Sitagliptin Alters Bone Composition in High-Fat-Fed Mice

Type 2 diabetes mellitus is recognized as a significant risk factor for fragility of bone. Among the newer anti-diabetic agents, dipeptidyl peptidase-4 inhibitors (DPP4i) have been reported to decrease the occurrence of bone fractures although the reason is unclear. The main aim of this study was to evaluate the impact of sitagliptin treatment on tissue bone strength and compositional parameters in the high-fat-fed mouse model. Male NIH swiss mice were allowed free access to high-fat diet for 150 days to induce chronic hyperglycemia and insulin resistance. Sitagliptin was administered once daily for 3 weeks. High-fat-fed mice administered with saline were used as controls. Bone strength was assessed at the organ and tissue level by three-point bending and nanoindentation, respectively. Bone microarchitecture was investigated by microcomputed tomography and bone composition was evaluated by Fourier transform infrared imaging and quantitative backscattered electron imaging. Administration of sitagliptin increased non-fasting insulin, improved glucose tolerance and increased insulin sensitivity. This was associated with clear ameliorations in bone strength at the organ and tissue level. No changes in trabecular or cortical microarchitectures were observed. On the other hand, higher values of Ca_mean, Ca_turn, collagen maturity, mineral/matrix ratio, mineral maturity and crystal size index were evidenced after sitagliptin treatment. Correlation analysis significantly linked the modifications of bone strength to changes in bone compositional parameters. These results bring new light on the mode of action of sitagliptin on bone physiology and demonstrate a benefit of DPP4i.

The GLP-1 Receptor Agonist Exenatide Ameliorates Bone Composition and Tissue Material Properties in High Fat Fed Diabetic Mice

Type 2 diabetes mellitus (T2DM) has recently been recognized as a significant risk factor for bone fragility. Careful investigations of bone mechanical properties in human studies suggested possible alterations of bone composition, although this axis has poorly been investigated. The main aim of this study was to evaluate the impact of high fat diet-induced diabetes and therapy using the clinically approved GLP-1 receptor agonist, exenatide, on tissue bone mechanical properties and compositional parameters. Male mice had free access to high fat diet for 16 weeks to induce diabetes prior to commencement of the study. Exenatide was administered twice daily by i.p. injection at a dose of 25 nmol/kg for 52 days. Normal and high fat diet fed (HFD) mice injected with saline were used as controls. Bone mechanical properties was assessed at the organ level by 3-point bending and at the tissue level by nanoindentation. Bone microarchitecture was investigated by microcomputed tomography and bone composition was evaluated by Fourier transform infrared imaging. HFD mice exhibited profound alterations of bone mechanical properties at both the organ and tissue level. Collagen maturity as well as trabecular and cortical bone microarchitectures were abnormal. Administration of exenatide, led to clear ameliorations in bone mechanical properties at the organ and tissue levels by modifications of both cortical microarchitecture and bone compositional parameters (collagen maturity, mineral crystallinity, carbonate/phosphate ratio, acid phosphate content). These results bring new light on the mode of action of exenatide in bone physiology and demonstrate the value of GLP-1 mimetics in the treatment of fragility fractures in diabetes.

A new stable GIP-Oxyntomodulin hybrid peptide improved bone strength both at the organ and tissue levels in genetically-inherited type 2 diabetes mellitus

Obesity and type 2 diabetes mellitus (T2DM) progress worldwide with detrimental effects on several physiological systems including bone tissue mainly by affecting bone quality. Several gut hormones analogues have been proven potent in ameliorating bone quality. In the present study, we used the leptin receptor-deficient db/db mice as a model of obesity and severe T2DM to assess the extent of bone quality alterations at the organ and tissue levels. We also examined the beneficial effects of gut hormone therapy in this model by using a new triple agonist ([d-Ala(2)]GIP-Oxm) active at the GIP, GLP-1 and glucagon receptors. As expected, db/db mice presented with dramatic alterations of bone strength at the organ level associated with deterioration of trabecular and cortical microarchitectures and an augmentation in osteoclast numbers. At the tissue level, these animals presented also with alterations of bone strength (reduced hardness, indentation modulus and dissipated energy) with modifications of tissue mineral distribution, collagen glycation and collagen maturity. The use of [d-Ala(2)]GIP-Oxm considerably improved bone strength at the organ level with modest effects on trabecular microarchitecture. At the tissue level, [d-Ala(2)]GIP-Oxm ameliorated bone strength reductions with positive effects on collagen glycation and collagen maturity. This study provides support for including gut hormone analogues as possible new therapeutic strategies for improving bone quality in bone complications associated to T2DM.

Stable Incretin Mimetics Counter Rapid Deterioration of Bone Quality in Type 1 Diabetes Mellitus

Type 1 diabetes mellitus is associated with a high risk for bone fractures. Although bone mass is reduced, bone quality is also dramatically altered in this disorder. However, recent evidences suggest a beneficial effect of the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) pathways on bone quality. The aims of the present study were to conduct a comprehensive investigation of bone strength at the organ and tissue level; and to ascertain whether enzyme resistant GIP or GLP-1 mimetic could be beneficial in preventing bone fragility in type 1 diabetes mellitus. Streptozotocin-treated mice were used as a model of type 1 diabetes mellitus. Control and streptozotocin-diabetic animals were treated for 21 days with an enzymatic-resistant GIP peptide ([D-Ala(2) ]GIP) or with liraglutide (each at 25 nmol/kg bw, ip). Bone quality was assessed at the organ and tissue level by microCT, qXRI, 3-point bending, qBEI, nanoindentation, and Fourier-transform infrared microspectroscopy. [D-Ala2]GIP and liraglutide treatment did prevent loss of whole bone strength and cortical microstructure in the STZ-injected mice. However, tissue material properties were significantly improved in STZ-injected animals following treatment with [D-Ala2]GIP or liraglutide. Treatment of STZ-diabetic mice with [D-Ala(2) ]GIP or liraglutide was capable of significantly preventing deterioration of the quality of the bone matrix. Further studies are required to further elucidate the molecular mechanisms involved and to validate whether these findings can be translated to human patients.

Alteration of the bone tissue material properties in type 1 diabetes mellitus: A Fourier transform infrared microspectroscopy study

Type 1 diabetes mellitus (T1DM) is a severe disorder characterized by hyperglycemia and hypoinsulinemia. A higher occurrence of bone fractures has been reported in T1DM, and although bone mineral density is reduced in this disorder, it is also thought that bone quality may be altered in this chronic pathology. Vibrational microscopies such as Fourier transform infrared microspectroscopy (FTIRM) represent an interesting approach to study bone quality as they allow investigation of the collagen and mineral compartment of the extracellular matrix in a specific bone location. However, as spectral feature arising from the mineral may overlap with those of the organic component, the demineralization of bone sections should be performed for a full investigation of the organic matrix. The aims of the present study were to (i) develop a new approach, based on the demineralization of thin bone tissue section to allow a better characterization of the bone organic component by FTIRM, (ii) to validate collagen glycation and collagen integrity in bone tissue and (iii) to better understand what alterations of tissue material properties in newly forming bone occur in T1DM. The streptozotocin-injected mouse (150 mg/kg body weight, injected at 8 weeks old) was used as T1DM model. Animals were randomly allocated to control (n = 8) or diabetic (n = 10) groups and were sacrificed 4 weeks post-STZ injection. Bones were collected at necropsy, embedded in polymethylmethacrylate and sectioned prior to examination by FTIRM. FTIRM collagen parameters were collagen maturity (area ratio between 1660 and 1690 cm(-1) subbands), collagen glycation (area ratio between the 1032 cm(-1) subband and amide I) and collagen integrity (area ratio between the 1338 cm(-1) subband and amide II). No significant differences in the mineral compartment of the bone matrix could be observed between controls and STZ-injected animals. On the other hand, as compared with controls, STZ-injected animals presented with significant higher value for collagen maturity (17%, p = 0.0048) and collagen glycation (99%, p = 0.0121), while collagen integrity was significantly lower by 170% (p = 0.0121). This study demonstrated the profound effect of early T1DM on the organic compartment of the bone matrix in newly forming bone. Further studies in humans are required to ascertain whether T1DM also lead to similar effect on the quality of the bone matrix.