Diurnal variation in salivary cortisol across age classes in Ache Amerindian males of Paraguay

Reproductive endocrinology and aging in human males: An evolutionary perspective

Due to its important role in fertility, reproductive endocrine function has been subject to natural selection in all organisms including human males. Moreover, reproductive endocrine function is subject to change as males age. Indeed, the biology of aging is also subject to natural selection. As males age, hormone function such as variation in testosterone can change as the result of general somatic degradation. However these changes are not universal and can differ between human male populations depending on lifestyle and ecological context. The degree to which this variation is adaptive remains an open question but recent evolutionary anthropology research has provided some clarity. While knowledge of evolutionary approaches has limitations, the benefits of understanding the origins and comparative context of reproductive endocrine function in older human males are significant. This paper discusses our present comprehension of reproductive endocrinology and aging in human males, with a focus on human diversity across varied lifestyles, ecologies, and environments. In addition, comparative great ape research is examined. Current research challenges and future directions related to the importance of evolutionary biology and human diversity for understanding human male aging are discussed.

Variation in diurnal cortisol patterns among the Indigenous Shuar of Amazonian Ecuador

OBJECTIVES

The hypothalamic-pituitary-adrenal (HPA) axis and its primary end product, the glucocorticoid cortisol, are major components of the evolved human stress response. However, most studies have examined these systems among populations in high-income settings, which differ from the high pathogen and limited resource contexts in which the HPA axis functioned for most of human evolution.

METHODS

We investigated variability in diurnal salivary cortisol patterns among 298 Indigenous Shuar from Amazonian Ecuador (147 males, 151 females; age 2-86 years), focusing on the effects of age, biological sex, and body mass index (BMI) in shaping differences in diurnal cortisol production. Saliva samples were collected three times daily (waking, 30 minutes post-waking, evening) for three consecutive days to measure key cortisol parameters: levels at waking, the cortisol awakening response, the diurnal slope, and total daily output.

RESULTS

Age was positively associated with waking levels and total daily output, with Shuar juveniles and adolescents displaying significantly lower levels than adults (p < .05). Sex was not a significant predictor of cortisol levels (p > .05), as Shuar males and females displayed similar patterns of diurnal cortisol production across the life course. Moreover, age, sex, and BMI significantly interacted to moderate the rate of diurnal cortisol decline (p = .027). Overall, Shuar demonstrated relatively lower cortisol concentrations than high-income populations.

CONCLUSIONS

This study expands the documented range of global variation in HPA axis activity and diurnal cortisol production and provides important insights into the plasticity of human stress physiology across diverse developmental and socioecological settings.

Wild chimpanzees exhibit humanlike aging of glucocorticoid regulation

Cortisol, a key product of the stress response, has critical influences on degenerative aging in humans. In turn, cortisol production is affected by senescence of the hypothalamic-pituitary-adrenal (HPA) axis, leading to progressive dysregulation and increased cortisol exposure. These processes have been studied extensively in industrialized settings, but few comparative data are available from humans and closely related species living in natural environments, where stressors are very different. Here, we examine age-related changes in urinary cortisol in a 20-y longitudinal study of wild chimpanzees (n = 59 adults) in the Kanyawara community of Kibale National Park, Uganda. We tested for three key features of HPA aging identified in many human studies: increased average levels, a blunted diurnal rhythm, and enhanced response to stressors. Using linear mixed models, we found that aging was associated with a blunting of the diurnal rhythm and a significant linear increase in cortisol, even after controlling for changes in dominance rank. These effects did not differ by sex. Aging did not increase sensitivity to energetic stress or social status. Female chimpanzees experienced their highest levels of cortisol during cycling (versus lactation), and this effect increased with age. Male chimpanzees experienced their highest levels when exposed to sexually attractive females, but this effect was diminished by age. Our results indicate that chimpanzees share some key features of HPA aging with humans. These findings suggest that impairments of HPA regulation are intrinsic to the aging process in hominids and are side effects neither of extended human life span nor of atypical environments.

Effects of inter-day and intra-day variation on salivary metabolomic profiles

BACKGROUND

Salivary secretion is an important parameter reflecting the health status of an individual and has been used clinically for the diagnosis of various oral diseases, such as xerostomia. Salivary metabolomic profiling is considered an emerging potential tool for the detection of various systemic diseases. To our knowledge, this is the first study to investigate the quantitative relationship between salivary secretion volume and salivary metabolomic profile.

METHODS

To evaluate inter- and intra-day variations in salivary secretion, 234 saliva samples were collected three times per day for three days from 13 subjects and analyzed. Capillary electrophoresis-mass spectrometry was used for non-targeted quantification of water-soluble metabolites.

RESULTS

No significant inter- or intra-day variations were observed in salivary secretion volume. No significant inter-day variations were observed in metabolomic patterns. In contrast, significant intra-day variations were observed in salivary metabolomic profiles. The difference was more obvious for stimulated saliva than for unstimulated saliva. These profile changes were independent of salivary secretion volume.

CONCLUSIONS

Our results indicated that diurnal change had a greater effect on salivary metabolomic profiles than the other factors. Hence, sampling time should be tightly controlled to minimize unexpected bias in the clinical use of salivary metabolomics.

Functional TSPO polymorphism predicts variance in the diurnal cortisol rhythm in bipolar disorder

INTRODUCTION

Psychosocial stress contributes to onset/exacerbation of mood episodes and alcohol use, suggesting dysregulated diurnal cortisol rhythms underlie episodic exacerbations in Bipolar Disorder (BD). However, mechanisms underlying dysregulated HPA rhythms in BD and alcohol use disorders (AUD) are understudied. Knowledge of associated variance factors have great clinical translational potential by facilitating development of strategies to reduce stress-related relapse in BD and AUD. Evidence suggests structural changes to mitochondrial translocator protein (TSPO) (a regulator of steroid synthesis) due to the single nucleotide polymorphism rs6971, may explain much of this variance. However, whether rs6971 is associated with abnormal HPA rhythms and clinical exacerbation in humans is unknown.

METHODS

To show this common TSPO polymorphism impacts HPA rhythms in BD, we tested whether rs6971 (dichotomized: presence/absence of polymorphism) predicted variance in diurnal cortisol rhythm (saliva: morning and evening for 3 days) in 107 BD (50 with and 57 without AUD) and 28 healthy volunteers of similar age and ethno-demographic distribution.

RESULTS

Repeated measures ANOVA confirmed effects BD (F5,525 = 3.0, p = 0.010) and AUD (F5,525 = 2.9, p = 0.012), but not TSPO polymorphism (p > 0.05). Interactions were confirmed for TSPO × BD (F5,525 = 3.9, p = 0.002) and for TSPO × AUD (F5,525 = 2.8, p = 0.017).

DISCUSSION

We identified differences in diurnal cortisol rhythm depending on presence/absence of common TSPO polymorphism in BD volunteers with or without AUD and healthy volunteers. These results have wide ranging implications but further validation is needed prior to optimal clinical translation.

Diurnal rhythm of follicle-stimulating hormone is associated with nonalcoholic fatty liver disease in a Chinese elderly population

OBJECTIVE

Previous studies have found that impairment of the circadian clock appears to contribute to the development of nonalcoholic fatty liver disease (NAFLD) and the circulating follicle-stimulating hormone (FSH) level showed a diurnal cycle. A recent study reported that a lower FSH level was associated with NAFLD. However, the effects of the diurnal rhythm of FSH on NAFLD have not been reported. The aim of this study was to evaluate whether the diurnal rhythm of FSH was associated with NAFLD in an elderly population.

STUDY DESIGN

We performed a cross-sectional study among 71 elderly patients between August 2015 and November 2015 at Fujian Provincial Hospital. Anthropometrics and tests for laboratory were performed for each patient. FSH was determined by radioimmunoassay. The FSH receptor (FSHR) expression was identified in liver and ovary tissue by immunohistochemical staining. NAFLD was diagnosed by sonographic features.

RESULTS

Of the 71 patients, 33 (42.9%) had NAFLD on their ultrasound. There were no significant differences between subjects with NAFLD and those without NAFLD in terms of age, sex, body mass index, waist-to-hip ratio, fasting plasma glucose, postload plasma glucose, liver enzyme, triglycerides, total cholesterol, high-density lipoprotein-cholesterol and low-density lipoprotein-cholesterol. Both the serum FSH levels of 8AM and 0AM showed no differences between the groups. The proportion of the 'normal' diurnal rhythm of FSH was higher among the patients with NAFLD (78.1% vs. 52.6%, P = .027). After adjusting for all potential confounders, the fully adjusted odds ratios (OR) of diurnal rhythm of FSH for NAFLD was 3.86 (95%CI: 1.01, 14.81, P = .049). Immunohistochemical staining showed that the FSHR protein was detected in human ovarian and hepatic tissues.

CONCLUSIONS

These results suggest that the 'normal' diurnal rhythm of FSH was independently associated with NAFLD in an elderly population. This study provides a novel insight into the diurnal rhythm of FSH in the pathogenesis of NAFLD.