Alteration of vitamin D metabolic enzyme expression and calcium transporter abundance in kidney involved in type 1 diabetes-induced bone loss

Eucommia ulmoides extract regulates oxidative stress to maintain calcium homeostasis and improve diabetic osteoporosis

Diabetic osteoporosis (DOP) is a secondary disease that severely affects the health and quality of life of patients with diabetes mellitus. This study aimed to explore the bone protective effect of aqueous extract of Eucommia ulmoides (EUL) in DOP mice. DOP mice were established using a high-sugar, high-fat diet and streptozotocin (STZ) (35 mg/kg for three consecutive days), and the EUL aqueous extract (2.5 g/kg/day) was orally administered for 6 weeks. The serum levels of oxidative stress-related factors, calcium, and phosphorus were assessed using biochemical assays. The osteoprotective effect of EUL was assessed using micro-computer tomography, three-point bending assay, histological analysis, and immunoblotting. Quantitative real-time polymerase chain reaction and western blotting were performed to detect the expression levels of calcium transport channel factors in the kidney and small intestine tissues. Furthermore, the expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the femur, kidney, and small intestine tissues were detected using western blotting and quantitative real-time polymerase chain reaction. EUL aqueous extract reduced blood glucose levels, increased body weight, and relieved symptoms in DOP mice (p < .05). It also increased bone mineral density, improved the bone microstructure, decreased the number of femoral osteoclasts, and increased the expression of femoral Runx2 and Bmp2 in DOP mice (p < .01). After 6 weeks of EUL aqueous extract administration, serum levels of SOD, CTA, calcium, and phosphorus were upregulated, whereas MDA levels were decreased (p < .01). The aqueous EUL extract also upregulated the expression of TRPV5, PMCA-1b, and CaBP-9 k in the kidney and small intestine of DOP mice (p < .01). Furthermore, the expression of Nrf2 and HO-1 in the kidney, small intestine, and femur tissues was increased (p < .01). EUL aqueous extract reduced blood glucose levels in DOP mice and regulated oxidative stress through the Nrf2/HO-1 pathway, thereby maintaining calcium homeostasis and ultimately improving bone quality. Our study suggested that EUL aqueous extract may be effective in the treatment of DOP.

Genetically determined type 1 diabetes mellitus and risk of osteoporosis

BACKGROUND

Observational evidence suggests that type 1 diabetes mellitus (T1DM) is associated with the risk of osteoporosis (OP). Nevertheless, it is not apparent whether these correlations indicate a causal relationship. To elucidate the causal relationship, a two-sample Mendelian randomization (MR) analysis was performed.

METHODS

T1DM data was obtained from the large genome-wide association study (GWAS), in which 6683 cases and 12,173 controls from 12 European cohorts were involved. Bone mineral density (BMD) samples at four sites were extracted from the GEnetic Factors for OSteoporosis (GEFOS) consortium, including forearm (FA) (n = 8,143), femoral neck (FN) (n = 32,735), lumbar spine (LS) (n = 28,498), and heel (eBMD) (n = 426,824). The former three samples were from mixed populations and the last one was from European. Inverse variance weighting, MR-Egger, and weighted median tests were used to test the causal relationship between T1DM and OP. A series of sensitivity analyses were then conducted to verify the robustness of the results.

RESULTS

Twenty-three independent SNPs were associated with FN-BMD and LS-BMD, twenty-seven were associated with FA-BMD, and thirty-one were associated with eBMD. Inverse variance-weighted estimates indicated a causal effect of T1DM on FN-BMD (odds ratio (OR) =1.033, 95 % confidence interval (CI): 1.012-1.054, p = 0.002) and LS-BMD (OR = 1.032, 95 % CI: 1.005-1.060, p = 0.022) on OP risk. Other MR methods, including weighted median and MR-Egger, calculated consistent trends. While no significant causation was found between T1DM and the other sites (FA-BMD: OR = 1.008, 95 % CI: 0.975-1.043, p = 0.632; eBMD: OR = 0.993, 95 % CI: 0.985-1.001, p = 0.106). No significant heterogeneity (except for eBMD) or horizontal pleiotropy was found for instrumental variables, suggesting these results were reliable and robust.

CONCLUSIONS

This study shows a causal relationship between T1DM and the risk of some sites of OP (FN-BMD, LS-BMD), allowing for continued research to discover the clinical and experimental mechanisms of T1DM and OP. It also contributes to the recommendation if patients with T1DM need targeted care to promote bone health and timely prevention of osteoporosis.

Potential Metabolic Pathways Involved in Osteoporosis and Evaluation of Fracture Risk in Individuals with Diabetes

Diabetes has a significant global prevalence. Chronic hyperglycemia affects multiple organs and tissues, including bones. A large number of diabetic patients develop osteoporosis; however, the precise relationship between diabetes and osteoporosis remains incompletely elucidated. The activation of the AGE-RAGE signaling pathway hinders the differentiation of osteoblasts and weakens the process of bone formation due to the presence of advanced glycation end products. High glucose environment can induce ferroptosis of osteoblasts and then develop osteoporosis. Hyperglycemia also suppresses the secretion of sex hormones, and the reduction of testosterone is difficult to effectively maintain bone mineral density. As diabetes therapy, thiazolidinediones control blood glucose by activating PPAR-γ. Activated PPAR-γ can promote osteoclast differentiation and regulate osteoblast function, triggering osteoporosis. The effects of metformin and insulin on bone are currently controversial. Currently, there are no appropriate tools available for assessing the risk of fractures in diabetic patients, despite the fact that the occurrence of osteoporotic fractures is considerably greater in diabetic individuals compared to those without diabetes. Further improving the inclusion criteria of FRAX risk factors and clarifying the early occurrence of osteoporosis sites unique to diabetic patients may be an effective way to diagnose and treat diabetic osteoporosis and reduce the risk of fracture occurrence.

Amelioration of Fructus Ligustri Lucidi and its phenol glycosides on hypercalciuria via stimulating PTH1R/PKA/TRPV5 signaling

BACKGROUND

Our early studies performed on aged rats, ovariectomized (OVX) rats and diabetic mice, indicated the calciotropic role of Fructus Ligustri Lucidi (FLL), the fruit of Ligustrum lucidum Ait., in mediating calcium homeostasis which was partially attributed to its stimulation on renal calcium reabsorption.

PURPOSE

This study aimed to explicate the underlying molecular mechanism and explore the potential bioactive ingredients in FLL.

STUDY DESIGN AND METHODS

The OVX C57BL/6 J mice were orally administered with low (FL, 75 mg/kg), middle (FM, 225 mg/kg) or high (FH, 675 mg/kg) dose of extract of Fructus Ligustri Lucidi for 10 weeks. The biological properties of trabecular bone were measured by micro-CT and H&E staining. The molecular expression was assessed by immunoblotting and immunostaining. The potential active components were identified by cell membrane chromatography (CMC) and explored in renal tubular cells with Fluo-3/AM fluorescent staining to indicate intracellular calcium level. The male mice fed with high calcium diet (1.2% Ca) and orally treated with active components for 3 weeks.

RESULTS

Treatment of OVX mice with FLL extract suppressed the elevation in urinary calcium level (FH, 0.081 ± 0.012, vs. OVX, 0.189 ± 0.038 mg/mg), and increased bone mineral density (FH, 62.41 ± 2.57, vs. OVX, 43.72 ± 8.43 mg/ccm) and percentage of trabecular bone area. It also decreased circulating PTH level (FH, 66.69 ± 10.94, vs. OVX, 303.50 ± 26.56 pg/ml) and up-regulated TRPV5 expression in renal cortex of OVX mice as well as enhanced the expression of PTH receptor (PTH1R) and the ratio of p-PKA/PKA. The PKA inhibitor H89 abolished the induction of serum, prepared from rats treated with FLL extract, on PKA/TRPV5 signaling in renal tubular cells. The CMC identified phenol glycosides, including salidroside and oleuropein, which increased intracellular calcium content, promoted expression of PTH1R and TRPV5 and ratio of p-PKA/PKA as well as decreased calcium excretion in urine of mice fed with high calcium diet.

CONCLUSION

Salidroside and oleuropein are major ingredients contributing to the anti-hypercalciuria effects of FLL via acting on PTH1R/PKA/TRPV5 signaling in kidney. Further translational research would be required.

A Naringin- and Icariin-Contained Herbal Formula, Gushukang, Ameliorated Aged Osteoporosis of Aged Mice with High Calcium Intake

Traditional herbal formula Gushukang (GSK) was clinically applied to treat primary osteoporosis and showed osteoprotective effect in ovariectomized rodent animals and regulatory action on calcium transporters. This study aimed to determine if GSK could ameliorate aged osteoporosis by modulating serum level of calciotropic hormones and improving calcium balance. 18-month-old male mice were orally administered with either GSK (0.38[Formula: see text]g/kg body weight) or calcitriol (1[Formula: see text][Formula: see text]g/kg body weight) combined with high calcium diet (HCD, 1.2% Ca) for 60 days. The aged mice fed with normal calcium diet (NCD, 0.6% Ca) were a negative control. Trabecular bone and cortical bone properties as well as calcium balance were determined. Treatment with GSK significantly increased 25(OH)D and 1,25-(OH)₂D levels in serum, moreover, it markedly attenuated trabecular bone micro-architectural deteriorations and elevated trabecular bone mass as well as strengthened cortical bone mechanical properties shown by the increase in maximal bending load and elastic modulus. Calcium balance, including urinary Ca excretion, fecal Ca level and net calcium retention, was remarkably improved by GSK, which up-regulated TRPV6 expression in duodenum and TRPV5 expression in kidney and down-regulated claudin-14 expression in duodenum and kidney. Additionally, 1-OHase and 24-OHase expression was significantly decreased (vs. NCD group) and increased (vs. HCD group), respectively, in kidney of GSK- and calcitriol-treated mice. Taken together, this study demonstrated the ameliorative effects of Gushukang on aged osteoporosis by effectively stimulating vitamin D production and improving calcium balance of aged mice with high dietary calcium supplement.

Andrographolide mitigates cartilage damage via miR-27-3p-modulated matrix metalloproteinase13 repression

BACKGROUND

As a potential anti-arthritic agent, Andrographolide (And) is capable of promoting chondrocyte proliferation and preventing apoptosis in pathologic condition. The present study aimed to explore the roles of And in in vivo and in vitro models of osteoarthritis (OA), as well as its underlying molecular mechanisms.

METHODS

An OA mouse model was established using anterior cruciate ligament transection operation on the left knee joint. The pathological changes of articular cartilage were assessed using safranin O staining. Chondrocyte proliferation and apoptosis were measured using cell a counting kit-8 assay and flow cytometry. Bioinformatics algorithms and a luciferase reporter assay were used to evaluate matrix metalloproteinase13 (MMP13) as a direct target of miR-27-3p.

RESULTS

And had the ability to prevent catabolism and facilitate anabolism of articular cartilage in an experimental OA model in mice. In addition, And alleviated chondrocyte apoptosis in in vitro and in vivo models of OA. We also found that both up-regulation of MMP13 and down-regulation of miR-27-3p in the proximal tibia of OA mice and interleukin (IL)-1β-stimulated chondrocytes were reversed by And administration simultaneously. MMP13 was validated as direct target of miR-27-3p and could be suppressed by overexpression of miR-27-3p in mouse chondrocyte. Furthermore, overexpression of miR-27-3p or MMP13 loss-of-function in chondrocytes could alleviate IL-1β-induced apoptosis.

CONCLUSIONS

These results indicated that miR-27-3p/MMP13 signaling axis might be a potential therapeutic target of And for preventing the progression of OA.

Association of increased renal Cyp24a1 gene expression with low plasma 1,25-dihydroxyvitamin D levels in rats with streptozotocin-induced diabetes

Decreases in plasma vitamin D concentrations have been reported in diabetes, although the mechanism involved in this decrease is unclear. Here, we investigated the association between Cyp24a1, a vitamin D catabolic enzyme, and abnormalities in vitamin D metabolism in streptozotocin-induced diabetes rats, an animal model of type 1 diabetes. Plasma 1,25-dihydroxyvitamin D [1,25(OH)₂D] levels were significantly lower in streptozotocin-induced diabetes rats and renal Cyp24a1 mRNA expression levels were increased. Western blotting analysis of streptozotocin-induced diabetes rats kidney tissues with anti-CYP24A1 antibody showed a strong signal around 40 kDa, which differs from the predicted 50–55 kDa molecular weight for full-length Cyp24a1 and could represent the Cyp24a1-splicing variant that lacks exons 1 and 2. We observed high levels of renal Cyp24a1-splicing variant mRNA expression in streptozotocin-induced diabetes rats. We also confirmed transcriptional up-regulation of endogenous Cyp24a1 mRNA expression through glucocorticoid receptors by glucocorticoid in opossum kidney proximal cells. Taken together, our results indicated that high Cyp24a1 expression levels may play a role in the decrease of plasma 1,25(OH)₂D levels in streptozotocin-induced diabetes rats. High plasma corticosterone levels in diabetes may affect transcriptional regulation to promote increases in Cyp24a1 expression.

Anomalous bone changes in ovariectomized type 2 diabetic rats: inappropriately low bone turnover with bone loss in an estrogen-deficient condition

Estrogen deprivation accelerates bone resorption, leading to imbalance of bone remodeling and osteoporosis in postmenopausal women. In the elderly, type 2 diabetes mellitus (T2DM) frequently coexists as an independent factor of bone loss. However, little is known about the skeletal changes in a combined condition of estrogen deficiency and T2DM. Herein, we performed ovariectomy (OVX) in nonobese Goto-Kakizaki (GK) T2DM rats to examine changes associated with calcium and phosphate metabolism and bone microstructures and strength. As expected, wild-type (WT) rats subjected to ovariectomy (OVX-WT) had low trabecular bone volume and serum calcium with increased dynamic histomorphometric and serum bone markers, consistent with the high turnover state. T2DM in GK rats also led to low trabecular volume and serum calcium. However, the dynamic histomorphometric markers of bone remodeling were unaffected in these GK rats, indicating the distinct mechanism of T2DM-induced bone loss. Interestingly, OVX-GK rats were found to have anomalous and unique changes in bone turnover-related parameters, i.e., decreased osteoblast and osteoclast surfaces with lower COOH-terminal telopeptide of type I collagen levels compared with OVX-WT rats. Furthermore, the levels of calciotropic hormones, i.e., parathyroid hormone and 1,25(OH)2D3, were significantly decreased in OVX-GK rats. Although the OVX-induced bone loss did not further worsen in GK rats, a three-point bending test indicated that OVX-GK bones exhibited a decrease in bone elasticity. In conclusion, T2DM and estrogen deficiency both led to microstructural bone loss, the appearance of which did not differ from each factor alone. Nevertheless, the combination worsened the integrity and suppressed the turnover, which might eventually result in adynamic bone disease.

Gushukang exerts osteopreserve effects by regulating vitamin D and calcium metabolism in ovariectomized mice

Calcium homeostasis plays vital roles in the management of bone health. Traditional herbal formula Gushukang (GSK) was clinically applied to treat primary osteoporosis. This study aimed to explore the osteoprotective effects of GSK and its roles in maintaining calcium homeostasis in ovariectomized (OVX) mice. The OVX mice were orally treated with low (0.38 g/kg), middle (0.76 g/kg) and high (1.52 g/kg) dose of GSK for 8 weeks. GSK treatment dramatically increased serum calcium level and decreased urinary calcium excretion as well as enhanced calcium content in bone of OVX mice. Serum level of 25-hydroxyvitamin D was significantly increased in OVX mice with exposure to GSK. Treatment with GSK improved bone mass and micro-structure of trabecular bone at distal metaphysis of femur and proximal metaphysis of tibia in OVX mice shown by safranin O staining and micro-CT measurement. GSK treatment at all doses up-regulated mRNA expression of calcium-binding protein-28k and vitamin D receptor in kidney of OVX mice, and dose-dependently decreased mRNA expression of claudin-14 and elevated mRNA expression of claudin-16 in duodenum of OVX mice. Taken together, GSK exerted beneficial effects on trabecular bone of OVX mice by improving calcium homeostasis via regulating paracellular calcium absorption in duodenum and transcellular calcium reabsorption in kidney.

Aqueous Extract of Mori Folium Exerts Bone Protective Effect Through Regulation of Calcium and Redox Homeostasis via PTH/VDR/CaBP and AGEs/RAGE/Nox4/NF-κB Signaling in Diabetic Rats

Purpose: The present study is aimed to explore whether the aqueous extract of Mori Folium (MF) exhibits bone protective effect by regulating calcium and redox homeostasis in diabetic rats, and to identify the signaling pathways involved in this process. Methods: Diabetic rats were established using high-sugar and high-fat diet and streptozotocin (STZ) (30 mg/kg for 3 consecutive days). The serum levels of osteocalcin (OC), insulin-like growth factor-1 (IGF-1), tartrate-resistant acid phosphatase (TRAP), phosphorus (P), calcium (Ca), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], parathormone (PTH), advanced glycation end products (AGEs), superoxide dismutase (SOD), and malondialdehyde (MDA), total antioxidant capacity (TAC), 8-hydroxy-2'-deoxyguanosine (8-OH-dG), and interleukin 6 (IL-6) were determined by ELISA or biochemical assays. Histopathological alterations in the femurs were evaluated by the stainings of hematoxylin-eosin (H&E) and alizarin red S. In addition, femoral strength was detected by a three-point bending assay, bone microstructure was detected with micro-computer tomography. Bone material properties were examined by Fourier-transform infrared spectroscopy. Furthermore, the expressions of IGF-1, runt-related transcription factor 2 (Runx2), osteoprotegerin (OPG), receptor activator of nuclear factor kappa-B ligand (RANKL), cathepsin K, AGEs, receptor of advanced glycation end products (RAGE), NADPH oxidase 4 (Nox4), and nuclear factor kappa-B (NF-κB) in the femurs and tibias, and the alterations in the levels of calcium-binding protein-28k (CaBP-28k), transient receptor potential V6 (TRPV6), and vitamin D receptor (VDR) in the kidneys and duodenums were determined by western blot and immunohistochemical analysis. Results: Treatment of diabetic rats with MF aqueous extract induces an increase in the levels of OC and IGF-1 as well as a decrease in TRAP level in serum. MF treatment also upregulates the expression of OPG, downregulates the expressions of AGEs, RAGE, Nox4, NF-κB, and RANKL, which leads to improve bone microstructure and strength exhibited by an increase in cortical area ratio, cortical thickness, and trabecular area ratio as well as ultimate load, elastic modulus, and bending stress in the femurs and tibias of diabetic rats. In addition, MF aqueous extract preserves bone material properties by decreasing the ratio of fatty acid/collagen and increasing the ratio of mineral/matrix in the femurs of diabetic rats. Moreover, MF treatment increases the levels of P, Ca, and 1,25(OH)2D3, and decreases the level of PTH in the serum, as well as upregulates the expressions of TRPV6 and VDR in the duodenums and CaBP-28k in the kidneys of diabetic rats. Additionally, MF has ability of rebuilding redox homeostasis and eliminating inflammatory stress by increasing the levels of SOD and TAC as well as decreasing the levels of IL-6, AGEs, MDA, and 8-OH-dG. Conclusions: MF treatment may improve bone quality through maintenance of calcium homeostasis via regulating the PTH/VDR/CaBP signaling, and elimination of oxidative stress via regulating the AGEs/RAGE/Nox4/NF-κB signaling. These results may suggest the potential of MF in preventing the development of diabetic osteoporosis.

Grain Amaranth Is Associated with Improved Hepatic and Renal Calcium Metabolism in Type 2 Diabetes Mellitus of Male Wistar Rats

Background

Dysregulation of calcium signaling is a hallmark of diabetes mellitus (DM) and grain amaranth (AG) has antidiabetic properties. Information on the mechanism of action of AG on blood, renal, and hepatic tissues is sparse, although it continues to be an important alternative medicinal plant in several developing countries. The objective of the study was to determine key changes in calcium levels and s100a1 protein levels and antioxidant and histopathologic changes in blood, renal, and hepatic tissues of male diabetic Wistar rats.

Materials and Methods

This was an experimental study in which 30 male Wistar rats were kept for 5 weeks (6 groups, N =5). Groups 1-IV had T2DM induced using Nicotinamide and Streptozotocin: Group I, Mixtard®; group II, positive control; group III, 25% AG; group IV, 50% AG. Furthermore, group V consisted of normal rats given 50% GA and group VI was negative control. Blood, renal, and hepatic tissues were collected and analyzed for calcium, s100a1 protein levels, and antioxidant and histopathological changes.

Results and Discussion

In blood, renal, and hepatic tissue, calcium and s100a1 levels were low during T2DM and these increased following AG supplementation. This was important for improved metabolic processes, thus leading to the low malondialdehyde (MDA) and glutathione peroxidase (GPx) activity in the tissues. Efficient antioxidant status was important for improved calcium signaling mechanisms, thus leading to improved tissue function and protection demonstrating the importance of AG as an alternative medicinal source through the calcium signaling pathway.

Conclusion

Grain amaranth exerts its antidiabetic properties through improved calcium homeostasis in blood, kidney, and liver.

Chinese herbal formulas for postmenopausal osteoporosis: A review of preclinical evidence on animal studies and molecular mechanism

Whether Chinese herbal formulas are effective in treatment of postmenopausal osteoporosis remains unclear. The aim of this study is to explore the experimental evidence of both in vitro and in vivo preclinical studies using Chinese herbal formulas in postmenopausal osteoporosis. Searches were applied to various databases with relevant keywords. Original in vivo and in vitro studies using Chinese herbal formulas to treat postmenopausal osteoporosis, and with full text available, were included. Er-Xian Decoction, Bu-Shen-Ning-Xin Decoction, Qing E Formula, Liuwei Dihuang Wan, and Xian-Ling-Gu-Bao Decoction, the most commonly studied formulas, were selected from the pool of Chinese medicine. The preclinical data indicated the potential use of Chinese herbal formulas in postmenopausal osteoporosis. The underlying mechanisms included bone morphogenetic protein (BMP), Wnt/[Formula: see text]-catenin, extracellular-signal-regulated kinase/c-Jun [Formula: see text] terminal kinase/mitogen-activated protein kinase (ERK/JNK/MAPK), estrogen receptor (ER), and osteoprotegerin/receptor activator of nuclear factor [Formula: see text]B ligand (OPG/RANKL) signaling pathways. This study demonstrated the anti-osteoporotic effect of Chinese herbal formulas targeting different pathways in bone metabolism. Further study with adequate sample size and follow-up time, appropriate controls, and optimal blinding is required.

Chinese single herbs and active ingredients for postmenopausal osteoporosis: From preclinical evidence to action mechanism

Postmenopausal osteoporosis is a systemic metabolic skeletal disease generally ascribable to a dearth of estrogen. Whether traditional Chinese medicine is effective in management of postmenopausal osteoporosis remains unclear. This article reviews the experimental evidence of both in vitro and in vivo preclinical studies with the theme of the application of Chinese single herbs and active ingredients in postmenopausal osteoporosis. It includes three single herbs (Herba Epimedium, Rhizoma Drynariae, and Salvia miltiorrhiza) and eight active ingredients (saikosaponins, linarin, echinacoside, sweroside, psoralen, poncirin, vanillic acid, and osthole). The experimental studies indicated their potential use as treatment for postmenopausal osteoporosis and investigated the underlying mechanisms including osteoprotegerin/receptor activator of nuclear factor κB ligand (OPG/RANKL), extracellular-signal-regulated kinase/c-Jun N terminal kinase/mitogen-activated protein kinase (ERK/JNK/MAPK), estrogen receptor (ER), bone morphogenetic protein (BMP), transforming growth factor (TGF)-β, Wnt/β-catenin, and Notch signaling pathways. This review contributes to a better understanding of traditional Chinese medicine and provides useful information for the development of more effective anti-osteoporosis drugs.

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

Differential response of bone and kidney to ACEI in db/db mice: A potential effect of captopril on accelerating bone loss

The components of renin-angiotensin system (RAS) are expressed in the kidney and bone. Kidney disease and bone injury are common complications associated with diabetes. This study aimed to investigate the effects of an angiotensin-converting enzyme inhibitor, captopril, on the kidney and bone of db/db mice. The db/db mice were orally administered by gavage with captopril for 8weeks with db/+ mice as the non-diabetic control. Serum and urine biochemistries were determined by standard colorimetric methods or ELISA. Histological measurements were performed on the kidney by periodic acid-schiff staining and on the tibial proximal metaphysis by safranin O and masson-trichrome staining. Trabecular bone mass and bone quality were analyzed by microcomputed tomography. Quantitative polymerase chain reaction and immunoblotting were applied for molecular analysis on mRNA and protein expression. Captopril significantly improved albuminuria and glomerulosclerosis in db/db mice, and these effects might be attributed to the down-regulation of angiotensin II expression and the expression of its down-stream profibrotic factors in the kidney, like connective tissue growth factor and vascular endothelial growth factor. Urinary excretion of calcium and phosphorus markedly increased in db/db mice in response to captopril. Treatment with captopril induced a decrease in bone mineral density and deterioration of trabecular bone at proximal metaphysis of tibia in db/db mice, as shown in the histological and reconstructed 3-dimensional images. Even though captopril effectively reversed the diabetes-induced changes in calcium-binding protein 28-k and vitamin D receptor expression in the kidney as well as the expression of RAS components and bradykinin receptor-2 in bone tissue, treatment with captopril increased the osteoclast-covered bone surface, reduced the osteoblast-covered bone surface, down-regulated the expression of type 1 collagen and transcription factor runt-related transcription factor 2 (markers for osteoblastic functions), and up-regulated the expression of carbonic anhydrase II (marker for bone resorption). Captopril exerted therapeutic effects on renal injuries associated with type 2 diabetes but worsened the deteriorations of trabecular bone in db/db mice; the latter of which was at least in part due to the stimulation of osteoclastogenesis and the suppression of osteogenesis by captopril.

Effect of the water fraction isolated from Fructus Ligustri Lucidi extract on bone metabolismviaantagonizing a calcium-sensing receptor in experimental type 1 diabetic rats

Osteoprotective effects of FLL water fraction by potentially regulating vitamin D metabolism and calcium transporters as well as CaSR.

Mechanisms involved in altered bone metabolism in diabetes: a narrative review

Many studies have shown that change in metabolism caused by diabetes can influence the bone metabolism in a way that quality and strength of bone is decreased. A 6 times and 2 times increased risk of fracture is reported in patients with type 1 and type 2 diabetes, respectively. There are several mechanisms by which diabetes can affect the bone. The fact that some of these mechanisms are acting in opposite ways opens the door for debate on pathways by which diabetes affects the bones. On the other hand, bone is not a simple organ that only get influence from other organs, but it is an endocrine organ that by secreting the agents such as osteocalcin, adiponectin and visfatin which can affect the insulin sensitivity and metabolism. In this paper we tried to briefly assess the latest finding in this matter.

MECHANISMS IN ENDOCRINOLOGY: Mechanisms and evaluation of bone fragility in type 1 diabetes mellitus

Subjects with type 1 diabetes mellitus (T1DM) have decreased bone mineral density and an up to sixfold increase in fracture risk. Yet bone fragility is not commonly regarded as another unique complication of diabetes. Both animals with experimentally induced insulin deficiency syndromes and patients with T1DM have impaired osteoblastic bone formation, with or without increased bone resorption. Insulin/IGF1 deficiency appears to be a major pathogenetic mechanism involved, along with glucose toxicity, marrow adiposity, inflammation, adipokine and other metabolic alterations that may all play a role on altering bone turnover. In turn, increasing physical activity in children with diabetes as well as good glycaemic control appears to provide some improvement of bone parameters, although robust clinical studies are still lacking. In this context, the role of osteoporosis drugs remains unknown.

2,3,5,4′-Tetrahydroxystilbene-2-O-β-d-glucoside exerted protective effects on diabetic nephropathy in mice with hyperglycemia induced by streptozotocin

This study demonstrated that the inhibition of the RAS with TSG effectively prevented renal injury in diabetic nephropathy.

An update on diabetes related skeletal fragility

There are several mechanisms by which diabetes could affect bone mass and strength. These mechanisms include insulin deficiency; hyperglycemia; the accumulation of advanced glycation end products that may influence collagen characteristics; marrow adiposity and bone inflammation. Furthermore, associated diabetic complications and treatment with thaizolidinediones may also increase risk of fracturing. The following article provides its readers with an update on the latest information pertaining to diabetes related bone skeletal fragility. In the authors' opinion, future studies are needed in order to clarify the impact of different aspects of diabetes metabolism, glycemic control, and specific treatments for diabetes on bone. Given that dual energy x-ray absorptiometry is a poor predictor of bone morbidity in this group of patients, there is a need to explore novel approaches for assessing bone quality. It is important that we develop a better understanding of how diabetes affects bone in order to improve our ability to protect bone health and prevent fractures in the growing population of adults with diabetes.

Protective effects of water fraction of Fructus Ligustri Lucidi extract against hypercalciuria and trabecular bone deterioration in experimentally type 1 diabetic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Ligustri Lucidi (FLL), the fruit of Ligustrum lucidum Ait, is a commonly prescribed herb to nourish the endocrine and renal systems and to strengthen the bones in Traditional Chinese Medicine. This study was aimed to determine the effects of water fraction of FLL ethanol extract (WF-EE) on urinary calcium excretion and trabecular bone properties in type 1 diabetic mice.

MATERIALS AND METHODS

The DBA/2J mice with type 1 diabetes induced by streptozotocin injection were orally administered with WF-EE. After 6 weeks of treatment, the level of biomarkers, including serum calcium, parathyroid hormone (PTH), and fibroblast growth factor-23 (FGF-23) and urine calcium, was measured. Micro-CT was performed to detect trabecular bone properties of the proximal tibial metaphysis. The expression of active calcium transporting proteins in kidney and duodenum was determined by RT-PCR, immunoblotting and immunostaining.

RESULTS

Type 1 diabetes induced hypercalciuria and trabecular bone deterioration. The WF-EE could significantly inhibit hypercalciuria and ameliorate the micro-structure of trabecular bone as well as increase serum PTH and FGF-23 levels in type 1 diabetic mice. The gene expressions of active calcium transporting proteins in duodenum were up-regulated, and the gene and protein expressions of calcium-sensing receptor (CaSR) in kidney were dramatically down-regulated in diabetic mice in response to the treatment with WF-EE.

CONCLUSIONS

The present study demonstrated the protective effects of the water fraction of Fructus Ligustri Lucidi ethanol extract against hypercalciuria and trabecular bone deterioration in experimentally type 1 diabetic mice, and the underlying mechanism may be attributed to its regulations on duodenal calcium transporting proteins and renal CaSR.

Time dependent changes in the intestinal Ca²⁺ absorption in rats with type I diabetes mellitus are associated with alterations in the intestinal redox state

The aim was to determine the intestinal Ca²⁺ absorption in type I diabetic rats after different times of STZ induction, as well as the gene and protein expression of molecules involved in both the transcellular and paracellular Ca²⁺ pathways. The redox state and the antioxidant enzymes of the enterocytes were also evaluated in duodenum from either diabetic or insulin-treated diabetic rats as compared to control rats. Male Wistar rats (150-200 g) were divided into two groups: 1) controls and 2) STZ-induced diabetic rats (60 mg/kg b.w.). A group of diabetic rats received insulin for five days. The insulin was adjusted daily to maintain a normal blood glucose level. Five 5 d after STZ injection, there was a reduction in the intestinal Ca²⁺ absorption, which was maintained for 30 d and disappeared at 60 d. Similar changes occurred in the GSH and (˙)O(2)(-) levels. The protein expression of molecules involved in the transcellular pathway increased at 5 and 30 d returning to control values at 60 d. Their mRNA levels declined considerably at 60 d. The gene and protein expression of claudin 2 was upregulated at 30 d. Catalase activity increased at 5 and 30 d normalizing at 60 d. To conclude, type I D.m. inhibits the intestinal Ca²⁺ absorption, which is transient leading to a time dependent adaptation and returning the absorptive process to normal values. The inhibition is accompanied by oxidative stress. When insulin is administered, the duodenal redox state returns to control values and the intestinal Ca²⁺ absorption normalizes.

Effects of angiotensin-converting enzyme inhibitor, captopril, on bone of mice with streptozotocin-induced type 1 diabetes

There are contradictory results about the effect of angiotensin-converting enzyme inhibitors (ACEIs) on bone. This study was performed to address the skeletal renin-angiotensin system (RAS) activity and the effects of the ACEI, captopril, on the bone of streptozotocin-induced type 1 diabetic mice. Histochemical assessment on bone paraffin sections was conducted by Safranin O staining and tartrate-resistant acid phosphatase staining. Micro-computed tomography was performed to analyze bone biological parameters. Gene and protein expression were determined by real-time polymerase chain reaction and immunoblotting, respectively. Type 1 diabetic mice displayed osteopenia phenotype and captopril treatment showed no osteoprotective effects in diabetic mice as shown by the reduction of bone mineral density, trabecular thickness and bone volume/total volume. The mRNA expression of ACE and renin receptor, and the protein expression of renin and angiotensin II were markedly up-regulated in the bone of vehicle-treated diabetic mice compared to those of non-diabetic mice, and these molecular changes of skeletal RAS components were effectively inhibited by treatment with captopril. However, treatment with captopril significantly elevated serum tartrate-resistant acid phosphatase 5b levels, reduced the ratio of osteoprotegerin/receptor activator of nuclear factor-κB ligand expression, increased carbonic anhydrase II mRNA expression and the number of matured osteoclasts and decreased transforming growth factor-β and osteocalcin mRNA expression in the tibia compared to those of diabetic mice. The present study demonstrated that the use of the ACEI, captopril, has no beneficial effect on the skeletal biological properties of diabetic mice. However, this could be attributed, at least partially, to its suppression of osteogenesis and stimulation of osteoclastogenesis, even though it could effectively inhibit high activity of local RAS in the bone of diabetic mice.

Diabetes mellitus and osteoporosis

Diabetes mellitus (particularly type 2) and osteoporosis are two very common disorders, and both are increasing in prevalence. Adolescents with type 1 diabetes mellitus may not reach potential peak bone mass, putting them at greater fracture risk. In adults with type 2 diabetes, fracture risk is increased and is not explained by the bone mineral density measured by dual-energy X-ray absorptiometry, still considered the gold standard predictor of fracture. In this review, we explore potential mechanisms behind the increased fracture risk that occurs in patients with diabetes, even those with increased bone mineral density. One potential link between diabetes and bone is the osteoblast-produced factor, osteocalcin. It remains to be established whether osteocalcin reflects or affects the connection between bone and glucose metabolism. Several other potential mediators of the effects of diabetes on bone are discussed.