Tight glycemic control by insulin, started in the preischemic, but not postischemic, period, protects against ischemic spinal cord injury in rabbits

Role of Insulin in Neurotrauma and Neurodegeneration: A Review

Insulin is a hormone typically associated with pancreatic release and blood sugar regulation. The brain was long thought to be “insulin-independent,” but research has shown that insulin receptors (IR) are expressed on neurons, microglia and astrocytes, among other cells. The effects of insulin on cells within the central nervous system are varied, and can include both metabolic and non-metabolic functions. Emerging data suggests that insulin can improve neuronal survival or recovery after trauma or during neurodegenerative diseases. Further, data suggests a strong anti-inflammatory component of insulin, which may also play a role in both neurotrauma and neurodegeneration. As a result, administration of exogenous insulin, either via systemic or intranasal routes, is an increasing area of focus in research in neurotrauma and neurodegenerative disorders. This review will explore the literature to date on the role of insulin in neurotrauma and neurodegeneration, with a focus on traumatic brain injury (TBI), spinal cord injury (SCI), Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Effect of moderately intense perioperative glucose control on renal allograft function: a pilot randomized controlled trial in renal transplantation

Recipient diabetes accounts for ~34% of end-stage renal disease in patients awaiting renal transplantation and has been linked to poor graft function. We conducted a single-center, open-label, randomized controlled trial to determine whether moderately intense glucose control during allograft reperfusion would reduce the incidence of poor graft function. Adult diabetics undergoing deceased donor renal transplant were randomized to moderately intense glucose control (n=30) or standard control (n=30). The primary outcome was poor graft function (dialysis within seven days of transplant or failure of serum creatinine to fall by 10% for three consecutive days). Recipients with moderately intense glucose control had less poor graft function in the intention-to-treat (43.3% vs 73.3%, P=.02) and per-protocol analysis (43.2% vs 81%, P<.01). Recipients with moderately intense control also had higher glomerular filtration rate (GFR) at 30 days after transplant in the per-protocol and intention-to-treat analyses. There were no episodes of severe hypoglycemia in either group and no differences in mortality, seizures, stroke, graft loss, or biopsy-proven rejection. Moderately intense glucose control at the time of allograft reperfusion reduces the incidence of poor graft function in diabetic renal transplant recipients and improves glomerular filtration rate at 30 days.

Metabolomic analysis of survival in carbohydrate pre-fed pigs subjected to shock and polytrauma

Hemorrhagic shock, a result of extensive blood loss, is a dominant factor in battlefield morbidity and mortality. Early rodent studies in hemorrhagic shock reported carbohydrate feeding prior to the induction of hemorrhagic shock decreased mortality. When repeated in our laboratory with a porcine model, carbohydrate pre-feed resulted in a 60% increase in death rate following hemorrhagic shock with trauma when compared to fasted animals (15/32 or 47% vs. 9/32 or 28%). In an attempt to explain the unexpected death rate for pre-fed animals, we further investigated the metabolic profiles of pre-fed non-survivors (n = 15) across 4 compartments (liver, muscle, serum, and urine) at specific time intervals (pre-shock, shock, and resuscitation) and compared them to pre-fed survivors (n = 17). As hypothesized, pre-fed pigs that died as a result of hemorrhage and trauma showed differences in their metabolic and physiologic profiles at all time intervals and in all compartments when compared to pre-fed survivors. Our data suggest that, although all animals were subjected to the same shock and trauma protocol, non-survivors exhibited altered carbohydrate processing as early as the pre-shock sampling point. This was evident in (for example) the higher levels of ATP and markers of greater anabolic activity in the muscle at the pre-shock time point. Based on the metabolic findings, we propose two mechanisms that connect pre-fed status to a higher death rate: (1) animals that die are more susceptible to opening of the mitochondrial permeability transition pore, a major factor in ischemia/reperfusion injury; and (2) loss of fasting-associated survival mechanisms in pre-fed animals.

The combination of insulin-like growth factor 1 and erythropoietin protects against ischemic spinal cord injury in rabbits

INTRODUCTION

Insulin-like growth factor 1 (IGF-1) and erythropoietin (EPO) have been reported to independently protect against ischemic spinal cord injury in rabbits. In the present study, we investigated whether the combination of IGF-1 and EPO protects against ischemic spinal cord injury in rabbits.

METHODS

Animals were assigned to 1 of 4 groups (n = 6 in each): a control group (saline), an IGF-1 group (IGF-1 0.3 mg/kg), an EPO group (EPO 800 U/kg), or an IGF-1 + EPO group (IGF-1 0.3 mg/kg + EPO 800 U/kg). Spinal cord ischemia was produced by occluding the abdominal aorta for 15 min. Saline, IGF-1, and EPO were administered intravenously just after the start of reperfusion. Hindlimb motor function was assessed daily for 7 days, after which histopathological evaluation was performed. To analyze phosphorylation of signal transduction molecules, animals were assigned to 1 of the 4 groups (n = 8 in each). Spinal cord ischemia and the treatment were the same as those described above. The spinal cords were removed at 15 or 30 min after reperfusion and used to analyze phosphorylation of signal transduction molecules. Four animals served as the preischemic control, and the spinal cord was removed just before the start of ischemia.

RESULTS

In the IGF-1 + EPO group, both neurological and histopathological outcomes were significantly improved as compared to the control group, which was consistent with the increase of Janus kinase-2 (JAK2) phosphorylation.

CONCLUSIONS

The combination of IGF-1 and EPO protects against ischemic spinal cord injury in rabbits. JAK2 might contribute to the protective effect.

The effects of glycemic control on seizures and seizure-induced excitotoxic cell death

Background

Epilepsy is the most common neurological disorder after stroke, affecting more than 50 million persons worldwide. Metabolic disturbances are often associated with epileptic seizures, but the pathogenesis of this relationship is poorly understood. It is known that seizures result in altered glucose metabolism, the reduction of intracellular energy metabolites such as ATP, ADP and phosphocreatine and the accumulation of metabolic intermediates, such as lactate and adenosine. In particular, it has been suggested that the duration and extent of glucose dysregulation may be a predictor of the pathological outcome of status. However, little is known about neither the effects of glycemic control on brain metabolism nor the effects of managing systemic glucose concentrations in epilepsy.

Results

In this study, we examined glycemic modulation of kainate-induced seizure sensitivity and its neuropathological consequences. To investigate the relationship between glycemic modulation, seizure susceptibility and its neuropathological consequences, C57BL/6 mice (excitotoxin cell death resistant) were subjected to hypoglycemia or hyperglycemia, followed by systemic administration of kainic acid to induce seizures. Glycemic modulation resulted in minimal consequences with regard to seizure severity but increased hippocampal pathology, irrespective of whether mice were hypoglycemic or hyperglycemic prior to kainate administration. Moreover, we found that exogenous administration of glucose following kainic acid seizures significantly reduced the extent of hippocampal pathology in FVB/N mice (excitotoxin cell death susceptible) following systemic administration of kainic acid.

Conclusion

These findings demonstrate that modulation of the glycemic index can modify the outcome of brain injury in the kainate model of seizure induction. Moreover, modulation of the glycemic index through glucose rescue greatly diminishes the extent of seizure-induced cell death following kainate administration. Our data support the hypothesis that deficient insulin signaling may represent a critical contributing factor in the susceptibility to seizure-induced cell death and this may be an important therapeutic target.

Intraoperative hyperglycemia augments ischemia reperfusion injury in renal transplantation: a prospective study

Background. Diabetes is a risk factor for delayed graft function in kidney transplantation, and hyperglycemia increases ischemia reperfusion injury in animal models. Methods. To explore the role of perioperative hyperglycemia in ischemia reperfusion injury, we conducted a prospective study of 40 patients undergoing living donor renal transplantation. Blood glucose levels were monitored intraoperatively, and serum samples were obtained at the time anesthesia was induced and one hour after allograft reperfusion. The percentage change in neutrophil gelatinase-associated lipocalin (NGAL), a protein whose expression is increased with renal ischemia, was then used to determine the extent of injury. Results. In a multivariate model including recipient, donor, and transplant factors, recipient blood glucose >160 mg/dL at the time of allograft reperfusion (β 0.19, P-value < 0.01), warm ischemia time >30 minutes (β 0.11, P-value 0.13), and recipient age (β 0.05, P-value 0.05) were associated with percentage change in NGAL. These same predictors were associated with the percentage change in creatinine on postoperative day 2. Conclusions. Hyperglycemia is associated with increased ischemic injury in renal transplantation. Both creatinine and NGAL, a marker of ischemic injury and renal function, fall less rapidly in patients with elevated blood glucose.

Insulin, synaptic function, and opportunities for neuroprotection

A steadily growing number of studies have begun to establish that the brain and insulin, while traditionally viewed as separate, do indeed have a relationship. The uptake of pancreatic insulin, along with neuronal biosynthesis, provides neural tissue with the hormone. As well, insulin acts upon a neuronal receptor that, although a close reflection of its peripheral counterpart, is characterized by unique structural and functional properties. One distinction is that the neural variant plays only a limited part in neuronal glucose transport. However, a number of other roles for neural insulin are gradually emerging; most significant among these is the modulation of ligand-gated ion channel (LGIC) trafficking. Notably, insulin has been shown to affect the tone of synaptic transmission by regulating cell-surface expression of inhibitory and excitatory receptors. The manner in which insulin regulates receptor movement may provide a cellular mechanism for insulin-mediated neuroprotection in the absence of hypoglycemia and stimulate the exploration of new therapeutic opportunities.

Does high-dose opioid anesthesia exacerbate ischemic spinal cord injury in rabbits?

PURPOSE

Intrathecal morphine given during a post-ischemic period has been reported to have the potential to exacerbate ischemic spinal cord injury. However, it remains unknown whether synthetic opioids administered systemically exacerbate ischemic injury. We sought to compare the damage of the spinal cord after transient spinal cord ischemia in rabbits anesthetized with three different regimens; isoflurane, fentanyl with isoflurane, and remifentanil with isoflurane.

METHODS

We assigned rabbits to three groups (n = 9 in each); an isoflurane group (isoflurane 1 minimum alveolar concentration [MAC]), a fentanyl group (isoflurane 0.5 MAC + 100 microg x kg(-1) i.v. fentanyl given over 30 min before aortic occlusion), and a remifentanil group (isoflurane 0.5 MAC + 1 microg x kg(-1) x min(-1) i.v. remifentanil started 30 min before aortic occlusion and maintained until 1 h after reperfusion). Spinal cord ischemia was produced by occluding the abdominal aorta for 13 min. Hindlimb motor function (score range: 4, normal to 0, paraplegia) was assessed daily for 7 days, and then the number of normal neurons in the anterior spinal cord was counted.

RESULTS

Severe motor dysfunction (score < or = 1) was observed in seven, four, and five animals in the isoflurane, fentanyl, and remifentanil groups, respectively. There were no significant intergroup differences in neurological scores. There were no differences in the numbers of normal neurons among the three groups (22 +/- 22, 42 +/- 30, 33 +/- 28, respectively).

CONCLUSION

Our results suggest that neither i.v. fentanyl nor i.v. remifentanil added to 0.5 MAC isoflurane exacerbated ischemic spinal cord injury in rabbits when compared to 1 MAC isoflurane.

Hyperglycaemia and neurological injury

PURPOSE OF REVIEW

Clinical and experimental data suggest that hypergylcaemia lowers the ischaemic neuronal threshold and worsens outcome in the presence of neurological injury from trauma, stroke and subarachnoid haemorrhage. This review aims to appraise the evidence for tight glycaemic control in patients with neurological injury.

RECENT FINDINGS

Hyperglycaemia can adversely affect outcome in critically ill patients. Intensive insulin therapy with tight glycaemic control has been advocated for improving outcome in these patients. However, the extent to which intensive insulin therapy and tight control of blood glucose improve outcome after ischaemic neurological insults remains unclear. The benefit of such treatment regimes may be negated by the increased frequency of hypoglycaemic episodes, which may aggravate neurological injury. Although it seems sensible to control hyperglycaemia in patients with neurological injury, the treatment must account for potential hypoglycaemic episodes.

SUMMARY

Clinical and experimental data suggest that hyperglycaemia lowers the ischaemic neuronal threshold in the presence of neurological injury. Tight glycaemic control may result in hypoglycaemia, which in itself can be detrimental. Therefore, it seems sensible that we should accept slightly less tight blood glucose control than in the critically ill patient without neurological injury.