Bone Structure and Predictors of Fracture in Type 1 and Type 2 Diabetes

MECHANISMS IN ENDOCRINOLOGY: Diabetes mellitus, a state of low bone turnover - a systematic review and meta-analysis

OBJECTIVE

To investigate the differences in bone turnover between diabetic patients and controls.

DESIGN

A systematic review and meta-analysis.

METHODS

A literature search was conducted using the databases Medline at PubMed and EMBASE. The free text search terms 'diabetes mellitus' and 'bone turnover', 'sclerostin', 'RANKL', 'osteoprotegerin', 'tartrate-resistant acid' and 'TRAP' were used. Studies were eligible if they investigated bone turnover markers in patients with diabetes compared with controls. Data were extracted by two reviewers.

RESULTS

A total of 2881 papers were identified of which 66 studies were included. Serum levels of the bone resorption marker C-terminal cross-linked telopeptide (-0.10 ng/mL (-0.12, -0.08)) and the bone formation markers osteocalcin (-2.51 ng/mL (-3.01, -2.01)) and procollagen type 1 amino terminal propeptide (-10.80 ng/mL (-12.83, -8.77)) were all lower in patients with diabetes compared with controls. Furthermore, s-tartrate-resistant acid phosphatase was decreased in patients with type 2 diabetes (-0.31 U/L (-0.56, -0.05)) compared with controls. S-sclerostin was significantly higher in patients with type 2 diabetes (14.92 pmol/L (3.12, 26.72)) and patients with type 1 diabetes (3.24 pmol/L (1.52, 4.96)) compared with controls. Also, s-osteoprotegerin was increased among patients with diabetes compared with controls (2.67 pmol/L (0.21, 5.14)).

CONCLUSIONS

Markers of both bone formation and bone resorption are decreased in patients with diabetes. This suggests that diabetes mellitus is a state of low bone turnover, which in turn may lead to more fragile bone. Altered levels of sclerostin and osteoprotegerin may be responsible for this.

Use of glucose-lowering drugs and risk of fracture in patients with type 2 diabetes

BACKGROUND

Diabetes mellitus is associated with an increased risk of hip fracture. The aim of this cohort study was to investigate whether glucose-lowering drugs influence the risk of hip fracture in patients with incident diabetes.

METHODS

A study was performed on a cohort of patients with incident type 2 diabetes. Diabetes diagnosis was defined using information from the Danish National Patient Registry and reimbursement information of glucose-lowering drugs from the Register of Medicinal Product Statistics. The period of observation was from 01.01.1996 till 31.12.2011. The primary exposure was glucose-lowering drugs and the primary endpoint was hip fracture. Unadjusted, adjusted, and propensity score adjusted Cox regressions were performed.

RESULTS

5244 patients with type 2 diabetes with a mean follow up of 5.5years were included in the study. Use of sulphonylureas within the last 90days was associated with hip fracture in patients with type 2 diabetes, hazard ratio 1.64 (95% confidence interval: 1.54,1.75), whereas ever use of sulohonylyreas was not associated with an increased risk of fractures. Use of sulphonylureas within the last 90days was also associated with an increased risk of fractures at other sites. Use of glitazones within the last 90days was associated with an increased risk of hip fracture, hazard ratio 2.07 (95% confidence interval: 1.39,3.07), whereas ever use was not associated with an increased risk.

CONCLUSIONS

Current use of sulphonylureas was associated with hip fracture in patients with type 2 diabetes. Speculatively, this may be due to hypoglycemia resulting in falls.

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

PURPOSE OF REVIEW

To describe the effects of type 1 diabetes on bone cells.

RECENT FINDINGS

Type 1 diabetes (T1D) is associated with low bone mineral density, increased risk of fractures, and poor fracture healing. Its effects on the skeleton were primarily attributed to impaired bone formation, but recent data suggests that bone remodeling and resorption are also compromised. The hyperglycemic and inflammatory environment associated with T1D impacts osteoblasts, osteocytes, and osteoclasts. The mechanisms involved are complex; insulinopenia, pro-inflammatory cytokine production, and alterations in gene expression are a few of the contributing factors leading to poor osteoblast activity and survival and, therefore, poor bone formation. In addition, the observed sclerostin level increase accompanied by decreased osteocyte number and enhanced osteoclast activity in T1D results in uncoupling of bone remodeling. T1D negatively impacts osteoblasts and osteocytes, whereas its effects on osteoclasts are not well characterized, although the limited studies available indicate increased osteoclast activity, favoring bone resorption.

Epidemiology of Skeletal Health in Type 1 Diabetes

The skeleton is adversely affected by type 1 diabetes (T1D). Patients with T1D of both sexes have an increased risk of fracture that begins in childhood and extends across the entire lifespan. T1D is characterized by mild to modest deficits in bone density, structure, and microarchitecture. Current evidence suggests that the observed bone deficits in T1D are the result of impaired bone formation rather than increased bone resorption. There is emerging data that bone quality is impaired in T1D, which may explain the findings that fracture risk is elevated out of proportion to the degree of bone mineral deficit. In this review, we summarize the current knowledge regarding the epidemiology of skeletal health in T1D. Given the high individual and societal burden of osteoporotic fracture, there is an urgent need to better understand the etiology of T1D-related bone disease so that clinical strategies to prevent fracture can be developed.

Bone Microarchitecture in Type 1 Diabetes: It Is Complicated

Patients with type 1 diabetes (T1DM) experience a disproportionate number of fractures for their bone mineral density (BMD). Differences in bone microarchitecture from those without the disease are thought to be responsible. However, the literature is inconclusive. New studies of the microarchitecture using three-dimensional imaging have the advantage of providing in vivo estimates of "bone quality," rather than examining areal BMD alone. There are drawbacks in that most studies have been done on those with less than a 30-year duration of T1DM, and the techniques used to measure vary as do the sites assessed. In addition to the rise in these imaging techniques, very recent literature presents evidence of an intimate relationship between skeletal health and vascular complications in T1DM. The following review provides an overview of the available studies of the bone microarchitecture in T1DM with a discussion of the burgeoning field of complications and skeletal health.

Changes in bone macro- and microstructure in diabetic obese mice revealed by high resolution microfocus X-ray computed tomography

High resolution microfocus X-ray computed tomography (HR-microCT) was employed to characterize the structural alterations of the cortical and trabecular bone in a mouse model of obesity-driven type 2 diabetes (T2DM). C57Bl/6J mice were randomly assigned for 14 weeks to either a control diet-fed (CTRL) or a high fat diet (HFD)-fed group developing obesity, hyperglycaemia and insulin resistance. The HFD group showed an increased trabecular thickness and a decreased trabecular number compared to CTRL animals. Midshaft tibia intracortical porosity was assessed at two spatial image resolutions. At 2 μm scale, no change was observed in the intracortical structure. At 1 μm scale, a decrease in the cortical vascular porosity of the HFD bone was evidenced. The study of a group of 8 week old animals corresponding to animals at the start of the diet challenge revealed that the decreased vascular porosity was T2DM-dependant and not related to the ageing process. Our results offer an unprecedented ultra-characterization of the T2DM compromised skeletal micro-architecture and highlight an unrevealed T2DM-related decrease in the cortical vascular porosity, potentially affecting the bone health and fragility. Additionally, it provides some insights into the technical challenge facing the assessment of the rodent bone structure using HR-microCT imaging.

Advanced Glycation Endproducts and Bone Material Strength in Type 2 Diabetes

CONTEXT

Skeletal deterioration, leading to an increased risk of fracture, is a known complication of type 2 diabetes mellitus (T2D). Yet plausible mechanisms to account for skeletal fragility in T2D have not been clearly established.

OBJECTIVE

The objective of the study was to determine whether bone material properties, as measured by reference point indentation, and advanced glycation endproducts (AGEs), as determined by skin autofluorescence (SAF), are related in patients with T2D.

DESIGN

This was a cross-sectional study.

SETTING

The study was conducted at a tertiary medical center.

PATIENTS

Sixteen postmenopausal women with T2D and 19 matched controls participated in the study.

MAIN OUTCOME MEASURES

Bone material strength index (BMSi) by in vivo reference point indentation, AGE accumulation by SAF, and circulating bone turnover markers were measured.

RESULTS

BMSi was reduced by 9.2% in T2D (P = .02) and was inversely associated with the duration of T2D (r = -0.68, P = .004). Increased SAF was associated with reduced BMSi (r = -0.65, P = .006) and lower bone formation marker procollagen type 1 amino-terminal propeptide (r = -0.63, P = .01) in T2D, whereas no associations were seen in controls. SAF accounted for 26% of the age-adjusted variance in BMSi in T2D (P = .03).

CONCLUSIONS

Bone material properties are impaired in postmenopausal women with T2D as determined by reference point indentation. The results suggest a role for the accumulation of AGEs to account for inferior BMSi in T2D.