Hormonal control of ketogenesis

Severe euglycemic diabetic ketoacidosis of multifactorial etiology in a type 2 diabetic patient treated with empagliflozin: case report and literature review

BACKGROUND

Sodium-glucose co-transporter-2 (SGLT-2) inhibitors are a relatively novel class of oral medications for the treatment of Type 2 DM with a generally acceptable safety profile. However, these agents have been associated with rare events of a serious and potentially life-threatening complication named euglycemic diabetic ketoacidosis (euDKA). euDKA is not identical with the typical diabetic ketoacidosis, as it often presents with serious metabolic acidosis but only mild to moderate glucose and anion gap elevation.

CASE PRESENTATION

We report a case of a 51-year old female with Type 2 DM treated with an SGLT-2 inhibitor, developing severe metabolic acidosis with only mild blood glucose elevation after a routine surgery. A careful evaluation of involved factors led to the diagnosis of euDKA, followed by cautious application of simple therapeutic measures that resulted in complete restoration of acidosis and glycemic control in less than 48-h.

CONCLUSIONS

Euglycemic ketoacidosis is a rare but rather serious complication of SGLT-2 inhibitors use, often with a multifactorial etiology. Its atypical presentation requires a high level of awareness by physicians as early recognition of this complication can quickly and safely restore acid-base balance.

Euglycaemic diabetic ketoacidosis as a complication of SGLT-2 inhibitors: epidemiology, pathophysiology, and treatment

INTRODUCTION

Sodium-glucose co-transporters 2 (SGLT-2) inhibitors are a relatively novel class of oral medications for the treatment of Type 2 Diabetes Mellitus, which lower plasma glucose by inhibiting glucose reabsorption in the proximal renal tubule. Apart from their hypoglycemic action, recent data suggest these agents have additional major cardioprotective and nephroprotective properties.

AREAS COVERED

This review summarizes the existing data on epidemiology, pathophysiology, and treatment of euglycaemic ketoacidosis (euDKA) as a complication of SGLT-2 inhibitor use.

EXPERT OPINION

Although SGLT-2 inhibitors have a relatively good adverse event profile, they have been associated with the serious and potentially life-threatening metabolic complication of euDKA. Data from major outcome trials suggest that the rate of DKA is quite low. However, the rate of DKA could be generally underestimated in clinical trials due to the atypical presentation of ketoacidosis, and even more so in real-life conditions. Management of this serious metabolic complication requires a proper understanding of its pathophysiology as well as increased awareness and early recognition of the potential risk factors involved. Following this, the institution of an array of simple supportive measures, could safely restore normal acid-base balance in most patients.

Diabetic ketoacidosis, sodium glucose transporter-2 inhibitors and the kidney

Diabetic ketoacidosis is a serious metabolic condition that may occur in patients with either Type 1 or Type 2 diabetes. The accumulation of ketoacids in the serum is a consequence of insulin deficiency and glucagon excess. Sodium Glucose Transporter 2 (SGLT2) inhibitors are novel therapeutic treatments for improving glucose homeostasis in patients with diabetes. Through reductions in glucose reabsorption by the kidney, they lower serum glucose in patients with Type 2 diabetes and they improve glucose control whether used alone or in combination with other therapies. Mechanistically, these drugs increase serum ketoacids and increase glucagon production, which in some individuals, can lead to formation of diabetic ketoacidosis. This review will first focus in how the kidney normally handles ketoacids, and second will discuss how the SGLT2 inhibitors affect the kidney in such a way so as to enhance the risk for development of ketoacidosis in susceptible individuals.

The fatty acid receptor GPR40 plays a role in insulin secretion in vivo after high-fat feeding

OBJECTIVE

The G-protein-coupled receptor GPR40 is expressed in pancreatic beta-cells and is activated by long-chain fatty acids. Gene deletion studies have shown that GPR40 mediates, at least in part, fatty acid-amplification of glucose-induced insulin secretion (GSIS) but is not implicated in GSIS itself. However, the role of GPR40 in the long-term effects of fatty acids on insulin secretion remains controversial. This study aimed to test the hypothesis that GPR40 plays a role in insulin secretion after high-fat feeding. RESEARCH DESIGN AND METHOD GPR40 knockout (KO) mice on a C57BL/6 background and their wild-type (WT) littermates were fed a high-fat diet (HFD) for 11 weeks. Glucose tolerance, insulin tolerance, and insulin secretion in response to glucose and Intralipid were assessed during the course of the diet period.

RESULTS

GPR40 KO mice had fasting hyperglycemia. They became as obese, glucose intolerant, and insulin resistant as their WT littermates given HFD and developed a similar degree of liver steatosis. Their fasting blood glucose levels increased earlier than those of control mice during the course of the HFD. The remarkable increase in insulin secretory responses to intravenous glucose and Intralipid seen in WT mice after HFD was of much lower magnitude in GPR40 KO mice.

CONCLUSIONS

GPR40 plays a role not only in fatty acid modulation of insulin secretion, but also in GSIS after high-fat feeding. These observations raise doubts on the validity of a therapeutic approach based on GPR40 antagonism for the treatment of type 2 diabetes.

Expression of mitochondrial tricarboxylate carrier TCC mRNA and protein in the rat brain

The tricarboxylate carrier protein catalyzes an electroneutral exchange across the mitochondrial inner membrane of tricarboxylate, dicarboxylate or phosphoenolpyruvate. We examined expression and localization of mitochondrial tricarboxylate carrier TCC mRNA and protein in the rat brain. TCC mRNA was ubiquitously expressed in all rat tissues examined and was abundant in brain, liver and kidney. TCC protein as well as mRNA was widely expressed in brain, and the protein expression was strong in neuronal cells in the hippocampus, the olfactory bulb, the corpus mamillare and the cerebellum. Our results suggest that this tricarboxylate carrier protein may contribute to biosynthesis and bioenergetics in neuronal cells in brain.

Diabetic ketoacidosis

Diabetic ketoacidosis (DKA) is a complex and potentially fatal metabolic disorder in patients with diabetes mellitus. An understanding of the pathophysiology of DKA is essential in order to optimize patient management. A combination of insulin deficiency, increased stress hormone levels, and volume depletion account for the laboratory abnormalities and clinical signs observed in these patients. Successful therapy depends upon correction of hyperglycemia, dehydration, and electrolyte and blood gas abnormalities.

Structure, function and regulation of the tricarboxylate transport protein from rat liver mitochondria

Recent progress is summarized on the structure, function, and regulation of the tricarboxylate (i.e., citrate) transport protein (CTP) from the rat liver mitochondrial inner membrane. The transporter has been purified and its reconstituted function characterized. A cDNA clone encoding the CTP has been isolated and sequenced, thus enabling a deduction of the complete amino acid sequence of this 32.6 kDa transport protein. Dot matrix analysis and sequence alignment indicate that based on structural considerations the CTP can be assigned to the mitochondrial carrier family. Hydropathy analysis of the transporter sequence indicates six putative membrane-spanning alpha-helices and has permitted the development of an initial model for the topography of the CTP within the inner membrane. The questions as to whether more than one gene encodes the CTP and whether more than one isoform is expressed remain unanswered at this time. Studies documenting a diabetes-induced alteration in the function of several mitochondrial anion transporters, which can be reversed by treatment with insulin, provide a physiologically/pathologically relevant experimental system for studying the molecular mechanism(s) by which mitochondrial transporters are regulated. Potential future research directions are discussed.

The effect of insulin supplementation on diabetes-induced alterations in the extractable levels of functional mitochondrial anion transport proteins

The effect of insulin supplementation on diabetes-induced alterations in the levels of functional mitochondrial anion transport proteins has been determined. The experimental approach consisted of the extraction of the pyruvate, dicarboxylate, and citrate transport proteins from the mitochondrial inner membrane with Triton X-114 using rat liver mitoplasts (prepared from control, diabetic, or insulin-supplemented diabetic animals) as the starting material, followed by the reconstitution of the function of each transporter in a proteoliposomal system. This experimental strategy permitted the quantification of the functional levels of these three transporters in the absence of the complications that arise when such measurements are carried out with intact mitochondria (or mitoplasts). We found that treatment of diabetic rats (i.e., animals that were injected with streptozotocin 3 weeks earlier) on a daily basis with insulin for 3 weeks resulted in a reversal of the diabetes-induced (a) increase in the extractable and reconstitutable total (and specific) transport activities of the pyruvate and dicarboxylate transporters and (b) decrease in the activity of the citrate transporter. These findings indicate that diabetes-induced alterations in the functional levels of mitochondrial anion transport proteins are a direct consequence of the insulin insufficiency that characterizes this disease. Furthermore, this study provides the first demonstration that insulin participates in the regulation of the functional levels of liver mitochondrial anion transport proteins.

Streptozotocin-induced alterations in the levels of functional mitochondrial anion transport proteins

The effect of streptozotocin-induced diabetes on the levels of functional mitochondrial anion transport proteins has been determined. The experimental approach utilized for these studies consisted of the extraction of each of four mitochondrial anion transport proteins from rat liver mitoplasts (isolated from diabetic and control animals) with the nonionic detergent Triton X-114, followed by the functional reconstitution of each transporter in a liposomal system via the freeze-thaw-sonication technique. This approach permitted the quantification of transporter function without the complications that occur when such measurements are carried out with intact mitochondria (or mitoplasts). We found that experimental diabetes caused an increase in the extractable and reconstitutable specific (and total) transport activities of the pyruvate and dicarboxylate transporters, a decrease in the activity of the citrate transporter, and no significant change in the activity of the phosphate transporter relative to control values. An examination of the time course of the appearance of changes in the reconstitutable activities of the pyruvate and citrate transporters following the injection of streptozotocin revealed differences. Thus, whereas the activity of the pyruvate transporter displayed the most pronounced increase (193%) 1 week following streptozotocin injection and then subsequently declined from this peak and plateaued at later times (99% and 96% increases at 3 and 8 weeks, respectively), the activity of the citrate transporter progressively decreased with time (31-51% decreases at 1-8 weeks). We suggest that the observed diabetes-induced changes in mitochondrial anion transporter function are predictable on the basis of diabetes-induced alterations in the activities of enzymes that constitute metabolic pathways to which these transporters either supply substrate or remove product. Furthermore, we speculate that mitochondrial anion transport proteins may be regulated in coordination with the enzymes of such associated metabolic pathways.