Oxidized LDL level is related to gene expression of tumour necrosis factor super family members in children and young adults with familial hypercholesterolaemia.

OBJECTIVE: Familial hypercholesterolaemia (FH) is associated with increased risk of premature atherosclerosis. Inflammation is a key event in atherogenesis, and we have previously reported an inflammatory imbalance between tumour necrosis factor (TNF)α and interleukin-10 in children with FH. Based on the potential role of TNF-related molecules in inflammation, we investigated the regulation of other members of the TNF superfamily (TNFSF)/TNF receptor superfamily (TNFRSF) in children and young adults with FH and matched healthy controls. METHODS: Expression of TNFSF/TNFRSF genes in peripheral blood mononuclear cells (PBMCs) was quantified in children and young adults with FH prior to (n = 42) and after statin treatment (n = 10) and in controls (n = 25) by quantitative real-time polymerase chain reaction. RESULTS: First we found that, compared with controls, the mRNA levels of OX40L, BAFFR and TRAILR1 were significantly higher, whereas TRAIL and TRAILR3 were significantly lower in children and young adults with FH. Secondly, levels of oxidized low-density lipoprotein (oxLDL) were significantly raised in the FH group, and correlated with the expression of OX40L, BAFFR and TRAILR1. Thirdly, oxLDL increased mRNA levels of BAFFR, TRAILR1 and TRAILR4 in PBMCs ex vivo from individuals with FH. Fourthly, OX40, acting through OX40L, enhanced the oxLDL-induced expression of matrix metalloproteinase-9 in THP-1 monocytes in vitro. Finally, after statin treatment in children with FH (n = 10), mRNA levels of OX40L and TRAILR1 decreased, whereas levels BAFF, TRAIL and TRAILR3 increased. CONCLUSION: Our findings suggest the involvement of some TNFSF/TNFRSF members and oxLDL in the early stages of atherogenesis; this may potentially contribute to the accelerated rate of atherosclerosis observed in individuals with FH.

Sun exposure rapidly reduces plasmacytoid dendritic cells and inflammatory dermal dendritic cells in psoriatic skin.

BACKGROUND: Interferon (IFN)-α-producing plasmacytoid dendritic cells (pDCs), inflammatory CD11c+CD1c- myeloid dendritic cells (mDCs) and macrophages have been found to contribute to the pathogenesis of psoriasis. Heliotherapy is a well-established treatment modality of this disease, although the details of how the effects are mediated are unknown. OBJECTIVES: To test the hypothesis that exposure to natural sun affects pathogenic DC subsets in lesional skin. METHODS: Skin biopsies were obtained from lesional and nonlesional skin in 10 patients with moderate to severe psoriasis subjected to controlled sun exposure on Gran Canaria. Biopsies were obtained at baseline, day 2 and day 16 and examined by immunohistochemistry. RESULTS: Sixteen days of heliotherapy had excellent clinical effect on patients with psoriasis, with significant reductions in Psoriasis Area and Severity Index (PASI) scores. In lesional skin pDC numbers and expression of MxA, a surrogate marker for IFN-α, were rapidly reduced. Inflammatory CD11c+CD1c- mDCs were significantly reduced whereas resident dermal CD11c+CD1c+ mDCs were unaffected. Expression levels of the maturation marker DC-LAMP (CD208) on mDCs were significantly reduced after sun exposure, as were the numbers of lesional dermal macrophages. A decrease of dermal DC subsets and macrophages was already observed after 1 day of sun exposure. An additional finding was that DC-SIGN (CD209) is primarily expressed on CD163+ macrophages and not DCs. CONCLUSIONS: The clinical improvement in psoriasis following sun exposure is associated with rapid changes in dermal DC populations and macrophages in lesional skin, preceding the clinical effect. These findings support the concept that these DC subsets are involved in the pathogenesis of psoriasis and suggest that sun-induced clinical benefit may partly be explained by its effect on dermal DCs.

Sun exposure induces rapid immunological changes in skin and peripheral blood in patients with psoriasis.

BACKGROUND: Ultraviolet (UV) radiation has immunosuppressive effects and heliotherapy is a well-described treatment modality for psoriasis. OBJECTIVES: To characterize early sun-induced immunological changes both local and systemic in patients with psoriasis. METHODS: Twenty patients with moderate to severe psoriasis were subjected to controlled sun exposure on Gran Canaria, Canary Islands, Spain. Psoriasis Area and Severity Index (PASI) scores were evaluated. Skin biopsies were obtained from lesional and nonlesional skin in 10 patients at baseline and on day 16 and from five additional patients on day 2. Specimens were examined with immunohistochemistry and polymerase chain reaction. Blood samples were obtained from all patients at the same time points and were examined for T-cell subsets and cytokine production. RESULTS: Significant clinical improvement was achieved during the study period. CD4+ and CD8+ T cells in lesional skin were significantly reduced in both the epidermis and dermis. In contrast, dermal FOXP3+ T cells were relatively increased. In the peripheral blood skin homing cutaneous lymphocyte-associated antigen (CLA)+ T cells were significantly decreased after only 1 day in the sun and in vitro stimulated peripheral blood mononuclear cells demonstrated reduced capacity to secrete cytokines after 16 days. CONCLUSIONS: Our data show that clinical improvement of psoriasis following sun exposure is preceded by a rapid reduction in local and systemic inflammatory markers, strongly suggesting that immune modulation mediated the observed clinical effect. We cannot completely rule out that other mechanisms, such as stress reduction, may contribute, but it is extensively documented that UV irradiation is a potent inducer of immunosuppression and we therefore conclude that the observed effect was primarily due to sun exposure.

Effect of climate therapy at Gran Canaria on vitamin D production, blood glucose and lipids in patients with psoriasis.

BACKGROUND: Climate therapy (heliotherapy) of psoriasis is an effective and natural treatment. Ultraviolet radiation (UVB) from the sun improves psoriasis and induces vitamin D(3) synthesis. OBJECTIVE: The aim of the study was to investigate the effect of climate therapy on vitamin D(3) synthesis, blood glucose, lipids and vitamin B12 in psoriasis patients. METHODS: Twenty Caucasian patients (6 women and 14 men; mean age, 47.2 years; range, 24-65) with moderate to severe psoriasis [mean Psoriasis Area and Severity Index (PASI) score 9.8; range, 3.8-18.8] received climate therapy at the Gran Canarias for 3 weeks. Blood samples were drawn before and after 15 days of sun exposure. In addition, the patients' individual skin UV doses based on UV measurements were estimated. RESULTS: Sun exposure for 15 days lead to a 72.8% (+/- 18.0 SD) reduction in the PASI score in psoriasis patients. Although no direct correlation was observed between PASI score improvement and UVB dose, the sun exposure improved the vitamin D, lipid and carbohydrate status of the patients. The serum concentrations of 25-hydroxyvitamin D [25(OH)D] increased from 57.2 +/- 14.9 nmol/L before therapy to 104.5 +/- 15.8 nmol/L (P < 0.0001) after 15 days of sun exposure; the serum levels of 1,25-dihydroxyvitamin D [1,25(OH)(2)D] increased from 146.5 +/- 42.0 to 182.7 +/- 59.1 pmol/L (P = 0.01); the ratio of low-density lipoprotein cholesterol and high-density lipoprotein cholesterol decreased from 2.4 to 1.9 (P < 0.001); and the haemoglobin A(1)c (HbA(1)c) levels decreased from 5.6 +/- 1.7% to 5.1 +/- 0.3% (P < 0.0001). CONCLUSION: Climate therapy with sun exposure had a positive effect on psoriasis, vitamin D production, lipid and carbohydrate status.

Endocytosed LDL and beta-VLDL follow different intracellular pathways in rat liver.

The intracellular transport of [125I]tyramine cellobiose low-density lipoprotein ([125ITC]LDL) and [131ITC]beta-very-low-density lipoprotein ([131ITC]beta-VLDL) in rat liver was studied by means of centrifugation in sucrose and Nycodenz gradients. At time-points up to 45 min after intravenous injection, the two ligands were found in endosomes with distinctly different buoyant densities. In the Nycodenz gradients [131ITC]beta-VLDL appeared at 1.08 g/ml partly coinciding with the distribution of the cation independent (alpha)mannose-6-phosphate receptor, whereas [125ITC]LDL was found at 1.13 mg/ml, where the degradation of [125ITC]LDL started. [131ITC]beta-VLDL, on the other hand, was transferred to denser vesicles, banding at 1.16 g/ml, and degradation started in these organelles, similar to that observed with asialoorosomucoid (ASOR) that was used as a control ligand. Since degradation products coincided with beta-N-acetylglucosaminidase we assume that these organelles are secondary lysosomes. [125ITC]LDL was subsequently also transferred to these dense secondary lysosomes, and the distribution of degraded [125ITC]LDL was therefore bimodal until [125ITC]LDL was completely cleared from the circulation. Furthermore our results show that the different intracellular pathways observed are not due to uptake in different liver cell types, since the bimodal distribution of [125ITC]LDL was also evident in purified liver parenchymal cells. The data suggest that LDL and beta-VLDL follow different endosomal pathways in the rat hepatocytes and that both pathways meet in a common final lysosome. The data also support the notion that LDL and beta-VLDL are taken up through different endocytic receptors. However, following estradiol treatment, both ligands seem to follow a common pathway. In this case the density distributions of the two ligands coincide and resemble the pathway of LDL observed in control animals. This may be due to a pronounced up-regulation of LDL receptors following estradiol treatment, and beta-VLDL may under these conditions be taken up via the LDL receptor.

Intracellular transport and degradation of chylomicron remnants in rat liver cells after in vivo endocytosis.

The intracellular transport and degradation of in vivo endocytosed chylomicron remnants labelled with 125I in the protein moiety was studied in rat liver cells by means of subcellular fractionation in Nycodenz and sucrose density gradients. Initially, the radioactivity was located in low-density endosomes and was sequentially transferred to light and dense lysosomes. Data from gel filtration of the light and dense lysosomal fractions showed radioactive material with a molecular weight of about 1000-2000, representing short peptide fragments or amino acids which remain attached to iodinated tyramine cellobiose. In addition, undegraded apoproteins accumulated in both types of lysosome. Our data suggest that endocytosed chylomicron remnant apoproteins are first located in low-density endosomes and are sequentially transferred to light and dense lysosomes. Furthermore, the degradation process starts in the light lysosomes.

Effect of cholesterol feeding on the susceptibility of lipoproteins to oxidative modification.

In previous studies we have shown that the liver endothelial and Kupffer cells in hypercholesterolemic rabbits are very active in endocytosis of low-density lipoprotein (LDL) and beta-very-low-density lipoprotein (beta-VLDL) (Nenseter et al. (1992) J. Lipid Res. 33, 867-877; Gudmundsen et al. (1993) J. Lipid Res. 34, 589-600). These data raised the question whether subfractions of LDL and beta-VLDL were modified in vivo to forms recognized by the scavenger/oxidized LDL receptors of the non-parenchymal liver cells. The purpose of the present study was to address this question by assessing the effect of cholesterol feeding on the susceptibility of the lipoproteins to oxidative modification in vitro. In addition, the effect of HDL on the lipid peroxidation of LDL was evaluated. LDL and beta-VLDL were isolated from rabbits given a diet supplemented with cholesterol (2% w/w) for 3 weeks. The extent of Cu(2+)-catalyzed oxidation of the lipoproteins was compared with that of LDL from control-fed rabbits. Extent of oxidation assessed by formation of conjugated dienes, lipid peroxides, thiobarbituric acid-reactive substances, relative electrophoretic mobility and uptake of lipoproteins by J774 macrophages suggested that LDL and beta-VLDL from the hypercholesterolemic rabbits were more susceptible to oxidation than LDL from normolipidemic rabbits. HDL protected LDL and beta-VLDL from lipid peroxidation in vitro. Taken together, the increased susceptibility of LDL and beta-VLDL to oxidative modification in vitro, combined with the low levels of alpha-tocopherol, and the reduced ratio of HDL to LDL cholesterol observed in the hypercholesterolemic rabbits, and the protective effect of HDL on the lipid peroxidation of LDL, support the probability that oxidative modification of LDL and beta-VLDL occur in vivo in the hypercholesterolemic rabbits.

Altered composition of HDL3 in FH subjects causing a HDL subfraction with less atheroprotective function.

BACKGROUND: Subjects with familial hypercholesterolemia (FH) are associated with increased risk of premature atherosclerosis and coronary artery disease (CAD). However, onset of clinically manifested CAD varies widely among subjects with heterozygous FH. The purpose of this study was to investigate whether FH subjects with an identical mutation in the low-density lipoprotein (LDL) receptor gene have a high-density lipoprotein (HDL)3 that is characterized by a less atheroprotective functions than that of healthy controls and within subgroups of FH. DESIGN: Twenty-two adults <75 years of age with FH and 17 healthy sex- and age-matched controls were included. HDL3 was isolated and the composition was characterized from each subject, and its ability to suppress tumor necrosis factor(TNF)-alpha stimulated expression of ICAM-1 on HUVEC was investigated. In addition, plasma level of soluble sICAM-1 and VCAM-1 was measured. RESULTS: Compared to controls, FH subjects had lower content of phospholipids in their HDL3 subfraction and a higher serum ICAM-1 level. No differences in sVCAM-1 were observed. HDL3 isolated from FH with body mass index(BMI)>25 and from FH subjects with premature CAD contained higher content of triglycerides compared to the HDL3 from FH subjects with BMI<25 and without CAD, respectively. Most important, when testing the function of HDL3 in the two FH subgroups characterized by elevated BMI and premature CAD, lower inhibition of ICAM-1 expression on HUVEC was observed. CONCLUSIONS: The altered composition of HDL3 from FH subjects with BMI>25 and FH subjects with premature CAD may be responsible for a HDL3 subfraction with less protective properties assessed as inhibition of ICAM-1 expression on HUVEC consequently leading to more proatherogenic endothelial surface.

Effect of folic acid treatment on endothelium-dependent vasodilation and nitric oxide-derived end products in hyperhomocysteinemic subjects.

PURPOSE: An elevated plasma homocysteine concentration is an independent risk factor for cardiovascular diseases. In this study, we tested the hypothesis that hyperhomocysteinemia induces endothelial dysfunction mediated, at least in part, through nitric oxide-dependent mechanisms and that folic acid supplementation improves endothelial function in hyperhomocysteinemic subjects. SUBJECTS AND METHODS: Endothelial function was evaluated in healthy controls and hyperhomocysteinemic subjects by measuring plasma levels of the nitric oxide-derived end products nitrite and nitrate and by assessing vasodilatory responses in the skin microcirculation and forearm vasculature. In the subjects with hyperhomocysteinemia, these measurements were repeated after 6 weeks and 12 months of folic acid supplementation. RESULTS: Compared with healthy controls, hyperhomocysteinemic subjects had significantly lower median plasma levels of nitric oxide-derived end products (12.1 microM [range 4.4 to 41.8] versus 24.6 microM [13.6 to 53.2]; P <0.001), a significantly lower endothelium-dependent vasodilatory response to acetylcholine (P <0.01), hyperemic response in the microcirculation (P <0.01), and total forearm blood flow during reactive hyperemia (P = 0.01). There was no significant difference in the endothelium-independent response. Folic acid treatment for 12 months increased the plasma level of nitric oxide-derived end products by 121% (95% confidence interval [CI], 72% to 170%), the vasodilatory response to acetylcholine by 124% (95% CI, 36% to 212%), and the ischemia-mediated hyperemic responses in the microcirculation by 60% (95% CI, 25% to 96%) and in the forearm vasculature by 47% (95% CI, 21% to 73%). CONCLUSIONS: Homocysteine appears to induce its atherogenic effect, at least in part, by depressing endothelial function, possibly through nitric oxide-dependent mechanisms. This effect can be reversed by folic acid supplementation.

Doxazosin treatment and peroxidation of low-density lipoprotein among male hypertensive subjects: in vitro and ex vivo studies.

Doxazosin is an antihypertensive drug that gives rise to 6- and 7-hydroxydoxazosin during hepatic metabolism. The structures of the hydroxymetabolites suggest that they may possess antioxidative properties. The aim of the present study was to examine whether doxazosin and 6- and 7-hydroxydoxazosin were able to scavenge free radicals and whether these compounds might protect low-density lipoprotein (LDL) against in vitro and ex vivo oxidation. Both 6- and 7-hydroxydoxazosin showed radical scavenging capacity as assessed by measuring scavenging of 1,1-diphenyl-2-picrylhydrazyl radicals. In vitro incubation with 10 microM 6- and 7-hydroxydoxazosin significantly reduced human mononuclear cell-mediated oxidation of LDL, measured as the formation of lipid peroxides and the relative electrophoretic mobility of LDL (to 10 and 6% of the control, respectively). Furthermore, formation of conjugated dienes in LDL during Cu2+-induced oxidation was significantly reduced in the presence of 5 microM 6- and 7-hydroxydoxazosin (to 28% of tmax [time to maximum] of control). However, treatment of hypertensive patients with increasing doses of doxazosin (from 1 to 8 mg/day) for 8 weeks altered neither Cu2+-catalyzed, 2,2'azobis-(2-amidinopropane hydrochloride)-initiated, nor cell-mediated oxidation of patient LDL ex vivo. Furthermore, the total antioxidative capacity of plasma was unaffected by treatment. In conclusion, the present study shows that 6- and 7-hydroxydoxazosin have radical scavenging properties and protect LDL against in vitro oxidation. However, treatment of hypertensive male subjects with increasing doses of doxazosin for 8 weeks did not affect ex vivo oxidation of LDL.

Omega-3 and omega-6 fatty acids in the insulin resistance syndrome. Lipid and lipoprotein metabolism and atherosclerosis.

Dietary fatty acids appear to be of significant importance for several of the most-common diseases in modern societies. To obtain more knowledge about the health consequences of dietary fatty acids, we depend upon a better understanding of the mechanisms of action of these fatty acids in vivo. With regard to the IRS, omega-3 PUFA may exert beneficial effects upon many of the associated pathophysiological metabolic changes. Omega-3 PUFA reduce fasting and postprandial TG, may improve insulin sensitivity (as shown in animal experiments), decrease platelet and leukocyte reactivity, alter immunological functions, and may slightly decrease blood pressure. Omega-3 PUFA may also beneficially influence vessel wall characteristics and blood rheology. Furthermore, both types of PUFA (omega-3 and omega-6) have been shown to inhibit cardiac arrhythmias in animals. The role of omega-3 PUFA in blood clotting and fibrinolysis still remains controversial, whereas omega-6 fatty acids may lead to increased oxidation of lipoproteins. Regardless of the effects on LDL oxidizability, both types of PUFA have shown beneficial effects on the development of atherosclerosis. As yet, little is known about the effect of specific omega-6 fatty acids with respect to the IRS. Potential adverse effects of dietary PUFA must not be neglected, but should be viewed in light of the beneficial effects of these agents.

Effects of partially hydrogenated fish oil, partially hydrogenated soybean oil and butter on the susceptibility of low density lipoprotein to oxidative modification in men.

OBJECTIVE: To study the effect of partially hydrogenated fish oil (PHFO-diet), partially hydrogenated soybean oil (PHSO-diet) and butterfat (butter-diet) on the susceptibility of low density lipoprotein (LDL) to in vitro oxidative modification. DESIGN: A strictly controlled, randomized, single-blind dietary study with cross-over design. SUBJECTS: Thirty-three healthy men aged from 21 to 46 years entered the study; 29 men completed the study. INTERVENTIONS: Fat provided approximately 35% of the energy intake in all three test diets, and the content of trans-fatty acids was 8.0, 8.5 and 0.9% of energy in the PHFO-, PHSO- and butter-diets, respectively. The subjects consumed all three test diets each during three weeks, in a single-blind, random order. LDL isolated from the participants given the three different diets was subjected to Cu(2+)-induced oxidation. RESULTS: No significant differences were seen on either conjugated dienes, lipid peroxides, uptake by macrophages or relative electrophoretic mobility of LDL. Vitamin E level in serum from subjects on the PHFO-diet was significantly higher compared to the two other diets. Furthermore, no significant differences were found in the composition of the LDL particle between the three diet groups. CONCLUSIONS: Our results indicate that consumption of trans-fatty acids does not alter the susceptibility of LDL to oxidative modification.

Omega-3 fatty acids--nutritional aspects.

Omega-3 fatty acids contain a double bond in the third position from the methyl group. The very long-chain (20 or 22 carbon atoms) omega-3 fatty acids are mostly found in fatty fish and fish oils. The omega-3 fatty acids are essential and may act as precursors for eicosanoids, altering membrane fluidity or binding to transcription factors. Dietary intake of omega-3 fatty acids reduces plasma concentration of triglycerides, probably by decreasing hepatic secretion of very low density lipoprotein (VLDL) and by increasing catabolism of chylomicrons. In addition, lipid peroxidation of omega-3 fatty acids may take place, with good and bad consequences. As the number of double bonds is high, the omega-3 fatty acids may easily react with oxygen radicals. We performed studies where 5 g/day of very long-chain omega-3 fatty acids was given as a supplement for four months along with vitamin E, whereas control groups received similar amounts of other oils. The unsaturation index was higher in fatty acids of LDL from individuals exposed to omega-3 fatty acids, and the amounts of cholesteryl esters and total lipids were lower compared with control LDL, whereas similar electrophoretic mobility and apolipoprotein B structure were observed. There was a decrease in the melting temperature of cholesteryl esters in omega-3 fatty acid-enriched LDL, but no change in the susceptibility of LDL to Cu2+ catalyzed lipid peroxidation, as measured by changes in amounts of lipid peroxides or in the uptake of LDL in macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased levels of C-reactive protein and interleukin-6 in hyperhomocysteinemic subjects.

OBJECTIVE: Elevated plasma homocysteine concentration is considered to be an independent risk factor for cardiovascular disease. However, the mechanisms by which hyperhomocysteinemia are related to vascular disease are unclear. High-sensitivity C-reactive protein (CRP), a marker of inflammation, has been reported to be an independent predictor of future myocardial infarction among clinically healthy individuals. Interleukin (IL)-6 is a regulator of CRP and has a key role in initiation of inflammation. The aim of this study was to investigate whether individuals with increased plasma homocysteine concentrations have altered levels of serum CRP and IL-6. MATERIAL AND METHODS: Serum concentrations of CRP and IL-6 were measured in 39 individuals with hyperhomocysteinemia and in 39 control subjects matched for gender, age and body mass index (BMI). In addition, the inflammatory effect of IL-6 on peripheral blood mononuclear cells was measured. RESULTS: Compared to controls, hyperhomocysteinemic subjects have elevated serum levels of CRP and IL-6 (p < or =0.001 and p < 0.005, respectively). Importantly, this raised level of IL-6 was also seen in hyperhomocysteinemic individuals without accompanying hypercholesterolemia or cardiovascular disease. IL-6 increased the release of monocyte chemoattractant protein-1 from peripheral blood mononuclear cells, with particularly enhancing effects in cells from patients with hyperhomocysteinemia. CONCLUSIONS: These data suggest that enhanced inflammation may be associated with homocysteine-related cardiovascular disease, possibly involving IL-6-related mechanisms.

Dietary polyunsaturates and peroxidation of low density lipoprotein.

Oxidative modification of low density lipoprotein is influenced by dietary polyunsaturates. Omega-6 polyunsaturated fatty acids enhance the susceptibility of low density lipoprotein to oxidation compared with monoenes. Most studies on omega-3 fatty acids also exhibit increased peroxidation of low density lipoprotein, although these data are more conflicting. Future studies should focus on additional information concerning dietary intake of antioxidants, fatty acids and lipid peroxides, as well as on the importance of low density lipoprotein oxidation in vivo.

Uptake and degradation of filamentous actin and vitamin D-binding protein in the rat.

Tissue uptake and degradation of 125I-tyramine-cellobiose-labelled filamentous actin, vitamin D-binding protein (DBP) and actin-DBP complex were studied in the rat. Actin and actin-DBP complex were cleared from plasma at a faster rate than was DBP. About 40% of injected actin was recovered in the liver between 10 and 30 min after administration. Of the total radioactivity recovered in the liver, about 35% and 40% was detected in parenchymal and endothelial cells respectively when labelled actin or DBP-actin complex was injected intravenously. When labelled DBP alone was injected, approx. 55% of the radioactivity recovered in liver was in the Kupffer cells. These results suggest that actin is targeting the DBP-actin complex to the endothelial and parenchymal liver cells. Filamentous actin was also taken up in large amounts and at a rapid rate in parenchymal as well as non-parenchymal liver cells in vitro. Our data indicate that the rat has a mechanism to clear actin and the DBP-actin complex from plasma and that both parenchymal and non-parenchymal liver cells are involved in this process.

Hepatic uptake of beta-VLDL in cholesterol-fed rabbits.

The hepatic uptake of intravenously injected beta-very low density lipoprotein (beta-VLDL) in rabbits fed 2% (w/w) cholesterol for 3 weeks was investigated. In vitro studies were also conducted to examine the specificity and the capacity of the uptake in isolated liver parenchymal cells. The hepatic uptake of beta-VLDL was 15.8 +/- 6.7% (n = 6) in the cholesterol-fed rabbits as compared to 26.6 +/- 7.5% (n = 6) of the injected dose in control rabbits (P < 0.05). Although this is a fractional reduction, it represents a more than 10-fold increase in absolute hepatic uptake of lipoproteins in the cholesterol-fed rabbits. In these animals the liver parenchymal, endothelial, and Kupffer cells took up 10.2 +/- 2.7%, 3.0 +/- 0.9%, and 1.8 +/- 0.4% of the injected dose, respectively, compared to 25.9 +/- 6.1%, 3.6 +/- 1.6%, and 1.5 +/- 0.8% of the injected dose in chow-fed controls. However, taking into account the high plasma lipoprotein levels in the cholesterol-fed rabbits, the absolute cellular uptake was 10-fold increased in the parenchymal liver cells and more than 20-fold increased in the nonparenchymal cells. In vitro results indicated a 40% down-regulation of the specific receptor for beta-VLDL in the parenchymal cells, and this, together with an increased competition for binding sites in the hypercholesterolemic rabbits, probably explains the reduced uptake of beta-VLDL in terms of % of injected dose observed in vivo. In vitro data suggested that the receptor involved in both hypercholesterolemic and normolipemic rabbits was the apolipoprotein (apo) B,E receptor. On a per cell basis, parenchymal cells from chow-fed control animals took up 2.4 +/- 0.8% of the injected dose per 10(9) cells; this uptake was reduced to 1.1 +/- 0.5% in hypercholesterolemic animals. No differences in uptake of beta-VLDL in nonparenchymal liver cells were observed on a per cell basis between the two feeding groups, indicating that binding sites involved in this uptake are not down-regulated by cholesterol feeding. On the contrary, the absolute uptake in the nonparenchymal liver cells is greatly increased in hypercholesterolemic rabbits as compared to controls. In cholesterol-fed rabbits the three different liver cell types took up approximately the same amount of beta-VLDL per cell. The liver nonparenchymal cells, therefore, assume a prominent role in uptake of beta-VLDL in hypercholesterolemic rabbits, accounting for more than 30% of the total hepatic uptake as compared to 16% in control animals.(ABSTRACT TRUNCATED AT 400 WORDS)