An accurate fully automated panel of plasma biomarkers for Alzheimer's disease

INTRODUCTION

There is a great need for fully automated plasma assays that can measure amyloid beta (Aβ) pathology and predict future Alzheimer's disease (AD) dementia.

METHODS

Two cohorts (n = 920) were examined: Panel A+ (n = 32 cognitively unimpaired [CU], n = 106 mild cognitive impairment [MCI], and n = 89 AD) and BioFINDER-1 (n = 461 CU, n = 232 MCI). Plasma Aβ42/Aβ40, phosphorylated tau (p-tau)181, two p-tau217 variants, ApoE4 protein, neurofilament light, and GFAP were measured using Elecsys prototype immunoassays.

RESULTS

The best biomarker for discriminating Aβ-positive versus Aβ-negative participants was Aβ42/Aβ40 (are under the curve [AUC] 0.83-0.87). Combining Aβ42/Aβ40, p-tau181, and ApoE4 improved the AUCs significantly (0.90 to 0.93; P< 0.01). Adding additional biomarkers had marginal effects (ΔAUC ≤0.01). In BioFINDER, p-tau181, p-tau217, and ApoE4 predicted AD dementia within 6 years in CU (AUC 0.88) and p-tau181, p-tau217, and Aβ42/Aβ40 in MCI (AUC 0.87).

DISCUSSION

The high accuracies for Aβ pathology and future AD dementia using fully automated instruments are promising for implementing plasma biomarkers in clinical trials and clinical routine.

Clock Drawing Test – low accuracy in early hours

Introduction

Early diagnostics of neurodegenerative disease and their comorbidities is linked to better treatment outcome and improved quality of life. The first patient assessment should lay strong foundations for the direction of the upcoming diagnostic procedure. Clock Drawing Test (CDT) is often used as an early screening instrument in geriatric patients presenting with cognitive disorders.

Objectives

The goal of the present study was to evaluate diagnostic accuracy of the CDT in a geriatric cohort with mild cognitive difficulties.

Methods

Out of a pool of in- and outpatient data presenting with subjective cognitive difficulties three diagnostic groups were formed – mild cognitive impairment, depressive disorder and healthy controls. CDT was scored using a quantitative scoring system with each aspect of the clock evaluated separately. CDT data was analysed for its discriminative value in early diagnostics of AD and DD.

Results

Logistic regression produced a significant model with a low percentage of explained variance in both DD and AD groups. Same CDT items were significant predictors for DD and AD pathology. ROC curve inspection allowed only a poor discrimination capability for the significant predictors.

Conclusions

Despite being a popular screening test, CDT is a poor choice for individuals presenting with a mild cognitive impairment. Using CDT alone might result in initial stages of neurodegeneration going undetected, thus depriving patients of early treatment options. Same error types were significant predictors in DD and AD. This indicates that CDT can detect a general impairment; however, an in-depth neuropsychological assessment is needed for differential diagnostics.

Disclosure

No significant relationships.

The relationship of weather with daily physical activity and the time spent out of home in older adults from Germany – the ActiFE study

Background

There is a need for a comprehensive evaluation of the associations between varieties of weather conditions on the time spent out-of-home (TOH) and on walking duration (WD) among older adults. We aim to investigate the extent to which various weather parameters (temperature, solar radiation, sunshine duration, humidity, windspeed, and rain) determine daily WD the TOH in older adults.

Methods

The ActiFE (Activity and Function in Older People in Ulm) study is a prospective study of participants aged 65 years or older who wore an accelerometer and kept a movement diary in up to three temporally separated waves from 2009 to 2018 for a duration up to seven days per wave (up to three weeks in summary). We used weather data from a weather station near the participants‘ homes. Age-adjusted and gender-stratified generalized mixed models were used to predict WD and TOH (with 95% confidence interval (CI)) within and between weather categories. Generalized additive models were computed for the single predictions at the weather quartile boundaries. Cubic splines (with 95% pointwise confidence bands (CB)) visualized the continuous course of the weather values.

Results

Higher temperatures, solar radiation and more hours of sunshine, led to an increase in WD and TOH, while higher precipitation, humidities and windspeeds led to a decrease. Women had in general higher WD and TOH times than men.

Conclusions

Our data suggest that weather parameters have a considerable influence on PA and TOH. Future analyses and interpretation of PA data should therefore account for weather parameters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11556-022-00286-0.

Seizures associated with antibodies against cell surface antigens are acute symptomatic and not indicative of epilepsy: insights from long-term data

Background

Clinicians have questioned whether any disorder involving seizures and neural antibodies should be called “(auto)immune epilepsy.” The concept of “acute symptomatic seizures” may be more applicable in cases with antibodies against neural cell surface antigens. We aimed at determining the probability of achieving seizure-freedom, the use of anti-seizure medication (ASM), and immunotherapy in patients with either constellation. As a potential pathophysiological correlate, we analyzed antibody titer courses.

Methods

Retrospective cohort study of 39 patients with seizures and neural antibodies, follow-up ≥ 3 years.

Results

Patients had surface antibodies against the N-methyl-d-aspartate receptor (NMDAR, n = 6), leucine-rich glioma inactivated protein 1 (LGI1, n = 11), contactin-associated protein-2 (CASPR2, n = 8), or antibodies against the intracellular antigens glutamic acid decarboxylase 65 kDa (GAD65, n = 13) or Ma2 (n = 1). Patients with surface antibodies reached first seizure-freedom (88% vs. 7%, P < 0.001) and terminal seizure-freedom (80% vs. 7%, P < 0.001) more frequently. The time to first and terminal seizure-freedom and the time to freedom from ASM were shorter in the surface antibody group (Kaplan–Meier curves: P < 0.0001 for first seizure-freedom; P < 0.0001 for terminal seizure-freedom; P = 0.0042 for terminal ASM-freedom). Maximum ASM defined daily doses were higher in the groups with intracellular antibodies. Seizure-freedom was achieved after additional immunotherapy, not always accompanied by increased ASM doses. Titers of surface antibodies but not intracellular antibodies decreased over time.

Conclusion

Seizures with surface antibodies should mostly be considered acute symptomatic and transient and not indicative of epilepsy. This has consequences for ASM prescription and social restrictions. Antibody titers correlate with clinical courses.

Electronic supplementary material

The online version of this article (10.1007/s00415-020-10250-6) contains supplementary material, which is available to authorized users.

Lazy Sundays: role of day of the week and reactivity on objectively measured physical activity in older people

Background

The aim of this study was to assess the effect of day of the week and wearing a device (reactivity) on objectively measured physical activity (PA) in older people.

Methods

Walking duration as a measure for PA was recorded from 1333 German community-dwelling older people (≥65 years, 43.8% women) over 5 days using accelerometers (activPAL). Least-square means of PA with 95%-confidence intervals (95%-CI) from multi-level analysis were calculated for each day of the week and each measurement day (days after sensor attachment).

Results

Walking duration on Sundays was significantly lower compared to working days (Sunday vs. Monday-Friday: − 12.8 min (95%-CI: − 14.7; − 10.9)). No statistically significant difference compared to working days was present for Saturdays. The linear slope for measurement day and walking duration was marginal and not statistically significant.

Conclusions

Studies using PA sensors in older people should assess Sundays and working days to adequately determine the activity level of the participants.

European multicentre double-blind placebo-controlled trial of Nilvadipine in mild-to-moderate Alzheimer's disease-the substudy protocols: NILVAD frailty; NILVAD blood and genetic biomarkers; NILVAD cerebrospinal fluid biomarkers; NILVAD cerebral blood flow

INTRODUCTION

In conjunction with the NILVAD trial, a European Multicentre Double-Blind Placebo Controlled trial of Nilvadipine in Mild-to-Moderate Alzheimer's disease (AD), there are four NILVAD substudies in which eligible NILVAD patients are also invited to participate. The main NILVAD protocol was previously published in BMJ Open (2014). The objectives of the NILVAD substudies are to determine whether frailty, cerebrospinal fluid (CSF), blood biomarker profile and Apolipoprotein E (APOE) status predict response to Nilvadipine, and to investigate the effect of Nilvadipine on cerebral blood flow and blood biomarkers.

METHODS AND ANALYSIS

All participants who fulfil criteria for the main NILVAD study are eligible for participation in the NILVAD substudies. Participation is subject to informed consent and whether the substudy is available at a particular NILVAD study site. Each substudy entails extra measurements during the course of the main NILVAD study. For example, in the blood and genetic biomarkers substudy, extra blood (30 mL) will be collected at week 0, week 13, week 52 and week 78, while in the cerebral blood flow substudy, participants will receive an MRI and transcranial Doppler measurements at week 0, week 26 and week 78. In the CSF substudy, 10 mL CSF is collected at week 0 and week 78.

ETHICS AND DISSEMINATION

All NILVAD substudies and all subsequent amendments have received ethical approval within each participating country, according to national regulations. Each participant provides written consent to participate. All participants remain anonymised throughout and the results of each substudy will be published in an international peer reviewed journal.

TRIAL REGISTRATION NUMBER

EUDRACT 2012-002764-27; Pre-results.

Serum Vitamin D Concentrations and Cognitive Function in a Population-Based Study among Older Adults in South Germany

Our objective was to investigate the associations of vitamin D serum levels with dementia and cognitive function in specific domains in community dwelling older adults. Between 2009 and 2010, we conducted a cross-sectional study in 1,373 individuals (56% men) aged 65+ years in the "Activity and Function in the Elderly in Ulm" (ActiFE) study. Dementia was defined as a Mini-Mental State Examination (MMSE) score ≤ 24. The 25-OHD serum level [ng/mL] was measured by an electrochemilumineszenz immunoassay (ECLIA). Logistic regression models were used to calculate odds ratios (OR)s for cognitive domains (cut-point: 10th percentile) by serum 25-OHD concentrations (both continuously and by cut-point of 20 ng/ml for vitamin D deficiency). Mean age of the study population was 75.6 (SD 6.6) years.We identified 75 participants (43% women) with dementia. 25-OHD concentrations were significantly lower in the participants with dementia compared to persons with a MMSE score >24. We also observed an association of continuous 25-OHD serum concentrations with prevalence of dementia (crude OR 1.05, 95% confidence interval (CI), 1.01-1.08, p-value 0.009) per 1 ng/mL decrease, after adjustment the OR was 1.03, 95% CI, 0.995-1.08 (p-value 0.09). Although vitamin D deficiency was tentatively associated with severity of dementia measured by MMSE (OR 1.35, 95% CI, 0.84-2.19), the association was not statistically significant. However, deficits in specific cognitive domains such as executive functions, wordlist encoding, and visual memory (encoding and recall) were significantly associated with low vitamin D concentration. Our results suggest an association between vitamin D deficiency and cognitive function in specific domains in community dwelling older adults.

Factors Associated with Greater Adherence to and Satisfaction with Transdermal Rivastigmine in Patients with Alzheimer's Disease and Their Caregivers

BACKGROUND/AIMS

Adherence to cholinesterase inhibitors is important in order to maximise treatment efficacy. This study aimed to investigate patient and caregiver factors associated with adherence to and satisfaction with transdermal rivastigmine treatment.

METHODS

Sociodemographic, clinical and psychosocial data were collected from 127 patients and their caregivers during the first follow-up visit after prescription. At the second follow-up, data were collected on 110 of the dyads. Adherence to and satisfaction with the treatment were assessed using the Medication Adherence Report Scale and an adapted version of the Alzheimer's Disease Caregiver Preference Questionnaire.

RESULTS

66.2% of the caregivers reported being adherent to, and 77.0% were satisfied with, the patch at the second follow-up. Factors predicting higher adherence at the second follow-up were caregivers' greater frequency of contact with patients, greater satisfaction with the information received about the patch, better tolerability of the patch and living at home with their caregivers. Greater concerns of the caregivers about the patch and the patients' belief in 'other' causes of their Alzheimer's disease predicted a lower adherence at the second follow-up.

CONCLUSIONS

Assessing and addressing caregivers' concerns about transdermal rivastigmine, improving doctor-patient/caregiver communication to increase caregiver satisfaction with information about the patch as well as providing education and support around patients' beliefs and tolerability of the patch could improve adherence to transdermal rivastigmine.

NILVAD protocol: a European multicentre double-blind placebo-controlled trial of nilvadipine in mild-to-moderate Alzheimer's disease

INTRODUCTION

This study is a European multicentre, randomised, double-blind, placebo-controlled trial investigating the efficacy and safety of nilvadipine as a disease course modifying treatment for mild-to-moderate Alzheimer's disease (AD) in a phase III study that will run for a period of 82 weeks with a treatment period of 78 weeks.

METHODS AND ANALYSIS

Adult patients, males and females over 50 years with mild-to-moderate AD as defined by the National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's disease and Related Disorders Association (NINCDS-ADRDA) criteria, will be included in the study. It aims to recruit a total of 500 patients with AD; 250 in the nilvadipine group and 250 in the placebo group. Participants will be randomised to receive nilvadipine, an 8 mg overencapsulated, sustained release capsule, or a matching overencapsulated placebo (sugar pill) for a period of 78 weeks of treatment. The primary efficacy outcome measure in this study is the change in cognitive function as assessed by the Alzheimer's disease Assessment Scale (ADAS-Cog 12) from baseline to the end of treatment duration (78 weeks). There are two key secondary outcome measures, the Clinical Dementia Rating Scale Sum of Boxes (CDR-sb) and the Disability Assessment for Dementia (DAD). If a statistically significant effect is seen in the primary outcome, CDR-sb will be considered to be a coprimary end point and only the DAD will contribute to the secondary outcome analysis.

ETHICS AND DISSEMINATION

The study and all subsequent amendments have received ethical approval within each participating country according to national regulations. Each participant will provide written consent to participate in the study. All participants will remain anonymised throughout and the results of the study will be published in an international peer-reviewed journal.

TRIAL REGISTRATION NUMBER

EUDRACT Reference Number: 2012-002764-27.

[Maintenance of health and relief for caregivers of elderly with dementia by using "initial case management": experiences from the Lighthouse Project on Dementia, Ulm, ULTDEM-study]

BACKGROUND

When facing the well-known demographic development with an increasing number of people suffering from dementia, there is a need of programmes to support nursing relatives and care at home. Many support services have been established in the past few years but they are rarely used by the relatives and the patients. The purpose of the Lighthouse Project Ulm (ULTDEM Study) was to prove the effectiveness of a single advisory approach in order to provide support services after care level classification and to relieve the burden placed on relatives caring for family members suffering from dementia ("initial case management").

METHODS

The ULTDEM Study is a prospective, open, randomized, controlled, interventional study with different parallel outcome measures (burden of caring, quality of life and mood). After the randomization, the interventional group was given comprehensive, individual advice about available treatment possibilities for dementia patients. Control group participants received standard treatment. Inclusion criteria were application of a care level (0 or 1) as well as dementia diagnosis. All participants (patients/relatives) underwent an initial and a 6 month comprehensive assessment.

RESULTS

Our results show that a single advisory approach does not lead to a significant difference in outcome measures in interventional and control groups. Those tendencies described have to be interpreted as clinically not relevant. Although utilization of support services increases, it remains similar in both study groups. A confirmatory interpretation has not been possible due to a lack of adjustment to the findings regarding multiple testing and an insufficient degree of recruitment. Possible causes will be discussed such as premature intervention during the course of the disease, a lack of intervention blinding, recruitment bias and lack of an influence on adherence with regard to the use of support services.

IMPLICATIONS

The study demonstrates that there is a substantial information deficit for persons affected by dementia and their relatives. Innovative ways still have to be developed to ensure that this information actually reaches the target audience.

The neurofilament heavy chain (NfH) in the cerebrospinal fluid diagnosis of Alzheimer's disease

BACKGROUND/AIMS

Attempting to improve the cerebrospinal fluid (CSF) diagnosis of Alzheimer's disease (AD), the neurofilament heavy chain isoform, NfH(SMI35) was compared to other CSF markers [total tau, phospho-tau, amyloid beta 1-42 (Abeta42), the ratio of amyloid beta fragments Abeta42/Abeta40 (Abeta ratio)].

METHODS

CSF levels were determined in patients with AD (n = 109), mild cognitive impairment (MCI, n = 25), frontotemporal dementia (n = 15), vascular dementia (VD, n = 41), and controls (n = 58).

RESULTS

CSF NfH(SMI35) was elevated in AD and VD as compared to controls (p < 0.05). Total tau was higher in AD as compared to controls (p < 0.05). CSF phospho-tau was elevated in AD as compared to controls and VD (p < 0.05 each). CSF Abeta42 and Abeta ratios in AD were lower than in MCI and controls (p < 0.05 each).

CONCLUSION

The diagnostic potential of NfH(SMI35) is not superior to that of other CSF markers.

Erythropoietin in the cerebrospinal fluid in neurodegenerative diseases

Erythropoietin (EPO) and its specific receptor (EPOR) have been proposed to act as an endogenous system protecting against neuronal injury and neurodegeneration. We measured EPO in cerebrospinal fluid (CSF) of patients with neurodegenerative diseases, and tested for a correlation with an established biomarker of neuro-axonal damage, tau protein. Patients with Alzheimer's disease (AD, N=40), vascular dementia (VD, N=19), frontotemporal lobe dementia (FTLD, N=5), ALS (N=30) and controls (N=49) were included. Cerebrospinal fluid and serum levels of EPO and tau were measured using ELISA techniques. We found CSF EPO in ALS to be lower than in controls (p=0.04), while no difference between patients with AD, VD, FTLD and controls was detectable. CSF EPO correlated with age (p<0.001) as well as with tau protein (p=0.002) in all patients pooled. In contrast to the upregulation of the EPO/EPOR system in brain tissue upon various conditions of neuronal distress, CSF EPO concentrations in neurodegenerative disease were found in the same range or even reduced as compared to controls. This may be due to a relative deficiency of endogenous CNS EPO in these conditions and/or to a more efficient extraction of free EPO molecules from brain intercellular fluid by increased numbers of EPOR.

Identification of novel biomarker candidates by differential peptidomics analysis of cerebrospinal fluid in Alzheimer's disease

The objective of this work was the application of peptidomics technologies for the detection and identification of reliable and robust biomarkers for Alzheimer's disease (AD) contributing to facilitate and further improve the diagnosis of AD. Using a new method for the comprehensive and comparative profiling of peptides, the differential peptide display (DPD), 312 cerebrospinal fluid (CSF) samples from AD patients, cognitively unimpaired subjects and from patients suffering from other primary dementia disorders were analysed as four independent analytical sets. By combination with a cross validation procedure, candidates were selected from a total of more than 6,000 different peptide signals based on their discriminating power. Twelve candidates were identified using mass-spectrometric techniques as fragments of the possibly neuroprotective neuroendocrine protein VGF and another one as the complement factor C3 descendent C3f. The combination of peptide profiling and cross validation resulted in the detection of novel potential biomarkers with remarkable robustness and a close relation to AD pathophysiology.

[Clinical presentation and prognosis of brain stem infarcts. An evaluation of the Stroke Databank of the German Stroke Foundation]

Due to the great variety of clinical classification systems and syndromes, a representative overview of the etiology and prognosis of brain stem infarctions is missing. From the German Stroke Data Bank we therefore investigated 455 patients with visible brainstem infarction on cerebral imaging in comparison to patients with other infarct localizations. Follow-up after 3 and 12 months assessed functional outcome and recurrence of cerebral ischemia. Of 455 patients with acute brainstem infarction, 115 had additional infarctions in other vascular territories. In the remaining 340 patients with isolated brainstem infarction, the classification was: small vessel disease in 36.2%, macroangiopathy in 22.6%, and cardioembolism in 11.2%. After 3 months, 10% of the patients with isolated brainstem infarction had died and 55.6% were functionally independent. Mortality was 43.5% in patients with combined brainstem infarction. Our study highlights the frequency of small vessel disease as well as the relatively favorable prognosis in isolated brainstem infarction and preserved consciousness.

Respiratory chain inhibition induces tolerance to focal cerebral ischemia

The authors show that the inhibitor of the succinate dehydrogenase, 3-nitroproprionic acid (3-NPA), which in high doses and with chronic administration is a neurotoxin, can induce profound tolerance to focal cerebral ischemia in the rat when administered in a single dose (20 mg/kg) 3 days before ischemia. Infarcts were approximately 70% and 35% smaller in the 3-NPA preconditioned groups of permanent and transient focal cerebral ischemia, respectively. This regimen of 3-NPA preconditioning neither induced necrosis, apoptosis, or any other histologically detectable damage to the brain, nor did it affect behavior of the animals. 3-NPA led to an immediate (1-hour) and long-lasting (3-day) decrease in succinate dehydrogenase activity (30% reduction) throughout the brain, whereas only a short metabolic impairment occurred (ATP decrease of 35% within 30 minutes, recovery within 2 hours). The authors found that 3-NPA induces a burst of reactive oxygen species and the free radical scavenger dimethylthiourea, when administered shortly before the 3-NPA stimulus, completely blocked preconditioning. Inhibition of protein synthesis with cycloheximide given at the time of 3-NPA administration completely inhibited preconditioning. The authors were unsuccessful in showing upregulation of mRNA for the manganese superoxide dismutase, and did not detect increased activities of the copper-zinc and manganese superoxide dismutases, prototypical oxygen free radicals scavenging enzymes, after 3-NPA preconditioning. The authors conclude that it is possible to pharmacologically precondition the brain against focal cerebral ischemia, a strategy that may in principal have clinical relevance. The data show the relevance of protein synthesis for tolerance, and suggests that oxygen free radicals may be critical signals in preconditioning.

Induction of ischemic tolerance in rat cortical neurons by 3-nitropropionic acid: chemical preconditioning

Sublethal ischemia leads to increased tolerance against subsequent ischemia. We investigated whether tolerance could also be elicited by mild respiratory-chain inhibition (chemical hypoxia) in a rat neuronal-cell enriched culture system. 3-Nitropropionic acid (3-NPA) caused a concentration-dependent inhibition of succinate-dehydrogenase. Two hours preconditioning with 3-NPA 24-48 h before oxygen-glucose deprivation (OGD) reduced neuronal damage morphologically and reduced lactate deydrogenase (LDH) release up to 72% compared to sham-treated sister cultures without 3-NPA. In an attempt to elucidate transcriptional mechanisms, we found no rapid translocation of the hypoxia-sensitive transcription factors N F-KB or hypoxia-inducible factor-I (HIF-I) at 3-NPA concentrations sufficient to trigger tolerance against OGD. In accordance to previous in vivo and brain slice data, we conclude that 3-NPA chemically induces tolerance against oxygen-glucose deprivation in vitro. However, the underlying mechanisms remain elusive.

[Molecular biology findings in amyotrophic lateral sclerosis]

At presently, the etiology and pathogenesis of amyotrophic lateral sclerosis (ALS) are unknown. In recent years, the genetic background of hereditary motor neuron diseases has been partly defined. In particular, these advances represent an opportunity to improve our understanding of the pathogenesis of the familial and sporadic forms of ALS and thus provide a basis for rational therapeutic approaches. In this article, recent findings on the pathogenesis of the familial form of ALS and their implications for the sporadic form are discussed.

Delayed increase of cell volume of single pyramidal cells in live rat hippocampal slices upon kainate application

Cell volume is an important physiologic parameter but is not directly accessible by conventional microscopy in vivo or in slice preparations. After staining of rat hippocampal slices with 1,1'-dioctadecyl-3,3,3',3'-tetramethylinso-carbocyanineperchlor ate (DiI), living single CA1 pyramidal cells were visualized by confocal microscopy while others in the illuminated area were recorded intracellularly. Resting membrane potential and action potentials were not affected by staining with DiI (4 microM) and repeated laser illumination (up to 600 times). A time- and dose-dependent increase of cell volume succeeds membrane depolarization upon bath application of kainate (40 microM and 100 microM) with a delay of several minutes indicating active regulation of cell volume. We conclude that cell swelling as visualized by confocal microscopy is a relatively late event of kainate excitotoxicity.

Cu,Zn SOD in German families with ALS

We studied the gene for Cu,Zn SOD in 15 German patients with familial ALS and did not find any mutation. Activity of the enzyme and its expression at the protein level was also normal in each patient and in 18 patients suffering from the sporadic form of ALS.

In vitro toxicological investigations of isoxazolinone amino acids of Lathyrus sativus

Two non-protein amino acids of Lathyrus sativus, beta-(isoxazoline-5-on-2-yl)-alanine (BIA) and its higher homologue alpha-amino-gamma-(isoxazoline-5-on-2-yl)-alanine (ACI) were tested for excitotoxic potential. BIA (0.5-2.0 mM) but not ACI (2.0 mM) produced a concentration-dependent neurodegeneration in mouse cortical explants. The neuronal damage was prevented by the prior and simultaneous application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), indicating that it was mediated by non-N-methyl-D-aspartate type receptors. BIA (0.5-2.0 mM) activated CNQX-sensitive currents which were significantly smaller than those activated by 3-N-oxalyl-L-2,3-diaminopropanoic acid (beta-ODAP) or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) in the majority of neurons. In a small number of cells, BIA (2 mM) produced currents which were similar in amplitude to those activated by beta-ODAP (50 microM). These results suggest that Lathyrus sativus plants engineered to block the synthesis of beta-ODAP may accumulate a neurotoxic precursor and therefore must be tested for the presence of both BIA and beta-ODAP.

Increase of ATP levels by glutamate antagonists is unrelated to neuroprotection

Succinic dehydrogenase in mouse cortical explant cultures was inhibited by 3-nitropropionic acid (3-NPA). ATP concentrations declined upon application of 3-NPA. At 4 h, ATP levels of cultures treated with 3-NPA alone were no different from those in cultures treated additionally with MK-801 (20 microM), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM) or a combination thereof. However, MK-801 and MK-801 plus CNQX mitigated morphological lesions caused by 3-NPA. CNQX alone did not influence the extent of morphological damage. In conclusion, MK-801, at concentrations which were neuroprotective against 3-NPA lesions in cortical explant cultures, did not modify 3-NPA dependent decreases in cellular ATP levels. These data indicate that the neuroprotective effects of glutamate receptor antagonists in this model are probably receptor mediated and do not involve effects on cellular metabolism.

Excitotoxicity, energy metabolism and neurodegeneration

There is increasing evidence that the neurotoxic effects of excitatory amino acids and their analogues are part of the pathogenesis of neuronal degeneration in acute and chronic neurological disease. Recent studies indicate that activation of excitatory amino acid receptors is also induced in the mechanism of neuronal damage induced by impairment of cellular energy metabolism. This article briefly summarizes the evidence for the presence of such a mechanism and discusses metabolic diseases in which excitatory amino acids alone or in combination with energy deficiency could play a pathogenetic role. In these and other metabolic diseases, antagonists to excitatory amino acid receptors may offer a therapeutic opportunity; however, there are potential limits that may prevent chronic use.

Inhibition of energy metabolism by 3-nitropropionic acid activates ATP-sensitive potassium channels

3-Nitropropionic acid (1 mM), which inhibits succinate dehydrogenase activity and reduces cellular energy, produces in the pyramidal cell layer of the hippocampal region CA1 a hyperpolarization for variable lengths of time before evoking an irreversible depolarization. Hyperpolarization is caused by an increased potassium conductance that is attenuated by glibenclamide (1-10 microM), a selective antagonist of ATP-sensitive potassium channels; in contrast, diazoxide (0.5 mM), an agonist at this channel, induces a hyperpolarization in CA1 neurons of rat hippocampal slices. The transient hyperpolarization after prolonged (ca. 1 h) application of 3-NPA is followed by a depolarization that is incompletely reversed by brief application of the glutamate antagonists (D-2-amino-5-phosphonopentanoic acid (APV), 6,7-dichloroquinoxaline-2,3-dione (CNQX), 3-(+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), 7-chloro-kynurenic acid (7Cl-KYN)). Early application of glibenclamide (within the initial 5 min) blocked or reduced hyperpolarization and accelerated the depolarization. These data suggest that metabolic inhibition by 3-NPA initially activates ATP-sensitive potassium channels. Events other than activation of glutamate receptors participate in the final depolarization resulting from uncoupling of oxidative phosphorylation.