The effect of fructose feeding on intestinal triacylglycerol production and de novo fatty acid synthesis in humans

A high fructose intake exacerbates postprandial plasma triacylglycerol (TAG) concentration, an independent risk factor for cardiovascular disease, although it is unclear whether this is due to increased production or impaired clearance of triacylglycerol (TAG)-rich lipoproteins. We determined the in vivo acute effect of fructose on postprandial intestinal and hepatic lipoprotein TAG kinetics and de novo lipogenesis (DNL). Five overweight men were studied twice, 4 weeks apart. They consumed hourly mixed-nutrient drinks that were high-fructose (30% energy) or low-fructose (<2% energy) for 11 hours. Oral 2H2O was administered to measure fasting and postprandial DNL. Postprandial chylomicron (CM)-TAG and very low-density lipoprotein (VLDL)-TAG kinetics were measured with an intravenous bolus of [2H5]-glycerol. CM and VLDL were separated by their apolipoprotein B content using antibodies. Plasma TAG (P<0.005) and VLDL-TAG (P=0.003) were greater, and CM-TAG production rate (PR, P=0.046) and CM-TAG fractional catabolic rate (FCR, P=0.073) lower when high-fructose was consumed, with no differences in VLDL-TAG kinetics. Insulin was lower (P=0.005) and apoB48 (P=0.039), apoB100 (P=0.013) and NEFA (P=0.013) were higher after high-fructose. Postprandial hepatic fractional DNL was higher than intestinal fractional DNL with high-fructose (P=0.043) and low-fructose (P=0.043). Fructose consumption had no effect on the rate of intestinal or hepatic DNL. We provide the first measurement of the rate of intestinal DNL in humans. Lower CM-TAG PR and CM-TAG FCR with high-fructose consumption suggests lower clearance of CM, rather than elevated production, may contribute to elevated plasma TAG, possibly due to lower insulin-mediated stimulation of lipoprotein lipase

Dose dependent effects of fructose and glucose on de novo palmitate and glycerol synthesis in an enterocyte cell model

Scope: Fructose exacerbates post-prandial hypertriacylglycerolaemia. This may be partly due to increased enterocyte de novo lipogenesis (DNL). It is unknown whether this is concentration-dependent or whether fructose has a greater effect on lipid synthesis than glucose. The dose-dependent effects of fructose and glucose on DNL and de novo triacylglycerol (TAG)-glycerol synthesis were investigated in an enterocyte model, Caco-2 cells. Methods and results: Caco-2 cells were treated for 96h with 5mM, 25mM or 50mM fructose or glucose, or 12.5mM fructose/12.5mM glucose mix. DNL was measured following addition of [13C2]-acetate to apical media. In separate experiments, [13C6]-fructose and [13C6]-glucose were used to measure DNL and de novo TAG-glycerol synthesis. DNL from [13C2]-acetate was detected following all treatments, with greater amounts in intracellular than secreted (media) samples (all P <0.05). DNL from [13C6]-fructose and [13C6]-glucose was also measurable. Intracellular synthesis was concentration-dependent for both glucose and fructose tracers (P=0.003, P=0.034, respectively) and was higher with 25mM glucose than 25mM fructose (P=0.025). DNL from fructose and glucose was <1%, but up to 70% of de novo TAG-glycerol was synthesised from glucose or fructose. Conclusion: Fructose is not a major source of DNL in Caco-2 cells but contributes substantially to de novo TAG-glycerol synthesis

Circulating pancreatic polypeptide concentrations predict visceral and liver fat content

CONTEXT AND OBJECTIVE: No current biomarker can reliably predict visceral and liver fat content, both of which are risk factors for cardiovascular disease. Vagal tone has been suggested to influence regional fat deposition. Pancreatic polypeptide (PP) is secreted from the endocrine pancreas under vagal control. We investigated the utility of PP in predicting visceral and liver fat. PATIENTS AND METHODS: Fasting plasma PP concentrations were measured in 104 overweight and obese subjects (46 men and 58 women). In the same subjects, total and regional adipose tissue, including total visceral adipose tissue (VAT) and total subcutaneous adipose tissue (TSAT), were measured using whole-body magnetic resonance imaging. Intrahepatocellular lipid content (IHCL) was quantified by proton magnetic resonance spectroscopy. RESULTS: Fasting plasma PP concentrations positively and significantly correlated with both VAT (r = 0.57, P < .001) and IHCL (r = 0.51, P < .001), but not with TSAT (r = 0.02, P = .88). Fasting PP concentrations independently predicted VAT after controlling for age and sex. Fasting PP concentrations independently predicted IHCL after controlling for age, sex, body mass index (BMI), waist-to-hip ratio, homeostatic model assessment 2-insulin resistance, (HOMA2-IR) and serum concentrations of triglyceride (TG), total cholesterol (TC), and alanine aminotransferase (ALT). Fasting PP concentrations were associated with serum ALT, TG, TC, low- and high-density lipoprotein cholesterol, and blood pressure (P < .05). These associations were mediated by IHCL and/or VAT. Fasting PP and HOMA2-IR were independently significantly associated with hepatic steatosis (P < .01). CONCLUSIONS: Pancreatic polypeptide is a novel predictor of visceral and liver fat content, and thus a potential biomarker for cardiovascular risk stratification and targeted treatment of patients with ectopic fat deposition

Novel hepatoselective insulin analog

Cel pracy. Zbadanie, czy tyroksylowy analog insuliny z ograniczonym dostępem do receptora w tkankach obwodowych wykazuje względnie wybiórcze powinowactwo do wątroby u ludzi. MATERIAŁ i metody. Pięć zdrowych osób otrzymywało podskórnie Na B1L-thyroksyl-insulinę (B1-T4-Ins) lub insulinę NPH w przypadkowej kolejności. Posługując się metodą klamry euglikemicznej i rozcieńczania znacznika izotopowego([D-6,6-2H2] glukozy), badano kinetykę insuliny oraz jej względny wpływ na wątrobową produkcję i obwodowy wychwyt glukozy. Pobierano próbki krwi w celu oznaczenia całkowitego stężenia insuliny immunoreaktywnej (bądź jej analogu) oraz w celu określenia stopnia wiązania analogu insuliny z białkami krwi, który badano metodą chromatografii cieczowej. Wyniki. Po podskórnym podaniu B1-T4-Ins była dobrze tolerowana i szybko wchłaniana. Analog cechował się długim czasem półtrwania w surowicy oraz wysokim stopniem wiązania (ok. 86%) z białkami. Jego czas działania, mierzony czasem wlewu glukozy niezbędnym do utrzymania euglikemii, był podobny do czasu działania insuliny NPH. Wpływ analogu na wątrobową produkcję glukozy był podobny do wpływu insuliny NPH, co wskazuje na podobny stopień oddziaływania. Analog w mniejszym stopniu działał na obwodowy wychwyt insuliny w porównaniu z insuliną NPH (p = 0,025), nie wpływał na szybkość przemian metabolicznych glukozy oraz wykazywał zmniejszoną zdolność do hamowania lipolizy (p < 0,05). Wnioski. U osób zdrowych B1-T4-Ins po podaniu podskórnym jest dobrze tolerowana, szybko się wchłania i ma wysoki stopień związania z białkami krwi, co odpowiada za długi czas połowicznego zaniku w surowicy. Analog ten wydaje się bardziej wybiórczy w oddziaływaniu na komórki wątroby, a zatem potencjalnie ma bardziej fizjologiczny profil działania w porównaniu z dotychczas stosowanymi preparatami insuliny.OBJECTIVE. To test whether a thyroxyl-insulin analog with restricted access to receptor sites in peripheral tissues displays relative hepatoselectivity in humans. RESEARCH DESIGN AND METHODS. Five normal human subjects received a subcutaneous bolus injection of either N B1 L-thyroxyl-insulin (B1-T4-Ins) or NPH insulin in random order. Insulin kinetics, relative effects on hepatic glucose production, and peripheral glucose uptake were studied using euglycemic clamp and stable isotope [D-6,6-2H2]glucose) dilution techniques. Blood samples were taken for the determination of total immunoreactive insulin/analog concentrations and for liquid chromatography to assess the protein binding of the analog in the circulation. RESULTS. After subcutaneous administration, B1-T4-Ins was well tolerated and rapidly absorbed. The analog had a long serum half-life and was highly protein bound (~86%). Its duration of action, as judged by the duration of infusion of exogenous glucose to maintain euglycemia, was similar to that of NPH insulin. The effect of the analogs on hepatic glucose production was similar to that of NPH insulin, indicating equivalent hepatic potency. The analog demonstrated less effect on peripheral glucose uptake than NPH insulin (P = 0,025), had no effect on metabolic clearance rate of glucose, and exhibited a reduced capacity to inhibit lipolysis (P < 0,05). CONCLUSIONS. When injected subcutaneously into normal human subjects, B1-T4-Ins is well tolerated, quickly absorbed, and highly protein bound, resulting in a long plasma half-life. This analog appears to have a hepatoselective action, and, therefore, has the potential to provide more physiological insulin action than the insulin preparations currently used

NAFLD exacerbates the effect of dietary sugar on liver fat and development of an atherogenic lipoprotein phenotype

This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Springer.${\bf Aims/hypothesis:}$ We aimed to test the hypothesis that the effects of dietary sugar on lipoprotein metabolism are influenced by non-alcoholic fatty liver disease (NAFLD). ${\bf Methods:}$ The effect of two 12 week, iso-energetic diets, high and low in non-milk extrinsic sugars (26% and 6% total energy), matched for macronutrient content, was examined in a randomised, cross-over study in men with NAFLD (n=11) and controls (n= 14). Lipoprotein kinetics and the sources of fatty acids for triacylglycerol (TAG) production were measured using stable isotope tracers. ${\bf Results:}$ Liver fat was higher after the high versus low-sugar diet in both groups (p<0.02), but men with NAFLD showed a relatively greater response than controls (p<0.05). After the high versus low-sugar diet, VLDL1-TAG production rate was higher in the controls (p <0.002) due to a greater contribution from splanchnic fatty acids (p<0.02) and de novo lipogenesis (p <0.002), whereas in NAFLD, VLDL2-TAG production rate was higher (p <0.05), due to a greater contribution from splanchnic fatty acids (p<0.02). There was no difference in the contribution of systemic NEFA to VLDL1 and VLDL2-TAG production rate between diets in either group. Intermediate density lipoprotein (IDL), LDL2 and LDL3-apolipoprotein B production rates and post-heparin hepatic lipase activity were all higher (p<0.05) on the high-sugar diet in NAFLD. ${\bf Conclusions:}$ A high sugar intake promoted a greater accumulation of liver fat in NAFLD than controls and increased VLDL-TAG production in both groups, due mainly to an increased contribution of fatty acids from splanchnic sources, which includes hepatic TAG storage pools. These effects may drive the formation of atherogenic lipoproteins.The work was supported by a UK government grant from the Biological Biotechnology Scientific Research Council (Grant no. BB/G009899/1); University of Surrey PhD scholarship for AM; Medical Research Council (body composition measurements) and infrastructure support from the National Institute of Health Research at the Cambridge Biomedical Research Centre

Dissociation between exercise-induced reduction in liver fat and changes in hepatic and peripheral glucose homoeostasis in obese patients with non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is associated with multi-organ (hepatic, skeletal muscle, adipose tissue) insulin resistance (IR). Exercise is an effective treatment for lowering liver fat but its effect on IR in NAFLD is unknown. We aimed to determine whether supervised exercise in NAFLD would reduce liver fat and improve hepatic and peripheral (skeletal muscle and adipose tissue) insulin sensitivity. Sixty nine NAFLD patients were randomized to 16 weeks exercise supervision (n=38) or counselling (n=31) without dietary modification. All participants underwent MRI/spectroscopy to assess changes in body fat and in liver and skeletal muscle triglyceride, before and following exercise/counselling. To quantify changes in hepatic and peripheral insulin sensitivity, a pre-determined subset (n=12 per group) underwent a two-stage hyperinsulinaemic euglycaemic clamp pre- and post-intervention. Results are shown as mean [95% confidence interval (CI)]. Fifty participants (30 exercise, 20 counselling), 51 years (IQR 40, 56), body mass index (BMI) 31 kg/m(2) (IQR 29, 35) with baseline liver fat/water % of 18.8% (IQR 10.7, 34.6) completed the study (12/12 exercise and 7/12 counselling completed the clamp studies). Supervised exercise mediated a greater reduction in liver fat/water percentage than counselling [Δ mean change 4.7% (0.01, 9.4); P<0.05], which correlated with the change in cardiorespiratory fitness (r=-0.34, P=0.0173). With exercise, peripheral insulin sensitivity significantly increased (following high-dose insulin) despite no significant change in hepatic glucose production (HGP; following low-dose insulin); no changes were observed in the control group. Although supervised exercise effectively reduced liver fat, improving peripheral IR in NAFLD, the reduction in liver fat was insufficient to improve hepatic IR

Ectopic lipid storage in non-alcoholic fatty liver disease is not mediated by impaired mitochondrial oxidative capacity in skeletal muscle

Background and Aims. Simple clinical algorithms including the Fatty Liver Index (FLI) and Lipid Accumulation Product (LAP) have been developed as a surrogate marker for Non-Alcoholic Fatty Liver Disease (NAFLD). These algorithms have been constructed using ultrasonography, a semi-quantitative method. This study aimed to validate FLI and LAP as measures of hepatic steatosis, as measured quantitatively by proton magnetic resonance spectroscopy (1H-MRS). Methods. Data were collected from 168 patients with NAFLD and 168 controls who had undergone clinical, biochemical and anthropometric assessment in the course of research studies. Values of FLI and LAP were determined, and assessed both as predictors of the presence of hepatic steatosis (liver fat >5.5 %) and of actual liver fat content, as measured by 1H MRS. The discriminative ability of FLI and LAP was estimated using the area under the Receiver Operator Characteristic curve (AUROC). Since FLI can also be interpreted as a predictive probability of hepatic steatosis, we assessed how well calibrated it was in our cohort. Linear regression with prediction intervals was used to assess the ability of FLI and LAP to predict liver fat content. Results. FLI and LAP discriminated between patients with and without hepatic steatosis with an AUROC of 0.79 (IQR= 0.74, 0.84) and 0.78 (IQR= 0.72, 0.83), although quantitative prediction of liver fat content was unsuccessful. Additionally, the algorithms accurately matched the observed percentages of patients with hepatic steatosis in our cohort. Conclusions. FLI and LAP may be used clinically, and for metabolic and epidemiological research, to identify patients with hepatic steatosis, but not as surrogates for liver fat content

Ethnic differences in beta cell function occur independently of insulin sensitivity and pancreatic fat in black and white men

Introduction It is increasingly recognized that type 2 diabetes (T2D) is a heterogenous disease with ethnic variations. Differences in insulin secretion, insulin resistance and ectopic fat are thought to contribute to these variations. Therefore, we aimed to compare postprandial insulin secretion and the relationships between insulin secretion, insulin sensitivity and pancreatic fat in men of black West African (BA) and white European (WE) ancestry.Research design and methods A cross-sectional, observational study in which 23 WE and 23 BA men with normal glucose tolerance, matched for body mass index, underwent a mixed meal tolerance test with C peptide modeling to measure beta cell insulin secretion, an MRI to quantify intrapancreatic lipid (IPL), and a hyperinsulinemic-euglycemic clamp to measure whole-body insulin sensitivity.Results Postprandial insulin secretion was lower in BA versus WE men following adjustment for insulin sensitivity (estimated marginal means, BA vs WE: 40.5 (95% CI 31.8 to 49.2) × 103 vs 56.4 (95% CI 48.9 to 63.8) × 103 pmol/m2 body surface area × 180 min, p=0.008). There was a significantly different relationship by ethnicity between IPL and insulin secretion, with a stronger relationship in WE than in BA (r=0.59 vs r=0.39, interaction p=0.036); however, IPL was not a predictor of insulin secretion in either ethnic group following adjustment for insulin sensitivity.Conclusions Ethnicity is an independent determinant of beta cell function in black and white men. In response to a meal, healthy BA men exhibit lower insulin secretion compared with their WE counterparts for their given insulin sensitivity. Ethnic differences in beta cell function may contribute to the greater risk of T2D in populations of African ancestry

Prandial Hypertriglyceridemia in Metabolic Syndrome is due to an Overproduction of both Chylomicron and VLDL Triacylglycerol

Abstract The aim was to determine whether fed very low density lipoprotein (VLDL) and chylomicron (CM) triacylglycerol (TAG) production rates are elevated in metabolic syndrome (MetS). Eight men with MetS (BMI 29.7± 1.1) and 8 lean age matched healthy men (BMI 23.1± 0.4) were studied using a frequent feeding protocol. After 4 hours of feeding an intravenous bolus of 2 H 5 -glycerol was administered to label VLDL1, VLDL2 and CM TAG. 13 C glycerol tripalmitin was administered orally as an independent measure of CM TAG metabolism. Hepatic and intestinal lipoproteins were separated by an immunoaffinity method. In MetS, fed TAG and the increment in TAG from fasting to feeding were higher (p=0.03, p&lt;0.05 respectively) than in lean men. Fed CM, VLDL1 and VLDL2 TAG pool sizes were higher (p=0.006, p=0.03, p&lt;0.02) and CM, VLDL1 and VLDL2 TAG production rates were higher (p&lt;0.002, p&lt;0.05, p=0.06) than in lean men. VLDL1, VLDL2 and CM TAG clearance rates were not different between groups. In conclusion prandial hypertriglyceridemia in men with MetS was due to an increased production rate of both VLDL and CM TAG. Since both groups received identical meals this suggests that in MetS the intestine is synthesising more TAG de novo for export in CMs.