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Abstracts

LE Magazine August 2007
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Natural stress relief

Psychiatric co-morbidity & diabetes.

Diabetes mellitus as well as psychiatric disorders are common. These may occur with one another and/or one may worsen the other. Psychological stress may follow screening for diabetes, as well as when diabetes is first identified. Acting through the hypothalamo-pituitary-adrenal axis, stress may initiate or worsen hyperglycaemia. Depression may be a risk factor for the development of diabetes; it also commonly occurs in subjects with diabetes. Identification and management are both important in preventing the disability. A variety of antipsychotic medications, especially the newer agents can induce weight gain, dyslipidaemia, insulin resistance and diabetes. Therefore in choosing a drug, one must consider the risk factors and screen for metabolic syndrome. Subjects with type 1 diabetes can have cognitive dysfunction, eating disorders and developmental disturbances. Physicians caring for people with diabetes must be trained to recognize and manage co-morbid psychiatric conditions that commonly occur. A biopsychosocial disease model for both conditions can leverage the social strengths and medical knowledge in developing countries.

Indian J Med Res. 2007 Mar;125(3):311-20

Attenuation of laboratory-induced stress in humans after acute administration of Melissa officinalis (Lemon Balm).

OBJECTIVE: Melissa officinalis (lemon balm) is contemporaneously used as a mild sedative and/or calming agent. Although recent research has demonstrated modulation of mood in keeping with these roles, no studies to date have directly investigated the effects of this herbal medication on laboratory-induced psychological stress. METHODS: In this double-blind, placebo-controlled, randomized, balanced crossover experiment, 18 healthy volunteers received two separate single doses of a standardized M. officinalis extract (300 mg, 600 mg) and a placebo, on separate days separated by a 7-day washout period. Modulation of mood was assessed during predose and 1-hour postdose completions of a 20-minute version of the Defined Intensity Stressor Simulation (DISS) battery. Cognitive performance on the four concurrent tasks of the battery was also assessed. RESULTS: The results showed that the 600-mg dose of Melissa ameliorated the negative mood effects of the DISS, with significantly increased self-ratings of calmness and reduced self-ratings of alertness. In addition, a significant increase in the speed of mathematical processing, with no reduction in accuracy, was observed after ingestion of the 300-mg dose. CONCLUSION: These results suggest that the potential for M. officinalis to mitigate the effects of stress deserves further investigation.

Psychosom Med. 2004 Jul-Aug;66(4):607-13.

Anxiety as an independent cardiovascular risk.

Anxiety itself, and anxiety disorders in particular, seem to represent an independent risk factor for cardiovascular diseases as important as obesity, hypertension, sendentary lifestyle or hyperlipidemia. Anxiety-related noradrenaline and HPA overactivity, excessive sympathetic nervous system activation, and the permanently elevated level of several neuropeptides and cytokines result in hypertension and arrhythmias, endothel lesions, detrimental hemodynamic changes and platelet overactivation facilitating thrombosis. Patients with severe and sustained anxiety usually have additional adverse health behaviors which further aggravate the hazards. Epidemiological studies agree in finding markedly increased incidence of myocardial infarct, coronary heart disease or other cardiovascular conditions, often with earlier age of onset, faster progression and higher letality, in anxiety disorder patients. Better recognition and adequate treatment of anxiety disorders may therefore contribute to curbing the excessive—and typically early-onset—cardiovascular morbidity and mortality in Hungary.

Neuropsychopharmacol Hung. 2006 Mar;8(1):5-11

L-Theanine reduces psychological and physiological stress responses.

L-Theanine is an amino acid contained in green tea leaves which is known to block the binding of L-glutamic acid to glutamate receptors in the brain. Because the characteristics of L-Theanine suggest that it may influence psychological and physiological states under stress, the present study examined these possible effects in a laboratory setting using a mental arithmetic task as an acute stressor. Twelve participants underwent four separate trials: one in which they took L-Theanine at the start of an experimental procedure, one in which they took L-Theanine midway, and two control trials in which they either took a placebo or nothing. The experimental sessions were performed by double-blind, and the order of them was counterbalanced. The results showed that L-Theanine intake resulted in a reduction in the heart rate (HR) and salivary immunoglobulin A (s-IgA) responses to an acute stress task relative to the placebo control condition. Moreover, analyses of heart rate variability indicated that the reductions in HR and s-IgA were likely attributable to an attenuation of sympathetic nervous activation. Thus, it was suggested that the oral intake of L-Theanine could cause anti-stress effects via the inhibition of cortical neuron excitation.

Biol Psychol. 2007 Jan;74(1):39-45

The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of theanine.

OBJECTIVE: Ingestion of the nonproteinic amino acid theanine (5-N-ethylglutamine) has been shown to increase oscillatory brain activity in the so-called alpha band (8-14 Hz) during resting electroencephalographic recordings in humans. Independently, alpha band activity has been shown to be a key component in selective attentional processes. Here, we set out to assess whether theanine would cause modulation of anticipatory alpha activity during selective attentional deployments to stimuli in different sensory modalities, a paradigm in which robust alpha attention effects have previously been established. METHODS: Electrophysiological data from 168 scalp electrode channels were recorded while participants performed a standard intersensory attentional cuing task. RESULTS: As in previous studies, significantly greater alpha band activity was measured over parieto-occipital scalp for attentional deployments to the auditory modality than to the visual modality. Theanine ingestion resulted in a substantial overall decrease in background alpha levels relative to placebo while subjects were actively performing this demanding attention task. Despite this decrease in background alpha activity, attention-related alpha effects were significantly greater for the theanine condition. CONCLUSION: This increase of attention-related anticipatory alpha over the right parieto-occipital scalp suggests that theanine may have a specific effect on the brain’s attention circuitry. We conclude that theanine has clear psychoactive properties, and that it represents a potentially interesting, naturally occurring compound for further study, as it relates to the brain’s attentional system.

Clin Neuropharmacol. 2007 Jan-Feb;30(1):25-38

Modulation of gamma and alpha activity during a working memory task engaging the dorsal or ventral stream.

Despite extensive experimental work in both animals and humans, the actual role of oscillatory brain activity for working memory maintenance remains elusive. Gamma band activity (30-100 Hz) has been hypothesized to reflect either the maintenance of neuronal representations or changing demands in attention. Regarding posterior alpha activity (8-13 Hz), it is under debate whether it reflects functional inhibition or neuronal processing required for the task. The aim of the present study was to further elucidate the role of oscillatory brain activity in humans using a working memory task engaging either the dorsal or ventral visual stream. We recorded brain activity using magnetoencephalography from subjects performing a delayed-match-to-sample task. Subjects were instructed to remember either the identity or the spatial orientation of shortly presented faces. The analysis revealed stronger alpha power around the parieto-occipital sulcus during retention of face identities (ventral stream) compared with the retention of face orientations (dorsal stream). In contrast, successful retention of face orientations was associated with an increase in gamma power in the occipital lobe relative to the face identity condition. We propose that gamma activity reflects the actual neuronal maintenance of visual representations, whereas the alpha increase is a result of functional inhibition.

J Neurosci. 2007 Mar 21;27(12):3244-51

Optimal sustained attention is linked to the spectral content of background EEG activity: greater ongoing tonic alpha (approximately 10 Hz) power supports successful phasic goal activation.

Efficient executive control frequently requires the timely activation or re-activation of a task-goal to enable purposeful behaviour. Additionally, more generalized factors such as alertness or neurological health will influence the efficiency with which control can be implemented. Goal-directed processes have been investigated by examining event-related potentials (ERPs), but much less is known about the involvement of background or ‘tonic’ processes reflected in the ongoing electroencephalogram (EEG), and how these affect the phasic processes expressed in the broad-band ERP. Here, we investigate the relationship between a key attention-sensitive tonic process--the alpha rhythm--and relevant phasic processes observed during a sustained attention paradigm in neurologically healthy subjects. We report that subjects with relatively higher tonic alpha power (approximately 10 Hz) show a larger-amplitude late positive ERP component that is thought to index goal activation and has been found to predict good sustained attention performance as defined by correct response patterns. Source localization results suggest that the neural generators responsible for oscillatory alpha activity, which are found primarily in the parietal and occipital lobes, are distinct from those giving rise to the late positive component. The results are discussed in terms of increased alpha synchrony facilitating goal-directed behaviour.

Eur J Neurosci. 2007 Feb;25(3):900-7

Induction of neutral endopeptidase (NEP) activity of SK-N-SH cells by natural compounds from green tea.

Deposition of amyloid beta-peptide as senile plaques in the brain is one of the neuropathological hallmarks of Alzheimer’s disease, which is the most prevalent progressive neurodegenerative disease leading to dementia. Neutral endopeptidase is one of the major beta-amyloid-degrading enzymes in the brain. To examine the influence of different polyphenols and other natural products from green tea extract (from Camellia sinensis, Theaceae), we used the neuroblastoma cell line SK-N-SH and studied the changes in the specific cellular neutral endopeptidase activity after long-term treatment with these substances. We have shown that caffeine leads to an increase in specific cellular neutral endopeptidase activity more than theophylline, theobromine or theanine. We have also shown that the combination of epicatechin, epigallocatechin and epigallocatechingallate with caffeine, theobromine or theophylline induced cellular neutral endopeptidase activity. It is suggested that the enhancement of cellular neutral endopeptidase activity by green tea extract and its natural products might be correlated with an elevated level of intracellular cyclic adenosine monophosphate.

J Pharm Pharmacol. 2006 Apr;58(4):495-501

Theanine and glutamate transporter inhibitors enhance the antitumor efficacy of chemotherapeutic agents.

Biochemical modulation has played an important role in the development of cancer chemotherapy. The combined effects of theanine, a specific amino acid in green tea, and glutamate transporter inhibitors on the antitumor activity of doxorubicin (DOX), were investigated and we clarified the biochemical mechanisms of action of these modulators. In M5076 ovarian sarcoma-bearing mice, theanine significantly enhanced the inhibitory effect of DOX on tumor growth and increased the DOX concentration in the tumor, compared to DOX-alone group. Furthermore, the oral administration of theanine or green tea similarly enhanced the antitumor activity of DOX. Moreover, the combination of theanine with DOX suppressed the hepatic metastasis of ovarian sarcoma. In contrast, an increase in DOX concentration was not observed in normal tissues, such as liver and heart. Namely, theanine did not enhance, rather it tended to normalize the increase of lipid peroxide (LPO) levels and reduction of glutathione peroxidase activity as indicators of the DOX-induced side toxicity. On the other hand, in vitro experiments proved that theanine inhibited the efflux of DOX from tumor cells, supporting a theanine-induced increase in the DOX concentration in tumors in vivo. Moreover, theanine significantly inhibited the glutamate uptake by M5076 cells similar to specific inhibitors. Two astrocytic high-affinity glutamate transporters, GLAST and GLT-1, were expressed in M5076 cells. These results suggested that the inhibition of DOX efflux was induced by theanine-mediated inhibition of glutamate transporters. The reduction in the concentration of glutamate in tumor cells caused by theanine induced decreases in the intracellular glutathione (GSH) and GS-DOX conjugate levels. As the expression of MRP5 in M5076 cells was confirmed, it is suggested that the GS-DOX conjugate was transported extracellularly via the MRP5/GS-X pump in M5076 cells and that theanine affected this route. Namely, theanine increases the concentration of DOX in a tumor in vivo through inhibition of the glutamate transporter via the GS-X pump. Similarly, dihydrokainate (DHK) and L-serine-O-sulfate (SOS), specific glutamate transporter inhibitors, indicated the enhancement of the DOX antitumor activity via inhibition of glutamate uptake. Therefore, we revealed the novel mechanism of enhancement of antitumor efficacy of DOX via the inhibition of glutamate transporters. Similarly, theanine enhanced the antitumor activities of other anthracyclines, cisplatin and irinotecan. Consequently, the modulating effect of theanine on the efficacy of antitumor agents is expected to be applicable in clinical cancer chemotherapy.

Biochim Biophys Acta. 2003 Dec 5;1653(2):47-59

Neuroprotective effect of gamma-glutamylethylamide (theanine) on cerebral infarction in mice.

In the present study, we examined the neuroprotective effect of gamma-glutamylethylamide (theanine) on the ischemic brain damage in a middle cerebral artery occlusion model in mice. Theanine was injected i.p. 3 h after the occlusion or immediately before and 3 h after the occlusion. Theanine (1 mg/kg) significantly decreased the size of the cerebral infarcts 1 day after the occlusion. In contrast, theanine did not affect the cerebral blood flow, brain temperature and physiological variables (pH, pCO(2), pO(2) and hematocrit) in this model. These results suggest that theanine directly provides neuroprotection against focal cerebral ischemia and may be clinically useful for preventing cerebral infarction.

Neurosci Lett. 2004 Jun 3;363(1):58-61

Effects of theanine, r-glutamylethylamide, on neurotransmitter release and its relationship with glutamic acid neurotransmission.

Theanine, r-glutamylethylamide, is one of the major amino acid components in green tea and many researchers have compared theanine’s effects with glutamic acid because the chemical structure is similar. In the previous study, we demonstrated that theanine can pass brain-blood barrier and may play as an agonist or an antagonist of some receptors. In this study, we investigated the effects of theanine on neurotransmitter release in the rat brain striatum by in vivo brain microdialysis and examined whether theanine affected glutamate transporters by comparing it with a glutamate transporter blocker, L-trans-Pyrrolidine-2,4-dicarboxylic acid (L-trans-2,4-PDC). Because we investigated whether the effects of theanine is similar to L-trans-2,4-PDC on the brain neurotransmission, we measured dopamine release and some amino acids release which are known as excitatory or inhibitory neurotransmitters from neurons by theanine or L-trans-2,4-PDC perfusion into the rat brain striatum. L-trans-2,4-PDC or theanine perfusion into the brain striatum caused dopamine release from dopaminergic neurons. In addition, L-trans-2,4-PDC perfusion increased glutamic acid, aspartic acid and, whereas theanine perfusion prevented aspartic acid release and increased glycine release. These results suggested that the mechanism of dopamine release caused by theanine is different from glutamate transporter blockers or glutamic acid. Further, L-trans-2,4-PDC cause excitatory neurotransmission, whereas theanine may inhibit excitatory neurotransmission and cause inhibitory neurotransmission via glycine receptors.

Nutr Neurosci. 2005 Aug;8(4):219-26

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