Speciation of iron in mouse liver during development, iron deficiency, IRP2 deletion and inflammatory hepatitis

Abstract

The iron content of livers from 57Fe-enriched C57BL/6 mice of different ages were investigated using Mössbauer spectroscopy, electron paramagnetic resonance (EPR), electronic absorption spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS). About 80% of the Fe in an adult liver was due to blood; thus removal of blood by flushing with buffer was essential to observe endogenous liver Fe. Even after exhaustive flushing, ca. 20% of the Fe in anaerobically dissected livers was typical of deoxy-hemoglobin. The concentration of Fe in newborn livers was the highest of any developmental stage (~ 1.2 mM). Most was stored as ferritin, with little mitochondrial Fe (consisting primarily of Fe/S clusters and haems) evident. Within the first few weeks of life, about half of ferritin Fe was mobilized and exported, illustrating the importance of Fe release as well as Fe storage in liver function. Additional ferritin Fe was used to generate mitochondrial Fe centres. From ca. 4 weeks of age to the end of the mouse’s natural lifespan, the concentration of mitochondrial Fe in liver was essentially invariant. A minor contribution from nonhaem high-spin FeII was observed in most liver samples and was also invariant with age. Some portion of these species may constitute the labile iron pool. Livers from mice raised on an Fe-deficient diet were highly Fe depleted; they were devoid of ferritin and contained 1/3 as much mitochondrial Fe as found in Fe-sufficient livers. In contrast, brains of the same Fe-deficient mice retained normal levels of mitochondrial Fe. Livers from mice with inflammatory hepatitis and from IRP2(−/−) mice hyper-accumulated Fe. These livers had high ferritin levels but low levels of mitochondrial Fe.

Mössbauer Spectra of Mouse Hearts Reveal Age-dependent Changes in Mitochondrial and Ferritin Iron Levels

“…The CD is due collectively to [Fe 4 S 4 ] 2ϩ clusters and low-spin Fe II hemes; the two types of centers cannot be resolved by MB spectroscopy because they are diamagnetic and have similar ␦ and ⌬E Q values. The CD dominates the spectrum of mitochondria isolated from brain, liver, and human cells (34,38,41), which allows us to assign this spectral feature to respiration-related complexes in that organelle.…”

“…Doing so increases TfR1 expression and decrease ferritin levels. IRP2 Ϫ/Ϫ mice accumulate large amounts of iron in the liver (33)(34)(35)(36), whereas IRP2 Ϫ/Ϫ brains contain WT levels of iron and WT MB features (34).…”

“…Nevertheless, we enriched mice with 57 Fe for this study. In earlier studies, we used MB spectroscopy to characterize the iron content of brain and liver (34,38,39). Here we use MB to probe the iron content of healthy mouse hearts during development.…”

Study of iron complexes in visceral organs and brain from a 57Fe enriched β-thalassaemia mouse model via Mössbauer spectroscopy

“…Besides the work by Bou-Abdallah et al [5], two other studies by Holmes-Hampton et al [12] and Chakrabarti et al [11] also used two doublets to describe this area of the spectrum from the liver and brain of healthy mice, but with different parameters. The authors attributed their sub-doublets to ferritin and to mitochondrial respiratory complexes ([Fe 4 S 4 ] 2+ clusters and low-spin Fe(II) haem centres).…”

“…Ferritin and haemosiderin isolated from iron-overloaded human spleens has also been investigated by MS, at the temperatures of 1.3 and 200K [10]. The brain, liver and hearts of 57 Fe enriched healthy mice were studied by various researchers [11][12][13]. Haemoglobin from residual blood, ferritin, mitochondrial iron, and mononuclear non-haem high-spin (NHHS) Fe(II) and Fe(III) species were identified in brain samples [12].…”