Defective glucose utilization in patients with functioning beta-cell tumors persists after tumor excision

Dysglycemia With Impaired Insulin Secretion After Resection of a High-Molecular-Weight IGF-II-Producing Tumor

Analysis of insulin and related glucoregulatory hormone secretion following high-molecular-weight insulin-like growth factor II (HMW-IGF-II)-releasing tumor excision has never been reported. In a man with chronic hypoglycemia-plasma glucose (PG), 2.1 mmol/L with undetectable serum insulin, less than 7.2 pmol/L on admission-the cause of the hypoglycemia was HMW-IGF-II in the serum secreted by an intrathoracic benign pleural solitary fibrous tumor (size: 15 × 17 × 12 cm). Removal of the tumor nullified serum HMW-IGF-II and hypoglycemia. Postoperative glucose metabolism was evaluated day 272 by 75 g oral glucose tolerance test (OGTT) and on days 5, 202, and 990 by fasted sampling. Glycated hemoglobin A1c (HbA1c) was 37 to 41 mmol/mol, fasting PG was 5.3 to 5.4 mmol/L, and 2-hour PG at 75 g OGTT was 6.9 mmol/L, indicating that he was at the prediabetes stage. Homeostasis Model Assessment 2 of Insulin Resistance and Homeostasis Model Assessment 2 of β-Cell levels were within the normal range but the Stumvoll first phase was lowered. Insulin sensitivity and secretion were compared to age-, sex-, and body mass index-matched controls with normal glucose metabolism. Long-term HMW-IGF-II exposure of pancreatic islet β cells caused the functional impairment, that is, suppressed glucose-stimulated insulin secretion (GSIS), leading to nondiabetic hyperglycemia. This fact suggests long-term HMW-IGF-II exposure of the islet β cell specifically dampens GSIS.

Concurrent insulinoma and impaired glucose tolerance suspected as owing to obesity

An obese 68-year-old woman was admitted for examination of fasting hypoglycaemia. A prolonged 18 h fast reduced her plasma glucose without suppressing insulin secretion, while plasma β-hydroxybutyrate levels were suppressed. Despite the prolonged fast, the glucose response to glucagon was increased by 25 mg/dL (1.39 mM) glucose, which is compatible with insulinoma. A 75 g oral glucose tolerance test (75 g OGTT) showed impaired glucose tolerance. An abdominal CT scan revealed a mass lesion in the uncinate process of the pancreas, a finding consistent with the results of angiography and selective artery calcium injection test. The patient then underwent a pancreaticoduodenectomy; the pancreatic mass was histologically diagnosed as benign insulinoma. After surgery, a prolonged 24 h fast caused no hypoglycaemia and the glucose tolerance capacity in 75 g OGTT improved. Eight months after surgery, the patient's body weight had reduced by 10 kg. This is therefore a case of concurrent insulinoma and impaired glucose tolerance.

Surgical removal of insulinoma restores glucose recovery from hypoglycaemia but does not normalize insulin action

In the present study we have evaluated the effects of chronic hyperinsulinaemia secondary to insulinoma, on insulin sensitivity and on counter-regulatory responses to hypoglycaemia. We studied six patients (M/F = 3/3; age = 40 +/- years), before and 6-9 months after surgical ablation of the neoplasia, by means of an euglycaemic-hyperinsulinaemic clamp (1 mU kg-1 min-1). Seven normal subjects (M/F = 4/3; age = 38 +/- 6 years) underwent the same experimental study as the control subjects. In insulinoma patients after 100 min of the euglycaemic-hyperinsulinaemic clamp, glycaemia was allowed to drop to a minimum value of 1.9 mmol L-1, and recovery evaluated after interrupting insulin infusion. During the entire study, 3-3H-glucose was infused to determine hepatic glucose production and glucose utilization. Surgical removal of the pancreatic adenoma was followed by a reduction in body weight (BMI = 25.7 +/- 1.9 vs. 23.0 +/- 1.6 kg m-2; P < 0.05), normalization of fasting plasma levels of glucose (2.94 +/- 0.16 vs. 4.83 +/- 0.11 mmol L-1), insulin (162 +/- 24 vs. 48 +/- 12 pmol L-1) and of basal hepatic glucose production (7.6 +/- 0.7 vs. 12.2 +/- 1.11 mumol kg-1 min-1). Before the operation, insulin-mediated glucose disposal was significantly lower than in the controls (30.8 +/- 3.1 vs. 49.1 +/- 3.1 mumol kg-1 min-1). Six to nine months after surgical removal of the adenoma, glucose utilization was unchanged (30.5 +/- 3.3 mumol kg-1 min-1) and still significantly lower than in controls (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin resistance in a case of coexisting insulinoma and type 2 diabetes

Hyperinsulinaemia due to pancreatic beta-cell tumours has been reported to lead to insulin resistance. A possible contribution of dysregulated insulin receptors to the impaired insulin action of insulinoma has not been explored. Therefore, we studied insulin receptor function in a patient with insulin-producing adenoma. This patient was rather unusual in that she was found to have a very large tumour and strikingly high circulating levels of insulin. In addition, her previous history included type 2 (non-insulin-dependent) diabetes mellitus. We confirmed decreased glucose utilization and metabolic clearance rate for glucose in presence of marked endogenous hyperinsulinaemia (approximately 2000 pM). 125I-labelled insulin binding capacity and receptor affinity for insulin were normal in her intact blood monocytes and erythrocytes. Insulin receptors were purified from the patient's tumour as well as from the pancreas, omental fat, liver and erythrocytes. All parameters of insulin binding to these receptors were normal. Thus, no evidence of receptor downregulation due to the marked hyperinsulinaemia was found. As expected, addition of insulin in vitro stimulated receptor autophosphorylation and tyrosine kinase activity of the receptors isolated from the liver, fat and erythrocytes. However, the basal tyrosine kinase activities of the tumour and pancreatic receptors were very high when isolated and further addition of insulin in vitro increased the protein kinase activity only slightly.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a euglycaemic clamp procedure as a diagnostic test in insulinoma patients

In 15 patients with insulinoma, six patients after successful removal of this tumour, two patients with previous pancreas resection because of hypoglycaemia elsewhere, and 10 control subjects, the diagnostic usefulness of euglycaemic clamp procedures (without exogenous insulin) was assessed in comparison with prolonged starvation. Only insulinoma patients developed sustained hypoglycaemia (less than or equal to 2.3 mmol l-1) within 2-44 h without caloric intake, because of inappropriately elevated immunoreactive insulin (IR-insulin) concentrations. IR-proinsulin values were elevated in most (7 out of 10), but not in all insulinoma patients. The steady-state glucose infusion rate necessary to maintain a stable plasma glucose concentration of 4.4-5.0 mmol l-1 was significantly (P less than or equal to 0.001) higher in insulinoma patients (2.5 +/- 0.6 mg kg-1 min-1) than in pancreas resected patients (0.6 +/- 0.2 mg kg-1 min-1), or in control subjects (0.5 +/- 0.1 mg kg-1 min-1). Due to a considerable degree of overlap, sensitivity (0.44) and specificity (0.95) were too low for such a procedure to qualify as a diagnostic test. There was no correlation of glucose infusion rates to IR-insulin values (r = 0.024, P = 0.461). One reason for this was the development of insulin resistance in some, but not in all insulinoma patients. When, in analogy to insulin/glucose ratios, a diagnostic index was derived by multiplying the steady state glucose infusion rate by the steady state IR-insulin concentration, the diagnostic accuracy was greatly increased (sensitivity and specificity 0.94, respectively), but still lower than that of 'amended' insulin/glucose ratios in fasting plasma or at the time of discontinuation of prolonged fasts (1.00). Somatostatin infusions inhibited insulin secretion (IR-C-peptide plasma concentrations) by 52-88% in subjects without insulinoma and in those insulinoma patients whose tumour cells ultrastructurally contained plenty of normal secretory granules, and to a lesser degree when only abnormal or virtually no secretory granules were present, i.e. in more de-differentiated tumours. In contrast to this significant (P = 0.036) association, malignancy, i.e. the presence of metastases, could not be predicted from whether or not insulin secretion was resistant to the inhibitory action of somatostatin. In conclusion, euglycaemic clamp experiments are less reliable for detecting or excluding a functioning insulinoma than the relation of glucose and insulin values during starvation. The inhibition of insulin secretion by somatostatin depends on the presence of normal beta-granules, and does not distinguish adenomas from carcinomas.