Aleksandra Mieczkowska

Use of glucagon-like peptide-1 receptor agonists and bone fractures: a meta-analysis of randomized clinical trials.

Patients with type 2 diabetes mellitus (T2DM) are at a higher risk of bone fractures independent of the use of antidiabetic medications. Furthermore, antidiabetic medications could directly affect bone metabolism. Recently, the use of dipeptidyl peptidase‐4 inhibitors has been associated with a lower rate of bone fracture. The aim of the present meta‐analysis was to assess whether patients with T2DM treated with glucagon‐like peptide‐1 receptor agonists (GLP‐1Ra) present a lower incidence of bone fracture compared with patients using other antidiabetic drugs.

Thiazolidinediones Induce Osteocyte Apoptosis by a G Protein-coupled Receptor 40-dependent Mechanism

Background: Thiazolidinediones (TZDs) mediate osteocyte apoptosis and sclerostin up-regulation by an unknown mechanism. Results: Osteocyte apoptosis is mediated through activation of Erk1/2 and p38, whereas sclerostin up-regulation is through peroxisome proliferator-activated receptor-γ (PPARγ) signaling. Conclusion: TZDs signal not exclusively through PPARγ, as thought, but also via a surface receptor called GPR40. Significance: Learning how TZDs signal in bone cells is crucial to prevent adverse effects associated with the use of these drugs. Thiazolidinediones (TZDs) represent an interesting treatment of type 2 diabetes mellitus. However, adverse effects such as heart problems and bone fractures have already been reported. Previously, we reported that pioglitazone and rosiglitazone induce osteocyte apoptosis and sclerostin up-regulation; however, the molecular mechanisms leading to such effects are unknown. In this study, we found that TZDs rapidly activated Erk1/2 and p38. These activations were mediated through Ras proteins and GPR40, a receptor expressed on the surface of osteocytes. Activation of this pathway led only to osteocyte apoptosis but not sclerostin up-regulation. On the other hand, TZDs were capable of activating peroxisome proliferator-activated receptor-γ, and activation of this signaling pathway led to sclerostin up-regulation but not osteocyte apoptosis. This study demonstrates two distinct signaling pathways activated in osteocytes in response to TZDs that could participate in the observed increase in fractures in TZD-treated patients.

Use of glucagon-like peptide-1 receptor agonists and bone fractures: A meta-analysis of randomized clinical trials (胰高血糖素样肽-1受体激动剂的使用与骨折的关系：一项对随机临床试验的meta分析)

Patients with type 2 diabetes mellitus (T2DM) are at a higher risk of bone fractures independent of the use of antidiabetic medications. Furthermore, antidiabetic medications could directly affect bone metabolism. Recently, the use of dipeptidyl peptidase‐4 inhibitors has been associated with a lower rate of bone fracture. The aim of the present meta‐analysis was to assess whether patients with T2DM treated with glucagon‐like peptide‐1 receptor agonists (GLP‐1Ra) present a lower incidence of bone fracture compared with patients using other antidiabetic drugs.

Optimal bone mechanical and material properties require a functional glucagon-like peptide-1 receptor

Bone is permanently remodeled by a complex network of local, hormonal, and neuronal factors that affect osteoclast and osteoblast biology. Among these factors, a role for gastrointestinal hormones has been proposed based on the evidence that bone resorption dramatically falls after a meal. Glucagon-like peptide-1 (GLP1) is one of these gut hormones, and despite several reports suggesting an anabolic effect of GLP1, or its stable analogs, on bone mass, little is known about the effects of GLP1/GLP1 receptor on bone strength. In this study, we investigated by three-point bending, quantitative X-ray microradiography, microcomputed tomography, qBEI, and FTIRI bone strength and bone quality in male Glp1r knockout (Glp1r KO) mice when compared with control WT animals. Animals with a deletion of Glp1r presented with a significant reduction in ultimate load, yield load, stiffness, and total absorbed and post-yield energies when compared with WT animals. Furthermore, cortical thickness and bone outer diameter were significantly decreased in deficient animals. The mineral quantity and quality were not significantly different between Glp1r KO and WT animals. On the other hand, the maturity of the collagen matrix was significantly reduced in deficient animals and associated with lowered material properties. Taken together, these data support a positive effect of GLP1R on bone strength and quality.

Glucose-dependent insulinotropic polypeptide (GIP) receptor deletion leads to reduced bone strength and quality

Bone is permanently remodeled by a complex network of local, hormonal and neuronal factors that affect osteoclast and osteoblast biology. In this context, a role for gastro-intestinal hormones has been proposed based on evidence that bone resorption dramatically falls after a meal. Glucose-dependent insulinotropic polypeptide (GIP) is one of the candidate hormones as its receptor, glucose-dependent insulinotropic polypeptide receptor (GIPR), is expressed in bone. In the present study we investigated bone strength and quality by three-point bending, quantitative x-ray microradiography, microCT, qBEI and FTIR in a GIPR knockout (GIPR KO) mouse model and compared with control wild-type (WT) animals. Animals with a deletion of the GIPR presented with a significant reduction in ultimate load (--11%), stiffness (-16%), total absorbed (-28%) and post-yield energies (-27%) as compared with WT animals. Furthermore, despite no change in bone outer diameter, the bone marrow diameter was significantly increased and as a result cortical thickness was significantly decreased by 20% in GIPR deficient animals. Bone resorption at the endosteal surface was significantly increased whilst bone formation was unchanged in GIPR deficient animals. Deficient animals also presented with a pronounced reduction in the degree of mineralization of bone matrix. Furthermore, the amount of mature cross-links of collagen matrix was significantly reduced in GIPR deficient animals and was associated with lowered intrinsic material properties. Taken together, these data support a positive effect of the GIPR on bone strength and quality.

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‐Ala2]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‐Ala2]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. J. Cell. Physiol. 230: 3009–3018, 2015.

Beneficial effects of a N-terminally modified GIP agonist on tissue-level bone material properties

Bone remodeling is under complex regulation from nervous, hormonal and local signals, including gut hormones. Among the gut hormones, a role for the glucose-dependent insulinotropic polypeptide (GIP) has been suggested. However, the rapid degradation of GIP in the bloodstream by the ubiquitous enzyme dipeptidyl peptidase-4 (DPP-4) precludes therapeutic use. To circumvent this problem, a series of N-terminally modified GIP agonists have been developed, with N-AcGIP being the most promising. The aims of the present study were to investigate the effects of N-AcGIP on bone at the micro-level using trabecular and cortical microstructural morphology, and at the tissue-level in rats. Copenhagen rats were randomly assigned into control or N-AcGIP-treated groups and received daily injection for 4 weeks. Bone microstructural morphology was assessed by microCT and dynamic histomorphometry and tissue-level properties by nanoindentation, qBEI and infra-red microscopy. Four week treatment with N-AcGIP did not alter trabecular or cortical microstructural morphology. In addition, no significant modifications of mechanical response and properties at the tissue-level were observed in trabecular bone. However, significant augmentations in maximum load (12%), hardness (14%), indentation modulus (13%) and dissipated energy (16%) were demonstrated in cortical bone. These beneficial modifications of mechanical properties at the tissue-level were associated with increased mineralization (22%) and collagen maturity (13%) of the bone matrix. Taken together, the results support a beneficial role of GIP, and particularly stable analogs such as N-AcGIP, on tissue material properties of bone.

Glucose-dependent insulinotropic polypeptide (GIP) directly affects collagen fibril diameter and collagen cross-linking in osteoblast cultures

Glucose-dependent insulinotropic polypeptide (GIP) is absolutely crucial in order to obtain optimal bone strength and collagen quality. However, as the GIPR is expressed in several tissues other than bone, it is difficult to ascertain whether the observed modifications of collagen maturity, reported in animal studies, were due to direct effects on osteoblasts or indirect through regulation of signals originating from other tissues. The aims of the present study were to investigate whether GIP can directly affect collagen biosynthesis and processing in osteoblast cultures and to decipher which molecular pathways were necessary for such effects. MC3T3-E1 cells were cultured in the presence of GIP ranged between 10 and 100pM. Collagen fibril diameter was investigated by electron microscopy whilst collagen maturity was determined by Fourier transform infra-red microspectroscopy (FTIRM). GIP treatment resulted in dose-dependent increases in lysyl oxidase activity and collagen maturity. Furthermore, GIP treatment shifted the collagen fiber diameter towards lower value but did not significantly affect collagen heterogeneity. GIP acted directly on osteoblasts by activating the adenylyl cyclase-cAMP pathway. This study provides evidences that GIP acts directly on osteoblasts and is capable of improving collagen maturity and fibril diameter.

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.

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.