Role of cholesterol ester pathway in the control of cell cycle in human aortic smooth muscle cells

Reversible translocation of acyl-CoA:cholesterol acyltransferase (ACAT) between the endoplasmic reticulum and vesicular structures

The enzyme acyl-CoA:cholesterol acyltransferase (ACAT) is normally localized in the endoplasmic reticulum (ER) where it can esterify cholesterol for storage in lipid droplets and/or the formation of lipoproteins. Here, we report that ACAT can translocate from the ER into vesicular structures in response to different ACAT inhibitors. The translocation was fast (within minutes), reversible and occurred in different cell types. Interestingly, oleic acid was able to fasten the re-translocation from vesicles back into the reticular ER network. The process of ACAT translocation could also be induced by cyclodextrins, cholesterol, lanosterol (but not 4-cholestene-3 one), 25-hydroxycholesterol, and by certain stress stimuli such as hyperosmolarity (sucrose treatment), temperature change, or high-density cultivation. In vitro esterification showed that ACAT remains fully active after it has been translocated to vesicles in response to hyperosmotic sucrose treatment of the cells. The translocation process was not accompanied by changes in the electrophoretic mobility of ACAT, even after chemical crosslinking. Interestingly, the protein synthesis inhibitor cycloheximide showed a stimulating effect on ACAT activity and prevented the translocation of ACAT from the ER into vesicles.

Pretransplant Systemic Lipidomic Profiles in Allogeneic Stem Cell Transplant Recipients

Simple Summary

Stem cell transplantation is used in the treatment of aggressive hematological malignancies and consists of initial high-dose and potentially lethal chemotherapy, followed by rescue with the transplantation of hematopoietic stem cells. Transplantation with stem cells from a healthy donor (i.e., allogeneic stem cells) has the strongest anti-cancer effect, but also the highest risk of severe toxicity. Furthermore, the clinical status at the time of transplantation (inflammation, fluid overload) is associated with posttransplant mortality, and immune-mediated acute graft-versus-host disease (GVHD) is a potential lethal complication. Finally, lipid metabolism regulates the proliferation and survival of both malignant hematological cells and immunocompetent cells that cause GVHD. Our study shows that the pretransplant lipid profiles differ between allotransplant recipients and can be used for the subclassification of patients and possibly to identify patients with an increased risk of death due to disease relapse or treatment toxicity. The therapeutic targeting of lipid metabolism should therefore be further explored in these transplant recipients.

Abstract

Allogeneic stem cell transplantation is used in the treatment of high-risk hematological malignancies. However, this treatment is associated with severe treatment-related morbidity and mortality. The metabolic status of the recipient may be associated with the risk of development of transplant-associated complications such as graft-versus-host disease (GVHD). To better understand the impact of the lipidomic profile of transplant recipients on posttransplant complications, we evaluated the lipid signatures of patients with hematological disease using non-targeted lipidomics. In the present study, we studied pretransplant serum samples derived from 92 consecutive patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS). A total of 960 lipid biochemicals were identified, and the pretransplant lipidomic profiles differed significantly when comparing patients with and without the risk factors: (i) pretransplant inflammation, (ii) early fluid overload, and (iii) patients with and without later steroid-requiring acute GVHD. All three factors, but especially patients with pretransplant inflammation, were associated with decreased levels of several lipid metabolites. Based on the overall concentrations of various lipid subclasses, we identified a patient subset characterized by low lipid levels, increased frequency of MDS patients, signs of inflammation, decreased body mass index, and an increased risk of early non-relapse mortality. Metabolic targeting has been proposed as a possible therapeutic strategy in allotransplant recipients, and our present results suggest that the clinical consequences of therapeutic intervention (e.g., nutritional support) will also differ between patients and depend on the metabolic context.

Progesterone Suppresses Cholesterol Esterification in APP/PS1 mice and a cell model of Alzheimer's Disease

AIMS

Cholesteryl ester(CE), generated from the mitochondria associated membrane (MAM), is involved in the pathogenesis of Alzheimer's Disease (AD). In theory, the different neuroprotective effects of progesterone in AD are all linked to MAM, yet the effect on cholesterol esterification has not been reported. Therefore, this study was aimed to investigate the regulation of progesterone on intracerebral CE in AD models and the underlying mechanism.

METHODS

APP/PS1 mice and AD cell model induced by Aβ 25-35 were selected as the research objects. APP/PS1 mice were daily administrated intragastrically with progesterone and The Morris Water Maze test was performed to detect the learning and memory abilities. Intracellular cholesterol was measured by Cholesterol/Cholesteryl Ester Quantitation Assay. The structure of MAMs were observed with transmission electron microscopy. The expression of acyl-CoA: cholesterol acyltransferase 1 (ACAT1), ERK1/2 and p-ERK1/2 were detected with western blotting, immunohistochemistry or immunofluorescence.

RESULTS

Progesterone suppressed the accumulation of intracellular CE, shortened the length of abnormally prolonged MAM in cortex of APP/PS1 mice. Progesterone decreased the expression of ACAT1, which could be blocked by progesterone receptor membrane component 1 (PGRMC1) inhibitor AG205. The ERK1/2 pathway maybe involved in the progesterone mediated regulation of ACAT1 in AD models, rather than the PI3K/Akt and the P38 MEPK pathways.

SIGNIFICANCE

The results supported a line of evidence that progesterone regulates CE level and the structure of MAM in neurons of AD models, providing a promising treatment against AD on the dysfunction of cholesterol metabolism.

Circ-Tulp4 promotes β-cell adaptation to lipotoxicity by regulating soat1 expression

This study aimed to identify circular RNAs differentially expressed in the islets of type 2 diabetes (T2DM) models and clarify their roles in the control of β-cell functions. Circular RNAs dysregulated in the islets of diabetic db/db mice were identified by high-throughput RNA sequencing. Then, the expression level of the selected circular RNA circ-Tulp4 was confirmed by real-time PCR in the islets of diabetic models and Min6 cells. MTS, EdU, western blot, flow cytometric analysis, and luciferase assay were performed to investigate the impact of circ-Tulp4 on β-cell functions. This study identified thousands of circular RNAs in mouse pancreatic islets. The circ-Tulp4 level significantly decreased in the diabetic models and altered in the Min6 cells under lipotoxic condition. The modulation of circ-Tulp4 level in Min6 cells regulated cell proliferation. Furthermore, an interaction was demonstrated between circ-Tulp4 and miR-7222-3p, which suppressed the expression of cholesterol esterification-related gene, sterol O-acyltransferase 1 (SOAT1). The accumulation of soat1 activated cyclin D1 expression, thus promoting cell cycle progression. These findings showed that circ-Tulp4 regulated β-cell proliferation via miR-7222-3p/soat1/cyclin D1 signaling. Our research suggested that circ-Tulp4 might be a potential therapeutic intervention for T2DM. Besides, soat1 might be important for β-cell adaptation to lipotoxicity.

High-density lipoprotein contribute to G0-G1/S transition in Swiss NIH/3T3 fibroblasts

High density lipoproteins (HDLs) play a crucial role in removing excess cholesterol from peripheral tissues. Although their concentration is lower during conditions of high cell growth rate (cancer and infections), their involvement during cell proliferation is not known. To this aim, we investigated the replicative cycles in synchronised Swiss 3T3 fibroblasts in different experimental conditions: i) contact-inhibited fibroblasts re-entering cell cycle after dilution; ii) scratch-wound assay; iii) serum-deprived cells induced to re-enter G1 by FCS, HDL or PDGF. Analyses were performed during each cell cycle up to quiescence. Cholesterol synthesis increased remarkably during the replicative cycles, decreasing only after cells reached confluence. In contrast, cholesteryl ester (CE) synthesis and content were high at 24 h after dilution and then decreased steeply in the successive cycles. Flow cytometry analysis of DiO-HDL, as well as radiolabeled HDL pulse, demonstrated a significant uptake of CE-HDL in 24 h. DiI-HDL uptake, lipid droplets (LDs) and SR-BI immunostaining and expression followed the same trend. Addition of HDL or PDGF partially restore the proliferation rate and significantly increase SR-BI and pAKT expression in serum-deprived cells. In conclusion, cell transition from G0 to G1/S requires CE-HDL uptake, leading to CE-HDL/SR-BI pathway activation and CEs increase into LDs.

Trypanosoma cruzi Epimastigotes Are Able to Manage Internal Cholesterol Levels under Nutritional Lipid Stress Conditions

Trypanosoma cruzi epimastigotes store high amounts of cholesterol and cholesteryl esters in reservosomes. These unique organelles are responsible for cellular digestion by providing substrates for homeostasis and parasite differentiation. Here we demonstrate that under nutritional lipid stress, epimastigotes preferentially mobilized reservosome lipid stocks, instead of lipid bodies, leading to the consumption of parasite cholesterol reservoirs and production of ergosterol. Starved epimastigotes acquired more LDL-NBD-cholesterol by endocytosis and distributed the exogenous cholesterol to their membranes faster than control parasites. Moreover, the parasites were able to manage internal cholesterol levels, alternating between consumption and accumulation. With normal lipid availability, parasites esterified cholesterol exhibiting an ACAT-like activity that was sensitive to Avasimibe in a dose-dependent manner. This result also implies that exogenous cholesterol has a role in lipid reservoirs in epimastigotes.

Cholesterol esterification as a mediator of proliferation of vascular smooth muscle cells and peripheral blood mononuclear cells during atherogenesis

BACKGROUND/AIMS

We determined growth rates, cholesterol esterification and mRNA levels for caveolin-1 (Cav-1), neutral cholesterol esters hydrolase (n-CEH) and ATP-binding cassette transporter (ABCA-1), in quiescent and growth-stimulated peripheral blood mononuclear cells (PBMCs) and intimal vascular smooth muscle cells (VSMCs) from blood and primary atherosclerotic plaques, respectively. These cells were cultured in the presence or absence of the mTOR inhibitor 40-O-(2-hydroxyethyl) rapamycin (RAD).

METHODS

The rate of cell proliferation was determined by 3H-thymidine incorporation into DNA and that of lipid metabolism by utilizing 14C-acetate and 14C-oleate as precursors. Lipid deposit in the vascular cells was evaluated by Oil Red O staining and lipid mass by thin layer chromatography-linked enzymatic assay.

RESULTS

Growth stimulation of PBMCs and VSMCs caused a rapid increase in intracellular cholesterol esterification and an accumulation of cholesterol esters (CEs) accompanied by a reduction of free cholesterol (FC) and Cav-1, ABCA-1 and n-CEH mRNAs. RAD reduced intracellular lipid accumulation in growth-stimulated cells and also increased expression of Cav-1, n-CEH and ABCA-1 genes.

CONCLUSION

Collectively, these data provide evidence that the determination of CEs in PBMCs may be an easy prescreening test to identify subjects at risk for vascular proliferative disease and that FC, CE, Cav-1, n-CEH and ABCA-1 may be suitable targets for antiproliferative therapies.

Acute-phase serum amyloid A: perspectives on its physiological and pathological roles

Serum amyloid A (SAA), a protein originally of interest primarily to investigators focusing on AA amyloidogenesis, has become a subject of interest to a very broad research community. SAA is still a major amyloid research topic because AA amyloid, for which SAA is the precursor, is the prototypic model of in vivo amyloidogenesis and much that has been learned with this model has been applicable to much more common clinical types of amyloid. However, SAA has also become a subject of considerable interest to those studying (i) the synthesis and regulation of acute phase proteins, of which SAA is a prime example, (ii) the role that SAA plays in tissue injury and inflammation, a situation in which the plasma concentration of SAA may increase a 1000-fold, (iii) the influence that SAA has on HDL structure and function, because during inflammation the majority of SAA is an apolipoprotein of HDL, (iv) the influence that SAA may have on HDL's role in reverse cholesterol transport, and therefore, (v) SAA's potential role in atherogenesis. However, no physiological role for SAA, among many proposed, has been widely accepted. None the less from an evolutionary perspective SAA must have a critical physiological function conferring survival-value because SAA genes have existed for at least 500 million years and SAA's amino acid sequence has been substantially conserved. An examination of the published literature over the last 40 years reveals a great deal of conflicting data and interpretation. Using SAA's conserved amino acid sequence and the physiological effects it has while in its native structure, namely an HDL apolipoprotein, we argue that much of the confounding data and interpretation relates to experimental pitfalls not appreciated when working with SAA, a failure to appreciate the value of physiologic studies done in the 1970-1990 and a current major focus on putative roles of SAA in atherogenesis and chronic disease. When viewed from an evolutionary perspective, published data suggest that acute-phase SAA is part of a systemic response to injury to recycle and reuse cholesterol from destroyed and damaged cells. This is accomplished through SAA's targeted delivery of HDL to macrophages, and its suppression of ACAT, the enhancement of neutral cholesterol esterase and ABC transporters in macrophages. The recycling of cholesterol during serious injury, when dietary intake is restricted and there is an immediate and critical requirement of cholesterol in the generation of myriads of cells involved in inflammation and repair responses, is likely SAA's important survival role. Data implicating SAA in atherogenesis are not relevant to its evolutionary role. Furthermore, in apoE(-/-) mice, domains near the N- and C- termini of SAA inhibit the initiation and progression of aortic lipid lesions illustrating the conflicting nature of these two sets of data.

A lipoprotein source of cholesteryl esters is essential for proliferation of CEM-CCRF lymphoblastic cell line

Tumour are characterised by a high content of cholesteryl esters (CEs) stored in lipid droplets purported to be due to a high rate of intracellular esterification of cholesterol. To verify whether and which pathways involved in CE accumulation are essential in tumour proliferation, the effect of CE deprivation, from both exogenous and endogenous sources, on CEM-CCRF cells was investigated. Cholesterol synthesis, esterification and content, low-density lipoprotein (LDL) binding and high-density lipoprotein (HDL)-CE uptake were evaluated in cultured in both conventional and delipidated bovine serum with or without oleic or linoleic acids, cholesteryl oleate, LDL and HDL. High content of CEs in lipid droplets in this cell line was due to esterification of both newly synthesised cholesterol and that obtained from hydrolysis of LDL; moreover, a significant amount of CE was derived from HDL-CE uptake. Cell proliferation was slightly affected by either acute or chronic treatment up to 400 μM with Sz-58035, an acyl-cholesteryl cholesterol esterification inhibitor (ACAT); although when the enzyme activity was continuously inhibited, CE content in lipid droplets was significantly higher than those in control cells. In these cells, analysis of intracellular and medium CEs revealed a profile reflecting the characteristics of bovine serum, suggesting a plasma origin of CE molecules. Cell proliferation arrest in delipidated medium was almost completely prevented in the first 72 h by LDL or HDL, although in subsequent cultures with LDL, it manifested an increasing mortality rate. This study suggests that high content of CEs in CEM-CCRF is mainly derived from plasma lipoproteins and that part of CEs stored in lipid droplets are obtained after being taken up from HDL. This route appears to be up-regulated according to cell requirements and involved in low levels of c-HDL during cancer. Moreover, the dependence of tumour cells on a source of lipoprotein provides a novel impetus in developing therapeutic strategies for use in the treatment of some tumours.

Cholesterol esterification during differentiation of mouse erythroleukemia (Friend) cells

Cholesterol is an essential constituent of all mammalian cell membranes and its availability is therefore a prerequisite for cellular growth and other functions. Several lines of evidence are now indicating an association between alterations of cholesterol homeostasis and cell cycle progression. However, the role of cholesterol in cell differentiation is still largely unknown. To begin to address this issue, in this study we examined changes in cholesterol metabolism and in the mRNA levels of proteins involved in cholesterol import and esterification (multi-drug resistance, MDR-3) and acylCoA: cholesterol acyltransferase (ACAT) and cholesterol export (caveolin-1) in Friend virus-induced erythroleukemia cells (MELC), in the absence or in the presence of the chemical inducer of differentiation, hexamethylene bisacetamide (HMBA). FBS-stimulated growth of MELC was accompanied by an immediate elevation of cholesterol synthesis and cholesterol esterification, and by an increase in the levels of MDR-3 and ACAT mRNAs. A decrease in caveolin-1 expression was also observed. However, when MELC were treated with HMBA, the inhibition of DNA synthesis caused by HMBA treatment, was associated with a decrease in cholesterol esterification and in ACAT and MDR-3 mRNA levels and an increase in caveolin-1 mRNA. Detection of cytoplasmic neutral lipids by staining MELC with oil red O, a dye able to evidence CE but not FC, revealed that HMBA-treatment also reduced growth-stimulated accumulation of cholesterol ester to approximately the same extent as the ACAT inhibitor, SaH. Overall, these results indicate for the first time a role of cholesterol esterification and of some related genes in differentiation of erythroid cells.

Inhibition of acyl-coenzyme A:cholesterol acyltransferase stimulates cholesterol efflux from macrophages and stimulates farnesoid X receptor in hepatocytes

We investigated the mechanism of spontaneous cholesterol efflux induced by acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibition, and how an alteration of cholesterol metabolism in macrophages impacts on that in HepG2 cells. Oleic acid anilide (OAA), a known ACAT inhibitor reduced lipid storage substantially by promotion of cholesterol catabolism and repression of cholesteryl ester accumulation without further increase of cytotoxicity in acetylated low-density lipoprotein-loaded THP-1 macrophages. Analysis of expressed mRNA and protein revealed that cholesterol 7alpha-hydroxylase (CYP7A1), oxysterol 7alpha- hydroxylase (CYP7B1), and cholesterol 27-hydroxylase (CYP27) were highly induced by ACAT inhibition. The presence of a functional cytochrome P450 pathway was confirmed by quantification of the biliary cholesterol mass in cell monolayers and extracelluar medium. Notably, massively secreted biliary cholesterol from macrophages suppressed the expression of CYP7 proteins in a farnesoid X receptor (FXR)-dependent manner in HepG2 cells. The findings reported here provide new insight into mechanisms of spontaneous cholesterol efflux, and suggest that ACAT inhibition may stimulate cholesterol-catabolic (cytochrome P450) pathway in lesion-macrophages, in contrast, suppress it in hepatocyte via FXR induced by biliary cholesterol (BC).

Antiprion activity of cholesterol esterification modulators: a comparative study using ex vivo sheep fibroblasts and lymphocytes and mouse neuroblastoma cell lines

Our studies on the role of cholesterol homeostasis in the pathogenesis of scrapie revealed abnormal accumulation of cholesterol esters in ex vivo peripheral blood mononuclear cells (PBMCs) and skin fibroblasts from healthy and scrapie-affected sheep carrying a scrapie-susceptible genotype compared to sheep with a resistant genotype. Similar alterations were observed in mouse neuroblastoma N2a cell lines persistently infected with mouse-adapted 22L and RML strains of scrapie that showed up to threefold-higher cholesterol ester levels than parental N2a cells. We now report that proteinase K-resistant prion protein (PrPres)-producing cell populations of subclones from scrapie-infected cell lines were characterized by higher cholesterol ester levels than clone populations not producing PrPres. Treatments with a number of drugs known to interfere with different steps of cholesterol metabolism strongly reduced the accumulation of cholesterol esters in ex vivo PBMCs and skin fibroblasts from scrapie-affected sheep but had significantly less or no effect in their respective scrapie-resistant or uninfected counterparts. In scrapie-infected N2a cells, inhibition of cholesterol esters was associated with selective antiprion activity. Effective antiprion concentrations of cholesterol modulators (50% effective concentration [EC(50)] range, 1.4 to 40 microM) were comparable to those of antiprion reference compounds (EC(50) range, 0.6 to 10 microM). These data confirm our hypothesis that abnormal accumulation of cholesterol esters may represent a biological marker of susceptibility to prion infection/replication and a novel molecular target of potential clinical importance.

Fibroblasts isolated from human pterygia exhibit altered lipid metabolism characteristics

To determine whether the fibrovascular proliferation observed in pterygium, may be, at least in part, mediated by an increased activity of cholesterol metabolism. The correlation between lipid metabolism and rate of growth was studied in human normal conjunctival (NCF) and primary pterygium fibroblasts (PFs) in primary culture. The expression of two proliferation markers (Ki-67 and p53) was evaluated by immunohistochemical staining techniques. Proliferation was evaluated by [(3)H]thymidine incorporation and by immunohistochemical assays. Lipid metabolism was evaluated by (14)C-oleate incorporated into cholesterol esters as well as by oil red O staining. Moreover, the cultures of pterygium fibroblasts were supplemented with two antiproliferative drugs in order to confirm the effective alterations in cholesterol metabolism related to proliferation. Immunohistochemistry of frozen sections from primary pterygium demonstrated an increased staining in Ki-67 and p53 compared with staining observed in normal conjunctiva. A dramatically increased activity of intracellular cholesterol metabolism was demonstrated in pterygium fibroblasts obtained from four different patients. This finding was confirmed by the reduction of cholesterol metabolism in pterygium fibroblasts treated with antiproliferative drugs. Collectively, these data support the hypothesis that alterations of cholesterol metabolism are involved in the development of pterygia. This finding may represent a target of new therapeutic approaches for treatment and prevention of pterygium.

Modulation of P-glycoprotein activity by cannabinoid molecules in HK-2 renal cells

1. Endogenous and synthetic cannabinoid molecules have been investigated as possible MDR-1/P-glycoprotein (P-gp) modulators in HK-2-immortalized renal cells, using calcein acetoxymethylester (calcein-AM) as a P-gp substrate. 2. Among the endocannabinoid molecules tested, anandamide (AEA), but not 2-arachidonoyl-glycerol (2-AG) or palmitoyl-ethanolamide (PEA), increased the intracellular fluorescence emitted by calcein, a metabolic derivative of the P-gp substrate calcein-AM, indicative of a reduction in transport capacity. 3. All the three synthetic cannabimimetics tested, that is, R-(+)-methanandamide (R(+)-MET), AM 251 and CP55,940 significantly increased calcein accumulation in the cytosol. 4. RT-PCR demonstrated that HK-2 cells do not express CB1 or CB2 cannabinoid receptors. 5. R(+)-MET, AM251 and CP55,940 were also evaluated as modulators of P-gp expression, by Western blot analysis. Only AM251 weakly enhanced the protein levels (by 1.2-fold) after a 4-day-long incubation with the noncytotoxic drug concentration 2 microM. 6. The present data provide the first evidence that the endocannabinoid AEA and different synthetic cannabinoids may inhibit the P-gp activity in vitro via a cannabinoid receptor-independent mechanism.

Hexadecylphosphocholine disrupts cholesterol homeostasis and induces the accumulation of free cholesterol in HepG2 tumour cells

Hexadecylphosphocholine (HePC) is a synthetic lipid belonging to the alkylphosphocholines (APC), a new group of antiproliferative agents that are proving to be promising candidates in anticancer therapy. We reported in a previous study that HePC interferes with phosphatidylcholine (PC) synthesis in HepG2 cells via both CDP-choline and phosphatidylethanolamine (PE) methylation. We have subsequently extended our studies to show that HePC interferes with sphingolipid metabolism by hindering the formation of sphingomyelin (SM), an effect accompanied by a substantial increase in the incorporation of the exogenous lipogenic precursors into ceramides. Interestingly, we demonstrate for the first time that HePC strongly inhibits the esterification of free cholesterol (FC) by acting at the level of acyl CoA:cholesterol acyltransferase (ACAT) (EC 2.3.1.26) activity. This effect is accompanied by a considerable increase in the synthesis of cholesterol, which leads to a rise in the levels of FC in cells. We are left in no doubt that the imbalance in the metabolism of membrane-lipid components vital to cell survival may well be responsible for the observed DNA fragmentation and activation of caspase-3, an enzyme involved in the cell apoptosis found in this study.

Cholesteryl esters in malignancy

Cholesteryl esters, formed by the esterification of cholesterol with long-chain fatty acids, on one hand, are the means by which cholesterol is transported through the blood by lipoproteins, on the other, the way cholesterol itself can be accumulated in the cells. Therefore, these important molecules play an active part in metabolic pathways that form the basis of cholesterol trafficking and homeostasis. The role of different regulatory mechanisms in cholesterol homeostasis in physiologic and neoplastic conditions with emphasis on intracellular content of cholesteryl esters is here reviewed. Numerous studies carried out on tumor cell lines, experimental tumors, and human tumors have shown an abnormal cholesterol metabolism that is reflected by an increase in intracellular cholesteryl esters due to an alteration in all the mechanisms that form the basis of regulation, in particular: cholesterol de novo biosynthesis; uptake of exogenous cholesterol LDL receptor mediated; cholesterol esterification mediated by the ACAT activity; cholesterol efflux HDL receptor mediated. The most recent analytic-spectroscopic applications that permit cholesteryl ester determination on tumor lipidic extracts and directly in vivo are also reported. This review gives an overview of cholesterol homeostasis in physiological and pathological conditions where cholesteryl esters are over-expressed.

Differential effects of delivery of omega-3 fatty acids to human cancer cells by low-density lipoproteins versus albumin

PURPOSE

Omega-3 (n-3) fatty acids (FA) have been proposed to confer tumor-inhibitory properties. In vivo, dietary FA are delivered to tumor cells by two main routes: low-density lipoproteins (LDL) and albumin complexes. High FA concentration in LDL and up-regulation of LDL receptors in tumor cells suggest that the LDL receptor pathway may be the major route for FA delivery. We compared effects of n-3FA delivered to human cancer cells by LDL and albumin.

EXPERIMENTAL DESIGN

LDL was isolated from plasma of African Green monkeys fed diets enriched in fish oil (n-3 FA) or linoleic acid (n-6FA) and used to deliver FA to MCF-7 and PC3 cancer cells. Cell proliferation, apoptosis, and changes in global gene expression were monitored.

RESULTS

Both LDL and albumin were effective in delivering FA to tumor cells and modifying the composition of cell phospholipids. The molar ratio of 20:4 (n-6) to 20:5 (n-3) in phosphatidylcholine and phosphatidylethanolamine was profoundly decreased. Although cell phospholipids were similarly modified by LDL and albumin-delivered FA, effects on cell proliferation and on transcription were markedly different. LDL-delivered n-3 FA were more effective at inhibiting cell proliferation and inducing apoptosis. Expression microarray profiling showed that a significantly higher number of genes were regulated by LDL-delivered than albumin-delivered n-3 FA with little overlap between the two sets of genes.

CONCLUSIONS

These results show the importance of the LDL receptor pathway in activating molecular mechanisms responsible for the tumor inhibitory properties of n-3FA.

High baseline serum total and LDL cholesterol levels are associated with MDR1 haplotypes in Brazilian hypercholesterolemic individuals of European descent

The MDR1 gene encodes the P-glycoprotein, an efflux transporter with broad substrate specificity. P-glycoprotein has raised great interest in pharmacogenetics because it transports a variety of structurally divergent drugs, including lipid-lowering drugs. The synonymous single-nucleotide polymorphism C3435T and the nonsynonymous single-nucleotide polymorphism G2677T/A in MDR1 have been indicated as potential determinants of variability in drug disposition and efficacy. In order to evaluate the effect of G2677T/A and C3435T MDR1 polymorphisms on serum levels of lipids before and after atorvastatin administration, 69 unrelated hypercholesterolemic individuals from São Paulo city, Brazil, were selected and treated with 10 mg atorvastatin orally once daily for four weeks. MDR1 polymorphisms were analyzed by PCR-RFLP. C3435T and G2677T polymorphisms were found to be linked. The allelic frequencies for C3435T polymorphism were 0.536 and 0.464 for the 3435C and 3435T alleles, respectively, while for G2677T/A polymorphism allele frequencies were 0.580 for the 2677G allele, 0.384 for the 2677T allele and 0.036 for the 2677A allele. There was no significant relation between atorvastatin response and MDR1 polymorphisms (repeated measures ANOVA; P > 0.05). However, haplotype analysis revealed an association between T/T carriers and higher basal serum total (TC) and LDL cholesterol levels (TC: 303 +/- 56, LDL-C: 216 +/- 57 mg/dl, respectively) compared with non-T/T carriers (TC: 278 +/- 28, LDL-C: 189 +/- 24 mg/dl; repeated measures ANOVA/Tukey test; P < 0.05). These data indicate that MDR1 polymorphism may have an important contribution to the control of basal serum cholesterol levels in Brazilian hypercholesterolemic individuals of European descent.

Host cell lipids control cholesteryl ester synthesis and storage in intracellular Toxoplasma

The intracellular protozoan Toxoplasma gondii lacks a de novo mechanism for cholesterol synthesis and therefore must scavenge this essential lipid from the host environment. In this study, we demonstrated that T. gondii diverts cholesterol from low-density lipoproteins for cholesteryl ester synthesis and storage in lipid bodies. We identified and characterized two isoforms of acyl-CoA:cholesterol acyltransferase (ACAT)-related enzymes, designated TgACAT1alpha and TgACAT1beta in T. gondii. Both proteins are coexpressed in the parasite, localized to the endoplasmic reticulum and participate in cholesteryl ester synthesis. In contrast to mammalian ACAT, TgACAT1alpha and TgACAT1beta preferentially incorporate palmitate into cholesteryl esters and present a broad sterol substrate affinity. Mammalian ACAT-deficient cells transfected with either TgACAT1alpha or TgACAT1beta are restored in their capability of cholesterol esterification. TgACAT1alpha produces steryl esters and forms lipid bodies after transformation in a Saccharomyces cerevisiae mutant strain lacking neutral lipids. In addition to their role as ACAT substrates, host fatty acids and low-density lipoproteins directly serve as Toxoplasma ACAT activators by stimulating cholesteryl ester synthesis and lipid droplet biogenesis. Free fatty acids significantly increase TgACAT1alpha mRNA levels. Selected cholesterol esterification inhibitors impair parasite growth by rapid disruption of plasma membrane. Altogether, these studies indicate that host lipids govern neutral lipid synthesis in Toxoplasma and that interference with mechanisms of host lipid storage is detrimental to parasite survival in mammalian cells.

Identification of variants in cyclin D1 (CCND1) and B-Cell CLL/lymphoma 2 (BCL2)

CCND1 is an important cell-cycle regulatory protein associated with cell proliferation, poor prognosis and recurrence in cancer, while BCL2 is an important anti-apoptotic protein that plays a vital role in the regulation of the life span by controlling the rate of apoptosis. Recent studies have shown that CCND1 and BCL2 may be responsible for the body mass and the regulation of various metabolic processes. In an effort to discover additional polymorphism(s), we scrutinized the genetic polymorphisms in the CCND1 and BCL2. By direct DNA sequencing in 24 individuals, we identified 22 sequence variants within the 16 kb of whole CCND1 gene: one in exon 4, 17 in introns and four in the 3' UTR region. We also found eight sequence variants within 7.5 kb exon-intron boundaries of BCL2 gene: one in promoter, three in exon 1, and four in the 3' UTR region. Haplotypes, their frequencies and linkage disequilibrium coefficients (| D'| and r(2)), among polymorphisms were estimated. Among identified variants, seven and six variants of CCND1 and BCL2 were genotyped in a larger series of subjects ( n=320). Statistical analyses of CCND1 and BCL2 polymorphisms with two metabolic phenotypes revealed no significant association. The information concerning genetic polymorphisms of CCND1 and BCL2 might provide valuable information for future genetic studies of diseases.