蓝靛果花色苷对高脂血症大鼠肝脏LDLR、ABCG1及ABCA1基因表达的影响

目的：研究蓝靛果花色苷对高脂血症大鼠肝脏低密度脂蛋白受体（low density lipoprotein receptor, LDLR）、三磷酸腺苷结合盒转运体G1（ATP-binding cassette transporter G1,ABCG1）及ABCA1基因表达的影响。 方法：选择2 月龄雄性Wistar大鼠60 只,将大鼠随机分为6 组,分别为基础饲料对照组（ND,1.2 g/（kg·d mb） 生理盐水灌胃）、高脂模型对照组（HFD,1.2 g/（kg·d mb）生理盐水灌胃）、阳性对照组（10 mg/（kg·d mb） 辛伐他汀片灌胃）,蓝靛果花色苷低、中、高剂量组（HFD＋L、HFD＋M、HFD＋H,分别给予4.0、40.0、 120.0 mg/（kg·d mb）的花色苷灌胃）,持续28 d。实验结束后,测定血清总胆固醇（total cholesterol,TC）、 甘油三酯（triglyceride,TG）、高密度脂蛋白胆固醇（high density lipoprotein cholesterol,HDL-C）、低密 度脂蛋白胆固醇（low density lipoprotein cholesterol,LDL-C）、载脂蛋白A（apolipoprotein A,Apo-A）及载 脂蛋白B（Apo-B）等血脂指标水平。取大鼠肝脏,利用实时荧光定量聚合酶链式反应测定大鼠肝脏组织中 LDLR、ABCG1、ABCA1 mRNA表达量,Western blot检测LDLR蛋白表达水平。结果：蓝靛果花色苷干预后, 与HFD组相比,花色苷均能不同程度地降低高血脂大鼠血清中TC、TG、LDL-C、Apo-B的含量（P＜0.05或 P＜0.01）,显著升高HDL-C及Apo-A的含量（P＜0.05或P＜0.01）。花色苷各剂量组LDLR蛋白和mRNA水平均增 高,与HFD组比较差异有显著性（P＜0.05）,ABCA1 mRNA和ABCG1 mRNA的表达水平也高于HFD组,尤其是花 色苷中、高剂量组差异明显（P＜0.05）。结论：40.0 mg/（kg·d mb）蓝靛果花色苷具有明显的调节血脂作用,其 作用机制可能是通过上调肝脏LDLR和ABC家族基因的表达,进而调节胆固醇逆转运过程。     

Theobromine Does Not Affect Fasting and Postprandial HDL Cholesterol Efflux Capacity,While It Decreases Fasting miR‐92a Levels in Humans

Scope

Chocolate consumption lowers cardiovascular disease risk, which might be attributed to the methylxanthine theobromine. These effects may be mediated through effects on HDL‐mediated cholesterol efflux, which may be affected by microRNA (miRNA) levels in the HDL particles. Therefore, the aim of this study is to investigate effects of theobromine consumption on fasting and postprandial cholesterol efflux and miRNAs levels.

Methods and results

Thirty overweight and 14 obese healthy men and women participated in this randomized, double‐blind crossover study. Participants consumed 500 mg d^?1 of theobromine or placebo for 4 weeks. ABCA1‐mediated cholesterol efflux was measured using J774 macrophages. MiRNAs levels (miR‐92a, miR‐223, miR‐135a*) were quantified in apolipoprotein B‐depleted serum. Theobromine consumption did not affect fasting and postprandial cholesterol efflux. Fasting miR‐223 and miR‐135a levels were unchanged, while miR‐92a levels were decreased (?0.21; p < 0.05). The high‐fat meal increased postprandial cholesterol efflux capacity (+4.3 percentage points; p ≤ 0.001), miR‐92a (+1.21; p < 0.001), and miR‐223 (+1.79; p < 0.001) levels, while a trend was found for miR‐135a (+1.08; p = 0.06).

Conclusion

Theobromine did not improve fasting and postprandial ABCA1‐mediated cholesterol efflux capacity, but decreased fasting miR‐92a levels. High‐fat meal intake increased postprandial cholesterol efflux and the three selected miRNAs levels.

     

The probiotic Lactobacillus rhamnosus BFE5264 and Lactobacillus plantarum NR74 promote cholesterol efflux and suppress inflammation in THP‐1 cells

BACKGROUND: The balance between the rate of cholesterol uptake/accumulation and the rate of cholesterol efflux is reflected in the amount of lipid accumulation in macrophages. Based upon the fact that liver X receptors (LXRs) play a role in cholesterol efflux, we studied the effects of probiotics on cholesterol efflux and anti‐inflammatory action in macrophages. We confirmed changes in LXR expression by treatment of LXR‐transfected CHO‐K1 cells with lactic acid bacteria (LAB), and co‐cultured THP‐1 cells with LAB to investigate changes in cholesterol efflux and inflammation. RESULTS: The experiment with CHO‐K1 cells showed upregulation of LXR‐β by LAB. Treatment of THP‐1 cells with LAB promoted LXR expression in THP‐1, which eventually led to significant upregulation of ABCA1 and ABCG1 expression. The treatment with live LAB also significantly promoted cholesterol efflux. LAB suppressed expression of interleukin (IL)‐1β and tumor necrosis factor (TNF)‐α, which resulted from activation of LXR. CONCLUSION: Our study shows that Lactobacillus rhamnosus BFE5264 and Lactobacillus plantarum NR74 activated LXR and induced cholesterol efflux by promoting expression of ABCA1 and ABCG1. Both strains also suppressed proinflammatory cytokines including IL‐1β and TNF‐α. This study could account for the observation that LAB may block foam cell formation by cholesterol efflux and immune modulation. © 2012 Society of Chemical Industry     

Dietary calcium decreases plasma cholesterol by down‐regulation of intestinal Niemann–Pick C1 like 1 and microsomal triacylglycerol transport protein and up‐regulation of CYP7A1 and ABCG 5/8 in hamsters

Scope: It has been shown that calcium supplementation favorably modifies plasma lipoprotein profile in postmenopausal women. The present study investigated the interaction of dietary calcium with genes of transporters, receptors and enzymes involved in cholesterol metabolism. Methods and results: Forty‐eight ovariectomized hamsters were fed one of the four diets containing 0, 2, 6 and 8 g calcium per kg. Plasma total cholesterol (TC), triacylglycerols (TG), and non‐high density lipoprotein cholesterol were dose‐dependently decreased, whereas high‐density lipoprotein cholesterol (HDL‐C) was dose‐dependently increased with the increasing dietary calcium levels. Dietary calcium had no effect on protein mass of hepatic sterol regulatory element binding protein‐2 (SREBP), liver X receptor‐alpha (LXR), 3‐hydroxy‐3‐methylglutaryl‐CoA reductase (HMGR), LDL receptor (LDLR) and cholesterol‐7α‐hydroxylase (CYP7A1). However, dietary calcium up‐regulated the mRNA levels of hepatic CYP7A1 and intestinal ATP binding cassette transporters (ABCG5/8) whereas it down‐regulated the intestinal Niemann‐Pick C1 like 1 (NPC1L1) and microsomal triacylglycerol transport protein (MTP). In addition, dietary calcium increased the activity of intestinal acyl coenzyme A: cholesterol acyltransferase 2, while it decreased plasma cholesteryl ester transport protein (CETP). Conclusion: Beneficial modification of lipoprotein profile by dietary calcium was mediated by sequestering bile acid absorption and enhancing excretion of fecal cholesterol, via up‐regulation of mRNA CYP7A1 and intestinal ABCG 5/8 with down‐regulation of mRNA NPC1L1 and MTP.     

Interactions between ABC‐transport proteins and the secondary Fusarium metabolites enniatin and beauvericin

Enniatins (ENN) and beauvericin (BEA) exert cytotoxic properties. Here, we observed that their impact on Ca²⁺‐homeostasis can be reversed by exogenous ATP. Thus, we investigated whether membrane‐located ATP‐binding cassette (ABC) transporters influence ENNs‐ and BEA‐induced cytotoxicity. In short‐term exposure assays breast cancer resistance protein (ABCG2)‐overexpression weakly but significantly reduced the cytotoxic activity of BEA but not ENNs. In contrast, multidrug resistance‐associated protein‐1 (ABCC1)‐ and P‐glycoprotein (ABCB1)‐overexpression was not protective under identical conditions. ABCG2‐mediated resistance against BEA was reversible by ABCG2 modulators. In long‐term exposure assays, ABCG2 and ABCB1 significantly protected against ENNs‐ and to a lesser extent BEA‐induced cytotoxicity. Moreover, both fusariotoxins potently inhibited the ABCG2‐ and ABCB1‐mediated efflux of specific fluorescent substrates, with BEA being more effective. Additionally, ATPase and photoaffinity‐labelling assays proofed interaction of both substances with ABCG2 and ABCB1. Remarkably, 2 years selection of KB‐3‐1 cells against both fusariotoxins resulted only in two‐fold ENNs but negligible BEA resistance. Interestingly, the selected sublines displayed upregulation of multidrug resistance proteins and crossresistance to other chemotherapeutics. Summarizing, ABCG2 and ABCB1 slightly but significantly protect human cells against ENNs‐ and BEA‐induced cytotoxicity. However, both mycotoxins potently interact with ABCB1 and ABCG2 transport functions suggesting influences on bioavailability of xenobiotics and pharmaceuticals.     

不同配比的荞麦日粮对高胆固醇血症小鼠肠道胆固醇吸收和菌群的影响（网络首发、推荐阅读）

研究不同比例荞麦日粮,对高胆固醇脂血症小鼠肠道胆固醇吸收和排出功能及肠道菌群的影响。小鼠分别饲喂AIN-93M标准饲料空白组,高胆固醇饲料模型组、高胆固醇饲料+荞麦低剂量组、高胆固醇饲料+荞麦高剂量组,饲喂12周。结果显示,不同比例荞麦日粮均能降低血液中胆固醇含量,修复小肠受损结构。相对于模型组,荞麦日粮组能提高小肠的ABCG5/ABCG8（ATP binding cassette transporter subfamily G members 5/8）信使核糖核酸（mRNA）表达量,减少NPC1L1（Niemann-Pick type C 1 like 1）蛋白的mRNA表达量,进而减少小肠对胆固醇的吸收。不同比例的荞麦日粮可以极显著升高小鼠肠ABCA1、SR- B1基因表达,提升肠道中胆固醇的逆向转运。相比模型组,高比例荞麦日粮大幅度促进肠道菌群的丰度,而低比例荞麦日粮对肠道菌群的丰度有负面作用。     

Anti-atherogenic effects of resveratrol via liver X receptor α-dependent upregulation of ATP-binding cassette transporters A1 and G1 in macrophages

Resveratrol (RSV), a phenolic component, is found in grape skins, peanuts, pistachios and red wine. RSV has protective activities in atherosclerosis, yet the detailed mechanisms are not fully elucidated. In the present study, we observed that RSV inhibited oxLDL-mediated lipid accumulation through the enhancement of cholesterol efflux in THP-1-derived macrophages and explored the possible underlying mechanisms. RSV dose-dependently enhanced the mRNA and protein levels of ATP-binding membrane cassette transporters A1 and G1 (ABCA1 and ABCG1) but had no effect on the mRNA expression of scavenger receptor class BI (SR-BI) in cholesterol homeostasis. Additionally, the functional inhibition of ABCA1 and ABCG1 with short hairpin RNA abrogated the effects of RSV on lipid accumulation. The upregulation of ABCA1 and ABCG1 by RSV depended on LXRα, as evidenced by an increase in the nuclear levels of LXRα through the induction of nuclear translocation. The functional inhibition of LXRα with a pharmacological inhibitor, geranylgeranyl pyrophosphate (GGPP), abolished the RSV-mediated protective effects in macrophages. These findings suggest that LXRα-dependent upregulation of ABCA1 and ABCG1 might mediate the beneficial effects of RSV, which ameliorated the oxLDL-mediated lipid accumulation in the process of lipid-laden foam cells formation.     

Identification of ABCA1 and ABCG1 in milk fat globules and mammary cells--implications for milk cholesterol secretion

The ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 play an important role in cellular cholesterol homeostasis, but their function in mammary gland (MG) tissue remains elusive. A bovine MG model that allows repeated MG sampling in identical animals at different functional stages was used to test whether 1) ABCA1 and ABCG1 protein expression and subcellular localization in mammary epithelial cells (MEC) change during the pregnancy-lactation cycle, and 2) these 2 proteins were present in milk fat globules (MFG). Expression and localization in MEC were investigated in bovine MG tissues at the end of lactation, during the dry period (DP), and early lactation using immunohistochemical and immunofluorescence approaches. The presence of ABCA1 and ABCG1 in MFG isolated from fresh milk was determined by immunofluorescence. The ABCA1 protein expression in MEC, expressed as arbitrary units, was higher during the end of lactation (12.2 ± 0.24) and the DP (12.5 ± 0.22) as compared with during early lactation (10.2 ± 0.65). In contrast, no significant change in ABCG1 expression existed between the stages. Throughout the cycle, ABCA1 and ABCG1 were detected in the apical (41.9 ± 24.8 and 49.0 ± 4.96% of cows, respectively), basal (56.2 ± 28.1 and 54.6 ± 7.78% of cows, respectively), or entire cytoplasm (56.8 ± 13.4 and 61.6 ± 14.4% of cows, respectively) of MEC, or showed combined localization. Unlike ABCG1, ABCA1 was absent at the apical aspect of MEC during early lactation. Immunolabeling experiments revealed the presence of ABCA1 and ABCG1 in MFG membranes. Findings suggest a differential, functional stage-dependent role of ABCA1 and ABCG1 in cholesterol homeostasis of the MG epithelium. The presence of ABCA1 and ABCG1 in MFG membranes suggests that these proteins are involved in cholesterol exchange between MEC and alveolar milk.     

Identification, sequence analysis and mRNA tissue distribution of the bovine sterol transporters ABCG5 and ABCG8

The family of ATP-binding cassette (ABC) transporters consists of several transmembrane proteins that use ATP hydrolysis as an energy source for the transport of a variety of substances through cellular membranes. Two members of this family, ABCG5 and ABCG8, are implicated in the intestinal absorption and biliar excretion of sterols. Cholesterol content in milk is highly variable among species, breeds, and individuals of the same species, but a potential application of these genes in lipid homeostasis in the mammary gland has never been addressed. In the present work, expression of ABCG5 and ABCG8 in the bovine was demonstrated for the first time and characterized by quantitative PCR. The entire coding region and promoter area were sequenced and screened for motifs involved in lipid homeostasis. Both ABCG5 and ABCG8 presented a high level of length and sequence identity with other mammalian species. In the intergenic promoter region, 2 GATA boxes, a liver receptor homolog-1 response element, and a nuclear factor-kappaB response element, important factors in other lipid regulatory processes, were identified. As expected, high expression levels of both ABCG5 and ABCG8 were present in liver and digestive tract samples, and interestingly, in the mammary gland, opening new avenues for further investigation about their potential role in lipid trafficking and excretion during lactation.     

The effect of co‐administered flavonoids on the metabolism of hesperetin and the disposition of its metabolites in Caco‐2 cell monolayers

Metabolism by phase II enzymes and transport from intestinal cells back into the lumen by ATP binding cassette (ABC) transporters limits the bioavailability of the flavanone hesperetin, the aglycone of hesperidin. This study investigates to what extent other flavonoids modulate the metabolism and transport of hesperetin by characterizing the effect of co‐administrating a series of flavonoids using Caco‐2 cell monolayers in a two‐compartment transwell system. Flavonoids may interfere with hesperetin metabolism and can also inhibit the apically located ABC transporter breast cancer resistance protein (ABCG2) which was previously shown to be responsible for the apical transport of hesperetin metabolites. Co‐exposure of Caco‐2 cell monolayers to hesperetin with specific flavonoids reduced the ratio of apical efflux to basolateral transport of hesperetin metabolites, and in some cases, also reduced the amount of hesperetin metabolites detected extracellularly. As intracellular accumulation of hesperetin metabolites did not account for this decrease, inhibition of metabolism of hesperetin is likely the underlying mechanism for the reduced metabolite formation and excretion. In spite of the reduction in metabolism the amount of hesperetin metabolites transported to the basolateral side significantly increased upon co‐exposure with specific flavonoids and therefore co‐administration of specific flavonoids could be a strategy to improve the bioavailability of hesperetin.     

Hypolipidemic Activity of Peony Seed Oil Rich in α‐Linolenic,is Mediated Through Inhibition of Lipogenesis and Upregulation of Fatty Acid β‐Oxidation

Peony seed oil (PSO) is a new resource food rich in α‐Linolenic Acid(ALA) (38.66%). The objective of this study was to assess the modulatory effect of PSO on lipid metabolism. Lard oil, safflower oil (SFO), and PSO were fed to wistar rats with 1% cholesterol in the diet for 60 d. Serum and liver lipids showed significant decrease in total cholesterol (TC), triglyceride (TG), and low density lipoprotein‐cholesterol (LDL‐C) levels in PSO fed rats compared to lard oil and SFO fed rats. ALA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), contents were significantly increased, whereas linoleic acid (LA), arachidonic acid (AA) levels decreased in serum and liver of PSO fed rats. Feeding PSO increased ALA level and decreased n‐6 to n‐3 polyunsaturated fatty acid (PUFA) ratio. The hypolipidemic result of PSO indicated that PSO participated in the regulation of plasma lipid concentration and cholesterol metabolism in liver. The decreased expression of sterol regulatory element‐binding proteins 1C (SREBP‐1c), acetyl‐CoA carboxylase (ACC), and fatty acid synthase (FAS)‐reduced lipid synthesis; Activation of peroxisome proliferator–activator receptor (PPARα) accompanied by increase of uncoupling protein2 (UP2) and acyl‐CoA oxidase (AOX) stimulated lipid metabolism and exerted an antiobesity effect via increasing energy expenditure for prevention of obesity.     

普洱茶茶色素对HepG2细胞脂质代谢的影响及作用机理

以正常培养和油酸诱导培养的人肝癌细胞系(human hepatocellular liver carcinoma cell line,Hep G2)细胞为模型,通过测定普洱茶茶色素对Hep G2细胞内甘油三酯(triglyceride,TG)和总胆固醇(total cholesterol,TC)含量,细胞中脂肪酸合成酶(fatty acid synthase,FAS)、固醇调节元件结合蛋白1c(sterol regulatory element binding protein 1c,SREBP-1c)、三磷酸腺苷结合转运子A1(ATP binding cassette transporter A1,ABCA1)、胆固醇7α-羟化酶(cholesterol 7α-hydroxylase,CYP7A1)的转录水平,磷酸化腺苷酸活化蛋白激酶(phospho-AMPactivated protein kinase,p-AMPK)的蛋白表达水平研究普洱茶茶色素的减肥降脂作用机制。结果显示,普洱茶茶色素能明显降低油酸诱导的Hep G2细胞模型中TG和TC含量,作用程度依赖于普洱茶的作用质量浓度。但对正常培养的Hep G2的TG、TC作用影响不显著。经过普洱茶茶色素作用油酸诱导Hep G2细胞24 h后,能显著下调细胞的FAS和SREBP-1c的m RNA表达水平(P0.05),显著上调ABCA1的转录水平(P0.05),且使CYP7A1的转录水平呈上升趋势,并显著上调p-AMPK蛋白的表达量(P0.05)。因此,普洱茶茶色素可通过调控上述调控因子和酶的表达而改善油酸诱导下Hep G2细胞的脂质代谢水平。     

五味子、黄芪混合多糖对大鼠高脂血症的降脂作用

为了观察五味子、黄芪混合多糖(Polysaccharide from mixed Schisandra chinensis and Astragalus membranaceus,SAP)对脂代谢紊乱的调节作用及其作用机制,采用高脂饮食喂养建立大鼠(Wistar)高脂血症模型,记录SAP干预期间大鼠每周体重变化。8周后检测其血清中甘油三酯(Triglyceride,TG)、总胆固醇(Total cholesterol,TC)、高密度脂蛋白胆固醇(High-density lipoprotein cholesterol,HDL-C)及低密度脂蛋白胆固醇(Low-density lipoprotein cholesterol,LDL-C)水平,肝组织中TG、TC水平,苏木素-伊红(HE)染色观察大鼠肝脏病理学变化,Western blot法检测肝脏中胆固醇代谢相关蛋白ATP结合盒转运蛋白A1(ATP-binding cassette transporter A1,ABCA1)、肝X受体α(Liver X receptors α,LXRα)和三磷酸结合盒转运体G1(ATP-binding cassette G1,ABCG1)的表达情况。结果表明,SAP(100 mg/kg)灌胃给药可显著降低高脂血症大鼠的体重、血清中TC、TG、LDL-C水平以及肝组织中TC、TG水平(P<0.05),显著增加血清中HDL-C水平(P<0.05),减轻肝脏组织中的脂质沉积,改善大鼠高脂血症。同时SAP显著提高了高脂血症大鼠肝脏中LXRα、ABCA1和ABCG1蛋白的表达(P<0.05)。综上所述,SAP对高脂血症大鼠有明显的调节血脂作用,且其作用机制可能与促进肝脏胆固醇代谢有关。     

Short communication: a polymorphism in ABCG2 in Bos indicus and Bos taurus cattle breeds

A single nucleotide change (A/C) in exon 14 is capable of encoding a substitution of tyrosine-581 to serine (Y581S) in the ABCG2 (ATP binding cassette, subfamily G, member 2) gene and affects milk production traits. The ABCG2^A allele decreases milk yield and increases protein and fat concentration. The allele frequencies were determined in 32 Bos taurus and 3 Bos indicus breeds; ABCG2^A was predominant in all populations. This allele approached fixation in 23 out of 35 breeds, including all 3 Bos indicus breeds. The ABCG2^C allele was found in the Belgian Blue (beef), Belgian Blue Mix, British Friesian, Bohemian Red, East Anatolian Red, German Angus, German Black Pied, German Brown, German Simmental, Israeli Holstein, Menorquina, and US Holstein breeds. Thus, the genetic gain expected from selection for ABCG2^A may be limited. The detection of ABCG2^C only in Bos taurus breeds may indicate that ABCG2^A is the ancestral allele, and that the Y581S substitution occurred after the separation of the Bos indicus and Bos taurus lineages.     

Cholesterol metabolism,transport, and hepatic regulation in dairy cows during transition and early lactation

The transition from the nonlactating to the lactating state represents a critical period for dairy cow lipid metabolism because body reserves have to be mobilized to meet the increasing energy requirements for the initiation of milk production. The purpose of this study was to provide a comprehensive overview on cholesterol homeostasis in transition dairy cows by assessing in parallel plasma, milk, and hepatic tissue for key factors of cholesterol metabolism, transport, and regulation. Blood samples and liver biopsies were taken from 50 multiparous Holstein dairy cows in wk 3 antepartum (a.p.), wk 1 postpartum (p.p.), wk 4 p.p., and wk 14 p.p. Milk sampling was performed in wk 1, 4, and 14 p.p. Blood and milk lipid concentrations [triglycerides (TG), cholesterol, and lipoproteins], enzyme activities (phospholipid transfer protein and lecithin:cholesterol acyltransferase) were analyzed using enzymatic assays. Hepatic gene expression patterns of 3-hydroxy-3-methylglutaryl-coenzyme A (HMGC) synthase 1 (HMGCS1) and HMGC reductase (HMGCR), sterol regulatory element-binding factor (SREBF)-1 and -2, microsomal triglyceride transfer protein (MTTP), ATP-binding cassette transporter (ABC) A1 and ABCG1, liver X receptor (LXR) α and peroxisome proliferator activated receptor (PPAR) α and γ were measured using quantitative RT-PCR. Plasma TG, cholesterol, and lipoprotein concentrations decreased from wk 3 a.p. to a minimum in wk 1 p.p., and then gradually increased until wk 14 p.p. Compared with wk 4 p.p., phospholipid transfer protein activity was increased in wk 1 p.p., whereas lecithin:cholesterol acyltransferase activity was lowest at this period. Total cholesterol concentration and mass, and cholesterol concentration in the milk fat fraction decreased from wk 1 p.p. to wk 4 p.p. Both total and milk fat cholesterol concentration were decreased in wk 4 p.p. compared with wk 1 and 14 p.p. The mRNA abundance of genes involved in cholesterol synthesis (SREBF-2, HMGCS1, and HMGCR) markedly increased from wk 3 a.p. to wk 1 p.p., whereas SREBF-1 was downregulated. The expression of ABCA1 increased from wk 3 a.p. to wk 1 p.p., whereas ABCG1 was increased in wk 14 p.p. compared with other time points. In conclusion, hepatic expression of genes involved in the biosynthesis of cholesterol as well as the ABCA1 transporter were upregulated at the onset of lactation, whereas plasma concentrations of total cholesterol, phospholipids, lipoprotein-cholesterol, and TG were at a minimum. Thus, at the gene expression level, the liver seems to react to the increased demand for cholesterol after parturition. Whether the low plasma cholesterol and TG levels are due to impaired hepatic export mechanisms or reflect an enhanced transfer of these compounds into the milk to provide essential nutrients for the newborn remains to be elucidated.     

Function of Candida glabrata ABC transporter gene,PDH1

The rapid increase in azole resistance during treatment of patients infected with Candida glabrata may be due to increased azole efflux mediated by ABC transporters, as occurs with increased expression of PDR5 in Saccharomyces cerevisiae. Two known C. glabrata homologues of PDR5 influencing azole susceptibility are PDH1 (CgCDR2) and CgCDR1. Disruption of PDH1 in a cgcdr1::ura3 strain increased susceptibility to rhodamine 6G, cycloheximide and chloramphenicol, and also increased rhodamine 6G accumulation, all properties of pdr5 null mutants. Overexpression of PDH1 in S. cerevisiae complemented the pdr5 mutation by reversing susceptibility to rhodamine 6G, chloramphenicol and cycloheximide, as well as by decreasing rhodamine 6G intracellular concentration. Expression of PDH1 in a C. glabrata cgcdr1::ura3 pdh1Delta::ura3 mutant using a multicopy plasmid almost completely restored the wild-type phenotype, showing that PDH1 at higher levels of expression can replace CgCDR1. Because PDH1 and CgCDR1 have both been reported to have upstream sequences similar to the Pdr1p- and Pdr3p-binding elements of PDR5, we sought similarities in regulation between the three genes. Abundance of PDH1 and CgCDR1 mRNA in C. glabrata was increased by rhodamine 6G, cycloheximide and oligomycin, properties in common with PDR5. PDH1, CgCDR1 and PDR5 have striking similarities in function and regulation.     

Moderately lipophilic carboxylate compounds are the selective inducers of the Saccharomyces cerevisiae Pdr12p ATP-binding cassette transporter

Saccharomyces cerevisiae displays very strong induction of a single ATP-binding cassette (ABC) transporter, Pdr12p, when stressed with certain weak organic acids. This is a plasma membrane pump catalysing active efflux of the organic acid anion from the cell. Pdr12p action probably allows S. cerevisiae to maintain lower intracellular levels of several weak organic acid preservatives than would be expected on the basis of the free equilibration of the acid across the cell membrane. This in turn facilitates growth in the presence of these preservatives and therefore yeast spoilage of food materials. Pdr12p appears to confer resistance to those carboxylic acids that, to a reasonable degree, partition into both the lipid bilayer and aqueous phases. Its gene (PDR12) is strongly induced by sorbate, benzoate and certain other moderately lipophilic carboxylate compounds, but not by organic alcohols or high levels of acetate. PDR12 induction reflects the operation of a previously uncharacterized S. cerevisiae stress response, for which the induction signal is probably a high intracellular pool of the organic acid anion.