Spatial social polarization and birth outcomes: preterm birth and infant mortality - New York City, 2010-14.

AIMS: This study assessed the relationship between spatial social polarization measured by the index of the concentration of the extremes (ICE) and preterm birth (PTB) and infant mortality (IM) in New York City. A secondary aim was to examine the ICE measure in comparison to neighborhood poverty. METHODS: The sample included singleton births to adult women in New York City, 2010-2014 ( n=532,806). Three ICE measures were employed at the census tract level: ICE - Income (persons in households in the bottom vs top 20th percentile of US annual household income), ICE -Race/Ethnicity (black non-Hispanic vs white non-Hispanic populations), and ICE - Income + Race/Ethnicity combined. Preterm birth was defined as birth before 37 weeks' gestation. Infant mortality was defined as a death before one year of age. A two-level generalized linear model with random intercept was utilized adjusting for individual-level covariates. RESULTS: Preterm birth prevalence was 7.1% and infant mortality rate was 3.4 per 1000 live births. Women who lived in areas with the least privilege were more likely to have a preterm birth or infant mortality as compared to women living in areas with the most privilege. After adjusting for covariates, this association remained for preterm birth (ICE - Income: Adjusted Odds Ratio (AOR) 1.16 (1.10-1.21); ICE - Race/Ethnicity: AOR 1.41 (1.34-1.49); ICE - Income + Race/Ethnicity: AOR 1.36 (1.29-1.43)) and IM (ICE - Race/Ethnicity (AOR 1.80 (1.43-2.28) and ICE - Income + Race/Ethnicity (AOR 1.54 (1.23-1.94)). High neighborhood poverty was associated with PTB only (AOR 1.09 (1.04-1.14). CONCLUSIONS: These results provide preliminary evidence for the use of the ICE measure in examining structural barriers to healthy birth outcomes.

Crystallization and preliminary crystallographic analysis of LipC12, a true lipase isolated through a metagenomics approach.

LipC12, a true lipase from family I.1 of bacterial lipases which was previously isolated through a metagenomics approach, contains 293 amino acids. Among lipases of known three-dimensional structure, it has a sequence identity of 47% to the lipase from Pseudomonas aeruginosa PAO1. Recombinant N-terminally His(6)-tagged LipC12 protein was expressed in Escherichia coli, purified in a homogenous form and crystallized in several conditions, with the best crystals being obtained using 2.0 M sodium formate and 0.1 M bis-tris propane pH 7.0. X-ray diffraction data were collected to 2.70 Å resolution. The crystals belonged to the tetragonal space group P4(1)22, with unit-cell parameters a = b = 58.62, c = 192.60 Å.

Mapping injustice, visualizing equity: why theory, metaphors and images matter in tackling inequalities.

This symposia discussed "Mapping injustice, visualizing equity: why theory, metaphors and images matter in tackling inequalities". It sought to provoke critical thinking about the current theories used to analyze the health impact of injustice, variously referred to as "health inequalities" in the UK, "social inequalities in health" in the US, and "health inequities" more globally. Our focus was the types of explanations, images, and metaphors these theories employ. Building on frameworks that emphasize politics, agency, and accountability, we suggested that it was essential to engage the general public in the politics of health inequities if progress is to be made. We showcased some examples of such engagement before inviting the audience to consider how this might apply in their own areas of responsibility.

Visions for the 20th International Epidemiological Association's World Congress of Epidemiology (WCE 2014).

During August 17th-21st, 2014, the University of Alaska Anchorage, along with other local, state, and federal agencies throughout Alaska, will host the 20(th) International Epidemiological Association's (IEA) World Congress of Epidemiology (WCE 2014). The theme for this Congress is "Global Epidemiology in a Changing Environment: The Circumpolar Perspective." The changing environment includes the full range of environments that shape population health and health inequities from the physical to the social and economic. Our circumpolar perspective on these environments includes views on how political systems, work, immigration, Indigenous status, and gender relations and sexuality affect the global world and the health of its people. Suggestions and insights from the 3(rd) North American Congress of Epidemiology (2011) and the first-ever joint regional workshop co-organized by the IEA North American Region and the IEA Latin American and Caribbean Region held at the 19(th) IEA World Congress of Epidemiology (2011) have helped direct the focus for WCE 2014. Since the Arctic regions are feeling the effects of climate change first, we believe focusing on the emerging data on the health impacts of climate change throughout the world will be an important topic for this Congress. This will include a broad range of more traditional epidemiology areas such as infectious disease epidemiology, environmental epidemiology, health disparities, and surveillance and emergency preparedness. Addressing health inequities and promoting health equity is likewise a key concern of the Congress. This Congress will also host presentations on injury epidemiology, occupational health, infectious diseases, chronic diseases, maternal and child health, surveillance and field epidemiology, mental health, violence (from self-directed, e.g., suicide, to interpersonal to structural), psychoactive substance use (including tobacco), and measures of subjective health. Attention will be given to epidemiology's theoretical frameworks and emphasizing knowledge translation, from epidemiology to health systems, to policy, and to the broader public. We also plan to offer many hands-on workshops including practical uses of epidemiology to improve health systems and reduce health inequities within and between countries; the manner in which epidemiology can inform public health practice; the understanding and use of the Dictionary of Epidemiology; and many others.

CD4+ but not CD8+ cells are essential for allorejection.

The generation of knockout mice with targeted gene disruption has provided a valuable tool for studying the immune response. Here we describe the use of CD4 and CD8 knockout mice to examine the role of CD4+ and CD8+ cells in initiating allotransplantation rejection. Pretreatment with a brief course of depletive anti-CD4 monoclonal antibody therapy allowed permanent survival of heart, but not skin, allografts transplanted across a major histocompatibility barrier. However, skin as well as heart grafts were permanently accepted in the CD4 knockout mice. Transfer of CD4+ cells into CD4 knockout recipient mice 1 d before skin engraftment reconstituted rejection, demonstrating that CD4+ cells are necessary for initiating rejection of allogeneic transplants. Major histocompatibility complex disparate heart and skin allografts transplanted into CD8 knockout recipients were rejected within 10 d. This study demonstrates that CD4+ but not CD8+ T cells are absolutely required to initiate allograft rejection.

Efficacy of the non-adenosine analogue A1 adenosine receptor agonist (BR-4935) on cardiovascular function after cardiopulmonary bypass.

BACKGROUND: We tested the hypothesis that pharmacological preconditioning with a newly developed, potent non-adenosine analogue A1AdoR agonist (BR-4935) improves biventricular cardiac and endothelial function after cardiopulmonary bypass. METHODS: Twelve anesthetized dogs underwent cardiopulmonary bypass. Dogs were divided into two groups: group 1 (n = 6) received saline vehicle, group 2 (n = 6) received BR-4935 before cardiopulmonary bypass. Biventricular hemodynamic variables were measured using a combined pressure-volume conductance catheter. Coronary blood flow, ATP content, malondialdehyde and myeloperoxidase levels and vasodilatative responses to acetylcholine and sodium nitroprusside were also determined. RESULTS: Administration of the A1AdoR agonist led to a significantly better recovery of left and right ventricular systolic function after 60 minutes of reperfusion. Although the vasodilatative response to sodium nitroprusside was similar in both groups, acetylcholine resulted in a significantly greater increase in coronary blood flow in the BR-4935 group. In addition, the ATP content was significantly higher in the same group. Furthermore, malondialdehyde and myeloperoxidase levels significantly decreased in the A1AdoR group. CONCLUSION: Pharmacological preconditioning with a new, potent non-adenosine analogue A1AdoR agonist improves biventricular function recovery and endothelial function after hypothermic cardiac arrest.

Bioluminescence: pH activity profiles of related luciferase fractions.

The 27, 000g supernatant from crude extracts of the dinoflagellate Gonyaulax can be fractionated into two components having luciferase activity that differ both in molecular weight (35, 000 and 150, 000) and in pH activity profile. The smaller component has activity over a broad range from pH 5 to 9, while the larger one is active only in the acid region. This clarifies the previous ambiguity in the literature regarding the optimum pH for the assay of luciferase.

Brain glutamate decarboxylase cloned in lambda gt-11: fusion protein produces gamma-aminobutyric acid.

Glutamate decarboxylase (GAD; E.C. 4.1.1.15) converts glutamate to gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the vertebrate central nervous system. This report describes the isolation of a GAD complementary DNA clone by immunological screening of a lambda gt-11 brain complementary DNA expression library. The fusion protein produced by this clone catalyzes the conversion of glutamate to GABA and carbon dioxide, confirming its identity as GAD. Antibodies to beta-galactosidase remove GAD enzymatic activity from solution, showing that this activity is associated with the fusion protein. In immunoblotting experiments all three available antisera to GAD reacted with the fusion polypeptide and with two major polypeptides (molecular size, 60,000 and 66,000 daltons) in brain extracts.

Cardiotonic agent milrinone stimulates resorption in rodent bone organ culture.

The cardiotonic agent amrinone inhibits bone resorption in vitro. Milrinone, an amrinone analog, is a more potent cardiotonic agent with lower toxicity. In contrast to amrinone, milrinone stimulated resorption in cultures of neonatal mouse calvaria and fetal rat limb bones. Threshold doses were 0.1 microM in calvaria and 0.1 mM in limb bones; maximal stimulation occurred in calvaria at 0.1 mM. Maximal responses to milrinone and parathyroid hormone were comparable. Milrinone concentrations below 0.1 mM did not affect calvarial cyclic AMP. 0.5 microM indomethacin inhibited milrinone effects in calvaria but usually not in limb bones. 3 nM calcitonin inhibited milrinone-stimulated resorption and there was no escape from this inhibition. Structural homology between milrinone and thyroxine has been reported. We find similarities between milrinone and thyroxine actions on bone, because prostaglandin production was crucial for the effects of both agents in calvaria but not in limb bones, and neither agent exhibited escape from calcitonin inhibition.

Human transforming growth factor-alpha stimulates bone resorption in vitro.

Tumor-derived transforming growth factors (TGF) have been proposed as possible mediators of hypercalcemia in malignancy. We have studied the action of recombinant human TGF-alpha in cultured bone cells and in bone explant cultures. In clonal UMR-106 rat osteosarcoma cells, TGF-alpha and epidermal growth factor (EGF) were equipotent in binding to the EGF receptor. TGF-alpha and EGF both stimulated resorption of neonatal mouse calvaria, and maximal responses were obtained with 10 ng/ml of TGF-alpha after 72 h in culture. The effects of both TGF-alpha and EGF in calvaria, but not those of parathyroid hormone, were inhibited by 5 X 10(-7) M indomethacin. Fetal rat limb bone cultures were less sensitive to TGF-alpha than neonatal mouse calvaria, with a concentration of 30 ng/ml being required to stimulate resorption in this system. The bone-resorbing activity of TGF-alpha in fetal rat bones was inhibited by 10 ng/ml calcitonin but not by 5 X 10(-7) M indomethacin. EGF at concentrations up to 300 ng/ml did not stimulate resorption of the limb bones at time periods up to 66 h. The results indicate that human TGF-alpha is a potent bone-resorbing agent, and support the concept that this growth factor exhibits some effects distinct from those of EGF. TGF-alpha could play an etiologic role in the hypercalcemia of malignancy.

Lifelong socioeconomic trajectory and premature mortality (35-65 years) in France: findings from the GAZEL Cohort Study.

BACKGROUND: Studies conducted in the UK and Scandinavia show an inverse association between lifetime socioeconomic position and adult mortality. However, there are virtually no data from other countries and few investigations have examined non-cardiovascular mortality in men and women. METHODS: Lifelong socioeconomic trajectories (father's occupation, own occupation in young adulthood and in mid-life) and premature (< or = 65 years) mortality (all-cause, smoking-related cancer, diseases of the circulatory system and external causes) in the French GAZEL Cohort Study (14,972 men and 5,598 women, followed up between 1990 and 2004) were studied. Hazard ratios (HRs) were estimated using Cox's regression models adjusted for age, marital status, tobacco smoking, alcohol consumption, body mass index, and fruit and vegetable consumption. RESULTS: Men and women who experienced lifelong disadvantage or downward intergenerational mobility were at high risk of dying prematurely compared with those with a favourable trajectory (age-adjusted HRs for all-cause mortality: cumulative disadvantage: HR 1.61, 95% confidence interval (CI) 1.26 to 2.06 in men and HR 1.95, 95% CI 1.10 to 3.47 in women; downward mobility: HR 1.87, 95% CI 1.35 to 2.58 in men and HR 2.05, 95% CI 1.12 to 3.75 in women). Associations were strongest for mortality due to chronic diseases (smoking-related cancers and diseases of the circulatory system). These associations were partly explained by marital status, body mass index, alcohol consumption, cigarette smoking, and fruit and vegetable consumption. CONCLUSIONS: In France, where the leading cause of premature death is cancer, lifelong socioeconomic position is associated with the risk of dying before the age of 65 years. Adult factors seem more relevant than childhood socioeconomic circumstances.

Breast cancer and serum organochlorines: a prospective study among white, black, and Asian women.

BACKGROUND: Five small case-control studies have examined the relationship between exposure to organochlorines and the risk of breast cancer and have found inconsistent results. In these studies, organochlorine levels in breast cancer patients were measured after (or at most 6 months before) diagnosis. PURPOSE: We tested the hypothesis that organochlorines are a risk factor for breast cancer, using prospectively gathered data on serum levels of DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] (the main metabolite of the pesticide DDT [2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane]) and polychlorinated biphenyls (PCBs). METHODS: Study subjects belonged to a cohort of 57,040 women (46,629 white, 8123 black, and 2288 Asian) from the San Francisco Bay Area who took a multiphasic health examination, independent of concern about risk of breast cancer, in the late 1960s. At that time, a sample of blood was obtained, then frozen and stored. Follow-up was through December 31, 1990. We conducted a nested case-control study of 150 case patients and 150 matched control subjects. A random sample of 50 women per racial/ethnic group who had been diagnosed with breast cancer more than 6 months after the multiphasic examination (mean follow-up = 14.2 years) was selected, and each case patient was matched to a cancer-free control subject. RESULTS: Matched analyses found no differences in the case patients' and control subjects' serum levels of DDE (mean difference = 0.2 parts per billion [ppb]; 95% confidence interval [CI] = -6.7, 7.2) or PCBs (mean difference = -0.4 ppb; 95% CI = -0.8, 0.1). DDE levels, however, tended to be higher among black case patients compared with black controls (mean difference = 5.7 ppb; 95% CI = -3.3, 14.8), and PCBs were lower among white case patients compared with white controls (mean difference = -0.6 ppb; 95% CI = -1.2, -0.1). Organochlorine levels were significantly higher among black and Asian women compared with white women. The mean difference for DDE was 11.0 ppb for black women (95% CI = 4.3, 17.6) and 12.6 ppb for Asian women (95% CI = 6.0, 19.2); for PCBs, the respective differences were 0.8 ppb for black women (95% CI = 0.2, 1.4) and 1.4 ppb for Asian women (95% CI = 0.8, 1.9). The results were not altered by adjusting for relevant confounders, and the lack of association between exposure to organochlorines and breast cancer was present regardless of length of follow-up, year of diagnosis, or the case patient's menopausal and estrogen-receptor status. CONCLUSION: The data do not support the hypothesis that exposure to DDE and PCBs increases risk of breast cancer. IMPLICATIONS: Future investigations must consider the biologic mechanisms involved and variations in exposure to chemical pollutants and of breast cancer incidence rates among diverse groups of women.

Characterization of the surface enhanced raman scattering (SERS) of bacteria.

The surface enhanced Raman scattering (SERS) of a number of species and strains of bacteria obtained on novel gold nanoparticle (approximately 80 nm) covered SiO(2) substrates excited at 785 nm is reported. Raman cross-section enhancements of >10(4) per bacterium are found for both Gram-positive and Gram-negative bacteria on these SERS active substrates. The SERS spectra of bacteria are spectrally less congested and exhibit greater species differentiation than their corresponding non-SERS (bulk) Raman spectra at this excitation wavelength. Fluorescence observed in the bulk Raman emission of Bacillus species is not apparent in the corresponding SERS spectra. Despite the field enhancement effects arising from the nanostructured metal surface, this fluorescence component appears "quenched" due to an energy transfer process which does not diminish the Raman emission. The surface enhancement effect allows the observation of Raman spectra of single bacterial cells excited at low incident powers and short data acquisition times. SERS spectra of B. anthracis Sterne illustrate this single cell level capability. Comparison with previous SERS studies reveals how the SERS vibrational signatures are strongly dependent on the morphology and nature of the SERS active substrates. The potential of SERS for detection and identification of bacterial pathogens with species and strain specificity on these gold particle covered glassy substrates is demonstrated by these results.

Demonstration of sodium/calcium exchange in rodent osteoblasts.

Based on the inhibition of stimulated Ca release from cultured bone by several different agents that alter Na transport, we proposed that hormonally stimulated bone resorption requires Na/Ca exchange. Calcemic hormones appear to interact primarily directly with the osteoblast, which then mediates the activation of osteoclast activity. In organ culture it is not possible to determine whether Na/Ca exchange is involved in this initiating step in the osteoblast or directly in osteoclast-mediated Ca release, and there have been no prior direct measurements of Na/Ca exchange in bone or bone cells. The purpose of this study was to demonstrate the presence of Na/Ca exchange transport in the osteoblast. Thus, we characterized Na-dependent Ca transport in osteoblast-like rat osteosarcoma cells (UMR-106) and primary bone cells isolated from neonatal mouse calvaria. Cells were loaded with the Ca-sensitive dye fura-2 in the presence of physiologic NaCl and the absence of Ca with or without 0.3 mM ouabain. Changes in free cytosolic Ca after the extracellular addition of 1.5 mM Ca were measured spectrofluorimetrically. An outward Na gradient was generated by decreasing extracellular Na while maintaining isotonicity. UMR-106 cells that were Na loaded by ouabain inhibition of Na,K-ATPase activity exhibited 30% greater Ca uptake than control cells. Similar results were obtained with primary bone cells. This uptake required extracellular Ca, was not inhibited by 200 microM verapamil, and was reversible upon reversal of the Na gradient. These data demonstrate the presence of a Na/Ca exchange transport system in osteoblasts.

Inhibition of bone resorption by alpha-difluoromethylornithine may not be mediated by polyamine depletion.

We have examined the effect of alpha-difluoromethylornithine (DFMO) on bone polyamine content and parathyroid hormone (PTH)- and calcitriol-stimulated bone resorption in cultures of neonatal mouse calvaria. Polyamine content in bone homogenates was determined by reverse-phase paired-ion HPLC. Treatment with 5 mM DFMO for 48 h reduced putrescine from 0.4 nmol/bone to nondetectable levels, slightly decreased spermidine, and did not affect spermine. Bone resorption elicited by 48 h of treatment with PTH or calcitriol was inhibited by concentrations of DFMO greater than or equal to 5 mM added 48 h prior to hormone. This observation supported the concept that polyamines may play a role in bone resorption. However, other observations cast uncertainty on this conclusion. Measurement of calvarial polyamine content at 2 h intervals revealed no increase in endogenous polyamines for up to 10.5 h after calcitriol addition. Although addition of putrescine restored bone polyamine content, exogenous polyamines failed to reverse the inhibitory effects of DFMO on calcitriol-stimulated resorption. These results suggest that a mechanism other than depletion of polyamines could be contributing to the inhibitory effect of DFMO on resorption.

Characterization of specific thyroid hormone receptors in bone.

Thyroid hormones stimulate bone turnover in vivo and increase Ca release from bone in vitro. To investigate further the effects of thyroid hormones in bone, we have characterized specific nuclear receptors for [125I]tri-iodothyronine (T3) in neonatal mouse calvaria. Maximal specific binding of [125I]T3 to isolated nuclei occurred within 60 min at 22 degrees C. [125I]T3 binding was completely and rapidly displaced by the addition of 10(-6) M unlabeled T3; the dissociation appears to be first order with t1/2 = 36 min. The IC50 for competition by unlabeled T3 was approximately 10(-8) M. The relative affinity of thyroxine (T4) for the receptor was approximately 10 X lower than T3, consistent with its lower biological potency in most target tissues for thyroid hormones. Only weak competition was observed with diiodotyrosine at concentrations up to 10(-4) M. We have previously shown that the cardiotonic agent milrinone stimulates bone resorption in vitro with characteristics similar to those of T4. Structural homology between milrinone and T4 was recently reported. Milrinone, like diiodotyrosine, was only a weak competitor for binding at concentrations up to 10(-4) M. Milrinone inhibited collagen synthesis in the calvaria. The results suggest that the effects of milrinone on bone turnover in calvaria in vitro are probably not mediated through a thyroid hormone receptor.

Conditioned medium from ras oncogene-transformed NIH 3T3 cells induces bone resorption in vitro.

Tumor-associated hypercalcemia is due, in part, to enhanced osteoclastic bone resorption induced by soluble factors elaborated from malignant cells. ras transformation of NIH 3T3 cells results in a 50-fold induction of cathepsin L mRNA and secretion of the corresponding protein. Since cathepsin L is an acid proteinase we asked whether conditioned medium from these cells would directly increase calcium release from bone in vitro. We tested conditioned medium obtained after 72 h culture of NIH 3T3 ras-transformed cells (DT) or nontransformed NIH 3T3 cells (3T3) and identical medium not exposed to cells (Ctl). Incubation of either live or dead neonatal mouse calvaria for 48 h in DT-conditioned medium increased calcium release compared to bones incubated with 3T3 medium. In both states the increased calcium release with DT medium was blocked by 0.25 mM E-64, a general cysteine proteinase inhibitor, and 1 microM Z-Phe-Ala-CH2F, a specific inhibitor of cathepsin L activity. Thus, conditioned medium from ras-transformed cells enhances calcium release in both live and dead bone. Since cathepsin L is the major protein secreted by these cells and the effect of DT-conditioned medium is blocked by a specific inhibitor of cathepsin L, these studies suggest that this acid proteinase acts directly on bone mineral to enhance net calcium release.

Mechanism of amphotericin B stimulation of net calcium efflux from neonatal mouse calvariae.

Amphotericin B is a polyene antifungal agent that binds to membrane sterols, creating aqueous pores that permit ion fluxes sufficient to cause cell lysis. It has also been shown to alter ion transport in mammalian cells, including proton secretion from renal tubular cells. The latter effect can lead to distal renal tubular acidosis in patients treated for systemic fungal infections. Based on the understanding that osteoclast-mediated bone resorption is dependent on proton secretion, we examined the effect of amphotericin B on calcium efflux from neonatal mouse calvariae in organ culture. Amphotericin B (5 micrograms/ml) stimulated net calcium efflux from calvariae within 24 h to a level almost as great as that produced by a maximally effective concentration of parathyroid hormone. The stimulated calcium efflux was completely inhibited by both 10 ng/ml salmon calcitonin, a physiologic inhibitor of osteoclast activity, and 4 x 10(-4) M acetazolamide, a specific inhibitor of carbonic anhydrase, the enzyme necessary for substantial proton generation by osteoclasts. These results indicate a direct effect of amphotericin B on bone in vitro to stimulate osteoclast-mediated calcium efflux.

Hormonal regulation of Na(+)-Ca2+ exchange in osteoblast-like cells.

We proposed a role for Na-Ca exchange in hormonally mediated bone resorption and recently characterized Na-dependent Ca transport in an osteoblast-like rat osteosarcoma cell line (UMR-106). To test whether calcemic agents alter Na(+)-Ca2+ exchange in osteoblasts, UMR cells were treated acutely or cultured in the absence or presence of calcemic agent for 24 h. Cells were then loaded with the Ca-sensitive dye fura-2 in the presence of 140 mM NaCl, no Ca, and the absence or presence of 0.3 mM ouabain. Cells were resuspended at 22 degrees C, and the fluorescence ratio at excitation wavelength of 340 and 380 nm was measured. An outward Na gradient was generated by removing extracellular Na and maintaining isotonicity with choline chloride. Na(+)-Ca2+ exchange was demonstrated by enhanced Ca uptake in ouabain-treated (Na-loaded) cells after the addition of 1.5 mM Ca. Acute addition of 10(-7) M PTH or 10(-6) M PGE2 had no effect on Na-dependent Ca uptake. However, 24 h treatment of cells with PTH, PGE2, or 1,25(OH)2D3 caused a dose-dependent inhibition of Na(+)-Ca2+ exchange. Using the Na-sensitive dye, SBFI, we also demonstrated that the effect was bidirectional; PTH inhibited Ca-dependent Na uptake comparably to its inhibition of Na-dependent Ca uptake. The effects of the calcemic agents were mimicked by 24 h treatment of the cells with 1 microM forskolin or 2 microM PMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Dichlorobenzamil inhibits stimulated bone resorption in vitro.

We have previously proposed that stimulated release of Ca from bone requires Na-Ca exchange. 3',4'-Dichlorobenzamil (DCB), an amiloride analog, has been shown to directly block Na-Ca exchange in cardiac tissue. To further test our hypothesis we have characterized the effect of DCB on basal and stimulated bone resorption from neonatal mouse calvaria in vitro. DCB inhibition of resorption from bones stimulated with 1 nM PTH was dose dependent. The IC50 was about 7 microM, and complete inhibition occurred at 10 microM. DCB alone inhibited basal Ca release at 10 microM. Amiloride, which is less potent as an inhibitor of Na-Ca exchange, had no effect on PTH-stimulated resorption at concentrations lower than 0.1 mM, but inhibited basal resorption at 10 microM. Stimulated Ca release was inhibited either by continuous treatment with DCB plus PTH for 72 h or by a short pretreatment with DCB alone, followed by removal of DCB before addition of PTH. At least 9-h pretreatment with DCB was necessary to block the subsequent response to PTH. The inhibitory effect of DCB pretreatment could be prevented if PTH was present together with DCB during pretreatment periods of 24 h or less. This reversibility suggests that the inhibition by DCB is not simply a toxic effect of the drug. DCB also inhibited resorption stimulated by 1,25-dihydroxyvitamin D3 or prostaglandin E2, which indicates that the effect of DCB is beyond the level of specific hormone-receptor interaction. Thus, the data are consistent with a role for Na-Ca exchange in the process of hormonally stimulated bone resorption.