Nicolas Rohleder

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.

A mechanism converting psychosocial stress into mononuclear cell activation

Little is known about the mechanisms converting psychosocial stress into cellular dysfunction. Various genes, up-regulated in atherosclerosis but also by psychosocial stress, are controlled by the transcription factor nuclear factor κB (NF-κB). Therefore, NF-κB is a good candidate to convert psychosocial stress into cellular activation. Volunteers were subjected to a brief laboratory stress test and NF-κB activity was determined in peripheral blood mononuclear cells (PBMC), as a window into the body and because PBMC play a role in diseases such as atherosclerosis. In 17 of 19 volunteers, NF-κB was rapidly induced during stress exposure, in parallel with elevated levels of catecholamines and cortisol, and returned to basal levels within 60 min. To model this response, mice transgenic for a strictly NF-κB-controlled β-globin transgene were stressed by immobilization. Immobilization resulted in increased β-globin expression, which could be reduced in the presence of the α1-adrenergic inhibitor prazosin. To define the role of adrenergic stimulation in the up-regulation of NF-κB, THP-1 cells were induced with physiological amounts of catecholamines for 10 min. Only noradrenaline resulted in a dose- and time-dependent induction of NF-κB and NF-κB-dependent gene expression, which depended on pertussis-toxin-sensitive G protein-mediated phosphophatidylinositol 3-kinase, Ras/Raf, and mitogen-activated protein kinase activation. Induction was reduced by α1- and β-adrenergic inhibitors. Thus, noradrenaline-dependent adrenergic stimulation results in activation of NF-κB in vitro and in vivo. Activation of NF-κB represents a downstream effector for the neuroendocrine response to stressful psychosocial events and links changes in the activity of the neuroendocrine axis to the cellular response.

A meta-analysis of structural brain abnormalities in PTSD.

This series of meta-analyses examined structural abnormalities of the hippocampus and other brain regions in persons with PTSD compared to trauma-exposed and non-exposed control groups. The findings were significantly smaller hippocampal volumes in persons with PTSD compared to controls with and without trauma exposure, but group differences were moderated by MRI methodology, PTSD severity, medication, age and gender. Trauma-exposed persons without PTSD also showed significantly smaller bilateral hippocampal compared to non-exposed controls. Meta-analyses also found significantly smaller left amygdala volumes in adults with PTSD compared to both healthy and trauma-exposed controls, and significantly smaller anterior cingulate cortex compared to trauma-exposed controls. Pediatric samples with PTSD exhibited significantly smaller corpus callosum and frontal lobe volumes compared to controls, but there were no group differences in hippocampal volume. The overall findings suggested a dimensional, developmental psychopathology systems model in which: (1) hippocampal volumetric differences covary with PTSD severity; (2) hippocampal volumetric differences do not become apparent until adulthood; and (3) PTSD is associated with abnormalities in multiple frontal-limbic system structures.

Psychosocial stress-induced activation of salivary alpha-amylase: an indicator of sympathetic activity?

Abstract: Assessment of sympathoadrenal medullary system (SAM) activity is only possible to date via measurement of catecholamines in blood plasma or via electrophysiological methods. Both ways of measurement are restricted to endocrinological or psychophysiological laboratories, as both require either immediate freezing of blood samples or complex recording devices. Efforts have therefore been undertaken to find a method comparable to salivary cortisol measurements, in which noninvasive samples can be taken at any place and stored at room temperature for sufficient time before later analysis in the laboratory. Salivary alpha‐amylase (sAA) is a candidate that may prove useful in this context. We show here that sAA activity is increased by acute psychosocial stress (Trier Social Stress Test) and that increases in sAA correlate with increases in norepinephrine. We further report that sAA exhibits a stable circadian pattern that mirrors that of salivary cortisol. In conclusion, the current data show that salivary alpha‐amylase may serve as an easy‐to‐use index for SAM activity. However, some questions remain to be answered; for example, what impact does salivary flow rate exert on stress‐induced sAA activity?

Determinants of salivary α-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.

Hypocortisolism and increased glucocorticoid sensitivity of pro-inflammatory cytokine production in Bosnian war refugees with posttraumatic stress disorder

BACKGROUND Posttraumatic stress disorder (PTSD) is associated with dysregulation of the hypothalamus pituitary adrenal (HPA) axis. Alterations include various responses to HPA axis stimulation, different basal hormone levels, and changes in glucocorticoid receptor (GR) numbers on lymphocytes. The functional significance of these latter changes remains elusive. METHODS Twelve Bosnian war refugees with PTSD and 13 control subjects were studied. On 2 consecutive days, they collected saliva samples after awakening and at 11, 15, and 20 hours. Glucocorticoid (GC) sensitivity was measured by dexamethasone (DEX) inhibition of lipopolysaccharide (LPS)-induced interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) production in whole blood. RESULTS The PTSD patients showed no cortisol response after awakening and had lower daytime cortisol levels (F = 14.57, p <.001). Less DEX was required for cytokine suppression in PTSD patients (IL-6: t = -2.82, p =.01; TNF-alpha: t = 5.03, p <.001), reflecting higher GC sensitivity of pro-inflammatory cytokine production. The LPS-stimulated production of IL-6, but not TNF-alpha, was markedly increased in patients (IL-6: F = 10.01, p <.004; TNF-alpha: F =.89, p =.34). CONCLUSIONS In refugees with PTSD, hypocortisolism is associated with increased GC sensitivity of immunologic tissues. Whether this pattern reflects an adaptive mechanism and whether this is sufficient to protect from detrimental effects of low cortisol remains to be investigated.

Salivary alpha amylase as marker for adrenergic activity during stress: Effect of betablockade

Free salivary cortisol is an established non-invasive marker of hypothalamus pituitary adrenal (HPA) axis activity. In contrast, such a well-characterized salivary marker for activity of the sympatho-adrenal medullar (SAM) system is still missing. As one potential candidate salivary alpha amylase (sAA) has been suggested. In humans increases in sAA levels have been observed in response to physiological and psychological stress. The present study aimed at exploring the effects of a pharmacological manipulation (betablockade) on sAA in the context of a stressful fMRI experiment on emotional information processing. Thirty young healthy subjects participated in a double blind group comparison study and received 80 mg of the betablocker (BB) propranolol or a placebo (PL). Salivary samples were obtained before and 90 min (pre-scan) and 135 min (post-scan) after drug application. In addition heart rate and blood pressure were assessed. During rest a significant drug by time interaction was observed, lowering sAA levels as well as heart rate and systolic blood pressure in the betablocker treatment group. During the scanning procedure, in which participants were confronted with highly negative emotional pictures, the significant increase in sAA levels in the PL group compared to the BB group persisted. No additional change was noticed in heart rate or blood pressure during scanning in the PL or BB group. The current pharmacological study in the human provides direct evidence for the sensitivity of sAA to changes in adrenergic activation, specifically in reaction to psychological stress.

Psychological determinants of the cortisol stress response: the role of anticipatory cognitive appraisal

Psychosocial stress is a potent activator of the hypothalamus-pituitary-adrenal (HPA) axis. While the physiological mechanisms of HPA axis responses to stress as well as its short and long-term consequences have been extensively examined, less is known why someone elicits an acute neuroendocrine stress response, i.e. what are the psychological processes involved and how are they related to the acute neuroendocrine stress response. To examine this question, a questionnaire to assess anticipatory cognitive appraisal processes was developed and administered to 81 male healthy subjects in a standardized psychosocial stress situation (Trier social stress test). Cortisol stress responses were assessed with repeated measurement of salivary free cortisol. Hierarchical regression analyses show that anticipatory cognitive appraisal, in contrast to general personality factors and retrospective stress appraisal is an important determinant of the cortisol stress response, explaining up to 35% of the variance of the salivary cortisol response. The reported results emphasize the importance of psychological stress processing for the understanding of psychobiological stress responses. Since stress and its biological consequences have been shown to be associated with the onset and the maintenance of somatic illnesses and psychiatric disorders, psychological processes are prime targets for prevention and intervention.

Altered cortisol awakening response in posttraumatic stress disorder

An altered function of the hypothalamic-pituitary-adrenal axis is assumed to be characteristic for Posttraumatic Stress Disorder (PTSD), although there is inconsistent empirical evidence. Only few studies examined the awakening cortisol response and a daytime profile in PTSD. Salivary cortisol levels were measured at seven intervals from awakening until 8 PM in trauma-exposed subjects with (N=29) and without PTSD (N=19) and in 15 non-exposed controls. While the three groups did not differ with respect to their first cortisol level immediately after awakening, the expected cortisol increase to awakening 15-60 min later was significantly lower in PTSD patients compared to non-PTSD subjects and healthy controls. This effect remained stable when trauma-exposed subjects with comorbid major depression were excluded from the analysis. A significant negative correlation between the overall cortisol secretion (AUC(G)) and overall PTSD symptomatology and hyper-arousal symptoms was found. The findings are discussed in light of the hypothesis of a counterregulation of hyper-arousal symptoms and chronic stress in PTSD.

Sex differences in glucocorticoid sensitivity of proinflammatory cytokine production after psychosocial stress.

Objective Men and women show marked differences in susceptibility to disorders related to the immune system. These gender differences have been proposed to be mediated by functional interactions of the hypothalamus-pituitary-adrenal (HPA) and hypothalamus-pituitary-gonadal (HPG) axes. A potential mechanism involved in this interaction is the glucocorticoid (GC) sensitivity of relevant target tissues for GC. Therefore, the aim of the study reported here was to investigate the impact of psychosocial stress and HPA axis activation on the GC sensitivity of proinflammatory cytokine production in men and women. Methods A total of 45 healthy subjects were investigated. Eighteen women in the luteal phase of their menstrual cycle and 27 men were exposed to a psychosocial stress test (Trier Social Stress Test). Salivary free cortisol levels were measured repeatedly after exposure to the stressor. GC sensitivity was assessed in vitro by dexamethasone inhibition of lipopolysaccharide-stimulated production of interleukin-6 and tumor necrosis factor-&agr;. Results The stress test induced significant increases in salivary free cortisol with no significant differences between men and women. In contrast, GC sensitivity and lipopolysaccharide-stimulated cytokine production showed large gender differences. In men GC sensitivity was markedly increased 1 hour after stress, whereas GC sensitivity decreased significantly in women. Similarly, lipopolysaccharide-induced cytokine production decreased in response to stress in men but increased in women. Conclusions These results demonstrate that despite similar free cortisol responses of men and women (studied in the luteal phase) to psychosocial stress, gender may exert differential effects on the immune system by modulating GC sensitivity of proinflammatory cytokine production.