Involvement of PKC-beta in PTH, TNF-alpha, and IL-1 beta effects on IL-6 promoter in osteoblastic cells and on PTH-stimulated bone resorption

HCV co-infection among people living with HIV Is associated with Higher fracture risk

INTRODUCTION

The purpose of this study was to predict the 10-year risk of fracture among people living with HIV (PLWH) using FRAX™, and to determine the risk factors related to a high probability of fractures.

METHODOLOGY

This study consisted of 288 subjects aged 40 years and above. The ten-year probability of major osteoporotic fractures (MOF) and hip fractures was assessed using the FRAX™ algorithm with bone mineral density (BMD) data. A logistic regression was used to determine risk factors related to a high probability of major osteoporotic fracture and hip fracture.

RESULTS

The median 10-year probability of fracture was 3.7% (IQR 2.2-6.2) for MOF and 0.8% (IQR 0.3-2.5) for hip fractures. In addition to old age, previous fracture history, and low T-scores, HCV co-infection was associated with a higher risk of hip fractures in PLWH (AOR: 4.3, 95% CI: 1.29-14.33). Old age and low T-scores were also associated with a high probability of MOF.

CONCLUSIONS

HCV co-infection among PLWH is associated with a higher risk of hip fracture. Sustained efforts in terms of pharmacologic and non-pharmacologic interventions in PLWH are necessary to prevent osteoporotic fractures, especially in those with HCV co-infections.

Veterans Aging Cohort Study Index as a Marker of Bone Disease in HIV-Infected Patients

People living with human immunodeficiency virus (HIV) infection have higher risk of low bone mineral density (BMD) and fragility fracture than general population. The aim of our retrospective study was to explore if HIV-specific Veterans Aging Cohort Study (VACS) Index and its specific components could help identify patients at risk for low BMD. A total of 195 HIV-infected patients with dual-energy X-ray absorptiometry (DXA) scan between 2007 and 2014 were included and DXA scan results were used to classify patients with osteopenia. VACS Index was calculated for all patients using laboratory values closest to the date of DXA scan. Logistic regression was used to assess the association between VACS Index score or individual components of VACS Index with the presence of low BMD after adjusting for confounding variables. A total of 109 (56%) patients were diagnosed with low BMD. VACS Index score was significantly associated with low BMD, with the odds of low BMD increasing 1.21 times for each 10 unit increase in VACS Index score [confidence interval (95% CI) 1.03-1.42; p = .02]. The two groups differed significantly on patient weights, proportion of white patients, and hepatitis C-coinfected patients. After adjusting for white race and weight, hepatitis C coinfection was significantly associated with increased risk of low BMD (odds ratio 24.4; 95% CI 7.45-80.16). VACS Index score, previously demonstrated to be a marker of frailty in HIV-infected patients, is significantly associated with risk of low BMD and could be used to develop a prediction tool to screen for low BMD in resource-limited setting where DXA scans are not easily available.

Improved fracture prediction using different fracture risk assessment tool adjustments in HIV-infected women

OBJECTIVES

A fracture risk assessment tool (FRAX) using clinical risk factors (CRFs) alone underestimates fracture risk in HIV-infected men. Our objective was to determine whether accuracy of FRAX would be improved by considering HIV as a cause of secondary osteoporosis, and further improved with addition of dual-energy X-ray absorptiometry parameters in HIV-infected women.

DESIGN

Subgroup analysis of Women's Interagency HIV Study.

METHODS

We included 1148 women (900 HIV-infected and 248 uninfected) over age 40 with data to approximate FRAX CRFs and 10-year observational data for incident fragility fractures; 181 (20%) HIV-infected women had dual-energy X-ray absorptiometry data. Accuracy of FRAX was evaluated by the observed/estimated ratios of fracture in four models: CRFs alone; CRFs with HIV included as a cause of secondary osteoporosis; CRFs and femoral neck bone mineral density (FN BMD); and CRFs, FN BMD and trabecular bone score.

RESULTS

FRAX using CRFs were less accurate in HIV-infected than uninfected women for major osteoporotic (observed/estimated ratio: 5.05 vs. 3.26, P < 0.001) and hip fractures (observed/estimated ratio: 19.78 vs. 7.94, P < 0.001), but improved when HIV was included as a cause of secondary osteoporosis. Among HIV-infected women, FRAX accuracy improved further with addition of FN BMD (observed/estimated ratio: 4.00) for hip fractures, but no further with trabecular bone score.

CONCLUSION

FRAX using CRFs alone underestimated fracture risk more in older HIV-infected women than otherwise similar uninfected women. Accuracy is improved when including HIV as a cause of secondary osteoporosis for both major osteoporotic and hip fractures, whereas addition of FN BMD only improved accuracy for hip fracture.

Hepatitis C virus coinfection as a risk factor for osteoporosis and fracture

PURPOSE OF REVIEW

With increased survival of HIV-infected patients, osteoporotic fractures have developed as a major cause of morbidity in these patients, and chronic hepatitis C virus (HCV) coinfection has emerged as a significant contributor to this increased fracture risk. The present article reviews the epidemiologic and clinical evidence for osteoporosis and increased fracture risk among HIV/HCV coinfected patients, and potential mechanisms for these outcomes with HCV coinfection.

RECENT FINDINGS

Epidemiologic studies suggest that HIV/HCV coinfected patients exhibit a three-fold increased fracture incidence compared with uninfected controls, and 1.2-2.4-fold increased fracture risk compared with HIV monoinfected patients. Recent reports suggest that chronic HCV coinfection is independently associated with reduced bone mineral density in HIV, but that it is not associated with significantly increased bone turnover. The deleterious impact of chronic HCV on BMD and fracture risk occurs even in the absence of advanced liver fibrosis or cirrhosis. New tools to assess bone quality, including the trabecular bone score, high-resolution peripheral quantitative computed tomography, and in-vivo microindentation, may help improve understanding of the mechanisms of HCV-associated skeletal fragility. The impact of approved antiosteoporosis medications and direct-acting antivirals for the treatment of chronic HCV infection on patients' bone health remain to be studied.

SUMMARY

Chronic HCV infection is an independent risk factor for osteoporosis and fractures among HIV-infected patients, even before the development of cirrhosis. The underlying mechanisms are being unraveled, but major questions persist regarding the optimal evaluation and management of bone health in HIV/HCV coinfected patients.

Structural Bone Deficits in HIV/HCV-Coinfected, HCV-Monoinfected, and HIV-Monoinfected Women

BACKGROUND

Coinfection with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) is associated with reduced bone mineral density (BMD) and increased fracture rates, particularly in women. The structural underpinnings for skeletal fragility in coinfected women have not been characterized. We used tibial peripheral quantitative computed tomography to evaluate skeletal parameters in women, by HIV/HCV status.

METHODS

We conducted a cross-sectional study among 50 HIV/HCV-coinfected, 51 HCV-monoinfected, and 50 HIV-monoinfected women. Tibial volumetric BMD and cortical dimensions were determined with peripheral quantitative computed tomography. Race-specific z scores for age were generated using 263 female reference participants without HIV infection or liver disease.

RESULTS

Coinfected participants had lower mean z scores for trabecular volumetric BMD (-0.85), cortical volumetric BMD (-0.67), cortical area (-0.61), and cortical thickness (-0.77) than reference participants (all P < .001). The smaller cortical dimensions were due to greater mean z scores for endosteal circumference (+0.67; P < .001) and comparable z scores for periosteal circumference (+0.04; P = .87). Trabecular volumetric BMD was lower in coinfected than in HCV- or HIV-monoinfected participants. HCV-infected women with stage 3-4 liver fibrosis had lower mean z scores for trabecular volumetric BMD, cortical thickness, and total hip BMD those with stage 0-2 fibrosis.

CONCLUSIONS

Compared with healthy reference patients, HIV/HCV-coinfected women had decreased tibial trabecular volumetric BMD, diminished cortical dimensions, and significant endocortical bone loss.

Biologics in paediatric Crohn's disease

Crohn's disease affects increasing numbers of children worldwide. Generally, childhood-onset disease runs a more severe course than in adults and has a greater impact on quality of life. Therapy in children must take account of a different set of risks for toxicity compared to adults, but also to their longevity. Biologic drugs present remarkable advantages in terms of disease control for children, especially in those whose disease cannot be controlled with conventional therapies, but their long-term risks are still being assessed. Data regarding biologic use in children is limited and mostly amounts to case series, but results have been promising, both in terms of controlling disease activity and improving growth parameters. Adverse reactions are infrequent in the short term, but loss of response is a long-term problem, particularly in children. More information is needed about very long term risks. Infliximab and adalimumab are the most studied agents in children, while there is relatively limited data on certolizumab and natalizumab. Further collection of data on these agents is still needed, but this should not restrict access to these agents for children in whom no other agent is effective.

Pediatric inflammatory bowel disease and bone health

Childhood and adolescence are important periods for bone development. Any disease that affects bone health has the potential to affect the bones not only in the short term but also later in life. Bone health abnormalities in patients with inflammatory bowel disease are being increasingly recognized. Screening the at-risk patient is important so that appropriate treatments can be instituted. Treatment options are limited to vitamin D and calcium supplementation, control of underlying disease activity, and appropriate physical activity. The role of bisphosphonates in these patients needs to be better studied, and treatment with bisphosphonates may be considered for some patients in consultation with a bone health expert.

Improvement in biomarkers of bone formation during infliximab therapy in pediatric Crohn's disease: results of the REACH study

BACKGROUND & AIMS

Crohn's disease (CD) is associated with altered bone metabolism. This study examined changes in bone formation and resorption after infliximab induction and associations between bone biomarkers, linear growth, and disease activity (Pediatric Crohn's Disease Activity Index [PCDAI]) after 54 weeks of infliximab therapy.

METHODS

One hundred twelve subjects ages 6-17 years with moderate to severe CD received infliximab induction (5 mg/kg/dose) at weeks 0, 2, and 6; week-10 responders were randomized to infliximab every 8 or every 12 weeks maintenance therapy. Serum bone-specific alkaline phosphatase (BSAP), N-terminal propeptide of type 1 collagen (P1NP), urine C-telopeptide of collagen cross-links (CTX-1), and deoxypyrodinoline (DPD) were collected at baseline and 10 weeks. PCDAI and height z-scores were assessed at baseline and at 10 and 54 weeks.

RESULTS

Models were adjusted for bone age, gender, height, and steroid use. Baseline BSAP and P1NP levels were negatively associated with PCDAI (both P = .01). BSAP and P1NP increased during induction (both P < .001) and were associated with 54-week increases in height z-score (P < .05 and P < .001, respectively). Improvements in P1NP were associated with 54-week decreases in PCDAI (P = .01). CTX-1 and DPD also increased during induction (P < .001 and P = .01, respectively) but were not associated with changes in PCDAI. Changes in CTX-1 were associated with improvements in height z-score (P < .002).

CONCLUSIONS

Infliximab therapy is associated with dramatic increases in BSAP and P1NP, consistent with inhibition of tumor necrosis factor-alpha effects on osteoblasts. The increases in CTX-1 and DPD likely reflect coupling of bone formation and resorption and increases in linear growth.

Regulation of matrix Gla protein by parathyroid hormone in MC3T3-E1 osteoblast-like cells involves protein kinase A and extracellular signal-regulated kinase pathways

Inhibition of osteoblast-mediated mineralization is one of the major catabolic effects of parathyroid hormone (PTH) on bone. Previously, we showed that PTH induces matrix gamma-carboxyglutamic acid (Gla) protein (MGP) expression and established that this induction is critical for PTH-mediated inhibition of osteoblast mineralization. In the present study, we focus on the mechanism through which PTH regulates MGP expression in osteoblastic MC3T3-E1 cells. Following transient transfection of these cells with a -748 bp murine MGP promoter-luciferase construct (pMGP-luc), PTH (10 (-7) M) induced promoter activity in a time-dependent manner with a maximal four- to six fold induction seen 6 h after PTH treatment. Both H-89 (PKA inhibitor) and U0126 (MEK inhibitor), suppressed PTH induction of MGP promoter activity as well as the MGP mRNA level. In addition, forskolin (PKA activator) stimulated MGP promoter activity and mRNA levels confirming that PKA is one of the signaling molecules required for regulation of MGP by PTH. Co-transfection of MC3T3-E1 cells with pMGP-luc and MEK(SP), a plasmid encoding the constitutively active form of MEK, led to a dose-dependent increase in MGP promoter activity. Both MGP promoter activity and MGP mRNA level were not affected by the protein kinase C (PKC) inhibitor, GF109203X. However, phorbol 12-myristate 13-acetate (PMA), a selective PKC activator induced MGP mRNA expression through activation of extracellular signal-regulated kinase (ERK). Taken together, these results indicate that PTH regulates MGP via both PKA- and ERK-dependent pathways.

Parathyroid hormone stimulates expression of the Notch ligand Jagged1 in osteoblastic cells

We previously demonstrated that activation of the Parathyroid Hormone Receptor (PTH1R) in osteoblastic cells increases the Notch ligand Jagged1 and expands hematopoietic stem cells (HSC) through Notch signaling. However, regulation of Jagged1 by PTH in osteoblasts is poorly understood. The present study demonstrates that PTH treatment increases Jagged1 levels in a subpopulation of osteoblastic cells in vivo and in UMR106 osteoblastic cells in vitro. Since PTH(1-34) activates both Adenylate Cyclase/Protein Kinase A (AC/PKA) and Protein Kinase C (PKC) downstream of the PTH1R in osteoblastic cells, we independently determined the effect of either pathway on Jagged1. Activation of AC with Forskolin or PKA with PTH(1-31) or cell-permeable cAMP analogues increased osteoblastic Jagged1. This PTH-dependent Jagged1 increase was blocked by H89 and PKI, specific PKA inhibitors. In contrast, PKC activation with phorbol ester (PMA) or PTH(13-34) did not stimulate Jagged1 expression, and PTH-dependent Jagged1 stimulation was not blocked by Gö6976, a conventional PKC inhibitor. Therefore, PTH treatment stimulates osteoblastic Jagged1 mainly through the AC/PKA signaling pathway downstream of the PTH1R. Since Jagged1/Notch signaling has been implicated not only in stromal-HSC interactions but also in osteoblastic differentiation, Jagged1 may play a critical role in mediating the PTH-dependent expansion of HSC, as well as the anabolic effect of PTH in bone.

Effects of calcitriol on type 5b tartrate-resistant acid phosphatase and interleukin-6 in secondary hyperparathyroidism

BACKGROUND/AIMS

Secondary hyperparathyroidism (SHP) is characterized by high bone turnover and elevated serum bone remodeling markers. Elevation of serum interleukin-6 (IL-6) levels is also characteristic of end-stage renal disease. This study investigates the effects of intravenous calcitriol on serum bone resorptive markers, namely, type 5b tartrate-resistant acid phosphatase (TRACP5b) and IL-6 in patients with SHP.

METHODS

Intravenous calcitriol therapy was given for 16 weeks to 24 patients on maintenance hemodialysis with plasma intact parathyroid hormone (iPTH) levels >300 pg/ml. Blood was drawn at baseline and every 4 weeks for 16 weeks for determination of the levels of biochemical parameters, iPTH, IL-6 and bone remodeling markers, including bone-specific alkaline phosphatase (bAP) and TRACP5b.

RESULTS

Only 21 patients responded to the calcitriol therapy, with significant decrements in serum iPTH after 4 weeks of therapy and thereafter. After 16 weeks of calcitriol therapy, 21 patients had significant decrements in serum iPTH (707.9 +/- 317.8 vs. 205.0 +/- 63.1 pg/ml, p < 0.01). Prior to treatment, a significant correlation was found between increased levels of serum iPTH and IL-6 levels (r = 0.45, p < 0.05). After treatment, there was also a significant and parallel lowering of levels of serum iPTH, IL-6 (8.52 +/- 3.59 vs. 7.24 +/- 2.81 pg/ml, p < 0.01), bAP (54.68 +/- 36.17 vs. 24.55 +/- 13.84 U/l, p < 0.01) and TRACP5b (3.41 +/- 1.89 vs. 1.80 +/- 0.55 U/l, p < 0.01). Our results additionally showed significant positive correlationsbetween baseline levels of serum IL-6 and those of iPTH, bAP and TRACP5b. After 16 weeks of calcitriol treatment, the correlation between IL-6 and iPTH levels lost significance but levels of serum IL-6, bAP and TRACP5b remained significantly correlated.

CONCLUSIONS

Elevated levels of serum IL-6 and bone remodeling markers, namely, bAP and TRACP5b which are common features of SHP, are effectively suppressed by calcitriol therapy. This indicates that hyperparathyroidism not only accelerates bone remodeling but may also aggravate inflammation in patients on maintenance hemodialysis.

Parathyroid hormone activates PKC-delta and regulates osteoblastic differentiation via a PLC-independent pathway

PTH exerts major effects upon bone by activating PTH/PTHrP receptors (PTH1Rs) expressed on osteoblasts. The PTH1R is capable of engaging multiple signaling pathways in parallel, including Gs/adenylyl cyclase (AC), Gq/phospholipase C/protein kinase C (PLC/PKC) and a distinct mechanism, involving activation of PKC via a PLC-independent pathway, that depends upon ligand determinants within the PTH(29-34) sequence. The involvement of PLC-dependent vs. PLC-independent PKC activation in PTH action was studied in clonal PTH1R-expressing murine calvarial osteoblasts ("Wt9") using two signal-selective analogs, [G1,R19]hPTH(1-28) and [G1,R19]hPTH(1-34). Both analogs lack PLC signaling but differ in their capacity to activate the PLC-independent PKC pathway. Both hPTH(1-34) and [G1,R19]hPTH(1-34), but not [G1,R19]hPTH(1-28), increased differentiation of Wt9 cells during a 16-day alternate-daily treatment protocol. Wt9 cells expressed PKC-betaI, -delta, -epsilon and -zeta, none of which exhibited net translocation to membranes in response to hPTH(1-34) or either analog. hPTH(1-34) induced activation of membrane-associated PKC-delta, however, and a time- and concentration-dependent increase in cytosolic [phospho-Thr505]PKC-delta which was maximal within 40 s at 100 nM in both Wt9 cells and primary osteoblasts. This response was mimicked by [G1,R19]hPTH(1-34) but not by [G1,R19]hPTH(1-28). Increased expression of bone sialoprotein (BSP) and osteocalcin (OC) mRNAs induced by PTH(1-34) and [G1,R19]hPTH(1-34) in Wt9 cells was blocked by rottlerin, a PKC-delta inhibitor. We conclude that PTH1Rs activate PKC-delta by a PLC-independent, PTH(29-34)-dependent mechanism that promotes osteoblastic differentiation.

Treatment with infliximab is associated with increased markers of bone formation in patients with Crohn's disease

OBJECTIVE

Osteoporosis is a common complication of Crohn's disease (CD). Glucocorticoid use and detrimental effects of inflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha) can lead to osteoporosis. The aim of this study was to assess the ability of treatment with the TNF-alpha antagonist infliximab to increase bone formation as measured by surrogate markers of bone turnover in patients with active CD.

METHODS

Sera from 38 prospectively enrolled CD patients were examined for levels of bone alkaline phosphatase (BAP), N-telopeptide of type I collagen (NTX), immunoreactive parathyroid hormone (iPTH), calcium, and pro-inflammatory cytokines at baseline and 4 weeks following infliximab infusion. Crohn's Disease Activity Index (CDAI), Inflammatory Bowel Disease Questionnaire (IBDQ), and glucocorticoid dose also were collected.

RESULTS

In this cohort, CDAI and IBDQ scores were significantly improved at week 4 (P<0.001). Infliximab therapy was associated with an increase in BAP, a marker of bone formation (P=0.010), whereas NTX, a marker of bone resorption, was not increased (P=0.801). Among 22 patients who were taking glucocorticoids, mean glucocorticoid dose decreased 36% (P<0.001; -7.9 mg).

CONCLUSIONS

Treatment with infliximab was associated with increased markers of bone formation (BAP) without increasing bone resorption (NTX). This effect may be due to a beneficial effect of TNF-alpha blockade on bone turnover, a beneficial effect on CD activity resulting in decreased glucocorticoid dose, or both. Studies of longer duration are needed to assess the effect of infliximab on bone mineral density.

IL-1β Induces IL-6 Expression in Human Orbital Fibroblasts: Identification of an Anatomic-Site Specific Phenotypic Attribute Relevant to Thyroid-Associated Ophthalmopathy

Human orbital fibroblasts exhibit a unique inflammatory phenotype. In the present study, we report that these fibroblasts, when treated with IL-1beta, express high levels of IL-6, a cytokine involved in B cell activation and the regulation of adipocyte metabolism. The magnitude of this induction is considerably greater than that in dermal fibroblasts and involves up-regulation of IL-6 mRNA levels. IL-1beta activates both p38 and ERK 1/2 components of the MAPK pathways. Disrupting these could attenuate the IL-6 induction. The up-regulation involves enhanced IL-6 gene promoter activity and retardation of IL-6 mRNA decay by IL-1beta. Dexamethasone completely blocked the effect of IL-1beta on IL-6 expression. Orbital fibroblasts also express higher levels of IL-6R than do skin-derived cells. When treated with rIL-6 (10 ng/ml), STAT3 is transiently phosphorylated. Thus, the exaggerated capacity of orbital fibroblasts to express high levels of both IL-6 and its receptor in an anatomic site-selective manner could represent an important basis for immune responses localized to the orbit in Graves' disease.

Rho and Rho kinase are involved in parathyroid hormone-stimulated protein kinase C alpha translocation and IL-6 promoter activity in osteoblastic cells

The role of small G-proteins in PTH-stimulated PKC translocation and IL-6 promoter expression in UMR-106 cells was determined. The effects of PTH(1-34) and PTH(3-34) in stimulating PKCalpha translocation and IL-6 were inhibited by agents that interfere with the activity of small G-proteins of the Rho family and with the downstream kinase Rho kinase.

INTRODUCTION

Activation of protein kinase C (PKC) is a signaling mechanism by which parathyroid hormone (PTH) modulates interleukin-6 (IL-6) in osteoblasts, leading to osteoclastogenesis and bone resorption. PKCalpha and PKCbetaI are translocated after treatment with PTH in UMR-106 osteoblastic cells; however, the pathway leading to PKC isozyme translocation is not established. Diacylglycerol (DAG) generation from phospholipase D (PLD) is one pathway of PKC activation, and PTH-mediated PLD activity is dependent on small G-proteins of the Rho family. This study investigated whether Rho proteins modulate the PKCalpha translocation and IL-6 promoter activity stimulated by PTH in UMR-106 cells.

MATERIALS AND METHODS

UMR-106 cells were treated with PTH(1-34) or PTH(3-34). PKC translocation was determined by immunofluorescence, Rho A activation by Rhotekin assay and by translocation assessed by Western blotting in membrane and cytosol fractions, and IL-6 promoter expression by luciferase assay.

RESULTS AND CONCLUSIONS

Inhibition of Rho proteins with Clostridium difficile toxin B or inhibition of Rho prenylation with GGTI attenuated PTH(1-34)- and PTH(3-34)-stimulated translocation of endogenous PKCalpha and IL-6 promoter activity. Expression of a constitutively active RhoA (RhoA63L) mimicked the effect of PTH(1-34) or PTH(3-34) to promote membrane localization of PKCalpha, whereas cells expressing a dominant negative RhoA (RhoA19N) did not respond to PTH(1-34) or PTH(3-34). The Rho kinase inhibitor Y27632 attenuated PTH(1-34)- and PTH(3-34)-stimulated PKCalpha translocation and IL-6 promoter activation. Rho seemed to be acting at a step before production of diacylglycerol (DAG), because the stimulation of PKCalpha translocation by the DAG mimetic phorbol 12,13 dibutyrate (PDBu) was unaffected by C. difficile toxin B or Y27632. These results indicate that Rho proteins are an important component of PTH signaling in osteoblastic cells and provide further demonstration of convergence between PKC and small G-protein signaling pathways.

Tumor necrosis factor-alpha in diabetic plasma increases the activity of core 2 GlcNAc-T and adherence of human leukocytes to retinal endothelial cells: significance of core 2 GlcNAc-T in diabetic retinopathy

A large body of evidence now implicates increased leukocyte-endothelial cell adhesion as a key early event in the development of diabetic retinopathy. We recently reported that raised activity of the glycosylating enzyme core 2 beta 1,6-N-acetylglucosaminyltransferase (GlcNAc-T) through protein kinase C (PKC)beta2-dependent phosphorylation plays a fundamental role in increased leukocyte-endothelial cell adhesion and capillary occlusion in retinopathy. In the present study, we demonstrate that following exposure to plasma from diabetic patients, the human promonocytic cell line U937 exhibits a significant elevation in core 2 GlcNAc-T activity and increased adherence to cultured retinal capillary endothelial cells. These effects of diabetic plasma on enzyme activity and cell adhesion, mediated by PKCbeta2-dependent phosphorylation of the core 2 GlcNAc-T protein, were found to be triggered by increased plasma levels of tumor necrosis factor (TNF)-alpha. Levels of enzyme activity in plasma-treated U937 cells were closely dependent on the severity of diabetic retinopathy, with the highest values observed upon treatment with plasma of patients affected by proliferative retinopathy. Furthermore, we noted much higher correlation, as compared with control subjects, between increased values of core 2 GlcNAc-T activity and cell adhesion properties. Based on the prominent role of TNF-alpha in the development of diabetic retinopathy, these observations further validate the significance of core 2 GlcNAc-T in the pathogenesis of capillary occlusion, thereby enhancing the therapeutic potential of specific enzyme inhibitors.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.

Impact of the mitogen-activated protein kinase pathway on parathyroid hormone-related protein actions in osteoblasts

Parathyroid hormone-related protein (PTHrP) regulates proliferation and differentiation of osteoblastic cells via binding to the parathyroid hormone receptor (PTH-1R). The cAMP-dependent protein kinase A pathway governs the majority of these effects, but recent evidence also implicates the MAPK pathway. MC3T3-E1 subclone 4 cells (MC4) were treated with the MAPK inhibitor U0126 and PTHrP. In differentiated MC4 cells, osteocalcin and bone sialoprotein gene expression were both down-regulated by PTHrP and also by inhibition of the MAPK pathway. PTHrP-mediated down-regulation of PTH-1R mRNA and up-regulation of c-fos mRNA were MAPK-independent, whereas PTHrP stimulation of fra-2 and interleukin-6 (IL-6) mRNA was MAPK-dependent. Luciferase promoter assays revealed that regulation of IL-6 involved the cAMP-dependent protein kinase A and MAPK pathways with a potential minor role of the protein kinase C pathway, and a promoter region containing an activator protein-1 site was necessary for PTHrP-induced IL-6 gene transcription. An alternative pathway, through cAMP/Epac/Rap1/MAPK, mediated ERK phosphorylation but was not sufficient for IL-6 promoter activation. Phosphorylation of the transcription factor CREB was also necessary but not sufficient for PTHrP-mediated IL-6 promoter activity. Most interesting, a bidirectional effect was found with PTHrP increasing phosphorylated ERK in undifferentiated MC4 cells but decreasing phosphorylated ERK in differentiated cells. These data indicate that inactivation of the MAPK pathway shows differential regulation of PTHrP-stimulated activator protein-1 members, blocks PTHrP-stimulated IL-6, and synergistically down-regulates certain osteoblastic markers associated with differentiation. These novel findings indicate that the MAPK pathway plays a selective but important role in the actions of PTHrP.

Characterization of the Interaction of Ingenol 3-Angelate with Protein Kinase C

Ingenol 3-angelate (I3A) is one of the active ingredients in Euphorbia peplus, which has been used in traditional medicine. Here, we report the initial characterization of I3A as a protein kinase C (PKC) ligand. I3A bound to PKC-alpha in the presence of phosphatidylserine with high affinity; however, under these assay conditions, little PKC isoform selectivity was observed. PKC isoforms did show different sensitivity and selectivity for down-regulation by I3A and phorbol 12-myristate 13-acetate (PMA) in WEHI-231, HOP-92, and Colo-205 cells. In all of the three cell types, I3A inhibited cell proliferation with somewhat lower potency than did PMA. In intact CHO-K1 cells, I3A was able to translocate different green fluorescent protein-tagged PKC isoforms, visualized by confocal microscopy, with equal or higher potency than PMA. PKC-delta in particular showed a different pattern of translocation in response to I3A and PMA. I3A induced a higher level of secretion of the inflammatory cytokine interleukin 6 compared with PMA in the WEHI-231 cells and displayed a marked biphasic dose-response curve for the induction. I3A was unable to cause the same extent of association of the C1b domain of PKC-delta with lipids, compared with PMA or the physiological regulator diacylglycerol, and was able to partially block the association induced by these agents, measured by surface plasmon resonance. The in vitro kinase activity of PKC-alpha induced by I3A was lower than that induced by PMA. The novel pattern of behavior of I3A makes it of great interest for further evaluation.

Role of protein kinase A, phospholipase C and phospholipase D in parathyroid hormone receptor regulation of protein kinase Cα and interleukin-6 in UMR-106 osteoblastic cells

Parathyroid hormone (PTH) stimulates both bone formation and resorption by activating diverse osteoblast signalling pathways. Upstream signalling for PTH stimulation of protein kinase C-alpha (PKCalpha) membrane translocation and subsequent expression of the pro-resorptive cytokine interleukin-6 (IL-6) was investigated in UMR-106 osteoblastic cells. PTH 1-34, PTH 3-34, PTHrP and PTH 1-31 stimulated PKCalpha translocation and IL-6 promoter activity. Pharmacologic intervention at the adenylyl cyclase (AC) pathway (forskolin, IBMX, PKI) failed to alter PTH 1-34- or PTH 3-34-stimulated PKCalpha translocation. The phosphoinositol-phospholipase C (PI-PLC) antagonist U73122 slightly decreased PTH 1-34-stimulated PKCalpha translocation; however, the control analogue U73343 acted similarly. Propranolol, an inhibitor of phosphatidic acid (PA) phosphohydrolase, decreased diacylglycerol (DAG) formation and attenuated PTH 1-34- and PTH 3-34-stimulated PKCalpha translocation and IL-6 promoter activity, suggesting a phospholipase D (PLD)-dependent mechanism. This is the first demonstration that PLD-mediated signalling leads to both PKC-alpha translocation and IL-6 promoter activation in osteoblastic cells.

The pathophysiology of bone disease in gastrointestinal disease

Reduced bone mass and the increased risk of fracture in gastrointestinal diseases have a multifactorial pathogenesis. Undoubtedly, genetics play an important role, but other factors such as systemic inflammation, malnutrition, hypogonadism, glucocorticoid therapy in inflammatory bowel disease (IBD) and other lifestyle factors, such as smoking or being sedentary, may contribute to reduced bone mass. At a molecular level the proinflammatory cytokines that contribute to the intestinal immune response in IBD and probably also in coeliac disease are also known to enhance bone resorption. The discovery of the role of the receptor to activated NFkappaB (RANK) interaction with its ligand RANKL in orchestrating the balance between bone resorption and formation may link mucosal and systemic inflammation with bone remodelling, since RANK-RANKL are also involved in lymphopoiesis and T-cell apoptosis. Low circulating leptin in response to weight loss in any gastrointestinal disease may be an important factor in reducing bone mass. This report will summarize current concepts regarding gastrointestinal diseases (primarily IBD, coeliac disease and postgastrectomy states) and low bone mass and fracture.

IL-1beta, TNF-alpha, TGF-beta, and bFGF expression in bone biopsies before and after parathyroidectomy

BACKGROUND

There is growing evidence pointing to an involvement of cytokines and growth factors in renal osteodystrophy. In this study, the expression of interleukin-l beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta), and basic fibroblast growth factor (bFGF) in bone biopsies taken from uremic patients before and 1 year after parathyroidectomy (PTX) was evaluated. Biochemical features and histomorphometric outcome were also studied.

METHODS

Iliac bone biopsies were taken before and 1 year after PTX in nine uremic patients with severe hyperparathyroidism (HPT). Immunohistochemical techniques were used to identify the expression of IL-1 beta, TNF-alpha, TGF-beta, and bFGF in these bone samples.

RESULTS

At the time of the second bone biopsy, the mean serum total alkaline phosphatase activity was normal, whereas mean serum intact parathyroid hormone (iPTH) level was slightly above the upper limit of normal values. Histomorphometric analysis showed a decrease in resorption parameters and static bone formation parameters after PTX. Dynamically, mineral apposition rate (MAR) and mineralization surface (MS/BS) decreased significantly. There was a marked local expression of IL-1beta, TNF-alpha, TGF-beta, and bFGF in bone biopsies before PTX, particularly in fibrous tissue and resorption areas. One year after PTX, IL-1beta decreased from 23.6 +/- 7.5% to 9.9 +/- 3.1%, TNF-alpha from 4.5 +/- 1.5% to 0.7 +/- 0.8%, TGF-beta from 49.6 +/- 9.8% to 15.2 +/- 4.6%, and bFGF from 50.9 +/- 12.7% to 12.9 +/- 7.9% (P < 0.001). A significant correlation was documented between cytokines and growth factors expression in bone with iPTH levels before and after PTX (P < 0.05).

CONCLUSIONS

Based on these results, we suggest that IL-1beta, TNF-alpha, TGF-beta, and bFGF are involved in bone remodeling regulation, acting as local effectors, possibly under the control of PTH.

Participation of protein kinase C beta in osteoclast differentiation and function

Protein kinase C (PKC) proteins have been shown to be involved in diverse cellular responses of various cell types. In experiments to identify genes regulated during osteoclast differentiation by a cDNA microarray approach, we found that the gene expression of PKC-betaII was upregulated in differentiated cells. Reverse transcription-polymerase chain reaction and Western blotting analyses also showed an increase in PKC-betaI as well as PKC-betaII during osteoclast formation in mouse bone marrow cell cultures in the presence of macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB ligand (RANKL). Use of an antisense oligonucleotide to PKC-betaII resulted in a reduction in the RANKL-driven osteoclastogenesis. Pharmacological intervention with PKC-beta activity by the specific inhibitor CG53353 suppressed cellular differentiation and fusion processes during osteoclastogenesis and inhibited bone-resorbing function of mature osteoclasts. PKC-beta inhibition abolished the ERK and MEK activation by macrophage-colony stimulating factor and RANKL in osteoclast precursor cells whereas the cytokine-induced NF-kappaB activation was not hampered by the PKC-beta inhibition. Our findings indicate that PKC-beta has a role in regulation of osteoclast formation and function potentially by participating in the ERK signaling pathway of M-CSF and RANKL.

Therapeutic Effects of Hominis placenta Injection into an Acupuncture Point on the Inflammatory Responses in Subchondral Bone Region of Adjuvant-Induced Polyarthritic Rat

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the synovial membrane in the joint, which leads to the progressive destruction of articular cartilage, ligament and bone. Several cytokines such as tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta), and interleukin 6 (IL-6) have been implicated in the pathological mechanisms of synovial tissue proliferation, joint destruction and programmed cell death in rheumatoid joint. In the Korean traditional medicine, Hominis placenta (HP) as an herbal component of herb-acupuncture has been widely used to treat chronic inflammatory diseases such as RA. To study the therapeutic effects of HP injection into the ST36 acupoint (HP herb-acupuncture) on the inflammatory responses of a subchondral region of rheumatoid joint, the polyarthritis-induced Sprague-Dawley (SD) rat was developed as a rheumatoid arthritis model by the intradermal injection of dried cells of Mycobacterium tuberculosis emulsified in squalene to the base of tail. After the onset stage (11 d after adjuvant injection) of polyarthritis, a fixed volume of HP extract was daily injected to Zusanli (ST36) acupoint on the rat's leg for 2 weeks. The body weight, paw volume of the knee joint and articular index were exploited as an assessment method addressing arthritic symptoms, and the expression profiles of TNF-alpha, IL-1beta and IL-6 at the subchondral bone of the joint were analyzed using an immunohistochemistry. After the treatment of arthritic rats with HP, the body weights and paw volumes of arthritic rats were almost restored to the levels of normal rats whereas the evaluation by the articular index was not remarkable. The TNF-alpha, IL-1beta and IL-6 positive cells in the immunohistological sections of subchondral bone region of the joint significantly decreased in HP-treated (ST36 acupoint) arthritic group as compared with those in non-treated or HP-treated (non-acupoint) ones, which was coincident with the behavioral studies. In conclusion, the HP herb-acupuncture was found to be effective to alleviate the arthritic symptoms in adjuvant-induced arthritis rats as regards the body weight, joint appearance and the expression profiles of inflammatory cytokines.

The PTH/PTHrP receptor can delay chondrocyte hypertrophy in vivo without activating phospholipase C

One G protein-coupled receptor (GPCR) can activate more than one G protein, but the physiologic importance of such activation has not been demonstrated in vivo. We have generated mice expressing exclusively a mutant form of the PTH/PTHrP receptor (DSEL) that activates adenylyl cyclase normally but not phospholipase C (PLC). DSEL mutant mice exhibit abnormalities in embryonic endochondral bone development, including delayed ossification and increased chondrocyte proliferation. Analysis of the differentiation of embryonic metatarsals in vitro shows that PTH(1-34) and forskolin inhibit, whereas active phorbol ester stimulates, hypertrophic differentiation. Thus, PLC signaling via the PTH/PTHrP receptor normally slows the proliferation and hastens the differentiation of chondrocytes, actions that oppose the dominant effects of PTH/PTHrP receptors and that involve cAMP-dependent signaling pathways.

Expression and function of classical protein kinase C isoenzymes in gastric cancer cell line and its drug-resistant sublines

AIM: To investigate the expression and function of classical protein kinase C (PKC) isoenzymes in inducing MDR phenotype in gastric cancer cells.

METHODS: Two cell lines were used in the study: gastric cancer cell SGC7901 and its drug-resistant cell SGC7901/VCR stepwise-selected by vincristine 0.3, 0.7 and 1.0 mg·L^-1, respectively. The expression of classical PKC (cPKC) isoenzymes in SGC7901 cells and SGC7901/VCR cells were detected using immunofluorescent cytochemistry, laser confocal scanning microscope and Western blot. The effects of anti-PKC isoenzymes antibody on adriamycin accumulation in SGC7901/VCR cells were determined using flow cytometric analysis.

RESULTS: (1) SGC7901 cells exhibited positive staining of PKC-α. SGC7901/VCR cells exhibited stronger staining of PKC-α than SGC7901 cells. The higher dosage vincristine selected, the much stronger staining of PKC-α was observed on SGC7901/VCR cells. (2) Both SGC7901 and SGC7901/VCR cells exhibited positive staining of PKC-β I and PKC-β II with no significant difference. (3) Compared with SGC7901, SGC7901/VCR cells had decreased adriamycin accumulation and retention. Accumulation of adriamycin in SGC7901 was 5.21 ± 2.56 mg·L^-1, in SGC7901/VCR 0.3 was 0.85 ± 0.29 mg·L^-1, in SGC7901/VCR 0.7 was 0.81 ± 0.32 mg·L^-1, and in SGC7901/VCR 1.0 was 0.80 ± 0.33 mg·L^-1; Retention of adriamycin in SGC7901 was 2.51 ± 1.23 mg·L^-1, in SGC7901/VCR 0.3 was 0.47 ± 0.14 mg·L^-1, in SGC7901/VCR 0.7 was 0.44 ± 0.15 mg·L^-1, and in SGC7901/VCR 1.0 was 0.41 ± 0.11 mg·L^-1. (4) Fluorescence intensity presented adriamycin accumulation in SGC7901/VCR cells was increased from 1.14 ± 0.36 to 2.71 ± 0.94 when cells were co-incubated with anti-PKC-α but not with anti-PKC-β I, PKC-α II and PKCγ antibodies.

CONCLUSION: PKC-α, but not PKC-β I, PKC-β II or PKCγ, may play a role in multidrug resistance of gastric cancer cells SGC7901/VCR.

Parathyroid hormone stimulates translocation of protein kinase C isozymes in UMR-106 osteoblastic osteosarcoma cells

Studies with antagonists have provided evidence that protein kinase C (PKC) is involved in several of the actions of parathyroid hormone (PTH) on bone. PTH increases total PKC activity in bone and bone cells. The current studies investigated whether PTH can activate specific PKC isozymes, as demonstrated by translocation of these isozymes from cytosolic to membrane fractions. The isozymes selected for study, alpha, betaI, delta, epsilon, and zeta, were shown previously by us to be present in normal osteoblasts and several osteosarcoma-derived osteoblastic cells. UMR-106 cells, a widely used osteoblastic cell line, were selected for the current study. PKC isozymes in whole cell lysates and cell fractions were visualized by western blotting; isozyme distribution was also visualized by immunofluorescence. The total amounts of the isozymes and their relative distribution between membrane and cytosolic fractions in untreated cells were stable over a range of passages (5-20 from initial plating). In untreated cells, the concentrations of PKC alpha, betaI, and zeta were higher in the cytosol, and PKC delta and epsilon were higher in the membrane fraction. Treatment with 1 or 10 nmol/L PTH for 1 or 5 min stimulated translocation of PKC alpha and betaI, with variable effects on the other isozymes. Treatment with phorbol-12,13-dibutyrate (PDBu), 1 micromol/L for 5 min, elicited similar effects to those of PTH on PKC alpha and betaI. Treatment with PDBu for 48 h resulted in a downregulation of PKC alpha, whereas a 48 h treatment with PTH did not cause downregulation. The results indicate that PTH can affect specific PKC isozymes, providing a mechanism for differential regulation of cellular actions through this pathway.