Glucagon as a determinant of fibrinolytic activity in men with different stages of glucose tolerance: impact of glucagon on fibrinolysis

A Glucagonoma Presenting as Cerebral Vein Thrombosis and Diabetes

Glucagonomas are rare pancreatic neuroendocrine tumors (pNETs), malignant in 80% of cases, thus highlighting the importance of early diagnosis and treatment. Primary manifestations are diabetes, dermatosis, depression, weight loss, and deep vein thrombosis. Unlike other pNETs, glucagonomas are associated with a higher incidence of thromboembolic events, often resulting in death. We present the case of a glucagonoma patient whose primary manifestation was cerebral sinus venous thrombosis (CS-VT). Early diagnosis enabled curative resection. The purpose of this paper is to review the underlying mechanisms associated with increased coagulopathy in glucagonomas.

Impaired Suppression of Glucagon in Obese Subjects Parallels Decline in Insulin Sensitivity and Beta-Cell Function

AIM

To examine the relationship between plasma glucagon levels and insulin sensitivity and insulin secretion in obese subjects.

METHODS

Suppression of plasma glucagon was examined in 275 obese Hispanic Americans with varying glucose tolerance. All subjects received a 2-hour oral glucose tolerance test (OGTT) and a subset (n = 90) had euglycemic hyperinsulinemic clamp. During OGTT, we quantitated suppression of plasma glucagon concentration, Matsuda index of insulin sensitivity, and insulin secretion/insulin resistance (disposition) index. Plasma glucagon suppression was compared between quartiles of insulin sensitivity and beta-cell function.

RESULTS

Fasting plasma glucagon levels were similar in obese subjects with normal glucose tolerance (NGT), prediabetes, and type 2 diabetes (T2D), but the fasting glucagon/insulin ratio decreased progressively from NGT to prediabetes to T2D (9.28 ± 0.66 vs 6.84 ± 0.44 vs 5.84 ± 0.43; P < 0.001). Fasting and 2-hour plasma glucagon levels during OGTT progressively increased and correlated positively with severity of insulin resistance (both Matsuda index and euglycemic hyperinsulinemic clamp). The fasting glucagon/insulin ratio declined with worsening insulin sensitivity and beta-cell function, and correlated with whole-body insulin sensitivity (Matsuda index, r = 0.81; P < 0.001) and beta-cell function (r = 0.35; P < 0.001). The glucagon/insulin ratio also correlated and with beta-cell function during OGTT at 60 and 120 minutes (r = -0.47; P < 0.001 and r = -0.32; P < 0.001).

CONCLUSION

Insulin-mediated suppression of glucagon secretion in obese subjects is impaired with increasing severity of glucose intolerance and parallels the severity of insulin resistance and beta-cell dysfunction.

Comparative effects of acute hypoglycemia and hyperglycemia on pro-atherothrombotic biomarkers and endothelial function in non-diabetic humans

BACKGROUND

The comparative effects of acute moderate hyperglycemia and hypoglycemia on in vivo endothelial function together with pro-inflammatory and pro-atherothrombotic responses in healthy individuals have not been determined.

METHODS

To investigate this question, 45 healthy subjects were compared during glucose clamp studies consisting of euinsulinemic hyperglycemia and hyperinsulinemic hyperglycemia (plasma glucose 11.1mmol/L, both with pancreatic clamps) and hyperinsulinemic euglycemia and hyperinsulinemic hypoglycemia (plasma glucose 5.1 and 2.9mmol/L, respectively). Two-dimensional Doppler ultrasound was used to determine brachial artery endothelial function.

RESULTS

Insulin levels during euinsulinemia hyperglycemia were 194±23 and (850±49-988±114) pmol/L during all hyperinsulinemic protocols. Responses of VCAM-1, ICAM-1, E-selectin, P-selectin, PAI-1, and IL-6 were increased (p<0.05-0.0001) during euinsulinemic hyperglycemia or hypoglycemia as compared to hyperinsulinemic euglycemia or hyperinsulinemic hyperglycemia. PAI-1 was increased (p<0.04) during hypoglycemia as compared to euinsulinemic hyperglycemia, and TNF-α responses were also increased during hypoglycemia as compared to hyperinsulinemic euglycemia or hyperinsulinemic hyperglycemia (p<0.05). In vivo endothelial function was similarly blunted by acute moderate hyperglycemia or hypoglycemia.

CONCLUSION

In summary, acute moderate hypoglycemia and euinsulinemic hyperglycemia can result in similar endothelial dysfunction and pro-atherothrombotic responses. Fibrinolytic balance was reduced by a greater extent by hypoglycemia as compared to moderate hyperglycemia. Acutely, hyperinsulinemia can prevent the acute pro-atherothrombotic and pro-inflammatory effects of moderate hyperglycemia but not hypoglycemia.

Acute effects of hyperinsulinemia and hyperglycemia on vascular inflammatory biomarkers and endothelial function in overweight and obese humans

We investigated the separate and combined effects of hyperglycemia and hyperinsulinemia on markers of endothelial function, proinflammatory and proatherothrombotic responses in overweight/obese nondiabetic humans. Twenty-two individuals (13 F/9 M, BMI 30.1 ± 4.1 kg/m(2)) were studied during four randomized, single-blind protocols. The pancreatic clamp technique was combined with 4-h glucose clamps consisting of either 1) euinsulinemia-euglycemia, 2) euinsulinemia-hyperglycemia, 3) hyperinsulinemia-hyperglycemia, or 4) hyperinsulinemia-euglycemia. Insulin levels were higher (998 ± 66 vs. 194 ± 22 pmol/l) during hyperinsulinemia compared with euinsulinemia. Glucose levels were 11.1 mmol/l during hyperinsulinemia compared with 5.1 ± 0.1 mmol/l during euglycemia. VCAM, ICAM, P-selectin, E-selectin, IL-6, adiponectin, and PAI-1 responses were all increased (P < 0.01-0.0001), and endothelial function was decreased (P < 0.0005) during euinsulinemia-hyperglycemia compared with other protocols. Hyperinsulinemia in the presence of hyperglycemia prevented the increase in proinflammatory and proatherothrombotic markers while also normalizing vascular endothelial function. We conclude that 4 h of moderate hyperglycemia can result in increases of proinflammatory markers (ICAM, VCAM, IL-6, E-selectin), platelet activation (P-selectin), reduced fibrinolytic balance (increased PAI-1), and disordered endothelial function in a group of obese and overweight individuals. Hyperinsulinemia prevents the actions of moderate hyperglycemia to reduce endothelial function and increase proinflammatory and proatherothrombotic markers.

Effect of linagliptin compared with glimepiride on postprandial glucose metabolism, islet cell function and vascular function parameters in patients with type 2 diabetes mellitus receiving ongoing metformin treatment

BACKGROUND

The goal of this study was to investigate the effects of linagliptin compared with glimepiride on alpha and beta cell function and several vascular biomarkers after a standardized test meal.

METHODS

Thirty-nine patients on metformin alone (age, 64 ± 7 years; duration of type 2 diabetes mellitus, 7.8 ± 4.5years, 27 male, 12 female; HbA1c , 57.2 ± 6.9 mmol/mol; mean ± SD) were randomized to receive linagliptin 5 mg (n = 19) or glimepiride (n = 20) for a study duration of 12 weeks. Glucagon-like peptide 1, blood glucose, insulin, intact proinsulin, glucagon, plasminogen activator inhibitor-1 (PAI-1), cyclic guanosinmonophosphat and asymetric dimethylarginin levels were measured in the fasting state and postprandial at 30-min intervals for a duration of 5 h. The areas under the curve (AUC0-300 min ) were calculated for group comparisons.

RESULTS

HbA1c , fasting and postprandial glucose levels improved in both groups. An increase in postprandial insulin (22595 ± 5984 pmol/L*min), postprandial intact proinsulin (1359 ± 658 pmol/L*min), postprandial glucagon (317 ± 1136 pg/mL*min) and postprandial PAI-1 levels (863 ± 467 ng/mL*min) could be observed during treatment with glimepiride, whereas treatment with linagliptin was associated with a decrease in postprandial insulin (-8007 ± 4204 pmol/L*min), intact proinsulin (-1771 ± 426 pmol/L*min), postprandial glucagon (-1597 ± 1831 pg/mL*min) and PAI-1 levels (-410 ± 276 ng/mL*min).

CONCLUSIONS

Despite an improvement in blood glucose control in both groups, linagliptin reduced postprandial insulin, proinsulin, glucagon and PAI-levels. These results indicate an improvement in postprandial alpha and beta cell function, as well as a reduced postprandial vascular risk profile during treatment with linagliptin.

Hyperglycemia enhances coagulation and reduces neutrophil degranulation, whereas hyperinsulinemia inhibits fibrinolysis during human endotoxemia

Type 2 diabetes is associated with altered immune and hemostatic responses. We investigated the selective effects of hyperglycemia and hyperinsulinemia on innate immune, coagulation, and fibrinolytic responses during systemic inflammation. Twenty-four healthy humans were studied for 8 hours during clamp experiments in which either plasma glucose, insulin, both, or none was increased, depending on randomization. Target plasma concentrations were 5 versus 12 mM for glucose, and 100 versus 400 pmol/L for insulin. After 3 hours, 4 ng/kg Escherichia coli endotoxin was injected intravenously to induce a systemic inflammatory and procoagulant response. Endotoxin administration induced cytokine release, activation of neutrophils, endothelium and coagulation, and inhibition of fibrinolysis. Hyperglycemia reduced neutrophil degranulation (plasma elastase levels, P < .001) and exaggerated coagulation (plasma concentrations of thrombin-antithrombin complexes and soluble tissue factor, both P < .001). Hyperinsulinemia attenuated fibrinolytic activity due to elevated plasminogen activator-inhibitor-1 levels (P < .001). Endothelial cell activation markers and cytokine concentrations did not differ between clamps. We conclude that in humans with systemic inflammation induced by intravenous endotoxin administration hyperglycemia impairs neutrophil degranulation and potentiates coagulation, whereas hyperinsulinemia inhibits fibrinolysis. These data suggest that type 2 diabetes patients may be especially vulnerable to prothrombotic events during inflammatory states.