Mitigation of helium irradiation-induced brain injury by microglia depletion

Background

Cosmic radiation exposures have been found to elicit cognitive impairments involving a wide-range of underlying neuropathology including elevated oxidative stress, neural stem cell loss, and compromised neuronal architecture. Cognitive impairments have also been associated with sustained microglia activation following low dose exposure to helium ions. Space-relevant charged particles elicit neuroinflammation that persists long-term post-irradiation. Here, we investigated the potential neurocognitive benefits of microglia depletion following low dose whole body exposure to helium ions.

Methods

Adult mice were administered a dietary inhibitor (PLX5622) of colony stimulating factor-1 receptor (CSF1R) to deplete microglia 2 weeks after whole body helium irradiation (⁴He, 30 cGy, 400 MeV/n). Cohorts of mice maintained on a normal and PLX5622 diet were tested for cognitive function using seven independent behavioral tasks, microglial activation, hippocampal neuronal morphology, spine density, and electrophysiology properties 4–6 weeks later.

Results

PLX5622 treatment caused a rapid and near complete elimination of microglia in the brain within 3 days of treatment. Irradiated animals on normal diet exhibited a range of behavioral deficits involving the medial pre-frontal cortex and hippocampus and increased microglial activation. Animals on PLX5622 diet exhibited no radiation-induced cognitive deficits, and expression of resting and activated microglia were almost completely abolished, without any effects on the oligodendrocyte progenitors, throughout the brain. While PLX5622 treatment was found to attenuate radiation-induced increases in post-synaptic density protein 95 (PSD-95) puncta and to preserve mushroom type spine densities, other morphologic features of neurons and electrophysiologic measures of intrinsic excitability were relatively unaffected.

Conclusions

Our data suggest that microglia play a critical role in cosmic radiation-induced cognitive deficits in mice and, that approaches targeting microglial function are poised to provide considerable benefit to the brain exposed to charged particles.

Pars plana vitrectomy for diabetic macular oedema: OCT and functional correlations

PURPOSE

A prospective study to evaluate the macular structural and functional effects of pars plana vitrectomy (PPV) for persistent diffuse clinically significant macular oedema (CSMO).

METHOD

A total of 12 patients with persistent diffuse CSMO were recruited and underwent assessment including best-corrected visual acuity, fundus fluorescein angiography, optical coherence tomography (OCT) and fine matrix mapping (FMM) at baseline and over a period of a year poststandard three-port PPV.

RESULTS

The median baseline ETDRS letters score for all 12 patients was 52 (range 41-63) while at 12 months it had increased to 65 (range of 27-68), an improvement of two complete ETDRS lines (P=0.037). Similarly, there was an improvement in the perifoveal cone thresholds (P=0.02). The foveal thickening for all 12 patients ranged from a median of 183 to 751 microm (normal range 126-180 microm) and the macular volume ranged from a median of 2.13 to 6.42 mm(3) (normal <1.66 mm(3)). After surgery, both the median foveal thickness (from 334 to 280 microm) and median macular volume (from 3.24 to 2.61 mm(3)) demonstrated decreases over 12 months (P=0.01). On baseline OCT, the patients fell into two anatomically distinct groups: Group 1 (n=4) had a dome-shaped thickened macula with a partial posterior hyaloid separation and a significantly higher foveal thickness and macular volume than Group 2 (n=8) which had a diffuse low-elevation profile of the thickened macula (P=0.007).

CONCLUSIONS

In this prospective study of PPV for persistent fovea-involving CSMO there was structural and functional improvement.

En face optical coherence tomography: a new method to analyse structural changes of the optic nerve head in rat glaucoma

AIM

To investigate en face optical coherence tomography (eOCT) and its use as an effective objective technique for assessing changes in the glaucomatous rat optic nerve head (ONH) in vivo, and compare it with confocal scanning laser ophthalmoscopy (cSLO).

METHODS

18 Dark Agouti (DA) rats with surgically induced ocular hypertension were imaged with eOCT and cSLO at regular intervals. Assessment included three dimensional (3D) topographic reconstructions, intensity z-profile plots, a new method of depth analysis to define a "multilayered" structure, and scleral canal measurements, in relation to the degree of intraocular pressure (IOP) exposure.

RESULTS

The increased depth resolution of the eOCT compared to the cSLO was apparent in all methods of analysis, with better discrimination of tissue planes. This was validated histologically. eOCT demonstrated several significant changes in imaged rat ONH which correlated with IOP exposure, including the area of ONH (p<0.01), separation between retinal vessel and scleral layers (p<0.05), and anterior scleral canal opening expansion (p<0.05).

CONCLUSION

eOCT appears to be effective in assessing rat ONH, allowing detailed structural analysis of the multilayered ONH structure. As far as the authors are aware, this is the first report of scleral canal expansion in a rat model. They suggest eOCT as a novel method for the detection of early changes in the ONH in glaucoma.

Diabetic macular oedema: pilot randomised trial of pars plana vitrectomy vs macular argon photocoagulation

INTRODUCTION

Focal macular photocoagulation for clinically significant macular oedema (CSME) is the proven method for treatment of this condition, but with little chance of visual improvement. Pars plana vitrectomy (PPV) may produce resolution of macular oedema and improvement in visual acuity. However, there have been no randomised trials to ascertain role of vitrectomy in the management of persistent CSME.

METHODS

Patients with persistent CSME despite previous macular photocoagulation and Snellen visual acuity 6/15 to 6/60 were recruited. Dilated fundoscopy, best-corrected visual acuity including Early Treatment Diabetic Retinopathy Study (ETDRS) vision, ocular coherence tomography and fundus fluorescein angiography (FFA) at baseline and up to 12 months post-treatment was performed. Exclusion criteria were signs of posterior vitreous detachment, macular traction or the taut posterior hyaloid face syndrome, or macular ischaemia on FFA. In all, 20 patients were randomised (10 in each arm) to either standard macular photocoagulation or PPV and removal of the posterior hyaloid face.

RESULTS

Of the 20 patients recruited, seven patients completed the protocol in the vitrectomy and eight in the laser arms, respectively. There was little evidence of any difference in the foveal thickness at 12 months between the two treatment arms despite a gradual improvement. Only one patient, from the vitrectomy arm, suffered moderate visual loss (defined as loss of 15 ETDRS letters) (our primary outcome).

DISCUSSION

In this pilot RCT, standard PPV provides little visual benefit compared to macular photocoagulation, but a larger definitive study is required to confirm this early appraisal.

Aging, carotid artery distensibility, and the Ser422Gly elastin gene polymorphism in humans

Elastin is a protein of the extracellular matrix that forms the major component of elastic fibers from the arterial wall thickness and plays an important role in elastic properties of large blood vessels. To study the relationships between the Ser422Gly polymorphism in exon 16 of the gene-encoding elastin and the distensibility of 2 different arteries, the radial artery (a muscular artery) and the common carotid artery (an elastic artery), we studied a cohort of 320 subjects (49+/-12 years of age) without evidence of cardiovascular disease and who had never been treated with cardiovascular drugs. Distensibility and elastic modulus were evaluated for the common carotid and the radial arteries with high-resolution echo-tracking devices (NIUS-02 and Wall Track System). The A-to-G nucleotide change corresponding to the Ser422Gly amino acid change was studied by digestion of polymerase chain reaction products with BstNI. Results indicate that genotype frequencies (AA=10%, AG=51%, GG=39%) were in agreement with the Hardy-Weinberg equilibrium. For the carotid artery, a significant decrease in distensibility was observed in subjects carrying the A allele (with AA+AG genotypes) compared with subjects with the GG genotype (13.8+/-6.4 kPa(-1). 10(-3) versus 15.9+/-6.2 kPa(-1). 10(-3), P<0.01), assuming a dominant effect of the A allele. Moreover, the presence of the A allele was associated with a significant increase in elastic modulus (0.98+/-0.40 kPa. 10(3) in subjects with AA+AG genotypes versus 0.83+/-0.41 kPa. 10(3) in subjects with GG genotypes, P<0.01). Multivariate analysis indicated that these results were observed after adjustment for age, gender, and mean arterial blood pressure (P<0.01). In contrast, no association was found between arterial parameters and genotypes for the radial artery. The 2-way analysis of covariance adjusted for mean arterial blood pressure indicated that the association between the A allele and distensibility of the carotid artery was observed only in subjects >50 years of age, assuming for carotid distensibility a significant age effect (P<0.01), genotype effect (P=0.01), and age-genotype interaction (P=0.04). The present results indicate a relationship between the Ser422Gly polymorphism and the distensibility of elastic arteries but not of muscular arteries and suggest that there is an age-genotype interaction for carotid artery distensibility.

Association between the apolipoprotein E polymorphism and arterial wall thickness in asymptomatic adults

OBJECTIVES

The polymorphism of the apolipoprotein E gene (epsilon2, epsilon3, epsilon4) affects plasma cholesterol but the relationship with artery wall thickness has indicated contradictory results. This study investigated the relationship between apolipoprotein E polymorphism and vascular phenotypes of the carotid and radial arteries, two arterial sites differently affected by atherosclerosis.

METHODS

We studied a cohort of 320 Caucasian subjects (age 49 +/- 12 years) without evidence of cardiovascular disease. Structural (internal diameter and wall thickness) and functional phenotypes (compliance, distensibility) were evaluated for the common carotid and the radial arteries using high resolution echo-tracking devices. Genotypes of apolipoprotein E were determined by allele-specific oligonucleotides hybridization. Because of the relative low frequency of some apolipoprotein E genotypes, they were designated as E2 (epsilon2/epsilon2, epsilon2/epsilon3), E3 (epsilon3/epsilon3), and E4 (epsilon4/epsilon4, epsilon3/epsilon4).

RESULTS

Apolipoprotein E allele frequencies were epsilon2 = 0.08, epsilon3 = 0.79, epsilon4 = 0.13. Subjects with epsilon4 allele had the highest levels of total serum cholesterol and low density lipoprotein cholesterol; subjects with epsilon2 allele had the lowest levels (P < 0.001). Considering carotid hypertrophy as intima-media thickness > 660 microm, and radial hypertrophy as intima-media thickness > 260 microm, a logistic regression model testing determinants of arterial hypertrophy (age, gender, weight, systolic blood pressure, smoking habits, and total serum cholesterol) observed a significant and positive association between carotid hypertrophy and epsilon2 allele carriers (P= 0.03). In contrast, no association was found between hypertrophy and apolipoprotein E genotypes for the radial artery. No association was observed between the apolipoprotein E genotypes and functional artery parameters.

CONCLUSIONS

In subjects without any evidence of cardiovascular disease, the presence of the epsilon2 allele is related to wall hypertrophy in carotid artery despite favourable effect on the lipid profile.

Skeletal muscle form and function after 4 hr ischemia-hypothermia

The purpose of this study was to examine the use of hypothermia to protect skeletal muscle from the effects of 4 hr of tourniquet ischemia. Muscle recovery was investigated at 6 weeks. Four hours of tourniquet ischemia was induced in two groups (n = 8 per group) of male, Wistar rats (344 +/- 15 g). In the ischemia-only group (IO), the ischemic leg was exposed to room temperature. In the ischemic-hypothermic group (IH), the ischemic leg was cooled to 5-8 degrees C throughout the ischemic period. The contralateral leg served as control. After 6 weeks, the isometric contractile function of the gastrocnemii of both the ischemic and nonischemic legs was determined. Following the functional assessment, the soleus and plantaris muscles were removed and weighed, and biopsies were taken for muscle fiber composition, mean fiber area, and myosin heavy chains (MHC) analysis. Differences between groups (P < 0.05) were determined using ANOVA. Muscle wet weight, tetanic forces, fiber area, fiber type, and MHC composition of IH group were the same as the control group. Yet, twitch tension and relaxation time were lower and longer in the IH group than control group. The tetanic force at 100 Hz of the IH group (12.62 +/- 0.73 N/g) was significantly greater than that of the IO group (2.12 +/- 0.84 N/g). The type 1 muscle fiber areas of plantaris in the IH (1.84 +/- 0.04 x 1000 microns 2) were significantly greater than those of the IO group (1.56 +/- 0.42 x 1000 microns 2).(ABSTRACT TRUNCATED AT 250 WORDS)