CCR3 plays a role in murine age-related cognitive changes and T-cell infiltration into the brain

Targeting immune-mediated, age-related, biology has the potential to be a transformative therapeutic strategy. However, the redundant nature of the multiple cytokines that change with aging requires identification of a master downstream regulator to successfully exert therapeutic efficacy. Here, we discovered CCR3 as a prime candidate, and inhibition of CCR3 has pro-cognitive benefits in mice, but these benefits are not driven by an obvious direct action on central nervous system (CNS)-resident cells. Instead, CCR3-expressing T cells in the periphery that are modulated in aging inhibit infiltration of these T cells across the blood-brain barrier and reduce neuroinflammation. The axis of CCR3-expressing T cells influencing crosstalk from periphery to brain provides a therapeutically tractable link. These findings indicate the broad therapeutic potential of CCR3 inhibition in a spectrum of neuroinflammatory diseases of aging.

Drug characteristics derived from kinetic modeling: combined 11C-UCB-J human PET imaging with levetiracetam and brivaracetam occupancy of SV2A

BACKGROUND

Antiepileptic drugs, levetiracetam (LEV) and brivaracetam (BRV), bind to synaptic vesicle glycoprotein 2A (SV2A). In their anti-seizure activity, speed of brain entry may be an important factor. BRV showed faster entry into the human and non-human primate brain, based on more rapid displacement of SV2A tracer ¹¹C-UCB-J. To extract additional information from previous human studies, we developed a nonlinear model that accounted for drug entry into the brain and binding to SV2A using brain ¹¹C-UCB-J positron emission tomography (PET) data and the time-varying plasma drug concentration, to assess the kinetic parameter K₁ (brain entry rate) of the drugs.

METHOD

Displacement (LEV or BRV p.i. 60 min post-tracer injection) and post-dose scans were conducted in five healthy subjects. Blood samples were collected for measurement of drug concentration and the tracer arterial input function. Fitting of nonlinear differential equations was applied simultaneously to time-activity curves (TACs) from displacement and post-dose scans to estimate 5 parameters: K₁ (drug), K₁(¹¹C-UCB-J, displacement), K₁(¹¹C-UCB-J, post-dose), free fraction of ¹¹C-UCB-J in brain (f_ND(¹¹C-UCB-J)), and distribution volume of ¹¹C-UCB-J (V_T(UCB-J)). Other parameters (K_D(drug), K_D(¹¹C-UCB-J), f_P(drug), f_P(¹¹C-UCB-J, displacement), f_P(¹¹C-UCB-J, post-dose), f_ND(drug), k_off(drug), k_off(¹¹C-UCB-J)) were fixed to literature or measured values.

RESULTS

The proposed model described well the TACs in all subjects; however, estimates of drug K₁ were unstable in comparison with ¹¹C-UCB-J K₁ estimation. To provide a conservative estimate of the relative speed of brain entry for BRV vs. LEV, we determined a lower bound on the ratio BRV K₁/LEV K₁, by finding the lowest BRV K₁ or highest LEV K₁ that were statistically consistent with the data. Specifically, we used the F test to compare the residual sum of squares with fixed BRV K₁ to that with floating BRV K₁ to obtain the lowest possible BRV K₁; the same analysis was performed to find the highest LEV K₁. The lower bound of the ratio BRV K₁/LEV K₁ was ~ 7.

CONCLUSIONS

Under appropriate conditions, this advanced nonlinear model can directly estimate entry rates of drugs into tissue by analysis of PET TACs. Using a conservative statistical cutoff, BRV enters the brain at least sevenfold faster than LEV.

Deep Longitudinal Proteomics Profiling Reveals Biological Pathways Responding to GRF6019 in Two AD Clinical Trials

Blood has been widely investigated to discover biomarkers and gain insights into the biology of aging and age-related diseases. Its protein composition provides insights into complex biological processes, as proteins are often direct regulators of cellular pathways. In clinical trials, selected proteins have been used as primary and secondary endpoints, but recent methodological developments allow the measurement of thousands of proteins with very high sensitivity and specificity. In two phase 2 clinical trials testing the safety, tolerability, and feasibility of infusions of the plasma fraction GRF6019 in Alzheimer's disease (AD), we measured more than 7000 proteins in plasma over the course of the clinical trials. Differential trajectories analysis revealed groups of proteins and pathways that were responding to GRF6019. Several pathways were relevant to the biology of aging and AD and our study suggests that deep proteomics profiling can inform on specific biological processes responding to treatment in clinical trials.

Safety and Tolerability of GRF6019 Infusions in Severe Alzheimer's Disease: A Phase II Double-Blind Placebo-Controlled Trial

BACKGROUND

The plasma fraction GRF6019 shows multiple benefits on brain aging in mice, including enhanced cognition, neurogenesis, and synaptic density, as well as reduced neuroinflammation.

OBJECTIVE

To evaluate the safety, tolerability, and preliminary efficacy of GRF6019 in patients with severe Alzheimer's disease (AD).

METHODS

A phase II, double-blind, placebo-controlled study in patients with severe AD (Mini-Mental State Examination score 0-10). Patients were randomized 2 : 1 to GRF6019 (N = 18) or placebo (N = 8) and received daily 250 mL intravenous infusions over 5 days. The primary endpoints were the rates of adverse events (AEs) and the tolerability of GRF6019 as assessed by the number of patients completing the study. Change from baseline in cognitive and functional assessments was also evaluated.

RESULTS

All patients completed 100%of study visits and infusions. The rate of AEs was similar in the GRF6019 (8/18 patients [44.4%]) and placebo (3/8 patients [37.5%]) groups, and there were no deaths or serious AEs. The most common AEs considered related to treatment were mild, transient changes in blood pressure in the GRF6019 group (hypotension: 2 patients [11.1%]; hypertension: 1 patient [5.6%]); there were no related AEs in the placebo group. The trial was not powered to detect statistically significant differences between treatment groups. At the end of the study, patients in both treatment groups remained stable or improved on all cognitive and functional endpoints.

CONCLUSION

GRF6019 demonstrated excellent safety, feasibility, and tolerability. Future trials designed to characterize the potential functional benefits of GRF6019 and related plasma fractions in severe AD are warranted.

Safety and tolerability of GRF6019 in mild-to-moderate Alzheimer's disease dementia

INTRODUCTION

This phase 2 trial evaluated the safety, tolerability, and feasibility of repeated infusions of the plasma fraction GRF6019 in mild-to-moderate Alzheimer's disease.

METHODS

In this randomized, double-blind, dose-comparison trial, 47 patients were randomized 1:1 to receive daily infusions of 100 mL (n = 24) or 250 mL (n = 23) of GRF6019 for 5 consecutive days over two dosing periods separated by a treatment-free interval of 3 months.

RESULTS

The mean (standard deviation [SD]) age of the enrolled patients was 74.3 (6.9), and 62% were women. Most adverse events (55%) were mild, with no clinically significant differences in safety or tolerability between the two dose levels. The mean (SD) baseline Mini-Mental State Examination score was 20.6 (3.7) in the 100 mL group and 19.6 (3.7) in the 250 mL group; at 24 weeks, the within-patient mean change from baseline was -1.0 points (95% confidence interval [CI], -3.1 to 1.1) in the 100 mL group and +1.5 points (95% CI, -0.4 to 3.3) in the 250 mL group. The within-patient mean change from baseline on the Alzheimer's Disease Assessment Scale-Cognitive subscale was -0.4 points (95% CI, -2.9 to 2.2) in the 100 mL group, while in the 250 mL group it was -0.9 points (95% CI, -3.0 to 1.2). The within-patient mean change from baseline on the Alzheimer's Disease Cooperative Study-Activities of Daily Living was -0.7 points in the 100 mL group (95% CI, -4.3 to 3.0) and -1.3 points (95% CI, -3.4 to 0.7) in the 250 mL group. The mean change from baseline on the Category Fluency Test, Clinical Dementia Rating Scale-Sum of Boxes, Alzheimer's Disease Cooperative Study-Clinical Global Impression of Change, and Neuropsychiatric Inventory Questionnaire was similar for both treatment groups and did not show any worsening.

DISCUSSION

GRF6019 was safe and well tolerated, and patients experienced no cognitive decline and minimal functional decline. These results support further development of GRF6019.

Padsevonil randomized Phase IIa trial in treatment-resistant focal epilepsy: a translational approach

Therapeutic options for patients with treatment-resistant epilepsy represent an important unmet need. Addressing this unmet need was the main factor driving the drug discovery program that led to the synthesis of padsevonil, a first-in-class antiepileptic drug candidate that interacts with two therapeutic targets: synaptic vesicle protein 2 and GABA_A receptors. Two PET imaging studies were conducted in healthy volunteers to identify optimal padsevonil target occupancy corresponding to levels associated with effective antiseizure activity in rodent models. Optimal padsevonil occupancy associated with non-clinical efficacy was translatable to humans for both molecular targets: high (>90%), sustained synaptic vesicle protein 2A occupancy and 10-15% transient GABA_A receptor occupancy. Rational dose selection enabled clinical evaluation of padsevonil in a Phase IIa proof-of-concept trial (NCT02495844), with a single-dose arm (400 mg bid). Adults with highly treatment-resistant epilepsy, who were experiencing ≥4 focal seizures/week, and had failed to respond to ≥4 antiepileptic drugs, were randomized to receive placebo or padsevonil as add-on to their stable regimen. After a 3-week inpatient double-blind period, all patients received padsevonil during an 8-week outpatient open-label period. The primary endpoint was ≥75% reduction in seizure frequency. Of 55 patients randomized, 50 completed the trial (placebo n = 26; padsevonil n = 24). Their median age was 36 years (range 18-60), and they had been living with epilepsy for an average of 25 years. They were experiencing a median of 10 seizures/week and 75% had failed ≥8 antiepileptic drugs. At the end of the inpatient period, 30.8% of patients on padsevonil and 11.1% on placebo were ≥75% responders (odds ratio 4.14; P = 0.067). Reduction in median weekly seizure frequency was 53.7% and 12.5% with padsevonil and placebo, respectively (unadjusted P = 0.026). At the end of the outpatient period, 31.4% were ≥75% responders and reduction in median seizure frequency was 55.2% (all patients). During the inpatient period, 63.0% of patients on placebo and 85.7% on padsevonil reported treatment-emergent adverse events. Overall, 50 (90.9%) patients who received padsevonil reported treatment-emergent adverse events, most frequently somnolence (45.5%), dizziness (43.6%) and headache (25.5%); only one patient discontinued due to a treatment-emergent adverse event. Padsevonil was associated with a favourable safety profile and displayed clinically meaningful efficacy in patients with treatment-resistant epilepsy. The novel translational approach and the innovative proof-of-concept trial design maximized signal detection in a small patient population in a short duration, expediting antiepileptic drug development for the population with the greatest unmet need in epilepsy.

Inverse changes in raphe and cortical 5-HT1B receptor availability after acute tryptophan depletion in healthy human subjects

Serotonergic neurotransmission plays a key role in the pathophysiology and treatment of various neuropsychiatric diseases. The purpose of this study was to investigate changes in serotonergic neurotransmission after acute tryptophan depletion (ATD) using positron emission tomography (PET) with [¹¹ C]P943, a 5-HT_1B receptor radioligand previously shown to be sensitive to changes in 5-HT. Five healthy subjects were scanned on a high resolution PET scanner twice on the same day, before and approximately 5 hours after ingesting capsules containing an amino acid mixture that lacks tryptophan. For each scan, emission data were acquired for 120 min after intravenous bolus injection of [¹¹ C]P943. Binding potential (BP_ND ) values were estimated from parametric images using the second version of the multilinear reference tissue model (MRTM2, t* = 20 min) with cerebellar grey matter used as a reference region. The change in [¹¹ C]P943 binding (ΔBP_ND , %) was calculated as (BP_ND,post  - BP_ND,pre )/(BP_ND,pre ) × 100, and correlation analysis was performed to measure linear associations of ΔBP_ND between raphe and other regions of interest (ROIs). ΔBP_ND ranged from -6% to 45% in the raphe, with positive values indicating reduced competition from 5-HT. In cortical regions, ΔBP_ND ranged from -28% to 7%. While these changes did not reach significance, there were significant negative correlations of ΔBP_ND of the raphe with those of cerebral cortical regions and the thalamus (e.g., r = -.96, p = .011 for average cortex). These findings support the hypothesis that raphe serotonin is a critical modulator of cortical serotonin release via projecting neurons in healthy human subjects.

A single-center, open-label positron emission tomography study to evaluate brivaracetam and levetiracetam synaptic vesicle glycoprotein 2A binding in healthy volunteers

OBJECTIVE

Brivaracetam (BRV) and levetiracetam (LEV) are antiepileptic drugs that bind synaptic vesicle glycoprotein 2A (SV2A). In vitro and in vivo animal studies suggest faster brain penetration and SV2A occupancy (SO) after dosing with BRV than LEV. We evaluated human brain penetration and SO time course of BRV and LEV at therapeutically relevant doses using the SV2A positron emission tomography (PET) tracer 11 C-UCB-J (EP0074; NCT02602860).

METHODS

Healthy volunteers were recruited into three cohorts. Cohort 1 (n = 4) was examined with PET at baseline and during displacement after intravenous BRV (100 mg) or LEV (1500 mg). Cohort 2 (n = 5) was studied during displacement and 4 hours postdose (BRV 50-200 mg or LEV 1500 mg). Cohort 3 (n = 4) was examined at baseline and steady state after 4 days of twice-daily oral dosing of BRV (50-100 mg) and 4 hours postdose of LEV (250-600 mg). Half-time of 11 C-UCB-J signal change was computed from displacement measurements. Half-saturation concentrations (IC50 ) were determined from calculated SO.

RESULTS

Observed tracer displacement half-times were 18 ± 6 minutes for BRV (100 mg, n = 4), 9.7 and 10.1 minutes for BRV (200 mg, n = 2), and 28 ± 6 minutes for LEV (1500 mg, n = 6). Estimated corrected half-times were 8 minutes shorter. The SO was 66%-70% for 100 mg intravenous BRV, 84%-85% for 200 mg intravenous BRV, and 78%-84% for intravenous 1500 mg LEV. The IC50 of BRV (0.46 μg/mL) was 8.7-fold lower than of LEV (4.02 μg/mL). BRV data fitted a single SO versus plasma concentration relationship. Steady state SO for 100 mg BRV was 86%-87% (peak) and 76%-82% (trough).

SIGNIFICANCE

BRV achieves high SO more rapidly than LEV when intravenously administered at therapeutic doses. Thus, BRV may have utility in treating acute seizures; further clinical studies are needed for confirmation.

Kinetic evaluation and test-retest reproducibility of [11C]UCB-J, a novel radioligand for positron emission tomography imaging of synaptic vesicle glycoprotein 2A in humans

Synaptic vesicle glycoprotein 2A (SV2A) is ubiquitously present in presynaptic terminals. Here we report kinetic modeling and test-retest reproducibility assessment of the SV2A positron emission tomography (PET) radioligand [11C]UCB-J in humans. Five volunteers were examined twice on the HRRT after bolus injection of [11C]UCB-J. Arterial blood samples were collected for measurements of radiometabolites and free fraction. Regional time-activity curves were analyzed with 1-tissue (1T) and 2-tissue (2T) compartment models to estimate volumes of distribution ( VT). Parametric maps were generated using the 1T model. [11C]UCB-J metabolized fairly quickly, with parent fraction of 36 ± 13% at 15 min after injection. Plasma free fraction was 32 ± 1%. Regional time-activity curves displayed rapid kinetics and were well described by the 1T model, except for the cerebellum and hippocampus. VT values estimated with the 2T model were similar to 1T values. Parametric maps were of high quality and VT values correlated well with time activity curve (TAC)-based estimates. Shortening of acquisition time from 120 min to 60 min had a negligible effect on VT values. The mean absolute test-retest reproducibility for VT was 3-9% across regions. In conclusion, [11C]UCB-J exhibited excellent PET tracer characteristics and has potential as a general purpose tool for measuring synaptic density in neurodegenerative disorders.

Imaging synaptic density in the living human brain

Chemical synapses are the predominant neuron-to-neuron contact in the central nervous system. Presynaptic boutons of neurons contain hundreds of vesicles filled with neurotransmitters, the diffusible signaling chemicals. Changes in the number of synapses are associated with numerous brain disorders, including Alzheimer's disease and epilepsy. However, all current approaches for measuring synaptic density in humans require brain tissue from autopsy or surgical resection. We report the use of the synaptic vesicle glycoprotein 2A (SV2A) radioligand [(11)C]UCB-J combined with positron emission tomography (PET) to quantify synaptic density in the living human brain. Validation studies in a baboon confirmed that SV2A is an alternative synaptic density marker to synaptophysin. First-in-human PET studies demonstrated that [(11)C]UCB-J had excellent imaging properties. Finally, we confirmed that PET imaging of SV2A was sensitive to synaptic loss in patients with temporal lobe epilepsy. Thus, [(11)C]UCB-J PET imaging is a promising approach for in vivo quantification of synaptic density with several potential applications in diagnosis and therapeutic monitoring of neurological and psychiatric disorders.

In vivo imaging of translocator protein, a marker of activated microglia, in alcohol dependence

Neuroinflammation may be a critical component of the neurobiology of alcohol use disorders, yet the exact nature of this relationship is not well understood. This work compared the brain and peripheral immune profile of alcohol-dependent subjects and controls. Brain levels of 18-kDa translocator protein (TSPO), a marker of microglial activation and neuroinflammation, were measured with [¹¹C]PBR28 positron emission tomography imaging in 15 healthy controls and 15 alcohol-dependent subjects. Alcohol-dependent subjects were imaged 1-4 days (n=14) or 24 days (n=1) after their last drink. Linear mixed modeling of partial-volume-corrected [¹¹C]PBR28 data revealed a main effect of alcohol dependence (P=0.034), corresponding to 10% lower TSPO levels in alcohol-dependent subjects. Within this group, exploratory analyses found a negative association of TSPO levels in the hippocampus and striatum with alcohol dependence severity (P<0.035). Peripheral immune response was assessed in a subset of subjects by measuring cytokine expression from monocytes cultured both in the presence and absence of lipopolysaccharide. Peripheral monocyte response to lipopolysaccharide stimulation was lower in alcohol-dependent subjects compared with controls for the proinflammatory cytokines interleukin-6 and interleukin-8. Thus, alcohol-dependent individuals exhibited less activated microglia in the brain and a blunted peripheral proinflammatory response compared with controls. These findings suggest a role for pharmaceuticals tuning the neuroimmune system as therapeutics for alcohol dependence.

OCD is associated with an altered association between sensorimotor gating and cortical and subcortical 5-HT1b receptor binding

Obsessive-compulsive disorder (OCD) is characterized by impaired sensorimotor gating, as measured using prepulse inhibition (PPI). This effect may be related to abnormalities in the serotonin (5-HT) system. 5-HT1B agonists can impair PPI, produce OCD-like behaviors in animals, and exacerbate OCD symptoms in humans. We measured 5-HT1B receptor availability using (11)C-P943 positron emission tomography (PET) in unmedicated, non-depressed OCD patients (n=12) and matched healthy controls (HC; n=12). Usable PPI data were obtained from 20 of these subjects (10 from each group). There were no significant main effects of OCD diagnosis on 5-HT1B receptor availability ((11)C-P943 BPND); however, the relationship between PPI and (11)C-P943 BPND differed dramatically and significantly between groups. 5-HT1B receptor availability in the basal ganglia and thalamus correlated positively with PPI in controls; these correlations were lost or even reversed in the OCD group. In cortical regions there were no significant correlations with PPI in controls, but widespread positive correlations in OCD patients. Positive correlations between 5-HT1B receptor availability and PPI were consistent across diagnostic groups only in two structures, the orbitofrontal cortex and the amygdala. Differential associations of 5-HT1B receptor availability with PPI in patients suggest functionally important alterations in the serotonergic regulation of cortical/subcortical balance in OCD.

Brivaracetam: Rationale for discovery and preclinical profile of a selective SV2A ligand for epilepsy treatment

Despite availability of effective antiepileptic drugs (AEDs), many patients with epilepsy continue to experience refractory seizures and adverse events. Achievement of better seizure control and fewer side effects is key to improving quality of life. This review describes the rationale for the discovery and preclinical profile of brivaracetam (BRV), currently under regulatory review as adjunctive therapy for adults with partial-onset seizures. The discovery of BRV was triggered by the novel mechanism of action and atypical properties of levetiracetam (LEV) in preclinical seizure and epilepsy models. LEV is associated with several mechanisms that may contribute to its antiepileptic properties and adverse effect profile. Early findings observed a moderate affinity for a unique brain-specific LEV binding site (LBS) that correlated with anticonvulsant effects in animal models of epilepsy. This provided a promising molecular target and rationale for identifying selective, high-affinity ligands for LBS with potential for improved antiepileptic properties. The later discovery that synaptic vesicle protein 2A (SV2A) was the molecular correlate of LBS confirmed the novelty of the target. A drug discovery program resulted in the identification of anticonvulsants, comprising two distinct families of high-affinity SV2A ligands possessing different pharmacologic properties. Among these, BRV differed significantly from LEV by its selective, high affinity and differential interaction with SV2A as well as a higher lipophilicity, correlating with more potent and complete seizure suppression, as well as a more rapid brain penetration in preclinical models. Initial studies in animal models also revealed BRV had a greater antiepileptogenic potential than LEV. These properties of BRV highlight its promising potential as an AED that might provide broad-spectrum efficacy, associated with a promising tolerability profile and a fast onset of action. BRV represents the first selective SV2A ligand for epilepsy treatment and may add a significant contribution to the existing armamentarium of AEDs.

Synthesis and Preclinical Evaluation of 11C-UCB-J as a PET Tracer for Imaging the Synaptic Vesicle Glycoprotein 2A in the Brain

The synaptic vesicle glycoprotein 2A (SV2A) is found in secretory vesicles in neurons and endocrine cells. PET with a selective SV2A radiotracer will allow characterization of drugs that modulate SV2A (e.g., antiepileptic drugs) and potentially could be a biomarker of synaptic density (e.g., in neurodegenerative disorders). Here we describe the synthesis and characterization of the SV2A PET radiotracer (11)C-UCB-J ((R)-1-((3-((11)C-methyl-(11)C)pyridin-4-yl)methyl)-4-(3,4,5-trifluorophenyl)pyrrolidin-2-one) in nonhuman primates, including whole-body biodistribution.

METHODS

(11)C-UCB-J was prepared by C-(11)C-methylation of the 3-pyridyl trifluoroborate precursor with (11)C-methyl iodide via the Suzuki-Miyaura cross-coupling method. Rhesus macaques underwent multiple scans including coinjection with unlabeled UCB-J (17, 50, and 150 μg/kg) or preblocking with the antiepileptic drug levetiracetam at 10 and 30 mg/kg. Scans were acquired for 2 h with arterial sampling and metabolite analysis to measure the input function. Regional volume of distribution (VT) was estimated using the 1-tissue-compartment model. Target occupancy was assessed using the occupancy plot; the dissociation constant (Kd) was determined by fitting self-blocking occupancies to a 1-site model, and the maximum number of receptor binding sites (Bmax) values were derived from baseline VT and from the estimated Kd and the nondisplaceable distribution volume (VND).

RESULTS

(11)C-UCB-J was synthesized with greater than 98% purity. (11)C-UCB-J exhibited high free fraction (0.46 ± 0.02) and metabolized at a moderate rate (39% ± 5% and 24% ± 3% parent remaining at 30 and 90 min) in plasma. In the monkey brain, (11)C-UCB-J displayed high uptake and fast kinetics. VT was high (∼25-55 mL/cm(3)) in all gray matter regions, consistent with the ubiquitous expression of SV2A. Preblocking with 10 and 30 mg/kg of levetiracetam resulted in approximately 60% and 90% occupancy, respectively. Analysis of the self-blocking scans yielded a Kd estimate of 3.4 nM and Bmax of 125-350 nM, in good agreement with the in vitro inhibition constant (Ki) of 6.3 nM and regional Bmax in humans. Whole-body biodistribution revealed that the liver and the brain are the dose-limiting organs for males and females, respectively.

CONCLUSION

(11)C-UCB-J exhibited excellent characteristics as an SV2A PET radiotracer in nonhuman primates. The radiotracer is currently undergoing first-in-human evaluation.

Brivaracetam, a selective high-affinity synaptic vesicle protein 2A (SV2A) ligand with preclinical evidence of high brain permeability and fast onset of action

OBJECTIVE

Rapid distribution to the brain is a prerequisite for antiepileptic drugs used for treatment of acute seizures. The preclinical studies described here investigated the high-affinity synaptic vesicle glycoprotein 2A (SV2A) antiepileptic drug brivara-cetam (BRV) for its rate of brain penetration and its onset of action. BRV was compared with levetiracetam (LEV).

METHODS

In vitro permeation studies were performed using Caco-2 cells. Plasma and brain levels were measured over time after single oral dosing to audiogenic mice and were correlated with anticonvulsant activity. Tissue distribution was investigated after single dosing to rat (BRV and LEV) and dog (LEV only). Positron emission tomography (PET) displacement studies were performed in rhesus monkeys using the SV2A PET tracer [11C]UCB-J. The time course of PET tracer displacement was measured following single intravenous (IV) dosing with LEV or BRV. Rodent distribution data and physiologically based pharmacokinetic (PBPK) modeling were used to compute blood-brain barrier permeability (permeability surface area product, PS) values and then predict brain kinetics in man.

RESULTS

In rodents, BRV consistently showed a faster entry into the brain than LEV; this correlated with a faster onset of action against seizures in audiogenic susceptible mice. The higher permeability of BRV was also demonstrated in human cells in vitro. PBPK modeling predicted that, following IV dosing to human subjects, BRV might distribute to the brain within a few minutes compared with approximately 1 h for LEV (PS of 0.315 and 0.015 ml/min/g for BRV and LEV, respectively). These data were supported by a nonhuman primate PET study showing faster SV2A occupancy by BRV compared with LEV.

SIGNIFICANCE

These preclinical data demonstrate that BRV has rapid brain entry and fast brain SV2A occupancy, consistent with the fast onset of action in the audiogenic seizure mice assay. The potential benefit of BRV for treatment of acute seizures remains to be confirmed in clinical studies.

Characterization in humans of 18F-MNI-444, a PET radiotracer for brain adenosine 2A receptors

PET with selective adenosine 2A receptor (A2A) radiotracers can be used to study a variety of neurodegenerative and neuropsychiatric disorders in vivo and to support drug-discovery studies targeting A2A. The aim of this study was to describe the first in vivo evaluation of (18)F-MNI-444, a novel PET radiotracer for imaging A2A, in healthy human subjects.

METHODS

Ten healthy human volunteers were enrolled in this study; 6 completed the brain PET studies and 4 participated in the whole-body PET studies. Arterial blood was collected for invasive kinetic modeling of the brain PET data. Noninvasive methods of data quantification were also explored. Test-retest reproducibility was evaluated in 5 subjects. Radiotracer distribution and dosimetry was determined using serial whole-body PET images acquired over 6 h post-radiotracer injection. Urine samples were collected to calculate urinary excretion.

RESULTS

After intravenous bolus injection, (18)F-MNI-444 rapidly entered the brain and displayed a distribution consistent with known A2A densities in the brain. Binding potentials ranging from 2.6 to 4.9 were measured in A2A-rich regions, with an average test-retest variability of less than 10%. The estimated whole-body radiation effective dose was approximately 0.023 mSv/MBq.

CONCLUSION

(18)F-MNI-444 is a useful PET radiotracer for imaging A2A in the human brain. The superior in vivo brain kinetic properties of (18)F-MNI-444, compared with previously developed A2A radiotracers, provide the opportunity to foster global use of in vivo A2A PET imaging in neuroscience research.

Comparison of standardized uptake values with volume of distribution for quantitation of [(11)C]PBR28 brain uptake

INTRODUCTION

[(11)C]PBR28 is a high-affinity ligand for the Translocator Protein 18 kDa (TSPO), which is considered to be a marker for microglial activation. Volume of distribution (VT) estimated with an arterial plasma input function is the gold standard for quantitation of [(11)C]PBR28 binding. However, arterial sampling is impractical at many PET sites for multiple reasons. Reference region modeling approaches are not ideal for TSPO tracers, as the existence of a true reference region cannot be assumed. Given that it would be desirable to have a non-invasive index of [(11)C]PBR28 binding, we elected to study the utility of the semi-quantitative metric, standardized uptake value (SUV) for use in brain [(11)C]PBR PET studies. The primary goal of this study was to determine the relationship between SUV and VT.

METHODS

We performed a retrospective analysis of data from sixteen [(11)C]PBR28 PET scans acquired in baboons at baseline and at multiple time points after IV injection of lipopolysaccharide, an endotoxin that transiently induces neuroinflammation. For each scan, data from 14 brain regions of interest were studied. VT was estimated with the Logan plot, using metabolite-corrected input functions. SUV was calculated with data from 30 to 60 minutes after [(11)C]PBR28 injection.

RESULTS

Within individual PET studies, SUV tended to correlate well with VT. Across studies, the relationship between SUV and VT was variable.

CONCLUSIONS

From study to study, there was variability in the degree of correlation between [(11)C]PBR28 VT and SUV. There are multiple physiological factors that may contribute to this variance.

ADVANCES IN KNOWLEDGE

As currently applied, the non-invasive measurement of SUV does not appear to be a reliable outcome variable for [(11)C]PBR28. Additional work is needed to discover the source of the discrepancy in SUV between [(11)C]PBR28 scans.

IMPLICATIONS FOR PATIENT CARE

There is a need to develop alternatives to arterial plasma input functions for TSPO ligands in order to facilitate multi-center trials.

Adenosine 2A receptor occupancy by tozadenant and preladenant in rhesus monkeys

Motor symptoms in Parkinson disease (PD) are caused by a loss of dopamine input from the substantia nigra to the striatum. Blockade of adenosine 2A (A(2A)) receptors facilitates dopamine D(2) receptor function. In phase 2 clinical trials, A(2A) antagonists (istradefylline, preladenant, and tozadenant) improved motor function in PD. We developed a new A(2A) PET radiotracer, (18)F-MNI-444, and used it to investigate the relationship between plasma levels and A(2A) occupancy by preladenant and tozadenant in nonhuman primates (NHP).

METHODS

A series of 20 PET experiments was conducted in 5 adult rhesus macaques. PET data were analyzed with both plasma-input (Logan graphical analysis) and reference-region-based (simplified reference tissue model and noninvasive Logan graphical analysis) methods. Whole-body PET images were acquired for radiation dosimetry estimates. Human pharmacokinetic parameters for tozadenant and preladenant were used to predict A(2A) occupancy in humans, based on median effective concentration (EC(50)) values estimated from the NHP PET measurements.

RESULTS

(18)F-MNI-444 regional uptake was consistent with A(2A) receptor distribution in the brain. Selectivity was demonstrated by dose-dependent blocking by tozadenant and preladenant. The specific-to-nonspecific ratio was superior to that of other A(2A) PET radiotracers. Pharmacokinetic modeling predicted that tozadenant and preladenant may have different profiles of A(2A) receptor occupancy in humans.

CONCLUSION

(18)F-MNI-444 appears to be a better PET radiotracer for A(2A) imaging than currently available radiotracers. Assuming that EC(50) in humans is similar to that in NHP, it appears that tozadenant will provide a more sustained A(2A) receptor occupancy than preladenant in humans at clinically tested doses.

Dopamine D₃ receptor alterations in cocaine-dependent humans imaged with [¹¹C](+)PHNO

BACKGROUND

Evidence from animal models and postmortem human studies points to the importance of the dopamine D₃ receptor (D₃R) in cocaine dependence (CD). The objective of this pilot study was to use the D₃R-preferring radioligand [(11)C](+)PHNO to compare receptor availability in groups with and without CD.

METHODS

Ten medically healthy, non-treatment seeking CD subjects (mean age 41 ± 8) in early abstinence were compared to 10 healthy control (HC) subjects (mean age 41 ± 6) with no history of cocaine or illicit substance abuse. Binding potential (BPND), a measure of available receptors, was determined with parametric images, computed using the simplified reference tissue model (SRTM2) with the cerebellum as the reference region.

RESULTS

BPND in CD subjects was higher in D₃R-rich areas including the substantia nigra ((SN) 29%; P=0.03), hypothalamus (28%; P=0.02) and amygdala (35%; P=0.03). No between-group differences were observed in the striatum or pallidum. BPND values in the SN (r=+0.83; P=0.008) and pallidum (r=+0.67; P=0.03) correlated with years of cocaine use.

CONCLUSIONS

Between-group differences suggest an important role for dopaminergic transmission in the SN, hypothalamus and amygdala in CD. Such findings also highlight the potential relevance of D₃R as a medication development target in CD.

The neuroinflammation marker translocator protein is not elevated in individuals with mild-to-moderate depression: a [¹¹C]PBR28 PET study

Depression is associated with systemic inflammation. In animals, systemic inflammation can induce neuroinflammation and activation of microglia; however, postmortem studies have not convincingly shown that there is neuroinflammation in depression. The purpose of this study was to use positron emission tomography (PET) with [¹¹C]PBR28, which binds to the neuroinflammation marker translocator protein 18 kDa (TSPO), to compare the level of TSPO between individuals with depression and control subjects. Ten individuals who were in an acute episode of major depression and 10 control subjects matched for TSPO genotype and other characteristics had a PET scan with arterial input function to quantify levels of TSPO in brain regions of interest (ROIs). Total volume of distribution (VT) of [¹¹C]PBR28 was used as a measure of total ligand binding. The primary outcome was the difference in VT between the two groups; this was assessed using a linear mixed model with group as a between-subject factor and region as a within-subject factor. There was no statistically significant difference in [¹¹C]PBR28 binding (VT) between the two groups. In fact, 7 of 10 individuals with depression had lower [¹¹C]PBR28 binding in all ROIs compared to their respective genotype-matched control subjects. Future studies are needed to determine whether individuals with mild-to-moderate depression have lower TSPO levels and to assess whether individuals with severe depression and/or with elevated levels of systemic inflammation might have higher TSPO levels than control subjects.

Bupropion pre-treatment of endotoxin-induced depressive symptoms

Increased levels of inflammatory cytokines may play a role in depression. Depressive symptoms can be induced in humans with administration of low-dose lipopolysaccharide (LPS; endotoxin), which activates the innate immune system and causes release of inflammatory cytokines. We previously found that pre-treatment with the serotonin reuptake inhibitor citalopram reduced LPS-induced fatigue and anhedonia. This is a follow-up study to determine whether LPS-induced symptoms could be reduced by pre-treatment with bupropion, a norepinephrine and dopamine reuptake inhibitor. In this double-blind, randomized, placebo-controlled, cross-over study, 10 healthy subjects received intravenous LPS (0.8 ng/kg) after oral pre-treatment with bupropion (75 mg twice a day) or placebo for 7 days. The Montgomery-Åsberg Depression Rating Scale (MADRS), the Profile of Mood States (POMS), and a visual analog scale (VAS) were used to measure depressive symptoms. Serum levels of inflammatory cytokines and chemokines were measured with electrochemiluminescence assays. The results of this study, which must be considered preliminary, showed that LPS administration was associated with (1) increase in serum levels of all cytokines and chemokines assayed; (2) increase in total MADRS score, mostly due to items 7 (lassitude) and 8 (anhedonia); (3) increase in fatigue; (4) decrease in vigor; and (5) decrease in social interest. Bupropion pre-treatment had no statistically significant effect on the innate immune response to LPS or on LPS-induced behavioral changes, suggesting that 1-week pre-treatment with bupropion does not inhibit LPS-induced fatigue and anhedonia, contrary to what was found previously with citalopram.

Transcranial magnetic stimulation of Wernicke's and Right homologous sites to curtail "voices": a randomized trial

BACKGROUND

Auditory/verbal hallucinations (AVHs) are accompanied by activation in Wernicke's and right homologous regions. Efficacy in curtailing AVHs via 1-Hz repetitive magnetic stimulation (rTMS) targeting a site in each region ("W" and "rW") was therefore studied.

METHODS

Patients with schizophrenia and AVHs (N = 83) were randomly allocated to double-masked rTMS versus sham stimulation, with blocks of five sessions given to W and rW in random order, followed by five sessions to the site yielding greater improvement. The primary outcome measure was the Hallucination Change Score (HCS). Hallucination frequency, total auditory hallucination rating scale score, and clinical global improvement were secondary outcome measures. Attentional salience of AVHs and neuropsychological measures of laterality were studied as predictors of site-specific response.

RESULTS

After 15 sessions, rTMS produced significant improvements relative to sham stimulation for hallucination frequency and clinical global improvement but not for HCS. After limiting analyses to patients whose motor threshold was detected consistently: 1) endpoint HCS demonstrated significantly greater improvement for rTMS compared with sham stimulation; 2) for high-salience AVHs, rTMS to rW after the first five sessions yielded significantly improved HCS scores relative to sham stimulation, whereas for low salience AVHs, rTMS to W produced this finding. Nondominant motor impairment correlated positively with hallucination improvement following rW rTMS.

CONCLUSIONS

One-hertz rTMS per our site-optimization protocol produced some clinical benefit in patients with persistent AVHs as a group, especially when motor threshold was consistently detected. Level of hallucination salience may usefully guide selection of W versus rW as intervention sites.

The application of PET imaging in psychoneuroimmunology research

Positron emission tomography (PET) imaging is a research tool that allows in vivo measurements of brain metabolism and specific target molecules. PET imaging can be used to measure these brain variables in a variety of species, including human and non-human primates, and rodents. PET imaging can therefore be combined with various experimental and clinical model systems that are commonly used in psychoneuroimmunology research.

Sex differences in decreased limbic and cortical grey matter volume in cocaine dependence: a voxel-based morphometric study

Structural neuroimaging studies have provided evidence of differences in local brain volume between cocaine-dependent and healthy control individuals. While sex differences in aetiology, course and brain dysfunction associated with chronic cocaine abuse have been previously documented, evidence of sex-specific differences in brain volume has not been examined thus far. This study examined sex-related differences in grey matter volume between cocaine-dependent and healthy control subjects using voxel-based morphometry. High-resolution T1 structural scans were obtained from 36 inpatient, treatment-engaged 3-week abstinent cocaine-dependent (CD) individuals. Fifty healthy control subjects were also scanned. Segmentation and registration were performed in SPM8, using New Segment and DARTEL, respectively. The whole-brain statistical analysis was conducted in SPM8 using random field-based cluster-size testing and family-wise error rate correction for multiple comparisons. CD patients were found to have less grey matter volume in anterior prefrontal cortex, including frontopolar and orbitofrontal cortices, and a posterior region surrounding the parietal-occipital sulcus. Female CD patients had less grey matter volume than female controls in left inferior frontal gyrus, insula, superior temporal gyrus and hippocampus. Male CD patients had less grey matter in a superior cortical region that included the precentral gyrus and the mid-cingulate. These sex differences in lower grey matter volume add to the evidence from functional neuroimaging for sex-specific differences in the neurophysiological changes associated with chronic cocaine use.

Omega-3 fatty acids for the treatment of depression: systematic review and meta-analysis

We conducted a meta-analysis of randomized, placebo-controlled trials of omega-3 fatty acid (FA) treatment of major depressive disorder (MDD) in order to determine efficacy and to examine sources of heterogeneity between trials. PubMed (1965-May 2010) was searched for randomized, placebo-controlled trials of omega-3 FAs for MDD. Our primary outcome measure was standardized mean difference in a clinical measure of depression severity. In stratified meta-analysis, we examined the effects of trial duration, trial methodological quality, baseline depression severity, diagnostic indication, dose of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in omega-3 preparations, and whether omega-3 FA was given as monotherapy or augmentation. In 13 randomized, placebo-controlled trials examining the efficacy of omega-3 FAs involving 731 participants, meta-analysis demonstrated no significant benefit of omega-3 FA treatment compared with placebo (standard mean difference (SMD)=0.11, 95% confidence interval (CI): -0.04, 0.26). Meta-analysis demonstrated significant heterogeneity and publication bias. Nearly all evidence of omega-3 benefit was removed after adjusting for publication bias using the trim-and-fill method (SMD=0.01, 95% CI: -0.13, 0.15). Secondary analyses suggested a trend toward increased efficacy of omega-3 FAs in trials of lower methodological quality, trials of shorter duration, trials which utilized completers rather than intention-to-treat analysis, and trials in which study participants had greater baseline depression severity. Current published trials suggest a small, non-significant benefit of omega-3 FAs for major depression. Nearly all of the treatment efficacy observed in the published literature may be attributable to publication bias.

Endotoxin-induced systemic inflammation activates microglia: [¹¹C]PBR28 positron emission tomography in nonhuman primates

Microglia play an essential role in many brain diseases. Microglia are activated by local tissue damage or inflammation, but systemic inflammation can also activate microglia. An important clinical question is whether the effects of systemic inflammation on microglia mediate the deleterious effects of systemic inflammation in diseases such as Alzheimer's dementia, multiple sclerosis, and stroke. Positron Emission Tomography (PET) imaging with ligands that bind to Translocator Protein (TSPO) can be used to detect activated microglia. The aim of this study was to evaluate whether the effect of systemic inflammation on microglia could be measured with PET imaging in nonhuman primates, using the TSPO ligand [(11)C]PBR28.

METHODS

Six female baboons (Papio anubis) were scanned before and at 1h and/or 4h and/or 22 h after intravenous administration of E. coli lipopolysaccharide (LPS; 0.1mg/kg), which induces systemic inflammation. Regional time-activity data from regions of interest (ROIs) were fitted to the two-tissue compartmental model, using the metabolite-corrected arterial plasma curve as input function. Total volume of distribution (V(T)) of [(11)C]PBR28 was used as a measure of total ligand binding. The primary outcome was change in V(T) from baseline. Serum levels of tumor necrosis factor alpha (TNFα), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and interleukin-8 (IL-8) were used to assess correlations between systemic inflammation and microglial activation. In one baboon, immunohistochemistry was used to identify cells expressing TSPO.

RESULTS

LPS administration increased [(11)C]PBR28 binding (F(3,6)=5.1, p=.043) with a 29 ± 16% increase at 1h (n=4) and a 62 ± 34% increase at 4h (n=3) post-LPS. There was a positive correlation between serum IL-1β and IL-6 levels and the increase in [(11)C]PBR28 binding. TSPO immunoreactivity occurred almost exclusively in microglia and rarely in astrocytes.

CONCLUSION

In the nonhuman-primate brain, LPS-induced systemic inflammation produces a robust increase in the level of TSPO that is readily detected with [(11)C]PBR28 PET. The effect of LPS on [(11)C]PBR28 binding is likely mediated by inflammatory cytokines. Activation of microglia may be a mechanism through which systemic inflammatory processes influence the course of diseases such as Alzheimer's, multiple sclerosis, and possibly depression.

Glucose metabolism in the insula and cingulate is affected by systemic inflammation in humans

Depression is associated with systemic inflammation, and the systemic inflammation caused by endotoxin administration elicits mild depressive symptoms such as fatigue and reduced interest. The neural correlates of depressive symptoms that result from systemic inflammation are poorly defined. The aim of this study was to use (18)F-FDG PET to identify brain regions involved in the response to endotoxin administration in humans.

METHODS

Nine healthy subjects received double-blind endotoxin (0.8 ng/kg) and placebo on different days. (18)F-FDG PET was used to measure differences in the cerebral metabolic rate of glucose in the following regions of interest: insula, cingulate, and amygdala. Serum levels of tumor necrosis factor-α and interleukin-6 were used to gauge the systemic inflammatory response, and depressive symptoms were measured with the Montgomery-Åsberg Depression Rating Scale and other scales.

RESULTS

Endotoxin administration was associated with an increase in Montgomery-Åsberg Depression Rating Scale, increased fatigue, reduced social interest, increased levels of inflammatory cytokines, higher normalized glucose metabolism (NGM) in the insula, and, at a trend level, lower NGM in the cingulate. Secondary analyses of insula and cingulate subregions indicated that these changes were driven by the right anterior insula and the right anterior cingulate. There was a negative correlation between peak cytokine levels and change in social interest and between peak cytokine levels and change in insula NGM. There was a positive correlation between the change in NGM in the insula and change in social interest.

CONCLUSION

Systemic inflammation in humans causes an increase in depressive symptoms and concurrent changes in glucose metabolism in the insula and cingulate-brain regions that are involved in interoception, positive emotionality, and motivation.

Citalopram reduces endotoxin-induced fatigue

Increased levels of inflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-6 (IL-6) may play a role in depression. Mild depressive-like symptoms can be induced in humans through activation of the innate immune system with endotoxin. Whether preventive treatment with antidepressants can reduce endotoxin-induced symptoms has never been tested. In a double-blind, randomized, placebo-controlled, cross-over study, we administered intravenous low-dose endotoxin (0.8 ng/kg) or placebo to 11 healthy subjects who had received oral pre-treatment with citalopram (10 mg twice a day) or placebo for 5 days. The Montgomery-Åsberg Depression Rating Scale, the State and Trait Anxiety Inventory, and a visual analog scale were used to measure depressive and anxiety symptoms and social anhedonia. Serum levels of TNF and IL-6 were measured with immunoassays. Compared to placebo, endotoxin administration increased serum levels of TNF and IL-6, and caused mild depressive-like symptoms, in particular lassitude and social anhedonia. While citalopram pre-treatment had no effect on the innate immune response to endotoxin, it reduced the endotoxin-induced MADRS total score by 50%, with a moderate effect size (Cohen's d=0.5). Most of the MADRS total score was due to the lassitude item, and citalopram pre-treatment specifically reduced endotoxin-induced lassitude with a large effect size (Cohen's d=0.9). These results suggest that subchronic pre-treatment with the serotonin-reuptake inhibitor citalopram blunts mood symptoms induced by acute immune system activation with endotoxin without inhibiting the peripheral immune response.

Clinically relevant doses of methylphenidate significantly occupy norepinephrine transporters in humans in vivo

BACKGROUND

Attention-deficit/hyperactivity disorder is a psychiatric disorder that starts in childhood. The mechanism of action of methylphenidate, the most common treatment for attention deficit hyperactivity disorder, is unclear. In vitro, the affinity of methylphenidate for the norepinephrine transporter (NET) is higher than that for the dopamine transporter (DAT). The goal of this study was to use positron emission tomography to measure the occupancy of brain norepinephrine transporter by methylphenidate in vivo in humans.

METHODS

We used (S,S)-[¹¹C] methylreboxetine ([¹¹C]MRB) to determine the effective dose 50 (ED₅₀) of methylphenidate for NET. In a within-subject design, healthy subjects (n = 11) received oral, single-blind placebo and 2.5, 10, and 40 mg of methylphenidate 75 min before [¹¹C]MRB injection. Dynamic positron emission tomography imaging was performed for 2 hours with the High Resolution Research Tomograph. The multilinear reference tissue model with occipital cortex as the reference region was used to estimate binding potential non-displaceable (BP(ND)) in the thalamus and other NET-rich regions.

RESULTS

BP(ND) was reduced by methylphenidate in a dose-dependent manner in thalamus and other NET-rich regions. The global ED₅₀ was estimated to be .14 mg/kg; therefore, the average clinical maintenance dose of methylphenidate (.35-.55 mg/kg) produces 70% to 80% occupancy of NET.

CONCLUSIONS

For the first time in humans, we demonstrate that oral methylphenidate significantly occupies NET at clinically relevant doses. The ED₅₀ is lower than that for DAT (.25 mg/kg), suggesting the potential relevance of NET inhibition in the therapeutic effects of methylphenidate in attention-deficit/hyperactivity disorder.

A critical review of human endotoxin administration as an experimental paradigm of depression

The syndrome called depression may represent the common final pathway at which different aetiopathogenic processes converge. One such aetiopathogenic process is innate immune system activation. Some depressed patients have increased levels of inflammatory cytokines and other immunologic abnormalities. It is not known whether immune system activation contributes to the pathogenesis of depressive symptoms. Supporting this possibility is the observation that in both rodents and humans, exogenous immune stimuli such as endotoxin can produce symptoms that resemble depression. A new approach to depression research would be to use immune stimuli to elicit depressive symptoms in humans. Here we review each of the symptoms elicited in humans by endotoxin administration, and compare this model to two other immune depression paradigms: interferon-alpha treatment and typhoid vaccine administration, to assess to what degree endotoxin administration represents a valid model of immune depression. We also review corresponding behavioral changes in rodents and the potential molecular pathways through which immune system activation produces each symptom.

Neurotrophin and Trk neurotrophin receptors in the inner ear of Salmo salar and Salmo trutta

Neurotrophins (NTs) and their signal transducing Trk receptors play a critical role in the development and maintenance of specific neuronal populations in the nervous system of higher vertebrates. They are responsible for the innervation of the inner ear cochlear and vestibular sensory epithelia. Neurotrophins and Trks are also present in teleosts but their distribution in the inner ear is unknown. Thus, in the present study, we used Western-blot analysis and immunohistochemistry to investigate the expression and cell localization of both NTs and Trk receptors in the inner ear of alevins of Salmo salar and Salmo trutta. Western-blot analysis revealed the occurrence of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), but not nerve growth factor (NGF), as well as all three Trk receptors, i.e. TrkA, TrkB and TrkC, the estimated molecular weights of which were similar to those expected for mammals. Specific immunoreactivity for neurotrophins was detected mainly in the sensory epithelia. In particular, BDNF immunoreactivity was found in the maculae of the utricle and saccule, whereas NT-3 immunoreactivity was present in the sensory epithelium of the cristae ampullaris. As a rule the sensory epithelia of the inner ear lacked immunoreactivity for Trks, thus excluding possible mechanisms of autocrinia and/or paracrinia. By contrast, overlapping subpopulations of neurons in the statoacoustic ganglion expressed TrkA (about 15%), TrkB (about 65%) and TrkC (about 45%). The present results demonstrate that, as in mammals and birds, the inner ear of teleosts expresses the components of the neurotrophin-Trk system, but their roles remain to be elucidated.

Caspase 1 deficiency reduces inflammation-induced brain transcription

The systemic inflammatory response syndrome (SIRS) is a life-threatening medical condition characterized by a severe and generalized inflammatory state that can lead to multiple organ failure and shock. The CNS regulates many features of SIRS such as fever, cardiovascular, and neuroendocrine responses. Central and systemic manifestations of SIRS can be induced by LPS or IL-1beta administration. The crucial role of IL-1beta in inflammation has been further highlighted by studies of mice lacking caspase 1 (casp1, also known as IL-1beta convertase), a protease that cleaves pro-IL-1beta into mature IL-1beta. Indeed, casp1 knockout (casp1(-/-)) mice survive lethal doses of LPS. The key role of IL-1beta in sickness behavior and its de novo expression in the CNS during inflammation led us to test the hypothesis that IL-1beta plays a major role modulating the brain transcriptome during SIRS. We show a gene-environment effect caused by LPS administration in casp1(-/-) mice. During SIRS, the expression of several genes, such as chemokines, GTPases, the metalloprotease ADAMTS1, IL-1RA, the inducible nitric oxide synthase, and cyclooxygenase-2, was differentially increased in casp1(-/-) mice. Our findings may contribute to the understanding of the molecular changes that take place within the CNS during sepsis and SIRS and the development of new therapies for these serious conditions. Our results indicate that those genes may also play a role in several neuropsychiatric conditions in which inflammation has been implicated and indicate that casp1 might be a potential therapeutic target for such disorders.

White matter lesion volumes and caudate volumes in late-life depression

BACKGROUND

Decreased caudate volumes and increased white matter lesions (WMLs) are associated both with aging and late-life depression, but the relationship between the two is unclear. We examined the association between WML and caudate volume, hypothesizing there would be a negative association, which would be stronger for WMLs located in anterior regions. We additionally hypothesized that this association would be stronger in depressed subjects.

METHOD

This MRI study included 182 elderly depressed and 64 elderly control subjects. Our imaging analysis procedures divided the brain into anterior and posterior halves. WML volume in each half was calculated, as were left and right caudate volumes. A statistical model incorporating WML volumes, age, total brain volume, diagnosis, and gender was used to examine caudate volumes.

RESULTS

WML volume was negatively associated with total and right caudate volume. This association was stronger for WMLs in the anterior half of the brain. Anterior WML volume was additionally negatively associated with right caudate volume in depressed subjects, but not in controls.

CONCLUSIONS

Using unadjusted levels of significance, WML volume is negatively associated with right caudate volume in both older populations, but with left caudate volume only in depressed individuals. When statistical corrections for multiple comparisons are used, the finding is limited to a negative association between WML volume and right caudate volume, primarily in depressed subjects. This study demonstrates one mechanism by which WMLs may disrupt frontostriatal circuits.

Age-dependent changes in the nervous and endocrine control of the thymus

The immune system, especially the thymus, undergoes age-related modifications leading to structural and functional changes in the lymphoid organs and immunocompetent cells. Nevertheless, the consequences of thymic involution in the peripheral pool of T-cells are still a matter of controversy. The control of the thymic function is very complex and involves intrathymic signals, the autonomic nervous system, and the endocrine system. Both thymocytes and thymic stromal cells express receptors for a wide range of hormones, as well as for neurotransmitters and neuropeptides, thus affecting thymocytes maturation. This review summarizes the age-dependent variations in the extrathymic components of the thymic microenvironment, i.e., vegetative nerves and hormones, and the possible effects of those changes in the immune function.

Identification, characterization, and gene expression profiling of endotoxin-induced myocarditis

In septic shock, reversible cardiac dysfunction starts within 24 h. Myocardial depressant factors are thought to cause myocyte dysfunction, resulting in alterations of intrinsic cardiac function. Nitric oxide is a myocardial depressant factor candidate. Here we identify endotoxin-induced myocarditis (EIM) a previously uncharacterized pathophysiological entity. Features of EIM include differential patterns of inducible NO synthase (NOS2) mRNA induction in the left (LV) and right (RV) ventricles during the systemic response inflammatory syndrome (SIRS) and the presence of myocarditis with focal areas of aseptic necrosis in the RV 24 h after SIRS induction. Even though clinical data lead to the presumption of myocardial injury in sepsis, the underlying pathophysiological mechanisms have not been previously elucidated. Gene expression profiling was used to test the hypothesis of differential LV and RV responses in EIM, and revealed novel patterns of qualitative and quantitative expansion of transcription. Those genes are novel targets for drug development in SIRS and sepsis. Our results demonstrate spatial and temporal heterogeneity of myocardial responses in EIM. These findings justify the design of treatments to ameliorate tissue injury in the RV. Because the complexity of the inflammatory response increases substantially as time elapses, we suggest a stepwise and multitarget therapeutic approach for SIRS and sepsis. Our findings can help identify innate immune pathways that could become targets for immunotherapy in the treatment of disease caused by potential bioterrorism agents.

Neurotrophins and the immune system

The neurotrophins are a family of polypeptide growth factors that are essential for the development and maintenance of the vertebrate nervous system. In recent years, data have emerged indicating that neurotrophins could have a broader role than their name might suggest. In particular, the putative role of NGF and its receptor TrkA in immune system homeostasis has become a much studied topic, whereas information on the other neurotrophins is scarce in this regard. This paper reviews what is known about the expression and possible functions of neurotrophins and their receptors in different immune tissues and cells, as well as recent data obtained from studies of transgenic mice in our laboratory. Results from studies to date support the idea that neurotrophins may regulate some immune functions. They also play an important role in the development of the thymus and in the survival of thymocytes.

Immunohistochemical localization of BDNF-, TrkB- and TrkA-like proteins in the teleost lateral line system

The lateral line system, formed of both superficial (pit organs) and canal neuromasts, is one of the major mechanosensory systems in fish. It has always been assumed that this system depends on neurotrophins and their cognate Trk receptors for development and maintenance, as has been shown in other mechanosensitive systems of vertebrates. However, until nowthis issue has not been specifically addressed. In this study we used immunohistochemistry to investigate the occurrence and localization both of neurotrophins (NGF-, BDNF- and NT-3-like) and of Trk-like proteins (TrkA-, TrkB-, TrkC-like) in alevins of Salmo salar and S. trutta. All cells in the pit organs of S. salar displayed strong immunoreactivity for TrkB-like and BDNF-like, whereas they were restricted to the hair cells in S. trutta. The hair, supporting and mantle cells of S. salar, and the mantle cells of S. trutta, also expressed TrkA-like immunoreactivity. In the canal neuromasts BDNF-, TrkA- and TrkB-like proteins were present in all cells, without differences between species. NGF-, NT-3- and TrkC-like immunoreactivity were never detected. The present results suggest that mechanoreceptive hair cells, as well as supporting cells, in the lateral line system are under the control of the BDNF-TrkB-like complex, and probably of ligands of TrkA-like receptors.

Involvement of the NGF receptors (Trka and p75lngfr) in the development and maintenance of the thymus

Nerve growth factor (NGF) and its main low- (p75LNGFR) and high-affinity (TrkA) receptors have been found in the vertebrate thymus, thus suggesting they are involved in the control of thymic function. However, its role in this organ is poorly known. In the present study we used combined morphological and immunohistochemical techniques to analyze the distribution of TrkA and p75LNGFR in the rat thymus, as well as the structural changes in the thymus of p75 LNGFR or TrkA deficient mice. In adult rats both TrkA and p75LNGFR were localized in a subset of thymic epithelial cells found primarily in the subcapsular and medullary thymic regions, regarded to be endodermal-derived cells. Consistently, animals with a non-functional TrkA, but not those lacking p75LNGFR, showed structural changes consisting of a decrease in the density of thymocytes, absence of cortico-medullary border, and large cysts lined of endodermal epithelium. These results strongly suggest a function of the TrkA-NGF system in thymic functions mediated by epithelial cells, as well as a role of TrkA in the development of the murine thymus. The function of p75LNGFR remains to be established.

Changes in the expression of the nerve growth factor receptors TrkA and p75LNGR in the rat thymus with ageing and increased nerve growth factor plasma levels

The nerve growth factor (NGF) receptors p75LNGR and TrkA are expressed by thymic epithelial cells. Presumably, the NGF-TrkA system is involved in the paracrine communication between thymic epithelial cells and thymocytes, whereas the functional role of p75LNGR is still unknown. The thymus of vertebrates undergoes age-related changes that in part depend on hormonal factors. In order to find out whether thymic epithelial cells are responsive to NGF during the whole lifespan of the rat, we studied NGF receptor expression in the thymus from birth to 2 years of age, using immunohistochemistry. Furthermore, to evaluate whether increased plasma levels of NGF affected the ageing process, either NGF or 4-methylcatechol (4MC), an inductor of NGF synthesis, was administered. Both TrkA and p75LNGR were expressed by a subpopulation of thymic epithelial cells during the whole age range studied and their expression peaked at around 3 months. TrkA was primarily found in subcortical and medullary epithelial cells, whereas p75LNGR was seen in a subpopulation of medullary cells. Cortical epithelial cells, neural crest-derived cells, other stromal cells and thymocytes were not immunoreactive for NGF receptors. Neither the administration of NGF nor the increased NGF plasma levels obtained after 4MC treatment seemed to affect the ageing of the thymus as assessed by morphological and immunohistochemical criteria, but this increase in NGF levels did produce a shift in the expression of p75LNGR from epithelial cells to ED1-positive macrophages in animals of 6 months and older. Present results indicate that the expression of p75LNGR and TrkA in the rat thymus undergoes age-dependent changes that parallel those of epithelial cells. NGF could therefore be important for thymus homeostasis, possibly acting on epithelial cells. Nevertheless, NGF did not seem to be able to prevent the involution of this organ, although it produced a switch in the expression of p75LNGR, the significance of which remains to be established.

TrkA is necessary for the normal development of the murine thymus

Nerve growth factor (NGF) and its signal-transducing receptor TrkA are expressed in the thymus. However, their possible role during thymic organogenesis is unknown. Here we analyze the thymus of trkA-kinase deficient 2-week-old mice. trkA-kinase +/+ and +/- mice had a normal thymus, whereas the thymus of trkA-kinase -/- mice showed lack of delimitation between the cortex and medulla, lower thymocyte density, and the presence of epithelial cell islands and numerous cysts lined with endodermal epithelium. The present results indicate that TrkA is necessary for the normal development of the thymus, and that its absence causes an arrest in the differentiation of endodermal epithelial cells. Whether this lack of differentiation has functional implication has yet to be determined.

Trk neurotrophin receptor-like proteins in the teleost Dicentrarchus labrax

In recent years, data have accumulated suggesting that the role of neurotrophins and Trk receptors may not be limited to the nervous system, and the presence of these substances has been detected in a variety of vertebrate and invertebrate non-nervous tissues. This study was designed to map the expression of immunoreactivity (IR) for Trk-like proteins in alevins of the teleost Dicentrarchus labrax, with particular emphasis on non-nervous structures. We used antibodies against specific epitopes of the intracellular domain of these proteins, a region that is highly conserved in phylogeny. Trk-like IR was seen in segregate cell populations of the nervous system, and non-nervous tissues. In the central nervous system TrkA-like and TrkC-like IR was abundant, whereas TrkB-like IR was restricted to a low number of brain areas. Expression of Trk-like protein IR was observed in the peripheral nervous system and sensory organs, with the exception of the lateral line organ. Outside the nervous system, TrkA-like IR was mainly found in different epithelia, TrkB-like IR in the endocrine and digestive system, and TrkC-like IR in the cardiovascular and immune systems. The gills showed IR for all three Trk-like proteins, whereas they were absent from the gonads. Furthermore, scattered cells positive for Trk-like proteins were found in most of the investigated tissues. The distribution of Trk-like IR in this teleost is compared with that of mammals and birds, which it often paralleled, and the possible role of neurotrophins and Trk-like receptor proteins in different non-neuronal tissues is discussed.

Expression of the neurotrophin receptor TrkB in rat spleen macrophages

Increasing evidence suggests that some members of the family of the neurotrophins could be involved in immune system functioning. Both neurotrophins and their tyrosine-kinase signal-transducing receptors, the so-called Trk receptors, have been detected in various lymphoid tissues in a number of species. Nevertheless, their cellular localisation remains unclear in most cases. In this study, we used immunohistochemical techniques to localise TrkB in the rat spleen (from 0 days to 2 years). Cells expressing TrkB-like immunoreactivity were found exclusively within the white pulp of the spleen, along the marginal zone-follicle border and inside the follicles and periarteriolar lymphoid sheaths. These cells probably represented macrophage subpopulations, since they expressed the ED3 rat macrophage antigen. No evidence of TrkB-like protein expression in lymphocytes or follicular dendritic cells could be found. Furthermore, the density of TrkB-immunoreactive cells was observed to increase with age. Although the role of TrkB ligands in these cells remains to be clarified, the present findings provide further evidence for the supposed role of neurotrophins in immune system homeostasis.

Expression of the TrkB neurotrophin receptor by thymic macrophages

Increasing evidence suggests that some members of the neurotrophic factor family of neurotrophins could be implicated in the regulation of immune responses. Neurotrophins, as well as their tyrosine kinase signal-transducing receptors (the so-called Trk neurotrophin receptors), have been detected in different lymphoid tissues, although their cellular localization is not well known. In this study we used single and double immunohistochemistry to localize TrkB in situ in the rat thymus (in animals from 0 days to 2 years of age), in cytospin preparations of rat thymic cells, and in two mouse monocyte-macrophage cell lines (RAW 264.7 and J774A.1). We found TrkB protein expression in a subpopulation of cells in the corticomedullary junction, which simultaneously expressed the rat macrophage marker ED1. The density of TrkB-expressing cells increased with age, reaching maximal values at 2 years. Conversely, no evidence of TrkB protein expression could be found in dendritic cells, epithelial cells or thymocytes. Thymic macrophages in cytospin preparations, as well as in the mouse monocyte macrophage cell lines, also expressed TrkB protein. Although the possible function of TrkB in the thymic macrophage remains to be clarified, present findings add further evidence to the proposed role of neurotrophins in the immune system.