: n=number, P-M=post-menopausal, CHD=coronary heart diseasse, FH=familial hypercholesterolaemia, HC=hypercholesterolaemic Methods: wk=weeks, stan est =stanol ester, marge=margarine, g=grams of stanol, EZE=ezetimibe Results: TC=total cholesterol, LDL-C,=LDL cholesterol.

6 Review 25 [4] Simons LA, Simons J, McManus P, Dudley J. Discontinuation rates for use of statins are high. Br Med J 2; 321: 184. [5] Cobb MM, Teitelbaum HS, Breslow JL. Lovastatin efficacy in reducing low-density lipoprotein cholesterol levels on high- vs low-fat diets. JAMA 1991; 265: [6] Chisholm A, Mann J, Sutherland W, Williams S, Ball M. Dietary management of patients with familial hypercholesterolaemia treated with simvastatin. Q J Med 1992; 85: [7] Saito Y, Yoshida S, Nakaya N, Hata Y, Goto Y. Comparison between morning and evening doses of simvastatin in hyperlipidemic subjects. A double-blind comparative study. Arterioscler Thromb 1991; 11: [8] Schachter M. Statins, drug interactions and cytochrome P45. Br J Cardiol 21; 8: [9] Bottorff M, Hansten P. Long-term safety of hepatic Hydroxymethyl Glutaryl Coenzyme A reductase inhibitors. Arch Int Med 2; 16: [1] Weber W. Drug firm withdraws statin from the market. Lancet 21; 358: 568. [11] Naoumova RP, Marais AD, Mountney J et al. Plasma mevalonic acid, an index of cholesterol synthesis in vivo, and responsiveness to HMG CoA reductase inhibitors in familial hypercholesterolaemia. Atherosclerosis 1996; 119: [12] Merck, data available on request, information package DA- ZCR27(3). [13] Pazzucconi F, Dorigotti F, Gianfranceschi G, et al. Therapy with HMG CoA reductase inhibitors: characteristics of the long-term permanence of hypocholesterolemic activity. Atherosclerosis 1995; 117: [14] Rubinstein A, Weintraub M. Escape phenomenon of lowdensity lipoprotein cholesterol during lovastatin treatment. Am J Cardiol 1995; 76: [15] Thompson GR. Poor responders to statins: a potential target for stanol esters. Eur Heart J Suppl 1991; 1 (Suppl S): S [16] Karayan L, Qiu S, Dufour R et al. Response to HMG CoA reductase inhibitors in heterozygous familial hypercholesterolaemia due to the 1-kb deletion ( French Canadian Mutation ) of the LDL receptor gene. Arterioscler Thromb 1994; 14: [17] Hernandez M, Montenegro J, Steiner M et al. Intestinal absorption of cholesterol is mediated by a saturable, inhibitable transporter. Biochim Biophys Acta 2; 1486: [18] Lee M-H, Lu K, Patel SB. Genetic basis of sitosterolemia. Curr Opin Lipidology 21; 12: [19] Berge KE, Tian H, Graft GA et al. Accumulation of dietary cholesterol in sitosterolemia caused by mutations in adjacent ABC transporters. Science 2; 29: [2] Dietschy JM, Turley SD, Spady DK. Role of liver in the maintenance of cholesterol and low density lipoprotein homeostasis in different animal species, including humans. J Lipid Res 1993; 34: [21] Thompson GR. Genetic influence on cholesterol absorption and its therapeutic consequences. In: Leeds AR, Gray J, eds. Dietary cholesterol as a cardiac risk factor: myth or reality? London, UK: Smith Gordon & Co Ltd., 21: [22] Sarkkinen E, Korhonen M, Erkkila A, Ebeling T, Uusitupa M. Effect of apolipoprotein E polymorphism on serum lipid response to the separate modification of dietary fat and dietary cholesterol. Am J Clin Nutr 1998; 68: [23] Kesaniemi YA, Enholm C, Miettinen TA. Intestinal cholesterol absorption efficiency in man is related to apoprotein E phenotype. J Clin Invest 1987; 8: [24] Miettinen TA, Strandberg TE, Gylling H, for the Finnish Investigators of the Scandinavian Simvastatin Survival Study Group. Noncholesterol sterols and cholesterol lowering by long-term simvastatin treatment in coronary patients. Relation to basal serum cholesterol. Arterioscl Thromb Vasc Biol 2; 2: [25] Naoumova RP, Marais AD, Mountney J et al. Plasma mevalonic acid, an index of cholesterol synthesis in vivo, and responsiveness to HMG CoA reductase inhibitors in familial hypercholesterolaemia. Atherosclerosis 1996; 119: [26] O Neill FH, Patel DD, Knight BL et al. Determinants of variable response to statin treatment in patients with refractory familial hypercholesterolemia. Arterioscler Thromb Vasc Biol 21; 21: [27] O Malley JP, Illingworth DR. The influence of apolipoprotein E phenotype on the response to lovastatin therapy in patients with heterozygous familial hypercholesterolemia. Metabolism 199; 39: [28] De Knijff P, Stalenhoef AFH, Mol MJTM et al. Influence of apoe polymorphism on the response to simvastatin treatment in patients with heterozygous familial hypercholesterolemia. Atherosclerosis 199; 83: [29] Ojala JP, Helve E, Ehnholm C, Aalto-Setala K, Kontula KK, Tikkanen MJ. Effect of apolipoprotein E polymorphism and XbaI polymorphism of apolipoprotein B on response to lovastatin treatment in familial and non-familial hypercholesterolaemia. J Intern Med 1991; 23: [3] Berglund L, Wiklund O, Eggertsen G et al. Apolipoprotein E phenotypes in familial hypercholesterolaemia: importance for expression of disease and response to therapy. J Int Med 1993; 233: [31] Carmena R, Roederer G, Mailloux H, Lussier-Cacan S, Davignon J. The response to lovastatin treatment in patients with heterozygous familial hypercholesterolemia is modulated by apolipoprotein E polymorphism. Metabolism 1993; 42: [32] Leitersdorf E, Eisenberg S, Eliav O et al. Genetic determinants of responsiveness to HMG-CoA reductase inhibitor fluvastatin in patients with molecularly defined heterozygous familial hypercholesterolemia. Circulation 1993; 87(4 Suppl): III [33] Karayan L, Qiu S, Betard C et al. Response to HMG CoA reductase inhibitors in heterozygous familial hypercholesterolemia due to the 1-kb deletion ( French Canadian mutation ) of the LDL receptor gene. Arterioscler Thromb 1994; 14: [34] Ordovas JM, Lopez-Miranda J, Perez-Jimenez F et al. Effect of apolipoprotein E and A-IV phenotypes on the low density lipoprotein response to HMG CoA reductase inhibitor therapy. Atherosclerosis 1995; 113: [35] Leren TP, Hjermann I. Is responsiveness to lovastatin in familial hypercholesterolaemia heterozygotes influenced by the specific mutation in the low-density lipoprotein receptor gene? Eur J Clin Invest 1995; 25: [36] Ballantyne CM, Herd JA, Stein EA et al. Apolipoprotein E genotypes and response of plasma lipids and progressionregression of coronary atherosclerosis to lipid-lowering drug therapy. J Am Coll Cardiol 2; 36: [37] Miettinen TA, Gylling H, Strandberg T, Sarna S, for the Finnish 4S Investigators. Baseline serum cholestanol as predictor of recurrent coronary events in subgroup of Scandinavian Simvastatin Survival Study. Br Med J 1998; 316: [38] Berger GMB, Pegoraro RJ, Patel SB et al. HMG-CoA reductase is not the site of the primary defect in phytosterolemia. J Lipid Res 1998; 39: [39] O Neill FH, Mandeno R, Thompson GR, Seed M. Enhancement of cholesterol-lowering effect of atorvastatin by stanol ester cereal bars. Atherosclerosis Suppl 21; 2/2: 11. [4] Bays H, Drehobl M, Rosenblatt S et al. Low-density lipoprotein cholesterol reduction by SCH58235 (ezetimibe), a novel inhibitor of intestinal cholesterol absorption in 243 hypercholesterolemic subjects: Results of a dose-response study. Atherosclerosis 2; 151: 135. [41] Thompson GR. Plant lipids that lower serum cholesterol. Eur Heart J 1999; 2: [42] Gylling H, Miettinen TA. Effects of inhibiting cholesterol absorption and synthesis on cholesterol and lipoprotein metabolism in hypercholesterolemic non-insulin-dependent diabetic men. J Lipid Res 1996; 37:

7 26 G. R. Thompson et al. [43] Gylling H, Radhakrishnan R, Miettinen TA. Reduction of serum cholesterol in postmenopausal women with previous myocardial infarction and cholesterol malabsorption induced by dietary sitostanol ester margarine: women and dietary sitostanol. Circulation 1997; 96: [44] Vuorio AF, Gylling H, Turtola H, Kontula K, Ketonen P, Miettinen TA. Stanol ester margarine alone and with simvastatin lowers serum cholesterol in families with familial hypercholesterolaemia caused by the FH North Karelia mutation. Arterioscler Thromb Vasc Biol 2; 2: 5 6. [45] Blair SN, Capuzzi DM, Gottlieb SO, Nguyen T, Morgan JM, Cater NB. Incremental reduction of serum total cholesterol and low-density lipoprotein cholesterol with the addition of plant stanol ester-containing spread to statin therapy. Am J Cardiol 2; 86: [46] Kosoglou T, Meyer I, Musiol B et al. Pharmacodynamic interaction between the new selective cholesterol absorption inhibitor ezetimibe and simvastatin. Atherosclerosis 2; 151: 135. [47] Gylling H, Miettinen TA. Sitostanol ester added to long-term simvastatin treatment of coronary patients with low and high basal cholesterol absorption. Atherosclerosis 1997; 134: 157. [48] Thompson GR, Naoumova RP. Novel lipid-regulating drugs. Exp Opin Invest Drugs 2; 9: