Biomedical subjects

James R Connor

Publications and source records attributed to James R Connor.

41 records · Page 3Linked to original sources

PubMed2002

H and L ferritin subunit mRNA expression differs in brains of control and iron-deficient rats.

The mRNA expression of ferritin subunits has not been studied thoroughly in the brain regions of iron-deficient rats. Sprague-Dawley rats (n = 26; 21 d old) were randomly assigned to an iron-deficient (3.5 mg Fe/kg diet) or a control diet (35 mg Fe/kg diet) for 6 wk. Ferritin protein and mRNA contents were quantified and the cellular expression of ferritin subunits in brain was determined. H and L ferritin had the same mRNA locations in nearly all brain regions. Both ferritin subunit mRNAs had heterogeneous distributions and there was a regional effect across brain regions. Iron deficiency did not affect the amount of ferritin mRNA in most brain regions, suggesting the post-transcriptional regulation of messengers by iron status. H ferritin protein was predominant in neurons and oligodendrocytes, whereas L ferritin protein and iron predominated in microglia cells and astrocytes as well as in oligodendrocytes and neurons. Ferritin mRNA was detectable only in neurons. Iron deficiency did not induce new types of cells containing either ferritin protein or mRNA. The fact that ferritin protein was found in four types of cells whereas mRNA was found in only one type of cell suggests that the site of ferritin synthesis is different from protein location in the brain. All of these data suggest that regulation of ferritin subunits is cellular and/or regional specific.

Animals↗

PubMed2002

Nitric oxide protects astrocytes from oxidative stress.

Oxidative stress in astrocytes has been observed in a number of pathological conditions, however the effect of nitric oxide on oxidatively stressed astrocytes remains unclear. The goal of this research was to determine how nitric oxide influences the mechanism of peroxide-induced oxidative stress in astrocytes. We used enriched mouse-astrocyte cultures and tertiary-butyl hydroperoxide to study astrocyte oxidative stress. Cellular integrity was measured at the ultrastructural level by electron microscopy and plasma membrane integrity measured by lactate dehydrogenase release. Mitochondrial swelling and disruption of cristae were observed by electron microscopy in the absence of damage to other organelles. Astrocytes exposed to peroxide eventually succumbed to necrotic loss of plasma membrane integrity. However, when astrocytes were subjected to oxidative stress in the presence of nitric oxide, mitochondrial integrity was preserved and cell death delayed. This protection of nitric oxide resembled that of iron chelation and nitric oxide reduced susceptibility usually associated with iron-loaded astrocytes exposed to oxidative stress. Taken together, these data suggest that nitric oxide can act as a powerful antioxidant for astrocytes preserving mitochondrial and cellular integrity during oxidative stress.

Animals↗

PubMed2002

The lipophilic iron compound TMH-ferrocene [(3,5,5-trimethylhexanoyl)ferrocene] increases iron concentrations, neuronal L-ferritin, and heme oxygenase in brains of BALB/c mice.

Mismanagement of intracellular iron is a key pathological feature of many neurodegenerative diseases. Our long-term goal is to use animal models to investigate the mechanisms of iron neurotoxicity and its relationship to neurodegenerative pathologies. The immediate aim of this experiment was to determine regional distribution of iron and cellular distribution of iron storage proteins (L- and H-ferritin) and an oxidative stress marker (heme oxygenase-1) in brains of mice fed the lipophilic iron compound (3,5,5-trimethylhexanoyl) (TMH)-ferrocene. We fed male and female weanling BALB/cj mice diets either deficient in iron (0 mg Fe/kg diet), adequate in iron (35 mg Fe/kg diet; control mice), or adequate in iron and supplemented with 0.1 or 1.0 g TMH-ferrocene/kg diet for 8 wk. Iron concentrations in cerebrum were higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p < 0.05). Liver iron concentrations were eightfold higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p < 0.0001). L-Ferritin and heme oxygenase-1 expression were elevated in striatum in mice fed 1.0 g TMH-ferrocene/kg diet. We conclude that administration of the lipophilic iron compound TMH-ferrocene leads to subtle perturbations of cellular iron within the brain, potentially representing a model of iron accumulation similar to that seen in various neuropathological conditions.

Animals↗

PubMedDate not supplied

Brain iron uptake in hypotransferrinemic mice: influence of systemic iron status.

The relationship of the heterogeneity of iron concentrations in the brain with the regulation of iron uptake into specific brain regions remains unresolved. We used hypotransferrinemic mice and an iron-deficient or control diet to explore whether plasma transferrin (Tf), transferrin saturation, and plasma iron levels influence the uptake of (59)Fe and whether there was brain region specificity. Weaning wild-type (+/+) and heterozygotic mice (+/hpx), were sorted randomly to either a iron-deficient diet or a control iron diet for 8 weeks, whereas homozygous mice (hpx/hpx) ate the control diet for 8 weeks before (59)Fe uptake studies. Iron-deficient heterozygous and wild-type mice both had significantly greater plasma Tf levels (37.5 and 42.5 microM) than control mice had (heterozygous and wild-type controls were 20 and 32.5 microM) and far more than homozygous mice (<0.2 microM) had, thus providing five distinct levels of plasma Tf concentrations. After intravenous injection of (59)Fe, brains of iron-deficient wild-type mice took up significantly more (59)Fe (0.15% dose) compared to control wild-type mice (0.056%) at 2 hr, a treatment effect that persisted through 24 hr. In contrast, diet had no effect in heterozygous mice. Importantly, homozygous mice had equivalent uptake to other groups (0.089% dose) by 24 hr. Early brain radioactivity varied by regions (hypothalamus and prefrontal cortex approximately 10-18% brain uptake > cerebellum, pons, thalamus, and striatum approximately 7-12% > cortex, hippocampus, and substantia nigra approximately 6-8%). This distribution of radioactivity changed over 24 hr in the hypothalamus of heterozygous mice, homozygous mice, and iron-deficient wild-type mice. Homozygous mice also showed higher uptake (13-15%) in some regions (hypothalamus and cerebellum) than in other regions. In wild-type and heterozygous mice, (59)Fe uptake was inversely related to brain Tf and was independent of regional brain iron concentrations and plasma Tf levels or saturation. These experimental data suggest that brain iron uptake may be constitutive and independent of plasma Tf, transferrin saturation, or regional brain iron concentration. The proteins and mechanisms responsible for additional iron uptake into specific regions, or perhaps the redistribution are unclear though the data are supportive of a non-transferrin-bound iron uptake pathway.

Analysis of Variance↗

PubMedDate not supplied

Pre- and postweaning iron deficiency alters myelination in Sprague-Dawley rats.

Iron deficiency in early life is associated with hypomyelination; however, the role which iron plays in myelinogenesis is not clearly established. In this study, we examined the effect of preweaning [postnatal days (PND) 4-14 and PND 4-21] and postweaning (PND 21-63) iron deficiency on hindbrain 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) activity (marker of oligodendrocyte metabolic activity) and myelin basic protein (MBP) concentrations. Both CNPase activity and concentrations in the cerebrum and hindbrain were significantly lower in pre- and postweaning iron-deficient rats. Similarly, MBP concentrations were also reduced (25-35%) in all three groups of iron-deficient animals. Iron-deficient animals also had significant alterations in the fatty acid composition of individual phospholipids within the hindbrain as well as changes in cytochrome oxidase activities. These studies show that postnatal iron deficiency, for as little as 10 days, can significantly alter the production of myelin and oligodendrocyte functioning. Importantly, postweaning iron deficiency was still associated with a decrease in CNPase activity and MBP concentrations despite occurring well past a likely key sensitive period of peak myelinogenesis at PND 8-12. This suggests that iron deficiency in later life, as well as during early postnatal growth, can effect the production and maintenance of myelin.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗