The theory of tracer experiments with 131I-labelled plasma proteins

Plasma kinetics of an LDL-like non-protein nanoemulsion and transfer of lipids to high-density lipoprotein (HDL) in patients with rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a systemic inflammatory disease associated with cardiovascular risk, but with normal plasma lipids.

OBJECTIVE

The aim was to investigate low-density lipoprotein (LDL) and high-density lipoprotein (HDL) metabolism in RA patients using radioactive nanoemulsions resembling an LDL lipid structure (LDE) as metabolic probes.

METHODS

Thirty patients with RA, 16 in remission and 14 in high activity, and 30 healthy controls were studied. LDE labeled with (14)C-cholesteryl ester ((14)C-CE) and (3)H-unesterified cholesterol ((3)H-UC) was intravenously injected followed by 24-hour plasma sampling. Fractional clearance rates (FCR, h(-1)) were calculated by compartmental analysis. Lipid transfers to HDL were assayed by incubating plasma samples with a donor nanoemulsion labeled with radioactive lipids; % lipids transferred to HDL were quantified after chemical precipitation.

RESULTS

LDL cholesterol, triglycerides, unesterified cholesterol, and oxidized LDL were equal in RA and controls, and HDL cholesterol was even higher in RA. Compared with controls, apolipoprotein B was lower, apolipoprotein A1 was equal, and apolipoprotein E was higher in RA. Decay curves of LDE labels were faster in RA patients than in controls ((14)C-CE: 0.072 ± 0.066 and 0.038 ± 0.027, P = .0115; (3)H-UC: 0.066 ± 0.042 and 0.035 ± 0.039; P < .0044). FCRs were equal in 2 RA subgroups. Transfer of UC, triglycerides, and phospholipids to HDL was equal between RA and controls, but CE transfer was lower in RA. HDL size was smaller in RA patients than in controls (8.5 ± 0.5 nm; 9.2 ± 0.8 nm, P < .0001).

CONCLUSION

RA patients were more efficient in removing atherogenic LDL from plasma, as indicated by higher CE and UC FCR, with in lower apolipoprotein B. This was unexpected because of the higher cardiovascular risk in RA.

Ezetimibe inhibits hepatic Niemann-Pick C1-Like 1 to facilitate macrophage reverse cholesterol transport in mice

OBJECTIVE

Controversies have arisen from recent mouse studies about the essential role of biliary sterol secretion in reverse cholesterol transport (RCT). The objective of this study was to examine the role of biliary cholesterol secretion in modulating macrophage RCT in Niemann-Pick C1-Like 1 (NPC1L1) liver only (L1(LivOnly)) mice, an animal model that is defective in both biliary sterol secretion and intestinal sterol absorption, and determine whether NPC1L1 inhibitor ezetimibe facilitates macrophage RCT by inhibiting hepatic NPC1L1.

APPROACH AND RESULTS

L1(LivOnly) mice were generated by crossing NPC1L1 knockout (L1-KO) mice with transgenic mice overexpressing human NPC1L1 specifically in liver. Macrophage-to-feces RCT was assayed in L1-KO and L1(LivOnly) mice injected intraperitoneally with [(3)H]-cholesterol-labeled peritoneal macrophages isolated from C57BL/6 mice. Inhibition of biliary sterol secretion by hepatic overexpression of NPC1L1 substantially reduced transport of [(3)H]-cholesterol from primary peritoneal macrophages to the neutral sterol fraction in bile and feces in L1(LivOnly) mice without affecting tracer excretion in the bile acid fraction. Ezetimibe treatment for 2 weeks completely restored both biliary and fecal excretion of [(3)H]-tracer in the neutral sterol fraction in L1(LivOnly) mice. High-density lipoprotein kinetic studies showed that L1(LivOnly) mice compared with L1-KO mice had a significantly reduced fractional catabolic rate without altered hepatic and intestinal uptake of high-density lipoprotein-cholesterol ether.

CONCLUSIONS

In mice lacking intestinal cholesterol absorption, macrophage-to-feces RCT depends on efficient biliary sterol secretion, and ezetimibe promotes macrophage RCT by inhibiting hepatic NPC1L1 function.

Apolipoprotein A-V modulates multiple atherogenic mechanisms in a mouse model of disturbed clearance of triglyceride-rich lipoproteins

OBJECTIVE

Apolipoprotein A-V plays an important role in reducing plasma triglyceride levels. We hypothesized that expression of apoA-V would inhibit atherogenesis in apoE(-/-) mice fed chow diet which is a known model of hypercholesterolemia. Our aim was to study this protective effect and to explore possible mechanisms.

METHODS AND RESULTS

ApoA-V(+/+)ApoE(-/-) mice expressing human apolipoprotein A-V (hapoA-V) were generated and compared to apoE(-/-) mice. Atherosclerotic aortic sinus lesion area was 70% smaller in hapoA-V(+/+)apoE(-/-). This was accompanied by a 58% reduction in lesion macrophage content. Furthermore, advanced atherosclerotic lesions in hapoA-V(+/+)apoE(-/-) mice showed features of a more stable plaque, manifested by 59% and 37% higher collagen and α-actin content, respectively. Plasma triglyceride and cholesterol levels in hapoA-V(+/+)apoE(-/-) mice were 47% and 33% lower, respectively. These were associated with a 33% reduction in very low density lipoprotein triglyceride production and 2-fold acceleration in triglyceride-rich lipoprotein clearance in hapoA-V(+/+)apoE(-/-) mice. In addition, hapoA-V(+/+)apoE(-/-) mice showed enhanced insulin sensitivity (25% and 15% improvement in glucose tolerance and insulin responsiveness, respectively). Finally, hapoA-V(+/+)apoE(-/-) displayed a milder systemic inflammatory response compared to apoE(-/-) mice, manifested by 22%, 65% and 15% lower plasma levels of TNFα, IL-1β and IL-6, respectively.

CONCLUSIONS

We showed that human apolipoprotein A-V is a potent modulator of atherosclerosis in mice through multiple modes of action. These findings may identify apoA-V as a potential therapeutic target for treatment of atherosclerosis.

Compartmental analysis and its manifold applications to pharmacokinetics

In this paper, I show how the concept of compartment evolved from the simple dilution of a substance in a physiological volume to its distribution in a network of interconnected spaces. The differential equations describing the fate of a substance in a living being can be solved, qualitatively and quantitatively, with the help of a number of mathematical techniques. A number of parameters of pharmacokinetic interest can be computed from the experimental data; often, the data available are not sufficient to determine some parameters, but it is possible to determine their range.

On the pathogenesis of acquired hypo-beta-lipoproteinemia. A case associated with sideroblastic anemia

A 71-year-old previously hypercholesterolemic woman developed gradually severe hypocholesterolemia of 1.55 mmol/l. Simultaneously she developed progressive sideroblastic anemia, altered erythrocyte morphology and defective platelet function. Hypo-beta-lipoproteinemia was demonstrated with abnormal lipid composition of both very low density (VLDL), low density (LDL) and high density lipoprotein (HDL) fractions. Other plasma lipids, as well as erythrocyte lipids, were normal. The fractional catabolic rate of homologous 125I-LDL was increased to 4-5-fold, while its rate of synthesis was normal. The patient's serum contained autoantibodies directed against LDL. It is concluded that her hypo-beta-lipoproteinemia was due to autoantibodies towards LDL causing an increased catabolism without any concomitant effect on the rate of LDL synthesis. It is suggested that acquired hypo-beta-lipoproteinemia can be subdivided into two types, one in which the primary defect is an increased catabolism due to immunoelimination, and another in which the primary defect is a decreased rate of LDL synthesis.

Deposition of free cholesterol in the blood vessels of patients with coronary artery disease: a possible novel mechanism for atherogenesis

A cholesterol-rich nanoemulsion (LDE) that mimics the composition of low-density lipoprotein (LDL) acquires apoE in the plasma and is taken-up by the cells by LDL receptors. In this study, to verify whether free cholesterol (FC) and the cholesteryl ester (CE) components of LDL are taken-up differently by the vessels. LDE labeled with (3)H-cholesterol and (14)C-cholesteryl oleate was injected into 20 coronary artery disease patients 24 h before a scheduled myocardial coronary artery bypass grafting. The plasma kinetics of both radiolabels was determined from plasma samples collected over 24 h, and fragments of vessels discarded during surgery were collected and analyzed for radioactivity. LDE FC was removed faster than CE. The radioactive counting of LDE CE was greater than that of LDE FC in the blood, but the uptake of FC was markedly greater than that of CE in all fragments: fivefold greater in the aorta (p = 0.04), fourfold greater in the internal thoracic artery (p = 0.03), tenfold greater in the saphenous vein (p = 0.01) and threefold in the radial artery (p = 0.05). In conclusion, the greater removal from plasma of FC compared with CE and the remarkably greater vessel tissue uptake of FC compared with CE suggests that, in the plasma, FC dissociates from the nanoemulsion particles and precipitates in the vessels. Considering LDE as an artificial nanoemulsion model for LDL, our results suggest that dissociation of FC from lipoprotein particles and deposition in the vessel wall may play a role as an independent mechanism in atherogenesis.

Evaluation in melanoma-bearing mice of an etoposide derivative associated to a cholesterol-rich nano-emulsion

A cholesterol-rich nano-emulsion (LDE) may be used as a vehicle to target antineoplastic drugs against cancer cells. The association of an etoposide derivative to LDE is stable and retains the cytotoxic activity of etoposide. We have evaluated the toxicity and antitumoral action of this new preparation in-vivo. Melanoma-bearing mice and control mice were administered LDE-etoposide oleate or commercial etoposide, either with or without radioactive labelling. The maximum tolerated dose (MTD), tissue distribution, plasma decay curves, pharmacokinetic parameters and antitumoral activity were determined. Association to LDE drastically reduced the drug toxicity, since MTD was approximately five-fold greater than in commercial etoposide. LDE-etoposide oleate was concentrated four-fold in the tumour compared with the normal adjacent tissues, was removed faster from plasma in tumour-bearing mice than in controls, and remained in the bloodstream longer than commercial etoposide. The tumour growth inhibition rate and survival were greater in animals treated with LDE-etoposide oleate compared with commercial etoposide. However, increasing the dose from 17 to 85 microM kg(-1) did not result in further improvement of the antitumour action. The incorporation of etoposide oleate to LDE resulted in markedly reduced toxicity and superior antitumoral activity. LDE-etoposide oleate is a promising new weapon for cancer treatment.

Cholesteryl ester transfer protein (CETP) expression enhances HDL cholesteryl ester liver delivery, which is independent of scavenger receptor BI, LDL receptor related protein and possibly LDL receptor

Cholesteryl ester transfer protein (CETP) is a hydrophobic plasma glycoprotein that mediates the transfer and exchange of cholesteryl ester (CE) and triglyceride (TG) between plasma lipoproteins, and also plays an important role in HDL metabolism. Previous studies have indicated that, compared to wild type mice, human CETP transgenic mice had significantly lower plasma HDL CE levels, which was associated with enhancement of HDL CE uptake by the liver. However, the mechanism of this process is still unknown. To evaluate the possibility that this might be directly mediated by CETP, we utilized CETP transgenic (CETPTg) mice with liver scavenger receptor BI (SR-BI) deficiency [i.e., PDZK1 gene knockout (PDZK1O)], and with receptor associated protein (RAP) overexpression, to block LDL receptor-related protein (LRP) and LDL receptor (LDLR). We found that (1) CETPTg/PDZK1O mice have significantly lower HDL-C than that of PDZK1 KO mice (36%, p<0.01); (2) CETPTg and CETPTg/PDZK1O mice have same HDL-C levels; (3) CETPTg/PDZK1O/RAP mice had significant lower plasma HDL-C levels than that of PDZK1O/RAP ones (50%, p<0.001); (4) there is no incremental transfer of HDL CE radioactivity to the apoB-containing lipoprotein fraction in mice expressing CETP; and (5) CETPTg/PDZK1O/RAP mice had significant higher plasma and liver [(3)H]CEt-HDL turnover rates than that of PDZK1O/RAP ones (50% and 53%, p<0.01, respectively). These results suggest that CETP expression in mouse increases direct removal of HDL CE in the liver and this process is independent of SR-BI, LRP, and possibly LDLR.

Adipose tissue-specific CETP expression in mice: impact on plasma lipoprotein metabolism

Adipose tissue appears to be a highly conserved site of cholesteryl ester transfer protein (CETP) expression across species. To investigate the impact of adipose CETP expression on lipid metabolism, we created adipose tissue-specific CETP transgenic (CETPTg) mice. CETP mRNA is predominantly expressed in adipose tissue. Plasma CETP mass and activity are readily detectable in CETPTg mice but not in controls. Plasma lipoprotein analysis shows marked reductions in HDL cholesterol and phospholipids, increases non-HDL lipids, decreases apolipoprotein A-I (apoA-I), and increases apoB. Unexpectedly, CETPTg adipocytes are significantly smaller than those in control mice (44%), triglyceride and cholesterol in adipose tissue were significantly decreased compared with controls (50% and 37%, respectively), and phospholipids showed no significant changes. To study the mechanism, we measured peroxisome proliferator-activated receptor gamma, sterol-regulatory element binding protein-1c, LPL, and hormone-sensitive lipase (HSL) in aP2-CETPTg adipose tissue and controls and found that, except for HSL, all mRNA levels are significantly decreased in the transgenic mice compared with controls (26, 33, and 22%). In conclusion, adipose tissue CETP makes a major contribution to CETP in the circulation, reduces HDL, and increases non-HDL cholesterol levels. Moreover, adipose tissue CETP expression changes triglyceride and cholesterol content and the size of adipocytes.

Adenovirus-mediated overexpression of sphingomyelin synthases 1 and 2 increases the atherogenic potential in mice

Sphingomyelin synthase 1 (SMS1) and SMS2 are two isoforms of SMS, the last enzyme for sphingomyelin (SM) biosynthesis. To evaluate the role of SMS in vivo in terms of plasma lipoprotein metabolism, we generated recombinant adenovirus vectors containing human SMS1 cDNA (AdV-SMS1), SMS2 cDNA (AdV-SMS2), or the reporter LacZ cDNA (AdV-LacZ) as a control. On day 7 after intravenous infusion of 2 x 10(11) particles of both AdV-SMS1 and AdV-SMS2 into mice, liver SMS1 and SMS2 mRNA levels as well as SMS activity were significantly increased (2.5-, 2.7-, 2.1-, and 2.3-fold, respectively; P < 0.001). Lipoprotein analysis indicated that AdV-SMS1 and AdV-SMS2 treatment caused no changes of total SM and cholesterol levels but significantly decreased HDL-SM and HDL-cholesterol (42% and 38%, and 27% and 25%, respectively; P < 0.05). It also significantly increased non-HDL-SM and non-HDL-cholesterol levels (50% and 35%, and 64% and 61%, respectively; P < 0.05) compared with AdV-LacZ controls. SDS-PAGE showed a significant increase in apolipoprotein B (apoB; P < 0.01) but no changes in apoA-I levels. Moreover, we found that non-HDL from both AdV-SMS1- and AdV-SMS2-treated mice was significantly aggregated after treatment with a mammalian sphingomyelinase, whereas lipoproteins from control animals did not aggregate. To investigate the mechanism of HDL changes, we measured liver scavenger receptor class B type I (SR-BI) levels by Western blot. We found that AdV-SMS1 and AdV-SMS2 mouse liver homogenates contained 50% and 55% higher SR-BI levels than in controls, whereas no change was observed in hepatic ABCA1 levels. An HDL turnover study revealed an increase of plasma clearance rates for [3H]cholesteryl oleyl ether-HDL but not for [125I]HDL in both AdV-SMS1 and AdV-SMS2 mice compared with controls. In conclusion, adenovirus-mediated SMS1 and SMS2 overexpression increased lipoprotein atherogenic potential. Such an effect may contribute to the increased plasma SM levels observed in animal models of atherosclerosis and in human patients with coronary artery disease.

Pharmacokinetics and tumor uptake of a derivatized form of paclitaxel associated to a cholesterol-rich nanoemulsion (LDE) in patients with gynecologic cancers

OBJECTIVE

A cholesterol-rich nanoemulsion termed LDE concentrates in cancer tissues after injection into the bloodstream. The association of a derivatized paclitaxel to LDE showed lower toxicity and increased antitumoral activity as tested in a B16 melanoma murine model. Here, the pharmacokinetics of LDE-paclitaxel oleate and the ability of LDE to concentrate the drug in the tumor were investigated in patients with gynecologic cancers.

METHODS

Either LDE-paclitaxel oleate doubly labeled with [(14)C]-cholesteryl oleate and [(3)H]-paclitaxel oleate or [(3)H]-paclitaxel-cremophor was intravenously injected into eight patients. Blood samples were collected over 24 h to determine the plasma decay curves. Fractional clearance rate (FCR) and pharmacokinetic parameters were calculated by compartmental analysis. Also, specimens of tumors and the corresponding normal tissues were excised during the surgery for radioactivity measurement.

RESULTS

The LDE and paclitaxel oleate FCR were similar (0.092 +/- 0.039 and 0.069 +/- 0.027 h(-1), respectively, n = 5, P = 0.390). FCR of paclitaxel oleate associated to LDE was smaller than that of paclitaxel-cremophor (0.231 +/- 0.128 h(-1), P = 0.028). Paclitaxel oleate T (1/2 )and AUC were greater than those of paclitaxel-cremophor (T (1/2 )=( )14.51 +/- 3.23 and 6.62 +/- 2.05 h and AUC = 2.49 +/- 0.35 and 1.26 +/- 0.40, respectively, P = 0.009, P = 0.004). The amount of paclitaxel and LDE-radioactive labels in the tumor was 3.5 times greater than in the normal tissues.

CONCLUSION

Paclitaxel oleate associated to LDE is stable in the bloodstream and has greater plasma half-life and AUC than those for paclitaxel-cremophor. LDE concentrates 3.5 times more paclitaxel in malignant tissues than in normal tissues. Therefore, association to LDE is an interesting strategy for using paclitaxel to treat gynecologic cancers.

Arterial graft maturation: The duration of thrombotic activity in Dacron aortobifemoral grafts measured by platelet and fibrinogen kinetics

Dacron is thrombogenic, hence small arterial grafts of this material frequently thrombose in the period prior to graft maturation. Anti-thrombotic therapy may therefore be indicated to preserve patency during this risk period. To evaluate the thrombogenicity of immature Dacron grafts, platelet and fibrinogen kinetics using 51Cr and 125I respectively were measured before operation and at 3, 6 and 9 months in 10 patients following aortobifemoral bypass and in 6 age-matched volunteers.

Platelet survival was reduced from 8.8±0.2 d before surgery to 7.4±0.24 d at 3 months. This was accompanied by an increase in platelet turnover from 39±2.4 × 109 l−1 d−1 to 46.9±2.9 × 109 l−1 d−1. Fibrinogen t1/2 fell from 3.72±0.13 d preoperatively to 3.36±0.11 d at 3 months, while fibrinogen fractional catabolic rate rose from 0.27±0.014 to 0.34±0.014. These changes were all significant (P &lt; 0.01). Fibrinogen consumption had returned to normal by 6 months following surgery but platelet kinetics only equated to pre-operative levels at 9 months. We suggest that Dacron grafts are thrombogenically active for about 9 months. When anti-thrombotic therapy is indicated it should be continued throughout this period.

Plasma kinetics of a cholesterol-rich microemulsion (LDE) in patients with Hodgkin's and non-Hodgkin's lymphoma and a preliminary study on the toxicity of etoposide associated with LDE

BACKGROUND

Neoplastic diseases are often associated with low plasma low-density lipoprotein (LDL) cholesterol and diminished LDL clearance due to upregulation in cancer cells of the receptors that internalize the lipoprotein. Thus, it is possible to use LDL or cholesterol-rich microemulsions (LDE) that bind to LDL receptors as carriers of antineoplastic agents to concentrate those drugs into cancer tissues. Our aim was to determine whether LDL cholesterol concentration plus LDE increased clearance occur in lymphomas.

PATIENTS AND METHODS

The LDE labeled with [(3) H]-cholesteryl oleate was injected into four Hodgkin's and 12 non-Hodgkin's lymphoma patients and into 16 healthy control subjects and the LDE plasma residence time (RT) was determined from sequential plasma samples. Two volunteers with relapsed/refractory lymphoma were treated with 300 mg/m(2) body surface etoposide associated with LDE in six cycles at 3-week intervals.

RESULTS

The LDL cholesterol was lower in lymphoma patients than in controls (94+/-52 and 115+/-16 mg/dL, p=0.0362, respectively). The LDE RT was 49% smaller in lymphoma patients than in controls (RT=21.9 and 45.7 h; p=0.0134), with positive correlation between RT and LDL cholesterol. LDE-etoposide showed no considerable toxicity in all cycles in the two treated patients and the disease remained stable during the treatment.

CONCLUSIONS

Our results suggest that lymphomas overexpress LDL receptors that make room for using LDE as drug-targeting vehicle and that the LDE-etoposide preparation is suitable for patient use.

Increased transvascular lipoprotein transport in diabetes: association with albuminuria and systolic hypertension

CONTEXT

Diabetes is associated with a highly increased risk of atherosclerosis, especially if hypertension or albuminuria is present.

OBJECTIVE

We hypothesized that the increased transvascular lipoprotein transport in diabetes may be further accelerated if hypertension or albuminuria is present, possibly explaining increased intimal lipoprotein accumulation and thus atherosclerosis.

DESIGN

The study was cross-sectional and was performed in 1999-2002.

SETTING

The study took place in the referral center.

PATIENTS

The patients included 60 with diabetes mellitus (27 with type 1 diabetes and 33 with type 2 diabetes) and 42 healthy controls. All were randomly recruited.

MAIN OUTCOME MEASURE

We used an in vivo method for measurement of transvascular transport of low-density lipoprotein (LDL). Autologous 131I-LDL was reinjected iv, and the 1-h fractional escape rate was taken as an index of transvascular transport.

RESULTS

Transvascular LDL transport was 1.8 (1.6-2.0), 2.3 (2.0-2.6), and 2.6 (1.3-4.0)%/[h x (liter/m2)] in healthy controls, diabetic controls, and diabetes patients with systolic hypertension or albuminuria, respectively (P = 0.013; F = 4.5; df =2; ANOVA). These differences most likely were not caused by altered hepatic LDL receptor expression, glycosylation of LDL, small LDL size, or medicine use.

CONCLUSIONS

Transvascular LDL transport is increased in patients with diabetes mellitus, especially if systolic hypertension or albuminuria is present. Accordingly, lipoprotein flux into the arterial wall could be increased in these patients, possibly explaining accelerated development of atherosclerosis.

Determining hepatic triglyceride production in mice: comparison of poloxamer 407 with Triton WR-1339

Triglyceride (TG), a water-insoluble energy-rich lipid, is secreted by the liver as part of very low density lipoproteins (VLDLs) to supply energy to extrahepatic tissues. Overproduction of VLDL is associated with increased risk of cardiovascular heart disease; this has renewed an interest in factors that affect hepatic TG production. The TG production rate is determined by measuring temporal increases in plasma TG under conditions in which TG hydrolysis by lipoprotein lipase (LPL) is inhibited. The nonionic detergent, Triton WR-1339 (Triton), has commonly been used to inhibit LPL for this purpose. Triton, in addition to inhibition of TG hydrolysis, has properties that have the potential to adversely influence lipoprotein metabolism. Another nonionic detergent, poloxamer 407 (P-407), also inhibits LPL. In these studies, we demonstrate that P-407 is comparable to Triton in the determination of TG production but without the unwanted side effects of Triton.

Plasma kinetics of free and esterified cholesterol in familial hypercholesterolemia: Effects of simvastatin

The objective of this study was to evaluate the kinetics of both free and esterified forms of cholesterol contained in a emulsion that binds to LDL receptors (LDE) in subjects with heterozygous familial hypercholesterolemia (FH), and the same subjects under the effects of high-dose simvastatin treatment, as compared with a control normolipidemic group (NL). Twenty-one FH patients (44.0 +/- 13.0 yr, 12 females, LDL cholesterol levels 6.93 +/- 1.60 mmol/L) and 22 normolipidemic patients (44.0 +/- 15.0, 10 females, LDL cholesterol levels 3.15 +/- 0.62 mmol/L) were injected intravenously with 14C-cholesteryl ester and 3H-cholesterol. FH patients were also evaluated after 2 mon of 40 or 80 mg/d simvastatin treatment, and plasma samples were collected over 24 h to determine the residence time (RT, in h) of both LDE labels, expressed as the median (25%; 75%). The RT of both 14C-cholesteryl ester and 3H-cholesterol were greater in FH than in NL [FH: 36.0 (20.5; 1191.0), NL: 17.0 (12.0-62.5), P = 0.015; and FH: 52.0 (30.0; 1515.0); NL 20.5 (14.0-30.0) P < 0.0001]. Treatment reduced LDL cholesterol by 36% (P < 0.0001), RT of 14C-cholesteryl ester by 49% (P = 0.0029 vs. baseline), and 3H-cholesterol RT by 44% (P = 0.019 vs. baseline). After treatment, the RT values of 14C-cholesteryl ester in the FH group approached the NL values (P = 0.58), but the RT of 3H-cholesterol was still greater than those for the NL group (P = 0.01). The removal of LDE cholesteryl esters and free cholesterol was delayed in FH patients. Treatment with a high dose of simvastatin normalized the removal of cholesterol esters but not the removal of free cholesterol.

Effects in post-menopausal women of transdermal estrogen associated with progestin upon the removal from the plasma of a microemulsion that resembles low-density lipoprotein (LDL)

OBJECTIVE

To evaluate the effects of transdermal estradiol and medroxyprogesterone acetate (MPA) treatment on the removal from the plasma of a cholesterol-rich microemulsion (LDE) that roughly resembles low-density lipoprotein (LDL) structure and that binds to LDL receptors.

METHODS

Ten healthy post-menopausal women were studied before and after 3-month treatment with transdermal estradiol in the following dosages administered every 3.5 days: 25, 50, 50, 100, 100, 50, 50 and 25 microg. From the 15th to the 21st day and from the 22nd to the 28th day of estrogen treatment, respectively, 10 and 5 mg q.d. MPA per oral were associated to the transdermal estrogen. The emulsion labeled with 14C-cholesteryl oleate was injected after 12 h fasting and its fractional catabolic rate (FCR) was calculated from the plasma decaying curves of the isotope.

RESULTS

Treatment reduced LDL-cholesterol levels by 8% only (149.0 +/- 36.0 mg/dl, 138.0 +/- 27.0 mg/dl; P = 0.046), but the FCR of LDE expressed in medians (25%; 75%) increased from 0.0054 (0.003; 0.052) h(-1) to 0.021 (0.009; 0.10) h(-1), P = 0.002.

CONCLUSION

The association used in this study so as to mimic the increasing-decreasing pattern of the hormonal ovarian production reduced modestly LDL-cholesterol levels but pronouncedly increased the lipoprotein removal as tested by LDE FCR.

Mutation in apolipoprotein B associated with hypobetalipoproteinemia despite decreased binding to the low density lipoprotein receptor

Mutations in apolipoprotein B (APOB) may reduce binding of low density lipoprotein (LDL) to the LDL receptor and cause hypercholesterolemia. We showed that heterozygotes for a new mutation in APOB have hypobetalipoproteinemia, despite a reduced binding of LDL to the LDL receptor. APOB R3480P heterozygotes were identified among 9,255 individuals from the general population and had reduced levels of apoB-containing lipoproteins. Most surprisingly, R3480P LDL bound with lower affinity to the LDL receptor than non-carrier LDL in vitro, and these results were confirmed by turnover studies of LDL in vivo. In very low density lipoprotein (VLDL) turnover studies, the amount of VLDL converted to LDL in R3480P heterozygotes was substantially reduced, suggesting that this was the explanation for the hypobetalipoproteinemia observed in these individuals. Our findings emphasized the importance of combining in vitro studies with both human in vivo and population-based studies, as in vitro studies often have focused on very limited aspects of complex mechanisms taken out of their natural context.

Improvement of paclitaxel therapeutic index by derivatization and association to a cholesterol-rich microemulsion: in vitro and in vivo studies

A cholesterol-rich microemulsion or nanoparticle termed LDE concentrates in cancer tissues after injection into the bloodstream. Here the cytotoxicity, pharmacokinetics, toxicity to animals and therapeutic action of a paclitaxel lipophilic derivative associated to LDE is compared with those of the commercial paclitaxel. Results show that LDE-paclitaxel oleate is stable. The cytostatic activity of the drug in the complex is diminished compared with the commercial paclitaxel due to the cytotoxicity of the vehicle Cremophor EL used in the commercial formulation. Competition experiments in neoplastic cultured cells show that paclitaxel oleate and LDE are internalized together by the LDL receptor pathway. LDE-paclitaxel oleate arrests the G(2)/M phase of cell cycle, similarly to commercial paclitaxel. Tolerability to mice is remarkable, such that the lethal dose (LD(50)) was ninefold greater than that of the commercial formulation (LD(50) = 326 microM and 37 microM, respectively). LDE concentrates paclitaxel oleate in the tumor roughly fourfold relative to the normal adjacent tissues. At equimolar doses, the association of paclitaxel oleate with LDE results in remarkable changes in the drug pharmacokinetic parameters when compared to commercial paclitaxel (t(1/2)=218 min and 184 min, AUC=1,334 microg h/ml and 707 microg h/ml and CL=0.125 ml/min and 0.236 ml/min, respectively). Finally, the therapeutic efficacy of the complex is pronouncedly greater than that of the commercial paclitaxel, as indicated by the reduction in tumor growth, increase in survival rates and % cure of treated mice. In conclusion, LDE-paclitaxel oleate is a stable complex and compared with paclitaxel toxicity is considerably reduced and activity is enhanced, which may lead to improved therapeutic index in clinical use.

Physiological importance of SR-BI in the in vivo metabolism of human HDL and LDL in male and female mice

The physiological role of murine scavenger receptor class B type I (SR-BI) was evaluated by in vivo clearances of human HDL3 and LDL in normal and SR-BI knockout (KO) mice. In normal mice, cholesteryl esters (CEs) were removed faster than proteins, indicating a selective uptake process from both HDL3 and LDL. SR-BI KO mice showed 80% losses of HDL-CE selective uptake and the complete loss of LDL-CE selective uptake in the first phase of clearance. However, the second phase was characterized by an acceleration of CE disappearance in SR-BI KO mice. Thus, SR-BI is the only murine receptor mediating HDL-CE selective uptake, whereas a SR-BI-independent pathway specific to LDL can rescue SR-BI deficiency. The analysis of LDL recovered 3 h after injection in mice from different genotypes revealed that LDLs are significantly depleted in CE (reduction from 19% to 50% of the CE/protein ratios). A smaller LDL size in comparison with that of noninjected LDL was also detectable but was more evident for LDL recovered from normal mice. All LDL preparations migrate faster than noninjected LDL on agarose-barbital gels. Thus, both SR-BI-dependent and -independent pathways lead to substantial changes in LDL.

Plasma kinetics of a cholesterol-rich microemulsion in subjects with heterozygous beta-thalassemia

Patients with beta-thalassemia trait have been reported to present lower plasma concentrations of low-density lipoprotein (LDL) and lower frequencies of acute myocardial infarction than normal subjects. In this study, the metabolism of LDL was tested in 12 patients with heterozygous beta-thalassemia trait (HBT) and 13 healthy subjects without the disease by determining the plasma kinetics of an artificially made cholesterol-rich microemulsion (LDE) that mimics the LDL metabolism and binds to LDL receptors. The emulsion was labeled with 14C-cholesterol ester and injected intravenously into the subjects. Blood samples were drawn at regular intervals over 24 hr to determine the plasma decay curve of the emulsion radioactive label and to estimate its plasma fractional clearance rate (FCR, in hr(-1)). FCR of the 14C-cholesterol ester was greater in HBT compared to controls (0.0631 +/- 0.0178 hr(-1) and 0.0501 +/- 0.0094 hr(-1), respectively; mean +/- SD, P = 0.022). No differences were found regarding LDL cholesterol plasma concentration between the two groups, but apolipoprotein B concentration was lower in HBT than in control subjects (80 +/- 44 and 96 +/- 14, respectively; mean +/- SD, P = 0.026). Our results show that LDE FCR is increased in HBT, indicating that LDL clearance is increased in patients with beta-thalassemia trait possibly due to the increased proliferation in the bone marrow of erythroid precursors.

PLTP deficiency improves the anti-inflammatory properties of HDL and reduces the ability of LDL to induce monocyte chemotactic activity

We reported that phospholipid transfer protein (PLTP) deficiency decreased atherosclerosis in mouse models. Because the decreased atherosclerosis was accompanied by a significant decrease in plasma HDL levels, we examined the properties of PLTP knockout (PLTP0) HDL and tested its ability to prevent LDL-induced monocyte chemotactic activity in human artery wall cell cocultures. We isolated HDL and LDL from LDL receptor knockout/PLTP knockout (LDLr0/PLTP0) mice and from apolipoprotein B transgenic (apoBTg)/PLTP0 mice as well as their controls. PLTP0 HDL was relatively rich in protein and depleted in phosphatidylcholine. Turnover studies revealed a 3.5- to 4.0-fold increase in the turnover of protein and cholesteryl ester in HDL from PLTP0 mice compared with control mice. The ability of HDL from LDLr0/PLTP0 and apoBTg/PLTP0 mice to prevent the induction of monocyte chemotactic activity in human artery wall cell cocultures exposed to human LDL was dramatically better than that in controls. Moreover, LDL from PLTP0 mice was markedly resistant to oxidation and induced significantly less monocyte chemotactic activity compared with that in controls. In vitro, PLTP0 HDL removed significantly more oxidized phospholipids from LDL than did control HDL. We conclude that PLTP deficiency improves the anti-inflammatory properties of HDL in mice and reduces the ability of LDL to induce monocyte chemotactic activity.

Scavenger receptor class B type I is solely responsible for the selective uptake of cholesteryl esters from HDL by the liver and the adrenals in mice

Scavenger receptor class B type I (SR-BI) has been identified as a functional HDL binding protein that can mediate the selective uptake of cholesteryl ester (CE) from HDL. To quantify the in vivo role of SR-BI in the process of selective uptake, HDL was labeled with cholesteryl ether ([(3)H] CEt-HDL) and (125)I-tyramine cellobiose ([(125)I]TC-HDL) and injected into SR-BI knockout (KO) and wild-type (WT) mice. In SR-BI KO mice, the clearance of HDL-CE from the blood circulation was greatly diminished (0.043 +/- 0.004 pools/h for SR-BI KO mice vs. 0.106 +/- 0.004 pools/h for WT mice), while liver and adrenal uptake were greatly reduced. Utilization of double-labeled HDL ([(3)H]CEt and [(125)I]TC) indicated the total absence in vivo of the selective decay and liver uptake of CE from HDL in SR-BI KO mice. Parenchymal cells isolated from SR-BI KO mice showed similar association values for [(3)H]CEt and [(125)I]TC in contrast to WT cells, indicating that in parenchymal liver cells SR-BI is the only molecule exerting selective CE uptake from HDL. Thus, in vivo and in vitro, SR-BI is the sole molecule mediating the selective uptake of CE from HDL by the liver and the adrenals, making it the unique target to modulate reverse cholesterol transport.

Transvascular lipoprotein transport in patients with chronic renal disease

BACKGROUND

While increased plasma cholesterol is a well-established cardiovascular risk factor in the general population, this is not so among patients with chronic renal disease. We hypothesized that the transvascular lipoprotein transport, in addition to the lipoprotein concentration in plasma, determines the degree of atherosclerosis among patients with chronic renal disease.

METHODS

We used an in vivo method for measurement of transvascular transport of low-density lipoprotein (LDL) in 21 patients with chronic renal disease and in 42 healthy control patients. Autologous 131-iodinated LDL was reinjected intravenously, and the 1-hour fractional escape rate was taken as index of transvascular transport.

RESULTS

Transvascular LDL transport tended to be lower in patients with chronic renal disease than in healthy control patients [3.3 (95% CI 2.4-4.2) vs. 4.2 (3.7-4.2)%/hour; NS]. However, this tendency disappeared when transvascular LDL transport was corrected for distribution volume of LDL [1.7 (1.2-2.2) vs. 1.8 (1.6-2.0) %/(hour x (L/m(2))); NS]. There was significant variation in transvascular LDL transport between diabetic patients with chronic renal disease, nondiabetic patients with chronic renal disease, and healthy control patients [5.0 (3.2-7.8) vs. 3.0 (2.2-3.8) vs. 4.2 (3.6-4.8) %/hour; P < 0.01 after adjustment for distribution volume of LDL]. This variation was unlikely caused by altered hepatic LDL receptor expression or glycosylation of LDL in diabetes patients.

CONCLUSION

Transvascular LDL transport may be increased in diabetic patients with chronic renal disease, suggesting that lipoprotein flux into the arterial wall is increased. A similar mechanism does not operate in nondiabetic patients with chronic renal disease.

Growth Hormone Induces Low-Density Lipoprotein Clearance but not Bile Acid Synthesis in Humans

OBJECTIVE

Growth hormone (GH) induces hepatic low-density lipoprotein (LDL) receptors and lowers plasma cholesterol. We characterized the influence of GH treatment on plasma LDL clearance in normal humans and investigated the relative role of LDL receptor (LDLR) activity and stimulation of bile acid synthesis in subjects with different LDLR expression.

METHODS AND RESULTS

Plasma clearance of autologous 125I-LDL was measured before and during 3 weeks of treatment with GH (0.1 IU/kg per day) in 9 healthy young males. Plasma LDL cholesterol was reduced by 13% and the fractional catabolic rate of LDL increased by 27%. More marked changes were seen in a patient with hypopituitarism substituted with GH (0.07 IU/kg per day) for 3 months. In a second study, GH dose-dependently reduced LDL cholesterol and increased Lp(a) levels in 3 groups of males: younger and elderly healthy subjects and heterozygous familial hypercholesterolemia (FH). No effect on bile acid synthesis measured by the plasma marker 7alpha-hydroxy-4-cholesten-3-one was observed. In an LDLR-deficient FH homozygote, LDL cholesterol was not affected by GH.

CONCLUSIONS

GH treatment reduces plasma LDL cholesterol by inducing LDL clearance. In humans, LDLR expression is a prerequisite for this effect, whereas it is not related to stimulation of bile acid synthesis.

Clearance of a 3H-labeled chylomicron-like emulsion following the acute phase of myocardial infarction

BACKGROUND

Plasma lipids may be altered during acute myocardial infarction and may not reflect patient baseline lipid profile. The metabolism of chylomicrons, the lipoproteins that carry the dietary lipids in the bloodstream has not yet been studied in acute myocardial infarction patients.

METHODS

In this study, a lipidic emulsion that mimics the intravascular behavior of chylomicrons labeled with cholesteryl oleate ((3)H-CO) was injected intravenously in 17 normolipidemic patients on the seventh and on the 45th day post-non complicated acute myocardial infarction after a 12-h fast. The plasma decay curve of the emulsion label was determined from blood samples collected during 60 min. Data were also compared with a group of 10 patients with chronic coronary artery disease.

RESULTS

In the acute myocardial infarction group, the plasma fractional catabolic rates of the emulsion (3)H-CO, expressed as median and confidence intervals, did not change from the seventh to the 45th day after the acute event [0.0773 (0.061, 0.1025) min(-1) vs. 0.0672 (0.00507, 0.1009) min(-1) P=0.61] and was similar to that determined in chronic coronary artery disease patients. High-density lipoprotein cholesterol and apolipoprotein AI were lower on the seventh day when compared to the 45th day post acute myocardial infarction (P=0.01 and P=0.004, respectively). No changes were found in LDL and total cholesterol as well as in plasma triglycerides in myocardial infarction group.

CONCLUSIONS

No changes were found in chylomicron metabolism is in the acute phase of myocardial infarction.

Metabolism of a cholesterol-rich microemulsion (LDE) in patients with multiple myeloma and a preliminary clinical study of LDE as a drug vehicle for the treatment of the disease

PURPOSE

Previously we have shown that cholesterol-rich microemulsions that bind to LDL receptors have the ability to concentrate in acute myeloid leukemia cells and in ovarian and breast carcinomas. Thus, LDE may be used as a vehicle for drugs directed against neoplastic cells. Indeed, we subsequently showed that when carmustine is associated with LDE the toxicity of the drug is significantly reduced in patients with advanced cancers. The aim of the present study was to verify whether LDE may be taken up by multiple myeloma cells and whether patients with multiple myeloma respond to treatment with LDE associated with carmustine.

METHODS

A total of 131 consecutive volunteer patients with recently diagnosed multiple myeloma classified as clinical stage IIIA had their plasma lipid profile determined. LDE plasma kinetics were performed in 14 of them. Cell uptake of LDE and the cytotoxicity of carmustine associated with the emulsion were evaluated in a multiple myeloma cell line. A pharmacokinetic study of LDE-carmustine was performed in three patients. Finally, an exploratory clinical study of LDE-carmustine (carmustine dose 180 mg/m(2) body surface every 4 weeks) was performed in seven untreated multiple myeloma patients.

RESULTS

LDL cholesterol was lower in the 131 multiple myeloma patients than in healthy controls and the fractional clearance rate (FCR, in units per minute) in the 14 multiple myeloma patients was twice that in 14 paired healthy control subjects. Moreover, entry of LDE into multiple myeloma cells was shown to be mediated by LDL receptors. Taken together, these findings indicate that LDE may target multiple myeloma. The exploratory clinical study showed that gammaglobulin decreased by 10-70% (mean 36%) after three cycles and by 25-75% (mean 44%) after six cycles. Furthermore, there was amelioration of symptoms in all patients. Cholesterol concentrations increased after treatment, suggesting that the treatment resulted in at least partial destruction of neoplastic cells with receptor upregulation. Side effects of the treatment were negligible.

CONCLUSIONS

Because it targets multiple myeloma and, when associated with an antineoplastic agent, produces therapeutic responses in patients with fewer side effects, LDE has the potential for use as a drug vehicle in the treatment of the disease.