High frequency vector-mediated transformation and gene replacement in Tetrahymena

Recently, we developed a mass DNA-mediated transformation technique for the ciliated protozoan Tetrahymena thermophila that introduces transforming DNA by electroporation into conjugating cells. Other studies demonstrated that a neomycin resistance gene flanked by Tetrahymena H4-I gene regulatory sequences transformed Tetrahymena by homologous recombination within the H4-I locus when microinjected into the macronucleus. We describe the use of conjugant electrotransformation (CET) for gene replacement and for the development of new independently replicating vectors and a gene cassette that can be used as a selectable marker in gene knockout experiments. Using CET, the neomycin resistance gene flanked by H4-I sequences transformed Tetrahymena, resulting in the replacement of the H4-I gene or integrative recombination of the H4-I/neo/H4-I gene (but not vector sequences) in the 5' or 3' flanking region of the H4-I locus. Gene replacement was obtained with non-digested plasmid DNA but releasing the insert increased the frequency of replacement events about 6-fold. The efficiency of transformation by the H4-I/neo/H4-I selectable marker was unchanged when a single copy of the Tetrahymena rDNA replication origin was included on the transforming plasmid. However, the efficiency of transformation using CET increased greatly when a tandem repeat of the replication origin fragment was used. This high frequency of transformation enabled mapping of the region required for H4-I promoter function to within 333 bp upstream of the initiator ATG. Similarly approximately 300 bp of sequence downstream of the translation terminator TGA of the beta-tubulin 2 (BTU2) gene could substitute for the 3' region of the H4-I gene. This hybrid H4-I/neo/BTU2 gene did not transform Tetrahymena when subcloned on a plasmid lacking an origin of replication, but did transform at high frequency on a two origin plasmid. Thus, the H4-I/neo/BTU2 cassette is a selectable marker that can be used for gene knockout in Tetrahymena. As a first step toward constructing a vector suitable for cloning genes by complementation of mutations in Tetrahymena, we also demonstrated that the vector containing 2 origins and the H4-I/neo/BTU2 cassette can co-express a gene encoding a cycloheximide resistant ribosomal protein.

Determinants for intracellular sorting of cytoplasmic and nuclear intermediate filaments

The mechanism by which nuclear and cytoplasmic filaments are sorted in vivo was studied by examining which lamin sequences are required to target an otherwise cytoplasmic IF protein, the small neurofilament subunit (NF-L), to the nuclear lamina. By swapping corresponding domains between NF-L and lamin A, nuclear envelope targeting of NF-L was shown to require the presence of the "head" domain, a 42-amino acid sequence unique to lamin rod domains, a nuclear localization signal and the CAAX motif. Replacement of the entire COOH-terminal tail of lamin A with that of NF-L had no discernible effect on nuclear localization of lamin A, provided the substituted NF-L tail contained a NLS and a CAAX motif. This chimeric protein exhibited characteristics more typical of lamin B than that of the parental lamin A. With regard to cytoplasmic assembly properties, substitution of the head domain of lamin A for that of NF-L did not substantially affect the ability of NF-L to coassemble with vimentin in the cytoplasm. In contrast, insertion of a 42-amino acid sequence unique to lamin rod domains into NF-L profoundly affected NF-L coassembly with vimentin indicating that the 42-amino acid insertion in lamins may be important for sorting lamins from cytoplasmic IF proteins.

Chromosomal assignment of 11 loci in the rat by mouse-rat somatic hybrids and linkage

Eleven rat genes have been assigned to rat chromosomes by use of mouse x rat somatic hybrids and/or use of linkage to known chromosome markers. Among them, the genes for the inducible nitric oxide synthase (Nos2) and for a vasoactive intestinal peptide receptor (Vipr) are potential candidates for genetic regulation of blood pressure and were localized to rat Chromosomes (Chrs) 10 and 8 respectively. Genes for gastric H,K-ATPase alpha subunit (Atp4a), Class I alcohol dehydrogenase (Adh), and aldolase C (Aldoc) were localized to Chrs 1, 2, and 10 respectively, and thus provide more DNA markers for genetic mapping of quantitative trait loci for blood pressure on those chromosomes. Genes for alkaline phosphatase (Alp1) and cardiac AE-3 Cl-/HCO3- exchanger (Ae3) were both localized to Chr 9. Genes for glutamate dehydrogenase (Glud) and gastric H,K-ATPase beta subunit (Atp4b) were localized to Chr 16. The ornithine decarboxylase (Odc) gene and ornithine decarboxylase pseudogene (Odcp) were localized to Chrs 6 and 11 respectively.

The genome reconstruction manager: a software environment for supporting high-throughput DNA sequencing

A new software system designed for use in high-throughput DNA sequencing laboratories is described. The Genome Reconstruction Manager (GRM) was developed from requirements derived from ongoing large-scale DNA sequencing projects. Object-oriented principles were followed in designing the system, and tools supporting object-oriented system development were employed for its implementation. GRM provides several advances in software support for high-throughput DNA sequencing: support for random, directed, and mixed sequencing strategies; a novel system for fragment assembly; a commercial object data-base management system for data storage; a client/server architecture for using network computational servers; and an underlying data model that can evolve to support fully automatic sequence reconstruction. GRM is currently being deployed for production use in high-throughput DNA sequencing projects.

Transcription factor GATA-2 is expressed in erythroid, early myeloid, and CD34+ human leukemia-derived cell lines

To understand the functional roles that the GATA factors may play during hematopoietic cell differentiation, we examined the expression of GATA factor mRNAs and protein products in various human cell lines. Blot hybridization analyses demonstrated that GATA-1 and GATA-2 mRNAs are expressed abundantly in a set of cell lines established from human myelogenous leukemia cells, but the expression pattern of each factor is distinct. GATA-2 mRNA is expressed in all cell lines tested that express erythroid markers, and, in addition, the mRNA is also expressed in three CD34+ cell lines and two early myeloid cell lines. In contrast, the expression of GATA-1 mRNA showed tight correlation to that of the erythroid/megakaryocytic lineage markers. We also found that the GATA-2 probe identifies two types of mRNA. Structural analysis of genomic DNA clones encoding human GATA-2 coupled with RNA blot analysis demonstrated that there exists an alternative use of polyadenylation consensus sequences in a single exon and this causes the molecular heterogeneity among GATA-2 mRNAs. Through immunochemical and immunohistochemical analyses using anti-GATA-1- and anti-GATA-2-specific antibodies, GATA-2 protein was clearly shown to be present in the nuclei of leukemia-derived early myeloid and CD34+ cell lines, whereas both GATA-1 and GATA-2 proteins are expressed in erythroid/megakaryocytic cell lines. Thus, the expression profile of GATA-2 is consistent with the hypothesis that GATA-2 plays unique roles for the transcriptional activation of genes in cells at an early stage of hematopoietic differentiation and in developing cells of the erythroid and myeloid lineages.

Influence of hydrocarbon tail structure on quinone binding and electron-transfer performance at the QA and QB sites of the photosynthetic reaction center protein

Binding free energies of 37 functional replacement quinone cofactors with systematically altered hydrocarbon tail structures have been determined for the QA and QB redox catalytic sites of the reaction center protein isolated from Rhodobacter sphaeroides and solubilized in aqueous and in hexane solutions. The first two and part of the third isoprene units of the 10-unit tail of the native ubiquinone-10 cofactor interact with the protein interior at each site. Contributions of the same tail structures to the binding free energies of quinones at the QA and QB sites are comparable, suggesting that the binding domains share common features. Comparison of the affinities of a homologous series of 10 n-alkyl-substituted ubiquinones resolves the binding forces along the length of the tail binding domain and shows that strong steric constraints oppose accommodation of the tail in its extended conformation. Differences in the contributions of identical tail substituents to ubiquinone- and menaquinone-QA site affinities, and tail-induced changes of up to 5-fold in the rates of QA site-mediated electron-transfer reactions, suggest that the tail adjusts the position of the quinone ring. Substitution of ubiquinone with the native 10-unit isoprene tail does not alter the affinity for the sites as determined in hexane solution. However, one- and two-isoprene-substituted quinones bind more tightly than analogs substituted with saturated-alkyl tail substituents. The sites therefore exhibit binding specificity for the native isoprene tail structure. Calculations indicate that the binding specificity arises primarily from a lower integrated torsion potential energy in the bound isoprene tails. The results suggest that the in vivo tail-protein interaction is designed to deter competitive interference of quinone function by amphiphilic species present in the native membrane.

Cloning and characterization of a secY homolog from Chlamydia trachomatis

Characterization of the genes involved in the process of protein translocation is important in understanding their structure-function relationships. However, little is known about the signals that govern chlamydial gene expression and translocation. We have cloned a 1.7 kb HindIII-PstI fragment containing the secY gene of Chlamydia trachomatis. The complete nucleotide sequence reveals three open reading frames. The amino acid sequence shows highest homology with Escherichia coli proteins L15, SecY and S13, corresponding to the spc-alpha ribosomal protein operons. The product of the C. trachomatis secY gene is composed of 457 amino acids with a calculated molecular mass of 50,195 Daltons. Its amino acid sequence shows 27.4% and 35.7% identity to E. coli and Bacillus subtilis SecY proteins, respectively. The distribution of hydrophobic amino acids in the C. trachomatis secY gene product is suggestive of it being an integral membrane protein with ten transmembrane segments, the second, third and seventh membrane segments sharing > 45% identity with E. coli SecY. Our results suggest that despite evolutionary differences, eubacteria share a similar protein export apparatus.

Electroporation-mediated replacement of a positively and negatively selectable beta-tubulin gene in Tetrahymena thermophila

Replacement of lysine-350 by methionine in the beta-tubulin gene of Chlamydomonas confers resistance to microtubule-depolymerizing drugs and increased sensitivity to the microtubule-stabilizing drug taxol. This mutation was created in cloned BTU1, one of two coexpressed beta-tublin genes of Tetrahymena thermophila. When introduced by electroporation, the mutated gene transformed Tetrahymena exclusively by gene replacement at the homologous locus. Taxol-sensitive transformants could be retransformed with a wild-type gene and selection for taxol resistance. Analyses of phenotypic assortment and of the mRNA in transformed cells suggest that complete replacement of the BTU1 gene in the polyploid macronucleus can be obtained. These studies demonstrate the utility of this marker for studying tublin gene function and show that electroporation allows facile gene replacement in Tetrahymena.

Coculture of primary rat hepatocytes and nonparenchymal cells permits expression of insulin-like growth factor binding protein-3 in vitro

In biological fluids, the insulin-like growth factors (IGFs) are associated with binding proteins (IGFBPs), which modify IGF distribution and action. Circulating IGFs are bound predominantly to IGFBP-3, of apparent hepatic origin, but regulation of IGFBP-3 has been difficult to dissect because of the lack of systems suitable for examining hepatic production of IGFBP-3 in vitro. In the present studies, IGFBP-3 expression was identified primarily in hepatic nonparenchymal cells, particularly Kupffer and sinusoidal endothelial cells. Coculture with hepatocytes enhanced the stability of nonparenchymal cells to express IGFBP-3 in vitro. IGFBP-3 in conditioned medium had apparent mol wt of 150-300 kilodaltons, suggesting formation of a ternary complex with IGFs and the acid-labile subunit. Expression and secretion of IGFBP-3 were hormonally responsive and strongly correlated (r = 0.79; P < 0.001), with 2- to 3-fold stimulation by added insulin or IGF-I (both P < 0.05), but not by added GH alone. Our findings suggest that GH may act indirectly to promote IGFBP-3 generation in vivo via increasing both the secretion of insulin and the hepatic production of IGF-I; in patients with diabetes mellitus, reduced circulating levels of IGFBP-3 despite high levels of GH may result from both insulin deficiency and inadequate hepatic production of IGF-I. Coculture of hepatic nonparenchymal and parenchymal cells should be useful for further analysis of the mechanism of IGFBP-3 regulation.

Human GATA-3 trans-activation, DNA-binding, and nuclear localization activities are organized into distinct structural domains

GATA-3 is a zinc finger transcription factor which is expressed in a highly restricted and strongly conserved tissue distribution pattern in vertebrate organisms, specifically, in a subset of hematopoietic cells, in cells within the central and peripheral nervous systems, in the kidney, and in placental trophoblasts. Tissue-specific cellular genes regulated by GATA-3 have been identified in T lymphocytes and the placenta, while GATA-3-regulated genes in the nervous system and kidney have not yet been defined. We prepared monoclonal antibodies with which we could dissect the biochemical and functional properties of human GATA-3. The results of these experiments show some anticipated phenotypes, for example, the definition of discrete domains required for specific DNA-binding site recognition (amino acids 303 to 348) and trans activation (amino acids 30 to 74). The signaling sequence for nuclear localization of human GATA-3 is a property conferred by sequences within and surrounding the amino finger (amino acids 249 to 311) of the protein, thereby assigning a function to this domain and thus explaining the curious observation that this zinc finger is dispensable for DNA binding by the GATA family of transcription factors.

[A study on Mechanism of prevention and treatment of gastric ulcer with Os sepiella in rats]

The Os Sepiella maiudrone (OSM) could markedly inhibit the stress-induced gastric mucosal lesions and promote the healing of acetic acid-induced gastric ulcer in rats were reported previously. In order to demonstrate its mechanism, the effects of OSM on acidity of gastric juice, combined mucus content in gastric wall, DNA synthesis, gastric movements, the gastric contents of prostaglandin E2 (PGE2) and cAMP of gastric tissue were examined. The results showed that OSM could neutralize the gastric acid, promote the production of cAMP and PGE2 in gastric tissue. These suggested that the neutralization of gastric acid and enhancing the gastric mucosal cytoprotection by OSM would play a role in preventing and curing gastric ulcers in rats.

[Spiral shaped bacteria in the human gastric biopsy]

Biopsy specimens from the gastric mucosa of 149 patients who underwent gastroduodenal endoscopy for upper gastrointestinal complaints were studied by light microscopy and culture. Spiral shaped bacteria were detected in four of the specimens by smears with Gram stain. The positive rate was 2.68%, but these bacteria and HP did not grow in culture. The characteristic helical morphology of the bacteria appears to be similar to that of the bacteria found in the stomach of cats and dogs. And what of significance in these cases is the presence of spiral shaped bacteria in association with chronic gastritis.

Treatment of acute experimental toxoplasmosis with investigational poloxamers

Because of the limited chemotherapeutic approaches available to treat reactivated latent Toxoplasma gondii infection manifested as toxoplasmic encephalitis in AIDS patients, investigation of novel chemotherapeutic agents is warranted. Several poloxamers (nonionic block copolymers composed of a central hydrophobic chain of polyoxypropylene flanked by two hydrophilic chains of polyoxyethylene) were tested for their abilities to alter the course of acute infection with a highly virulent T. gondii in mice. The effect varied markedly with the length of the constituent chains of the copolymers. The most effective preparations were highly effective when administered after infection and afforded remarkable protection against 10 to 1,000 100% lethal doses of T. gondii. Protection was dose dependent, and multiple treatments were more effective than single treatment. These preliminary findings warrant additional studies to determine whether this novel form of antitoxoplasma chemotherapy may prove promising in the treatment or prevention of acute toxoplasmic encephalitis in humans.

Drosophila Rrp1 complements E. coli xth nfo mutants: protection against both oxidative and alkylation-induced DNA damage

Drosophila Rrp1 protein has four tightly associated enzymatic activities: DNA strand transfer, ssDNA renaturation, dsDNA 3'-exonuclease and apurinic/apyrimidinic (AP) endonuclease. The carboxy-terminal region of Rrp1 is homologous to Escherichia coli exonuclease III and several eukaryotic AP endonucleases. All members of this protein family cleave abasic sites. Rrp1 protein was expressed under the control of the E. coli RNA polymerase tac promoter (pRrp1-tac) in two repair deficient E. coli strains (BW528 and LG101) lacking both exonuclease III (xth) and endonuclease IV (nfo). Rrp1 confers resistance to killing by oxidative, antitumor and alkylating agents that damage DNA (hydrogen peroxide, t-butylhydroperoxide, bleomycin, methyl methanesulfonate, and mitomycin C). Complementation of the repair deficiency by Rrp1 provides up to a two log increase in survival and requires the C-terminal nuclease region of Rrp1, but not its N-terminal region. The AP endonuclease activity in extracts from the repair deficient strain LG101 is increased up to 12-fold when the strain contains pRrp1-tac. These results indicate that pRrp1-tac directs the synthesis of active enzyme, and that the nuclease activities of Rrp1 are likely to be the cause of the increased resistance to DNA damage of the mutant cells.

Erythroid transcription factor GATA-1 is abundantly transcribed in mouse testis

The transcription factor GATA-1 is a fundamental regulator of genes in haematopoietic cell lineages and belongs to a family of factors that bind to the consensus sequence WGATAR. The GATA motif was originally identified in cis-regulatory regions of globin and other erythroid-specific genes, but the range of genes controlled by the GATA factors has since expanded. Members of the GATA transcription factor family share a conserved zinc-finger DNA-binding domain, but the expression profile of each GATA factor is distinct. Here we show that a testis form of murine (m)GATA-1 messenger RNA is transcribed from a promoter located 5' to the erythroid first exon, and the remaining exons (which encode the mGATA-1 protein) are used in common by both testis and erythroid transcripts. We use an anti-mGATA-1 monoclonal antibody to show that the factor expressed in erythroid cells is the same as that found in the seminiferous tubules of murine testis. The GATA-1-expressing cells in 10-week-old testis were found only in contact with the basement membrane of seminiferous tubules, suggesting that GATA-1 regulates genes during the earliest stages of spermatogenesis.

Functional analysis of the human platelet-derived growth factor A-chain promoter region

The platelet-derived growth factor (PDGF) A-chain gene is a developmentally regulated gene that is expressed in high levels in a limited number of normal and transformed cell lines and in cells stimulated by cytokines, including PDGF itself. We have now analyzed potential regulatory elements in 3.6 kilobase pairs (kb) of the 5'-flanking sequences of the human PDGF A-chain gene using reporter gene constructs and transient transfection analyses. The region between base pairs (bp) -618 and +392 (relative to the transcription initiation site) is sufficient for optimal promoter activity. A highly G + C region containing three contiguous Sp1 binding sites between bp -150 and -33 contributes over 80% of promotor activity. DNase I footprinting analyses indicates that Sp1 binds to and protects over 57 bp of this G + C region. A functional serum response element is located within bp -477 and -468 and positively regulates induction of PDGF A by PDGF. A negative regulatory (silencer) element is located from -1.9 to -0.9 kb. The results suggest that the major constitutive expression of the PDGF A-chain gene requires a highly G + C-rich region containing three Sp1 binding sites and that induction of the PDGF A-chain gene by PDGF is mediated by a SRE located at bp -477 to -468.

Biotransformation of caffeine, paraxanthine, theobromine and theophylline by cDNA-expressed human CYP1A2 and CYP2E1

Six human cytochrome P450s expressed in HepG2 cells using vaccinia virus cDNA-directed expression, were used to study the biotransformation of caffeine and its metabolites. CYP1A2 alone was responsible for caffeine 3-demethylation and paraxanthine 7-demethylation; in addition, 1A2 catalysed virtually all reactions related to caffeine and its metabolites. The metabolic profile of caffeine biotransformation by CYP1A2 averaged 81.5% for paraxanthine, 10.8% for theobromine and 5.4% for theophylline formation. It remained quite uniform when caffeine concentrations were varied. The most striking finding was that CYP2E1 (the ethanol-inducible form) had major influences upon caffeine metabolism: in particular, it catalysed the formation of theophylline and theobromine from caffeine. Thus, the in vivo metabolite profiling of caffeine may reveal CYP2E1 activities in addition to the previously documented activities of CYP1A2, polymorphic N-acetyltransferase and xanthine oxidase.

Interleukin-4 is an autocrine growth factor secreted by the L-428 Reed-Sternberg cell

Recent evidence indicates that Reed-Sternberg (RS) cells from many cases of Hodgkin's disease have features of activated lymphocytes and that lymphokines from activated lymphocytes induce proliferation of L-428 RS cells. It is shown here that a lymphokine similar to a lymphokine secreted by activated lymphocytes is secreted by L-428 cells. This lymphokine has a molecular weight approximately equal to 68,000 daltons, identical to glycosylated recombinant interleukin-4 (rIL-4), and cross-reacts with monoclonal anti-IL-4 in Western immunoblotting. This Hodgkin's cell growth factor (HCGF) is 100% neutralized by polyclonal anti-IL-4 antibodies and competes for the IL-4 receptor. After acid-elution, the L-428 RS cell has been shown to have 3,396 +/- 120 high-affinity receptor sites/cell. HCGF competes with rIL-4 for this receptor and L-428 cells contain mRNA for IL-4. Although all evidence indicates that IL-4 is an important secreted autocrine growth factor for L-428 RS cells, anti-IL-4 has no effect on the sustained serum-free growth of these Hodgkin's cells, suggesting that either the IL-4 receptor and the IL-4 receptor-growth factor complex are protected from antibody inhibition or other mechanisms are responsible for the sustained proliferation of L-428 RS cells.

Physicochemical characterization of recombinant human nerve growth factor produced in insect cells with a baculovirus vector

Recombinant human nerve growth factor (rhNGF) secreted by insect cells was purified by ion-exchange and reversed-phase chromatography to near homogeneity. The N-terminus of the secreted molecule was analogous to that of mouse salivary gland NGF. In its native conformation, the insect cell produced rhNGF molecules were homodimers consisting of 120 amino acid polypeptide chains. Mature rhNGF was found not to be significantly glycosylated (less than 0.08 mol of N-acetylglucosamine/mol of protein). The rhNGF was homogeneous with regard to molecular weight and amino acid sequence. Isoelectric focusing resolved the rhNGF into one major and one minor component. Because rhNGF from insect cells can be obtained in large quantities, purified to near homogeneity, and is similar to natural NGF with regard to physicochemical properties and biological activity, it is suitable for further evaluation in animal models as a therapeutic molecule for neurodegenerative diseases such as Alzheimer's disease.

Inhibition of succinate-ubiquinone reductase by nitrosalicyl-N-alkylamides

The abilities of eight nitrosalicyl-N-alkylamides to inhibit succinate-ubiquinone reductase were compared. These compounds possess both a nitro group at 3- or 5-position of the benzyl ring, and a methyl, decyl, dodecyl or tetradecyl group subsituted for the amide hydrogen of salicylamide. The result shows the following: (a) 3-Nitrosalicyl-N-alkylamides are stronger inhibitors than 5-nitrosalicyl-N-alkylamides when they have the same alkyl group. (b) The inhibitory abilities of both 3-and 5-nitrosalicyl-N-alkylamides increase with increasing alkyl group length. (c) Kinetic data show that the inhibition by 3-nitrosalicyl-N-tetradecylamide is noncompetitive with respect to the electron acceptor Q2.

Reactive hyperemia in term neonates and adults--a laser Doppler fluxmetry study of skin microcirculation

The reactivities of neonatal and adult microcirculation have been studied and compared. The cutaneous reactive hyperemia after 1 and 4 min of arterial occlusion (AO) was measured with a laser-Doppler fluxmeter in 21 healthy neonates and 10 adults. Local skin temperature, mean arterial blood pressure (MAP), and skin prick hematocrit were also determined at the same time. The magnitude of neonatal reactive hyperemia was approximately one-third that of the adult response regardless of the duration of AO. In both groups, with age-specific regressions, the hyperemic blood flow response after 4 min of AO developed more slowly in subjects with low MAP and was of low magnitude in subjects with high hematocrit values. In response to a prolongation of AO, from 1 to 4 min, the magnitude and duration of hyperemia increased significantly and similarly in both neonates and adults. We conclude that compared to adults neonates have a less pronounced ability to increase skin microcirculation in response to local ischemia. The normally low blood pressure and high hematocrit in newborn infants contribute further to this conclusion.

High-performance liquid chromatographic (HPLC) and HPLC-mass spectrometric (MS) analysis of the degradation of the luteinizing hormone-releasing hormone (LH-RH) antagonist RS-26306 in aqueous solution

The kinetics of the degradation of an LH-RH antagonist, RS-26306,1, in aqueous solution from pH 1 to pH 11 were studied by reverse-phase HPLC. The pH-rate profiles at 50, 60, and 80 degrees C were U-shaped with the rate law of kobs = kHaH + kw + kOHaOH. The predicted 25 degrees C shelf life at the pH of maximum stability, pH approximately 5, is greater than 10 years. The products from the degradation were analyzed by HPLC-MS using thermospray ionization. Below pH 3, the primary product, 2, forms from the acid-catalyzed deamidation of the C-terminal amide. Above pH 7, epimerization of the individual amino acids is the principal reaction. Between pH 4 and pH 6, intramolecular serine-catalyzed peptide hydrolysis becomes important, yielding a tripeptide, 3, and a heptapeptide, 4. At the pH of maximum stability all three pathways for degradation are observed.

Drug-excipient incompatibility studies of the dipeptide angiotensin-converting enzyme inhibitor, moexipril hydrochloride: dry powder vs wet granulation

The drug-excipient incompatibility screen for moexipril hydrochloride (1) using various isothermal stress methods is reported herein. It was found that most of the commonly used filters, disintegrants, lubricants, glidants, and coating agents were incompatible with 1 in dry powder mixtures; moisture and basic (or alkalizing) agents were determined to be the dominant destabilizing factors. In wet granulations, basic agents, however, were found to suppress drug degradation even in the presence of moisture. Supported by the product distribution studies, the stabilization is proposed to involve the neutralization of the acidic drug by the basic excipients.

Bioavailability improvement of mycophenolic acid through amino ester derivatization

The potential bioavailability improvement of mycophenolic acid (MPA), 1, through ester derivatization was evaluated in monkeys at a dose of 20 mg/kg in this study. The acetyl solketal ester 3 was found to have excellent partition properties but poor aqueous solubility. Thus, even though it can be converted rapidly to MPA by plasma and liver enzymes, it showed poor oral bioavailability (56% of MPA) in monkeys. The bioavailability of the morpholinoethyl ester 4 and the acetyl morpholinoethyl ester 5, on the other hand, was found to be 236 and 150% that of MPA, respectively. Since ester 5 has greater aqueous solubility, but similar chemical stability and enzymatic hydrolysis rates compared to ester 4, the better bioavailability of ester 4 may result from its greater partitioning into the gastrointestinal membranes.

An unexpected pH effect on the stability of moexipril lyophilized powder

Because of the limited stability of moexipril (RS-10085; 1) in aqueous solution, lyophilized parenteral formulations were evaluated as a function of pH in this study. In general, the lyophilized powder of 1 showed about two orders of magnitude less reactivity at 50 degree C than in aqueous solution at pH values below 3 or above 6. At pH 5.1, however, the lyophilized powder had maximum reactivity, with the rate actually comparable to that observed in aqueous solution. When the distribution of the two major products, diketopiperazine (DKP) 2 and ester hydrolysis analogue 3, was compared to the observed kinetics as a function of pH, it was clear that removal of water via lyophilization suppressed the spontaneous k1 cyclization process, the spontaneous k3 hydrolysis process, and the specific base-catalyzed k4 hydrolysis process. The overall spontaneous k2 cyclization process, however, was not affected by lyophilization. The latter result is accounted for by the increased equilibrium constant for the formation of the tetrahedral intermediate, To, as a result of lyophilization. This study demonstrates that stability data in solution can not be used for predicting the stability of moexipril in lyophilized powder form.

Studies of safe maximal daily dietary Se-intake in a seleniferous area in China. Part II: Relation between Se-intake and the manifestation of clinical signs and certain biochemical alterations in blood and urine

Selenosis occurs in areas of Enshi county because of the high Se content of the food. Morphological changes in finger-nails were used as the main criterion for clinical diagnosis of selenosis. Pathological nails were observed to occur almost only in adults, not at all in young children and very seldom in teenagers. Symptoms of selenosis in susceptible patients were found at or above an Se-intake of 910 micrograms/d, corresponding to a blood Se level of 1.05 mg/L. There was no evidence for an increased susceptibility to dental caries due to high Se consumption, and an increase in Se-intake seems unlikely to reduce the beneficial effects of fluoride on caries. No abnormalities of liver or heart were seen by supersonic B or electrocardiographic examinations. The biochemical investigations showed that with increasing whole blood Se the ratio of plasma Se to erythrocyte Se tended to decrease. As Se-intake increases to over 750 micrograms daily, the ratio decreases to near a minimal level. Reduced glutathione in whole blood decreases within a blood Se range of 1.01 to 2.28 micrograms in the high Se area. The amount of trimethylselenonium ion excreted in urine increased with the increase of urinary Se. Cases with prolonged prothrombin time occurred as blood Se increased to a level above 1 mg/L. The white blood cell count also increased significantly. Quantitative values were obtained only for ratio of plasma-Se to erythrocyte-Se for prothrombin time and for maintenance of nail Symptoms of susceptible patients. The overall results indicated that a daily Se-intake of 750-850 micrograms [corrected] might be the marginal level of safe intake. When other variable factors are also taken into consideration a daily Se-intake of 400 micrograms [corrected] is suggested as the maximum daily safe intake. At this level of Se-intake the corresponding approximate tissue Se levels are: whole blood 0.559 mg/L, plasma 0.327 mg/L, urine excretion 173 micrograms/d, hair 3.60 mg/kg, toe-nails 4.25 mg/kg, and finger-nails 4.70 mg/kg.

Studies of safe maximal daily dietary selenium intake in a seleniferous area in China. I. Selenium intake and tissue selenium levels of the inhabitants

Studies of marginal safe Se-intake have been carried out in a seleniferous section of China since 1985. Three areas with low, medium and high Se levels were selected for this study. The respective average daily Se-intake (mean +/- SE) was 70.5 +/- 4.8 micrograms, 194.7 +/- 22.9 micrograms and 1438.2 +/- 76.3 micrograms for males, and 62.0 +/- 3.6 micrograms, 198.1 +/- 23.8 micrograms and 1238.5 +/- 64.6 micrograms for females (average body weight: male 55 Kg, female 53 Kg). When the increasing rate of Se-intake was compared with the corresponding tissue-Se levels it was found that the whole blood Se-level reflected more closely the physiological range of Se-intake, while at higher Se-intakes it became less sensitive than the levels in hair, finger-nail and toe-nail, which were comparable to the sensitivity of urine. It is suggested that hair, finger- and toe-nail may all act as excretory organs when excess amounts of Se are ingested. Hair- and blood-Cd are somewhat higher in residents of the high Se area, but whether they have influenced human Se-metabolism at the high level of Se-intake is not yet known. Significant correlations on log-log plots were obtained between levels of daily Se-intake and whole blood r = 0.878), breast milk (r = 0.899) and 24-h-urine (r = 0.859). Highly significant correlations on log-log plots between levels of tissue were also obtained: urine Se--plasma Se (r = 0.968), whole blood Se--hair Se (r = 0.952), fingernail Se--toenail Se (r = 0.919), hair Se--fingernail Se (r = 0.914), hair Se--toenail Se (r = 0.891), whole blood Se--toenail Se (r = 0.849) and whole blood Se--fingernail Se (r = 0.836). The highly significant correlations found between the Se-intake and the tissue-Se level, and also between the Se levels of various tissues, could possibly conveniently be used to convert the known tissue-Se level to the corresponding Se-intake. Taken together with the wide range of Se-intakes and corresponding tissue-Se levels this would provide the necessary conditions for studying the marginal and maximal safe Se-intakes in humans.

Preformulation stability studies of the new dipeptide angiotensin-converting enzyme inhibitor RS-10029

The degradation kinetics, products, and mechanisms of RS-10029 (2), 2-[2-[(1-carboxylic acid)-3-phenylpropyl]amino-1-oxopropyl] 6,7-dimethoxy- 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (S,S,S), in aqueous solutions from pH 1 to pH 13 were studied at 50, 60, and 80 degrees C. Pseudo-first-order kinetics were obtained throughout the entire pH range studied, and the log(rate)-pH profile reflected four kinetic processes (ko, k'o, k"o, and kOH) as well as the three pka's of 2. Excellent mass balance (greater than 96%) was obtained for the four major products 3-6 throughout the entire pH range studied even though four other minor products can be detected by high-performance liquid chromatography (HPLC). At pH 8.0 and below, intramolecular aminolysis leading to diketopiperazine (DKP) 5 accounted for greater than 65% of the neutral or water-catalyzed (ko and k'o) processes. Amide hydrolysis leading to products 3 and 4 and epimerization of DKP 5 to the (R,S,S) diastereomer 6 accounted for the remaining 35% of the neutral or water catalyzed processes. At pH values above 8.0, DKP 5 formation begins to decrease as the amide hydrolysis increases so that both mechanisms account for the neutral or water-catalyzed k"o process. Above pH 11.0 amide hydrolysis dominates and is responsible for the specific base-catalyzed (kOH) process. The four minor products detected by HPLC are two diastereomers (7 and 8) of 2 and the two diastereomers (9 and 10) of the DKP 5. The stability results between 2 and its ester prodrug (1) are compared.

Inhibitors of cyclic AMP phosphodiesterase. 4. Synthesis and evaluation of potential prodrugs of lixazinone (N-cyclohexyl-N-methyl-4-[(1,2,3,5-tetrahydro-2- oxoimidazo[2,1-b]quinazolin-7-yl)-oxy]butyramide, RS-82856)

The cyclic AMP phosphodiesterase (cAMP PDE) inhibitor and cardiotonic agent lixazinone (N-cyclohexyl-N-methyl-4-[(1,2,3,5-tetrahydro-2- oxoimidazo[2,1-b]quinazolin-7-yl)oxy]butyramide, RS-82856, 1) and its acid and base addition salts were found to be insufficiently soluble in formulations suitable for intravenous administration. These results prompted an investigation into potential prodrugs with enhanced aqueous solubility designed to deliver 1 by three distinct mechanisms: (1) decarboxylation of alpha-carboxamides; (2) hydrolytic loss of a solubilizing N-1-(acyloxy)methyl or (N,N-dialkylamino)methyl moiety; or (3) intramolecular closure of a guanidino ester or amide. The target compounds were evaluated as delivery systems for 1 by three criteria: (1) chemical conversion rate to 1 under physiological conditions; (2) inhibition of type IV cAMP PDE at a fixed time point; and (3) in vivo inotropic activity in anesthetized dogs by both intravenous and oral administration. Release of 1 from 4a (series 1) was found to be too slow to be of value as a prodrug of 1, since decarboxylation could be induced only by strong acid, conditions under which hydrolytic ring opening was found to severely compete. Conversely, 1 was released too readily on exposure of (N,N-dialkylamino)methyl derivatives such as 8d (series 2) to physiological conditions, although no large increase in aqueous solubility was realized. Finally, both the physicochemical and in vitro studies indicated that ring closure of the guanidinium esters and amides 17a-k (series 3) to 1 was quantitative and pH- and time-dependent, suggesting the possibility of delivery of the open, water-soluble prodrug form, followed by closure to 1 in plasma. Detailed examination of these agents in vivo, however, demonstrated that only those compounds that rapidly cyclized to 1, as measured by plasma levels of 1, exhibited inotropic activity, indicating that the open prodrug form was not efficiently absorbed upon oral administration.

John Caffey Award. Intussusception reduction in children by rectal insufflation of air

Air was used as the contrast medium for colonic studies in 282 patients with suspected intussusception. Intussusception was documented in 118 of these patients (42%), and reduction was achieved in 89 (75%) of those 118. Twenty-nine patients, in whom the intussusception could not be reduced with air, underwent surgery. Seven of these patients required surgical resection of devitalized bowel. In seven others, the intussusception was reduced by the surgeon with difficulty; in 12, surgical reduction was achieved easily. Three perforations occurred with the use of air. These patients were treated surgically without sequelae. This pilot study of 282 patients suggests that air is a safe substitute for hydrostatic reduction of intussusception.

Transient opacification of the urinary pathways by amorphous debris in children with leukemia

Our index patient, a 14-year-old male on chemotherapy for acute lymphatic leukemia had extensive opacification of the urinary tract on the preliminary film for an intravenous urogram. Sonography and computed tomography also demonstrated dense material in the calyces, renal pelves and ureters. Since then, we have found another patient, a 9-year-old female with acute lymphatic leukemia who was not receiving chemotherapy, with a similar pattern on sonography and computed tomography. These densities unlike those in our first patient were not visible on a plain film of the abdomen. All of the material disappeared spontaneously in both patients.

Diketopiperazine formation, hydrolysis, and epimerization of the new dipeptide angiotensin-converting enzyme inhibitor RS-10085

The degradation kinetics, products, and mechanisms of RS-10085(1), 2-[2-(1-ethoxycarbonyl)-3-phenylpropyl]amino-1-oxopropyl]-6,7- dimethoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid(S,S,S), in aqueous solution were investigated at 40, 60, and 80 degrees C from pH 1 to pH 13. Pseudo-first-order kinetics were observed throughout the pH range studied and the log(rate)-pH profiles reflected four kinetic processes (ko, k'o, k'o, and kOH) as well as the two pKa's of 1. Excellent (greater than 98%) mass balance was obtained through products 2-5. At pH 4 or below, intramolecular cyclization leading to diketopiperazine 5 accounted for greater than 93% of the observed neutral- or water-catalyzed processes (ko and k'o). At pH levels greater than 5, hydrolysis giving 2 predominated and was responsible for the observed neutral- or water-catalyzed (k''o) and specific base-catalyzed (kOH) kinetic processes. Some epimerization leading to the S,S,R drug isomer (4) was also observed at pH levels greater than 7. The relative acidity of the protons at the three chiral centers of 1 was qualitatively compared and was used to explain the observed specificity in epimerization.