Bioimaging Metallomics

The visualization of the mineral and protein distribution in the same histological sections of rat calcified growth plate cartilage

OBJECTIVE

To determine whether the combination of scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and immunostaining would visualize the mineral and protein distribution in the same histological sections.

METHODS

Paraffin sections of fixed rat hindlimbs were processed for SEM-EDX and subsequently for immunofluorescence staining.

RESULTS

The localization of calcium, phosphorus, and carbon with type II collagen could be visualized in the same region of calcified growth plate cartilage on the same section.

CONCLUSIONS

The combination of SEM-EDX and immunostaining is effective for visualizing mineral and protein distribution in the same histological sections.

Correlative transmission electron microscopy and high-resolution hard X-ray fluorescence microscopy of cell sections to measure trace element concentrations at the organelle level

Metals are essential for life and their concentration and distribution in organisms are tightly regulated. Indeed, in their free form, most transition metal ions are toxic. Therefore, an excess of physiologic metal ions or the uptake of non-physiologic metal ions can be highly detrimental to the organism. It is thus fundamental to understand metal distribution under physiological, pathological or environmental conditions, for instance in metal-related pathologies or upon environmental exposure to metals. Elemental imaging techniques can serve this purpose, by allowing the visualization and the quantification of metal species in tissues down to the level of cell organelles. Synchrotron radiation-based X-ray fluorescence (SR-XRF) microscopy is one of the most sensitive techniques to date, and great progress was made to reach nanoscale spatial resolution. Here we propose a correlative method to couple SR-XRF to electron microscopy (EM), with the possibility to quantify selected elemental contents in a specific organelle of interest with 50 × 50 nm² raster scan resolution. We performed EM and SR-XRF on the same section of hepatocytes exposed to silver nanoparticles, in order to identify mitochondria through EM and visualize Ag co-localized with these organelles through SR-XRF. We demonstrate the accumulation of silver in mitochondria, which can reach a 10-fold higher silver concentration compared to the surrounding cytosol. The sample preparation and experimental setup can be adapted to other scientific questions, making the correlative use of SR-XRF and EM suitable to address a large panel of biological questions related to metal homeostasis.

Understanding the relationship between viral infections and trace elements from a metallomics perspective: implications for COVID-19

Recently, the World Health Organization (WHO) declared a pandemic situation due to a new viral infection (COVID-19) caused by a novel virus (Sars-CoV-2). COVID-19 is today the leading cause of death from viral infections in the world. It is known that many elements play important roles in viral infections, both in virus survival, and in the activation of the host's immune system, which depends on the presence of micronutrients to maintain the integrity of its functions. In this sense, the metallome can be an important object of study for understanding viral infections. Therefore, this work presents an overview of the role of trace elements in the immune system and the state of the art in metallomics, highlighting the challenges found in studies focusing on viral infections.

Subcellular Imaging of Localization and Transformation of Silver Nanoparticles in the Oyster Larvae

To accurately assess the behavior and toxicity of silver nanoparticles (AgNPs), it is essential to understand their subcellular distribution and biotransformation. We combined both nanoscale secondary ion mass spectrometry (NanoSIMS) and electron microscopy to investigate the subcellular localization of Ag and in situ chemical distribution in the oyster larvae Crassostrea angulata after exposure to isotopically enriched ¹⁰⁹AgNPs. Oyster larvae directly ingested particulate Ag, and in vivo dissolution of AgNPs occurred. The results collectively showed that AgNPs were much less bioavailable than Ag⁺, and the intracellular Ag was mainly originated from the soluble Ag, especially those dissolved from the ingested AgNPs. AgNPs absorbed on the cell membranes continued to release Ag ions, forming inorganic Ag-S complexes extracellularly, while Ag-organosulfur complexes were predominantly formed intracellularly. The internalized Ag could bind to the sulfur-rich molecules (S-donors) in the cytosol and/or be sequestered in the lysosomes of velum, esophagus, and stomach cells, as well as in the digestive vacuoles of digestive cells, which could act as a detoxification pathway for the oyster larvae. Ag was also occasionally incorporated into the phosphate granules, rough endoplasmic reticulum, and mitochondria. Our work provided definite evidence for the partial sulfidation of AgNPs after interaction with oyster larvae and shed new light on the bioavailability and fate of nanoparticles in marine environment.

Across the spectrum: integrating multidimensional metal analytics for in situ metallomic imaging

To know how much of a metal species is in a particular location within a biological context at any given time is essential for understanding the intricate roles of metals in biology and is the fundamental question upon which the field of metallomics was born. Simply put, seeing is powerful. With the combination of spectroscopy and microscopy, we can now see metals within complex biological matrices complemented by information about associated molecules and their structures. With the addition of mass spectrometry and particle beam based techniques, the field of view grows to cover greater sensitivities and spatial resolutions, addressing structural, functional and quantitative metallomic questions from the atomic level to whole body processes. In this perspective, I present a paradigm shift in the way we relate to and integrate current and developing metallomic analytics, highlighting both familiar and perhaps less well-known state of the art techniques for in situ metallomic imaging, specific biological applications, and their use in correlative studies. There is a genuine need to abandon scientific silos and, through the establishment of a metallomic scientific platform for further development of multidimensional analytics for in situ metallomic imaging, we have an incredible opportunity to enhance the field of metallomics and demonstrate how discovery research can be done more effectively.