Induction of gene pattern changes associated with dysfunctional lipid metabolism induced by dietary fat and exposure to a persistent organic pollutant

Particulate matter air pollutants and cardiovascular disease: Strategies for intervention

Air pollution is consistently linked with elevations in cardiovascular disease (CVD) and CVD-related mortality. Particulate matter (PM) is a critical factor in air pollution-associated CVD. PM forms in the air during the combustion of fuels as solid particles and liquid droplets and the sources of airborne PM range from dust and dirt to soot and smoke. The health impacts of PM inhalation are well documented. In the US, where CVD is already the leading cause of death, it is estimated that PM2.5 (PM < 2.5 μm in size) is responsible for nearly 200,000 premature deaths annually. Despite the public health data, definitive mechanisms underlying PM-associated CVD are elusive. However, evidence to-date implicates mechanisms involving oxidative stress, inflammation, metabolic dysfunction and dyslipidemia, contributing to vascular dysfunction and atherosclerosis, along with autonomic dysfunction and hypertension. For the benefit of susceptible individuals and individuals who live in areas where PM levels exceed the National Ambient Air Quality Standard, interventional strategies for mitigating PM-associated CVD are necessary. This review will highlight current state of knowledge with respect to mechanisms for PM-dependent CVD. Based upon these mechanisms, strategies for intervention will be outlined. Citing data from animal models and human subjects, these highlighted strategies include: 1) antioxidants, such as vitamins E and C, carnosine, sulforaphane and resveratrol, to reduce oxidative stress and systemic inflammation; 2) omega-3 fatty acids, to inhibit inflammation and autonomic dysfunction; 3) statins, to decrease cholesterol accumulation and inflammation; 4) melatonin, to regulate the immune-pineal axis and 5) metformin, to address PM-associated metabolic dysfunction. Each of these will be discussed with respect to its potential role in limiting PM-associated CVD.

Effects of di (2-ethylhexyl) phthalate and high-fat diet on lipid metabolism in rats by JAK2/STAT5

Exposure to di (2-ethylhexyl) phthalate (DEHP) induces lipid metabolism disorder and high-fat diet (HD) may have joint effects with DEHP. We aim to clarify the role of JAK2/STAT5 pathway in the process and reveal the effects of HD on the toxicity of DEHP. Wistar rats (160 animals) were fed with HD or normal diet (ND) respectively and exposed to DEHP 0, 5, 50, and 500 mg/kg/day for 8 weeks. Lipid levels, as well as the morphology of liver and adipose, mRNA levels, and protein levels of JAK2, STAT5A, STAT5B, FAS, ap2, and PDK4 were detected. The results showed that DEHP exposure leads to increased weight gain. The JAK2/STAT5 pathway was activated in adipose after DEHP exposure and promoted the expression of FAS, ap2, and PDK4 in ND rats. While in the liver, JAK2 was inhibited, and lipid synthesis and accumulation were increased. However, rats exposed to DEHP in combination with HD showed a complete disorder of lipid metabolism. Therefore, we conclude that DEHP affects lipid metabolism through regulating the JAK2/STAT5 pathway and promotes adipogenesis and lipid accumulation. High-fat diet may have a joint effect with DEHP on lipid metabolism disorder.

The impact of maternally derived dioxins on embryonic development and hepatic AHR signaling in a long-lived apex predator

Dioxins and related contaminants are highly pervasive in aquatic systems and elicit deleterious effects in exposed organisms. Because dioxins exhibit a proclivity to bioaccumulate, long-lived predatory species are particularly vulnerable to their persistence in the environment. We have previously reported elevated expression of CYP1A2, a biomarker of dioxin exposure, in American alligator embryos collected from the Tom Yawkey Wildlife Center (YWC). This coastal population inhabits a system with historical dioxin contamination associated with industrial activities. Herein, we utilize ecological attributes of the alligator to address the persistence of dioxins and furans in yolk and their potential to drive changes in hepatic function. Specifically, we assess variation in expression of AHR signaling components in embryos and its connection to contaminant levels in matched yolk samples. Compared to a reference population, TEQ levels and total penta-, hexa-, octa-substituted CDDs were elevated at YWC. Contrary to predictions, TEQ levels were not significantly related to hepatic AHR1B or CYP1A2 expression. However, a significant association was detected between expression of both factors and embryo:yolk mass ratios, wherein decreasing embryo mass was negatively associated with CYP1A2 but positively associated with AHR1B. These findings suggest that variation in embryonic metabolism and developmental progression likely influence AHR signaling and dioxin toxicity in alligators and potentially other oviparous species. While dioxin concentrations observed in alligators in this study are lower than historical values reported for other wildlife species inhabiting this system, they indicate the continued presence and possible long-term influence of these contaminants in a high trophic status species.

Dioxin-like PCB 126 Increases Systemic Inflammation and Accelerates Atherosclerosis in Lean LDL Receptor-Deficient Mice

Exposure to dioxins and related persistent organic pollutants likely contributes to cardiovascular disease (CVD) risk through multiple mechanisms including the induction of chronic inflammation. Epidemiological studies have shown that leaner individuals may be more susceptible to the detrimental effects of lipophilic toxicants because they lack large adipose tissue depots that can accumulate and sequester these pollutants. This phenomenon complicates efforts to study mechanisms of pollutant-accelerated atherosclerosis in experimental animal models where high-fat feeding and adipose expansion limit the bioavailability of lipophilic pollutants. Here, we investigated whether a model dioxin-like pollutant, PCB 126, could increase inflammation and accelerate atherosclerosis in Ldlr-/- mice fed a low-fat atherogenic diet. We fed Ldlr-/- mice the Clinton/Cybulsky diet (10% kcal fat, 0.15% cholesterol) and sacrificed mice at 8, 10, or 12 weeks postPCB (2 doses of 1 μmol/kg) or vehicle gavage. To characterize this novel model, we examined the effects of PCB 126 on markers of systemic inflammation, hematological indices, fatty livers, and atherosclerotic lesion size. Mice exposed to PCB 126 exhibited significantly increased plasma inflammatory cytokine levels, increased circulating biomarkers of CVD, altered platelet, and red blood cell counts, increased accumulation of hepatic fatty acids, and accelerated atherosclerotic lesion formation in the aortic root. PCB 126 also increased circulating neutrophils, monocytes, and macrophages as determined by flow cytometry analysis. Exposure to dioxin-like PCB 126 increases inflammation and accelerates atherosclerosis in mice. This low-fat atherogenic diet may provide a useful tool to study the mechanisms linking exposure to lipophilic pollutants to increased risk of CVD.

Relationship Between the Content of Chlorinated Hydrocarbons and Fatty Acid Composition of Milk Fat

Introduction

Reports that the presence of persistent organic pollutants in fat may affect fatty acid metabolism prompted this research aiming to study the relationship between the contents of γ-HCH and DDT, DDE, DDD, and ΣDDT, and fatty acid composition of milk fat.

Material and Methods

The material consisted of 50 samples of cow and mare milk, collected in 2015. Ludwicki’s and the Röse-Gottlieb and IDF Standard methods were used to prepare the samples. Statistical analyses were conducted using Statistica 12.0.

Results

There was a negative correlation between the content of γ-HCH and C16:1, C17:1, C18:1c9, C18:1c9c12, and ΣMUFA in cow milk fat and C13:0, C14:0, and C10:1 in mare milk fat. A positive correlation was observed between γ-HCH and C6:0 to C12:0, C14:0, C18:1t16, and ΣSFA in cow milk fat, and between this compound and C14:0iso, C16:1, C17:1, C18:1c9,11, and ΣMUFA in mare milk fat. A negative correlation between the contents of ΣDDT and C16:1, C17:1, C18:1c9,11,13 and ΣMUFA in cow milk fat and C16:0iso, C17:0, and C18:3 in mare milk fat was noted. A positive correlation was found between the contents of ΣDDT and saturated and polyunsaturated fatty acids and ΣSFA and ΣPUFA in cow milk fat, and C18:2c9c12 in mare milk fat.

Conclusion

The correlation between the content of selected organochlorine compounds and the composition of fatty acids in cow and mare milk fat indicates the strong influence of these environmental pollutants on the nutritional value of milk fat.

Relationship between the content of chlorinated hydrocarbons and fatty acid composition of milk fat

Introduction

Reports that the presence of persistent organic pollutants in fat may affect fatty acid metabolism prompted this research aiming to study the relationship between the contents of γ-HCH and DDT, DDE, DDD, and ΣDDT, and fatty acid composition of milk fat.

Material and Methods

The material consisted of 50 samples of cow and mare milk, collected in 2015. Ludwicki’s and the Röse-Gottlieb and IDF Standard methods were used to prepare the samples. Statistical analyses were conducted using Statistica 12.0.

Results

There was a negative correlation between the content of γ-HCH and C16:1, C17:1, C18:1c9, C18:1c9c12, and ΣMUFA in cow milk fat and C13:0, C14:0, and C10:1 in mare milk fat. A positive correlation was observed between γ-HCH and C6:0 to C12:0, C14:0, C18:1t16, and ΣSFA in cow milk fat, and between this compound and C14:0iso, C16:1, C17:1, C18:1c9,11, and ΣMUFA in mare milk fat. A negative correlation between the contents of ΣDDT and C16:1, C17:1, C18:1c9,11,13 and ΣMUFA in cow milk fat and C16:0iso, C17:0, and C18:3 in mare milk fat was noted. A positive correlation was found between the contents of ΣDDT and saturated and polyunsaturated fatty acids and ΣSFA and ΣPUFA in cow milk fat, and C18:2c9c12 in mare milk fat.

Conclusion

The correlation between the content of selected organochlorine compounds and the composition of fatty acids in cow and mare milk fat indicates the strong influence of these environmental pollutants on the nutritional value of milk fat.

Determinants of serum organochlorine pesticide and polychlorinated biphenyl levels in middle-aged Korean adults

The serum levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were measured in a middle-aged Korean population and investigated associations with age, gender, body mass index (BMI), metabolic syndrome (MS), type 2 diabetes mellitus (T2DM), and dietary habits. The median concentrations of 22 OCPs and 34 PCBs in the serum samples were 483 and 216 ng g^-1 lipid, respectively. The most abundant compound was p,p'-DDE, followed by PCB 153, β-HCH, PCB 118, and PCB 180. The results of multiple linear regression and other statistical analyses revealed that serum OCP and PCB levels were higher in women and were positively correlated with age. BMI was positively associated with serum OCP and PCB levels, reflecting the influence of food intake and the preserving effect of body fat. MS and T2DM were significantly associated with serum OCP and PCB levels. The intake of animal foods had positive associations with serum OCP and PCB levels, whereas the intake of phytogenic foods showed negative associations, presumably because of contamination levels in food items and food matrices that governs absorption and excretion of OCPs and PCBs in the body. The relationship between dietary habits and serum OCP and PCB levels were different in participants with MS compared to healthy participants, suggesting MS may alter the influence of food intake on serum OCP and PCB levels.

The fate of technical-grade chlordane in mice fed a high-fat diet and its roles as a candidate obesogen

Epidemiological studies indicate that exposure to persistent organic pollutants is positively associated with the prevalence of obesity. To delineate the potential role of technical-grade chlordane in obesity development, chlordane metabolism and chlordane-induced metabolic changes were investigated in mice fed high-fat diet (HFD) over a 6-week period. Gas chromatography-electron capture detector analysis showed that HFD induced more accumulation of technical chlordane in the liver, muscle and adipose tissue. The enantioselectivities of oxychlordane in selected tissues were also influenced by HFD. ¹H NMR-based liver metabolome indicated that technical chlordane can enhance the metabolic alterations induced by HFD. Compared with the low-fat diet (LFD) group, no differences were observed in the LFD + chlordane group. However, as many as 16 metabolites were significantly different between the HFD group and HFD + chlordane group. Moreover, compared to the LFD + chlordane group, the abundances of 24 metabolites significantly increased or decreased in the HFD + chlordane group. Twenty metabolites were altered in the HFD group compared to the LFD group. Tryptophan profiling suggested that both chlordane and HFD can disturb tryptophan catabolism. These interactions between technical chlordane and HFD suggest that technical chlordane is a candidate obesogen.

Brain in situ hybridization maps as a source for reverse-engineering transcriptional regulatory networks: Alzheimer's disease insights

Microarray data have been a valuable resource for identifying transcriptional regulatory relationships among genes. As an example, brain region-specific transcriptional regulatory events have the potential of providing etiological insights into Alzheimer Disease (AD). However, there is often a paucity of suitable brain-region specific expression data obtained via microarrays or other high throughput means. The Allen Brain Atlas in situ hybridization (ISH) data sets (Jones et al., 2009) represent a potentially valuable alternative source of high-throughput brain region-specific gene expression data for such purposes. In this study, Allen Brain Atlas mouse ISH data in the hippocampal fields were extracted, focusing on 508 genes relevant to neurodegeneration. Transcriptional regulatory networks were learned using three high-performing network inference algorithms. Only 17% of regulatory edges from a network reverse-engineered based on brain region-specific ISH data were also found in a network constructed upon gene expression correlations in mouse whole brain microarrays, thus showing the specificity of gene expression within brain sub-regions. Furthermore, the ISH data-based networks were used to identify instructive transcriptional regulatory relationships. Ncor2, Sp3 and Usf2 form a unique three-party regulatory motif, potentially affecting memory formation pathways. Nfe2l1, Egr1 and Usf2 emerge among regulators of genes involved in AD (e.g. Dhcr24, Aplp2, Tia1, Pdrx1, Vdac1, and Syn2). Further, Nfe2l1, Egr1 and Usf2 are sensitive to dietary factors and could be among links between dietary influences and genes in the AD etiology. Thus, this approach of harnessing brain region-specific ISH data represents a rare opportunity for gleaning unique etiological insights for diseases such as AD.

MRNA expression of genes regulating lipid metabolism in ringed seals (Pusa hispida) from differently polluted areas

There is a growing concern about the ability of persistent organic pollutants (POPs) to influence lipid metabolism. Although POPs are found at high concentrations in some populations of marine mammals, for example in the ringed seal (Pusa hispida) from the Baltic Sea, little is known about the effects of POPs on their lipid metabolism. An optimal regulation of lipid metabolism is crucial for ringed seals during the fasting/molting season. This is a physiologically stressful period, during which they rely on the energy stored in their fat reserves. The mRNA expression levels for seven genes involved in lipid metabolism were analyzed in liver and/or blubber tissue from molting ringed seals from the polluted Baltic Sea and a less polluted reference location, Svalbard (Norway). mRNA expression of genes encoding peroxisome proliferator-activated receptors (PPAR) α and γ and their target genes acyl-coenzyme A oxidase 1 (ACOX1) and cluster of differentiation 36 (CD36) were analyzed in liver. mRNA expression level of genes encoding PPARβ, PPARγ and their target genes encoding fatty acid binding protein 4 (FABP4) and adiponectin (ADIPOQ) were measured in inner and middle blubber layers. In addition, we evaluated the influence of molting status on hepatic mRNA expression of genes encoding PPARs and their target genes in ringed seals from Svalbard. Our results show higher mRNA expression of genes encoding hepatic PPARγ and adipose PPARβ, FABP4, and ADIPOQ in the Baltic seals compared to the Svalbard seals. A positive relationship between mRNA expressions of genes encoding hepatic PPARγ, adipose FABP4, adipose ADIPOQ and ΣPOP concentrations was observed. These findings suggest that lipid metabolism may be affected by contaminant exposure in the Baltic population. mRNA expression of genes encoding PPARβ, PPARγ, FABP4 and ADIPOQ were similar between the mid and inner adipose layer. Hepatic mRNA expression of genes encoding PPARα and PPARγ was higher in the pre-molting individuals compared to the molting ones highlighting differential regulation of these metabolic sensors through the molting period.

Chronic exposure to PCBs (Aroclor 1254) exacerbates obesity-induced insulin resistance and hyperinsulinemia in mice

Evidence from recent epidemiological studies has emerged implicating exposure to environmental toxicants as a novel risk factor for the development of type 2 diabetes (T2D) and the metabolic syndrome in the general population. Humans and other organisms in high trophic levels of the food chain consume persistent organic pollutants (POP) through their diet. Few experimental studies demonstrating cause and effect are available and evidence for a direct association between accumulation of POP and T2D is preliminary; however, the possibility exists that lipophilic chemicals that accumulate in fatty tissue may disrupt cellular function and metabolic homeostasis. Chronic exposure of diabetes-prone C57B/6 mice to a polychlorinated biphenyl (PCB) mixture (Aroclor 1254, 36 mg/kg/wk, 20 wk) alone or in combination with high-fat diet impairs carbohydrate metabolism was compared to vehicle-treated control animals. Specifically, PBC exposure was found to produce hyperinsulinemia in both lean and diet-induced obese mice and exacerbated whole-body insulin resistance in obese mice. These changes in carbohydrate metabolism in response to Aroclor 1254 occurred without marked effect on body weight in both lean and obese mice. Our results demonstrate a causative association between PCB exposure and obesity-induced insulin resistance and hyperinsulinemia independent of body weight changes, an observation that contributes to a growing body of evidence suggesting that exposure to environmental pollutants represents a novel risk factor contributing to the diabetes epidemic.

N-acetylcysteine (NAC) diminishes the severity of PCB 126-induced fatty liver in male rodents

Potent aryl hydrocarbon receptor agonists like PCB 126 (3,3',4,4',5-pentachlorobiphenyl) cause oxidative stress and liver pathology, including fatty liver. Our question was whether dietary supplementation with N-acetylcysteine (NAC), an antioxidant, can prevent these adverse changes. Male Sprague-Dawley rats were fed a standard AIN-93G diet (sufficient in cysteine) or a modified diet supplemented with 1.0% NAC. After one week, rats on each diet were exposed to 0, 1, or 5μmol/kg body weight PCB 126 by i.p. injection (6 rats per group) and euthanized two weeks later. PCB-treatment caused a dose-dependent reduction in growth, feed consumption, relative thymus weight, total glutathione and glutathione disulfide (GSSG), while relative liver weight, glutathione transferase activity and hepatic lipid content were dose-dependently increased with PCB dose. Histologic examination of liver tissue showed PCB 126-induced hepatocellular steatosis with dose dependent increase in lipid deposition and distribution. Dietary NAC resulted in a reduction in hepatocellular lipid in both PCB groups. This effect was confirmed by gravimetric analysis of extracted lipids. Expression of CD36, a scavenger receptor involved in regulating hepatic fatty acid uptake, was reduced with high dose PCB treatment but unaltered in PCB-treated rats on NAC-supplemented diet. These results demonstrate that NAC has a protective effect against hepatic lipid accumulation in rats exposed to PCB 126. The mechanism of this protective effect appears to be independent of NAC as a source of cysteine/precursor of glutathione.

Chronic exposure to contaminated drinking water stimulates PPAR expression in mice livers

Mice were fed with source water (SW) and tap water (TW) for 90 d to evaluate hepatotoxicity induced by the drinking water. Histopathologic observation showed no obvious damage to hepatic tissue in the SW and TW groups. However, microarray analysis indicated that the SW and TW exposures affected many metabolic pathways, among which PPAR (peroxisome proliferator-activated receptors) signaling was most susceptible. Immunohistochemical staining demonstrated that both PPAR-α and PPAR-γ were significantly increased in the exposure groups compared to control. Enzyme-linked immunosorbent assay revealed that PPAR-α expression level was increased from 23.37±0.53 ng g(-1) liver weight in control group to 26.60±1.43 ng g(-1) liver weight in SW group and 27.68±1.10 ng g(-1) liver weight in TW group (p<0.05). For PPAR-γ, the expression level was also significantly enhanced from 0.83±0.07 ng g(-1) liver weight in control group to 1.11±0.20 ng g(-1) liver weight in SW group and 1.16±0.07 ng g(-1) liver weight in TW group (p<0.05). The SW and DW posed no obvious hepatotoxicity on mice and PPAR-α/-γ could be used as a novel biomarker to assess public health risk induced by slightly contaminated drinking water.

Nutrition can modulate the toxicity of environmental pollutants: implications in risk assessment and human health

BACKGROUND

The paradigm of human risk assessment includes many variables that must be viewed collectively in order to improve human health and prevent chronic disease. The pathology of chronic diseases is complex, however, and may be influenced by exposure to environmental pollutants, a sedentary lifestyle, and poor dietary habits. Much of the emerging evidence suggests that nutrition can modulate the toxicity of environmental pollutants, which may alter human risks associated with toxicant exposures.

OBJECTIVES

In this commentary, we discuss the basis for recommending that nutrition be considered a critical variable in disease outcomes associated with exposure to environmental pollutants, thus establishing the importance of incorporating nutrition within the context of cumulative risk assessment.

DISCUSSION

A convincing body of research indicates that nutrition is a modulator of vulnerability to environmental insults; thus, it is timely to consider nutrition as a vital component of human risk assessment. Nutrition may serve as either an agonist or an antagonist (e.g., high-fat foods or foods rich in antioxidants, respectively) of the health impacts associated with exposure to environmental pollutants. Dietary practices and food choices may help explain the large variability observed in human risk assessment.

CONCLUSION

We recommend that nutrition and dietary practices be incorporated into future environmental research and the development of risk assessment paradigms. Healthful nutrition interventions might be a powerful approach to reduce disease risks associated with many environmental toxic insults and should be considered a variable within the context of cumulative risk assessment and, where appropriate, a potential tool for subsequent risk reduction.

Cytochrome P450 isozyme protein verified in the skin of southern hemisphere humpback whales (Megaptera novaeangliae): implications for biochemical biomarker assessment

Large mysticete whales represent a unique challenge for chemical risk assessment. Few epidemiological investigations are possible due to the low incidence of adult stranding events. Similarly their often extreme life-history adaptations of prolonged migration and fasting challenge exposure assumptions. Molecular biomarkers offer the potential to complement information yielded through tissue chemical analysis, as well as providing evidence of a molecular response to chemical exposure. In this study we confirm the presence of cytochrome P450 reductase (CPR) and cytochrome P450 isoenzyme 1A1 (CYP1A1) in epidermal tissue of southern hemisphere humpback whales (Megaptera novaeangliae). The detection of CYP1A1 in the integument of the humpback whale affords the opportunity for further quantitative non-destructive investigations of enzyme activity as a function of chemical stress.

The role of caveolae in endothelial cell dysfunction with a focus on nutrition and environmental toxicants

Complications of vascular diseases, including atherosclerosis, are the number one cause of death in Western societies. Dysfunction of endothelial cells is a critical underlying cause of the pathology of atherosclerosis. Lipid rafts, and especially caveolae, are enriched in endothelial cells, and down-regulation of the caveolin-1 gene may provide protection against the development of atherosclerosis. There is substantial evidence that exposure to environmental pollution is linked to cardiovascular mortality, and that persistent organic pollutants can markedly contribute to endothelial cell dysfunction and an increase in vascular inflammation. Nutrition can modulate the toxicity of environmental pollutants, and evidence suggests that these affect health and disease outcome associated with chemical insults. Because caveolae can provide a regulatory platform for pro-inflammatory signalling associated with vascular diseases such as atherosclerosis, we suggest a link between atherogenic risk and functional changes of caveolae by environmental factors such as dietary lipids and organic pollutants. For example, we have evidence that endothelial caveolae play a role in uptake of persistent organic pollutants, an event associated with subsequent production of inflammatory mediators. Functional properties of caveolae can be modulated by nutrition, such as dietary lipids (e.g. fatty acids) and plant-derived polyphenols (e.g. flavonoids), which change activation of caveolae-associated signalling proteins. The following review will focus on caveolae providing a platform for pro-inflammatory signalling, and the role of caveolae in endothelial cell functional changes associated with environmental mediators such as nutrients and toxicants, which are known to modulate the pathology of vascular diseases.

Differential gene expression in liver and small intestine from lactating rats compared to age-matched virgin controls detects increased mRNA of cholesterol biosynthetic genes

Background

Lactation increases energy demands four- to five-fold, leading to a two- to three-fold increase in food consumption, requiring a proportional adjustment in the ability of the lactating dam to absorb nutrients and to synthesize critical biomolecules, such as cholesterol, to meet the dietary needs of both the offspring and the dam. The size and hydrophobicity of the bile acid pool increases during lactation, implying an increased absorption and disposition of lipids, sterols, nutrients, and xenobiotics. In order to investigate changes at the transcriptomics level, we utilized an exon array and calculated expression levels to investigate changes in gene expression in the liver, duodenum, jejunum, and ileum of lactating dams when compared against age-matched virgin controls.

Results

A two-way mixed models ANOVA was applied to detect differentially expressed genes. Significance calls were defined as a p < 0.05 for the overall physiologic state effect (lactation vs. control), and a within tissue pairwise comparison of p < 0.01. The proportion of false positives, an estimate of the ratio of false positives in the list of differentially expressed genes, was calculated for each tissue. The number of differentially expressed genes was 420 in the liver, 337 in the duodenum, 402 in the jejunum, and 523 in the ileum. The list of differentially expressed genes was in turn analyzed by Ingenuity Pathways Analysis (IPA) to detect biological pathways that were overrepresented. In all tissues, sterol regulatory element binding protein (Srebp)-regulated genes involved in cholesterol synthesis showed increased mRNA expression, with the fewest changes detected in the jejunum. We detected increased Scap mRNA in the liver only, suggesting an explanation for the difference in response to lactation between the liver and small intestine. Expression of Cyp7a1, which catalyzes the rate limiting step in the bile acid biosynthetic pathway, was also significantly increased in liver. In addition, decreased levels of mRNA associated with T-cell signaling were found in the jejunum and ileum. Several members of the Solute Carrier (SLC) and Adenosine Triphosphate Binding Cassette (ABC) superfamilies of membrane transporters were found to be differentially expressed; these genes may play a role in differences in nutrient and xenobiotic absorption and disposition. mRNA expression of SLC39a4_predicted, a zinc transporter, was increased in all tissues, suggesting that it is involved in increased zinc uptake during lactation. Microarray data are available through GEO under GSE19175.

Conclusions

We detected differential expression of mRNA from several pathways in lactating dams, including upregulation of the cholesterol biosynthetic pathway in liver and intestine, consistent with Srebp activation. Differential T-Cell signaling in the two most distal regions of the small intestine (ileum and jejunum) was also noted, as well as differential expression of transporters that likely play a key role in nutrient uptake.