Interaction of Human Arylamine N-Acetyltransferase 1 with Different Nanomaterials

Abstract

Humans are exposed to nanoparticles in the environment as well as those in nanomaterials developed for biomedical applications. However, the safety and biologic effects of many nanoparticles remain to be elucidated. Over the past decade, our understanding of the interaction of proteins with various nanomaterials has grown. The protein corona can determine not only how nanoparticles interact with cells but also their biologic effects and toxicity. In this study, we describe the effects that several different classes of nanoparticles exert on the enzymatic activity of the cytosolic protein human arylamine N-acetyltransferase 1 (NAT1), a drug-metabolizing enzyme widely distributed in the body that is also responsible for the activation and detoxification of known carcinogens. We investigated three metal oxides (zinc oxide, titanium dioxide, and silicon dioxide), two synthetic clay nanoparticles (layered double hydroxide and layered silicate nanoparticles), and a self-assembling thermoresponsive polymeric nanoparticle that differ in size and surface characteristics. We found that the different nanoparticles induced very different responses, ranging from inhibition to marked enhancement of enzyme activity. The layered silicates did not directly inactivate NAT1, but was found to enhance substrate-dependent inhibition. These differing effects demonstrate the multiplicity of nanoparticle-protein interactions and suggest that enzyme activity may be compromised in organs exposed to nanoparticles, such as the lungs or reticulo-endothelial system.

Treatment of Rats with Apocynin Has Considerable Inhibitory Effects on Arylamine N-Acetyltransferase Activity in the Liver

“…To date, panoply of diverse sulphydryl reactive compounds has been used as irreversible inhibitors of mammalian NATs, only to elucidate the involvement of a Cys residue in the catalytic mechanism of NATs 39 51 52 53 54 55 or propose hypotheses for the putative endogenous role of human NATs 56 57 58 . Other recent studies have also shown irreversible inhibition of human NAT isoforms by different heavy metals 59 60 , and some of the oxidizing products resulting from the oxidation metabolism of aromatic amines 61 . The eventuality that apocynin could act as covalent inhibitor of NAT enzymes would have offered some advantages in drug design, since specific covalent inhibitors are usually associated with lower doses and a longer duration of action, and avoiding resistance 62 .…”

“…Other recent studies have also shown irreversible inhibition of human NAT isoforms by different heavy metals5960, and some of the oxidizing products resulting from the oxidation metabolism of aromatic amines61. The eventuality that apocynin could act as covalent inhibitor of NAT enzymes would have offered some advantages in drug design, since specific covalent inhibitors are usually associated with lower doses and a longer duration of action, and avoiding resistance62.…”

Back to Basics: Exploiting the Innate Physico‐chemical Characteristics of Nanomaterials for Biomedical Applications

“…The mode of inhibition in this case involves the binding of the NM to the active site of NAT1, thus preventing NAT1 from binding to the target substrate. Interestingly, the more negative the surface charge of the NM, the lower the LD50 concentration needed to inhibit the NAT1 activity, highlighting the importance of considering NM charge as a critical design parameter to inhibit enzymatic activity …”

Carbon black and titanium dioxide nanoparticles induce distinct molecular mechanisms of toxicity

“…Interaction of nanomaterials with proteins essential for cellular functions could inactivate them either by conformational changes and/or denaturation. Both CB and TiO 2 nanoparticles were shown to inhibit enzyme activity and induce conformational changes in Arylamine N-Acetyletransferase-1 44,45 , a xenobiotic metabolizing enzyme involved in activation/detoxification of carcinogens. Although in this case both nanomaterials induce similar effects, the magnitude of the response varies hugely.…”