Current Drug Targets - Volume 14, Issue 13, 2013

Fracture healing is a process of recovering injured bone tissue forms and functions. Osteoporosis can delay the healing process, which contributes to personal suffering and loss of activities. Osteoporosis patients tend to lose bone mass at the metaphyseal region which require treatment to increase bone mass. Postmenopausal osteoporosis is the most common osteoporosis that occurs in women which subsequently resulted in fractures even under slight trauma. Estrogen Replacement Therapy (ERT), the recommended therapy for postmenopausal osteoporosis, is associated with higher risk of breast cancer, ovarian cancer and cardiovascular diseases. As osteoporotic fractures are becoming a public health issue, alternative treatment is now being thoroughly explored. The potential agent is statins, the HMG-CoA reductase inhibitor which is widely used for hypercholesterolemia treatment. Statins have been found to increase bone mass by stimulation of Bone morphogenetic protein-2 (BMP-2) expression and Vascular Endothelial Growth Factor (VEGF) production. However, these bone forming effects were achieved at very high systemic doses. Therefore, studies on locally applied statins are required to further explore the ability of statins to stimulate bone formation at acceptable doses for better fracture healing. This review highlights the animal and clinical studies on fracture healing promotions by statins and the mechanisms involved.

Osteoporosis is posing a tremendous healthcare problem globally. Much effort has been invested in finding novel antiosteoporotic agents to stop the progression of this disease. Tocotrienol, one of the isoforms of vitamin E, is poised as a potential antiosteoporotic agent. Previous studies showed that tocotrienol as a single isomer or as a mixture demonstrated both anabolic and antiresorptive effects in various rodent models of osteoporosis. In vitro experiments further demonstrated that tocotrienol could up-regulate genes related to osteoblastogenesis and modify receptor activator of nuclear factor kappa B signaling against osteoclastogenesis. Additionally, tocotrienol was also shown to be a strong 3- hydroxy-3-methyl-glutaryl-CoA reductase down-regulator with a mechanism different from that of statins. Inhibition of the mevalonate pathway affects both osteoblast and osteoclast formation in favor of the former. Tocopherol, a more commonly used isoform of vitamin E does not possess similar effects. Tocotrienol is also a potent antioxidant. It can scavenge free radicals and prevent oxidative damage on osteoblast thus promoting its survival. It may also up-regulate the antioxidant defense network in osteoclast and indirectly act against free radical signaling essential in osteoclastogenesis. The effects of tocotrienol on Wnt/β-catenin signaling essential in osteoblastogenesis have not been determined. More mechanistic studies need to be conducted to illustrate the antiosteoporotic effects of tocotrienol. Clinical trials are also required to confirm its effects in humans. In conclusion, tocotrienol demonstrates great potential as an antiosteoporotic agent and much research effort should be invested to develop it as an agent to curb osteoporosis.

Bone quality assessment is important in assessments of potential agents for the prevention and treatment of osteoporosis. Bone density, microarchitecture and strength are important determinants in osteoporotic study which are widely studied using Dual-Energy X-ray Absorptiometry (DXA), histomorphometry and radiological imaging techniques. In recent years, high resolution micro-CT has become feasible for in vitro or in vivo evaluation of bone architecture. Three-dimensional images of micro-CT reflected high correlations with the conventional histomorphometry and DXA. In comparison to other imaging techniques, micro-CT is the most effective tool in detecting early bone changes for fracture prediction and assessments of potential anti-osteoporotic agents. It is crucial to define an ideal setting with safe radiation doses and appropriate methods for image reconstruction and segmentation to obtain high resolution images. Micro-CT evaluation provides a better insight of bone structure as well as non-metric parameters such as connectivity density, structural model index (SMI) and degree of anisotropy (DA). This non- invasive imaging technique is also equipped with finite element analysis for evaluation of bone biomechanical strength. Micro-CT allows a compressive understanding of the relationships between bone density, microarchitecture and strength which is fundamental to development of pharmacological interventions.

Osteoporosis is a common complication observed in rheumatoid arthritis (RA). Accelerated bone loss is always a matter of concern. The pathogenesis of RA may be important for better understanding of the bone loss. The mechanism involved in the bone loss in RA is not well understood although cytokines such as interleukin 1 and tumour necrosis factor α (TNF α) have been strongly implicated. TNF α antagonists have revolutionised the treatment of RA in the recent years. Beyond the control of disease activity in RA, accumulating evidence suggests that this form of therapy may provide beneficial effects to the bone metabolism and remodeling. An extensive search of the literature was performed in the Medline, Scopus and EBSCO databases to evaluate the documented research on the effects of TNF α antagonists in RA on bone mineral density and bone turnover markers. The available data based on our systematic review, depict a significant association between TNF α antagonists treatment and suppression of bone resorption.

Anti-osteoporotic drugs are available for treatment of osteoporosis and for preventing osteoporosis complications especially fractures. Most of the current anti-osteoporotic drugs are administered orally or parenterally to target the osteoporosis-affected bones. However, bone is a peripheral organ with limited blood supply. Therefore, the drugs delivered are exposed to various physicochemical and biological factors which affect the bioavailability of the drugs. In preclinical research, the dose of a potential anti-osteoporotic agent used in animal model may be too high for human application when administered via the conventional route of administration. The current anti-osteoporotic drugs need to be administered at higher doses to account for pharmacological interactions. However, this will expose the patients to adverse effects such as the cancer risks of postmenopausal women who took estrogen replacement therapy. There is also problem with patient compliance as anti-osteoporotic drugs may have to be taken for prolonged duration. The current deliveries of drugs need to be improved to overcome these problems. This review discussed several potential drug delivery systems which are able to contain the anti-osteoporosis drugs and release them slowly to the targeted bone. Among them are various carriers, polymers and microsponges, which may not only increase drug efficacy but also reduce adverse effects. The delivery systems allow the drugs to be administered locally at the targeted bone for longer duration, therefore reducing drug frequency and improving patient’s compliance. It is hoped that these delivery systems may be applicable for the treatment of osteoporosis in the future to keep tab of the rising osteoporotic fracture incidence.

This review explores the effects of pomegranate on the pathogenesis of bone loss in osteoporosis, osteoarthritis and rheumatoid arthritis. A systematic review of the literature was conducted to identify the relevant studies on pomegranate and osteoporosis/osteoarthritis/rheumatoid arthritis. A comprehensive search was conducted in Medline and CINAHL for relevant studies published between the years 1946 to 2012. The main inclusion criteria were research articles published in English, studies had to report the association or effect of pomegranate and these bone and joint diseases: osteoporosis, osteoarthritis or rheumatoid arthritis. The literature search identified 35 potentially relevant articles, whereby 8 met the inclusion criteria. Two animal studies, two combinations of animal and in vitro studies, three in vitro studies and one human study were included in this review. All the studies reported positive effects of pomegranate extract or juice on osteoporosis, osteoarthritis and rheumatoid arthritis. This evidence-based review highlighted the potential of pomegranate extract being used for treating bone loss in osteoporosis, osteoarthritis and rheumatoid arthritis. Further studies are required to identify the active ingredients and molecular mechanisms before controlled human observational studies are conducted to provide stronger evidence.

Skeletal tissue undergoes continuous remodeling which makes it unique among other body tissues. Osteoporosis is a common bone metabolic disorder affecting both men and women. Osteoporosis and its complications mainly osteoporotic fractures, have a high impact on health and economy. Current approved medications are associated with numerous side effects, which limit their use. Identification of a new and safe therapy is mandatory. Statins, also known as HMGCoA reductase inhibitors, are frequently used for the treatment of hypercholesterolemia and for the prevention of morbidity and mortality associated with cardiovascular disease. Statins improved bone health status in intact and ovariectomised rodents following high clinically intolerable oral doses. However, this beneficial effect of statins could not be significantly demonstrated in humans. The reason behind this discrepancy might be due to the safety and bioavailability of the currently used oral statins. Vitamin E, especially the tocotrienols at the dose 60 mg/kg/day provided significant antiosteoporotic effects in different animal models of osteoporosis. The use of the aforementioned dose of tocotrienols was shown to be safe in both humans and animals. Enhancement of bone formation and reduction of bone resorption were achieved more effectively by a combination of tocotrienols and statins than by either treatment when supplemented separately at clinically tolerable doses. Therefore, the adverse effects associated with high statin doses might be avoided with the coadministration of tocotrienols. Moreover, the combination therapy strategy might be useful for patients who are at high risk of osteoporosis, cardiovascular events and hypercholesterolaemia.

Osteoporosis is a pathologic process characterized by low bone mass with skeletal fragility and an increased risk of fracture. It occurs due to an imbalance between bone resorption and formation. Although current antiresorptive therapy halts bone loss, it does not cure the condition as it also inhibits bone formation. Recent preclinical and clinical trials suggest that the inhibition of resorption by cathepsin K inhibitors increases bone formation. Cathepsin K is a papainlike cysteine protease with high potent collagenase activity and predominantly expressed in osteoclasts. While allowing demineralization, cathepsin K inhibitors suppress the degradation of type I collagen (the major organic matrix of bone) and thus enhancing bone formation. Many of these inhibitors have passed preclinical studies and are presently in clinical trials at different stages of advancement. This review explores the promising role of cathepsin K as a novel antiresorptive for the treatment of osteoporosis.

Osteoporosis is the most common bone disease in humans; it represents a major public health problem. This chronic disease is characterized by increase in bone fracture due to: reduced bone mass, deterioration of micro architectural and decreased bone strength, bone fragility; and bone mineral density 2.5 or more standard deviations below the normal mean. Secondary osteoporosis is a common cause of osteoporosis, and there are many underlying risk factors for osteoporosis. Chronic alcohol abuse is one of the modifiable risk factors in osteoporosis. There is evidence of correlation between chronic alcohol abuse and low bone mass. Alcohol is directly toxic to the bone; with increased incidence of fractures and complications. Although there is a paucity of studies regarding alcohol induced osteoporosis therapy, it can be classified into antiresorptive therapy and anabolic therapy. Bisphosphonates have been demonstrated to be clinically relevant to prevent bone damage associated with alcohol use while parathyroid hormone increased bone mineralization as well as bone formation in alcohol treated rats. Vitamin D supplementation could prevent bone toxicity in chronic drinkers. This review discussed the pathogenesis of alcohol-induced osteoporosis and the agents available for its treatment. Other potential therapies are also discussed.