Dietary silver nanoparticles can disturb the gut microbiota in mice

Abstract

BackgroundHumans are increasingly exposed via the diet to Ag nanoparticles (NP) used in the food industry. Because of their anti-bacterial activity, ingested Ag NP might disturb the gut microbiota that is essential for local and systemic homeostasis. We explored here the possible impact of dietary Ag NP on the gut microbiota in mice at doses relevant for currently estimated human intake.MethodsMice were orally exposed to food (pellets) supplemented with increasing doses of Ag NP (0, 46, 460 or 4600 ppb) during 28 d. Body weight, systemic inflammation and gut integrity were investigated to determine overall toxicity, and feces DNA collected from the gut were analyzed by Next Generation Sequencing (NGS) to assess the effect of Ag NP on the bacterial population. Ag NP were characterized alone and in the supplemented pellets by scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX).ResultsNo overall toxicity was recorded in mice exposed to Ag NP. Ag NP disturbed bacterial evenness (α-diversity) and populations (β-diversity) in a dose-dependent manner. Ag NP increased the ratio between Firmicutes (F) and Bacteroidetes (B) phyla. At the family level, Lachnospiraceae and the S24-7 family mainly accounted for the increase in Firmicutes and decrease in Bacteroidetes, respectively. Similar effects were not observed in mice identically exposed to the same batch of Ag NP-supplemented pellets aged during 4 or 8 months and the F/B ratio was less or not modified. Analysis of Ag NP-supplemented pellets showed that freshly prepared pellets released Ag ions faster than aged pellets. STEM-EDX analysis also showed that Ag sulfidation occurred in aged Ag NP-supplemented pellets.ConclusionsOur data indicate that oral exposure to human relevant doses of Ag NP can induce microbial alterations in the gut. The bacterial disturbances recorded after Ag NP are similar to those reported in metabolic and inflammatory diseases, such as obesity. It also highlights that Ag NP aging in food, and more specifically sulfidation, can reduce the effects of Ag NP on the microbiota by limiting the release of toxic Ag ions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-016-0149-1) contains supplementary material, which is available to authorized users.

Review of the effects of silver nanoparticle exposure on gut bacteria

“…Using Sprague-Dawley rats, Williams et al (2015) confirmed that AgNPs induced dose-dependent changes in ileal-mucosal microbial populations, as well as intestinal gene expression, and promoted an apparent shift in the gut microbiota toward a greater proportion of gram-negative bacteria. Another study showed that AgNPs altered bacterial evenness (α-diversity) and populations (β-diversity) and increased the ratio of Bacteroides to Firmicutes in a dose-dependent manner (van den Brule et al, 2016). Similarly, Sarkar et al (2015) detected dose-dependent changes in the gut microbial population of AgNP-exposed fish.…”

“…Experimental animals can be exposed to AgNPs by gavage (Hadrup et al, 2012) or drinking water (Pineda et al, 2012) or by adding them to food (van den Brule et al, 2016). Consequently, different exposure methods can cause deviations in the actual contact dose of the animal and might affect the toxicity of the AgNPs to gut bacteria.…”

“…Several studies indicated that Ag + ions are potentially lethal to pathogens (Liu et al, 1998;Park et al, 2009) and that the mechanisms associated with AgNP toxicity are largely explained by the action of Ag + . For example, by limiting the release of toxic Ag + , the sulfurization of AgNPs can reduce their effects on microbiota in mice, specifically F/B ratio (van den Brule et al, 2016).…”

“…The antibacterial effect of AgNPs is considerably greater than that of macro-Ag, which can be attributed to the release of Ag ions (Ag + ) and "particle-specific" effects; however, there remains a lack of consensus on the underlying mechanisms (Morones et al, 2005;van den Brule et al, 2016). In this review, we summarize some of the possible mechanisms through which AgNPs exert their bactericidal effects.…”

The antihyperlipidemic effects of fullerenol nanoparticles via adjusting the gut microbiota in vivo

“…The impacts of nanoparticles (NPs) on the gut microbiota have also attracted increasing attention. The nanoparticles of titanium dixoide (TiO 2 ), Zinc and silver have been reported to be able to change the gut microbial community, but their modulating effects on the gut microbiota remain controversial among different research groups [15][16][17][18][19][20].…”