Long-term use of thiazolidinediones and fractures in type 2 diabetes: a meta-analysis

Revitalization of pioglitazone: the optimum agent to be combined with a sodium-glucose co-transporter-2 inhibitor

The recently completed EMPA-REG study showed that empagliflozin significantly decreased the major adverse cardiac events (MACE) endpoint, which comprised cardiovascular death, non-fatal myocardial infarction (MI) and stroke, in patients with high-risk type 2 diabetes (T2DM), primarily through a reduction in cardiovascular death, without a significant decrease in either MI or stroke. In the PROactive study, pioglitazone decreased the MACE endpoint by a similar degree to that observed in the EMPA-REG study, through a marked reduction in both recurrent MI and stroke and a modest reduction in cardiovascular death. These observations suggest that pioglitazone might be an ideal agent to combine with empagliflozin to further reduce cardiovascular events in patients with high-risk diabetes as empagliflozin also promotes salt/water loss and would be expected to offset any fluid retention associated with pioglitazone therapy. In the present paper, we provide an overview of the potential benefits of combined pioglitazone/empagliflozin therapy to prevent cardiovascular events in patients with T2DM.

Does Sitagliptin Affect the Rate of Osteoporotic Fractures in Type 2 Diabetes? Population-Based Cohort Study

CONTEXT

Type 2 diabetes and osteoporosis are both common, chronic, and increase with age, whereas type 2 diabetes is also a risk factor for major osteoporotic fractures (MOFs). However, different treatments for type 2 diabetes can affect fracture risk differently, with metaanalyses showing some agents increase risk (eg, thiazolidinediones) and some reduce risk (eg, sitagliptin).

OBJECTIVE

To determine the independent association between new use of sitagliptin and MOF in a large population-based cohort study.

DESIGN, SETTING, AND SUBJECTS

A sitagliptin new user study design employing a nationally representative Unites States claims database of 72 738 insured patients with type 2 diabetes. We used 90-day time-varying sitagliptin exposure windows and controlled confounding by using multivariable analyses that adjusted for clinical data, comorbidities, and time-updated propensity scores.

MAIN OUTCOMES

We compared the incidence of MOF (hip, clinical spine, proximal humerus, distal radius) in new users of sitagliptin vs nonusers over a median 2.2 years follow-up.

RESULTS

At baseline, the median age was 52 years, 54% were men, and median A1c was 7.5%. There were 8894 new users of sitagliptin and 63 834 nonusers with a total 181 139 person-years of follow-up. There were 741 MOF (79 hip fractures), with 53 fractures (4.8 per 1000 person-years) among new users of sitagliptin vs 688 fractures (4.0 per 1000 person-years) among nonusers (P = .3 for difference). In multivariable analyses, sitagliptin was not associated with fracture (adjusted hazard ratio 1.1, 95% confidence interval 0.8-1.4; P = .7), although insulin (P < .001), sulfonylureas (P < .008), and thiazolidinedione (P = .019) were each independently associated with increased fracture risk.

CONCLUSIONS

Even in a young population with type 2 diabetes, osteoporotic fractures were not uncommon. New use of sitagliptin was not associated with fracture, but other commonly used second-line agents for type 2 diabetes were associated with increased risk. These data should be considered when making treatment decisions for those with type 2 diabetes at particularly high risk of fractures.

Assessment of bone turnover and bone quality in type 2 diabetic bone disease: current concepts and future directions

Substantial evidence exists that in addition to the well-known complications of diabetes, increased fracture risk is an important morbidity. This risk is probably due to altered bone properties in diabetes. Circulating biochemical markers of bone turnover have been found to be decreased in type 2 diabetes (T2D) and may be predictive of fractures independently of bone mineral density (BMD). Serum sclerostin levels have been found to be increased in T2D and appear to be predictive of fracture risk independent of BMD. Bone imaging technologies, including trabecular bone score (TBS) and quantitative CT testing have revealed differences in diabetic bone as compared to non-diabetic individuals. Specifically, high resolution peripheral quantitative CT (HRpQCT) imaging has demonstrated increased cortical porosity in diabetic postmenopausal women. Other factors such as bone marrow fat saturation and advanced glycation endproduct (AGE) accumulation might also relate to bone cell function and fracture risk in diabetes. These data have increased our understanding of how T2D adversely impacts both bone metabolism and fracture risk.

Associations with fracture in patients with diabetes: a nested case-control study

OBJECTIVES

Diabetes mellitus is associated with an increased risk of fractures, which is not fully explained by bone mineral density and common risk factors. The aim of this study is to investigate the association of medication and biochemical markers on the risk of fracture in a diabetes population.

DESIGN AND SETTING

A nested case-control study was conducted based on Danish diabetes patients from The Danish National Hospital Discharge Registry.

PARTICIPANTS

The cases of the study were diabetes patients with a fracture (n=24,349), and controls were diabetes patients with no fracture (n=132,349). A total of 2627 diabetes patients were available for an analysis of patient characteristics, comorbidities, biochemical parameters and drug usage.

RESULTS

Age (OR=1.02, 95% CI 1.01 to 1.04), diabetes duration (OR=1.06, 95% CI 1.02 to 1.09), a diagnosis of previous fracture (OR=2.20, 95% CI 1.55 to 3.11), an alcohol-related diagnosis (OR=2.94, 95% CI 1.76 to 4.91), total cholesterol level (OR=2.50, 95% CI 1.20 to 5.21) and the usage of antiepileptics (OR=2.12, 95% CI 1.39 to 3.59) all increased the odds of fracture. Low-density lipoprotein cholesterol levels decreased the odds of fracture (OR =0.34, 95% CI 0.16 to 0.74), where the level of 3.04-5.96 mmol/L was optimal with regard to fracture risk.

CONCLUSIONS

Low-density lipoprotein cholesterol may improve our understanding of fractures in diabetes patients, and it may be added to current fracture risk models in diabetes patients.

Association Between Chronic Conditions and Physical Function Among Veteran and Non-Veteran Women With Diabetes

PURPOSE OF THE STUDY

To compare the number of chronic conditions among a list of 12 and their association with physical function among postmenopausal non-Veteran and Veteran women with diabetes.

DESIGN AND METHODS

Among women with diabetes from the Women's Health Initiative, we compared the average number of chronic conditions between non-Veterans and Veterans and the association between total number of chronic conditions on subsequent RAND-36 physical function. To examine associations between each condition and subsequent physical function, we compared women with diabetes plus one chronic condition to women with diabetes alone using linear regression in separate models for each condition and for non-Veterans and Veterans.

RESULTS

Both non-Veterans (N = 23,542) and Veterans (N = 618) with diabetes had a median of 3 chronic conditions. Decreases in physical function for each additional condition were larger among Veterans than non-Veterans (-6.3 vs. -4.1 points). Decreases in physical function among women with diabetes plus one chronic condition were greater than that reported for diabetes alone for all combinations and were more pronounced among Veterans (non-Veterans: -11.1 to -24.2, Veterans: -16.6 to -40.4 points). Hip fracture, peripheral artery disease, cerebrovascular disease, and coronary disease in combination with diabetes were associated with the greatest decreases in physical function.

IMPLICATIONS

Chronic conditions were common among postmenopausal women with diabetes and were associated with large declines in physical function, particularly among Veterans. Interventions to prevent and reduce the impact of these conditions and facilitate coordination of care among women with diabetes may help them maintain physical function.

Efficacy and Safety of Risedronate in Osteoporosis Subjects with Comorbid Diabetes, Hypertension, and/or Dyslipidemia: A Post Hoc Analysis of Phase III Trials Conducted in Japan

Many osteoporotics have comorbid diabetes mellitus (DM), hypertension (HT), and dyslipidemia (DL). However, whether such comorbidities alter response to anti-osteoporotic treatment is unknown. We did post hoc analyses of combined data from three risedronate Japanese phase III trials to determine whether the presence of DM, HT, or DL affects its efficacy and safety. Data from 885 subjects who received 48-week treatment with risedronate were collected and combined from the three phase III trials. They were divided into two groups by the presence or absence of comorbidities: DM (n = 53) versus non-DM (n = 832); HT (n = 278) versus non-HT (n = 607); and DL (n = 292) versus non-DL (n = 593). Bone mineral density (BMD), urinary type 1 collagen N-telopeptide (uNTX), and serum bone-specific alkaline phosphatase (BAP) were measured at baseline and sequentially until 48 weeks. BMD or bone markers were not different between any of the two groups. Overall, BMD was increased by 5.52%, and uNTX and BAP were decreased by 35.4 and 33.8%, respectively. Some bone markers were slightly lower in DM and DL subjects, but the responses to risedronate were not significantly different. Statin users had lower uNTX and BAP, but showed no difference in the treatment response. All the other medications had no apparent effect. Adverse event incidence was marginally higher in DL compared with non-DL (Relative risk 1.06; 95% confidence interval 1.01-1.11), but was not related to increase in any specific events. Risedronate shows consistent safety and efficacy in suppressing bone turnover and increasing BMD in osteoporosis patients with comorbid DM, HT, and/or DL.

Determinants of bone strength and quality in diabetes mellitus in humans

There is growing evidence that the higher fracture rate observed in patients with type 2 diabetes mellitus (T2DM) is associated with normal, or even increased, areal bone mineral density (aBMD) by DXA. This has led to the hypothesis that patients with T2DM may have abnormalities in bone microarchitecture and/or material composition - i.e., key determinants of bone "quality." Consistent with this hypothesis, several studies using high-resolution peripheral quantitative computed tomography (HRpQCT) have demonstrated preserved indices of trabecular microarchitecture but increased cortical porosity in T2DM patients. In addition, a recent study using a novel in vivo microindentation device found an impairment in a measure of bone material properties (bone material strength index, BMSi) in postmenopausal women with longstanding T2DM; notably, the reduction in BMSi was associated with chronic glycemic control, suggesting that the skeleton should be included as another target organ subject to diabetic complications. The underlying pathogenesis of skeletal fragility in T2DM remains to be defined, although high levels of advanced glycation endproducts (AGEs) may play a role. In addition, T2DM is associated with reduced bone turnover, perhaps with an imbalance between bone resorption and bone formation. Although several studies have found increased serum sclerostin levels in patients with T2DM, the role of these increased levels in mediating the observed increases in cortical porosity or reduction in BMSi remains to be defined. Thus, although bone quality appears to be impaired in T2DM, the pathogenesis of these abnormalities and their relationship to the increased fracture risk observed in these patients needs further study.

Orthopedic complications in diabetes

Diabetes is associated with a number of lower extremity orthopedic conditions and complications including fractures, Charcot neuroarthropathy, plantar ulcers, and infection. These complications are of significant clinical concern in terms of morbidity, mortality, and socioeconomic costs. A review of each condition is discussed, with particular emphasis on the clinical importance, diagnostic considerations, and orthopedic treatment recommendations. The goal of the article is to provide a clinical picture of the challenges that orthopedic surgeons confront, and highlight the need for specific clinical guidelines in diabetic patients.

Effects of diabetes drugs on the skeleton

Type 2 diabetes is associated with increased fracture risk and the mechanisms underlying the detrimental effects of diabetes on skeletal health are only partially understood. Antidiabetic drugs are indispensable for glycemic control in most type 2 diabetics, however, they may, at least in part, modulate fracture risk in exposed patients. Preclinical and clinical data clearly demonstrate an unfavorable effect of thiazolidinediones on the skeleton with impaired osteoblast function and activated osteoclastogenesis. The negative effect of thiazolidinediones on osteoblastogenesis includes decreased activity of osteoblast-specific transcription factors (e.g. Runx2, Dlx5, osterix) and decreased activity of osteoblast-specific signaling pathways (e.g. Wnt, TGF-β/BMP, IGF-1). In contrast, metformin has a positive effect on osteoblast differentiation due to increased activity of Runx2 via the AMPK/USF-1/SHP regulatory cascade resulting in a neutral or potentially protective effect on bone. Recently marketed antidiabetic drugs include incretin-based therapies (GLP-1 receptor agonists, DPP-4 inhibitors) and sodium-glucose co-transporter 2 (SGLT2)-inhibitors. Preclinical studies indicate that incretins (GIP, GLP-1, and GLP-2) play an important role in the regulation of bone turnover. Clinical safety data are limited, however, meta-analyses of trials investigating the glycemic-lowering effect of both, GLP-1 receptor agonists and DPP4-inhibitors, suggest a neutral effect of incretin-based therapies on fracture risk. For SGLT2-inhibitors recent data indicate that due to their mode of action they may alter calcium and phosphate homeostasis (secondary hyperparathyroidism induced by increased phosphate reabsorption) and thereby potentially affect bone mass and fracture risk. Clinical studies are needed to elucidate the effect of SGLT2-inhibitors on bone metabolism. Meanwhile SGLT2-inhibitors should be used with caution in patients with high fracture risk, which is specifically true for the use of thiazolidinediones.

Increased Circulating Adiponectin in Response to Thiazolidinediones: Investigating the Role of Bone Marrow Adipose Tissue

BACKGROUND

Bone marrow adipose tissue (MAT) contributes to increased circulating adiponectin, an insulin-sensitizing hormone, during caloric restriction (CR), but whether this occurs in other contexts remains unknown. The antidiabetic thiazolidinediones (TZDs) also promote MAT expansion and hyperadiponectinemia, even without increasing adiponectin expression in white adipose tissue (WAT).

OBJECTIVES

To test the hypothesis that MAT expansion contributes to TZD-associated hyperadiponectinemia, we investigated the effects of rosiglitazone, a prototypical TZD, in wild-type (WT) or Ocn-Wnt10b mice. The latter resist MAT expansion during CR, leading us to postulate that they would also resist this effect of rosiglitazone.

DESIGN

Male and female WT or Ocn-Wnt10b mice (C57BL/6J) were treated with or without rosiglitazone for 2, 4, or 8 weeks, up to 30 weeks of age. MAT content was assessed by osmium tetroxide staining and adipocyte marker expression. Circulating adiponectin was determined by ELISA.

RESULTS

In WT mice, rosiglitazone caused hyperadiponectinemia and MAT expansion. Compared to WT mice, Ocn-Wnt10b mice had significantly less MAT in distal tibiae and sometimes in proximal tibiae; however, interpretation was complicated by the leakage of osmium tetroxide from ruptures in some tibiae, highlighting an important technical consideration for osmium-based MAT analysis. Despite decreased MAT in Ocn-Wnt10b mice, circulating adiponectin was generally similar between WT and Ocn-Wnt10b mice; however, in females receiving rosiglitazone for 4 weeks, hyperadiponectinemia was significantly blunted in Ocn-Wnt10b compared to WT mice. Notably, this was also the only group in which tibial adiponectin expression was lower than in WT mice, suggesting a close association between MAT adiponectin production and circulating adiponectin. However, rosiglitazone significantly increased adiponectin protein expression in WAT, suggesting that WAT contributes to hyperadiponectinemia in this context. Finally, rosiglitazone upregulated uncoupling protein 1 in brown adipose tissue (BAT), but this protein was undetectable in tibiae, suggesting that MAT is unlikely to share thermogenic properties of BAT.

CONCLUSION

TZD-induced hyperadiponectinemia is closely associated with increased adiponectin production in MAT but is not prevented by the partial loss of MAT that occurs in Ocn-Wnt10b mice. Thus, more robust loss-of-MAT models are required for future studies to better establish MAT's elusive functions, both on an endocrine level and beyond.

Chinese Herbal Medicine Treatment Improves the Overall Survival Rate of Individuals with Hypertension among Type 2 Diabetes Patients and Modulates In Vitro Smooth Muscle Cell Contractility

Type 2 diabetes (T2D) is a chronic, multifactorial, and metabolic disorder accounting for 90% diabetes cases worldwide. Among them, almost half of T2D have hypertension, which is responsible for cardiovascular disease, morbidity, and mortality in these patients. The Chinese herbal medicine (CHM) prescription patterns of hypertension individuals among T2D patients have yet to be characterized. This study, therefore, aimed to determine their prescription patterns and evaluate the CHM effect. A cohort of one million randomly sampled cases from the National Health Insurance Research Database (NHIRD) was used to investigate the overall survival rate of CHM users, and prescription patterns. After matching CHM and non-CHM users for age, gender and date of diagnosis of hypertension, 980 subjects for each group were selected. The CHM users were characterized with slightly longer duration time from diabetes to hypertension, and more cases for hyperlipidaemia. The cumulative survival probabilities were higher in CHM users than in non-CHM users. Among these top 12 herbs, Liu-Wei-Di-Huang-Wan, Jia-Wei-Xiao-Yao-San, Dan-Shen, and Ge-Gen were the most common herbs and inhibited in vitro smooth muscle cell contractility. Our study also provides a CHM comprehensive list that may be useful in future investigation of the safety and efficacy for individuals with hypertension among type 2 diabetes patients.

Diabetes and bone: biological and environmental factors

PURPOSE OF REVIEW

Type 1 and type 2 diabetes mellitus are known to increase fracture risk. It is known that type 1 diabetes mellitus is associated with lower bone mineral density, but for type 2 diabetes mellitus, the real risk of increasing osteoporotic fractures is not explained by bone mineral density, which was found to be normal or paradoxically higher than controls in several studies, thus claiming for further investigations. This review summarizes some of the newest findings about factors that contribute to bone alterations in diabetic patients.

RECENT FINDINGS

Most recent evidences showed that bone of diabetic patients presents a cortical porosity which is not captured by the bidimensional densitometric measurements as performed by dual energy X-ray absorptiometry. Other studies investigated bone matrix searching for molecular mechanisms underlying the reduced bone strength in diabetic patients. The loss of bone biomechanical properties in diabetes has been associated to the glycated collagen matrix induced by hyperglycemia. Other studies analyzed the effect on bone microarchitecture of the most common antidiabetic drugs.

SUMMARY

Disease management of fracture risk in diabetic patients needs new methodologies of assessment that also take into account bone quality and evaluation of clinical risk factors, including balance, visual, and neurological impairments.

COMPARISON OF THE LONG-TERM EFFECTS OF LIRAGLUTIDE AND GLIMEPIRIDE MONOTHERAPY ON BONE MINERAL DENSITY IN PATIENTS WITH TYPE 2 DIABETES

OBJECTIVE

Patients with type 2 diabetes have an increased risk of fragility fractures; the cause is unclear but is likely multifactorial. Some diabetes treatments induce bone loss, accentuating underlying skeletal fragility and increasing fracture risk. This subgroup analysis aimed to compare long-term effects of liraglutide and glimepiride on bone mineral density (BMD) in patients with type 2 diabetes.

METHODS

LEAD-3, a 52-week, double-blind, active-control, phase III, multicenter trial, investigated the efficacy of liraglutide (1.2 and 1.8 mg/day) versus glimepiride monotherapy in type 2 diabetes. A 52-week, open-label extension followed, in which participants remained on randomized therapy. A subgroup of participants underwent BMD measurement by dual-energy X-ray absorptiometry at baseline, 52, and 104 weeks. The main outcome measure was change from baseline in total body BMD at 52 and 104 weeks, assessed by analysis of covariance.

RESULTS

A total of 746 patients with type 2 diabetes aged 19 to 79 years were randomized into the main trial. Of these, 61 patients (20 assigned to liraglutide 1.8 mg/day, 23 to liraglutide 1.2 mg/day, 18 to glimepiride 8 mg/day) had BMD measurements. Baseline age, body mass index, diabetes duration, glycated hemoglobin, and total BMD were similar across treatment groups. There was no apparent difference in mean total BMD change from baseline in patients receiving liraglutide 1.8 or 1.2 mg/day or glimepiride 8 mg/day at 52 or 104 weeks.

CONCLUSION

In this small subgroup analysis, liraglutide monotherapy did not negatively affect total BMD in a 2-year prospective study, suggesting it may not exacerbate the consequences of bone fragility.

Effects of TZD Use and Discontinuation on Fracture Rates in ACCORD Bone Study

CONTEXT

In trials, thiazolidinediones (TZDs) increase fracture risk in women, but the effects of discontinuation are unknown.

OBJECTIVE

The objective was to investigate the effects of TZD use and discontinuation on fractures in women and men.

DESIGN

This was a longitudinal observational cohort study using data from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial bone ancillary study. Duration of TZD use and discontinuation during ACCORD, assessed every 2-4 months at clinic visits, were modeled as time-varying covariates in proportional hazards models for occurrence of first non-spine fracture.

PARTICIPANTS

We studied a total of 6865 participants in ACCORD BONE.

MAIN OUTCOME MEASURES

Main outcome measures were centrally adjudicated non-spine fracture.

RESULTS

Average age was 62.4 (SD, 6.6) years; average duration of diabetes was 11.1 (SD, 7.8) years. Rosiglitazone was used by 74% and pioglitazone by 13% of participants. During a mean follow-up of 4.8 (SD, 1.5) years, 262 men and 287 women experienced at least one non-spine fracture. The fracture rate was higher in women with 1-2 years of TZD use (hazard ratio [HR] = 2.32; 95% confidence interval [CI], 1.49, 3.62) or >2 years of TZD use (HR = 2.01; 95% CI, 1.35, 2.98), compared with no use. The fracture rate was reduced in women who had discontinued TZD use for 1-2 years (HR = 0.57; 95% CI, 0.35, 0.92) or > 2 years (HR = 0.42; 95% CI, 0.24, 0.74) compared with current users. TZD use and discontinuation were not associated with non-spine fractures in men.

CONCLUSIONS

TZD use was associated with increased non-spine fractures in women, but not men, with type 2 diabetes. When women discontinued TZD use, the fracture effects were attenuated.

Drug-induced osteoporosis: from Fuller Albright to aromatase inhibitors

Many commonly prescribed medications, such as selective serotonin reuptake inhibitors, proton pump inhibitors, thiazolidinediones, aromatase inhibitors, and androgen deprivation therapy, have been associated with adverse skeletal effects. The levels of evidence in support of a causal relationship between drug use and the development of bone loss and fractures are variable. For some drugs, a causal relationship is suspected (but not proven) based on observational studies, while in others causality is firmly established with randomized, controlled clinical trials. The mechanism of action for skeletal damage is poorly understood for some drugs and well known for others. Guidelines for managing bone health in patients taking some medications with potential skeletal toxicity have been developed using the best available evidence and expert opinion. This is a review of selected medications that have been associated with bone loss and fractures, with recommendations for clinical care.

The effect of thiazolidinediones on bone mineral density and bone turnover: systematic review and meta-analysis

AIMS/HYPOTHESIS

Thiazolidinediones (TZDs) are associated with an increased risk of fracture but the mechanism is unclear. We sought to determine the effect of TZDs on bone mineral density (BMD) and bone turnover markers.

METHODS

PubMed, EMBASE and Cochrane CENTRAL databases were searched from inception until January 2015 for randomised controlled trials comparing TZDs with metformin, sulfonylureas or placebo, and those reporting changes in BMD and/or bone turnover markers. The primary outcome was percentage change in BMD from baseline and results were pooled with random effects meta-analyses.

RESULTS

In all, 18 trials were included in the primary analyses and another two were included in the sensitivity analyses (n = 3,743, 50% women, mean age 56 years, median trial duration 48 weeks). TZDs decreased BMD at the lumbar spine (difference -1.1% [95% CI -1.6, -0.7]; p < 0.0001), total hip (-1.0% [-1.4, -0.6]; p < 0.0001) and forearm (-0.9% [-1.6, -0.3]; p = 0.007). There were statistically non-significant decreases in BMD at the femoral neck (-0.7% [-1.4, 0.0]; p = 0.06) and total body (-0.3% [-0.5, 0.0]; p = 0.08). Five trials (n = 450) showed no statistically significant difference in percentage change in BMD between the TZD group and controls up to 1 year following TZD withdrawal. In 14 trials, the effect of TZD treatment on turnover markers varied considerably between individual studies.

CONCLUSIONS/INTERPRETATION

Treatment with TZDs results in modest bone loss that may not be reversed 1 year after cessation of treatment.

Optimal glycaemic control in elderly people with type 2 diabetes: what does the evidence say?

The global prevalence of type 2 diabetes mellitus (T2DM) is rising in an ageing population through a combination of lifestyle changes and greater longevity. However, by excluding participants aged over 70 years, most major interventional trials on which current diabetes therapeutic guidelines are based have failed to provide specific evidence to support the prescribed management of diabetes in elderly people. While diabetes per se has a significant impact on the elderly person, the side effects of medications, particularly hypoglycaemia, prevent optimisation of diabetes treatment. Hypoglycaemia is associated with significant morbidity, to which elderly people are often more vulnerable because of factors such as the effects of ageing, progressive renal impairment, frailty, polypharmacy and cognitive decline. T2DM is associated with accelerated cognitive decline in some individuals, and recurrent severe hypoglycaemia has been implicated as a potential contributory factor. Although the evidence for selection of appropriate glycaemic targets in elderly patients is sparse, it is now acknowledged that prevention of hypoglycaemia must influence individualisation of treatment goals in this vulnerable group. This should also be reflected by the choice of anti-diabetes agents that are initiated when diet and lifestyle advice is ineffective. Recently developed international guidelines, which have specifically addressed the management of diabetes in elderly people, highlight the importance of a pragmatic management approach rather than attempting to achieve a generic glycated haemoglobin goal and are summarised in this article.

Change in estimated glomerular filtration rate and fracture risk in the Action to Control Cardiovascular Risk in Diabetes Trial

OBJECTIVE

Patients with type 2 diabetes (T2DM) are at increased risk of fracture. High prevalence of chronic kidney disease (CKD) in T2DM may contribute to bone fragility, but whether dynamic change in kidney function is associated with fracture risk is unclear.

RESEARCH DESIGN AND METHODS

To evaluate the association of pre-randomization baseline estimated glomerular filtration (eGFR) and its change over time with subsequent fracture risk in the Bone substudy of Action to Control Cardiovascular Risk in Diabetes (ACCORD) Trial, we conducted an observational study of 2262 women and 4737 men with T2DM and with at least 2 eGFR values.

RESULTS

During a mean follow-up of 4.40±1.54 years, 235 women and 223 men sustained a new non-vertebral fracture. In multivariable adjusted sex-specific models, pre-randomization baseline eGFR was not a significant predictor of fracture risk in either men or women. However, a steeper decline in eGFR was associated with greater risk of fracture in women (hazard ratio [HR] per standard deviation [SD] decrement in eGFR slope, 1.30; 95% CI 1.17-1.44) but not men (HR per SD decrement in eGFR slope, 0.97; 95%CI 0.82-1.13). Accounting for competing risk of death modestly attenuated the association in women (HR per SD decrement in eGFR slope, 1.19; 95% CI 1.04-1.37), with the relationship in men remaining non-significant (HR per SD decrement in eGFR slope, 0.96; 95% CI 0.77-1.18).

CONCLUSIONS

Declining kidney function predicts fracture risk in women but not in men with T2DM. Future studies should investigate the mechanisms for these associations.

Glycemic Control with Thiazolidinedione Is Associated with Fracture of T2DM Patients

Objective

Diabetes is a common diseases and a major problem worldwide. Diabetic osteopathy might be elevated in diabetic patients and is usually caused by bone fracture. Several diabetes medications, such as thiazolidinediones (TZDs), could lead to increased risks of fracture.

Methods

We used the nationwide database to identified 32466 patients who had developed type 2 diabetes from 2000 to 2010 as the diabetic cohort and, from that group, we selected 3427 diabetic patients who had developed bone fracture to survey the possible risk factors, includng commonly used diabetes medication.

Results

We found that TZDs might present increased risks for fracture in patients who used it for an extended period (7 to 730 days before the index date), especially in female patients younger than 64 years old, for whom the risk was elevated from a 1.74- to a 2.58-fold odds ratio.

Conclusions

We recommend that clinics follow up with non-osteoporotic female patients younger than 64 years old who are using TZDs, to avoid the associated risks of fracture.

Oral anti-diabetic drugs and fracture risk, cut to the bone: safe or dangerous? A narrative review

Fracture risk is higher in older adults with type 2 diabetes and may be influenced by treatments for diabetes. Oral anti-diabetic drugs have different effects on bone metabolism. The purpose of this review is to describe the effects of these drugs on bone metabolism and fracture risk. Osteoporosis is a progressive skeletal disorder that is characterized by compromised bone strength and increased risk of fracture. This condition has become an important global health problem, affecting approximately 200 million people worldwide. Another chronic and highly prevalent condition is diabetes mellitus, which affects more than 380 million people; both type 1 and type 2 diabetes are risk factors for fracture. Type 2 diabetes, in particular, is associated with impaired bone strength, although it is characterized by normal or elevated bone mineral density. Several therapeutic strategies are available to achieve the best outcomes in the management of diabetes mellitus but these have different effects on bone metabolism. The purpose of this narrative review is to describe the effects of oral hypoglycemic agents (metformin, sulfonylureas, thiazolidinediones, meglitinides, dipeptidyl peptidase-4 inhibitors, glucagon-like peptide-1 receptor agonists and sodium-dependent glucose transporter 2 inhibitors) on bone metabolism and on the risk of developing fragility fractures in patients with type 2 diabetes. Both diabetes and osteoporosis represent a significant burden in terms of healthcare costs and quality of life. It is very important to choose therapies for diabetes that ensure good metabolic control whilst preserving skeletal health.

Bone cells and bone turnover in diabetes mellitus

Substantial evidence exists that in addition to the well-known complications of diabetes, increased fracture risk is an important morbidity. This risk is probably due, at least in part, to altered bone remodeling and bone cell function in diabetes. Circulating biochemical markers of bone formation, including P1NP, osteocalcin and bone-specific alkaline phosphatase have been found to be decreased in type 2 diabetes (T2D) and may be predictive of fractures independently of bone mineral density (BMD). These findings have been corroborated by preliminary histomorphometric data. Reductions in the bone resorption marker serum CTx in T2D have also been reported. Serum sclerostin levels have been found to be increased in T2D and appear to be predictive of fracture risk independent of BMD. Other factors such as bone marrow fat saturation, advanced glycation endproduct (AGE) accumulation, and microarchitectural changes might also relate to bone cell function and fracture risk in diabetes.

The prevention of fragility fractures in diabetic patients

Patients with diabetes mellitus (DM) are at greater risk of fractures mostly due to not only extraskeletal factors, such as propensity to falls, but also to bone quality alteration, which reduces bone strength. In people with DM, insulin deficit and hyperglycemia seem to play a role in determining bone formation alteration by AGE accumulation which directly influences osteoblast activity. Although there are conflicting data in the literature, adequate glycemic control with hypoglycemic treatment may be an important element in preventing bone tissue alterations in both type 1 and type 2 DM. Diabetes status is a predictive of future hip and major osteoporosis fractures independently of BMD and FRAX probability. Attention should be paid to the use of thiazolidinediones, especially in older women, because the direct negative effect on bone could exceed the positive effect of glycemic control. Systematic screening for complications and fall prevention efforts, along with calcium and vitamin D repletion and adequate physical activity, represents the mainstay of fracture prevention in DM patients. All anticatabolic drugs (raloxifene, bisphosphonates, denosumab) seem to be effective in DM patients. On the basis of pathophysiological evidence that suggests low bone formation in DM patients, osteoanabolic therapies such as teriparatide might represent an important therapeutic option for DM patients with severe osteoporosis and/or multiple fractures. The search for better methods for the identification of fragility fracture risk in the growing population of adult and elderly subjects with DM might be considered a clinical priority which could improve the prevention of fracture in DM patients.

The impact of diabetes and diabetes medications on bone health

Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fragility fractures despite increased body weight and normal or higher bone mineral density. The mechanisms by which T2DM increases skeletal fragility are unclear. It is likely that a combination of factors, including a greater risk of falling, regional osteopenia, and impaired bone quality, contributes to the increased fracture risk. Drugs for the treatment of T2DM may also impact on the risk for fractures. For example, thiazolidinediones accelerate bone loss and increase the risk of fractures, particularly in older women. In contrast, metformin and sulfonylureas do not appear to have a negative effect on bone health and may, in fact, protect against fragility fracture. Animal models indicate a potential role for incretin hormones in bone metabolism, but there are only limited data on the impact of dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 agonists on bone health in humans. Animal models also have demonstrated a role for amylin in bone metabolism, but clinical trials in patients with type 1 diabetes with an amylin analog (pramlintide) have not shown a significant impact on bone metabolism. The effects of insulin treatment on fracture risk are inconsistent with some studies showing an increased risk and others showing no effect. Finally, although there is limited information on the latest class of medications for the treatment of T2DM, the sodium-glucose co-transporter-2 inhibitors, these drugs do not seem to increase fracture risk. Because diabetes is an increasingly common chronic condition that can affect patients for many decades, further research into the effects of agents for the treatment of T2DM on bone metabolism is warranted. In this review, the physiological mechanisms and clinical impact of diabetes treatments on bone health and fracture risk in patients with T2DM are described.

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.

Diabetes medications and bone

Type 2 diabetes mellitus (T2DM) is a common chronic disease that may be associated with an increased risk of fracture. Evidence that thiazolidinediones (TZDs) increase fracture risk in women with T2DM has focused attention on the skeletal effects of treatments for diabetes. Only scant, low-quality evidence is available for non-TZD diabetes medications and bone health, but it suggests that there are no clinically important effects.

Antidiabetic therapy in post kidney transplantation diabetes mellitus

Post-transplantation diabetes mellitus (PTDM) is a common complication after kidney transplantation that affects up to 40% of kidney transplant recipients. By pathogenesis, PTDM is a diabetes form of its own, and may be characterised by a sudden, drug-induced deficiency in insulin secretion rather than worsening of insulin resistance over time. In the context of deteriorating allograft function leading to a re-occurrence of chronic kidney disease after transplantation, pharmacological interventions in PTDM patients deserve special attention. In the present review, we aim at presenting the current evidence regarding efficacy and safety of the modern antidiabetic armamentarium. Specifically, we focus on incretin-based therapies and insulin treatment, besides metformin and glitazones, and discuss their respective advantages and pitfalls. Although recent pilot trials are available in both prediabetes and PTDM, further studies are warranted to elucidate the ideal timing of various antidiabetics as well as its long-term impact on safety, glucose metabolism and cardiovascular outcomes in kidney transplant recipients.

Adverse skeletal effects of drugs - beyond Glucocorticoids

Osteoporotic fractures are an important public health problem with significant individual and societal costs. In addition to the major risk factors for osteoporotic fracture, low bone mineral density (BMD), age, low body weight and history of fracture or falls, some drugs are now considered to be important secondary risk factor for bone loss and fracture, particularly amongst predisposed individuals. Currently available data are often generated from small observational clinical studies, making risk assessment and development of management guidelines difficult. In many cases, the exposed population has a low baseline risk for fracture and additional assessment and treatment may not be necessary. In this review, we focus on drugs other than glucocorticoids identified as potentially causing adverse skeletal effects, summarizing the existing evidence from preclinical and clinical studies, and suggest recommendations for patient management.

Insights into bone fragility in diabetes: the crucial role of bone quality on skeletal strength

Meta-analyses have revealed that the relative risk of hip fractures in patients with type 1 and type 2 diabetes mellitus is higher than that in non-diabetic subjects. The risk of fracture in patients with diabetes mellitus increases along with a decrease in bone mineral density (BMD) similarly to those in non-diabetic patients. However, the observed risk of fracture is higher than expected one by BMD in both type 1 and type 2 diabetic patients, indicating that precise estimation of bone fragility by BMD values in patients with diabetes is difficult. Bone strength consists of BMD and bone quality, for this reason, poor bone quality is a most suitable and explicable cause for elevated fracture risk in this population. This bone fragility observed in patients with diabetes mellitus is caused by unique pathogenesis in diabetes, suggesting that osteoporosis in diabetic patients may be one of the diabetic complications and that specific diagnostic criteria for this osteoporosis is required. Bone quality indicators closely related to bone fragility are required to be identified to establish a diagnostic method for osteoporosis in patients with diabetes mellitus.

A review of the treatment of type 2 diabetes in children

The incidence of type 2 diabetes and obesity in children and adolescents has risen at staggering rates. Studies have shown that treating type 2 diabetes with oral medications in children may be more difficult than treating in adults. Compounding this problem is the fact that most of the medications available for treating type 2 diabetes have not been studied in children. Recently, the American Diabetes Association and the Pediatric Endocrine Society have collaborated to create a guideline for the treatment of type 2 diabetes in children. Similar to the treatment of adults with type 2 diabetes, metformin remains the mainstay of therapy along with diet and exercise. Adjunctive therapy should be based on the limited clinical evidence available as well as on patient preference. In order to avoid detrimental microvascular and macrovascular complications, patients, clinicians, and family members should work together to ensure adequate treatment of type 2 diabetes in children.

Oral antihyperglycemic treatment options for type 2 diabetes mellitus

Table 3 provides an overview of the oral antihyperglycemic drugs reviewed in this article. A 2011 meta-analysis by Bennett and colleagues found low or insufficient quality of evidence favoring an initial choice of metformin, SUs, glinides, TZDs, or (table see text) DPP-4 inhibitors (alpha-glucosidase inhibitors, bromocriptine mesylate, and SGLT2 inhibitors were not included in this meta-analysis) with regard to the outcomes measures of all-cause mortality, cardiovascular events and mortality, and incidence of microvascular disease (retinopathy, nephropathy, and neuropathy) in previously healthy individuals with newly diagnosed T2DM. Likewise, the Bennett and colleagues meta-analysis judged these drugs to be of roughly equal efficacy with regard to reduction of HbA1c (1%–1.6%) from the pretreatment baseline. The ADOPT clinical trial of 3 different and, at the time, popular, oral monotherapies for T2DM provides support for the consensus recommendation of metformin as first-line therapy. The ADOPT trial showed slightly superior HbA1c reduction for rosiglitazone compared with metformin, which was in turn superior to glyburide. However, significant adverse events, including edema, weight gain, and fractures, were more common in the rosiglitazone-treated patients. The implication of this trial is that the combination of low cost, low risk, minimal adverse effects, and efficacy of metformin justifies use of this agent as the cornerstone of oral drug treatment of T2DM. Judicious use of metformin in groups formerly thought to be at high risk for lactic acidosis (ie, those with CHF, chronic kidney disease [eGFR >30 mL/min/1.73 m2], and the elderly) may be associated with mortality benefit rather than increased risk. Secondary and tertiary add-on drug therapy should be individualized based on cost, personal preferences, and overall treatment goals, taking into account the wishes and priorities of the patient.

Sodium glucose co-transporter inhibitors for the management of diabetes mellitus: an opinion paper from the Endocrine and Metabolism Practice and Research Network of the American College of Clinical Pharmacy

Type 2 diabetes mellitus (T2DM) carries a high prevalence in the United States and worldwide. Therefore, the number of medication classes being developed and studied has grown. The individualized management of diabetes is accomplished by evaluating a medication's efficacy, safety, and cost, along with the patient's preference and tolerance to the medication. Sodium glucose co-transporter 2 inhibitors are a new therapeutic class indicated for the treatment of diabetes and have a unique mechanism of action, independent of beta-cell function. The first agent approved by the Food and Drug Administration (FDA) was canagliflozin in March 2013. Two agents - dapagliflozin and empagliflozin - were FDA-approved in January and July 2014, respectively. A clear understanding of the new class is needed to identify its appropriate use in clinical practice. Members of the American College of Clinical Pharmacy Endocrine and Metabolism Practice and Research Network reviewed available literature regarding this therapeutic class. The article addresses the advantages, disadvantages, emerging role, and patient education for sodium glucose co-transporter 2 inhibitors. Key limitations for this article include limited access to clinical trial data not published by the pharmaceutical company and limited data on products produced outside the United States.

Type 2 diabetes pharmacoepidemiology update 2014: safety versus efficacy

The number of available options for type 2 diabetes has increased steadily over the last decade. These include the insulins, metformin, sulfonylureas, thiazolidinediones, incretin-based therapies, and sodium-glucose cotransporter 2 inhibitors. In this paper, the safety and efficacy of these agents are reviewed with a view on updated findings that have emerged over the last few years. Most drugs for type 2 diabetes effectively lower glycated hemoglobin. Their efficacy is in the range of approximate 0.8-1.5 % reduction in glycated hemoglobin for most agents. No drug for type 2 diabetes has been shown to reduce cardiovascular risk in a clinical trial which represents a gap in the therapeutic armamentarium for type 2 diabetes. Recent evidence has linked the thiazolidinediones to bladder cancer and raised concerns about pancreatic cancer with incretins, which requires further confirmation. The rapidly emerging evidence in the field of pharmacoepidemiology of diabetes will continue to provide answers to important questions on safety and efficacy in 2015 and beyond.

Secondary osteoporosis: pathophysiology & diagnosis

Osteoporosis is a skeletal disease characterized by decreased bone mass and microarchitectural changes in bone tissue that increase the susceptibility to fracture. Secondary osteoporosis is loosely defined as low bone mineral density or increased risk of fragility fracture caused by any factor other than aging or postmenopausal status. The purpose of this review is to discuss the current understanding of the pathophysiology and contribution to fracture risk of many of the more common causes of secondary osteoporosis, as well as diagnostic considerations, outlined by organ system. While not comprehensive, included are a wide array of diseases, conditions, and medications that have been associated with bone loss and susceptibility to fractures. The hope is to highlight the importance to the general clinician of screening for and treating the osteoporosis in these patients, so to limit the resultant increased morbidity associated with fractures.

Identification of patient profile for treatment

The WHO clinical definition of osteoporosis, based on a measurement of bone mineral density (BMD) by Dual Energy X-ray Absorptiometry, has been used globally since the mid-1990s. However, although this definition identifies those at greatest individual risk of fracture, in the population overall a greater total number of fractures occur in individuals with BMD values above the osteoporosis threshold. The inclusion of clinical risk factors, with or without BMD, in fracture prediction algorithms can improve the identification of individuals at high fracture risk; thus a number of web-based tools have been developed, the most commonly used globally being FRAX(®). In this review, we will discuss the epidemiology of osteoporosis, clinical risk factors for fragility fracture, and how this knowledge is being used to aid risk stratification. Importantly, research is on-going to demonstrate the clinical efficacy and cost-effectiveness of such case-finding strategies.

Bayesian methods including nonrandomized study data increased the efficiency of postlaunch RCTs

OBJECTIVES

Findings from nonrandomized studies on safety or efficacy of treatment in patient subgroups may trigger postlaunch randomized clinical trials (RCTs). In the analysis of such RCTs, results from nonrandomized studies are typically ignored. This study explores the trade-off between bias and power of Bayesian RCT analysis incorporating information from nonrandomized studies.

STUDY DESIGN AND SETTING

A simulation study was conducted to compare frequentist with Bayesian analyses using noninformative and informative priors in their ability to detect interaction effects. In simulated subgroups, the effect of a hypothetical treatment differed between subgroups (odds ratio 1.00 vs. 2.33). Simulations varied in sample size, proportions of the subgroups, and specification of the priors.

RESULTS

As expected, the results for the informative Bayesian analyses were more biased than those from the noninformative Bayesian analysis or frequentist analysis. However, because of a reduction in posterior variance, informative Bayesian analyses were generally more powerful to detect an effect. In scenarios where the informative priors were in the opposite direction of the RCT data, type 1 error rates could be 100% and power 0%.

CONCLUSION

Bayesian methods incorporating data from nonrandomized studies can meaningfully increase power of interaction tests in postlaunch RCTs.

Thiazolidinedione-induced lipid droplet formation during osteogenic differentiation

Chronic administration of the insulin-sensitising drugs, thiazolidinediones (TZDs), results in low bone mineral density and 'fatty bones'. This is thought to be due, at least in part, to aberrant differentiation of progenitor mesenchymal stem cells (MSCs) away from osteogenesis towards adipogenesis. This study directly compared the effects of rosiglitazone, pioglitazone, and netoglitazone treatment on osteogenesis and adipogenesis in MSCs derived from subcutaneous (SC) or visceral (PV) white adipose tissue. MSCs were isolated from adipose tissue depots of male Wistar rats and characterised using flow cytometry. The effects of TZD treatment on osteogenic and adipogenic differentiation were assessed histologically (day 14) and by quantitative PCR analysis (Pparγ2 (Pparg2), Ap2 (Fabp4), Adipsin (Adps), Msx2, Collagen I (Col1a1), and Alp) on days 0, 7, and 10. Uniquely, lipid droplet formation and mineralisation were found to occur concurrently in response to TZD treatment during osteogenesis. Compared with SC MSCs, PV MSCs were more prone to lipid accumulation under controlled osteogenic and adipogenic differentiation conditions. This study demonstrated that the extent of lipid accumulation is dependent on the nature of the Ppar ligand and that SC and PV MSCs respond differently to in vitro TZD treatment, suggesting that metabolic status can contribute to the adverse effects associated with TZD treatment.

Bone damage in type 2 diabetes mellitus

This review focuses on the mechanisms determining bone fragility in patients with type 2 diabetes mellitus (T2DM). Despite bone mineral density (BMD) is usually normal or more often increased in these patients, fracture incidence is high, probably because of altered bone "quality". The latter seems to depend on several, only partly elucidated, mechanisms, such as the increased skeletal content of advanced glycation end-products causing collagen deterioration, the altered differentiation of bone osteogenic cells, the altered bone turnover and micro-architecture. Disease duration, its severity and metabolic control, the type of therapy, the presence or absence of complications, as like as the other known predictors for falls, are all relevant contributing factors affecting fracture risk in T2DM. In these patients the estimate of fracture risk in the everyday clinical practice may be challenging, due to the lower predictive capacity of both BMD and risk factors-based algorithms (e.g. FRAX).

Risk of fracture with thiazolidinediones: an updated meta-analysis of randomized clinical trials

OBJECTIVE

The use of thiazolidinediones (TZDs) has been associated with increased fracture risk. We performed a comprehensive literature review and meta-analysis to estimate the risk of fractures with TZDs

METHODS

We searched MEDLINE, Embase and the Cochrane Database, from inception to May 2014. We included all randomized trials that described the risk of fractures or changes in bone mineral density (BMD) with TZDs. We pooled data with odds ratios (ORs) for fractures and the weighted mean difference in BMD. To assess heterogeneity in results of individual studies, we used Cochran's Q statistic and the I(2) statistic.

RESULTS

We included 24,544 participants with 896 fracture cases from 22 randomized controlled trials. Meta-analysis showed that the significantly increased incidence of fracture was found in women (OR=1.94; 95%CI: 1.60-2.35; P<0.001), but not in men (OR=1.02; 95%CI: 0.83-1.27; P=0.83). For women, the fracture risk was similar in rosiglitazone (OR=2.01; 95%CI: 1.61-2.51; P<0.001) and pioglitazone (OR=1.73; 95%CI: 1.18-2.55; P=0.005) treatment and appeared to be similar for participants aged <60years old (OR=1.89; 95%CI: 1.51-2.36; P<0.001) and aged ≥60years old (OR=2.07; 95%CI: 1.51-2.36; P<0.001). There was a non-significant trend towards increased risk of fractures in different cumulative durations of TZD exposure. TZD treatment was also associated with significant changes in BMD among women at the lumbar spine(weighted mean difference: -0.49%, 95%CI: -0.66% to -0.32%; P<0.001), the femoral neck (weighted mean difference: -0.34%, 95%CI: -0.51% to -0.16%; P<0.001) and the hip(weighted mean difference: -0.33%, 95%CI: -0.52% to -0.14%; P<0.001).

CONCLUSIONS

Our results suggest that TZD treatment is associated with an increased risk of fractures in women, effects of rosiglitazone and pioglitazone are similar, fracture risk is independent of age and fracture risk has no clear association with duration of TZD exposure.

Medication-induced osteoporosis: screening and treatment strategies

Drug-induced osteoporosis is a significant health problem and many physicians are unaware that many commonly prescribed medications contribute to significant bone loss and fractures. In addition to glucocorticoids, proton pump inhibitors, selective serotonin receptor inhibitors, thiazolidinediones, anticonvulsants, medroxyprogesterone acetate, aromatase inhibitors, androgen deprivation therapy, heparin, calcineurin inhibitors, and some chemotherapies have deleterious effects on bone health. Furthermore, many patients are treated with combinations of these medications, possibly compounding the harmful effects of these drugs. Increasing physician awareness of these side effects will allow for monitoring of bone health and therapeutic interventions to prevent or treat drug-induced osteoporosis.

Retinaldehyde dehydrogenase 1 deficiency inhibits PPARγ-mediated bone loss and marrow adiposity

PPARγ, a ligand-activated nuclear receptor, regulates fundamental aspects of bone homeostasis and skeletal remodeling. PPARγ-activating anti-diabetic thiazolidinediones in clinical use promote marrow adiposity, bone loss, and skeletal fractures. As such, delineating novel regulatory pathways that modulate the action of PPARγ, and its obligate heterodimeric partner RXR, may have important implications for our understanding and treatment of disorders of low bone mineral density. We present data here establishing retinaldehyde dehydrogenase 1 (Aldh1a1) and its substrate retinaldehyde (Rald) as novel determinants of PPARγ-RXR actions in the skeleton. When compared to wild type (WT) controls, retinaldehyde dehydrogenase-deficient (Aldh1a1(-/-)) mice were protected against bone loss and marrow adiposity induced by either the thiazolidinedione rosiglitazone or a high fat diet, both of which potently activate the PPARγ-RXR complex. Consistent with these results, Rald, which accumulates in vivo in Aldh1a1(-/-) mice, protects against rosiglitazone-mediated inhibition of osteoblastogenesis in vitro. In addition, Rald potently inhibits in vitro adipogenesis and osteoclastogenesis in WT mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) respectively. Primary Aldh1a1(-/-) HSCs also demonstrate impaired osteoclastogenesis in vitro compared to WT controls. Collectively, these findings identify Rald and retinoid metabolism through Aldh1a1 as important novel modulators of PPARγ-RXR transactivation in the marrow niche.

Pathophysiological role of enhanced bone marrow adipogenesis in diabetic complications

Diabetes leads to complications in select organ systems primarily by disrupting the vasculature of the target organs. These complications include both micro- (cardiomyopathy, retinopathy, nephropathy, and neuropathy) and macro-(atherosclerosis) angiopathies. Bone marrow angiopathy is also evident in both experimental models of the disease as well as in human diabetes. In addition to vascular disruption, bone loss and increased marrow adiposity have become hallmarks of the diabetic bone phenotype. Emerging evidence now implicates enhanced marrow adipogenesis and changes to cellular makeup of the marrow in a novel mechanistic link between various secondary complications of diabetes. In this review, we explore the mechanisms of enhanced marrow adipogenesis in diabetes and the link between changes to marrow cellular composition, and disruption and depletion of reparative stem cells.