Pharmacokinetics and biodistribution of squalene-containing emulsion adjuvant following intramuscular injection of H5N1 influenza vaccine in mice.

Squalene is a component of oil-in-water emulsion adjuvants developed for potential use in some influenza vaccines. The biodistribution of the squalene-containing emulsion adjuvant (AddaVax™) alone and as part of complete H5N1 vaccine was quantified in mechanistically and toxicologically relevant target tissues up to 336 h (14 days) following injection into quadriceps muscle. At 1 h, about 55% of the intramuscularly injected dose of squalene was detected in the local quadriceps muscles and this decreased to 26% at 48 h. Twenty-four hours after the injection, approximately 5%, 1%, and 0.6% of the injected dose was detected in inguinal fat, draining lymph nodes, and sciatic nerve, respectively. The peak concentration for kidney, brain, spinal cord, bone marrow, and spleen was each less than 1% of the injected dose, and H5N1 antigen did not significantly alter the biodistribution of squalene to these tissues. The area-under-blood-concentration curve (AUC) and peak blood concentration (Cmax) of squalene were slightly higher (20-25%) in the presence of H5N1 antigen. A population pharmacokinetic model-based statistical analysis identified body weight and H5N1 antigen as covariates influencing the clearance of squalene. The results contribute to the body of knowledge informing benefit-risk analyses of squalene-containing emulsion vaccine adjuvants.

2,3-Oxidosqualene cyclase protects liver cells from the injury of intermittent hypoxia by regulating lipid metabolism.

PURPOSE: 2,3-Oxidosqualene cyclase (OSC), an important enzyme of cholesterol biosynthesis, catalyzes the highly selective cyclization of 2,3-monoepoxysqualene to lanosterol. Intermittent hypoxia (IH) is a hallmark feature in obstructive sleep apnea (OSA) which is increasingly recognized as an independent risk factor for liver injury. The aim of this study was to determine the effect of IH on OSC expression and evaluate the role of OSC in the IH-induced apoptosis in hepatic cell line human liver cell (HL-02). METHODS: HL-02 cells were exposed to normoxia or IH. Cell Counting Kit-8 (CCK-8) assay was used to value cell proliferation, and flow cytometry was used to determine cell apoptosis. The expression of OSC messenger RNA (mRNA) was evaluated by quantitative real-time PCR, and the expression of OSC protein was determined by Western blot. To further investigate the function of OSC in IH-induced apoptosis, oxidosqualene cyclase-enhanced green fluorescence protein (OSC-EGFP) plasmid was constructed to over-express OSC protein. Triglyceride content in HL-02 cells was analyzed by oil red staining or Triglyceride Quantification Kit. RESULTS: We found that IH inhibited HL-02 cell proliferation and accelerated cell apoptosis. IH decreased OSC expression, and over-expression of OSC could protect HL-02 cells against the IH-induced hepatic cell injury. Moreover, over-expression of OSC could attenuate IH-induced cellular triglyceride accumulation. CONCLUSIONS: These findings suggest that OSC are involved in IH-induced hepatic cell injury. These results may contribute to the further understanding of the mechanism underlying the liver injury in OSA patients.

A first-generation physiologically based pharmacokinetic (PBPK) model of alpha-tocopherol in human influenza vaccine adjuvant.

Alpha (α)-tocopherol is a component of a new generation of squalene-containing oil-in-water (SQ/W) emulsion adjuvants that have been licensed for use in certain influenza vaccines. Since regulatory pharmacokinetic studies are not routinely required for influenza vaccines, the in vivo fate of this vaccine constituent is largely unknown. In this study, we constructed a physiologically based pharmacokinetic (PBPK) model for emulsified α-tocopherol in human adults and infants. An independent sheep PBPK model was also developed to inform the local preferential lymphatic transfer and for the purpose of model evaluation. The PBPK model predicts that α-tocopherol will be removed from the injection site within 24h and rapidly transfer predominantly into draining lymph nodes. A much lower concentration of α-tocopherol was estimated to peak in plasma within 8h. Any systemically absorbed α-tocopherol was predicted to accumulate slowly in adipose tissue, but not in other tissues. Model evaluation and uncertainty analyses indicated acceptable fit, with the fraction of dose taken up into the lymphatics as most influential on plasma concentration. In summary, this study estimates the in vivo fate of α-tocopherol in adjuvanted influenza vaccine, may be relevant in explaining its immunodynamics in humans, and informs current regulatory risk-benefit analyses.

Cholesterol precursors: more than mere markers of biosynthesis.

PURPOSE OF REVIEW: Circulating levels of cholesterol precursors in the body have proven their value over the years as indicators of in-vivo cholesterol synthesis. However, there is growing interest in their potential as markers of various disease states. The purpose of this review is to evaluate current literature on cholesterol precursors as disease markers. RECENT FINDINGS: Firstly, we focus on studies linking circulating squalene with the risk of cardiovascular disease. Secondly, we explore the interplay between cholesterol precursors (7-dehydrocholesterol and desmosterol) and the enzymes that act upon them (DHCR7 and DHCR24) in the context of liver disease. For instance, recent findings indicate that circulating desmosterol is elevated in nonalcoholic steatohepatitis. This may be linked to this regulatory cholesterol precursor being produced in and effluxed from hepatocytes, or alternatively from lipid-laden hepatic macrophages (Kupffer cells), which play an important role in the cause of nonalcoholic steatohepatitis. Desmosterol is also implicated in Hepatitis C virus replication, and hence may also be involved in viral fatty liver disease, possibly contributing to virus pathogenicity and/or host defense. Furthermore, there is increasing evidence that the activity of DHCR7 may affect chronic liver diseases by influencing vitamin D levels. SUMMARY: Beyond their accepted application as markers of cholesterol synthesis, cholesterol precursors have potential both as disease indicators, and for providing deeper insights into the disease process.

Elevated serum squalene and cholesterol synthesis markers in pregnant obese women with gestational diabetes mellitus.

We examined serum cholesterol synthesis and absorption markers and their association with neonatal birth weight in obese pregnancies affected by gestational diabetes mellitus (GDM). Pregnant women at risk for GDM (BMI >30 kg/m²) were enrolled from maternity clinics in Finland. GDM was determined from the results of an oral glucose tolerance test. Serum samples were collected at six time-points, one in each trimester of pregnancy, and at 6 weeks, 6 months, and 12 months postpartum. Analysis of serum squalene and noncholesterol sterols by gas-liquid chromatography revealed that in subjects with GDM (n = 22), the serum Δ8-cholestenol concentration and lathosterol/sitosterol ratio were higher (P < 0.05) than in the controls (n = 30) in the first trimester, reflecting increased cholesterol synthesis. Also, subjects with GDM had an increased ratio of squalene to cholesterol (100 × µmol/mmol of cholesterol) in the second (11.5 ± 0.5 vs. 9.1 ± 0.5, P < 0.01) and third (12.1 ± 0.8 vs. 10.0 ± 0.7, P < 0.05) trimester. In GDM, the second trimester maternal serum squalene concentration correlated with neonatal birth weight (r = 0.70, P < 0.001). In conclusion, in obesity, GDM associated with elevated serum markers of cholesterol synthesis. Correlation of maternal serum squalene with neonatal birth weight suggests a potential contribution of maternal cholesterol synthesis to newborn weight in GDM.

Familial combined hyperlipidemia is associated with alterations in the cholesterol synthesis pathway.

OBJECTIVE: Familial combined hyperlipidemia (FCH) is a common familial lipid disorder characterized by increases in plasma total cholesterol, triglyceride, and apolipoprotein B-100 levels. In light of prior metabolic and genetic research, our purpose was to ascertain whether FCH cases had significant abnormalities of plasma markers of cholesterol synthesis and absorption as compared to unaffected kindred members. METHODS AND RESULTS: Plasma levels of squalene, desmosterol, and lathosterol (cholesterol synthesis markers) and campesterol, sitosterol, and cholestanol (cholesterol absorption markers) were measured by gas-liquid chromatography in 103 FCH patients and 240 normolipidemic relatives (NLR). Squalene, desmosterol, and lathosterol levels were 6% (0.078), 31%, (P<0.001) and 51% (P<0.001) higher in FCH as compared to NLR, and these differences were especially pronounced in women. An interaction with obesity was also noted for a subset of these markers. We did not observe any apparent differences for the cholesterol absorption markers among FCH patients and NLR. CONCLUSIONS: Our data indicate that both men and women with FCH have alterations in the cholesterol synthesis pathway, resulting in 51% higher levels of lathosterol (and additionally desmosterol in women). Plasma levels of the cholesterol precursor sterol squalene were only slightly increased (6%), suggesting enhanced conversion of squalene to lathosterol in this disorder.

Insulin sensitivity regulates cholesterol metabolism to a greater extent than obesity: lessons from the METSIM Study.

Cholesterol synthesis is upregulated and absorption downregulated in insulin resistance and in type 2 diabetes. We investigated whether alterations in cholesterol metabolism are observed across the glucose tolerance status, from normoglycemia through impaired glucose tolerance to type 2 diabetes, in 781 randomly selected men 45 to 70 years of age from a population-based Metabolic Syndrome in Men Study. Cholesterol metabolism was assayed using surrogate serum markers, squalene, and noncholesterol sterols. The study population was classified into subgroups according to glucose tolerance as follows: normoglycemia, impaired fasting glucose, impaired glucose tolerance, and type 2 diabetes. LDL cholesterol did not differ between the groups. Cholesterol synthesis markers were lowest and absorption markers highest in normoglycemia. Sitosterol was lower in subjects with impaired fasting glucose compared with normoglycemic subjects (113 +/- 7 vs. 136 +/- 3 10(2) mumol/mmol of cholesterol, P < 0.05). LDL cholesterol was not associated with lathosterol/sitosterol ratio, a marker of cholesterol metabolism. Peripheral insulin sensitivity evaluated by the Matsuda index was associated with the lathosterol/sitosterol ratio in the entire population (r = -0.457, P < 0.001) and with that of lathosterol/cholestanol independently of obesity. In conclusion, cholesterol metabolism was altered already from subjects with impaired fasting glucose. Upregulated cholesterol synthesis was associated with peripheral insulin resistance independent of obesity.

Plant stanol ester spreads as components of a balanced diet for pregnant and breast-feeding women: evaluation of clinical safety.

Clinical safety of consuming plant stanol ester spreads during pregnancy and lactation, the impact on maternal and infant serum and breast-milk cholesterol and the ratios (micromol/mmol of cholesterol) of synthesis and absorption markers were evaluated. Pregnant women (n 21) were randomised to control and dietary intervention groups, the intervention including advice to follow a balanced diet and to consume spreads enriched with plant stanol esters. Participants were followed during and after pregnancy and their infants up to 1 year of age. A mean 1.1 (sd 0.4) g consumption of plant stanols during pregnancy and 1.4 (sd 0.9) g 1 month post-partum increased sitostanol and the markers for cholesterol synthesis, lathosterol, lathosterol/campesterol and lathosterol/sitosterol, and reduced a marker for cholesterol absorption, campesterol, in maternal serum. In breast milk, desmosterol was lower in the intervention group, while no differences were detected between the groups in infants' serum. Plant stanol ester spread consumption had no impact on the length of gestation, infants' growth or serum beta-carotene concentration at 1 and 6 months of age, but the cholesterol-adjusted serum beta-carotene concentration was lowered at 1 month in the intervention group. Plant stanol ester spread consumption appeared safe in the clinical setting, except for potential lowering of infants' serum beta-carotene concentration, and was reflected in the markers of cholesterol synthesis and absorption in mothers' serum, encouraging further studies in larger settings.

Effect of gestational diabetes mellitus on newborn cholesterol metabolism.

BACKGROUND AND AIMS: Impaired glucose metabolism during pregnancy may associate with changes in fetal cholesterol metabolism. We investigated if gestational diabetes mellitus (GDM) affects newborn cholesterol metabolism as determined by cord blood squalene and non-cholesterol sterols. Furthermore, we examined potential correlations between cord blood and maternal serum non-cholesterol sterols. METHODS: Pregnant women at risk for GDM (BMI>30 kg/m2) were enrolled from maternity clinics in Finland. GDM was determined from the results of an oral glucose tolerance test. Serum samples were taken in the third trimester of pregnancy, and cord blood samples collected from their newborns at birth. Squalene and non-cholesterol sterols were analyzed from serum and cord blood by gas liquid chromatography. All women with GDM were in good glycaemic control. RESULTS: The ratios of squalene and non-cholesterol sterols to cholesterol (100 × µmol/mmol of cholesterol) in cord blood did not differ between the infants born to mothers with GDM (n = 15) or mothers with normal glucose tolerance (n = 13). The ratios of sitosterol and campesterol to cholesterol in the cord blood correlated with the corresponding maternal serum ratios (r = 0.70, p < 0.0001) in both groups. CONCLUSIONS: In obese women under good glycaemic control, GDM did not affect newborn cholesterol metabolism. Cord blood sitosterol and campesterol ratios to cholesterol correlated with the corresponding maternal serum ratios thus potentially reflecting maternal-fetal cholesterol transport.

Simultaneous determination of gemcitabine and gemcitabine-squalene by liquid chromatography-tandem mass spectrometry in human plasma.

Gemcitabine-squalene is a new prodrug that self-organizes in water forming nanoassemblies. It exhibits better anti-cancer properties in vitro and in vivo than gemcitabine. A liquid chromatography/tandem mass spectrometry assay of gemcitabine-squalene and gemcitabine was developed in human plasma in order to quantitate gemcitabine and its squalene conjugate. After protein precipitation with acetonitrile/methanol (90/10, v/v), the compounds were analyzed by reversed-phase high performance liquid chromatography and detected by tandem mass spectrometry using multiple reaction monitoring. The method was linear over the concentration range of 10-10,000 ng/ml of human plasma for both compounds with an accuracy lower than 10.4% and a precision below 14.8%. The method showed a lower limit of quantitation of 10 ng/ml of human plasma for dFdC and dFdC-SQ. A preliminary in vivo study in mice was shown as application of the method as no significant difference between human and mice plasma for the analysis of dFdC and dFdC-SQ was demonstrated.

Cholesterol absorption and synthesis in children with type 1 diabetes.

OBJECTIVE: The levels of the surrogate markers of cholesterol absorption (cholestanol and plant sterols) and synthesis (cholesterol precursors) in serum have suggested that in adult type 1 diabetes, cholesterol absorption is high and synthesis is low compared with type 2 diabetic or control subjects. Accordingly, these findings were further studied in children with type 1 diabetes. RESEARCH DESIGN AND METHODS: Forty-eight children with diabetes were compared with 79 age- and sex-matched control subjects. The serum ratios of cholesterol absorption and synthesis markers were measured with gas-liquid chromatography. The study population was divided into triads (combining the two lowest triads) by serum cholestanol ratios of the control subjects indicating low to high cholesterol absorption efficiency. RESULTS: The ratios of the absorption and synthesis markers were similar in case and control subjects, and they were negatively related to each other in control subjects, being less consistent in diabetic patients. Thus, high cholesterol absorption was associated with low synthesis. Plant sterol ratios increased significantly with increasing cholestanol triads in both groups, but the values in the lowest triads were higher in case versus control subjects. CONCLUSIONS: Homeostasis between cholesterol absorption and synthesis is maintained in control children and somewhat less consistently in those with diabetes. The higher plant sterol ratios in diabetic versus control subjects in the lowest cholestanol triads suggest that cholesterol absorption is higher in children with diabetes versus control subjects but only within the range of low cholesterol absorption.

Cholesterol absorption and synthesis in pediatric kidney, liver, and heart transplant recipients.

BACKGROUND: Hypercholesterolemia after organ transplantation is common. Previously, we observed higher serum total cholesterol (TC) concentrations in our pediatric kidney than liver or heart transplant recipients. To find an explanation to the observed difference, our kidney recipients' cholesterol synthesis and absorption efficiency was compared to those of liver and heart recipients. METHODS: Serum noncholesterol sterol ratios (10 x mmol to the mol of TC, surrogate estimates of hepatic cholesterol synthesis and intestinal absorption) were studied in 50 pediatric kidney, 25 liver and 12 heart transplant recipients without diabetes or cholestasis, and in 29 controls. RESULTS: The kidney recipients had lower Delta-cholesterol (P=0.031), similar lathosterol and higher desmosterol ratios (markers of cholesterol synthesis) (P=0.020), and similar campesterol and sitosterol ratios (markers of cholesterol absorption) when compared to the controls. The liver recipients had lower campesterol ratios than the kidney recipients and controls (P=0.002). Glomerular filtration rates were not associated with the ratios of noncholesterol sterols. Multivariate analysis showed markers of cholesterol synthesis to be lower and absorption to be higher in the kidney than the liver or the heart transplant recipients. Weight-adjusted dosages of immunosuppressive agents were associated with some ratios of noncholesterol sterols and cholestanol though these varied between the transplant recipient groups. CONCLUSIONS: Serum TC concentration in kidney recipients was not significantly associated with absorption efficiency or synthesis of cholesterol, though kidney transplantation was associated with low synthesis and high absorption efficiency of cholesterol. Immunosuppressive therapy with cyclosporine and methylprednisolone may modulate absorption efficiency and synthesis of cholesterol.

Postprandial behavior of plasma squalene and non-cholesterol sterols in men with varying cholesterol absorption.

BACKGROUND: The purpose of this study was to investigate, whether low vs. high absorption of cholesterol affects the postprandial lipid clearance (squalene as the surrogate marker) and postprandial cholesterol metabolism evaluated with plasma levels of cholesterol absorption (cholestanol and plant sterols) and synthesis markers (desmosterol and lathosterol). METHODS: Fifteen normo- or mildly hypercholesterolemic men were divided into low or high cholesterol absorbers on the basis of plasma cholestanol to cholesterol ratio and they volunteered to an oral fat load test containing fat 35 g/m(2) body surface. RESULTS: Plasma squalene to cholesterol ratio did not differ between the groups throughout the postprandial follow-up of 8 h. The level differences in the plasma absorption and synthesis markers seen at baseline remained between the groups, so that in high absorbers the absorption markers remained high and synthesis markers low throughout the postprandial follow-up. The postprandial response curves of desmosterol (p<0.05) and lathosterol (p=0.052) to cholestanol decreased linearly in the low, but not in the high absorbers. CONCLUSIONS: Low vs. high absorption of cholesterol does not affect the first 8-h postprandial lipid clearance. The metabolic profile of cholesterol is maintained postprandially. The postprandial decrease in cholesterol synthesis differs in low vs. high absorbers especially through the desmosterol pathway.

Effects of plant stanol esters supplied in a fat free milieu by pastilles on cholesterol metabolism in colectomized human subjects.

BACKGROUND AND AIM: Nutritional products containing fat-soluble phytosterol esters for serum cholesterol lowering have traditionally been oil-based. Their cholesterol-lowering efficacy when provided by low-fat vehicles with a diet of normal fat content is questionable. The aims of the present study were to find out whether 1-week consumption of plant stanol esters in pastilles alters absorption percentage of labeled esterified and free cholesterol and fecal elimination of sterols, including phytosterols (n = 9), and to define the impact of dietary fat on intestinal sterol ester hydrolysis (n = 8) in colectomized human subjects. METHODS AND RESULTS: Levels of lipoprotein cholesterol and triacylglycerols, non-cholesterol sterols and squalene in serum, neutral sterols, non-cholesterol sterols, fat and bile acids in feces, cholesterol absorption efficiency and cholesterol synthesis were analyzed at baseline and at the end of the treatment period. Analyses of esterified and free cholesterol and phytosterols were performed during diets with normal and low-fat content. Serum levels of total and low-density lipoprotein cholesterol decreased by 9% and 14%, respectively (P < 0.01 for both), and absorption of 3H-esterified and 14C-free cholesterol decreased in proportion to baseline values (r = -0.58, P < 0.05) by over 40% (P < 0.01) in colectomized patients with stanol ester pastilles. Fecal elimination of cholesterol was increased by about 35% and almost 60% of campestanol and sitostanol esters were hydrolyzed during their transit in gastrointestinal tract when consumed with a normal fat diet (mean daily fat 93 +/- 13g ) for 1 week. The hydrolysis of plant stanol esters was more pronounced with a normal than with a low-fat diet (70% versus 40%, P < 0.001). CONCLUSIONS: We conclude that plant stanol esters provided in fat free milieu exert favourable effects on serum lipid profile by decreasing absorption of cholesterol in colectomized human subjects, even though the intestinal hydrolysis of plant stanol esters is weaker on low than normal fat diet.

Fate of intravenously administered squalene in the rat.

To investigate the metabolism of serum squalene rats were given intravenously serum or isolated lipoprotein containing [3H]squalene and [14C]cholesterol. Labeled squalene disappeared multiexponentially from serum and the rate of disappearance was consistently faster than for [14C]cholesterol. [3H]Squalene given by injection did not accumulate in tissues, but was rapidly cyclized to sterols, resulting in the labeling of serum methyl sterols and cholesterol as well as biliary and fecal sterols and bile acids. Independent of the form of administration, the fractional conversion of squalene to serum cholesterol was less than one. This was caused by the fact that [3H]squalene was eliminated initially more rapidly than serum [14C]cholesterol in the feces and was converted to a greater extent than serum cholesterol to bile acids, whereas both labels were eliminated in parallel as neutral sterols. The results support the role of newly synthesized hepatic cholesterol as the preferred substrate of bile acid synthesis.

Independent association of serum squalene and noncholesterol sterols with coronary artery disease in postmenopausal women.

OBJECTIVES: The purpose of the study was to investigate whether cholesterol metabolism is associated with coronary artery disease (CAD) in postmenopausal women. BACKGROUND: Although hypercholesterolemia, a predominant risk factor of CAD, is related to cholesterol metabolism, the association between cholesterol metabolism and CAD is not well known. METHODS: In addition to conventional coronary risk factors, fasting serum squalene, delta8-cholestenol, desmosterol, lathosterol (indicators of cholesterol synthesis), cholestanol, campesterol and sitosterol (indicators of cholesterol absorption) were measured in 48 50- to 55-year-old consecutive women with angiographically verified CAD and in 61 age-matched healthy controls. RESULTS: The coronary patients had elevated ratios of squalene (p < 0.001), desmosterol (p = 0.005), campesterol (p = 0.028) and sitosterol (p = 0.022) to cholesterol, but had lower respective lathosterol value (p = 0.041) compared with the controls, despite similar serum cholesterol levels. Adjusted for age, body mass index, family history of CAD, smoking, hypertension, serum triglycerides, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol level and glycosylated hemoglobin A1c% (GHbA1c), the ratios of squalene (odds ratio, 1.36; 95% confidence interval, 1.17 to 1.57), lathosterol (0.98; 0.97 to 0.99), campesterol (1.01; 1.00 to 1.01) and sitosterol (1.01; 1.00 to 1.03) were significantly associated with the risk of CAD. In addition, family history of CAD and GHbA1c% were also independently related to the presence of CAD. CONCLUSIONS: The results suggest that women with elevated ratios of serum squalene, campesterol and sitosterol to cholesterol and low respective lathosterol values have enhanced risk for CAD. Thus, enhanced absorption and reduced synthesis of cholesterol may be related to coronary atherosclerosis.

Cholesterol absorption, synthesis, and fecal output in postmenopausal women with and without coronary artery disease.

Hypercholesterolemia is a prominent risk factor for coronary artery disease (CAD), yet cholesterol metabolism has not been evaluated in women with CAD. The objective of this study was to determine the interrelations of CAD, serum squalene and sterols, and cholesterol metabolism with each other in postmenopausal women. For this purpose, we measured serum squalene and sterols and fecal steroids (cholesterol and bile acids) and squalene by gas-liquid chromatography and evaluated cholesterol absorption and synthesis in postmenopausal women with CAD (n=29) and age-matched controls (n=20). On similar dietary lipid intake, the cholesterol absorption efficiency and mean serum cholesterol level were comparable, but the squalene-to-cholesterol ratio was higher in cases than in controls. The presence of CAD was inversely associated with fecal total steroids (logistic regression coefficient beta/SE=-2.11, P=0.04) and cholesterol synthesis (beta/SE=-2.14, P=0.04) and turnover (beta/SE=-2.19, P=0.03) after adjustment for dietary cholesterol, family history of CAD, smoking, low and high density lipoprotein cholesterol, and serum triglyceride levels. A high serum squalene ratio was not related to cholesterol synthesis but was inversely related to fecal squalene excretion, which was lower in cases than in controls. In conclusion, the presence of CAD in postmenopausal women is independently associated with altered cholesterol metabolism, as reflected by low synthesis and inefficient elimination of cholesterol.

Low synthesis and high absorption of cholesterol characterize type 1 diabetes.

OBJECTIVE: Streptozotocin-induced type 1 diabetes in experimental animals inhibits cholesterol synthesis and increases cholesterol absorption. In contrast to human type 2 diabetes, virtually no information is available on cholesterol synthesis and absorption in type 1 diabetes. RESEARCH DESIGN AND METHODS: We studied the variables of cholesterol metabolism in 27 patients with type 1 diabetes and in 10 patients with type 2 diabetes matched for body weight, using cholesterol precursor sterol ratios to cholesterol as surrogate markers of synthesis, and those of cholestanol and plant sterols of cholesterol absorption. Glucose control was good in all subjects. RESULTS: Total and HDL cholesterol and LDL triglycerides were higher in type 2 than in type 1 diabetes. Serum sterols, measured also in VLDL, intermediate-density lipoprotein (IDL), LDL, and HDL, were transported up to >90% by LDL and HDL in type 1 diabetes. The ratios of all absorption sterols in serum and in each lipoprotein were higher, and those of the synthesis markers, especially cholestenol and lathosterol, were lower in type 1 than in type 2 diabetes. CONCLUSIONS: In contrast to type 2 diabetes, the findings in type 1 diabetes could be related to low expression of ABC G/5 G/8 genes, resulting in high absorption of cholesterol and sterols in general and low synthesis of cholesterol.

Cholesterol metabolism in diabetes: the effect of insulin on the kinetics of plasma squalene.

The turnover of isotopically labeled squalene formed in plasma from [14C]mevalonate has been used to measure cholesterol synthesis in diabetics over a 7-h period. Five patients were studied while in poor diabetic control (mean daytime glycemia, 349 mg/dl) and at a later date once improved control was established by multiple daily insulin injections (mean glycemia, 175 mg/dl). This degree of diabetic control resulted in an increase in the fractional conversion of [14C]mevalonic acid to [14C]squalene from 55.2 +/- 1% to 67.5 +/- 4% (P less than 0.025). These data together with the area under the squalene specific activity curve yeild an estimated rate of cholesterol synthesis based on the likely assumption that mevalonate pool size did not decrease. Insulinization increased this calculated mean rate of cholesterol synthesis from 961 +/- 151 to 1206 +/- 223 mg/day (P less than 0.025). The use of squalene kinetics to evaluate changes in cholesterol synthesis deserves further study, particularly in metabolically unstable states such as diabetes in which conventional methods for measuring cholesterol synthesis are difficult to apply and to interpret.

Reduced triglyceridemia and increased high density lipoprotein cholesterol levels after treatment with acipimox, a new inhibitor of lipolysis.

Acipimox (5-methylpyrazine carboxylic acid 4-oxide) is a new inhibitor of lipolysis with long-lasting activity, whose plasma lipid lowering potential was demonstrated in early clinical trials. The hypolipidemic effect of acipimox was investigated in two double-blind cross-over trials versus placebo. The first trial, carried out in 12 type IV patients, showed a significant triglyceride lowering effect (-35%) following 4 weeks of drug administration at a 250 tid dose. The same regimen, maintained for 9 weeks in 18 type IIA patients, failed to induce a significant reduction of total cholesterolemia. However, in 10 subjects, in whom lipoprotein cholesterol fractionation was carried out, a significant reduction of low density and highly significant increase in high density lipoprotein cholesterol levels (respectively -11% and +20%) were observed.