In vivo formation of natural HgSe nanoparticles in the liver and brain of pilot whales.

Zuzana Gajdosechova,Glenn Woods,Erik H Larsen,Mohammed M Lawan,Katrin Loeschner,Peter M Kopittke,Andrew Brownlow,Fiona L Read,Andrea Raab,Enzo Lombi,Kirk G Scheckel,Eva M Krupp,Dagmar S Urgast,Jörg Feldmann

doi:10.1038/srep34361

Abstract

To understand the biochemistry of methylmercury (MeHg) that leads to the formation of mercury-selenium (Hg-Se) clusters is a long outstanding challenge that promises to deepen our knowledge of MeHg detoxification and the role Se plays in this process. Here, we show that mercury selenide (HgSe) nanoparticles in the liver and brain of long-finned pilot whales are attached to Se-rich structures and possibly act as a nucleation point for the formation of large Se-Hg clusters, which can grow with age to over 5 μm in size. The detoxification mechanism is fully developed from the early age of the animals, with particulate Hg found already in juvenile tissues. As a consequence of MeHg detoxification, Se-methionine, the selenium pool in the system is depleted in the efforts to maintain essential levels of Se-cysteine. This study provides evidence of so far unreported depletion of the bioavailable Se pool, a plausible driving mechanism of demonstrated neurotoxic effects of MeHg in the organism affected by its high dietary intake.

Highlights

Metabolic roles, they are exceptionally efficient redox catalysts due to a completely ionized Se-cysteine moiety at physiological pH13
Deposition of Hg LCF included mercury selenide (HgSe) particles could lead to reduced Se bioavailability and subsequent deficiency, which predisposes to a variety of biological pathologies including epilepsy[15], coordination disorder[16], autoimmune and infectious diseases[17]
Considering that the biochemistry of MeHg detoxification is largely unknown, the use of Se:Hg molar ratio to identify the detoxification abilities of an organism may prove to be flawed. Such an assumption would hold if the only Hg species present in the tissue would be in the form of HgSe particles, and thereby it would be plausible to assume that organism with molar ratio above 1 has enough bioavailable Se to support vital biological functions

Summary

Introduction

Metabolic roles, they are exceptionally efficient redox catalysts due to a completely ionized Se-cysteine moiety at physiological pH13. Deposition of HgSe particles could lead to reduced Se bioavailability and subsequent deficiency, which predisposes to a variety of biological pathologies including epilepsy[15], coordination disorder[16], autoimmune and infectious diseases[17]. To address these issues, we investigated in vivo formation of natural HgSe particles in a pod of stranded long-finned pilot whales (Globicephala melas), with age of the animal and the potency of the environmentally relevant dose of dietary MeHg to disrupt the Se-proteins synthesis. This has not been previously investigated despite the substantial indications of the interaction between Hg and Se, and we conducted a multi-method analytical approach on brain and liver samples of the stranded whales

Methods

Results

Discussion

Conclusion