Difference in the cellular response following THP-1 derived phagocytic monocyte cells exposure to commercial aluminum-based adjuvants and aluminum-containing vaccines

BACKGROUND

Aluminum-based adjuvants (ABAs) enhance the immune response following vaccine injection. Their mechanisms of action are not fully understood, and their bio-persistency have been described associated with long-term adverse effects.

METHODS

We evaluated and compared the cellular effects of the two main ABAs and whole vaccines on ATP production, ROS generation and cytokines production (IL-6 and IL-10), using THP-1 cells.

RESULTS

ABAs altered the cell energy metabolism by increasing ROS production after 24 h and reducing ATP production after 48 h. In addition, both ABAs and whole vaccines induced different kinetics of IL-6 production, whereas only ABAs induced IL-10 secretion.

CONCLUSION

This study showed clearly, for a first time, a difference in cellular response to the ABAs and whole vaccines which should be taken into consideration in future studies focusing on the effect of ABA in vaccines. Future studies on ABAs should also pay attention to mitochondrial function alterations following exposure to ABA-containing vaccines.

Physico-chemical properties of aluminum adjuvants in vaccines: Implications for toxicological evaluation

Aluminum salts have been used as adjuvants in human vaccines since 1932. The most used adjuvants are Al oxyhydroxide (AlOOH) and Al hydroxyphosphate (AlOHPO₄). Al adjuvants have different physico-chemical properties. The differences in these properties are not well documented and not considered by the Food and Drug Administration (FDA), though they can largely influence biological effects of the adjuvants which are particulate components. In this study, different physico-chemical properties including the shape, size and charge of particles have been evaluated under different conditions in three Al adjuvants containing-vaccines and two corresponding commercial adjuvants suspensions. The results showed that the two Al adjuvants have different shapes, sizes and charges but both form aggregates. In addition, a clear effect of dilution on the size of the aggregates was observed. Moreover, different sizes of Al particles were measured for both Al oxyhydroxide adjuvant alone or in the vaccine, at identical concentrations, displaying the impact of adsorbed proteins on the size of aggregates in the case of the vaccine. Taken together, this paper suggests the importance to evaluate, before any biological and especially toxicological impact study, the whole physico-chemical properties of Al particle without restricting to the sole evaluation of the injected concentration. Furthermore, any modification of these mentioned parameters during manipulation, before animal or cell exposure, should be considered. In a more global way, the fixed "safe dose" of Al adjuvants should be specific for each type of Al adjuvant independently or for a mix of the two compounds, due to their different properties.

Physical and chemical characterization of McIntyre Powder: An aluminum dust inhaled by miners to combat silicosis

McIntyre Powder (MP) is a finely ground aluminum powder that was used between 1943 and 1979 as a prophylaxis for silicosis. Silicosis is a chronic lung disease caused by the inhalation of crystalline silica dust and was prevalent in the Canadian mining industry during this time period. The McIntyre Research Foundation developed, patented, and produced the MP and distributed it to licensees in Canada, the United States, Mexico, Chile, Belgian Congo, and Western Australia. In the province of Ontario, Canada it is estimated that at least 27,500 miners between 1943 and 1979 were exposed to MP. The present study was undertaken to examine the chemical and physical characteristics of two variations of MP (light grey and black). Chemical analyses (using X-ray Fluorescence and Inductively Coupled Plasma approaches) indicate that the black MP contains significantly higher concentrations of aluminum and metal impurities than the light grey MP (p < 0.001). X-ray diffractometry shows that while aluminum hydroxide dominates the aluminum speciation in both variations, the higher total aluminum content in the black MP is attributable to a greater proportion of elemental aluminum. Physical characterization (using electron microscopy, light microscopy, and dynamic light scattering) indicates that the light grey MP consists of particles ranging from 5 nm to 5 µm in diameter. Atomic Force Microscopy shows that the light grey MP particles in the nanoparticle range (<100 nm) have a mode between 5 and 10 nm. Consequently, it is possible that inhaled smaller MP nanoparticles may be transported via blood and lymph fluid circulation to many different organs including the brain. It is also possible for inhaled larger MP particles to deposit onto lung tissue and for potential health effects to arise from inflammatory responses through immune activation. This MP characterization will provide crucial data to help inform future toxicological, epidemiological, and biological studies of any long-term effects related to the inhalation of aluminum dust and nanomaterials.

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

Aluminium (Al) oxyhydroxide (Alhydrogel^®), the main adjuvant licensed for human and animal vaccines, consists of primary nanoparticles that spontaneously agglomerate. Concerns about its safety emerged following recognition of its unexpectedly long-lasting biopersistence within immune cells in some individuals, and reports of chronic fatigue syndrome, cognitive dysfunction, myalgia, dysautonomia and autoimmune/inflammatory features temporally linked to multiple Al-containing vaccine administrations. Mouse experiments have documented its capture and slow transportation by monocyte-lineage cells from the injected muscle to lymphoid organs and eventually the brain. The present study aimed at evaluating mouse brain function and Al concentration 180days after injection of various doses of Alhydrogel^® (200, 400 and 800μg Al/kg of body weight) in the tibialis anterior muscle in adult female CD1 mice. Cognitive and motor performances were assessed by 8 validated tests, microglial activation by Iba-1 immunohistochemistry, and Al level by graphite furnace atomic absorption spectroscopy. An unusual neuro-toxicological pattern limited to a low dose of Alhydrogel^® was observed. Neurobehavioural changes, including decreased activity levels and altered anxiety-like behaviour, were observed compared to controls in animals exposed to 200μg Al/kg but not at 400 and 800μg Al/kg. Consistently, microglial number appeared increased in the ventral forebrain of the 200μg Al/kg group. Cerebral Al levels were selectively increased in animals exposed to the lowest dose, while muscle granulomas had almost completely disappeared at 6 months in these animals. We conclude that Alhydrogel^® injected at low dose in mouse muscle may selectively induce long-term Al cerebral accumulation and neurotoxic effects. To explain this unexpected result, an avenue that could be explored in the future relates to the adjuvant size since the injected suspensions corresponding to the lowest dose, but not to the highest doses, exclusively contained small agglomerates in the bacteria-size range known to favour capture and, presumably, transportation by monocyte-lineage cells. In any event, the view that Alhydrogel^® neurotoxicity obeys "the dose makes the poison" rule of classical chemical toxicity appears overly simplistic.

Fluorescent nanodiamonds as a relevant tag for the assessment of alum adjuvant particle biodisposition

BACKGROUND

Aluminum oxyhydroxide (alum) is a crystalline compound widely used as an immunologic adjuvant of vaccines. Concerns linked to alum particles have emerged following recognition of their causative role in the so-called macrophagic myofasciitis (MMF) lesion in patients with myalgic encephalomyelitis, revealing an unexpectedly long-lasting biopersistence of alum within immune cells and a fundamental misconception of its biodisposition. Evidence that aluminum-coated particles phagocytozed in the injected muscle and its draining lymph nodes can disseminate within phagocytes throughout the body and slowly accumulate in the brain further suggested that alum safety should be evaluated in the long term. However, lack of specific staining makes difficult the assessment of low quantities of bona fide alum adjuvant particles in tissues.

METHODS

We explored the feasibility of using fluorescent functionalized nanodiamonds (mfNDs) as a permanent label of alum (Alhydrogel(®)). mfNDs have a specific and perfectly photostable fluorescence based on the presence within the diamond lattice of nitrogen-vacancy centers (NV centers). As the NV center does not bleach, it allows the microspectrometric detection of mfNDs at very low levels and in the long-term. We thus developed fluorescent nanodiamonds functionalized by hyperbranched polyglycerol (mfNDs) allowing good coupling and stability of alum:mfNDs (AluDia) complexes. Specificities of AluDia complexes were comparable to the whole reference vaccine (anti-hepatitis B vaccine) in terms of particle size and zeta potential.

RESULTS

In vivo, AluDia injection was followed by prompt phagocytosis and AluDia particles remained easily detectable by the specific signal of the fND particles in the injected muscle, draining lymph nodes, spleen, liver and brain. In vitro, mfNDs had low toxicity on THP-1 cells and AluDia showed cell toxicity similar to alum alone. Expectedly, AluDia elicited autophagy, and allowed highly specific detection of small amounts of alum in autophagosomes.

CONCLUSIONS

The fluorescent nanodiamond technology is able to overcome the limitations of previously used organic fluorophores, thus appearing as a choice methodology for studying distribution, persistence and long-term neurotoxicity of alum adjuvants and beyond of other types of nanoparticles.

Structural basis for the association of MAP6 protein with microtubules and its regulation by calmodulin

Microtubules are highly dynamic αβ-tubulin polymers. In vitro and in living cells, microtubules are most often cold- and nocodazole-sensitive. When present, the MAP6/STOP family of proteins protects microtubules from cold- and nocodazole-induced depolymerization but the molecular and structure determinants by which these proteins stabilize microtubules remain under debate. We show here that a short protein fragment from MAP6-N, which encompasses its Mn1 and Mn2 modules (MAP6(90-177)), recapitulates the function of the full-length MAP6-N protein toward microtubules, i.e. its ability to stabilize microtubules in vitro and in cultured cells in ice-cold conditions or in the presence of nocodazole. We further show for the first time, using biochemical assays and NMR spectroscopy, that these effects result from the binding of MAP6(90-177) to microtubules with a 1:1 MAP6(90-177):tubulin heterodimer stoichiometry. NMR data demonstrate that the binding of MAP6(90-177) to microtubules involve its two Mn modules but that a single one is also able to interact with microtubules in a closely similar manner. This suggests that the Mn modules represent each a full microtubule binding domain and that MAP6 proteins may stabilize microtubules by bridging tubulin heterodimers from adjacent protofilaments or within a protofilament. Finally, we demonstrate that Ca(2+)-calmodulin competes with microtubules for MAP6(90-177) binding and that the binding mode of MAP6(90-177) to microtubules and Ca(2+)-calmodulin involves a common stretch of amino acid residues on the MAP6(90-177) side. This result accounts for the regulation of microtubule stability in cold condition by Ca(2+)-calmodulin.

Anionic polyelectrolyte adsorption on mica mediated by multivalent cations: a solution to DNA imaging by atomic force microscopy under high ionic strengths

Adsorption of DNA molecules on mica, a highly negatively charged surface, mediated by divalent or trivalent cations is considered. By analyzing atomic force microscope (AFM) images of DNA molecules adsorbed on mica, phase diagrams of DNA molecules interacting with a mica surface are established in terms of concentrations of monovalent salt (NaCl) and divalent (MgCl2) or multivalent (spermidine, cobalt hexamine) salts. These diagrams show two transitions between nonadsorption and adsorption. The first one arises when the concentration of multivalent counterions is larger than a limit value, which is not sensitive to the monovalent salt concentration. The second transition is due to the binding competition between monovalent and multivalent counterions. In addition, we develop a model of polyelectrolyte adsorption on like-charged surfaces with multivalent counterions. This model shows that the correlations of the multivalent counterions at the interface between DNA and mica play a critical role. Furthermore, it appears that DNA adsorption takes place when the energy gain in counterion correlations overcomes an energy barrier. This barrier is induced by the entropy loss in confining DNA in a thin adsorbed layer, the entropy loss in the interpenetration of the clouds of mica and DNA counterions, and the electrostatic repulsion between DNA and mica. The analysis of the experimental results provides an estimation of this energy barrier. We then discuss some important issues, including DNA adsorption under physiological conditions.

A new approach to DNA bending by polyamines and its implication in DNA condensation

Polyamines are known to induce dynamical bending of DNA molecules. This mechanism is very important since many DNA binding proteins (DNAse, transcription factor, etc.) exert their action by their ability to bend DNA. We propose an analytical model which describes the dynamical bending of DNA by polyamine ions in highly diluted DNA solutions. The bending probability depends on the entropy loss of polyamines due to their localization. This localization is facilitated by the electrostatic repulsion between multivalent counterions condensed on DNA, which reduces the entropy loss in counterion localization. Therefore DNA bending by polyamines depends on the competition between monovalent counterions and polyamines. We find that the bending probability is weak for a low binding ratio of polyamines (i.e. number of bound polyamines per base pair), whereas a high bending probability can be reached at large polyamine binding ratio. In addition, we describe a new mechanism of DNA bending. It occurs with the help of thermal agitation, which initiates the bending and favours the polyamine localization. This model provides further insights into DNA bending by polyamines and its implication in DNA condensation. A qualitative estimation of the DNA bending probability is obtained by measuring the cleavage efficiency of DNA by bleomycin versus spermidine concentration. Indeed, a local helix distortion by polyamines results in an amplification of the double-strand cleavage by bleomycin. The measurement of the bleomycin amplification is performed by analysing images of DNA molecules with atomic force microscope. Some features of the dynamical bending indicate that condensation and bending are interrelated.

Studying the effect of a charged surface on the interaction of bleomycin with DNA using an atomic force microscope

The cleavage of DNA caused by the antitumoral drug bleomycin has been investigated using atomic force microscopy (AFM). This work deals with the effect that adsorbing DNA onto a positively- or negatively-charged surface has on the double-strand cleavage of DNA by Fe(III)/bleomycin. Quantitative analysis of the number of breaks per DNA molecule, in bulk and at the surface of the mica substrate, has been performed by analyzing AFM images. It turns out that the cleavage of DNA is strongly inhibited by a positively-charged surface. Our experiments can be interpreted using a simple electrostatic model. This paper is a first step in the study of DNA accessibility to ligand such as bleomycin, using AFM in liquids.

Adsorption of DNA to mica mediated by divalent counterions: a theoretical and experimental study

The adsorption of DNA molecules onto a flat mica surface is a necessary step to perform atomic force microscopy studies of DNA conformation and observe DNA-protein interactions in physiological environment. However, the phenomenon that pulls DNA molecules onto the surface is still not understood. This is a crucial issue because the DNA/surface interactions could affect the DNA biological functions. In this paper we develop a model that can explain the mechanism of the DNA adsorption onto mica. This model suggests that DNA attraction is due to the sharing of the DNA and mica counterions. The correlations between divalent counterions on both the negatively charged DNA and the mica surface can generate a net attraction force whereas the correlations between monovalent counterions are ineffective in the DNA attraction. DNA binding is then dependent on the fractional surface densities of the divalent and monovalent cations, which can compete for the mica surface and DNA neutralizations. In addition, the attraction can be enhanced when the mica has been pretreated by transition metal cations (Ni(2+), Zn(2+)). Mica pretreatment simultaneously enhances the DNA attraction and reduces the repulsive contribution due to the electrical double-layer force. We also perform end-to-end distance measurement of DNA chains to study the binding strength. The DNA binding strength appears to be constant for a fixed fractional surface density of the divalent cations at low ionic strength (I < 0.1 M) as predicted by the model. However, at higher ionic strength, the binding is weakened by the screening effect of the ions. Then, some equations were derived to describe the binding of a polyelectrolyte onto a charged surface. The electrostatic attraction due to the sharing of counterions is particularly effective if the polyelectrolyte and the surface have nearly the same surface charge density. This characteristic of the attraction force can explain the success of mica for performing single DNA molecule observation by AFM. In addition, we explain how a reversible binding of the DNA molecules can be obtained with a pretreated mica surface.

The Strength of Long-Range Forces across Thin Liquid Films

We present experimental results on the instability of thin liquid polydimethylsiloxane films intercalated between a solid substrate and a liquid surrounding medium. The instability is induced by long-range van der Waals forces across the film. From the characteristic wavelength of the instability and from the apparent contact angle of the equilibrium structures, we deduce an effective Hamaker constant (A132) about 2-3 orders of magnitude higher than what is expected from calculations based on the individual Hamaker constants. With air as the surrounding medium, we obtain the expected values. Copyright 1999 Academic Press.