Use of cholesterol precursors to assess changes in cholesterol synthesis under non-steady-state conditions

Determining the mechanisms of dietary turnip rapeseed oil on cholesterol metabolism in men with metabolic syndrome

We have earlier reported the reduction of total cholesterol, low-density lipoprotein (LDL) cholesterol and oxidized LDL caused by short-term modification of diet with cold-pressed turnip rapeseed oil (CPTRO) instead of butter. The aim of this supplementary study was to determine whether the beneficial effects resulted from altered cholesterol metabolism during the intervention.Thirty-seven men with metabolic syndrome (MetS) completed an open, randomized and balanced crossover study. Subjects' usual diet was supplemented with either 37.5 g of butter or 35 mL of CPTRO for 6-8 weeks. Otherwise normal dietary habits and physical activity were maintained without major variations. Serum non-cholesterol sterols were assayed with gas-liquid chromatography and used as surrogate markers of whole-body cholesterol synthesis and absorption efficiency. Serum proprotein convertase subtilisin/kexin type 9 (PCSK9) concentration was analyzed with Quantikine ELISA Immunoassay. Serum cholesterol synthesis markers and serum cholestanol (absorption marker), all as ratios to cholesterol, did not differ between the periods. Serum campesterol and sitosterol ratios to cholesterol were significantly increased after the administration of CPTRO resulting from the increased intake of 217 mg/day of plant sterols in CPTRO. Serum PCSK9 concentration did not differ between CPTRO and butter periods.The reduction in serum cholesterol by 7.2% after consumption of rapeseed oil could not be explained by changes in cholesterol absorption, synthesis or PCSK9 metabolism in MetS.ClinicalTrials.gov NCT01119690.

Geranylgeraniol prevents the simvastatin-induced PCSK9 expression: Role of the small G protein Rac1

Statins are known to increase the plasma levels of proprotein convertase subtilisin kexin type 9 (PCSK9) through the activation of the sterol responsive element binding protein (SREBP) pathway due to the inhibition of cholesterol biosynthesis. In the present study, we explore a possible role of the prenylated proteins on the statin-mediated PCSK9 induction in Caco-2 cells. Simvastatin (40μM) induced both PCSK9 mRNA (10.7±3.2 fold) and protein (2.2±0.3 fold), after 24h incubation. The induction of PCSK9 mRNA was partially, but significantly, prevented by the co-incubation with mevalonate (MVA), farnesol (FOH) and geranylgeraniol (GGOH), while a complete prevention was observed on secreted PCSK9, evaluated by ELISA assay. Under the same experimental conditions, MVA, GGOH, but not FOH, prevented the activation of the PCSK9 promoter by simvastatin in a SRE-dependent manner. Simvastatin reduced by -35.7±15.2% the Rac1-GTP levels, while no changes were observed on RhoA- and Cdc42-GTP. This effect was prevented by MVA and GGOH. A Rac inhibitor, and N17Rac1 dominant negative mutant, significantly induced PCSK9 levels, and a suppression of Rac1 expression by siRNA, counteract the effect of simvastatin on the induction of PCSK9 mRNA. Finally, simvastatin, and Rac inhibitor inhibited the nuclear translocation of STAT3 and its knock-down by siRNA increased significantly the susceptibility of Caco-2 to simvastatin on PCSK9 expression. Taken together, the present study reveal a direct role of Rac1 on simvastatin-mediated PCSK9 expression via the reduction of STAT3 nuclear translocation.

Clinical utility of serum markers of cholesterol absorption and synthesis

PURPOSE OF REVIEW

The serum noncholesterol sterols are widely used today in clinical lipid research as surrogate markers of cholesterol absorption and synthesis. Their applicability and some aspects related to their analysis, use, and interpretations are discussed.

RECENT FINDINGS

The serum markers of cholesterol metabolism have been carefully validated in several populations and during different interventions. If the homeostasis between cholesterol absorption and synthesis is lost, the markers cannot be used as surrogates. The markers have been applied in large population and cohort studies to find out how cholesterol metabolism is related to coronary artery disease. Most of the large studies suggested that increased levels of the markers of cholesterol absorption may conceivably be a risk factor for coronary artery disease.

SUMMARY

Results even from large population studies vary from population to population. The large number of factors, which interfere with cholesterol metabolism, such as age, sex, BMI, diet, health status, medication, and genetic background, and differences in the analysis methods of the serum markers should be taken into consideration when interpreting the data.

De novo lipogenesis and cholesterol synthesis in humans with long-standing type 1 diabetes are comparable to non-diabetic individuals

BACKGROUND

Synthesis of lipid species, including fatty acids (FA) and cholesterol, can contribute to pathological disease. The purpose of this study was to investigate FA and cholesterol synthesis in individuals with type 1 diabetes, a group at elevated risk for vascular disease, using stable isotope analysis.

METHODS

Individuals with type 1 diabetes (n = 9) and age-, sex-, and BMI-matched non-diabetic subjects (n = 9) were recruited. On testing day, meals were provided to standardize food intake and elicit typical feeding responses. Blood samples were analyzed at fasting (0 and 24 h) and postprandial (2, 4, 6, and 8 hours after breakfast) time points. FA was isolated from VLDL to estimate hepatic FA synthesis, whereas free cholesterol (FC) and cholesteryl ester (CE) was isolated from plasma and VLDL to estimate whole-body and hepatic cholesterol synthesis, respectively. Lipid synthesis was measured using deuterium incorporation and isotope ratio mass spectrometry.

RESULTS

Fasting total hepatic lipogenesis (3.91 ± 0.90% vs. 5.30 ± 1.22%; P = 0.41) was not significantly different between diabetic and control groups, respectively, nor was synthesis of myristic (28.60 ± 4.90% vs. 26.66 ± 4.57%; P = 0.76), palmitic (12.52 ± 2.75% vs. 13.71 ± 2.64%; P = 0.65), palmitoleic (3.86 ± 0.91% vs. 4.80 ± 1.22%; P = 0.65), stearic (5.55 ± 1.04% vs. 6.96 ± 0.97%; P = 0.29), and oleic acid (1.45 ± 0.28% vs. 2.10 ± 0.51%; P = 0.21). Postprandial lipogenesis was also not different between groups (P = 0.38). Similarly, fasting synthesis of whole-body FC (8.2 ± 1.3% vs. 7.3 ± 0.8%/day; P = 0.88) and CE (1.9 ± 0.4% vs. 2.0 ± 0.3%/day; P = 0.96) and hepatic FC (8.2 ± 2.0% vs. 8.1 ± 0.8%/day; P = 0.72) was not significantly different between diabetic and control subjects.

CONCLUSIONS

Despite long-standing disease, lipogenesis and cholesterol synthesis was not different in individuals with type 1 diabetes compared to healthy non-diabetic humans.

Cholesterol metabolism in active Crohn's disease

Hypocholesterolemia has been investigated as a typical feature of critical illness and is connected with poor prognosis. Crohn's disease is an inflammatory process and is associated with several metabolic disturbances. In recent decades clinical studies have established a link between lipid metabolism and systemic inflammation. In our study we examined the serum profile of cholesterol (total cholesterol, LDL- and HDL-cholesterol) and changes in the cholesterol absorption/synthesis process by determination of plasma non-cholesterol sterol (squalene, lathosterol, campesterol, sitosterol) concentrations. Serum concentrations of total cholesterol, LDL- and HDL-cholesterol and non-cholesterol sterols were evaluated in 24 patients with active Crohn's disease during a period of 28 days. We detected lower serum levels of total cholesterol (P < 0.001), LDL- and HDL-cholesterol (P < 0.05) in the patients with active Crohn's disease than in the control group. In addition, the patients had significantly lower plasma levels of lathosterol (P < 0.001) and higher concentrations of squalene, although without significant differences. A significant decrease of campesterol plasma levels (P < 0.001) was detected, but lower plasma concentrations of sitosterol were without statistical significance. The active phase of Crohn's disease is characterized by altered metabolism of lipids, mainly of cholesterol. Our results show abnormalities in plasma concentrations of non-cholesterol sterols and provide evidence that the process of cholesterol synthesis and absorption is altered in active Crohn's disease.

Determination of key intermediates in cholesterol and bile acid biosynthesis by stable isotope dilution mass spectrometry

For more than a decade, we have developed stable isotope dilution mass spectrometry methods to quantify key intermediates in cholesterol and bile acid biosynthesis, mevalonate and oxysterols, respectively. The methods are more sensitive and reproducible than conventional radioisotope (RI), gas-chromatography (GC) or high-performance liquid chromatography (HPLC) methods, so that they are applicable not only to samples from experimental animals but also to small amounts of human specimens. In this paper, we review the development of stable isotope dilution mass spectrometry for quantifying mevalonate and oxysterols in biological materials, and demonstrate the usefulness of this technique.

Lipid metabolism in active Crohn's disease: pre-results

BACKGROUND

Crohn's disease (CD) is a chronic relapsing disease. Especially acute period may be associated with metabolic disturbances. Alteration of lipid metabolism has been described in critically ill patients and hypocholesterolemia is associated with poor prognosis. The human organism acquires cholesterol by two principal processes - synthesis de novo, and absorption from the diet. It is possible to assess, using cholesterol synthesis markers (lathosterol) and cholesterol absorption markers (sitosterol, campesterol) the leading form of cholesterol acquisition.

AIM

The aim of this study is assess the association between the lipid profile in plasma and the plasma concentration of sterols in active CD patients and in control subjects.

METHOD

Routine laboratory tests, CDAI, lipid and non-cholesterol sterols plasma levels were performed on days 3, 14 and 28. The metabolic parameters have been compared with a control cohort of 100 healthy blood donors.

RESULTS

Presently, complete data for 8 patients are available The serum total cholesterol, LDL and HDL cholesterol, and triglyceride concentrations were lower in patients with acute Crohn's disease than in the control group. Moreover lathosterol, campesterol and sitosterol concentrations were lower, whereas squalene concentration was higher than in controls. As mentioned above, complete data are not currently available. Therefore statistical analysis has not been finished.

CONCLUSION

Our pre-results show substantial abnormalities in the concentrations of plasma lipids and non-cholesterol sterols, which are presented as markers of cholesterol requirement, in patients with acute CD.

Acute effects of pravastatin on cholesterol synthesis are associated with SLCO1B1 (encoding OATP1B1) haplotype *17

OBJECTIVE

The aim was to investigate whether polymorphisms in the SLCO1B1 gene, encoding the hepatic uptake transporter OATP1B1, influence the short-term effects of pravastatin on cholesterol synthesis.

METHODS

We determined plasma concentrations of lathosterol and cholesterol up to 12 h after intake of a single dose of 40 mg pravastatin in 41 healthy Caucasian subjects, in whom SLCO1B1 single nucleotide polymorphisms (SNP; 521T>C and -11187G>A) and haplotypes (*15B and *17) had been previously shown to be associated with considerably elevated plasma pravastatin levels.

RESULTS

The effects of pravastatin on plasma lathosterol concentration and lathosterol to cholesterol concentration ratio, which are established markers of the rate of cholesterol synthesis in vivo, were significantly smaller among the three heterozygous carriers of the SLCO1B1 *17 haplotype (containing the -11187G>A, 388A>G and 521T>C SNPs) as compared with non-carriers. Significant inverse relationships were found between pravastatin area under the concentration-time curve (AUC) values and effects of pravastatin on lathosterol and lathosterol to cholesterol ratio among the whole study population.

CONCLUSION

These results suggest that uptake of pravastatin into hepatocytes is impaired in carriers of the SLCO1B1 haplotype *17, resulting in higher plasma pravastatin concentrations but lower concentrations of pravastatin in hepatocytes and thereby in a smaller inhibitory effect on cholesterol synthesis. The cholesterol-lowering response to pravastatin may be impaired in carriers of the *17 haplotype.

Quantitative analysis of simvastatin and its β-hydroxy acid in human plasma using automated liquid–liquid extraction based on 96-well plate format and liquid chromatography-tandem mass spectrometry

An assay based on automated liquid-liquid extraction (LLE) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been developed and validated for the quantitative analysis of simvastatin (SV) and its beta-hydroxy acid (SVA) in human plasma. A Packard MultiProbe II workstation was used to convert human plasma samples collected following administration of simvastatin and quality control (QC) samples from individual tubes into 96-well plate format. The workstation was also used to prepare calibration standards and spike internal standards. A Tomtec Quadra 96-channel liquid handling workstation was used to perform LLE based on 96-well plates including adding solvents, separating organic from aqueous layer and reconstitution. SV and SVA were separated through a Kromasil C18 column (50 mm x 2 mm i.d., 5 microm) and detected by tandem mass spectrometry with a TurboIonspray interface. Stable isotope-labeled SV and SVA, 13CD(3)-SV and 13 CD(3)-SVA, were used as the internal standards for SV and SVA, respectively. The automated procedures reduced the overall analytical time (96 samples) to 1/3 of that of manual LLE. Most importantly, an analyst spent only a fraction of time on the 96-well LLE. A limit of quantitation of 50 pg/ml was achieved for both SV and SVA. The interconversion between SV and SVA during the 96-well LLE was found to be negligible. The assay showed very good reproducibility, with intra- and inter-assay precision (%R.S.D.) of less than 7.5%, and accuracy of 98.7-102.3% of nominal values for both analytes. By using this method, sample throughput should be enhanced at least three-fold compared to that of the manual procedure.

Deuterium uptake and plasma cholesterol precursor levels correspond as methods for measurement of endogenous cholesterol synthesis in hypercholesterolemic women

To assess the validity of two techniques used to measure human cholesterol synthesis, the rate of uptake of deuterium (D) into plasma free cholesterol (FC), and plasma cholesterol precursor (squalene, lanosterol, desmosterol and lathosterol) levels were compared in 14 women [65-71 yr with low density lipoprotein-cholesterol (LDL-C) > or = 3.36 mmol x L(-1)]. Subjects consumed each of six diets for 5-wk periods according to a randomized crossover design. The experimental diets included a baseline diet (39% energy as fat, 164 mg chol x 4.2 MJ(-1)) and five reduced-fat diets (30% of energy as fat), where two-thirds of the fat was either soybean oil; squeeze, tub or stick margarines; or butter. Fractional and absolute synthesis rates (FSR and ASR) of FC were determined using the deuterium incorporation (DI) method, while cholesterol precursor levels were measured using gas-liquid chromatography. Data were pooled across diets for each variable and correlation coefficients were calculated to determine if associations were present. There was good agreement among levels of the various cholesterol precursors. In addition, FSR in pools/d (p x d(-1)) and ASR in grams/d (g x d(-1)) were strongly associated with lathosterol (r= 0.72 and 0.71, P= 0.0001), desmosterol (r= 0.75 and 0.75, P = 0.0001), lanosterol (r = 0.67 and 0.67), and squalene (r = 0.69 and 0.68) when levels of the precursors were expressed as micromol x mmol(-1) C. Significant but lower correlations were observed between the D uptake and plasma cholesterol precursor levels when the latter were expressed in absolute amounts (micromol x L(-1)). The wide range of fatty acid profiles of the experimental diets did not influence the degree of association between methods. In conclusion, the DI method and levels of some cholesterol precursors correspond as methods for shortterm measurement of cholesterol synthesis.

Cholesterol synthesis is increased in mixed hyperlipidaemia

We showed previously that hypertriglyceridaemia, but not hypercholesterolaemia, is correlated with increases in cholesterol synthesis and apolipoprotein B secretion in patients with secondary hypertriglyceridaemia. The aim of the present study was to compare the rate of cholesterol synthesis, using fasting plasma mevalonic acid (MVA) as an index, in patients with primary mixed hyperlipidaemia (type IIb phenotype, n=45) and primary hypercholesterolaemia (type IIa phenotype, n=92). LDL cholesterol was significantly higher in types IIa (6.38+/-0.18 mmol/l) and IIb (5.89+/-0.25 mmol/l) compared to 40 normolipidaemic controls (2. 99+/-0.1 mmol/l, P<0.0001), whereas serum triglyceride was higher in type IIb (2.62 (range 2.2-3.0) mmol/l) than type IIa (1.22 (range 0. 85-1.60) mmol/l, P<0.001) and controls (0.90 (range 0.68-1.24) mmol/l, P<0.001). Similarly, MVA was higher in type IIb (7.0+/-0.46 ng/ml) than IIa (5.6+/-0.23 ng/ml, P<0.0) and controls (5.6+/-0.36 ng/ml, P<0.05). Plasma MVA correlated positively with serum triglyceride (r=0.22, P=0.004) and negatively with LDL cholesterol (r=-0.21, P=0.014). These results are in accordance with previous observations that VLDL-apolipoprotein B secretion and cholesterol synthesis are linked and demonstrate that the latter is increased in mixed hyperlipidaemia.