Background and aim: ApoE and apoC-III are important components of lipoprotein metabolism. While the function of both apoproteins is relatively well understood, little is known about the in vivo metabolism of these proteins, partly because of the lack of a standardized method to isolate these apoproteins in large sample numbers.Methods and results: We developed a new reverse phase HPLC method (acetonitril/ phosphate gradient; Aquapore RP-300, 7 mu m, 220 X 4.6 mm) to isolate a number of different apoproteins, including apoC-III and apoE from VLDL. This method was then used in a study which aimed at determining VLDL-apoE-3 and VLDL-apoC-III metabolism. In addition VLDL-apoB and LDL-apoB metabolism was determined. Endogenous labeling with d(3)-leucine, mass spectrometry and multicompartmental modeling was used in 6 normolipidemic healthy mate subjects. Tracer/tracee ratios of free plasma leucine, VLDL-apoE, -apoC-III, -apoB, and LDL-apoB leucine were determined over 60 h following a bolus of d(3)-leucine (5 mg kg(-1)). In all subjects sufficient apoC-III could be isolated by reverse phase HPLC to derive metabolic parameters, white apoE metabolic parameters could only be determined if apoE plasma concentration was 0.75 mg dl(-1) or higher. Compared to VLDL-apoB (FCR 10.4 +/- 3.3 d(-1), production 17.8 +/- 4.5 mg kg(-1) d(-1)), VLDL-apoE-3 (FCR 1.03 +/- 0.11 d(-1), production 0.50 +/- 0.29 mg kg(-1) d(-1)) and VLDL-apoC-III (FCR 1.67 +/- 1.22 d(-1), production 0.44 +/- 0.24 mg kg(-1) d(-1)) parameters were much tower. This indicates that apoE-3 and apoC-III recirculate in plasma and that only a small fraction of apoE and apoC-III on VLDL is newly synthesized.Conclusions: We conclude that HPLC methodology can be used to isolate VLDL-apoC-III and apoE for metabolic studies and that the metabolic fate of apoC-III and apoE is different from that of apoB because both apoproteins recycle through the VLDL fraction. (C) 2005 Elsevier B.V. All rights reserved.

Kinetics of apo B and apo AI were assessed in 8 patients with mixed hyperlipidemia at baseline and after 8 weeks of atorvastatin 80 mg q.d. and micronised fenofibrate 200 mg q.d. in a cross-over study. Both increased hepatic production and decreased catabolism of VLDL accounted for elevated cholesterol and triglyceride concentrations at baseline. Atorvastatin significantly decreased triglyceride, total, VLDL and LDL cholesterol and apo B concentrations (-65%, -36%, -57%, -40% and -33%, respectively, P < 0.05). Kinetic analysis revealed that atorvastatin stimulated the catabolism of apo B containing lipoproteins, enhanced the delipidation of VLDL1 and decreased VLDL1 production. Fenofibrate lowered triglycerides and VLDL cholesterol (-57% and -64%, respectively, P < 0.05) due to enhanced delipidation of VLDL1 and VLDL2 and increased VLDL1 catabolism. Changes of HDL particle composition accounted for the increase of HDL cholesterol during atorvastatin and fenofibrate (18% and 23%, P < 0.01). Only fenofibrate increased apo AI concentrations through enhanced apo AI synthesis (45%, P < 0.05). We conclude that atorvastatin exerts additional beneficial effects on the metabolism of apo B containing lipoproteins unrelated to an increase in LDL receptor activity. Fenofibrate but not atorvastatin increases apo Al production and plasma turnover.

Kinetics of apo B and apo AI were assessed in 8 patients with mixed hyperlipidemia at baseline and after 8 weeks of atorvastatin 80 mg q.d. and micronised fenofibrate 200 mg q.d. in a cross-over study. Both increased hepatic production and decreased catabolism of VLDL accounted for elevated cholesterol and triglyceride concentrations at baseline. Atorvastatin significantly decreased triglyceride, total, VLDL and LDL cholesterol and apo B concentrations (−65%, −36%, −57%, −40% and −33%, respectively, P < 0.05). Kinetic analysis revealed that atorvastatin stimulated the catabolism of apo B containing lipoproteins, enhanced the delipidation of VLDL1 and decreased VLDL1 production. Fenofibrate lowered triglycerides and VLDL cholesterol (−57% and −64%, respectively, P < 0.05) due to enhanced delipidation of VLDL1 and VLDL2 and increased VLDL1 catabolism. Changes of HDL particle composition accounted for the increase of HDL cholesterol during atorvastatin and fenofibrate (18% and 23%, P < 0.01). Only fenofibrate increased apo AI concentrations through enhanced apo AI synthesis (45%, P < 0.05). We conclude that atorvastatin exerts additional beneficial effects on the metabolism of apo B containing lipoproteins unrelated to an increase in LDL receptor activity. Fenofibrate but not atorvastatin increases apo AI production and plasma turnover.

Drug Prescribing for Patients with Chronic Kidney Disease in General Practice: a Cross-Sectional Study

Polycystic ovary syndrome (PCOS) is characterized by various endocrine and metabolic abnormalities, whose mutual associations and symptoms are still not clear. In the present study, fifteen PCOS patients and fifteen controls, matched for age and body weight, were investigated. Endocrine profiles were evaluated by the nafarelin and the adrenocorticotropin (ACTH) test. Insulin sensitivity was determined by an intravenous insulin tolerance test. Patients showed a significant predominance of abdominal adiposity [waist-to-hip ratio (WHR), 0.86 +/- 0.05 vs. 0.79 +/- 0.04] with markedly higher fasting insulin levels (+75%) and reduced insulin sensitivity (-37%). Fasting insulin, testosterone and free androgen index were positively correlated with the body mass index (BMI). In contrast, insulin sensitivity and BMI were inversely correlated in patients only. In the nafarelin test increases of 17-OH-progesterone and androstenedione were higher in patients and positively correlated with fasting insulin levels. Lipoprotein profiles showed trends towards higher triglycerides, lower HDL-cholesterol and a preponderance of small, dense LDL in patients. In PCOS higher triglycerides and lower HDL cholesterol were correlated with insulin sensitivity. It is concluded that PCOS patients show metabolic abnormalities combined with a more adroid type of adiposity when compared to cyclic controls of similar BMI.

Lipoprotein(a) is a risk factor for cardiovascular disease composed of an apolipoprotein B-containing lipoprotein to which a second protein, apolipoprotein(a), is attached. We investigated in seven subjects with Lp(a) levels of 39–85 mg/dl the metabolism of four apo B-containing lipoproteins (VLDL1, VLDL2, IDL and LDL) together with that of apo B and apo(a) isolated from Lp(a). Rates of secretion, catabolism and where appropriate, transfer were determined by intravenous administration of d3-leucine, mass spectrometry for measurements of leucine tracer/tracee ratios and kinetic data analysis using multicompartmental metabolic modeling. Apo B in Lp(a) was secreted at a rate of 0.28 (0.17–0.40) mg/kg per day. It was found to originate from two sources — 53% (43–67) were derived from preformed lipoproteins, i.e. IDL and LDL, the remainder was accounted for by apo B, directly secreted by the liver. The fractional catabolic rates (FCRs) of apo B and of apo(a) prepared from Lp(a) were determined as 0.27 (0.16–0.38) and 0.24 (0.12–0.40) pools per day, respectively, which is less than half of the FCR observed for LDL. Our in vivo data from humans support the view that Lp(a) assembly is an extracellular process and that its two protein components, apo(a) and apo B, are cleared from the circulation at identical rates.

BACKGROUND:Dyslipidemia (predominantly hypertriglyceridemia) is frequently seen in patients receiving antiretroviral combination therapy (ART). However, the underlying mechanisms and long-term risks (e.g., cardiovascular events) are still unclear. OBJECTIVES/METHODS:In 5 patients with ART-associated dyslipidemia, stable isotope labeled amino acid tracer (d3-Leu) kinetic analysis over 12 days was used to investigate the metabolism of apolipoprotein B-containing lipoproteins (very low density lipoproteins [VLDL]1, VLDL2, intermediate density lipoproteins [IDL] and low density lipoproteins [LDL]). Data were compared with those in 6 healthy normolipidemic controls. RESULTS:The patients under ART showed significantly increased fasting triglycerides (359 vs. 77 mg/dl) and VLDL (54 vs. 15 mg/dl), compared with controls. They had significantly higher total cholesterol (213 vs. 157 mg/dl) and there was a nonsignificant trend toward higher LDL (136 vs. 93 mg/dl), and toward lower HDL (26 vs. 46 mg/dl). The ratio of large, buoyant LDL1 over small, dense LDL2 was markedly reduced in patients under ART (0.80 vs. 2.00). Total apo B synthesis was significantly increased (25.5 vs. 14.5 mg/kg/d) and shifted toward triglyceride rich VLDL1 (18.5 vs. 8.7 mg/kg/d) in patients receiving ART. There was also a significantly reduced rate of apo B lipoprotein transfer from VLDL1 to VLDL2 (3.7 vs. 20.7 pools/d). In addition, all patients revealed insulin resistance. CONCLUSIONS:These data indicate that increased triglycerides in HIV-infected patients with ART are primary due to reduced rates of VLDL transfer into denser lipoproteins implying a lower rate of lipoprotein lipase-mediated delipidation. In addition, total apo B synthesis was increased and shifted toward triglyceride-rich VLDL1. Overall, this lipoprotein profile in patients with ART-associated dyslipidemia implies an increased risk for cardiovascular events.

Apheresis is a treatment option for patients with severe hypercholesterolemia and coronary artery disease. It is unknown whether such therapy changes kinetic parameters of lipoprotein metabolism, such as apolipoprotein B (apoB) secretion rates, conversion rates, and fractional catabolic rates (FCR). We studied the acute effect of apheresis on metabolic parameters of apoB in five patients with drug-resistant hyperlipoproteinemia, using endogenous labeling with D(3)-leucine, mass spectrometry, and multicompartmental modeling. Patients were studied prior to and immediately after apheresis therapy. The two tracer studies were modeled simultaneously, taking into account the non-steady-state concentrations of apoB. The low density lipoprotein (LDL)-apoB concentration was 120+/-32 mg dl(-1) prior to and 52+/-18 mg dl(-1) immediately after apheresis therapy. The metabolic studies indicate that no change in apoB secretion (13.9+/- 4.9 mg kg(-1) day(-1)) is required to fit the tracer and apoB mass data obtained before and after apheresis and that in four of the five patients the LDL-apoB FCR (0.21+/-0.02 day(-1)) was not altered after apheresis. In one subject the LDL-apoB FCR temporarily increased from 0.22 day(-1) to 0.35 day(-1) after apheresis. The conversion rate of very low density lipoprotein (VLDL)-apoB to LDL-apoB is temporarily decreased from 76 to 51% after apheresis and thus less LDL-apoB is produced after apheresis. We conclude that an acute reduction of LDL-apoB concentration does not affect apoB secretion or LDL-apoB FCR, but that apoB conversion to LDL is temporarily decreased. Thus, in most patients the decreased rate of delivery of neutral lipids or apoB to the liver does not result in an upregulation of LDL receptors or in decreased apoB secretion.

Corticosteroid-binding globulin (CBG) is the principal transport protein of glucocorticoids. Approximately 80–90% of serum cortisol binds to CBG with high affinity and only about 5% of cortisol remain unbound and is considered biologically active. CBG seems to modulate and influence the bioavailability of cortisol to local tissues. In this review, we will discuss physicochemical properties of CBG and structure of CBG in the mechanisms of binding and release of cortisol. This review describes several factors affecting CBG functions, such as genetic factors or temperature. Furthermore, clinical implications of CBG abnormalities and the measurement of CBG and its use for assessment of free cortisol levels are described in this review.

Apolipoprotein B (apoB) metabolism was investigated in 20 men with plasma triglyceride 0.66–2.40 mmol/l and plasma cholesterol 3.95–6.95 mmol/l. Kinetics of VLDL1 (Sf 60–400), VLDL2 (Sf 20–60), IDL (Sf 12–20), and LDL (Sf 0–12) apoB were analyzed using a trideuterated leucine tracer and a multicompartmental model which allowed input into each fraction. VLDL1 apoB production varied widely (from 5.4 to 26.6 mg/kg/d) as did VLDL2 apoB production (from 0.18 to 8.4 mg/kg/d) but the two were not correlated. IDL plus LDL apoB direct production accounted for up to half of total apoB production and was inversely related to plasma triglyceride (r = −0.54, P = 0.009). Percent of direct apoB production into the IDL/LDL density range (r = 0.50, P < 0.02) was positively related to the LDL apoB fractional catabolic rate (FCR). Plasma triglyceride in these subjects was determined principally by VLDL1 and VLDL2 apoB fractional transfer rates (FTR), i.e., lipolysis. IDL apoB concentration was regulated mainly by the IDL to LDL FTR (r = −0.71, P < 0.0001). LDL apoB concentration correlated with VLDL2 apoB production (r = 0.48, P = 0.018) and the LDL FCR (r = −0.77, P < 0.001) but not with VLDL1, IDL, or LDL apoB production. Subjects with predominantly small, dense LDL (pattern B) had lower VLDL1 and VLDL2 apoB FTRs, higher VLDL2 apoB production, and a lower LDL apoB FCR than those with large LDL (pattern A). Thus, the metabolic conditions that favored appearance of small, dense LDL were diminished lipolysis of VLDL, resulting in a raised plasma triglyceride above the putative threshold of 1.5 mmol/l, and a prolonged residence time for LDL. This latter condition presumably permitted sufficient time for the processes of lipid exchange and lipolysis to generate small LDL particles. —Packard, C. J., T. Demant, J. P. Stewart, D. Bedford, M. J. Caslake, G. Schwertfeger, A. Bedynek, J. Shepherd, and D. Seidel. Apolipoprotein B metabolism and the distribution of VLDL and LDL subfractions.

The association between plasma triglyceride levels and coronary heart disease may be explained by the metabolism of triglyceride-apolipoprotein (apo) B100-containing lipoproteins to an atherogenic low density lipoprotein (LDL) fraction. Apo B100 is secreted into the plasma compartment mainly as large triglyceride-rich very low density lipoprotein1 (VLDL1) particles and smaller, comparatively cholesterol ester-rich VLDL2. Both forms of VLDL undergo stepwise delipidation to LDL. A dual tracer VLDL technique has investigated the metabolism of apo B-containing lipoproteins and established that about one-third of the VLDL2 pool is transferred to LDL compared with less than 20% of VLDL1. In addition, LDL derived from VLDL1 has a longer plasma residence time than LDL from VLDL2. A series of experiments using a stable isotope tracer technique showed that the LDL fractional catabolic rate was inversely correlated with plasma triglyceride concentration, which itself is largely determined by VLDL1 concentration. In subjects with triglyceride concentrations between 150-200 mg. dl-1 (1.36 - 2.26 mmol .1(-1)), the prevailing small dense LDL is derived to a larger extent from VLDL precursors, rather than entering the plasma as LDL or IDL, and catabolized more slowly than the large buoyant LDL prevailing in subjects with lower triglyceride levels. These two independent methods show that triglyceride-rich VLDL is the precursor of slowly catabolized LDL particles which constitute an atherogenic lipoprotein subfraction.

TO THE EDITOR: Protease inhibitors are a crucial component of highly active antiretroviral therapy for HIV infection. However, the use of these drugs is associated with hyperglycemia, hyperlipidemia, and lipodystrophy [1-3]. The underlying mechanisms leading to these metabolic alterations are unknown. We evaluated peripheral insulin sensitivity in 24 HIV-positive patients treated with protease inhibitors, 8 therapy-naive HIV-positive patients, and 18 HIV-negative controls (Figure 1) using an intravenous insulin tolerance test [4]. Figure 1. Insulin sensitivity of 18 HIV-negative controls (squares), 8 HIV-positive therapy-naive patients (diamonds), and 24 HIV-positive patients treated with protease inhibitors (11 with normal glucose tolerance [black triangles] and 13 with abnormal tolerance [white triangles]). Patients treated with protease inhibitors had a significantly lower median insulin sensitivity (67 mol/L per minute) than did untreated patients (156 mol/L per minute; P < 0.001) and controls (177 mol/L per minute; P < 0.001). Untreated patients did not differ significantly from controls (P > 0.2). With stratification according to oral glucose tolerance, insulin sensitivity was significantly higher in the treated patients with normal glucose tolerance (121 mol/L per minute; n = 11) than in those with impaired or diabetic glucose tolerance (55 mol/L per minute; n = 13). We used the mean insulin sensitivity of the HIV-negative controls 2 SDs (92 mol/L per minute) to distinguish between normal and abnormal insulin sensitivity. All controls and untreated patients had normal insulin sensitivity. All treated patients with impaired (n = 4) or diabetic (n = 9) oral glucose tolerance had abnormal insulin sensitivity. Of note, in the treated patients with normal oral glucose tolerance, both normal (n = 5) and abnormal (n = 6) insulin sensitivity was seen. These data suggest that treatment with protease inhibitors can lead to abnormal insulin sensitivity. In some patients, this can result in impaired or even diabetic oral glucose tolerance. A possible explanations for the reported peripheral insulin resistance is interference with insulin receptors or glucose transporters. Other factors, such as perturbance of insulin secretion or alterations of anti-insulinergic factors, may also be involved. Abnormal insulin sensitivity was seen in patients treated with all currently available protease inhibitors (indinavir, nelfinavir, ritonavir, and saquinavir).

Background: The use of protease inhibitors in the treatment of HIV-1 infection is associated with the new onset of diabetes mellitus, hyperlipidaemia and lipodystrophy. It is unclear whether these findings are coincidental or whether they reflect a causative effect of protease inhibitors. Objective: To evaluate the effect of treatment with protease inhibitors on insulin sensitivity, oral glucose tolerance and serum lipids in HIV-infected patients in order to determine whether treatment with protease inhibitors can cause peripheral insulin resistance. Design: Cross-sectional controlled study in HIV-infected patients treated with protease inhibitors to assess insulin sensitivity, oral glucose tolerance and changes in serum lipids. Methods: Sixty-seven patients treated with protease inhibitors, 13 therapy-naive patients and 18 HIV-negative control subjects were tested for insulin sensitivity (intravenous insulin tolerance test). In a subgroup of 24 treated patients, oral glucose tolerance was determined. Serum lipids prior to and under treatment with protease inhibitors were compared. Results: Patients on protease inhibitors had a significantly decreased insulin sensitivity when compared with therapy-naive patients (median, 75 and 156 μmol/l/min, respectively; p <0.001). All treated patients with impaired (n = 4) or diabetic (n = 9) oral glucose tolerance, and four out of 11 patients with normal glucose tolerance showed peripheral insulin resistance; all therapy-naive patients had normal insulin sensitivity. Treatment with protease inhibitors led to a significant increase in total triglycerides and cholesterol in the 67 treated patients (median increase, 113 and 37 mg/ml, respectively). Conclusion: Treatment with protease inhibitors is associated with peripheral insulin resistance, leading to impaired or diabetic oral glucose tolerance in some of the patients, and with hyperlipidaemia. Overall, there is a large variation in the severity and clinical presentation of protease inhibitor-associated metabolic side-effects.

BACKGROUND The nephrotic syndrome is characterized by proteinuria, hypoalbuminemia and hyperlipidemia. Despite intensive research it is not clear at present what the causal links are between these pathological findings. METHODS Stable isotope labeled amino acid tracer kinetic analysis was used to simultaneously investigate the metabolism of four apolipoprotein B-containing lipoproteins (VLDL1, VLDL2, IDL and LDL) and albumin in seven patients with nephrotic syndrome and marked hypercholesterolemia, in two additional nephrotic patients with concomitant renal failure and mixed hyperlipidemia, and in a matched group of normolipidemic controls. RESULTS Increased concentrations of VLDL2, IDL and LDL were due to (a) impaired VLDL2 and IDL delipidation, (b) reduced LDL catabolism, and (c) a trend towards an increased rate of total apolipoprotein B production. The rate of fractional albumin elimination was three times higher in patients than in controls and the rate of albumin synthesis was increased by 45%. No correlations were detectable between rates of apolipoprotein B production and the rate of albumin synthesis. CONCLUSIONS The results of this study suggest that hyperlipidemia in nephrotic syndrome is predominantly the result of delayed lipoprotein delipidation and catabolism. There is no evidence that it is driven by a general increase of the rate of hepatic protein synthesis.