Trafficking of superparamagnetic iron oxide particles (Combidex) from brain to lymph nodes in the rat

Abstract

Central nervous system (CNS) drainage may occur via connections to the vasculature, but in animal models up to 50% occurs via perivascular, perineural and primitive lymphatic drainage to cervical lymph nodes. We evaluated efflux of particles from the brain to cervical lymph nodes in normal rats, using Combidex iron oxide-based magnetic resonance imaging (MRI) agent. After intracerebral, intraventricular, intracarotid or intravenous injection of Combidex in normal Long Evans rats, particle localization was assessed by MRI and histochemistry for iron and the dextran coat (n = 27). Intraventricular or intracerebral injection, but not intracarotid administration of Combidex (100 micro g), resulted in MRI signal changes in the deep cervical lymph nodes around the carotid artery, and, less strongly, in the superficial cervical nodes. Within 2 h of Combidex administration, iron was histologically localized in cervical lymph nodes, with patched staining of capsule and peripheral sinus consistent with delivery via multiple afferent lymphatic vessels. Lymph node staining in groups receiving CNS Combidex was significantly different from controls (P < 0.0001) and was significantly localized in the deep vs. superficial cervical lymph nodes (P = 0.0003). The trafficking of the superparamagnetic iron particles from the CNS in the rat could be visualized by MRI and histology. Combidex provides a powerful tool to rapidly assess drainage of virus-sized particles from the CNS.

Magnetic resonance imaging of viral particle biodistribution in vivo

“…Moreover, as CSF clearance is reportedly rapid 26 with 1 h turnover in rats, 27 after 2 h (the/any) unbound bUSPIO or non-endocytosed bUS-PIO-Baavi particles are likely to have diluted and escaped from CSF as reported previously. 24 The transduction efficiency of the bUSPIO-labeled Baavi in choroid plexus cells in vivo is in line with our previous findings 14 of baculovirus without avidin.…”

“…signal loss) to be a few millimeters larger than the area actually confirmed by histochemical methods. 24 The loss of the MRI signal during time studied here may be explained by choroid plexus cell turnover or even cell proliferation as a response to injury. 25 After intracerebral administration, USPIO particles have been observed to accumulate in cervical lymph nodes via CSF efflux, 24 which agrees with our previous findings of baculovirus systemic escape to ectopic tissues.…”

“…24 The loss of the MRI signal during time studied here may be explained by choroid plexus cell turnover or even cell proliferation as a response to injury. 25 After intracerebral administration, USPIO particles have been observed to accumulate in cervical lymph nodes via CSF efflux, 24 which agrees with our previous findings of baculovirus systemic escape to ectopic tissues. 14 These observations could explain the fate of non-uptaken bUSPIO and bUSPIO-Baavi complexes that are not taken up.…”

In vivo leukocyte labeling with intravenous ferumoxides/protamine sulfate complex and in vitro characterization for cellular magnetic resonance imaging

“…For blood count analysis, 0.5 ml of whole blood collected in EDTA microtubes were analyzed in duplicate on a Hemavet 850 (CDC Technologies, Oxford, CT). Iron histochemistry was performed using Prussian blue staining with or without diaminobenzidine (DAB) enhancement (29). Cells or tissues were fixed, washed, and incubated for 20 -30 min with 2% potassium ferrocyanide in 3.7% hydrochloric acid, followed by an incubation in hydrogen peroxide-activated DAB solution for 5-10 min.…”

“…MRI was performed on a Siemens Magnetom Trio 3T scanner using a custom rat head coil as previously described (29). T1, T2, and T2*-weighted sequences were acquired with the following parameters: coronal T1 weighted spin echo, repetition time ( For in vitro MR assessment, mononuclear leukocytes, plasma, and whole blood were isolated from rats 2 h after an intravenous injection with Fe-Pro complex, ferumoxytol (20 mg/kg) ϩ protamine sulfate (2 mg/kg), or protamine alone following the procedure described above.…”