title: Slow CCL2-dependent translocation of biopersistent particles from muscle to brain.
abstract: BACKGROUND
  Long-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).
  
  
  METHODS
  On 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.
  
  
  RESULTS
  Intramuscular 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.
  
  
  CONCLUSIONS
  Nanomaterials 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.
authors.affiliation: Inserm, U955, 8 rue du Général Sarrail, Créteil, 94010, France.
authors.forename: Zakir
authors.initials: Z
authors.lastname: Khan
authors.forename: Christophe
authors.initials: C
authors.lastname: Combadière
authors.forename: François-Jérôme
authors.initials: FJ
authors.lastname: Authier
authors.forename: Valérie
authors.initials: V
authors.lastname: Itier
authors.forename: François
authors.initials: F
authors.lastname: Lux
authors.forename: Christopher
authors.initials: C
authors.lastname: Exley
authors.forename: Meriem
authors.initials: M
authors.lastname: Mahrouf-Yorgov
authors.forename: Xavier
authors.initials: X
authors.lastname: Decrouy
authors.forename: Philippe
authors.initials: P
authors.lastname: Moretto
authors.forename: Olivier
authors.initials: O
authors.lastname: Tillement
authors.forename: Romain K
authors.initials: RK
authors.lastname: Gherardi
authors.forename: Josette
authors.initials: J
authors.lastname: Cadusseau
mesh_terms: D000276:Adjuvants, Immunologic / Q000493:pharmacokinetics*; D000534:Alum Compounds / Q000493:pharmacokinetics*; D000818:Animals; D001208:Asia; D001812:Blood-Brain Barrier / Q000276:immunology; D001921:Brain / Q000276:immunology* / Q000378:metabolism; D002465:Cell Movement; D018932:Chemokine CCL2 / Q000097:blood / Q000378:metabolism*; D006801:Humans; D007114:Immunization / Q000009:adverse effects; D007273:Injections, Intramuscular / Q000009:adverse effects; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000276:immunology; D009132:Muscles / Q000276:immunology* / Q000378:metabolism; D053758:Nanoparticles; D014018:Tissue Distribution; D014612:Vaccines / Q000008:administration & dosage / Q000009:adverse effects; D014771:Virion / Q000472:pathogenicity*
chemical_list: D000276:Adjuvants, Immunologic; D000534:Alum Compounds; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D014612:Vaccines; C041524:aluminum sulfate
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