Physiology of the Hypothalamic–Pituitary–Adrenocortical Axis

Assessing the risk of low energy availability, bone mineral density and psychological strain in endurance athletes

BACKGROUND

Adequate energy intake is crucial for athletic performance and recovery. However, many endurance athletes experience Low Energy Availability (LEA), which, if prolonged, can detrimentally impact both health and performance.

METHODS

A total of 55 endurance athletes (23 females; 45  ±  13 years, 1.64  ±  0.06 m, 64.4  ±  11.4 kg and 32 males; 44  ±  13 years, 1.76  ±  0.18 m, 78.8  ±  9.2 kg) underwent physical assessments and completed questionnaires on dietary habits, training loads, and psychological stress. Dual-Energy X-ray Absorptiometry (DEXA) scans measured bone mineral density (BMD) in the lumbar L1-L4 spine, and body composition. Risk of LEA burnout, and psychological strain were assessed using sport-specific questionnaires.

RESULTS

Seventy-seven percent of female athletes were identified as at risk of LEA by the LEAF-Q. These females had higher body weight and fat percentage than those at low risk of LEA. Male athletes had a higher prevalence of low lumbar BMD (31%) compared to females, associated with older age, and longer training histories. Although only 9% of female athletes had low-BMD, those affected had a history of amenorrhea and were identified as at risk of LEA by the LEAF-Q.

CONCLUSION

A high proportion of endurance athletes had low-BMD and were at risk of LEA. This underscores the need for targeted nutritional strategies to mitigate the risks associated with LEA and promote overall athlete well-being.

Impacts of predation risk on learning and memory of free-living mice

In predator-prey interactions, responses to predation risk typically involve behavioural, morphological or physiological changes. Laboratory-based studies have also shown changes in prey cognition (i.e. learning and memory), with individuals often showing impairment. However, an ecological perspective predicts that wild animals should conserve their cognitive ability, given that many risk responses require robust cognition. Here, we simulated predation risk and used a field-adapted version of the Morris Water Maze (MWM) to investigate how chronic predation risk affects cognition in wild white-footed mice (Peromyscus leucopus). We found that 24 days' exposure to predation risk did not impair learning. However, those exposed to risk had a 25% reduction of their short-term memory. Twelve days post-risk exposure, we found no performance differences between risk-exposed and control mice. Additionally, risk-exposed mice displayed greater exploration with a higher probability of completing the MWM in their initial trial. Given that prey integrate multiple pieces of information to shape their behaviour, the lack of learning impairment and altered exploration strategies may help mice respond to predation risk. However, the tendency of memory impairment suggests there are consequences for cognition when experiencing increased predation risk.

Mindfulness-Based Interventions and the Hypothalamic-Pituitary-Adrenal Axis: A Systematic Review

BACKGROUND

Numerous studies have evaluated the effect that mindfulness-based interventions (MBIs) have on multiple health outcomes. For its part, stress is a natural response to environmental disturbances and within the associated metabolic responses, alterations in cortisol levels and their measurement in different tissues are a way to determine the stress state of an individual. Therefore, it has been proposed that MBIs can modify cortisol levels.

METHODS AND RESULTS

The objective of this systematic review was to analyze and summarize the different studies that have evaluated the effect of MBIs on cortisol levels. The following databases were consulted: MEDLINE, AMED, CINAHL, Web of Science, Science Direct, PsycINFO, SocINDEX, PubMed, the Cochrane Library and Scopus. The search terms "mindfulness", "mindfulness-based interventions" and "cortisol" were used (and the search was limited to studies from January 1990 to May 2024). In order to reduce selection bias, each article was scrutinized using the JBI Critical Appraisal Checklist independently by two authors. We included those studies with specified intervention groups with at least one control group and excluded duplicate studies or those in which the intervention or control group was not adequately specified. Significant changes in cortisol following MBIs were found in 25 studies, while 10 found no changes. The small sample size, lack of randomization, blinding, and probable confounding and interaction variables stand out in these studies.

CONCLUSION

MBIs have biological plausibility as a means of explaining a positive effect on cortisol levels; however, the weakness of the studies and the absence of robust designs makes it difficult to establish a causal association between both variables.

REGISTRATION NUMBER

INPLASY2024110017.

Thyroid, Gonadal and Adrenal Dysfunction in Kidney Transplant Recipients: A Review for the Clinician

While chronic kidney disease-associated mineral and bone disorders (CKD-MBD) prevail in the endocrinological assessment of CKD patients, other endocrine abnormalities are usually overlooked. CKD is associated with significant thyroid, adrenal and gonadal dysfunction, while persistent and de novo endocrinological abnormalities are frequent among kidney transplant recipients (KTR). Low T3 levels prior to transplantation may help identify those at risk for delayed graft function and are often found in KTR. Thyroid surveillance after kidney transplantation should be considered due to structural anomalies that may occur. Despite the rapid recovery of gonadal hormonal secretion after renal transplantation, fertility is not completely restored. Testosterone may improve anemia and general symptoms in KTR with persistent hypogonadism. Female KTR may still experience abnormal uterine bleeding, for which estroprogestative administration may be beneficial. Glucocorticoid administration suppresses the hypothalamic-pituitary-adrenal axis in KTR, leading to metabolic syndrome. Patients should be informed about signs and symptoms of hypoadrenalism that may occur after glucocorticoid withdrawal, prompting adrenal function assessment. Clinicians should be more aware of the endocrine abnormalities experienced by their KTR patients, as these may significantly impact the quality of life. In clinical practice, awareness of the specific endocrine dysfunctions experienced by KTR patients ensures the correct management of these complications in a multidisciplinary team, while avoiding unnecessary treatment.

Discovery of a novel 2-spiroproline steroid mimetic scaffold for the potent inhibition of 11β-HSD1

11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) has been identified as the primary enzyme responsible for the activation of hepatic cortisone to cortisol in specific peripheral tissues, resulting in the concomitant antagonism of insulin action within these tissues. Dysregulation of 11β-HSD1, particularly in adipose tissues, has been associated with a variety of ailments including metabolic syndrome and type 2 diabetes mellitus. Therefore, inhibition of 11β-HSD1 with a small nonsteroidal molecule is therapeutically desirable. Implementation of a scaffold-hopping approach revealed a 3-point pharmacophore for 11β-HSD1 that was utilized to design a 2-spiroproline derivative as a steroid mimetic scaffold. Reiterative optimization provided valuable insight into the bioactive conformation of our novel scaffold and led to the discovery of several leads, such as compounds 39 and 51. Importantly, deleterious hERG inhibition and pregnane X receptor induction were mitigated by the introduction of a 4-hydroxyl group to the proline ring system.

Stress and the Gut-Brain Axis: Implications for Cancer, Inflammation and Sepsis

BACKGROUND

The gut-brain axis has been discussed, directly or indirectly, for centuries, with the ideas of the gut affecting anything from moods to overall physiology being discussed across the centuries. With a recent explosion in research that looks to the microbiota as a mechanistic link between the gut and the brain, one sees that the gut-brain axis has various means of communication, such as through the vagus nerve and the enteric nervous system and can use the metabolites in the gut to communicate to the brain.

METHODS

The purpose of this review is to view the gut-brain axis through the lens of stress and how stress, from the prenatal period all the way through adulthood can impact the physiology of a human being. Studies have shown multiple mechanisms of measurable change with disruption in the microbiota that lead to behavioral changes. There are also effects of gut inflammation on the brain and the corresponding systemic response observed.

CONCLUSION

The overall literature is encouraging that the more understanding of the gut-brain axis, the greater ability to wield that understanding for therapeutic benefits.

Chronic exposure to inhaled, traffic-related nitrogen dioxide and a blunted cortisol response in adolescents

BACKGROUND

Chronic health effects of traffic-related air pollution, like nitrogen dioxide (NO₂), are well-documented. Animal models suggested that NO₂ exposures dysregulate cortisol function.

OBJECTIVES

We evaluated the association between traffic-related NO₂ exposure and adolescent human cortisol concentrations, utilizing measures of the cortisol diurnal slope.

METHODS

140 adolescents provided repeated salivary cortisol samples throughout one day. We built a land use regression model to estimate chronic NO₂ exposures based on home and school addresses. We then generated model-based estimates of the association between cortisol and NO₂ exposure one year prior to cortisol sampling, examining changes in cortisol diurnal slope. The final model was adjusted other criteria pollutants, measures of psychosocial stress, anthropometry, and other demographic and covariates.

RESULTS

We observed a decrease in diurnal slope in cortisol for adolescents exposed to the estimated 75th percentile of ambient NO₂ (high exposure) relative to those exposed at the 25th percentile (low exposure). For a highly exposed adolescent, the log cortisol was lower by 0.06 µg/dl at waking (95% CI: -0.15, 0.02), 0.07 µg/dl at 30 min post waking (95% CI: -0.15, 0.02), and higher by 0.05 µg/dl at bedtime (95% CI: 0.05, 0.15), compared to a low exposed adolescent. For an additional interquartile range of exposure, the model-based predicted diurnal slope significantly decreased by 0.12 (95% CI: -0.23, -0.01).

CONCLUSIONS

In adolescents, we found that increased, chronic exposure to NO₂ and the mixture of pollutants from traffic sources was associated with a flattened diurnal slope of cortisol, a marker of an abnormal cortisol response which we hypothesize may be a mechanism through which air pollution may affect respiratory function and asthma in adolescents.

Shared Dysregulation of Homeostatic Brain-Body Pathways in Depression and Type 2 Diabetes

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of shared dysregulation of the hypothalamic-pituitary-adrenal (HPA) and brain-gut-microbiome (BGM) axes associated with depression and type 2 diabetes (T2D). Clinical implications and future research are also discussed.

RECENT FINDINGS

Both depression and T2D are associated with dysregulation of the HPA and BGM axes. These pathways regulate immune function, glucose metabolism, and sleep, which are altered in both illnesses. Dysregulation of homeostatic brain-body pathways may be positively influenced through different therapeutic actions, including psychotherapy, healthy eating, physical activity, sleep promotion, and certain anti-inflammatory or antidepressant medications. While the causal nature of the relationship between depression and T2D remains unclear, these conditions share dysregulation of homeostatic brain-body pathways that are central to mental and physical health. Better understanding of this dysregulation may provide opportunities for interventions that could benefit both conditions. Future research should examine the additive burden of depression and T2D on HPA and BGM dysregulation and better differentiate depression from emotional distress.