Changes in Bone Turnover With Exposure to a GLP-1 Receptor Agonist

The purpose of this study is to determine changes in bone turnover markers and calcitonin following the initiation of exenatide compared to placebo in postmenopausal women wtih type 2 diabetes.

Hypothesis 1a: Bone resorption (measured by osteocalcin and bone-specific alkaline phosphatase) will be lower and bone formation (measured by type I collagen crosslinked aminoterminal peptide in urine (Urine NTX)) will be higher when subjects are treated with exenatide compared to when subjects are treated with placebo.

Hypothesis 1b: Calcitonin levels will not vary significantly between periods of treatment with exenatide vs. placebo.

Patients with Type 2 Diabetes Mellitus (T2DM) are at an increased risk of fracture, despite having bone mineral density (BMD) levels similar to age and sex matched cohorts. Recent studies have indicated that changes in incretin (INtestinal seCRETion of INsulin) hormones in the setting of T2DM may play a role in bone metabolism. Two of these incretin hormones, gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), have been shown to be involved in bone turnover regulation, in addition to their effect in increasing insulin secretion and decreasing glucagon secretion in a glucose-dependent manner. In addition, the rise in glucagon-like peptide-2 (GLP-2) in the postprandial state has been found to have a direct effect on reduced bone resorption in a non-fasting state and treatment with GLP-2 improved BMD in postmenopausal women. Due to their glucose lowering effects, incretin hormones have been a therapeutic target for the treatment of T2DM through GLP-1 receptor agonists (i.e. exenatide) or inhibition of incretin hormone metabolism via dipeptidyl peptidase 4 (DPP-4)inhibitors. The GLP-1 receptor analog exenatide leads to an approximate 13-fold increased GLP-1 effect compared to approximate doubling of incretin hormone levels with current DDP-4 inhibitors. In rodent models, calcitonin levels rise significantly following treatment with GLP-1 receptor agonists, leading to c-cell hyperplasia. However, review of calcitonin changes in humans and cynomolgus monkeys treated with GLP-1 receptor agonists have not shown similar results.

Eligibility Criteria:
Inclusion Criteria:

* Postmenopausal women (as defined by age ≥45 years old or amenorrhea for \>2years)
* Type 2 DM currently not on diabetes-specific medication(s) or treated with monotherapy of metformin or a sulfonylurea. Patients treated with insulin monotherapy will also be eligible if the total daily dose of insulin is ≤10units. If on a medication for diabetes prior to study entry, the medication can be discontinued for 2 weeks prior to study initiation.
* Hemoglobin A1c (HbA1c) of 6.5-9.0%

Exclusion Criteria:

* Use of an incretin mimetic (i.e. exenatide, liraglutide), a DPP-4 inhibitor (i.e. sitagliptin, saxagliptin), a thiazolidinedione, or oral glucocorticoids in the 6 months prior to the study will not be eligible
* Known osteoporosis or patients treated with an osteoporosis-specific medication (bisphosphonate, teriparatide) or estrogen (including Selective Estrogen Receptor Modulators (SERMs)) or those who anticipate imminent treatment with one of these medications will be excluded from the study
* Chronic kidney disease (calculated GFR \<30 ml/min) or a disease known to affect bone turnover (i.e. Paget Disease, Osteogenesis Imperfecta, HIV) will be excluded from the study.
* History of pancreatitis