Metabolic analysis of mouse brains that have compromised iron storage

Periodic limb movements during sleep: a narrative review

Objective

Using narrative review techniques, this paper evaluates the evidence for separable underlying patho-mechanisms of periodic limb movements (PLMs) to separable PLM motor patterns and phenotypes, in order to elucidate potential new treatment modalities.

Background

Periodic limb movement disorder (PLMD) is estimated to occur in 5–8% of the paediatric population and 4–11% of the general adult population. Due to significant sleep fragmentation, PLMD can lead to functional impairment, including hyperactivity and delayed language development in children, and poor concentration and work performance in adults. Longitudinal data demonstrate that those with PLMD are at greater risk of depression and anxiety, and a 4-fold greater risk of developing dementia. PLMD has been extensively studied over the past two decades, and several key insights into the genetic, pathophysiological, and neural correlates have been proposed. Amongst these proposals is the concept of separable PLM phenotypes, proposed on the basis of nocturnal features such as the ratio of limb movements and distribution throughout the night. PLM phenotype and presentation, however, varies significantly depending on the scoring utilized and the nocturnal features examined, across age, and co-morbid clinical conditions. Furthermore, associations between these phenotypes with major neurologic and psychiatric disorders remain controversial.

Methods

In order to elucidate potential divergent biological pathways that may help clarify important new treatment modalities, this paper utilizes narrative review and evaluates the evidence linking PLM motor patterns and phenotypes with hypothesised underlying patho-mechanisms. Distinctive, underlying patho-mechanisms include: a pure motor mechanism originating in the spinal cord, iron deficiency, dopamine system dysfunction, thalamic glutamatergic hyperactivity, and a more cortical-subcortical interplay. In support of the latter hypothesis, PLM rhythmicity appears tightly linked to the microarchitecture of sleep, not dissimilarly to the apnoeic/hypopneic events seen in obstructive sleep apnea (OSA).

Conclusions

This review closes with a proposal for greater investigation into the identification of potential, divergent biological pathways. To do so would require prospective, multimodal imaging clinical studies which may delineate differential responses to treatment in restless legs syndrome (RLS) without PLMS and PLMS without RLS. This could pave the way toward important new treatment modalities.

The importance of eukaryotic ferritins in iron handling and cytoprotection

Ferritins, the main intracellular iron storage proteins, have been studied for over 60 years, mainly focusing on the mammalian ones. This allowed the elucidation of the structure of these proteins and the mechanisms regulating their iron incorporation and mineralization. However, ferritin is present in most, although not all, eukaryotic cells, comprising monocellular and multicellular invertebrates and vertebrates. The aim of this review is to provide an update on the general properties of ferritins that are common to various eukaryotic phyla (except plants), and to give an overview on the structure, function and regulation of ferritins. An update on the animal models that were used to characterize H, L and mitochondrial ferritins is also provided. The data show that ferritin structure is highly conserved among different phyla. It exerts an important cytoprotective function against oxidative damage and plays a role in innate immunity, where it also contributes to prevent parenchymal tissue from the cytotoxicity of pro-inflammatory agonists released by the activation of the immune response activation. Less clear are the properties of the secretory ferritins expressed by insects and molluscs, which may be important for understanding the role played by serum ferritin in mammals.

Thalamic glutamate/glutamine in restless legs syndrome: increased and related to disturbed sleep

OBJECTIVE

To evaluate possible abnormal increase in thalamic glutamate/glutamine levels for restless legs syndrome (RLS) indicating increased glutamatergic activity producing arousal that at night disrupts and shortens sleep.

METHODS

(1)H MRS of the right thalamus was performed using a 1.5 T GE MRI scanner and the PROBE-P (PRESS) on 28 patients with RLS and 20 matched controls. The Glx signal (combination of mostly glutamate [Glu] and glutamine [Gln]) was assessed as a ratio to the total creatine (Cr). This study tested 2 primary hypotheses: 1) higher thalamic Glx/Cr for patients with RLS than controls; 2) thalamic Glx/Cr correlates with increased wake during the sleep period.

RESULTS

The Glx/Cr was higher for patients with RLS than controls (mean ± SD 1.20 ± 0.73 vs 0.80 ± 0.39, t = 2.2, p = 0.016) and correlated significantly with the wake time during the sleep period (r = 0.61, p = 0.007) and all other RLS-related polysomnographic sleep variables (p < 0.05) except for periodic leg movements during sleep (PLMS)/hour.

CONCLUSIONS

The primary findings introduce 2 new related dimensions to RLS: abnormalities in a major nondopaminergic neurologic system and the arousal disturbance of sleep. The strong relation of the arousal sleep disturbance to glutamate and the lack of relation to the PLMS motor features of RLS contrasts with the reverse for dopamine of a limited relation to arousal sleep disturbance but strong relation to PLMS. Understanding this dichotomy and the interaction of these 2 differing systems may be important for understanding RLS neurobiology and developing better treatments for RLS.

Iron supplementation dose for perinatal iron deficiency differentially alters the neurochemistry of the frontal cortex and hippocampus in adult rats

BACKGROUND

Long-term prefrontal cortex (PFC)- and hippocampus-based cognitive deficits are the sequelae of perinatal iron deficiency, despite iron supplementation starting in the newborn period. Whether high-dose iron supplementation prevents these deficits is yet to be determined.

METHODS

Perinatal iron deficiency was induced in rat pups using a low-iron (3 mg/kg diet) diet during gestation until postnatal day (P)8. Iron was supplemented using a standard (40 mg/kg diet) or a 10-fold higher (400 mg/kg diet) iron-containing diet until P21. PFC and hippocampal neurochemistry was determined using in vivo (1)H nuclear magnetic resonance (NMR) spectroscopy at 9.4 Tesla on P90.

RESULTS

Both standard and 10-fold higher iron supplementation doses corrected anemia and brain iron deficiency by P21. The neurochemical profile of the PFC in both supplementation groups was comparable with the control group. In the hippocampus, standard-dose iron supplementation resulted in lower concentrations of N-acetylaspartate (NAA) and phosphoethanolamine (PE) and higher concentrations of N-acetylaspartylglutamate (NAAG) and glycerophosphocholine + phosphocholine (GPC + PC). High-dose iron supplementation resulted in lower PE and higher GPC + PC concentrations.

CONCLUSION

The iron supplementation dose for perinatal iron deficiency differentially alters the neurochemical profile of the PFC and hippocampus in adults. The neurochemical changes suggest altered glutamatergic neurotransmission, hypomyelination, and abnormal phospholipid metabolism in the formerly iron-deficient (FID) hippocampus.

Ferritin nanoparticles as magnetic resonance reporter gene

Dynamic imaging of gene expression in live animals is among the exciting challenges of molecular imaging. To achieve that, one of the approaches is to use reporter genes that encode for the synthesis of easily detectable products. Such reporter genes can be designed to be expressed under the control of the regulatory elements included in a promoter region of a gene of interest, thus allowing the use of the same reporter gene for the detection of multiple genes. The most commonly used reporter genes include the firefly light-generating enzyme luciferase and the green fluorescent protein detectable by bioluminescence and fluorescence optical imaging, respectively. Over the last years a number of studies demonstrated the ability to use the iron-binding protein ferritin as a reporter gene that allows the detection of gene expression by magnetic resonance imaging (MRI). MRI provides high spatial resolution and soft tissue contrast for deep tissues along with a large arsenal of functional and anatomical contrast mechanisms that can be correlated with gene expression, and can potentially be translated into clinical use.

Gestational and lactational iron deficiency alters the developing striatal metabolome and associated behaviors in young rats

Gestational and early postnatal iron deficiency occurs commonly in humans and results in altered behaviors suggestive of striatal dysfunction. We hypothesized that early iron deficiency alters the metabolome of the developing striatum and accounts for abnormalities in striatum-dependent behavior in rats. Sixteen metabolite concentrations from a 9-11 microL volume within the striatum were serially assessed in 10 iron-deficient and 10 iron-sufficient rats on postnatal days 8, 22 (peak anemia), and 37 (following recovery from anemia) using (1)H NMR spectroscopy at 9.4 tesla. Chin-elicited bilateral forelimb placing and vibrissae-elicited unilateral forelimb placing were also assessed on these days. Iron deficiency altered metabolites indexing energy metabolism, neurotransmission, glial integrity, and myelination over time (P < 0.05). Successful development of behaviors was delayed in the iron-deficient group (P < or = 0.01). Alterations in creatine, glucose, glutamine, glutamate, N-acetylaspartate, myo-inositol, and glycerophosphorylcholine + phosphorylcholine concentrations accounted for 77-83% of the behavioral variability during peak anemia on postnatal day 22 in the iron-deficient group. Correction of anemia normalized the striatal metabolome but not the behaviors on postnatal day 37. These novel data imply that alterations in the metabolite profile of the striatum likely influence later neural functioning in early iron deficiency.