Food deprivation increases post-heparin lipoprotein lipase activity in humans

OBJECTIVE: To study the effect of fasting on lipoprotein lipase (LPL) activity in human post-heparin plasma, representing the functional pool of LPL. DESIGN: Fourteen healthy volunteers were recruited for the study. The subjects were fasted for 30 h. Activities of LPL and hepatic lipase (HL), and LPL mass, were measured in pre- and post-heparin plasma in the fed and in the fasted states, respectively. For comparison, LPL and HL activities were measured in pre- and post-heparin plasma from fed and 24-h-fasted guinea pigs. RESULTS: Fasting caused a significant drop in the levels of serum insulin, triglycerides and glucose in the human subjects. Post-heparin LPL activity increased from 79 +/- 6.4 mU mL-1 in the fed state to 112 +/- 10 mU mL-1 in the fasted state (P < 0.01), while LPL mass was 361 +/- 29 in the fed state and 383 +/- 28 in the fasted state, respectively (P = 0.6). In contrast, fasting of guinea pigs caused an 80% drop in post-heparin LPL activity. The effect of fasting on human and guinea pig post-heparin HL activity were moderate and statistically not significant. CONCLUSIONS: In animal models such as rats and guinea pigs, post-heparin LPL activity decreases on fasting, presumably due to down-regulation of adipose tissue LPL. In humans, fasting caused increased post-heparin LPL activity.     

Exaggerated postprandial lipaemia and lower post-heparin lipoprotein lipase activity in middle-aged men

An exaggerated postprandial lipaemic response is thought to play a central role in the development of an atherogenic lipoprotein phenotype, a recognized lipid risk factor for coronary heart disease. A small number of limited studies have compared postprandial lipaemia in subjects of varying age, but have not investigated mechanisms underlying age-associated changes in postprandial lipaemia. In order to test the hypothesis that impaired lipaemia in older subjects is associated with loss of insulin sensitivity, the present study compared the postprandial lipaemic and hormone responses for 9 h following a standard mixed meal in normolipidaemic healthy young and middle-aged men. Lipoprotein lipase (LPL) and hepatic lipase (HL) activities were determined in post-heparin plasma 9 h postprandially and on another occasion under fasting conditions. Postprandial plasma glucose (P<0.02), retinyl ester (indirect marker for chylomicron particles; P<0.005) and triacylglycerol (TAG)-rich lipoprotein (density<1.006 g/ml fraction of plasma) TAG (P<0.05) and retinyl ester (P<0.005) responses were higher in middle-aged men, whereas plasma insulin responses were lower in this group (P<0.001). Fasting and 9 h postprandial LPL and HL activities were also significantly lower in the middle-aged men compared with the young men (P<0.006). In conclusion, the higher incremental postprandial TAG response in middle-aged men than young men was attributed to the accumulation of dietary-derived TAG-rich lipoproteins (density<1.006 g/ml fraction of plasma) and occurred in the absence of marked differences in fasting TAG levels between the two groups. Fasting and postprandial LPL and HL activities were markedly lower in middle-aged men, but lack of statistical associations between measures of insulin response and post-heparin lipase activities, as well as between insulin and measures of postprandial lipaemia, suggest that this lower activity cannot be attributed to lack of sensitivity of lipases to activation by insulin. Alternatively, post-heparin lipase activities may not be good markers for the insulin-sensitive component of lipase that is activated postprandially.     

Tissue-specific regulation of lipoprotein lipase in humans: effects of fasting

BACKGROUND: We have previously reported that the activity of lipoprotein lipase (LPL) measured in postheparin plasma from humans fasted for 30 h is increased relative to the fed state. This is in contrast to laboratory animals, where the strong down-regulation of LPL in their adipose tissue on fasting is reflected in decreased levels of LPL activity in postheparin plasma. MATERIALS AND METHODS: To search for the tissue source of the increase in LPL activity on fasting of humans, young, healthy subjects were fasted for 10, 20 or 30 h, and LPL was measured in plasma (pre- and postheparin) and in biopsies from subcutaneous adipose tissue (abdominal) and from a skeletal muscle (tibialis anterior). Both LPL activity and LPL protein mass were measured in the tissue homogenates. Values after fasting were compared with values from postprandial samples obtained 2 h after a meal. RESULTS: Fasting for up to 30 h did not alter LPL activity in basal plasma (preheparin). LPL activity in postheparin plasma remained unchanged after 10 and 20 h of fasting, but was increased by 50% after 30 h (P < 0.05). Ten hours of fasting caused a 25% (P < 0.05) decrease in LPL activity in subcutaneous adipose tissue, while LPL activity in skeletal muscle remained unchanged. After 30 h of fasting, both LPL activity and mass had decreased by approximately 50% (P < 0.05) in adipose tissue, but had increased by approximately 100% (P < 0.05) in muscle. CONCLUSIONS: The increase in postheparin plasma LPL activity after 30 h of total food deprivation of healthy human subjects seemed to reflect an increased activity and mass of LPL in skeletal muscle.     

Relationship between lipoprotein lipase activity and plasma sex steroid level in obese women.

In obese women (n = 16) at their weight, fasting adipose tissue lipoprotein lipase (LPL) activity, obtained by elution with serum and heparin at 4 degrees and 37 degrees C, was inversely correlated to plasma estradiol levels (r = -0.724; P = 0.002) and (r = -0.641; P = 0.010), respectively. Furthermore, fasting postheparin plasma LPL activity during a heparin infusion, showed an even stronger inverse correlation to plasma estradiol when measured at 60 min (r = -0.815; P less than 0.001). None of the above parameters was correlated to the body mass index. Postprandial LPL activity in postheparin plasma, measured 10 min after a heparin injection, showed a strong positive correlation with plasma free testosterone (r = 0.780; P = 0.001). Neither of these parameters was correlated with the body mass index. The origin of this LPL activity is presently unknown but could conceivably represent a pool of LPL from skeletal muscle. Since it has been shown convincingly that estrogen decreases adipose tissue LPL activity in the rat, the present studies strongly suggest that estradiol is a major negative regulator of fasting adipose tissue LPL activity in women.     

Effect of estrogen on post-heparin lipolytic activity. Selective decline in hepatic triglyceride lipase.

The rise in plasma triglyceride (TG) levels associated with estrogen administration has been thought to arise from impaired clearance because of the uniform suppression of post-heparin lipolytic activity (PHLA). Recently PHLA has been shown to consist of two activities: hepatic TG lipase and extrahepatic lipoprotein lipase (LPL). To determine whether estrogen might induce a selective decline in one of these activities, both hepatic TG lipase and extrahepatic LPL were measured in post-heparin plasma from 13 normal women before and after 2 wk of treatment with ethinyl estradiol (1 mug/kg per day). Hepatic TG lipase and extrahepatic LPL were determined by two techniques: (a) separation by heparin-Sepharose column chromatography, and (b) selective inhibition with specific antibodies to post-heparin hepatic TG lipase and milk LPL. Estrogen uniformly depressed hepatic TG lipase as measured by affinity column (-68 +/- 12%, mean +/- SD, P less than 0.001) or antibody inhibition (-63 +/- 11%, P less than 0.001). Extrahepatic LPL was not significantly changed by affinity column (-22 +/- 40%) or antibody inhibition (-3 +/- 42%). Direct measurement of adipose tissue LPL from buttock fat biopsies also showed no systematic change in the activated form of LPL measured as heparin-elutable LPL (+64 +/- 164%) or in the tissue form of LPL measured in extracts of acetone-ether powders (+21 +/- 77%). The change in hepatic TG lipase correlated with the change in PHLA (r = 0.969, P less than 0.01). However, neither the change in PHLA nor hepatic TG lipase correlated with the increase in TG during estrogen. The decrease in PHLA during estrogen thus results from a selective decline in hepatic TG lipase.     

Post-heparin plasma lipoprotein lipase, but not hepatic lipase activity, is related to plasma adiponectin in type 2 diabetic patients and healthy subjects

The aim of this study was to determine the relationships of plasma adiponectin with post-heparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities, and to evaluate whether plasma adiponectin contributes to diabetes-associated dyslipidaemia. Plasma adiponectin, post-heparin plasma lipase activities, lipoproteins and insulin sensitivity (hyperinsulinaemic euglycaemic clamp) were measured in 24 male type 2 diabetic patients and 24 age-matched healthy men. Plasma triglycerides (P < 0.01) and apolipoprotein B levels (P < 0.01) were higher, and HDL cholesterol was lower (P < 0.05) in type 2 diabetic patients. Plasma adiponectin, as well as LPL and HL activities were not significantly different between diabetic and healthy subjects. Multiple regression analysis showed that LPL activity was positively related with plasma adiponectin (P < 0.05). In contrast, HL activity was positively related with body mass index (P < 0.02) and waist/hip ratio (P < 0.05, multiple r = 0.74), but not with plasma adiponectin. Plasma adiponectin was positively associated with insulin sensitivity (P = 0.001), age (P < 0.02) and LPL activity (P < 0.05, multiple r = 0.64), but not with the presence of diabetes and HL activity. Plasma triglycerides were negatively related with LPL activity (P = 0.002) and positively with the diabetic state (P = 0.001, multiple r = 0.58). HDL cholesterol was positively related with plasma adiponectin (P = 0.003) and negatively with HL activity (P < 0.02) as well as with the presence of diabetes (P = 0.05, multiple r = 0.59). We conclude that post-heparin plasma LPL activity, but not HL activity, is related with plasma adiponectin. Plasma adiponectin appears to be a determinant of plasma triglycerides via an effect on LPL activity. It seems unlikely that plasma adiponectin predicts the effects of the diabetic state as such on high plasma triglycerides and low HDL cholesterol.     

Lipoprotein lipase activity of adipose tissue, skeletal muscle and post-heparin plasma in primary endogenous hypertriglyceridaemia: relation to lipoprotein pattern and to obesity

The lipoprotein lipase (LPL) activity was determined from heparin eluates of adipose tissue and skeletal muscle and from post-heparin plasma of sixty-five males with hypertriglyceridaemia and of seventy males with normal serum lipid levels. The patients were subgrouped by their lipoprotein concentrations into types 2b, 4 and 5. The mean LPL activity of adipose tissue (per tissue weight) of nonobese type 2b, 4 and 5 patients was reduced to 54%, 41% and 13%, respectively, of the corresponding value of normolipidaemic men. On the other hand, among obese hyperglyceridaemic men only those with type 5 showed a decreased LPL activity in adipose tissue (44%). The mean skeletal muscle LPL was subnormal in nonobese type 4 (55%) and in type 5 patients (34%) but was normal in type 2b and in obese type 4 patients. The post-heparin plasma LPL activity was significantly reduced in all nonobese hyperglyceridaemic groups but was normal in obese patients apart from cases with type 5 who had low values. One exceptional subject with type 5 had high post-heparin plasma LPL activity. It is concluded that a low LPL activity may be a crucial factor in the pathogenesis of hypertriglyceridaemia in nonobese subjects and in patients having type 5 disorder.     

Decreased plasma lipoprotein lipase in hypoadiponectinemia: an association independent of systemic inflammation and insulin resistance

OBJECTIVE: Adiponectin is a plasma protein expressed in adipose tissue. Hypoadiponectinemia is associated with low HDL cholesterol and high plasma triglycerides, which also characterize lipoprotein lipase (LPL) deficiency syndromes. Recently, dramatically increased LPL activity was reported in mice overexpressing adiponectin. We therefore speculated that adiponectin may directly affect LPL in humans. RESEARCH DESIGN AND METHODS: We measured plasma adiponectin and postheparin LPL in 206 nondiabetic men and in a second group of 110 patients with type 2 diabetes. Parameters were correlated with markers of systemic inflammation (C-reactive protein [CRP]) and insulin resistance (homeostatis model assessment of insulin resistance [HOMA-IR]). RESULTS: Nondiabetic subjects with decreased plasma adiponectin had lower LPL activity (r=0.42, P <0.0001). This association of plasma adiponectin with LPL activity was confirmed in the second group of patients with type 2 diabetes (r=0.37, P <0.0001). Multivariate analysis revealed that adiponectin was the strongest factor influencing LPL activity, accounting for 23% of the variation in LPL activity in nondiabetic subjects and for 26% of the variation in LPL activity in type 2 diabetic patients. These associations were independent of plasma CRP and HOMA-IR. CONCLUSIONS: These results demonstrate an association of decreased postheparin LPL activity with low plasma adiponectin that is independent of systemic inflammation and insulin resistance. Therefore, LPL may represent a link between low adiponectin levels and dyslipidemia in both nondiabetic individuals and patients with type 2 diabetes.     

Restoration of early insulin secretion after a meal in type 2 diabetes: effects on lipid and glucose metabolism

BACKGROUND: In type 2 diabetes (T2D) insulin secretion after a meal is delayed; this may have an impact on the development of hyperglycaemia and hyperlipidaemia. DESIGN: To investigate this, a meal was given to 15 T2D (age 52 +/- 2 years, BMI 25 +/- 0.8 kg m(-2)) on three different occasions: (1) without treatment, (2) after 120 mg of nateglinide before the meal (acute treatment), and (3) after 3 months of nateglinide (120 mg t.i.d., chronic treatment). Fifteen healthy subjects (CON, age 48 +/- 2 years, BMI 24 +/- 0.5 kg m(-2)) were also studied. Blood was withdrawn for 360 min from veins draining the anterior abdominal subcutaneous adipose tissue (AD) and from an arterialized hand vein. Blood flow (BF) in AD was measured with (133)Xe. Lipoprotein lipase activity (LPL) was calculated as the triacylglycerol (TAG) flux across AD, and hormone-sensitive lipase (HSL) as the glycerol flux minus LPL. RESULTS: (1) In T2D the increase in prandial insulin secretion was delayed; postprandial nonesterified fatty acid (NEFA) and TAG levels in blood were increased, while BF, LPL and TAG clearance were blunted vs. CON. (2) Acute or chronic nateglinide treatment induced a prompt increase in prandial insulin secretion, resulting in a decrease in blood glucose and NEFA levels owing to suppression of HSL, while BF, LPL and TAG clearance remained suppressed. CONCLUSIONS: In T2D, restoration of early phase insulin secretion improved postprandial hyperglycaemia and suppressed endogenous lipolysis, resulting in suppression of NEFA levels. These results suggest that in nonobese T2D, metabolic defects may result, to a large extent, from the delay in prandial insulin secretion.     

Carbohydrate and fat have different effects on plasma leptin concentrations and adipose tissue leptin production

Leptin is secreted by adipocytes and plays a role in the regulation of food intake. However, the regulation of leptin production by adipose tissue is unclear. We have investigated whether a mixed meal or a high-fat load given orally, or a pure fat load given intravenously, stimulates adipose tissue leptin production. Six volunteers were studied on two occasions following an overnight fast. On one occasion they consumed tomato soup containing 40 g of triacylglycerol (as Intralipid) and 9.6 g of carbohydrate; on the other occasion Intralipid was infused intravenously over 4 h to give the same fat load. A further eight subjects consumed a mixed meal (containing 37 g of fat and 100 g of carbohydrate) after an overnight fast. Paired blood samples were obtained from an arterialized hand vein and a vein draining subcutaneous adipose tissue at baseline and for 6 h following the meals or the start of the infusion. After both the intravenous and oral fat loads, the arterialized and adipose venous plasma leptin concentrations decreased over 6 h (both P<0.001), as did the leptin veno--arterial difference (P=0.01). Following the mixed meal, there was a slight increase in the arterialized plasma leptin concentration (P=0.02) and a more marked increase in the adipose venous plasma leptin concentration (P=0.03) and in the adipose tissue leptin veno--arterial difference (P=0.01), all peaking at 240 min. We conclude that the increase in plasma leptin concentration observed after meals is not simply a result of an energy load, but is in response to a signal that is not present following a fat load without carbohydrate.