© 2001 American Heart Association, Inc.
Atherosclerosis and Lipoproteins |
Determinants of Variable Response to Statin Treatment in Patients With Refractory Familial Hypercholesterolemia
From the Imperial College School of Medicine (F.H.O., G.W.T., G.R.T.) and the MRC Clinical Sciences Centre (D.D.P., B.L.K., C.K.Y.N., M.B., A.K.S., R.P.N.), Hammersmith Hospital, London, England.
Correspondence to Dr Rossitza P. Naoumova, MD, PhD, MRC Clinical Sciences Centre, Hammersmith Hospital, Du Cane Road, London, W12 0NN, UK. E-mail rossi.naoumova{at}csc.mrc.ac.uk
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Abstract—Interindividual variability in low density lipoprotein (LDL) cholesterol (LDL-C) response during treatment with statins is well documented but poorly understood. To investigate potential metabolic and genetic determinants of statin responsiveness, 19 patients with refractory heterozygous familial hypercholesterolemia were sequentially treated with placebo, atorvastatin (10 mg/d), bile acid sequestrant, and the 2 combined, each for 4 weeks. Levels of LDL-C, mevalonic acid (MVA), 7-
-OH-4-cholesten-3-one, and leukocyte LDL receptor and
hydroxymethylglutaryl coenzyme A reductase mRNA were
determined after each treatment period. Atorvastatin (10 mg/d) reduced
LDL-C by an overall mean of 32.5%. Above-average responders (
LDL-C
-39.5%) had higher basal MVA levels (34.4±6.1 µmol/L) than did
below-average responders (LDL-C -23.6%,
P<0.02; basal MVA 26.3±6.1
µmol/L, P<0.01). Fewer good
responders compared with the poor responders had an apolipoprotein E4
allele (3 of 11 versus 6 of 8, respectively;
P<0.05). There were no
baseline differences between them in 7--OH-4-cholesten-3-one,
hydroxymethylglutaryl coenzyme A reductase mRNA, or LDL
receptor mRNA, but the latter increased in the good responders on
combination therapy (P<0.05).
Severe mutations were not more common in poor than in good responders.
We conclude that poor responders to statins have a low basal rate of
cholesterol synthesis that may be secondary to a
genetically determined increase in cholesterol absorption,
possibly mediated by apolipoprotein E4. If so, statin responsiveness
could be enhanced by reducing dietary cholesterol intake or
inhibiting
absorption.
Key Words: familial hypercholesterolemia • statins • apolipoprotein E • cholesterol • hydroxymethylglutaryl coenzyme A reductase
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Familial hypercholesterolemia (FH) is caused by mutations in the gene encoding the LDL receptor, resulting in either deficient gene expression or the expression of defective LDL receptors. The lack of functioning LDL receptors results in decreased catabolism of LDL and its consequent accumulation in plasma. In homozygous1 and heterozygous2 individuals, hypercholesterolemia is more severe with mutations causing null alleles than with mutations resulting in defective receptors.
Hydroxymethylglutaryl coenzyme A (HMG CoA) reductase catalyzes the rate-limiting step in cholesterol synthesis, namely, the conversion of HMG CoA to mevalonic acid (MVA), and its activity is rapidly regulated at the transcriptional, translational, and protein levels.3 HMG CoA reductase inhibitors (statins) have been very effective in treating FH, but we4 and others5 6 have reported large variations in interindividual plasma cholesterol responses to statins, irrespective of the statin and dose used. Whether the nature of the LDL receptor mutation influences the degree of cholesterol lowering achieved by statins is controversial, with evidence for5 7 8 and against6 9 10 11 12 this hypothesis. However, the extent of variability documented by Karayan et al6 in >100 patients, all with the same mutation, as well as in non-FH subjects without LDL receptor mutations suggests that other factors play a major role in determining the response to statins.
One potential determinant of statin responsiveness is the
apoE genotype. Data in
FH13 and
non-FH14 subjects suggest
that possession of an 
4 allele results in a lesser reduction in
LDL cholesterol (LDL-C) than is seen in those with 2 or
3 alleles, although this was not confirmed in other
reports.15 16 17
Previously, we showed that statin responsiveness was associated with the rate of cholesterol synthesis before treatment.4 Similar findings have been reported by Miettinen et al.18 Other factors that might influence the interindividual response to statins are whether these drugs differentially affect bile acid synthesis and any variability in the rate at which they are metabolized by the cytochrome P-450 pathway.
The object of the present study was to further elucidate the mechanisms underlying the large variations observed in plasma cholesterol response when FH patients are treated with statins.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Subjects
Twenty-one subjects with refractory heterozygous FH attending the lipid clinic at Hammersmith Hospital, London, were enrolled in the present study, 19 of whom completed it. Being refractory to treatment was defined as having an LDL-C level of
5 mmol/L despite taking simvastatin (40 mg/d) plus
at least 1 other drug, ie, cholestyramine, bezafibrate, or nicotinic
acid. All patients had definite FH according to established
criteria,19 including tendon
xanthomas in the patient or a first-degree relative. This diagnosis was
later confirmed by mutational analysis in all but 3 instances,
with 1 instance proving to be a case of familial defective apoB-100
(FDB). Details of the subjects are summarized in
Table 1
.
|
The present study was approved by the Research Ethics Committee of the Hammersmith Hospitals NHS Trust, and written informed consent was obtained from all participants.
Experimental Protocol
Participants in this single-blind placebo-controlled
study underwent 4 sequential treatment regimens, each of 4-week
duration. All maintained their habitual diet, which was low in
cholesterol and saturated fat. The treatment regimens, in
chronological order, were as follows: placebo, atorvastatin (10 mg/d),
bile acid sequestrant (BAS, 8 to 16 g/d cholestyramine or 10 to 20 g/d
colestipol), and BAS plus atorvastatin (10 mg/d). After each treatment
period, blood was collected between 9:00 and 10:00
AM after an overnight fast.
Samples were assayed for levels of serum total cholesterol,
HDL cholesterol, LDL-C, triglycerides, plasma
MVA, plasma 7--OH-4-cholesten-3-one (7--OHC), mononuclear
leukocyte LDL receptor mRNA, and HMG CoA reductase mRNA. Compliance
with treatment was verified by tablet and sachet
counts.
Analysis
Plasma MVA concentration is an indicator of the
activity of HMG CoA
reductase.6 20 21
MVA was extracted from fasting plasma and quantified by gas
chromatography/mass spectrometry, as described
previously.22 Plasma
7--OHC is a validated marker of the activity of
cholesterol-7- hydroxylase, the rate-limiting enzyme in
bile acid
synthesis.23 24 25
7--OHC was extracted from plasma and quantified by
high-performance liquid chromatography as
described by Axelson et
al.23
Mononuclear leukocytes were isolated from whole blood by using Ficoll-Paque density gradients adapted from Boyum.26 RNA was isolated from the samples by using an RNAgents total RNA isolation kit (Promega). Before reverse transcription, the RNA was DNase-treated (DNAase, Ambion Inc). Total RNA (1.8 µg) was subsequently reverse-transcribed by using random hexamers (Roche Molecular Biochemicals). Controls without reverse transcriptase were included for all samples. The cDNA obtained was used in real-time quantitative polymerase chain reactions on the ABI PRISM 7700 Sequence Detection System (PE Applied Biosystems). The following oligonucleotide sets were used for quantifying HMG CoA reductase and LDL receptor mRNA, respectively: 5'-FAM-CGTCTTCCACGTGCTTGTGACTCTGC-TAMRA-3' (fluorescent probe) with 5'-ATGACTCGTGGCCCAGTTG-3' and 5'-TCGAGCCAGGCTTTCACTTC-3' (primers) and 5'-FAM-CCCAACCTGAGGAACCTGGTCGCT-TAMRA-3' (fluorescent probe) with 5'-CTGGACCGGAGCGAGTACAC-3' and 5'-TGGGTGCTGCAGATCATTCTC-3' (primers). Target mRNA quantities were expressed as relative values, and a standard curve of a common RNA mixture was included on every 96-well reaction plate. The obtained target mRNA values were normalized to ß-actin, which was quantified with the use of a commercially available probe/primer set (PE Applied Biosystems). All samples and standards were assayed in triplicate. Comparisons of RNA quantities were performed according to the threshold cycle of each sample. (The threshold cycle is directly related to the initial amount of RNA present in the sample.)
ApoE phenotyping was performed by agarose gel electrofocusing and immunoblotting, as described by McDowell et al.27 LDL receptor mutations were identified by sequencing amplified fragments of LDL receptor mRNA. If the mutation could not be identified from the mRNA sequences, the genomic sequence of the 18 exons of the LDL receptor was determined, as is fully described elsewhere.28 Mutations were classified as mild, severe, or in the epidermal growth factor (EGF) domain, as defined previously.11 FDB was diagnosed by using a molecular screening technique as described by Tybjaerg-Hansen et al.29
Cytochrome P-450 3A4 (CYP3A4) activity was assessed by measuring the 24-hour urinary excretion of 6-ß-hydroxycortisol with the use of commercially available ELISA kits (Stabiligen); (CYP3A4) activity was then expressed as the ratio of the excretion of 6-ß-hydroxycortisol to the excretion of urinary free cortisol, as described by Zhiri et al.30 This ratio reflects the hepatic activity of CYP3A4.
Statistical Analysis
Data were checked for normality and transformed
logarithmically if skewed. Statistical significances were tested with
2-tailed or paired t tests and
ANOVA. Random-effects regression was used to analyze the
significance of the intergroup differences on the various treatments.
The 
2 test was used for analysis
of apoE phenotype frequency. A value of
P
0.05 was considered
significant.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
After a 1-month period of treatment with atorvastatin (10 mg daily), serum LDL-C levels were reduced by an average of 32.6%, with the range varying between 46.9% and 8.9%. The mean reduction in serum LDL-C was used to arbitrarily divide the subjects into 2 groups. Eleven subjects whose LDL-C decreased by an above-average value were designated as "good responders," whereas 8 subjects with a below-average reduction were classified as "poor responders."
Serum lipid and lipoprotein levels at the end of each
treatment regimen are shown in
Table 2. Retrospective analysis showed that mean
LDL-C values did not differ significantly between the good and poor
responders (9.4 and 9.8 mmol/L, respectively;
P>0.1) when they were on
placebo, and they had similar triglyceride levels (2.5 and
2.1 mmol/L, respectively;
P>0.1). By definition, LDL-C
levels decreased more markedly in good than in poor responders after 1
month on 10 mg atorvastatin daily (-39.5% versus -23.6%,
respectively), with the difference between the 2 groups being
significant (P<0.02). The sex
of the individual had no significant effect on LDL-C
reductions.
|
In contrast, there were no significant differences in LDL-C
between the 2 groups when they were treated with BAS or a combination
of atorvastatin and BAS. Although the difference between the groups on
combination therapy was not significant, there was a trend for the good
responders to show a greater reduction in LDL-C (-41.9% versus
-30.9% for good versus poor responders, respectively). The decreases
in LDL-C in both groups with each treatment regimen are graphically
represented in
Figure 1.
|
Whereas there were no changes in HDL
cholesterol, triglyceride levels were decreased
by atorvastatin and increased by BAS, with the latter effect being
largely eliminated when the 2 drugs were given in combination. The
magnitude of these changes was similar in good and poor responders
(Table 2
).
As shown in
Table 3, the mean MVA level in the good responders on
placebo was 34.4 µmol/L, whereas in the poor responders, the mean was
26.3 µmol/L. The difference in these mean baseline MVA levels is
statistically significant
(P<0.01). On atorvastatin (10
mg/d), the mean MVA levels decreased to 22.3 µmol/L in both groups.
Differences between MVA levels in the good and poor responders on BAS
and the combination of BAS and atorvastatin (10 mg/d) therapy were not
statistically significant.
|
No significant changes from baseline values were detected in
7--OHC levels after treatment with atorvastatin (10 mg/d) for 1
month. As expected, treatment with BAS substantially increased
7--OHC levels in both groups. Compared with BAS treatment alone,
coadministration of atorvastatin (10 mg/d) with BAS reduced the levels
of 7--OHC by 56% in poor responders. In comparison, the good
responders showed a decrease of only 8% on combination therapy, so
that both groups ended up with similar values
(Table 3). Statistical analysis showed no
significant difference in 7--OHC between the 2 groups after any of
the 3 treatment regimens.
No statistically significant changes were detected in the relative LDL receptor and HMG CoA reductase mRNA levels in mononuclear leukocytes under any of the treatment regimens with the exception of LDL receptor mRNA on the statin/resin combination. Despite substantial variability, the good responders had a significant increase (44%, P=0.05) in their level of LDL receptor mRNA on the statin/resin combination compared with baseline values.
LDL receptor mutations were identified in all subjects,
apart from 3 poor responders, 1 of whom was shown to have FDB. No
mutation was detected in the other 2 subjects. As shown in
Figure 2, mild, severe, and EGF domain mutations of the LDL
receptor were distributed evenly among good and poor responders. A
severe mutation is defined as one in which the mutant gene would
produce little or no functional LDL receptor protein, whereas single
amino acid substitutions in regions of the LDL receptor gene that would
not be expected to have a major effect on LDL receptor function were
classified as mild mutations. Mutations in the EGF precursor domain
cannot be classified as either mild or severe on the basis of amino
acid substitution; thus, these were assigned as a separate
group.
|
Possession of an 4 allele (E3/4 and E4/4) was
significantly more frequent among poor responders (6 of 8) than among
good responders (3 of 11,
P<0.05). If the subjects are
grouped according to whether they had an 4 allele or an 2 or
3 allele (E2/3, E2/4, and E3/3), the latter showed a significantly
greater (P0.02) reduction in
LDL-C after the administration of atorvastatin
(Figure 3).
|
The ratio of urinary 6-ß-hydroxycortisol to free cortisol did not differ significantly between good and poor responders at baseline (7.9±0.8 versus 8.5±1.9, respectively).
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
These results confirm and extend our previous findings in FH patients in South Africa treated with high doses of atorvastatin, simvastatin, or pravastatin, which showed that compared with good responders, poor responders had a lower basal level and a smaller decrease of plasma MVA on statins.6 In the present study of British patients with refractory FH treated with low-dose atorvastatin, the spectrum of LDL receptor mutations differed from those in the South Africans, most of whom had the Afrikaner 1 or 2 mutations. However, in neither study was the extent of reduction in LDL-C on treatment attributable to the underlying LDL receptor defect, inasmuch as mild and severe mutations were evenly distributed among good and poor responders, as has been shown in several previous studies.6 9 10 11 12 That mild and severe mutations were evenly distributed can be adduced from the observation that baseline LDL-C levels were similar in good and poor responders. However, our group of patients was too small for any definite conclusion to be drawn about the impact of the severity of the LDL receptor mutation on therapeutic response.
We and others have justified the use of fasting plasma MVA
as an index of HMG CoA reductase activity and, thus, of
cholesterol
synthesis.6 20 21
Hence, our results imply that patients in whom basal HMG CoA reductase
activity is downregulated and whose rate of cholesterol
synthesis is therefore low respond less well to statins than do
patients with a higher rate of cholesterol synthesis. A
possible explanation for these findings stems from the analysis
of apoE phenotypes, which showed a significantly higher
prevalence of the 4 allele among poor responders and of the 2
and 3 alleles among good responders. Subjects with an 4
allele had a significantly smaller decrease in LDL-C on
atorvastatin than did those with 2 or 3 alleles. Ojala
et al31 also observed that 6
weeks of treatment with 40 mg/d lovastatin resulted in a
smaller reduction in total cholesterol in FH subjects with
an E3/4 phenotype compared with those with an E3/3
phenotype (22.6% versus 27.4%,
P=0.023), although this
difference was no longer significant after 12 weeks of
treatment.
A possible mechanism whereby apoE polymorphism might
determine the response to statins comes from the work of Kesaniemi et
al,32 who measured
cholesterol absorption and synthesis in a group of
middle-aged Finns. Those with an 2 allele (E2/2, E2/3, or E2/4)
absorbed less and synthesized more cholesterol than did
those with an 3 allele (E3/3), whereas those with an 4
allele (E3/4 or E4/4) absorbed the most and synthesized the least.
In another Finnish study, compared with those with an 3 allele,
subjects with an 4 allele showed a more marked increase in LDL-C
after switching from a low cholesterol to a high
cholesterol diet, implying greater absorption of dietary
cholesterol.33
Because the prevalence of an 4 allele in the present study
was significantly higher among the poor responders (75%) than the good
responders (27%), we hypothesize that poor responders have a higher
efficiency of cholesterol absorption. Higher absorption
efficiency is equated with a higher uptake of chylomicron remnant
cholesterol by the liver, which, in turn, will downregulate
HMG CoA reductase activity because the enzyme is subject to feedback
regulation by cholesterol. This is in accord with the MVA
data, which indicate that the HMG CoA reductase is more downregulated
at baseline in the poor responders than in the good responders. We
conclude that in the poor responders, a genetically determined increase
in cholesterol absorption downregulates HMG CoA reductase,
as supported by the data of Miettinen et
al,18 and renders the enzyme
refractory to pharmacological inhibition. Although the lesser decrease
in LDL-C of poor responders might be ascribed to poor compliance, this
would not explain why their pretreatment MVA levels were significantly
lower than those of good responders.
How can we reconcile the marked changes in plasma LDL and MVA on the various treatment regimens with the relative lack of change in mononuclear leukocytes? Previous studies have shown good correlation between mRNA levels of HMG CoA reductase and LDL receptor in the liver and in mononuclear leukocytes.34 Contrary to these findings, the present findings demonstrated no significant changes in mononuclear leukocyte mRNA apart from a rise in LDL receptor mRNA levels in the good responders during combined treatment with atorvastatin and BAS. An increase in LDL degradation in vitro, indicative of increased expression of LDL receptors, has previously been documented in mononuclear leukocytes obtained from FH heterozygotes treated with a BAS.35 The apparent lack of response of mononuclear leukocyte HMG CoA reductase mRNA to inhibition (statin) and stimulation (BAS) in the present study could be ascribed to various causes. One difference between the present study and that of Powell and Kroon34 is that we used FH patients, whereas they studied non-FH individuals. Alternatively, the lack of significant change in HMG CoA reductase mRNA in the mononuclear leukocytes could reflect the extent to which atorvastatin is sequestered by the liver, resulting in the absence of any inhibitory activity in plasma on the morning after the dose of the previous night, as documented for lovastatin.36 Thus, plasma MVA seems to be a better index of changes in hepatic cholesterol synthesis during lipid-lowering drug therapy than is leukocyte HMG CoA reductase mRNA, at least in FH patients.
Studies by Stein and colleagues37 38 suggested that LDL-C reductions with simvastatin in patients with raised cholesterol and triglycerides were less than those seen in patients with hypercholesterolemia alone. However, in our FH patients, the difference between baseline triglyceride levels in the good and poor responders (2.5 versus 2.1 mmol/L) was statistically insignificant and cannot be invoked as the explanation for their variable response to statins.
Measurement of 7--OHC was undertaken to ascertain whether
statins could induce a decrease in bile acid synthesis by limiting the
availability of cholesterol, the substrate for
7--hydroxylase. Our previous data, obtained by using atorvastatin
(10 to 40 mg) daily, suggest that this would only occur under
circumstances in which bile acid synthesis has been therapeutically
upregulated.39 The levels of
7--OHC, a well-authenticated marker of bile acid synthesis, did not
differ significantly between the good and poor responders on
atorvastatin; hence, a differential effect on bile acid synthesis
cannot explain the variation in LDL response nor the differences in MVA
levels. The increase in 7--OHC after BAS was more marked in the poor
than in the good responders; this difference disappeared when they were
treated with atorvastatin and BAS in combination.
Finally, we could find no difference between the 2 groups in terms of CYP3A4 activity, which suggests that the rate of metabolism of atorvastatin did not differ significantly between good and poor responders. Thus, of the various factors we investigated, only a low basal rate of cholesterol synthesis differentiated the poor from the good responders. We suggest that upregulation of cholesterol synthesis by therapeutic inhibition of cholesterol absorption might enhance their response to statins.
Received September 7, 2000; accepted February 2, 2001.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Moorjani S, Roy M, Torres A, Betard C, Gagne C, Lambert M, Brun D, Davignon J, Lupien P. Mutations of low-density-lipoprotein-receptor gene, variation in plasma cholesterol, and expression of coronary heart disease in homozygous familial hypercholesterolaemia. Lancet. 1993;341:1303–1306.[Medline] [Order article via Infotrieve]
2.
Gudnason V, Day IN,
Humphries SE. Effect on plasma lipid levels of different classes of
mutations in the low-density lipoprotein receptor gene in patients with
familial hypercholesterolemia.
Arterioscler Thromb. 1994;14:1717–1722.
3. Goldstein JL, Brown MS. Regulation of the mevalonate pathway. Nature. 1990;343:425–430.[Medline] [Order article via Infotrieve]
4. Naoumova RP, Marais AD, Mountney J, Firth JC, Rendell NB, Taylor GW, Thompson GR. Plasma mevalonic acid, an index of cholesterol synthesis in vivo, and responsiveness to HMG-CoA reductase inhibitors in familial hypercholesterolaemia. Atherosclerosis. 1996;119:203–213.[Medline] [Order article via Infotrieve]
5. Leitersdorf E, Eisenberg S, Eliav O, Friedlander Y, Berkman N, Dann EJ, Landsberger D, Sehayek E, Meiner V, Wurm M, et al. Genetic determinants of responsiveness to the HMG-CoA reductase inhibitor fluvastatin in patients with molecularly defined heterozygous familial hypercholesterolemia. Circulation. 1993;87(suppl III):III-35–III-44.
6.
Karayan L, Qiu S,
Betard C, Dufour R, Roederer G, Minnich A, Davignon J, Genest J Jr.
Response to HMG CoA reductase inhibitors in heterozygous
familial hypercholesterolemia due to the 10-kb
deletion ("French Canadian mutation") of the LDL-receptor gene.
Arterioscler Thromb. 1994;14:1258–1263.
7. Jeenah M, September W, Graadt van Roggen F, de Villiers W, Seftel H, Marais D. Influence of specific mutations at the LDL-receptor gene locus on the response to simvastatin therapy in Afrikaner patients with heterozygous familial hypercholesterolaemia. Atherosclerosis. 1993;98:51–58.[Medline] [Order article via Infotrieve]
8. Kajinami K, Yagi K, Higashikata T, Inazu A, Koizumi J, Mabuchi H. Low-density lipoprotein receptor genotype-dependent response to cholesterol lowering by combined pravastatin and cholestyramine in familial hypercholesterolemia. Am J Cardiol. 1998;82:113–117.[Medline] [Order article via Infotrieve]
9. 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;25:967–973.[Medline] [Order article via Infotrieve]
10. Vuorio AF, Ojala JP, Sarna S, Turtola H, Tikkanen MJ, Kontula K. Heterozygous familial hypercholesterolaemia: the influence of the mutation type of the low-density-lipoprotein receptor gene and PvuII polymorphism of the normal allele on serum lipid levels and response to lovastatin treatment. J Intern Med. 1995;237:43–48.[Medline] [Order article via Infotrieve]
11. Sun XM, Patel DD, Knight BL, Soutar AK, the Familial Hypercholesterolaemia Regression Study Group. Influence of genotype at the low density lipoprotein (LDL) receptor gene locus on the clinical phenotype and response to lipid-lowering drug therapy in heterozygous familial hypercholesterolaemia. Atherosclerosis. 1998;136:175–185.[Medline] [Order article via Infotrieve]
12. Sijbrands EJ, Lombardi MP, Westendorp RG, Leuven JA, Meinders AE, Van der Laarse A, Frants RR, Havekes LM, Smelt AH. Similar response to simvastatin in patients heterozygous for familial hypercholesterolemia with mRNA negative and mRNA positive mutations. Atherosclerosis. 1998;136:247–254.[Medline] [Order article via Infotrieve]
13. 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;42:895–901.[Medline] [Order article via Infotrieve]
14. Ordovas JM, Lopez-Miranda J, Perez-Jimenez F, Rodriguez C, Park JS, Cole T, Schaefer EJ. Effect of apolipoprotein E and A-IV phenotypes on the low density lipoprotein response to HMG CoA reductase inhibitor therapy. Atherosclerosis. 1995;113:157–166.[Medline] [Order article via Infotrieve]
15. O’Malley JP, Illingworth DR. The influence of apolipoprotein E phenotype on the response to lovastatin therapy in patients with heterozygous familial hypercholesterolemia. Metabolism. 1990;39:150–154.[Medline] [Order article via Infotrieve]
16. De Knijff P, Stalenhoef AF, Mol MJ, Gevers Leuven JA, Smit J, Erkelens DW, Schouten J, Frants RR, Havekes LM. Influence of apo E polymorphism on the response to simvastatin treatment in patients with heterozygous familial hypercholesterolemia. Atherosclerosis. 1990;83:89–97.[Medline] [Order article via Infotrieve]
17. Berglund L, Wiklund O, Eggertsen G, Olofsson SO, Eriksson M, Linden T, Bondjers G, Angelin B. Apolipoprotein E phenotypes in familial hypercholesterolaemia: importance for expression of disease and response to therapy. J Intern Med. 1993;233:173–178.[Medline] [Order article via Infotrieve]
18.
Miettinen TA,
Strandberg TE, Gylling H. Noncholesterol sterols and
cholesterol lowering by long-term simvastatin
treatment in coronary patients: relation to basal serum
cholestanol. Arterioscler Thromb Vasc
Biol. 2000;20:1340–1346.
19. Scientific Steering Committee on behalf of the Simon Broome Register Group. Risk of fatal coronary heart disease in familial hypercholesterolaemia. BMJ. 1991;303:893–896.
20. Pappu AS, Illingworth DR. Contrasting effects of lovastatin and cholestyramine on low-density lipoprotein cholesterol and 24-hour urinary mevalonate excretion in patients with heterozygous familial hypercholesterolemia. J Lab Clin Med. 1989;114:554–562.[Medline] [Order article via Infotrieve]
21. Yoshida T, Honda A, Tanaka N, Matsuzaki Y, He B, Osuga T, Kobayashi N, Ozawa K, Miyazaki H. Simultaneous determination of mevalonate and 7 alpha-hydroxycholesterol in human plasma by gas chromatography-mass spectrometry as indices of cholesterol and bile acid biosynthesis.J Chromatogr. 1993;613:185–193.[Medline] [Order article via Infotrieve]
22. Naoumova RP, Cummings MH, Watts GF, Rendell NB, Taylor GW, Sonksen PH, Thompson GR. Acute hyperinsulinaemia decreases cholesterol synthesis less in subjects with non-insulin-dependent diabetes mellitus than in non-diabetic subjects. Eur J Clin Invest. 1996;26:332–340.[Medline] [Order article via Infotrieve]
23.
Axelson M, Aly A,
Sjovall J. Levels of 7 -hydroxy-4-cholesten-3-one in plasma reflect
rates of bile acid synthesis in man. FEBS
Lett. 1988;239:324–328.[Medline]
[Order article via Infotrieve]
24.
Axelson M,
Bjorkhem I, Reihner E, Einarsson K. The plasma level of 7
-hydroxy-4-cholesten-3-one reflects the activity of hepatic
cholesterol 7 -hydroxylase in man.
FEBS Lett. 1991;284:216–218.[Medline]
[Order article via Infotrieve]
25.
Sauter G, Berr F,
Beuers U, Fischer S, Paumgartner G. Serum concentrations of
7-hydroxy-4-cholesten-3-one reflect bile acid synthesis in humans.
Hepatology. 1996;24:123–126.[Medline]
[Order article via Infotrieve]
26. Boyum A. Isolation of mononuclear cells and granulocytes from human blood. Scand J Clin Lab Invest. 1968;97(suppl):77–89.
27.
McDowell IF,
Wisdom GB, Trimble ER. Apolipoprotein E phenotype determined by
agarose gel electrofocusing and immunoblotting.
Clin Chem. 1989;35:2070–2073.
28. Bourbon M. Identification of mutations in the low density lipoprotein-receptor gene of patients with heterozygous familial hypercholesterolaemia [master’s thesis]. London, England: University of London; 1997.
29. Tybjaerg-Hansen A, Gallagher J, Vincent J, Houlston R, Talmud P, Dunning AM, Seed M, Hamsten A, Humphries SE, Myant NB. Familial defective apolipoprotein B-100: detection in the United Kingdom and Scandinavia, and clinical characteristics of ten cases. Atherosclerosis. 1990;80:235–242.[Medline] [Order article via Infotrieve]
30. Zhiri A, Wellman-Bednawska M, Siest G. ELISA of 6-beta-hydroxycortisol in human urine: diurnal variations and effects of antiepileptic therapy. Clin Chim Acta. 1986;157:267–276.[Medline] [Order article via Infotrieve]
31. 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;230:397–405.[Medline] [Order article via Infotrieve]
32. Kesaniemi YA, Ehnholm C, Miettinen TA. Intestinal cholesterol absorption efficiency in man is related to apoprotein E phenotype. J Clin Invest. 1987;80:578–581.
33. 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;68:1215–1222.[Abstract]
34. Powell EE, Kroon PA. Low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl coenzyme A reductase gene expression in human mononuclear leukocytes is regulated coordinately and parallels gene expression in human liver. J Clin Invest. 1994;93:2168–2174.
35.
Sundberg EE,
Illingworth DR. Effects of hypolipidemic therapy on
cholesterol homeostasis in freshly isolated mononuclear
cells from patients with heterozygous familial
hypercholesterolemia.
Proc Natl Acad Sci
U S A. 1983;80:7631–7635.
36.
Hagemenas FC,
Illingworth DR. Cholesterol homeostasis in mononuclear
leukocytes from patients with familial
hypercholesterolemia treated with
lovastatin.
Arteriosclerosis. 1989;9:355–361.
37. Stein EA, Davidson MH, Dobs AS, Schrott H, Dujovne CA, Bays H, Weiss SR, Melino MR, Stepanavage ME, Mitchel YB, for the Expanded Dose Simvastatin US Study Group. Efficacy and safety of simvastatin 80 mg/day in hypercholesterolemic patients. Am J Cardiol. 1998;82:311–316.[Medline] [Order article via Infotrieve]
38. Stein E, Plotkin D, Bays H, Davidson M, Dujovne C, Korenman S, Stepanavage M, Mercuri M. Effects of simvastatin (40 and 80 mg/day) in patients with mixed hyperlipidemia. Am J Cardiol. 2000;86:406–411.[Medline] [Order article via Infotrieve]
39.
Naoumova RP,
O’Neill FH, Dunn S, Neuwirth CK, Taylor GW, Axelson M, Thompson GR.
Effect of inhibiting HMG-CoA reductase on 7
-hydroxy-4-cholesten-3-one, a marker of bile acid synthesis:
contrasting findings in patients with and without prior up-regulation
of the latter pathway. Eur J Clin
Invest. 1999;29:404–412.[Medline]
[Order article via Infotrieve]
This article has been cited by other articles:
 |
|
 |
|
  G. S. Saini, T. A. Wani, A. Gautam, B. Varshney, T. Ahmed, K. S. Rajan, K. K. Pillai, and J. K. Paliwal Validation of the LC-MS/MS method for the quantification of mevalonic acid in human plasma and determination of the matrix effect J. Lipid Res., October 1, 2006; 47(10): 2340 - 2345. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. S. Christidis, E. N. Liberopoulos, A. I. Kakafika, G. A. Miltiadous, M. Cariolou, E. S. Ganotakis, D. P. Mikhailidis, and M. S. Elisaf The effect of apolipoprotein e polymorphism on the response to lipid-lowering treatment with atorvastatin or fenofibrate. Journal of Cardiovascular Pharmacology and Therapeutics, September 1, 2006; 11(3): 211 - 221. [Abstract] [PDF]
|
|
|
|
 |
|
 X.-M. Sun, E. R. Eden, I. Tosi, C. K. Neuwirth, D. Wile, R. P. Naoumova, and A. K. Soutar Evidence for effect of mutant PCSK9 on apolipoprotein B secretion as the cause of unusually severe dominant hypercholesterolaemia Hum. Mol. Genet., May 1, 2005; 14(9): 1161 - 1169. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G.R. Thompson, F. O'Neill, and M. Seed Why some patients respond poorly to statins and how this might be remedied Eur. Heart J., February 1, 2002; 23(3): 200 - 206. [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||