Abstract
BackgroundWe posit that the same mononuclear phagocytes (MP) that serve as target cells and vehicles for a host of microbial infections can be used to improve diagnostics and drug delivery. We also theorize that physical and biological processes such as particle shape, size, coating and opsonization that affect MP clearance of debris and microbes can be harnessed to facilitate uptake of nanoparticles (NP) and tissue delivery.MethodsMonocytes and monocyte-derived macrophages (MDM) were used as vehicles of superparamagnetic iron oxide (SPIO) NP and immunoglobulin (IgG) or albumin coated SPIO for studies of uptake and distribution. IgG coated SPIO was synthesized by covalent linkage and uptake into monocytes and MDM investigated related to size, time, temperature, concentration, and coatings. SPIO and IgG SPIO were infused intravenously into naïve mice. T2 measures using magnetic resonance imaging (MRI) were used to monitor tissue distribution in animals.ResultsOxidation of dextran on the SPIO surface generated reactive aldehyde groups and permitted covalent linkage to amino groups of murine and human IgG and F(ab')2 fragments and for Alexa Fluor® 488 hydroxylamine to form a Schiff base. This labile intermediate was immediately reduced with sodium cyanoborohydride in order to stabilize the NP conjugate. Optical density measurements of the oxidized IgG, F(ab')2, and/or Alexa Fluor® 488 SPIO demonstrated ∼50% coupling yield. IgG-SPIO was found stable at 4°C for a period of 1 month during which size and polydispersity index varied little from 175 nm and 200 nm, respectively. In vitro, NP accumulated readily within monocyte and MDM cytoplasm after IgG-SPIO exposure; whereas, the uptake of native SPIO in monocytes and MDM was 10-fold less. No changes in cell viability were noted for the SPIO-containing monocytes and MDM. Cell morphology was not changed as observed by transmission electron microscopy. Compared to unconjugated SPIO, intravenous injection of IgG-SPIO afforded enhanced and sustained lymphoid tissue distribution over 24 hours as demonstrated by MRI.ConclusionsFacilitated uptake of coated SPIO in monocytes and MDM was achieved. Uptake was linked to particle size and was time and concentration dependent. The ability of SPIO to be rapidly taken up and distributed into lymphoid tissues also demonstrates feasibility of macrophage-targeted nanoformulations for diagnostic and drug therapy.
Highlights
The ability of monocytes to migrate to the sites of inflammation, infection, and tissue degeneration makes them attractive vehicles to deliver contrast agents for diagnosis or drugs as therapeutic modalities [1]
bicinchoninic acid (BCA) reagent was added to each collected fraction and the optical density (OD) was measured at 540 nm
superparamagnetic iron oxide (SPIO) reacted with IgG yielded higher BCA reactivity compared to control SPIO due to the presence of increased protein moieties, while the proportion of free IgG in the second peak was lower
Summary
The ability of monocytes to migrate to the sites of inflammation, infection, and tissue degeneration makes them attractive vehicles to deliver contrast agents for diagnosis or drugs as therapeutic modalities [1]. Obstacles in realizing this goal center on both cell uptake of drug and monocyte trafficking to tissues known as sites of disease [10]. We demonstrated that after ex vivo loading of monocytes and MDM with NP, the cells readily distribute NP within and throughout body tissues [3]. If any drug is to be used in the clinic, it need be formulated for parenteral use Achieving this has proven difficult, as any NP given would be rapidly distributed to the liver, where it would be metabolized and degraded. We posit that the same mononuclear phagocytes (MP) that serve as target cells and vehicles for a host of microbial infections can be used to improve diagnostics and drug delivery. We theorize that physical and biological processes such as particle shape, size, coating and opsonization that affect MP clearance of debris and microbes can be harnessed to facilitate uptake of nanoparticles (NP) and tissue delivery
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