Alexander Cegan

Circulating Palmitoleate Strongly and Independently Predicts Insulin Sensitivity in Humans

OBJECTIVE We investigated whether palmitoleate, which prevents insulin resistance in mice, predicts insulin sensitivity in humans. RESEARCH DESIGN AND METHODS The fasting fatty acid pattern in the plasma free fatty acid (FFA) fraction was determined in 100 subjects at increased risk for type 2 diabetes. Insulin sensitivity was estimated during an oral glucose tolerance test (OGTT) at baseline and after 9 months of lifestyle intervention and measured during the euglycemic-hyperinsulinemic clamp (n = 79). RESULTS Circulating palmitoleate (OGTT:F ratio = 8.2, P = 0.005; clamp:F ratio = 7.8, P = 0.007) but not total FFAs (OGTT:F ratio = 0.6, P = 0.42; clamp:F ratio = 0.7, P = 0.40) correlated positively with insulin sensitivity, independently of age, sex, and adiposity. High baseline palmitoleate predicted a larger increase in insulin sensitivity. For 1-SD increase in palmitoleate, the odds ratio for being in the highest versus the lowest tertile of adjusted change in insulin sensitivity was 2.35 (95% CI 1.16–5.35). CONCLUSIONS Circulating palmitoleate strongly and independently predicts insulin sensitivity, suggesting that it plays an important role in the pathophysiology of insulin resistance in humans.

Hepatic Lipid Composition and Stearoyl-Coenzyme A Desaturase 1 mRNA Expression Can Be Estimated from Plasma VLDL Fatty Acid Ratios

BACKGROUND Stearoyl-coenzyme A desaturase 1 (SCD1) catalyzes the limiting step of monounsaturated fatty acid synthesis in humans and is an important player in triglyceride generation. SCD1 has been repeatedly implicated in the pathogenesis of metabolic and inflammatory diseases. Therefore it is of great importance to determine SCD1 activity in human samples. In this study we aimed to evaluate a hepatic SCD1 activity index derived from plasma VLDL triglyceride composition as a tool to estimate hepatic SCD1 expression in humans. Additionally, we further evaluated commonly used fatty acid ratios [elongase, de novo lipogenesis, and Delta5 and Delta6 desaturase] in plasma VLDL and hepatic lipid fractions. DESIGN AND METHODS Liver biopsies and plasma samples were simultaneously collected from 15 individuals. Plasma VLDL was obtained by ultracentrifugation. Hepatic and plasma VLDL lipids were fractionated by thin-layer chromatography, and the fatty acid composition of each fraction was analyzed by gas chromatography. Hepatic SCD1 expression was determined by real-time PCR. RESULTS Hepatic SCD1 mRNA expression was associated with the product/precursor ratios (16:1/16:0 and 18:1/18:0) of hepatic lipid fractions. The 16:1/16:0 ratio in hepatic and VLDL triglycerides as well as the 18:1/18:0 ratio in plasma VLDL were closely associated with hepatic SCD1 expression. The hepatic de novo lipogenesis index from triglycerides was associated with expression of lipogenic genes [fatty acid synthase (FASN), acetyl-Coenzyme A carboxylase alpha (ACACA), and sterol regulatory element binding transcription factor 1 (SREBP-1)] and is closely reflected by the de novo lipogenesis index in VLDL triglycerides. CONCLUSION We demonstrated for the first time that hepatic SCD1 expression can be estimated noninvasively from routine blood samples by measuring the SCD1 activity index in fasting plasma VLDL.

Induction of stearoyl-CoA desaturase protects human arterial endothelial cells against lipotoxicity

Endothelial lipotoxicity has been implicated in the pathogenesis of multiple stages of cardiovascular disease from early endothelial dysfunction to manifest atherosclerosis and its complications. Saturated free fatty acids are the major inducers of endothelial cell apoptosis and inflammatory cytokines. In humans, the enzyme human stearoyl-CoA desaturase-1 (hSCD-1) is the limiting step of the desaturation of saturated to monounsaturated fatty acids. Since we could demonstrate the expression of SCD-1 in primary human arterial endothelial cells (HAECs), we aimed to prove a beneficial role of upregulated hSCD-1 expression. In contrast to other cells that are less susceptible to lipotoxicity, hSCD-1 was not upregulated in HAECs upon palmitate treatment. Following that, we could show that upregulation of hSCD-1 using the LXR activator TO-901317 in HAECs protects the cells against palmitate-induced lipotoxicity, cell apoptosis, and expression of inflammatory cytokines IL-6 and IL-8. Increased hSCD-1 activity was determined as increased C16:1/16:0 ratio and enhanced triglyceride storage in palmitate treated cells. The beneficial effect was clearly attributed to enhanced hSCD-1 activity. Overexpression of hSCD-1 blocked palmitate-induced cytotoxicity, and knockdown of hSCD-1 using siRNA abolished the protective effect of TO-901317 in HEK-293 cells. Additionally, inhibition of hSCD-1 with 10/12 CLA blocked the effect of TO-901317 on palmitate-induced lipotoxicity, cell apoptosis, and inflammatory cytokine induction in HAECs. We conclude that upregulation of hSCD-1 leads to a desaturation of saturated fatty acids and facilitates their esterification and storage, thereby preventing downstream effects of lipotoxicity in HAECs. These findings add a novel aspect to the atheroprotective actions of LXR activators in cardiovascular disease.

Hepatic Glucokinase Expression Is Associated with Lipogenesis and Fatty Liver in Humans

BACKGROUND/AIMS Glucokinase (GCK) phosphorylates glucose to form glucose 6-phosphate and thereby regulates hepatic glucose disposal and activates hepatic lipogenesis. Hepatic GCK activity is regulated on the level of GCK mRNA expression and by the inhibitory glucokinase regulatory protein. In this study, we aimed to investigate the relation between GCK mRNA expression and markers of lipogenesis as well as liver fat content in human liver biopsies. Additionally, we investigated whether genetic variation in the liver specific GCK promoter determines liver fat content in humans. METHODS Hepatic mRNA expression and liver triglyceride content was analyzed in 50 human liver biopsies. In a second cohort of 330 individuals, liver fat was precisely measured by 1H magnetic resonance spectroscopy. RESULTS Hepatic GCK mRNA expression is associated with triglyceride content in human liver biopsies (r = 0.50, P = 0.0002). Furthermore, hepatic GCK mRNA expression is associated with lipogenic gene expression (fatty acid synthase, r = 0.49, P = 0.0003; acetyl-coenzyme A carboxylase-α, r = 0.44, P = 0.0015, and acetyl-coenzyme A carboxylase-β, r = 0.48, P = 0.0004) and the de novo lipogenesis index (r = 0.36, P = 0.01). In support of these findings, the single-nucleotide polymorphism rs2041547 in the liver-specific GCK promoter is associated with liver fat content in prediabetic individuals (P = 0.047). CONCLUSIONS In this study, we demonstrate for the first time that GCK mRNA expression is associated with markers of de novo lipogenesis and liver triglyceride content in humans. This suggests that increased GCK activity may induce fatty liver and its metabolic and hepatic consequences in humans. Thus, the widely used approach to nonspecifically activate β-cell and hepatic GCK to treat diabetes mellitus is therefore questionable and may cause serious side effects.

The Insulin Effect on Cerebrocortical Theta Activity Is Associated with Serum Concentrations of Saturated Nonesterified Fatty Acids

CONTEXT Insulin action in the brain contributes to adequate regulation of body weight, neuronal survival, and suppression of endogenous glucose production. We previously demonstrated by magnetoencephalography in lean humans that insulin stimulates activity in beta and theta frequency bands, whereas this effect was abolished in obese individuals. OBJECTIVE The present study aims to define metabolic signals associated with the suppression of the cerebrocortical response in obese humans. DESIGN AND SETTING We determined insulin-mediated modulation of spontaneous cerebrocortical activity by magnetoencephalography during a hyperinsulinemic euglycemic clamp and related it to measures of ectopic fat deposition and mediators of peripheral insulin resistance. Visceral fat mass and intrahepatic lipid content were quantified by magnetic resonance imaging and spectroscopy. Multiple regression analysis was used to analyze associations of cerebrocortical insulin sensitivity and metabolic markers related to obesity. PARTICIPANTS Forty-nine healthy, nondiabetic humans participated in the study. RESULTS In a multiple regression, insulin-mediated stimulation of theta activity was negatively correlated to body mass index, visceral fat mass, and intrahepatic lipid content. Although fasting saturated nonesterified fatty acids mediated the correlations of theta activity with abdominal and intrahepatic lipid stores, adipocytokines displayed no independent correlation with insulin-mediated cortical activity in the theta frequency band. CONCLUSIONS Thus, insulin action at the level of cerebrocortical activity in the brain is diminished in the presence of elevated levels of saturated nonesterified fatty acids.

Neuroactive steroids, their precursors, and polar conjugates during parturition and postpartum in maternal and umbilical blood: 1. Identification and simultaneous determination of pregnanolone isomers.

A rapid method for the identification and measurement of four pregnanolone isomers and their polar conjugates in human plasma was developed using a simple quadrupole GC/MS system with electron impact ionization. Steroid levels were measured in the plasma of 13 and three women at delivery with subarachnoidal and epidural analgesia, respectively, and in corresponding samples of umbilical plasma. A good correlation (r=0.94, P<0.001, n=8) was found between the allopregnanolone in maternal plasma determined by GC/MS and that measured by RIA. Epipregnanolone (3beta-hydroxy-5beta-pregnan-20-one) was identified and measured for the first time in human plasma; its concentration in both maternal and umbilical plasma was much lower than that of other pregnanolone isomers. The levels of 3beta-hydroxy-pregnanolone isomers were significantly higher in the umbilical plasma than in the maternal plasma, while the differences in 3alpha-hydroxy-isomers were insignificant. The differences in conjugates were insignificant except in the case of allopregnanolone, the levels of which were lower in umbilical plasma. In all of the pregnanolone isomers, a significantly lower conjugated/unconjugated steroid ratio was found in the umbilical plasma than in the maternal plasma. The possible role of the sulfatation of pregnanolone isomers around parturition is discussed.

High hepatic SCD1 activity is associated with low liver fat content in healthy subjects under a lipogenic diet.

CONTEXT Increased hepatic de novo lipogenesis (DNL) in response to dietary sugar is implicated in the pathophysiology of fatty liver. Saturated fatty acids are the product of DNL and exert lipotoxic effects that promote liver fat accumulation. Desaturation of fatty acids by stearoyl-CoA desaturase 1 (SCD1) can prevent these deleterious effects. Here we investigated whether DNL and SCD1 are activated in parallel by dietary sugar and influence liver fat accumulation. METHODS In 20 healthy subjects (eight females and 12 males, aged 30.5 ± 2.0 yr, body mass index 25.9 ± 0.5 kg/m(2)) who received a 4-wk lipogenic diet supplemented with 150 g/d of monosaccharides, hepatic SCD1 activity and DNL were determined using validated fatty acid ratios (16:1n-7/16:0; 16:0/18:2n-6) in very low-density lipoprotein triglycerides. Liver fat content was measured by localized (1)H-magnetic resonance spectroscopy. RESULTS At baseline, liver fat content was positively associated with the DNL (r = 0.54, P = 0.01) but not the SCD1 activity index (r = 0.16, P = 0.49). Dietary sugar supplementation increased liver fat content and DNL and SCD1 activity indices (+33, +19, and +8%, respectively). The increase of the DNL index was strongly related to the changes in liver fat content during the sugar supplementation (r = 0.75, P = 0.0001) but showed no association with changes in the SCD1 activity (P > 0.35). After the monosaccharide supplementation, the DNL index was still positively associated with liver fat content (r = 0.52, P = 0.02), whereas SCD1 activity showed a strong negative correlation with liver fat content (r = -0.63, P = 0.002). CONCLUSIONS DNL is closely linked with hepatic steatosis under dietary conditions rich in monosaccharides. Our data suggest that the individual hepatic SCD1 activity is a determinant of liver fat accumulation under lipogenic dietary conditions.

Neuroactive steroids, their precursors and polar conjugates during parturition and postpartum in maternal blood: 2. Time profiles of pregnanolone isomers

Time profiles of the pregnanolone isomers epipregnanolone (3 beta-hydroxy-5 beta-pregnan-20-one), allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one), pregnanolone (3 alpha-hydroxy-5 beta-pregnan-20-one), and isopregnanolone (3 beta-hydroxy-5 alpha-pregnan-20-one) were measured around parturition and in the postpartum period in the serum of 13 and three women with subarachnoidal and epidural analgesia, respectively. In addition, the levels of polar conjugates of all pregnanolone isomers were followed during parturition. GC/MS analysis was used for the measurement of steroid levels. Changes in concentrations of free steroids exhibited a similar pattern, with a fall primarily within the first hour after delivery. The decrease in conjugated steroids was shifted to the interval within the first hour and first day after delivery, and the changes were more pronounced. The time profile of the conjugated/free steroid ratio exhibited a significant decrease within the first hour and the first day after delivery in all of the isomers investigated. A decrease was also observed in the ratio of 3 alpha/3 beta-isomers and 5 alpha/5 beta-isomers around parturition. The possible physiological consequences of the findings are indicated.

Relationships between hepatic stearoyl-CoA desaturase-1 activity and mRNA expression with liver fat content in humans

Stearoyl-CoA desaturase-1 (SCD1) has gained much interest as a future drug target to treat fatty liver and its consequences. However, there are few and inconsistent human data about expression and activity of this important enzyme. We investigated activity and expression of SCD1 and their relationships with liver fat (LF) content in human liver samples. Fifty subjects undergoing liver surgery were studied. SCD1 activity was estimated from the ratio of oleate (C18:1) to stearate (C18:0) within lipid subfractions. Furthermore, SCD1 mRNA expression and LF content were measured. Similarly to previous studies, we observed a strong positive correlation between LF content and the C18:1/C18:0 ratio in the combined fatty acid (FA) fractions (r = 0.96, P < 0.0001), which could be interpreted as higher SCD1 activity with increasing LF. However, hepatic SCD1 mRNA expression did not correlate with LF (r = 0.16, P = 0.13). To solve these conflicting data, we analyzed the FA composition of hepatic lipid subfractions. With increasing LF content the amount of FAs from the triglyceride (TG) fraction increased (r = 0.96, P < 0.0001), whereas the FAs from the phospholipid (PL) fraction remained unchanged (r = -0.17, P = 0.19). Of these two major lipid fractions, the C18:1/C18:0 ratio in TG was 16-fold higher than in PL. Supporting the SCD1 mRNA expression data, the C18:1/C18:0 ratio of the TG or PL fraction did not correlate with LF (r = 0.26, P = 0.12 and r = 0.08, P = 0.29). We provide novel information that SCD1 activity and mRNA expression appear not to be elevated in subjects with high LF content. We suggest that the FA composition of lipid subclasses, rather than of mixed lipids, should be analyzed to estimate SCD1 activity.

Cerebrospinal Fluid Fatty Acids in Glucocerebrosidase-Associated Parkinson's Disease

Heterozygous mutations in the glucocerebrosidase gene lead to an increased risk for and to more severe alpha‐synuclein‐associated pathology in Parkinsons disease. As both glucocerebrosidase and alpha‐synuclein interact with fatty acids, we hypothesized that cerebrospinal fluid fatty acid levels are altered in these Parkinsons disease patients.