Migration of intradermally injected quantum dots to sentinel organs in mice

Abstract

Topical exposure to nanoscale materials is likely from a variety of sources including sunscreens and cosmetics. Because the in vivo disposition of nanoscale materials is not well understood, we have evaluated the distribution of quantum dots (QDs) following intradermal injection into female SKH-1 hairless mice as a model system for determining tissue localization following intradermal infiltration. The QD (CdSe core, CdS capped, poly[ethylene glycol] coated, 37 nm diameter, 621 nm fluorescence emission) were injected intradermally (ID) on the right dorsal flank. Within minutes following intradermal injection, the highly UV fluorescent QD could be observed moving from the injection sites apparently through the lymphatic duct system to regional lymph nodes. Residual fluorescent QD remained at the site of injection until necropsy at 24 h. Quantification of cadmium and selenium levels after 0, 4, 8, 12, or 24 h in multiple tissues, using inductively coupled plasma mass spectrometry (ICP-MS), showed a time-dependent loss of cadmium from the injection site, and accumulation in the liver, regional draining lymph nodes, kidney, spleen, and hepatic lymph node. Fluorescence microscopy corroborated the ICP-MS results regarding the tissue distribution of QD. The results indicated that (1) ID injected nanoscale QD remained as a deposit in skin and penetrated the surrounding viable subcutis, (2) QD were distributed to draining lymph nodes through the sc lymphatics and to the liver and other organs, and (3) sentinel organs are effective locations for monitoring transdermal penetration of nanoscale materials into animals.

FIGURE 1

Characterization of QD using TEM. The QD were characterized using TEM and the average QD CdSe core size was nail shaped with an 8.4 ± 1.92 nm length and 5.8 ± 0.97 nm width, resulting in an aspect ratio of 1.45.

FIGURE 2

Panels A,B: Female SKH-1 hairless mice were injected with 5 μL saline (A) or 5 μL of QD solution (B) and digital images were taken following ultraviolet-A illumination. The tracking of red fluorescent QD into the lymphatics is shown in the lower panel (arrow). Panels C–H: Twenty-four hours after injection, the mice were sacrificed, and the tissues were removed, preserved in formalin, and sectioned for microscopic examination. Bright field (panels C, E, G) and fluorescence (panels D, F, H) images were taken of intradermal injection site skin (panels C, D; bar = 200 μm), right axillary lymph node (panels E, F; bar = 500 μm), and right brachial lymph node (panels G,H; bar = 500 μm). The red fluorescent QD are visible in sections of the lymph nodes.

FIGURE 3

The percent of the initial dose of cadmium that remained at the site of injection of the CdSe QD. The skin that contained the site of injection was removed, completely digested using HNO3, and the total cadmium was detected using ICP-MS (mean ± standard error). Values indicated by an asterisk (*) were significantly different (p 0.05) than the value at 0 hr, while values indicated with the cross (^†) were not significantly different from each other (p>0.05).

FIGURE 4

Distribution of cadmium in organs following intradermal injection of CdSe QD. The data are expressed as mean ± standard error for: liver (solid circle); regional lymph nodes (open circle); kidney (open diamond). Values indicated by an asterisk (*) were significantly different (p<0.05) than the value in the same organ at 0 hr.

FIGURE 5

Distribution of cadmium in organs following intradermal injection of CdSe QD. The data are expressed as mean ± standard error for: hepatic lymph node (solid circle); spleen (open circle); heart (open diamond). Values indicated by an asterisk (*) were significantly different (p<0.05) than the value in the same organ at 0 hr.