The Glutathione Synthesis Gene <i>Gclm</i> Modulates Amphiphilic Polymer-Coated CdSe/ZnS Quantum Dot–Induced Lung Inflammation in Mice

<div><p>Quantum dots (QDs) are unique semi-conductor fluorescent nanoparticles with potential uses in a variety of biomedical applications. However, concerns exist regarding their potential toxicity, specifically their capacity to induce oxidative stress and inflammation. In this study we synthesized CdSe/ZnS core/shell QDs with a tri-n-octylphosphine oxide, poly(maleic anhydride-alt-1-tetradecene) (TOPO-PMAT) coating and assessed their effects on lung inflammation in mice. Previously published <i>in vitro</i> data demonstrated these TOPO-PMAT QDs cause oxidative stress resulting in increased expression of antioxidant proteins, including heme oxygenase, and the glutathione (GSH) synthesis enzyme glutamate cysteine ligase (GCL). We therefore investigated the effects of these QDs <i>in vivo</i> in mice deficient in GSH synthesis (<i>Gclm</i> +/− and <i>Gclm</i> −/− mice). When mice were exposed via nasal instillation to a TOPO-PMAT QD dose of 6 µg cadmium (Cd) equivalents/kg body weight, neutrophil counts in bronchoalveolar lavage fluid (BALF) increased in both <i>Gclm</i> wild-type (+/+) and <i>Gclm</i> heterozygous (+/−) mice, whereas <i>Gclm</i> null (−/−) mice exhibited no such increase. Levels of the pro-inflammatory cytokines KC and TNFα increased in BALF from <i>Gclm</i> +/+ and +/− mice, but not from <i>Gclm</i> −/− mice. Analysis of lung Cd levels suggested that QDs were cleared more readily from the lungs of <i>Gclm</i> −/− mice. There was no change in matrix metalloproteinase (MMP) activity in any of the mice. However, there was a decrease in whole lung myeloperoxidase (MPO) content in <i>Gclm</i> −/− mice, regardless of treatment, relative to untreated <i>Gclm</i> +/+ mice. We conclude that in mice TOPO-PMAT QDs have <i>in vivo</i> pro-inflammatory properties, and the inflammatory response is dependent on GSH synthesis status. Because there is a common polymorphism in humans that influences GCLM expression, these findings imply that humans with reduced GSH synthesis capabilities may be more susceptible to the pro-inflammatory effects of QDs.</p></div

mRNA expression of stress-response genes as measured by qRT-PCR.

<p>The effects of saline and TOPO-PMAT QD administration on A) <i>Gclc</i>, B) <i>Gclm</i>, C) <i>Hmox1</i>, D) <i>Mt1</i> and E) <i>Mt2</i> mRNA expression are shown. Data represent the mean ± S.E.M., * = p<0.05 relative to saline treated <i>Gclm</i> +/− mice. The number of replicates is indicated in each bar.</p

mRNA expression of inflammatory cytokine genes as measured by qRT-PCR.

<p>The effects of saline or TOPO-PMAT QD administration on A) <i>Il1β</i>, B) <i>Mcp1</i>, C) <i>Tnfα</i>, D) <i>Gmcsf</i> and E) <i>KC</i> mRNA expression are shown. Data represent the mean ± S.E.M. of the indicated number of replicates in each bar.</p