Protection against T1DM-Induced Bone Loss by Zinc Supplementation: Biomechanical, Histomorphometric, and Molecular Analyses in STZ-Induced Diabetic Rats

Abstract

Several studies have established an association between diabetes and alterations in bone metabolism; however, the underlying mechanism is not well established. Although zinc is recognized as a potential preventive agent against diabetes-induced bone loss, there is no evidence demonstrating its effect in chronic diabetic conditions. This study evaluated the effects of zinc supplementation in a chronic (90 days) type 1 diabetes-induced bone-loss model. Male Wistar rats were distributed in three groups: control, type 1 diabetes mellitus (T1DM), and T1DM plus zinc supplementation (T1DMS). Serum biochemical analysis; tibia histomorphometric, biomechanical, and collagen-content analyses; and femur mRNA expression were evaluated. Relative to T1DM, the zinc-supplemented group showed increased histomorphometric parameters such as TbWi and BAr and decreased TbSp, increased biomechanical parameters (maximum load, stiffness, ultimate strain, and Young’s modulus), and increased type I collagen content. Interestingly, similar values for these parameters were observed between the T1DMS and control groups. These results demonstrate the protective effect of zinc on the maintenance of bone strength and flexibility. In addition, downregulation of OPG, COL1A, and MMP-9 genes was observed in T1DMS, and the anabolic effects of zinc were evidenced by increased OC expression and serum ALP activity, both related to osteoblastogenesis, demonstrating a positive effect on bone formation. In contrast, T1DM showed excessive bone loss, observed through reduced histomorphometric and biomechanical parameters, characterizing diabetes-associated bone loss. The bone loss was also observed through upregulation of OPG, COL1A, and MMP-9 genes. In conclusion, zinc showed a positive effect on the maintenance of bone architecture and biomechanical parameters. Indeed, OC upregulation and control of expression of OPG, COL1A, and MMP-9 mRNAs, even in chronic hyperglycemia, support an anabolic and protective effect of zinc under chronic diabetic conditions. Furthermore, these results indicate that zinc supplementation could act as a complementary therapy in chronic T1DM.

Effects of Type 1 Diabetes on Osteoblasts, Osteocytes, and Osteoclasts

“…Skeletal alkaline phosphatase, another late marker of osteoblast activity, has been found to be low in diabetic children and adults, confirming poor osteoblast function [32, 33], as well as in most animal models of STZ-induced diabetes [10, 8, 27]. Expression of other key genes important for osteoblast bone metabolism and remodeling such as proteolytic members of the metalloproteinase family MMP2 (matrix metallopeptidase 2) and MMP9 were found to be increased in an animal model of STZ-induced diabetes [11], whereas in a model pairing STZ-induced diabetes with distraction osteogenesis, MMP9 and MMP13 were decreased [5]. Interestingly, in vitro studies have suggested that some of the hyperglycemic effects on the expression of genes encoding extracellular matrix proteins such as osteonectin, osteopontin, and collagen I can be attributed to osmotic changes [37-39].…”

“…The Wnt/beta catenin pathway, which is essential for osteoblast differentiation and regulation of bone formation in differentiated osteoblasts, has also been shown to be down regulated in the bone of STZ-induced diabetic animals [10], partly due to increased expression of sclerostin and dickkopf-related protein 1 (Dkk1), two inhibitors of Wnt signaling. Interestingly, several studies describing altered expression of osteoblast regulating genes, such as Runx2, Dlx5, Osx, ALP, OC, Col1 and osteoclast genes, including osteoprotegerin (OPG), MMP9 and receptor activator of nuclear factor kappa-B ligand (RANKL) in diabetic bones, found that zinc supplementation can prevent these dysregulations and protect bones from diabetes induced damage [11, 12]. …”

“…Genes coding for the RANKL/RANK/OPG system and the corresponding markers were found to be altered in humans with T1D and insulinopenic animal models. Some studies found increased OPG gene expression in young patients with T1D [2] and in chronic hyperglycemic conditions in vivo [11] and in vitro [37], which suggests a decreased osteoclast differentiation and a possible adaptive protection against excessive bone resorption in diabetes. Others found downregulation of OPG expression in STZ-induced diabetes in mice [46].…”

Zanthoxylum alkylamides ameliorate protein metabolism disorder in STZ-induced diabetic rats

“…Therefore, in recent years, the pathogenesis of T1DM has been examined intensely in research. STZ is widely used in the construction of the diabetes model experiment because it can specifically destruct pancreatic beta cells, which cause T1DM (Bortolin et al 2015, Carlos et al 2015, Lin & Sun 2015. In this experiment, the FBG levels of the normal control group were maintained within the normal range (4-6 mmol/L) throughout the feeding period.…”

Relationship between glycemic control and OPG gene polymorphisms with lower bone mineral density in patients with type 1 Diabetes mellitus

“…More than 50% of patients with T1DM have bone loss compared to healthy age-matched subjects (Muñoz-Torres et al, 1996;Kemink et al, 2000) markers of bone formation plasma insulin-like growth factor I (IGF-I), and a variety of bone-related changes are known to be influenced by hyperglycemia such as femoral neck geometry, microarchitecture and biomechanical markers of bone turnover (Starup-Linde, 2013;Bortolin et al, 2015;. However, the association between T1DM and bone mineral density (BMD) is controversial.…”