Longitudinal assessment of marrow fat content using three-point Dixon technique in osteoporotic rabbits

The assessment of marrow adiposity in type 1 diabetic rabbits through magnetic resonance spectroscopy is linked to bone resorption

Background

Enhanced marrow adiposity is frequently linked with a decline in bone density. The underlying mechanisms responsible for bone loss in diabetes are not well understood. In this investigation, we employed an alloxan-induced diabetes rabbit model to unravel the association between marrow fat content and bone resorption, utilizing magnetic resonance spectroscopy.

Methods

Forty 4-month-old male New Zealand rabbits were randomly allocated into two groups: a control group and an alloxan-induced diabetic group, each consisting of 20 rabbits. Biochemical analyses covered plasma glucose, enzyme levels, lipid profiles, blood urea nitrogen, creatinine levels, and markers of bone turnover. Quantification of bone marrow adipose tissue utilized both MR spectroscopy and histological examinations. Dual-energy X-ray absorptiometry and microcomputed tomography were employed to determine bone density and trabecular bone microarchitectures. The expression levels of marrow adipocyte markers (peroxisome proliferator-activated receptor-gamma2, CCAAT/enhancer-binding protein-α, and fatty acid binding protein 4) and markers of bone resorption [tartrate-resistant acid phosphatase (TRACP) and cathepsin K] were assessed using RT-PCR.

Results

Diabetic rabbits exhibited significant increases in marrow fat fraction (MFF) over time (MFF increased by 13.2% at 1.5 months and 24.9% at 3 months relative to baseline conditions, respectively). These changes were accompanied by the deterioration of trabecular microarchitectures. Marrow adipogenesis was evident through a 31.0% increase in adipocyte size, a 60.0% rise in adipocyte number, a 103.3% increase in the percentage of adipocyte area, and elevated mRNA expressions of marrow adipocyte markers. Osteoclast markers (TRACP and cathepsin K RNA and serum TRACP5b levels) were elevated in diabetic rabbits. MFF exhibited a robust correlation with trabecular bone microarchitectures. A significant positive correlation was identified between ΔMFF and serum ΔTRACP5b levels. Moreover, MFF at 3 months showed a strong positive correlation with serum TRACP5b levels (r = 0.763), as well as with the mRNA expression of osteoclast markers, including TRACP (r = 0.784) and cathepsin K (r = 0.659), all with p <0.001.

Conclusions

Rabbits with type 1 diabetes experience an expansion of marrow adiposity, and this enhanced marrow adiposity is associated with increased osteoclast activity.

Preliminary Study of Confounder-Corrected Fat Fraction and R2* Mapping of Bone Marrow in Children With Acute Leukemia

BACKGROUND

The bone marrow (BM) evaluation of acute leukemia (AL) mainly depends on invasive BM puncture biopsy. Noninvasive and accurate MR examination technology has potential clinical application value in the BM evaluation of AL patients. Multi-gradient-echo (MGRE) has been found useful to evaluate changes in BM fat and iron content, but has not yet been applied in AL.

PURPOSE

To explore the diagnostic capability of BM infiltration of quantitative BM fat fraction (FF) and R2* values obtained from a 3D MGRE sequence in children with primary AL.

STUDY TYPE

Prospective.

POPULATION/SUBJECTS

Sixty-two pediatric patients with untreated AL and 68 healthy volunteers. AL patients were divided into acute lymphoblastic leukemia (ALL) (n = 39) and acute myeloid leukemia (AML) (n = 23) groups.

FIELD STRENGTH/SEQUENCE

3T, 3D chemical-shift-encoded multi-gradient-echo, T1WI, T2WI, T2_STIR.

ASSESSMENT

BM FF and R2* values were assessed by manually drawing regions of interest at the L3, L4, ilium, and 1 cm below the bilateral trochanter of the femur (upper femur).

STATISTICAL TESTS

Independent sample t-tests, variance analysis, Spearman correlation.

RESULTS

BM FF and R2* at L3, L4, ilium, and upper femur, FFtotal and R2*total were significantly lower in the AL than control group. BM FF did not significantly differ between ALL and AML groups (PL3  = 0.060, PL4  = 0.086, Pilium  = 0.179, Pupper femur  = 0.149, and Ptotle  = 0.097, respectively). The R2* was significantly lower in ALL group than AML group for L3, L4, and R2*total . BM FF was moderately positively correlated with R2* in ALL group, and strongly positively correlated in AML group. Area under the receiver operating characteristic curves showed that BM FF had higher AUC in AL, ALL, and AML (all AUC = 1.000) than R2* (0.976, 0.996, and 0.941, respectively).

DATA CONCLUSION

MGRE-MRI mapping can be applied to measure BM FF and R2* values, and help evaluate BM infiltration and iron storage in children with AL.

EVIDENCE LEVEL

1 Technical Efficacy: 2.

The effects of PPARγ inhibitor on bones and bone marrow fat in aged glucocorticoid-treated female rats

Progressive bone marrow (BM) fat accumulation is a common bone loss characteristic in older populations and glucocorticoid (GC)-induced skeletal destruction that is inversely associated with bone synthesis and directly associated with increased peroxisomal proliferator-activated receptor gamma (PPARγ) expression. PPARγ inhibition is an efficient therapeutic strategy for aged- and GC-related skeletal disorders. This study aimed to evaluate the effect of PPARγ inhibition on aged GC-treated female rats. It was hypothesised that bisphenol A diglycidyl ether (BADGE) could inhibit marrow adiposity and improve osteogenesis by inhibiting PPARγ, thereby preventing GC-induced osteoporosis (GIO). Female Sprague-Dawley rats (n = 32, age = 18 months) were randomly allocated to one of the following groups: (1) control, (2) BADGE (30 mg/kg/day, intraperitoneal), (3) methylprednisolone (MP; 30 mg/kg/day, subcutaneous), and (4) MP + BADGE. After eight weeks of treatment, bone density (BD) and trabecular bone microarchitectures were quantified by micro-computed tomography (CT), and BM adipocytes were quantified by histopathology. Additionally, mRNA and protein expression of adipogenic and osteogenic markers were quantified by reverse transcription-quantitative polymerase chain reaction. Furthermore, serum bone turnover biomarker levels were quantified by enzyme-linked immunosorbent assay. MP treatment led to marrow adipogenesis and bone deterioration. However, rats treated with MP + BADGE showed lower marrow adipogenesis, as indicated by smaller marrow adipocyte diameter, decreased density and area percentages, reduced expression of marrow adipogenic genes and proteins, improved BD and trabecular microarchitectures, increased expression of osteogenic genes and proteins, and higher levels of serum bone formation markers. These results were consistent with the differences observed between control and BADGE mono-treated rats. In conclusion, BADGE treatment attenuates BM adiposity and improves bone formation in aged GC-treated female rats by inhibiting PPARγ. Therefore, PPARγ might be a potential target for treating GIO in older populations.

Effects of Total Flavonoids of Epimedium on Bone Marrow Adipose Tissue in Ovariectomized Rats

Bone marrow adipose tissue has brown fat characteristics. Several studies have demonstrated that total flavonoids of Epimedium (TFE) could prevent bone loss and reduce the white adiposity in bone marrow induced by ovariectomy (OVX) in rats. However, the effects of TFE on marrow brown fat in OVX rats remain unclear. In this word, we addressed this question expected to provide a new target for preventing and treating osteoporosis. Thirty-six 3-month-old female Sprague-Dawley rats were equally divided into Sham controls, OVX controls, and OVX treated with TFE. Chemical shift coding magnetic resonance was performed to detect marrow fat fraction at the left femur at baseline, 6 and 12 weeks post-OVX. Bone mineral density at the lumbar spine and femur was measured by dual-energy x-ray absorptiometry. Serum bone biomarkers by ELISA, trabecular bone microarchitecture at the proximal tibia by micro-CT, quantitative parameters of marrow adipocyte by hematoxylin, and eosin staining were evaluated. The marrow adipocyte gene and protein expressions profile were determined by real-time quantitative PCR and immunostaining in whole tibiae. We found that TFE treatment could decrease bone turnover rate and improved bone mineral density and trabecular microarchitecture in OVX rats. OVX resulted in marrow adipogenesis as evidenced by increased marrow fat fraction, larger marrow adipocyte size, increased adipocyte number and percentage of adipocyte area, marrow white adipocyte gene, and protein expression, including PPARγ2 and FABP4. These pathological changes induced by estrogen deficiency were restored by TFE treatment. TFE also increased brown adipocyte expressions of the transcription factor Ucp1 and Prdm16 in whole tibiae. There was no detectible protein expression of brown adipocyte markers in the proximal tibia. Taken together, TFE regulation of bone marrow adiposity in OVX rats is mediated, at least in part, via maintaining the reciprocity of white and brown adipose tissue.

Reporting Guidelines, Review of Methodological Standards, and Challenges Toward Harmonization in Bone Marrow Adiposity Research. Report of the Methodologies Working Group of the International Bone Marrow Adiposity Society

The interest in bone marrow adiposity (BMA) has increased over the last decade due to its association with, and potential role, in a range of diseases (osteoporosis, diabetes, anorexia, cancer) as well as treatments (corticosteroid, radiation, chemotherapy, thiazolidinediones). However, to advance the field of BMA research, standardization of methods is desirable to increase comparability of study outcomes and foster collaboration. Therefore, at the 2017 annual BMA meeting, the International Bone Marrow Adiposity Society (BMAS) founded a working group to evaluate methodologies in BMA research. All BMAS members could volunteer to participate. The working group members, who are all active preclinical or clinical BMA researchers, searched the literature for articles investigating BMA and discussed the results during personal and telephone conferences. According to the consensus opinion, both based on the review of the literature and on expert opinion, we describe existing methodologies and discuss the challenges and future directions for (1) histomorphometry of bone marrow adipocytes, (2) ex vivo BMA imaging, (3) in vivo BMA imaging, (4) cell isolation, culture, differentiation and in vitro modulation of primary bone marrow adipocytes and bone marrow stromal cell precursors, (5) lineage tracing and in vivo BMA modulation, and (6) BMA biobanking. We identify as accepted standards in BMA research: manual histomorphometry and osmium tetroxide 3D contrast-enhanced μCT for ex vivo quantification, specific MRI sequences (WFI and H-MRS) for in vivo studies, and RT-qPCR with a minimal four gene panel or lipid-based assays for in vitro quantification of bone marrow adipogenesis. Emerging techniques are described which may soon come to complement or substitute these gold standards. Known confounding factors and minimal reporting standards are presented, and their use is encouraged to facilitate comparison across studies. In conclusion, specific BMA methodologies have been developed. However, important challenges remain. In particular, we advocate for the harmonization of methodologies, the precise reporting of known confounding factors, and the identification of methods to modulate BMA independently from other tissues. Wider use of existing animal models with impaired BMA production (e.g., Pfrt^-/-, Kit^W/W-v) and development of specific BMA deletion models would be highly desirable for this purpose.

Sclerostin Antibody Mitigates Estrogen Deficiency-Inducted Marrow Lipid Accumulation Assessed by Proton MR Spectroscopy

Sclerostin knock-out mice or sclerostin antibody (Scl-Ab) treated wild-type mice displayed decreased marrow adiposity. But the effects of Scl-Ab on estrogen deficiency-induced marrow fat expansion remain elusive. In this work, 45 female New Zealand rabbits were equally divided into sham-operation, ovariectomy controls, and ovariectomy treated with Scl-Ab for 5 months. MR spectroscopy was performed to longitudinally assess marrow fat fraction at baseline conditions, 2.5 and 5 months post-operatively, respectively. We evaluated bone mineral density (BMD), bone structural parameters, serum bone biomarkers, and quantitative parameters of marrow adipocytes. Ovariectomized rabbits markedly exhibited expansion of marrow fat in a time-dependent manner, with a variation of marrow fat fraction (+17.8%) at 2.5 months relative to baseline and it was maintained until 5 months (+30.4%, all P < 0.001), which was accompanied by diminished BMD and deterioration of trabecular microstructure. Compared to sham controls, adipocyte mean diameter, adipocyte density and adipocytes area percentage was increased by 42.9, 68.3, and 108.6% in ovariectomized rabbits, respectively. Scl-Ab treatment increased serum bone formation marker and alleviated the ovariectomy escalation of serum bone resorption marker. It remarkably lessened the ovariectomy-mediated deterioration of BMD, and morphometric characteristics of trabecular bone. Marrow fat fraction was decreased significantly with Scl-Ab to levels matching that of sham-operated controls and correlated positively with reductions in adipocyte mean diameter, percentage adipocyte volume per marrow volume, and adipocyte density. Taken together, early Scl-Ab treatment reverts marrow fat expansion seen in ovariectomized rabbits in addition to having a beneficial effect on bone mass and microstructural properties.

Bone marrow adipose amount influences vertebral bone strength

Association of bone marrow adipose and microstructure with bone strength in osteoporotic rats using MR Dixon analysis and micro-CT was evaluated. A total of 40 female Sprague-Dawley rats (6-month-old) were divided randomly into sham-operated (SHAM, n=20) group and ovariectomized (OVX, n=20) group. Fat fraction (FF) was measured by two-point Dixon method with MR imaging at the baseline, 4th, 8th and 12th week, respectively. After sacrifice by anesthesia, the fifth lumbar vertebrae bone was sampled for micro-CT scanning. The biomechanical analysis was also performed. FF in osteoporotic rats significantly increases with time, which correlates with bone microstructure parameters. Compared with biomechanical test, FF showed negative correlation with break stress and elastic modulus. It also suggested that loss of bone mass was accompanied with the increase of adipose tissue content in vertebrae bone marrow. The impairment of bone strength leads to the risk of brittle fracture. In conclusion, the bone marrow adipose amount obtained by MR Dixon and microstructure by micro-CT correlates to bone strength in osteoporotic rats.

Effect of Leptin on Marrow Adiposity in Ovariectomized Rabbits Assessed by Proton Magnetic Resonance Spectroscopy

OBJECTIVE

Leptin acts to influence bone metabolism through indirect hypothalamic relay and direct peripheral pathways. Leptin enhances the differentiation of mesenchymal stem cells to the osteoblast rather than the adipocyte lineage, but the in vivo impacts of leptin on ovariectomy (OVX)-induced marrow adiposity are poorly understood. In this work, we aimed to address this question.

METHODS

Forty-five female New Zealand rabbits were divided into sham + vehicle, OVX + vehicle, and OVX + leptin for 5 months. Magnetic resonance spectroscopy and dual-energy x-ray absorptiometry were performed to longitudinally evaluate marrow fat fraction and bone density at 0, 2.5, and 5 months, respectively. At the end of experiment, quantitative parameters of marrow adipocytes were assessed by histopathology.

RESULTS

Estrogen-deficient rabbits markedly exhibited expansion of marrow fat in a time-dependent manner, with a variation of marrow fat fraction (+19.7%) at 2.5 months relative to baseline conditions, and it was maintained until 5 months (+49.2%; all P < 0.001), which was accompanied by diminished bone density. Adipocyte diameter, density, and adipocytes area percentage in the OVX controls was increased by 50.7%, 76.3%, and 135.5%, respectively, relative to the sham controls (all P < 0.001). These OVX-induced marrow adiposity and bone loss were partly restored by leptin treatment. Treatment with leptin prevented OVX-induced increases in bone turnover in rabbits.

CONCLUSIONS

Early leptin administration inhibits the adipogenic effect of estrogen deficiency in terms of reverting marrow fat expansion seen in OVX rabbits. Magnetic resonance spectroscopy may be a useful tool for longitudinal and interventional assessments in osteoporosis.

Renal fat fraction and diffusion tensor imaging in patients with early-stage diabetic nephropathy

OBJECTIVE

To investigate the renal fat fraction and water molecular diffusion features in patients with early-stage DN using Dixon imaging and diffusion tensor imaging (DTI).

METHODS

Sixty-one type 2 diabetics (normoalbuminuria: n = 40; microalbuminuria: n = 21) and 34 non-diabetic volunteers were included. All participants received three-point Dixon imaging and DTI using a 3.0-T magnetic resonance imager. The fat fraction [FF] and DTI features [fractional anisotropy (FA), apparent diffusion coefficient (ADC), tract counts and length from DTI tractography] were collected. All image features were compared between cohorts using one-way ANOVA with Bonferroni post-hoc analysis.

RESULTS

Renal FF in the microalbuminuric group was significantly higher than in the normoalbuminuric and control groups (5.6% ± 1.3%, 4.7% ± 1.1% and 4.3% ± 0.5%, respectively; p < 0.001). Medullary FA in the microalbuminuric group was the lowest (0.31 ± 0.06) in all cohorts. The tract counts and length in the renal medulla were significantly lower in the microalbuminuric group than in the other two groups.

CONCLUSIONS

Dixon imaging and DTI are able to detect renal lipid deposition and water molecule diffusion abnormalities in patients with early-stage DN. Both techniques have the potential to noninvasively evaluate early renal impairment in type 2 diabetes.

KEY POINTS

• Dixon imaging demonstrated renal fat deposition in early-stage DN; • Renal fractional anisotropy decreased in patients with early-stage DN; • Renal tractography demonstrated reduced track counts and length in early-stage DN.

Magnetic Resonance Spectroscopy-Detected Change in Marrow Adiposity Is Strongly Correlated to Postmenopausal Breast Cancer Risk

PURPOSE

To determine whether marrow fat fraction (FF) is correlated with postmenopausal breast cancer risk and clinicopathological characteristics of breast cancer.

METHODS

Fifty-six patients with newly diagnosed and histologically confirmed postmenopausal breast cancer and 56 healthy controls underwent serologic test and magnetic resonance spectroscopy-based FF measurements. Data were analyzed by logistic multivariate regression models to determine the independent predictors of breast cancer risk and clinicopathological characters of breast cancer.

RESULTS

Patients with breast cancer had higher FF than that of the controls. Marrow FF showed positive association with serum leptin levels (r = 0.607, P < .001) in the cases, but no relationship was found in the controls. In the univariate analysis, both levels of leptin and marrow FF were significantly associated with breast cancer risk and clinicopathological characteristics of breast cancer. In the multivariable model with adjustment for established breast cancer risk factors, serum leptin was a significant predictor of breast cancer risk (OR 1.746; 95% CI, 1.226-2.556) and clinicopathological characteristics of breast cancer including TNM, tumor size, lymph node status, and histological grade (OR 1.461-1.695); but when marrow FF was additionally added to the regression model, marrow FF but not leptin levels was observed to be an independent risk factor for breast cancer risk (OR 1.940; 95% CI, 1.306-2.910) and clinicopathological characteristics of breast cancer (OR 1.770-1.903).

CONCLUSION

Marrow adiposity is a predictor of postmenopausal breast cancer risk and clinicopathological characteristics of breast cancer.

Differential effects of bisphenol A diglicydyl ether on bone quality and marrow adiposity in ovary-intact and ovariectomized rats

Bisphenol A diglycidyl ether (BADGE), a PPARγ2 antagonist, has been shown to inhibit marrow adipogenesis and promote bone formation in intact animals. We investigated the impact of BADGE on a new and more clinically relevant physiological model, the ovariectomized (OVX) rat model. Forty female Wistar rats were divided into four treatment groups for 12 wk (n = 10/group): sham+vehicle, sham+BADGE, OVX+vehicle, and OVX+BADGE. Postmortem analyses included MRI, micro-CT, serological test, histomorphometry, biomechanical tests, RT-PCR, and Western blot. Overall, OVX induced a sequential marrow fat expansion accompanied by bone deterioration. Compared with OVX controls, BADGE reduced fat fraction of the distal femur by 36.3%, adipocyte density by 33.0%, adipocyte size by 28.6%, adipocyte volume percentage by 57.8%, and adipogenic markers PPARγ2 and C/EBPα by ∼50% in OVX rats. Similar results were observed in sham rats vs. vehicle. BADGE could promote bone quality in sham rats; however, BADGE did not significantly improve trabecular microarchitecture, biomechanical strength, and dynamic histomorphometric parameters except for trabecular separation in OVX rats. We concluded that early BADGE treatment at a dose of 30 mg/kg attenuates marrow adiposity in ovary-intact and OVX rats and stimulates bone formation in ovary-intact rats but does not significantly rescue bone quality in OVX rats.