Vertebral marrow fat content and diffusion and perfusion indexes in women with varying bone density: MR evaluation

Analysis of bone marrow fatty acid composition using high-resolution proton NMR spectroscopy

High-resolution 1H NMR spectroscopy as a complementary method in the analysis of human bone marrow fatty acid (FA) composition was examined. Marrow FA composition in 10 bone samples measured by NMR and gas chromatography (GC) were compared. NMR T1 relaxation time of FA was determined and reproducibility tests were performed to assess the variability. Good correlations were obtained between the NMR and GC results for omega-6 polyunsaturated fatty acid (PUFA) (Spearman r, 0.878), omega-3 PUFA (0.895), monounsaturated FA (0.964) and saturated FA (0.939). The NMR method tended to overestimate saturated FA and underestimate omega-3/omega-6 ratio compared to GC results. T1 relaxation time of marrow FA was 0.56-3.65s. Coefficient of variation of the NMR method was 0.6-8.2% in intra-experimental and 0.2-8.4% in inter-experimental measurements. This study demonstrates a complementary role for 1H NMR spectroscopy as an additional analytical tool in human lipid research.

Elevated adipogenesis of marrow mesenchymal stem cells during early steroid-associated osteonecrosis development

Background

Increased bone marrow lipid deposition in steroid-associated osteonecrosis (ON) implies that abnormalities in fat metabolism play an important role in ON development. The increase in lipid deposition might be explained by elevated adipogenesis of marrow mesenchymal stem cells (MSCs). However, it remains unclear whether there is a close association between elevated adipogenesis and steroid-associated ON development.

Objective

The present study was designed to test the hypothesis that there might be a close association between elevated adipogenesis and steroid-associated ON development.

Methods

ON rabbit model was induced based on our established protocol. Dynamic-MRI was employed for local intra-osseous perfusion evaluation in bilateral femora. Two weeks after induction, bone marrow was harvested for evaluating the ability of adipogenic differentiation of marrow MSCs at both cellular and mRNA level involving adipogenesis-related gene peroxisome proliferator-activated receptor gamma2 (PPARγ2). The bilateral femora were dissected for examining marrow lipid deposition by quantifying fat cell number, fat cell size, lipid deposition area and ON lesions. For investigating association among adipogenesis, lipid deposition and perfusion function with regard to ON occurrence, the rabbits were divided into ON⁺ (with at least one ON lesion) group and ON^- (without ON lesion) group. For investigating association among adipogenesis, lipid deposition and perfusion function with regard to ON extension, the ON⁺ rabbits were further divided into sub-single-lesion group (SON group: with one ON lesion) and sub-multiple-lesion group (MON group: with more than one ON lesion).

Results

Local intra-osseous perfusion index was found lower in either ON⁺ or MON group when compared to either ON^- or SON group, whereas the marrow fat cells number and area were much larger in either ON⁺ or MON group as compared with ON^- and SON group. The adipogenic differentiation ability of MSCs and PPARγ2 expression in either ON⁺ or MON group were elevated significantly as compared with either ON^- or SON group.

Conclusion

These findings support our hypothesis that there is a close association between elevated adipogenesis and steroid-associated osteonecrosis development.

Quantitative and diffusion MR imaging as a new method to assess osteoporosis

BACKGROUND AND PURPOSE

The role of advanced MR imaging techniques in demonstrating the microarchitectural changes in osteoporosis has been recently investigated. Our aim was to determine the role of quantitative and diffusion MR imaging in the diagnosis of osteoporosis compared with dual-energy x-ray absorptiometry (DEXA).

MATERIALS AND METHODS

Fifty-one subjects underwent both DEXA and conventional MR imaging with diffusion and apparent diffusion coefficient (ADC) mapping. T1, T2, diffusion signal intensity, and ADC values were calculated and compared with bone mineral attenuation (BMD). Results were obtained from L1 to L4 of each patient with a total of 204 lumbar vertebrae.

RESULTS

Both T1 and T2 signal intensities tended to increase when both diffusion and ADC values decreased with reducing BMD.

CONCLUSIONS

An inverse relationship between BMD and T1 and T2 signal intensities and a direct relationship between diffusion and ADC values were present in this pilot group. The T1/diffusion signal-intensity ratio could be a reliable diagnostic indicator of osteoporosis.

Type I diabetic bone phenotype is location but not gender dependent

Bone is highly dynamic and responsive. Bone location, bone type and gender can influence bone responses (positive, negative or none) and magnitude. Type I diabetes induces bone loss and increased marrow adiposity in the tibia. We tested if this response exhibits gender and location dependency by examining femur, vertebrae and calvaria of male and female, control and diabetic BALB/c mice. Non-diabetic male mice exhibited larger body, muscle, and fat mass, and increased femur BMD compared to female mice, while vertebrae and calvarial bone parameters did not exhibit gender differences. Streptozotocin-induced diabetes caused a reduction in BMD at all sites examined irrespective of gender. Increased marrow adiposity was evident in diabetic femurs and calvaria (endochondrial and intramembranous formed bones, respectively), but not in vertebrae. Leptin-deficient mice also exhibit location dependent bone responses and we found that serum leptin levels were significantly lower in diabetic compared to control mice. However, in contrast to leptin-deficient mice, the vertebrae of T1-diabetic mice exhibit bone loss, not gain. Taken together, our findings indicate that TI-diabetic bone loss in mice is not gender, bone location or bone type dependent, while increased marrow adiposity is location dependent.