Karen M. Powers

Parkinson’s disease risks associated with dietary iron, manganese, and other nutrient intakes

Background: Dietary influences on oxidative stress have been thought to play important role in the etiology of PD. Objective: To examine associations of PD with dietary nutrients, including minerals, vitamins, and fats. Methods: A population-based case-control study was conducted among newly diagnosed case (n = 250) and control subjects (n = 388) identified between 1992 and 2002 from enrollees of the Group Health Cooperative health maintenance organization in western Washington state. Controls were frequency matched to cases on sex and age. In-person interviews elicited data on food frequency habits during most of adult life. Nutrient intakes were calculated and analyzed by adjusting each person’s nutrient intake by their total energy intake (the nutrient density technique). Results: Subjects with an iron intake in the highest quartile compared with those in the lowest quartile had an increased risk of PD (odds ratio = 1.7, 95% CI: 1.0, 2.7, trend p = 0.016). There was an apparent joint effect of iron and manganese; dietary intake above median levels of both together conferred a nearly doubled risk compared with lower intakes of each nutrient (odds ratio = 1.9, 95% CI: 1.2, 2.9). No strong associations were found for either antioxidants or fats. Conclusion: A high intake of iron, especially in combination with high manganese intake, may be related to risk for PD.

Combined Effects of Smoking, Coffee, and NSAIDs on Parkinson's Disease Risk

Inverse associations of Parkinsons disease (PD) with cigarette smoking, coffee drinking, and nonsteroidal anti‐inflammatory drug (NSAID) use have been reported individually, but their joint effects have not been examined. To quantify associations with PD for the individual, two‐way and three‐way combinations of these factors, a case–control association study with 1,186 PD patients and 928 controls was conducted. The study setting was the NeuroGenetics Research Consortium. Subjects completed a structured questionnaire regarding smoking, coffee, and NSAID consumption. Odds ratios were calculated using unconditional logistic regression. Smoking, coffee, and over the counter NSAID use as individual factors exhibited significantly reduced risks of 20% to 30%. The two‐way and three‐way combinations were associated with risk reduction of 37% to 49%, and 62%, respectively. Smoking and coffee exhibited significant inverse risk trends with increasing cumulative exposures, suggesting dose–response relations. With respect to the combination of all three exposures, persons who were at the highest exposure strata for smoking and coffee and used NSAIDs had an estimated 87% reduction in risk (OR = 0.13, 95% CI = 0.06–0.29). Whether this finding reflects true biologic protection needs to be investigated.

Effect of mannitol on cerebrospinal fluid dynamics and brain tissue edema

Mannitol is used widely to decrease intracranial pressure (ICP); however, the mechanism by which this effect occurs is unclear. This study was designed to examine the effects of mannitol on cerebrospinal fluid (CSF) formation rate (Vf), resistance to reabsorption of CSF (Ra), and brain tissue water content (BTWC). Eighteen New Zealand White rabbits were allocated into one of three groups and studied at baseline and at two sequential doses of 20% mannitol: 0.75 g/kg followed by 4.4 mg.kg-1.min-1, and 2.0 g/kg (1.25 g/kg added to the initial dose of 0.75 g/kg) followed by 8.6 mg.kg-1.min-1. In Group 1, closed ventriculocisternal perfusion (VCP) was performed to determine changes in ICP due to mannitol. In Group 2, the increase in CSF osmolality due to mannitol was determined. In Group 3, mock CSF was used for open VCP to determine Vf and Ra. At the conclusion of each study, brain tissue samples were taken for determination of BTWC. Mannitol increased CSF and plasma osmolality. Ra was increased by 104% with the low dose of mannitol and not significantly changed by the high dose. Mannitol decreased BTWC, Vf (by 49% with the high dose), ICP, and hematocrit. The authors conclude that two of the mechanisms contributing to decreased ICP with mannitol are: 1) decreased CSF volume as indicated by decreased Vf, and 2) decreased brain tissue volume as indicated by decreased BTWC.

Occupational factors and risk of Parkinson's disease: A population-based case-control study.

BACKGROUND Parkinsons disease (PD) has been associated with various workplace factors, but the evidence is inconsistent. OBJECTIVE To estimate the risk of PD associated with various jobs and workplace exposures. METHODS We conducted a population-based, case-control study of 404 incident PD cases and 526 age and sex-matched controls, collecting self-reported work histories including job titles and exposures to various industrial toxicants. Relative risks of PD from these exposures were estimated with odds ratios (OR) and 95% confidence intervals (CI) using logistic regression. RESULTS Risk was not significantly affected by farming work, by metal work, or by exposure to pesticides, metals, or solvents. CONCLUSIONS These findings do not provide support for the hypothesis that workplace factors affect the risk of PD.

Comparison of Amsorb®, Sodalime, and Baralyme®. Degradation of volatile anesthetics and formation of carbon monoxide and compound A in swine in vivo

Background Consequences of volatile anesthetic degradation by carbon dioxide absorbents that contain strong base include formation of compound A from sevoflurane, formation of carbon monoxide (CO) and CO toxicity from desflurane, enflurane and isoflurane, delayed inhalation induction, and increased anesthetic costs. Amsorb® (Armstrong Ltd., Coleraine, Northern Ireland) is a new absorbent that does not contain strong base and does not form CO or compound A in vitro. This investigation compared Amsorb®, Baralyme® (Chemetron Medical Division, Allied Healthcare Products, St. Louis, MO), and sodalime effects on CO (from desflurane and isoflurane) and compound A formation, carboxyhemoglobin (COHb) concentrations, and anesthetic degradation in a clinically relevant porcine in vivo model. Methods Pigs were anesthetized with desflurane, isoflurane, or sevoflurane, using fresh or partially dehydrated Amsorb®, Baralyme®, and new and old formulations of sodalime. Anesthetic concentrations in the fresh (preabsorber), inspired (postabsorber), and end-tidal gas were measured, as were inspired CO and compound A concentrations and blood oxyhemoglobin and COHb concentrations. Results For desflurane and isoflurane, the order of inspired CO and COHb formation was dehydrated Baralyme® >> soda-lime > Amsorb®. For desflurane and Baralyme®, peak CO was 9,700 ± 5,100 parts per million (ppm), and the increase in COHb was 37 ± 14%. CO and COHb increases were undetectable with Amsorb®. Oxyhemoglobin desaturation occurred with desflurane and Baralyme® but not Amsorb® or sodalime. The gap between inspired and end-tidal desflurane and isoflurane did not differ between the various dehydrated absorbents. Neither fresh nor dehydrated Amsorb® caused compound A formation from sevoflurane. In contrast, Baralyme® and sodalime caused 20–40 ppm compound A. The gap between inspired and end-tidal sevoflurane did not differ between fresh absorbents, but was Amsorb® < sodalime < Baralyme® with dehydrated absorbents. Conclusion Amsorb® caused minimal if any CO formation, minimal compound A formation regardless of absorbent hydration, and the least amount of sevoflurane degradation. An absorbent like Amsorb®, which does not contain strong base or cause anesthetic degradation and formation of toxic products, may have benefit with respect to patient safety, inhalation induction, and anesthetic consumption (cost).

Probenecid-inhibitable efflux transport of valproic acid in the brain parenchymal cells of rabbits: a microdialysis study.

Delivery of valproic acid (VPA) to the human brain is relatively inefficient as reflected by a low brain-to-unbound plasma concentration ratio (< or =0.5) at steady state. Previous pharmacokinetic studies suggested that the unfavorable brain-to-plasma gradient is maintained by coupled efflux transport processes at both the brain parenchymal cells and blood-brain barrier (BBB); one or both of the efflux transporters are inhibitable by probenecid. The present study in rabbits utilized microdialysis to measure drug concentration in the brain extracellular fluid (ECF) of the cerebral cortex during steady-state i.v. infusion with VPA alone or with VPA plus probenecid. Probenecid co-infusion elevated VPA concentration in the brain tissue surrounding the tip of the microdialysis probe to a greater extent than in the ECF (230% versus 47%). Brain intracellular compartment (ICC) concentration was estimated. In control rabbits, the ICC concentration was 2.8+/-0.28 times higher than the ECF concentration. Probenecid co-infusion elevated the ICC-to-ECF concentration ratio to 4.2+/-0.44, which confirms the existence of an efflux transport system in brain parenchymal cells. The ECF-to-unbound plasma concentration ratio was well below unity (0.029), indicating an uphill efflux transport of VPA across the BBB. Co-infusion of probenecid did not have a significant effect on VPA efflux at the BBB as evidenced by a minimal change in the ECF-to-unbound plasma concentration ratio. This study suggests the presence of distinctly different organic anion transporters for the efflux of VPA at the parenchymal cells and capillary endothelium in the brain.

Posttreatment with propofol terminates lidocaine-induced epileptiform electroencephalogram activity in rabbits: effects on cerebrospinal fluid dynamics.

There are no controlled studies to determine whether propofol given after the onset of lidocaine-induced seizures (posttreatment) stops lidocaine-induced seizures. In this study, we determined whether posttreatment with propofol abolishes lidocaine-induced epileptiform electroencephalogram (EEG) activity as effectively as does midazolam, and cerebrospinal fluid (CSF) dynamics during lidocaine-induced epileptiform EEG activity and its treatment. EEG activity and CSF dynamics were determined in two groups of anesthetized rabbits at each of four experimental conditions: baseline, lidocaine-induced epileptiform activity, treatment with midazolam (n = 6) or propofol (n = 6), and return to baseline. The analog EEG signal was converted into a set of digital parameters using aperiodic analysis, and CSF dynamics were determined using ventriculocisternal perfusion. Propofol (3.8 +/- 1.3 mg/kg) stopped epileptiform activity, as did midazolam (2.0 +/- 1.7 mg/kg). The rates of CSF formation or reabsorption and resistances to CSF reabsorption or flow at the arachnoid villi did not differ among conditions or between groups. Our results indicate that propofol and midazolam both terminate epileptiform activity without changing CSF dynamics. Implications: Propofol may be an alternative to benzodiazepines for treating lidocaine-induced epileptiform electroencephalogram activity in patients. (Anesth Analg 1998;87:900-6)

No associations between Parkinson's disease and polymorphisms of the quinone oxidoreductase (NQO1, NQO2) genes

Reactive oxygen species derived from dopamine metabolism can induce oxidative stress and thus may contribute to Parkinsons disease (PD) pathogenesis. The quinone oxidoreductases, nicotinamide adenine dinucleotide (phosphate) (NAD[P]H): quinone oxidoreductase 1 (NQO1) and dihydronicotinamide riboside (NRH): quinone oxidoreductase 2 (NQO2) detoxify quinones and quinonoid compounds. We investigated associations of genetic polymorphisms of NQO1 (C609T) and NQO2 (I/D, 29 base pairs) with PD in a population-based case-control study of 190 idiopathic PD cases and 305 unrelated controls matched on age and sex. No associations were detected for either gene variant or for any allele combinations.

Effect of para-aminohippurate on the efflux of valproic acid from the central nervous system of the rabbit.

Recently we investigated the mechanisms mediating the transport of valproic acid (VPA) between blood and brain. In one study efflux of valproic acid (VPA) from rabbit brain was inhibited by probenecid. Efflux of VPA decreased when probenecid was given intravenously but not when probenecid was given by ventriculocisternal (VC) perfusion indicating that the major site of probenecid-sensitive transport was at the brain capillary endothelium and not at the choroid plexus. In another study VPA transport into rat brain was inhibited by para-aminohippurate (PAH). The purpose of the present study were to determine (a) if the efflux of VPA from rabbit brain was also inhibited by PAH, and (b) whether efflux of VPA could occur at the choroid plexus via an PAH-selective transport system. Six control rabbits received VPA by intravenous infusion and tracer concentrations of [3H]VPA and [14C]PAH by VC perfusion. Rabbits in the PAH group (n = 6) received identical treatment with VPA, tracer concentrations of [3H]VPA and [14C]PAH and, in addition, received 20 mM PAH by VC perfusion. PAH had no effect on the VC extraction ratio of [3H]VPA or the steady-state brain concentration of intravenously administered VPA. It is concluded that the efflux of VPA at the rabbit blood-brain barrier is mediated by a transporter different from the PAH-like transporter responsible for the uptake of VPA into rat brain. In addition, the finding that VC perfusion with PAH had no effect on the VC extraction of [3H]VPA provides further evidence that the choroid plexus plays a negligible role in removal of VPA from the CNS.

Intravenous lidocaine decreases but cocaine does not alter the rate of cerebrospinal fluid formation in anesthetized rabbits

Considering that adrenergic stimulation was reported to decrease the rate of cerebrospinal fluid (CSF) formation (Vf), it was hypothesized that cocaine might exert a similar effect. Accordingly, the present study was designed to examine the effects of low, moderate, and high doses of cocaine on Vf and resistance to reabsorption of CSF (Ra). Because cocaine possesses both adrenergic-stimulating and local anesthetic properties, the present study examined the effects of lidocaine, a local anesthetic without adrenergic-stimulating properties, as a comparison treatment to cocaine. New Zealand white rabbits (n = 17) weighing 3.5-4.3 kg were anesthetized with halothane. A needle was inserted into the left lateral cerebral ventricle and a catheter was inserted into the cisterna magna to permit ventriculocisternal perfusion with mock CSF labeled with blue dextran. A1 each of four experimental conditions, control and three doses of cocaine or lidocaine, fluid volumes and concentrations of blue dextran in timed samples of cisternal outflow were used to determine Vf and the rate of reabsorption of CSF (Va). In turn, Va at normal and elevated CSF pressures (+6 cmH2O) were used to determine Ra. For both the cocaine group (n = 9) and the lidocaine group (n = 8) the three drug doses were 0.5 mg.kg-1 followed by 1.0 microgram.kg-1.min-1, 1.5 mg.kg-1 followed by 3.0 micrograms.kg-1.min-1, and 4.5 mg.kg-1 followed by 9.0 micrograms.kg-1.min-1 i.v. Cocaine caused no significant change of Vf or Ra. In the lidocaine group there was a dose/time-related decrease of Vf (although the slope relating Vf to dose/time was not significantly different from that in the cocaine group), but no significant change of Ra. It is concluded that during halothane anesthesia cocaine does not decrease Vf, a finding not consistent with previous reports that adrenergic stimulation decreases Vf. Decrease of Vf with lidocaine is consistent with previous reports of similar dose-related effects of thiopental, etomidate, midazolam, and fentanyl on Vf.