Reversibility of Brain Glucose Transport and Metabolism in T2DM: an Intervention Study

Specific Aim 1: To compare brain glucose transport and metabolism in age, BMI, and HbA1c matched T2DM individuals with either long duration of diabetes or short duration of diabetes using brain 1H MRSI during hyperglycemic clamp

Hypothesis: T2DM individuals with chronic uncontrolled diabetes will have lower brain glucose levels as compared with age, BMI, and HbA1c matched T2DM individuals with shorter duration of diabetes.

Screening visit: Volunteers will be screened at the Yale New Haven Hospital (YNHH) Hospital Research Unit (HRU) or Yale Center for Clinical Investigation (YCCI) Church street Research Unit (CSRU) with a medical history and exam. Blood tests will be collected for A1C, ALT, TSH, Hgb and Creatinine. A urine pregnancy test will be performed on all women of childbearing potential, and women who are pregnant will be excluded.

Continuous Glucose Monitoring (CGM): Participants will wear for 14 days prior to the MRSI scanning sessions a CGM (FreeStyle Libre Pro glucose monitoring system) to continuously monitor their interstitial blood glucose levels. Given that this data is blinded, patients will be informed that it is not a replacement for self-monitoring of blood glucose. Subjects should continue their normal testing routine while wearing the sensor. CGM placement will take place at the HRU or CSRU. Those not already using CGM in their usual care will be trained in its proper use by experienced study staff. Patients already using CGM will be allowed to use their usual CGM, however, they will also be asked to wear a second blinded study sensor. Subjects will be provided with our contact information in the event that they have any questions, concerns or issues related to the CGM. Intense exercise may cause the sensor to loosen due to sweat or movement of the sensor. If the CGM sensor falls off while the subject is wearing it, subjects will be asked to return to the HRU or CSRU so that a new sensor can be re-inserted.

The CGM consists of a sensor that measures glucose levels from the interstitial tissue. The sensor is sterile and comes in an unopened package. It has a plastic wire-like tip that is placed under the skin and continuously measures the glucose levels. A trained study staff member will insert the CGM wirelike tip under the volunteer's skin with the use of the CGM sensor insertion kit. Each sensor is single use only and disposable. The FreeStyle Libre Pro does not require any calibration, as is the case with other CGM devices. This means that no finger sticks are required for its use.

CGM removal: After 14 days of wearing the CGM, it will be removed by a trained study staff member on the on the same day as the subject's scan. To remove the sensor, the adhesive patch will be gently peeled off from the skin, together with the sensor. Removal of the sensor is a painless procedure. The sensor will be discarded after use.

MRSI scanning and Hyperglycemic Clamp: Participants will arrive at MRRC at 7AM on the morning of the study after an 8 hour overnight fast. A urine pregnancy test will be performed on all women of childbearing potential, and women who are pregnant will be excluded. Following IV placements and baseline blood collection, at ~8 AM all T2DM subjects will receive insulin infusion to keep plasma glucose levels at ~100-110 mg/dl. Once glucose levels are stabilized, the subjects will be transferred into the 4T scanner for the hyperglycemia clamp.

Subjects will lie supine in a 4.0 T whole-body magnet interfaced to a Bruker AVANCE spectrometer (Bruker Instruments) with the head immobilized with foam inserts on top of a radiofrequency probe consisting of a 1H coil, as previously described by our group. A nurse experienced with working in a MRS environment will be with subjects at all times. If patients express discomfort or anxiety and ask to be removed from the scanner, the session will be immediately terminated.

Following the 45-minute baseline scan, subjects will remain in the scanner for continuous scanning during the hyperglycemic clamp. An infusion of 20% dextrose at a variable rate to maintain plasma glucose levels at 220 mg/dL for 2 hours. Glucose infusion rates will be adjusted in response to plasma glucose levels measured every 5-10 minutes. Subjects will be able to take breaks as needed during the 2 hours hyperglycemic clamp and MRS scan. During the clamp study a series of hormones will be obtained including insulin levels, GLP1, leptin and free fatty acids.

Neurocognitive testing: Participants will undergo a panel of cognitive testing to assess working memory, learning and executive function; visual, verbal and episodic memory; attention, information processing and reaction time; social and emotion recognition, decision making and response control (CANTAB Cognitive research software, Cambridge Cognition).

Specific Aim 2: To assess the impact that duration of diabetes has on reversibility of brain glucose transport kinetics as assessed by 1H MRSI scanning before and after a 12-week intervention to improve glycemic control

Hypothesis: Participants with shorter duration of diabetes (<5 years) will have greater magnitude of restoration of brain glucose transport parameters compared to T2DM participants with longer duration of diabetes (>5 years).

Subjects: Subjects from Aim 1 will undergo intensification of their diabetes management for a period of 12-week and at the end of the intervention they will undergo 1H MRSI scanning to measure intracerebral and plasma glucose levels at euglycemia and following 2 hours of hyperglycemia using the clamp technique (target glucose 220 mg/dl) in the occipital region. (Figure 2)

Intensification of insulin regimen/Nutrition visit:

The intensification of the diabetes regimens will be managed by Dr. Sanchez Rangel, a fully trained attending endocrinologist, and will follow the general strategies outlined in the Position Statement of the American Diabetes Association and the European Association for the Study of Diabetes. All participants will receive exercise and dietary counseling from Mary Savoye, a nutritionist and registered dietician with extensive experience with working with individuals with diabetes and obesity, and who has worked with Dr. Sanchez Rangel on her current pilot. The weight goal will be to have no more than 5% weight change. Participants will have regular phone and in-person MD and nutritionist communication over the course of the 12-week study. All individuals will be asked to perform SMBG at least 4 times a day (before breakfast, lunch, dinner, and bedtime). The daily SMBG records will be sent to Dr. Sanchez Rangel weekly for review to guide adjustment of insulin regimens. Target blood glucose levels will be between 80-130 mg/dl before meals and between < 180 mg/dl at bedtime. Individuals not at goal glycemic targets will undergo intensification of their regimen. Throughout the study, individuals will be contacted via telephone call, email or through additional clinic visits as deemed necessary for maintenance of glycemic control. All individuals will receive education regarding the detection and proper management of hypoglycemia.

Continuous Glucose Monitoring (CGM): Identical to Aim 1.

MRSI scanning and Hyperglycemic Clamp: Study design will be identical to Aim 1

Neurocognitive testing: Study design will be identical to Aim 1