Impact of improved glycaemic control on rates of hypoglycaemia in insulin dependent diabetes mellitus

Zinc release contributes to hypoglycemia-induced neuronal death

Neurons exposed to zinc exhibit activation of poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme that normally participates in DNA repair but promotes cell death when extensively activated. Endogenous, vesicular zinc in brain is released to the extracellular space under conditions causing neuronal depolarization. Here, we used a rat model of insulin-induced hypoglycemia to assess the role of zinc release in PARP-1 activation and neuronal death after severe hypoglycemia. Zinc staining with N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ) showed depletion of presynaptic vesicular zinc from hippocampal mossy fiber terminals and accumulation of weakly bound zinc in hippocampal CA1 cell bodies after severe hypoglycemia. Intracerebroventricular injection of the zinc chelator calcium ethylene-diamine tetraacetic acid (CaEDTA) blocked the zinc accumulation and significantly reduced hypoglycemia-induced neuronal death. CaEDTA also attenuated the accumulation of poly(ADP-ribose), the enzymatic product of PARP-1, in hippocampal neurons. These results suggest that zinc translocation is an intermediary step linking hypoglycemia to PARP-1 activation and neuronal death.

Repetitive hypoglycemia in young rats impairs hippocampal long-term potentiation

Mechanisms underlying cognitive dysfunction in young diabetic children are poorly understood, and may include synaptic dysfunction from insulin-induced hypoglycemia. We developed a model of repetitive insulin-induced hypoglycemia in young rats and examined hippocampal long-term potentiation, an electrophysiologic assay of synaptic plasticity, 3-5 d after the last hypoglycemic event. Three hypoglycemic events between postnatal d 21-25 produced modest cortical (17 +/- 2.9 dead neurons per section in parasagittal cortex), but not hippocampal, neuron death quantified by Fluoro-Jade B staining. There was no change in neurogenesis in the hippocampal dentate granule cell region by quantification of bromodeoxyuridine incorporation. Although normal baseline hippocampal synaptic responses were elicited from hippocampal slices from hypoglycemic animals, long-term synaptic potentiation could not be induced in hippocampal slices from rats subjected to hypoglycemia. These results suggest that repetitive hypoglycemia in the developing brain can cause selective impairment of synaptic plasticity in the absence of cell death, and without complete disruption of basal synaptic transmission. We speculate that impaired synaptic plasticity in the hippocampus caused by repetitive hypoglycemia could underlie memory and cognitive deficits observed in young diabetic children, and that cortical neuron death caused by repetitive hypoglycemia in the developing brain may contribute to other neurologic, cognitive, and psychological problems sometimes encountered in diabetic children.

Hypoglycemic neuronal death and cognitive impairment are prevented by poly(ADP-ribose) polymerase inhibitors administered after hypoglycemia

Severe hypoglycemia causes neuronal death and cognitive impairment. Evidence suggests that hypoglycemic neuronal death involves excitotoxicity and DNA damage. Poly(ADP-ribose) polymerase-1 (PARP-1) normally functions in DNA repair, but promotes cell death when extensively activated by DNA damage. Cortical neuron cultures were subjected to glucose deprivation to assess the role of PARP-1 in hypoglycemic neuronal death. PARP-1-/- neurons and wild-type, PARP-1+/+ neurons treated with the PARP inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone both showed increased resistance to glucose deprivation. A rat model of insulin-induced hypoglycemia was used to assess the therapeutic potential of PARP inhibitors after hypoglycemia. Rats subjected to severe hypoglycemia (30 min EEG isoelectricity) accumulated both nitrotyrosine and the PARP-1 product, poly(ADP-ribose), in vulnerable neurons. Treatment with PARP inhibitors immediately after hypoglycemia blocked production of poly(ADP-ribose) and reduced neuronal death by >80% in most brain regions examined. Increased neuronal survival was also achieved when PARP inhibitors were administered up to 2 hr after blood glucose correction. Behavioral and histological assessments performed 6 weeks after hypoglycemia confirmed a sustained salutary effect of PARP inhibition. These results suggest that PARP-1 activation is a major factor mediating hypoglycemic neuronal death and that PARP-1 inhibitors can rescue neurons that would otherwise die after severe hypoglycemia.

Hypoglycemic neuronal death and cognitive impairment are prevented by poly(ADP-ribose) polymerase inhibitors administered after hypoglycemia

Severe hypoglycemia causes neuronal death and cognitive impairment. Evidence suggests that hypoglycemic neuronal death involves excitotoxicity and DNA damage. Poly(ADP-ribose) polymerase-1 (PARP-1) normally functions in DNA repair, but promotes cell death when extensively activated by DNA damage. Cortical neuron cultures were subjected to glucose deprivation to assess the role of PARP-1 in hypoglycemic neuronal death. PARP-1-/- neurons and wild-type, PARP-1+/+ neurons treated with the PARP inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone both showed increased resistance to glucose deprivation. A rat model of insulin-induced hypoglycemia was used to assess the therapeutic potential of PARP inhibitors after hypoglycemia. Rats subjected to severe hypoglycemia (30 min EEG isoelectricity) accumulated both nitrotyrosine and the PARP-1 product, poly(ADP-ribose), in vulnerable neurons. Treatment with PARP inhibitors immediately after hypoglycemia blocked production of poly(ADP-ribose) and reduced neuronal death by >80% in most brain regions examined. Increased neuronal survival was also achieved when PARP inhibitors were administered up to 2 hr after blood glucose correction. Behavioral and histological assessments performed 6 weeks after hypoglycemia confirmed a sustained salutary effect of PARP inhibition. These results suggest that PARP-1 activation is a major factor mediating hypoglycemic neuronal death and that PARP-1 inhibitors can rescue neurons that would otherwise die after severe hypoglycemia.

Hypoglycemia in children with type 1 diabetes: current issues and controversies

Hypoglycemia is a common complication of insulin therapy, particularly in the young. For children and adolescents with diabetes, the risk of hypoglycemia may not only prevent optimal glycemic control but can also add significantly to the psychosocial burden of the disease. Recently, surveys employing prospective monitoring techniques have allowed more precise information to be gained about rates of hypoglycemia, its clinical associations, and the impact of new therapies and technologies. A number of reports have estimated rates of hypoglycemic comas and convulsions to be approximately 20 events per 100 patient years in children on current conventional therapy. There is evidence that the introduction of new analog short- and longer-acting insulins and the more widespread use of continuous subcutaneous infusion therapies may allow improvements in glycemic control to occur without the usual increased rate of severe hypoglycemic episodes. The use of glucose sensor technology has brought into focus the widespread occurrence of asymptomatic hypoglycemia. Asymptomatic hypoglycemia has long been recognized, particularly at night, when the combination of excessive insulin action and suppressed counter-regulatory hormone responses put children at special risk of hypoglycemia. Hypoglycemia unawareness is common in the young and is associated with an increased risk of severe hypoglycemia. Whether episodes of severe hypoglycemia have long-term consequences is controversial. Early studies suggesting that the developing brain is sensitive to permanent neurological damage as a result of hypoglycemia have not been confirmed in more recent reports. Many studies have not found convincing evidence of neurological sequelae of the hypoglycemic events that are an inevitable complication of insulin therapy. The question, however, remains under active investigation. Continued prospective monitoring of hypoglycemia rates and consequences has become an essential component of diabetes management.

Characteristics of glycemic control in young children with type 1 diabetes

BACKGROUND

The Diabetes Control and Complications Trial (DCCT) demonstrated that the rate-limiting step to the intensification of diabetes management in adolescents and adults was hypoglycemia. Young children were presumed to be at even greater risk for hypoglycemia with severe consequences, particularly if they had HbA1c levels < 8%.

SUBJECTS

A retrospective chart review was performed on 148 patients with type 1 diabetes on insulin injection therapy who were < 8 yr of age (mean age 5.7 +/- 1.5, mean diabetes duration 3.0 +/- 1.4 yr) followed quarterly from July 1999 to June 2001.

METHODS

The subjects were divided into two groups based on their mean HbA1c values (< 8 vs. > or = 8%) averaged over the 2-yr time period. The following variables were analyzed comparing the two groups: age, duration of diabetes, insulin dose, severe hypoglycemic episodes, episodes of diabetic ketoacidosis (DKA), percentage of glucose levels above, within, and below the target range, and number of diabetes home-management competencies obtained.

RESULTS

Patients with HbA1c < 8% spent more time within target range (40.0 vs. 29.5%, p = 0.0001) and less time above their target range (36.9 vs. 51.2%, p = 0.0003). There was no difference in the percentage of glucose levels below target (23.2 vs. 19.4%, p = NS), percentage of severe hypoglycemic episodes (3 vs. 7 episodes per 100 patient-yr, p = NS), or episodes of DKA (1 vs. 3 episodes per 100 patient-yr, p = NS) between the two groups. SUBJECTS with lower HbA1c levels had acquired more home-management competencies (4.0 vs. 3.5, p = 0.01).

CONCLUSIONS

If families are competent in fundamental diabetes management, young children can achieve HbA1c levels < 8.0% without increasing the risk of hypoglycemia.

Predictors of glycaemic control and hypoglycaemia in children and adolescents with type 1 diabetes from NSW and the ACT

OBJECTIVES

To audit glycaemic control and incidence of severe hypoglycaemia in children and adolescents with type 1 diabetes in New South Wales (NSW) and the Australian Capital Territory (ACT).

DESIGN

A multicentre, population-based, cross-sectional study from 1 September to 31 December, 1999.

PARTICIPANTS

1190 children and adolescents aged 1.2-15.8 years with type 1 diabetes, identified from three hospital-based paediatric diabetes units, four private city-based paediatric practices and 18 regional outreach clinics in NSW and the ACT.

MAIN OUTCOME MEASURES

HbA(1c) level and incidence of severe hypoglycaemia (defined by unconsciousness or seizures).

RESULTS

The response rate was 67% (1190 of a target group of 1765). The median HbA(1c) level was 8.2% (interquartile range, 7.6%-9.1%). Significant predictors of HbA1c level in a multiple regression model were duration (b = 0.05; 95% CI, 0.02-0.07) and insulin dose/kg (b = 0.46; 95% CI, 0.27-0.66). At least one episode of severe hypoglycaemia in the previous three months was reported in 6.7%, and the rate of severe hypoglycaemia was 36/100 patient-years. Significant predictors of hypoglycaemia in a Poisson regression model were younger age (P = 0.03), male sex (P = 0.04), longer diabetes duration (P = 0.02), and > 3 daily insulin injections (P = 0.02), but not HbA(1c) level. Children with diabetes had higher BMI standard deviation scores compared with population standards, and those in the highest quartile of BMI standard deviation score were younger, had shorter diabetes duration and had higher HbA(1c) level.

CONCLUSIONS

Many children and adolescents with type 1 diabetes have suboptimal glycaemic control, placing them at high risk of developing microvascular complications. Those with longer diabetes duration are at increased risk of suboptimal glycaemic control and severe hypoglycaemia and should be targeted for interventional strategies.

Hypoglycemia: a complication of diabetes therapy in children

Hypoglycemia is the most common acute complication in insulin-treated type 1 diabetic patients. Most surveys have demonstrated that the tighter the glycemic control, and the younger the patient, the greater the frequency of both mild and severe hypoglycemia. However, people in poor metabolic control, with high glycosylated hemoglobin levels, are not protected from experiencing severe hypoglycemia. Focusing on the pediatric population, we review new or controversial issues surrounding the prevalence of hypoglycemia, its causes, its consequences and preventive strategies, and discuss possible mechanisms underlying the variability of responses to hypoglycemia.

Hypoglycemia in children with type 1 diabetes mellitus. Risk factors, cognitive function, and management

This article examines the relationship between hypoglycemia and brain function in children with type 1 diabetes. Hypoglycemic episodes occurring in the first 5 years of life may permanently disrupt cognitive function in a subset of children with diabetes, and a single acute episode of hypoglycemia may produce a transient reduction in mental efficiency, alter the electroencephalogram, and increase regional cerebral blood flow. Because iatrogenic development of hypoglycemic unawareness and autonomic failure are the most likely mediators of moderately severe hypoglycemia, medical management efforts should be directed at the prevention of frequently recurring, mild hypoglycemia.

An assessment of paediatric diabetes care in three centres in Russia and in Southampton, UK. The Paediatric Teams in Moscow, Tula, Tambov, Southampton

AIMS

Young people in Russia with diabetes have an increased morbidity and a 10-fold increase in mortality compared with many European countries. This joint international study was set up to compare of care and outcomes against published guidelines in three Russian centres and one UK centre.

METHODS

An assessment of the diabetic care of 368 children, based on the principles of the St Vincent Declaration, was undertaken in each centre. Data on prevalence, management, control and complications were collected in young people with diabetes < 16 years of age in each of the four centres over a 4-week period.

RESULTS

The prevalence of diabetes was greater in Southampton (1:702 vs. 1:1378). At diagnosis Russian children had a higher incidence of ketoacidosis (69 vs. 29%) and stayed in hospital longer (30 vs. 3 days). In management Russian children received more injections per day (5 vs. 2). There was no significant difference in insulin dose for those under 10 years between countries (Southampton 0.69 U/kg vs. Russian 0.73 U/kg, P=NS). Older Russian children did not increase their insulin dosage, while children over 10 years in Southampton received significantly more insulin than the Russian children (Southampton 1.0 U/kg vs. Russian 0.77 U/kg, P< or =0.001). Twenty-nine per cent of the Russian children reported that they had insufficient insulin and 14% had to buy extra. HbA1c was higher in the Russian children (9.8% vs. 8.3%), increasing significantly with age. The Russian children showed a height deficit which correlated with HbA1c and diabetes duration. The Southampton children were heavier and with a higher body-mass index and their HbA1c did not rise similarly as in Russia. Severe hypoglycaemia was more common in the Southampton children (32 vs. 12%). Retinopathy was reported in 12% of the Russian children (Southampton 0%) and systolic blood pressure > 95th centile in 21% (Southampton 8%).

CONCLUSIONS

This study demonstrates a significant difference in diabetic control and complications between the two countries which could be partially explained by a decreased availability and prescribing of insulin and blood glucose monitoring in Russia. Southampton has an education and management policy based on ambulatory care resulting in reduced hospital stay.

Type 1 diabetes mellitus in early childhood: glycemic control and associated risk of hypoglycemic reactions

OBJECTIVE

To assess the level of glycemic control and to determine whether more normal glycemic control, as measured by glycosylated hemoglobin, leads to frequent hypoglycemic episodes in young patients with type 1 diabetes mellitus.

MATERIAL AND METHODS

We undertook a retrospective review of the medical records of 59 children with type 1 diabetes diagnosed at age 9 years or younger, who underwent follow-up at our institution for at least 2 years. For each follow-up, insulin requirements, levels of glycosylated hemoglobin, and frequency of hypoglycemic reactions were analyzed for three age-groups--0 to 2 years, 2 to 5 years, and 5 to 9 years old.

RESULTS

The mean glycosylated hemoglobin for the first 2 years after diagnosis of type 1 diabetes was higher in children 0 to 2 years old in comparison with the other age-groups. This increased glycosylated hemoglobin occurred despite increased administration of insulin, expressed in units per kilogram daily, to these children (P < 0.05). Severe hypoglycemic reactions were more common in infants (55%) and children between 2 and 5 years old (45%) than in children from 5 to 9 years old (13%). In all age-groups, the mean glycosylated hemoglobin value closest to a hypoglycemic event and the mean glycosylated hemoglobin value for the 2-year study period were similar but were both less than 8% (the standard established by the Diabetes Control and Complications Trial). Most reactions had no clear cause in the youngest age-group, whereas a specific reason could usually be determined in children 2 to 5 years old.

CONCLUSION

Tight glycemic control is achievable in young patients with type 1 diabetes mellitus. Such tight control, however, may lead to an increase in the frequency of severe hypoglycemic reactions in this patient population. Our data support the guideline that children younger than 5 years should have a higher goal for premeal plasma glucose levels.