Heather Clair

Endothelial Progenitor Cells and Vascular Dysfunction in Children with Obstructive Sleep Apnea

RATIONALE Endothelial dysfunction is a potential complication of obstructive sleep apnea syndrome (OSAS) in children ascribed to systemic inflammatory changes. However, not all children with OSAS will manifest endothelial dysfunction. OBJECTIVES The variability in endothelial function in pediatric OSAS may be related to the ability to recruit repair mechanisms such as endothelial progenitor cells (EPCs). METHODS Prepubertal nonhypertensive children with or without polysomonographically confirmed OSAS had endothelial function assessed in a morning fasted state using a modified hyperemic test involving cuff-induced occlusion of the radial and ulnar arteries. Blood was drawn and EPCs were assessed by flow cytometry and triple staining using antibodies against CD133, CD34, and vascular endothelial growth factor receptor-2 after isolation of peripheral blood mononuclear cells. SDF-1 levels were measured by ELISA. MEASUREMENTS AND MAIN RESULTS Eighty children with OSAS (mean age 8.2 +/- 1.4 yr, mean body mass index [BMI] z-score, 1.43 +/- 0.3) and 20 controls (CO) matched for BMI, age, sex, and ethnicity were studied. Significant delays to peak capillary reperfusion after occlusion release (Tmax) occurred in OSAS children, but substantial variability was present. Despite similar OSAS severity, EPC counts, and stromal cell-derived factor-1 (SDF-1) levels were significantly lower among the 20 OSAS children with the longest Tmax, when compared with either the 20 children with normal Tmax values or to CO ( P < 0.01). Furthermore, Tmax was significantly and inversely correlated with EPCs (r(2), 0.51; P < 0.01), but neither EPCs nor Tmax were associated with apnea-hyponea index (AHI). CONCLUSIONS Endothelial dysfunction is frequently present in OSAS. Variance in endothelial functional phenotype may not only reside in the individual susceptibility but also in the ability to recruit endothelial repair mechanisms.

Increased Cellular Proliferation and Inflammatory Cytokines in Tonsils Derived From Children With Obstructive Sleep Apnea

Adenotonsillar hypertrophy is the major pathophysiological mechanism underlying obstructive sleep apnea (OSA) and recurrent tonsillitis (RI) in children. The increased expression of various mediators of the inflammatory response in tonsils of patients with OSA prompted our hypothesis that the enhanced local and systemic inflammation in children with OSA would promote tonsillar proliferation. Mixed cell cultures from tonsils recovered during adenotonsillectomy in children with OSA and RI were established, and proliferative rates were assessed. Cells were also cultured to determine the levels of proinflammatory cytokines and antioxidant protein levels and mRNA expression. Global cell proliferative rates from OSA tonsils were significantly higher than RI (p < 0.01), with CD3+, CD4+, and CD8+ cell proliferation being higher in OSA (p < 0.05). Moreover, proinflammatory cytokines, such as TNF-α, IL-6, and IL-1α, were highly expressed in OSA-derived tonsils. Furthermore, thioredoxin (TRX), an antioxidant protein, was also highly expressed in OSA tonsils at the mRNA and protein levels (p < 0.01). Thus, T cells are in a highly proliferative state in the tonsils of children with OSA and are associated with increased production of proinflammatory cytokines and TRX, when compared with children with RI.

Hypoxia differentially regulates the expression of neuroglobin and cytoglobin in rat brain

Neuroglobin (Ngb) and Cytoglobin (Cygb) are new members of the globin family and display heterotopic expression patterns. To examine the effect of different hypoxia profiles on expression of Ngb and Cygb in rodent brain, rats were exposed to either sustained hypoxia (SH; 10% O(2)) or intermittent hypoxia (IH; 10% and 21% O(2) alternating every 90 s) for 1, 3, 7 and 14 days, and mRNA and protein expression of Ngb and Cygb were assessed in brain cortex. SH increased Ngb mRNA and protein expression throughout the exposure, while IH only elicited slight increases in Ngb expression at day 1. Neither SH nor IH elicited increases in Cygb expression. Thus, hypoxic stimulus presentation is a major determinant of the regulation of hypoxic sensitive genes such as Ngb. Furthermore, disparities between Ngb and Cygb responses to hypoxia further suggest that these two globins may play divergent roles in brain.

Toxicant-associated Steatohepatitis

Hepatotoxicity is the most common organ injury due to occupational and environmental exposures to industrial chemicals. A wide range of liver pathologies ranging from necrosis to cancer have been observed following chemical exposures both in humans and in animal models. Toxicant-associated fatty liver disease (TAFLD) is a recently named form of liver injury pathologically similar to alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD). Toxicant-associated steatohepatitis (TASH) is a more severe form of TAFLD characterized by hepatic steatosis, inflammatory infiltrate, and in some cases, fibrosis. While subjects with TASH have exposures to industrial chemicals, such as vinyl chloride, they do not have traditional risk factors for fatty liver such as significant alcohol consumption or obesity. Conventional biomarkers of hepatotoxicity including serum alanine aminotransferase activity may be normal in TASH, making screening problematic. This article examines selected chemical exposures associated with TAFLD in human subjects or animal models and concisely reviews the closely related NAFLD and ALD.

Nuclear receptors and nonalcoholic fatty liver disease

Nuclear receptors are transcription factors which sense changing environmental or hormonal signals and effect transcriptional changes to regulate core life functions including growth, development, and reproduction. To support this function, following ligand-activation by xenobiotics, members of subfamily 1 nuclear receptors (NR1s) may heterodimerize with the retinoid X receptor (RXR) to regulate transcription of genes involved in energy and xenobiotic metabolism and inflammation. Several of these receptors including the peroxisome proliferator-activated receptors (PPARs), the pregnane and xenobiotic receptor (PXR), the constitutive androstane receptor (CAR), the liver X receptor (LXR) and the farnesoid X receptor (FXR) are key regulators of the gut:liver:adipose axis and serve to coordinate metabolic responses across organ systems between the fed and fasting states. Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease and may progress to cirrhosis and even hepatocellular carcinoma. NAFLD is associated with inappropriate nuclear receptor function and perturbations along the gut:liver:adipose axis including obesity, increased intestinal permeability with systemic inflammation, abnormal hepatic lipid metabolism, and insulin resistance. Environmental chemicals may compound the problem by directly interacting with nuclear receptors leading to metabolic confusion and the inability to differentiate fed from fasting conditions. This review focuses on the impact of nuclear receptors in the pathogenesis and treatment of NAFLD. Clinical trials including PIVENS and FLINT demonstrate that nuclear receptor targeted therapies may lead to the paradoxical dissociation of steatosis, inflammation, fibrosis, insulin resistance, dyslipidemia and obesity. Novel strategies currently under development (including tissue-specific ligands and dual receptor agonists) may be required to separate the beneficial effects of nuclear receptor activation from unwanted metabolic side effects. The impact of nuclear receptor crosstalk in NAFLD is likely to be profound, but requires further elucidation. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Identification of Environmental Chemicals Associated with the Development of Toxicant-associated Fatty Liver Disease in Rodents

Background: Toxicant-associated fatty liver disease (TAFLD) is a recently identified form of nonalcoholic fatty liver disease (NAFLD) associated with exposure to industrial chemicals and environmental pollutants. Numerous studies have been conducted to test the association between industrial chemicals/environmental pollutants and fatty liver disease both in vivo and in vitro. Objectives: The objective of the article is to report a list of chemicals associated with TAFLD. Methods: Two federal databases of rodent toxicology studies—Toxicological Reference Database (ToxRefDB; Environmental Protection Agency) and Chemical Effects in Biological Systems (CEBS, National Toxicology Program)—were searched for liver end points. Combined, these 2 databases archive nearly 2,000 rodent studies. Toxicant-associated steatohepatitis (TASH) descriptors including fatty change, fatty necrosis, Oil red O-positive staining, steatosis, and lipid deposition were queried. Results: Using these search terms, 123 chemicals associated with fatty liver were identified. Pesticides and solvents were the most frequently identified chemicals, while polychlorinated biphenyls (PCBs)/dioxins were the most potent. About 44% of identified compounds were pesticides or their intermediates, and >10% of pesticide registration studies in ToxRefDB were associated with fatty liver. Fungicides and herbicides were more frequently associated with fatty liver than insecticides. Conclusion: More research on pesticides, solvents, metals, and PCBs/dioxins in NAFLD/TAFLD is warranted due to their association with liver damage.

Transcriptional landscape of bone marrow-derived very small embryonic-like stem cells during hypoxia

BackgroundHypoxia is a ubiquitous feature of many lung diseases and elicits cell-specific responses. While the effects of hypoxia on stem cells have been examined under in vitro conditions, the consequences of in vivo oxygen deprivation have not been studied.MethodsWe investigated the effects of in vivo hypoxia on a recently characterized population of pluripotent stem cells known as very small embryonic-like stem cells (VSELs) by whole-genome expression profiling and measuring peripheral blood stem cell chemokine levels.ResultsWe found that exposure to hypoxia in mice mobilized VSELs from the bone marrow to peripheral blood, and induced a distinct genome-wide transcriptional signature. Applying a computationally-intensive methodology, we identified a hypoxia-induced gene interaction network that was functionally enriched in a diverse array of programs including organ-specific development, stress response, and wound repair. Topographic analysis of the network highlighted a number of densely connected hubs that may represent key controllers of stem cell response during hypoxia and, therefore, serve as putative targets for altering the pathophysiologic consequences of hypoxic burden.ConclusionsA brief exposure to hypoxia recruits pluripotent stem cells to the peripheral circulation and actives diverse transcriptional programs that are orchestrated by a selective number of key genes.

Polychlorinated biphenyls disrupt hepatic epidermal growth factor receptor signaling

Abstract 1. Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that disrupt hepatic xenobiotic and intermediary metabolism, leading to metabolic syndrome and nonalcoholic steatohepatitis (NASH). 2. Since phenobarbital indirectly activates Constitutive Androstane Receptor (CAR) by antagonizing growth factor binding to the epidermal growth factor receptor (EGFR), we hypothesized that PCBs may also diminish EGFR signaling. 3. The effects of the PCB mixture Aroclor 1260 on the protein phosphorylation cascade triggered by EGFR activation were determined in murine (in vitro and in vivo) and human models (in vitro). EGFR tyrosine residue phosphorylation was decreased by PCBs in all models tested. 4. The IC50 values for Aroclor 1260 concentrations that decreased Y1173 phosphorylation of EGFR were similar in murine AML-12 and human HepG2 cells (∼2–4 μg/mL). Both dioxin and non-dioxin-like PCB congeners decreased EGFR phosphorylation in cell culture. 5. PCB treatment reduced phosphorylation of downstream EGFR effectors including Akt and mTOR, as well as other phosphoprotein targets including STAT3 and c-RAF in vivo. 6. PCBs diminish EGFR signaling in human and murine hepatocyte models and may dysregulate critical phosphoprotein regulators of energy metabolism and nutrition, providing a new mechanism of action in environmental diseases.

Liver Disease in a Residential Cohort With Elevated Polychlorinated Biphenyl Exposures

Endocrine and metabolism disrupting chemicals (EDCs/MDCs) have been associated with environmental liver diseases including toxicant-associated steatohepatitis (TASH). TASH has previously been characterized by hepatocellular necrosis, disrupted intermediary metabolism, and liver inflammation. Polychlorinated biphenyls (PCBs) are environmental EDCs/MDCs associated with the genesis and progression of steatohepatitis in animal models and human liver injury in epidemiology studies. The cross-sectional Anniston Community Health Survey (ACHS) investigates ortho-substituted PCB exposures and health effects near a former PCB manufacturing complex. The rates of obesity, diabetes, and dyslipidemia were previously determined to be high in ACHS. In this study, 738 ACHS participants were categorized by liver disease status using the serum cytokeratin 18 biomarker. Associations between PCB exposures and mechanistic biomarkers of intermediary metabolism, inflammation, and hepatocyte death were determined. The liver disease prevalence was high (60.2%), and 80.7% of these individuals were categorized as having TASH. Sex and race/ethnicity differences were noted. TASH was associated with increased exposures to specific PCB congeners, insulin resistance, dyslipidemia, proinflammatory cytokines, and liver necrosis. These findings are consistent with PCB-related steatohepatitis. ΣPCBs was inversely associated with insulin resistance/production, leptin, and hepatocyte apoptosis, while other adipocytokines were increased. This is possibly the largest environmental liver disease study applying mechanistic biomarkers ever performed and the most comprehensive analysis of PCBs and adipocytokines. It provides insight into the mechanisms of PCB-related endocrine and metabolic disruption in liver disease and diabetes. In the future, associations between additional exposures and liver disease biomarkers will be evaluated in the ACHS and follow-up ACHS-II studies.