Tag: stress response

High-fidelity discrete modeling of the HPA axis: a study of regulatory plasticity in biology

Abstract:

BACKGROUND: The hypothalamic-pituitary-adrenal (HPA) axis is a central regulator of stress response and its dysfunction has been associated with a broad range of complex illnesses including Gulf War Illness (GWI) and Chronic Fatigue Syndrome (CFS). Though classical mathematical approaches have been used to model HPA function in isolation, its broad regulatory interactions with immune and central nervous function are such that the biological fidelity of simulations is undermined by the limited availability of reliable parameter estimates.

METHOD: Here we introduce and apply a generalized discrete formalism to recover multiple stable regulatory programs of the HPA axis using little more than connectivity between physiological components. This simple discrete model captures cyclic attractors such as the circadian rhythm by applying generic constraints to a minimal parameter set; this is distinct from Ordinary Differential Equation (ODE) models, which require broad and precise parameter sets. Parameter tuning is accomplished by decomposition of the overall regulatory network into isolated sub-networks that support cyclic attractors. Network behavior is simulated using a novel asynchronous updating scheme that enforces priority with memory within and between physiological compartments.

RESULTS: Consistent with much more complex conventional models of the HPA axis, this parsimonious framework supports two cyclic attractors, governed by higher and lower levels of cortisol respectively. Importantly, results suggest that stress may remodel the stability landscape of this system, favoring migration from one stable circadian cycle to the other. Access to each regime is dependent on HPA axis tone, captured here by the tunable parameters of the multi-valued logic. Likewise, an idealized glucocorticoid receptor blocker alters the regulatory topology such that maintenance of persistently low cortisol levels is rendered unstable, favoring a return to normal circadian oscillation in both cortisol and glucocorticoid receptor expression.

CONCLUSION: These results emphasize the significance of regulatory connectivity alone and how regulatory plasticity may be explored using simple discrete logic and minimal data compared to conventional methods.

Source: Sedghamiz H, Morris M, Craddock TJA, Whitley D, Broderick G. High-fidelity discrete modeling of the HPA axis: a study of regulatory plasticity in biology. BMC Syst Biol. 2018 Jul 17;12(1):76. doi: 10.1186/s12918-018-0599-1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6050677/ (Full article)

Chronic Fatigue Syndrome Linked To Impaired Stress Response

Subtle alterations of a hormonal stress response system called the HPA axis may play a role in chronic fatigue syndrome, according to a study in the November/December issue of Psychosomatic Medicine.

A smoothly functioning hypothalamus-pituitary-adrenal, or HPA, axis helps the body remain stable under physiological and psychological stress through the actions of three hormones. First, the brain portion called the hypothalamus secretes a hormone that stimulates the pituitary gland to secrete a second hormone. This second hormone causes the adrenal glands to create cortisol.

Problems can occur at any point in this process and result in a variety of diseases. A research team led by Jens Gaab, Ph.D., of the Center for Psychobiological and Psychosomatic Research at the University of Trier in Trier, Germany; and the Institute of Psychology at the University of Zürich in Switzerland are proposing that chronic fatigue syndrome may be one of them.

Chronic fatigue syndrome is characterized by debilitating fatigue that can include including muscle aches, low-grade fever and sleep disturbances. Its cause is not understood.

Gaab and colleagues recruited approximately 40 study participants between the ages of 30 and 50. Half of the participants were chronic fatigue sufferers and the other half were healthy volunteers. All participants completed questionnaires measuring fatigue, depression and coping skills.

To examine the HPA axis in action, participants were given blood, cardiovascular and saliva tests before and after taking two stress tests. The first, a psychosocial stress test, involved preparing for a fake job interview and completing an arithmetic problem before an audience while under the impression they were being videotaped. The second test measured physical stress on a stationary bicycle.

Participants were also given a series of insulin injections known as the insulin tolerance test. “The ITT is considered the gold standard for testing the integrity of the entire HPA axis,” Gaab says.

The researchers found significantly lower response levels of one of the HPA hormones, called ACTH, among the chronic fatigue patients compared with the healthy volunteers, during both stress tests as well as the ITT test. In fact, the chronic fatigue patients had significantly lower levels of the hormone before the testing even began.

“These results suggest that on a central level, subtle dysregulations of the HPA axis exist” in chronic fatigue syndrome patients, Gaab says, adding that future studies should include repeated evaluation of the HPA axis over the course of the syndrome.

Gaab and colleagues note that the possible role of cortisol in chronic fatigue syndrome still merits investigation, as low doses of hydrocortisone have shown some positive results in chronic fatigue patients.

Source: Center For The Advancement Of Health. “Chronic Fatigue Syndrome Linked To Impaired Stress Response.” ScienceDaily. ScienceDaily, 27 November 2002. https://www.sciencedaily.com/releases/2002/11/021126202215.htm

Allostatic overload in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating condition characterised by diverse symptoms such as fatigue, pain, sleep disturbance and autonomic dysfunction. There remains to be a singular biomarker identified for this illness, hence numerous theories about its development and perpetuation have been posited in the literature.

This brief report presents the model of ‘allostasis’ as a framework for understanding ME/CFS, specifically the notion that the physiological mechanisms employed in the body to deal with stress termed here as ‘allostatic states’ (e.g. elevation of inflammatory cytokines), may in and of themselves contribute to the perpetuation of the disorder. This theoretical assertion has important consequences for the understanding of ME/CFS and treatment; rather than searching for a singular pathogen responsible for this condition, ME/CFS can be conceptualised as a maladaptive stress disorder and interventions aimed at addressing the allostatic states may be incorporated into current symptom management programmes.

Copyright © 2013 Elsevier Ltd. All rights reserved.

 

Source: Arroll MA. Allostatic overload in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Med Hypotheses. 2013 Sep;81(3):506-8. doi: 10.1016/j.mehy.2013.06.023. Epub 2013 Jul 11. https://www.ncbi.nlm.nih.gov/pubmed/23850395

 

Loss of stress response as a consequence of viral infection: implications for disease and therapy

Abstract:

Herein, we propose that viral infection can induce a deficient cell stress response and thereby impairs stress tolerance and makes tissues vulnerable to damage. Having a valid paradigm to address the pathological impacts of viral infections could lead to effective new therapies for diseases that have previously been unresponsive to intervention. Host response to viral infections can also lead to autoimmune diseases like type 1 diabetes. In the case of Newcastle disease virus, the effects of viral infection on heat shock proteins may be leveraged as a therapy for cancer. Finally, the search for a specific virus being responsible for a condition like chronic fatigue syndrome may not be worthwhile if the disease is simply a nonspecific response to viral infection.

 

Source: Hooper PL, Hightower LE, Hooper PL. Loss of stress response as a consequence of viral infection: implications for disease and therapy. Cell Stress Chaperones. 2012 Nov;17(6):647-55. doi: 10.1007/s12192-012-0352-4. Epub 2012 Jul 14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3468676/ (Full article)

 

Associations between neuroendocrine responses to the Insulin Tolerance Test and patient characteristics in chronic fatigue syndrome

Abstract:

OBJECTIVE: Subtle dysregulations of the hypothalamic-pituitary-adrenal (HPA) axis have been proposed as an underlying pathophysiological mechanism in chronic fatigue syndrome (CFS). This study attempted to assess the relationship between patient characteristics and HPA axis functioning using a neuroendocrine challenge test.

METHOD: A test battery designed to assess different dimensions of CFS was given to 18 CFS patients and 17 controls. To evaluate the integrity of the HPA axis, the Insulin Tolerance Test (ITT), a centrally acting neuroendocrine challenge test, was performed on patients and controls. ACTH, salivary free cortisol and total plasma cortisol levels were assessed as a measure of the HPA axis stress response. Correlations of patient characteristics were calculated with integrated responses for all endocrine parameters.

RESULTS: CFS patients had a significantly reduced area under the ACTH response curve (AUC) in the ITT. The AUC was significantly associated with the duration of CFS symptoms (r = -.592, P = .005) and the severity of fatigue symptomatology (r = -.41, P = .045). In addition, duration of CFS was correlated with the severity of fatigue symptoms (r = .38, P = .045). Similar associations were not observed for cortisol parameters.

CONCLUSION: It has been postulated that neuroendocrine dysregulations observed in CFS are of an acquired nature. The results of a strong association between the integrated ACTH response and the duration of CFS emphasizes the need to consider factors known to be risk factors for the chronicity of CFS symptoms, such as profound inactivity, deconditioning and sleep abnormalities, as possible candidates for secondary causes of neuroendocrine dysregulations in CFS.

Copyright 2004 Elsevier Inc.

 

Source: Gaab J, Engert V, Heitz V, Schad T, Schürmeyer TH, Ehlert U. Associations between neuroendocrine responses to the Insulin Tolerance Test and patient characteristics in chronic fatigue syndrome.  J Psychosom Res. 2004 Apr;56(4):419-24. http://www.ncbi.nlm.nih.gov/pubmed/15094026