Biomedical subjects

Q H Meng

Publications and source records attributed to Q H Meng.

At least 19 recordsLinked to original sources

PubMed2006

Ten-year experience with living related donated splenic transplantation for the treatment of hemophilia A.

AIM: Six cases of hemophilia A treated with living related donated splenic transplantation (LRDST) were performed over 10 years. METHODS: We reviewed the six consecutive cases of LRDST from 1992 to 2002. Three patients received whole spleen allografts and the other three, partial spleen allografts. All allografts were transplanted to the extraperitoneal space in the right iliac fossa by an end-to-end anastomosis between the splenic artery and the internal iliac artery and an end-to-side anastomosis between the splenic vein and the external (or common) iliac vein. After the operation, a combined regimen with cyclosporine, azathioprine, anti-lymphocyte globulin, OKT3, was administered to suppress the immune reaction. RESULTS: The functional period of the allografts varied between 30 days to 4 years. Patient factor-VIII (F-VIII) levels rose from less than 5% before operation to 15% to 56% postoperatively. One patient died from central nervous system complications. Another lost his graft because exogenous F-VIII was not supplemented in timely fashion at the onset of rejection. And the third could no longer afford the expensive immunosuppressive drugs at 2 years after the operation and eventually lost the spleen. The remaining three patients presently have regained self-support, among whom one has survived for 4 years. CONCLUSION: Though the sample pool is relatively small, our clinical observations tend to confirm LRDST as a feasible, effective treatment for hemophilia A.

Drug Therapy, Combination↗

PubMed2001

Increased expression of inducible nitric oxide synthase and cyclo-oxygenase-2 in the airway epithelium of asthmatic subjects and regulation by corticosteroid treatment.

BACKGROUND: Nitric oxide (NO) and prostanoids are mediators of vascular and bronchial tone that are postulated to be involved in asthma. Increased levels of both are found in asthmatic subjects and are synthesised by enzymes that have cytokine inducible forms: inducible NO synthase (iNOS) and cyclo-oxygenase-2 (COX-2), respectively. We hypothesised that the in vivo expression of iNOS and COX-2 in the airways would be increased in asthma, and that these cytokine inducible enzymes may represent targets for regulation by corticosteroid treatment. METHODS: Bronchial biopsy specimens were obtained from three groups of subjects: atopic asthmatics treated with beta(2) agonists alone (n=7), atopic asthmatics additionally receiving regular treatment with corticosteroids (n=8), and non-asthmatic control subjects (n=10). Expression of iNOS and COX-2 mRNA and immunoreactive protein was studied using in situ hybridisation and quantitative immunohistochemistry. RESULTS: Immunoreactivity and the hybridisation signal for iNOS and COX-2 were mainly localised in the airway epithelium. The proportion of epithelium immunostained was significantly greater in the non-steroid treated asthmatic subjects (iNOS 8.6 (1.8)%; COX-2 26.3 (4.6)%) than either the steroid treated asthmatics (iNOS 3.4 (1.0)%, p=0.009; COX-2 13.0 (0.6)%, p=0.0015) or the non-asthmatic controls (iNOS 4.2 (0.9)%, p=0.018; COX-2 11.6 (0.6)%, p=0.0003). Similarly, the hybridisation signal was stronger in the non-steroid treated group of asthmatic subjects than in the other two groups. CONCLUSIONS: These findings highlight the potential role of the airway epithelium both as a contributor to the inflammatory process in asthma and as a target for inhaled corticosteroid treatment in this disease.

Adrenal Cortex Hormones↗

PubMed2001

BRCA1 is differentially expressed in human tumor cells.

Mutations of the human breast cancer susceptibility gene 1 (BRCA1) confers a risk for breast, ovarian and prostate cancers and BRCA1 exerts multiple biological functions. Using Western blot and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assays, we have determined the expression of endogenous BRCA1 protein and mRNA in forty-three human tumor cell lines established from eleven types of human tumor tissues. BRCA1 was differentially expressed in tumor cell lines. No significant association was found between BRCA1 expression and the p53 gene status of cell lines. The disruption of wild-type p53 by either the human papillomavirus E6 oncogene or the mutant p53 gene (143Ala-->Val) did not cause any significant alteration in basal level of BRCA1 expression, while the knockout of p21 (-/-) by homologous recombination assay and Blocking Gadd45 expression by constitutive antisense expression slightly increased BRCA1 protein expression. Therefore, although the functional significance of the differential expression in human tumor cells is currently unknown, the present data provide a valuable background for further study of BRCA1 in tumor cell lines.

BRCA1 Protein↗

PubMed2000

Neutrophils enhance expression of inducible nitric oxide synthase in human normal but not cystic fibrosis bronchial epithelial cells.

The bronchial epithelium in cystic fibrosis (CF) expresses very low levels of the inducible form of nitric oxide synthase (iNOS). The product of iNOS, nitric oxide (NO), mediates anti-microbial effects and can reduce neutrophil sequestration in the lung. Heavy neutrophilic infiltration of the pulmonary epithelium is a major feature of the end-stage CF lung. This study hypothesized that the system whereby the pulmonary epithelium protects itself against exaggerated neutrophilic infiltration by producing NO is compromised in CF. Human neutrophils were activated by incubation with cytokines, added to monolayers of normal (16HBE14o-) and CF (CFBE41o-) bronchial epithelial cells and co-cultured for up to 72 h. Marked up-regulation of iNOS protein expression was seen in normal bronchial epithelial cells following neutrophil co-culture but the CF cells showed a significantly smaller increase (p<0.001). To determine whether the relative lack of protein was due to a defect in translation, RT-PCR of iNOS mRNA was carried out and a pattern of mRNA expression was seen paralleling that of the protein. The reduced production of NO by CF compared with normal epithelium was shown by the presence of significantly (p<0.001) less accumulated nitrites in medium after co-culture with neutrophils. In summary, this study shows that the normal production of NO by bronchial epithelium in response to contact with neutrophils is lacking in CF. As NO has been shown to oppose neutrophil sequestration, its relative lack in CF may underlie the heavy neutrophilic infiltration that characterizes the disease.

Bronchi↗

PubMed2000

An integrin-targeted non-viral vector for pulmonary gene therapy.

Gene therapy offers potential for the treatment of severe respiratory diseases. However, the vectors which are currently available have drawbacks limiting their therapeutic application. Here we report on an integrin-targeted, non-viral gene delivery system for pulmonary gene transfer. We demonstrate that this vector can deliver the lacZ reporter gene to the lung, transfecting bronchial epithelium and parenchymal cells with similar efficiency to an adenoviral vector and with greater efficiency than a cationic liposome. In addition, vector administration can be repeated leading to further gene expression without inducing inflammation. The advantages of this novel gene delivery system provide considerable potential for targeted gene therapy in vivo. Gene Therapy (2000) 7, 393-400.

Animals↗

PubMed2000

Expression of low and high density lipoprotein receptor genes in human adrenals.

Corticosteroids are synthesized from cholesterol which may arise from de novo synthesis or from the uptake of low or high density lipoproteins (LDL or HDL). In the present study, we compared the expression and regulation patterns of LDL receptor and CLA-1 (CD36 and LIMPII Analogous-1, an HDL receptor) genes in adult human adrenocortical tissues to shed more light on the relative contribution of LDL and HDL in human adrenal steroidogenesis. By screening 64 normal and pathological adrenal samples by Northern blotting, we found a positive correlation between LDL receptor and CLA-1 mRNA expression in the adrenal tissues (r=0.547; spearman rank correlation test P<0.01). Adrenal tissues adjacent to Cushing's adenomas contained consistently less LDL receptor and CLA-1 mRNA than normal adrenals (Mann-Whitney P<0.05). In primary cultures of normal adrenal cells, accumulation of both LDL receptor and CLA-1 mRNAs was upregulated by ACTH in a dose- and time-dependent manner, with an earlier induction of LDL receptor than CLA-1 mRNA expression. (Bu)(2)cAMP also increased the levels of these two mRNAs. Addition of LDL, but not HDL, into the culture medium increased cortisol production in untreated adrenocortical cells. Both LDL and HDL enhanced ACTH-induced cortisol production, with the effect of LDL much stronger than that of HDL. Our data show that LDL receptor and CLA-1's expression is ACTH-dependent and occurs in parallel in human adrenal tissues. LDL rather than HDL may be used as the preferential source of cholesterol for steroidogenesis in human adult adrenocortical cells.

Adrenal Glands↗

PubMed1999

Antioxidant protection of lipoproteins containing estrogens: in vitro evidence for low- and high-density lipoproteins as estrogen carriers.

Some recent studies have reported that low-density lipoprotein (LDL) isolated from estrogen-treated postmenopausal women exhibited increased oxidation resistance ex vivo. However, the underlying mechanisms responsible for this effect are not clear. We explored the possibility that lipophilic derivatives of 17beta-estradiol (E(2)) could be incorporated into LDL and high-density lipoprotein (HDL) particles inhibiting lipoprotein oxidation. Introduction of small amounts of esterified E(2) into lipoproteins by means of incubation of free E(2) and E(2) 17-stearate in plasma did not result in any antioxidant effect. Using an artificial transfer system (Celite dispersion), larger amounts of E(2) esters could be incorporated into lipoproteins. Concentrations ranging between 0.27 and 1.38 molecules/LDL particle for E(2) 17-stearate and between 0.36 and 1.93 molecules/LDL particle for E(2) 17-oleate resulted in increased Cu(2+)-induced oxidation resistance of LDL as indicated by statistically significant lag time prolongations. Significant prolongations of lag times were also observed for HDL following incorporation of E(2) esters using Celite as transfer system. Our results suggest that free E(2) can be esterified and incorporated into lipoproteins during incubation in plasma. However, incorporation of supraphysiologic concentrations of E(2) esters into lipoproteins by means of the artificial transfer system was required in order to reduce their oxidation susceptibility.

Adult↗

PubMed1999

Incorporation of esterified soybean isoflavones with antioxidant activity into low density lipoprotein.

We have recently reported that dietary intake of soybean isoflavone phytoestrogens resulted in increased oxidation resistance of isolated low density lipoprotein (LDL). In order to explore the underlying mechanisms we designed two types of in vitro experiments. First, we prepared several different isoflavone fatty acid esters to increase their lipid solubility and studied their incorporation into LDL. Second, the oxidation resistance of the isoflavone-containing LDLs was investigated with Esterbauer's 'conjugated diene' method using Cu2+ as prooxidant. Unesterified daidzein and genistein as well as genistein stearic acid esters were incorporated into LDL to a relatively small extent (0.33 molecules per LDL particle, or less) and they did not significantly influence oxidation resistance. The oleic acid esters of isoflavones were incorporated more effectively, reaching a level of 2.19 molecules per LDL particle or more, and the 4',7-O-dioleates of daidzein and genistein exhibited prolongations of lag times by 46% (P<0.05) and 202% (P<0.01), respectively. A smaller but significant increase in lag time (20.5%, P<0.01) was caused by daidzein 7-mono-oleate. In summary, esterification of soybean isoflavones daidzein and genistein with fatty acids at different hydroxyl groups provided lipophilicity needed for incorporation into LDL. Some isoflavone oleic acid esters increased oxidation resistance of LDL following their incorporation.

Antioxidants↗

PubMed1999

Antiproliferative efficacy of lipophilic soy isoflavone phytoestrogens delivered by low density lipoprotein particles into cultured U937 cells.

Some fat-soluble bioactive substances incorporated into low density lipoprotein (LDL) may be delivered into cells via LDL receptor pathway influencing cellular functions. In this study, we synthesized a number of fat-soluble isoflavone esters and investigated their incorporation into LDL as well as their delivery into U937 cells. Using an artificial transfer system (Celite dispersion), genistein and daidzein oleates and daidzein dilinoleate were efficiently incorporated into LDL with concentrations ranging between 2.7 to 16.9 isoflavone molecules/LDL particle, while much smaller amounts of unesterified isoflavones and genistein stearates were transferred into LDL. LDL containing 7-oleates or 4',7-dioleates of genistein and daidzein significantly reduced U937 cell proliferation by 36-43%. The strongest inhibitory effect was shown by daidzein 4',7-dilinoleate with 93% reduction of cell proliferation. Neither of the 4'-oleates of genistein and daidzein contained in LDLs exhibited antiproliferative effects although they were incorporated into LDL. In summary, we demonstrated that isoflavones made fat-soluble by esterification can be incorporated into LDL in vitro and delivered into cultured U937 cells via the LDL-receptor pathway, reducing the cell proliferation.

Antineoplastic Agents, Phytogenic↗

PubMed1998

Lack of inducible nitric oxide synthase in bronchial epithelium: a possible mechanism of susceptibility to infection in cystic fibrosis.

Cystic fibrosis (CF) is an inherited disorder associated with severe inflammation and repeated bacterial infection and colonization in the lung. Airway epithelium is involved in defence against bacteria, but this system may be defective in CF. Pro-inflammatory cytokines can stimulate the expression of inducible nitric oxide synthase (iNOS), an enzyme generating nitric oxide, which functions as an important mediator in host defence mechanisms. To understand better the poor resistance to infections in the CF lung, the expression of the iNOS gene was investigated in explanted lungs from patients with cystic fibrosis (n = 13), bronchiectasis (n = 3), emphysema (n = 14), and in normal lungs (n = 8). In addition, bronchial epithelial cell lines were examined to study iNOS gene expression in vitro. Strong immunoreactivity for iNOS was seen in inflammatory cells and bronchial epithelium in all the diseased lungs, except for bronchial epithelium in CF. Quantitative analysis showed a significant reduction in the area of epithelium immunostained in CF [CF 6.8 +/- 1.6 (% +/- SEM); emphysema 18.2 +/- 2.8; normal 9.6 +/- 0.8, P < 0.01], regardless of steroid treatment. These results were supported by in situ hybridization of iNOS mRNA, which showed a pattern of gene expression in CF, emphysema, and normal lung which paralleled that of protein immunoreactivity. Stimulation with cytokines (IL-1 beta, TNF-alpha, and IFN-gamma) increased the expression of iNOS mRNA detected by reverse transcriptase-polymerase chain reaction (RT-PCR) in cultures of normal (16HBE14o-), but not CF (CFBE41o-, with delta F508 CFTR mutation) epithelial cells. Expression of iNOS in inflammatory cells suggests that the gene is normal in CF. Absence of iNOS from bronchial epithelium may be due to low expression of the gene resulting from abnormalities in the signalling system that normally causes induction, such as cytokine receptors, second messengers or transcription factors. The resulting deficiency of the nitric oxide defence system may be relevant to the susceptibility of CF patients to pulmonary bacterial colonization.

Adult↗

PubMed1997

Immunoreactive endothelin in bronchial biopsy specimens: increased expression in asthma and modulation by corticosteroid therapy.

BACKGROUND: The human endothelin (ET) family comprises three 21-amino-acid peptides, which are potent bronchoconstrictors and have a number of other biologic properties relevant to the pathophysiology of asthma. OBJECTIVE: We sought to compare the expression of immunoreactive ET in bronchial biopsy specimens from subjects with asthma treated only with inhaled beta2-agonists, subjects with asthma treated with beta2-agonists and corticosteroids, and control subjects without asthma. METHODS: Biopsy specimens were obtained by fiberoptic bronchoscopy and stained immunohistochemically with a specific ET antiserum. Epithelial ET expression was quantitated by using a computer-assisted system of image analysis. Numbers of inflammatory cells and depth of subepithelial collagen deposition were also determined. RESULTS: Immunoreactive ET was principally localized in the airway epithelium. The proportion of epithelium immunostained was significantly increased in the subjects with asthma not treated with steroids (35.4% +/- 3.8%) compared with that of both the control subjects (16.2% +/- 1.9%, p < 0.0001) and the subjects with asthma treated with steroids (14.3% +/- 2.0%, p < 0.0001). The last two groups did not differ significantly from one another. There were no significant correlations between ET expression and either physiologic parameters or indexes of airway inflammation and remodeling. CONCLUSION: Bronchial epithelial expression of immunoreactive ET is increased in subjects with asthma receiving treatment only with beta2-agonists but not in subjects with asthma also receiving corticosteroid therapy. These findings are consistent with the hypothesis that ET is implicated in the pathophysiology of asthma.

Adrenal Cortex Hormones↗

PubMed1997

Influence of apolipoprotein A-1 promoter polymorphism on lipid levels and responses to dietary change in Finnish adults.

OBJECTIVES: To analyse the association between the G/A polymorphism in the apolipoprotein A-1 (apo A-1) promoter region and plasma lipid levels, as well as their responses to dietary change, in Finnish adults. SUBJECTS AND DESIGN: Blood samples from 86 subjects (42 men. 44 women) who attended a dietary intervention study carried out in North Karelia in 1993 were available for the current analysis. The diet study consisted of a 2-week baseline period, followed by an 8-week intervention period, and an 8-week switchback period. INTERVENTION: Diet was modified to a low-fat, low-cholesterol diet during the dietary intervention. MAIN OUTCOME MEASURES: Fasting plasma lipid, lipoprotein and apoliprotein levels were determined. RESULTS: At baseline, the high-density lipoprotein (HDL) cholesterol and apo A-1 levels were higher (P < 0.01) and the triglyceride levels were lower (P < 0.05) in men, but not in women, with the A allele. The differences in HDL cholesterol and apo A-1 levels between genotypes remained during the lowfat, low-cholesterol diet and switchback periods. Apart from the difference between responses in apo A-1 during switchback to the original diet, lipid responses to dietary change did not differ significantly between genotypes. CONCLUSION: Our findings indicate a significant association between the apo A-1 promoter polymorphism and plasma apo A-1 and HDL-cholesterol in men. In theory, the higher plasma HDL-cholesterol and apo A-1 levels in the GA/AA group may confer some protection against coronary artery disease. The differences in HDL-cholesterol and apo A-1 levels between genotypes persisted during different diets suggesting that the possible benefit is independent of fat and cholesterol intake.

Adult↗

PubMed1997

Effects of ozone on epithelium and sensory nerves in the bronchial mucosa of healthy humans.

Neuropeptides released from sensory nerves during inflammation have potent effects on bronchomotor tone, airway secretion, and inflammatory cells. We investigated the effects of ozone on sensory nerves by exposing 12 healthy, nonsmoking subjects to 0.2 ppm ozone and filtered air (FA) for 2 h on separate occasions, with intermittent exercise and rest. Spirometry was performed at baseline and 15 min after exposures, and bronchoscopy (bronchial biopsy and bronchoalveolar lavage [BAL]) was done 6 h after exposure. Frozen sections were immunostained for the anatomic neural marker protein gene peptide (PGP) 9.5 and the sensory neutropeptides substance P (SP) and calcitonin-gene-related peptide (CGRP). Nerves in the submucosa were quantified by image analysis. A trend toward an increase in the levels of polymorphonuclear leukocytes (PMNs) (air versus ozone, median [interquartile range]: 3.5 [2 to 5.3%] versus 9.8 [4.2 to 16.3%], p = 0.07) and ciliated epithelial cells (median [interquartile range]: 1.6 [1.3 to 3.4%] versus 5 [2.2 to 9.8%], p = 0.05) was observed in the BAL fluid (BALF). There was a significant decrease in SP immunoreactivity following ozone exposure (median [interquartile range]: 0.6 [0.05 to 1.2] versus 0.15 [0.08 to 0.18], p < 0.05). A significant inverse correlation was observed between SP immunoreactivity and: (1) percent PMNs and ciliated epithelial cells in the BALF; and (2) percent change in FEV1 following exposure to ozone. These findings indicate that short-term exposure to 0.2 ppm ozone causes epithelial shedding and stimulates subepithelial sensory nerves to release SP into the airways. The release of SP could contribute to bronchoconstriction and subsequent neutrophil infiltration into the airways.

Adult↗

PubMed1996

Analysis of novel apolipoprotein B mutations using a modified U937 cell line LDL binding assay.

The U937 myelomonocyte proliferation assay can be used to detect patients with familial defective apolipoprotein B-100 (FDB). Previous studies have employed electronic cell counting to assess cell proliferation. We simplified the assay using 3H-thymidine incorporation DNA analysis to measure cell growth. We tested the modified method by analyzing the effects of different concentrations of native low density lipoproteins (LDL), methylated LDL, as well as LDLs obtained from patients with FDB on cell growth. Methylation of LDL to various degrees reduced cell proliferation correspondingly, and LDLs obtained from FDB patients decreased cell growth confirming that the modified method was able to detect binding defective species of LDL. We applied this method to analyze three novel apoB polymorphisms recently characterized in this laboratory (apoB His1896-->Arg, apoB Asn1887-->Ser, apoB Ala4454-->Thr), which did not significantly alter U937 cell proliferation. Our results show that this simplified assay can be used for screening for LDL variants with defective binding.

Alleles↗

PubMed1996

Neurochemical mediators of anxiety have inconsistent effects on hypothalamic self-stimulation in rats.

We studied effects of anxiogenic and anxiolytic compounds on the electric self-stimulation of the medial fore-brain bundle in male rats to find out if there is a link between reward and anxiety-related behaviours. The cholecystokinin agonist, caerulein (25-100 micrograms/kg) and the 5-HT agonist 1-(3-chlorophenyl)piperazine (0.2-1 mg/kg) dose-dependently inhibited the electric self-stimulation. The 5-HT2A antagonist, ketanserin, at 2.5 mg/kg, increased the self-stimulation at high currents but not at threshold current. The 5-HT3 antagonist ondansetron (10 and 100 micrograms/kg). The alpha 1-adrenergic antagonist, prazosin (0.125 and 0.5 mg/kg), the beta-adrenergic antagonist, propranolol (5 and 10 mg/kg) and the alpha 2-adreno-receptor antagonist, atipamezole (4 mg/kg), did not affect the self-stimulation. Nor did the benzodiazepine agonist, diazepam (5-15 mg/kg), a benzodiazepine receptor antagonist flumazenil (at 10 and 25 mg/kg) or the inverse agonist of benzodiazepine receptors, N-methyl-beta-carboline-3-carboxamide (10 and 20 mg/kg), cause any substantial changes of the self-stimulation. We conclude that only two anxiolytic drugs (caerulein and 1-(3-chlorophenyl)piperazine) suppress the electric self-stimulation. These findings indicate that anxiogenicity as such is not able to weaken the hypothalamic electric self-stimulation. Anxiety and reward are apparently mediated through separate neural pathways.

Amphetamine↗

PubMed1995

Apolipoprotein A-I conformation in reconstituted discoidal lipoproteins varying in phospholipid and cholesterol content.

The effects of the size and cholesterol content on the conformation of apolipoprotein A-I (apoA-I) have been studied in reconstituted discoidal lipoproteins containing two apoA-I per particle (Lp2A-I). The immunoreactivity of a series of 13 epitopes distributed along the apoA-I sequence has been evaluated in Lp2A-I with a phospholipid/apoA-I molar ratio ranging from 31 to 156 and in Lp2A-I with constant phospholipids but varying in cholesterol content from 0 to 22 molecules. The results are compatible with a three domain structure in apoA-I in which the central domain is located between residues 99 and 143 and postulated to be a hinged domain that responds differentially to changes in phospholipid and cholesterol contents. Increasing the phospholipid content results in significant changes of epitope immunoreactivity throughout the N-terminal and central domains of apoA-I with fewer modifications in the C-terminal domain. In contrast, increasing Lp2A-I of two central epitopes, A11 (residues 99-132) and 5F6 (residues 118-148), and an extreme N-terminal epitope, 4H1 (residues 2-8). Interestingly, the effects of increasing cholesterol or phospholipids on these epitopes are opposite. This suggests a specific effect of cholesterol on the central domain tertiary structure between residues 99 and 143. Competition binding assays among pairs of antibodies binding to apoA-I on Lp2A-I are best explained by invoking inter- as well as intramolecular competitions. The specificity of the intermolecular competitions suggests an N to C termini arrangement of the two apoA-I molecules around the disc. Increasing the phospholipid content of Lp2A-I mainly increases the competitions between 3G10 and antibodies binding to most adjacent epitopes. Simultaneously as Lp2A-I enlarges, several of these antibodies also enhance the binding of 3G10. This has been interpreted as evidence of a structural rearrangement of apoA-I as a result of the size increase where the alpha-helix (residues 99-121) that contains the 3G10 epitope is increasingly interacting with lipids resulting in the enhanced expression of this epitope. The increasing interactions of apoA-I helices with lipids in the enlarging disc are compatible with previous reports of a greater apoA-I stability in the large discs. By contrast, cholesterol has limited but specific effects on antibody competitions and decreases the interaction of the N-terminal domain with the domain containing 3G10, either by direct cholesterol protein interaction or by modification of the lipid phase packing.

Antibodies, Monoclonal↗

PubMed1995

Role of apolipoprotein A-I in cholesterol transfer between lipoproteins. Evidence for involvement of specific apoA-I domains.

A series of monoclonal antibodies against epitopes spanning different domains of apoA-I have been tested for their effects on unesterified cholesterol transfer between low density lipoprotein (LDL) and well-defined homogenous lipoproteins reconstituted with phosphatidylcholine, cholesterol, and apoA-I (LpA-I). Antibodies 2G11 (reacting between residues 25 and 110), A05 (residues 25-82), A03 (residues 135-140), A44 and r5G9 (residues 149-186), and 4A12 (residues 173-205) significantly inhibit cholesterol transfer from LDL to Lp2A-I while they enhance transfer in the opposite direction, thus causing an increased net transfer to LDL. Most of these monoclonal antibodies (mAbs) also enhance phospholipid transfer to LDL but in a lesser and variable proportion relative to cholesterol. Their epitopes are mainly contained within domains that are predicted to be amphipathic alpha-helices. In contrast, mAbs 4H1 (residues 2-8), 3G10 (residues 96-121), and 5F6 (residues 116-141) have little or no effect on either cholesterol or phospholipid transfer, and the epitopes for these three mAbs have been shown in earlier studies to be structurally and functionally related. Their immunoreactivity responds similarly to variation in lipoprotein cholesterol content, and the antibodies binding to these sites compete with one another and have similar effects on the cholesterol esterification reaction. Thus, the current results are compatible with the hypothesis that they form an integrated domain with a common function in cholesterol metabolism, possibly as part of a hinge domain. Most mAbs were found to increase significantly the alpha-helicity of apoA-I in the Lp2A-I immunecomplexes, suggesting that they may increase the stability of the lipid-bound apoA-I. However, not unexpectedly, there is no correlation between the effects of mAbs on alpha-helicity and their effects on cholesterol or phospholipid transfer since each mAb has a discrete effect on these transfers. These studies demonstrate the specificity of LpA-I particles in cholesterol transport and document the existence of apoA-I domains with different functions in cholesterol transport.

Antibodies, Monoclonal↗

PubMed1995

Effect of LpA-I composition and structure on cholesterol transfer between lipoproteins.

The effect of high density lipoprotein composition on the rates of unesterified cholesterol exchange between low density lipoproteins (LDL) and well-defined homogeneous discoidal lipoproteins (LpA-I) reconstituted with phosphatidylcholine, cholesterol, and apolipoprotein A-I (apoA-I) has been investigated. LpA-I containing cholesterol and 2, 3, and 4 apoA-I molecules per particle differed in their ability to accept or donate cholesterol. A significant cholesterol exchange occurs between LDL and Lp2A-I (7.8 and 9.6 nm), while there is little or no cholesterol exchange detectable between LDL and Lp3A-I (10.8 and 13.4 nm) and Lp4A-I (17.0 nm) complexes. The cholesterol transfer from LDL to the cholesterol-free Lp2A-I (9.6 nm), Lp3A-I (13.4 nm), and Lp4A-I (17.0 nm) particles also shows significant cholesterol transfer to Lp2A-I, while there is no detectable transfer to Lp3- and 4A-I particles. The rates of cholesterol transfer to cholesterol-free and cholesterol-containing Lp2A-I appear to differ significantly. Cholesterol transfer from LDL to cholesterol-free Lp2A-I is zero order with respect to acceptor concentrations when the Lp2A-I/LDL ratio is above 10. Transfer rates from LDL to cholesterol-free Lp2A-I are faster for the smaller Lp2A-I (8.5 nm) than to the larger Lp2A-I (9.7 nm) and exhibit half-times (t1/2) at 25 degrees C of 4.0 and 5.3 h, respectively. In contrast, cholesterol transfer from LDL to cholesterol-containing Lp2A-I remains dependent upon acceptor concentrations to an acceptor/donor particle ratio of 80. In addition, transfer from LDL to cholesterol-containing Lp2A-I is faster to the 9.6 nm than to 7.8 nm particles, with t1/2 of 1.4 and 2.3 h, respectively. The rates of cholesterol transfer from Lp2A-I to LDL are higher than in the opposite direction, in particular for the small Lp2A-I (7.8 nm), which has a t1/2 of approximately 50 min. The results show that changes in the composition and structure of apoA-I-containing particles have a significant effect on inter-lipoprotein exchange of cholesterol. This suggests that the kinetics of cholesterol transfer to and from reconstituted discoidal LpA-I particles cannot be fully explained by passive aqueous diffusion.

Apolipoproteins A↗