Long-lasting and transmission-blocking activity of antibodies to Plasmodium falciparum elicited in mice by protein conjugates of Pfs25

Malaria is a leading cause of morbidity and mortality, estimated to cause >1 million childhood deaths annually. Plasmodium falciparum causes the most severe form of the disease. There is as yet no licensed vaccine for this disease, despite over a half century of research. In this study, we investigated a transmission-blocking vaccine candidate, the ookinete surface protein Pfs25. Antibodies against Pfs25, drawn in during a bite, can block parasite development in the mosquito midgut, preventing transmission to other individuals. Pfs25 is a low-molecular-weight protein, by itself not immunogenic. To increase its immunogenicity, we investigated several methods of conjugating Pfs25 to itself and to other proteins: recombinant Pseudomonas aeruginosa exotoxin A, and ovalbumin, using amide, hydrazone, or thioether linkages. All conjugates were immunogenic and induced booster responses in mice. The scheme to form amide bonds between proteins by using adipic acid dihydrizide as a linker produced the most immunogenic conjugates. Adsorption of the conjugates onto aluminum hydroxide further increased the antibody response. Remarkably, the antibody levels 3 or 7 months after the last injection were significantly higher than those 1 wk after that injection. The observed transmission-blocking activity of immune sera correlated with antibody levels measured by ELISA.     

Metabolic abnormalities, insulin resistance, and metabolic syndrome in children with primary hypertension

BACKGROUND: We sought to describe the prevalence of metabolic abnormalities and of metabolic syndrome (MS) and its relationship to target-organ damage in children with primary hypertension (PH). METHODS: Patients included 113 children with untreated PH at a mean age of 14.6 years (range, 5 to 18 years). The control group consisted of 134 healthy children at a mean age of 13.5 years (range, 5 to 20 years). We performed a cross-sectional assessment of anthropometric and biochemical cardiovascular risk factors, homeostatic metabolic assessment (HOMA-IR), the insulin sensitivity index (ISI[0,120]), and adiponectin. RESULTS: Metabolic syndrome, as defined by classic criteria, was present in 4 of 134 (3%) of controls versus 23 of 113 (20.4%) patients (P=.0001), but when PH was not taken as a criterion of MS, MS was diagnosed in 6.2% of patients (no significance). Left-ventricular hypertrophy (LVH) was found in 46 of 113 patients (40.7%), and severe LVH was found in 14 of 113 patients (12.5%). Patients with LVH had a greater body mass index, greater waist-to-hip-ratio, and greater number of parameters of metabolic syndrome (overall P<.05). Carotid (cIMT) and femoral superficial artery intima-media thicknesses correlated positively with HOMA-IR and negatively with ISI[0.120] and serum adiponectin (P<.05). The main predictor for cIMT was adiponectin (R2=0.178, beta=-0.466, P=.002). Left-ventricular hypertrophy was predicted (R2=0.332) by body mass index-standard deviation score (beta=0.551, P=.005) and HOMA-IR (beta=0.380, P=.04). CONCLUSIONS: Metabolic syndrome, as defined by classic criteria, was diagnosed in 20% of children with PH, but when PH was not a criterion, MS was present in 6.2% of patients. Irrespective of the definition of MS, the applied markers of MS and insulin resistance were the main predictors of target-organ damage.     

Depressed dopamine activity in caudate and preliminary evidence of limbic involvement in adults with attention-deficit/hyperactivity disorder

CONTEXT: Attention-deficit/hyperactivity disorder (ADHD) is the most prevalent psychiatric disorder of childhood. There is considerable evidence that brain dopamine is involved in ADHD, but it is unclear whether dopamine activity is enhanced or depressed. OBJECTIVE: To test the hypotheses that striatal dopamine activity is depressed in ADHD and that this contributes to symptoms of inattention. DESIGN: Clinical (ADHD adult) and comparison (healthy control) subjects were scanned with positron emission tomography and raclopride labeled with carbon 11 (D2/D3 receptor radioligand sensitive to competition with endogenous dopamine) after placebo and after intravenous methylphenidate hydrochloride (stimulant that increases extracellular dopamine by blocking dopamine transporters). The difference in [11C]raclopride's specific binding between placebo and methylphenidate was used as marker of dopamine release. Symptoms were quantified using the Conners Adult ADHD Rating Scales. SETTING: Outpatient setting. PARTICIPANTS: Nineteen adults with ADHD who had never received medication and 24 healthy controls. RESULTS: With the placebo, D2/D3 receptor availability in left caudate was lower (P < .05) in subjects with ADHD than in controls. Methylphenidate induced smaller decrements in [11C]raclopride binding in left and right caudate (blunted DA increases) (P < .05) and higher scores on self-reports of "drug liking" in ADHD than in control subjects. The blunted response to methylphenidate in caudate was associated with symptoms of inattention (P < .05) and with higher self-reports of drug liking (P < .01). Exploratory analysis using statistical parametric mapping revealed that methylphenidate also decreased [11C]raclopride binding in hippocampus and amygdala and that these decrements were smaller in subjects with ADHD (P < .001). CONCLUSIONS: This study reveals depressed dopamine activity in caudate and preliminary evidence in limbic regions in adults with ADHD that was associated with inattention and with enhanced reinforcing responses to intravenous methylphenidate. This suggests that dopamine dysfunction is involved with symptoms of inattention but may also contribute to substance abuse comorbidity in ADHD.     

Amphetamine and mCPP Effects on Dopamine and Serotonin Striatalin vivo Microdialysates in an Animal Model of Hyperactivity

In the neonatally 6-hydroxydopamine (6-OHDA)-lesioned rat hyperlocomotor activity, first described in the 1970s, was subsequently found to be increased by an additional lesion with 5,7-dihydroxytryptamine (5,7-DHT) (i.c.v.) in adulthood. The latter animal model (i.e., 134 microg 6-OHDA at 3 d postbirth plus 71 microg 5,7-DHT at 10 weeks; desipramine pretreatments) was used in this study, in an attempt to attribute hyperlocomotor attenuation by D,L-amphetamine sulfate (AMPH) and m-chlorophenylpiperazine di HCl (mCPP), to specific changes in extraneuronal (i.e., in vivo microdialysate) levels of dopamine (DA) and/or serotonin (5-HT). Despite the 98-99% reduction in striatal tissue content of DA, the baseline striatal microdialysate level of DA was reduced by 50% or less at 14 weeks, versus the intact control group. When challenged with AMPH (0.5 mg/kg), the microdialysate level of DA went either unchanged or was slightly reduced over the next 180 min (i.e., 20 min sampling), while in the vehicle group and 5,7-DHT (alone) lesioned group, the microdialysate level was maximally elevated by approximately 225% and approximately 450%, respectively--and over a span of nearly 2 h. Acute challenge with mCPP (1 mg/kg salt form) had little effect on microdialysate levels of DA, DOPAC and 5-HT. Moreover, there was no consistent change in the microdialysate levels of DA, DOPAC, and 5-HT between intact, 5-HT-lesioned rats, and DA-lesioned rats which might reasonably account for an attenuation of hyperlocomotor activity. These findings indicate that there are other important neurochemical changes produced by AMPH- and mCPP-attenuated hyperlocomotor activity, or perhaps a different brain region or multiple brain regional effects are involved in AMPH and mCPP behavioral actions.     

Visual and flight performance recovery after PRK or LASIK in helicopter pilots

INTRODUCTION: Refractive surgery, specifically photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK), is becoming more accepted in the military environment. Determination of the impact on visual performance in the more demanding aviation environment was the impetus for this study. METHODS: A prospective evaluation of 20 Black Hawk pilots pre-surgically and at 1 wk, 1 mo, and 6 mo postsurgery was conducted to assess both PRK and LASIK visual and flight performance outcomes on the return of aviators to duty. RESULTS: Of 20 pilots, 19 returned to flight status at 1 mo after surgery; 1 PRK subject was delayed due to corneal haze and subjective visual symptoms. Improvements were seen under simulator night and night vision goggle flight after LASIK; no significant changes in flight performance were measured in the aircraft. Results indicated a significantly faster recovery of all visual performance outcomes 1 wk after LASIK vs. PRK, with no difference between procedures at 1 and 6 mo. Low contrast acuity and contrast sensitivity only weakly correlated to flight performance in the early post-operative period. DISCUSSION: Overall flight performance assessed in this study after PRK and LASIK was stable or improved from baseline, indicating a resilience of performance despite measured decrements in visual performance, especially in PRK. More visually demanding flight tasks may be impacted by subtle changes in visual performance. Contrast tests are more sensitive to the effects of refractive surgical intervention and may prove to be a better indicator of visual recovery for return to flight status.     

Synthesis and positron emission tomography studies of carbon-11-labeled imatinib (Gleevec)

INTRODUCTION: Imatinib mesylate (Gleevec) is a well known drug for treating chronic myeloid leukemia and gastrointestinal stromal tumors. Its active ingredient, imatinib ([4-[(4-methyl-1-piperazinyl)methyl]-N-[4-methyl-3-[[4-(3-pyridyl)-2-pyrimidinyl]amino]phenyl]benzamide), blocks the activity of several tyrosine kinases. Here we labeled imatinib with carbon-11 as a tool for determining the drug distribution and pharmacokinetics of imatinib, and we carried out positron emission tomography (PET) studies in baboons. METHODS: [N-(11)C-methyl]imatinib was synthesized from [(11)C]methyl iodide and norimatinib was synthesized by the demethylation of imatinib (isolated from Gleevec tablets) according to a patent procedure [Collins JM, Klecker RW Jr, Anderson LW. Imaging of drug accumulation as a guide to antitumor therapy. US Patent 20030198594A1, 2003]. Norimatinib was also synthesized from the corresponding amine and acid. PET studies were carried out in three baboons to measure pharmacokinetics in the brain and peripheral organs and to determine the effect of a therapeutic dose of imatinib. Log D and plasma protein binding were also measured. RESULTS: [N-(11)C-methyl]imatinib uptake in the brain is negligible (consistent with P-glycoprotein-mediated efflux); it peaks and clears rapidly from the heart, lungs and spleen. Peak uptake and clearance occur more slowly in the liver and kidneys, followed by accumulation in the gallbladder and urinary bladder. Pretreatment with imatinib did not change uptake in the heart, lungs, kidneys and spleen, and increased uptake in the liver and gallbladder. CONCLUSIONS: [N-(11)C-methyl]imatinib has potential for assessing the regional distribution and kinetics of imatinib in the human body to determine whether the drug targets tumors and to identify other organs to which the drug or its labeled metabolites distribute. Paired with tracers such as 2'deoxy-2'-[(18)F]fluoro-D-glucose ((18)FDG) and 3'deoxy-3'-[(18)F]fluorothymidine ((18)FLT), [N-(11)C-methyl]imatinib may be a useful radiotracer for planning chemotherapy, for monitoring response to treatment and for assessing the role of drug pharmacokinetics in drug resistance.     

Synthesis and positron emission tomography studies of C-11-labeled isotopomers and metabolites of GTS-21, a partial alpha7 nicotinic cholinergic agonist drug

INTRODUCTION: (3E)-3-[(2,4-dimethoxyphenyl)methylene]-3,4,5,6-tetrahydro-2,3'-bipyridine (GTS-21), a partial alpha7 nicotinic acetylcholine receptor agonist drug, has recently been shown to improve cognition in schizophrenia and Alzheimer's disease. One of its two major demethylated metabolites, 4-OH-GTS-21, has been suggested to contribute to its therapeutic effects. METHODS: We labeled GTS-21 in two different positions with carbon-11 ([2-methoxy-(11)C]GTS-21 and [4-(11)C]GTS-21) along with two corresponding demethylated metabolites ([2-methoxy-(11)C]4-OH-GTS-21 and [4-methoxy-(11)C]2-OH-GTS-21) for pharmacokinetic studies in baboons and mice with positron emission tomography (PET). RESULTS: Both [2-(11)C]GTS-21 and [4-methoxy-(11)C]GTS-21 showed similar initial high rapid uptake in baboon brain, peaking from 1 to 3.5 min (0.027-0.038%ID/cc) followed by rapid clearance (t(1/2)<15 min), resulting in low brain retention by 30 min. However, after 30 min, [2-methoxy-(11)C]GTS-21 continued to clear while [4-methoxy-(11)C]GTS-21 plateaued, suggesting the entry of a labeled metabolite into the brain. Comparison of the pharmacokinetics of the two labeled metabolites confirmed expected higher brain uptake and retention of [4-methoxy-(11)C]2-OH-GTS-21 (the labeled metabolite of [4-methoxy-(11)C]GTS-21) relative to [2-methoxy-(11)C]4-OH-GTS-21 (the labeled metabolite of [2-methoxy-(11)C]GTS-21), which had negligible brain uptake. Ex vivo studies in mice showed that GTS-21 is the major chemical form in the mouse brain. Whole-body dynamic PET imaging in baboon and mouse showed that the major route of excretion of C-11 is through the gallbladder. CONCLUSIONS: The major findings are as follows: (a) extremely rapid uptake and clearance of [2-methoxy-(11)C]GTS-21 from the brain, which may need to be considered in developing optimal dosing of GTS-21 for patients, and (b) significant brain uptake of 2-OH-GTS-21, suggesting that it might contribute to the therapeutic effects of GTS-21. This study illustrates the value of comparing different label positions and labeled metabolites to gain insight on the behavior of a central nervous system drug and its metabolites in the brain, providing an important perspective on drug pharmacokinetics.     

Quantification of rodent cerebral blood flow (CBF) in normal and high flow states using pulsed arterial spin labeling magnetic resonance imaging

PURPOSE: To implement a pulsed arterial spin labeling (ASL) technique in rats that accounts for cerebral blood flow (CBF) quantification errors due to arterial transit times (dt)-the time that tagged blood takes to reach the imaging slice-and outflow of the tag. MATERIALS AND METHODS: Wistar rats were subjected to air or 5% CO(2), and flow-sensitive alternating inversion-recovery (FAIR) perfusion images were acquired. For CBF calculation, we applied the double-subtraction strategy (Buxton et al., Magn Reson Med 1998;40:383-396), in which data collected at two inversion times (TIs) are combined. RESULTS: The ASL signal fell off more rapidly than expected from TI = one second onward, due to outflow effects. Inversion times for CBF calculation were therefore chosen to be larger than the longest transit times, but short enough to avoid systematic errors caused by outflow of tagged blood. Using our method, we observed a marked regional variability in CBF and dt, and a region dependent response to hypercapnia. CONCLUSION: Even when flow is accelerated, CBF can be accurately determined using pulsed ASL, as long as dt and outflow of the tag are accounted for.