Effects of unsaturated free fatty acids on adhesion and on gene expression of extracellular matrix macromolecules in human osteoblast-like cell cultures

Arachidonic acid in aging: New roles for old players

BACKGROUND

Arachidonic acid (AA), one of the most ubiquitous polyunsaturated fatty acids (PUFAs), provides fluidity to mammalian cell membranes. It is derived from linoleic acid (LA) and can be transformed into various bioactive metabolites, including prostaglandins (PGs), thromboxanes (TXs), lipoxins (LXs), hydroxy-eicosatetraenoic acids (HETEs), leukotrienes (LTs), and epoxyeicosatrienoic acids (EETs), by different pathways. All these processes are involved in AA metabolism. Currently, in the context of an increasingly visible aging world population, several scholars have revealed the essential role of AA metabolism in osteoporosis, chronic obstructive pulmonary disease, and many other aging diseases.

AIM OF REVIEW

Although there are some reviews describing the role of AA in some specific diseases, there seems to be no or little information on the role of AA metabolism in aging tissues or organs. This review scrutinizes and highlights the role of AA metabolism in aging and provides a new idea for strategies for treating aging-related diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

As a member of lipid metabolism, AA metabolism regulates the important lipids that interfere with the aging in several ways. We present a comprehensivereviewofthe role ofAA metabolism in aging, with the aim of relieving the extreme suffering of families and the heavy economic burden on society caused by age-related diseases. We also collected and summarized data on anti-aging therapies associated with AA metabolism, with the expectation of identifying a novel and efficient way to protect against aging.

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius)

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

Human proximal tubular cells can form calcium phosphate deposits in osteogenic culture: role of cell death and osteoblast-like transdifferentiation

Nephrocalcinosis is a clinicopathological entity characterized by microscopic calcium crystals in the renal parenchyma, within the tubular lumen or in the interstitium. Crystal binding to tubular cells may be the cause underlying nephrocalcinosis and nephrolithiasis. Pathological circumstances, such as acute cortical necrosis, may induce healthy cells to acquire a crystal-binding phenotype. The present study aimed to investigate whether human renal proximal tubular cells (HK-2 cells) can form calcium phosphate deposits under osteogenic conditions, and whether apoptosis and/or osteogenic-like processes are involved in cell calcification. HK-2 cells were cultured in standard or osteogenic medium for 1, 5, and 15 days. Von Kossa staining and ESEM were used to analyze crystal deposition. Apoptosis was investigated, analyzing caspase activation by in-cell Western assay, membrane translocation of phosphotidylserine by annexin V-FITC/propidium iodide staining, and DNA fragmentation by TUNEL assay. qRT/PCR, immunolabeling and cytochemistry were performed to assess osteogenic activation (Runx2, Osteonectin, Osteopontin and ALP), and early genes of apoptosis (BAX, Bcl-2). HK-2 cell mineralization was successfully induced on adding osteogenic medium. Calcium phosphate deposition increased in a time-dependent manner, and calcified cell aggregates exhibited characteristic signs of apoptosis. At 15 days, calcifying HK-2 cells revealed osteogenic markers, such as Runx2, ALP, osteonectin and osteopontin. Monitoring the processes at 1, 5, and 15 days showed apoptosis starting already after 5 days of osteogenic induction, when the first small calcium phosphate crystals began to appear on areas where cell aggregates were in apoptotic conditions. The cell death process proved caspase-dependent. The importance of apoptosis was reinforced by the time-dependent increase in BAX expression, starting from day 1. These findings strongly support the hypothesis that apoptosis triggered HK-2 calcification even before any calcium phosphate crystal deposition or acquisition of an osteogenic phenotype.

Caspase-independent programmed cell death triggers Ca2PO4 deposition in an in vitro model of nephrocalcinosis

Nephrocalcinosis involves the deposition of microscopic crystals in the tubular lumen or interstitium. While the clinical, biochemical, and genetic aspects of the diseases causing nephrocalcinosis have been elucidated, little is known about the cellular events in this calcification process. We previously reported a phenomenon involving the spontaneous formation of Ca2PO4 nodules in primary papillary renal cells from a patient with medullary nephrocalcinosis harboring a rare glial cell-derived neurotrophic factor (GDNF) gene variant. We also demonstrated that cultivating GDNF-silenced human kidney-2 (HK-2) cells in osteogenic conditions for 15 days triggered Ca2PO4 deposits. Given the reportedly close relationship between cell death and pathological calcification, aim of the present study was to investigate whether apoptosis is involved in the calcification of GDNF-silenced HK-2 cells under osteogenic conditions. Silenced and control cells were cultured in standard and osteogenic medium for 1, 5, and 15 days, and any Ca2PO4 deposition was identified by means of von Kossa staining and environmental SEM (ESEM) analyses. Based on the results of annexin V and propidium iodide (PI) analysis, and terminal deoxynucleotidyl transferase dUTP-biotin nick end labeling (TUNEL) assay, the silenced cells in the osteogenic medium showed a significant increase in the percentage of cells in the late phase of apoptosis and an increased Ca2PO4 deposition at 15 days. The results of quantitative real-time PCR (qRT-PCR) of BAX and BCL2, and in-cell Western analysis of caspases indicated that the cell death process was independent of caspase-3, -6, -7, and -9 activation, however. Using this model, we provide evidence of caspase-independent cell death triggering the calcification process in GDNF-silenced HK-2 cells.

Age-Related Loss in Bone Mineral Density of Rats Fed Lifelong on a Fish Oil-Based Diet Is Avoided by Coenzyme Q10 Addition

During aging, bone mass declines increasing osteoporosis and fracture risks. Oxidative stress has been related to this bone loss, making dietary compounds with antioxidant properties a promising weapon. Male Wistar rats were maintained for 6 or 24 months on diets with fish oil as unique fat source, supplemented or not with coenzyme Q10 (CoQ10), to evaluate the potential of adding this molecule to the n-3 polyunsaturated fatty acid (n-3 PUFA)-based diet for bone mineral density (BMD) preservation. BMD was evaluated in the femur. Serum osteocalcin, osteopontin, receptor activator of nuclear factor-κB ligand, ostroprotegerin, parathyroid hormone, urinary F₂-isoprostanes, and lymphocytes DNA strand breaks were also measured. BMD was lower in aged rats fed a diet without CoQ10 respect than their younger counterparts, whereas older animals receiving CoQ10 showed the highest BMD. F₂-isoprostanes and DNA strand breaks showed that oxidative stress was higher during aging. Supplementation with CoQ10 prevented oxidative damage to lipid and DNA, in young and old animals, respectively. Reduced oxidative stress associated to CoQ10 supplementation of this n-3 PUFA-rich diet might explain the higher BMD found in aged rats in this group of animals.

PUFAs, Bone Mineral Density, and Fragility Fracture: Findings from Human Studies

Osteoporosis is a global health problem that leads to an increased incidence of fragility fracture. Recent dietary patterns of Western populations include higher than recommended intakes of n-6 (ω-6) polyunsaturated fatty acids (PUFAs) relative to n-3 (ω-3) PUFAs that may result in a chronic state of sterile whole body inflammation. Findings from human bone cell culture experiments have revealed both benefits and detriments to bone-related outcomes depending on the quantity and source of PUFAs. Findings from observational and randomized controlled trials suggest that higher fatty fish intake is strongly linked with reduced risk of fragility fracture. Moreover, human studies largely support a greater intake of total PUFAs, total n-6 (ω-6) fatty acid, and total n-3 (ω-3) fatty acid for higher bone mineral density and reduced risk of fragility fracture. Less consistent evidence has been observed when investigating the role of long chain n-3 (ω-3) PUFAs or the ratio of n-6 (ω-6) PUFAs to n-3 (ω-3) PUFAs. Aspects to consider when interpreting the current literature involve participant characteristics, study duration, diet assessment tools, and the primary outcome measure.

Saturated and monounsaturated fatty acid status is associated with bone strength estimated by calcaneal ultrasonography in Inuit women from Nunavik (Canada): a cross-sectional study

OBJECTIVE

The aim of this study is to examine the relationship between the status in selected saturated (SFAs) and monounsaturated (MUFAs) fatty acids and the Stiffness Index (SI) in Inuit women from Nunavik (Northern Quebec, Canada).

DESIGN

Cross-sectional descriptive study.

SETTING

Inuit population from 14 communities who participated to Qanuippitaa? How are we? Nunavik Inuit Health Survey in 2004.

PARTICIPANTS

187 Inuit women aged 35-72 years.

MEASUREMENTS

SI was determined by ultrasonography (Achilles InSight device) at the right calcaneus of participants. SFAs and MUFAs contents of erythrocyte membrane phospholipids were measured after transmethylation by gas chromatography coupled with a flame ionization detector. Several factors known to be associated with bone strength were concomitantly recorded. Multiple linear regression was used to investigate relations between selected SFAs, MUFAs and SI, taking into consideration several potential confounders and covariates.

RESULTS

Total SFAs, in particular behenic acid, and cis-vaccenic acid among MUFAs were negatively associated with SI (β = -0.028, SE = 0.011, p = 0.0084; β = -0.060, SE = 0.023, p = 0.0093 and β = -0.087, SE = 0.019, p <0.0001, respectively), whereas total cis-MUFAs and specifically oleic acid were positively associated with SI (β = 0.036, SE = 0.011, p = 0.0008; β = 0.037, SE = 0.011, p = 0.0014, respectively) after adjustment for several covariates.

CONCLUSION

Saturated and monounsaturated fatty acid status is associated with bone strength estimated by calcaneal SI values in Inuit women from Nunavik.

Long-chain polyunsaturated fatty acids may mutually benefit both obesity and osteoporosis

The overconsumption of n-6 polyunsaturated fatty acids (PUFA), resulting in a high ratio of n-6 to n-3 PUFA, may contribute to the increased pathogenesis of obesity and osteoporosis by promoting low-grade chronic inflammation (LGCI). As evidence suggests, both obesity and osteoporosis are linked on a cellular and systemic basis. This review will analyze if a relationship exists between LGCI, fat, bone, and n-3 PUFA. During the life cycle, inflammation increases, fat mass accumulates, and bone mass declines, thus suggesting that a connection exists. This review will begin by examining how the current American diet and dietary guidelines may fall short of providing an anti-inflammatory dose of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It will then define LGCI and outline the evidence for a relationship between fat and bone. Inflammation as it pertains to obesity and osteoporosis and how EPA and DHA can alleviate the associated inflammation will be discussed, followed by some preliminary evidence to show how mesenchymal stem cell (MSC) lineage commitment may be altered by inflammation to favor adipogenesis. Our hypothesis is that n-3 PUFA positively influence obesity and osteoporosis by reducing LGCI, ultimately leading to a beneficial shift in MSC lineage commitment. This hypothesis essentially relates the need for more focused research in several areas such as determining age and lifestyle factors that promote the shift in MSC commitment and if current intakes of EPA and DHA are optimal for fat and bone.

S100A16 inhibits osteogenesis but stimulates adipogenesis

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have the capacity to differentiate into osteoblasts and adipocytes. Bone marrow adipogenesis exerts an inhibitory effect on osteogenesis, which leads to osteoporosis. S100A16, a novel member of the S100 family, is ubiquitously expressed, and markedly enhances adipogenesis. The aim of this study was to demonstrate, in the mouse BM-MSC model, whether S100A16 significantly stimulates adipogenic, rather than osteogenic differentiation. The overexpression of S100A16 led to a significant increase in Oil Red O staining (a marker of adipocyte differentiation) but a decrease in Alizarin Red S staining (a marker of osteoblast differentiation). In contrast, reducing the expression of S100A16 resulted in minimal Oil Red O staining but increased Alizarin Red S staining. During differentiation into osteoblasts, RUNX2 expression increased fourfold in the S100A16(KO+/-) BM-MSCs, but only increased by approximately 1.5-fold in the S100A16(TG+/+) BM-MSCs. And BMP2 occurred in the same changes. Upon induction of BM-MSC differentiation into adipocytes, peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer binding protein-α expression were significantly higher in the cells overexpressing S100A16 protein but lower in the cells with reduced expression of S100A16 protein, compared with the control cells, which were BM-MSCs derived from C57/BL6. S100A16 increased PPARγ promoter luciferase activity and decreased RUNX2 promoter luciferase activity. ERK1/2 phosphorylation was stimulated during osteogenesis, whereas p-JNK phosphorylation was increased by stimulation of adipogenesis. Our results suggest that S100A16 inhibits osteogenesis but stimulates adipogenesis by increasing the transcription of PPARγ and decreasing the transcription of RUNX2. The ERK1/2 pathway is involved in the regulation of osteogenesis whereas the JNK pathway is involved in adipogenesis.

Aging and bone loss: new insights for the clinician

It is well known that the underlying mechanisms of osteoporosis in older adults are different than those associated with estrogen deprivation. Age-related bone loss involves a gradual and progressive decline, which is also seen in men. Markedly increased bone resorption leads to the initial fall in bone mineral density. With increasing age, there is also a significant reduction in bone formation. This is mostly due to a shift from osteoblastogenesis to predominant adipogenesis in the bone marrow, which also has a lipotoxic effect that affects matrix formation and mineralization. We review new evidence on the pathophysiology of age-related bone loss with emphasis upon the mechanism of action of current osteoporosis treatments. New potential treatments are also considered, including therapeutic approaches to osteoporosis in the elderly that focus on the pathophysiology and potential reversal of adipogenic shift in bone.

Absence of glutamine supplementation prevents differentiation of murine calvarial osteoblasts to a mineralizing phenotype

Osteoblasts in vitro differentiate from a proliferating to a mineralizing phenotype upon transfer to a medium rich in beta-glycerophosphate and ascorbic acid. The nutritional requirements of the cells at different stages of this differentiation process are not known. In other cell types, nutritional supplementation during surgery can improve the outcome in terms of speed of patient recovery and prognosis. There is therefore the potential for supplementation at the site of fracture repair or bone grafting with critical osteoblast nutritional factors to potentially accelerate healing. In this study we investigate which common cell nutrients are required for the proliferating and mineralizing stages of osteoblast differentiation. Medium containing 5.5 mM glucose was sufficient to achieve maximal proliferation of primary calvarial osteoblasts and human osteoblast cell lines, with some added benefit of additional glutamine supplementation. However, when cells were stimulated to mineralize, glucose was insufficient to support their energetic requirements. Only when cells were supplemented with glucose together with glutamine were high levels of osteocalcin expression observed together with mineralized nodules in culture, suggesting that this would be a useful combination to assess in cultures of primary human osteoblasts to determine whether it may have beneficial effects during fracture surgery, bone grafting, and fixation of uncemented arthroplasty implants.

[Senile osteoporosis: an update]

Knowledge of the mechanisms underlying the development of osteoporosis in the elderly has advanced greatly in the past few years. After an initial sudden loss of bone mineral mass in the peri-menopausal period there follows a more progressive and gradual loss that has also been seen in men. This initial drop in bone mass is due to a significant increase in bone resorption. There is also a significant reduction in bone formation with age that is mainly due to osteoblastogenesis in the bone marrow passing to a second plane, transferring its main role to adipogenesis. In this article, the latest evidence on the pathophysiology of senile osteoporosis is reviewed, highlighting the mechanisms of action of available treatments. Potential future treatments are also considered, which include new therapeutic approaches based on the pathophysiology of osteoporosis in the elderly, mainly on the potential reversibility of the adipogenesis.

Evaluation of the lipid-rich layer of reamer aspirate

The fatty layer of aspirate obtained by reaming the femoral shaft using a reamer/irrigator/aspirator (RIA) device was characterized for fatty acid content and the presence of adult stem cells. Gas chromatography analysis was performed on samples taken from multiple patients to determine and compare the fatty acid contents of aspirate lipid samples. All four patients had the same four fatty acids present in the highest percentages: oleic, palmitic, linoleic and stearic. After successful isolation from bulk material, cells isolated from this lipid-rich layer were studied to determine their osteogenic and growth potential on a clinically available ceramic bone graft substitute. The results of metabolic activity and intracellular protein assays indicated that the ceramics supported growth of the cells isolated from the aspirate fat layer, although levels of alkaline phosphatase (ALP) expression were low for cells grown on the ceramics. Cells will not transition along the osteogenic pathway when they are actively dividing, and active growth may have contributed to the lack of ALP expression in this study. Isolated cells grown on tissue culture plastic expressed significant levels of the bone marker ALP. The results of this study suggest that cells isolated from the fat layer of RIA aspirate proliferate on ceramic bone void filler and have the potential to differentiate along an osteogenic pathway. Previously considered waste, the lipid-rich fat layer of aspirate may be a source of mesenchymal stem cells that, either alone or in conjunction with currently available synthetic bone graft material, could be used to stimulate new bone growth.

A study of bone marrow and subcutaneous fatty acid composition in subjects of varying bone mineral density

Osteoporosis is associated with an increase in marrow fat. Fats, particularly polyunsaturated fats, either in co-cultures or diet, have been shown to significantly influence bone remodeling. Whether the increase in marrow fat seen in osteoporosis is also associated with a change in fatty acid composition is not known. This study was undertaken to investigate the fatty acid composition in subjects of varying bone mineral density (BMD). Samples of marrow fat and subcutaneous fat from 126 subjects (98 females, 34 males, mean age 69.7+/-10.5 years) undergoing orthopedic surgery were analyzed for fatty acid composition by gas chromatography. These results were correlated with BMD assessed by DXA. A total of 22 fatty acids were identified in marrow and subcutaneous fat. Significant differences in fatty acid composition existed between marrow and subcutaneous fat as well as between marrow fat samples obtained from the proximal femur and proximal tibia. Other than cis-7-hexadecenoic acid [C16:1 (n=9)] and docosanoic acid [C22:0], no difference in marrow fatty acid composition was evident between subject groups of varying BMD (normal, low bone mass, and osteoporosis). In conclusion, there exists a wide range of individual fatty acids in marrow fat. Marrow fatty acid composition differs from that of subcutaneous fat and varies between predominantly erythropoetic and fatty marrow sites. Other than cis-7-hexadecenoic acid [C16:1 (n=9)] and docosanoic acid [C22:0], no difference in marrow fatty acid composition was evident between subjects of varying BMD.

Understanding the mechanisms of senile osteoporosis: new facts for a major geriatric syndrome

Knowledge of the underlying mechanisms of osteoporosis in older adults has significantly advanced in recent years. There is an acute loss of bone mineral density in the peri-menopausal period, followed by a more gradual and progressive decline, which is also seen in men. Markedly increased bone resorption leads to the initial fall in bone mineral density. With increasing age, there is also a significant reduction in bone formation. This is mostly due to a shift from osteoblastogenesis to predominant adipogenesis in the bone marrow. This study reviews new evidence on the pathophysiology of senile osteoporosis, with emphasis upon the mechanism of action of current osteoporosis treatments. New potential treatments are also considered, including therapeutic approaches to osteoporosis in elderly people that focus on the pathophysiology and potential reversal of the adipogenic shift in bone.