Stromal-Initiated Changes in the Bone Promote Metastatic Niche Development

More than 85% of advanced breast cancer patients suffer from metastatic bone lesions, yet the mechanisms that facilitate these metastases remain poorly understood. Recent studies suggest that tumor-derived factors initiate changes within the tumor microenvironment to facilitate metastasis. However, whether stromal-initiated changes are sufficient to drive increased metastasis in the bone remains an open question. Thus, we developed a model to induce reactive senescent osteoblasts and found that they increased breast cancer colonization of the bone. Analysis of senescent osteoblasts revealed that they failed to mineralize bone matrix and increased local osteoclastogenesis, the latter process being driven by the senescence-associated secretory phenotype factor, IL-6. Neutralization of IL-6 was sufficient to limit senescence-induced osteoclastogenesis and tumor cell localization to bone, thereby reducing tumor burden. Together, these data suggest that a reactive stromal compartment can condition the niche, in the absence of tumor-derived signals, to facilitate metastatic tumor growth in the bone.

Autotaxin and LPA receptors represent potential molecular targets for the radiosensitization of murine glioma through effects on tumor vasculature

Despite wide margins and high dose irradiation, unresectable malignant glioma (MG) is less responsive to radiation and is uniformly fatal. We previously found that cytosolic phospholipase A2 (cPLA₂) is a molecular target for radiosensitizing cancer through the vascular endothelium. Autotaxin (ATX) and lysophosphatidic acid (LPA) receptors are downstream from cPLA₂ and highly expressed in MG. Using the ATX and LPA receptor inhibitor, α-bromomethylene phosphonate LPA (BrP-LPA), we studied ATX and LPA receptors as potential molecular targets for the radiosensitization of tumor vasculature in MG. Treatment of Human Umbilical Endothelial cells (HUVEC) and mouse brain microvascular cells bEND.3 with 5 µmol/L BrP-LPA and 3 Gy irradiation showed decreased clonogenic survival, tubule formation, and migration. Exogenous addition of LPA showed radioprotection that was abrogated in the presence of BrP-LPA. In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells. Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation. However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect. Using heterotopic tumor models of GL-261, mice treated with BrP-LPA and irradiation showed a tumor growth delay of 6.8 days compared to mice treated with irradiation alone indicating that inhibition of ATX and LPA receptors may significantly improve malignant glioma response to radiation therapy. These findings identify ATX and LPA receptors as molecular targets for the development of radiosensitizers for MG.

Phase II study of dasatinib in relapsed or refractory chronic lymphocytic leukemia

PURPOSE

Chronic lymphocytic leukemia (CLL) cells treated with dasatinib in vitro undergo apoptosis via inhibition of Lyn kinase. Thus, in this study we tested the activity of dasatinib in patients with relapsed CLL.

EXPERIMENTAL DESIGN

Patients were eligible for this phase II trial if they had documented CLL/SLL and had failed at least 1 prior therapy with a fludarabine-containing regimen and if they required therapy according to NCI-WG criteria. The starting dose of dasatinib was 140 mg daily.

RESULTS

Fifteen patients were enrolled, with a median age of 59 and a median of 3 prior regimens. All patients had received fludarabine, and 5 were fludarabine-refractory. Eleven of the 15 (73%) had high risk del(11q) or del(17p) cytogenetics. The primary toxicity was myelosuppression, with grade 3 or 4 neutropenia and thrombocytopenia in 10 and 6 patients, respectively. Partial responses by NCI-WG criteria were achieved in 3 of the 15 patients (20%; 90% CI: 6-44). Among the remaining 12 patients, 5 had nodal responses by physical exam, and 1 patient had a nodal and lymphocyte response but with severe myelosuppression. Pharmacodynamic studies indicated apoptosis in peripheral blood CLL cells within 3 to 6 hours after dasatinib administration, associated with downregulation of Syk (spleen tyrosine kinase) mRNA.

CONCLUSIONS

Dasatinib as a single agent has activity in relapsed and refractory CLL.

Wnt signaling in the niche enforces hematopoietic stem cell quiescence and is necessary to preserve self-renewal in vivo

Wingless (Wnt) is a potent morphogen demonstrated in multiple cell lineages to promote the expansion and maintenance of stem and progenitor cell populations. Wnt effects are highly context dependent, and varying effects of Wnt signaling on hematopoietic stem cells (HSCs) have been reported. We explored the impact of Wnt signaling in vivo, specifically in the context of the HSC niche by using an osteoblast-specific promoter driving expression of the paninhibitor of canonical Wnt signaling, Dickkopf1 (Dkk1). Here we report that Wnt signaling was markedly inhibited in HSCs and, unexpectedly given prior reports, reduction in HSC Wnt signaling resulted in reduced p21Cip1 expression, increased cell cycling, and a progressive decline in regenerative function after transplantation. This effect was microenvironment determined, but irreversible if the cells were transferred to a normal host. Wnt pathway activation in the niche is required to limit HSC proliferation and preserve the reconstituting function of endogenous hematopoietic stem cells.

Quantitative ex vivo detection of rodent retinal ganglion cells by immunolabeling Brn-3b

To evaluate the neuroprotective potential of drug candidates to treat human glaucoma, a short-term rodent model of retinal ganglion cell death was employed. Transient ischemia applied to the rodent retina, with subsequent reperfusion for 1-4 weeks, produces an experimental retinal ganglion cell death that is quantifiable. A widely used method to detect viable retinal ganglion cells involves surgical injection of labeling compounds into the superior colliculus of the rodent brain, the retrograde transport of the compounds along the axons to the retina, and subsequent microscopic evaluation of the retina. In order to circumvent the labor intensive and invasive surgery of this method, we sought an alternative means of assessing retinal ganglion cell survival that would be more suitable for high-throughput analysis. We therefore developed a method of immunolabeling whole retinas ex vivo with an antibody to Brn-3b, an antigen expressed in a subpopulation of retinal ganglion cells, that allows for detection of a representative retinal ganglion cell population. Fluorescently tagged Brn-3b immunolabeled retinas were flat-mounted, digitally imaged, and assessed using image analysis software. We determined that 60 min of ischemia caused a 49% and a 32% decrease in Brn-3b positive retinal ganglion cells in Lewis rats after 4 weeks reperfusion, and Sprague-Dawley rats after 2 weeks reperfusion, respectively. In Swiss Webster ND4 mouse retinas subjected to 45 min ischemia and 7 days reperfusion, we found a 70% decrease in Brn-3b positive cells. Thus, ex vivo immunolabeling of retinal ganglion cells using antibody to Brn-3b provides an alternative to other methods of quantifying retinal ganglion cells.

A selective and oral small molecule inhibitor of vascular epithelial growth factor receptor (VEGFR)-2 and VEGFR-1 inhibits neovascularization and vascular permeability

Vascular endothelial growth factor (VEGF) is a key driver of the neovascularization and vascular permeability that leads to the loss of visual acuity in diabetic retinopathy and neovascular age-related macular degeneration. Our aim was to identify an orally active, selective small molecule kinase inhibitor of vascular endothelial growth factor receptor (VEGFR)-2 with activity against both VEGF-induced angiogenesis and vascular permeability. We used a biochemical assay to identify 3-[5-methyl-2- (2-oxo-1,2-dihydro-indol-3-ylidenemethyl)-1H-pyrrol-3-yl]-proprionic acid (SU10944), a pyrrole indolinone, which is a potent ATP-competitive inhibitor of VEGFR-2 (Ki of 21 +/- 5 nM). In cellular assays, SU10944 inhibited VEGF-induced receptor autophosphorylation (IC50 of 227 +/- 80 nM) as well as downstream signaling (IC50 of 102 +/- 27 nM). In biochemical assays, SU10944 exhibits potent inhibitory activity against VEGFR-1; weak activity against other related subgroup members, including stem cell factor receptor (SCFR), platelet-derived growth factor receptor beta (PDGFRbeta), and fibroblast growth factor receptor-1 (FGFR-1); and no detectable activity against other protein tyrosine kinases such as epidermal growth factor receptor (EGFR), Src, and hepatocyte growth factor receptor. In cellular assays, the selectivity for SU10944 to inhibit VEGFR is maintained compared with other tyrosine kinases (IC50 for SCFR of 1.6 +/- 0.3 microM, for PDGFRbeta of 30.6 +/- 13.3 microM, for FGFR-1 of >50 microM, and for EGFR of >50 microM). Upon oral administration, SU10944 gave a clear dose response in the corneal micropocket model with an ED50 value for inhibition of neovascularization of approximately 30 mg/kg and a maximum inhibition of 95% at 300 mg/kg. Similarly, upon oral administration in the Miles assay, SU10944 potently inhibited VEGF-induced vascular permeability. Our data indicate that small molecule inhibitors of VEGFR signaling have the potential to ameliorate VEGF-induced neovascularization as well as vascular permeability.

Pharmacology of celecoxib in rat brain after kainate administration

Prostaglandin E(2) (PGE(2)) is the major prostaglandin produced both centrally and in the periphery in models of acute and chronic inflammation, and its formation in both locations is blocked by cyclooxygenase-2 (COX-2) inhibitors such as celecoxib. In animal models of inflammation, PGE(2) inhibition in the brain may occur secondarily to a peripheral action by inhibiting local PG formation that elicits increased firing of pain fibers and consequent activation of PG synthesis in the central nervous system (CNS). Celecoxib was studied in the kainate-induced seizure model in the rat, a model of direct central prostaglandin induction, to determine whether it can act directly in the CNS. In the kainate-treated rat brain there was increased PGE(2), PGF(2alpha), and PGD(2) production, with COX activity and PGE(2) formation increased about 7-fold over normal. We quantitated mRNA levels for enzymes involved in the prostaglandin biosynthetic pathways and found that both COX-2 and PGE synthase (PGEs) mRNA levels were increased in the brain; no changes were found for expression of COX-1 or PGD synthase mRNA. By Western blot analysis, COX-2 and PGEs were induced in total brain, hippocampus, and cortex, but not in the spinal cord. Immunohistological studies showed that COX-2 protein expression was enhanced in neurons. Dexamethasone treatment reduced the expression of both COX-2 and PGEs in kainate-treated animals. Celecoxib reduced the elevated PGE(2) levels in brain of kainate-treated rats and inhibited induced COX activity, demonstrating the ability of this compound to act on COX-2 in CNS. Doses of celecoxib that inhibited brain COX-2 were lower than those needed for anti-inflammatory activity in adjuvant arthritis, demonstrating a potent direct central action of the compound.

Cyclooxygenase-2 inhibition by celecoxib reduces proliferation and induces apoptosis in angiogenic endothelial cells in vivo

Cyclooxygenase-2 (COX-2) is expressed within neovascular structures that support many human cancers. Inhibition of COX-2 by celecoxib delays tumor growth and metastasis in xenograft tumor models as well as suppresses basic fibroblast growth factor 2 (FGF-2)-induced neovascularization of the rodent cornea. The present studies were undertaken to evaluate possible mechanisms of the antiangiogenic and anticancer effects of celecoxib. Prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)) were increased in rat corneas implanted with slow-release pellets containing FGF-2 (338.6 ng of PGE(2)/g and 17.53 ng of TXB(2)/g) compared with normal rat corneas (63.1 ng of PGE(2)/g and 2.0 ng of TXB(2)/g). Celecoxib at 30 mg/kg/day p.o. inhibited angiogenesis (78.6%) and prostaglandin production by 78% for PGE(2) (72.65 ng/g) and 68% for TXB(2) (5.55 ng/g). Decreased prostaglandin production in corneas was associated with a 2.5-fold cellular increase in apoptosis and a 65% decrease in proliferation. Similar reductions in proliferation were observed in neovascular stroma (65-70%) of celecoxib-treated (dietary 160 ppm/day) xenograft tumors as well as in tumor cells (50-75%). Apoptosis was also increased in the tumor cells (2.2-3.0-fold) in response to celecoxib. Thus, the antitumor activity of celecoxib may be attributable, at least in part, to a direct effect on host stromal elements, such as the angiogenic vasculature.

Role of cyclooxygenases in angiogenesis

Angiogenesis is the process by which new blood vessels are formed. This process supports normal physiology as well as contributes to progression of disease. Progressive rheumatoid arthritis and growth of tumors are two pathologies to which angiogenesis contributes. In arthritis, we know that prostaglandins (PGs) and the enzyme cyclooxygenase-2, which catalyses prostaglandin production, are inflammatory mediators. These mediators are involved in rheumatoid arthritis and cancer-induced angiogenic processes. We discuss, herein, recent findings on the expression of cyclooxygenases in both rheumatoid arthritis and human cancer, and the links between COX-2, PGs, and angiogenesis. We also propose a model for the possible mechanistic interaction of the various cell types involved in angiogenesis.

Celecoxib inhibits N-butyl-N-(4-hydroxybutyl)-nitrosamine-induced urinary bladder cancers in male B6D2F1 mice and female Fischer-344 rats

Epidemiological studies have shown that nonsteroidal anti-inflammatory drugs (NSAIDs) may have a role in the prevention of human cancers. A number of preclinical studies have also suggested that inhibition of cyclooxygenase (COX) with NSAIDs has an anticancer effect in animal models of colon, urinary bladder, skin, and breast. In these studies, we evaluated the COX-2 inhibitor celecoxib in two rodent models of urinary bladder cancer. Male B6D2F1 mice treated with N-butyl-N-(4-hydroxybutyl)-nitrosamine (OH-BBN) developed transitional and squamous cell urinary bladder cancers, many of which grew rapidly and caused substantial morbidity that required sacrifice of the mice. Groups of mice received various daily doses of celecoxib in the diet (1250, 500, or 200 mg/kg of diet) beginning 7 days before the initiation of 12 weekly doses of OH-BBN. Mice were checked weekly for the presence of palpable urinary bladder masses. The study was terminated at 8 months following the initial treatment with OH-BBN. The percentage of mice with large palpable bladder lesions, which necessitated sacrifice of the mice, was 40% in the OH-BBN control group. In contrast, only 10% of all celecoxib-treated mice required sacrifice before the scheduled termination of the experiment, implying that all three doses of celecoxib inhibited the formation of large palpable lesions. Celecoxib did not significantly alter the incidence of preneoplastic bladder lesions, but did dose-dependently decrease the total number of urinary bladder cancers/mouse, palpable plus microscopic, by 77, 57, and 43% at dosages of 1250, 500, and 200 mg of celecoxib/kg of diet, respectively. In the second model, female Fischer-344 rats were administered OH-BBN twice/week for a period of 8 weeks. After 8 months, all rats developed preneoplastic lesions, whereas roughly 60% of the rats developed relatively small urinary bladder cancers. Rats were treated continually with celecoxib in the diet (500 or 1000 mg/kg of diet) beginning either 1 week prior to the initial OH-BBN treatment or beginning 1 week following the last OH-BBN treatment. Neither celecoxib treatment regimen significantly altered the number of preneoplastic lesions. Whereas celecoxib treatment initiated prior to OH-BBN administration decreased cancer incidence roughly 65%, celecoxib treatment initiated beginning 1 week after the last dose of OH-BBN profoundly decreased cancer incidence (>95%). Celecoxib did not alter the body weights of the mice or rats, or cause other signs of toxicity at any of the doses studied. Taken together these results demonstrate that: (a) celecoxib effectively inhibits tumor growth and enhances survival in the mouse model of urinary bladder cancer; and (b) celecoxib profoundly inhibits development of urinary bladder cancers in the rat model even when administered following the last dose of OH-BBN. Clinical trials will be necessary to determine whether COX-2 inhibitors will provide a clinical benefit in human bladder cancer.

Antiangiogenic and antitumor activities of cyclooxygenase-2 inhibitors

We provide evidence that cyclooxygenase (COX)-2-derived prostaglandins contribute to tumor growth by inducing newly formed blood vessels (neoangiogenesis) that sustain tumor cell viability and growth. COX-2 is expressed within human tumor neovasculature as well as in neoplastic cells present in human colon, breast, prostate, and lung cancer biopsy tissue. COX-1 is broadly distributed in normal, as well as in neoplastic, tissues. The contribution of COX-2 to human tumor growth was indicated by the ability of celecoxib, an agent that inhibits the COX-2 enzyme, to suppress growth of lung and colon tumors implanted into recipient mice. Mechanistically, celecoxib demonstrated a potent antiangiogenic activity. In a rat model of angiogenesis, we observe that corneal blood vessel formation is suppressed by celecoxib, but not by a COX-1 inhibitor. These and other data indicate that COX-2 and COX-2-derived prostaglandins may play a major role in development of cancer through numerous biochemical mechanisms, including stimulation of tumor cell growth and neovascularization. The ability of celecoxib to block angiogenesis and suppress tumor growth suggests a novel application of this anti-inflammatory drug in the treatment of human cancer.

Upregulation of COX-2 during cardiac allograft rejection

BACKGROUND

The hypothesis that cyclooxygenase-2 (COX-2) is involved in the myocardial inflammatory response during cardiac allograft rejection was investigated using a rat heterotopic abdominal cardiac transplantation model.

METHODS AND RESULTS

COX-2 mRNA and protein in the myocardium of rejecting cardiac allografts were significantly elevated 3 to 5 days after transplantation compared with syngeneic controls (n=3, P<0.05). COX-2 upregulation paralleled in time and extent the upregulation of iNOS mRNA, protein, and enzyme activity in this model. COX-2 immunostaining was prominent in macrophages infiltrating the rejecting allografts and in damaged cardiac myocytes. Prostaglandin (PG) levels in rejecting allografts were also higher than in native hearts. Because NO has been reported to modulate PG synthesis by COX-2, additional transplants were performed using animals treated with a selective COX-2 inhibitor (SC-58125) and a selective inhibitor of the inducible nitric oxide synthase (iNOS) N-aminomethyl-L-lysine. At posttransplant day 5, inhibitor administration resulted in a significant reduction of COX-2 mRNA expression (3764+/-337 versus 5110+/-141 arbitrary units, n=3, P<0.05) and iNOS enzymatic activity (1.7+/-0.4 versus 22.8+/-14. 4 nmol/mg protein, n=3, P<0.01) compared with vehicle-treated allogeneic transplants. Allograft survival in treated animals was increased modestly from 5.4 to 6.4 days (P<0.05). However, apoptosis of cardiac myocytes (TUNNEL method) was only marginally reduced relative to vehicle controls in treated graft recipients. The intensity of allograft rejection was also similar in the treated and untreated allografts.

CONCLUSIONS

The data indicates that COX-2 expression is enhanced in parallel with iNOS in the myocardium during cardiac allograft rejection.

Selective inhibition of inducible cyclooxygenase 2 in vivo is antiinflammatory and nonulcerogenic

We have examined the role of cyclooxygenase 2 (COX-2) in a model of inflammation in vivo. Carrageenan administration to the subcutaneous rat air pouch induces a rapid inflammatory response characterized by high levels of prostaglandins (PGs) and leukotrienes in the fluid exudate. The time course of the induction of COX-2 mRNA and protein coincided with the production of PGs in the pouch tissue and cellular infiltrate. Carrageenan-induced COX-2 immunoreactivity was localized to macrophages obtained from the fluid exudate as well as to the inner surface layer of cells within the pouch lining. Dexamethasone inhibited both COX-2 expression and PG synthesis in the fluid exudate but failed to inhibit PG synthesis in the stomach. Furthermore, NS-398, a selective COX-2 inhibitor, and indomethacin, a nonselective COX-1/COX-2 inhibitor, blocked proinflammatory PG synthesis in the air pouch. In contrast, only indomethacin blocked gastric PG and, additionally, produced gastric lesions. These results suggest that inhibitors of COX-2 are potent antiinflammatory agents which do not produce the typical side effects (e.g., gastric ulcers) associated with the nonselective, COX-1-directed antiinflammatory drugs.

Brain natriuretic peptide-like immunoreactive innervation of the cardiovascular and cerebrovascular systems in the rat

Atrial natriuretic peptide is a potent dilator of aorta and renal and cerebral arteries and inhibits sympathetic tone in the heart in several mammalian species. We examined the possibility that a molecule related to porcine brain natriuretic peptide (pBNP), which acts at the same receptor sites as atrial natriuretic peptide, might provide an alternative source of natriuretic peptide to the cardiovascular system in the rat. An antiserum against pBNP demonstrated profuse immunoreactive innervation of the heart, cerebrovascular tree, and renal arteries. pBNP-like immunoreactive fibers ran in bundles along the surface of the heart, innervating the atria most heavily and penetrating the ventricular myocardium along the coronary arteries. There was greater density of innervation of the right side of the heart compared with the left, particularly in the ventricles, suggesting a parasympathetic origin. The entire cerebrovascular tree was innervated by immunoreactive pBNP fibers, with the densest concentration of immunoreactive fibers along the surface of the internal carotid, middle cerebral, posterior communicating, and anterior cerebral arteries. The proximal renal arteries were not innervated, but as they approached the kidney, they were invested by bundles of immunoreactive pBNP fibers. These axons followed the major branches of the renal artery into the kidney parenchyma, running along the surface of the arterioles up to their entrance into the renal glomeruli. No immunoreactive innervation of the aorta or proximal brachiocephalic, subclavian, or carotid arteries was seen. A substance related to pBNP may serve as a neuromodulator regulating cardiac output as well as blood flow in certain vascular beds.

Brain natriuretic peptides: differential localization of a new family of neuropeptides

Brain natriuretic peptide (BNP) is a recently discovered neuropeptide, isolated from the porcine brain, that is highly homologous to atriopeptin (AP), the atrial natriuretic peptide. We used a set of highly selective antisera against the two peptides to map their differential distribution immunohistochemically in the rat central nervous system. BNP immunoreactivity has a distinct distribution, involving many central autonomic and endocrine control structures that contain little if any AP immunoreactivity. AP and BNP belong to a family of neuropeptides that may be important in central cardiovascular control.

Reversible induction of right ventricular atriopeptin synthesis in hypertrophy due to hypoxia

Right ventricular hypertrophy produced in rats exposed to 10% oxygen for 3 weeks resulted in a ninefold increase in atriopeptin immunoreactivity (APir) and a 160-fold increase in atriopeptin messenger RNA (AP mRNA) in the right ventricular myocardium. A small but significant increase in left ventricular APir and AP mRNA was also present, probably representing the interventricular septum. Right atrial APir was decreased by 50%, but left atrial APir was not different from normoxic controls. Purification of ventricular tissue extracts by high-performance liquid chromatography revealed primarily the high molecular weight prohormone. The development of right ventricular hypertrophy and right ventricular APir content followed a similar time course, each evident at 7 days of hypoxia and reaching a plateau at 14 days. Hypoxia followed by normoxia caused right ventricular APir to fall to control levels within 3 days, despite persistent right ventricular hypertrophy. This data demonstrates that hypoxia can reversibly induce extra-atrial expression of atriopeptin synthesis in the cardiac ventricle.

Heparin interferes with the biological effectiveness of atriopeptin

The chromatographic mobility of atriopeptin-28 or of the prohormone is markedly altered by preincubation of the peptides with heparin before separation on reverse-phase high performance liquid chromatography. Protamine prevented the heparin effect and reestablished the original migration pattern of the atrial peptides. The addition of heparin to either rat or human plasma samples did not interfere with the atriopeptin immunoreactivity. The influence of heparin on the biological activity of the atriopeptin-28 in anesthetized rats was also investigated. Infusion of heparin (30 U/min) significantly reduced the dose-dependent fall of blood pressure produced by atriopeptin-28, but did not interfere with the hypotensive effect of nitroglycerin. Similarly, infusion of heparin in volume-expanded rats markedly decreased the diuresis produced by atriopeptin-28 without altering the urine volume excreted in response to furosemide. These data suggest that the highly charged molecule heparin can modify the physical and biological properties of atriopeptins, perhaps by binding to the numerous arginine residues (i.e., 5 arginine residues in atriopeptin-28) in the atriopeptin molecules.

Development, validation and application of an enzyme immunoassay (EIA) of atriopeptin

A rapid, convenient, and sensitive enzyme immunoassay (EIA) for atriopeptin (AP) has been developed. The tracer-ligand for the assay is the 24-amino acid peptide, AP24, which has been covalently coupled to the tetrameric form of acetylcholinesterase (AChE) (EC 3.1.1.7). Tracer, unknown, and primary antibody are incubated in a 96-well microtiter plate precoated with secondary antibody. After washing, a colorimetric reaction is used to measure acetylcholinesterase activity. A direct linear correlation was obtained when comparing the conventional radioimmunoassay and the EIA by using the same primary antibody to assay: plasma samples (rat or human), HPLC column fractions, or atrial extracts. Besides being technically much less demanding and not requiring the use of the radioisotopes, the EIA is more sensitive than the radioimmunoassay and thereby lends itself to a "flash" same-day assay of samples.

Thromboxane synthase is preferentially conserved in activated mouse peritoneal macrophages

Resident macrophages isolated from uninfected animals produce large quantities of arachidonic acid (AA) metabolites. Immunizing animals with protein antigens or bacteria activates macrophages and causes an 80% reduction in the cyclooxygenase and lipoxygenase metabolites relative to resident cells. Since some products have been shown to modulate immune functions, we examined how the AA metabolic enzyme activities regulate the products that are synthesized. We demonstrate that the cyclooxygenase, 5-lipoxygenase, prostacyclin synthase, and probably prostaglandin (PG) endoperoxide E-isomerase activities were decreased in activated peritoneal macrophages. In sharp contrast, thromboxane synthase activity was selectively unchanged or enhanced in the activated macrophages. Thus the immune response appears to modulate the activity of the AA and PG endoperoxide-dependent enzymes, thus dictating a major shift in the profile of metabolites synthesized by macrophages.

Cellular interactions and exaggerated arachidonic acid metabolism in rabbit renal injury

Cell cultures from explants of the rabbit hydronephrotic kidney (HNK) cortex consisted of fibroblasts and an esterase-positive cell that phagocytizes zymosan. Cortical cell cultures from the contralateral kidney (CLK) contained only the fibroblast. The HNK cultures exhibited an endotoxin-induced prostaglandin (PG) E2 (three - fourfold) release indicative of the presence of macrophages, whereas no response was observed in the CLK cultures. At bradykinin concentrations as low as 10(-9)M there was a 20-fold stimulation of PGE2 from the HNK cultures and a sevenfold stimulation in the CLK cultures. The heterogeneous population of cells in the HNK cultures was separated using a mild trypsin treatment which permits passage of only the fibroblasts. The HNK-passaged cultures contained no phagocytic cells and did not release PGE2 in response to endotoxin. The passaged HNK cultures released less PGE2 in response to bradykinin as compared to primary cultures and had a decreased cyclooxygenase activity as determined by exogenous arachidonic acid conversion to PGE2. Conditioned media from adherent rabbit peripheral blood mononuclear cells stimulated basal PGE2 production (two - threefold) from both the HNK and CLK cultures. These findings demonstrated the similarity of the PGE2 production by cultured HNK cortical cells as compared to the ex vivo perfused HNK.

Inducible plasmid-determined resistance to arsenate, arsenite, and antimony (III) in escherichia coli and Staphylococcus aureus

Plasmids in both Escherichia coli and Staphylococcus aureus contain an "operon" that confers resistance to arsenate, arsenite, and antimony(III) salts. The systems were always inducible. All three salts, arsenate, arsenite, and antimony(III), were inducers. Mutants and a cloned deoxyribonucleic acid fragment from plasmid pI258 in S. aureus have lost arsenate resistance but retained resistances to arsenite and antimony, demonstrating that separate genes are involved. Arsenate-resistant arsenite-sensitive S. aureus plasmid mutants were also isolated. In E. coli, plasmid-determined arsenate resistance and reduced uptake were additive to that found with chromosomal arsenate resistance mutants. Arsenate resistance was due to reduced uptake of arsenate by the induced plasmid-containing cells. Under conditions of high arsenate, when some uptake could be demonstrated with the induced resistant cells, the arsenate was rapidly lost by the cells in the absence of extracellular phosphate. Sensitive cells retained arsenate under these conditions. When phosphate was added, phosphate-arsenate exchange occurred. High phosphate in the growth medium protected cells from arsenate, but not from arsenite or antimony(III) toxicity. We do not know the mechanisms of arsenite or antimony resistance. However, arsenite was not oxidized to less toxic arsenate. Since cell-free medium "conditioned" by prior growth to induced resistant cells with toxic levels of arsenite or antimony(III) retained the ability to inhibit the growth of sensitive cells, the mechanism of arsenite and antimony resistance does not involve conversion of AsO2- or SbO+ to less toxic forms or binding by soluble thiols excreted by resistant cells.