Attenuated sympathoadrenal responses, but not severe hypoglycemia, during aggressive glycemic therapy of early type 2 diabetes

Role of the Adrenal Medulla in Hypoglycaemia-Associated Autonomic Failure-A Diabetic Perspective

Hypoglycaemia-associated autonomic failure (HAAF) is characterised by an impairment in adrenal medullary and neurogenic symptom responses following episodes of recurrent hypoglycaemia. Here, we review the status quo of research related to the regulatory mechanisms of the adrenal medulla in its response to single and recurrent hypoglycaemia in both diabetic and non-diabetic subjects with particular focus given to catecholamine synthesis, enzymatic activity, and the impact of adrenal medullary peptides. Short-term post-transcriptional modifications, particularly phosphorylation at specific residues of tyrosine hydroxylase (TH), play a key role in the regulation of catecholamine synthesis. While the effects of recurrent hypoglycaemia on catecholamine synthetic enzymes remain inconsistent, long-term changes in TH protein expression suggest species-specific responses. Adrenomedullary peptides such as neuropeptide Y (NPY), galanin, and proenkephalin exhibit altered gene and protein expression in response to hypoglycaemia, suggesting a potential role in the modulation of catecholamine secretion. Of note is NPY, since its antagonism has been shown to prevent reductions in TH protein expression. This review highlights the need for further investigation into the molecular mechanisms involved in the adrenal medullary response to hypoglycaemia. Despite advancements in our understanding of HAAF in non-diabetic rodents, a reliable diabetic rodent model of HAAF remains a challenge.

Minimizing the risk of hypoglycemia with vildagliptin: Clinical experience, mechanistic basis, and importance in type 2 diabetes management

Even if the true incidence of hypoglycemia in type 2 diabetes mellitus (T2DM) remains difficult to estimate, with highly variable rates reported in the literature, it is likely more common than previously thought. While most hypoglycemic episodes in T2DM are considered "mild," they still have a substantial clinical impact. Severe hypoglycemia also exists in T2DM, with recent landmark studies prompting much debate about the potential role of severe hypoglycemia in cardiovascular morbidity and mortality, even though there is currently no definitive evidence for causality. The challenge in the treatment of T2DM remains the achievement of optimal glycemic control to lower the risk for long-term complications while avoiding hypoglycemia. Successful treatment strategies should therefore include careful selection of therapies to prevent hypoglycemia, starting early in the disease management process, in order to best preserve counterregulation. The dipeptidyl peptidase-4 inhibitor, vildagliptin, is a good treatment option to minimize the risk of hypoglycemia over time, while maintaining good glucose control. Extensive clinical experience is available for vildagliptin, with data published for all stages of the condition and with the low hypoglycemic potential stemming from a solid mechanistic basis.

Avoiding hypoglycaemia while achieving good glycaemic control in type 2 diabetes through optimal use of oral agent therapy

BACKGROUND

Patients with type 2 diabetes appear to be at relatively low risk of severe hypoglycaemia and hypoglycaemia unawareness in the early stages of disease. However, declining endogenous insulin secretory capacity due to beta-cell dysfunction/failure eventually produces vulnerability similar to type 1 diabetes. Severe hypoglycaemia itself is associated with serious morbidity and sometimes mortality, and represents an important barrier to achieving glycaemic goals and thus may reduce the protection from diabetes-related morbidity provided by good glycaemic control. Achieving an optimal balance of good glycaemic control and low risk of hypoglycaemia is key to providing optimum care in individuals with type 2 diabetes. This article discusses the issues related specifically to hypoglycaemia associated with oral agent therapy and how these agents may be best employed to provide an optimal balance between hypoglycaemia and good glycaemic control.

METHODS

Embase and Medline searches from 1998 to 2009 using the search terms DPP-4 inhibitors, metformin, oral agents, sulphonylureas, thiazolidinediones AND hypoglycaemia were conducted to identify relevant articles. The limitations inherent in this retrospective, narrative review of previously published publications chosen at the author's discretion are acknowledged.

FINDINGS

Failure to address even mild hypoglycaemia and glycaemic control early in the course of the disease may compromise the success of treatment in the longer term. Metformin, thiazolidinediones and DPP-4 inhibitors, either as monotherapy or in combination with each other, have a well-characterised low propensity to cause hypoglycaemia compared with other therapies.

CONCLUSIONS

Metformin, thiazolidinediones and DPP-4 inhibitors appear to be the most appropriate oral options for minimising the risk of hypoglycaemia. Early and ongoing attention to hypoglycaemia should form an integral part of any long-term glucose control strategy.