Review of the direct and indirect effects of hyperglycemia on the HPA axis in T2DM and the co-occurrence of depression

Type 2 diabetes mellitus (T2DM) is characterized by persistent hyperglycemia which is further associated with hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Several studies have shown that HPA axis hyperactivity is heightened in the chronic hyperglycemic state with severe hyperglycemic events more likely to result in a depressive disorder. The HPA axis is also regulated by the immune system. Upon stress, under homeostatic conditions, the immune system is activated via the sympatho-adrenal-medullary axis resulting in an immune response which secretes proinflammatory cytokines. These cytokines aid in the activation of the HPA axis during stress. However, in T2DM, where there is persistent hyperglycemia, the immune system is dysregulated resulting in the elevated concentrations of these cytokines. The HPA axis, already activated by the hyperglycemia, is further activated by the cytokines which all contribute to a diagnosis of depression in patients with T2DM. However, the onset of T2DM is often preceded by pre-diabetes, a reversible state of moderate hyperglycemia and insulin resistance. Complications often seen in T2DM have been reported to begin in the pre-diabetic state. While the current management strategies have been shown to ameliorate the moderate hyperglycemic state and decrease the risk of developing T2DM, research is necessary for clinical studies to profile these direct effects of moderate hyperglycemia in pre-diabetes on the HPA axis and the indirect effects moderate hyperglycemia may have on the HPA axis by investigating the components of the immune system that play a role in regulating this pathway.

The relationship between adipose tissue RAAS activity and the risk factors of prediabetes: a systematic review and meta-analysis

METHODS

This systematic review was developed in compliance with the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-2020) standards. This was accomplished by searching clinical MeSH categories in MEDLINE with full texts, EMBASE, Web of Science, PubMed, Cochrane Library, Academic Search Complete, ICTRP and ClinicalTrial.gov. Reviewers examined all the findings and selected the studies that satisfied the inclusion criteria. The Downs and Black Checklist was used to assess for bias, followed by a Review Manager v5. A Forrest plot was used for the meta-analysis and sensitivity analysis. The protocol for this review was registered with PROSPERO CRD42022320252.

RESULTS

The clinical studies (n = 2) comprised 1065 patients with prediabetes and 1103 normal controls. The RAAS measurements were completed in the adipose tissue. The RAAS components, renin and aldosterone were higher in the prediabetic (PD) compared to the control [mean difference (MD) = 0.16, 95% CI 0.16 (-0.13, 0.45), p = 0.25]. Furthermore, the PD group demonstrated higher triglycerides mean difference [MD = 7.84, 95% CI 7.84 (-9.84, 25.51), p = 0.38] and increased BMI [MD = 0.13, 95% CI 0.13 (-0.74, 0.99), p = 0.77] compared to the control. The overall quality of the studies was fair with a median score and range of 17 (16-18).

CONCLUSION

The current study highlights the relationship between increased BMI, RAAS and insulin resistance which is a predictor of prediabetes. The renin is slightly higher in the prediabetes group without any statistical significance, aldosterone is rather negatively associated with prediabetes which may be attributed to the use of anti-hypertensive treatment.

Investigating the Association Between Diet-Induced "Leaky Gut" and the Development of Prediabetes

INTRODUCTION

Chronic consumption of a high-calorie diet compromises the gut microbiota and the integrity of the intestinal wall, which causes translocation of bacterial lipopolysaccharides (LPS) into the blood. This elicits the secretion of pro-inflammatory cytokines, resulting in inflammation. However, how a high-fat high carbohydrate diet affects intestinal permeability and its possible role in the development of prediabetes have not been investigated. This study investigated the effects of HFHC diet-induced prediabetes on gut microbiota and intestinal permeability in male Sprague Dawley rats.

METHODS

The animals were randomly assigned into the non-prediabetic (NPD) and diet-induced prediabetic (PD) groups (n=6) for 20 weeks. Then, the fecal samples were analyzed to measure the gut microbiota level of Firmicutes, Bacteroidetes, and Proteobacteria in both animal groups. Blood glucose, plasma insulin, serum zonulin, plasma LPS, soluble CD14, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), C-reactive protein (CRP), and intestinal fatty-acid binding protein (IFABP) concentrations were measured.

RESULTS

The PD group had a reduction in the Firmicutes and an increase in Bacteroidetes and Proteobacteria levels compared to those in the NPD group. Blood glucose, insulin concentration, serum zonulin, and plasma sCD14 concentrations in the PD group increased significantly, while plasma LPS concentrations were similar to the NPD group. Concentrations of plasma TNF-α, IL-6, CRP, and IFABP, an intracellular protein expressed in the intestine, increased in PD compared to the NPD group.

CONCLUSIONS

the study results cumulatively suggest that chronic consumption of the HFHC diet may be associated with the dysregulation of gut microbiota, leading to increased intestinal permeability.

The Relationship between Renin-Angiotensin-Aldosterone System (RAAS) Activity, Osteoporosis and Estrogen Deficiency in Type 2 Diabetes

Type 2 diabetes (T2D) is associated with a plethora of comorbidities, including osteoporosis, which occurs due to an imbalance between bone resorption and formation. Numerous mechanisms have been explored to understand this association, including the renin-angiotensin-aldosterone system (RAAS). An upregulated RAAS has been positively correlated with T2D and estrogen deficiency in comorbidities such as osteoporosis in humans and experimental studies. Therefore, research has focused on these associations in order to find ways to improve glucose handling, osteoporosis and the downstream effects of estrogen deficiency. Upregulation of RAAS may alter the bone microenvironment by altering the bone marrow inflammatory status by shifting the osteoprotegerin (OPG)/nuclear factor kappa-Β ligand (RANKL) ratio. The angiotensin-converting-enzyme/angiotensin II/Angiotensin II type 1 receptor (ACE/Ang II/AT1R) has been evidenced to promote osteoclastogenesis and decrease osteoblast formation and differentiation. ACE/Ang II/AT1R inhibits the wingless-related integration site (Wnt)/β-catenin pathway, which is integral in bone formation. While a lot of literature exists on the effects of RAAS and osteoporosis on T2D, the work is yet to be consolidated. Therefore, this review looks at RAAS activity in relation to osteoporosis and T2D. This review also highlights the relationship between RAAS activity, osteoporosis and estrogen deficiency in T2D.

Diet-induced prediabetes: Effects on the activity of the renin-angiotensin-aldosterone system (RAAS) in selected organs

Derangements often observed with type 2 diabetes (T2D) are associated with disturbances in renin-angiotensin-aldosterone system (RAAS) activity. A positive correlation between local RAAS activity and the complications observed in T2D has been noted. However, the detrimental ramifications due to moderate hyperglycemia noted in prediabetes and the affected organ system and mechanistic pathways are not elucidated. Hence, this study investigated the effects of diet-induced prediabetes on RAAS in various organs.

MATERIALS AND METHODS

Male Sprague-Dawley rats were separated into two groups: non-pre-diabetic (NPD) through exposure to standard rat chow and diet-induced prediabetic (PD) group by exposure to a high-fat high carbohydrate diet for 32 weeks. RAAS activity in the skeletal muscle, adipose tissue, liver, pancreas and heart was determined through the analysis of RAAS components such as; renin, angiotensinogen, angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor (AT1R) via PCR as well as the quantification of angiotensin II and aldosterone concentration. Furthermore, NADPH oxidase, SOD and GPx1 concentrations were determined in the skeletal muscle, pancreas and heart in addition to the hepatic triglycerides.

RESULTS

The RAAS components were elevated in the PD group when compared to the NPD. This was further accompanied by increased NADPH oxidase and reduced SOD and GPx1 concentrations in the selected organs, in addition to the elevated hepatic triglycerides concentration in the PD by comparison to NPD.

CONCLUSION

Due to these observed changes, we suggest that local RAAS activity in the prediabetic state in selected organs elicits the derangements noted in T2D.

The dysregulation of the hypothalamic-pituitary-adrenal axis in diet-induced prediabetic male Sprague Dawley rats

BACKGROUND

Altered function of the hypothalamic-pituitary-adrenal (HPA) axis in type 2 diabetic patients, a condition preceded by pre-diabetes, has been shown to increase the risk of depression as well as cause downstream effects resulting in upregulation of gluconeogenesis and dyslipidemia. In addition, stress, either psychological from managing diabetes or lifestyle related, further activates the HPA axis causing an exaggerated stress response. This study investigated the activity of the HPA axis in selected markers of glucose handling, and the stress response relative to components of the HPA axis in a diet-induced pre-diabetic rat model.

METHODS

Sprague Dawley Rats were randomly divided into non-pre-diabetic group (NPD) and pre-diabetic group (PD) (n = 6, per group) over a 20-week induction period and a further 12-week experimental period to get 32 weeks. At the end of the 20 and 32-week periods, glucose handling using the Homeostasis Model Assessment indices, adrenocorticotropic (ACTH) and corticosterone (CORT) concentrations were measured. Stress was induced and the forced swim test were performed in the 12-week experimental week. At the end of 32 weeks glucocorticoid and mineralocorticoid hippocampal receptors were also measured.

RESULTS

Impaired glucose handling in the PD group as well as increase in corticosterone was observed at the end of both 20 and 32-week periods by comparison to NPD groups. No changes were observed in ACTH concentration at week 20 while, at week 32, a decrease in plasma ACTH concentration was observed in the PD group by comparison to the NPD group. The stressed-induced animals were stressed using the forced swim test: the behaviour observed showed an increase in immobility time in the PD stressed group by comparison to the NPD group. This was followed by the observation of a decrease in ACTH and CORT concentration in the PD stressed group by comparison to the NPD stressed group. Mineralocorticoid and glucocorticoid receptors gene expression were elevated in the stressed PD group relative to the stressed NPD group.

CONCLUSION

These observations, together, suggest that diet-induced pre-diabetes is associated with impaired HPA axis activity and deteriorating response to stress.

The Pathogenesis of Fever-Induced Febrile Seizures and Its Current State

Febrile seizures, commonly in children between the ages of 3 months to 5 years, are a neurological abnormality characterized by neuronal hyper-excitability, that occur as a result of an increased core body temperature during a fever, which was caused by an underlying systemic infection. Such infections cause the immune system to elicit an inflammatory response resulting in the release of cytokines from macrophages. The cytokines such as interleukin (IL)- 1β, IL-6, and tumour necrosis factor-α (TNF-α) combat the infection in the localized area ultimately spilling over into circulation resulting in elevated cytokine levels. The cytokines, along with pathogen-associated molecular patterns (PAMPs) expressed on pathogens for example, lipopolysaccharide (LPS), interact with the blood brain barrier (BBB) causing a ‘leaky’ BBB which facilitates cytokines and LPS entry into the central nervous system. The cytokines activate the microglia which release their own cytokines, specifically IL1β. IL-β interacts with the brain endothelium resulting in the activation of cyclooxygenase 2 which catalyzes the production of prostaglandin 2 (PGE2). PGE2 enters the hypothalamic region and induces a fever. Abnormally increased IL-1β levels also progressively increases excitatory (glutamatergic) neurotransmission, and decreases inhibitory (GABAergic) neurotransmission, thus mediating the pathogenesis of convulsions. Current treatments for febrile seizures present with side effects that are detrimental to health, which fosters the need for an alternative, more affordable treatment with fewer adverse side effects, and 1 that is easily accessible, especially in low income areas that are also affected by other underlying socio-economic factors, in which febrile seizures are of growing concern.