The chemical fate of the Cd/Se/Te-based quantum dot 705 in the biological system: toxicity implications

Abstract

QD705 is a cadmium/selenium/tellurium (Cd/Se/Te)-based quantum dot with good potential for biomedical applications. Although the biological fate of QD705 is established, its chemical fate in the biological system is still unknown. Since the chemical nature of Cd in QD705 (either stays as bounded Cd or becomes free Cd) is closely related to the toxicity of this nanocrystal, information on its chemical fate is critically needed. In this study we investigated the chemical fate of QD705 in the kidneys of mice. We used the molar ratio of Cd and Te (increased Cd/Te ratio signifies increased Cd release from QD705) and the induction of tissue metallothionein (MT) as markers for elevated free Cd in tissues. Our study indicated that 100% of QD705 (measured as Cd) was still retained in the body 16 weeks after exposure, with significant time redistribution to the kidneys. Furthermore, there were an elevation in both the molar Cd/Te ratio and MT-1 expression in the kidneys, suggesting that free Cd was released from QD705. Thus QD705 is not as stable or biologically inert as many may have once believed. Our study demonstrated that free Cd indeed can be released from QD705 in the kidneys and increases the risk of renal toxicity.

Transport of Nanoparticles through the Placental Barrier

“…This ambiguity undermines the reliability of the ICP-AES method for the assessment of NP concentration in vivo. CdTe QD degradation in vivo and toxicity due to Cd 2+ leakage are possible and the fact was reported earlier Lin et al 2009). Consequently, lower Cd accumulation after coating the nanoparticles can be explained in two ways: a) the coating stabilizes the CdTe core and minimizes Cd 2+ release; b) the coating increases the overall NP size, which results in reduced penetration through placental barrier.…”

Clinical significance of metallothioneins in cell therapy and nanomedicine

“…Thus, QD-705 is not stable or biologically inert as free Cd released from QD-705 may increase the risk of nephrotoxicity because MTs bind these metal NPs and are specifically induced to prevent nephrotoxicity. 54 …”

Time-dependent toxicity of cadmium telluride quantum dots on liver and kidneys in mice: histopathological changes with elevated free cadmium ions and hydroxyl radicals

“…[23][24][25] When QDs degrade (ie, surface atoms are lost and QDs decrease in size), blue shifts in the fluorescence-excitation spectra and decreases in the quantum yield are observed. 31 However, using fluorescence intensity to quantify QDs in tissues has been deemed to be problematic, due to the high and variable background fluorescence that results from the tissues.…”

“…32 Furthermore, Lin et al reported that only free Cd 2+ dissociated from QDs, not QDs themselves, could induce MT production in tissues. 25 Therefore, an elevation in MT expression can be used as a good biological index of QD degradation in vivo. To reduce the effects of other metals on MT expression, CdTe QDs were selected in the present study rather than core-shell-structured CdTe/ZnS QDs.…”

“…These results confirmed that QDs were indeed degraded in vivo. 23,25 ROS can damage important biomolecules and subsequently inflict harmful effects on an organism. The three major types of ROS are ⋅O 2 -, H 2 O 2 , and ⋅OH, a highly reactive species that can modify purine and pyrimidine bases and cause strand breaks that result in DNA damage.…”