John I. Malone

Red Cell Sorbitol: An Indicator of Diabetic Control

SUMMARY Intact human erythrocytes accumulate intracellular sorbitol in response to the mediums glucose concentration during in vitro incubations. Sorbitol was identified and measured both enzymatically and by gas-liquid chromatography. The sorbitol produced is most likely a result of the activity of aldose reductase, since (1) a low glucose concentration in the medium elicits this response, and (2) this activity is completely blocked by tetramethylene glutaric acid, a specific inhibitor of aldose reductase. Erythrocyte sorbitol levels in insulin-dependent diabetics are clearly above those of nondiabetics after an 8 h fast. A good correlation exists between red cell sorbitol content and coincident plasma glucose concentrations. Individual exceptions to this rule exist, however, and suggest that red cell sorbitol levels may provide information about in vivo polyol pathway activity that may be important in the pathogenesis of diabetes-associated complications.

Hyperglycemia not hypoglycemia alters neuronal dendrites and impairs spatial memory

Background/Objective:  We previously reported that chronic hyperglycemia, but not hypoglycemia, was associated with the reduction of neuronal size in the rat brain. We hypothesized that hyperglycemia‐induced changes in neuronal structure would have negative consequences, such as impaired learning and memory. We therefore assessed the effects of hyperglycemia and hypoglycemia on neuronal dendritic structure and cognitive functioning in young rats.

Red blood cell sorbitol as an indicator of polyol pathway activity: inhibition by sorbinil in insulin-dependent diabetic subjects

In a double-blind crossover study of 15 diabetic patients, elevated red blood cell (RBC) sorbitol levels were reduced by oral doses of the potent aldose reductase inhibitor, sorbinil (250 mg o.d.), to near-normal ranges. In diabetic rats with severe hyperglycemia, oral sorbinil (5 mg/kg) dramatically reduced (80–90%) sorbitol levels in tissues without affecting blood glucose; the RBC dose-response curve was similar to that in lens and sciatic nerve. In streptozotocin-treated rats with varying degrees of diabetes sorbitol levels in the lens, sciatic nerve, and RBC were elevated in proportion to the degree of hyperglycemia. RBC sorbitol levels in these animals were positively correlated with the levels in lens and sciatic nerve. These results establish that orally administered sorbinil is effective in lowering elevated sorbitol levels, and strongly suggest that the reduction seen in RBC sorbitol levels in human diabetic subjects is likely to reflect comparable effects of the drug in less accessible tissues associated with the long-term complications of diabetes.

Cerebral adema complicating diabetic ketoacidosis in childhood

Three patients who developed fatal cerebral edema in the diabetes camp setting were reviewed with 14 previously reported instances in persons under 21 years of age. Seven occurred in the initial episode of diabetic ketoacidosis. Minimal blood glucose levels less than 250 mg/dl were recorded in 8/17. Rate of fluid administration, rate of Na or K infusion, and hyponatremia or hypokalemia were not consistent factors. Two of the 17 patients received oral fluids only. An etiologic role for rate of blood glucose correction or speed of hydration was not substantiated by this experience and review.

Type 2 diabetes mellitus among Florida children and adolescents, 1994 through 1998

OBJECTIVES This study was undertaken to examine the trends in the diagnosis of Type 2 diabetes mellitus among children and adolescents with new-onset diabetes seen from 1994 through 1998 at the three university-based diabetes centers in Florida. METHODS Data were abstracted from medical records and patients were categorized as having Type 1 or Type 2 diabetes. RESULTS There were 569 patients classified with Type 1 diabetes and 92 with Type 2 diabetes. The proportion of patients diagnosed with Type 2 diabetes increased over the five years from 9.4% in 1994 to 20.0% in 1998 (chi-square test for trend = 8.2; p=0.004). There was not an associated net increase in the total number of new diabetes patients referred over time (chi-square test for trend = 0.6, p=0.4). Those with Type 2 diabetes were more likely to have a body mass index in the 85th-94th percentile [odds ratio (OR) = 8.5; 95% confidence interval (CI) 2.5, 28.8], have a body mass index >or=95th percentile (OR = 6.8; 95% CI 2.6, 17.7), Hispanic ethnicity (OR = 6.2; 95% CI 2.2, 17.9), black race (OR = 2.8; 95% CI 1.3, 6.2), female gender (OR = 2.2; 95% CI 1.2, 4.3), and older age (OR = 1.4 for each one-year increment in age; 95% CI 1.3, 1.6), compared with those having Type 1 diabetes. CONCLUSIONS From 1994 through 1998, there was a significant overall increase in the percentage of children referred with new-onset diabetes who were considered to have Type 2 diabetes. Factors associated with the diagnosis of Type 2 diabetes relative to Type 1 diabetes include body mass index >/=85th percentile, Hispanic ethnicity, black race, female gender, and older age.

A comparison of insulin lispro and buffered regular human insulin administered via continuous subcutaneous insulin infusion pump

This study compared glycemic control achieved with insulin lispro or buffered regular human insulin in patients with Type 1 diabetes treated with continuous subcutaneous insulin infusion (CSII) using an external insulin pump. In this 24-week multicenter, randomized, two-way crossover, open-label trial, 58 patients on CSII with adequate glycemic control received either insulin lispro or buffered regular human insulin for 12 weeks, followed by the alternate treatment for another 12 weeks. Efficacy and safety measures included hemoglobin A(1c) (HbA(1c)) at baseline and endpoint, home blood glucose monitoring, hypoglycemia, and frequency of pump catheter occlusion. Patients consumed a standard test meal on three occasions, with determinations of fasting, 1- and 2-h postprandial glucose values. Insulin lispro use was associated with a significantly lower HbA(1c) than was buffered regular human insulin (7.41+/-0.97 vs. 7.65+/-0.85 mmol/l; P=.004). Fasting serum glucose values before the test meal were similar between the two therapies. The 1-h (11.16+/-4.29 vs. 13.20+/-4.68 mmol/l; P=.012) and 2-h (9.64+/-4.10 vs. 12.53+/-4.64 mmol/l; P=.001) postprandial glucose concentrations were significantly lower during treatment with insulin lispro. No differences between treatments were observed in basal or bolus insulin doses, weight gain, or the incidence and rate of hypoglycemia, hyperglycemia, or pump occlusions. When used in external pumps, insulin lispro provides better glycemic control than buffered regular human insulin with a similar adverse event profile.

Diabetic vascular changes in children.

The microvascular complications of diabetes are demonstrated in the eye at a very early stage with the use of retinal ftuorescein angiography. One hundred and fifty-four children who have had diabetes mellitus for durations varying from one month to 18 years had their retinal vasculature evaluated with fluorescein angiography. Seventy-five per cent of the children examined had vascular abnormalities, including 20 children who had diabetes for one year or less. Twenty-five per cent of the children showed no vascular abnormalities. This included one child who had diabetes for 12 years. The severity of the vascular abnormalities increased with the duration of diabetes. Vascular abnormalities did not appear related to diabetic management or control. The possibility of two types of diabetes, one with and the other without associated vascular abnormalities, is suggested.

Oral Insulin Therapy to Prevent Progression of Immune‐Mediated (Type 1) Diabetes

Abstract: Repeated ingestion of insulin has been suggested as an immune tolerization therapy to prevent immune‐mediated (type 1) diabetes. We performed a placebo‐controlled, two‐dose, oral insulin tolerance trial in newly diagnosed (< 2 years) diabetic patients who had required insulin replacement for less than 4 weeks and were found to have cytoplasmic islet cell autoantibodies (ICAs). No oral hypoglycemic agents were permitted during the trial. Endogenous insulin reserves were estimated at six‐month intervals by plasma C‐peptide responses to a mixed meal. Positive ICAs were found in 262 (31%) of the 846 patients screened. Of the 197 who agreed to participate, 187 could be followed for 6 to 36 months. Endogenous insulin retention was dependent upon initial stimulated C‐peptide response, age at diabetes onset, and numbers of specific islet cell autoantibodies found. Oral insulin improved plasma C‐peptide responses in patients diagnosed at ages greater than 20 years, best seen at the low (1 mg/day) over the high (10 mg/day) insulin dose (P= .003 and P= .01, respectively). In patients diagnosed before age 20 years, the 1 mg dose was ineffective, whereas the 10 mg dose actually accelerated C‐peptide loss (P= .003). There were no adverse effects. If confirmed, these findings suggest that diabetic patients over age 20 years with ICA evidence of late‐onset immune‐mediated diabetes should be considered for oral insulin at 1 mg/day to better retain endogenous insulin secretion.

Diabetic Cardiomyopathy and Carnitine Deficiency

This study was designed to study the pathogenesis of cardiomyopathy in animals with longstanding (6 months) diabetes mellitus. Male Wistar rats were made diabetic by the injection of streptozotocin (35 mg/kg) intraperitoneal at 6 months of age. Myocardial contractility was evaluated at 1 year of age by an echocardiogram. Blood was collected at that time to measure blood glucose and hemoglobin A1c as an indicator of metabolic control. Serum carnitine was also measured on the same sample to evaluate the availability of this substance so essential for fatty acid metabolism in the myocardium. Myocardial anatomy was evaluated by both light and electron microscopy after the animals had diabetes for 6 months. It was found that the left ventricular volume was greater at the end of systole and diastole. There was the suggestion of left ventricular fractional shortening and calculated reduced ejection fraction indicating decreased contractility consistent with cardiomyopathy. The hearts had no evidence of coronary vascular occlusion, and the serum cholesterol was normal. Myocardial ultrastructure revealed abnormal-appearing mitochondria consistent with carnitine deficiency. Serum and myocardial carnitine levels in the animals with diabetes and reduced myocardial function were low. Carnitine levels and metabolism could be important in the pathogenesis of diabetic cardiomyopathy.

Hyperglycemic brain injury in the rat

Children with diabetes onset before 5 years of age have reduced neurocognitive function. This problem has been attributed to hypoglycemia, a complication of insulin therapy. The eye, kidney, and nerve complications of diabetes (hyperglycemia) have been reduced by intensified insulin therapy which is associated with a 3-fold increase in severe hypoglycemia and therefore is not recommended for children less than 13 years of age. Since hyperglycemia is much more common than intermittent hypoglycemia during early childhood diabetes, it is important to determine if hyperglycemia affects brain growth and development. Rats were exposed to 4 weeks of either continuous hyperglycemia (diabetes) or intermittent (3 h, 3 times/week) hypoglycemia from 4 to 8 weeks of age. The brains of these animals were compared to those of similarly aged normal control animals. The cell number was increased, and the cell size reduced in the cortex of diabetic animals as assessed by DNA/wet weight of brain and protein/DNA content. Reduced amounts of protein, fatty acids, and cholesterol/microgram DNA also indicate smaller cells with reduced myelin content in the cortex of the diabetic animals. Histologic evaluation of these brains confirmed the biochemical findings. These observations require further confirmation and evaluation but indicate that continuous hyperglycemia may be more damaging than intermittent hypoglycemia to the developing brain. This is an important consideration for the management of diabetes mellitus in young children.