Neale Scott Mason

A (polycation:heparin) complex releases growth factors with enhanced bioactivity

Growth factors are potent molecules that regulate cell functions including survival, self renewal, differentiation and proliferation. High-efficacy delivery of growth factors will be a powerful tool for regenerative medicine. Decades of intense research have significantly advanced the field of controlled delivery. There is, however, still a great unmet need for new methods that can improve overall efficacy of growth factor delivery. Here, we report a new growth factor delivery vehicle formed by self assembly of heparin and a biocompatible polycation, poly(ethylene argininylaspartate diglyceride) (PEAD). Of the many heparin-binding growth factors, we chose FGF-2 and NGF to demonstrate the potential of the [PEAD:heparin] delivery vehicle. The delivery vehicle incorporates both growth factors with high efficiency, controls their release, maintains the bioactivity of FGF-2 and increases the bioactivity of NGF relative to bolus delivery. [PEAD:heparin] appears to be a promising delivery matrix for many heparin-binding growth factors and may lead to efficient growth factor delivery for a variety of diseases and disabilities.

Amyloid-β 11C-PiB-PET imaging results from 2 randomized bapineuzumab phase 3 AD trials

Objective: To evaluate the effects of bapineuzumab on brain β-amyloid (Aβ) burden using 11C-Pittsburgh compound B (11C-PiB)-PET. Methods: Two phase 3 clinical trials, 1 each in apolipoprotein APOE ε4 carriers and noncarriers, were conducted in patients with mild to moderate Alzheimer disease dementia. Bapineuzumab, an anti-Aβ monoclonal antibody, or placebo, was administered by IV infusion every 13 weeks for 78 weeks. PET substudies assessed change in brain fibrillar Aβ over 71 weeks using an 11C-PiB-PET standardized uptake value ratio (SUVr) global cortical average (GCA) comprising the average SUVr from 5 cortical regions of interest with cerebellar gray matter as the reference region. Results: A total of 115 carriers and 39 noncarriers were analyzed. The difference (δ) in mean baseline to 71 week change in 11C-PiB-PET GCA between bapineuzumab and placebo was significant in carriers (0.5 mg/kg vs placebo δ = −0.101; p = 0.004) and in pooled analyses of both carriers and noncarriers (0.5 mg/kg vs placebo δ = −0.068; p = 0.027; 1.0 mg/kg vs placebo δ = −0.133; p = 0.028) but not in the noncarrier trial separately. Analyses by individual region of interest and in mild disease yielded findings similar to the main trial results. Conclusions: The 11C-PiB-PET imaging results demonstrated reduction of fibrillar Aβ accumulation in patients with Alzheimer disease treated with bapineuzumab; however, as no clinical benefit was observed, the findings are consistent with the hypotheses that bapineuzumab may not have been initiated early enough in the disease course, the doses were insufficient, or the most critical Aβ species were inadequately targeted.

Gender, personality, and serotonin-2A receptor binding in healthy subjects

The vulnerability to mood disorders, impulsive-aggression, eating disorders, and suicidal behavior varies greatly with gender, and may reflect gender differences in central serotonergic function. We investigated the relationships of gender, mood, impulsivity, aggression and temperament to 5HT(2A) receptor binding in 21 healthy subjects using [18F]altanserin and PET neuroimaging. Binding potentials in pre-defined regions-of-interest (ROI) were calculated using the Logan graphical method, corrected for partial volume effects, and compared by gender with age co-varied. SPM analysis was used for voxel level comparisons. Altanserin binding (BP(P)) was greater in male than female subjects in the following nine ROIs: hippocampus (HIP) and Lt. HIP, lateral orbital frontal cortex (LOF) and Lt. LOF, left medial frontal cortex (Lt. MFC), left medial temporal cortex (Lt. MTC), left occipital cortex (Lt. OCC), thalamus (THL) and Lt. THL. Differences in Lt. HIP and Lt. MTL remained significant after Bonferroni correction. Gender differences were noted in the co-variation of psychological traits with BP(P) values in specific ROIs. Among males alone, aggression was negatively correlated with BP(P) values in Lt. LOF and Lt. MFC, and Suspiciousness positively correlated in LOF, Lt. LOF and Lt. MFC. Among female subjects alone, Negativism was positively correlated with BP(P) values in HIP, and Verbal Hostility in Lt. HIP. Altanserin binding in Lt. MTC was positively correlated with Persistence, with no significant gender effect. Gender differences in 5HT(2A) receptor function in specific ROIs may mediate expression of psychological characteristics such as aggression, suspiciousness and negativism. Future studies of 5HT(2A) receptor function and its relationship to behavior should control for gender.

In vivo evidence for low striatal vesicular monoamine transporter 2 (VMAT2) availability in cocaine abusers.

OBJECTIVE Positron emission tomography (PET) imaging studies in cocaine abusers have shown that low dopamine release in the striatum following an amphetamine challenge is associated with higher relapse rates. One possible mechanism that might lead to lower amphetamine-induced dopamine release is low availability of dopamine storage vesicles in the presynaptic terminals for release. Consistent with this hypothesis, postmortem studies have shown low levels of vesicular monoamine transporter, type 2 (VMAT2), the membrane protein that regulates the size of the vesicular dopamine pool, in cocaine abusers relative to healthy subjects. To confirm the postmortem findings, the authors used PET and the VMAT2 radioligand [¹¹C]-(+)-dihydrotetrabenazine (DTBZ) to assess the in vivo VMAT2 availability in a group of 12 recently abstinent cocaine-dependent subjects and matched healthy comparison subjects. METHOD [¹¹C]DTBZ nondisplaceable binding potential (BP(ND)) was measured by kinetic analysis using the arterial input function or, if arterial input was unavailable, by the simplified reference tissue method. RESULTS [¹¹C]DTBZ BP(ND) was significantly lower in the cocaine abusers than in the comparison subjects in the limbic striatum (10.0% lower), associative striatum (-13.4%), and sensorimotor striatum (-11.5%). CONCLUSIONS The results of this in vivo PET study confirm previous in vitro reports of low VMAT2 availability in the striatum of cocaine abusers. It also suggests a compensatory down-regulation of the dopamine storage vesicles in response to chronic cocaine abuse and/or a loss of dopaminergic terminals. Further research is necessary to understand the clinical relevance of this observation to relapse and outcome in abstinent cocaine abusers.

Decreased Prefrontal Cortical Dopamine Transmission in Alcoholism

OBJECTIVE Basic studies have demonstrated that optimal levels of prefrontal cortical dopamine are critical to various executive functions such as working memory, attention, inhibitory control, and risk/reward decisions, all of which are impaired in addictive disorders such as alcoholism. Based on this and imaging studies of alcoholism that have demonstrated less dopamine in the striatum, the authors hypothesized decreased dopamine transmission in the prefrontal cortex in persons with alcohol dependence. METHOD To test this hypothesis, amphetamine and [11C]FLB 457 positron emission tomography were used to measure cortical dopamine transmission in 21 recently abstinent persons with alcohol dependence and 21 matched healthy comparison subjects. [11C]FLB 457 binding potential, specific compared to nondisplaceable uptake (BPND), was measured in subjects with kinetic analysis using the arterial input function both before and after 0.5 mg kg-1 of d-amphetamine. RESULTS Amphetamine-induced displacement of [11C]FLB 457 binding potential (ΔBPND) was significantly smaller in the cortical regions in the alcohol-dependent group compared with the healthy comparison group. Cortical regions that demonstrated lower dopamine transmission in the alcohol-dependent group included the dorsolateral prefrontal cortex, medial prefrontal cortex, orbital frontal cortex, temporal cortex, and medial temporal lobe. CONCLUSIONS The results of this study, for the first time, unambiguously demonstrate decreased dopamine transmission in the cortex in alcoholism. Further research is necessary to understand the clinical relevance of decreased cortical dopamine as to whether it is related to impaired executive function, relapse, and outcome in alcoholism.

Cocaine Abuse in Humans Is Not Associated with Increased Microglial Activation: An 18-kDa Translocator Protein Positron Emission Tomography Imaging Study with [11C]PBR28

Basic science investigations have consistently shown that repeated exposure to psychostimulant drugs, such as cocaine, activate the immune response and lead to inflammatory changes in the brain. No previous in vivo studies have confirmed this observation in chronic cocaine-abusing humans. To test this hypothesis, we used positron emission tomography imaging to measure the binding of [11C]PBR28 to the 18 kDa translocator protein (TSPO), a marker for microglial activation in a group of 15 recently abstinent cocaine abusers and 17 matched healthy controls. [11C]PBR28 volumes of distribution expressed relative to total plasma ligand concentration (VT) were measured in subjects with kinetic analysis using the arterial input function. Subjects were also genotyped for the TSPO alanine147 threonine (Ala147Thr, rs6971) polymorphism that has been shown to influence the in vivo binding of PBR28 to TSPO. Consistent with previous reports, the TSPO Ala147Thr genotype predicted the in vivo binding of [11C]PBR28. No significant differences in [11C]PBR28 VT were observed in the cortical and subcortical regions in cocaine abusers compared with healthy controls. The results of this in vivo study do not support increased TSPO expression and, by extension, microglial activation in chronic cocaine-abusing humans. Further research with more direct markers of microglial activation is necessary to conclusively rule out neuroinflammation in cocaine dependence.

Effects of serotonin-2A receptor binding and gender on personality traits and suicidal behavior in borderline personality disorder.

Impulsivity and aggressiveness are personality traits associated with a vulnerability to suicidal behavior. Behavioral expression of these traits differs by gender and has been related to central serotonergic function. We assessed the relationships between serotonin-2A receptor function, gender, and personality traits in borderline personality disorder (BPD), a disorder characterized by impulsive-aggression and recurrent suicidal behavior. Participants, who included 33 BPD patients and 27 healthy controls (HC), were assessed for Axis I and II disorders with the Structured Clinical Interview for DSM-IV and the International Personality Disorders Examination, and with the Diagnostic Interview for Borderline Patients-Revised for BPD. Depressed mood, impulsivity, aggression, and temperament were assessed with standardized measures. Positron emission tomography with [(18)F]altanserin as ligand and arterial blood sampling was used to determine the binding potentials (BPND) of serotonin-2A receptors in 11 regions of interest. Data were analyzed using Logan graphical analysis, controlling for age and non-specific binding. Among BPD subjects, aggression, Cluster B co-morbidity, antisocial PD, and childhood abuse were each related to altanserin binding. BPND values predicted impulsivity and aggression in BPD females (but not BPD males), and in HC males (but not HC females.) Altanserin binding was greater in BPD females than males in every contrast, but it did not discriminate suicide attempters from non-attempters. Region-specific differences in serotonin-2A receptor binding related to diagnosis and gender predicted clinical expression of aggression and impulsivity. Vulnerability to suicidal behavior in BPD may be related to serotonin-2A binding through expression of personality risk factors.

Imaging of dopamine D2/3 agonist binding in cocaine dependence: a [11C]NPA positron emission tomography study.

Objective: Positron emission tomography (PET) studies performed with [11C]raclopride have consistently reported lower binding to D2/3 receptors and lower amphetamine‐induced dopamine (DA) release in cocaine abusers relative to healthy controls. A limitation of these studies that were performed with D2/3 antagonist radiotracers such as [11C]raclopride is the failure to provide information that is specific to D2/3 receptors configured in a state of high affinity for the agonists (i.e., D2/3 receptors coupled to G‐proteins, D2/3 HIGH). As the endogenous agonist DA binds with preference to D2/3 HIGH relative to D2/3 LOW receptors (i.e., D2/3 receptors uncoupled to G‐proteins) it is critical to understand the in vivo status of D2/3 HIGH receptors in cocaine dependence. Thus, we measured the available fraction of D2/3 HIGH receptors in 10 recently abstinent cocaine abusers (CD) and matched healthy controls (HC) with the D2/3 antagonist and agonist PET radiotracers [11C]raclopride and [11C]NPA. Methods:[11C]raclopride and [11C]NPA binding potential (BP) (BPND) in the striatum were measured with kinetic analysis using the arterial input function. The available fraction of D2/3 HIGH receptors, i.e., % RHIGH available = D2/3 HIGH/(D2/3 HIGH + D2/3 LOW) was then computed as the ratio of [11C]NPA BPND/[11C]raclopride BPND. Results:No differences in striatal [11C]NPA BPND (HC = 1.00 ± 0.17; CD = 0.97 ± 0.17, P = 0.67) or available % RHIGH (HC = 39% ± 5%; CD = 41% ± 5%, P = 0.50) was observed between cocaine abusers and matched controls. Conclusions: The results of this [11C]NPA PET study do not support alterations in D2/3 HIGH binding in the striatum in cocaine dependence. Synapse, 2011.

Improved Working Memory but No Effect on Striatal Vesicular Monoamine Transporter Type 2 after Omega-3 Polyunsaturated Fatty Acid Supplementation

Studies in rodents indicate that diets deficient in omega-3 polyunsaturated fatty acids (n–3 PUFA) lower dopamine neurotransmission as measured by striatal vesicular monoamine transporter type 2 (VMAT2) density and amphetamine-induced dopamine release. This suggests that dietary supplementation with fish oil might increase VMAT2 availability, enhance dopamine storage and release, and improve dopamine-dependent cognitive functions such as working memory. To investigate this mechanism in humans, positron emission tomography (PET) was used to measure VMAT2 availability pre- and post-supplementation of n–3 PUFA in healthy individuals. Healthy young adult subjects were scanned with PET using [11C]-(+)-α-dihydrotetrabenzine (DTBZ) before and after six months of n–3 PUFA supplementation (Lovaza, 2 g/day containing docosahexaenonic acid, DHA 750 mg/d and eicosapentaenoic acid, EPA 930 mg/d). In addition, subjects underwent a working memory task (n-back) and red blood cell membrane (RBC) fatty acid composition analysis pre- and post-supplementation. RBC analysis showed a significant increase in both DHA and EPA post-supplementation. In contrast, no significant change in [11C]DTBZ binding potential (BPND) in striatum and its subdivisions were observed after supplementation with n–3 PUFA. No correlation was evident between n–3 PUFA induced change in RBC DHA or EPA levels and change in [11C]DTBZ BPND in striatal subdivisions. However, pre-supplementation RBC DHA levels was predictive of baseline performance (i.e., adjusted hit rate, AHR on 3-back) on the n-back task (y = 0.19+0.07, r2 = 0.55, p = 0.009). In addition, subjects AHR performance improved on 3-back post-supplementation (pre 0.65±0.27, post 0.80±0.15, p = 0.04). The correlation between n-back performance, and DHA levels are consistent with reports in which higher DHA levels is related to improved cognitive performance. However, the lack of change in [11C]DBTZ BPND indicates that striatal VMAT2 regulation is not the mechanism of action by which n–3 PUFA improves cognitive performance.

PET Measurement of Endogenous Neurotransmitter Activity Using High and Low Affinity Radiotracers

Functional imaging of the in vivo competition of dopamine-D 2 radioligands with endogenous dopamine has provided indirect measures of dopamine activity. Binding parameter changes ( > 20%) have been observed for [ 11 C]raclopride positron emission tomography studies performed after d-amphetamine administration, and this sensitivity has been partially attributed to its low D 2 receptor affinity. In this work, a d-amphetamine pretreatment/bolus radiotracer injection paradigm was used to examine binding parameter changes for the high and low affinity benzamides, [ 18 F]fallypride and [ 11 C]raclopride; and a preliminary examination of [ 18 F]fallypride extrastriatal D 2 binding at baseline and after haloperidol pretreatment was performed. [ 11 C]aclopride studies were performed in baboons at baseline and after d-amphetamine pretreatment (0.6 mg/kg, n = 3 or 1.0 mg/kg, n = 2). Two baboons had additional [ 18 F]fallypride studies at baseline and after d-amphetamine, and a third baboon was studied at baseline and after haloperidol pretreatment (1 mg/kg). Kinetic analyses provided distribution volume (DV) and DV-de-rived binding potential (BP DV ) estimates. For [ 11 C]raclopride, the average striatal BP DV change was – 26 ± 2.6% for the 0.6-mg/kg amphetamine dose, with slightly greater changes of −31 and −39% after the 1.0-mg/kg dose. Lower striatal changes were observed for [ 18 F]fallypride: – 14% (0.6 mg/kg) and – 29% (1.0 mg/kg). Baseline regional BP DV values were highly correlated (r 2 > 0.9) with human D 2 receptor rank order but did not correlate after 1 mg/kg haloperidol pretreatment (r 2 0.1).Functional imaging of the in vivo competition of dopamine-D2radioligands with endogenous dopamine has provided indirect measures of dopamine activity. Binding parameter changes (> 20%) have been observed for [11C]raclopride positron emission tomography studies performed after d-amphetamine administration, and this sensitivity has been partially attributed to its low D2 receptor affinity. In this work, a d-amphetamine pretreatment/bolus radiotracer injection paradigm was used to examine binding parameter changes for the high and low affinity benzamides, [18F]fallypride and [11C]raclopride; and a preliminary examination of [18F]fallypride extrastriatal D2 binding at baseline and after haloperidol pretreatment was performed. [11C]aclopride studies were performed in baboons at baseline and after d-amphetamine pretreatment (0.6 mg/kg, n = 3 or 1.0 mg/kg, n = 2). Two baboons had additional [18F]fallypride studies at baseline and after d-amphetamine, and a third baboon was studied at baseline and after haloperidol pretreatment (1 mg/kg). Kinetic analyses provided distribution volume (DV) and DV-de-rived binding potential (BPDV) estimates. For [11C]raclopride, the average striatal BPDV change was –26 ± 2.6% for the 0.6-mg/kg amphetamine dose, with slightly greater changes of −31 and −39% after the 1.0-mg/kg dose. Lower striatal changes were observed for [18F]fallypride: –14% (0.6 mg/kg) and –29% (1.0 mg/kg). Baseline regional BPDVvalues were highly correlated (r2 > 0.9) with human D2 receptor rank order but did not correlate after 1 mg/kg haloperidol pretreatment (r2 < 0.1).