Polysorbate-stabilized solid lipid nanoparticles as colloidal carriers for intravenous targeting of drugs to the brain: Comparison of plasma protein adsorption patterns

Plasma proteins enriched on the surface of drug-delivery-purpose nanoparticles are regarded as key factors for determination of in vivo organ distribution after intravenous injection. Polysorbate 80-coated polybutylcyanoacrylate (PBCA) nanoparticles, preferentially adsorbing apolipoprotein E (apoE) on their surface, have previously been considered to deliver various drugs to the brain. In the present study, in vivo well tolerable solid lipid nanoparticles (SLN) using different types of polysorbates as stabilizers were produced. The influence of the different surfactants on in vitro adsorption of human plasma proteins was investigated using two-dimensional polyacrylamide gel electrophoresis (2-DE). Possible correlations of different amounts of adsorbed apoE to the hydrophilic-lipophilic balance (HLB) of the polysorbates are shown and discussed. Apolipoprotein C-II, albumin and immunoglobulin G, which are also decisive plasma proteins with regard to site-specific drug delivery of intravenously injected carriers to the brain, are compared with regard to adsorption. Moreover, certain similarities to the plasma protein adsorption patterns of previously analysed brain-specific PBCA nanoparticles could be detected. Despite some differences in adsorption behavior of proteins on the surface of polysorbate-stabilized SLN and PBCA nanoparticles, we conclude that in both cases polysorbate 80 might have the highest potential to deliver drugs to the brain.

Effects of apolipoproteins on dalargin transport across the blood-brain barrier

Antinociceptive activity of dalargin (7.5 mg/kg) adsorbed on poly(butyl)cyanoacrylate nanoparticles with different coating was studied on outbred albino mice by the tail-flick test. poly(butyl)cyanoacrylate nanoparticles without coating did not increase the antinociceptive activity of dalargin and hence, did not increase its transport across the blood-brain barrier. poly(butyl)cyanoacrylate nanoparticles coated with apolipoprotein B, apolipoprotein E, and polysorbate 80 increased the transport of dalargin across the blood-brain barrier. Delivery of dalargin to the brain was most effective in case of using poly(butyl)cyanoacrylate nanoparticles with polysorbate 80 coating and subsequent supercoating with apolipoprotein E.

Covalent Linkage of Apolipoprotein E to Albumin Nanoparticles Strongly Enhances Drug Transport into the Brain

Drug delivery to the brain is becoming more and more important but is severely restricted by the blood-brain barrier. Nanoparticles coated with polysorbates have previously been shown to enable the transport of several drugs across the blood-brain barrier, which under normal circumstances is impermeable to these compounds. Apolipoprotein E was suggested to mediate this drug transport across the blood-brain barrier. In the present study, apolipoprotein E was coupled by chemical methods to nanoparticles made of human serum albumin (HSA-NP). Loperamide, which does not cross the blood-brain barrier but exerts antinociceptive effects after direct injection into the brain, was used as model drug. Apolipoprotein E was chemically bound via linkers to loperamide-loaded HSA-NP. This preparation induced antinociceptive effects in the tail-flick test in ICR mice after i.v. injection. In contrast, nanoparticles linked to apolipoprotein E variants that do not recognize lipoprotein receptors failed to induce these effects. These results indicate that apolipoprotein E attached to the surface of nanoparticles facilitates transport of drugs across the blood-brain barrier, probably after interaction with lipoprotein receptors on the brain capillary endothelial cell membranes.

Estrogen facilitates neurite extension via apolipoprotein E in cultured adult mouse cortical neurons

Literature review suggests a close relationship between estrogen and apolipoprotein E (ApoE) in the central nervous system. Epidemiology studies show that estrogen replacement therapy (ERT) decreases the morbidity from several chronic neurological diseases. Alleles of ApoE modify the risk for and progression of the same diseases. ApoE levels in the rodent brain vary during the estrous cycle and increase after 17beta-estradiol administration. Both estradiol and ApoE3, the most common isoform of human ApoE, increase the extent of neurite outgrowth in culture. Combined, these observations suggest a common mechanism whereby estrogen may increase ApoE levels to facilitate neurite growth. We tested this hypothesis by characterizing the effects of estradiol and ApoE isoforms on neurite outgrowth in cultured adult mouse cortical neurons. Estradiol increased ApoE levels and neurite outgrowth. ApoE2 increased neurite length more so than ApoE3 in the presence of estradiol. Estradiol had no effect on neurite outgrowth from mice lacking the ApoE gene or when only ApoE4, the isoform of ApoE that is associated with increased risk of neurological disease, was exogenously supplied. Cultures from mice transgenic for human ApoE3 or ApoE4 showed the same isoform-specific effect. Neuronal internalization of recombinant human ApoE3 was greater than ApoE4, and ApoE3 was more effective than ApoE4 in facilitating neuronal uptake of a fatty acid. We conclude that estradiol facilitates neurite growth through an ApoE-dependent mechanism. The effects of ERT on chronic neurological diseases may vary with ApoE genotype. The clinical use of ERT may require ApoE genotyping for optimal efficacy.

Comparative in vivo metabolism of apolipoproteins E2 and E4 in heterozygous apoE2/4 subjects

Apolipoprotein E (apoE) exists in three common forms in humans: the wild-type apoE3 and two common genetic variants, apoE2 and apoE4. Although previous studies have examined the metabolism of the different apoE isoforms in human subjects, they have not involved direct comparison of two different isoforms in subjects heterozygous for the same two isoforms. We conducted this study to directly compare the catabolism of apoE2 and apoE4 in heterozygous E2/4 subjects in vivo. Iodine 131-labeled apoE2 and iodine 125-labeled apoE4 were simultaneously injected into three E4/2 heterozygous subjects. The mean residence time of apoE4 (0.40 +/- 0.01 day) was found to be one-third that of apoE2 (1.20 +/- 0.18 day). ApoE2 was present primarily in high-density lipoprotein, whereas apoE4 was present equally in very low density and high-density lipoprotein. In all lipoprotein subfractions, apoE4 was catabolized at a much faster rate than apoE2. In conclusion, E4 is catabolized three times faster than apoE2 in heterozygous E2/4 subjects, indicating that these two apoE isoproteins have distinct metabolic pathways.

Transfer of antisense oligodeoxynucleotides against endothelin receptors A and B into human coronary smooth muscle cells and endothelial cells by apolipoprotein E peptide: an in vitro study

Antisense oligodeoxynucleotides (AS-ODNs) are a new generation of therapeutic agents for gene therapy. To develop a new approach in regulating the expression of endothelin (ET) receptor, N,N-dipalmitylglycyl-apolipoprotein E (129-169) peptide (dpGapoE), an efficient gene delivery system, was used to transfect phosphorothioated AS-ODNs against nucleotides of human ET type A (ETA) receptors in human coronary smooth muscle cells (HCSMCs) and type B (ETB) receptors in human coronary endothelial cells (HCECs). After transfection, translocation to the nuclei and concentration in nuclear structures were observed in approximately 40% of HCSMCs and 60% of HCECs, respectively, at 48 h by fluorescence microscopy. Both the cellular ETA mRNA concentration in HCSMCs and ETB mRNA concentration in HCECs significantly declined. This approach may enable gene regulation in vivo and could be used to regulate vascular tone and constriction through ET receptors.

Apolipoprotein-mediated transport of nanoparticle-bound drugs across the blood-brain barrier

Recent studies have shown that drugs that are normally unable to cross the blood-brain barrier (BBB) following intravenous injection can be transported across this barrier by binding to poly(butyl cyanoacrylate) nanoparticles and coating with polysorbate 80. However, the mechanism of this transport so far was not known. In the present paper, the possible involvement of apolipoproteins in the transport of nanoparticle-bound drugs into the brain is investigated. Poly(butyl cyanoacrylate) nanoparticles loaded with the hexapeptide dalargin were coated with the apolipoproteins AII, B, CII, E, or J without or after precoating with polysorbate 80. In addition, loperamide-loaded nanoparticles were coated with apolipoprotein E alone or again after precoating with polysorbate 80. After intravenous injection to ICR mice the antinociceptive threshold was measured by the tail flick test. Furthermore, the antinociceptive threshold of polysorbate 80-coated dalargin-loaded nanoparticles was determined in ApoEtm1Unc and C57BL/6J mice. The results show that only dalargin or loperamide-loaded nanoparticles coated with polysorbate 80 and/or with apolipoprotein B or E were able to achieve an antinociceptive effect. This effect was significantly higher after polysorbate-precoating and apolipoprotein B or E-overcoating. With the apolipoprotein E-deficient ApoEtm1Unc mice the antinociceptive effect was considerably reduced in comparison to the C57BL/6J mice. These results suggest that apolipoproteins B and E are involved in the mediation of the transport of drugs bound to poly(butyl cyanoacrylate) nanoparticles across the BBB. Polysorbate 80-coated nanoparticles adsorb these apolipoproteins from the blood after injection and thus seem to mimic lipoprotein particles that could be taken up by the brain capillary endothelial cells via receptor-mediated endocytosis. Bound drugs then may be further transported into the brain by diffusion following release within the endothelial cells or, alternatively, by transcytosis.

Uptake and internalization of exogenous apolipoprotein E3 by cultured human central nervous system neurons

Apolipoprotein E (apoE) has been confirmed as a risk factor for late-onset Alzheimer's disease (AD) and is associated with neurofibrillary tangles and senile plaques, the microscopic pathological characteristics of AD. There has been no direct evidence that human central nervous system neurons can take up and internalize exogenous apoE, which may be important in order for apoE to be involved in the development of the disease. This paper demonstrates by immunohistochemistry and confocal microscopy that cultured human brain neurons can take up and internalize exogenous recombinant human apoE3. We confirm that neurons express the low-density lipoprotein receptor-related protein (LRP) but do not express the low-density lipoprotein receptor. We also demonstrate that the LRP mediates the neuronal uptake of apoE.

Isoform-specific effects of apolipoproteins E2, E3, and E4 on cerebral capillary sequestration and blood-brain barrier transport of circulating Alzheimer's amyloid beta

Cerebral capillary sequestration and blood-brain barrier (BBB) permeability to apolipoproteins E2 (apoE2), E3 (apoE3), and E4 (apoE4) and to their complexes with sA beta(1-40), a peptide homologous to the major form of soluble Alzheimer's amyloid beta, were studied in perfused guinea pig brain. Cerebrovascular uptake of three apoE isoforms was low, their blood-to-brain transport undetectable, but uptake by the choroid plexus significant. Binding of all three isoforms to sA beta(1-40) in vitro was similar with a K(D) between 11.8 and 12.9 nM. Transport into brain parenchyma and sequestration by BBB and choroid plexus were negligible for sA beta(1-40)-apoE2 and sA beta(1-40)-apoE3, but significant for sA beta(1-40)-apoE4. After 10 min, 85% of sA beta(1-40)-apoE4 taken up at the BBB remained as intact complex, whereas free sA beta(1-40) was 51% degraded. Circulating apoE isoforms have contrasting effects on cerebral capillary uptake of and BBB permeability of sA beta. ApoE2 and apoE3 completely prevent cerebral capillary sequestration and blood-to-brain transport of sA beta(1-40). Conversely, apoE4, by entering brain microvessels and parenchyma as a stable complex with sA beta, reduces peptide degradation and may predispose to cerebrovascular and possibly enhance parenchymal amyloid formation under pathological conditions.

Human recombinant apolipoprotein E redirects lipopolysaccharide from Kupffer cells to liver parenchymal cells in rats In vivo

Chylomicrons have been shown to protect mice and rats against a lethal dose of lipopolysaccharide and may serve as a therapeutic means to protect against endotoxemia. However, the requisite of isolation from human lymph hampers pharmaceutical application. Recently, we developed recombinant chylomicrons from commercially available lipids and human recombinant apolipoprotein E. The current study explored the effectiveness of these apoE-enriched emulsions in redirecting LPS from Kupffer cells to liver parenchymal cells. Upon injection into rats, 125I-LPS rapidly and specifically associated with the liver (64.3+/-3.1% of the injected dose) and spleen (4.1+/-0.7%). The uptake of LPS by the spleen was four- to fivefold reduced upon incubation with the apoE-enriched emulsion or free apoE (P < 0.0001), but not with emulsion alone or Lipofundin. Within the liver, 125I-LPS mainly associated with Kupffer cells. The uptake by Kupffer cells was eight- to ninefold reduced by the apoE-enriched emulsion or apoE alone (P < 0.01), and a 19.6-fold increased uptake ratio by liver parenchymal cells over Kupffer cells was observed. The emulsion without apoE had no effect on the in vivo kinetics of LPS. LPS interacted selectively with the apoE moiety of the recombinant chylomicron. Emulsion-associated and free apoE bound approximately two molecules of LPS, possibly by its exposed hydrophilic domain involving arginine residues. We anticipate that the protecting effect of endogenous chylomicrons against LPS-induced endotoxemia may result from the apoE moiety and that human recombinant apoE may serve as a therapeuticum to protect against endotoxemia.

Hepatic production of very low density lipoprotein, catabolism of low density lipoprotein, biliary lipid secretion, and bile salt synthesis in rats fed a bean (Phaseolus vulgaris) diet

Rats fed a bean diet develop a significant hypocholesterolemia. The catabolism of low density lipoprotein (LDL; d 1.019-1.063 g/ml) was studied in vivo and in vitro in the isolated perfused liver of rats fed either a casein or a bean diet. The clearance of LDL was significantly increased by 100% from 0.38 +/- 0.04 to 0.63 +/- 0.04 ml/h x 100 g body wt in vivo in the bean-fed rat. Similarly, the clearance of homologous and heterologous (human) LDL was also increased by 100% in the isolated perfused liver of bean-fed animals. Spleen, kidney, and hepatic cholesterogenesis was increased by 150% in these animals. Bile salt synthesis was increased from 1.54 +/- 0.02 to 2.84 +/- 0.09 nmol/min x g liver wt (P < 0.02) and biliary cholesterol output by 200% from 0.81 +/- 0.03 to 2.18 +/- 0.04 nmol/min x g (P < 0.02) in the isolated perfused liver of rats fed a bean diet. These results explained the depletion of hepatic cholesterol and were consistent with the LDL turnover studies, suggesting that apoB/E receptor activity was increased in these animals. ApoB and triglyceride secretion in the d < 1.060 g/ml lipoprotein fraction of liver perfusates remained normal in the bean-fed rats. In contrast, total sinusoidal cholesterol output isolated in the d < 1.060 g/ml fraction significantly decreased by 100% after 90 min of perfusion. Cholesterol output in the d > 1.060 g/ml lipoprotein fraction was unmodified by the bean diet. These data demonstrate that key metabolic pathways of hepatic cholesterol are modified in the bean-fed rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective labelling of hepatic fatty acids in vivo. Studies on the synthesis and secretion of glycerolipids in the rat

1. We describe a method for the selective labelling of hepatic fatty acids in the rat in vivo. It relies on (i) the rapid and preferential uptake of cholesteryl ester from chylomicron and/or very-low-density-lipoprotein remnants by the liver [Holder, Zammit & Robinson (1990) Biochem. J. 272, 735-741] (without prior exchange of the ester to other lipoproteins in the plasma), and (ii) the very short half-life of the cholesteryl ester in the liver. The 14C-labelled fatty acid moiety generated by cholesteryl ester hydrolysis was shown to be utilized by the liver for glycerolipid synthesis in a very similar pattern to that demonstrated for exogenous fatty acids by isolated cultured hepatocytes in previous studies. 2. Starvation (24 h) was shown to decrease the proportion of fatty acid utilized for glycerolipid synthesis, but to result in a proportionately smaller effect on incorporation into phospholipid. This was accompanied by a decrease in the fraction of synthesized triacylglycerol that was secreted by the liver. 3. Streptozotocin-diabetes did not affect the phospholipid/triacylglycerol ratio, but resulted in a small, but significant, decline in the fraction of triacylglycerol secreted by the liver. 4. In both starved and diabetic animals fatty acid esterification to the glycerol moiety constituted a smaller proportion of the total disposal of label. 5. These findings appear to validate the present method for the selective labelling of liver fatty acids in vivo in a non-invasive manner. Other possible uses for the method are suggested.

Intravenous infusion of apolipoprotein E accelerates clearance of plasma lipoproteins in rabbits

Plasma cholesterol levels in cholesterol-fed rabbits were markedly reduced by the intravenous infusion or bolus injection of recombinant human apo E or rabbit plasma apo E. Administration of 6-70 mg of apo E resulted in an approximately 20-40% acute reduction in plasma cholesterol levels within 2-3 h. Plasma cholesterol levels remained reduced for 4-8 h after the administration of apo E. Furthermore, the intravenous injection of apo E reduced the plasma cholesterol levels in Watanabe heritable hyperlipidemic rabbits. The addition of apo E to [14C]cholesterol-labeled canine thoracic duct lymph or [14C]cholesterol-labeled chylomicrons resulted in accelerated plasma clearance of these diet-induced lipoproteins in normal rabbits, with the uptake occurring primarily in the liver. This study suggests that the amount or availability of apo E in the plasma of cholesterol-fed rabbits may be rate limiting for the normal clearance of diet-induced remnant lipoproteins.

Increased clearance of plasma cholesterol after injection of apolipoprotein E into Watanabe heritable hyperlipidemic rabbits

Apolipoprotein E (apoE) is known to play an important role in lipoprotein metabolism. We have studied the effect of apoE on the metabolism of plasma cholesterol by injecting apoE intravenously into rabbits deficient in low density lipoprotein receptors [Watanabe heritable hyperlipidemic (WHHL) rabbits]. Approximately 30 mg of apoE was injected per rabbit; a total of five WHHL rabbits were used. One hour later, plasma cholesterol levels fell 8.3% (from 488 +/- 192 to 446 +/- 174 mg/dl). After 3 hr, cholesterol levels had fallen by 19% (to 392 +/- 152 mg/dl). The reduced levels were maintained for at least 8 hr after injection of apoE. Cholesterol in very low density lipoproteins (VLDLs) and intermediate density lipoproteins fell rapidly during the first 2 hr after injection, followed by a reduction in the low density lipoprotein cholesterol level. Changes in apolipoprotein B levels in each lipoprotein fraction were very similar to those of cholesterol. Plasma apoE levels 3 min after injection were elevated 3-fold to 22.8 +/- 6.3 mg/dl and returned to initial levels 8 hr after injection. The rate of removal of intravenously injected 125I-labeled VLDL that had been incubated with apoE was 3-fold higher than that of unmodified VLDL. From these results, we conclude that the injected apoE is incorporated into VLDLs and that VLDL particles carrying more apoE are removed from the blood more rapidly, resulting in reduced formation of low density lipoprotein and lowered cholesterol levels.

Apolipoprotein E is released by rat sciatic nerve during segmental demyelination and remyelination

Apolipoprotein E (apo E) is synthesized and released in greatly increased amounts by peripheral nerve following Wallerian degeneration; it has been suggested that this protein may function in the transport of degenerated myelin lipid. The purpose of this study was to determine if the amount of apo E released by rat peripheral nerve is increased following selective demyelination, in the absence of significant axonopathy. Using an immunoturbidimetric assay, release of apo E from excised sciatic nerve segments was measured during the phases of acute demyelination and remyelination caused by tellurium (Te) toxicity, during segmental demyelination in chronic lead (Pb) poisoning, and during Wallerian degeneration following nerve crush. Morphologic changes were examined in contralateral sciatic nerves by nerve-fiber teasing or by light and electron microscopy of transverse sections. As in previous studies, the amount of apo E released from the nerves was greatly increased following Wallerian degeneration due to nerve crush. In Te neuropathy, increased release of apo E was first detected on the fourth day of Te exposure, corresponding temporally to the acute onset of paralysis and segmental demyelination. Apolipoprotein E release rose steeply to a maximum of ten times the control values by day 9 and then gradually waned during the next five weeks, corresponding to a period of active remyelination and resolution of the neuropathy. In the demyelinating neuropathy of chronic lead poisoning, apo E release was increased four times over control animals after seven weeks of exposure, with less than 10% of teased fibers showing early paranodal demyelination and no evidence of remyelination.(ABSTRACT TRUNCATED AT 250 WORDS)