Anti-anabolic Effects Research Articles

FRI170 Ultrasound-Based Evaluation Of Muscles And Tendons In Patients With Cushing Syndrome

Abstract Disclosure: B. Bolayir: None. F. Gogus: None. B. Demir: None. M.M. Yalcin: None. J. Meray: None. A. Altinova: None. F.S. Toruner: None. M.Y. Akturk: None. Background: Myopathy, being induced by antianabolic and catabolic effects of excess corticosteroids is one of the characteristic features of Cushing Syndrome (CS). Muscle thickness which has been shown to be correlated with muscle cross sectional area can be used as an indicator of muscle mass. Although many studies have demonstrated effects of corticosteroids on collagen metabolism and case reports documented rupture of tendons in patients with chronic exposure to corticosteroids, tendon changes of patients with endogenous hypercortisolism have not been studied. Ultrasound, although not studied well in this group of patients, can be an alternative imaging method that provides information about muscle and tendon thickness. The aim of this study was to investigate muscle, tendon thicknesses and serum levels of myostatin in patients with CS. Methods: Twenty-two patients with CS and nineteen healthy control subjects similar for age, sex, height and weight were enrolled. Lower extremity tendon and muscle groups’ thickness were evaluated by ultrasound. Serum myostatin levels were measured by ELISA. Results: Age, height, weight and body mass index were similar between groups (p>0.05). The thicknesses of rectus femoris, vastus medialis, vastus lateralis, gastrocnemius medialis and gastrocnemius lateralis were lower in the CS group than control group (p≤0.001). However, thickness of soleus muscle was not significantly different between the groups (p > 0.05). No significant difference was revealed between groups in terms of Achilles and patellar tendon thickness (p>0.05). Median serum myostatin levels were found to be lower in the CS group than the control group (p<0.001).Conclusions: Ultrasound based measurement of muscle thickness can be used to assess and monitor steroid-induced changes of muscle mass. The fact that the thickness of the proximal muscles of lower extremity was found to be lower by ultrasound in patients with CS in our study supports the proximal myopathy feature of CS. Besides that, it was shown that the gastrocnemius lateralis and medialis thicknesses, which are the distal muscles of the lower extremity, were also shown to be lower in the Cushing group. On the other hand, CS might not affect the thickness of the lower extremity tendons. Moreover, the mechanism of the decrease in the level of myostatin, the negative regulator of muscle growth, in patients with needs to be elucidated with CS further studies. Presentation: Friday, June 16, 2023

All-trans Retinoic Acid and Beta-Carotene Increase Sclerostin Production in C2C12 Myotubes.

Sclerostin is a protein secreted by osteocytes whose encoding gene SOST is regulated by mechanical stimuli, cytokines, and all-trans retinoic acid (ATRA) and mediates antianabolic effects on bone formation as an inhibitor of the canonical Wnt/β-catenin pathway. Interestingly, skeletal muscle has recently been identified as another source of sclerostin, suggesting that the musculature may play an important role in maintaining bone mass. However, regulators of muscular SOST expression are virtually unknown. This study investigates the influence of ATRA and the provitamin A derivative beta-carotene (β-C) on sclerostin synthesis in muscle cells. The impact of ATRA, its synthetic analog TTNPB, and β-C on Sost transcription was analyzed by qRT-PCR in C2C12 myotubes and the secreted sclerostin protein by ELISA. ATRA strongly increases the sclerostin synthesis in C2C12 myotubes in a dose-dependent manner. The stimulating effect of ATRA and TTNPB on Sost is largely reduced in the presence of the retinoic acid receptor inhibitor AGN193109. β-C also increases the Sost expression, but this effect vanishes when β-C is coincubated with beta-carotene 15,15'-monooxygenase 1 (BCMO1)-specific siRNA. Thus, ATRA is a potent stimulator of sclerostin release in muscle cells. β-C can also increase Sost mRNA abundance, but this effect depends on the conversion to a retinoid.

Sclerostin as a biomarker of physical exercise in osteoporosis: A narrative review.

Osteoporosis, a disease of low bone mass, is characterized by reduced bone mineral density (BMD) through abnormalities in the microarchitecture of bone tissue. It affects both the social and economic areas, therefore it has been considered a lifestyle disease for many years. Bone tissue is a dynamic structure exhibiting sensitivity to various stimuli, including mechanical ones, which are a regulator of tissue sclerostin levels. Sclerostin is a protein involved in bone remodeling, showing an anti-anabolic effect on bone density. Moderate to vigorous physical activity inhibits secretion of this protein and promotes increased bone mineral density. Appropriate exercise has been shown to have an osteogenic effect. The effectiveness of osteogenic training depends on the type, intensity, regularity and frequency of exercise and the number of body parts involved. The greatest osteogenic activity is demonstrated by exercises affecting bone with high ground reaction forces (GRF) and high forces exerted by contracting muscles (JFR). The purpose of this study was to review the literature for the effects of various forms of exercise on sclerostin secretion.

Anticytokine Activity Enhances Osteogenesis of Bioactive Implants.

In dental clinical practice, systemic steroids are often applied at the end of implant surgeries to reduce postsurgical inflammation (tissue swelling, etc.) and to reduce patient discomfort. However, the use of systemic steroids is associated with generalized catabolic effects and with a temporarily reduced immunological competence. We hypothesize that by applying locally anticytokine antibodies (antitumor necrosis factor alpha and anti-interleukin-1 beta) together with a bioactive osteogenic implant at the time of the surgical intervention for the placement of a construct, we will be able to achieve the same beneficial effects as those using systemic steroids but are able to avoid the generalized antianabolic effects and the reduced immunocompetence effects, associated with the systemic use of steroids. In an adult rat model, a collagen sponge, soaked with the osteogenic agent bone morphogenetic protein-2, was used as an example for a bioactive implant material and was surgically placed subcutaneously. In the acute inflammatory phase after implantation (2 days after surgery) we investigated the local inflammatory tissue response, and 18 days postsurgically the efficiency of local osteogenesis (to assess possible antianabolic effects). We found that the negative control groups, treated postsurgically with systemic steroids, showed a significant suppression of both the inflammatory response and the osteogenetic activity, that is, they were associated with significant general antianabolic effects, even when steroids were used only at a low dose level. The local anticytokine treatment, however, was able to significantly enhance new bone formation activity, that is, the anabolic activity, over positive control values with BMP-2 only. However, the anticytokine treatment was unable to reduce the local inflammatory and swelling responses.

Inferior alveolar nerve transection disturbs innate immune responses and bone healing after tooth extraction.

Coordination between the nervous and innate immune systems to maintain bone homeostasis is largely uncharacterized. The present study investigated the sensory-immune interaction in resting alveolar bone and healing socket by surgical sensory denervation. Bone histomorphometry and immunohistochemistry showed that sensory denervation resulted in moderate suppression of bone remodeling, with a proinflammatory milieu manifested by increased neutrophil recruitment and possible alternations in macrophage phenotypes along the resting bone surface. This denervation effect intensified when bone remodeling was triggered by tooth extraction, as revealed by disrupted temporospatial variations in macrophage subpopulations and neutrophil infiltration, which were closely associated with a dramatic decline in socket bone filling and residual ridge height. Antagonism of calcitonin gene-related peptide (CGRP) brought about similar antianabolic and proinflammatory effects as sensory denervation, suggesting that sensory nerves may monitor the bony milieu by CGRP. Depletion of macrophages, rather than neutrophils, ruled out CGRP effects, illustrating that macrophages were the primary immune mechanism that linked sensory innervation, innate immunity, and bone. The data support that sensory innervation is required for control of innate immune responses and maintenance of bone homeostasis. Sensory neuropeptides, such as CGRP, are a possible target for the development of proanabolic treatments in bone disease by modulating innate immune responses.

Transient receptor potential ankyrin 1 (TRPA1) as a factor and drug target in osteoarthritis: TRPA1 mediates fibroblast growth factor 2 expression in chondrocytes

Purpose: Transient receptor potential ankyrin 1 (TRPA1) is a membrane-associated cation channel, which is known to be involved in nociception and neurogenic inflammation. TRPA1 is widely expressed in neurons, and according to more recent findings, also in non-neuronal cells, including synoviocytes and keratinocytes. TRPA1 acts as a chemosensor of pungent environmental compounds, but it is also activated by agents formed endogenously in inflammatory and hypoxic conditions such as those found in osteoarthritic joints. We have recently shown in monosodium iodoacetate-induced experimental osteoarthritis that TRPA1 activation mediates inflammation, cartilage degradation and pain (Moilanen et al. Osteoarthritis Cartilage 2015). We have also shown that TRPA1 is functionally expressed in human chondrocytes, where it mediates inflammatory effects (Nummenmaa et al. Arthritis Res Ther 2016). Further, we found that anti-inflammatory drugs dexamethasone and aurothiomalate downregulate the expression of TRPA1 in human chondrocytes (Nummenmaa et al. RMD Open 2017), revealing TRPA1 as a potential mediator and drug target in osteoarthritis. Fibroblast growth factor 2 (FGF-2) belongs to the fibroblast growth factor family, which is a large group of molecules involved in the regulation of connective tissue development and metabolism. FGF-2 is found in the synovial fluid and cartilage of osteoarthritis patients, and has previously been associated with the pathogenesis of osteoarthritis. In the present study, we investigated the functional consequences of TRPA1 activation in chondrocytes focusing in particularly on the expression of FGF-2. Methods: Chondrocytes were isolated from cartilage tissue from wild type (WT) and TRPA1 deficient (knock-out, KO) mice and cultured in the absence or presence of IL-1β. Total RNA was isolated and genome-wide expression analysis was carried out with next generation RNA sequencing (NGS) method with Illumina HiSeq2500 at the Institute for Molecular Medicine Finland. Results from the RNA sequencing analysis were verified by quantitative RT-PCR. Primary human OA chondrocytes were isolated from cartilage samples obtained from patients undergoing knee replacement surgery. Chondrocytes were cultured in the presence of the TRPA1-inducing cytokine IL-1β alone and together with the selective TRPA1 antagonist HC-030031. For experiments investigating the effects of FGF-2 in chondrocytes, the cells were cultured in the presence of FGF-2. Expression of FGF-2 subsequent to TRPA1 activation was measured by quantitative RT-PCR, and aggrecan, collagen II and MMP-enzymes by quantitative RT-PCR/immunoassay. Results: The expression of FGF-2 was significantly downregulated in chondrocytes from TRPA KO mice compared to WT mice. The downregulation of FGF-2 was verified by performing quantitative RT-PCR analysis on the sequenced samples, and on a larger set of corresponding samples. The results were confirmed using primary human OA chondrocytes. Pharmacological inhibition of TRPA1 with the selective antagonist HC-030031 downregulated FGF-2 expression in these cells. We further investigated the effects of FGF-2 in human OA chondrocytes, and found that FGF-2 upregulated the production of cartilage matrix degrading enzymes MMP-1 and MMP-13, and downregulated the expression of cartilage matrix components aggrecan and collagen II. Conclusions: The results revealed a hitherto unknown role for TRPA1 in the regulation of FGF-2 expression in chondrocytes. Further, FGF-2 was confirmed to have catabolic and anti-anabolic effects in human OA chondrocytes. Inhibition of TRPA1 and subsequent downregulation of FGF-2 could therefore have beneficial effects on the balance of catabolic and anabolic mediators within OA cartilage. These results together with our recent data discussed above support the concept of TRPA1 as a potential mediator and drug target in osteoarthritis.

Commensal Gut Microbiota Immunomodulatory Actions in Bone Marrow and Liver have Catabolic Effects on Skeletal Homeostasis in Health

Despite knowledge the gut microbiota regulates bone mass, mechanisms governing the normal gut microbiota’s osteoimmunomodulatory effects on skeletal remodeling and homeostasis are unclear in the healthy adult skeleton. Young adult specific-pathogen-free and germ-free mice were used to delineate the commensal microbiota’s immunoregulatory effects on osteoblastogenesis, osteoclastogenesis, marrow T-cell hematopoiesis, and extra-skeletal endocrine organ function. We report the commensal microbiota has anti-anabolic effects suppressing osteoblastogenesis and pro-catabolic effects enhancing osteoclastogenesis, which drive bone loss in health. Suppression of Sp7(Osterix) and Igf1 in bone, and serum IGF1, in specific-pathogen-free mice suggest the commensal microbiota’s anti-osteoblastic actions are mediated via local disruption of IGF1-signaling. Differences in the RANKL/OPG Axis in vivo, and RANKL-induced maturation of osteoclast-precursors in vitro, indicate the commensal microbiota induces sustained changes in RANKL-mediated osteoclastogenesis. Candidate mechanisms mediating commensal microbiota’s pro-osteoclastic actions include altered marrow effector CD4+T-cells and a novel Gut-Liver-Bone Axis. The previously unidentified Gut-Liver-Bone Axis intriguingly implies the normal gut microbiota’s osteoimmunomodulatory actions are partly mediated via immunostimulatory effects in the liver. The molecular underpinnings defining commensal gut microbiota immunomodulatory actions on physiologic bone remodeling are highly relevant in advancing the understanding of normal osteoimmunological processes, having implications for the prevention of skeletal deterioration in health and disease.

Sclerostin inhibition promotes TNF-dependent inflammatory joint destruction.

Sclerostin, an inhibitor of the Wnt/β-catenin pathway, has anti-anabolic effects on bone formation by negatively regulating osteoblast differentiation. Mutations in the human sclerostin gene (SOST) lead to sclerosteosis with progressive skeletal overgrowth, whereas sclerostin-deficient (Sost(-/-)) mice exhibit increased bone mass and strength. Therefore, antibody-mediated inhibition of sclerostin is currently being clinically evaluated for the treatment of postmenopausal osteoporosis in humans. We report that in chronic TNFα (tumor necrosis factor α)-dependent arthritis, fibroblast-like synoviocytes constitute a major source of sclerostin and that either the lack of sclerostin or its antibody-mediated inhibition leads to an acceleration of rheumatoid arthritis (RA)-like disease in human TNFα transgenic (hTNFtg) mice with enhanced pannus formation and joint destruction. Inhibition of sclerostin also failed to improve clinical signs and joint destruction in the partially TNFα-dependent glucose-6-phosphate isomerase-induced arthritis mouse model, but ameliorated disease severity in K/BxN serum transfer-induced arthritis mouse model, which is independent of TNF receptor signaling, thus suggesting a specific role for sclerostin in TNFα signaling. Sclerostin effectively blocked TNFα- but not interleukin-1-induced activation of p38, a key step in arthritis development, pointing to a previously unrealized protective role of sclerostin in TNF-mediated chronic inflammation. The possibility of anti-sclerostin antibody treatment worsening clinical RA outcome under chronic TNFα-dependent inflammatory conditions in mice means that caution should be taken both when considering such treatment for inflammatory bone loss in RA and when using anti-sclerostin antibodies in patients with TNFα-dependent comorbidities.

The growth endocrine axis and inflammatory responses after laparoscopic cholecystectomy.

It is well known that conventional surgery leads to detrimental immune and catabolic responses, thus there is growing interest in the effect of minimally invasive techniques on postoperative endocrine and immune function. The aim of this prospective study was to evaluate the growth hormone (GH)/insulin-like growth factor-1 (IGF-1)/IGF binding protein-3 (IGFBP-3) axis and acute phase (interleukin-6, IL-6, and C-reactive protein, CRP) responses in patients who underwent laparoscopic cholecystectomy. Twenty-nine patients (16 women, 13 men; age: 58+8 years) with a history of uncomplicated symptomatic cholelithiasis participated in the study. Blood samples were collected prior to and at 24 hrs and 48 hrs after laparoscopic cholecystectomy. Serum concentrations of GH, IGF-1, IGFBP-3, and IL-6 were determined by standard sandwich enzyme-linked immunosorbent assay (ELISA), while CRP was measured by nephelometry. ANOVA with repeated measures and Tukey's post-hoc test were used to evaluate changes in serum measurements. The laparoscopic cholecystectomy resulted in a significant postoperative increase in circulating levels of IL-6 (p=0.031), which is the main cytokine responsible for inducing the acute inflammatory response, and of the acute phase protein CRP (p=0.005). A significant increase in GH levels at 24 hrs (p=0.034) and decrease of IGF-1 on both postoperative days were also found (p=0.045, 0.044), while no changes were documented in IGFBP-3 levels. Significant correlations were revealed between postoperative levels of the acute phase proteins and growth axis hormones (p<0.05 - 0.001). Our findings suggest that laparoscopic cholecystectomy induces acute phase endocrine and immune responses. These changes may represent a state of systemic inflammation and GH resistance, compatible with possible cytokine-induced anti-anabolic or catabolic effects even after this minimally invasive cholecystectomy.

Meniscus is more susceptible than cartilage to catabolic and anti-anabolic effects of adipokines

This study compared the effects on cartilage and meniscus matrix catabolism and biosynthesis of several adipokines implicated in osteoarthritis (OA). Bovine cartilage and meniscus explants were cultured for 1 or 9 days in serum-free medium alone or with 0.02, 0.2, or 2 μg/ml of leptin, visfatin, adiponectin, or resistin. Media were supplemented with (3)H-proline or (35)S-sodium sulfate to evaluate protein and sulfated glycosaminoglycan (sGAG) accumulation on the last day of culture. Explants were assayed for radiolabel, sGAG, and DNA contents. Cultured media were assayed for sGAG, nitrite and lactate dehydrogenase. Cartilage tissue was minimally affected by adipokines, with only the highest resistin dose increasing sGAG release and nitrite production compared to controls. In sharp contrast, meniscus tissue was responsive to several adipokines, with elevated sGAG and nitrite release following treatment with resistin, leptin, or visfatin. Cartilage sGAG content was unaltered by adipokine treatment whereas meniscal sGAG content significantly decreased with resistin dosage. Protein ((3)H) incorporation was unaffected by adipokine treatment in both tissues. sGAG ((35)S) incorporation did not significantly vary with adipokine treatment in cartilage but was inhibited by treatment with leptin, visfatin, and resistin in meniscus. Our results indicate that meniscal tissue is more susceptible to adipokine-stimulated catabolism than is cartilage. Resistin had the strongest effect of the adipokines tested, inducing sGAG release in both tissues and depleting sGAG content in meniscus. These results suggest that increased adipokine levels due to obesity or joint injury may alter the mechanical integrity of the knee joint through biological pathways.

Haem oxygenase-1 induction reverses the actions of interleukin-1β on hypoxia-inducible transcription factors and human chondrocyte metabolism in hypoxia

HO-1 (haem oxygenase-1) catalyses the degradation of haem and possesses anti-inflammatory and cytoprotective properties. The role of inflammatory mediators in the pathogenesis of OA (osteoarthritis) is becoming increasingly appreciated. In the present study, we investigated the effects of HO-1 induction in OA and healthy HACs (human articular chondrocytes) in response to inflammatory cytokine IL-1 β (interleukin-1β) under hypoxic conditions. Hypoxia was investigated as it is a more physiological condition of the avascular cartilage. Hypoxic signalling is mediated by HIFs (hypoxia-inducible factors), of which there are two main isoforms, HIF-1α and HIF-2α. Normal and OA chondrocytes were stimulated with IL-1β. This cytokine suppresses HO-1 expression and exerts both catabolic and anti-anabolic effects, while increasing HIF-1α and suppressing HIF-2α protein levels in OA chondrocytes in hypoxia. Induction of HO-1 by CoPP (cobalt protoporphyrin IX) reversed these IL-1β actions. The hypoxia-induced anabolic pathway involving HIF-2α, SOX9 [SRY (sex determining region Y)-box 9] and COL2A1 (collagen typeII α1) was suppressed by IL-1β, but importantly, levels were restored by HO-1 induction, which down-regulated TNFα (tumour necrosis factor α), MMP (matrix metalloproteinase) activity and MMP-13 protein levels. Depletion of HO-1 using siRNA (small interfering RNA) abolished the CoPP effects, further demonstrating that these were due to HO-1. The results of the present study reveal the different mechanisms by which HO-1 exerts protective effects on chondrocytes in physiological levels of hypoxia.

Pharmacological advances in the management of osteoporosis

Osteoporosis is a worldwide health problem with a high prevalence. Agents for the treatment of osteoporosis are classified as antiresorptives, anabolic agents and drugs with combined anabolic and anti-resorptive actions. Although many drugs with proven efficacy are available for the treatment of osteoporosis their effectiveness has been limited by side-effects, concurrent comorbidities, and inadequate long-term compliance. Additionally, conventional antiresorptives such as aminobisphosphonates profoundly suppress bone resorption and formation which might contribute to the pathogenesis of osteonecrosis of the jaw. Various novel antiresorptive agents are in development. This overview aims to discuss in brief some of the most promising novel treatments which include: bazedoxifene a new selective estrogen receptor modulator, denosumab, PTH rP (parathyroid hormone related protein), odanacatib and other bone anabolic agents such antibodies against sclerostin and dickkopf-1. Denosumab, a fully human monoclonal antibody to receptor activator of nuclear factor kappa B ligand (RANKL) an anti-resorptive agent with a low side effect profile has been proven efficacious. Bazedoxifene has also proven its efficacy. Odanacatib, an inhibitor of cathepsin K, which is an osteoclast enzyme required for resorption of bone matrix is under assessment as an anti-resorptive agent with no antianabolic effects and is showing promising results. Anabolic agents act by stimulating formation of new bone. Novel agents in development include: antibodies to sclerostin and dickkopf-1, proteins that target molecules involved in Wnt signaling, a pathway that regulates gene transcription of proteins that are important for osteoblast function; an antagonist to the calcium-sensing receptor; and an activin receptor fusion protein, which functions as an activin antagonist and has shown promise as an anabolic agent in early human trials. Sri Lanka Journal of Diabetes, Endocrinology and Metabolism 2012; 2 : 92-100 DOI: http://dx.doi.org/10.4038/sjdem.v2i2.4779

Des-acyl ghrelin exhibits pro-anabolic and anti-catabolic effects on C2C12 myotubes exposed to cytokines and reduces burn-induced muscle proteolysis in rats

Although ghrelin and GHRP-2 have been shown to inhibit skeletal muscle proteolysis in rats with burn injury, the effects of des-acyl ghrelin (DAG) have not been reported. In this paper, we demonstrate that continuous 24h administration of DAG attenuated burn-induced EDL muscle proteolysis, and normalized elevated TNFα mRNA. Combined treatment of cultured C2C12 myotubes with TNFα and IFN-γ (TNF+IFN) inhibited protein synthesis and increased protein breakdown; DAG abolished both effects. PI3 kinase inhibition by LY294002 and mTOR inhibition by rapamycin blocked the reversal of the anti-anabolic effects of TNF+IFN-treated myotubes by DAG. DAG also reversed or attenuated the TNF+IFN-induced reduction in phosphorylation of Akt, FOXO1, 4E-BP-1, and GSK-3β in myotubes. Furthermore, DAG attenuated the atrophy signal, phospho-NF-κB, and the mRNA expression of MAFbx and MuRF1, upregulated by TNF+IFN in C2C12 myotubes. We conclude that DAG reduces muscle cachexia produced by injury and proinflammatory cytokines, and that DAG or DAG-based compounds may be useful in treating wasting disorders.

The effects of 20-hydroxyecdysone and 17β-estradiol on the skin of ovariectomized rats

20-hydroxyecdysone has numerous favorable effects on a variety of organs, including the skin, where it improves wound healing. It is devoid of estrogenic and androgenic effects. Therefore, application of 20-hydroxyecdysone might be a new approach to improve skin conditions in postmenopausal women, and this was investigated in ovariectomized (OVX) rats. After ovariectomy, rats received Ecd (18, 57, or 116 mg/animal/day) or 17β-estradiol (E₂)-3-benzoate (60 μg/kg body weight) in food for 12 weeks, and skin samples were evaluated histologically to quantify two dermal layers, the subcutaneous fat and muscle layers. Epidermal thickness was lowest in the OVX animals, slightly higher in the E₂-treated animals, and significantly higher in the Ecd-treated animals. Dermal thickness was lowest in the intact and E₂-treated animals and highest in the Ecd-treated animals. The subcutaneous fat layer was thickest in the OVX animals, thinner in the intact animals, and intermediate in the Ecd-treated animals. The muscle layer was smallest in the OVX and intact animals and significantly larger in the E₂- and Ecd-treated animals. The number of proliferating cell nuclear antigen antibody-positive cells was lowest in OVX controls and significantly higher in all other groups. The Ecd-induced increases in epidermal and dermal thickness are suggestive of functional changes of the skin. The decreased amounts of subcutaneous fat in the E₂- and Ecd-treated animals point to either a fat catabolic or an antianabolic effect. The ovariectomy-induced decrease in subcutaneous musculature was prevented by Ecd but not by E₂. The stimulatory effects of Ecd on epidermal and dermal thickness and the muscle-increasing effects in the skin of OVX rats may indicate functional changes of the skin.

Fibroblast growth factor 2: good or bad guy in the joint?

Fibroblast growth factor 2 (FGF2) is a highly abundant growth factor found within the pericellular matrix of articular chondrocytes, but studies investigating its role have been conflicting. The paper reported by Yan and colleagues in the previous issue of Arthritis Research & Therapy proposes that differences in responses to FGF2 are most likely due to changes in the balance between the two major articular cartilage FGF receptors, FGFR1 and FGFR3. They show that the catabolic and anti-anabolic effects of FGF2 are mediated primarily through FGFR1 whereas the beneficial effects are through FGFR3. This balance is dynamic and is altered in disease and following growth factor stimulation in vitro.

Psychotropic drugs have contrasting skeletal effects that are independent of their effects on physical activity levels

Popular psychotropic drugs, like the antidepressant selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), and the mood stabilizer lithium, may have skeletal effects. In particular, preclinical observations suggest a direct negative effect of SSRIs on the skeleton. A potential caveat in studies of the skeletal effects of psychotropic drugs is the hypoactive (skeletal unloading) phenotype they induce. The aim of this study was to investigate the contribution of physical inactivity to the skeletal effects of psychotropic drugs by studying bone changes in cage control and tail suspended mice treated with either vehicle, SSRI, TCA or lithium. Tail suspension was used to control for drug differences on physical activity levels by normalizing skeletal loading between groups. The psychotropic drugs were found to have contrasting skeletal effects which were independent of drug effects on animal physical activity levels. The latter was evident by an absence of statistical interactions between the activity and drug groups. Pharmacological inhibition of the 5-hydroxytryptamine (5-HT) transporter (5-HTT) using a SSRI reduced in vivo gains in lower extremity BMD, and negatively altered ex vivo measures of femoral and spinal bone density, architecture and mechanical properties. These effects were mediated by a decrease in bone formation without a change in bone resorption suggesting that the SSRI had anti-anabolic skeletal effects. In contrast, glycogen synthase kinase-3[beta] (GSK-3[beta]) inhibition using lithium had anabolic effects improving in vivo gains in BMD via an increase in bone formation, while TCA-mediated inhibition of the norepinephrine transporter had minimal skeletal effect. The observed negative skeletal effect of 5-HTT inhibition, combined with recent findings of direct and indirect effects of 5-HT on bone formation, are of interest given the frequent prescription of SSRIs for the treatment of depression and other affective disorders. Likewise, the anabolic effect of GSK-3[beta] inhibition using lithium reconfirms the importance of Wnt/beta-catenin signaling in the skeleton and it's targeting by recent drug discovery efforts. In conclusion, the current study demonstrates that different psychotropic drugs with differing underlying mechanisms of action have contrasting skeletal effects and that these effects do not result indirectly via the generation of animal physical inactivity.

Prostaglandin E2 and its cognate EP receptors control human adult articular cartilage homeostasis and are linked to the pathophysiology of osteoarthritis

To elucidate the pathophysiologic links between prostaglandin E(2) (PGE(2)) and osteoarthritis (OA) by characterizing the catabolic effects of PGE(2) and its unique receptors in human adult articular chondrocytes. Human adult articular chondrocytes were cultured in monolayer or alginate beads with and without PGE(2) and/or agonists of EP receptors, antagonists of EP receptors, and cytokines. Cell survival, proliferation, and total proteoglycan synthesis and accumulation were measured in alginate beads. Chondrocyte-related gene expression and phosphatidylinositol 3-kinase/Akt signaling were assessed by real-time reverse transcription-polymerase chain reaction and Western blotting, respectively, using a monolayer cell culture model. Stimulation of human articular chondrocytes with PGE(2) through the EP2 receptor suppressed proteoglycan accumulation and synthesis, suppressed aggrecan gene expression, did not appreciably affect expression of matrix-degrading enzymes, and decreased the type II collagen:type I collagen ratio. EP2 and EP4 receptors were expressed at higher levels in knee cartilage than in ankle cartilage and in a grade-dependent manner. PGE(2) titration combined with interleukin-1 (IL-1) synergistically accelerated expression of pain-associated molecules such as inducible nitric oxide synthase and IL-6. Finally, stimulation with exogenous PGE(2) or an EP2 receptor-specific agonist inhibited activation of Akt that was induced by insulin-like growth factor 1. PGE(2) exerts an antianabolic effect on human adult articular cartilage in vitro, and EP2 and EP4 receptor antagonists may represent effective therapeutic agents for the treatment of OA.

Correction of Metabolic Acidosis to Ameliorate Wasting in Chronic Kidney Disease: Goals and Strategies

Metabolic acidosis is an important cause of protein-energy wasting, commonly observed in chronic kidney disease (CKD). This wasting is, in part, a result of the imbalance between protein degradation and synthesis induced by metabolic acidosis. The increase in protein degradation seen with metabolic acidosis is largely secondary to increased activities of the adenosine triphosphate-dependent, ubiquitin-proteasome system and branched-chain ketoacid dehydrogenase. Studies consistently have shown increased protein degradation with lower serum bicarbonate levels and/or arterial pH; however, the evidence for the anti-anabolic effects of metabolic acidosis is less consistent. In contrast to these metabolic studies, many cross-sectional studies have shown a direct relationship between the severity of metabolic acidosis and the adequacy of nutritional status in CKD patients. Moreover, lower serum bicarbonate levels have been associated with better survival in some epidemiologic studies of patients undergoing maintenance hemodialysis. It is likely that these relationships are confounded by the direct association of dietary protein intakes with metabolic acidosis-controlling the survival data for measures of dietary protein intakes, malnutrition, and inflammation shows a rather steep increase in the risk of death with lower serum bicarbonate levels. Two randomized controlled studies have shown that correction of metabolic acidosis is associated with reduction in risk for hospitalization in chronic peritoneal dialysis patients; the studies in maintenance hemodialysis patients have been small and inconsistent. For now, metabolic studies and data from clinical trials lend support to the recommendations made by the Nutrition Workgroup of the Kidney Disease Outcomes Quality Initiative to maintain serum bicarbonate levels of 22 mEq/L or greater in all CKD patients. Limited data suggest that a higher serum bicarbonate level (around 24 mEq/L) may be even more beneficial, particularly in chronic peritoneal dialysis patients.

Cartilage biomarkers in hemodialysis patients and the effect of β 2-microglobulin on articular chondrocytes

Dialysis-related amyloidosis (DRA) is a severe complication of maintenance hemodialysis (HD). Given the predominant deposition of beta(2)-microglobulin (beta2m) fibrils on articular cartilage in early DRA, we investigated the significance of beta2m and its relationship to distinct cartilage biomarkers in early DRA diagnosis in HD patients. Furthermore, we assessed the effects of beta2m on articular chondrocytes in vitro. Serum samples from 133 patients were collected before and after HD. Type II collagen cleavage product (C2C), procollagen II c-propeptide (CPII), aggrecan chondroitin sulfate 846 epitope (CS-486) and cartilage oligomeric matrix protein (COMP) levels were determined by enzyme-linked immunosorbent assay. Primary bovine articular chondrocytes were cultured as monolayers and incubated with beta2m at 1.5mg/l and 20mg/l. Cartilage glucosaminoglycan synthesis was measured by [(35)S]sulfate incorporation. mRNA expression of interleukin (IL)-1beta, matrix metalloproteinases (MMPs)-3 and -9 was measured by reverse-transcriptase polymerase chain reaction (RT-PCR). Incubation with beta2m at 20mg/l significantly decreased matrix biosynthesis. PCR analysis revealed an increase of IL-1beta, as well as MMPs-3 and -9 on the mRNA level. C2C/CPII, CS-486 and COMP levels were increased only in a subset of patients without a significant correlation with beta2m concentrations. A subgroup analysis elucidated an increase in type II collagen degradation during the first years of HD, as shown by the elevation of C2C/CPII ratio. beta2m exerted anti-anabolic effects on articular chondrocytes in vitro and might be involved in cartilage degradation in HD patients. beta2m serum levels, however, did not reflect cartilage degradation in DRA. The assessment of C2C/CPII, CS-486 or COMP concentrations apparently has minor relevance in DRA diagnosis in HD patients. However, the increased type II collagen breakdown within 5 years after HD onset possibly mirrors the early stages of DRA. Thus, the C2C/CPII ratio could be employed in longitudinal studies, since it may reflect a risk for DRA related arthropathy development in a subset of patients.

Haem oxygenase‐1 regulates catabolic and anabolic processes in osteoarthritic chondrocytes

Pro-inflammatory cytokines, matrix metalloproteinases (MMPs) and other catabolic factors participate in the pathogenesis of cartilage damage in osteoarthritis (OA). Pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) mediate cartilage degradation and might be involved in the progression of OA. Previously, we found that haem oxygenase-1 (HO-1) is down-regulated by pro-inflammatory cytokines and up-regulated by IL-10 in OA chondrocytes. The aim of this study was to determine whether HO-1 can modify the catabolic effects of IL-1beta in OA cartilage and chondrocytes. Up-regulation of HO-1 by cobalt protoporphyrin IX significantly reduced glycosaminoglycan degradation elicited by IL-1beta in OA cartilage explants but increased glycosaminoglycan synthesis and the expression of collagen II in OA chondrocytes in primary culture, as determined by radiometric procedures, immunoblotting and immunocytochemistry. HO-1 decreased the activation of extracellular signal-regulated kinase 1/2. This was accompanied by a significant inhibition in MMP activity and expression of collagenases MMP-1 and MMP-13 at the protein and mRNA levels. In addition, HO-1 induction caused a significant increase in the production of insulin-like growth factor-1 and a reduction in the levels of insulin-like growth factor binding protein-3. We have shown in primary culture of chondrocytes and articular explants from OA patients that HO-1 counteracts the catabolic and anti-anabolic effects of IL-1beta. Our data thus suggest that HO-1 may be a factor regulating the degradation and synthesis of extracellular matrix components in OA.