Prevalence and predictors of osteopenia and osteoporosis in adults with Type 1 diabetes

The association of serum ionized calcium and vitamin D with adult cognitive performance

BACKGROUND

High serum calcium levels have been associated with cognitive decline in older adults. These associations have not been studied in younger adults. The possible association of vitamin D with cognitive function, independent of calcium, is unknown.

METHODS

A cross-sectional study of associations of serum ionized calcium and 25-hydroxyvitamin D levels with cognitive function in younger adults (20-59 years) and older adults (60-90 years) was conducted using data from the US third National Health and Nutrition Examination Survey (NHANES III).

RESULTS

Neither serum ionized calcium nor 25-hydroxyvitamin D was associated with cognitive function in either age group. For example, the confounder-adjusted mean difference in reaction time in young adults was 0.00 (95% confidence interval = -0.07 to 0.06) per 1 SD calcium.

CONCLUSION

Our results do not support an important role for calcium or vitamin D in cognitive performance in adults.

Low serum osteoprotegerin levels in normoalbuminuric type 1 diabetes mellitus

The aim of this study is to establish whether abnormal mineral metabolism is present in patients with type 1 DM with normal renal function and in the absence of microalbuminuria. Serum levels of 1,25-dihydroxyvitamin D, osteoprotegerin (OPG) and receptor activator for nuclear factor kappa β ligand (RANKL) and other determinants of bone metabolism were measured in 35 patients with type 1 DM and in 25 age-, sex- and ethnicity-matched healthy controls. Serum OPG (1.98 vs. 2.98 pmol/l: P = 0.001), 1,25-dihydroxyvitamin D (41.1 vs. 48.2 pmol/l: P = 0.035) and magnesium (0.84 vs. 0.89 mmol/l P = 0.029) levels were significantly lower in patients with type 1 DM compared to normal controls. RANKL levels were similar in both groups. The groups did not differ with respect to calcium, phosphate, PTH, 25-hydroxyvitamin D, tubular reabsorption of phosphate and cross-linked N-telopeptides of type 1-collagen levels. Abnormalities of mineral metabolism including low serum OPG and 1,25-dihydroxyvitamin D levels occur in patients with type 1 DM with normal renal function and in the absence of microalbuminuria. These abnormalities may promote altered bone metabolism and vascular pathology.

Overexpression of heme oxygenase-1 increases human osteoblast stem cell differentiation

Human bone marrow mesenchymal stem cells (MSCs) are pleiotrophic cells that differentiate to either adipocytes or osteoblasts as a result of crosstalk by specific signaling pathways including heme oxygenase (HO)-1/-2 expression. We examined the effect of inducers of HO-1 expression and inhibitors of HO activity on MSC differentiation to the osteoblast and following high glucose exposure. MSC cultured in osteogenic medium increased expression of osteonectin, Runt-related transcription factor 2 (RUNX-2), osteocalcin, and alkaline phosphatase. HO-1 expression during differentiation was initially decreased and then followed by a rebound increase after 15 days of culture. Additionally, the effect of HO-1 on osteoblasts appears different to that seen in adipocyte stem cells. On addition of a cobalt compound, the resultant induction of HO-1 decreases adipogenesis. Moreover, glucose (30 mM) inhibited osteoblast differentiation, as evidenced by decreased bone morphogenetic protein (BMP)-2, osteonectin, osteocalcin, and osteoprotegerin (OPG). In contrast, MSC-derived adipocytes were increased by glucose. Increased HO-1 expression increased the levels of osteonectin, OPG, and BMP-2. Inhibition of HO activity prevented the increase in osteonectin and potentiated the decrease of osteocalcin and OPG in cells exposed to high glucose levels. Furthermore, targeting HO-1 expression increased pAMPK and endothelial nitric oxide synthase (eNOS) and restored osteoblastic markers. Our findings suggest that targeting HO-1 gene expression attenuates the hyperglycemia-mediated decrease in MSC-derived osteoblast differentiation. Finally, the mechanism underlying the HO-1-specific cell effect on osteoblasts and adipocytes is yet to be explored. Thus, the targeting of HO-1 gene expression presents a portal to increase osteoblast function and differentiation and attenuate osteoporosis by promoting bone formation.

Vitamin D receptor gene, biochemical bone markers and bone mineral density in Mexican women on dialysis

BACKGROUND

The influence of the Bsm1 polymorphism of the vitamin D receptor (VDR) gene on mineral and bone disorders in chronic kidney disease (CKD) is still under discussion. The aim of this study was to analyse the relationship between VDR polymorphism, bone mineral density (BMD), biochemical bone markers and clinical factors in women on peritoneal dialysis (PD) and haemodialysis (HD).

METHODS

In a cross-sectional study, 197 women (42 +/- 10 years; 25% with diabetes mellitus (DM); body mass index (BMI) 25.26 +/- 4.77 kg/m(2)) treated by PD (72%) or HD (28%) underwent measurements of BMD (measured at the calcaneus by quantitative ultrasound; expressed as T- and Z-scores) and plasma total calcium (tCa), intact parathyroid hormone 1-84 (iPTH), phosphorus, albumin, glucose, osteoprotegerin (OPG), fetuin-A, intact osteocalcin-49 and N-MID fragment 1-43 aa (N-MID osteocalcin) N-terminal propeptide of type 1 procollagen (PINP) and C-terminal telopeptide-beta aspartic acid (BCL). DNA was extracted from peripheral blood. PCR products were digested with Bsm1 to analyse VDR polymorphism.

RESULTS

The Z-score of BMD was -1.1 +/- 1.03. According to the values of osteopenia (T-score = -1.0), patients with higher BMD were younger, had lower frequency of amenorrhoea and diabetes and had higher serum creatinine and fetuin levels as well as lower levels of PINP. In a stepwise multivariate logistics analysis, osteopenia was associated with presence of genotype BB+Bb (OR = 3.26, P < or = 0.003) and age (OR = 0.95, P = 0.050). According to the B allele, bb: n = 126 (64%) and BB+Bb: n = 71(36%), group bb had significantly higher mean Z-scores (-0.97 +/- 1.0 vs -1.3+/-0.92; P < or = 0.021).

CONCLUSIONS

The high frequency of osteopenia observed in female CKD patients on dialysis is associated with age and genetic predisposition as revealed by its association to the Bsm1 VDR polymorphism.

HO-1 expression increases mesenchymal stem cell-derived osteoblasts but decreases adipocyte lineage

Human bone marrow mesenchymal stem cells (MSC) are pleiotropic cells that differentiate to either adipocytes or osteoblasts as a result of cross-talk by specific signaling pathways including heme oxygenase (HO)-1/-2 expression. We examined the effect of inducers of HO-1 expression and inhibitors of HO activity on MSC differentiation to the osteoblast and adipocyte lineage. HO-1 expression is increased during osteoblast stem cell development but remains elevated at 25 days. The increase in HO-1 levels precedes an increase in alkaline phosphatase (AP) activity and an increase in BMP, osteonectin and RUNX-2 mRNA. Induction of HO-1 by osteogenic growth peptide (OGP) was associated with an increase in BMP-2 and osteonectin. Exposure of MSC to high glucose levels decreased osteocalcin and osteogenic protein expression, which was reversed by upregulation of the OGP-mediated increase in HO-1 expression. The glucose-mediated decrease in HO-1 resulted in decreased levels of pAMPK, pAKT and the eNOS signaling pathway and was reversed by OGP. In contrast, MSC-derived adipocytes were increased by glucose. HO-1 siRNA decreased HO-1 expression but increased adipocyte stem cell differentiation and the adipogenesis marker, PPARgamma. Thus, upregulation of HO-1 expression shifts the balance of MSC differentiation in favor of the osteoblast lineage. In contrast, a decrease in HO-1 or exposure to glucose drives the MSC towards adipogenesis. Thus, targeting HO-1 expression is a portal to increased osteoblast stem cell differentiation and to the attenuation of osteoporosis by the promotion of bone formation.

Diabetes and skeletal health

Osteoporosis and diabetes affect a large proportion of the elderly population. The prevalence of diabetes and osteoporosis is increasing. Compared with individuals without diabetes, both men and women with diabetes have a higher risk of fractures, particularly at the hip, with consequent significant morbidity and mortality. Type 1 diabetes is associated with decreased bone mass and although bone mass data for Type 2 diabetes may or may not be decreased, there is evidence of altered bone quality in diabetes. The mechanisms involved include effects of insulin, insulin-like growth factor 1, cytokines, advanced glycation end products, and altered calcium homeostasis. In addition, a drug-induced increase in the incidence of fractures has been noted with the use of thiazolidinediones (TZDs). TZDs improve insulin sensitivity and have multitude other beneficial effects. Osteoblasts and adipocytes are derived from a common multipotential mesenchymal stem cell progenitor, with activation of peroxisome proliferator-activated receptor γ2 by both currently available TZDs (i.e. rosiglitazone and pioglitazone) stimulating adipogenesis and inhibiting osteoblastogenesis. The use of both rosiglitazone and pioglitazone is associated with an increased fracture risk, with changes in bone turnover markers and decreased bone mineral density.