COMPARISON OF PEROXIDASE RESPONSE TO MENTAL ARITHMETIC STRESS IN SALIVA OF SMOKERS AND NON-SMOKERS

Effect of Combined Ingestion of L-Theanine and L-Arginine for Short-Term Psychological Stress in Young Adults: A Randomized Placebo-Controlled Study

l-Theanine, the most abundant amino acid component in green tea, has anti-stress effects and refreshes the mental state. A recent study demonstrated that l-arginine, the second most abundant amino acid in green tea, might enhance the anti-stress effects of l-theanine. The aim of this study was to evaluated the effects of combined ingestion of l-theanine and l-arginine on psychological stress in humans. A randomized placebo-controlled trial was conducted including 120 healthy young adults (mean age 22.4 y, 63.3% female). Subjects were randomly assigned to theanine (200 mg l-theanine), combined theanine/arginine (200 mg l-theanine, 50 mg l-arginine), or placebo groups. After consuming a test beverage, we administered a stress-loading test (Uchida-Kraepelin performance test) and performed salivary alpha-amylase activity (sAA) measurements to assess the physiological stress response at 0 min (immediately after), 5 min, and 15 min. The changes in sAA at 15 min after the stress-loading test were -2.75 (11.2) kIU/L in the theanine/arginine group, -0.40 (11.5) kIU/L in the theanine group, and 6.95 (18.6) kIU/L in the placebo group. The values in the theanine/arginine (p=0.007) and theanine (p=0.02) groups differed significantly from those in the placebo group. However, the difference between theanine/arginine and theanine groups, was not statistically significant (p=0.74). From this study, no clear conclusion could be drawn regarding the potentiating effect of theanine and arginine combined ingestion on anti-stress effects in human.

Effect of Oral Administration of Lactiplantibacillus plantarum SNK12 on Temporary Stress in Adults: A Randomized, Placebo-Controlled, Double-Blind, Parallel-Group Study

Mouse studies have reported anti-stress effects of Lactiplantibacillus plantarum SNK12 (SNK). Specifically, oral SNK administration increased mRNA levels of hippocampal neurotrophic factor and gamma-aminobutyric acid receptor in mice with sub-chronic mild stress-induced social defeat; moreover, it improved depressive behavior. We aimed to evaluate the efficacy of SNK ingestion against stress in healthy adults. We used the Uchida–Kraepelin test for the stress load, with a low-dose (50 mg/day), high-dose (150 mg/day), and placebo groups (dextrin). The primary outcome was the psychological evaluation as measured by the Profile of Mood States 2nd Edition (POMS2) using total mood disturbance (TMD) scores. The secondary outcomes were the score of each POMS2 item, salivary cortisol as a stress marker, and autonomic balance with the low frequency (LF)/ high frequency (HF) ratio. Compared with the placebo group, the SNK ingestion group showed significantly lower TMD scores. Additionally, compared with the placebo group, the high-dose group showed significantly lower scores for Tension-Anxiety and Confusion-Bewilderment, while the low-dose group showed significantly lower Anger-Hostility scores, salivary cortisol levels, and LF/HF scores. Our findings suggest that SNK ingestion could relieve stress (negative feelings, anxiety, tension, embarrassment, confusion, anger, and hostility) resulting from the temporary load caused by work and study.

Physical Activity and Psychological Stress Detection and Assessment of Their Effects on Glucose Concentration Predictions in Diabetes Management

OBJECTIVE

Continuous glucose monitoring (CGM) enables prediction of the future glucose concentration (GC) trajectory for making informed diabetes management decisions. The glucose concentration values are affected by various physiological and metabolic variations, such as physical activity (PA) and acute psychological stress (APS), in addition to meals and insulin. In this work, we extend our adaptive glucose modeling framework to incorporate the effects of PA and APS on the GC predictions.

METHODS

A wristband conducive of use by free-living ambulatory people is used. The measured physiological variables are analyzed to generate new quantifiable input features for PA and APS. Machine learning techniques estimate the type and intensity of the PA and APS when they occur individually and concurrently. Variables quantifying the characteristics of both PA and APS are integrated as exogenous inputs in an adaptive system identification technique for enhancing the accuracy of GC predictions. Data from clinical experiments illustrate the improvement in GC prediction accuracy.

RESULTS

The average mean absolute error (MAE) of one-hour-ahead GC predictions with testing data decreases from 35.1 to 31.9 mg/dL (p-value = 0.01) with the inclusion of PA information, and it decreases from 16.9 to 14.2 mg/dL (p-value = 0.006) with the inclusion of PA and APS information.

CONCLUSION

The first-ever glucose prediction model is developed that incorporates measures of physical activity and acute psychological stress to improve GC prediction accuracy.

SIGNIFICANCE

Modeling the effects of physical activity and acute psychological stress on glucose concentration values will improve diabetes management and enable informed meal, activity and insulin dosing decisions.

Detection of cognitive impairment by choice auditory reaction time (ART) and visual reaction time (VRT) s during acute mental stress in young hypertensives: A case control study

BACKGROUND

Acute stress is known to be associated with both negative and positive influences on cognitive performance. Hypertension is one of the risk factors for lowered cognitive performance. Mental stress testing is easier to administer and can be regulated by the investigator. Mental arithmetic, using serial subtraction, is the most widely used method to administer stress. Reaction time (RT) is widely used to assess cognitive domains like attention, execution, and psychomotor speed. Researchers have shown that choice reaction times are delayed in hypertension. It is not known whether acute mental stress improves or deteriorates attention, execution, and psychomotor speed in hypertension. We hypothesized in the present study that acute mental stress deteriorates cognitive function in hypertensives without overt cerebro-vascular disease or other vascular risk factors.

METHODS

After getting medical ethical clearance from our institution, this case-control study was carried out over eight months (January 2017 to September 2017). 60 subjects between the age group of 35 to 55 years were included in the study. They were divided into 2 groups. Group 1 consisted of 30 diagnosed cases of hypertension with at least two years of duration. Group 2 consisted of 30 sex and age-matched controls. MMSE was performed to assess the cognitive function in these groups. Simple (S) and choice (C) auditory reaction time (ART) and visual reaction time (VRT) were measured at rest and acute mental stress in these groups to assess cognitive function. The predictive value of VRTC resting and VRTC during acute mental stress among hypertensives for cognitive dysfunction was calculated by using the receiver operating characteristic (ROC) curve.

RESULTS

There was a significant difference between ART and VRT, both simple and choice in hypertensive and non-hypertensive subjects, and these reaction times further increased during mental stress. (P<0.001). VCRT can be a predictor of cognitive dysfunction in hypertensives and during acute mental stress.

CONCLUSION

A significant difference in cognitive functions in hypertensive and non-hypertensive subjects exists, and this further deteriorates with acute mental stress.

Xanthine oxidase-lactoperoxidase system and innate immunity: Biochemical actions and physiological roles

The innate immune system in mammals is the first-line defense that plays an important protective role against a wide spectrum of pathogens, especially during early life before the adaptive immune system develops. The enzymes xanthine oxidase (XO) and lactoperoxidase (LPO) are widely distributed in mammalian tissues and secretions, and have a variety of biological functions including in innate immunity, provoking much interest for both in vitro and in vivo applications. The enzymes are characterized by their generation of reactive oxygen and nitrogen species, including hydrogen peroxide, hypothiocyanite, nitric oxide, and peroxynitrite. XO is a major generator of hydrogen peroxide and superoxide that subsequently trigger a cascade of oxidative radical pathways, including those produced by LPO, which have bactericidal and bacteriostatic effects against pathogens including opportunistic bacteria. In addition to their role in host microbial defense, reactive oxygen and nitrogen species play important physiological roles as second messenger cell signaling molecules, including cellular proliferation, differentiation and gene expression. There are several indications that the reactive species generated by peroxide have positive effects on human health, particularly in neonates; however, some important in vivo aspects of this system remain obscure. The primary dependence of the system on hydrogen peroxide has led us to propose it is particularly relevant to neonate mammals during milk feeding.

The Significance of Lactoperoxidase System in Oral Health: Application and Efficacy in Oral Hygiene Products

Lactoperoxidase (LPO) present in saliva are an important element of the nonspecific immune response involved in maintaining oral health. The main role of this enzyme is to oxidize salivary thiocyanate ions (SCN^-) in the presence of hydrogen peroxide (H₂O₂) to products that exhibit antimicrobial activity. LPO derived from bovine milk has found an application in food, cosmetics, and medical industries due to its structural and functional similarity to the human enzyme. Oral hygiene products enriched with the LPO system constitute an alternative to the classic fluoride caries prophylaxis. This review describes the physiological role of human salivary lactoperoxidase and compares the results of clinical trials and in vitro studies of LPO alone and complex dentifrices enriched with bovine LPO. The role of reactivators and inhibitors of LPO is discussed together with the possibility of using nanoparticles to increase the stabilization and activity of this enzyme.

Midday and nadir salivary cortisol appear superior to cortisol awakening response in burnout assessment and monitoring

Burnout and work-related stress symptoms of anxiety disorder and depression cause prolonged work absenteeism and early retirement. Hence, reliable identification of patients under risk and monitoring of treatment success is highly warranted. We aimed to evaluate stress-specific biomarkers in a population-based, “real-world” cohort (burnouts: n = 40, healthy controls: n = 26), recruited at a preventive care ward, at baseline and after a four-month follow up, during which patients received medical and psychological treatment. At baseline, significantly higher levels of salivary cortisol were observed in the burnout group compared to the control group. This was even more pronounced in midday- (p < 0.001) and nadir samples (p < 0.001) than for total morning cortisol secretion (p < 0.01). The treatment program resulted in a significant reduction of stress, anxiety, and depression scores (all p < 0.001), with 60% of patients showing a clinically relevant improvement. This was accompanied by a ~30% drop in midday cortisol levels (p < 0.001), as well as a ~25% decrease in cortisol nadir (p < 0.05), although not directly correlating with score declines. Our data emphasize the potential usefulness of midday and nadir salivary cortisol as markers in the assessment and biomonitoring of burnout.

Black tea aroma inhibited increase of salivary chromogranin-A after arithmetic tasks

Background

Growing attention has been paid to the effects of food flavor components on alleviating negative brain functions caused by stressful lifestyles. In this study, we investigated the alleviating effect of two kinds of black tea aromas on physical and psychological stress induced by the Uchida-Kraepelin test, based on salivary chromogranin-A (CgA) levels as a stress marker and subjective evaluations (Profile of Mood States).

Results

Compared with the water exposure control, inhaling black tea aroma (Darjeeling and Assam in this study) induced lower salivary CgA concentration levels after 30 min of mental stress load tasks. This anti-stress effect of black tea aroma did not differ between the two tea types even though the concentration of the anti-stress components in the Darjeeling tea aroma was higher than that in the Assam aroma. However, Darjeeling tea aroma tended to decrease the tension and/or anxiety score immediately after the first exposure.

Conclusions

Inhaling black tea aroma may diminish stress levels caused by arithmetic mental stress tasks, and Darjeeling tea aroma tended to improve mood before mental stress load.

sIgA, peroxidase and collagenase in saliva of smokers aggressive periodontal patients

BACKGROUND

Tobacco smoking is strongly associated with destructive periodontal disease, alveolar bone loss and poor response to periodontal therapy. The aim of this study was to investigate the effect of smoking on antimicrobials and destructive proteins in the saliva of patients with generalized aggressive periodontal disease.

MATERIAL AND METHODS

The study group consisted of 55 adult subjects. They were classified according to their clinical diagnoses either as having generalized aggressive periodontitis (n = 27; 13 smokers and 14 non-smokers) or as periodontitis-free control group (n = 28; 14 smokers and 14 non-smokers). Total proteins, sIgA, peroxidase and collagenase were quantified in whole saliva. Data were analyzed using one-way ANOVA and Tukey tests.

RESULTS

Statistical differences were found between smokers with periodontal disease and healthy control subjects for sIgA, and between non-smokers with periodontal disease and healthy control subjects for peroxidase. Collagenase activity was higher in smokers and non-smokers with periodontal disease, and tobacco use was found to increase collagenase activity in healthy subjects.

CONCLUSION

Whole saliva from all patients with periodontal disease had higher sIgA and lower peroxidase content. Smokers with periodontitis had higher sIgA than smokers without periodontitis. Smokers with and without periodontitis had higher collagenase activity than non-smokers (with and without periodontitis).

The effect of clinical setting on the unstimulated salivary flow rate

OBJECTIVE

Unstimulated whole saliva (UWS) sialometry uses the spitting method to assess occurrence of hyposalivation. This study compares the UWS flow rates in volunteers sitting in a laboratory or in a clinical setting, in order to evaluate the influence of environment on salivary secretion.

DESIGN

25 healthy volunteers were recruited and divided into two groups to perform UWS sialometry under the two different settings (T1). Eleven weeks later, the participants repeated the same test (T2). At a unique time point and under the clinical setting, 18 patients complaining of xerostomia also performed the UWS sialometry; these values were used as control to corroborate findings.

RESULTS

Different scenarios - laboratory one vs. clinical one - did not affect measurements of mean UWS flow rates. Both intra- and inter-individual variabilities, reported as standard error of the mean (SEM) and within-subject variance (WSV), resulted below the threshold of 0.1g/min. A significant difference was found between UWS flow rates from healthy volunteers and those from patients with xerostomia (p<0.05). Test/retest reliability showed a moderate correlation of datasets collected at the two time points from healthy volunteers (T1 vs. T2, 11 weeks later): under laboratory and clinical settings, Pearson's coefficients of correlation were r=0.62 and r=0.32, respectively.

CONCLUSIONS

Type of environment did not influence UWS sialometry via spitting method, which appeared reliable for intra-day analysis of the salivary flow rate, although prone to physiological variations over time.

Masticatory performance alters stress relief effect of gum chewing

PURPOSE

We evaluated the effects of gum chewing on the response to psychological stress induced by a calculation task and investigated the relationship between this response and masticatory performance.

METHODS

Nineteen healthy adult volunteers without dental problems undertook the Uchida-Kraepelin (UK) test (30 min of reiterating additions of one-digit numbers). Before and immediately after the test, saliva samples were collected from the sublingual area of the participants. Three min after the UK test, the participants were made to chew flavorless gum for 3 min, and the final saliva samples were collected 10 min after the UK test. The experiment was performed without gum chewing on a different day. Masticatory performance was evaluated using color-changing chewing gum.

RESULTS

Salivary CgA levels at immediately and 10 min after the UK test were compared with and without gum chewing condition. Two-way repeated measures analysis of variance revealed significant interaction between gum chewing condition and changes in CgA levels during post 10 min UK test period. A significant correlation was found between changes in CgA levels and masticatory performance in all participants.

CONCLUSION

Our results indicate that gum chewing may relieve stress responses; however, high masticatory performance is required to achieve this effect.

Salivary α-amylase reflects change in attentional demands during postural control: comparison with probe reaction time

PURPOSE

The influence of attention on postural control and the relationship between attention and falling has been reported in previous studies. Although a dual-task procedure is commonly used to measure attentional demand, such procedures are affected by allocation policy, which is a mental strategy to divide attention between simultaneous tasks. Therefore, we examined the effectiveness of salivary α-amylase, which is a physiological method for measuring attentional demand during postural control.

METHOD

Sixteen healthy participants performed a postural-control task using the Balance System, which is a device that can be calibrated to a specific stability level ("Level 1 = least stable" to "Level 8 = most stable"). Levels 1, 2, and 3 were used for this study. Dependent variables measured were overall stability index, which represents the variance of platform displacement in degrees from a horizontal plane; probe reaction time, which was measured using a sound stimulator and recorder; and salivary α-amylase, which was measured using a portable salivary amylase analyzer.

RESULTS

As stability level of the test task decreased, both stability index and probe reaction time significantly increased. In addition, we identified a positive moderate correlation between probe reaction time and salivary α-amylase.

CONCLUSIONS

Our results suggest that salivary α-amylase and probe reaction time reflect the change in attentional demands during a postural-control task and that salivary α-amylase may be an effective tool for evaluating attentional demands during postural control because it is noninvasive and simple to perform.

Intake of green tea inhibited increase of salivary chromogranin A after mental task stress loads

BACKGROUND

Green tea has become renowned for its health benefits. In this study, we investigated the anti-stress effect of two kinds of green tea against a mental stress task load.

METHODS

Warm water, ordinary green tea (Sagara), and shaded white tea, which contains more amino acid components than Sagara, were used as test samples in a randomized cross-over design study. Eighteen students (nine male and nine female) participated in three experimental trials on different days at intervals of seven days. Saliva was collected before beverage intake and after performing the mental stress load tasks. Concentration of chromogranin A (CgA) in the saliva was used as an index of autonomic nervous system activity.

RESULTS

CgA level increased after the mental tasks, but intake of green tea inhibited this increase; the anti-stress effect was even greater after consumption of shaded white tea. Intake of shaded white tea also lowered Total Mood Disturbance (TMD) score on the Profile of Mood States (POMS); subjects in this condition tended to perform more calculations in the arithmetic task than those in the warm water treatment condition.

CONCLUSIONS

Salivary CgA concentration levels increased after mental stress load tasks, but ingestion of green tea inhibited this increase. This anti-stress effect was larger after the consumption of shaded white tea than after Sagara. Shaded white tea intake also lowered TMD score (POMS) and tended to improve performance on an arithmetic task compared to warm water, suggesting that shaded white tea might also improve mood during and after mental stress load.

Affective and inflammatory responses among orchestra musicians in performance situation

A number of studies have shown that mental challenge under controlled experimental conditions is associated with elevations in inflammatory markers such as interleukin-6 (IL-6) and C-reactive protein (CRP). However, relatively little work has been done on the effects of 'naturalistic' stressors on acute changes in inflammatory markers. The present study examined whether perceived arousal, valence and dominance in musicians are associated with pro-inflammatory and oxidative responses to a concert situation. Blood and salivary samples obtained from 48 members of a symphony orchestra on the day of rehearsal (i.e., control situation) and on the following day of premiere concert (i.e., test situation) were used to determine changes in salivary cortisol, pro-inflammatory markers (plasma myeloperoxidase, serum CRP, plasma IL-6), oxidative stress markers (paraoxonase1 activity and malondialdehyde), and homocysteine, a risk factor for vascular disease. Results of regression analyses showed a significant trend to increased myeloperoxidase (MPO) response in individuals with low valence score. Both affective states, valence and arousal, were identified as significant predictors of cortisol response during concert. In addition, control levels of plasma malondialdehyde were positively correlated with differences in IL-6 levels between premiere and rehearsal (r=.38, p=.012), pointing to higher oxidative stress in individuals with pronounced IL-6 response. Our results indicate that stress of public performance leads to increased concentrations of plasma MPO (20%), IL-6 (27%) and salivary cortisol (44%) in musicians. The decreasing effect of pleasantness on the MPO response was highly pronounced in non-smokers (r=-.60, p<.001), suggesting a significant role of emotional valence in stress-induced secretion of MPO. Additional studies are needed to assess the generalizability of these findings to other 'naturalistic' stress situations.

Development of a saliva collection device for use in the field

BACKGROUND

For monitoring biomarkers, saliva has several distinct advantages over other biological fluids. Saliva sampling is relatively non-invasive and enables the collection from either adults or infants under many different circumstances. However, there is no collection device that can be speedily used for analysis in the field. The aim of the present study was to evaluate the suitability of a new device, termed Muddler, compared with commercially available collection devices.

METHODS

Saliva was collected from healthy volunteers. The collection devices such as Muddler, eye sponge, Salivette® Cotton (SC) and Salivette® Synthetic (SS) were evaluated in terms of the volume and/or composition of the collected saliva. The amounts of immunoglobulin A (IgA) and lactofferin in saliva were assessed by the enzyme-linked immunosorbent assays with the corresponding antibodies. Amylase activity was measured using a commercially available kit, and high molecular weight complexes including mucin were assessed by SDS-PAGE staining.

RESULTS

A newly developed Muddler, which was made of plastic plate, was the best device for collecting a constant volume of saliva among all the devices examined in the present study. Furthermore, Muddler can collect without change in composition of salivary proteins such as IgA, lactoferrin, amylase, and mucin complex, whereas the levels of the salivary proteins obtained with all the commercial devices used were clearly different from those in original saliva.

CONCLUSIONS

The newly developed Muddler was the best collection device in terms of the accuracy of collection and the reliability of measurements among all the devices examined in the present study.

Influência do fumo na atividade da amilase salivar e na curva glicêmica

OBJETIVO: Determinar a atividade da amilase salivar e a relação com a glicemia, antes e após a ingestão de carboidratos em fumantes e não fumantes, uma vez que in vitro a exposição da saliva à fumaça do cigarro induz à redução da atividade da amilase salivar e poderia influenciar na absorção dos carboidratos da dieta. MÉTODOS: Foram avaliados voluntários fumantes (n=10) e não fumantes (n=10). Realizou-se coletas da saliva antes e após o fumo e determinou-se a glicemia antes e após a ingestão de 72g de carboidratos. Para glicemia usaram-se tempos de 0, 15, 30, 60, 120 minutos. A determinação da atividade da amilase salivar foi realizada por meio de kits comerciais. A glicemia foi determinada utilizando o aparelho Glicomiter (Accu-Chek-Roche). As análises estatísticas foram realizadas no software Sigmastat, utilizou-se o método Teste t pareado (p<0,05). RESULTADOS: O aumento da glicemia aos 15, 30, 60 e 90 minutos foi de 3,9; 11,9; 34,8 e 22,7% para os não fumantes e 4,9; 6,5; 13,8 e 9,7% para os fumantes, respectivamente. No pico máximo de absorção tem-se uma glicemia de 21,0 % maior nos pacientes não fumantes. A atividade da amilase salivar antes e após alimentação apresentou-se 75,0% menor nos indivíduos fumantes. CONCLUSÃO: Estes resultados sugerem que o fumo inibe a amilase e influencia na diminuição da digestão/absorção de carboidratos, consequentemente na concentração de glicose sanguínea, reduzindo assim o aporte energético ingerido.

Salivary alpha-amylase as a non-invasive biomarker for the sympathetic nervous system: current state of research

Development of new biomarkers is a constantly evolving field of research endeavor in psychoneuroendocrinology. Salivary biomarkers have received special attention since they are readily accessible and easily obtained. Salivary alpha-amylase (sAA) has been proposed as a sensitive biomarker for stress-related changes in the body that reflect the activity of the sympathetic nervous system (SNS), and a growing body of research is accumulating to support the validity and reliability of this parameter. However, questions remain to be answered before sAA can be accepted as an index of SNS activity. This review describes sAA as an emerging biomarker for stress and provides an overview of the current literature on stress-related alterations in sAA. It critically discusses how sAA might reflect changes in the autonomic nervous system. Finally, current and future fields for the application of sAA measurement are outlined.

Determinants of salivary alpha-amylase in humans and methodological considerations

Salivary alpha-amylase (sAA) has been proposed as a marker for activity of the sympathetic nervous system (SNS). Recent studies in support of this hypothesis have led to an increased number of researchers integrating amylase measurements into their study designs. Salivary alpha-amylase is produced locally in the salivary glands, controlled by the autonomic nervous system. This entails some methodological consequences and potential pitfalls that might lead to increased error variance and thus prevent successful testing of hypotheses. The goal of this review is to summarize basic and recent findings on methodological issues and potential factors influencing sAA measurement, and to derive a set of recommendations enabling researchers to successfully using sAA in psychoneuroendocrinological experiments.

The effectiveness of the Uchida-Kraepelin test for psychological stress: an analysis of plasma and salivary stress substances

Background

The hypothalamic-pituitary-adrenocortical (HPA) axis and sympathetic adrenomedullary (SAM) system are the major stress-response pathways. Plasma adrenocorticotropic hormone (ACTH) represents HPA axis activity, while plasma catecholamines are used as markers of the SAM system. Salivary alpha amylase (AA), chromogranin A (CgA), and immunoglobulin A (IgA) are candidate markers of stress activation, although their role has not been established. The Uchida-Kraepelin (U-K) test is a questionnaire that requires intense concentration and effort, and has been used as a tool to induce mental stress. However, it is not clear whether or not the test is effective as a psychological/mental stressor.

Methods

In this study, normal young women took the U-K test and serial measurements of plasma ACTH and catecholamines (dopamine, noradrenaline, and adrenaline) (n = 10), as well as salivary AA, CgA, and IgA (n = 16) before, during and after the test.

Results

We found no changes in any of these parameters at any time point during or after the U-K test.

Conclusion

Our findings indicate that the U-K test is not a suitable for measuring the psychological/mental stress of young women because the plasma data showed that it did not affect the HPA axis and SAM system. The U-K test should be employed carefully as a psychological/mental stressor due to insufficient scientific evidence of its effectiveness. In addition, salivary AA, CgA, and IgA should not simply be compared with previous reports, because the mechanism of secretion and normal range of each salivary parameter remain unknown. Salivary AA, CgA, and IgA may not be suitable candidate markers of psychological/mental stress.