DNA vaccination using the fragment C of botulinum neurotoxin type A provided protective immunity in mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.

Insulin inhibits angiotensinogen gene expression via the mitogen-activated protein kinase pathway in rat kidney proximal tubular cells

The present study aimed to investigate the molecular mechanism(s) of insulin action on angiotensinogen (ANG) secretion and gene expression in kidney proximal tubular cells exposed to high levels of glucose. Immortalized rat proximal tubular cells (IRPTC) were cultured in monolayer. The levels of rat ANG and ANG messenger RNA in the IRPTC were quantified by a specific RIA for rat ANG (RIA-rANG) and by an RT-PCR assay. Insulin inhibited the stimulatory effect of a high level of glucose (25 mM) and phorbol 12-myristate 13-acetate, an activator of protein kinase C) on the secretion of ANG and the expression of the ANG messenger RNA in IRPTC. This inhibitory action of insulin on the ANG secretion and gene expression was blocked by PD98059 (an inhibitor of mitogen-activated protein kinase kinase) but not by Wortmannin (an inhibitor of phosphatidylinositol-3-kinase). PD98059 was effective in inhibiting the phosphorylation of MEK 1/2 and p44/42 MAP kinase in IRPTC stimulated by insulin. These studies demonstrate that insulin prevents the stimulatory effect of high levels of glucose on the expression of the renal ANG gene in IRPTC, at least in part, via the MAPK kinase signal transduction pathway, subsequently inhibiting the activation of the local renal renin-angiotensin system.

Glucocorticoid metabolism in proximal tubules modulates angiotensin II-induced electrolyte transport

The hormonal interactions that regulate electrolyte transport in the proximal tubule are complex and incompletely understood. Since endogenous glucocorticoids and angiotensin II each can affect electrolyte transport in this renal segment, we hypothesized that local metabolism of glucocorticoids by the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) might alter the response to angiotensin II. Studies were conducted in cultured origin defective SV-40 transformed immortalized renal proximal tubule cells (IRPTC) derived from weanling Wistar rat kidney. The 11beta-HSD contained in these cells uses NADP+, has an apparent Km for corticosterone of 1.6 microM, but functions only as a dehydrogenase (corticosterone --> 11-dehydro-corticosterone). When mounted in modified Ussing chambers, IRPTC generate a transmembrane current, and angiotensin II (10 pM to 10 microM) increases this sodium-dependent current. Cells incubated with corticosterone (100 nM) and the 11beta-HSD inhibitor carbenoxolone (CBX) (1 microM) for 24 hr and then acutely stimulated with angiotensin (10 nM) show a greater rise in current than do cells exposed to corticosterone alone and stimulated with angiotensin (corticosterone + CBX: 64.2% +/- 20.5% vs. corticosterone: 18.8% +/- 5.9%; P < 0.02 at 180 min)[mean +/- SE percentage above baseline, n = 8/group]. Cells exposed to corticosterone (100 nM) or CBX (1 microM) alone for 24 hr and then stimulated with angiotensin II (10 nM) had responses similar to controls. Thus glucocorticoids can enhance angiotensin II-induced electrolyte transport in proximal tubule epithelial cells when local 11beta-HSD is inhibited.

Rat proximal tubule cell line transformed with origin-defective SV40 DNA: autocrine ANG II feedback

The renal proximal tubule (PT) is a major site for a complete tissue renin-angiotensin system (RAS) and produces endogenous angiotensin II (ANG II). The present studies demonstrate autocrine RAS feedback in a line of origin-defective SV40 plasmid transformed immortalized rat PT cells (IRPTC) designated as line 93-p-2-1, which are highly differentiated and express all RAS components. Receptor competition assays and Southern blot following RT-PCR demonstrated that these IRPTC express AT1 and AT2 angiotensin receptor subtypes. Autocrine RAS feedback was examined following exposure to ANG II (10(-8) M), and it was noted that angiotensinogen mRNA increases significantly by 1 h and remains elevated through 24 h. The AT1 blocker losartan prevents this increase. Moreover, ANG II upregulates expression of ANG II receptor mRNA (both AT1 and AT2). Thus the present studies demonstrate positive ANG II feedback with angiotensinogen and ANG II receptors in PTC, suggesting that the main site of such intrarenal feedback in vivo is within PT. ANG II secreted by line 93-p-2-1 is increased by isoproterenol, suggesting beta-adrenergic regulation in IRPTC.

Molecular mechanisms of glucose action on angiotensinogen gene expression in rat proximal tubular cells

BACKGROUND

Clinical studies have shown that the angiotensin-converting enzyme (ACE) inhibitors or angiotensin II (Ang II) receptor antagonists decrease proteinuria and slow the progression of nephropathy in diabetes, indicating that Ang II plays an important role in the development of nephropathy. We have previously reported that high levels of glucose stimulate the expression of rat angiotensinogen (ANG) gene in opossum kidney (OK) proximal tubular cells. We hypothesized that the stimulatory effect of D(+)-glucose on the expression of the ANG gene in kidney proximal tubular cells is mediated via de novo synthesis of diacylglycerol (DAG) and the protein kinase C (PKC) signal transduction pathway.

METHODS

Immortalized rat proximal tubular cells (IRPTCs) were cultured in monolayer. The stimulatory effect of glucose on the activation of polyol pathway and PKC signal transduction pathway in IRPTCs was determined. The immunoreactive rat ANG (IR-rANG) in the culture medium and the cellular ANG mRNA were measured with a specific radioimmunoassay and a reverse transcription-polymerase chain reaction assay, respectively.

RESULTS

D(+)-glucose (25 mM) markedly increased the intracellular levels of sorbitol, fructose, DAG, and PKC activity as well as the expression of IR-rANG and ANG mRNA in IRPTCs. These stimulatory effects of D(+)-glucose (25 mM) were blocked by an inhibitor of aldose reductase, Tolrestat. PKC inhibitors also inhibited the stimulatory effect of D(+)-glucose (25 mM) on the expression of the IR-rANG in IRPTCs. The addition of phorbol 12-myristate 13-acetate further enhanced the stimulatory effect of D(+)-glucose (25 mM) on the expression of the IR-rANG in IRPTCs and blocked the inhibitory effect of Tolrestat.

CONCLUSION

These studies suggest that the stimulatory effect of a high level of D(+)-glucose (25 mM) on the expression of the ANG gene in IRPTCs is mediated, at least in part, via the de novo synthesis of DAG, an activator of PKC signal transduction pathway.

Synergistic effect of dexamethasone and isoproterenol on the expression of angiotensinogen in immortalized rat proximal tubular cells

To investigate whether the expression of angiotensinogen (ANG) in rat kidney proximal tubules is stimulated by dexamethasone and isoproterenol, immortalized rat proximal tubular cells (IRPTC) were cultured in a monolayer. Immunoreactive rat ANG (IR-rANG) in the culture medium was measured by a specific radioimmunoassay (RIA) for rANG. This RIA was developed by employing rabbit antiserum against the purified recombinant rat ANG (rANG). The purified rANG from plasma and the iodinated rANG were used as the hormone standard and tracer, respectively. The RIA is specific for rat ANG and it has no cross-reactivity with other pituitary hormone preparations or other rat plasma proteins. The sensitivity of detection of the RIA is approximately 2 ng of rANG. The levels of IR-rANG in the culture media of IRPTC ranged from 2 to 5 ng/ml/24 hr/10(6) cells. The addition of dexamethasone (10(-13) to 10(-5) M) stimulated the expression and secretion of rANG from IRPTC in a dose-dependent manner, whereas the addition of isoproterenol alone had no effect. However, a combination of both dexamethasone and isoproterenol synergistically stimulated the expression and secretion of rANG by IRPTC. The synergistic effect of dexamethasone and isoproterenol was blocked by the presence of RU 486 (a glucocorticoid receptor antagonist) or propranolol (beta-adrenoceptor blocker). These studies suggest that the addition of dexamethasone and isoproterenol acts synergistically to stimulate the expression and secretion of ANG protein in rat proximal tubules in vivo.

Immortalized rat proximal tubule cells produce membrane bound and soluble megalin

Megalin (gp330), a glycoprotein receptor found on renal proximal tubule cells and several other epithelial cells, is deduced to be a type I integral membrane protein, but may also exist as a cell surface form lacking a cytoplasmic domain. Furthermore, soluble megalin products have been detected in urine, and in culture medium of a rat yolk sac carcinoma cell line, combined with receptor associated protein (RAP). Permanent renal cell lines expressing megalin were unavailable until the recent description of two immortalized rat proximal tubule cell lines (IRPTC). The present study demonstrated megalin on IRPTC surface by immunofluorescence, without surface staining for RAP, which was, however, readily detected within cells. Antibodies to ectodomain megalin epitopes immunoprecipitated megalin products both from cell lysates and culture medium, whereas antibodies to cytoplasmic domain epitopes precipitated megalin only from lysates. Western blots showed two major megalin products in medium, a prominent band at approximately 200 kDa, and a fainter band above 400 kDa, slightly below intact megalin in cell lysates. Anti-receptor associated protein antibodies immunoprecipitated megalin from IRPTC lysates, but not from media. We propose that portions of megalin are spontaneously produced by IRPTC, probably either by cleavage in the ectodomain or release of forms lacking a cytoplasmic domain.

[Effect of adrenomedullin on mesenteric microvessels and microlymphatics in rat]

The dilatant effect of adrenomedullin (ADM), a novel peptide of 52 amino acids, on the mesenteric microvessels and microlymphatics was investigated under microscopic observation. 10(-6) mol/L ADM could also ameliorate alteration of the hemorheology induced by 10(-5) mol/L norepinephrine (NE) or 10(-7) mol/L endothelin (ET). However, this ameliorative response was markedly inhibited in the presence of NG-nitro-L-arginine (L-NNA), an inhibitor for production of nitric oxide.

Kinetic characterization of the endogenous glutathione transferase activity of octopus lens S-crystallin

The kinetic mechanism of the endogenous glutathione transferase (GST) activity of octopus S-crystallin was investigated by steady-state kinetics. Biphasic double-reciprocal plots were obtained for both glutathione and the hydrophobic substrate 1-chloro-2,4-dinitrobenzene (CDNB). Substrate inhibition was observed only for CDNB with Ksi value of 29.7 +/- 0.01 mM. The catalytic constant for S-crystallin was three orders of magnitude smaller than that for the digestive gland GST of the same species. The initial-velocity studies indicated that the enzyme reaction might conform to a steady-state random Bi-Bi kinetic mechanism, being similar to the reaction of GST from other sources. The pH-rate profiles also suggest that the same chemical mechanism for the nucleophilic aromatic substitution between GSH and CDNB was employed for S-crystallin. The interaction of Tyr7 with the bound GSH lowered the pKa value of the sulfhydryl group of GSH to 6.82-6.85, which is 2.32-2.35 pH unit smaller than that found in aqueous solution. This lowering of pKa value produces the thiolate anion of GSH, a better nucleophile to attack the ipso carbon of CDNB, resulting in formation of Meisenheimer complex intermediate. Removing the chloride ion from this intermediate complex produces the conjugate product. Using the method devised by Wang and Srivastava (Anal. Biochem. 216, 15-26, 1994), the functional unit of the dimeric S-crystallin was estimated to be a monomer. The possible biological implications of the endogenous detoxification ability of cephalopods S-crystallin are discussed.

Kinetic mechanism of octopus hepatopancreatic glutathione transferase in reverse micelles

Octopus glutathione transferase (GST) was enzymically active in aerosol-OT [sodium bis-(2-ethylhexyl)sulphosuccinate]/iso-octane reverse micelles albeit with lowered catalytic constant (kcat). The enzyme reaction rate was found to be dependent on the [H2O]/[surfactant] ratio (omega(o)) of the system with maximum rate observed at omega(o) 13.88, which corresponded to vesicles with a core volume of 64 nm3. According to the physical examinations, a vesicle of this size is barely large enough to accommodate a monomeric enzyme subunit. Dissociation of the enzyme in reverse micelles was confirmed by cross-linking of the associated subunits with glutaraldehyde and separation of the monomers and dimers with electrophoresis in the presence of SDS. The kinetic properties of the enzyme were investigated by steady-state kinetic analysis. Both GSH and 1-chloro-2,4-dinitrobenzene (CDNB) showed substrate inhibition and the Michaelis constant for CDNB was increased by 36-fold to 11.05 mM in reverse micelles. Results on the initial-velocity and product-inhibition studies indicate that the octopus GST conforms to a steady-state sequential random Bi Bi mechanism. The results from a log kcat versus pH plot suggest that amino acid residues with pKa values of 6.56 0.07 and 8.81 0.17 should be deprotonated to give optimum catalytic function. In contrast, the amino acid residue with a pKa value of 9.69 0.16 in aqueous solution had to be protonated for the reaction to proceed. We propose that the pKa1 (6.56) is that for the enzyme-bound GSH, which has a pKa value lowered by 1.40-1.54 pH units compared with that of free GSH in reverse micelles. The most probable candidate for the observed pKa2 (8.81) is Tyr7 of GST. The pKa of Tyr7 is 0.88 pH unit lower than that in aqueous solution and is about 2 pH units below the normal tyrosine. This tyrosyl residue may act as a base catalyst facilitating the dissociation of enzyme-bound GSH. The possible interaction of GST with plasma membrane in vivo is discussed.

Metal-catalyzed oxidation and cleavage of octopus glutathione transferase by the Cu(II)-ascorbate system

Glutathione transferase (GST) from octopus hepatopancreas was rapidly inactivated by micromolar concentration of Cu(II) in the presence of ascorbate at neutral pH and 0 degree C. Omitting the metal ion or ascorbate, or replacing the Cu(II) with Fe(II) did not result in any inactivation. Glutathione or the conjugation product of glutathione and 1-chloro-2,4-dinitrobenzene offered complete protection of the enzyme from Cu(II)-induced inactivation. 1-Chloro-2,4-dinitrobenzene, however, did not provide any protection. The inactivation was time and Cu(II) concentration dependent. The dependence of inactivation rate on Cu(II) concentration displayed saturation kinetics, which suggests that the inactivation occurs in two steps with Cu(II) binding with the enzyme first (KdCu = 260 microM), then the locally generated free radicals modify the essential amino acid residues in the active center, which results in enzyme inactivation. The Cu(II)-ascorbate system is, thus, an affinity reagent for the octopus GST. The enzyme inactivation was demonstrated to be followed by protein cleavage. Native octopus GST has a subunit M(r) of 24,000. The inactivated enzyme was cleaved at the C-terminal domain (domain II) of the enzyme molecule and resulted in the formation of peptide fragment of M(r) 15,300, which has the identical N-terminal amino acid sequence as the native enzyme. The other half of the peptide with M(r) approximately 7700 was visible in the gels only after silver staining, which also revealed a minor cleavage site, also located at the domain II, to produce peptide fragments of M(r) approximately 11,300 and 8300. The oxygen carrier molecule in the cephalopods' blood is the copper-containing hemocyanin, which during turnover will release Cu(II). Our results indicate that Cu(II) catalyzes a site-specific oxidation of the essential amino acid residues at the C-terminus of GST causing enzyme inactivation. The modified-enzyme is then affinity cleaved at the putative metal binding site. The ability of octopus GST to bind with free Cu(II) may have important biological implications to enable cephalopods to avoid copper-induced cellular toxicity.

Activity of the molluscicidal plant Millettia thonningii (Leguminosae) toward Biomphalaria glabrata eggs

A dichloromethane extract of the seeds of the molluscicidal west African legume Millettia thonningii was tested for ovicidal activity toward Biomphalaria glabrata egg masses. The extract was found to be highly ovicidal at concentrations as low as 5 mg/L. Embryonic development of the snails in egg masses was monitored using photomicrographs from which embryonic diameters were estimated. Such measurements revealed that ovicidal effects were developmentally stage specific and normally induced a curtailment of development during the gastrula to trochophore transition.

NF-kappa B and transcriptional control of renal epithelial-inducible nitric oxide synthase

Expression of the inducible isoform of nitric oxide synthase (iNOS) is subject to strict tissue specific transcriptional control. Recently, the NF-kappa B/Rel family of transcription factors, and particularly c-rel, was shown to mediate bacterial lipopolysaccharide (LPS) induction of iNOS in macrophages. Since LPS is only a weak inducer of iNOS in most nonimmune cells, we investigated the role of NF-kappa B in the regulation of iNOS expression in mouse renal epithelial cells. We report that LPS activates NF-kappa B in renal epithelium, but that this is not sufficient for induction of iNOS activity. The NF-kappa B complexes activated by LPS in renal epithelium differ from those in macrophages in that they lack c-rel, which may explain the absence of iNOS induction in renal epithelium. Conversely, LPS and interferon-gamma (IFN) synergize to induce renal epithelial iNOS. Functional iNOS promoter analysis indicate that this synergistic induction requires NF-kappa B. We conclude that NF-kappa B is necessary but not sufficient for the induction of renal epithelial iNOS expression, and that in contrast to macrophages, c-rel does not appear to play a major role in the regulation of renal epithelial iNOS.

Steady-state kinetics and chemical mechanism of octopus hepatopancreatic glutathione transferase

The kinetic mechanism of glutathione S-transferase (GST) from Octopus vulgaris hepatopancreas was investigated by steady-state analysis. Initial-velocity studies showed an intersecting pattern, which suggests a sequential kinetic mechanism for the enzyme. Product-inhibition patterns by chloride and the conjugate product were all non-competitive with respect to glutathione or 1-chloro-2,4-dinitrobenzene (CDNB), which indicates that the octopus digestive gland GST conforms to a steady-state sequential random Bi Bi kinetic mechanism. Dead-end inhibition patterns indicate that ethacrynic acid ([2,3-dichloro-4-(2-methyl-enebutyryl) phenoxy]acetic acid) binds at the hydrophobic H-site, norophthalmic acid (gamma-glutamylalanylglycine) binds at the glutathione G-site, and glutathione-ethacrynate conjugate occupied both H- and G-sites of the enzyme. The chemical mechanism of the enzyme was examined by pH and kinetic solvent-isotope effects. At pH (and p2H) = 8.011, in which kcat. was independent of pH or p2H, the solvent isotope effects on V and V/KmGSH were near unity, in the range 1.069-1.175. An inverse isotope effect was observed for V/KmCDNB (0.597), presumably resulting from the hydrogen-bonding of enzyme-bound glutathione, which has pKa of 6.83 +/- 0.04, a value lower by 2.34 pH units than the pKa of glutathione in aqueous solution. This lowering of the pKa value for the sulphydryl group of the bound glutathione was presumably due to interaction with the active site Tyr7, which had a pKa value of 8.46 +/- 0.09 that was raised to 9.63 +/- 0.08 in the presence of glutathione thiolate. Subsequent chemical reaction involves attacking of thiolate anion at the electrophilic substrate with the formation of a negatively charged Meisenheimer complex, which is the rate-limiting step of the reaction.

Autocrine inhibition of Na+/K(+)-ATPase by nitric oxide in mouse proximal tubule epithelial cells

An inducible nitric oxide synthase has recently been described in proximal tubule epithelium. To investigate the effects of proximal tubule NO on Na+/K(+)-ATPase, we induced NO production in mouse proximal tubule epithelial cells by treatment with lipopolysaccharide (LPS) and interferon-gamma (IFN gamma) followed by determinations of ouabain-sensitive ATPase activity. Na+/K(+)-ATPase activity decreased after 4 h of LPS/IFN gamma treatment, reaching maximal inhibition after 24 h (34% reduction in activity). The inhibition of Na+/K(+)-ATPase activity by LPS/IFN gamma was prevented by simultaneous incubation with N omega-nitro L-arginine and markedly blunted by removal of L-arginine from the medium. The NO donors sodium nitroprusside and SIN-1 also inhibited Na+/K(+)-ATPase activity to a similar extent than LPS/IFN gamma. However, treatment with 8-pCPT-cGMP only modestly reduced Na+/K(+)-ATPase activity. Interestingly, superoxide dismutase prevented the inhibitory effects of NO on Na+/K(+)-ATPase activity, suggesting a role for peroxynitrite in this inhibition. We conclude that NO generated by mouse proximal tubule epithelial cell iNOS inhibits Na/K ATPase activity in an autocrine fashion and that this inhibition is accompanied by a reduction in Na-dependent solute transport.

Temperature-sensitive SV40 immortalized rat proximal tubule cell line has functional renin-angiotensin system

Immortalized rat proximal tubule cell (IRPTC) lines should be useful for investigation of proximal tubule (PT) regulation and function but previously have been unavailable. We now report the establishment and characterization of an immortalized transformed, temperature-sensitive IRPTC cell line containing renin-angiotensin system (RAS) components. Primary PT cells prepared from male Wistar rats (4-5 wk old) after collagenase digestion, sieving, and Percoll gradient were cultured on collagen-coated T-75 flasks in Dulbecco's modified Eagle's medium containing 5% fetal calf serum. Subconfluent PT cells were transfected with the temperature-sensitive SV40 mutant viruses (tsA SV40) by direct exposure. After 7-8 wk, several clones were obtained, from which one has been characterized and designated as line 3-2. This cell line appears stable up to 45 passages. Clonal cells transformed with this virus exhibit a transformed phenotype at a permissive temperature of 34 degrees C and grow in multiple layers. When the cells are subsequently placed at a nonpermissive temperature of 41 degrees C, they return to morphology similar to that of untransformed cells of the same lineage. At either 34 degrees C or 41 degrees C, this cell line expresses a variety of PT markers including alkaline phosphatase, cytokeratin, carbonic anhydrase, and glucose transporter isoform 2 (GLUT2), while not expressing factor VIII. Uniquely, these cells also appear to express PT proteins gp330 and CHIP28, markers which are usually lost in cultured cells. Furthermore, the cell line expresses protein and mRNA components of RAS, including angiotensinogen, angiotensin converting enzyme, and renin. The IRPTC cell line expresses few angiotensin II (ANG II) receptors at 34 degrees C, the permissive temperature. However, at the nonpermissive temperature, 41 degrees C, IRPTC expresses ANG II receptor (dissociation constant of 0.7 nM; maximum binding capacity of 265 fmol/mg protein). ANG II (10(-8) M) induced a transient rise in cytoplasmic Ca2+ concentration, which was nearly abolished with losartan but not PD-123319, suggesting this finding is AT1 receptor mediated. This cell line should provide an excellent model of PT and should make it possible to study the cell and molecular biology of the RAS, as well as other regulatory systems of the PT.

Guanosine triphosphate cyclohydrolase I regulates nitric oxide synthesis in renal proximal tubules

The synthesis of nitric oxide by proximal tubule-inducible nitric oxide synthase requires tetrahydrobiopterin as a cofactor. To determine whether tetrahydrobiopterin synthesis is required for nitric oxide production, nitrite release by mouse proximal tubule cells treated with 2,4-diamino-6-hydroxypyrimidine, an inhibitor of the rate-limiting enzyme in the de novo synthesis of tetrahydrobiopterin from guanosine triphosphate, guanosine triphosphate cyclohydrolase I, was measured. Treatment with lipopolysaccharide (0.1 micrograms/mL) and interferon-gamma (100 U/mL) for 12 h increased nitrite production from 2.7 +/- 0.2 to 25.4 +/- 1.3 nmol/mg of protein (P < 0.001; N = 9). 2,4-Diamino-6-hydroxypyrimidine (6 mM) reduced lipopolysaccharide/interferon-gamma-induced nitrite production by 53.1 +/- 3.4%. Sepiapterin, a substrate for tetrahydrobiopterin synthesis via the dihydrofolate reductase-dependent pterin salvage pathway, prevented the inhibition by 2,4-diamino-6-hydroxypyrimidine, an effect that was blocked by methotrexate. In conclusion, guanosine triphosphate cyclohydrolase I activity is required for cytokine-induced nitric oxide production by proximal tubular epithelium. The inhibition of guanosine triphosphate cyclohydrolase I could prove useful in the treatment of nitric oxide-mediated renal disorders.

Molecular-Structure of bis(ethane-1,2-diolato)( tetraphenylporphyrinato )phosphorus(V) chloride: [P( tpp )(OCH2CH2OH)2]+Cl -

The structure of bis(ethane-1,2-diolato)( tetraphenylporphyrinato )phosphorus(V) chloride, [P( tpp )(OCH2CH2OH)2]+Cl -, has been confirmed by X-ray diffraction. The cation displays an octahedral coordination about the phosphorus atom and exhibits a ruffled porphyrin geometry with a core size of 1.841 Ǻ. It crystallizes in the orthorhombic space group P212121, with a 12.524(3), b 25.177(5), c 14.275(3) Ǻ, and Z = 4. Refinement based on 4194 observed reflections led to a final R value of 5.1%. The displacement of the phosphorus atom from the porphyrin mean plane is 0.014 Ǻ. The geometry around the phosphorus centre of the [P( tpp )(OCH2CH2OH)2]+Cl- molecule has P-O(1) 1.643(4), P-O(3) 1.642(4) and P- Np 1.841(4) Ǻ. n.m.r. spectroscopy provides a complementary method for the investigation of the ethane-1,2-diolate ligand. The 13C resonances (24°C) of this axial ligand were observed at 62.9 [P-O-C-C-OH, with 2J(P,C) 16.1 Hz] and 57.8 ppm [P-O-C-C-OH with 3J(P,C) 19.1 Hz].

Isolation and characterization of octopus hepatopancreatic glutathione S-transferase. Comparison of digestive gland enzyme with lens S-crystallin

Glutathione S-transferase from Octopus vulgaris hepatopancreas was purified to apparent homogeneity by single glutathione-Sepharose-4B affinity chromatography with overall yield 46% and purification 249-fold. The enzyme was a homodimer with subunit M(r) 24,000, which was smaller than that of the octopus lens S-crystallin (M(r) 27,000) with glutathione-S-transferase-like structure. Both proteins showed substrate specificities similar to alpha/pi-type isozyme of glutathione S-transferase. Under native conditions, both proteins exhibited multiple forms upon polyacrylamide gel electrophoresis or isoelectric focusing, albeit with distinct mobilities; however, only one kind of N-terminal amino acid sequence was determined for the multiple forms of each protein. The hepatopancreatic GST, with pI value 6.6-7.3, dissociated into two monomers in an acidic or alkaline environment. Two amino acid residues, with pKa values 5.69 +/- 0.14 and 9.03 +/- 0.11 were involved in the subunit interactions of the hepatopancreatic enzyme.

Distribution and function of cardiac angiotensin AT1- and AT2-receptor subtypes in hypertrophied rat hearts

To determine distribution and function of cardiac angiotensin (ANG) II receptor AT1 and AT2 subtypes in left ventricular (LV) hypertrophy (LVH), ANG II (10(-8) M) was infused into isolated rat hearts with hypertrophy from aortic banding and into sham-operated controls. ANG II was infused alone or in the presence of AT1 inhibitor [losartan (10(-5) M) or CL-329167 (10(-7) M)] or AT2 inhibitor [CG-42112A (10(-8) M]. ANG II alone caused less increase in coronary vascular resistance (CVR) in LVH compared with control hearts (19 vs. 39%; P < 0.01), although baseline CVR was higher in LVH hearts. This was prevented by AT1 but not AT2 antagonists. ANG II also increased LV end-diastolic pressure in LVH hearts, signifying decreased diastolic relaxation that was prevented by AT1 but not AT2 inhibition. Characterization of ANG II binding sites in LV membrane preparations revealed similar dissociation constants between groups (1.6 +/- 0.95 vs. 2.2 +/- 2.0 nM; not significant) but lower maximum binding capacity in the LVH group (21.1 +/- 5.9 vs. 33.5 +/- 3.0 fmol/mg protein; P < 0.05). Competition assays demonstrated that control left ventricles contain predominantly the AT1 subtype (68.8 +/- 20%), whereas LVH ventricles contain primarily the putative AT2 subtype (59.8% +/- 10.8%; P < 0.05). This suggests that receptor subtype redistribution occurs in LVH with AT1 subtype down-regulation. Nonetheless, the AT1 subtype mediates the effects of ANG II on coronary tone and diastolic dysfunction in pressure-overload hypertrophy.

Renin and angiotensinogen mRNA expression in the kidneys of rats subjected to long-term bile duct ligation

Activation of antinatriuretic systems such as the renin-angiotensin system, is of major importance in the pathogenesis of sodium retention in cirrhosis. In this study, we studied the intrarenal renin-angiotensin system by measuring renin and angiotensinogen mRNA expression in the kidney of rats subjected to long-term bile duct ligation in a phase before the development of ascites, when sodium retention is already present. Experiments were performed in sham-operated and bile duct-ligated rats 3 wk after surgery. Balance studies showed lower sodium excretion and greater sodium retention in the bile duct-ligated rats compared with the control animals. Plasma renin activity (4.41 +/- 1.01 ng Angiotensin I/ml/hr in the bile duct-ligated group vs. 4.20 +/- 0.74 in the controls) and plasma renin concentration were not different between the two groups. However, plasma renin substrate was significantly decreased in bile duct-ligated animals. Total kidney renin mRNA was significantly higher in the bile duct-ligated animals (0.83 +/- 0.14 densitometric units vs. 0.44 +/- 0.04 in the controls), as determined on Northern-blot analysis and densitometric quantitation. Angiotensinogen mRNA expression in the kidneys of bile duct-ligated rats was significantly decreased (0.09 +/- 0.01 densitometric units) compared with that of the controls (0.21 +/- 0.03). These results indicate that sodium-retaining, nonascitic bile duct-ligated rats show abnormalities of the intrarenal renin angiotensin system that precede changes in plasma renin activity. Our data suggest that the intrarenal renin angiotensin system may participate in the initiation of the renal pathophysiological abnormalities present in bile duct-ligated rats.

Purification and kinetic mechanism of the glutathione S-transferase from C6/36, an Aedes albopictus cell line

Glutathione S-transferase from an Aedes albopictus cell line, C6/36, was purified to apparent homogeneity by a single glutathione-Sepharose 4B affinity chromatography, with an overall yield of 66% and 226-fold purification. The enzyme is presumably a homodimer with subunit M(r) 23,000, which is similar to the enzyme isolated from other sources. Under native conditions, the enzyme exhibited multiple forms upon isoelectric focusing or polyacrylamide gel electrophoresis, and all these forms retained enzymatic activity. The pI value of the purified enzyme was distributed between approximately 4.7 and 5.4 with major form at 4.9. The purified enzyme lost 63% activity at -20 degrees C within 1 week. Stability of the purified enzyme was greatly improved by the addition 10 mg/ml of bovine serum albumin, under which only 7% activity was lost after 1 week at -20 degrees C. Activation energy for the enzyme-catalyzed conjugation of glutathione with 1-chloro-2,4-dinitrobenzene was found to be 49.1 kJ/mol. The enzyme could utilize 1-chloro-2,4-dinitrobenzene and ethacrynic acid as substrate, but not bromosulfophthalein, cumene hydroperoxide, or trans-4-phenyl-3-buten-2-one. The initial-velocity and product-inhibition studies indicated that the enzyme reaction conformed to a steady-state random Bi-Bi kinetic mechanism, which was similar to the glutathione S-transferase from other sources. The kinetic data also indicated a synergistic effect between the binding of glutathione G-site and that of organic electrophilic substrate in the H-site of the enzyme active center. The biological significance of the conjugation reaction is discussed.

Angiotensin converting enzyme in renal ontogeny: hypothesis for multiple roles

Angiotensin converting enzyme (ACE) has multiple effects both as the enzyme which cleaves angiotensin II from angiotensin I and as that which breaks down bradykinin. The present study examines ACE mRNA and protein expression in the rat kidney during development. Changes in distribution and expression during development are consistent with suggestions that the renin angiotensin system is important in growth modulation, vascular development and regulation, and protein reabsorption.

Regulation of intrarenal and circulating renin-angiotensin systems in severe heart failure in the rat

OBJECTIVE

Activation of the intrarenal renin-angiotensin system may contribute to the pathophysiology of heart failure by accelerating the generation of angiotensin II at local sites within the kidneys. Activation of the local intrarenal renin-angiotensin system occurs in rats and with mild heart failure. The aim of the present study was to examine components of the circulating as well as the intrarenal renin-angiotensin system in rats with severe heart failure.

METHODS

Six weeks after experimental myocardial infarction (heart failure, HF; n = 8) or sham operation (control, C; n = 6), haemodynamics and the circulating and intrarenal components of the renin-angiotensin system were studied.

RESULTS

HF rats were characterised by large infarctions (scar tissue > 40% of the left ventricular circumference). In comparison to sham operated controls, large myocardial infarctions resulted in severe heart failure with decreased systolic [108(SEM 3) mm Hg v 132(3) in C; p < 0.001] and diastolic arterial blood pressure [83(3) mm Hg v 95(2) in C; p < 0.05], decreased left ventricular systolic pressure [109(3) mm Hg v 132(3) in C; p < 0.005] and increased left ventricular end diastolic pressure [27(2) mm Hg v 5(1) in C; p < 0.0001]. In rats with severe heart failure, the circulating renin-angiotensin system was activated, with an increase in plasma renin activity (3.5-fold, p < 0.05) and plasma angiotensin II concentration (threefold, p < 0.01). In parallel, the intrarenal renin-angiotensin system was activated in severe heart failure. Increases occurred in renal renin mRNA level (1.7-fold, p < 0.01), renal angiotensinogen mRNA level (1.8-fold, p < 0.05), and renal angiotensin II concentration (twofold, p < 0.05) compared to C. Intrarenal angiotensin II concentrations exceeded plasma levels by a factor of 50 and were positively correlated with renal angiotensinogen mRNA levels (r = 0.874, p < 0.001), suggesting that local synthesis is the major source of angiotensin II found in the kidney.

CONCLUSIONS

The intrarenal renin-angiotensin system may be selectively activated in mild heart failure, while both circulating and intrarenal renin-angiotensin systems are induced as the extent of left ventricular function worsens.