Slow CCL2-dependent translocation of biopersistent particles from muscle to brain

Abstract

BackgroundLong-term biodistribution of nanomaterials used in medicine is largely unknown. This is the case for alum, the most widely used vaccine adjuvant, which is a nanocrystalline compound spontaneously forming micron/submicron-sized agglomerates. Although generally well tolerated, alum is occasionally detected within monocyte-lineage cells long after immunization in presumably susceptible individuals with systemic/neurologic manifestations or autoimmune (inflammatory) syndrome induced by adjuvants (ASIA).MethodsOn the grounds of preliminary investigations in 252 patients with alum-associated ASIA showing both a selective increase of circulating CCL2, the major monocyte chemoattractant, and a variation in the CCL2 gene, we designed mouse experiments to assess biodistribution of vaccine-derived aluminum and of alum-particle fluorescent surrogates injected in muscle. Aluminum was detected in tissues by Morin stain and particle induced X-ray emission) (PIXE) Both 500 nm fluorescent latex beads and vaccine alum agglomerates-sized nanohybrids (Al-Rho) were used.ResultsIntramuscular injection of alum-containing vaccine was associated with the appearance of aluminum deposits in distant organs, such as spleen and brain where they were still detected one year after injection. Both fluorescent materials injected into muscle translocated to draining lymph nodes (DLNs) and thereafter were detected associated with phagocytes in blood and spleen. Particles linearly accumulated in the brain up to the six-month endpoint; they were first found in perivascular CD11b+ cells and then in microglia and other neural cells. DLN ablation dramatically reduced the biodistribution. Cerebral translocation was not observed after direct intravenous injection, but significantly increased in mice with chronically altered blood-brain-barrier. Loss/gain-of-function experiments consistently implicated CCL2 in systemic diffusion of Al-Rho particles captured by monocyte-lineage cells and in their subsequent neurodelivery. Stereotactic particle injection pointed out brain retention as a factor of progressive particle accumulation.ConclusionNanomaterials can be transported by monocyte-lineage cells to DLNs, blood and spleen, and, similarly to HIV, may use CCL2-dependent mechanisms to penetrate the brain. This occurs at a very low rate in normal conditions explaining good overall tolerance of alum despite its strong neurotoxic potential. However, continuously escalating doses of this poorly biodegradable adjuvant in the population may become insidiously unsafe, especially in the case of overimmunization or immature/altered blood brain barrier or high constitutive CCL-2 production.

Non-linear dose-response of aluminium hydroxide adjuvant particles: Selective low dose neurotoxicity

“…Alhydrogel® biopersistence was confirmed in a variety of laboratory animal models up to 6-12 months post-injection, in both the injected muscle (Verdier et al, 2005;Authier et al, 2006;Khan et al, 2013;Eidi et al, 2015) and distant lymphoid organs . Particles traffic from an injected tissue to the dLNs is size-dependent, smaller particles (20-200 nm) being able to drain in a free form whereas medium-sized particles (0.5-2 µm) are exclusively subjected to cell transportation (Manolova et al, 2008).…”

“…This compound spontaneously forms micron-sized agglomerates (Johnston et al, 2002), subjected to slight size variations after antigen adsorption and in vivo interactions with phosphate, organic acid and proteinaceous environments. A series of recent reports from our laboratory have shown that translocation of aluminium hydroxide may be specifically related to monocyte lineage cell uptake of this poorly biodegradable compound (Khan et al, 2013;Crépeaux et al, 2015;Eidi et al, 2015), likely resulting from phagocytosis or macropinocytosis (Mao et al, 2013).…”

“…Previous studies from our laboratory have shown that alum particles, as other poorly degradable particles, may not stay entirely localized in the injected tissue in mice, but can disseminate within phagocytic cells to regional lymph nodes and then to more distant sites and to the brain (Khan et al, 2013;Crépeaux et al, 2015;Eidi et al, 2015). In contrast to a previous belief, alum is characterized by striking biopersistence within immune cells in both the injected muscle, and the draining lymph nodes (dLNs) and spleen, where it may be found in conspicuous quantities 9 months after injection .…”

FDG-PET/CT Brain Findings in a Patient With Macrophagic Myofasciitis

“…Cortico-subcortical brain lesions are possibly of inflammatory or toxic origin. Experimental data evidenced that after intramuscular injections of aluminum hydroxide, aluminum particles can translocate into the brain tissue where they remain trapped [10]. However, to our knowledge, there is no pathological or radiological evidence for brain damage specifically associated with MMF.…”

What is the risk of aluminium as a neurotoxin?

“…Aluminium is, of course, a powerful immunogen, being the preferred adjuvant in vaccination and immunotherapy. This activity as an adjuvant, and concomitantly as an antigen, at injection sites in skin or muscle must also be considered for focal accumulations of aluminium within the CNS and such reactivity may underlie aluminium's suggested roles in autoimmunity [3][4][5].…”