Lipids as modulators of bone remodelling

Nutrition and Kidney Stone Disease

The prevalence of kidney stone disease is increasing worldwide. The recurrence rate of urinary stones is estimated to be up to 50%. Nephrolithiasis is associated with increased risk of chronic and end stage kidney disease. Diet composition is considered to play a crucial role in urinary stone formation. There is strong evidence that an inadequate fluid intake is the major dietary risk factor for urolithiasis. While the benefit of high fluid intake has been confirmed, the effect of different beverages, such as tap water, mineral water, fruit juices, soft drinks, tea and coffee, are debated. Other nutritional factors, including dietary protein, carbohydrates, oxalate, calcium and sodium chloride can also modulate the urinary risk profile and contribute to the risk of kidney stone formation. The assessment of nutritional risk factors is an essential component in the specific dietary therapy of kidney stone patients. An appropriate dietary intervention can contribute to the effective prevention of recurrent stones and reduce the burden of invasive surgical procedures for the treatment of urinary stone disease. This narrative review has intended to provide a comprehensive and updated overview on the role of nutrition and diet in kidney stone disease.

Understanding the local actions of lipids in bone physiology

The adult skeleton is a metabolically active organ system that undergoes continuous remodeling to remove old and/or stressed bone (resorption) and replace it with new bone (formation) in order to maintain a constant bone mass and preserve bone strength from micro-damage accumulation. In that remodeling process, cellular balances--adipocytogenesis/osteoblastogenesis and osteoblastogenesis/osteoclastogenesis--are critical and tightly controlled by many factors, including lipids as discussed in the present review. Interest in the bone lipid area has increased as a result of in vivo evidences indicating a reciprocal relationship between bone mass and marrow adiposity. Lipids in bones are usually assumed to be present only in the bone marrow. However, the mineralized bone tissue itself also contains small amounts of lipids which might play an important role in bone physiology. Fatty acids, cholesterol, phospholipids and several endogenous metabolites (i.e., prostaglandins, oxysterols) have been purported to act on bone cell survival and functions, the bone mineralization process, and critical signaling pathways. Thus, they can be regarded as regulatory molecules important in bone health. Recently, several specific lipids derived from membrane phospholipids (i.e., sphingosine-1-phosphate, lysophosphatidic acid and different fatty acid amides) have emerged as important mediators in bone physiology and the number of such molecules will probably increase in the near future. The present paper reviews the current knowledge about: (1°) bone lipid composition in both bone marrow and mineralized tissue compartments, and (2°) local actions of lipids on bone physiology in relation to their metabolism. Understanding the roles of lipids in bone is essential to knowing how an imbalance in their signaling pathways might contribute to bone pathologies, such as osteoporosis.

Harnessing the power of yeast to elucidate the role of sphingolipids in metabolic and signaling processes pertinent to psychiatric disorders

The development of therapies for neuropsychiatric disorders is hampered by the lack of understanding of the mechanisms underlying their pathologies. While aberrant sphingolipid metabolism is associated with psychiatric illness, the role of sphingolipids in these disorders is not understood. The genetically tractable yeast model can be exploited in order to elucidate the cellular consequences of sphingolipid perturbation. Hypotheses generated from studies in yeast and tested in mammalian cells may contribute to our understanding of the role of sphingolipids in psychiatric disorders and to the development of new treatments. Here, we compare sphingolipid metabolism in yeast and mammalian cells, discuss studies implicating sphingolipids in psychiatric disorders and propose approaches that utilize yeast in order to elucidate sphingolipid function and identify drugs that target sphingolipid synthesis.

Perinatal maternal dietary supplementation of ω3-fatty acids transiently affects bone marrow microenvironment, osteoblast and osteoclast formation, and bone mass in male offspring

It is increasingly evident that micronutrient environment experienced before birth and in infancy is important for achieving optimal bone mass by adolescence and maintaining bone health. This study determined whether maternal supplementation with ω3-polyunsaturated fatty acids (n3FA) improved offspring bone growth and adult bone mass. Female rats were fed a diet containing 0.1% (control, n = 10) or 1% (n3FA, n = 11) docosahexanoic acid (DHA) during pregnancy and lactation. Offspring were weaned onto a control rat chow diet. Tibial growth plate and metaphysis structure, osteoblast/osteoclast density and differentiation, and gene expression were assessed in offspring at 3 wk (weaning), 6 wk (adolescent), and 3 months (adult). Maternal n3FA supplementation elevated offspring plasma n3FA levels at 3 and 6 wk. Although total growth plate heights were unaffected at any age, the resting zone thickness was increased in both male and female offspring at 3 wk. In n3FA males, but not females, bone trabecular number and thickness were increased at 3 wk but not other ages. The wk 3 n3FA males also exhibited an increased bone volume, an increased osteoblast but decreased osteoclast density, and lower expression of osteoclastogenic cytokines receptor activator of nuclear factor-κB ligand, TNF-α, and IL-6. No effects were seen at 6 wk or 3 months in either sex. Thus, perinatal n3FA supplementation is associated with increased bone formation, decreased resorption, and a higher bone mass in males, but not in females, at weaning; these effects do not persist into adolescence and adulthood and are unlikely to produce lasting improvements in bone health.

Response of human bone marrow stromal cells, MG-63, and SaOS-2 to titanium-based dental implant surfaces with different topography and surface energy

OBJECTIVES

Osseointegration is dependent on different parameters of the implant surface like surface roughness and physicochemical properties. In vitro studies using a wide variety of surface parameters and cell lines make it difficult to address the influence of a single parameter. With this study the influence of surface topography and energy on different osteoblast derived cell lines, namely MG-63 and SaOS-2 and of human mesenchymal stromal cells (hMSC) were investigated.

MATERIAL AND METHODS

Cells were cultured on polished (POL) and sandblasted/hot acid etched (SBA) titanium surfaces which were partly alkaline treated (SBA NaOH). Cell morphology, metabolic activity, tissue non-specific alkaline phosphatase (TNAP) activity and prostaglandin E(2) (PGE(2) ) formation were determined.

RESULTS

Impaired spreading was found on both SBA surfaces. Proliferation after 4 and 7 days increased on POL compared to both SBA surfaces. TNAP activity of hMSC and MG-63 was increased on POL compared to both SBA surfaces whereas SaOS-2 did not discriminate between the three surfaces. PGE(2) formation of hMSC and MG-63 was on both SBA surfaces after 2 days significantly higher than on POL.

CONCLUSIONS

The results of this study show that surface roughness has a distinct influence on proliferation and differentiation of osteoblasts. However, variations in physicochemical properties seem to have little influence under the used experimental conditions. It is suggested that more sever and long-lasting modifications of surface chemistry would have an influence on osteoblastic cells.

The effect of polyunsaturated fatty acids on bone health

The essential polyunsaturated fatty acids (PUFAs) are divided into two classes, n-3 (ω-3) and n-6 (ω-6) and their dietary precursors are α-linolenic (ALA) and linoleic acid (LA), respectively. PUFAs are precursors of a wide range of metabolites, for example eicosanoids like prostaglandins and leukotrienes, which play critical roles in the regulation of a variety of biological processes, including bone metabolism.

A large body of evidence supports an effect of PUFA on bone metabolism which may be mediated by regulation of osteoblastogenesis and osteoclast activity, change of membrane function, decrease in inflammatory cytokines, such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumour necrosis factor alpha (TNF-α), modulation of peroxisome proliferators-activated receptor γ (PPARγ) and influence in NO secretion and NO synthase.

Animal studies have shown that a higher dietary omega-3/omega-6 fatty acids ratio is associated with beneficial effects on bone health. Human studies conducted in elderly subjects suggest that omega-3 instead of omega-6 has a positive effect on bone metabolism. In spite of increasing evidence, studies conducted in humans do not allow us to draw a definitive conclusion on the usefulness of PUFAs in clinical practice.

Effect of n-3 fatty acid supplementation on urinary risk factors for calcium oxalate stone formation

PURPOSE

Findings are inconsistent in a few studies of the effect of n-3 fatty acid supplementation on urinary calcium and oxalate excretion in stone formers. We evaluated the physiological effects of supplementation with eicosapentaenoic acid and docosahexaenoic acid on urinary risk factors for calcium oxalate stone formation under standardized conditions.

MATERIALS AND METHODS

We studied 15 healthy subjects initially while consuming a standardized diet for 5 days (control phase). During consecutive intervention phases 1-5-day standardized diet, 2-20-day free diet and 3-5-day standardized diet participants received 900 mg eicosapentaenoic acid and 600 mg docosahexaenoic acid daily. While ingesting the standardized diets, daily 24-hour urine samples were collected.

RESULTS

After short-term supplementation with eicosapentaenoic acid and docosahexaenoic acid in phase 1 we noted no changes in urinary parameters compared to the control phase. After 30-day supplementation with eicosapentaenoic acid and docosahexaenoic acid in phase 3 relative supersaturation with calcium oxalate decreased significantly by 23% from a mean ± SD of 2.01 ± 1.26 to 1.55 ± 0.84 due to significantly decreased urinary oxalate excretion (p = 0.023). Other urinary variables were not affected by supplementation.

CONCLUSIONS

Results show that 30-day n-3 fatty acid supplementation effectively decreases urinary oxalate excretion and the risk of calcium oxalate crystallization. The mechanism of the physiological effect may be decreased cellular oxalic acid exchange attributable to an altered fatty acid pattern of membrane phospholipids with concomitant changes in oxalate transporter activity. Calcium oxalate stone formers may benefit from long-term n-3 fatty acid supplementation.

Differential effect of chondroitin-4-sulfate on the immediate and delayed prostaglandin E2 release from osteoblasts

The present study examines the effect of chondroitin-4-sulfate (C4S) on the immediate (non-inflammatory conditions) and the delayed (inflammatory conditions) prostaglandin E(2) (PGE(2)) release from rat calvarial osteoblasts. An immediate low release of PGE(2) was induced by PAF, phorbol ester and arachidonic acid but not by IL1beta, TNF-alpha and LPS whereas a delayed high release of PGE(2) was induced by the inflammatory agents IL1beta, TNF-alpha and LPS but not by PAF, phorbol ester and arachidonic acid. C4S had no effect on the immediate PGE(2) release but inhibited the delayed release of PGE(2). IL1beta, TNF-alpha and LPS enhanced the expression of COX-2 and mPGES1 whereas phorbol ester enhanced COX-2 expression only. PAF and arachidonic acid had no effect on the expression of COX-2 and mPGES1. C4S inhibited the enhanced expression of COX-2 and mPGES1 but had no effect on the IL1beta-induced decrease of I-kappaBalpha and nuclear translocation of NF-kappaB. These results indicate that the beneficial effects of C4S in bone inflammatory diseases might be due to a specific inhibition of the delayed high PGE(2) release from osteoblasts.

Conjugated linoleic acid prevents growth attenuation induced by corticosteroid administration and increases bone mineral content in young rats

Corticosteroids are a common therapy in many disease states, despite frequent and potentially serious side effects. Nutritional supplementation with conjugated linoleic acid (CLA) has been shown to increase fat-free mass, whereas supplementation with n-3 and n-6 fatty acids has been shown to increase bone mineral density (BMD). To determine whether CLA can attenuate the side effects of 8 weeks of corticosteroid administration, we randomized twenty-four 5-week-old male Sprague-Dawley rats into 1 of 4 groups: control; control + methylprednisolone (7 mg.kg-1.week-1); CLA diet (1% CLA w/w); or CLA plus methylprednisolone. Body composition, bone mineral content (BMC), and BMD were assessed with dual-energy X-ray absorptiometry at the onset and at the end of the 8-week intervention. The mechanical properties of bone were determined using 3-point femur bending at the end of the intervention. Methylprednisolone resulted in an attenuation of the increase in body mass and lean mass over the 8 weeks (p < 0.05). CLA prevented the methylprednisolone-induced attenuation of body mass and lean mass accumulation. CLA also resulted in a greater increase in BMC (p < 0.05) in the lumbar spine. The energy at failure of the isolated femurs was increased with CLA (p < 0.05). Dietary CLA prevents many of the growth- and bone-related side effects arising from 8 weeks of corticosteroid administration, results in greater increases in BMC and BMD, and can contribute to an improvement in some of the mechanical properties of bone.

The effect of a low-carbohydrate diet on bone turnover

INTRODUCTION

Low-carbohydrate diets have become popular as weight loss techniques. These diets are high in protein, saturated fats, and omega-6 fatty acids. They also lead to a ketogenic state. These factors could lead to increased bone turnover. This study was designed to see whether a low-carbohydrate diet would lead to increased bone turnover in humans.

METHODS

Thirty patients (15 study subjects and 15 controls) were recruited for this 3-month study. The 15 patients on the diet were instructed to consume less than 20 g of carbohydrates per day for the 1st month and then less than 40 g per day for months 2 and 3. Control subjects had no restrictions on their diet. The primary end point was urinary N-telopeptide (UNTx) at 3 months. Secondary end points included UNTx at 1 month, bone-specific alkaline phosphatase (BSAP) at 1 month, bone turnover ratio (BSAP/UNTx) at 1 month, and weight loss.

RESULTS

The mean UNTx in the study subjects increased by 1.6 [95% confidence interval (CI) +/-22.8] compared with an increase of 1.9 (95% CI +/-17.6) in the controls at 3 months (p=0.86). The mean UNTx decreased by 2.2 (95% CI +/-27.2) and 3.1 (95% CI +/-17.6) at 1 month in the dieters and controls, respectively (p=0.36). The mean BSAP decreased by 0.53 (95% CI +/-2.96) in the dieters and increased by 0.34 (95% CI +/-2.92) in the controls at 1 month (p=0.27). The bone turnover ratio increased by 0.08 (95% CI +/-0.81) in the dieters and by 0.05 (95% CI +/- 0.27) in the controls at 1 month (p=0.78). The dieters lost 6.39 kg versus 1.05 kg for the controls at 3 months (p=0.0008).

CONCLUSIONS

Although the patients on the low-carbohydrate diet did lose significantly more weight than the controls did, the diet did not increase bone turnover markers compared with controls at any time point. Further, there was no significant change in the bone turnover ratio compared with controls.

Peripheral blood mononuclear cell fatty acid composition and inflammatory mediator production in adult Crohn's disease

BACKGROUND & AIMS

Crohn's disease (CD) is associated with nutritional deficiencies, altered plasma concentrations of polyunsaturated fatty acids (PUFA) and an anti-inflammatory response to fish oil that contains n-3 PUFA. This suggests that, in CD, immune cells may have altered n-3 PUFA composition with functional consequences. The aim of this study is to investigate n-3 and n-6 PUFA composition and synthetic function of peripheral blood mononuclear cells (PBMC) in the basal state.

METHODS

A case control study of 52 adult CD patients and healthy, age- and sex-matched controls. Composition of PBMC and plasma phospholipids were measured by gas chromatography and production of tumour necrosis factor-alpha, prostaglandin E2 (PGE2) and interferon-gamma (IFN-gamma) by PBMC were measured by ELISA.

RESULTS

CD was associated with higher concentrations of eicosapentaenoic acid and other n-3 PUFA, and lower arachidonic acid (AA) (n-6 PUFA) in PBMC. This was not explained by differences in dietary fat intake. Lower rates of production of PGE2 and IFN-gamma by PBMC were noted in quiescent and active CD, respectively, compared to controls.

CONCLUSIONS

CD is associated with a greater availability, and not a deficiency, of n-3 PUFA in PBMC, but lower concentrations of AA, and lower rates of production of PGE2 and IFN-gamma, compared to healthy controls.

Expression of LRP1 by human osteoblasts: a mechanism for the delivery of lipoproteins and vitamin K1 to bone

Accumulating clinical and experimental data show the importance of dietary lipids and lipophilic vitamins, such as vitamin K1, for bone formation. The molecular mechanism of how they enter the osteoblast is unknown. Here we describe the expression of the multifunctional LRP1 by human osteoblasts in vitro and in vivo. We provide evidence that LRP1 plays an important role in the uptake of postprandial lipoproteins and vitamin K1 by human osteoblasts.

INTRODUCTION

Chylomicrons (CM) and their remnants (CR) represent the postprandial plasma carriers of dietary lipids. Dietary vitamin K1 is known to be transported in the circulation as part of CM/CR and is required by osteoblasts as an essential co-factor for the gamma-carboxylation of bone matrix proteins. The molecular mechanisms underlying the delivery of lipophilic substances to bone are not understood. In this study, the expression and function of CM/CR receptors was examined in human osteoblasts.

MATERIALS AND METHODS

Four human osteoblast-like cell lines were analyzed: two osteosarcoma lines (MG63, SaOS-2) and two telomerase-immortalized human bone marrow stromal cell lines (hMSC-TERT [4] and [20]) after 1,25(OH)2 vitamin D3 induction of osteoblastic differentiation (hMSC-TERT-OB). Receptor expression was examined by Western blotting and immunohistochemistry of normal human bone sections. Endocytotic receptor function was analyzed by cellular uptake assays using fluorescent and radiolabeled human CR. Vitamin K1-enriched CR (CR-K1) were generated in vivo after oral vitamin administration and vitamin K1 uptake by osteoblasts was measured by HPLC. The effect of CR-K1 uptake on osteocalcin carboxylation was measured by ELISA.

RESULTS

Osteoblasts exhibit high levels of protein expression of the CR receptors LRP1 and LDLR. VLDLR is expressed to a lower degree. Immunohistochemistry of normal human bone sections showed strong LRP1 expression by osteoblasts and marrow stromal cells. Uptake of fluorescent CR by osteoblasts resulted in the typical pattern of receptor-mediated endocytosis. CR uptake was stimulated by the exogenous addition of the lipoprotein receptor ligands apolipoprotein E and lipoprotein lipase. Uptake was reduced by the known LRP1 inhibitors RAP, lactoferrin, and suramin, but not by LDL, which exclusively binds to the LDLR. Vitamin K1 uptake by hMSC-TERT-OB after incubation with CR-K1 was also shown to be sensitive to LPL stimulation and the LRP1 specific inhibitor lactoferrin. CR-K1 uptake into osteoblasts stimulated the gamma-carboxylation of osteocalcin.

CONCLUSION

Human osteoblasts express receptors of the LDLR family with a capacity for vitamin K1 uptake through CR endocytosis, a novel mechanism for the delivery of dietary lipids and lipophilic vitamins to human bone. The current data suggest that, among the expressed receptors, LRP1 plays a predominant role.

Dietary fat composition modifies the effect of boron on bone characteristics and plasma lipids in rats

Female and male rats weighing about 170 g and 200 g, respectively, were fed diets (approximately 70 microg boron/kg) in a factorial arrangement with supplemental boron at 0 (deficient) and 3 (adequate) mg/kg and canola oil or palm oil at 75 g/kg of diet as variables. After 5 weeks, six females in each treatment were bred. Dams and pups continued on their respective dietary treatments through gestation, lactation and post-weaning. Thirteen weeks after weaning, plasma and bones were collected from 12 male and 12 female offspring in each treatment. Boron supplementation increased femur strength measured by the breaking variable bending moment; tibial calcium and phosphorus concentrations; and plasma alkaline phosphatase. Femur breaking stress was greatest in boron-supplemented rats fed canola oil, and lowest in boron-deprived females fed canola oil; this group also exhibited the lowest femur bending moment. Minerals associated with bone organic matrix, zinc and potassium, were increased by boron supplementation in tibia. Plasma phospholipids were decreased by boron deprivation in females, but not males. Plasma cholesterol was decreased in boron-supplemented males by replacing canola oil with palm oil. The findings suggest that a diet high in omega-3 alpha-linolenic acid promotes femur strength best when the dietary boron is adequate.

Biomechanical bone strength and bone mass in young male and female rats fed a fish oil diet

The study objective was to determine if male and female rats fed a diet rich in fish oil had femurs and vertebrae that were stronger and more resistant to fracture than rats not fed omega-3 long chain polyunsaturated fatty acids. Weanling rats were randomized to a control or a fish oil diet for 5 weeks. Feeding fish oil to males had no effect on biomechanical strength properties of femurs and vertebrae as measured by three point bending and compression, respectively. In contrast, females fed fish oil had reduced length growth and a lower vertebral peak load. These effects may have been partly mediated by a lower food intake but were not associated with differences in serum IGF-I, estradiol or urinary calcium. The effect of consuming a fish oil diet into later adulthood should be investigated to determine if femur strength is also affected among females.

Protective role of n-3 lipids and soy protein in osteoporosis

It is well established that bone loss due to estrogen deficiency after menopause is greater in women consuming higher quantities of animal protein than in women consuming vegetable protein, particularly soy protein. Besides the dietary protein source altering bone loss, it has also been postulated recently that the source of a higher n-6/n-3 ratio in dietary oils is implicated in causing osteoporosis. Both animal and human studies have indicated that an increased intake of n-6 fatty acids from vegetable oils elevates prostaglandin E(2) levels as well as pro-inflammatory cytokines such as IL-1, IL-6 and TNF-alpha. Interestingly, it has been found that lack of estrogen also increases the production of these cytokines by immune cells and thereby activates osteoclasts during the peri-menopausal period. We speculated that the use of n-3 fatty acids and soy protein, which are known to act as anti-inflammatory and down regulate pro-inflammatory cytokines, may also protect against bone loss by decreasing osteoclast activation and bone resorption. Similar to the results of others, our ongoing studies indeed show that the bone loss in ovariectomized mice is significantly attenuated by feeding diets enriched with either fish oil or soy protein when compared to corn oil and casein-fed mice. One of the mechanisms appears to be decreasing the activation of receptor activator of NF-kappaB ligand (RANKL) on T cells, which has been found to increase osteoclast activation along with increasing pro-inflammatory cytokines in OVX mice. Since hormone replacement therapy has been found to cause adverse effects, further both animal and human studies are required with moderate soy protein and fish oil supplements in understanding the mechanisms involved in altering immune function and bone loss during menopause in women and aging in men.

Skeletal biology, functional asymmetry and the origins of "Handedness"

The past decade has witnessed the (re)emergence of a debate as to whether handedness is apomorphic within hominins. There are both qualitative and quantitative arguments, some which draw non-human primates into the handed sphere and others which exclude them. Ultimate questions concern origins of structural asymmetry of both brain and body and lateralized behaviours with implications for tool use and language. Lateralization is thus an important realm of phylogenetic study, and archaeologists and psychologists alike have sought to identify handedness within material culture. However, hand preference for tool manufacture and use among extant non-human primates, such as Cebus and Pan, suggests that the archaeological record may well be mute regarding the origins of laterality. In this paper, an argument is put forward positioning skeletal biology as a viable approach to the handedness origins issue. Behaviour is a mediator of the complementary processes of geometric modelling (change in size and shape) and histological remodelling (disuse osteopenia; microfracture repair); therefore, directional asymmetry in the pattern of skeletal modelling and remodelling is a putative signal of lateralized activity.