Purpose

Type 2 diabetes (T2D) is a growing worldwide disease that is known to negatively influence bone quality¹. Patients with T2D have increased fracture risk despite normal or even elevated bone mineral density (BMD) ². Recently, the association of bone marrow fat (BMF) with bone quality and strength has been a focus of research. Several studies demonstrated that increased BMF is highly associated with low BMD, poor bone structure or increased fracture risk^3,4. MR spectroscopy (MRS) is a non-invasive, in-vivo technique that is widely used to quantify BMF and provides several biomarkers for better understanding the relationship between altered BMF and bone diseases^5,6. The purpose of this study is to quantify and compare the BMF of T2D patients and healthy controls at the spine and lower extremities using MRS technique. We hypothesize that T2D patients will have altered BMF and bone marrow composition biomarkers at the vertebrae and distal tibia.

Methods

Participants with T2D and diabetes pharmacologic treatment for a minimum of 3 years were frequency matched for age, sex, and body mass index (BMI) with non-diabetic controls and enrolled in this study. For the vertebral scans, 37 T2D patients (17 males and 20 females; mean age = 61.3±5.5 years) and 36 controls (13 males and 23 females; mean age = 62.7±5.5 years) were included. For the distal tibia scans, 30 T2D patients (15 males and 15 females; mean age = 62.5±5.4 years) and 32 controls (13 males and 19 females; mean age = 60.7±5.6 years) were included. All participants were underwent DXA imaging and completed medical history questionnaires. They were included in the study only if they had a DXA T-score between 0 and −2.4 and did not take bone-active medications. Before performing MRS, a sagittal T2‐weighted fast spin echo (FSE) sequence (TR/TE = 4500/68ms, bandwidth = ±31.25 kHz/pixel; flip angle = 142° [vertebral] or 111° [distal Tibia]; FOV = 24mm [vertebral] or 16mm [distal tibia], slice thickness = 5mm) was performed on a 3T whole-body scanner (MR750, GE Healthcare) for visual inspection of bone fractures and leisions as well as for prescription of the MRS acquisition box. Single voxel MRS data were acquired using Stimulated Echo Acquisition Mode (STEAM) method with the sequence parameters: TR/TE = 3000/20ms [vertebral] or 3000/30ms [distal tibia]; BW=5 kHz; data point=4096. For vertebral scans, the volume of interest (15 x 12 x 12 mm) was located in the center of the vertebral bodies L3 and L4. For distal tibia scans, the 15 x 10 x 10 mm single voxel was located with the center 34.5 mm proximal to the joint line. MRS data were analyzed using in-house software based on previous work⁷. Each individual channel data were processed with frequency and phase corrections and then combined using the peak at 1.3ppm. Smoothing (line broadening = 15) was applied on the combined signal to remove noise. Spectra data were fitted using a Voigt model ⁸, and each biomarker was calculated as follows: (1) fat content (FC) = total lipids/water+total lipids, (2) unsaturated content (UC) = unsaturated lipid (5.3 ppm)/water+total lipids, (3) Saturated content (SC) = saturated lipid (1.3 ppm)/water+total lipids, and (4) residual content (RC) = residual lipid (2.0 ppm)/water+total lipids. Generalized estimating equations (accounting for multiple measurements per person) were used to assess the relationship between T2D and MRS outcomes in vertebral regions L3 and L4. Linear regression was used to assess the relationship between T2D and MRS outcomes in the distal tibia.

Results

Examples of MRS data and fitting results are demonstrated in Fig. 1. In men, at the vertebra, UC was significantly lower in T2D patients compared to controls (coeff. = -0.61; 95%CI = [-1.08 -0.14]; p=0.011). FC trended lower in T2D patients compared to controls (coeff. = -3.96; 95%CI = [-8.48 0.56]; p=0.086) (Fig.2). In men, at the distal tibia, FC, UC, SC, and RC were similar between groups (Fig 3). In women, no significant differences were found between groups at either anatomic site (P>0.05).

Discussion and Conclusions

We present a sex-stratified analysis of BMF and marrow composition, the results suggest a sex-specific relationship between T2D and marrow composition. In men (but not in women) we found lower unsaturated lipid levels within vertebral bone marrow in patients with T2D compared to controls. Contrary to our expectations, we did not find increased overall fat content in either T2D group. Previous reports are inconsistent, with some studies reporting decreased unsaturated lipid levels and increased overall fat content in T2D and others reporting no differences in unsaturated lipid and overall fat content between T2D and controls^9-13.Taken as a whole, these data suggest that T2D may change vertebral marrow composition, which may be a factor in the development of diabetic bone pathology. However, more detailed analyses and larger cohort studies are necessary. Ongoing research will focus on longitudinal analyses to confirm the associations of BMF alterations with bone quality and strength, and particularly in the development of pathological porosity in T2D progression.

Acknowledgements

This study is supported by NIH NIAMS R01AR069670, NIH NIAMS R01AR076159 and UCSF Academic Senate Committee on Research

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