Mechanisms of the blunting of the sympatho-adrenal response: a theory

Blockade of Acid-Sensing Ion Channels Attenuates Recurrent Hypoglycemia-Induced Potentiation of Ischemic Brain Damage in Treated Diabetic Rats

Diabetes is a chronic metabolic disease and cerebral ischemia is a serious complication of diabetes. Anti-diabetic therapy mitigates this complication but increases the risk of exposure to recurrent hypoglycemia (RH). We showed previously that RH exposure increases ischemic brain damage in insulin-treated diabetic (ITD) rats. The present study evaluated the hypothesis that increased intra-ischemic acidosis in RH-exposed ITD rats leads to pronounced post-ischemic hypoperfusion via activation of acid-sensing (proton-gated) ion channels (ASICs). Streptozotocin-diabetic rats treated with insulin were considered ITD rats. ITD rats were exposed to RH for 5 days and were randomized into Psalmotoxin1 (PcTx1, ASIC1a inhibitor), APETx2 (ASIC3 inhibitor), or vehicle groups. Transient global cerebral ischemia was induced overnight after RH. Cerebral blood flow was measured using laser Doppler flowmetry. Ischemic brain injury in hippocampus was evaluated using histopathology. Post-ischemic hypoperfusion in RH-exposed rats was of greater extent than that in control rats. Inhibition of ASICs prevented RH-induced increase in the extent of post-ischemic hypoperfusion and ischemic brain injury. Since ASIC activation-induced store-operated calcium entry (SOCE) plays a role in vascular tone, next we tested if acidosis activates SOCE via activating ASICs in vascular smooth muscle cells (VSMCs). We observed that SOCE in VSMCs at lower pH is ASIC3 dependent. The results show the role of ASIC in post-ischemic hypoperfusion and increased ischemic damage in RH-exposed ITD rats. Understanding the pathways mediating exacerbated ischemic brain injury in RH-exposed ITD rats may help lower diabetic aggravation of ischemic brain damage.

Associations Between the Knowledge of Different Food Categories and Glycemia in Chinese Adult Patients With Type 2 Diabetes

This study aims to evaluate the levels of knowledge of different food categories and analyze the association between the levels of dietary knowledge and glycemia in Chinese adult patients with type 2 diabetes mellitus (T2DM). A cross-sectional study design was adopted. A total of 334 patients with T2DM were recruited from six hospitals from July to October 2014 in China. The Diabetes Dietary Knowledge Scale was utilized to obtain dietary knowledge. The results showed the item examining knowledge of carbohydrates received the highest score, whereas the item examining knowledge of healthy fats received the lowest score. The item "nuts" (B = -0.49; 95% confidence interval [CI] = [0.38, 0.99]) was associated with the incidence of hyperglycemia. The item "foods when hypoglycemic" (B = 0.42; 95% CI = [1.22, 2.07]) was associated with the incidence of hypoglycemia. There were different knowledge levels of different food categories in patients with T2DM, and these have implications for blood glucose control.

Differential effects of type 2 diabetes on brain glycometabolism in rats: focus on glycogen and monocarboxylate transporter 2

Astrocyte-neuron lactate shuttle (ANLS) is a pathway that supplies glycogen-derived lactate to active neurons via monocarboxylate transporter 2 (MCT2), and is important for maintaining brain functions. Our study revealed alterations of ANLS with hippocampal hyper-glycogen levels and downregulated MCT2 protein levels underlying hippocampal dysfunctions as a complication in type 2 diabetic (T2DM) animals. Since T2DM rats exhibit brain dysfunctions involving several brain regions, we examined whether there might also be T2DM effects on ANLS's disturbances in other brain loci. OLETF rats exhibited significantly higher glycogen levels in the hippocampus, hypothalamus, and cerebral cortex than did LETO rats. MCT2 protein levels in OLETF rats decreased significantly in the hippocampus and hypothalamus compared to their controls, but a significant correlation with glycogen levels was only observed in the hippocampus. This suggests that the hippocampus may be more vulnerable to T2DM compared to other brain regions in the context of ANLS disruption.

The risk for hypoglycemia during Ramadan fasting in patients with adrenal insufficiency

OBJECTIVES

The risk for hypoglycemia during Ramadan fasting in patients with adrenal insufficiency (AI) is not fully known. The aims of this study were to evaluate this risk objectively and to determine the associated factors.

METHODS

This prospective case-crossover study included 25 women and 5 men with known and treated AI and a median age of 38.5 y. Patients underwent clinical examination and a fasting blood sample was collected to measure glucose, urea, creatinine, sodium, potassium, cortisol, growth hormone and free thyroxine. A 24-h continuous glucose monitoring system (CGMS) using iPro2 (Medtronic, Parsippany, NJ, USA) with Enlite sensor (Medtronic) was performed for each patient during a Ramadan fasting day then again during a nonfasting day.

RESULTS

Interstitial glucose levels during the 24-h period, the fasting period, and the fasting period after exclusion of the 5 postprandial hours were significantly lower during the fasting day than on the nonfasting day. Hypoglycemia occurred in three patients (10%) during the fasting day but not during the nonfasting day (P = 0.23). Hypoglycemia was asymptomatic in two cases. Male sex was significantly associated with the occurrence of hypoglycemia.

CONCLUSION

Interstitial glucose levels were lower during fasting in patients with AI. However, the risk for hypoglycemia was not increased.

Whole genome expression profiling associates activation of unfolded protein response with impaired production and release of epinephrine after recurrent hypoglycemia

Recurrent hypoglycemia can occur as a major complication of insulin replacement therapy, limiting the long-term health benefits of intense glycemic control in type 1 and advanced type 2 diabetic patients. It impairs the normal counter-regulatory hormonal and behavioral responses to glucose deprivation, a phenomenon known as hypoglycemia associated autonomic failure (HAAF). The molecular mechanisms leading to defective counter-regulation are not completely understood. We hypothesized that both neuronal (excessive cholinergic signaling between the splanchnic nerve fibers and the adrenal medulla) and humoral factors contribute to the impaired epinephrine production and release in HAAF. To gain further insight into the molecular mechanism(s) mediating the blunted epinephrine responses following recurrent hypoglycemia, we utilized a global gene expression profiling approach. We characterized the transcriptomes during recurrent (defective counter-regulation model) and acute hypoglycemia (normal counter-regulation group) in the adrenal medulla of normal Sprague-Dawley rats. Based on comparison analysis of differentially expressed genes, a set of unique genes that are activated only at specific time points after recurrent hypoglycemia were revealed. A complementary bioinformatics analysis of the functional category, pathway, and integrated network indicated activation of the unfolded protein response. Furthermore, at least three additional pathways/interaction networks altered in the adrenal medulla following recurrent hypoglycemia were identified, which may contribute to the impaired epinephrine secretion in HAAF: greatly increased neuropeptide signaling (proenkephalin, neuropeptide Y, galanin); altered ion homeostasis (Na+, K+, Ca2+) and downregulation of genes involved in Ca2+-dependent exocytosis of secretory vesicles. Given the pleiotropic effects of the unfolded protein response in different organs, involved in maintaining glucose homeostasis, these findings uncover broader general mechanisms that arise following recurrent hypoglycemia which may afford clinicians an opportunity to modulate the magnitude of HAAF syndrome.

Posttranscriptional regulation of adrenal TH gene expression contributes to the maladaptive responses triggered by insulin-induced recurrent hypoglycemia

Acute metabolic stress such as insulin-induced hypoglycemia triggers a counterregulatory response during which the release of catecholamines (epinephrine), the activation of tyrosine hydroxylase (TH) enzyme and subsequent compensatory catecholamine biosynthesis occur in the adrenal medulla. However, recurrent exposure to hypoglycemia (RH), a consequence of tight glycemic control in individuals with type 1 and type 2 diabetes compromises this physiological response. The molecular mechanisms underlying the maladaptive response to repeated glucose deprivation are incompletely understood. We hypothesize that impaired epinephrine release following RH reflects altered regulation of adrenal catecholamine biosynthesis. To test this hypothesis, we compared the effect of single daily (RH) and twice-daily episodes of insulin-induced hypoglycemia (2RH) on adrenal epinephrine release and production in normal rats. Control animals received saline injections under similar conditions (RS and 2RS, respectively). Following 3 days of treatment, we assessed the counterregulatory hormonal responses during a hypoglycemic clamp. Changes in adrenal TH gene expression were also analyzed. The counterregulatory responses, relative TH transcription and TH mRNA levels and Ser40-TH phosphorylation (marker for enzyme activation) were induced to a similar extent in RS, 2RS, and RH groups. In contrast, epinephrine and glucagon responses were attenuated in the 2RH group and this was associated with a limited elevation of adrenal TH mRNA, rapid inactivation of TH enzyme and no significant changes in TH protein. Our results suggest that novel posttranscriptional mechanisms controlling TH mRNA and activated TH enzyme turnover contribute to the impaired epinephrine responses and may provide new therapeutic targets to prevent HAAF.

Composite efficacy parameters and predictors of hypoglycaemia in basal-plus insulin therapy--a combined analysis of 713 type 2 diabetic patients

AIMS

We aimed to identify predictors of hypoglycaemia in patients with poorly controlled type 2 diabetes treated with a single daily bolus of insulin glulisine on top of insulin glargine and oral antidiabetic drugs (basal-plus regimen).

METHODS

We retrospectively analysed four large basal-plus trials including 713 patients (47% female) with type 2 diabetes, mean age of 59.9 ± 9.5 years and diabetes duration of 11 ± 7.0 years. Predictors for symptomatic, severe and nocturnal hypoglycaemia were identified by multivariate logistic regression analyses, calculation of odds ratios (ORs) and Wald 95% confidence intervals (CIs).

RESULTS

Mean numbers of hypoglycaemic events per year were 4.64 ± 11.4 (symptomatic < 60 mg/dl), 0.59 ± 2.28 (nocturnal) and 0.03 ± 0.22 (severe). A total of 44.5% of patients reached the composite endpoint of glycated haemoglobin (HbA1c) <7.0% plus no severe hypoglycaemia, and 26.7% reached the composite of HbA1c <7.0% plus no symptomatic hypoglycaemia. Predictors of nocturnal and symptomatic hypoglycaemia were female gender (OR 1.82; 95% CI 1.07-3.11 and OR 1.89; 95% CI 1.31-2.78), diabetes duration >10 versus <5 years (OR 2.61; 95% CI 1.03-6.59 and OR 2.01; 95% CI 1.15-3.51) and higher basal insulin dose (per unit of increase) (OR 1.01; 95% CI 1.00-1.03 and OR 1.01; 95% CI 1.00-1.02). Conversely, a higher body mass index (BMI) (27-30 vs. <27 kg/m(2) and >30 vs. <27 kg/m(2) ) conferred a reduced risk of symptomatic hypoglycaemia with an OR of 0.53 (95% CI 0.31-0.90) and an OR of 0.61 (95% CI 0.39-0.97).

CONCLUSIONS

Female gender, a long diabetes duration and higher basal insulin dose were predictors of hypoglycaemia, while protection was provided by BMI > 30. These results may help to successfully establish basal-plus insulin regimen in individual patients on their transition from basal-only to basal-bolus treatment.

A retrospective study on the incidence and risk factors of severe hypoglycemia in primary care

AIMS

To investigate the incidence and risk factors of severe hypoglycemia (SH) in primary care. SH was defined as hypoglycemia with coma, or the need of glucose or glucagon injection.

METHODS

We performed a cross-sectional retrospective study in patients with diabetes treated in primary care in Germany. We analyzed an unselected sample of participants with type 1 (n = 373) and type 2 diabetes (n = 4481) who participated in an insurance plan from the health care insurer Deutsche BKK. Data of participants with type 1 diabetes are as follows: women, n = 155 (42%); age, 49±16 years; diabetes duration, 20+13 years; BMI, 28±6 kg/m2; GHb, 7.1+1.5%; GHb≤7%, n = 263 (71%); GHb≥8.5%, n = 48 (13%). Data of participants with type 2 diabetes: women, n = 1979 (44%); age, 66±10 years; diabetes duration, 8±7 years; BMI, 30±5 kg/m2; GHb, 6.6±1.3%; GHb≤7%, n = 3747 (84%); GHb≥8.5%, n = 360 (8%); insulin therapy, n = 1175 (26%).

RESULTS

The incidence of SH in type 1 diabetes: 1.3% (CI: 0.4%, 3.1%) per year; type 2 diabetes with insulin therapy: 0.9% (CI: 0.5%, 1.7%); without insulin therapy: 0.3% (CI: 0.1%, 0.6%). The event rate was 0.02 SH per patient/year in type 1 diabetes and 0.01 in type 2 diabetes, respectively. Low BMI, GHb, insulin therapy and female gender were associated with an increased risk of SH.

CONCLUSIONS

In primary care, patients with diabetes can achieve good glycemic control with very rare events of SH. Due to low incidence, SH would have been an inappropriate parameter to evaluate the outcome quality of diabetes therapy in primary care.

Respiration and autonomic regulation and orexin

Orexin, a small neuropeptide released from neurons in the hypothalamus with widespread projections throughout the central nervous system, has broad biological roles including the modulation of breathing and autonomic function. That orexin activity is fundamentally dependent on sleep-wake state, and circadian cycle requires consideration of orexin function in physiological control systems in respect to these two state-related activity patterns. Both transgenic mouse studies and focal orexin receptor antagonism support a role for orexins in respiratory chemosensitivity to CO₂ predominantly in wakefulness, with further observations limiting this role to the dark period. In addition, orexin neurons participate in the regulation of sympathetic activity, including effects on blood pressure and thermoregulation. Orexin is also essential in physiological responses to stress. Orexin-mediated processes may operate at two levels: (1) in sleep-wake and circadian states and (2) in stress, for example, the defense or "fight-or-flight" response and panic-anxiety syndrome.