Robert P Hoffman

Von Willebrand Factor and Von Willebrand Factor-Cleaving Metalloprotease Activity in Escherichia coli O157:H7-Associated Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) usually occurs after infection with Shiga toxin-producing bacteria. Thrombotic thrombocytopenic purpura, a disorder with similar clinical manifestations, is associated with deficient activity of a circulating metalloprotease that cleaves von Willebrand factor at the Tyr842-Met843 peptide bond in a shear stress-dependent manner. We analyzed von Willebrand factor-cleaving metalloprotease activity and the status of von Willebrand factor in 16 children who developed HUS after Escherichia coli O157:H7 infection and in 29 infected children who did not develop this complication. Von Willebrand factor-cleaving metalloprotease activity was normal in all subjects, but von Willebrand factor size was decreased in the plasma of each of 16 patients with HUS. The decrease in circulating von Willebrand factor size correlated with the severity of thrombocytopenia and was proportional to an increase in von Willebrand factor proteolytic fragments in plasma. Immunohistochemical studies of the kidneys in four additional patients who died of HUS demonstrated glomerular thrombi in three patients, and arterial and arteriolar thrombi in one patient. The glomerular thrombi contained fibrin but little or no von Willebrand factor. A decrease in large von Willebrand factor multimers, presumably caused by enhanced proteolysis from abnormal shear stress in the microcirculation, is common in HUS.

Dissociation of sympathoexcitatory and vasodilator actions of modestly elevated plasma insulin levels

Objective: To determine sympathetic and vascular responses to modest increases in plasma insulin level. Background: Most studies of sympathetic and vascular actions of insulin have evaluated high plasma insulin levels (>50µU/ml). Those levels increase sympathetic nerve activity but also cause vasodilation. Hypertension and obesity are associated with only modestly elevated fasting insulin levels. Methods: We investigated the effects of a 90min low-dose hyperinsulinemic euglycemic clamp on muscle sympathetic nerve activity (microneurography), forearm vascular resistance (plethysmography), heart rate, blood pressure and central venous pressure. Insulin and vehicle sessions were performed in 12 normal subjects. Results: Plasma insulin levels were elevated from values of 10±2 in the fasting state to 25±3µU/ml during insulin infusion. Insulin levels did not change during vehicle administration. Muscle sympathetic nerve activity increased from 16±2 to 25±3 bursts/min during the insulin session and did not change during vehicle administration. In contrast to muscle sympathetic nerve activity, forearm vascular resistance did not change during insulin administration (from 50±3 to 51±4U). Forearm vascular resistance tended to fall during vehicle administration (from 45±2 to 37 ±3 U). There were no changes in heart rate, blood pressure and central venous pressure that could be attributed to insulin. Conclusion: Modest elevations of plasma insulin levels produce sympathetic activation similar to that caused by high levels, but, in contrast to high levels, modest elevations in plasma insulin level do not decrease forearm vascular resistance. The present findings suggest a dissociation between sympathoexcitatory and vascular actions of insulin at low plasma levels.

Hypoglycemia increases muscle sympathetic nerve activity in IDDM and control subjects

OBJECTIVE The relationship between the increase in adrenomedullary catecholamine secretion and the sympathetic response to hypoglycemia is not well understood in humans. To explore this relationship more closely, we directly recorded muscle sympathetic nerve activity (MSNA) in control subjects and in insulin-dependent diabetes mellitus (IDDM) subjects without clinically evident diabetic complications. RESEARCH DESIGN AND METHODS Twelve IDDM subjects (22.5 ± 3.9 years of age, diabetes duration of 9.8 ± 8.3 years) and 12 age-matched control subjects were studied. MSNA was measured during insulin infusion (720 pM·m–2 ·min–1) with 30-min periods of 1) euglycemia, 2) hypoglycemia (target plasma glucose, 2.8 mM), and 3) recovery. The effect of increased insulin dose (1,440 pM· m–2 · min–1) was studied in six subjects in each group, and the effect of prolonged hypoglycemia (1 h) was studied in five IDDM subjects and four control subjects. RESULTS MSNA levels increased in IDDM and control subjects, 31 ± 8 and 29 ± 6%, respectively, above euglycemia during hypoglycemia and returned to euglycemic levels during recovery. MSNA levels during hypoglycemia were lower in IDDM subjects than in control subjects (26 ± 3 vs. 35 ± 2 bursts/min, P < 0.01). Importantly, no relationships were found between the MSNA and epinephrine responses to hypoglycemia in either group. Increasing the insulin infusion rate did not alter the MSNA response to hypoglycemia. During prolonged hypoglycemia, MSNA remained elevated above euglycemic levels throughout hypoglycemia. CONCLUSIONS These results demonstrate that insulin-induced hypoglycemia increases muscle sympathetic neural outflow in IDDM and control subjects. The lack of correlation between the MSNA and epinephrine responses to hypoglycemia indicates that the adrenomedullary and peripheral sympathetic responses to hypoglycemia are independently mediated.

Plasma Catecholamine Responses to Hypoglycemia in Children and Adolescents With IDDM

Objective The goal of this study was to assess whether children and adolescents with insulin-dependent diabetes mellitus (IDDM) have decreased catecholamine responses to insulin-induced hypoglycemia as has been reported in adults and to explore the pathogenesis of the decreased response in terms of possible relationships to autonomic neuropathy or hyperinsulinism. Research Design and Methods A before-and-after trial on the effects of 3 days of intensive insulin therapy was conducted on 60 subjects with IDDM (age 15.4 ± 2.6 yr, duration of diabetes 7.8 ± 3.5 yr). The control group consisted of 5 children with non-growth hormone-deficient short stature (age 14.8 ± 3.2 yr). Hypoglycemia was induced with an intravenous insulin bolus (0.15–0.75 U/kg) after insulin withdrawal and 3 days of intensive insulin therapy in diabetic subjects on an inpatient basis to assess the role of hyperinsulinism in suppressing the catecholamine response to hypoglycemia. Control subjects were studied once and received an insulin bolus of 0.1 µU/kg. Autonomic neuropathy was assessed by computerized assessment of the basal R-R variation during inspiration and expiration and the pancreatic polypeptide response to hypoglycemia. Results Basal plasma catecholamine levels were lower in diabetic subjects after intensive insulin therapy than in control subjects (P = 0.008). The peak and incremental catecholamine responses after insulin withdrawal and intensive insulin therapy in IDDM subjects were significantly decreased compared with control subjects (P < 0.001). Peak catecholamine responses to hypoglycemia in IDDM were decreased after intensive insulin therapy (P = 0.002). This was particularly true in those with plasma glucose nadir levels of < 2.2 mmol (P < 0.001). The diminished catecholamine responses were primarily due to decreased peak epinephrine responses after intensive insulin therapy compared with insulin withdrawal (P = 0.011). There were no significant correlations between the catecholamine response to hypoglycemia and age, duration of diabetes, pancreatic polypeptide, or R-R interval. Conclusions These results suggest that children and adolescents with IDDM after insulin withdrawal have diminished catecholamine response to hypoglycemia compared with control subjects and indicate that short-term intensive insulin therapy diminishes this response further. Thus, hyperinsulinism may play a role in suppressing the catecholamine response to hypoglycemia. There is no evidence for a clinical or subclinical role of autonomic neuropathy to explain the altered catecholamine responses.

Glucagon Responses to Hypoglycemia in Children and Adolescents With IDDM

To investigate plasma glucagon counterregulatory responses to hypoglycemia, an intravenous insulin bolus was given over 2 min to 73 children, aged 8.5–18.8 yr, with diabetes duration 1.2–17.1 yr. The plasma glucagon responses of the 61 children without glucagon antibodies or abnormal glucagon molecules were compared with those of 13 nondiabetic control subjects, aged 8.3–18.3 yr. Glucagon increments from baseline (73 ± 10 pg/ml) and peak glucagon responses (212 ± 13 pg/ml) were markedly lower in diabetic patients than in control subjects (341 ± 49 and 462 ± 51 pg/ml, respectively, P < .001). Glucagon responses were found to correlate positively with the age of the patients at the time of testing (r = .478, P < .001) and inversely with metabolic control as measured by glycosylated hemoglobin (r = −.342, P < .02). There was no relationship between glucagon responses and diabetes duration. There was also no relationship between the glucagon increments and free-insulin levels during the test. Glucose recovery from the nadir was impaired in diabetic subjects compared with control subjects and correlated inversely with free-insulin levels. However, glucose recovery did not correlate with the rise of plasma glucagon. Glucose recovery was not different in patients with glucagon antibodies. In this study, we have demonstrated a deficient glucagon response to hypoglycemia in children with insulin-dependent diabetes mellitus. However, the clinical significance of this deficit is not clear.

Muscle Sympathetic Nerve Activity Is Higher in Intensively versus Conventionally Treated IDDM Subjects

OBJECTIVE To determine whether poor long–term glycemie control may play a role in the lower muscle sympathetic nerve activity (MSNA) levels in insulindependent diabetes mellitus (IDDM). RESEARCH DESIGN AND METHODS Intraneural electrodes were used to record MSNA from the peroneal nerve at baseline and during euglycemic insulin infusion (120 mU · m−2 · min−1) in 16 IDDM subjects enrolled in the Diabetes Control and Complications Trial (DCCT), 8 intensively treated (HbAlc 7.1 ± 1.2%) and 8 conventionally treated (HbA1c 9.0 ± 1.5%; P < 0.05). RESULTS Fasting plasma glucose levels tended to be higher at baseline in the conventionally treated group (11.3 ± 1.7 mmol/l) than in the intensively treated group (7.4 ±1.1 mmol/l, P < 0.1), but did not differ during insulin infusion (conventional, 5.0 ± 0.3 mmol/l; intensive, 5.1 ± 0.4 mmol/l). Plasma free insulin levels did not differ between groups either before or during insulin infusion. The intensively treated group had significantly higher MSNA levels than the conventionally treated group both in the fasting state (16.2 ± 2.7 vs. 10.5 ± 4.4 bursts/min, P < 0.05) and during insulin infusion with euglycemia (27.8 ± 2.1 vs. 17.5 ± 5.2 bursts/min). CONCLUSIONS MSNA levels in intensively treated IDDM subjects are higher than in conventionally treated subjects. These results suggest that improved long-term glycemie control is associated with increased sympathetic neural outflow to muscle. The mechanism for this effect remains unclear.

Munchausen's Syndrome by Proxy Mistaken for IDDM

When parents fabricate acute or chronic diseases for their child, a rare form of child abuse known as Munchausens syndrome by proxy exists (1). We report the case of a child who presented with a 2-yr history of insulin-dependent diabetes mellitus (IDDM) and seizures and who was receiving insulin therapy. A 5-yr-old white male originally came to our attention when he was admitted to a local hospital because he had had seizures at home earlier in the day. His mother reported a 4-yr history of seizures controlled with phenobarbital. She reported a 2-yr history of IDDM. The mother described herself as having diabetes herself and as a diabetes educator. She was employed by a hospital supply store/pharmacy. She reported that the patients diabetes was controlled with 4 U of combined NPH and regular insulin daily. He had no history of diabetic ketoacidosis. While he was hospitalized his mother stayed at his bedside. She did all of his care, including his blood glucose monitoring and insulin administration. All of the blood glucose levels performed at the bedside by the mother were reported to be elevated; the plasma glucose levels performed by the laboratory were all within normal limits. The patients HbA1c concentration was 5.5%. No signs or symptoms of hyperglycemia or hypoglycemia were observed nor was any seizure activity. The mother was unable to recall the name of the doctor who had made the diagnosis of IDDM in another state and stated that his records were lost. After a 2-day hospitalization, he was discharged with an appointment to return to the diabetes clinic at the University of Florida Health Science Center Jacksonville. In the next month, she missed three scheduled appointments. At this time, we reported the mother to the state board that governs child abuse on the basis of medical neglect. Unknown to us, the very same week, the patients grandmother also reported his mother on the grounds that she did not give him insulin daily and that the mother was emotionally unstable. The patient was placed in his grandmothers care and she brought him to the clinic. The patients grandmother finally presented us with the history of how the diagnosis of IDDM was made. His mother had made the diagnosis herself by testing his blood before and after a pancake and syrup breakfast. He was begun on insulin without hospitalization under the supervision of a physician, whose name no one could recall. The mother placed him on the combination insulin on the recommendation of a salesman. The grandmother reported that the patient often went 3-4 days without insulin with no adverse effects. She did report that he was more inclined to hypoglycemia when he received his insulin after not having any for a number of days. The grandmother reported that the only person who had ever witnessed the patient seize was his mother. On one occasion, the mother reportedly locked herself in the room with him and piled pillows on his face before claiming that he was seizing. The last relevant information that the grandmother reported was that the patient had been referred to state authorities two other times in the past for medical neglect and/or possible Munchausens syndrome by proxy. He was admitted to rule out IDDM and seizure disorder. On the 1st day of hospitalization he was taken off insulin. Plasma blood glucose levels were measured every 2 h. All results were between 4.4 and 6.4 mM. On the 2nd day he was challenged with a mixed meal. His fasting and stimulated plasma glucose and insulin

Complement C3 and C4 Genetics and Cardiometabolic Risk in Adolescents

Background: Although not usually manifest until adulthood, evidence indicates that cardiometabolic disease has its origins in pediatrics. If we are truly to decrease cardiometabolic disease we must understand the pathophysiology of cardiometabolic risk in childhood. Individuals with the F polymorphism of the complement C3 gene have increased rates of myocardial infarction and athereosclerosis. Individuals with increased gene copy number of the complement C4 long and A genes have decreased longevity. Methods: C3 F vs. S genotype and C4A, C4B, C4L and C4s gene copy number were measured in 59 non-Hispanic white subjects (29 female, age=15.3±1.7 years, BMI=22.4.1±5.9 kg/m2,, mean±SD). Endothelial function (reactive hyperemia (RH), venous occlusion plethysmography), arterial stiffness (augmentation index (AI), arterial tonometry), lipids, interleukin-6 (IL-6), c-reactive protein, plasminogen activator inhibitor 1 (PAI1) insulin sensitivity and secretion (oral glucose tolerance test) were used to assess cardiometabolic risk. BMI percentile, waist circumference and percent body fat (air displacement) were measured to assess adiposity. Results: Forty percent of subjects had at least one C3F allele. These subjects were found to have increased waist circumference (78±18 vs. 70±11 cm, p=0.029) and higher HDL levels (55±14 vs. 46±11 mg/dl, p=0.024) compared to those with only the S allele. Increased C4L (r=0.34, p=0.017) and C4A (r=0.33, p=0.019) gene copy number were associated with decreased endothelial function. Multiple linear regression including percent body fat and either C4L or C4A showed that both relationships became more significant. Conclusions: In adolescent the C3 F polymorphism gene is associated with increased central obesity but surprisingly increased HDL. Increased C4L and C4A gene copy are associated with decreased endothelial function. This could explain their association with deceased longevity. Disclosure R.P. Hoffman: None. M.M. Copenhaver: None. C. Yu: None.

10 Insulin Response to Glucose Predicts Endothelial Dysfunction in Adolescence

Background: Insulin resistance is known to affect endothelial function in adults leading to cardiovascular disease. It is important to assess adolescent changes during puberty and how they relate to carbohydrate and insulin physiology.Design/Methods: Strain gauge plethysmography and radial arterial tonometry were used to determine the percent change in forearm vascular resistance (mean arterial pressure/forearm blood flow; reactive hyperemia; RH) following 5 min of upper arm vascular occlusion after overnight fast in 14 healthy Caucasians (age 14.3±2.0 years; BMI 19.8±3.0 kg/m2; mean SD) the frequently sampled intravenous glucose tolerance test, IVGTT, and minimum model were used to assess insulin sensitivity (SI), glucose effectiveness (SG) and acute insulin response to glucose (AIRG).Results: The RH was negatively correlated with AIRG (r=-0.74, p=0.022) and tended to positively correlate with log disposition index (AIRGxSI) (r=0.62, p=0.056) (figure 1). No relations between RH and SG or SI.Conclusions: These results demonstrate that Caucasian adolescents with a high acute insulin response have poorer endothelial function. Thus high insulin levels may impair endothelial function and increase risk of cardiovascular disease. The relationship between DI and RH suggest that even in adolescence there is a close relationship between risk for type 2 diabetes and cardiovascular disease.

Relationship between Glucose Metabolism and Height and Weight Velocity in Early Puberty 440

Relationship between Glucose Metabolism and Height and Weight Velocity in Early Puberty 440