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.

High-fat, high-carbohydrate diet-induced prediabetes preconception in Sprague-Dawley rats as a risk factor for the development of preeclampsia: assessing changes in placental metabolic insults

Introduction

Hyperglycemia preconception deranges the establishment of a functional placenta; however, the risk of developing preeclampsia (PE) in prediabetic patients remains obscure. The aim was to assess abnormal placental changes as a risk factor for the development of PE in high-fat, high-carbohydrate (HFHC) diet-induced prediabetic (PD) rats.

Methods

HFHC diet-induced female prediabetic Sprague-Dawley rats were mated, and blood glucose concentrations, mean arterial pressure (MAP), and body weights were monitored on gestational days (GNDs) 0, 9, and 18. On GND 18, animals were euthanized. Blood and placentas were collected for biochemical analysis.

Results

Prediabetic rats showed significantly increased blood glucose concentration, proinflammatory cytokines, MAP, placental weight, and fetoplacental ratio compared with non-prediabetic (NPD) rats. Prediabetic rats showed significantly decreased placental vascular endothelial growth factor receptor 1 (VEGFR1) and placental growth factor (PLGF) and plasma nitric oxide (NO) compared with NPD.

Discussion

Prediabetes may have promoted endothelial dysfunction in the placenta and hypoxia, thus reducing PLGF and VEGFR1, which may have promoted proinflammation, endothelial dysfunction associated with NO decline, and hypertension, which is also observed in preeclamptic patients. Prediabetes may have promoted lipogenesis in placentas and fetuses that may have induced macrosomia and IUGR, also observed in preeclamptic patients. The findings from this study highlight the need for screening and monitoring of prediabetes during pregnancy to reduce the risk of developing preeclampsia.

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.

DPP4 Inhibitors: Could they be One of the Solutions for COVID-19 Patients with Prediabetes?

Recent reports suggest that prediabetes is a risk factor for developing severe COVID-19 complications through underlying mechanisms involving undiagnosed sub-clinical inflammation. However, we remain without a clinical approach for managing COVID-19 in prediabetic cases. The subclinical inflammation in prediabetes is associated with elevated DPP4 levels and activity. DPP4 has pleiotropic actions, including glycaemia regulation and immuno-modulation. Recently, DPP4 has been recognised as a co-receptor for COVID-19 for entering host cells. In addition to improving glycaemia, DPP4 inhibition is associated with reduced inflammation. In this submission, we explore the potential use of DPP4 inhibitors as therapeutic agents for prediabetic patients in managing the deleterious effects of COVID-19. DPP4 inhibitors (gliptins), such as linagliptin and sitagliptin, have therapeutic effects, which have been shown to extend beyond glycaemic control with no risk of hypoglycaemia. By the nature of their mechanism of action, gliptins are not associated with hypoglycaemia, unlike their anti-glycaemic counterparts, as they mainly target postprandial glycaemia. Moreover, DPP4 inhibitors may represent a safer option for prediabetic individuals in managing prediabetes either as a prophylactic or curative treatment for COVID-19. We envisage that beyond improved glycaemic control, the use of DPP4 inhibitors would also alleviate the cytokine storm, resulting in a reduction in the severity of COVID-19 symptoms and consequently reducing the morbidity and mortality in prediabetic COVID- 19 patients.

Evaluation of the effects of bredemolic acid on selected markers of glucose homeostasis in diet-induced prediabetic rats

CONTEXT

Pentacyclic triterpenes (such as maslinic acid) are natural anti-diabetic agents that ameliorate glucose metabolism in diet-induced prediabetes. However, the effects of bredemolic acid (BA), maslinic acid isomer, is yet unknown in prediabetic (PD) conditions.

OBJECTIVES

To investigate the effects of BA on some glucose homeostasis parameters in high-fat high-carbohydrate (HFHC) diet-induced PD rats.

METHODS

Thirty-six (36) male rats (150-180 g) were divided into two groups, the normal diet (ND) non-prediabetic, NPD (n = 6) and the HFHC diet PD groups (n = 30). The PD animals were further sub-divided into five groups (n = 6) where they were treated with BA for 12 weeks while monitoring changes in blood glucose, caloric intake, and body weight.

RESULTS

Diet-induced prediabetes resulted in increased body weight, caloric intake, glycated haemoglobin, and glucose tolerance. BA treatment ameliorated glucose tolerance, lowered plasma insulin and increased expression of glucose transporter 4 (GLUT 4) in rats.

CONCLUSIONS

BA administration restored glucose homeostasis in diet-induced prediabetes regardless of diet intervention.

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 effects of Momordica balsamina methanolic extract on haematological function in streptozotocin-induced diabetic rats: Effects on selected markers

BACKGROUND

Chronic hyperglycaemia-induced haematological changes increase the risk of cardiovascular complications in diabetic patients. The administration of insulin injection as a bolus is accompanied with increased blood viscosity, which is not recommended for patients with congestive heart failure. Momordica balsamina methanolic extract (MB) has previously been shown to possess anti-hyperglycaemic and renal dysfunction ameliorative effects; however, the haematological effects of MB have not been shown. The current study therefore, investigated the short-term effects MB on selected haematological parameters in streptozotocin (STZ)-induced diabetic rats.

METHODS

Briefly, the air-dried Momordica balsamina leaves were sequentially extracted with methanol to yield a methanolic extract. STZ-induced diabetic rats were divided into untreated and treated groups with insulin (170 μg kg^-1 s.c.) and metformin (500 mg kg^-1 p.o.) MB (250 mg kg^-1 p.o.). MB was administered twice daily for the 5-week experimental period. Blood glucose concentration was monitored weekly. Animals were sacrificed terminally. Blood and kidneys were collected for haematological and biochemical analysis respectively.

RESULTS

Treatment with MB significantly decreased blood glucose concentration and improved erythropoietin secretion, thus significantly increasing red blood cell production in treated diabetic animals by comparison to untreated animals. MB also significantly improved haemoglobin concentrations and moderately increased erythrocyte indices specifically, mean corpuscular volume (MCV), mean corpuscular haemoglobin concentration (MCHC) and mean corpuscular haemoglobin (MCH) to no significance by comparison to untreated diabetic animals. MB treatment decreased the oxidative stress evoked by the induction of diabetes while improving the antioxidant status of treated animals by comparison to untreated animals respectively.

CONCLUSIONS

Administration of Momordica balsamina methanolic extract protects against some injurious haematological changes induced by hyperglycaemia, which may reduce the risks of cardiovascular complications.