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Intestinal Cholesterol Absorption Inhibitor Ezetimibe Added to Cholestyramine for Sitosterolemia and Xanthomatosis

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Intestinal Cholesterol Absorption Inhibitor Ezetimibe Added to Cholestyramine for Sitosterolemia and Xanthomatosis
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  Ezetimibe Effectively Reduces Plasma Plant Sterols inPatients With Sitosterolemia G. Salen, MD*; K. von Bergmann, MD*; D. Lütjohann, PhD; P. Kwiterovich, MD; J. Kane, MD, PhD;S.B. Patel, MD, PhD; T. Musliner, MD; P. Stein, MD; B. Musser, PhD;and the Multicenter Sitosterolemia Study Group  Background  —Sitosterolemia is a recessively inherited disorder that results from mutations in either ABCG5 or G8proteins, with hyperabsorption of dietary sterols and decreased hepatic excretion of plant sterols and cholesterol. As aconsequence of markedly elevated plasma and tissue sitosterol and campesterol levels, premature atherosclerosisdevelops.  Methods and Results —In this multicenter, double-blind, randomized, placebo-controlled study, we examined whethertreatment with ezetimibe, an inhibitor of cholesterol absorption, reduces plant sterol levels in patients withsitosterolemia. After a 3-week placebo run-in, 37 patients were randomized to receive placebo (n  7) or ezetimibe 10mg/d (n  30) for 8 weeks. Sitosterol concentrations decreased by 21% ( P  0.001) in patients treated with ezetimibecompared with a nonsignificant 4% rise in those on placebo (between-group  P  0.001). The reduction in sitosterol frombaseline was progressive, with further decline observed at each subsequent biweekly visit. Campesterol alsoprogressively declined, with a mean decrease after 8 weeks of 24% with ezetimibe and a mean increase of 3% withplacebo treatment (between-group  P  0.001). Reductions in plant sterol concentrations were similar irrespective of whether patients were undergoing concomitant treatment with resin or statin. Reductions in total sterols andapolipoprotein B were also observed. Ezetimibe was well tolerated, with no serious treatment-related adverse events ordiscontinuations due to adverse events being reported. Conclusions —Ezetimibe produced significant and progressive reductions in plasma plant sterol concentrations in patientswith sitosterolemia, consistent with the hypothesis that ezetimibe inhibits the intestinal absorption of plant sterols as wellas cholesterol, leading to reductions in plasma concentrations.  ( Circulation . 2004;109:966-971.)Key Words:  ezetimibe    sitosterolemia    cholesterol    coronary disease S itosterolemia is a rare, autosomal recessively inheritedsterol storage disease in which markedly increased tissueand plasma plant sterol concentrations can lead to prematureatherosclerosis and early cardiovascular death. 1–4 Sitosterol-emia is caused by complete mutations in either the ABCG5 orABCG8 genes, located in a head-to-head organization onhuman chromosome 2p21. 5–7 These genes encode ATP bind-ing cassette (ABC) proteins that belong to the G family andmay work together to pump sterols (cholesterol and plantsterols) from the brush border of enterocytes into the intesti-nal lumen and from the liver into bile. 8 Normally,  500 mgof cholesterol and half as much plant sterols (predominatelysitosterol and campesterol) are consumed in the diet eachday. 9,10 Approximately 50% of the cholesterol,   20% of campesterol, and  7% of sitosterol are absorbed. 11–13 Despitetheir close structural similarity, plant sterols are recognized asdistinct from cholesterol by the liver and are preferentiallyexcreted into bile. 11,14,15 Because of their lower intestinalabsorption and preferential biliary excretion, plant sterolsoccur in very low concentrations in the plasma of normalindividuals. 16–18 In contrast, patients with sitosterolemia havemarkedly increased plant sterol absorption and diminishedbiliary excretion of these sterols. 11,13,19–21 These 2 defectscombine to lead to marked elevations of plant sterol plasmaconcentrations and consequent increases in total body storesand tissue levels. 3,14,19,20 The clinical consequences of tissueplant sterol accumulation include premature atherosclerosisand coronary heart disease at a young age, 1–4 tendon xantho- Received April 22, 2003; de novo received September 30, 2003; accepted November 17, 2003.From the UMDNJ-New Jersey Medical School, Newark, NJ, and VA Medical Center, East Orange, NJ (G.S.); Department of Clinical Pharmacology,University of Bonn (K.V.B., D.L.), Bonn, Germany; Johns Hopkins University (P.K.), Baltimore, Md; University of California at San Francisco (J.K.),San Francisco, Calif; Medical University of South Carolina (S.B.P.), Charleston, SC; and Merck Research Laboratories (T.M., P.S., B.M.), Rahway, NJ.*Drs Salen and von Bergmann contributed equally to this work.Dr Kane is a recipient of a clinical research grant for evaluation of ezetimibe in phytosterolemia from Merck & Co, Inc. Dr von Bergmann offeredconsultancy services to Merck Sharpe and Dohme and Shering Plough (in Germany, Essex Pharma); he also gave lectures at symposia organized by thesecompanies. This work is paid, and travel costs are covered.Reprint requests to Dr Gerald Salen, University of Medicine and Dentistry of New Jersey, 185 S Orange Ave, MSB-H538, Newark, NJ 07103. E-mailSalenGe@UMDNJ.edu© 2004 American Heart Association, Inc. Circulation  is available at http://www.circulationaha.org DOI: 10.1161/01.CIR.0000116766.31036.03  966  Clinical Investigation and Reports  mas similar to those observed in patients with homozygousfamilial hypercholesterolemia, hematologic sequelae includ-ing chronic hemolytic anemia and thrombocytopenia, andabnormal liver function tests. 1,3,4,22 Available treatments for sitosterolemia include a dietrestricted in cholesterol and plant sterols, bile salt-bindingresins, ileal bypass surgery, or LDL immunoabsorption. 3,4 Despite treatment, most patients continue to have markedlyelevated concentrations of plant sterols and associated com-plications. Thus, current therapy is often inadequate to treatpatients with sitosterolemia.Ezetimibe is a novel inhibitor of intestinal cholesterolabsorption in humans, 23 shown to significantly lower plasmacholesterol and LDL cholesterol (LDL-C) concentrations inpatients with hypercholesterolemia. 24 – 26 Ezetimibe undergoesglucuronidation in the intestine and liver, and both the parentcompound and its glucuronide localize to the brush border of the small intestine, where they block the absorption of dietaryand biliary sources of cholesterol without affecting absorp-tion of triglycerides, bile acids, or fat-soluble vitamins. 27,28 Inpatients with mild to moderate hypercholesterolemia,ezetimibe reduces plasma concentrations of sitosterol andcampesterol, 23 most likely by reducing the absorption of theseplant sterols. The purpose of the present study was todetermine whether ezetimibe would also block the intestinalabsorption of plant sterols and thus lead to lower plant sterolconcentrations in patients with sitosterolemia. Methods Patients Patients aged  10 years with a diagnosis of sitosterolemia who hadplasma sitosterol levels   0.12 mmol/L (normal range  0.0239 mmol/L) despite current treatment were eligible to partic-ipate. Patients with poorly controlled diabetes or active liver or renaldisease were excluded. Patients were expected to have been on astable regimen of diet and/or medications for at least 4 weeks beforethe screening visit. If considered clinically appropriate, patientstaking bile salt-binding resins had these agents discontinued beforeentry into the study because it was not known whether resins mightlower ezetimibe concentrations. If it was not considered appropriateto modify the bile salt-binding medication that the patient wastaking, patients could be enrolled while undergoing their currentresin treatment. In these patients, ezetimibe was given at least 2hours before or after bile acid – binding resins. Other treatments,including diet and statins, were continued but were expected toremain stable during the double-blind treatment period. Study Design This was a randomized, double-blind, placebo-controlled studyconducted in 23 centers worldwide. After a 3-week single-blindplacebo run-in period, patients were randomized (in a 4:1 ratio) toreceive ezetimibe 10 mg/d or placebo. Given the relative rarity of this disorder, it was not expected that sufficient patients would beavailable to have an adequately powered study to assess between-group differences. Thus, the primary end point was percent changefrom baseline (defined as the average of the week    1 and therandomization visit) to end point (defined as the average of weeks 6and 8) in sitosterol concentrations, and the 4:1 randomization ratiowas used to ensure that sufficient patients would receive treatmentwith ezetimibe. More patients participated than expected, whichprovided sufficient power to assess both between- and within-groupdifferences in plant sterols. Blood specimens collected with EDTAwere obtained after an overnight fast at screening, at randomization,and after 2, 4, 6, and 8 weeks of treatment. The study protocol wasapproved by the institutional review boards at the participating sites,and all subjects or their legal guardians gave informed writtenconsent. Analytical Methods All laboratory analyses other than those for sterols and geneticanalyses were performed at Medical Research Laboratories, High-land Heights, Ky, or its subsidiary, Clinical Research Laboratories,Brussels, Belgium, according to published procedures. 29 – 31 Sterolswere analyzed by capillary gas-liquid chromatography (GLC). 13,19 VLDL (density  1.006 g/mL) was isolated from plasma by prepar-ative ultracentrifugation, and cholesterol was measured in the VLDLfraction and the infranatant by GLC. Plasma HDL cholesterol(HDL-C) was also measured by GLC after lipoproteins that con-tained apolipoprotein B had been precipitated with heparin-manganese. Cholesterol in the LDL fraction was taken as thedifference between the cholesterol content of the infranatant andHDL fraction. The chromatographic quantification of lathosterol wasperformed by GLC-mass spectrometry-selected ion monitoring(GLC-MS-SIM). 13 For mutational analyses, informed consent wasobtained for the confirmation of known mutational analyses reportedpreviously. 6,7 In all cases, known mutations were confirmed by directsequencing of polymerase chain reaction products. 7 Achilles tendon thickness was measured by lateral foot radiogra-phy; x-ray films were centrally read by a radiologist blinded totreatment group assignment and to sequence (baseline or end of study). Radiographs were only available at baseline and end of studyin 24 patients (6 placebo, 18 ezetimibe) because radiography wasgenerally not performed in patients younger than 18 years of age. TABLE 1. Baseline Characteristics of the Study Population Placebo(n  7)Ezetimibe10 mg/d(n  30) Age, yMean 37.6 37.0Range 13–57 9–72 Age subgroup, n (%)  18 y 1 (14) 4 (13)  18 y 6 (86) 26 (87)Gender, n (%)Female 6 (86) 18 (60)Male 1 (14) 12 (40)Race, n (%)White 6 (86) 27 (90) Asian 0 (0) 1 (3)Hispanic 1 (14) 2 (7)Body weight, kgMean 63.0 67.5Range 38.9–90.5 37.2–103.6Time since diagnosis, yMean 15.4 15.0Range 6–32 0–32Prior treatment of sitosterolemia, n (%)None 0 (0) 10 (33)Statins 2 (29) 8 (27)Bile salt-binding resins 4 (57) 11 (37)Ileal bypass surgery 2 (29) 3 (10) Apheresis 0 (0) 1 (3) Salen et al Ezetimibe in Patients With Sitosterolemia  967   Statistical Analysis The primary efficacy variable was the within-group mean percentchange in plasma sitosterol from baseline to end point. Key second-ary variables were the within-group percent changes in plasmacampesterol and in LDL-C. For all efficacy variables, percent changewas assessed with summary statistics and 95% CIs. The assumptionof normality was assessed by the Shapiro-Wilk statistic. Between-group differences were estimated with 95% CI. As prespecifiedbefore unblinding, a modified intention-to-treat analysis was per-formed without the single patient undergoing apheresis, who wasexcluded from the primary analysis given the distinctly differentongoing therapy; hence, the efficacy results are presented based on29 patients treated with ezetimibe and 7 patients given placebo. Results A total of 39 patients were screened, and 37 patients wererandomized into the double-blind treatment period. Patientbaseline characteristics are presented in Table 1. The 2treatment groups were similar in age and body weight.However, the placebo group had a greater proportion of females than the ezetimibe treatment group. Most patientswere undergoing medical therapies for sitosterolemia, whichincluded bile salt-binding resins in 15 patients (10 of whomcontinued such therapy during the double-blind treatmentperiod) and statins in 10 patients. In addition, 5 patients hadhad prior ileal bypass surgery to treat their disease. Mostpatients had had the diagnosis of sitosterolemia for manyyears at the time of recruitment, with an average durationsince diagnosis of    15 years. Mutational analyses wereperformed in 29 subjects who gave informed consent; 28 of these were mutant for ABCG8, and 1 was mutant forABCG5. This was expected, because almost all white sitos-terolemic individuals are mutant for ABCG8, and all Japa-nese and Chinese patients are mutant for ABCG5. 7 Thepresent study cohort included only 1 Japanese proband.Clinically overt coronary artery disease was present in 12patients (32.4%). Of note, 9 patients (24.3%) either had aorticstenosis (by examination and/or echocardiography) or ahistory of aortic valve replacement surgery. Low plateletcounts (  100 000) were present in 11 patients (29.7%), andlow hemoglobin was observed in 5 patients (13.5%), consis-tent with prior observations of hematologic complications inpatients with sitosterolemia. Finally, abnormal liver enzymelevels at baseline were common, with 25 patients (67.6%)having elevations in 1 or more liver function tests; aspartateaminotransferase was elevated in 12 patients (32.4%), alanineaminotransferase in 14 patients (35.1%), and    -glutamyltransferase in 5 patients (13.5%). Baseline lipid values areprovided in Table 2. Plant sterol and lipid concentrationswere generally similar between the 2 treatment groups andshowed the expected dramatic elevations in both sitosteroland campesterol but relatively normal concentrations of cholesterol in the lipid fractions. Efficacy of Ezetimibe on Plant and OtherSterol Concentrations Treatment with ezetimibe 10 mg/d resulted in a mean percentchange in plasma sitosterol levels from baseline to end pointof   21.0% ( P  0.001) compared with a nonsignificant 4.0%increase in the placebo group (Table 2). The between-groupdifference in mean percent change in sitosterol was  25.0%(95% CI   36.7% to   13.2%;  P  0.001). The reduction inplasma sitosterol during the double-blind period was progres-sive beginning at week 2, with greater reduction frombaseline observed at each subsequent visit (Figure 1A). Ahigh proportion of patients (27/29, 93%) had reductions insitosterol with ezetimibe treatment; 25 (86%) of 29 patientshad a   15% decrease and 10 (34%) of 29 had a   25%decrease from baseline in sitosterol concentrations. In con-trast, only 1 (14%) of 7 patients in the placebo-treated grouphad a decrease of   15%, and none had a decrease of   25%. TABLE 2. Baseline and Percent Change From Baseline Lipid and Apolipoprotein Values Sterol or ApolipoproteinPlacebo Ezetimibe 10 mg/dBetween-GroupDifference(95% CI)BaselineMean,mmol/L%Change(SE)95%CI for %ChangeBaselineMean,mmol/L%Change(SE)95%CI for %ChangeSitosterol 0.44 4.0 (5.3)   6.9 to 14.8 0.50   21.0 (2.8)   26.7 to  15.3   25.0 (  36.7 to  13.6)Campesterol 0.23 3.2 (5.5)   7.9 to 14.3 0.27   24.3 (2.9)   30.7 to  18.4   27.5 (  39.6 to  15.4)Lathosterol 0.012   7.2 (5.1)   20.2 to 5.9 0.007 10.6 (6.1)   1.9 to 23.2 17.8 (  7.9 to 43.4)LDL-C* 2.31 16.7 (19.7)   31.6 to 64.9 2.47   13.6 (4.0)   21.7 to  5.5 NA LDL sterols 3.11 18.4 (7.7) 2.8 to 34.0 3.39   14.9 (4.1)   23.2 to  6.6   33.3 (  50.4 to  16.2)HDL sterols 1.27 5.5 (5.0)   4.7 to 15.7 1.42 2.2 (2.6)   3.2 to 7.6   3.3 (  14.4 to 7.8)HDL-C (GC) 0.86 8.3 (6.1)   4.2 to 20.7 1.03 6.2 (3.2)   0.4 to 12.8   2.1 (  15.6 to 11.5)Cholesterol (GC) 3.75 8.0 (6.1)   11.3 to 27.3 4.35   4.8 (3.2)   14.9 to 5.3   12.8 (  26.4 to 0.7)Total sterols 5.29 3.7 (4.8)   6.2 to 13.5 5.62   8.7 (2.5)   13.9 to  3.5   12.4 (  23.1 to  1.7)Triglyceride* 2.2   20.8 (6.9)   37.6 to  4.0 1.66   2.1 (8.1)   18.7 to 14.6 NA  Apo A-I (mg/dL) 146.7 0.6 (4.2)   7.9 to 9.2 159.0 6.5 (2.2) 2.0 to 11.0 5.9 (  3.4 to 15.2) Apo B (mg/dL) 128.2 3.1 (4.5)   6.1 to 12.2 129.9   12.7 (2.4)   17.5 to  7.9   15.8 (  25.8 to  5.8)Lath:Chol ratio 0.41   7.2 (11.2)   30.1 to 15.8 0.18 10.6 (5.6)   0.8 to 22.1 37.3 (1.0 to 73.7) Apo indicates apolipoprotein; GC, gas chromatography; and Lath:Chol, lathosterol:cholesterol.*LDL-C and triglyceride results presented as median, given nonnormal distribution of results, and hence, between-group differences are not provided.  968 Circulation  March 2, 2004  Results for the primary efficacy variable were examined insubgroups defined by patient baseline characteristics, includ-ing concomitant usage of bile salt-binding resins, statins,median baseline sitosterol, and gender. The results of theanalyses indicate that the response to 10 mg of ezetimibe wasconsistent across these subgroups (Figure 2). There were toofew patients under the age of 18 years to perform meaningfulsubgroup analysis by age; however, inspection of individualplasma sitosterol responses suggested that the effect of ezetimibe on sitosterol was similar in subjects under age 18and those 18 years and older.Plasma campesterol was reduced by 24.3% ( P  0.001) inthe 29 patients treated with ezetimibe compared with anonsignificant 3.2% rise in the 7 subjects given placebo. Thisresulted in a between-group difference of 27.5% ( P  0.001;Table 2). As with plasma sitosterol, plasma campesteroldecreased progressively over the 8-week treatment period(Figure 1B).Table 2 provides mean changes from baseline in lipids andapoproteins. For LDL-C measured by GLC, the medianpercent change was   13.6% for patients treated withezetimibe compared with a 16.7% rise for those givenplacebo. This difference was not statistically significant.LDL-C was relatively low at baseline, with a median value of 2.43 mmol/L. Patients with baseline LDL-C above the me-dian level had a median change of    17.5% compared with1.5% in patients whose LDL-C at baseline was lower than themedian value. Total sterols (including cholesterol and plantsterols) and apolipoprotein B were reduced in the ezetimibegroup (  8.7% and   12.7%, respectively) and increasedslightly in patients on placebo (3.7% and 3.1%, respectively).The between-group differences (  12.4% and   15.8%, re-spectively) were significant ( P  0.05 for both). Both totalsterols and apolipoprotein B were decreased at week 2 andremained generally stable throughout the study. No signifi-cant effects of ezetimibe on HDL sterols, HDL-C, apoli-poprotein A-I, or triglycerides were observed. In theezetimibe-treated group, plasma lathosterol (a cholesterolprecursor) and the ratio of lathosterol to cholesterol increasedprogressively, which indicates enhanced biosynthesis. Levelsin the placebo group did not change. After 8 weeks, thebetween-group difference in the ratio of lathosterol to cho-lesterol was 37.3% ( P  0.044). Achilles Tendon Radiography At baseline, the mean Achilles tendon thickness, measured byradiography, was 15.7 mm in the placebo group (n  6) and18.2 mm in the ezetimibe group (n  18). After 8 weeks of treatment, Achilles tendon thickness decreased slightly in theezetimibe-treated group (  0.6%), and modestly increased inthe placebo-treated group (8%) for a significant ( P  0.013)between-group difference of    8.6% (95% CI   15.1% to  2.0%). Safety and Tolerability Ezetimibe was generally well tolerated, and all patientscompleted the double-blind treatment period. Overall, 21(70%) of 30 ezetimibe-treated patients and 2 (40%) of 7placebo-treated subjects reported 1 or more adverse experi-ences. The most commonly reported adverse experiences Figure 1.  Mean percent change from baseline in plasma con-centration of sitosterol (A) and campesterol (B) over time and atend point in 2 treatment groups. Avg. indicates average; Wks.,weeks. Figure 2.  Point estimate and 95% CI response to ezetimibe 10mg/d in sitosterol in various subgroups of population, definedby baseline characteristics. For baseline sitosterol subgroup,median sitosterol concentration used was based on all random-ized subjects; 18 subjects (6 placebo and 12 ezetimibe) hadplasma sitosterol levels at or below median at baseline, and 18subjects (1 placebo and 17 ezetimibe) had baseline sitosterollevels above median. BSBR indicates bile salt-binding resin. Salen et al Ezetimibe in Patients With Sitosterolemia  969  were in the gastrointestinal system in the ezetimibe-treatedgroup, with occurrences in 12 patients (40%). Six of theseevents were considered by the investigator to be possibly orprobably related to the study drug. The gastrointestinaladverse events reported were generally mild and of shortduration and included mild abdominal pain, diarrhea, looseand frequent bowel movements, nausea, and toothache.Safety laboratory studies remained essentially stable dur-ing the treatment period. Platelet count increased slightly inthe ezetimibe-treated group by a mean of 17 800 ( P  0.05)but also rose in the placebo-treated group by a mean of 26 700 (between-group  P  NS). Hematocrit rose by 1.1% inthe ezetimibe-treated group and decreased by 0.2% in theplacebo-treated group. Renal and liver function tests re-mained essentially unchanged during the double-blind treat-ment period; no patient receiving ezetimibe experiencedelevations in aspartate aminotransferase or alanine amino-transferase of    3-fold or in creatine kinase   10-fold theupper limit of normal. Discussion In sitosterolemic individuals, plant sterol absorption is in-creased and hepatic removal is slowed. 11,13,14,19 – 21 The neteffect leads to a progressive accumulation of plant sterols invirtually every tissue except brain, where the blood-brainbarrier prevents the uptake of circulating plant sterols (as wellas cholesterol). 1 Increased cholesterol absorption at the high-normal level is also noted in patients with sitosterolemia. 12 – 19 As a result of plant sterol accumulation, individuals withsitosterolemia are at high risk of atherosclerosis and coronaryheart disease – related morbidity and mortality. 1 – 4 Treatment of patients with sitosterolemia has only beenpartially effective; bile salt-binding resins lower plant sterolsbut do not lead to normalization, and plasma sterol levelsoften do not decline when patients are treated with statindrugs that inhibit HMG-CoA reductase activity. 3,32,33 Indeed,activities of many of the enzymes along the cholesterolbiosynthesis pathway are reduced in liver biopsy samplesfrom sitosterolemic individuals, which perhaps accounts forthe lack of efficacy of the statin drugs. 34 There are no prior,adequately controlled clinical trials of medications for thetreatment of sitosterolemia; hence, the extent of efficacy withother agents is not known. Low-sterol diets are difficult forpatients to maintain and are often unsuccessful in substan-tially lowering plant sterol levels; paradoxical increases inplasma plant sterol levels have even been observed. 33 Thus, asignificant need exists for new, effective treatments forsitosterolemia.The results of the present study demonstrated that treatmentwith ezetimibe produced significant reductions from baseline insitosterol and campesterol, the predominant plant sterols, as wellas reductions in total sterols and apolipoprotein B concentra-tions. Plant sterols declined even if the subjects were alsoreceiving treatment with bile salt-binding resins or statins, andezetimibe was similarly effective in both men and women withthe disease and in patients with higher or lower sitosterolconcentrations at baseline. Plant sterol levels declined progres-sively, although they remained significantly above the normalrange and likely did not reach plateau in the present study.LDL-C reduction with ezetimibe did not achieve statisticalsignificancerelativetoplacebo;however,baselineLDL-Clevelswere low, and it appeared that individuals with higher baselineLDL-C concentrations had more pronounced reductions.Whether this indicates greater efficacy in patients with elevatedbaseline LDL-C or a regression to the mean phenomenon canonly be assessed with additional study in this patient population.Ezetimibe was well tolerated, with no discontinuations related toadverse experiences. Although more adverse experiences wereobserved in the active-treatment group, the number of patients inthe placebo group was quite small, which limits any meaningfulconclusions. Nonetheless, the majority of adverse experienceswere mild, transient, and resolved despite continued treatment.Ezetimibe has been shown to block the intestinal absorptionof both cholesterol 27 and phytosterols (Harry Davis, PhD,Schering-Plough Research Institute, unpublished observation,2000); however, the exact mechanism of action has not beendefined. The fact that ezetimibe blocks the uptake of cholesteroland plant sterols suggests that they may be absorbed through acommon mechanism. Ezetimibe does not appear to affect theexpression of the ABCG5 or ABCG8 genes directly. 35 Theeffect of ezetimibe on the function of the ABCG5/G8 proteinscannot be assessed because assays to test for the putative activityof these proteins are not available.An important observation was that ezetimibe reducedplasma total cholesterol levels rapidly, with essentially thefull reduction observed by the second week of double-blindtreatment. Cholesterol synthesis increased, as evidenced bythe 35% rise in plasma ratio of lathosterol to cholesterol(Table 2). The rise in cholesterol synthesis may explain thefailure to see a further decline in total cholesterol. Becauseplant sterols cannot be synthesized by the human body,progressive decline in these sterols may reflect continuedtissue depletion.Whether the complications of sitosterolemia, includingatherosclerosis, hemolysis, and low platelet counts, may bereversed with ezetimibe treatment remains to be seen. Al-though small increases in platelet counts and hematocrit wereobserved in the ezetimibe-treated group, a rise in plateletswas also observed in patients given placebo. It is interestingthat Achilles tendon thickness by radiography, used to assesschange in Achilles tendon xanthoma, decreased in theezetimibe-treated group relative to the placebo group after 8weeks of treatment. Whether such a change can be substan-tiated with more dramatic reductions in thickness with long-term treatment must await further study. Nonetheless, thismay be an indication that tissue stores of plant sterols wereaffected by ezetimibe treatment. A trial of long-term treat-ment is planned to determine whether ezetimibe will lowerplant sterol levels further, leading to evidence of diminutionin tissue stores and a reduction in cardiovascular disease. Appendix Coinvestigators of the Multicenter SitosterolemiaStudy Group Canada, David Mymin, MD (Winnipeg, Manitoba), and JiriFrohlich, MD (Vancouver, BC); Finland, Tatu Miettinen, MD(HYKS, Helsinki); France, Eric Bruckert, MD (Paris); Germany,Klaus von Bergmann, MD; Dieter L ü tjohann, PhD; and Thomas  970 Circulation  March 2, 2004
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