Edward G. Flickinger

Insulin receptor kinase in human skeletal muscle from obese subjects with and without noninsulin dependent diabetes.

We have studied the structure and function of the insulin receptors in obese patients with and without noninsulin dependent diabetes mellitus (NIDDM) and in nonobese controls using partially purified receptors from muscle biopsies. Insulin binding was decreased in obesity due to reduced number of binding sites but no differences were observed in insulin binding between obese subjects with or without NIDDM. The structural characteristics of the receptors, as determined by affinity labeling methods and electrophoretic mobility of the beta-subunit, were not altered in obese or NIDDM compared to normal weight subjects. Furthermore, the ability of insulin to stimulate the autophosphorylation of the beta-subunit and the phosphoamino acid composition of the phosphorylated receptor were the same in all groups. However, insulin receptor kinase activity was decreased in obesity using Glu4:Tyr1 as exogenous phosphoacceptor without any appreciable additional defect when obesity was associated with NIDDM. Thus, our data are supportive of the hypothesis that in muscle of obese humans, insulin resistance is partially due to decreased insulin receptors and insulin receptor kinase activity. In NIDDM the defect(s) in muscle is probably distal to the insulin receptor kinase.

An in vitro human muscle preparation suitable for metabolic studies: decreased insulin stimulation of glucose transport in muscle from morbidly obese and diabetic subjects

We have developed an in vitro muscle preparation suitable for metabolic studies with human muscle tissue and have investigated the effects of obesity and non-insulin-dependent diabetes mellitus (NIDDM) on glucose transport. Transport of 3-O-methylglucose and 2-deoxyglucose was stimulated approximately twofold by insulin in muscle from normal nonobese subjects and stimulation occurred in the normal physiological range of insulin concentrations. In contrast to insulin stimulation of 3-O-methylglucose and 2-deoxyglucose transport in muscle from normal, nonobese subjects, tissue from morbidly obese subjects, with or without NIDDM, were not responsive to insulin. Maximal 3-O-methylglucose transport was lower in muscle of obese than nonobese subjects. Morbidly obese patients, with or without NIDDM, have a severe state of insulin resistance in glucose transport. The novel in vitro human skeletal muscle preparation herein described should be useful in investigating the mechanism of this insulin resistance.

Insulin-like growth factor I binding in hepatocytes from human liver, human hepatoma, and normal, regenerating, and fetal rat liver.

Insulin-like growth factor-I (IGF-I) in human hepatoma cells (HEP-G2) has, in addition to its effect on cell growth, short-term metabolic effects acting through its own receptor. We have demonstrated that normal human hepatocytes, compared with HEP-G2 cells, have virtually no IGF-I binding sites. Because the rate of growth is the major difference between the hepatoma and the normal liver, we asked if normal liver might express IGF-I binding sites under physiologic growth conditions. Indeed, whereas adult rat hepatocytes have low IGF-I binding sites similar to those in human liver, hepatocytes from regenerating liver after 3 d subtotal hepatectomy have an approximately sixfold increase (P less than 0.005) and those from fetal rat liver a approximately 12-fold increase (P less than 0.005), to levels comparable to those in the HEP-G2 cells. The specificity of 125I IGF-I binding to its receptor was demonstrated by competition studies with monoclonal antibodies directed toward the IGF-I and the insulin receptors, with unlabeled IGF-I and insulin and by affinity labeling experiments. Thus, if IGF-I has any short-term metabolic functions in the adult human liver, it is not through interaction with its own receptor. Autocrine regulation by IGF-I of liver growth appears possible since IGF-I binding sites are expressed under pathological and physiological conditions of growth. The mechanism that couples these two phenomena remains to be elucidated.

Studies on the mechanism of insulin resistance in the liver from humans with noninsulin-dependent diabetes. Insulin action and binding in isolated hepatocytes, insulin receptor structure, and kinase activity.

We have developed a method to isolate insulin-responsive human hepatocytes from an intraoperative liver biopsy to study insulin action and resistance in man. Hepatocytes from obese patients with noninsulin-dependent diabetes were resistant to maximal insulin concentration, and those from obese controls to submaximal insulin concentration in comparison to nonobese controls. Insulin binding per cell number was similar in all groups. However, insulin binding per surface area was decreased in the two obese groups because their hepatocytes were larger. In addition, the pool of detergent-extractable receptor was further decreased in diabetics. Insulin receptors in all groups were unaltered as determined by affinity-labeling methods. However, insulin-stimulated insulin receptor kinase activity was decreased in diabetics. Thus, in obesity, decreased surface binding could explain resistance to submaximal insulin concentrations. In diabetes, diminished insulin-stimulated protein kinase activity and decreased intracellular pool of receptors could provide an explanation for postinsulin-binding defect(s) of insulin action in human liver.

Long-term studies of mental health after the greenville gastric bypass operation for morbid obesity

From February 1, 1980, to May 1, 1989, 462 patients underwent the Greenville gastric bypass at the East Carolina University School of Medicine. The operation effectively maintained satisfactory weight loss after 9 years (mean weight preoperatively, 293 lbs; at 24 months, 179 lbs; at 96 months, 194 lbs). The gastric bypass favorably affected non-insulin-dependent diabetes, hypertension, and physical and role functioning. In the most recent 157 patients, our studies were extended to study the effects of the gastric bypass on mental health. The significant improvements in mental health indices that were observed 6 and 12 months after surgery eroded by the end of 2 years. This return of the mental health indices to the preoperative status, plus the late occurrence of 3 suicides and 2 deaths from alcohol abuse among the total 462 patients, suggest that long-term follow-up and continued emotional support are essential ingredients for successful bariatric surgery.

IGF-I–Stimulated Glucose Transport in Human Skeletal Muscle and IGF-I Resistance in Obesity and NIDDM

Based on the observation that insulinlike growth factor I (IGF-I) can stimulate glucose utilization in nondiabetic subjects and that the action of the IGF-I receptor is normal in the skeletal muscle of patients with noninsulin-dependent diabetes mellitus (NIDDM), it seems possible that IGF-I might provide an effective acute treatment for the hyperglycemia of NIDDM. Using our recently developed in vitro human muscle preparation, we investigated the hypothesis that IGF-I might be an effective alternative to insulin in stimulating glucose transport in diabetic muscle. Abdominal muscle samples from nonobese nondiabetic, obese nondiabetic, and obese NIDDM patients were obtained during elective abdominal surgery. Plasma levels of IGF-I in diabetic patients were lower than those in either of the nondiabetic groups. Binding studies with wheat-germ–agglutinin–chromatography–purified receptors demonstrated the presence of IGF-I receptors in human muscle, with IGF-I binding being ∼24% that of insulin. There was no change in IGF-I binding in muscle from obese or diabetic subjects, and the structural characteristics of the IGF-I receptor were not altered, as determined by electrophoretic mobility. IGF-I stimulated glucose transport approximately twofold in incubated muscle from control subjects, but there was no IGF-I stimulation of transport in muscle from obese subjects with or without NIDDM. These results confirm a previous report that human muscle contains receptors for IGF-I and demonstrate for the first time that IGF-I can stimulate glucose transport in human muscle. However, muscle from obese subjects with or without NIDDM is resistant to the action of IGF-I.

The bypassed stomach

Retrograde duodenogastroscopy solves the problem of postoperative evaluation of the gastric bypass patient. The stomach may be bypassed to treat morbid obesity, but it no longer need be inaccessible. Endoscopic gastritis is rare in the proximal gastric pouch but common in the distal gastric segment and may be related to the presence of bile. Although the gastric mucosa is histologically normal in half of the gastric bypass patients, acute and chronic gastritis, regenerative changes, and intestinal metaplasia may develop in either or both segments. The causes and implications of these endoscopic and histologic findings are unknown.

Insulin-Receptor Kinase Activity of Adipose Tissue From Morbidly Obese Humans With and Without NIDDM

We have determined glucose transport, insulin binding, and insulin-receptor kinase activity in adipose tissue from morbidly obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM). The insulin sensitivity and responsiveness of glucose transport in freshly isolated adipocytes were significantly reduced in NIDDM subjects compared with nondiabetics. This was due in part to decreased insulin binding in adipocytes. Reduced specific 125I-labeled insulin binding was also observed in crude detergent extracts and partially purified insulin receptors from adipose tissue. In addition, the basal and insulin-stimulated tyrosine-specific protein kinase activity per milligram of protein was significantly decreased in NIDDM patients compared with nondiabetics. The differences between maximally insulin-stimulated and basal kinase activities expressed by insulin-binding activity were also significantly reduced in NIDDM subjects. We conclude that insulin resistance in morbidly obese patients with NIDDM is due to both insulin-binding and postbinding defects. One of the postbinding defects in NIDDM appears to be impaired insulin-receptor kinase activity of fat tissue.

Intraoperative video panendoscopy for diagnosing sites of chronic intestinal bleeding

Intraoperative video panendoscopy was performed in 14 patients with chronic, recurrent gastrointestinal bleeding. All of the study patients had undergone extensive and expensive diagnostic testing including multiple radiographic contrast studies of the gastrointestinal tract, upper and lower endoscopy, nuclear bleeding scans, and selective mesenteric angiography without definition of the bleeding source. Intraoperative video panendoscopy, employing a segmental advance and look technique, allowed visualization and transillumination of the entire gut and identified mucosal disease in 13 patients (93 percent). Angiodysplasia of the colon and small intestine was the most common pathologic finding. Intraoperative video panendoscopy significantly influenced the operation performed in 13 patients (93 percent). Postoperative complications were minimal, with none being directly attributable to intraoperative video panendoscopy. Bleeding was totally controlled in 10 patients (71 percent) during a mean follow-up period of 25 months. Intraoperative video panendoscopy is a valuable technique for assisting in the management of the patient with recurrent gastrointestinal bleeding.

Long-term effect of insulin on glucose transport and insulin binding in cultured adipocytes from normal and obese humans with and without non-insulin-dependent diabetes.

We have tested the hypothesis that in vitro exposure of insulin-resistant adipocytes with insulin results in improved insulin action. A primary culture system of adipocytes from obese subjects with or without non-insulin-dependent diabetes mellitus (NIDDM) and nonobese control subjects has been developed. The adipocytes when cultured in serum-free medium do not lose their original characteristics in regard to insulin binding and glucose transport. The adipocytes from three groups were incubated with insulin (0, 10(-10) M, and 10(-7) M) for 24 h at 37 degrees C, receptor-bound insulin was dissociated, and basal and insulin (1 X 10(-11)-10(-7) M)-stimulated glucose transport and 125I-insulin binding were determined. The 24-h insulin exposure of adipocytes from control subjects decreased basal and insulin-stimulated glucose transport. The effects of 1 X 10(-7) M insulin were more pronounced than 1 X 10(-10) M insulin. Similarly, insulin exposure decreased insulin sensitivity and responsiveness of cultured adipocytes from obese and NIDDM patients. The insulin-induced reduction in insulin sensitivity and responsiveness for glucose transport in three groups were due to alterations at insulin binding and postbinding levels. In conclusion, insulin induces insulin resistance in control adipocytes and further worsens the insulin resistance of adipocytes from obese and NIDDM subjects. For insulin to improve the insulin resistance of adipocytes from NIDDM patients, either more prolonged in vitro insulin exposure and/or other hormonal factors might be required.