Positron emission tomographic investigations of central muscarinic cholinergic receptors with three isomers of [76Br]BrQNP

We studied the potential of three radiobrominated isomers of BrQNP, (Z(-,-)-[⁷⁶Br]BrQNP,E(-,-)-[⁷⁶Br]BrQNP andE(-,+)-[⁷⁶Br]BrQNP), as suitable radioligands for imaging of central muscarinic cholinergic receptors in the human brain. These radioligands were stereospecifically prepared by electrophilic radiobromodestannylation of the respective tributylstannyl precursors using no-carrier-added [⁷⁶Br]BrNH₄ and peracetic acid. Preliminary pharmacological characterizations were determined by biodistribution, autoradiography, competition, displacement and metabolite studies in rats. The (-,-)-configuration presented important specific uptakes in brain muscarinic cholinergic receptor (mAChR)-rich structures and in heart, low metabolization rates and an apparent M₂ selectivity. The (-,+)-configuration revealed more rapid clearance, lower uptake, a higher metabolization rate and an apparent M₁ selectivity. Reversibility of the binding was confirmed for the three radiotracers. Positron emission tomography in the living baboon brain revealed high and rapid uptake in the brain and accumulation in the mAChR-rich structures studied. At 30 min p.i., theE(-,-)-radiotracer reached a plateau in cortex, pons and thalamus with concentrations of 29%, 24% and 19% ID/l, respectively.Z(-,-)-[⁷⁶Br]BrQNP also accumulated in these structures, reaching a maximal uptake (27% ID/l) in the cortex 2 h p.i. At 5 min p.i. a plateau (17% ID/l) was only observed in the cortex for theE(-,+)-[⁷⁶Br]BrQNP; by contrast, the other structures showed slow washout. After 3 weeks, the (-,-)-radiotracers were studied in the same baboon pretreated with dexetimide (1 mg/kg), a well-known muscarinic antagonist. In all the mAChR structures, the highly reduced uptake observed after this preloading step indicates that these radiotracers specifically bind to muscarinic receptors.Z(-,-)-[⁷⁶Br]BrQNP, which is displaced in higher amounts from M₂ mAChR-enriched structures, reveals an M₂ affinity. The two isomers having the (-,-)-configuration are potential probes for investigating central muscarinic receptors. The absolute configuration on the acetate chiral centre influences their muscarinic subtype selectivity and thecis-trans isomerism of the vinyl moiety affects their specific fixation.     

Cervical bruits: clinical correlates of stenosis

To analyze the relationship among characteristics of buits, degree of underlying stenosis, and neurologic symptom complexes, the authors studied 157 patients with bruits undergoing digital subtraction angiography. Symptom status assignment (definite lateralizing, possible lateralizing, vertebrobasilar, diffuse, and asymptomatic) and cervical auscultation for location, duration, and other bruit characteristics were performed independently. Bruit occurrence was associated with stenosis of greater than or equal to 50% of the underlying vessel with the association being no stronger at higher levels of stenosis (greater than or equal to 80%). No relationship existed between the side of bruit and side of symptoms in those with lateralized symptoms. The authors found more severe degrees of carotid stenosis in two symptomatic groups (vertebrobasilar insufficiency [VBI] and definite lateralized) compared with asymptomatic patients. Those with VBI had more high-grade stenosis, whereas those with lateralized symptoms had more occlusions, which tended to be ipsilateral to the symptoms.     

Maternal renal insufficiency: A cause of congenital rickets and secondary hyperparathyroidism

We present a case of a newborn with congenital rickets and radiographic evidence of secondary hyperparathyroidism in which the infant's mother had severe, longstanding untreated renal insufficiency.     

Small bowel transplantation: Effects on function of nonadrenergic, noncholinergic nerves

Previous work from our laboratory showed that spontaneous contractile activity of jejunal smooth muscle increases after small bowel transplantation. Our aim was to determine whether small bowel transplantation alters the function of nonadrenergic, noncholinergic (NANC) nerves. Seven groups of rats, (n ≥7 in each group) were studied as follows: 1 week after sham celiotomy and 1 week and 8 weeks after 45 minutes of ischemia/ reperfusion (IR1 and IR8), jejunal and ileal transection and reanastomosis (TR1 and TR8), or orthotopic small bowel transplantation (TX1 and TX8). Contractility of jejunal circular muscle strips was studied in vitro. Spontaneous contractile activity increased in the IR1, TR1, and TX1 and TX1 and TX8 groups (P<0.01). Under NANC conditions, spontaneous activity increased in TR1 and in both TX1 and TX8 (P<0.01) despite the lack of an increase in the frequency of contraction in TX1. Electrical field stimulation inhibited contractile activity at low frequencies, but under NANC conditions this inhibition persisted at higher frequencies. The calculated equieffective frequency (F₁₀₀) that produced a response equal to baseline contractile activity was similar in all groups, but under NANC conditions was greater in TX1 (P<0.025). Functional alterations of NANC nerves are partly responsible for the increase in spontaneous activity in rat jejunal circular muscle strips after a limited ischemia/reperfusion injury, after selective disruption of enteric neural continuity (transection/reanastomosis), and after small bowel transplantation. These findings may provide important insight into graft dysfunction after small bowel transplantation in humans. Supported by United States Public Health Service grant DK 39337 from the National Institutes of Health and by the Mayo Foundation.     

Novel antiepileptic drug levetiracetam decreases dyskinesia elicited by L-dopa and ropinirole in the MPTP-lesioned marmoset.

Long-term dopamine replacement therapy of Parkinson's disease leads to the occurrence of dyskinesias. Altered firing patterns of neurons of the internal globus pallidus, involving a pathological synchronization/desynchronization process, may contribute significantly to the genesis of dyskinesia. Levetiracetam, an antiepileptic drug that counteracts neuronal (hyper)synchronization in animal models of epilepsy, was assessed in the MPTP-lesioned marmoset model of Parkinson's disease, after coadministration with (1) levodopa (L-dopa) or (2) ropinirole/L-dopa combination. Oral administration of levetiracetam (13-60 mg/kg) in combination with either L-dopa (12 mg/kg) alone or L-dopa (8 mg/kg)/ropinirole (1.25 mg/kg) treatments was associated with significantly less dyskinesia, in comparison to L-dopa monotherapy during the first hour after administration. Thus, new nondopaminergic treatment strategies targeting normalization of abnormal firing patterns in basal ganglia structures may prove useful as an adjunct to reduce dyskinesia induced by dopamine replacement therapy without affecting its antiparkinsonian action.     

Cancer risk due to occupational exposure to polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) demonstrate carcinogenic activity in animal models. Although some epidemiologic studies have implicated PAHs as risk factors for human cancer, the evidence reported to date has not been consistent. The purpose of this report is to describe the associations between occupational exposure to PAHs in the workplace and each of 14 types of cancer. A population-based, case-control study was carried out in Montreal to investigate associations between a large variety of environmental and occupational exposures on the one hand, and several types of cancer on the other. A detailed job history was obtained from each subject along with information on a number of potential confounders. Each job history was reviewed by a team of experts, who used this information to construct a corresponding history of occupational exposures. Among the PAH exposures considered were benzo(a)pyrene (B(a)P) and five categories of PAHs defined on the basis of the source material, namely, wood, petroleum, coal, other sources, and any source. Altogether, 3,730 cancer patients and 533 population controls were interviewed and their job exposure histories coded. For each of 14 types of cancer analyzed, three control groups were available: other cancer patients, population controls, and the pooled set of cancer and population controls. The associations between 14 cancer types and 6 PAH exposures were analyzed using logistic regression methods. For most types of cancer evaluated, there was no evidence of excess risk due to PAHs at the levels encountered in the occupations in which PAH exposure has been prevalent in the Montreal area. For a few cancer sites–the esophagus, the pancreas, and the prostate gland–there were suggestions of excess risk; these observations are noteworthy hypotheses for further investigation. For lung cancer, there appeared to be an increased risk due to PAHs among nonsmokers and light smokers, but not among heavy smokers.     

Intravenous colistin sulphomethate in acute respiratory exacerbations in adult patients with cystic fibrosis

BACKGROUND: Patients with cystic fibrosis have received more intravenous antibiotic courses as median survival has steadily increased. A number of centres have adopted a policy of regular (three monthly) rather than on demand intravenous antipseudomonal antibiotics. More widespread bacterial antibiotic resistance has resulted from this increased antibiotic use. Most Pseudomonas aeruginosa strains remain fully sensitive to colistin but its use has been resisted owing to concerns about neurotoxicity and nephrotoxicity. A study was carried out to assess the safety and efficacy of intravenous colistin in the treatment of acute respiratory exacerbations in adult patients with cystic fibrosis. METHODS: Patients with chronic Pseudomonas aeruginosa colonisation who presented with protocol defined respiratory tract exacerbations were randomised to receive treatment for 12 days with either colistin (2 MU tds intravenously) alone or with a second anti- pseudomonal antibiotic. Comparisons of the absolute values of respiratory function tests on days 1, 5, and 12 and of overnight oxygen saturation on days 1 and 12 were the primary outcome measures. Patient's weight, clinical and chest radiographic scores, and peripheral blood markers of inflammation were also documented. The effect of each treatment regimen individually was assessed by the change in clinical measurements from baseline values. Adverse renal effects were monitored by measurement of serum levels of urea and electrolytes, creatinine clearance, and ward urine testing. Neurotoxicity was monitored by direct questioning for symptoms. RESULTS: Fifty three patients, 18 of whom entered the study twice, were enrolled. The mean forced expiratory volume in one second (FEV1) increased significantly in both groups, mean forced vital capacity (FVC) only with dual therapy. Both groups showed a non-significant increase in overnight oxygen saturation. All patients showed clinical improvement. Thirty seven adverse neurological events (two severe) were reported in 33 patients in the monotherapy group and 37 (none severe) in 36 patients in the dual therapy group. One patient withdrew because of severe weakness and dizziness. All other adverse neurological events were well tolerated and resolved during or shortly after treatment. Significant changes were seen in mean serum urea levels in both groups, but in only four patients to a level above the normal range, and in creatinine clearance in the dual therapy group. At 24 month follow up no long term adverse consequences from intravenous colistin were found in patients who completed the study. CONCLUSIONS: Intravenous colistin is an effective treatment for Pseudomonas aeruginosa associated pulmonary exacerbations in patients with cystic fibrosis. Assessment of the individual effect of each treatment regimen suggests a greater efficacy when colistin is combined with a second antibiotic to which the pseudomonas shows in vitro sensitivity. Changes in renal function should be monitored.