Torsten Plösch

The breast cancer resistance protein protects against a major chlorophyll-derived dietary phototoxin and protoporphyria

The breast cancer resistance protein (BCRP/ABCG2) is a member of the ATP-binding cassette family of drug transporters and confers resistance to various anticancer drugs. We show here that mice lacking Bcrp1/Abcg2 become extremely sensitive to the dietary chlorophyll-breakdown product pheophorbide a, resulting in severe, sometimes lethal phototoxic lesions on light-exposed skin. Pheophorbide a occurs in various plant-derived foods and food supplements. Bcrp1 transports pheophorbide a and is highly efficient in limiting its uptake from ingested food. Bcrp1−/− mice also displayed a previously unknown type of protoporphyria. Erythrocyte levels of the heme precursor and phototoxin protoporphyrin IX, which is structurally related to pheophorbide a, were increased 10-fold. Transplantation with wild-type bone marrow cured the protoporphyria and reduced the phototoxin sensitivity of Bcrp1−/− mice. These results indicate that humans or animals with low or absent BCRP activity may be at increased risk for developing protoporphyria and diet-dependent phototoxicity and provide a striking illustration of the importance of drug transporters in protection from toxicity of normal food constituents.

The role of nutrition on epigenetic modifications and their implications on health

Nutrition plays a key role in many aspects of health and dietary imbalances are major determinants of chronic diseases including cardiovascular disease, obesity, diabetes and cancer. Adequate nutrition is particularly essential during critical periods in early life (both pre- and postnatal). In this regard, there is extensive epidemiologic and experimental data showing that early sub-optimal nutrition can have health consequences several decades later. The hypothesis that epigenetic mechanisms may link such nutritional imbalances with altered disease risk has been gaining acceptance over recent years. Epigenetics can be defined as the study of heritable changes in gene expression that do not involve alterations in the DNA sequence. Epigenetic marks include DNA methylation, histone modifications and a variety of non-coding RNAs. Strikingly, they are plastic and respond to environmental signals, including diet. Here we will review how dietary factors modulate the establishment and maintenance of epigenetic marks, thereby influencing gene expression and, hence, disease risk and health.

The liver X-receptor gene promoter is hypermethylated in a mouse model of prenatal protein restriction

Prenatal nutrition as influenced by the nutritional status of the mother has been identified as a determinant of adult disease. Feeding low-protein diets during pregnancy in rodents is a well-established model to induce programming events in offspring. We hypothesized that protein restriction would influence fetal lipid metabolism by inducing epigenetic adaptations. Pregnant C57BL/6J mice were exposed to a protein-restriction protocol (9% vs. 18% casein). Shortly before birth, dams and fetuses were killed. To identify putative epigenetic changes, CG-dinucleotide-rich region in the promoter of a gene (CpG island) methylation microarrays were performed on DNA isolated from fetal livers. Two hundred four gene promoter regions were differentially methylated upon protein restriction. The liver X-receptor (Lxr) alpha promoter was hypermethylated in protein-restricted pups. Lxr alpha is a nuclear receptor critically involved in control of cholesterol and fatty acid metabolism. The mRNA level of Lxra was reduced by 32% in fetal liver upon maternal protein restriction, whereas expression of the Lxr target genes Abcg5/Abcg8 was reduced by 56% and 51%, respectively, measured by real-time quantitative PCR. The same effect, although less pronounced, was observed in the fetal intestine. In vitro methylation of a mouse Lxra-promoter/luciferase expression cassette resulted in a 24-fold transcriptional repression. Our study demonstrates that, in mice, protein restriction during pregnancy interferes with DNA methylation in fetal liver. Lxra is a target of differential methylation, and Lxra transcription is dependent on DNA methylation. It is tempting to speculate that perinatal nutrition may influence adult lipid metabolism by DNA methylation, which may contribute to the epidemiological relation between perinatal/neonatal nutrition and adult disease.

Relation between hepatic expression of ATP-binding cassette transporters G5 and G8 and biliary cholesterol secretion in mice

BACKGROUND/AIM Mutations in genes encoding the ATP-binding cassette (ABC)-transporters ABCG5 and ABCG8 underlie sitosterolemia, which is characterized by elevated plasma levels of phytosterols due to increased intestinal absorption and impaired biliary secretion of sterols. The aim of our study was to correlate the expression levels of Abcg5 and Abcg8 to biliary cholesterol secretion in various (genetically-modified) mouse models. METHODS Bile was collected from genetically-modified mice fed a chow diet, or from mice fed either a chow diet, or chow supplemented with either 1% diosgenin, 0.1% simvastatin, or a synthetic liver X receptor agonist, for determination of biliary lipids. Livers and small intestines were harvested and expression levels of Abcg5, Abcg8 and Abcb4 were determined by real-time polymerase chain reaction. RESULTS Intestinal expression of Abcg5 and Abcg8 did not show much variation between the various models. In contrast, a linear correlation between hepatic expression levels of Abcg5 and Abcg8 and biliary cholesterol secretion rates was found. This relation was independent of Abcb4-mediated phospholipid secretion. However, in diosgenin-fed mice showing cholesterol hypersecretion, hepatic Abcg5 and Abcg8 expression levels remained unchanged. CONCLUSIONS Our results strongly support a role for Abcg5 and Abcg8 in regulation of biliary cholesterol secretion, but also indicate the existence of a largely independent route of cholesterol secretion.

The role of maternal-fetal cholesterol transport in early fetal life: Current insights

ABSTRACT The importance of maternal cholesterol as an exogenous cholesterol source for the growing embryo was first reported in studies of Smith-Lemli-Opitz syndrome. Although most of the fetuss cholesterol is synthesized by the fetus itself, there is now growing evidence that during the first weeks of life, when most organs develop, the fetus largely depends on maternal cholesterol as its cholesterol source. The maternal-fetal cholesterol transport mechanism, by transporters in both the yolk sac and placenta, is becoming better understood. This minireview summarizes current insights on maternal-fetal cholesterol transport based on in vitro and in vivo studies. As the prevalence of maternal diseases, such as diabetes, obesity, and the metabolic syndrome that adversely affect maternal cholesterol levels, is now rapidly reaching epidemic proportions, we urgently need to determine the impact of these maternal conditions on the developing human fetus.

More than just a gut instinct - The potential interplay between a baby's nutrition, its gut microbiome and the epigenome

Substantial evidence links early postnatal nutrition to the development of obesity later in life. However, the molecular mechanisms of this connection must be further elucidated. Epigenetic mechanisms have been indicated to be involved in this process, referred to as metabolic programming. Therefore, we propose here that early postnatal nutrition (breast and formula feeding) epigenetically programs the developing organs via modulation of the gut microbiome and influences the body weight phenotype including the predisposition to obesity. Specifically, the early-age food patterns are known to determine the gross composition of the early gut microbiota. In turn, the microbiota produces large quantities of epigenetically active metabolites, such as folate and short chain fatty acids (butyrate and acetate). The spectrum of these produced metabolites depends on the composition of the gut microbiota. Hence, it is likely that changes in gut microbiota that result in altered metabolite composition might influence the epigenome of directly adjacent intestinal cells, as well as other major target cell populations, such as hepatocytes and adipocytes. Nuclear receptors and other transcription factors (the PPARs, LXR, RXR, and others) could be physiologically relevant targets of this metabolite-induced epigenetic regulation. Ultimately, transcriptional networks regulating energy balance could be manipulated. For these reasons, we postulate that early nutrition may influence the baby epigenome via microbial metabolites, which contributes to the observed relationship between early nutrition and adult obesity.

Maternal western diet primes non‐alcoholic fatty liver disease in adult mouse offspring

Metabolic programming via components of the maternal diet during gestation may play a role in the development of different aspects of the metabolic syndrome. Using a mouse model, we aimed to characterize the role of maternal western‐type diet in the development of non‐alcoholic fatty liver disease (NAFLD) in the offspring.

The Liver X Receptor (LXR) and its Target Gene ABCA1 are Regulated Upon Low Oxygen in Human Trophoblast Cells: A Reason for Alterations in Preeclampsia?

OBJECTIVES The Liver X receptors (LXR) alpha and beta and their target genes such as the ATP-binding cassette (ABC) transporters have been shown to be crucially involved in the regulation of cellular cholesterol homeostasis. The aim of this study was to characterize the role of LXR alpha/beta in the human placenta under normal physiological circumstances and in preeclampsia. STUDY DESIGN We investigated the expression pattern of the LXRs and their target genes in the human placenta during normal pregnancy and in preeclampsia. Placental explants and cell lines were studied under different oxygen levels and pharmacological LXR agonists. MAIN OUTCOME MEASURES Gene expressions (Taqman PCR) and protein levels (Western Blot) were combined with immunohistochemistry to analyze the expression of LXR and its target genes. RESULTS In the human placenta, LXRA and LXRB expression increased during normal pregnancy. This was paralleled by the expression of their prototypical target genes, e.g., the cholesterol transporter ABCA1. Interestingly, early-onset preeclamptic placentae revealed a significant upregulation of ABCA1. Culture of JAr trophoblast cells and human first trimester placental explants under low oxygen lead to increased expression of LXRA and ABCA1 which was further enhanced by the LXR agonist T0901317. CONCLUSIONS LXRA together with ABCA1 are specifically expressed in the human placenta and can be regulated by hypoxia. Deregulation of this system in early preeclampsia might be the result of placental hypoxia and hence might have consequences for maternal-fetal cholesterol transport.

The ABC of hepatic and intestinal cholesterol transport

The liver and (small) intestine are key organs in maintenance of cholesterol homeostasis: both organs show active de novo cholesterogenesis and are able to transport impressive amounts of newly synthesized and diet-derived cholesterol via a number of distinct pathways. Cholesterol trafficking involves the concerted action of a number of transporter proteins, some of which have been identified only recently. In particular, several ATP-binding cassette (ABC) transporters fulfil critical roles. For instance, the ABCG5/ABCG8 couple is crucial for hepatobiliary and intestinal cholesterol excretion, while ABCA1 is essential for high-density lipoprotein formation and, hence, for inter-organ trafficking of the highly water-insoluble cholesterol molecules. Very recently, the Niemann-Pick C1-like 1 protein has been identified as a key player in cholesterol absorption by the small intestine and may represent a target of the cholesterol absorption inhibitor ezetimibe. Alterations in hepatic and intestinal cholesterol transport affect circulating levels of atherogenic lipoproteins and thus the risk for cardiovascular disease. This review specifically deals with the processes of hepatobiliary cholesterol excretion and intestinal cholesterol absorption as well as the interactions between these important transport routes. During the last few years, insight into the mechanisms of hepatic and intestinal cholesterol transport has greatly increased not in the least by the identification of involved transporter proteins and the (partial) elucidation of their mode of action. In addition, information has become available on (transcription) factors regulating expression of the encoding genes. This knowledge is of great importance for the development of a tailored design of novel plasma cholesterol-lowering strategies.

The origin of fetal sterols in second-trimester amniotic fluid: endogenous synthesis or maternal-fetal transport?

OBJECTIVE Cholesterol is crucial for fetal development. To gain more insight into the origin of the fetal cholesterol pool in early human pregnancy, we determined cholesterol and its precursors in the amniotic fluid of uncomplicated, singleton human pregnancies. STUDY DESIGN Total sterols were characterized by gas chromatography-mass spectrometry in the second-trimester amniotic fluid of 126 healthy fetuses from week 15 until week 22. RESULTS The markers of cholesterol biosynthesis, lanosterol, dihydrolanosterol, and lathosterol, were present in low levels until the 19th week of gestation, after which their levels increased strongly. β-sitosterol, a marker for maternal-fetal cholesterol transport, was detectable in the amniotic fluid. The total cholesterol levels increased slightly between weeks 15 and 22. CONCLUSION Our results support the hypothesis that during early life the fetus depends on maternal cholesterol supply because endogenous synthesis is relatively low. Therefore, maternal cholesterol can play a crucial role in fetal development.