Testing Glial Pathways to HAAF in Human Subjects Using Carbon 13 Magnetic Resonance Spectroscopy

Following the detection of severe hypoglycemia by the central nervous system (CNS), a series of physiological countermeasures are triggered which return serum glucose to euglycemic levels. This vital homeostatic response frequently becomes dysfunctional in both type 1 and type 2 diabetics, leaving them particularly vulnerable to life threatening bouts of hypoglycemia. This dysfunction, often termed hypoglycemia-associated autonomic failure (HAAF), is thought to be caused by maladaptive changes in the CNS. Currently, progress towards rectifying this HAAF is severely hindered by a lack of knowledge regarding the exact nature of these maladaptive changes and the antecedent events which cause them. Previous work by the PI, as well as others, has identified altered glial metabolism as a potential biological substrate driving HAAF. The alterations in glial metabolism associated with HAAF are strikingly similar to those induced by prolonged dietary restriction in rodents. This raises the intriguing possibility that HAAF may be driven by glial adaptations, normally induced only by prolonged starvation, which are triggered in diabetic individuals by treatment-induced exposure to severe hypoglycemia. The primary goal of our pilot project is to conduct a prospective observational study in humans to test the hypothesis that prolonged fasting will induce changes in glial metabolism similar to those previously measured in individuals with HAAF. The investigators will accomplish this goal via the following specific aims: Aim 1: Using a prospective observational study design in humans, test whether a 72 hour fast will induce acute alterations in glial metabolism, Aim 2: Determine if changes in plasma glucose and leptin levels following prolonged fasting are correlated with changes in glial adaptation. The investigators will utilize innovative 13C magnetic resonance spectroscopy to measure alterations in glial metabolism and substrate preference following acute dietary restriction in healthy young individuals. By demonstrating that metabolic adaptations of glial cells induced by prolonged fasting are similar to those previously associated with HAAF, the investigators can provide key insights into the precursors that may lead to the development of HAAF in diabetic individuals.

Inclusion criteria

• Male
• BMI 20.0-24.9 kg/m2
• 18-40 years old
• Willing to reside at Pennington Biomedical for 4 days

Exclusion criteria

• Type 1 diabetes mellitus
• Type 2 diabetes mellitus
• Fasting glucose ≥ 110 mg/dL (determined at screening visit)
• Hyperketonuria >15 mg/dL, (determined at screening visit)
• Contraindication to MRI
• History of or current eating disorder
• History of obsessive compulsive disorder
• Current use of any medication (excluding over-the-counter pain medication)
• Contraindication to prolonged fasting
• Consume >10 alcoholic drinks/week