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Organisationseinheit der BAM
An immunohistochemical method is described to visualize the distribution of metallothioneins 1/2 (MT 1/2) and metallothionein 3 (MT 3) in human ocular tissue. It is making use of (a) antibodies conjugated to gold nanoclusters (AuNCs) acting as labels, and (b) laser ablation (LA) coupled to inductively coupled plasma – mass spectrometry (ICP-MS).Water-soluble fluorescent AuNCs (with an average size of 2.7 nm) were synthesized and then conjugated to antibody by carbodiimide coupling. The surface of the modified AuNCs was then blocked with hydroxylamine to avoid nonspecific interactions with biological tissue. Immunoassays for MT 1/2 and MT 3 in ocular tissue sections (5 μm thick) from two post mortem human donors were performed. Imaging studies were then performed by fluorescence using confocal microscopy, and LA-ICP-MS was performed in the retina to measure the signal for gold. Signal amplification by the >500 gold atoms in each nanocluster allowed the antigens (MT 1/2 and MT 3) to be imaged by LA-ICP-MS using a laser spot size as small as 4 μm. The image patterns found in retina are in good agreement with those obtained by conventional fluorescence immunohistochemistry which was used as an established reference method.
Oxidative stress is produced by an imbalance between free radical production and biological system's ability to detoxify the reactive intermediates and repair the resulting damage. In the human eye the main causes of oxidative stress are the daily exposure to sunlight, chemical insults and the special microenvironment with abundant photo-sensitizers. For this reason, oxidative stress has been associated several ocular diseases, like aged-related macular degeneration (AMD). On the other hand, Metallothioneins (MTs) are a family of low molecular weight (6–7 kDa), cysteine-rich (30%) and metal-binding proteins. The cysteine residues can bind metal atoms such as zinc, copper, and cadmium via thiolate bonds. These proteins have a wide range of functions including defense against oxidative damage, intracellular storage and transport and metabolism of metal ions. The antioxidant properties of MTs reside in their capacity to capture and neutralize free radicals by binding and transferring zinc ions in a redox-dependent fashion, forming the antioxidant system Zinc-Metalothionein (Zn-MT).
Highly sensitive analytical tools are required to study the relationship between Zn and MTs in sections from ocular tissues. These methodologies should permit the simultaneous localization (bioimaging) of metals and proteins. Laser ablation (LA) coupled to ICP-MS has shown a huge potential for bioimaging studies in biological tissues. In addition, the use of metal nanoclusters (NCs) as elemental tags will provide signal amplification, compared with other tags traditionally employed (e.g. polymeric tags). To this end, antibodies with gold nanoclusters (AuNCs) will be used in combination with LA-ICP-MS for the detection of different metallothioneins (MT 1/2 and 3) directly into the ocular tissue sections.
- Methods:
The AuNCs synthesized were bioconjugated with an Anti-MT 1/2 antibody and with Anti-MT 3 antibody. Next, using ocular tissue sections (5 microns thick) from different donors the immunoassays were performed. After the immunoassay protocol, imaging studies were carried out by LA-ICP-MS as well as by fluorescence (confocal microscope) in order to compare both methodologies.
- Results:
The MTs (measuring the Au signal) and the coordinated metals distribution (Zn and Cu) were successfully carried out in human ocular tissues, including sclera, choroid, retina and retinal pigment epithelium regions. The image patterns found in ocular tissues were in agreement with those reported by conventional immunohistochemistry.
- Conclusions:
It is possible to know the distribution of MT proteins and different coordinated metals using bioconjugated AuNCs and LA-ICP-MS. Proposed analytical tools could help to better understand the roles of the antioxidant system Zinc-Metalothionein in the eye.
An immunohistochemical method is described to visualize the distribution of metallothioneins 1/2 (MT 1/2) and metallothionein 3 (MT 3) in human ocular tissue. It is making use of (a) antibodies conjugated to gold nanoclusters (AuNCs) acting as labels, and (b) laser ablation (LA) coupled to inductively coupled plasma – mass spectrometry (ICP-MS). Water-soluble fluorescent AuNCs (with an average size of 2.7 nm) were synthesized and then conjugated to antibody by carbodiimide coupling. The surface of the modified AuNCs was then blocked with hydroxylamine to avoid nonspecific interactions with biological tissue. Immunoassays for MT 1/2 and MT 3 in ocular tissue sections (5 μm thick) from two post mortem human donors were performed. Imaging studies were then performed by fluorescence using confocal microscopy, and LA-ICP-MS was performed in the retina to measure the signal for gold. Signal amplification by the >500 gold atoms in each nanocluster allowed the antigens (MT 1/2 and MT 3) to be imaged by LA-ICP-MS using a laser spot size as small as 4 μm. The image patterns found in retina are in good agreement with those obtained by conventional fluorescence immunohistochemistry which was used as an established reference method.