Zinc deficiency induces vascular pro-inflammatory parameters associated with NF-kappaB and PPAR signaling.

OBJECTIVES: Marginal intake of dietary zinc can be associated with increased risk of cardiovascular diseases. In the current study we hypothesized that vascular dysfunction and associated inflammatory events are activated during a zinc deficient state. DESIGN: We tested this hypothesis using both vascular endothelial cells and mice lacking the functional LDL-receptor gene. RESULTS: Zinc deficiency increased oxidative stress and NF-kappaB DNA binding activity, and induced COX-2 and E-selectin gene expression, as well as monocyte adhesion in cultured endothelial cells. The NF-kappaB inhibitor CAPE significantly reduced the zinc deficiency-induced COX-2 expression, suggesting regulation through NF-kappaB signaling. PPAR can inhibit NF-kappaB signaling, and our previous data have shown that PPAR transactivation activity requires adequate zinc. Zinc deficiency down-regulated PPARalpha expression in cultured endothelial cells. Furthermore, the PPARgamma agonist rosiglitazone was unable to inhibit the adhesion of monocytes to endothelial cells during zinc deficiency, an event which could be reversed by zinc supplementation. Our in vivo data support the importance of PPAR dysregulation during zinc deficiency. For example, rosiglitazone induced inflammatory genes (e.g., MCP-1) only during zinc deficiency, and adequate zinc was required for rosiglitazone to down-regulate pro-inflammatory markers such as iNOS. In addition, rosiglitazone increased IkappaBalpha protein expression only in zinc adequate mice. Finally, plasma data from LDL-R-deficient mice suggest an overall pro-inflammatory environment during zinc deficiency and support the concept that zinc is required for proper anti-inflammatory or protective functions of PPAR. CONCLUSIONS: These studies suggest that zinc nutrition can markedly modulate mechanisms of the pathology of inflammatory diseases such as atherosclerosis.

Benzo[a]pyrene induces intercellular adhesion molecule-1 through a caveolae and aryl hydrocarbon receptor mediated pathway.

Toxicologic and epidemiologic studies have linked benzo[a]pyrene (B[a]P) exposure with cardiovascular diseases such as atherosclerosis. The mechanisms of action leading to these diseases have not been fully understood. One key step in the development of atherosclerosis is vascular endothelial dysfunction, which is characterized by increased adhesiveness. To determine if B[a]P could lead to increased endothelial adhesiveness, the effects of B[a]P on human endothelial cell intercellular adhesion molecule-1 (ICAM-1) expression was investigated. B[a]P was able to increase ICAM-1 protein only after pretreatment with the aryl hydrocarbon receptor (AhR) agonist beta-naphthoflavone (beta-NF). Knockdown of AhR by siRNA or treatment with AhR antagonist alpha-naphthoflavone (alpha-NF) eliminated the induction of ICAM-1 from B[a]P, confirming the necessity of AhR in this process. Likewise, B[a]P only increased monocyte adhesion to the vascular endothelium when cells were pretreated with beta-NF. Experiments were done to define a signaling mechanism. B[a]P increased phosphorylation of MEK and p38-MAPK, and inhibitors to these proteins blunted the ICAM-1 induction. B[a]P was also able to increase AP-1 DNA binding and phosphorylation of cJun. Phosphorylation of cJun was disrupted by MEK and p38-MAPK inhibitors linking the signaling cascade. Finally, the importance of membrane microdomains, caveolae, was demonstrated by knockdown of the structural protein caveolin-1. Disruption of caveolae eliminated the B[a]P-induced ICAM-1 expression. These data suggest a possible pro-inflammatory mechanism of action of B[a]P involving caveolae, leading to increased vascular endothelial adhesiveness, and this inflammation may be a critical step in the development of B[a]P-induced atherosclerosis.

Alumina nanoparticles induce expression of endothelial cell adhesion molecules.

Nanotechnology is a rapidly growing industry that has elicited much concern because of the lack of available toxicity data. Exposure to ultrafine particles may be a risk for the development of vascular diseases due to dysfunction of the vascular endothelium. Increased endothelial adhesiveness is a critical first step in the development of vascular diseases, such as atherosclerosis. The hypothesis that alumina nanoparticles increase inflammatory markers of the endothelium, measured by the induction of adhesion molecules as well as the adhesion of monocytes to the endothelial monolayer, was tested. Following characterization of alumina nanoparticles by transmission electron microscopy (TEM), electron diffraction, and particle size distribution analysis, endothelial cells were exposed to alumina at various concentrations and times. Both porcine pulmonary artery endothelial cells and human umbilical vein endothelial cells showed increased mRNA and protein expression of VCAM-1, ICAM-1, and ELAM-1. Furthermore, human endothelial cells treated with alumina particles showed increased adhesion of activated monocytes. The alumina particles tended to agglomerate at physiological pH in serum-containing media, which led to a range of particle sizes from nano to micron size during treatment conditions. These data show that alumina nanoparticles can elicit a proinflammatory response and thus present a cardiovascular disease risk.

Renin inhibition reduces hypercholesterolemia-induced atherosclerosis in mice.

The role of the renin angiotensin system (RAS) in atherosclerosis is complex because of the involvement of multiple peptides and receptors. Renin is the rate-limiting enzyme in the production of all angiotensin peptides. To determine the effects of renin inhibition on atherosclerosis, we administered the novel renin inhibitor aliskiren over a broad dose range to fat-fed LDL receptor-deficient (Ldlr(-/-)) mice. Renin inhibition resulted in striking reductions of atherosclerotic lesion size in both the aortic arch and the root. Subsequent studies demonstrated that cultured macrophages expressed all components of the RAS. To determine the role of macrophage-derived angiotensin in the development of atherosclerosis, we transplanted renin-deficient bone marrow to irradiated Ldlr(-/-) mice and observed a profound decrease in the size of atherosclerotic lesions. In similar experiments, transplantation of bone marrow deficient for angiotensin II type 1a receptors failed to influence lesion development. We conclude that renin-dependent angiotensin production in macrophages does not act in an autocrine/paracrine manner. Furthermore, in vitro studies demonstrated that coculture with renin-expressing macrophages augmented monocyte adhesion to endothelial cells. Therefore, although previous work suggests that angiotensin peptides have conflicting effects on atherogenesis, we found that renin inhibition profoundly decreased lesion development in mice.

Impact of nutrition on PCB toxicity.

Studies are evolving which suggest that nutritional intervention can modify pathologies of diseases associated with environmental toxic insults. The diet is a major route of exposure to environmental toxins, such as persistent organic pollutants and heavy metals. Many persistent organics, such as polychlorinated biphenyls (PCBs), bioaccumulate in our bodies and "bioremediation" is extremely difficult. Furthermore, many environmental toxins induce signaling pathways that are oxidative stress-sensitive and similar or the same as the ones associated with the etiology and early pathology of many chronic diseases. There is now increasing evidence that exposure to PCBs can contribute to the development of inflammatory diseases such as atherosclerosis. Activation, chronic inflammation, and dysfunction of the vascular endothelium are critical events in the initiation and acceleration of atherosclerotic lesion formation. Our studies indicate that an increase in cellular oxidative stress and an imbalance in antioxidant status are critical events in PCB-mediated induction of inflammatory genes and endothelial cell dysfunction. We also have evidence that the plasma membrane microdomains called caveolae play an important role in endothelial activation and toxicity mediated by coplanar PCBs. Caveolae are particularly abundant in endothelial cells and play a major role in endothelial trafficking and the regulation of signaling pathways associated with the pathology of vascular diseases. There is a great need to further explore this nutritional paradigm in environmental toxicology and to improve our understanding of the relationship between nutrition and lifestyle, exposure to environmental toxins and disease. Our studies suggest that certain dietary fats can increase the risk of environmental insult induced by PCBs, while other dietary factors may provide protection. Nutrition may provide the most sensible means to develop primary intervention and prevention strategies of diseases associated with many environmental toxic insults.

Environmental toxicity, nutrition, and gene interactions in the development of atherosclerosis.

There is substantial evidence from epidemiological studies that the pathology of cardiovascular diseases is linked in part to environmental pollution. Many environmental contaminants, and especially persistent organic pollutants, are risk factors for atherosclerosis because they may exacerbate an underlying disease by altering gene expression patterns. Many mechanisms and signaling pathways associated with the pathology of "modern" diseases are similarly modulated by poor dietary habits and environmental pollutants. Many genes induced in diseases associated with vascular dysfunction such as atherosclerosis are oxidative stress-sensitive, suggesting that an imbalance in cellular oxidative stress and antioxidant status is a critical underlying factor. One of the emerging issues in modern toxicological sciences is the modification of environmental toxicity by nutrients. Evidence is emerging which suggests that antioxidant nutrients and related bioactive compounds common in fruits and vegetables protect against environmental toxic insult to the vascular endothelium by down-regulation of signaling pathways involved in inflammatory responses associated with vascular diseases such as atherosclerosis. Thus, the concept that nutrition may modify or ameliorate the toxicity of environmental chemicals may have implications for understanding the complex interaction of environmental toxicity and disease development.

Modification of environmental toxicity by nutrients: implications in atherosclerosis.

We hypothesize that nutrition can modulate the toxicity of environmental pollutants and thus modulate health and disease outcome associated with chemical insult. There is now increasing evidence that exposure to persistent organic pollutants, such as PCBs, can contribute to the development of inflammatory diseases such as atherosclerosis. Activation, chronic inflammation, and dysfunction of the vascular endothelium are critical events in the initiation and acceleration of atherosclerotic lesion formation. Our studies indicate that an increase in cellular oxidative stress and an imbalance in antioxidant status are critical events in PCB-mediated induction of inflammatory genes and endothelial cell dysfunction. Furthermore, we have found that specific dietary fats can further compromise endothelial dysfunction induced by selected PCBs and that antioxidant nutrients (such as vitamin E and dietary flavonoids) can protect against endothelial cell damage mediated by these persistent organic pollutants. Our recent data suggest that membrane lipid rafts such as caveolae may play a major role in the regulation of PCB-induced inflammatory signaling in endothelial cells. In addition, PCB- and lipid-induced inflammation can be down-regulated by ligands of anti-atherogenic peroxisome proliferator-activated receptors (PPARs). We hypothesize that PCBs contribute to an endothelial inflammatory response in part by down-regulating PPAR signaling. Our data so far support our hypothesis that antioxidant nutrients and related bioactive compounds common in fruits and vegetables protect against environmental toxic insult to the vascular endothelium by down-regulation of signaling pathways involved in inflammatory responses and atherosclerosis. Even though the concept that nutrition may modify or ameliorate the toxicity of environmental chemicals is provocative and warrants further study, the implications for human health could be significant. More research is needed to understand observed interactions of PCB toxicity with nutritional interventions.