Methionine down-regulates TLR4/MyD88/NF-κB signalling in osteoclast precursors to reduce bone loss during osteoporosis

Ferulic acid may target MyD88-mediated pro-inflammatory signaling - Implications for the health protection afforded by whole grains, anthocyanins, and coffee

Higher dietary intakes of anthocyanins have been linked epidemiologically to decreased risk for metabolic syndrome, type 2 diabetes and cardiovascular events; clinical trials and rodent studies evaluating ingestion of anthocyanin-rich extracts confirm favorable effects of these agents on endothelial function and metabolic syndrome. However, these benefits of anthocyanins are lost in rats whose gut microbiome has been eliminated with antibiotic treatment - pointing to bacterial metabolites of anthocyanins as the likely protective agents. A human pharmacokinetic assessment of orally administered cyanidin-3-O-glucoside, a prominent anthocyanin, has revealed that, whereas this compound is minimally absorbed, ferulic acid (FA) is one of its primary metabolites that appears in plasma. FA is a strong antioxidant and phase 2 inducer that has exerted marked anti-inflammatory effects in a number of rodent and cell culture studies; in particular, FA is highly protective in rodent models of diet-induced weight gain and metabolic syndrome. FA, a precursor for lignan synthesis, is widely distributed in plant-based whole foods, mostly in conjugated form; whole grains are a notable source. Coffee ingestion boosts plasma FA owing to gastrointestinal metabolism of chlorogenic acid. Hence, it is reasonable to suspect that FA mediates some of the broad health benefits that have been associated epidemiologically with frequent consumption of whole grains, anthocyanins, coffee, and unrefined plant-based foods. The molecular basis of the anti-inflammatory effects of FA may have been clarified by a recent study demonstrating that FA can target the adaptor protein MyD88; this plays an essential role in pro-inflammatory signaling by most toll-like receptors and interleukin-1β. If feasible oral intakes of FA can indeed down-regulate MyD88-dependent signaling, favorable effects of FA on neurodegeneration, hypothalamic inflammation, weight gain, adipocyte and beta cell function, adiponectin secretion, vascular health, and cartilage and bone integrity can be predicted. Since FA is well tolerated, safe, and natural, it may have great potential as a protective nutraceutical, and clinical trials evaluating its effects are needed.

Role of Toll-Like Receptor 4 on Osteoblast Metabolism and Function

Inflammation is a process whose main function is to fight against invading pathogens or foreign agents. Nonetheless, it is widely accepted that inflammation takes part in multiple processes in a physiological or pathophysiological context. Among these processes the inflammation has been closely related to bone metabolism. It is well-known that in systemic inflammatory diseases such as rheumatoid arthritis the inflammatory environment contributes to the reduction of the bone mineral density. This has been further evidenced in different animals models of osteoporosis where the deletion of key inflammatory molecules dramatically reduced the bone loss. On the contrary, it is also well-known that certain degree of inflammation is required to allow bone fractures healing. In fact, excessive use of anti-inflammatory drugs inhibits bone fracture consolidation. The innate immune responses (IIRs) contribute to the development and maintenance of the inflammation. These responses have been observed in cells of the musculoskeletal system. Chondrocytes and osteoblasts are equipped with the molecular repertoire necessary to setting up these IIR, including the expression of several toll-like receptors. Specifically, toll-like receptor 4 (TLR4) activation in mesenchymal stem cells, osteoblasts, and osteocytes has been involved in catabolic and anabolic process. Accordingly, in this review we have summarized the current knowledge about the physiology of TLR4, including its signaling, and its endogenous agonists. In addition we have focused on its role on osteoblast metabolism and function.

TLR4 Inactivation in Myeloid Cells Accelerates Bone Healing of a Calvarial Defect Model in Mice

Supplemental Digital Content is available in the text.

Background:

Toll-like receptor 4 (TLR4) has been implicated in inflammation-induced bone destruction in various chronic bone diseases; however, its direct influence on bone healing is not well understood. The authors’ previous study showed accelerated bone healing with higher osteoclastogenesis gene expression in toll-like receptor 4 knockout mice (TLR4^-/-). This study aimed to further elucidate the underlying cellular mechanisms during fracture healing by generating a myeloid cell-specific toll-like receptor 4 knockout model (Lyz-TLR4^-/- mice).

Methods:

Calvarial defects, 1.8 mm in diameter, were created in wild-type, TLR4^-/-, and Lyz-TLR4^-/- mice. Bone healing was investigated using micro–computed tomography and histologic, histomorphometric, and immunohistochemistry analyses. Primary bone marrow–derived cells were also isolated from wild-type, TLR4^-/-, and Lyz-TLR4^-/- mice to measure their osteoclast differentiation and resorption properties.

Results:

A similar faster bone healing response, with active intramembranous bone formation, intense osteopontin staining, and more osteoblast infiltration, was observed in TLR4^-/- and Lyz-TLR4^-/- mice. Tartrate-resistant acid phosphatase staining showed more osteoclast infiltration in Lyz-TLR4^-/- mice than in wild-type mice at day 7. Primary bone marrow–derived cells isolated from TLR4^-/- and Lyz-TLR4^-/- mice presented enhanced osteoclastogenesis and resorption activity compared with those from wild-type mice. Comparable M0, M1, and M2 macrophage infiltration was found among all groups at days 1, 4, and 7.

Conclusions:

This study revealed that inactivation of toll-like receptor 4 in myeloid cells enhanced osteoclastogenesis and accelerated healing response during skull repair. Together with the role of toll-like receptor 4 in inflammation-mediated bone destruction, it suggests that toll-like receptor 4 might regulate inflammation-induced osteoclastogenesis under different clinical settings.

Low bone mineral density is a common finding in patients with homocystinuria

Homocystinuria (HCU) due to deficiency of cystathionine beta-synthetase is associated with increased plasma levels of homocysteine and methionine and is characterized by developmental delay, intellectual impairment, ocular defects, thromboembolism and skeletal abnormalities. HCU has been associated with increased risk for osteoporosis in some studies, but the natural history of HCU-related bone disease is poorly understood. The objective of this study was to characterize bone mineral density (BMD) measured by dual energy X-ray absorptiometry (DXA) in a multi-center, retrospective cohort of children and adults with HCU. We identified 19 subjects (9 males) aged 3.5 to 49.2 years who had DXA scans performed as a part of routine clinical care from 2002-2010. The mean lumbar spine (LS) BMD Z-score at the time of first DXA scan in this cohort was -1.2 (± SD of 1.3); 38% of participants had low BMD for age (as defined by a Z-score ≤-2). Homocysteine and methionine were positively associated with LS BMD Z-score in multiple linear regression models. Our findings suggest that low BMD is common in both children and adults with HCU and that routine assessment of bone health in this patient population is warranted. Future studies are needed to clarify the relationship between HCU and BMD.

Protective effect of porcine placenta in a menopausal ovariectomized mouse

Menopause is a significant physiological phase that occurs as women's ovaries stop producing ovum and the production of estrogen declines. Human placenta and some amino acids are known to improve menopausal symptoms. In this study, we investigated that porcine placenta extract (PPE) and arginine (Arg), a main amino acid of PPE, would have estrogenic activities in ovariectomized (OVX) mice as a menopause mouse model, human breast cancer cell line (MCF-7) cells, and human osteoblast cell line (MG-63) cells. PPE or Arg significantly inhibited the body weight and increased the vagina weight compared to the OVX mice. PPE or Arg ameliorated the vaginal atrophy in the OVX mice. The levels of 17β-estradiol and the activities of alkaline phosphatase (ALP) were significantly increased by PPE or Arg in the serum of OVX mice. Trabecular bone parameters such as bone mineral density and porosity were also improved by PPE or Arg in the OVX mice. In the MCF-7 and MG-63 cells, PPE or Arg significantly increased the cell proliferation, estrogen receptor β mRNA expression, and estrogen-response elements luciferase activity. Finally, PPE or Arg increased the activations of ALP and extracellular signal-regulated kinase 1/2 in the MG-63 cells. These results indicate that PPE or Arg would have estrogenic and osteoblastic activity. Therefore, PPE or Arg may be useful as new pharmacological tools for treating menopausal symptoms including osteoporosis. Free Korean abstract: A Korean translation of this abstract is freely available at http://www.reproduction-online.org/content/150/3/173/suppl/DC1.

A metabolomics study of the inhibitory effect of 17-beta-estradiol on osteoclast proliferation and differentiation

Estradiol is a major drug used clinically to alleviate osteoporosis, partly through inhibition of the activity of osteoclasts, which play a crucial role in bone resorption. So far, little is known about the effects of estradiol on osteoclast metabolism. In this study, ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC/MS)-based metabolomics strategy was used to investigate the metabolite response to 17β-estradiol in mouse osteoclast RAW264.7, a commonly used cell model for studying osteoporosis. Our results showed that the application of estradiol altered the levels of 27 intracellular metabolites, including lysophosphatidylcholines (LysoPCs), other lipids and amino acid derivants. The changes of all the 27 metabolites were observed in the study of estradiol induced osteoclast proliferation inhibition (1 μM estradiol applied), while the changes of only 18 metabolites were observed in the study of differentiation inhibition (0.1 μM estradiol applied). Further pathway impact analysis determined glycerophospholipid metabolism as the main potential target pathway of estradiol, which was further confirmed by LCAT (phosphatidylcholine-sterol acyltransferase) activity changes and lipid peroxidative product (MDA, methane dicarboxylic aldehyde) changes caused by estradiol. Additionally, we found that estradiol significantly decreased intracellular oxidative stress during cell proliferation but not during cell differentiation. Our study suggested that estradiol generated a highly condition-dependent influence on osteoclast metabolism.