Neuroprotection by donepezil against glutamate excitotoxicity involves stimulation of ��7 nicotinic receptors and internalization of NMDA receptors

BACKGROUND AND PURPOSE

Glutamate excitotoxicity may be involved in ischaemic injury to the CNS and some neurodegenerative diseases, such as Alzheimer''s disease. Donepezil, an acetylcholinesterase (AChE) inhibitor, exerts neuroprotective effects. Here we demonstrated a novel mechanism underlying the neuroprotection induced by donepezil.

EXPERIMENTAL APPROACH

Cell damage in primary rat neuron cultures was quantified by lactate dehydrogenase release. Morphological changes associated with neuroprotective effects of nicotine and AChE inhibitors were assessed by immunostaining. Cell surface levels of the glutamate receptor sub-units, NR1 and NR2A, were analyzed using biotinylation. Immunoblot was used to measure protein levels of cleaved caspase-3, total NR1, total NR2A and phosphorylated NR1. Immunoprecipitation was used to measure association of NR1 with the post-synaptic protein, PSD-95. Intracellular Ca²⁺ concentrations were measured with fura 2-acetoxymethylester. Caspase 3-like activity was measured using enzyme substrate, 7-amino-4-methylcoumarin (AMC)-DEVD.

KEY RESULTS

Levels of NR1, a core subunit of the NMDA receptor, on the cell surface were significantly reduced by donepexzil. In addition, glutamate-mediated Ca²⁺ entry was significantly attenuated by donepezil. Methyllycaconitine, an inhibitor of α7 nicotinic acetylcholine receptors (nAChR), inhibited the donepezil-induced attenuation of glutamate-mediated Ca²⁺ entry. {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002, a phosphatidyl inositol 3-kinase (PI3K) inhibitor, had no effect on attenuation of glutamate-mediated Ca²⁺ entry induced by donepezil.

CONCLUSIONS AND IMPLICATIONS

Decreased glutamate toxicity through down-regulation of NMDA receptors, following stimulation of α7 nAChRs, could be another mechanism underlying neuroprotection by donepezil, in addition to up-regulating the PI3K-Akt cascade or defensive system.     

Adjuvant! Online is overoptimistic in predicting survival of Asian breast cancer patients

Background: Adjuvant! Online is a free web-based tool which predicts 10-year breast cancer outcomes and the efficacy of adjuvant therapy in patients with breast cancer. As its prognostic performance has only been validated in high income Caucasian populations, we validated the model in a middle income Asian setting.Methods: Within the University Malaya Hospital-Based Breast Cancer Registry, all 631 women who were surgically treated for invasive non-metastatic breast cancer between 1993 and 2000 were identified. The discriminative performance of Adjuvant! Online was tested using receiver operating characteristic (ROC) analysis. Calibration of the model was evaluated by comparing predicted 10-year overall survival with observed 10-year survival.Findings: Adjuvant! Online was fairly capable in discriminating between good and poor survivors, as attested by the area under ROC curve of 0.73 (95% Confidence Interval: 0.69–0.77). Overall, Adjuvant! Online predicted 10 year survival (70.3%) was significantly higher than the observed 10 year survival (63.6%, difference of 6.7%; 95% CI: 3.0–10.4%). The model was especially overoptimistic in women under 40 years and in women of Malay ethnicity, where survival was overestimated by approximately 20% (95% CI: 9.8–29.8%) and 15% (95% CI: 5.3–24.5%) respectively.Interpretation: Even though Adjuvant! Online is capable of discriminating between good and poor survivors, it systematically overestimates survival. These findings suggest that the model requires adaptation prior to use in Asian settings.     

Hemicerebellectomy impairs the modulation of cutaneomuscular reflexes by the motor cortex following repetitive somatosensory stimulation

We examined the cutaneomuscular reflex of the plantaris muscle of rats in response to cutaneous stimulation in isolation and in conjunction with subthreshold high-frequency trains of stimuli applied on the motor cortex, prior to and following repetitive peripheral stimulation. The cutaneomuscular reflex was also investigated under the same paradigm following hemicerebellectomy. The enhancement of cutaneomuscular responses associated with subthreshold high-frequency trains of stimulation following repetitive peripheral stimulation was prevented by hemicerebellectomy. Our results suggest that the pathways passing through the cerebellum are involved in the calibration of cutaneomuscular responses.     

Modulation of excitability as an early change leading to structural adaptation in the motor cortex

The excitability of the motor cortex is a function of single cell excitability, synaptic strength, and the balance between excitatory cells and inhibitory cells. Sustained periods of sensory stimulation enhance the excitability in the motor cortex. This adaptation, which represents an early change in cortical network function effective in motor learning and recovery from a motor deficit, is followed by longer-lasting changes, such as modifications in cortical somatotopy, and by structural plasticity. Interventions aiming at increasing excitability also positively affect learning processes. Recent studies highlight that the cerebellum, especially the interpositus nucleus, plays a key function in the adaptation of the motor cortex to repeated trains of peripheral stimulation. Interpositus neurons, which receive inputs from the sensorimotor cortex and the spinal cord, are involved in somesthetic reflex behaviors and assist the cerebral cortex in transforming sensory signals to motor-oriented commands by acting via the cerebello-thalamo-cortical projections. Moreover, climbing fibers originating in the inferior olivary complex and innervating the nucleus interpositus mediate highly integrated sensorimotor information derived from spinal modules. The intermediate cerebellum allows the motor cortex to tune the gain of polysynaptic responses originating from the spinal cord after repetitive trains of peripheral stimulation, allowing an online calibration of cutaneo-muscular responses.     

Predictors of Axillary Lymph Node Metastases in Breast Cancer: Is There a Role for Minimal Axillary Surgery?

Introduction  Axillary nodal status is one of the most important prognostic factors in breast cancer. In the present study we used it to determine the predictors of axillary lymph node metastases in breast cancer and to determine if there is a group of patients in whom minimal axillary surgery is indicated. Methods  This article reports a retrospective study of 953 patients with T1 and T2 invasive breast carcinomas seen in the University Malaya Medical Centre between January 2001 and December 2005, where axillary dissection was done. Results  Of the 953 patients, 283 (29.7%) had breast-conserving surgery, and the rest had mastectomies. In this series, 463 patients (48.6%) were younger than 50 years of age; 365 patients (38.3%) had lymph node involvement. The Malays tend to have more axillary node metastases (45.1%) than the Chinese (36.9%); however, there was no significant relationship between age and race and lymph node involvement. Some 23.9% of grade 1 cancers were node positive, compared to 42.9% of grade 2/3 cancers. Tumor size ranged from 0.2 cm to 5 cm; 55.5% of tumors were T2 (>2–5 cm). There were only 13 (1.4%) T1a tumors (>0.1–0.5 cm). Node involvement was documented in 7.7% of T1a tumors, 12.3% of T1b tumors (>0.5–1 cm), 29.2% of T1c tumors, and 48.2% of T2 tumors. In patients who had no lymphovascular invasion (LVI), 24.4% had axillary node metastases, compared with 52.2% of patients where LVI was reported. On univariate analysis, our study found that tumor diameter >2 cm, presence of lymphovascular invasion, and higher tumor grade (2 & 3) were factors significantly associated with a higher risk of nodal metastases. On multivariate analysis, however, only lymphovascular invasion and tumor size were independent predictors based on the logistic regression. Conclusions  In T1 tumors, axillary lymph node dissection will overtreat almost 75% of cases; therefore a sentinel lymph node biopsy is justified in these tumors. Sentinel lymph node biopsy has been shown to reduce the complications of formal axillary dissection, such as shoulder stiffness, pain, and lymphedema. In patients with T2 tumors, where almost 45% have lymph node involvement, sentinel node biopsy may not be cost effective.     

Malignant rhabdoid tumors of the central nervous system. Report of a case

Primitive malignant rhabdoid tumor of the central nervous system are extremely rare. Less than 70 cases are reported in the literature. This tumor grows during the first months of life and prognosis is very poor. We report a case of primitive malignant rhabdoid tumor in a 17-year-old young adult. To our knowledge it is the first such case reported in the literature. We review the clinical feature, the neuradiological and therapeutical aspects.     

A multigene RT-PCR assay used to predict recurrence in early breast cancer: two presentations with contradictory results

During the 2003 San Antonio Breast Cancer Symposium two studies were presented that were designed to validate a recurrence score, derived from a 21-gene RT-PCR assay, in patients with axillary node-negative breast cancer. This recurrence score was highly predictive for the risk of recurrence in 668 patients treated in a large multicenter trial with adjuvant tamoxifen. However, no prognostic value was found in a small group of patients who were retrospectively selected in a single institution and who did not receive any adjuvant systemic therapy. Further validation is needed to establish the prognostic and predictive role of this assay in clinical management.