The influence of age on low density lipoprotein metabolism: effects of cholestyramine treatment in young and old healthy male subjects

OBJECTIVE

The plasma concentration of low density lipoproteins (LDL) increases with age, mainly as the result of a reduced clearance of LDL. Because the conversion of cholesterol to bile acids is reduced with age, we hypothesized that the response of plasma LDL to stimulation of bile acid production would be different in young and old subjects.

DESIGN, SUBJECTS AND SETTING

Comparison of the response to cholestyramine treatment in two groups of normolipidaemic, normal weight males: seven young (23-34 years) and eight old (64-73 years). Outpatients at the metabolic ward of a university hospital given a standardized diet of natural type.

INTERVENTION

Cholestyramine was given 8 g b.i.d. for 3 weeks and continued during the second LDL turnover study.

MAIN OUTCOME MEASURES

Kinetics of autologous radiolabelled LDL before and during treatment. Mean values of lipoprotein lipid levels obtained during the two turnover studies. Changes in LDL particle composition and LDL receptor affinity between the two study periods.

RESULTS

Both age groups responded with decreased levels of LDL cholesterol and apolipoprotein-B (apoB), the change being more pronounced in the old subjects. The LDL apoB fractional catabolic rate was increased by approximately 11% in both groups. In contrast, there was a reduced ability in the old subjects to sustain their production rates for LDL apoB with resin therapy, resulting in a 23% reduction in LDL input. No effect on the apparent LDL apoB synthesis rate was observed in the young subjects. LDL particles isolated from cholestyramine-treated subjects were triglyceride-enriched and cholesterol-depleted, and showed a lowered affinity for the LDL receptor in tissue culture studies.

CONCLUSIONS

The results demonstrate that stimulation of bile acid production by cholestyramine treatment decreases LDL cholesterol levels in both young and old subjects. This therapy increases LDL apoB elimination in both age groups, but reduction of apparent LDL apoB production is only seen in old subjects.

Importance of estrogen receptors in hepatic LDL receptor regulation

Treatment with pharmacological doses of estrogen is the most potent way to stimulate hepatic LDL receptor expression in vivo. The mechanism for this effect is unclear, in part because of difficulties in inducing this stimulation in vitro. A fundamental question, whether estrogen receptors (ERs) mediate this stimulation, has not been addressed. The aim of the current study was to determine the involvement of ERs in the estrogen-induced stimulation of LDL receptors. Treatment of rats with high doses of ethynylestradiol for 7 days increased the hepatic LDL receptor protein and mRNA levels four- and threefold, respectively. LDL receptor stimulation in estrogen-treated rats was not due to their reduced food intake because hepatic LDL receptor expression did not increase in rats fasted for 72 hours. Treatment with antiestrogen (tamoxifen or clomiphene) abolished the LDL receptor stimulatory effect of ethynylestradiol at both the protein and mRNA levels. Antiestrogen alone had no effect on hepatic LDL receptor expression and did not influence the strong resistance to dietary cholesterol normally present in rats. It is concluded that ERs are critically involved in the induction of hepatic LDL receptor expression by ethynylestradiol. The known role of growth hormone for the expression of hepatic ERs may therefore play a role in the modulation of the effects of estrogen on cholesterol metabolism and hepatic LDL receptors in the rat.

Lipoprotein metabolism in the fat Zucker rat: reduced basal expression but normal regulation of hepatic low density lipoprotein receptors

Hyperlipoproteinemia is one of the phenotypic characteristics of the fat Zucker rat that carries a mutation in the leptin receptor gene. In the present study, we studied the regulation of hepatic low density lipoprotein (LDL) receptor expression in lean and fat Zucker rats. Compared with lean rats, the fat ones had a pronounced (approximately 60%) reduction in hepatic LDL receptor expression, whereas the levels of receptor messenger RNA (mRNA) were not reduced. Fat rats had increased levels of very low density lipoproteins and high density lipoproteins, but their plasma apo B100 within LDL was reduced. Challenge with 2% dietary cholesterol for 8 days suppressed hepatic LDL receptor expression in lean animals to similar levels as seen in fat ones, whereas the reduction in mRNA levels was much less pronounced. Treatment with ethynylestradiol (5 mg/kg BW per day) for 4 days strongly stimulated hepatic LDL receptor expression in both lean and fat rats; this treatment also increased LDL receptor mRNA levels, but to a lesser extent. In conclusion, the basal expression of hepatic LDL receptors is reduced in fat Zucker rats, but the capacity for the regulation of the receptors remains intact.

Hepatic cholesterol metabolism in human obesity

Hepatic cholesterol metabolism was studied in operative liver biopsies from 17 morbidly obese subjects and compared with that in samples from 15 nonobese controls. The aim was to understand the mechanisms causing the hypersecretion of cholesterol into bile. The content of cholesteryl esters was increased threefold in the liver of obese subjects compared with that of the controls (P < .0001). The activity and the messenger RNA (mRNA) level of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the rate limiting enzyme for cholesterol synthesis, were higher in the obese subjects compared with the nonobese subjects (75% and 140%, respectively; P < .01). In the obese subjects, the activity and mRNA level of cholesterol 7alpha-hydroxylase, which regulates the catabolism of cholesterol to bile acids, were also increased by 140% (P < .05) and 180% (P = .06), respectively, as compared with the controls. There was a significant correlation between the activities and the mRNA levels of cholesterol 7alpha-hydroxylase among the obese subjects (r = +0.65, P < .01). The activities of acyl-coenzyme A:cholesterol acyltransferase (ACAT), which governs cholesteryl ester formation, in obese and nonobese patients were 12.5 +/- 1.7 and 8.1 +/- 1.2 pmol/min/mg protein, respectively (P < .05), and the low-density lipoprotein (LDL) receptor mRNA levels were 5.3 +/- 0.7 and 4.5 +/- 0.9 molecules of mRNA/microg of RNA, respectively. We conclude that the activities of three key enzymes in hepatic cholesterol metabolism were increased in morbidly obese subjects compared with nonobese controls, as were mRNA levels of HMG CoA reductase and cholesterol 7alpha-hydroxylase. The mRNA level of the LDL receptor in the obese subjects was not significantly changed. The hypersecretion of cholesterol occurring in obesity is neither due to a reduced conversion of cholesterol to bile acids nor to a decreased esterification of hepatic cholesterol but may be due to an increased synthesis of cholesterol.

Growth hormone and bile acid synthesis. Key role for the activity of hepatic microsomal cholesterol 7alpha-hydroxylase in the rat

Growth hormone (GH) has an important role in the regulation of hepatic LDL receptor expression and plasma lipoprotein levels. This investigation was undertaken to characterize the effects of GH on hepatic cholesterol and bile acid metabolism in the rat. In hypophysectomized (Hx) rats, the activities of the rate-limiting enzymes in cholesterol and bile acid biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) and cholesterol 7alpha-hydroxylase (C7alphaOH), were reduced by 71 and 64%, respectively. HMG CoA reductase mRNA levels were reduced by 37%, whereas C7alphaOH mRNA was increased by 81%. LDL receptor expression was reduced by 18% in Hx rats, without any change in the LDL receptor mRNA levels. Although the normal diurnal variation of C7alphaOH activity was preserved in Hx rats, the activity of C7alphaOH was much reduced both at midday and midnight. Total hepatic cholesterol was increased by 14% in Hx animals whereas microsomal cholesterol was unchanged. The rate of cholesterol esterification was enhanced (by 38%) in liver microsomes from Hx rats. Stepwise hormonal substitution of Hx rats showed that GH, but not thyroid hormone or cortisone, was essential to normalize the enzymatic activity of C7alphaOH. GH also normalized the altered plasma lipoprotein pattern in Hx rats, and increased the fecal output of bile acids. The latter effect was particularly evident when GH was combined with cortisone and thyroid hormone. Also in normal rats, GH stimulated C7alphaOH activity. In conclusion, GH has an essential role to maintain a normal enzymatic activity of C7alphaOH, and this, at least in part, explains the effects of GH on hepatic cholesterol metabolism. GH is also of critical importance to normalize the altered plasma lipoprotein pattern in Hx rats.

Novel effects of histamine on lipoprotein metabolism: suppression of hepatic low density lipoprotein receptor expression and reduction of plasma high density lipoprotein cholesterol in the rat

Histamine has been shown to be involved in atherosclerosis and coronary heart disease. Little information is available regarding the effects of histamine on lipoprotein metabolism. In the current study, we investigated the effects of histamine on the expression of hepatic low density lipoprotein (LDL) receptors and on plasma lipoproteins in the rat. Injection of compound 48/80 (C48/80, a histamine releaser) or histamine reduced hepatic LDL receptor expression, but not LDL receptor messenger RNA levels. Oral administration of polymyxin B (an antiendotoxin antibiotic and a histamine releaser) before the injection of C48/80 or histamine did not attenuate their effects. Polymyxin B itself had effects similar to those of C48/80 and histamine on LDL receptors. These results suggest that the effects of histamine are not mediated by the induction of gut-derived endotoxemia. Histamine H2 agonists (dimaprit and impromidine), but not H1 agonists (2-methylhistamine and 2-thiazolylethylamine), also reduced hepatic LDL receptor expression. The suppressive effect of C48/80 on hepatic LDL receptor expression was not attenuated by either the H1 antagonist (chlorpheniramine) or the H2 antagonist (cimetidine). Administration of C48/80 also reduced plasma high density lipoprotein (HDL) cholesterol. The H1 antagonist (chlorpheniramine), but not the H2 antagonist (cimetidine), almost completely reversed the effect of C48/80 on plasma HDL cholesterol. In conclusion, histamine suppresses hepatic LDL receptor expression via a non-H1 receptor-mediated pathway, and histamine reduces plasma HDL cholesterol via an H1 receptor-mediated pathway.

Simvastatin impairs mitogen-induced proliferation of malignant B-lymphocytes from humans--in vitro and in vivo studies

Chronic lymphocytic leukemia (CLL) cells express lower low density lipoprotein (LDL) receptor activity and higher 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity than normal mononuclear blood cells indicating that CLL cells may depend on cholesterol synthesis for their proliferation. We studied the effects of competitive inhibitors of HMG-CoA reductase on malignant lymphocyte proliferation in vitro and in vivo. Tumor B-cells from 13 patients with CLL, hairy cell leukemia, or immunoblastic B-cell lymphoma were cultured for 4 d in the presence of B-cell mitogens and cholesterol synthesis inhibitors. Simvastatin and lovastatin suppressed, in a concentration-dependent manner, the mitogen-induced cellular thymidin uptake in medium with 10% human AB-serum or lipoprotein-deficient serum. Pravastatin was active only in medium with lipoprotein-deficient serum. Ten previously untreated patients with CLL received simvastatin orally, 40 mg daily for 12 wk. Mean reductions in total plasma and LDL cholesterol were 30% (range 9-46%) and 37% (range 16-63%), respectively. Cells from four patients showed moderate to minor increases in the degradation rate of 1251-LDL suggesting that the need for exogenous cholesterol had increased, three patients showed an increase in HMG-CoA reductase activity, and the cells from one patient showed both. There was no significant change in the clinical disease status during medication. However, four of the ten patients developed a therapy-demanding progressive disease during the subsequent year. Further clinical studies with cholesterol synthesis inhibitors in leukemia are warranted.

Low-density lipoprotein metabolism and its association to plasma lipoprotein(a) in the nephrotic syndrome

Patients with nephrotic syndrome have multiple abnormalities of lipoprotein metabolism, but the cause and exact nature of these abnormalities have not been established. In the present study we have determined the kinetics of plasma low-density lipoprotein (LDL) apoB in seven nephrotic patients demonstrating an elevated LDL apoB production rate (25.7 +/- 6.4 vs. 13.1 +/- 0.3 mgkg-1 day-1; P < 0.001) but a normal LDL apoB fractional catabolic rate (FCR) (0.31 +/- 0.04 vs. 0.33 +/- 0.008 pools day-1; NS) compared with 41 healthy control subjects. However, two out of the seven patients had a markedly low LDL apoB-FCR. Serum albumin was inversely correlated with the LDL apoB production rate (R = -0.82; P < 0.05). Plasma lipoprotein (a) [Lp(a)] levels were significantly (P < 0.001) increased in the nephrotic patients compared with control subjects. Significant correlations were observed between log Lp(a) and LDL apoB production rate (R = 0.90; P < 0.01), VLDL-cholesterol (R = 0.95; P < 0.001) and VLDL-triglycerides (R = 0.80; P < 0.05) respectively. In summary, the present study suggests that nephrotic hyperlipidaemia may be caused by at least two independent mechanisms. The elevated LDL apoB production rate is highly correlated with the prevailing levels of serum albumin, whereas some nephrotic patients seem to have a decreased LDL apoB clearance, suggesting impaired LDL receptor-mediated clearance. The present results also suggest that the elevated plasma Lp(a) levels in nephrosis are related to an increased hepatic synthesis rather than a decreased catabolism of lipoproteins.

No influence of simvastatin treatment on platelet function in vivo in patients with hypercholesterolemia

Hypercholesterolemia is associated with platelet activation. Reduction of plasma cholesterol levels by the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin has been found to improve certain aspects of platelet function in vitro and in vivo, but controlled trials are largely lacking. The present randomized, double-blind, crossover study was performed to evaluate whether 10- to 12-week treatment with simvastatin or placebo affects platelet function in vivo in 23 hypercholesterolemic men. Measurements were performed at rest and during mental stress. Simvastatin treatment reduced plasma total cholesterol levels by 18 +/- 2% and low density lipoprotein cholesterol levels by 26 +/- 2% (P < .001 for both), whereas high density lipoprotein cholesterol levels increased slightly (6 +/- 2%, P < .05). Platelet aggregability as assessed by filtragometry ex vivo was unaffected by simvastatin treatment both at rest and during mental stress. Plasma beta-thromboglobulin levels, which reflect platelet secretion, were also unaltered by simvastatin treatment both at rest (antilog of the mean: 20.2 versus 20.0 ng/mL during placebo) and during mental stress. Moreover, nocturnal excretion of 11-dehydrothromboxane B2 in urine did not differ between placebo and active treatment: 218 versus 216 ng/mmol creatinine, respectively. The corresponding values for urinary excretion of high-molecular-weight beta-thromboglobulin were 1.78 versus 1.92 ng/mmol creatinine. Thus, simvastatin treatment had no clear-cut effect on platelet function, as assessed by four different in vivo related platelet function variables, in hypercholesterolemic men.

Secretion and composition of bile after human liver transplantation: studies on the effects of cyclosporine and tacrolimus

Cyclosporine (CsA) and tacrolimus (FK506) have recently been reported to inhibit canalicular transport of bile acids in vitro and thereby possibly induce cholestasis. A relative reduction of chenodeoxycholic acid (CDCA) has been observed after liver transplantation when CsA is used as immunosuppressant. We tested the hypothesis that CsA induces cholestasis and reduces CDCA secretion as compared with treatment with monoclonal antibodies (OKT3), and that CsA differs from FK506 with regard to its effects on biliary lipid secretion. Bile flow, biliary lipid secretion rates, and biliary bile acid composition were determined during the first 10 days after transplantation in 29 liver transplant recipients. Two prospective randomized studies were performed that compared CsA and OKT3 and compared CsA- and FK506-based regimens. In study 1, bile acid output averaged 0.75+/-0.15 micromol/min in the CsA I group and 0.54+/-0.11 micromol/min in the OKT3 group on postoperative day 1. Bile flow and bile acid output then increased, and there was no significant difference between the two groups. The relative proportion of CDCA decreased to the same extent in both groups. In study 2, mean bile acid outputs on postoperative day 1 were 0.57+/-0.26 micromol/min and 0.55+/-0.15 micromol/min in the CsA 2 and FK506 groups, respectively. The following increase in bile acid secretion was significantly larger in the FK506 group. After transplantation, the relative proportion of CDCA decreased with time in both groups, but the reduction was more rapid in the FK506 group. In conclusion, CsA did not inhibit bile secretion during short-term treatment after liver transplantation. Compared with patients given CsA-based treatment, patients with FK506-based treatment recovered bile secretion more rapidly.

Haemostatic markers, inflammatory parameters and lipids in male and female patients in the Angina Prognosis Study in Stockholm (APSIS). A comparison with healthy controls

OBJECTIVES

To investigate haemostatic markers (especially fibrinolysis), inflammatory parameters and lipids in patients with stable angina pectoris. Special attention was paid to differences between male and female patients, and to the reactivity to exercise or the diurnal variation of certain parameters.

SUBJECTS

Eight hundred and nine patients (31% females) and a matched healthy control group (n = 50).

RESULTS

The patients had signs of disturbed fibrinolysis, with elevated plasma levels of tissue plasminogen activator (tPA) antigen and plasminogen activator inhibitor (PAI-1) activity at rest, and attenuated responses of tPA antigen and activity to exercise. Elevated levels of fibrinogen, white blood cell counts and orosomucoid were found, suggesting increased inflammatory activity, as well as a more disturbed lipid profile (higher triglycerides and lower HDL cholesterol levels) than among controls. Female patients had higher HDL cholesterol and lower triglyceride levels than male patients, but higher platelet counts and signs of enhanced platelet activity (beta-thromboglobulin excretion). In addition, female patients had lower white blood cell counts, suggesting lesser inflammatory activity.

CONCLUSIONS

Patients with stable angina pectoris have signs of markedly disturbed fibrinolysis both at rest and in response to exercise, as well as signs of enhanced inflammatory activity and dyslipidemia. The observed sex differences suggest that male patients with stable angina pectoris may have a more lipid-related disease, whereas it may be more dependent on platelet function in females.

Contrasting effects of growth hormone and insulin-like growth factor I on the biological activities of endotoxin in the rat

We previously demonstrated that GH potentiates the biological activities of endotoxin in the rat. In the present study, we wanted to determine if the potentiating effects of GH on the biological activities of endotoxin could be reproduced by insulin-like growth factor I (IGF-I). Endotoxin (5 mg/kg BW) was injected in rats primed with or without GH or IGF-I for 3 days. As expected, endotoxin administration markedly increased circulating tumor necrosis factor (TNF) and interferon-gamma (IFN gamma) and induced organ injury, hypoglycemia, and hyperlipidemia. In GH-primed rats, endotoxin induced a further increase of serum IFN gamma (but not TNF); and five out of six of those rats died within 15 h after giving endotoxin. However, little difference between endotoxin-treated rats with and without IGF-I priming could be seen. Furthermore, IGF-I infusion altered blood glucose, urea, and circulating ICF-I levels more than GH infusion. Therefore, IGF-I does not enhance the biological activities of endotoxin in the rat, suggesting that the enhancement of endotoxin effects by GH is via an IGF-I-independent pathway. Priming rats by GH (but not by IGF-I) induced a further increased response of serum IFN gamma but not TNF to subsequent endotoxin challenge, suggesting that IFN gamma rather than TNF is likely to be involved in this process.

Metabolism and excretion of ropivacaine in humans

The pharmacokinetics, biotransformation, and urinary excretion of ropivacaine (Naropin), a new local anesthetic agent, have been studied in six healthy male volunteers after a 15-min iv infusion of 152 mumol (50 mg) of [14C]ropivacaine, with a specific radioactivity of 22.5 kBq/mumol (8.8 kBq/mg). Blood, urine, and feces were collected for up to 96 hr after administration. The plasma and urine samples were analyzed for unchanged ropivacaine and for four of its metabolites, i.e. 3-OH-2',6'-pipecoloxylidide (3-OH-PPX), 4-OH-ropivacaine, 3-OH-ropivacaine, and the N-dealkylated metabolite PPX, using GC and HPLC methods. The presence of 2,6-xylidine in plasma was also analyzed. The metabolites were quantified after acidic hydrolysis. The radioactivity could be followed in plasma for up to 14 hr after administration, with ropivacaine being the predominant compound in the early samples. The concentrations of the aforementioned metabolites in plasma were below or just above the lower limit of quantification, and no 2,6-xylidine was detected. The maximum plasma concentration of ropivacaine was 5.9 +/- 2.6 microM (1.6 +/- 0.7 mg/liter), with an elimination half-life of 2.0 +/- 0.3 hr and a total plasma clearance of 397 +/- 127 ml/min. The maximum plasma concentration value for the total radioactivity was 5.5 +/- 2.4 microM (1.5 +/- 0.7 mg/liter) and the elimination half-life was 5.4 +/- 2.9 hr. [14C]Ropivacaine and its metabolites were mainly excreted in the urine, with a total recovery of 86 +/- 3% in the urine and 9 +/- 1% in the feces after 96 hr. Most of the radioactivity (about 68%) was excreted within 12 hr. Ropivacaine was extensively metabolized, and only 1 +/- 0.6% of the dose was excreted unchanged in the urine. The major metabolite identified in the urine was conjugated 3-OH-ropivacaine, which was excreted to an extent of 37 +/- 3% of the dose. The urinary excretion of 4-OH-ropivacaine was < 1%, whereas the N-dealkylated metabolites PPX and 3-OH-PPX accounted for 2 and 3% of the dose, respectively. An additional hydroxylated metabolite, 2-OH-methyl-ropivacaine, was tentatively identified in the urine of some volunteers, accounting for about 4-15% of the dose.

Reduction in serum levels of antimitochondrial (M2) antibodies following immunoglobulin therapy in severe combined immunodeficient (SCID) mice reconstituted with lymphocytes from patients with primary biliary cirrhosis (PBC)

The effect of gammaglobulin treatment on autoantibody production was investigated in SCID mice reconstituted with human peripheral blood mononuclear cells (PBMC) obtained from patients with PBC. All reconstituted mice displayed the presence of human antimitochondrial antibodies (alpha M2Ab) of both IgG and IgM types before treatment with human immunoglobulin. Two weeks after i.p. injection of 20 x 10(6) PBMC into SCID mice, i.p. treatment with various preparations of human immunoglobulin was initiated. In control animals treated with saline, serum levels of human alpha M2Ab of the IgG type increased with time, peaking around 4 weeks after reconstitution. In contrast, human IgG autoantibodies rapidly decreased in all animals treated with human IgG. Treatment with a human IgM preparation had no effect on serum levels of alpha M2Ab of the IgG type. The results may suggest that the pronounced reduction of specific IgG autoantibodies was due to an increased catabolism of human IgG, including the autoantibodies, in the gammaglobulin-treated mice. Although the production of human alpha M2Ab in reconstituted mice could be easily shown, PBC-specific liver lesions or bile duct destruction were not observed, irrespective of treatment protocol.

VLDL receptor mediates the uptake of human chylomicron remnants in vitro

The VLDL receptor has been described as a new member of the LDL receptor supergene family that specifically binds VLDL in vitro via apolipoprotein E and lipoprotein lipase. Both apolipoprotein E and lipoprotein lipase are constituents of chylomicron remnants, another triglyceride-rich lipoprotein which has been proposed as a physiological ligand for the VLDL receptor. We used human chylomicron remnants to study their uptake into LDL, receptor-deficient Chinese hamster ovary cells overexpressing the human VLDL receptor. The uptake into these cells was compared to that into cells transfected with an empty transfection vector. Human chylomicron remnants were produced in vitro by hydrolysis with lipoprotein lipase, and were labeled with 125I. The uptake of these remnants into the cells overexpressing the VLDL receptor was found to be about 3-fold higher than the uptake into the control cells. The addition of a surplus of either apolipoprotein E or inactivated lipoprotein lipase to the remnants led to an increase in particle uptake. The chylomicron remnant uptake was inhibited by addition of the 39 kDa receptor associated protein These in vitro experiments strongly support the idea that the VLDL receptor is a physiological receptor for chylomicron remnants. The increase of receptor-mediated uptake induced by the addition of apoE or lipoprotein lipase underlines the role of these two proteins in this process.

Gemfibrozil reduces thrombin generation in patients with combined hyperlipidaemia, without influencing plasma fibrinogen, fibrin gel structure or coagulation factor VII

A double-blind, placebo-controlled, cross-over study was conducted in 21 men with combined hyperlipoproteinaemia to examine if lipid-lowering treatment with gemfibrozil (10-12 weeks) affects blood coagulation and fibrin gel structure at rest or during mental stress. Gemfibrozil lowered plasma triglycerides by 57 +/- 4%, whereas high density lipoprotein (HDL) cholesterol increased by 22 +/- 5%. Gemfibrozil lowered the triglyceride content of low density lipoprotein (LDL). Gemfibrozil reduced the plasma concentrations of thrombin-antithrombin complex (TAT) and prothrombin fragment F1 + 2 (F1 + 2), both at rest and during mental stress. However, there were no effects of gemfibrozil treatment on the plasma concentrations of fibrinogen, factor VII antigen, activated factor VII (VIIa) or activated factor XII (XIIa), or on fibrin gel structure. Acute mental stress per se did not influence coagulation factors, reaction products or fibrin gel structure, or their responses to the study drug. Thus, gemfibrozil reduced thrombin generation in men with combined hyperlipoproteinaemia, without influencing the plasma levels of fibrinogen, VIIa and XIIa, or fibrin gel structure. Attenuation of thrombin generation may contribute to the primary-preventive effects of gemfibrozil on coronary heart disease.

Hormonal regulation of serum lipoprotein (a) levels: effects of parenteral administration of estrogen or testosterone in males

When given orally, estrogens, as well as androgens, lower serum lipoprotein (a)[Lp(a)]levels. To determine whether these effects occur also after parenteral administration of steroids, Lp(a) levels were determined in two groups of elderly males suffering from prostatic carcinoma, who were randomized to treatment with parenteral estrogen (n = 8) or orchidectomy (n = 6). One group of healthy male volunteers (n = 9) was studied after parenteral administration of testosterone. Estrogen was given as im polyestradiol phosphate, 240 mg twice monthly, and testosterone was given as im injections, 250 mg/week. In the orchidectomized subjects, Lp(a) levels increased by 20% by month 3 after treatment (P < 0.05). In spite of drastic changes in serum hormone levels, no change in Lp(a) levels was observed in the estrogen-treated subjects. Concomitantly, low-density lipoprotein cholesterol levels were lowered by 15% and high-density lipoprotein cholesterol levels increased by 20%. Testosterone administration lowered Lp(a) levels by 20% (P < 0.05). No significant changes in serum lipid levels were observed in the testosterone-treated subjects or in the orchidectomy group. Thus, during parenteral administration of estrogens or androgens, diverging effects on Lp(a) and serum lipoproteins were observed. In particular, the mode of administration of estrogen influenced the response in Lp(a) levels. This suggests that the regulatory role of sex hormones on serum Lp(a) levels may depend on their capability to influence hepatic metabolic pathways of Lp(a).

Bile acid kinetics and biliary lipid composition in cystic fibrosis

AIMS/METHODS

Bile acid kinetics and biliary lipid composition were studied in seven patients, aged 17-70 years with cystic fibrosis. All patients were of normal height and weight, and were in good clinical condition. Ultrasonography indicated a small gallbladder in one and non-visualized gallbladder in two patients. Serum concentrations of cholesterol and transaminases were essentially normal. Substitution with pancreatic enzymes was discontinued at least 1 week before the investigation. Bile acid kinetics were determined by the isotope dilution technique using [24-14C] cholic and [24-14C] chenodeoxycholic acids.

RESULTS

The mean pool size of cholic acid was 3.3 (range 0.8-6.9) mmol, and that of chenodeoxycholic acid 2.3 (1.2-2.7) mmol, corresponding to 49 +/- 16 and 36 +/- 4 mumol/kg, respectively. The mean synthesis of cholic acid was 1.3 (0.5-3.6) mmol/day and of chenodeoxycholic acid 0.8 (0.2-1.7) mmol/ day and related to body weight 20 +/- 6 and 12 +/- 3 mumol.kg.day-1, respectively. Fractional turnover rates averaged 0.48 (0.24-0.67) and 0.36 (0.10-0.65) day-1, respectively. The kinetic values were not significantly different from controls, aged 21 to 68 years. The biliary lipid composition of fasting gallbladder bile showed a low-normal molar percentage of cholesterol, and in no case was bile supersaturated. The duodenal bile acid concentration was similar in patients and controls, but the bile acid distribution was significantly different; cholic acid constituted a higher percentage (p < 0.001) and chenodeoxycholic and deoxycholic acid lower percentages (p < 0.05 and p < 0.01, respectively) in cystic fibrosis patients than in controls.

CONCLUSIONS

The findings of normal concentrations of bile acids in duodenal bile and normal to large pool sizes of bile acids in all patients, despite a marked fat malabsorption, are in contrast to some previous reports. The data indicate that biliary lipid metabolism is normal in well-nourished and well-controlled adult patients with cystic fibrosis.

Expression of very low density lipoprotein receptor in the vascular wall. Analysis of human tissues by in situ hybridization and immunohistochemistry

The recently cloned very low density lipoprotein (VLDL) receptor binds triglyceride-rich, apolipoprotein-E-containing lipoproteins with high affinity. The observation that VLDL receptor mRNA is abundantly expressed in extracts of tissues such as skeletal muscle and heart, but not liver, has led to the hypothesis that this receptor may facilitate the peripheral uptake of triglyceride-rich lipoproteins. However, little information is available concerning the types of cells that express this receptor in vivo. As expression of the VLDL receptor in the vascular wall might have important implications for the uptake and transport of triglyceride-rich lipoproteins, and perhaps facilitate the development of atherosclerosis in hypertriglyceridemic individuals, we used in situ hybridization and immunohistochemistry to determine whether VLDL receptor mRNA and protein was expressed in human vascular tissue. We observed expression of the receptor by both endothelial and smooth muscle cells within normal arteries and veins, as well as within atherosclerotic plaques. In the latter, the VLDL receptor was also expressed by macrophage-derived foam cells. The widespread distribution of the VLDL receptor in vascular tissue suggests a potentially important role for this receptor in normal and pathophysiological vascular processes.

Gemfibrozil treatment of combined hyperlipoproteinemia. No improvement of fibrinolysis despite marked reduction of plasma triglyceride levels

Hypertriglyceridemia is linked to impaired fibrinolytic function, and lipid-lowering treatment with fibric acid derivatives could hypothetically improve fibrinolysis in this condition. We therefore conducted a double-blind, placebo-controlled, crossover study of gemfibrozil treatment on fibrinolytic function in 21 men with combined hyperlipoproteinemia. Measurements were performed at rest and during mental stress and after venous occlusion. The patients had clearly disturbed fibrinolytic function, with elevated plasminogen activator inhibitor-1 (PAI-1) activity at rest ( approximately 25 U/mL; reference, <15 U/mL). Gemfibrozil reduced plasma total and VLDL cholesterol as well as all triglyceride fractions, whereas HDL cholesterol increased (P <.001 for all). Total triglyceride levels were reduced by 57 +/- 4% (from 5.3 to 2.1 mmol/L). Fasting serum insulin levels were not altered by gemfibrozil treatment. Plasma levels of PAI-1 activity and tissue-type plasminogen activator (TPA) activity or antigen were unaffected by gemfibrozil treatment both at rest and during the provocations. The levels of D-dimer, plasmin/antiplasmin complex, and fibrinogen were also uninfluenced by gemfibrozil treatment. Mental stress elevated plasma TPA (P=.0036) and lowered PAI-1 (P=.0012) activity during placebo but not gemfibrozil treatment (P=.28 and P=.17, respectively), but treatment effects did not differ by ANOVA on delta values (ie, stress minus rest). Venous occlusion reduced PAI-1 activity, whereas TPA and plasmin/antiplasmin complex increased during both treatments. Thus, gemfibrozil treatment did not improve fibrinolysis or lower fibrinogen levels in men with combined hyperlipoproteinemia despite marked reduction of plasma triglyceride levels. It seems unlikely that improved fibrinolysis explains the primary preventive effect of gemfibrozil.

Growth hormone potentiates the in vivo biological activities of endotoxin in the rat

To investigate if growth hormone (GH) alters the effects of endotoxin in rats, endotoxin (5 mg kg-1 body weight) was injected into normal rats and into rats primed with GH for 3 days. Endotoxin had injurious effects on renal and liver function and induced hypoglycaemia and hyperlipidaemia as expected. GH-primed rats became extremely sick after endotoxin challenge and had more marked abnormalities of renal and liver function and much more pronounced hypoglycaemia and hyperlipidaemia than non-primed rats. It is concluded that growth hormone potentiates the in vivo biological activities of endotoxin in the rat. The results may also suggest that caution should be exerted when considering GH treatment in catabolic situations with endotoxaemia and that special attention should be paid to the prevention of infection during GH therapy in such situations.

Increased prevalence of atherosclerotic wall changes in patients with hyperlipidaemia after renal transplantation

OBJECTIVES

The initial aim of this study was to evaluate the possibility of influencing atherosclerosis in hyperlipidaemic renal transplant patients by lowering blood lipids with gemfibrozil treatment.

DESIGN

Although this double-blind, randomized trial was stopped after 6 months owing to the suspicion of drug interference, we report here on the results of baseline ultrasonographic examinations.

SETTING

The outpatient clinic at the Department of Transplantation Surgery, Huddinge University Hospital, Huddinge, Sweden.

SUBJECTS AND METHODS

The carotid arteries were examined in 16 out of the 19 kidney transplant patients included in the study using an ultrasonographic duplex scanner.

MAIN OUTCOME MEASURES

Plaque occurrence and the common carotid intima-media thickness of the renal transplant recipients were compared to the same parameters in a normotensive control group of approximately the same age from a previous study.

RESULTS

An increased prevalence of plaque (75% of the patients having plaque on one or both sides) was seen in the hyperlipidaemic renal transplant patients in comparison with the control group (16%; P < 0.001). The common carotid intima-media complex was thicker (P < 0.05), and the lumen diameter and the calculated cross-sectional intima-media area were greater (P < 0.01-0.001) in the transplant recipients.

CONCLUSIONS

Markedly increased atherosclerotic wall changes are seen in the carotid arteries of patients with hyperlipidaemia after renal transplantation.

Endotoxin suppresses rat hepatic low-density lipoprotein receptor expression

Endotoxin induces hyperlipidaemia in experimental animals. In the current study, we investigated whether endotoxin alters hepatic low-density lipoprotein (LDL) receptor expression in rats. Endotoxin treatment suppressed hepatic LDL receptor expression in a dose- and time-dependent manner. Eighteen hours after intraperitoneal injection of increasing amounts of endotoxin, LDL receptor and its mRNA levels were determined by ligand blot and solution hybridization respectively. LDL receptor expression was inhibited by about 70% at a dose of 500 micrograms/100 g body weight. However, LDL receptor mRNA levels were markedly increased in all endotoxin-treated groups at this time point (by 83-136%; P < 0.001). Time-course experiments showed that LDL receptor expression was already reduced by 48% 4 h after endotoxin injection and was maximally reduced (by 63-65%) between 8 and 18 h. Changes in hepatic LDL receptor mRNA showed a different pattern. By 4 h after endotoxin injection, LDL receptor mRNA had decreased by 78% (P < 0.001). However, by 8 h after endotoxin injection, LDL receptor mRNA had returned to levels similar to controls, and 18 and 24 h after endotoxin injection, they were increased by about 60% (P < 0.05). Separation of plasma lipoproteins by FPLC demonstrated that endotoxin-induced changes in plasma triacylglycerols and cholesterol were due to accumulation of plasma apolipoprotein B-containing lipoproteins among very-low-density lipoprotein, intermediate-density lipoprotein and LDL. It is concluded that endotoxin suppresses hepatic LDL receptor expression in vivo in rats.

Regulation of rat hepatic low density lipoprotein receptors. In vivo stimulation by growth hormone is not mediated by insulin-like growth factor I

Growth hormone (GH) has an important role in the regulation of hepatic LDL receptor expression and plasma lipoprotein levels. This investigation was undertaken to evaluate if these effects of GH on hepatic LDL receptors are direct or mediated by insulin-like growth factor I (IGF-I). Two models were studied in which substitution with GH is important for the regulation of hepatic LDL receptors: hypophysectomized rats receiving high-dose ethynylestradiol or challenge with dietary cholesterol. The hypophysectomized rats were hormonally substituted by infusion with dexamethasone and L-thyroxine, and either GH or IGF-I. In both models, GH was essential for maintaining normal expression of LDL receptors. In contrast, despite fully normalized plasma levels, IGF-I did not support the expression of hepatic LDL receptors. Analysis of plasma lipoproteins revealed that substitution with GH, but not with IGF-I, reduced LDL and intermediate density lipoproteins. In addition, determination of hepatic mRNA levels for apo B-100 and apo B-48 indicated that GH may be more effective than IGF-I in the promotion of apo B mRNA editing. In conclusion, GH has specific effects on hepatic LDL receptor expression and plasma lipoprotein levels that are not mediated by IGF-I.