Renal glucose production during insulin-induced hypoglycemia

Effect of Dapagliflozin on Renal and Hepatic Glucose Kinetics in T2D and NGT Subjects

Acute and chronic sodium-glucose cotransporter 2 (SGLT-2) inhibition increases endogenous glucose production (EGP). However, the organ-liver versus kidney-responsible for the increase in EGP has not been identified. In this study, 20 subjects with type 2 diabetes (T2D) and 12 subjects with normal glucose tolerance (NGT) received [3-3H]glucose infusion (to measure total EGP) combined with arterial and renal vein catheterization and para-aminohippuric acid infusion for determination of renal blood flow. Total EGP, net renal arteriovenous balance, and renal glucose production were measured before and 4 h after dapagliflozin (DAPA) and placebo administration. Following DAPA, EGP increased in both T2D and NGT from baseline to 240 min, while there was a significant time-related decrease after placebo in T2D. Renal glucose production at baseline was <5% of basal EGP in both groups and did not change significantly following DAPA in NGT or T2D. Renal glucose uptake (sum of tissue glucose uptake plus glucosuria) increased in both T2D and NGT following DAPA (P < 0.05 vs. placebo). The increase in renal glucose uptake was entirely explained by the increase in glucosuria. A single dose of DAPA significantly increased EGP, which primarily is explained by an increase in hepatic glucose production, establishing the existence of a novel renal-hepatic axis.

ARTICLE HIGHLIGHTS

Approach to the Hypoglycemic Patient

Hypoglycemia is commonly encountered in the emergency department. Patients can present with a myriad of symptoms and its presentation can mimic other more serious diagnoses. Despite the relative ease of its management, clinicians often miss the diagnosis or mismanage it even when discovered. Glucose is an important energy source for the brain and failing to recognize hypoglycemia or mismanaging it can lead to permanent neurologic disability or death. Although it is important to replenish glucose in a rapid fashion, it is equally important to discover and manage the underlying etiology to prevent further episodes of hypoglycemia.

Hormonal, Metabolic and Hemodynamic Adaptations to Glycosuria in Type 2 Diabetes Patients Treated with Sodium-Glucose Co-Transporter Inhibitors

BACKGROUND & INTRODUCTION

The advent of the sodium-glucose cotransporter-2 inhibitors [SGLT-2i] provides an additional tool to combat diabetes and complications. The use of SGLT-2i leads to effective and durable glycemic control with important reductions in body weight/fat and blood pressure. These agents may delay beta-cell deterioration and improve tissue insulin sensitivity, which might slow the progression of the disease.

METHODS & RESULTS

In response to glycosuria, a compensatory rise in endogenous glucose production, sustained by a decrease in plasma insulin with an increase in glucagon has been described. Other possible mediators have been implicated and preliminary findings suggest that a sympathoadrenal discharge and/or rapid elevation in circulating substrates (i.e., fatty acids) or some yet unidentified humoral factors may have a role in a renal-hepatic inter-organ relationship. A possible contribution of enhanced renal gluconeogenesis to glucose entry into the systemic circulation has not yet been ruled out. Additionally, tissue glucose utilization decreases, whereas adipose tissue lipolysis is stimulated and, there is a switch to lipid oxidation with the formation of ketone bodies; the risk for keto-acidosis may limit the use of SGLT-2i. These metabolic adaptations are part of a counter-regulatory response to avoid hypoglycemia and, as a result, limit the SGLT-2i therapeutic efficacy. Recent trials revealed important cardiovascular [CV] beneficial effects of SGLT-2i drugs when used in T2DM patients with CV disease. Although the underlying mechanisms are not fully understood, there appears to be "class effect". Changes in hemodynamics and electrolyte/body fluid distribution are likely involved, but there is no evidence for anti-atherosclerotic effects.

CONCLUSION

It is anticipated that, by providing durable diabetes control and reducing CV morbidity and mortality, the SGLT-2i class of drugs is destined to become a priority choice in diabetes management.

Effects of Late Gestational Fetal Exposure to Dexamethasone Administration on the Postnatal Hypothalamus-Pituitary-Adrenal Axis Response to Hypoglycemia in Pigs

BACKGROUND

Prenatal glucocorticoid administration alters the activity of the fetal hypothalamic-pituitary-adrenocortical axis (HPAA), and correspondingly the adenocorticotropic hormone (ACTH) and cortisol levels after birth. The dosages required for these effects are critically discussed. Activation of the HPAA is related to metabolic syndrome and diabetes mellitus. Hypoglycemia is the classic side effect of antidiabetic treatment. We hypothesized that a low dosage of dexamethasone in late pregnancy alters the HPAA response to hypoglycemia in pigs.

METHODS

12 pregnant sows were randomly assigned to two groups which received either a low-dose intramuscular injection (99th and 100th day of gestation) of dexamethasone (0.06 μg/kg body weight) or vehicle. Three months after birth, 18 dexamethasone-treated anaesthetized offspring and 12 control offspring underwent a 75 min hypoglycemic clamp (blood glucose below 4 mmol/L) procedure. Heart rate (HR), blood pressure, ACTH and cortisol levels and body weight (at birth and after three months) were recorded.

RESULTS

Dexamethasone-treated animals exhibited significantly elevated ACTH (139.9 ± 12.7 pg/mL) and cortisol (483.1 ± 30.3 nmol/L) levels during hypoglycemia as compared to the control group (41.7 ± 6.5 pg/mL and 257.9 ± 26.7 nmol/L, respectively), as well as an elevated HR (205.5 ± 5.7 bpm) and blood pressure (systolic: 128.6 ± 1.5, diastolic: 85.7 ± 0.7 mmHg) response as compared to the control group (153.2 ± 4.5 bpm; systolic: 118.6 ± 1.6, diastolic: 79.5 ± 1.4 mmHg, respectively; p < 0.001).

CONCLUSIONS

Low-dose prenatal administration of dexamethasone not only exerts effects on the HPAA (ACTH and cortisol concentration) and vital parameters (HR and diastolic blood pressure) under baseline conditions, but also on ACTH, HR and systolic blood pressure during hypoglycemia.

Renal glucose release during hypoglycemia is partly controlled by sympathetic nerves - a study in pigs with unilateral surgically denervated kidneys

Catecholamines are known to increase renal glucose release during hypoglycemia. The specific extent of the contribution of different sources of catecholamines, endocrine delivery via circulation or release from autonomous sympathetic renal nerves, though, is unknown. We tested the hypothesis that sympathetic renal innervation plays a major role in the regulation of renal gluconeogenesis. For this purpose, instrumented adolescent pigs had one kidney surgically denervated while the other kidney served as a control. A hypoglycemic clamp with arterial blood glucose below 2 mmol/L was maintained for 75 min. Arteriovenous blood glucose difference, inulin clearance, p-aminohippurate clearance, and sodium excretion were measured in intervals of 15 min separately for both kidneys. Blood glucose was lowered to 0.84 ± 0.33 mmol/L for 75 min. The side-dependent renal net glucose release (SGN) decreased significantly after the unilateral ablation of renal nerves. In the linear mixed model, renal denervation had a significant inhibitory effect on renal net glucose release (P = 0.036). The SGN of the ablated kidney decreased by 0.02 mmol/min and was equivalent to 43.3 ± 23.2% of the control (nonablated) kidney in the pigs. This allows the conclusion that renal glucose release is partly controlled by sympathetic nerves. This may be relevant in humans as well, and could explain the increased risk of severe hypoglycemia of patients with diabetes mellitus and autonomous neuropathy. The effects of denervation on renal glucose metabolism should be critically taken into account when considering renal denervation as a therapy in diabetic patients.

Insulin therapy and hypoglycaemia: the size of the problem

BACKGROUND AND METHODS

Hypoglycaemia is a fact of life for people with diabetes mellitus. Mild, asymptomatic episodes occur once or twice a week in insulin-treated diabetic subjects. Asymptomatic hypoglycaemia, including nocturnal hypoglycaemia, occurs in about 25% of diabetic subjects treated with insulin therapy. Mild hypoglycaemia, if recurrent, induces unawareness of hypoglycaemia and impairs glucose counterregulation, which in turn predisposes to severe hypoglycaemia. Even brief hypoglycaemia can cause profound dysfunction of the brain. Prolonged, severe hypoglycaemia can cause permanent neurological sequels. In addition, it is possible that hypoglycaemia may accelerate the vascular complications of diabetes by increasing platelet aggregation and/or fibrinogen formation. Finally, hypoglycaemia may be fatal. Hypoglycaemia induced by insulin as treatment of type 1 diabetes mellitus (T1 DM) is not the consequence of diabetes, but invariably of the non-physiological replacement of insulin.

RESULTS

A number of studies have demonstrated that by moving from non-physiological to more physiological models of insulin therapy, most of the hypoglycaemia problems may be overcome, the percentage of glycated hemoglobin (A1c) decreased, and the quality of life improved. Interestingly, in T1 DM with hypoglycaemia unawareness, prevention of hypoglycaemia reverses not only unawareness but also improves glucose counterregulation, primarily the responses of adrenaline.

CONCLUSIONS

In order to best prevent hypoglycaemia, insulin should preferably be given as continuous subcutaneous infusion via a minipump (the 'golden standard') or multiple daily insulin administrations with insulin analogues (basal insulin glargine, meal insulin rapid-acting insulin analogues) in T1 DM.

Role of human liver, kidney, and skeletal muscle in postprandial glucose homeostasis

Recent studies indicate a role for the kidney in postabsorptive glucose homeostasis. The present studies were undertaken to evaluate the role of the kidney in postprandial glucose homeostasis and to compare its contribution to that of liver and skeletal muscle. Accordingly, we used the double isotope technique along with forearm and renal balance measurements to assess systemic, renal, and hepatic glucose release as well as glucose uptake by kidney, skeletal muscle, and splanchnic tissues in 10 normal volunteers after ingestion of 75 g of glucose. We found that, during the 4.5-h postprandial period, 22 +/- 2 g (30 +/- 3% of the ingested glucose) were initially extracted by splanchnic tissues. Of the remaining 53 +/- 2 g that entered the systemic circulation, 19 +/- 3 g were calculated to have been taken up by skeletal muscle and 7.5 +/- 1.7 g by the kidney (26 +/- 3 and 10 +/- 2%, respectively, of the ingested glucose). Endogenous glucose release during the postprandial period (16 +/- 2 g), calculated as the difference between overall systemic glucose appearance and the appearance of ingested glucose in the systemic circulation, was suppressed 61 +/- 3%. Surprisingly, renal glucose release increased twofold (10.6 +/- 2.5 g) and accounted for ~60% of postprandial endogenous glucose release. Hepatic glucose release (6.7 +/- 2.2 g), the difference between endogenous and renal glucose release, was suppressed 82 +/- 6%. These results demonstrate a hitherto unappreciated contribution of the kidney to postprandial glucose homeostasis and indicate that postprandial suppression of hepatic glucose release is nearly twofold greater than had been calculated in previous studies (42 +/- 4%), which had assumed that there was no renal glucose release. We postulate that increases in postprandial renal glucose release may play a role in facilitating efficient liver glycogen repletion by permitting substantial suppression of hepatic glucose release.

Phosphoenolpyruvate carboxykinase is necessary for the integration of hepatic energy metabolism

We used an allelogenic Cre/loxP gene targeting strategy in mice to determine the role of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) in hepatic energy metabolism. Mice that lack this enzyme die within 3 days of birth, while mice with at least a 90% global reduction of PEPCK, or a liver-specific knockout of PEPCK, are viable. Surprisingly, in both cases these animals remain euglycemic after a 24-h fast. However, mice without hepatic PEPCK develop hepatic steatosis after fasting despite up-regulation of a variety of genes encoding free fatty acid-oxidizing enzymes. Also, marked alterations in the expression of hepatic genes involved in energy metabolism occur in the absence of any changes in plasma hormone concentrations. Given that a ninefold elevation of the hepatic malate concentration occurs in the liver-specific PEPCK knockout mice, we suggest that one or more intermediary metabolites may directly regulate expression of the affected genes. Thus, hepatic PEPCK may function more as an integrator of hepatic energy metabolism than as a determinant of gluconeogenesis.

Important role of the kidney in human carbohydrate metabolism

Recent studies using a combination of isotope and balance techniques have shown that, in the postabsorptive state, the human kidney contributes substantially to overall glucose production and consumption. The kidney may contribute as much as the liver to gluconeogenesis and play an important role in the counterregulation of hypoglycemia. Furthermore, increased renal glucose production may contribute to fasting hyperglycemia found in type I and type II diabetes mellitus. Finally, loss of renal tissue as a consumer of glucose could explain the insulin resistance of uremia. We hypothesize that the human kidney may play a more important role in human carbohydrate metabolism than previously appreciated.

Insulin regulation of renal glucose metabolism in humans

Eighteen healthy subjects had arterialized hand and renal veins catheterized after an overnight fast. Systemic and renal glucose and glycerol kinetics were measured with [6,6-2H2]glucose and [2-13C]glycerol before and after 180-min peripheral infusions of insulin at 0.125 (LO) or 0.25 (HI) mU. kg-1. min-1 with variable [6, 6-2H2]dextrose or saline (control). Renal plasma flow was determined by plasma p-aminohippurate clearance. Arterial insulin increased from 37 +/- 8 to 53 +/- 5 (LO) and to 102 +/- 10 pM (HI, P < 0.01) but not in control (35 +/- 8 pM). Arterial glucose did not change and averaged 5.2 +/- 0.1 (control), 4.7 +/- 0.2 (LO), and 5.1 +/- 0. 2 (HI) micromol/ml; renal vein glucose decreased from 4.8 +/- 0.2 to 4.5 +/- 0.2 micromol/ml (LO) and from 5.3 +/- 0.2 to 4.9 +/- 0.1 micromol/ml (HI) with insulin but not saline infusion (5.3 +/- 0.1 micromol/ml). Endogenous glucose production decreased from 9.9 +/- 0. 7 to 6.9 +/- 0.5 (LO) and to 5.7 +/- 0.5 (HI) micromol. kg-1. min-1; renal glucose production decreased from 2.5 +/- 0.6 to 1.5 +/- 0.5 (LO) and to 1.2 +/- 0.6 (HI) micromol. kg-1. min-1, whereas renal glucose utilization increased from 1.5 +/- 0.6 to 2.6 +/- 0.7 (LO) and to 2.9 +/- 0.7 (HI) micromol. kg-1. min-1 after insulin infusion (all P < 0.05 vs. baseline). Neither endogenous glucose production (10.0 +/- 0.4), renal glucose production (1.1 +/- 0.4), nor renal glucose utilization (0.8 +/- 0.4) changed in the control group. During insulin infusion, systemic gluconeogenesis from glycerol decreased from 0.67 +/- 0.05 to 0.18 +/- 0.02 (LO) and from 0.60 +/- 0.04 to 0.20 +/- 0.02 (HI) micromol. kg-1. min-1 (P < 0.01), and renal gluconeogenesis from glycerol decreased from 0.10 +/- 0.02 to 0.02 +/- 0.02 (LO) and from 0.15 +/- 0.03 to 0.09 +/- 0.03 (HI) micromol. kg-1. min-1 (P < 0.05). In contrast, during saline infusion, systemic (0.66 +/- 0.03 vs. 0.82 +/- 0.05 micromol. kg-1. min-1) and renal gluconeogenesis from glycerol (0.11 +/- 0.02 vs. 0. 41 +/- 0.04 micromol. kg-1. min-1) increased (P < 0.05 vs. baseline). We conclude that glucose production and utilization by the kidney are important insulin-responsive components of glucose metabolism in humans.

Effects of beta-adrenergic blockade on hepatic and renal glucose production during hypoglycemia in conscious dogs

To investigate the role of beta-adrenergic mechanisms in the counterregulatory response of the liver and kidney to hypoglycemia, we studied 10 dogs before and after a 2-h constant infusion of insulin (4 mU. kg-1. min-1) either without (n = 4) or with (8 micrograms/min, n = 6) propranolol and variable dextrose to maintain hypoglycemia, 7 days after surgical placement of sampling catheters in left renal and hepatic veins and femoral artery. Systemic glucose appearance (Ra) and endogenous (EGP), hepatic (HGP), and renal (RGP) glucose production were measured by a combination of arteriovenous difference and peripheral infusion of [6-3H]glucose, renal blood flow with a flow probe, and hepatic plasma flow by indocyanine green clearance. Without beta-adrenergic blockade, arterial glucose decreased from 5.12 +/- 0.02 to 2.53 +/- 0.07 mmol/l, glucose Ra increased from 17.8 +/- 0.7 to 30.5 +/- 2.5 (P < 0.01) when EGP was 22.2 +/- 0.5, HGP from 13.5 +/- 1.1 to 19.3 +/- 1.3, and RGP from 2. 4 +/- 1.0 to 8.6 +/- 0.9 micromol. kg-1. min-1 (all P < 0.05). When propranolol was infused, glucose decreased from 5.97 +/- 0.02 to 2. 71 +/- 0.03 mmol/l, glucose Ra increased from 16.3 +/- 1.0 to 25.1 +/- 1.6 when EGP was 9.9 +/- 0.4, HGP decreased from 14.4 +/- 0.7 to 10.4 +/- 0.6, and RGP decreased from 3.8 +/- 1.3 to 1.1 +/- 0.8 micromol. kg-1. min-1 (all P < 0.05). Our data indicate that beta-adrenergic blockade impairs glucose recovery during sustained hypoglycemia, in part, by preventing the simultaneous compensatory increase in HGP and RGP.