Orlistat fails to alter postprandial plasma lipid excursions or plasma lipases in normal-weight male volunteers

Lipoprotein composition in patients with type 1 diabetes mellitus: Impact of lipases and adipokines

OBJECTIVE

High cardiovascular mortality in patients with type 1 diabetes (T1DM) is widely recognized. Paradoxically, these patients have been shown to have elevated HDL-C and reduced apoB-containing lipoproteins. The purpose of this investigation was to further characterize the lipoprotein composition in T1DM and to assess the role that lipases and adipokines may play in these differences.

METHODS

T1DM patients (89) attending the Diabetes Clinic at the University of Miami and 42 healthy controls were recruited. Clinical characteristics, lipoprotein composition (by ultracentrifugation and HPLC), leptin, and adiponectin were measured in the full cohort, while a subgroup had LPL and hepatic lipase measured.

RESULTS

Subjects were predominately Caucasian and Hispanic. HgbA1c's were above goal while their mean duration of diabetes was >20 years. LPL was 2-fold elevated in diabetic women versus controls (+107%{p=0.001}) with no difference in men. Hepatic lipase was reduced 50% {p<0.001} in women but increased 50% {p=0.079} in men. Leptin was similar to controls in women but reduced in men (-60%{p<0.001}). Adiponectin was elevated in both genders (men: +55%{p=0.018}; women: +46%{p=0.007}). LDL-C was reduced in both diabetic men (-33%{p<0.001}) and women (-24%{p<0.001}) while HDL-C trended higher only in men (+13%{p=0.064}). Both total apoB (men: -31%{p<0.001}; women: -17%{p=0.016}) and triglycerides (men: -49%{p<0.001}; women: -31%{p=0.011}) were reduced in both genders while total apoA-I was increased in both (men: +31%{p<0.001}; women: +19%{p=0.008}). Both men and women had increases in LpA-I (+66%{p<0.001}; +40%{p=0.001}) which accounted for essentially the entire increase in HDL mass. VLDL lipids (men: -53→70%; women: -31→57%) were lower as was apoB (particle number) in men (-51{p<0.001}) with a similar trend in women (-35%{p=0.066}). Cholesterol esters in the particle core were depleted in both genders relative to both apoB (men: -41%; women: -37%) and triglycerides (men: -38%; women: -34%) (all{p<0.009}). There were similar differences in IDL. HDL-L lipids (except triglycerides) (men: +45→74%; women: +49→77%{p<0.006}), apoA-1 (men: +162%; women: +117%{p<0.001}), and apoA-II (men: +64%{p=0.008}; women: +55%{p=0.014}) were higher in T1DM patients. These differences produced dramatic increases in LpA-I (men: +221%; women +139%{p<0.001}) and total HDL-L mass (men: +85%; women: +78%{p<0.001}). ApoM (men: +190%; women: +149%{p<0.001}) was also dramatically increased. Conversely, HDL-D lipids were lower in both genders (-20%→50%) while apoA-I was not different in either. ApoA-II was lower only in the diabetic women (-25%{p=0.015}). LPL activity correlated primarily with IDL(-), LDL(-), HDL-L(+), and HDL-D(-) only in the women. HL correlated weakly with VLDL(+), LDL(+), HDL-L(-), and HDL-D(+) in women but had much stronger correlations with VLDL(-), IDL(-), and HDL-L(+). Adiponectin correlated with VLDL(-), IDL(-), LDL(-), HDL-L(+), and HDL-D(-) in women but only HDL-L(+) and HDL-D(-) in men. Leptin correlated with very few parameters in women but did correlate weakly with several HDL-L(-) and HDL-M(-) parameters.

CONCLUSION

Lipoprotein composition and adipokine concentrations in both genders as well as lipase activities in the women would be expected to reduce the atherosclerotic risk in these patients with T1DM. These data suggest that there are functional lipoprotein abnormalities responsible for their CV risk that are not reflected in their plasma concentrations.

Elevated Lipoprotein Lipase Activity Does Not Account for the Association Between Adiponectin and HDL in Type 1 Diabetes

CONTEXT

Increased high-density lipoprotein cholesterol (HDL-C) is common in type 1 diabetes (T1D) and is associated both with hyperadiponectinemia and with elevated lipoprotein lipase activity (LPL). Because adiponectin has been shown to increase LPL expression, elevated LPL may link the hyperadiponectinemia in T1D with increased HDL.

OBJECTIVE

The purpose of this study was to determine whether LPL activity accounts for the association between adiponectin and HDL in T1D.

DESIGN, PARTICIPANTS, AND SETTING

A cohort of 127 patients with T1D attending the Diabetes Clinic at the University of Miami and 103 healthy control subjects were recruited.

MAIN OUTCOME MEASURE

HDL-C and adiponectin were measured in the full cohort and in a subgroup, HDL subfractions were obtained by ultracentrifugation, and LPL and hepatic lipase were measured in postheparin plasma.

RESULTS

Total HDL-C and the lowest density HDL subfraction, apolipoprotein A-I, LPL activity, and adiponectin levels were higher in subjects with T1D than in control subjects (P < .05). Both adiponectin and LPL activity were directly associated with total HDL-C and its lowest density subfraction, but adiponectin and LPL were not correlated (P = 0.13). Adiponectin alone explained 11.6% and adiponectin plus LPL explained 23.8% of the HDL-C variance. In a multivariate model, adiponectin remained an independent predictor of HDL-C along with LPL and serum creatinine, explaining together 27% of HDL-C variance.

CONCLUSIONS

Adiponectin was strongly associated with HDL-C in T1D, suggesting that hyperadiponectinemia is linked to the elevated HDL-C in this population. However, this relationship is independent of the association between LPL and HDL-C. Thus, elevated adiponectin and LPL activity are independently related to increased HDL-C in T1D.

Inhibition of SREBP1 sensitizes cells to death ligands

Evasion of death receptor ligand-induced apoptosis contributs to cancer development and progression. To better understand mechanisms conferring resistance to death ligands, we screened an siRNA library to identify sequences that sensitize resistant cells to fas activating antibody (CH-11). From this screen, we identified the Sterol-Regulatory Element-Binding Protein 1 (SREBP1), a transcription factor, which regulates genes involved in cholesterol and fatty acid synthesis including fatty acid synthase. Inhibition of SREBP1 sensitized PPC-1 and HeLa to the death receptor ligands CH-11 and TRAIL. In contrast, DU145 prostate cancer cells that are resistant to death ligands despite expressing the receptors on their cell surface remained resistant to CH-11 and TRAIL after knockdown of SREBP1. Consistent with the effects on cell viability, the addition of CH-11 activated caspases 3 and 8 in HeLa but not DU145 cells with silenced SREBP1. We demonstrated that knockdown of SREBP1 produced a marked decrease in fatty acid synthase expression. Furthermore, genetic or chemical inhibition of fatty acid synthase with shRNA or orlistat, respectively, recapitulated the effects of SREBP1 inhibition and sensitized HeLa but not DU145 cells to CH-11 and TRAIL. Sensitization to death receptor ligands by inhibition of fatty acid synthase was associated with activation of caspase 8 prior to caspase 9. Neither silencing of SREBP1 or fatty acid synthase changed basal expression of the core death receptor components Fas, caspase 8, FADD, caspase 3 or FLIP. Thus, inhibition of SREBP1 or its downstream target fatty acid synthase sensitizes resistant cells to death ligands.

Orlistat accentuates the fat-induced fall in blood pressure in older adults

Postprandial hypotension may be influenced by the digestion of fat. The aim of the present study was to evaluate the hypothesis that products of fat digestion mediate the hypotensive response to fat. In part A of the study, nine healthy older subjects were studied on three separate occasions in randomised order. Blood pressure, heart rate (HR), plasma TAG and gastric emptying were measured following the ingestion of equivolaemic drinks: (1) 300 ml of high-fat drink (88 % fat); (2) fat drink mixed with 120 mg orlistat (lipase inhibitor); (3) water (control). In part B of the study, ten healthy older subjects were studied on two separate occasions. Blood pressure, HR, plasma TAG and superior mesenteric artery flow were measured during 90 min intraduodenal infusions of 10 % intralipid (2·7 ml/min), with and without 120 mg orlistat. Oral fat ingestion was associated with decreases in systolic and diastolic blood pressures (both P = 0·0001) that were greater when orlistat was co-administered (both P < 0·05), and an increase in HR (P = 0·0001) that was inhibited by orlistat co-administration (P < 0·03). Gastric emptying was slowed by oral fat digestion, and orlistat administration inhibited this slowing (P < 0·04). Intraduodenal fat infusion was not associated with changes in blood pressure but increased HR (P < 0·0001), an effect attenuated by orlistat (P < 0·05). In conclusion, orlistat potentiates the hypotensive response to oral fat in older adults, possibly as a result of faster gastric emptying of fat. The results do not support a role for fat digestion in lowering blood pressure.

Short-term administration of orlistat reduced daytime triglyceridemia in obese women with the metabolic syndrome

The objective of this prospective, controlled, randomized study was to evaluate the effect of orlistat administration for 10 days on daytime capillary triglyceridemia in obese women with metabolic syndrome (MetSyn). Thirty-two obese, nondiabetic women with MetSyn were evaluated. The presence of MetSyn was defined according to the National Cholesterol Education Program (NCEP)-Adult Treatment Panel III (ATP III) criteria. Patients were randomized into 2 similar groups: group A (orlistat), mean age 50.1 -/+ 8.2 years, received a low-calorie diet combined with orlistat 120 mg tid for 10 days and group B (control), mean age 51.2 -/+ 9.1 years, received only the low-calorie diet for the same period of time. Anthropometric, lipids, and parameters of insulin resistance were measured before and after 10 days of intervention. Capillary triglycerides (TGc) were measured at 6 different time points during the day and daytime triglyceridemia was expressed as area under the curve of TGc (AUC-TGc). Most anthropometric measurements (body weight, body mass index, waist circumference, and percentage of fat mass) and most metabolic parameters (total cholesterol [TC], fasting venous triglycerides [TGfv], high-density lipoprotein cholesterol [HDL-C] levels, fasting glucose [FG], fasting insulin [FI], and homeostasis model for assessment [HOMA] for insulin resistance index) decreased significantly in both groups, while waist-to-hip ratio (WHR) and systolic (SBP) and diastolic blood pressure (DBP) did not change significantly in both groups and low-density lipoprotein cholesterol (LDL-C) levels decreased only in the orlistat group. Following minimal weight loss, TGc at most time points and AUC-TGc were significantly reduced only in group A. In group A, AUG-TGc decreased by 17% from 36.4 -/+11.8 to 30.2 -/+9.9 mmol/Lxh(-1) (p < 0.001), and this reduction was significantly greater compared with the control group (p < 0.05) and remained significant after percentage of weight loss was taken into account. This decrease of AUC-TGc significantly correlated with the decrease of HOMA index (p < 0.05, r = 0.39) and the decrease of TGfv (p < 0.001, r = 0.62). The tolerability of orlistat was very good and side effects were transient and of minimal intensity. In conclusion, short-term administration of orlistat significantly reduced daytime triglyceridemia in obese, nondiabetic women with MetSyn. This reduction could offer cardiovascular benefits in these high-risk patients. Long-term studies with more patients are needed to reach definite conclusions.

The use of orlistat in the treatment of obesity, dyslipidaemia and Type 2 diabetes

Orlistat (tetrahydrolipstatin) is an inhibitor of gastrointestinal lipases, especially pancreatic lipase. It is used as an adjunct to diet and exercise in order to achieve weight loss in obese individuals (body mass index > 30 kg/m2) or in overweight individuals (body mass index > 27 kg/m2) with other risk factors for atherosclerotic vascular disease, such as hypertension, dyslipidaemia or diabetes. Short- and long-term studies of up to 4 years duration have shown the drug to have significant benefits in weight loss, as well as in the reduction in lipids, glucose and haemoglobin A1c, and in time to onset of Type 2 diabetes compared with diet alone or placebo groups. The incremental amount of weight loss that orlistat produces is modest, but sufficient to result in improvement in obesity comorbidities such as elevated blood pressure, dyslipidaemia and hyperglycaemia compared with diet and exercise alone. Orlistat should only be prescribed for individuals who are motivated to adhere to lifestyle modifications, especially dietary fat restriction.

Effect of orlistat on postprandial lipemia, NMR lipoprotein subclass profiles and particle size

Evidence suggests that metabolic phenomena during postprandial lipemia may be important in the pathogenesis of atherosclerosis. Both lipid concentrations and lipoprotein subclass patterns may be important cardiovascular risk modifiers. The pancreatic lipase inhibitor orlistat reduces fat absorption by 30% and is used for the treatment of overweight and obesity. We evaluated the effect of orlistat on postprandial lipemia and lipoprotein particle distribution after moderate-and high-fat meals in healthy volunteers. In this double-blind, randomized, cross-over study, 10 healthy young men received orlistat 120 mg plus a high-fat meal (HFO), orlistat plus a moderate-fat meal (MFO) or placebo plus a high-fat meal (HFP). Plasma triacylglycerol, glucose, insulin, and free fatty acids were measured at baseline (fasting) and postprandially for 8h. Lipoprotein subclass profile was assessed by nuclear magnetic resonance spectroscopy. The 8h postprandial mean triacylglycerol area under the curve (AUC) was significantly lower with MFO and HFO (0.79 versus 1.33 mmol/lh) versus HFP (4.33 mmol/lh; p=0.02). Mean change in large VLDL subclass concentration during the 4-8h and mean VLDL size after 8h was significantly lower with HFO and MFO versus HFP (p<0.001). Small HDL particle concentration decreased significantly with HFP versus MFO or HFO (p<0.001). There was no significant difference in postprandial concentrations of glucose, insulin or free fatty acids on the different regimens. The lowering of postprandial triacylglycerol AUC, shorter postprandial lipemia, lower concentration of large triacylglycerol-rich particles and decrease of VLDL particle size supports the hypothesis of a less atherogenic postprandial lipoprotein profile following orlistat ingestion.

Orlistat: a review of its use in the management of patients with obesity

Orlistat is an inhibitor of gastrointestinal lipases and, therefore, prevents the absorption of dietary fat. This agent reduces weight in obese adults and adolescents with or without comorbidities (including type 2 diabetes mellitus, hypercholesterolaemia, hypertension, metabolic syndrome) who received up to 4 years of therapy in conjunction with a hypocaloric diet. In obese patients, orlistat in combination with a hypocaloric diet improved metabolic risk factors and reduced the risk of developing type 2 diabetes. Furthermore, this agent was cost effective in patients with obesity, particularly those with type 2 diabetes. Orlistat is generally well tolerated, with gastrointestinal adverse events being most commonly reported. Orlistat, in addition to lifestyle and dietary intervention, is thus an attractive option for the treatment of patients with obesity, especially those with associated comorbidities or at risk of developing type 2 diabetes.

Combination of gemfibrozil and orlistat for treatment of combined hyperlipidemia with predominant hypertriglyceridemia

OBJECTIVE

To present a case of combined hyperlipidemia with predominant hypertriglyceridemia unresponsive to conventional diet and single-agent drug therapy but successfully treated with a combination of gemfibrozil and orlistat.

METHODS

We describe a nonobese Asian Indian man with combined hyperlipidemia. Predominant hypertriglyceridemia was unresponsive to conventional therapy. Orlistat was added to the maximal dose of gemfibrozil, and baseline lipid profiles were compared with posttreatment values after repeated challenges with each drug individually and in combination. The relevant literature was also reviewed.

RESULTS

At baseline, the patient's serum triglyceride level was 766 mg/dL and total cholesterol level was 241 mg/dL. On repeated measurements 4 months later, these values were 959 mg/dL and 309 mg/dL, respectively. With use of a reduced-fat diet and gemfibrozil (600 mg orally twice a day), serum triglyceride levels were 830 mg/dL and 909 mg/dL on two different occasions. Combination treatment with the same dosage of gemfibrozil and orlistat at 120 mg orally three times a day reduced triglyceride levels to 279 mg/dL and 244 mg/dL on two separate occasions. Rechallenges with drug monotherapy yielded triglyceride levels of up to 1,159 mg/dL with gemfibrozil alone and of up to 896 mg/dL with orlistat alone. A reduction of serum triglyceride levels to 269 mg/dL and 224 mg/dL occurred when combined treatment with both gemfibrozil and orlistat was reinstituted on two additional occasions.

CONCLUSION

The combination of gemfibrozil and orlistat was extremely effective in reducing serum triglyceride levels in this patient with combined hyperlipidemia and predominant hypertriglyceridemia, whereas either one of these agents, when used alone, was ineffective. Determining the mechanisms of this synergy will necessitate further investigation. Additional studies of the use of the gemfibrozil-orlistat combination in patients who have combined hyperlipidemia with predominant hypertriglyceridemia are needed.

Postprandial lipemia--effect of lipid-lowering drugs

Exaggerated postprandial hyperlipidemia has been associated with cardiovascular disease. The mechanisms underlying this association are likely to depend on a multitude of effects. Potentially atherogenic remnants of triglyceride-rich lipoproteins (TRL) accumulate in the postprandial state. In addition, TRL may promote the formation of small dense LDL. There are some indications that the postprandial period is a hypercoagulable state and endothelial function seems to be hampered after acute fat intake. Conventional lipid lowering drugs such as statins and fibrates have the potency of reducing postprandial hyperlipidemia, but the fibrates seem to be more effective in this respect. There is a complete lack of prospective studies linking inefficient postprandial lipid metabolism with clinical endpoints and there is also a need to include investigations of postprandial lipid metabolism in the evaluation of novel drugs affecting lipid metabolism and insulin resistance.

[Inhibitors of absorption as anti-obesity drugs]

There are two types of anti-obesity agents which are classified as inhibitors of absorption: inhibitors of lipid and carbohydrate absorption. Inhibitors of lipid absorption consist of lipase inhibitor (orlistat, Nomma Herb's extract (CT-II) and fat substitute (olestra, sucrose polyester). Orlistat is now available as an anti-obesity drug in the USA and Europe. CT-II may be useful as a functional diet. Application of fat substitute is still limited in snack food. As for inhibitors of carbohydrate absorption, alpha-glucosidase inhibitors are now available as anti-diabetic drugs. To develop these agents for anti-obesity drug, solution of adverse effects on the gastrointestinal tract are necessary.

Physiological levels of mammalian uncoupling protein 2 do not uncouple yeast mitochondria

We assessed the ability of human uncoupling protein 2 (UCP2) to uncouple mitochondrial oxidative phosphorylation when expressed in yeast at physiological and supraphysiological levels. We used three different inducible UCP2 expression constructs to achieve mitochondrial UCP2 expression levels in yeast of 33, 283, and 4100 ng of UCP2/mg of mitochondrial protein. Yeast mitochondria expressing UCP2 at 33 or 283 ng/mg showed no increase in proton conductance, even in the presence of various putative effectors, including palmitate and all-trans-retinoic acid. Only when UCP2 expression in yeast mitochondria was increased to 4 microg/mg, more than an order of magnitude greater than the highest known physiological concentration, was proton conductance increased. This increased proton conductance was not abolished by GDP. At this high level of UCP2 expression, an inhibition of substrate oxidation was observed, which cannot be readily explained by an uncoupling activity of UCP2. Quantitatively, even the uncoupling seen at 4 microgram/mg was insufficient to account for the basal proton conductance of mammalian mitochondria. These observations suggest that uncoupling of yeast mitochondria by UCP2 is an overexpression artifact leading to compromised mitochondrial integrity.

Overexpression of UCP-3 in Skeletal Muscle of Mice Results in Increased Expression of Mitochondrial Thioesterase mRNA

Mice overexpressing human UCP-3 in skeletal muscle (UCP-3tg) are lean despite overeating, have increased metabolic rate, and their skeletal muscle mitochondria show increased proton conductance. The true function of UCP-3 however, has yet to be determined. It is assumed that UCP-3tg mice have increased fatty acid beta-oxidation to fuel their increased metabolic rate. In this study we have quantified skeletal muscle mRNA levels of a number of genes involved in fatty acid metabolism. mRNA levels of uncoupling protein-2, carnitine palmitoyl transferase-1beta and fatty acid binding proteins, and transporters were unchanged when compared to wild-type mice. Lipoprotein lipase mRNA was slightly, but significantly, increased by 50%. The most notable change in gene expression was a threefold increase in mitochondrial thioesterase (MTE-1) expression. In the face of a chronic increase in mitochondrial uncoupling these changes suggest that increased flux of fatty acids through the beta-oxidation pathway does not necessarily require marked changes in expression of genes involved in fatty acid metabolism. The large increase in MTE-1 both confirms the importance of this gene in situations where mitochondrial beta-oxidation is increased and supports the hypothesis that UCP-3 exports fatty acids generated by MTE-1 in the mitochondrion.

Postprandial lipid handling

The etiological importance of postprandial lipid metabolism in the development of coronary artery disease is now well established. Since then, the work of Patsch and others has helped to establish the etiological importance of postprandial lipid metabolism in the development of coronary artery disease. Dietary and pharmacological interventions have been shown to produce dramatic improvement in postprandial lipid handling in high risk groups and have potential to prevent coronary artery disease through these effects. Research effort continues to focus on the complex mechanisms which underlie defects in postprandial lipid handling, with a view to understanding how lifestyle variables such as diet can be modified to prevent coronary artery disease.