Use of Intranasal Insulin as Neuroprotection From Hyperglycemia in Rat Model of Extremely Preterm Infants

Background: Hyperglycemia is common in extremely preterm infants (EPI) and is a risk factor for increased mortality and morbidity, including abnormal neurodevelopment. Hippocampus-mediated cognitive deficits are common in this population. In a rat model of insulinopenic hyperglycemia, abnormal neurochemistry in the hippocampus was found, with lactate, glutamate (Glu):glutamine (Gln) ratio lower and Phosphorylated Creatinine (PCr):Creatinine (Cr) higher. Intranasal insulin has been shown to improve cognitive function in animal models of Alzheimer’s disease and type 2 diabetes mellitus, as well as in adult human studies of Alzheimer’s disease. No study has previous investigated the use of intranasal insulin on preventing the long-term effects of hyperglycemia in the EPI population. Objective: To determine whether administration of intranasal insulin during early postnatal days would negate the effects of hyperglycemia on the developing hippocampus in neonatal rat model of streptozotocin (STZ)-induced hyperglycemia. Design/Methods: STZ (80mg/kg IP) was injected on postnatal day (P) 2, and littermates in the control group were injected with an equivalent volume of citrate buffer. STZ pups were randomized to intranasal insulin, 3U twice daily from P3-P6 (STZ + INS) or left untreated (STZ). Neurochemical profile (consisting of 20 metabolites, PCr:Cr and Glu:Gln ratios) of the hippocampus was evaluated using ultra-high-field (9.4 T) magnetic resonance spectroscopy (MRS) on P7 (acute effects) and P56 (long-term effects) compared with the control group (CON)(N=6/group). Results: Mean glucose values from P3-P6 were higher in STZ groups (STZ = 279.0 +/- 132.2 mg/dL, STZ+INS = 274.4 +/- 89.5 mg/dL, CONT = 128.4 +/- 15.1 mg/dL). The neurochemical profile was different at both P7 and P56. On P7, compared with the control, the taurine (Tau) was higher in the STZ groups (p = 0.007. At P56, PCr:Cr was higher in the STZ group compared to CONT and STZ+INS groups (p = 0.04). No difference noted between the STZ+INS and CONT groups. No other metabolites were altered. Conclusion: Neonatal hyperglycemia alters the acute and long-term neurochemical profile in the hippocampus of developing rats. The increase in PCr:Cr ratio in the STZ group indicates lower demand for ATP and PCr, secondary to decreased neuronal activity, which has been demonstrated in previous studies. PCr:Cr ratio of the STZ+INS group was no different than control, indicating that intranasal insulin reverses the negative effect on neuronal activity caused by neonatal hyperglycemia.