Iron distribution in the liver and duodenum during seasonal iron overload in Svalbard reindeer

Evaluation of the use of reindeer droppings for monitoring essential and non-essential elements in the polar terrestrial environment

Excess or toxic metals, non-metals and metalloids can be eliminated from the organism by deposition in inert tissue (e.g. fur) or excretion with body secretions, urine and faeces. Droppings are one of the main routes for the elimination of multiple elements and they can be collected without direct contact with the animal. Contaminant concentration has been examined in non-lethally collected tissues of several species (especially reptilian, avian and mammalian). However, studies on species residing in polar areas are still limited, especially of mammals from the European Arctic. Reindeers are the only large herbivores living in Svalbard, being an essential part of the Arctic terrestrial ecosystem. Although reindeer presence has a high impact on their surroundings, those huge mammals are rarely part of ecotoxicological studies regarding metal pollution. In this paper, the droppings of Svalbard reindeer were used as a non-invasively collected tissue to examine the excretion pathway of 30 elements. Samples were collected in mesic and moss tundra, representing summer, winter and winter-transitional excretion. For more than a half of the studied elements, significant differences occurred between the samples collected in the two tundra types. The feasibility of older and fresh samples was assessed based on summer droppings, and significant differences were found for K, As, Mn, Na, Ni, and Sb concentrations. No relevant differences in element levels were observed for samples collected from adult females, adult males and calves, except for zinc and potassium. Results show that reindeer droppings are an important vector for the transfer of many metals, non-metals and metalloids including calcium, phosphorus, zinc, aluminium and lead. As a sedentary species, feeding on local food sources, Svalbard reindeer is a valuable indicator of trace element presence in the polar terrestrial ecosystem.

Svalbard reindeer as an indicator of ecosystem changes in the Arctic terrestrial ecosystem

Over the years, noticeable effort has been directed towards contaminant determination in multiple biotic samples collected from the inhabitants of the Arctic. Little consideration has been given to polar herbivores, however, especially those from the European parts of the Arctic. To provide a broader perspective, we aimed to decipher trace element concentration in hairs of the key species in the Arctic, namely the Svalbard reindeer (Rangifer tarandus platyrhynchus), and to recognise whether diet variations could correspond with forward exposure. The effect of habitat and diet was investigated using the ratios of stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N), and previous literature studies on vegetation from the areas of interest. Analysis was performed for eighteen elements in total, both toxic and essential. Metals were present in a decreasing order Fe > Zn > Ba > Cu > Pb > Cr > Ni > V > Ga =La > Rb > As > Li > Co > Hg > Cd > Cs > Be. Similarity in trends in the studied subpopulations was observed for many metals. A significant log-linear correlation was observed for most of the elements, excluding nitrogen and carbon isotopes signature. Extremely high iron levels were determined in some of the samples, suggesting past iron overload. Zinc, in contrast to the remaining metals, did not correlate well with any other element. Mercury was determined at very low levels, in accordance with previous literature regarding its concentrations in moss and lichen species in Svalbard. The analysis of stable isotopes showed a high variation in nitrogen isotopes signatures. Further research is required to properly evaluate the potential health risks and ecological implications of elevated exposure.

Iron-rich ferritin in the hypoxia-tolerant rodent Spalax ehrenbergi: a naturally-occurring biomarker confirms the internalization and pathways of intracellular macromolecules

The discovery of pits/caveolae in the plasmalemma advanced the study of macromolecule internalization. "Transcytosis" describes the transport of macromolecular cargo from one front of a polarized cell to the other within membrane-bounded carrier(s), via endocytosis, intracellular trafficking and exocytosis. Clathrin-mediated transcytosis is used extensively by epithelial cells, while caveolae-mediated transcytosis mostly occurs in endothelial cells. The internalization pathways were monitored by various markers, including radioisotopes, nanoparticles, enzymes, immunostains, and fluorophores. We describe an internalization pathway identified using a naturally-occurring biomarker, in vivo assembled ferritin, containing electron-dense iron cores. Iron, an essential trace metal for most living species and iron homeostasis, is crucial for cellular life. Ferritin is a ubiquitous and highly conserved archeoprotein whose main function is to store a reserve iron supply inside the cytoplasm in a non-toxic form. Ferritin is present in all organisms which have a metabolic requirement for iron and in even in organisms whose taxonomic rank is very low. The newborns of the blind mole, Spalax ehrenbergi, are born and live in a hypoxic environment and have significant iron overload in their liver and heart, but their iron metabolism has not been previously studied. These newborns, which are evolutionarily adapted to fluctuations in the environmental oxygen, have a unique ability to sequester transplacental iron and store it in ferritin without any signs of iron toxicity. Using the ferrihydrite cores of ferritin, we were able to monitor the ferritin internalization from portals of its entry into the cytosol of hepatocytes and cardiomyocytes and into the lysosomes.

Protective effects of crude garlic by reducing iron-mediated oxidative stress, proliferation and autophagy in rats

The impact of garlic, known for its antioxidant activities, on iron metabolism has been poorly investigated. The aim of this work was to study the effect of crude garlic pre-treatment on iron-mediated lipid peroxidation, proliferation and autophagy for 5 weeks. Rats were fed distilled water or garlic solution (1 g/kg body weight) by gavage for the first 3 weeks as pre-treatment and received a basal diet supplemented or not with ferrous sulfate (650 mg Fe/kg diet) for the last 2 weeks of treatment. Immunohistochemistry labeling and ultrastuctural observations were used to evaluate the iron deleterious effects in the liver. Iron supplementation induced cell proliferation predominantly in non parenchymal cells comparing to hepatocytes, but not apoptosis. In addition, iron was accumulated within the hepatic lysosomes where it triggers autophagy as evidenced by the formation of autophagic vesicles detected by LC3-II staining. It also induced morphologic alterations of the mitochondrial membranes due to increased lipid peroxidation as shown by elevated iron and malondialdehyde concentrations in serum and tissues. Garlic pre-treatment reduced iron-catalyzed lipid peroxidation by decreasing the malondialdehyde level in the liver and colon and by enhancing the status of antioxidants. In addition, garlic reduced the iron-mediated cell proliferation and autophagy by lowering iron storage in the liver and protected mitochondrial membrane. Based on these results, garlic treatment significantly prevented iron-induced oxidative stress, proliferation and autophagy at both biochemical and histological levels due to its potent free radical scavenging and antioxidant properties.