Intestinal ammonium transport by ammonium and hydrogen exchange

BACKGROUND

Ionized ammonia (NH3) transport in the intestine has not been previously established as a mechanism of acidosis in urinary intestinal diversion or hepatic failure.

STUDY DESIGN

The purpose of this study was to establish that ionized transport of ammonium (NH4) occurs in the intestine and to characterize the mechanism of its transport using the methodology of brush border membrane vesicles and acridine orange fluorescence.

RESULTS

An NH4/H exchange was demonstrated and found to be the dominant mechanism causing a pH change when NH4 is transported across the lumenal membrane. Ionized NH4 transport was demonstrated to occur against an NH3 concentration gradient. The Km was 1.02 mmol and the Vmax was 247 U/sec. The Hill coefficient was 0.97, indicating a single port. Ammonium hydrogen exchange could be inhibited by amiloride but not by bumetanide. Sodium, potassium or chloride, or both, did not effect the NH4/H exchanger.

CONCLUSIONS

This study establishes that ionized NH4 transport occurs across the small intestine brush border in exchange for a hydrogen ion.

Octopus S-crystallins with endogenous glutathione S-transferase (GST) activity: sequence comparison and evolutionary relationships with authentic GST enzymes

S-Crystallin is a major protein present in the lenses of cephalopods (octopus and squid). To facilitate the cloning of this crystallin gene, cDNA was constructed from the poly(A)+ mRNA of octopus lenses, and amplified by PCR for nucleotide sequencing. Sequencing of 10 of 15 positive clones coding for this crystallin revealed three distinct S-crystallin isoforms with 61-64% identity in nucleotide sequences and 42-58% similarity in amino acid sequences when compared with homologous crystallins in squid lenses. These charge-isomeric crystallins also show between 26 and 33% amino acid sequence identity to four major classes of glutathione S-transferase (GST), a major detoxification enzyme present in most mammalian tissues. For further analysis, expression of one of the S-crystallin cDNAs was carried out in the bacterial expression system pQE-30, and the S-crystallin protein produced in Escherichia coli was purified to homogeneity to determine the enzymic properties. We found that the expressed octopus S-crystallin possessed much lower GST activity than the authentic GSTs from other tissues. Sequence comparison and construction of phylogenetic trees for S-crystallins from squid and octopus lenses and various classes of GSTs revealed that S-crystallins represent a multigene family which is structurally related to Alpha-class GSTs and probably derived from the ancestral GST by gene duplication and subsequent multiple mutational substitutions.

Rapid recovery of rat brain intracellular pH after cardiac arrest and resuscitation

We studied the intracellular pH in rat cerebral cortex of rats subjected to reversible total cerebral ischemia by cardiac arrest and resuscitation. Brain acidoses was more pronounced during ischemia in hyperglycemic rats (6.21 +/- 0.14) than in normoglycemic rats (6.56 +/- 0.07). Brain tissue lactate accumulated proportionally. Nevertheless, within 5 min of reperfusion, pHi in both normoglycemic and hyperglycemic groups had recovered to baseline levels, i.e. near 7.1-7.2, despite the fact that lactate concentrations were still elevated. These results demonstrate a rapid reversal of ischemic acidosis during recovery from 10 min of cardiac arrest, and suggest that acidosis, per se, may not be responsible for neuronal damage following cardiac arrest and resuscitation, even in hyperglycemic conditions.

Function of human Fc gamma RIIA and Fc gamma RIIIB

Fc gamma RIIA (CD32), a conventional type I transmembrane protein, and Fc gamma RIIIB (CD16B), which has a glycan phosphatidylinositol (GPI) membrane anchor, are both expressed on human neutrophils. Although some details remain to be elucidated, signaling following crosslinking of Fc gamma RIIA requires the activation of tyrosine kinases of both Src-family kinases and Syk, resulting in tyrosine phosphorylation of Shc, phospholipase C gamma isozymes, and a [Ca2+]i transient. Ligation of neutrophil Fc gamma RIIIB triggers a [Ca2+]i transient, and degranulation, although probably not ADCC or an oxidative burst. However, the mechanism for signal transduction by Fc gamma RIIIB, which lacks a transmembrane domain, is not known. Fc gamma RIIA and Fc gamma RIIIB appear to synergize with each other, leading to suggestions that the GPI-anchored Fc gamma RIIIB utilizes the Fc gamma RIIA signaling apparatus. The relevance of proposed specialized membrane domains enriched in GPI-anchored proteins, sphingomyelin and glycolipids to the signaling properties of Fc gamma RIIIB likewise remains to be explored.

Characterization of cloned human dopamine D1 receptor-mediated calcium release in 293 cells

Dopamine (DA) D1 receptors are generally known to couple only to Gs and cAMP production. Recently, D1 receptors expressed in mouse Ltk- cells have been shown to induce cAMP production, phosphoinositide (PI) hydrolysis, and calcium mobilization [Mol. Endocrinol. 6: 1815-1824 (1992)]. To further evaluate second messenger systems that could be activated by the D1 receptor, we examined the effects of DA, (R)-(+)-SKF-38393, and DA antagonists on cAMP production and calcium release in human embryonic kidney 293 cells stably expressing three different levels (Bmax = 0.12, 1.4, and 23 pmol/mg of protein) of the human D1 receptor. DA and (R)-(+)-SKF-38393 activated cAMP production and calcium release in all three D1-293 clones, and their potency was proportional to receptor density. The efficacy of SKF-38393 was also increased with receptor density in both cAMP and calcium studies. The effect of DA on calcium release consisted of a transient peak response (< 20 sec) that declined to an ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid-sensitive plateau level above the base-line (>5 min). The effect of DA on cAMP and calcium release was selectively inhibited by SCH23390, a selective D1 antagonist, and not by spiperone, a selective D2 antagonist. DA did not induce PI hydrolysis in any of the three receptor-expressing clones. A 24-hr pretreatment with cholera toxin (2 micrograms/ml) greatly attenuated the effect of DA on cAMP formation and calcium release. To address how DA could activate calcium release without enhancing PI hydrolysis, the effects of forskolin, thapsigargin, and isoproterenol (Iso) were studied. Similarly to the effects of DA, forskolin and Iso stimulated cAMP production and calcium release from D1-293 cells. Cells that were stimulated with Iso or forskolin showed a reduced response to subsequent addition of DA. Pretreatment of D1-293 cells with thapsigargin, a selective Ca2+-ATPase inhibitor, elicited calcium release from the inositol-1, 4, 5-trisphosphate-sensitive calcium store and attenuated the response to subsequent addition of DA. Carbachol stimulated PI hydrolysis and calcium release but had little effect on cAMP production. Prestimulation with carbachol abolished the calcium response to DA, Iso, or forskolin. These studies indicate that D1 receptor-mediated calcium mobilization in 293 cells is dependent on cAMP production and the cAMP-dependent calcium store is part of the inositol-1,4,5-trisphosphate-sensitive calcium pool.

Influence of dye and protein location on photosensitization of the plasma membrane

Two membrane-photosensitizing dyes were used to investigate whether selected sites in the plasma membrane vary in their sensitivity to damage by singlet oxygen (1O2*) and, if so, what factors are responsible for the variation. The relative ability of Rose bengal (RB) and merocyanine 540 (MC540), both of which localize in the plasma membrane and produce 1O2*, to photosensitize five plasma membrane functions in P388D1 cells was evaluated. The five membrane functions assessed were: plasma membrane potential, proline transport, facilitated glucose diffusion, 5'-nucleotidase activity, and dye exclusion. Photosensitization efficiency by RB varied by a factor of 188 for these membrane functions, whereas for MC540 a range of only 24 was found. RB was a more efficient photosensitizer than MC540 but the relative efficiencies varied with the membrane function. The wide range of P50 values for RB suggests that it binds selectively to membrane sites where it causes damage with high efficiency; possibly a non-1O2* mechanism is involved. In contrast, MC540 photosensitized the three membrane functions involving integral membrane proteins about equally suggesting that differences are due to small variations in the distribution of MC540 in the plasma membrane and/or variations in the inherent reactivity of the membrane targets with 1O2*. The results indicate that the lability of membrane sites to photosensitization depends both on their inherent reactivity with 1O2* and the relative location of specific protein and dye molecules.

Enhancement of Nile blue derivative-induced photocytotoxicity by nigericin and low cytoplasmic pH

The mechanism of photocytotoxicity mediated by a lysosomotropic photosensitizer, Nile blue derivative (NBS-61), in relation to lysosome destruction was examined by lowering the intracellular pH with low extracellular pH and an ionophore, nigericin. The treatment performed after photoirradiation had minimal effect on the cytotoxicity. However, when the treatment was initiated before photoirradiation, it caused a three orders of magnitude enhancement on cytotoxicity with a two orders of magnitude enhancement by nigericin alone. This effect on cytotoxicity resembles closely that observed on photosensitization mediated by chloroaluminum phthalocyanine. The enhancement in this case has been attributed to the synergistic interaction between photodamage and perturbation of ion transports across mitochondrial or plasma membranes by nigericin. Because these are not the main sites of localization for Nile blue photosensitizers nor their initial targets of photocytotoxic action, data from the present study suggest the possibility of an intracellular dye translocation induced by nigericin, which redistributes the Nile blue photosensitizer from lysosomes to other sites, as a possible cause of the enhancement of cytotoxicity.

Novel Asp32-replacement tetrapeptide analogues as potent and selective CCK-A agonists

A series of novel CCK tetrapeptide analogues of the general formula Boc-Trp-Lys(Tac)-N(R)-(CH2)nCON(R')Phe-NH2 (Tac = o-tolylaminocarbonyl), where R,R' = H or Me and n = 1-5, have been synthesized and tested. These analogues, which lack an acidic residue at the penultimate position, demonstrated surprisingly high CCK-A receptor affinity and selectivity. The effect of N-methylation pattern on CCK-A receptor affinity showed consistent trends for analogues in which n = 1, 2, or 3, with the di-N-methylated analogues having the highest affinity in each case. However, none of these analogues had full agonist activity, as measured by percent maximal PI hydrolysis. Two conformationally constrained analogues also demonstrated high CCK-A receptor affinity and selectivity, as well as nearly maximal agonist activity. In addition, one of these conformationally-constrained analogues demonstrated anorectic activity in rats.

Changes in energy metabolites, cGMP and intracellular pH during cortical spreading depression

The spatial and temporal distribution of cerebral metabolites and pHi were examined in the cortex during spreading depression. Acidification and marked depression in the energy status of the tissue was evident at the wavefront of spreading depression. In its aftermath, the residual activation of glycolysis and accumulation of cGMP persisted for minutes after a relatively rapid restoration of high-energy phosphates and pHi.

Evidence that the guanosine substrate of the Tetrahymena ribozyme is bound in the anti conformation and that N7 contributes to binding

The group I self-splicing introns are RNA enzymes that catalyze phosphodiester-exchange reactions. These ribozymes have a highly specific binding site for guanosine, a substrate for the first self-splicing reaction (Bass & Cech, 1984). The binding site for guanosine has been localized to a specific region of the ribozyme (Michel et al., 1989), but the conformation of the bound guanosine substrate remains unknown. Most analogs of guanosine with substituents at C8 have a preference for the syn conformation; however, some C8-substituted analogs have the potential to form a hydrogen bond between the C8 substituent and the 5'-hydroxyl that would stabilize the anti conformation; we have found that analogs with the potential to form such a hydrogen bond are more active substrates than those that cannot form such a hydrogen bond. These observations led us to test 8-5'-O-cycloguanosine, which is locked in the anti conformation, and 8-(alpha-hydroxyisopropyl)guanosine, which is locked in the syn conformation; the former is active as a substrate, while the latter is inactive. These results strongly suggest that guanosine is bound to the ribozyme in the anti conformation and provide an additional constraint on structural models of this RNA enzyme. We have also examined a series of N7-substituted guanosine analogs; this position had previously been assumed to be unimportant for substrate binding since 7-methylguanosine is an excellent substrate. However, we have found that 7-deazaguanosine and 7-methyl-7-deazaguanosine are less active substrates than guanosine. We discuss several models for the role of N7 in guanosine binding.

Tetrapeptide CCK-A agonists: effect of backbone N-methylations on in vitro and in vivo CCK activity

N-Methylation of backbone amide bonds was conducted on a tetrapeptide that had been identified previously (Shiosaki, K.; et al. J. Med. Chem. 1991, 34, 2387-2842) as a potent and selective CCK-A agonist. N alpha-Methylation at the position corresponding to Asp32 (CCK-33 numbering) was consistent with high affinity, efficacy, and selectivity for the CCK-A receptor. Combination of this (N-Me)Asp with the (N-Me)Phe modification also provided a highly active analogue. The observation of parallel structure-binding affinity profiles with respect to sites of N-methylation in the C-terminal regions of tetrapeptide vs heptapeptide CCK analogues suggests that the two series interact similarly with the CCK-A receptor.

Novel CCK analogues and bombesin: a detailed analysis between phosphoinositide breakdown and high-dose inhibition of pancreatic enzyme secretion in three rodent species

Cholecystokinin octapeptide (26-33) (CCK-8) stimulates pancreatic amylase secretion in a biphasic manner. Amylase secretion is stimulated in a dose-dependent manner up to a maximal level, but reduced secretion is observed at supramaximal concentrations. The downward portion of the dose-response curve has been referred to as "high-dose" inhibition. Recent studies with CCK-8 and Boc-Tyr(SO3H)-Nle-Gyl-Trp-Nle-Asp-2-phenylethylester (JMV-180) using rat acini have suggested that activation of the low-affinity CCK receptor leads to enhanced phosphoinositide (PI) breakdown, which in turn is responsible for high-dose inhibition of enzyme release. However, the secretory effect of JMV-180 varied considerably between rat and mouse. To explore further the relationship between PI breakdown and high-dose inhibition, we compared the effects of JMV-180 as well as the novel cholecystokinin tetrapeptide (30-33) Trp-Met-Asp-Phe-NH2 analogs A-70874 and A-57282, using rat, mouse and guinea pig pancreatic acini. The maximal secretory activity of CCK-8 was lowest (approximately 10% of total cellular amylase) in mouse, as compared with guinea pig and rat (approximately 15-20% of total amylase). The efficacies of A-70874, A-57282 and JMV-180 for stimulation of PI breakdown, relative to CCK-8, were 100, 100 and 45%, respectively, in mouse; 95, 70 and 20%, respectively, in rat and 75, 40 and 0%, respectively, in guinea pig.(ABSTRACT TRUNCATED AT 250 WORDS)

Tetrapeptide CCK agonists: structure-activity studies on modifications at the N-terminus

We had reported earlier on a novel series of potent and selective tetrapeptide cholecystokinin-A (CCK-A) agonists of the general structure Boc-Trp-Lys[epsilon-Y]-Asp-N(R)PheNH2 [Y = amides, ureas; R = H, Me] that were potent anorectic agents in rats. In an effort to optimize the potency, selectivity, stability, and efficacy of our lead candidate A-71623 [R = Me, Y = o-tolylaminocarbonyl; Tac] toward development of a clinical candidate, we have explored a series of analogues in which the N-terminal Boc functionality was systematically replaced with various amides, ureas, carbamates, and sulfonamides of differing size, hydrophobicity, and stereoelectronic properties. In general, these analogues maintained good potency and selectivity for the CCK-A receptor (guinea pig pancreas), as well as potent anorectic activity in rats. Those analogues exhibiting equal or superior activity compared to A-71623 but differing physicochemical properties may represent superior drug candidates.

Cloning and characterization of a truncated dopamine D1 receptor from goldfish retina: stimulation of cyclic AMP production and calcium mobilization

Receptors for dopamine are present on horizontal cells of fish retina that are linked to the activation of adenylate cyclase. In the present study, the goldfish (Carassius auratus) gene that encodes these receptors, referred to as gfD1, was isolated and analyzed. A single open reading frame within the gfD1 gene encodes a protein of 363 amino acids that is highly homologous with dopamine D1 receptors from rats and humans. Interestingly, the carboxyl terminus of gfD1 lacks 80 amino acids that are present in the mammalian receptor sequences. RNA analysis using the polymerase chain reaction demonstrated that the gene is expressed in the goldfish retina and is intronless within the coding region. The fact that gfD1 encodes a dopamine D1 receptor was demonstrated through pharmacological analysis of transfected cells. Both the gfD1 receptor and the human D1 receptor expressed in mammalian cells had high affinity for SCH-23390 and other D1-specific ligands. In addition, the gfD1 receptor and the human D1 receptor were able to stimulate the accumulation of cAMP in response to SKF-38393 or dopamine. Interestingly, stimulation of both the gfD1 and human receptors with dopamine also resulted in an increase in intracellular Ca2+. Finally, long term pretreatment of transfected cells with dopamine resulted in the desensitization and down-regulation of both the goldfish and human receptors.

Double bond isosteres of the peptide bond: synthesis and biological activity of cholecystokinin (CCK) C-terminal hexapeptide analogs

New and existing methodologies were used to prepare a series of modified CCK analogs in which each amide bond was replaced by a trans-alkene unit. The data indicate that every amide linkage at C-terminal tetrapeptide (CCK-4) region is crucial for biological activity. While the amide bond beyond the Trp residue in the N-terminal direction can be replaced by a trans-alkene and still retain most of the binding potency and functional activity.

Regulation of manganese superoxide dismutase and other antioxidant genes in normal and leukemic hematopoietic cells and their relationship to cytotoxicity by tumor necrosis factor

Myeloid cells are a major source of superoxide and other oxygen metabolites. As a protective mechanism, cells express antioxidant enzymes including manganese superoxide dismutase (Mn-SOD), copper-zinc SOD (Cu/Zn-SOD), and glutathione peroxidase (GSX-PX). Even though hematopoietic cells are a major source of oxidants, little is known of their expression of antioxidants. We found that seven myeloid leukemic cell lines blocked at different stages of differentiation constitutively expressed Mn-SOD, Cu/Zn-SOD, and GSX-PX RNAs. Level of Mn-SOD activities paralleled levels of Mn-SOD RNA. Terminal differentiation of native HL-60 cells to either granulocytes or macrophages did not alter levels of Mn-SOD RNA but markedly decreased cell division. Myeloid leukemic lines sensitive to cytotoxic effects of tumor necrosis factor (TNF) as well as normal peripheral blood lymphocytes and monocytes, dramatically increased their levels of Mn-SOD RNA in the presence of TNF. In contrast, Cu/Zn-SOD and GSX-PX RNA levels did not increase in these same cells. TNF-resistant leukemic lines had higher constitutive levels of Mn-SOD RNA and activity; and these levels did not change in the presence of TNF. Antisense but not random oligonucleotides to Mn-SOD markedly increased the sensitivity to the inhibitory effects of TNF for both the native HL-60 (TNF-sensitive) and K562 (TNF-resistant) cell lines. Further studies showed that the antisense oligonucleotides entered the cells and resulted in decreased levels of Mn-SOD RNA. The data suggest that Mn-SOD may provide protection against cytotoxicity of TNF in hematopoietic cells.

Identification and characterization of type A endothelin receptors in MMQ cells

Recently the identification of endothelin (ET) receptors and ET in the pituitary gland has induced much interest in studying the potential role of ET in neuroendocrine regulation. MMQ, isolated from rat pituitary, is a prolactin-secreting cell line. Similar to primary pituitary cells, the secretory response in MMQ cells is regulated by calcium and cAMP. In this report, by combining radioligand binding, cross-linking, and reverse transcription-polymerase chain reaction (RT-PCR) techniques, we characterized the properties of ET receptors in MMQ cells. 125I-ET-1 bound to membranes prepared from MMQ cells in a time-dependent manner, reaching a plateau at 150 min at 25 degrees. 125I-ET-1 binding was inhibited by ET-1 with an IC50 value of 0.17 nM but was only partially (approximately 60%) inhibited by 1 microM ET-3. BQ123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu]) and FR139317 (cC6N-L-Leu-D-Trp-Me-D-2Pya-OH), two antagonists that are selective for the ETA receptor, inhibited 125I-ET-1 binding with IC50 values of 5 nM and 0.9 nM, respectively. RT-PCR detected mRNA for the ETA receptor but not the ETB receptor. RT-PCR detected mRNA for both ETA and ETB receptors in control experiments using rat kidney RNA. 125I-ET-1 binding was saturable, reaching a plateau at 0.1 nM. Scatchard analysis of the data from saturation studies yielded a straight line, with Bmax and Kd values of 0.11 pmol/mg and 0.038 nM, respectively. The number of receptors was 6.6 x 10(10) sites/mg of protein or 13,200 sites/cell. Cross-linking studies using bis(sulfosuccinimidyl)suberate revealed an apparent molecular mass of 65 kDa for the ET receptor. Labeling of the 65-kDa protein was abolished by ET-1, BQ123, or FR139317 at 0.1 microM. ET-1 stimulated the formation of total inositol phosphates in a dose-dependent manner, with an EC50 of 0.1 nM. The phosphatidylinositol hydrolysis response was also inhibited by BQ123 and FR139317. We conclude that MMQ cells express the ETA receptor, which is coupled to phosphatidylinositol hydrolysis. MMQ cells may be useful for elucidating the mechanisms through which ET exerts its regulatory effects on pituitary cells.

Photodynamic destruction of lysosomes mediated by Nile blue photosensitizers

Previous studies have established that a number of Nile blue derivatives are potent photosensitizers and that they are localized primarily in the lysosomes. The present study examines whether the lysosome is a main target of the photocytotoxic action mediated by these sensitizers. Chosen for this study were NBS-6I and sat-NBS, which represented, respectively, derivatives with high and moderate degrees of lysosomal. This is indicated by the light-and drug-dose-dependent losses of acid phosphatase staining particles, reduction of hexosaminidase in the lysosome-containing subcellular fraction, and impairment of the lysosomes to take up and sequester acridine orange. Ultrastructurally, swollen and ruptured lysosomes were seen as one of the first evidences of cell damage mediated by these photosensitizers. However, the study also showed that sat-NBS, which is less lysosomal selective, was less effective in mediating lysosomal destruction. Also, the degree of lysosomal destruction mediated by sat-NBS did not parallel the degree of cytotoxicity generated. This implies that for derivatives that are not exclusively localized in the lysosome, other subcellular sites may also be damaged by the photodynamic action and may play a role in the photocytotoxic process.

The role of AP-1 in matrix metalloproteinase gene expression

In an effort to understand the mechanism of matrix metalloproteinase (MMP) induction, lapine synoviocytes were isolated and incubated with phorbol myristate acetate (PMA) and autocrine "cell-activating factors" (CAF), agents which significantly increase MMP mRNA abundance. AP-1 complexes, formed by c-fos and c-jun which bind to 5' residues of the MMP genes, seem causally related to MMP gene expression in response to PMA. However, although AP-1 DNA binding activity is strongly induced following exposure of synoviocytes to CAF, MMP gene expression in response to CAF does not correlate well with AP-1 activity and is not inhibited by antisense DNA to fos and jun. We hypothesize that there is a CAF-response factor involved in MMP gene expression and that this factor competes with the binding of the AP-1 complex to its target response element.

Peripheral cholecystokinin type A receptors mediate oxytocin secretion in vivo

Cholecystokinin-octapeptide (CCK8) administered intraperitoneally (i.p.) in rats induces a rapid elevation in serum oxytocin (OT). The receptor subtype mediating this action of CCK was investigated with selective CCK-A and CCK-B receptor agonists and antagonists. CCK8 and A-71623, a potent CCK-A selective agonist, were similar in efficacy and potency for stimulating OT secretion. Both compounds at 10 nmol/kg elicited approximately one-half the response of 100 nmol/kg, which elevated serum OT to approx. 20 to 30-fold above basal level. The potent CCK-B selective agonist, A-63387, at doses up to 100 nmol/kg did not increase serum OT. MK-329, a CCK-A receptor selective antagonist, at a dose of 20 nmol/kg fully inhibited the action of 20 nmol/kg CCK8, while 100 nmol/kg of (R)L-365,260, a CCK-B selective antagonist, had no effect on the CCK8 response. These results, together with previous lesion studies, suggest that vagal CCK-A receptors in the periphery mediate the activation of the oxytocinergic pathway in vivo.

Biochemical characterization of crystallins from pigeon lenses: structural and sequence analysis of pigeon delta-crystallin

Crystallins from pigeon eye lenses were isolated and purified by gel-permeation chromatography and characterized by gel electrophoresis, amino-acid composition and sequence analysis. Alpha- and beta-crystallins could be obtained in relatively pure forms by single-step size-exclusion chromatography whereas an extra step of ion-exchange chromatography was needed for the separation of delta-crystallin from the beta-crystallin fraction. In contrast to most characterized vertebrate species, a large amount of glycogen is eluted as a high molecular form in the first peak of the gel filtration column. Pigeon delta-crystallin, similar to duck and reptilian delta-crystallins, exists as a tetrameric structure of about 200 kDa in the native form and is composed of one major subunit of 50 kDa with heterogeneous isoelectric points spreading in a range of 4.7 to 6.8. In contrast to those obtained from duck, goose and caiman, delta-crystallin isolated from the pigeon lens possessed very little argininosuccinate lyase activity. However, pigeon delta-crystallin can still cross-react with the antibody against enzymically active duck delta-crystallin as revealed by the sensitive immunoblotting technique. It was also shown that the delta-crystallin content of the total pigeon soluble proteins decreased with the age of the animal. Structural analysis of purified delta-crystallin fraction was made with respect to its amino-acid composition and protein primary sequence. N-terminal sequence analysis indicated the presence of blocked amino-termini in all crystallin fractions of pigeon lenses. Therefore, a sequence analysis of PCR (polymerase chain reaction) amplified delta-crystallin cDNA was employed to deduce the protein sequence of this crystallin. Structural comparison of delta-crystallin sequences from pigeon, chicken and duck lenses casts some doubts on the recent claim that His-89-->Gln mutation in the chicken delta-crystallin may account for the loss of argininosuccinate lyase activity in this avian species, as compared to high enzymic activity in the duck crystallin (Barbosa et al. (1991) J. Biol. Chem. 266, 5286-5290).

Characterization of the novel CCK analogs JMV-180, JMV-320, and JMV-332 in H345 cells

The interaction of the novel CCK analogs JMV-180, JMV-320, and JMV-332 with CCK-B/gastrin receptors on small cell lung cancer (SCLC) cells was investigated. JMV-180, JMV-320, and JMV-332 potently inhibited specific binding of 125I-CCK-8 to CCK-B/gastrin receptors expressed on the SCLC cell line NCI-H345 (H345) with IC50 values of 4.9, 1.8, and 7.0 nM, respectively. JMV-320 and JMV-332 stimulated intracellular calcium ([Ca2+]i) release in a dose-dependent manner in cells preloaded with indo-1. JMV-180 did not stimulate [Ca2+]i but inhibited the [Ca2+]i release elicited by 10 nM CCK-8 in a dose-dependent manner. These data indicate that JMV-320 and JMV-332 function as CCK-B/gastrin receptor agonists while JMV-180 functions as a CCK-B/gastrin receptor antagonist in H345 cells.

Sequence analysis of pigeon delta-crystallin gene and its deduced primary structure. Comparison of avian delta-crystallins with and without endogenous argininosuccinate lyase activity

delta-Crystallin is a major lens protein present in the avian and reptilian lenses. To facilitate the cloning of the delta-crystallin gene, cDNA was constructed from the poly(A)+ RNA of pigeon lenses, amplified by the polymerase chain reaction (PCR). The PCR product was then subcloned into pUC19 vector and transformed into E. coli strain JM109. Plasmids purified from the positive clones were prepared for nucleotide sequencing by the dideoxynucleotide chain-termination method. Sequencing two clones, containing 1.4 kb DNA inserts coding for delta-crystallin allowed the construction of a complete, full-length reading frame of 1,417 bp covering a deduced protein sequence of 466 amino acids, including the universal translation-initiating methionine. The pigeon delta-crystallin shows 88, 83 and 69% sequence identity to duck delta 2, chicken delta 1 crystallins and human argininosuccinate lyase respectively. It is also shown that, in contrast to duck delta 2 crystallin which has a high argininosuccinate lyase activity, pigeon delta-crystallin appears to contain very low activity of this enzyme, despite the fact that they share a highly homologous structure. A structural comparison of delta-crystallins with or without enzymatic activity suggested several amino acid replacements which may account for the loss of argininosuccinate lyase activity in the lenses of certain avian species.

Both CCK-A and CCK-B/gastrin receptors are present on rabbit vagus nerve

Cholecystokinin (CCK) receptors on vagal afferents have been implicated in many of the actions of the brain-gut peptide CCK, including satiety. Autoradiographic studies in rats have demonstrated the presence of CCK-A-type receptors on vagus nerves. However, direct and detailed characterization of this important CCK receptor site has never been reported with membrane-binding techniques. Using 125I-Bolt-on-Hunter-CCK octapeptide (125I-BH-CCK-8) and the recently discovered selective agonists and antagonists of CCK receptors, we have delineated the properties of CCK receptors on rabbit vagus nerve. 125I-BH-CCK-8 binding sites appeared to be homogeneous by the Scatchard analysis, with a dissociation constant of 0.14 nM and a maximum binding of 72 fmol/mg protein. However, competition studies using selective CCK ligands showed that the vagal CCK receptors are heterogeneous. A71378, a selective CCK-A agonist, showed biphasic displacement curves, with the high-affinity portion (less than 10 nM) accounting for approximately 60% and the low-affinity portion for approximately 40%. Competitive binding studies using A63387, a selective CCK-B/gastrin receptor agonist, also showed biphasic displacement curves, with the high-affinity portion (less than 30 nM) at approximately 40% and the low-affinity portion at approximately 60%. Under conditions which selectively examined vagal CCK-A or CCK-B/gastrin receptors, we demonstrated that a number of CCK subtype selective agonists and antagonists possessed similar affinities for the vagal CCK-A and -B/gastrin receptors as those found on the guinea pig pancreas (CCK-A) and cerebral cortex (CCK-B), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and biological activity of CCK heptapeptide analogues. Effects of conformational constraints and standard modifications on receptor subtype selectivity, functional activity in vitro, and appetite suppression in vivo

A series of modifications of the CCK7 analogue (des-NH2)Tyr(SO3-)-Nle-Gly-Trp-Nle-Asp-Phe-NH2 was prepared and tested for binding to guinea pig CCK-A and CCK-B receptors and in CCK-A-mediated functional assays. Selected analogues also were tested for appetite suppressant activity in rats. Several conformationally restricted residues in the C-terminal tetrapeptide region, including delta Z-Phe33, (N-Me)Phe33, (N-Me)Asp32, (N-Me)Leu31, and 3PP31 (3PP = trans-3-n-propyl-L- proline) were found to be acceptable modifications at one or both receptor subtypes. The (N-Me)Asp32 and (N-Me)Leu31 modifications afforded potent and selective CCK-A and CCK-B ligands, respectively. SAR studies in the N-terminal acyldipeptide region examined structural requirements for the side chain at position 28, where Gly and Pro replacements were found to possess high affinity at both receptor subtypes. Other conformationally restrictive modifications were less active. All of the analogues that showed high affinity (less than 10 nM) for the CCK-A receptor also were full agonists in amylase release and most were full or nearly full agonists in the phosphoinositide (PI) turnover assay, the most notable exception being the delta Z-Phe33 analogue, which showed 69% of the maximal response in the PI assay. Potent activity in suppression of food intake in rats was found for selected analogues.

Facile cloning and sequencing of S-crystallin genes from octopus lenses based on polymerase chain reaction

S-crystallin is a major lens protein present in the octopus and squid of Cephalopods. To facilitate the cloning of the protein, cDNA was constructed from the poly(A)+RNA of octopus lenses, and amplification by polymerase chain reaction (PCR) was carried out with two primers designed according to the 5'- and 3'-coding regions of S-crystallin gene. Sequencing two of 15 positive clones obtained shows 37-44% similarity in nucleotide and 23-30% similarity in amino acid sequences as compared with mammalian glutathione S-transferases (GST), revealing that S-crystallins exist as a multigene family and probably derived from GST by gene duplication and subsequent mutational base replacements.

Both CCK-A and CCK-B/gastrin receptors mediate pepsinogen release in guinea pig gastric glands

We evaluated the affinity of cholecystokinin octapeptide (CCK-8), gastrin, and subtype-selective CCK agonists for CCK/gastrin receptors and compared it with the ability of these peptides to stimulate phosphoinositide (PI) hydrolysis and pepsinogen release in guinea pig gastric glands. Competitive binding studies using 125I-labeled Bolton-Hunter-CCK-8 and 125I-gastrin showed the presence of CCK-B/gastrin receptors in gastric glands and dispersed chief cells. In contrast, the potency of peptides in stimulating PI hydrolysis in both gastric glands and dispersed chief cells displayed a profile similar to CCK-A receptors found in pancreatic acini, i.e., CCK-8 = A 71378 greater than A 71623 greater than A 70874 much greater than A 72962 = CCK-8 (desulfated) greater than gastrin II greater than gastrin I. In general, the rank order of potency of peptides for stimulation of PI hydrolysis correlated well with their ability to stimulate pepsinogen release. At concentrations greater than 10 microM, efficacies of gastrin I and II in stimulating pepsinogen release from gastric glands were near 90% of the maximal activity of CCK-8. The inhibitory potency of MK-329, a selective CCK-A receptor antagonist, was similar against either CCK-8 (10 nM) or gastrin I (10 microM), except that a minor portion (approximately 30-40%) of gastrin I-induced pepsinogen release was insensitive to MK-329. The MK-329-insensitive component was inhibited by CI-988, a potent and selective CCK-B/gastrin receptor antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of potent and selective CCK-A receptor agonists from Boc-CCK-4: tetrapeptides containing Lys(N epsilon)-amide residues

A series of Boc-CCK-4 derivatives represented by the general structure Boc-Trp-Lys(N epsilon-COR)-Asp-Phe-NH2, where R is an aromatic, heterocyclic, or aliphatic group, are potent and selective CCK-A receptor agonists. These amide-bearing compounds complement the previously described urea-based tetrapeptides (Shiosaki et al. J. Med. Chem. 1991, 34, 2837-2842); structure-activity studies revealed parallel as well as divergent trends between these two series. A significant correlation was observed between pancreatic binding affinity and the resonance constant R of the phenyl substituent in one particular series of derivatives. Sulfation of phenolic amides appended onto the epsilon-amino group of the lysine did not affect affinity for the CCK-A receptor in contrast to the 500-fold increase in binding potency observed upon sulfation of CCK-8, suggesting that the lysine appendage and the sulfated tyrosine in CCK-8, both key structural elements that impart high affinity for the CCK-A receptor, are interacting differently with the receptor. The amide-bearing tetrapeptides are full agonists relative to CCK-8 in stimulating pancreatic amylase release while being partial agonists in eliciting phosphoinositide (PI) hydrolysis. Both effects were blocked by selective CCK-A receptor antagonists.

Intracellular pH in rat brain in vivo and in brain slices

Intracellular pH can be measured quantitatively in rat brain in vivo and in vitro using spectrophotometric detection of the vital dye neutral red. This method preserves spatial information and is compatible with microhistochemistry. The intracellular pH indicated by this method is in close agreement with that indicated by 31P-NMR spectroscopy. During ischemia, intracellular acidification is correlated with tissue lactate accumulation. The spatial distribution of pH values becomes more heterogeneous as the tissue becomes more acidic. Resuscitation from total cerebral ischemia produced by cardiac arrest results in rapid intracellular realkalinization. This realkalinization is at least partially inhibited by amiloride pretreatment. Some neuronal populations, especially in the hippocampal CA1 and CA4 regions, may become more acidic during ischemia and realkalinize more slowly after reperfusion than other tissue regions. The intracellular pH of hippocampal brain slice preparations is more alkaline than expected from in vivo studies. The intracellular pH of the brain slice can be acidified to near neutrality by specific inhibitors of the sodium/hydrogen ion exchanger.

The synovial activation of chondrocytes: evidence for complex cytokine interactions involving a possible novel factor

Preparations of lapine synovial 'chondrocyte activating factors' (CAF) were analyzed for the presence of individual cytokines which modulate the production of neutral metalloproteinases (NMPs) and prostaglandin E2 (PGE2) by articular chondrocytes. A combination of different biochemical analyses suggested that synovial fibroblasts secrete IL-1 alpha, which activated chondrocytes directly, bFGF, which potentiated the activity of IL-1, and TGF-beta 1, which produced a bivalent response. TGF-beta 1 suppressed NMP synthesis by chondrocytes, but enhanced PGE2 synthesis. The IL-1 receptor antagonist protein (IRAP) eliminated chondrocyte activation by IL-1, but only partially inhibited activation by CAF. Thus, CAF may contain a cytokine in addition to IL-1 which activates chondrocytes. This putative additional factor was more thermosensitive than IL-1, and had an apparent molecular weight of approx. 20,000 when estimated by size exclusion chromatography. Of a variety of purified cytokines tested for their ability to induce NMPs in chondrocytes, only IL-1 was active. This favours the possibility that the activity which resists suppression by IRAP reflects the presence of a novel cytokine.

Distribution of intracellular pH in the rat brain cortex after global ischemia as measured by color film histophotometry of neutral red

Tissue acidosis is an important determinant of cell viability following cerebral ischemia. Because of the heterogeneity of tissue response to metabolic stress, a method for measuring intracellular pH (pHi) that preserves spatial information would be desirable. Histophotometry of the pH indicator dye Neutral red offers such a possibility. The purpose of our study was to determine the distribution of pHi following complete irreversible ischemia and show the correlation of mean pHi measured by Neutral red and [31P]NMR in the same brain. Three rats were studied in the anesthetized state. A pHi range was obtained by total cerebral ischemia at various pre-arrest plasma glucose concentrations. The data show that mean pHi calculated by Neutral red was strongly correlated to pHi determined from [31P]NMR (slope: 0.99 +/- 0.08; P less than 0.001, r2 = 0.96). Within each brain, 80-110 discrete samples were analyzed by histophotometry. The pHi distribution of those samples broadened in those rat brains with greater acidosis, suggesting a heterogeneity of response by the tissue to ischemia and the presence of multiple pHi pools. Our results demonstrate the need to use methods which maintain spatial resolution such as is available with histophotometry.

Isolation of a crotalase-like protease with alpha-fibrinogenase activity from the western diamondback rattlesnake, Crotalus atrox

Venom toxins were isolated from rattlesnake (Crotalus atrox) venom by cation-exchange chromatography. Seven major fractions could be obtained by single-step ion-exchange chromatography with two fractions showing essentially apparent homogeneity by SDS-gel electrophoresis. All fractions showed various extents of specific proteolytic activity against alpha- or beta-chains of fibrinogen molecules. Further characterization of one of the purified fractions with alpha-fribrinogenase activity indicated that it is a single-chain thrombin-like protease with a molecular mass of about 30 kDa. It is relatively heat stable, inhibited by phenylmethanesulfonyl fluoride, N alpha-p-tosyl-L-phenylalanine chloromethyl ketone and N alpha-p-tosyl-L-lysine chloromethyl ketone but not by soybean trypsin inhibitor and beta-mercaptoethanol. Amino acid analysis showed that the enzyme possesses an amino acid composition very similar to thrombin and crotalase characterized before from the closely related snake venoms. N-Terminal sequence analysis of the enzyme corroborated the close similarity between this enzyme and those sequences of crotalase and kallikrein-like enzymes characterized from the same Crotalidae snake family. This study is in contrast to the previous reports which indicated a lack of thrombin- and crotalase-like enzyme in the venom of Western diamondback rattlesnake.

Cholecystokinin antagonists: (R)-tryptophan-based hybrid antagonists of high affinity and selectivity for CCK-A receptors

The intriguing structural similarities of glutamic acid based cholecystokinin (CCK) antagonists (A-64718 and A-65186) and the benzodiazepine CCK antagonist MK-329 (L-364,718) have been reported. Efforts to include the weak CCK antagonist benzotript into this construct utilizing a similar approach have resulted in a novel series of benzotript-based hybrid antagonists N alpha-(3'-quinolylcarbonyl)-(R)-tryptophan di-n-pentylamide (9, A-67396), N alpha-(4',8'-dihydroxy-2'-quinolylcarbonyl)-(R)-tryptophan di-n-pentylamide (23, A-70276), and N alpha-(3'-quinolylcarbonyl)-(R)-5'-hydroxytryptophan di-n-pentylamide (36, A-71134) which possess respectively binding affinities of 23, 21, and 11 nM for the pancreatic CCK-A receptor and which inhibit CCK8-induced amylase secretion. Compound 9 possesses a selectivity of greater than 500-fold for the pancreatic CCK-A receptor over the CCK-B receptor.

Inducible synthesis of collagenase and other neutral metalloproteinases by cells of aortic origin

In view of the possible link between collagenase and the formation of aortic aneurysms we have determined whether cells within the aorta are able to synthesize this enzyme. Explanted cells obtained from fragments of lapine abdominal aorta secreted little or no collagenase. Two related metalloproteinases, gelatinase and stromelysin, were also produced at very low levels. Treatment with purified human monocyte interleukin-1 beta, partially purified lapine, synovial IL-1 or phorbol myristate acetate strongly induced the synthesis of all these enzymes. These activators also increased synthesis of prostaglandin E2. The identity of collagenase was confirmed by detection of the characteristic TCA and TCB breakdown fragments of collagen and by demonstration of collagenase mRNA within activated aortic cells. Unactivated aortic cells contained no detectable collagenase mRNA, suggesting a pretranslational level of regulation. Aortic cells thus possess the ability to express several neutral metalloproteinases and, if a sufficient inflammatory stimulus was present, they might do so in arteries undergoing aneurysmal degeneration.

Photodynamic therapy of malignant tumors--recent developments

Photodynamic therapy (PDT) is a promising new cancer treatment modality in which tumor cells are killed as a result of photoactivation of a tumor-localizing photosensitizing agent. Since activating light can be targeted specifically to tumors, and tumor-selective photosensitizing agents are being developed, this treatment has the potential to induce highly selective destruction of malignant cells. To date, PDT has been applied to a large variety of human carcinomas, resulting in successful eradication of single tumor nodules and several types of superficial tumors. Current research is aimed at improving the efficacy and tumor-selectivity and tumor destruction. The most immediate benefits of PDT are likely to be seen in patients treated with a combination of this and other forms of therapy.

Synovial activation of chondrocytes: evidence for complex cytokine interactions

Synoviocytes secrete factors which induce the synthesis of neutral metalloproteinases (NMP) and prostaglandin E2 (PGE2) by chondrocytes in a response called "chondrocyte activation". We analyzed synovial chondrocyte activating factors (CAF) for the presence of cytokines which modulated the NMP production by articular chondrocytes. These studies suggested the presence of several other cytokines in addition to interleukin-1 (IL-1). Both resting and activated synoviocytes contained mRNA for basic fibroblast growth factor (bFGF) which is a synergist for IL-1 induced NMP production, and secreted bFGF into their culture media. They also expressed mRNA for transforming growth factor beta (TGF beta) which inhibits IL-1 induced NMP production. These cells also produce tumor necrosis factor alpha (TNF alpha) and trace amounts of interleukin-6 (IL-6). In addition to these there is evidence for a synovial activator of chondrocytes which is distinct from IL-1. Since a number of recombinant cytokines including TNF alpha, IL-6 and bFGF failed to activate chondrocytes, this could be a novel cytokine.

Boc-CCK-4 derivatives containing side-chain ureas as potent and selective CCK-a receptor agonists

Novel Boc-CCK-4 derivatives were communicated recently as having high potency and selectivity for the CCK-A receptor (Shiosaki et al. J. Med. Chem. 1990, 33, 2950-2952). While Boc-CCK-4 binds selectively to the CCK-B receptor, replacement of the methionine with an N epsilon-substituted lysine dramatically reversed receptor selectivity, leading to the development of this novel series of tetrapeptides. A detailed structure-activity analysis of a series of urea-substituted tetrapeptides, represented by the general structure Boc-Trp-Lys(N epsilon-CO-NHR)-Asp-Phe-NH2, revealed that a number of substituted phenyl, naphthyl, and aliphatic urea residues in the lysine side chain yielded potent and selective CCK-A ligands. These tetrapeptides elicit full agonist responses in stimulating pancreatic amylase release that are effectively blocked by a selective CCK-A receptor antagonist. Conversion of the urea to a thiourea significantly reduced CCK-A binding potency as did replacement of the lysine with the homologous ornithine or homolysine. Tetrapeptides that were partial agonists (less than 80% efficacy) in phosphoinositide (PI) hydrolysis relative to CCK-8 did not exhibit high-dose inhibition of amylase secretion in guinea pig acini.

Excitatory effects of cholecystokinin octapeptide on rat nodose ganglion cells in vitro

Cholecystokinin octapeptide (CCK-8) applied by pressure evoked in the majority of rat nodose ganglion cells a rapid depolarization associated with a fall of membrane resistance and in a few cells a slow depolarization accompanied by an increase of membrane resistance. The fast depolarizations were increased and decreased by membrane hyperpolarization and depolarization; the extrapolated reversal potential was about -10 mV. The response was depressed in a Na-free solution and by d-tubocurarine (10-100 microM) but not in a Cl-deficient solution. It is concluded that CCK-8 depolarized the nodose ganglion cells by increasing cation conductances and in a few cells it also produced a slow excitation, the mechanism of which remains to be established.

Lysosomal localization and mechanism of uptake of Nile blue photosensitizers in tumor cells

Nile blue derivatives have been shown to be potentially effective photosensitizers for photodynamic therapy of malignant tumors. Results of a previous study suggested that the high accumulation of these dyes in cells may be the result of dye aggregation, partition in membrane lipids, and/or sequestration in subcellular organelles. In this report, results of studies are presented from an investigation of the subcellular localization and mechanism of accumulation of these dyes in cells in vitro. A video-enhanced fluorescence microscopy was used, and a punctate pattern of fluorescence was seen, most of which was localized in the perinuclear region with extracellular dye concentrations between 1 to 100 nM. These particles resembled characteristic particles identified by standard lysosomal dyes. At higher dye concentrations (1 microM or above), fluorescence in the perinuclear region was too intense to resolve into discrete cellular structures, while fluorescence in other cellular structures including mitochondria and cytomembranes was visible. At even higher dye concentrations (10-100 microM), Nile blue derivatives were seen with a light microscope as blue particles, the size and location of which resembled the punctate fluorescence described above. Results which further suggest that the lysosome is the main site of dye localization include (a) histochemical staining of dye-loaded cells with the lysosomal marker enzyme acid phosphatase, which showed similar localization of the enzyme-staining and dye-containing particles, (b) phototreatment of dye-loaded cells which obliterated the majority of the acid phosphatase-stained particles, and (c) treatments with agents affecting the membrane pH gradient reduced the uptake and enhanced the efflux of dyes, while agents that alter cellular membrane potentials had no effect on dye accumulation. The uptake of the dyes was partially inhibited by inhibitors of oxidative phosphorylation indicating that at least part of the process is energy dependent. These findings, together with previous results showing that the cellular uptake of these dyes is highly concentrative and proportional to the extracellular dye concentration over a wide range, are consistent with the hypothesis that the dyes are mainly localized in the lysosomes via an ion-trapping mechanism. Results of the present study also suggest that the lysosomes may be an intracellular target for photodynamic killing of tumor cells mediated by Nile blue photosensitizers and that lysosomotropic photosensitization may be a strategy for effective and selective destruction of tumor cells.

1,25-Dihydroxyvitamin D3 receptor RNA: expression in hematopoietic cells

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] induces differentiation and inhibits proliferation of myeloid leukemic cells from various lines and patients; these effects are probably mediated through the 1,25(OH)2D3 receptor. Little is known of expression of 1,25(OH)2D3 receptor RNA in hematopoietic cells. We examined the expression and modulation of expression of 1,25(OH)2D3 receptor RNA in various proliferating and nonproliferating hematopoietic cells. Constitutive expression of 1,25(OH)2D3 receptor RNA was detected in various kinds of hematopoietic cells, including macrophages and activated T lymphocytes, as well as in cell lines KG-1 (myeloblasts), HL-60 (promyelocytes), ML-3 (myelomonoblasts), U937, THP-1 (monoblasts), K562 (erythroblasts), and S-LB1 (HTLV-1-transfected T lymphocytes). Receptor transcripts were 4.6 kilobases (kb), and no variant sizes were observed. All cell lines examined in this group also expressed 1,25(OH)2D3 receptors. Most B lymphocyte lines expressed negligible levels of 1,25(OH)2D3 receptor RNA and protein; however; analysis of a lymphoid/myeloid somatic hybrid suggested that suppression of expression of 1,25(OH)2D3 receptor RNA in B lymphocytes may be a dominant characteristic. HL-60 cells were cultured with 10(-7) mol/L 1,25(OH)2D3 for 24 to 72 hours, and levels of expression of 1,25(OH)2D3 receptor and its RNA were examined. Levels of RNA coding for the receptor were not modulated by exposure to high levels of ligand. Levels of occupied 1,25(OH)2D3 receptor protein increased in these HL-60 cells; but the total number of 1,25(OH)2D3 receptors decreased about 50% at 24 hours and returned toward normal at 72 hours. Steady-state levels of 1,25(OH)2D3 receptor RNA were not affected by terminal differentiation of HL-60 toward either granulocytes or macrophages. Nondividing macrophages from normal individuals also expressed 1,25(OH)2D3 receptor RNA. In contrast, nondividing peripheral blood lymphocytes from normal individuals did not express 1,25(OH)2D3 receptor RNA; with stimulation of proliferation of these cells, accumulation of 1,25(OH)2D3 receptor RNA increased markedly. Half-life (t1/2) of 1,25(OH)2D3 receptor RNA in T lymphocytes was short (1 hour) as determined by measuring decay of the message after addition of actinomycin D. Consistent with this short t1/2, accumulation of 1,25(OH)2D3 receptor RNA increased in cells as their protein synthesis was inhibited. Further studies are required to understand the physiologic role of 1,25(OH)2D3 receptors in myeloid cells and proliferating T lymphocytes.

Characterization of two novel cholecystokinin tetrapeptide (30-33) analogues, A-71623 and A-70874, that exhibit high potency and selectivity for cholecystokinin-A receptors

Based on their relative affinities for cholecystokinin octapeptide (26-33) (CCK-8), cholecystokinin tetrapeptide (30-33) (CCK-4), desulfated CCK-8, and gastrin, cholecystokinin (CCK) receptors have been classified as CCK-A (alimentary) and CCK-B (brain). Selective nonpeptide antagonists of CCK-A and CCK-B receptors, as well as highly selective CCK-A and CCK-B peptide agonists, have been described. We report here the characterization of two novel CCK-4-based peptides, A-71623 and A-70874. In radioligand binding assays, the IC50 values for A-71623 and A-70874 were 3.7 and 4.9 nM in guinea pig pancreas (CCK-A) and 4500 and 710 nM in cerebral cortex (CCK-B), respectively. Both were agonists in stimulating pancreatic amylase release, and their stimulatory effects were potently inhibited by the CCK-A antagonist L-364,718. A-71623 was a full agonist and A-70874 was a partial agonist (approximately 80%) in stimulating phosphoinositide breakdown in pancreas. Both peptides also were potent agonists in stimulating CCK-A receptors in the ileum. They were, however, weak and behaved as partial agonists in calcium studies in NCI-H345 cells, which possess CCK-B/gastrin receptors. In guinea pig gastric glands, the affinities of A-71623 and A-70874 for the CCK-B/gastrin receptor were 11 and 1.6 microM, respectively. These results demonstrate that A-71623 and A-70874 are potent and selective agonists at CCK-A receptors. The preferential interaction of these novel CCK-4 analogs with CCK-A receptors is in contrast to other CCK-4-based peptides, which are primarily selective for CCK-B receptors. In addition, A-71623 and A-70874 are the first two examples of potent CCK-A agonists that do not contain a tyrosine residue whose sulfation is required for potent CCK-A agonist activity of larger peptides.

Photosensitization, uptake, and retention of phenoxazine Nile blue derivatives in human bladder carcinoma cells

The overall goal of our research is to develop effective new photosensitizers for tumor-selective photodynamic therapy. Phenoxazine dyes, including several Nile blue analogues, are known to localize selectively in animal tumors. Structural modifications yielded several series of analogues with substantially higher 1O2 yields and different photochemical and physicochemical properties. This study examined the photosensitization potency, cellular uptake, and retention of these derivatives in human bladder carcinoma cells (MGH-U1) in culture. Nile blue derivatives containing halogens and/or sulfur substitutes were selected to exhibit different 1O2 yields, pKa values, and hydrophobicities. The effectiveness of these derivatives in mediating photokilling of tumor cells in vitro corresponded well with the 1O2 yields of these compounds, indicating that structural modifications which resulted in increased 1O2 yields enhanced potency in mediating photocytotoxicity in vitro. Using derivatives (sat-NBS and sat-NBS-61) with the highest 1O2 quantum yield (0.35 and 0.821), over 90% cell kill was achieved at a sensitizer concentration of 5 x 10(-8) M, about 3 orders of magnitude more effective than hematoporphyrin derivative, the only sensitizer currently available clinically. This result suggests that some of the oxazine derivatives could potentially be effective photosensitizers. The correspondence between 1O2 yield and photosensitizing potency, together with results showing enhanced photocytotoxicity in the presence of D2O and reduced photocytotoxicity under hypoxic conditions, strongly suggests that the generation of 1O2 is a major mechanism mediating the photocytotoxic effect. The uptake of Nile blue derivatives by cells in culture exhibited a pattern of rapid initial uptake followed by a gradual increase in cellular dye contents. The uptake does not correlate directly with the individual pKa values or hydrophobicities of the derivatives, indicating that the structural modifications that increased 1O2 yields did not significantly alter the uptake and retention of Nile blue derivatives. The highly concentrative uptake by and slow efflux from dye-loaded cells were consistent with an active mechanism for the cellular accumulation of these dyes. On the other hand, the retention of the compounds was directly proportional to dye concentration in the medium over a 1000-fold range of concentrations, and the uptake could proceed at temperatures below 2 degrees C; these observations excluded endocytosis or a carrier-mediated mechanism for the uptake. The uptake was also unaffected by the presence of serum in the medium. Based on these results, we hypothesize that Nile blue derivatives transport across the cell membrane possibly as deprotonated forms and, upon entering the cell, either partition into lipophilic areas of the cell membranes and/or become sequestered in certain intracellular organelles.

Detection of exfoliated bladder cancer cells by monoclonal antibodies to tumor-associated cell surface antigens

Monoclonal antibodies (Mabs) to human tumor antigens have potential for tumor detection and treatment. For bladder carcinoma, the detection of exfoliated tumor cells in urinary specimens may be accomplished with Mabs reacting to tumor cell-surface components. This method may be useful for screening and monitoring carcinogen-exposed workers. A Mab generated by our laboratory, 3G2-C6, reacts with high affinity to a cell-surface component expressed by bladder tumor cells. The potential utility of this Mab in detecting exfoliated tumor cells was evaluated in bladder wash specimens. The Mab method detected positive cells in 87% (56/64) of specimens from patients with bladder cancer, including a great majority with grade 1 tumor and carcinoma in situ, superior to the routine cytology done on the same specimens. Cells in specimens from patients with urinary calculi, chronic cystitis, and history of bladder cancer also reacted with the Mab, suggesting that other stimuli can induce antigen expression. The Mab method can also be performed on urine samples, thus allowing evaluation of the ability of the Mab to identify premalignant, malignant, and other abnormal exfoliated cells in urine. The Mab method represents a unique opportunity to develop noninvasive detection of bladder cancer and to monitor and screen bladder cancer high-risk groups.

Multi-drug resistance of a doxorubicin-resistant bladder cancer cell line

A bladder tumor cell line resistant to doxorubicin (MGH-U1R) has been established previously by culturing a human transitional cell carcinoma cell line (MGH-U1) in increasing concentrations of the drug. MGH-U1R is 40 times more resistant to doxorubicin than MGH-U1. In the present study, MGH-U1R was evaluated for its multi-drug resistance or pleiotropism by testing against other chemotherapeutic agents. MGH-U1R was found to be 188 times more resistant to vinblastine and 13 times more resistant to etoposide than MGH-U1, while remained sensitive to bleomycin. Taken together with earlier evidence that the resistance of MGH-U1R to doxorubicin can be reversed by a calcium-channel blocker verapamil, and the measured over-expression of the mdr1 gene in these cells, MGH-U1R has the characteristic multiple drug resistance properties similar to other established doxorubicin resistant carcinoma cell lines. MGH-U1R may be a useful model for the development of strategies in overcoming drug-resistance in the treatment of transitional cell carcinoma.

The effect of verapamil on a multi-drug resistant bladder carcinoma cell line and its potential as an intravesical chemotherapeutic agent

A human bladder transitional cell carcinoma cell line, MGH-U1R, exhibits reproducible resistance to doxorubicin. We examined the effects on survival of this cell line caused by verapamil, which has been shown to reverse multi-drug resistance in vitro in other neoplastic cell lines. Both MGH-U1R and MGH-U1, the non-resistant parent cell line, were treated with varying concentrations of doxorubicin alone, verapamil alone, or both drugs simultaneously, all for one hour. Cells were then grown in drug-free medium for 10 days, stained, and counted. Standard survival curves were calculated. Verapamil alone had no significant cytotoxicity. Verapamil at concentrations of 16 micrograms./ml. and 32 micrograms./ml. decreased the IC50 of doxorubicin for MGH-U1R by a factor of 2.5. Using H3-verapamil, we also examined the systemic and local absorption of this drug resulting from intravesical verapamil administration in rabbits. All animals were treated for one hour, and multiple serum samples were drawn during treatment. Verapamil was found in high concentrations in the mucosa, less in the adventitia, and was absent in venous blood. Verapamil effectively reverses resistance to doxorubicin of MGH-U1R in vitro. The intravesical use of verapamil appears to be safe, and may prove to be a useful adjunct in the intravesical therapy of some bladder tumors.

A71378: a CCK agonist with high potency and selectivity for CCK-A receptors

Receptors for the brain and gut peptide cholecystokinin (CCK) have been classified into two classes, CCK-A and CCK-B. To date, peptide analogues with selectivity for the CCK-B receptors have been identified, and selective antagonists for CCK-A and CCK-B receptors have been reported as well; until now, there have been no reports of highly selective CCK-A agonists. Herein we describe the properties of A71378 [desamino-Try(SO3H)-Nle-Gly-Trp-Nle-(N-methyl)Asp-Phe-NH2], a highly selective CCK-A receptor ligand. Characterization of A71378 was carried out in the guinea pig pancreas, cortex, gastric gland, and ileum, as well as in NCI-H345 cells. The IC50 values of A71378 for the pancreatic CCK-A, cortical CCK-B, and gastrin receptor were 0.4 nM, 300 nM, and 1,200 nM, respectively. A71378 proved to be a potent agonist in eliciting pancreatic amylase secretion (EC50 = 0.16 nM) and ileal muscle contraction (EC50 = 3.7 nM). In contrast, A71378 was relatively weak (EC50 = 600 nM) in mobilizing intracellular calcium from NCI-H345 cells, which express CCK-B/gastrin receptors. The high potency and selectivity of A71378 for the CCK-A over CCK-B and gastrin receptors is unprecedented among CCK peptides. Studies on CCK-7 analogues indicate that N-methylation of the Asp residue is responsible for the observed selectivity for CCK-A receptors. This discovery of a selective CCK-A agonist should prove valuable for studies aimed at understanding the physiological roles of CCK-A receptors in the brain and periphery.