A Brain Penetrant Mutant IDH1 Inhibitor Provides In Vivo Survival Benefit

Mutations in IDH1 are highly prevalent in human glioma. First line treatment is radiotherapy, which many patients often forego to avoid treatment-associated morbidities. The high prevalence of IDH1 mutations in glioma highlights the need for brain-penetrant IDH1 mutant-selective inhibitors as an alternative therapeutic option. Here, we have explored the utility of such an inhibitor in IDH1 mutant patient-derived models to assess the potential therapeutic benefits associated with intracranial 2-HG inhibition. Treatment of mutant IDH1 cell line models led to a decrease in intracellular 2-HG levels both in vitro and in vivo. Interestingly, inhibition of 2-HG production had no effect on in vitro IDH1 mutant glioma cell proliferation. In contrast, IDH1 mutant-selective inhibitors provided considerable survival benefit in vivo. However, even with near complete inhibition of intratumoral 2-HG production, not all mutant glioma models responded to treatment. The results suggest that disruption of 2-HG production with brain-penetrant inhibitors in IDH1 mutant gliomas may have substantial patient benefit.

Biomarker-driven phase 2 study of MK-2206 and selumetinib (AZD6244, ARRY-142886) in patients with colorectal cancer

PURPOSE

PI3K/AKT/mTOR and RAS/RAF/MEK pathways are frequently dysregulated in colorectal cancer (CRC). We conducted a biomarker-driven trial of the combination of MK-2206, an allosteric AKT 1/2/3 inhibitor, and selumetinib, a MEK 1/2 inhibitor, in patients with CRC to evaluate inhibition of phosphorylated ERK (pERK) and AKT (pAKT) in paired tumor biopsies.

PATIENTS AND METHODS

Adult patients with advanced CRC were enrolled in successive cohorts stratified by KRAS mutation status. Initially, 12 patients received oral MK-2206 90 mg weekly with oral selumetinib 75 mg daily in 28-day cycles. Following an interim analysis, the doses of MK-2206 and selumetinib were increased to 135 mg weekly and 100 mg daily, respectively. Paired tumor biopsies were evaluated for target modulation.

RESULTS

Common toxicities were gastrointestinal, hepatic, dermatologic, and hematologic. Of 21 patients enrolled, there were no objective responses. Target modulation did not achieve the pre-specified criteria of dual 70 % inhibition of pERK and pAKT levels in paired tumor biopsies.

CONCLUSION

Despite strong scientific rationale and preclinical data, clinical activity was not observed. The desired level of target inhibition was not achieved. Overlapping toxicities limited the ability to dose escalate to achieve exposures likely needed for clinical activity, highlighting the challenges in developing optimal combinations of targeted agents.

Chk1 versus Cdc25: Chking One’s Levels of Cellular Proliferation

This review summarizes recent studies which have provided new insight into the mechanisms by which the DNA damage response kinase, Chk1 inhibits the dual specificity phosphatase, Cdc25, and thereby regulates cell cycle progression. Recently, Chk1 has been shown to not only regulate Cdc25A degradation but also its ability to interact with various Cdk complexes through phosphorylation of the carboxy-terminus of the phosphatase. Surprisingly, these effects appear to be specific for Chk1, but not Chk2, which may explain the recently reported in vivo haploinsufficiency phenotype observed in the mammary gland using a Chk1 conditional mouse model.

Effects of an oral allosteric AKT inhibitor (MK-2206) on human nasopharyngeal cancer in vitro and in vivo

Aim

Protein kinase B (AKT) signaling frequently is deregulated in human cancers and plays an important role in nasopharyngeal carcinoma (NPC). This preclinical study investigated the effect of MK-2206, a potent allosteric AKT inhibitor, on human NPC cells in vitro and in vivo.

Methods

The effect of MK-2206 on the growth and proliferation of CNE-1, CNE-2, HONE-1, and SUNE-1 cells was assessed by Cell Counting Kit 8 and colony formation assay. Flow cytometry was performed to analyze cell cycle and apoptosis. The effects of MK-2206 on the AKT pathway were analyzed by Western blotting. Autophagy induction was evaluated via electron microscopy and Western blot. To test the effects of MK-2206 in vivo, CNE-2 cells were subcutaneously implanted into nude mice. Tumor-bearing mice were treated orally with MK-2206 or placebo. Tumors were harvested for immunohistochemical analysis.

Results

In vitro, MK-2206 inhibited the four NPC cell line growths and reduced the sizes of the colonies in a dose-dependent manner. At 72 and 96 hours, the half maximal inhibitory concentration (IC₅₀) values of MK-2206 in CNE-1, CNE-2, and HONE-1 cell lines were 3–5 μM, whereas in SUNE-1, IC₅₀ was less than 1 μM, and MK-2206 induced cell cycle arrest at the G1 phase. However, our study found no evidence of apoptosis. MK-2206 induced autophagy in NPC cells, as evidenced by electron microscopy and Western blot, and inhibited the growth of tumors that were subcutaneously implanted in mice. Inhibition of downstream phosphorylation through the PRAS40 and S6 pathways seems to be the main mechanism for the MK-2206-induced growth inhibition.

Conclusion

Our preclinical study suggests that MK-2206’s antiproliferative effect may be useful for NPC treatment; however, strategies for reinforcing this effect are needed to maximize clinical benefit.

The DNA-damage effector checkpoint kinase 1 is essential for chromosome segregation and cytokinesis

Defective genome maintenance mechanisms, involving DNA repair and cell-cycle checkpoint pathways, initiate genetic instability in many sporadic and hereditary cancers. The DNA damage effector Checkpoint kinase 1 (Chk1) is a critical component of DNA replication, intra-S phase, and G(2)/M phase checkpoints and a recently reported mitotic spindle-assembly checkpoint. Here, we report for the first time that haploinsufficiency of Chk1 in mice resulted in multiple mitotic defects and enhanced binucleation. We observed that Aurora B, a critical cytokinetic regulator and a recently identified Chk1 substrate, was mislocalized in mitotic Chk1(+/-) mammary epithelia. Chk1 also exhibited distinct mitotic localization patterns and was active during unperturbed mitosis and cytokinesis in mammalian cells. Active Chk1 expression was not dependent on treatment with spindle poisons such as colcemid during mitosis and cytokinesis. Furthermore, two different complementary approaches demonstrated that abrogation of Chk1 in mitotic mammalian cells resulted in cytokinetic regression and binucleation, increased chromosome lagging and/or nondisjunction, and abnormal localization of Aurora B at late mitotic structures. Thus, Chk1 is a multifunctional kinase that serves as a nexus between the DNA damage response and the mitotic exit pathways during cell-cycle progression to prevent genomic instability and cancer.

Pitfalls of the application of microdialysis in clinical oncology: controversial findings with docetaxel

Microdialysis is a novel and minimally invasive sampling technique, based on the diffusion of analytes from the interstitial compartment through a semi-permeable membrane, and enables direct assessment of tissue disposition and penetration of drugs. Variable antitumor responses may be associated with differences in tumor vascularity, capillary permeability or tumor interstitial pressure resulting in variable delivery of anticancer agents. In preparation of pharmacokinetic studies, aimed at measuring docetaxel concentrations in healthy and malignant tissues in vivo, in pre-clinical as well as clinical studies, in vitro recovery experiments were performed. In contrast to published data, the recovery experiments suggest that docetaxel has a very low recovery as a result of non-specific binding to currently available microdialysis catheters. Here we discuss our findings with docetaxel in a historical perspective and we report on our experience using polysorbate 80 to eliminate the non-specific binding and its effects on the recovery of docetaxel.

Chk1 is haploinsufficient for multiple functions critical to tumor suppression

The haploinsufficient tumor suppressor Chk1 is essential for embryonic cells, but the consequences of Chk1 loss in adult tissues are unknown. Using conditional Chk1 mice, we find that proliferating mammary cells lacking Chk1 undergo apoptosis leading to developmental defects. Conditional Chk1 heterozygosity increased the number of S phase cells and caused spontaneous DNA damage. Chk1+/- epithelia also exhibit a miscoordinated cell cycle in which S phase cells display an early mitotic phenotype. These cells maintain high levels of Cdc25A, which can promote inappropriate cell cycle transitions. Thus, Chk1 heterozygosity results in three distinct haploinsufficient phenotypes that can contribute to tumorigenesis: inappropriate S phase entry, accumulation of DNA damage during replication, and failure to restrain mitotic entry.

Adenomatous hyperplastic polyp of the gall bladder associated with cholelithiasis in a child

Polyps of the gall bladder are uncommon conditions in children. We present a case report of a 14-year-old girl who had calculous cholecystitis and an adenomatous hyperplastic polyp of the gall bladder. She was treated by laparoscopic cholecystectomy.

A randomised placebo-controlled trial of vaginal misoprostol for cervical priming before hysteroscopy in postmenopausal women

OBJECTIVE

To investigate the effectiveness of misoprostol given vaginally for cervical priming before hysteroscopy in postmenopausal women.

DESIGN

Double-blind randomised controlled study.

SETTING

Regional hospital, Hong Kong.

PARTICIPANTS

One hundred women with postmenopausal bleeding scheduled for hysteroscopy from October 1998 to September 2001 were randomly assigned to receive either misoprostol or placebo vaginally before the operation.

MAIN OUTCOME MEASURES

The number of women requiring cervical dilatation, outcome of hysteroscopy and side effects of the medication were assessed.

RESULTS

Forty-eight women receiving misoprostol and 48 women receiving placebo were compared. The mean degree of endocervical diameter estimated by Hegar's dilator was similar between the treatment group and the control group. A similar number of women in the treatment group and the control group required cervical dilatation. The operative times for both groups were similar. The incidence of side effects was comparable in both groups. The most common side effects for misoprostol were febrile episodes and diarrhoea. There was no cervical tear nor uterine perforation encountered in both groups. The mean duration of hospital stay in both groups were similar. Subanalysis of results were similar in women receiving vaginal medication at least five hours before the operation.

CONCLUSION

Vaginal misoprostol was not shown to reduce the need for cervical dilatation in postmenopausal women. It cannot convert diagnostic hysteroscopy from a hospital procedure into an office one in postmenopausal women with tight cervical os.

Review of effects of water pollution on the breeding success of waterbirds, with particular reference to ardeids in Hong Kong

Predatory waterbirds, such as ardeids, are susceptible to bioaccumulation of pollutants through the ingestion of contaminated food sources. High body burdens of contaminants, including PCBs, PAHs, cadmium, mercury, lead, copper, zinc and arsenic have been detected in many bird species worldwide. There is a paucity of literature, however, linking contaminant body burden and effects on reproductive success in waterbirds. This review is a synthesis of pertinent literature on this topic, with specific reference to contaminant residues in various tissue types, relationship between body burden and reproductive success, and the use of biomarkers to predict more serious adverse affects. The impetus for this review was the development of a conservation strategy and management plan (commissioned by the Agriculture, Fisheries and Conservation Department of Hong Kong Special Administrative Region (SAR)) for an important wetland in Hong Kong that supports many threatened waterbirds, including ardeids.

Dynamics of leptomycin B-sensitive nucleocytoplasmic flux of parathyroid hormone-related protein

Parathyroid hormone-related protein is responsible for hypercalcemia induced by various tumors. The similarity of its N-terminus to that of parathyroid hormone enables parathyroid hormone-related protein to share parathyroid hormone's signaling properties, but the rest of the molecule possesses distinct functions including a role in the nucleus/nucleolus in reducing apoptosis and enhancing cell proliferation. We have previously shown that parathyroid hormone-related protein nuclear import is mediated by importin beta1. Here we use fluorescence recovery after photobleaching for the first time to show that, in living cells, parathyroid hormone-related protein is exported from the nucleus in a leptomycin B-sensitive manner, implicating CRM1 as the parathyroid hormone-related protein nuclear export receptor. Leptomycin B treatment significantly reduced the rate of nuclear export 4 -10-fold, thereby increasing parathyroid hormone-related protein concentration in the nucleus/nucleolus about 2-fold. Intriguingly, this also led to a 2-fold reduced nuclear import rate. Inhibiting the nuclear export of a protein able to shuttle between nucleus and cytoplasm through distinct receptors thus can also affect nuclear import, indicating that the subcellular localization of a protein containing distinct nuclear import and export signals is the product of an integrated system. Although there have been several recent studies examining the dynamics of intranuclear transport using fluorescence recovery after photobleaching, this represents, to our knowledge, the first use of the technique to examine the kinetics of nucleocytoplasmic flux in living cells.

Cellular stress regulates the nucleocytoplasmic distribution of the protein-tyrosine phosphatase TCPTP

Specific cellular stresses, including hyperosmotic stress, caused a dramatic but reversible cytoplasmic accumulation of the otherwise nuclear 45-kDa variant of the protein-tyrosine phosphatase TCPTP (TC45). In the cytoplasm, TC45 dephosphorylated the epidermal growth factor receptor and down-regulated the hyperosmotic stress-induced activation of the c-Jun N-terminal kinase. The hyperosmotic stress-induced nuclear exit of TC45 was not inhibited by leptomycin B, indicating that TC45 nuclear exit was independent of the exportin CRM-1. Moreover, hyperosmotic stress did not induce the cytoplasmic accumulation of a green fluorescent protein-TC45 fusion protein that was too large to diffuse across the nuclear pore. Our results indicate that TC45 nuclear exit may occur by passive diffusion and that cellular stress may induce the cytoplasmic accumulation of TC45 by inhibiting nuclear import. Neither p42(Erk2) nor the stress-activated c-Jun N-terminal kinase or p38 mediated the stress-induced redistribution of TC45. We found that only those stresses that stimulated the metabolic stress-sensing enzyme AMP-activated protein kinase (AMPK) induced the redistribution of TC45. In addition, specific pharmacological activation of the AMPK was sufficient to cause the accumulation of TC45 in the cytoplasm. Our studies indicate that specific stress-activated signaling pathways that involve the AMPK can alter the nucleocytoplasmic distribution of TC45 and thus regulate TC45 function in vivo.

Determination of microcystins in cyanobacterial blooms by solid-phase microextraction-high-performance liquid chromatography

A solid-phase microextraction (SPME) method was applied to study microcystin (MC) profiles in a natural Microcystis sp. bloom in a freshwater pond in Guangzhou, China. Three dominant MC variants, namely MC-LR, MC-YR, and MC-RR, were quantified. Simultaneous study of their total, extracellular, and intracellular profiles was made possible using SPME coupled to high-performance liquid chromatography. The total and intracellular concentrations of MC-LR in the bloom were 8.67 x 10(-2) microg/ ml and 1.93 mg/g, respectively. The corresponding concentrations of MC-YR were 1.20 x 10(-3) microg/ml and 0.06 mg/g, respectively, and those of MC-RR were 5.57 x 10(-2) microg/ml and 1.49 mg/g, respectively. Only MC-LR was detectable in the extracellular phase (1.49 x 10(-2) microg/ml) of the bloom, and its concentration was 14% of the intracellular content. Mass balance consideration revealed that only 71.1% of total MC-LR, 36.0% of total MC-YR, and 67.4% of total MC-RR within the cyanobacterial cells were released into the aqueous phase immediately after cell lysis.

Nuclear import of Creb and AP-1 transcription factors requires importin-beta 1 and Ran but is independent of importin-alpha

Although the specific role of transcription factors (TFs) is nuclear, surprisingly little is known in quantitative terms regarding the pathways by which TFs localize in the nucleus. In this study, we use direct binding assays, native gel electrophoresis, and fluorescence polarization measurements to show for the first time that the cAMP-response element binding protein (CREB) and related AP-1 and jun and fos constituents are recognized by importin beta1 (Impbeta) with nanomolar affinity. We reconstitute the nuclear import of these TFs in vitro, demonstrating dependence on cytosolic factors, and show that this is due to the requirement for Impbeta, since antibodies to Impbeta, but not to importin alpha (Impalpha), inhibit nuclear accumulation significantly. We show that Impbeta is necessary and sufficient for docking of CREB at the nuclear envelope; that Ran is essential for CREB nuclear import is demonstrated by the reduction of nuclear accumulation effected by RanGTPgammaS but not RanGDP, and by dissociation of the Impbeta-CREB-GFP complex by RanGTPgammaS but not RanGDP as demonstrated using fluorescence polarization assays. The results support the existence of an Impbeta1- and Ran-mediated nuclear import pathway for CREB and related constitutively nuclear TFs, which is Impalpha-independent and thus distinct from import pathways utilized by inducible TFs.

Effects of radiation therapy on vascular responsiveness

The use of radiation therapy to inhibit vascular proliferative diseases has produced encouraging results in several clinical trials. However, little is known about the possible side effects of radiation on vascular responsiveness. Our goal was to study the in vitro vascular responses of the rabbit aorta to various agonists immediately after several regimens of radiation therapy administered at doses prescribed in clinical protocols and at two different dose rates. High-dose-rate radiation was administered either by brachytherapy, using a gamma source, iridium 192, or an external electron beam producing beta radiation. Low-dose-rate radiation was administered by brachytherapy using a liquid-filled balloon with the beta emitter 32P. Vascular reactivity after the various regimens of irradiation was determined using the organ bath pharmacology assay. Various agonists were applied to the rabbit aorta to produce full cumulative concentration-response curves. Radiation, administered using an external electron beam, did not alter endothelium-dependent relaxation of the aorta induced by acetylcholine. However, the use of a catheter-based system to deliver radiation disrupted the endothelial cell lining of the vessel, causing a lack of relaxation by acetylcholine. Therefore, to compare all modalities of radiation therapy on vascular responsiveness, the agonists used in this study are known to act directly on the smooth muscle. Radiation therapy had no effect on the contractile responses induced by the following agonists: phenylephrine and potassium chloride. Vascular dilatation induced by nitroglycerin, a nitric oxide donor, was unaffected by radiation therapy. The contractile response induced by des-Arg9-bradykinin, a kinin B1 receptor agonist, was significantly increased twofold to threefold by all types of irradiation under study. This enhanced response is attributable to an increase of mRNA levels coding for this receptor. In all cases, radiation therapy did not alter the effective concentration producing 50% of maximal responsiveness (EC50) and did not reduce the vascular responsiveness induced by agonists. Taken together, we conclude that radiation therapy does not hinder endothelium-independent vascular responsiveness and increases the kinin B1 receptor-mediated vasoconstriction.

Molecular dissection of the importin beta1-recognized nuclear targeting signal of parathyroid hormone-related protein

Produced by various types of solid tumors, parathyroid hormone-related protein (PTHrP) is the causative agent of humoral hypercalcemia of malignancy. The similarity of PTHrP's amino-terminus to that of parathyroid hormone enables it to share some of the latter's signalling properties, but its carboxy-terminus confers distinct functions including a role in the nucleus/nucleolus in reducing apoptosis and enhancing cell proliferation. PTHrP nuclear import occurs via a novel importin beta1-mediated pathway. The present study uses several different direct binding assays to map the interaction of PTHrP with importin beta using a series of alanine mutated PTHrP peptides and truncated human importin beta1 derivatives. Our results indicate that PTHrP amino acids 83-93 (KTPGKKKKGK) are absolutely essential for importin beta1 recognition with residues 71-82 (TNKVETYKEQPL) additionally required for high affinity binding; residues 380-643 of importin beta1 are required for the interaction. Binding of importin beta1 to PTHrP is reduced in the presence of the GTP-bound but not GDP-bound form of the guanine nucleotide binding protein Ran, consistent with the idea that RanGTP binding to importin beta is involved in the release of PTHrP into the nucleus following translocation across the nuclear envelope. This study represents the first detailed examination of a modular, non-arginine-rich importin beta1-recognized nuclear targeting signal.

Nuclear targeting signal recognition: a key control point in nuclear transport?

Recent progress indicates that there are multiple pathways of nucleocytoplasmic transport which involve specific targeting sequences, such as nuclear localization sequences (NLSs), and cytosolic receptor molecules of the importin/karyopherin superfamily which recognise and dock the NLS-containing proteins at the nuclear pore. This first step of nuclear import/export is of central importance, with the affinity of the importin-targeting sequence interaction a critical parameter in determining transport efficiency. Different importins possess distinct NLS-binding specificities, which allows the system to be modulated through differential expression of the importins themselves, as well as through competition between different importins for the same protein, and between different proteins for the same importin. The targeting sequence-importin interaction can also be influenced directly by phosphorylation increasing the affinity of the interaction with importins or by targeting sequence masking through phosphorylation or specific protein binding. Targeting sequence recognition thus appears to represent a key control point in the regulation of nuclear transport. BioEssays 22:532-544, 2000.

Nuclear targeting signal recognition: a key control point in nuclear transport?

Recent progress indicates that there are multiple pathways of nucleocytoplasmic transport which involve specific targeting sequences, such as nuclear localization sequences (NLSs), and cytosolic receptor molecules of the importin/karyopherin superfamily which recognise and dock the NLS-containing proteins at the nuclear pore. This first step of nuclear import/export is of central importance, with the affinity of the importin-targeting sequence interaction a critical parameter in determining transport efficiency. Different importins possess distinct NLS-binding specificities, which allows the system to be modulated through differential expression of the importins themselves, as well as through competition between different importins for the same protein, and between different proteins for the same importin. The targeting sequence-importin interaction can also be influenced directly by phosphorylation increasing the affinity of the interaction with importins or by targeting sequence masking through phosphorylation or specific protein binding. Targeting sequence recognition thus appears to represent a key control point in the regulation of nuclear transport. BioEssays 22:532-544, 2000.

Nuclear and nucleolar localization of parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) was first discovered as the factor causing hypercalcaemia produced by solid tumours frequently associated with the head and neck, breast, lung and kidney. The homology of its amino-terminus to parathyroid hormone (PTH; eight of the first 13 residues are identical), enables it to share the same receptor and perform similar biological functions to PTH. The sequences of PTHrP C-terminal to its PTH-like region confer functions such as transplacental calcium transport, renal bicarbonate excretion and in vitro osteoclast inhibition. Recent findings have shown that PTHrP is a nuclear/nucleolar protein in certain tissues and that this localization is cell cycle-regulated, mediated by the middle portion of the molecule, and involves the nuclear import receptor importin beta1. The present review discusses what is known about the pathway by which PTHrP localizes to the nucleus/nucleolus and the putative roles it may have there.

Nuclear targeting signal recognition: a key control point in nuclear transport?

Recent progress indicates that there are multiple pathways of nucleocytoplasmic transport which involve specific targeting sequences, such as nuclear localization sequences (NLSs), and cytosolic receptor molecules of the importin/karyopherin superfamily which recognise and dock the NLS-containing proteins at the nuclear pore. This first step of nuclear import/export is of central importance, with the affinity of the importin-targeting sequence interaction a critical parameter in determining transport efficiency. Different importins possess distinct NLS-binding specificities, which allows the system to be modulated through differential expression of the importins themselves, as well as through competition between different importins for the same protein, and between different proteins for the same importin. The targeting sequence-importin interaction can also be influenced directly by phosphorylation increasing the affinity of the interaction with importins or by targeting sequence masking through phosphorylation or specific protein binding. Targeting sequence recognition thus appears to represent a key control point in the regulation of nuclear transport. BioEssays 22:532-544, 2000.

Toxicology and evaluation of microcystins

This paper reviews the toxicity and tumor-promoting properties of microcystins. Methods for screening and/or identification of microcystins in environmental samples are discussed and compared. Specific emphasis is placed on newly developed extraction/detection methods, e.g., solid phase microextraction (SPME) technique, and capillary electrophoresis coupled with laser-induced fluorescence detection. The results of a kinetic analysis of the effects of microcystins on phosphorylase-a binding to phosphatase-2A using a surface plasmon resonance biosensor are also presented.

A fluorescent cholesterol analog traces cholesterol absorption in hamsters and is esterified in vivo and in vitro

The fluorescent cholesterol analog 22-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3beta-ol (fluoresterol) was characterized as a tool for exploring the biochemistry and cell biology of intestinal cholesterol absorption. Hamsters absorbed fluoresterol in a concentration- and time-dependent manner, with an efficiency of about 15-30% that of cholesterol. Fluoresterol absorption was blocked by compounds known to inhibit cholesterol absorption, implying that fluoresterol interacts with those elements of the normal pathway for cholesterol absorption on which the inhibitors act. Confocal microscopy of small intestinal tissue demonstrated that fluoresterol was taken up by absorptive epithelial cells and packaged into lipoprotein particles, suggesting a normal route of intracellular trafficking. Uptake of fluoresterol was confirmed by biochemical analysis of intestinal tissue, and a comparison of [(3)H] cholesterol and fluoresterol content in the mucosa suggested that fluoresterol moved through the enterocytes more rapidly than did cholesterol. This interpretation was supported by measurements of fluoresterol esterification in the mucosa. Four hours after hamsters were given fluoresterol and [(3)H]cholesterol orally, 44% of the fluoresterol in the intestinal mucosa was esterified, compared to 8% of the [(3)H]cholesterol. Caco-2 cells took up 2- to 5-fold more [(3)H]cholesterol than fluoresterol from bile acid micelles, and esterified 21-24% of the fluoresterol but only 1-4% of the [(3)H]cholesterol. Thus fluoresterol apparently interacts with the proteins required for cholesterol uptake, trafficking, and processing in the small intestine.

Determination of polychlorinated biphenyls in human blood serum by SPME

We report a direct immersion SPME-GC/mu ECD method for the determination of non-volatile pollutants (Aroclor 1254) in human blood plasma using an enzymatic proteolytic approach to overcome the protein fouling problem. A nonspecific serine protease, Proteinase K, is used to remove the fouling interference. Significant improvement in relative repeatability from 28.9% to 3.4% (n = 10) was obtained. Analyte recovery up to 93% and detection limit of 1.0 ppb (total PCB) were achieved.

Calcitonin receptor antibodies in the identification of osteoclasts

Osteoclasts are the cells responsible for bone resorption, and their number and rate of formation are critical in determining bone mass. To identify and quantify osteoclasts, as well as to study their formation in bone and in osteoclastogenic cultures, osteoclast-specific cell markers are required. Only the calcitonin receptor (CTR) expression unambiguously identifies osteoclasts and distinguishes them from macrophage polykaryons. However, present autoradiographic methods for CTR detection are cumbersome and time consuming. We have developed rabbit polyclonal antibodies specific for the C-terminal intracellular domain of the mouse and rat Cla CTR. These antibodies labeled HEK-293 cells stably transfected with CTR (but not untransfected HEK-293 cells). This labeling is abrogated by preabsorbing the antibodies with the recombinant antigen. The antibodies immunostained primary mouse and rat osteoclasts as well as osteoclasts in sections of mouse bone. Osteoclasts (both mononuclear and multinucleated) formed from mouse bone marrow or spleen cells cocultured with osteoblasts in the presence of 1,25 dihydroxyvitamin D3 and prostaglandin E2 were also specifically immunostained by the CTR antibodies. Cocultures incubated under conditions that did not allow osteoclastogenesis (i.e., omission of mediators or osteoblasts, or culture for less than 4 days) were not immunostained by CTR antibodies. Autoradiographic detection of 125I-labeled salmon calcitonin combined with CTR immunohistochemistry showed that both methods labeled the same cells. A CTR polyclonal antibody and monoclonal antibody F4/80 were used in combination to show immunofluorescence labeling of murine osteoclasts and macrophage populations, respectively, in marrow/osteoblast cocultures. These results indicate that simple and rapid CTR antibody-based methods can be used to identify osteoclasts, and can be used to characterize the antigenic profile of osteoclasts by using double immunofluorescence analysis.

Phosphorylation at the cyclin-dependent kinases site (Thr85) of parathyroid hormone-related protein negatively regulates its nuclear localization

Parathyroid hormone-related protein (PTHrP) is expressed by a wide variety of cells and is considered to act as a secreted factor; however, evidence is accumulating for it to act in an intracrine manner. We have determined that PTHrP localizes to the nucleus at the G1 phase of the cell cycle and is transported to the cytoplasm when cells divide. PTHrP contains a putative nuclear localization sequence (NLS) (residues 61-94) similar to that of SV40 T-antigen, which may be implicated in the nuclear import of the molecule. We identified that Thr85 immediately prior to the NLS of PTHrP was phosphorylated by CDC2-CDK2 and phosphorylation was cell cycle-dependent. Mutation of Thr85 to Ala85 resulted in nuclear accumulation of PTHrP, while mutation to Glu85 to mimic a phosphorylated residue resulted in localization of PTHrP to the cytoplasm. Combined, the data demonstrate that the intracellular localization of PTHrP is phosphorylation- and cell cycle-dependent, and such control further supports a potential intracellular role (10,34,35) for PTHrP.

Importin beta recognizes parathyroid hormone-related protein with high affinity and mediates its nuclear import in the absence of importin alpha

Parathyroid hormone-related protein (PTHrP), expressed in a range of tumors, has endocrine, autocrine/paracrine, and intracrine actions, some of which relate to its ability to localize in the nucleus. Here we show for the first time that extracellularly added human PTHrP (amino acids 1-108) can be taken up specifically by receptor-expressing UMR106.01 osteogenic sarcoma cells and accumulate to quite high levels in the nucleus and nucleolus within 40 min. Quantitation of recognition by the nuclear localization sequence (NLS)-binding importin subunits indicated that in contrast to proteins containing conventional NLSs, PTHrP is recognized exclusively by importin beta and not by importin alpha. The sequence of PTHrP responsible for binding was mapped to amino acids 66-94, which includes an SV40 large tumor-antigen NLS-like sequence, although sequence determinants amino-terminal to this region were also necessary for high affinity binding (apparent dissociation constant of approximately 2 nM for importin beta). Nuclear import of PTHrP was assessed in vitro using purified components, demonstrating that importin beta, together with the GTP-binding protein Ran, was able to mediate efficient nuclear accumulation in the absence of importin alpha, whereas the addition of nuclear transport factor NTF2 reduced transport. The polypeptide ligand PTHrP thus appears to be accumulated in the nucleus/nucleolus through a novel, NLS-dependent nuclear import pathway independent of importin alpha and perhaps also of NTF2.

PTHrP and cell division: expression and localization of PTHrP in a keratinocyte cell line (HaCaT) during the cell cycle

Parathyroid hormone-related protein (PTHrP) is highly expressed in normal skin keratinocytes, and its involvement in growth and differentiation processes in these cells has been implicated by several lines of evidence which include the use of antisense PTHrP (Kaiser et al., 1994, Mol. Endocrinol., 8:139-147). In this study, we have investigated whether PTHrP expression and its subcellular localization is linked to cell cycle progression in a human keratinocyte cell line (HaCat), which constitutively expresses and secretes PTHrP. PTHrP mRNA and immunoreactive PTHrP were assessed in asynchronous dividing cells and in cells blocked at G1 or G2 + M phases of the cell cycle using several different protocols. The response of PTHrP mRNA expression was examined following readdition of serum in the continued presence of cycle blockers, and after release from cell cycle block, or from cell synchronization by serum deprivation. PTHrP expression was greatest in actively dividing cells when cells were in S and G2 + M phases of the cell cycle and were lowest in quiescent G1 cells. Most notable were the high levels of PTHrP mRNA and protein in cells at G2 + M phase of the cell cycle at division. Furthermore, PTHrP was localized to the nucleolus in quiescent cells, but redistributed to the cytoplasm when cells were actively dividing. Taken together, these results support a role for PTHrP in cell division in keratinocytes. In asynchronously growing cells, PTHrP expression fell as cells became confluent at a time when cell growth is inhibited and cells begin to differentiate. Mitogen stimulation of HaCaT cells resulted in a rapid increase in PTHrP mRNA expression, but was dependent upon cells being in the G1 phase of the cell cycle. Cells blocked in G1 responded to mitogen both in the continued presence of aphidicolin or when released from block. Cells blocked at G2 + M with colcemid expressed high levels of PTHrP mRNA and protein, and PTHrP mRNA did not respond further to mitogen in the continued presence of blocker. However, in cells released from block at G2 + M by addition of serum, an increase in PTHrP expression was seen coincident with the progression of cells into G1. In contrast, in a squamous cancer cell line (COLO16), basal PTHrP expression was high and was not altered during the cell cycle or by cell cycle block, consistent with association of its dysregulated expression in malignant cells. The results of this study suggest that PTHrP may have two roles in the cell cycle; one in G1 in response to mitogen, and a second at cell division when its expression is high and it is relocated from the nucleolus to the cytoplasm.

PC8 [corrected], a new member of the convertase family

A novel subtilisin-like protein, PC8, was identified by PCR using degenerate primers to conserved amino acid residues in the catalytic region of members of the prohormone convertase family. PC8 was predicted to be 785 residues long and was structurally related to the mammalian convertases furin, PACE4, PC1 and PC2, sharing more than 50% amino acid identity over the catalytic region with these family members. PC8 possessed the catalytically important Asp, His, Asn and Ser amino acids, the homo B domain of this family of enzymes and a C-terminal hydrophobic sequence indicative of a transmembrane domain. Structurally, PC8 is more related to furin and PACE4 than to PC1 or PC2. Like furin and PACE4, PC8 mRNA was found to be widely expressed; this is in contrast with PC1 and PC2, which have a restricted distribution. Two transcripts, of 4.5 and 3.5 kb, were detected in both human cell lines and rat tissues. Unlike furin and PACE4, both of which map to chromosome 15, PC8 maps to chromosome 11q23-11q24, suggesting that this gene may have resulted from an ancient gene duplication event from either furin or PACE4, or conversely that these genes arose from PC8.

False 'hematuria' due to bacteriuria

OBJECTIVE

To determine the effects of bacteriuria on dipstick urinalysis for microhematuria.

DESIGN

Selection of urine samples with dipstick readings of at least one plus (+) for blood, followed by microscopic examination and bacterial culture, from patients with signs and symptoms of urinary tract diseases.

SETTING

A large teaching hospital in Melbourne, Australia.

PATIENTS

Two hundred forty-six inpatients and outpatients being investigated for signs and symptoms of urinary tract diseases.

RESULTS

Seventeen (7%) of 246 patients having within-reference erythrocyte counts had polymicrobic cultures. One hundred nine patients had slight hematuria (1 x 10(7) to 6 x 10(7) cells/L). Of these, 21 bacteriuric patients had significantly higher dipstick findings than 88 abacteriuric patients (P < .005, Fisher's Exact Probability Test, two-tailed). Hydroperoxidase was detected in 80% of isolates (in 27 of 27 gram-negative bacilli cultures, in 6 of 6 staphylococci cultures, and in 3 of 12 streptococci cultures) on agar medium and in 69% of isolates in urine.

CONCLUSION

These results show that patients without hematuria but with bacteriuria may give a false-positive dipstick reading for blood.

The effects of endurance exercise on dystrophic mdx mice. II. Contractile properties of skinned muscle fibres

Dystrophic (mdx) mice were subjected to a 15 week exercise programme consisting of endurance swimming. Single fibres from the extensor digitorum longus (EDL, fast-twitch) and soleus (SOL, mixed fast- and slow-twitch) muscles were attached to a sensitive force-recording apparatus, and activated in Ca(2+)- and Sr(2+)-buffered solutions. In addition to the normal well-defined fibre types in these muscles, a small number of fibres were also sampled from the soleus of both experimental groups, which were 'Intermediate' to the other two SOL fibre types. Type IIB fibres from the EDL and type IIA fibres from the soleus of the Swim group were significantly less sensitive to Ca2+ and Sr2+ compared with those fibres sampled from the sedentary (Sedent) group, suggesting that endurance exercise was able to modify Ca(2+)- and Sr(2+)-activated contractile characteristics. The swim-trained (Swim) group's increased incidence of SOL fibres with characteristics intermediate to those of the fast- and slow-twitch fibre types suggests a possible exercise-induced fibre type transformation as an adaptation to the functional demand.

MK 287: a potent, specific, and orally active receptor antagonist of platelet-activating factor

MK 287 (L-680,573), a tetrahydrofuran analog, potently inhibited [3H]C18-PAF binding to human platelet, polymorphonuclear leukocyte (PMN) and lung membranes with K1 values of 6.1 +/- 1.5, 3.2 +/- 0.7, and 5.49 +/- 2.3 nM, respectively. The inhibitory effects are stereospecific and competitive. The racemate, L-668,750 is less potent and the enantiomer, L-680,574 is 20-fold less potent than MK 287. Inhibition of the binding of [3H]C18-PAF to human PMN membranes by MK 287 was associated with the reduction of the affinity of the radioligand but not the number of the receptor sites. Binding of other radioligands (e.g., LTB4, LTC4, C5a, FMLP) to their specific receptors was unaltered at 1-10 microM MK 287. [3H]MK 287 bound to membranes from human platelets and PMNs: KD = 2.1 +/- 0.6 and 2.9 +/- 1.2 nM, respectively. When examined on isolated human cells, MK 287 potently and selectively inhibited PAF-induced aggregation of platelets in plasma (ED50 = 56 +/- 38 nM) or gel-filtered platelets (ED50 = 1.5 +/- 0.5 nM) and elastase release from PMNs (ED50 = 4.4 +/- 2.6 nM). In studies in vivo, MK 287 inhibited PAF-induced lethality in mice (ED50 = 0.8 mg/kg orally) and PAF-induced bronchoconstriction in guinea pigs (ED50 = 0.18 mg/kg intraduodenally and 0.19 mg/kg intravenously). Inhibition of PAF-induced bronchoconstriction was accompanied by parallel rightward shifts in concentration-response curves for PAF-induced platelet aggregation measured ex vivo.

L-659,989: a useful probe in the detection of multiple conformational states of PAF receptors

L-659,989 is a potent, specific and competitive platelet-activating factor (PAF) receptor antagonist. The 2,5-tritium labeled L-659,989, similar to [3H]PAF, specifically binds to rabbit platelet membranes with an equilibrium dissociation constant (KD) of 1.60 (+/- 0.20) nM in 10 mM MgCl2. However, guanosine 5'-triphosphate (GTP) and several cations affect the specific binding of [3H]PAF and of [3H]L-659,989 to rabbit platelet membranes in different ways. K+, Mg2+, Ca2+ and Mn2+ potentiate the specific binding of both ligands. Na+ and Li+ inhibit the specific [3H]PAF binding, but enhance the binding of [3H]L-659,989; GTP reduces the [3H]PAF binding but has no effect on the binding of [3H]-L-659,989. Ni2+ inhibits the [3H]L-659-989 binding, but has no effect on the binding of [3H]PAF. In the presence of 150 mM NaCl, [3H]L-659,989 exhibits identical KD and detectable binding sites (Bmax) values as those in the presence of 10 mM MgCl2, while KD And Bmax values of [3H]PAF are dramatically reduced in the presence of 150 mM NaCl compared to those in 10 mM MgCl2. These results suggest the existence of multiple conformational states of the PAF specific receptor and that PAF and L-659,989 bind differently to those states. In the presence of 150 mM NaCl and 1 mM GTP, receptors appear to exist in a single conformational state with an equilibrium dissociation constant (KB) of 0.93 microM for PAF as derived from the Schild plot. In isolated rabbit platelets pretreated with 10 microM ETH 227, a Na(+)-specific ionophore, the detectable [3H]PAF binding sites drop from 260 to 100 binding sites per platelet, but the binding sites for [3H]L-659,989 remain roughly the same. The Na+ binding sites which modulate the conformation of PAF receptors are therefore protected from extracellular Na+ until ionophore is added, and are probably located on the cytoplasmic side of the plasma membrane.

Survival of Gardnerella vaginalis in human urine

The authors studied the survival of Gardnerella vaginalis in human urine and determined conditions for optimum recovery on agar media. Gardnerella counts declined by greater than 99.9% in urine held at 37 degrees C for 24 hours, whereas the falloff was negligible at 4 degrees C. Viability was lost after 6 hours in urine with pH of 5, and only 0.01% cells survived in urine with pH of 7. In contrast, greater than 90% cells survived exposure at pH of 6. Dialysis to remove small molecular weight (less than 14,000) inhibitors did not enhance survival. Co-cultivation with Ureaplasma urealyticum and the addition of glycogen improved survival. Maximum recovery from urine required anaerobic incubation on enriched agar medium (pH 6.5-7.5) for at least 48 hours. Gardnerella vaginalis survives poorly in human urine at 37 degrees C. Culture for these bacteria requires prolonged anaerobic incubation.

Comparative bioavailability study of two brands of prazosin-containing tablets in healthy volunteers

The bioavailability of two prazosin formulations was studied in 12 healthy volunteers. 1 Subject left the study. Based on the statistical tests of the pharmacokinetic parameters of prazosin in 11 volunteers, such as t 1/2, Cmax, tmax and AUC, it could be concluded that both preparations had comparable bioavailabilities.

Characterization of platelet-activating factor (PAF) receptor by specific binding of [3H]L-659,989, a PAF receptor antagonist, to rabbit platelet membranes: possible multiple conformational states of a single type of PAF receptors

(trans)-2-(3-Methoxy-5-methylsulfonyl-4-propoxyphenyl)-5-(3,4,5- trimethoxyphenyl)tetrahydrofuran (L-659,989) is a potent and orally active platelet-activating factor (PAF)-specific and competitive receptor antagonist. The 2,5-tritium-labeled L-659,989 ([3H]L-659,989) specifically binds to rabbit platelet membranes with an equilibrium dissociation constant (KD) of 1.60 +/- 0.20 nM in 10 mM MgCl2. Several selected PAF analogs and PAF receptor antagonists show equilibrium inhibition constants roughly similar to those found in the specific [3H]PAF binding assay. Other pharmacological agents with no PAF antagonistic activities do not inhibit the specific binding of [3H]L-659,989. K+ and divalent cations such as Mg2+, Ca2+, and Mn2+ potentiate the specific [3H]L-659,989 binding. Na+ and Li+ also enhance but GTP shows no effect on the specific binding of [3H]L-659,989. However, Ni2+ inhibits the specific binding. Scatchard analysis demonstrates that the potentiating effect of these cations is due to an increase in the detectable receptor number for L-659,989. In 10 mM MgCl2 [3H]L-659,989 shows higher receptor number than [3H]PAF. Under various ionic conditions with or without GTP, in which [3H] L-659,989 binding remains approximately the same, C16-PAF shows different potencies in competing against the specific [3H] L-659,989 binding. These results demonstrate the existence of multiple conformational states of the PAF-specific receptor. The variation in the detectable receptor number under different conditions is due to the coexistence of the high and low affinity states and the fact that the low affinity state(s) of the receptor with KD value(s) possibly in the micromolar range cannot be detected in the Scatchard analysis with the radioligand at nanomolar concentrations. In the presence of 150 mM NaCl and 1 mM GTP, receptors exist in a single conformational state with an equilibrium dissociation constant (KB) of 0.931 microM for PAF.

Biochemical and pharmacological characterization of L-659,989: an extremely potent, selective and competitive receptor antagonist of platelet-activating factor

L-659,989 [trans-2-(3-methoxy-5-methylsulfonyl-4-propoxy-phenyl)-5-(3,4,5- trimethoxyphenyl)tetrahydrofuran] is a p.o. active and extremely potent, selective and competitive platelet-activating factor (PAF) receptor antagonist. It inhibited [3H]PAF binding to either rabbit platelet or rabbit polymorphonuclear leukocyte membranes with an equilibrium inhibition constant (Kl) of 1.1 nM; whereas in human platelet, human polymorphonuclear leukocyte or human lung membranes, L-659,989 was about 10 times less potent with a Kl of 14.3 nM. The structural specificity of L-659,989 was demonstrated by the low activity of its cisisomer which was about 100 to 200 times less potent, also the (-)-L-659,989 was found to be 20- to 30-fold more potent than (+)-L-659,989. In both [3H]PAF binding and PAF-induced platelet aggregation inhibition, L-659,989 was found to be a competitive inhibitor with an equilibrium dissociation constant (KB) of 1.5 and 1.7 nM, respectively, in rabbit platelets. Even up to 6 microM concentration, L-659,989 showed no inhibition on the aggregation of rabbit platelets in plasma induced by ADP, arachidonic acid, collagen or thrombin. In an in vivo model, it inhibited guinea pig bronchoconstriction induced by i.v. infusion of 75 ng/kg of PAF with ED50 values of 13 micrograms/kg i.v. and 0.5 mg/kg p.o.

Prevalence of Gardnerella vaginalis in the urinary tract

Midstream urine samples from 106 patients presenting to the Casualty Department of The Royal Melbourne Hospital with frequency or dysuria were cultured for Gardnerella vaginalis and conventional uropathogens. Urine samples collected via an open-end catheter from 70 healthy pregnant women were examined similarly. Midstream urine and other samples, including the seminal fluids and swabs of the mouths, throats, rectums, and vaginas of 33 healthy subjects, were cultured for G. vaginalis. Another 15 female patients with proven G. vaginalis bacteriuria were given a bladder washout localization test to determine the site of infection in the urinary tract. G. vaginalis in counts greater than 10(3) CFU/ml was recovered from the midstream urine of 27 of 106 patients (25%), 7 of whom also harbored conventional pathogens in counts greater than 10(4) CFU/ml. Another 11 patients with cultures negative for G. vaginalis yielded greater than 10(4) CFU of conventional pathogens per ml. G. vaginalis was cultured (greater than 10(3) CFU/ml) from catheter samples of 19 of 70 healthy pregnant women (27%), 6 of whom also harbored greater than 10(3) CFU of conventional uropathogens per ml. Two women yielded growths of conventional pathogens only. Midstream urine samples from 13 of 13 healthy males were free of G. vaginalis, whereas 5 of 20 healthy nonpregnant females yielded greater than 10(3) CFU of G. vaginalis per ml from midstream urine samples. G. vaginalis was recovered from 4 of 12 semen samples and from urethral samples from four of seven males and four of eight females. All four culture-positive females also harbored G. vaginalis in their vaginas. There was no evidence of oral or rectal carriage of G. vaginalis in 15 healthy subjects. Localization studies with 15 female patients having underlying renal disease showed that 11 patients harbored G. vaginalis in their kidneys. The result suggest that colonization or infection of the bladder and upper urinary tract by G. vaginalis is very largely a phenomenon of females, with the highest frequency in pregnant women. The prevalence of G. vaginalis in the urinary tracts of healthy females is similar to that of symptomatic subjects. However, G. vaginalis in counts greater than 10(5) CFU/ml is more likely to be associated with urinary tract symptoms. In males, this bacterial species infects the genital tract rather than the urinary tract.

Species difference in the specific receptors of platelet activating factor

Relative potencies of platelet activating factor (PAF) and PAF analogs and several PAF receptor antagonists when inhibiting the [3H]PAF specific binding to human and rabbit platelet membranes and membrane fragments of human lung tissues were compared. In rabbit platelets, L-652,731 was found to be most potent in the list of PAF receptor antagonists with an equilibrium inhibition constant (Ki) of 9.83 (+/- 2.92) X 10(-9) M followed by L-653,150 greater than kadsurenone congruent to Ono-6240 greater than ginkgolide B greater than CV-3988 greater than L-651,142, whereas in human platelets the relative potencies of these PAF receptor antagonists were as follows: Ono-6240 greater than L-653,150 congruent to L-652,731 congruent to kadsurenone greater than ginkgolide B greater than CV-3988 greater than L-651,142. Ono-6240 was the most potent one with a Ki of 4.86 (+/- 1.44) X 10(-8) M which was roughly two times more potent than that in rabbit platelets, whereas the affinity of L-652,731 was about ten times less in human platelets (Ki = 1.03 (+/- 0.15) X 10(-7) M) compared to that in rabbit platelets (Ki = 9.83 (+/- 2.92) X 10(-9) M). These variations between species among PAF antagonists strongly suggest that there exists a species difference at or near the binding site of the receptor of platelet activating factor. The relative potency of these PAF receptor antagonists in human lung membranes differed very little from that in human platelets and was found to be Ono-6240 greater than L-653,150 congruent to kadsurenone congruent to L-652,731 greater than ginkgolide B greater than CV-3988 greater than L-651,142. Even though C16-PAF showed slightly higher potency in human lung, and CV-3988 and Ono-6240 showed slightly lower, the difference was too small to suggest that there is a difference in the PAF receptors between human platelets and human lung tissues.

Specific binding of [3H]dihydrokadsurenone to rabbit platelet membranes and its inhibition by the receptor agonists and antagonists of platelet-activating factor

Kadsurenone inhibits specifically and competitively the specific binding of 3H-labeled platelet-activating factor ([3H]PAF) to rabbit platelet membranes. Since the 5-propyl analog of kadsurenone (dihydrokadsurenone) retains roughly the same potency as kadsurenone, [3H]dihydrokadsurenone was therefore synthesized through tritiation of kadsurenone. Specific binding of [3H]dihydrokadsurenone in rabbit platelet membranes is saturable. Scatchard analysis of binding data reveals the presence of a single class of binding sites with an equilibrium dissociation constant (KD) of 16.81 ( +/- 0.57) nM. The total number (Bmax) of detectable binding sites is 2.27 ( +/- 0.09) pmol/mg protein. Both C16- and C18-PAF fully displace the specific binding of (3H]dihydrokadsurenone (5 nM) with an identical ED50 of 3.6 X 10(-9) M. Dihydrokadsurenone and kadsurenone also displace the specific binding with roughly the same potency (ED50 = 4.4 X 10(-8) M). Several other PAF analogs and PAF receptor antagonists tested show relative potencies roughly similar to those found in the [3H]PAF-specific binding assay. Other pharmacological agents with no PAF antagonistic activities did not inhibit the specific binding of [3H]dihydrokadsurenone. These results agree with our previous conclusion that kadsurenone is a specific and competitive receptor antagonist and strongly suggest that PAF and the PAF receptor antagonists tested may interact at a common binding site in the PAF receptor.

Ionic and GTP regulation of binding of platelet-activating factor to receptors and platelet-activating factor-induced activation of GTPase in rabbit platelet membranes

Specific binding of 3H-labeled platelet-activating factor (PAF) to rabbit platelet membranes was found to be regulated by monovalent and divalent cations and GTP. At 0 degrees C, inhibition of [3H]PAF binding by sodium is specific, with an ED50 of 6 mM, while Li+ is 25-fold less effective. On the contrary, K+, Cs+, and Rb+ enhance the binding. The divalent cations, Mg2+, Ca2+, and Mn2+ enhance the specific binding 8-10-fold. From both Scatchard and Klotz analyses, the inhibitory effect of Na+ is apparently due to an increase in the equilibrium dissociation constant (KD) of PAF binding to its receptors. However, the Mg2+-induced enhancement of the PAF specific binding may be attributed to an increased affinity of the receptor and an increased availability of the receptor sites. In the presence of Na+, PAF receptor affinity decreased with increasing temperature with a 100-fold sharp discontinuous decrease in receptor affinity at 24 degrees C. In contrast, the Mg2+-induced increase is independent of temperature suggesting that the Mg2+ regulatory site is different from Na+ regulatory site. [3H]PAF binding is also specifically inhibited by GTP; other nucleotides have little effect. PAF also stimulates hydrolysis of [gamma-32P]GTP with an ED50 of 0.7 nM, whereas 3-O-hexadecyl-2-O-acetyl-sn-glyceryl-1-phosphorylcholine showed no activity even at 10 microM. Moreover, such stimulatory effect of PAF is dependent on Na+ and can be abolished by the PAF-specific receptor antagonist, kadsurenone, but not by an inactive analog, kadsurin B. These results suggest that the PAF receptor may be coupled with the adenylate cyclase system via an inhibitory guanine nucleotide regulatory protein.

Release of platelet activating factor and its involvement in the first phase of carrageenin-induced rat foot edema

Platelet activating factor (PAF), a potent lipid-like vasoactive agent, induced rat foot edema when it was injected subplantarly. The edema reached its maximum 1 h after PAF challenge. Indomethacin did not inhibit the peak edematous response whereas both PAF antagonists, kadsurenone and L-652,731, inhibit the PAF-induced rat foot edema (PFE). Both PAF antagonists also partially block the first phase of the carrageenin-induced rat foot edema (CFE). Using the inhibition of [3H]PAF receptor binding to prepared rabbit platelet membranes, release of PAF or PAF-like materials in carrageenin-injected rat hindpaw was observed. These results suggest that the released PAF or PAF-like materials together with the released histamine and kinin evoke the first phase hindpaw edema in the rats. Indomethacin or PAF antagonist, administered alone, does not block the first phase or the second phase of CFE, respectively. However, PAF antagonist potentiated the inhibitory effects of indomethacin suggesting that the released PAF may also be involved in the biosynthesis of prostaglandins to initiate the second phase of rat CFE.

trans-2,5-Bis-(3,4,5-trimethoxyphenyl)tetrahydrofuran. An orally active specific and competitive receptor antagonist of platelet activating factor

trans-2,5-Bis(3,4,5-trimethoxyphenyl)tetrahydrofuran (L-652,731) is found to be a potent and orally active platelet activating factor (PAF)-specific and competitive receptor antagonist. It potently inhibits [3H]PAF (1 nM) binding to receptor sites on rabbit platelet membranes with an ED50 of 2 X 10(-8) M under the assay condition without the addition of mono- or divalent cations. In a comparative study, it is more potent than CV-3988, kadsurenone, and ginkgolide B as a receptor antagonist. The equilibrium dissociation constants (KB) of L-652,731 obtained either from the inhibition of receptor binding or from the inhibition of PAF-induced aggregation of gel-filtered rabbit platelet are 2.7 X 10(-8) and 2.1 X 10(-8) M, respectively. The agreement of these KB determinations based on receptor and cellular function suggests that L-652,731 does not inhibit other steps following PAF-receptor binding. L-652,731 does not antagonize the binding of several radioligands to their respective receptor. It shows no inhibitory effect on platelet aggregation induced by other aggregating agents including thrombin, collagen, A-23187, arachidonic acid, epinephrine, and ADP. L-652,731 is orally active; it inhibits PAF-induced rat cutaneous vascular permeability with an ED50 of 30 mg/kg orally. Significant inhibitory results of L-652,731 suggest that PAF may be partially involved in cutaneous vascular permeability induced by histamine and bradykinin.

Characterization of cutaneous vascular permeability induced by platelet-activating factor in guinea pigs and rats and its inhibition by a platelet-activating factor receptor antagonist

Mechanisms of platelet-activating factor (PAF)-induced increases of cutaneous vascular permeability in guinea pigs and in rats were further explored. PAF so far is the most potent vasoactive mediator, being more than 1000-fold more potent than histamine and bradykinin in both species. In guinea pigs, there is a time delay of 5 to 10 minutes before PAF action, whereas, in the rat, the increased vasopermeability occurs immediately following the intradermal PAF injection. Relative vasoactive potencies of PAF and several structure-related analogues in both species correlate very well with their relative inhibition of the binding of 3H-PAF to specific receptor sites on isolated rabbit platelet plasma membranes and their aggregatory abilities of rabbit platelets. Furthermore, the PAF-induced cutaneous vascular permeability is inhibitable by a competitive specific PAF receptor antagonist, kadsurenone, suggesting that binding of PAF to its specific receptor site is the first step to initiate its action of increased cutaneous vascular permeability. Several pure cyclooxygenase inhibitors, including indomethacin, diflunisal, and flurbiprofen, and the dual cyclooxygenase/lipoxygenase inhibitor, BW755C, but not the histamine antagonists, inhibit the PAF-induced vasopermeability in guinea pigs. The inhibition by indomethacin or BW755C can be fully reversed by coinjection intradermally with PAF and prostaglandin E1 but not leukotriene B4. Also, prostaglandin E1 but not leukotriene B4 enhances the guinea pig in vivo response to PAF in this model. However, in rats, none of the cyclooxygenase inhibitors, histamine antagonists, or BW755C inhibit the PAF effect of cutaneous phenomena even though prostaglandin E1 also enhances the PAF potency of the increased cutaneous vascular permeability. Kadsurenone, a competitive specific receptor antagonist, inhibits both histamine- and bradykinin-induced rat cutaneous vascular permeability which suggests that PAF may be involved in the vasopermeability induced by histamine and bradykinin.

Specific binding sites for platelet activating factor in human lung tissues

Specific and saturable binding of [3H]-labeled 1-0-alkyl-2-0-acetyl-sn-glycero-3-phosphocholine (PAF) to membrane preparations of human lung tissues is demonstrated. The equilibrium dissociation constant (KD) was determined by Scatchard analysis to be 4.9 (+/- 1.7) X 10(-10)M and the maximal number of binding sites was estimated to be 140 (+/- 37) fmole/mg protein. The binding site is PAF specific and its selectivity toward PAF analogs is very similar to that in rabbit platelets. Two PAF receptor antagonists, kadsurenone and ginkgolide B, previously characterized in platelet systems, also displace the binding of [3H]-PAF to human lung homogenates. These data indicate that human lung tissues contain PAF specific receptors, and binding of PAF to these receptor sites may be the first step to initiate PAF-induced lung pathophysiology.

Synthetic glycopeptide substrates for receptor-mediated endocytosis by macrophages

Mammalian macrophages contain a transport system that binds and internalizes glycoproteins with exposed mannose residues. This system and analogous systems on other types of cells require substrates to bear multiple nonreducing terminal residues of the appropriate sugar for effective uptake. Small multivalent synthetic glycopeptides with mannose residues covalently linked through a spacer arm to the alpha- and epsilon-amino groups of lysine, dilysine, and trilysine are competitive inhibitors of rat alveolar macrophage uptake of the neoglycoprotein mannosyl-bovine serum albumin with inhibition constants in the microM range. Various compounds could be covalently attached to the alpha-carboxyl group of these glycopeptides with substantial retention of inhibitory potency. This uptake system does not recognize galactose residues, and the galactosyl analog of an inhibitory mannosylpeptide did not inhibit uptake of mannosyl-bovine serum albumin. The trimannosyldilysine ligand is not only an inhibitor but also a substrate for specific uptake by macrophage, as shown with an 125I-labeled derivative. Macrophages bound 6.4 x 10(5) molecules per cell at 0 degrees C with a dissociation constant of 2 microM. At 21 degrees C the cells could internalize the labeled conjugate with an apparent Michaelis constant of 6 microM and a maximal velocity of 1.7 x 10(5) molecules per min per cel. The dissociation constant and Michaelis constant are similar to the inhibition constant of 9 microM determined at 21 degrees C for inhibition by this conjugate at mannosyl-bovine serum albumin uptake. These synthetic substrates may be useful in targeting pharmacologic agents to macrophages, and analogous compounds may target such agents to other types of cell.