Chemical Genetics Uncovers Novel Inhibitors of Lignification, Including p-Iodobenzoic Acid Targeting CINNAMATE-4-HYDROXYLASE

Plant secondary-thickened cell walls are characterized by the presence of lignin, a recalcitrant and hydrophobic polymer that provides mechanical strength and ensures long-distance water transport. Exactly the recalcitrance and hydrophobicity of lignin put a burden on the industrial processing efficiency of lignocellulosic biomass. Both forward and reverse genetic strategies have been used intensively to unravel the molecular mechanism of lignin deposition. As an alternative strategy, we introduce here a forward chemical genetic approach to find candidate inhibitors of lignification. A high-throughput assay to assess lignification in Arabidopsis (Arabidopsis thaliana) seedlings was developed and used to screen a 10-k library of structurally diverse, synthetic molecules. Of the 73 compounds that reduced lignin deposition, 39 that had a major impact were retained and classified into five clusters based on the shift they induced in the phenolic profile of Arabidopsis seedlings. One representative compound of each cluster was selected for further lignin-specific assays, leading to the identification of an aromatic compound that is processed in the plant into two fragments, both having inhibitory activity against lignification. One fragment, p-iodobenzoic acid, was further characterized as a new inhibitor of CINNAMATE 4-HYDROXYLASE, a key enzyme of the phenylpropanoid pathway synthesizing the building blocks of the lignin polymer. As such, we provide proof of concept of this chemical biology approach to screen for inhibitors of lignification and present a broad array of putative inhibitors of lignin deposition for further characterization.

The relationship between chemical structure and antimicrobial activity of selected nicotinates, p-iodobenzoates, picolinates and isonicotinates

Alkaline metal, calcium and magnesium p-iodobenzoates and alkaline metal nicotinates, as well as sodium and potassium picolinic and isonicotinates were investigated by means of their antimicrobial and chemical properties. The quality estimation of the influence of metal cation coordinated to the carboxylic anion of the series of studied compounds on their antimicrobial activity as well as on the vibrational structure of whole complex in water solution was done. The changes in antimicrobial properties and in charge distribution of the complex along the position of nitrogen atom in the aromatic ring in sodium and potassium complexes were investigated. The analysis of influence of iodine substituent in para position on the change of electronic charge distribution of carboxylate anion and aromatic ring was done. The relationship between electronic properties estimated by vibrational spectroscopy and antimicrobial activity of studied complexes was investigated.

Mechanisms of antitumor action of methyl-3,5-diiodo-4-(4'-methoxyphenoxy)benzoate: drug-induced protein dephosphorylations and inhibition of the permissive action of ceramide on growth factor induced cell proliferation

The tumoricidal mechanism of methyl-3,5-diiodo-4-(4'-methoxypropoxy)benzoate (DIME), or DIPE, has been analyzed beyond its first recognized cellular site, which is the inhibition of tubulin polymerization. DIME (or DIPE) pretreatment of Eras cells for 3 days abolished ceramide basic fibroblast growth factor (bFGF)-induced glycolysis, coinciding with a block produced by the phosphoprotein dephosphorylation of cdc 25 by protein phosphatase 2A (PP2A). Protein dephosphorylation is directly activated by DIME (or DIPE), and enzyme activities that are dependent on P-proteins are significantly down-regulated (e.g. Topo I and II, MAP-kinase, and cdc-cyclin kinase). Purified PP2A is one target of activation by DIME (or DIPE), and an alkaline phosphatase isoenzyme is also induced by the drug. It is proposed that the pleiotropic effects of DIME (or DIPE) on cancer cells involve the activation of protein dephosphorylations, as well as inhibition of tubulin polymerization.

Synthesis of the catechols of natural and synthetic estrogens by using 2-iodoxybenzoic acid (IBX) as the oxidizing agent

A method for the synthesis of 2-hydroxyestrone/estradiol, 4-hydroxyestrone/estradiol, 3'-hydroxydiethylstilbestrol, 3'-hydroxyhexestrol, and 3'-hydroxydienestrol is reported, in which 2-iodoxybenzoic acid (IBX) and the corresponding phenolic estrogen are reacted. Treatment of the natural estrogens, estrone/estradiol, with stoichiometric amounts of IBX in dimethylformamide initially yielded a mixture of estrone/estradiol-2,3- and -3,4-quinones, which were reduced in situ to the corresponding catechols by treatment with a 1 M aqueous solution of ascorbic acid. Chromatographic separation of the reaction products afforded 2- and 4-hydroxyestrone/estradiol in good overall yields (79%). In the case of the synthetic estrogens containing two identical phenolic rings, protection of one ring is a prerequisite for the synthesis of the monocatechol. Thus, diethylstilbestrol and dienestrol were protected at one phenol ring as their methyl ethers. The resulting monophenols were treated with stoichiometric amounts of IBX for 1 h, followed by treatment with 1 M aqueous ascorbic acid to obtain the corresponding catechols in more than 70% yield. Furthermore, the catechol of diethylstilbestrol, protected at one ring, was reduced by catalytic hydrogenation at the C3-C4 double bond to obtain 3'-hydroxyhexestrol in 90% yield. Removal of the protected methoxy groups of the synthetic estrogen catechols was carried out by treatment with a 1 M solution of boron tribromide in dichloromethane. This method is highly efficient for the preparative scale synthesis of catechols of both natural and synthetic estrogens.

The novel tubulin-binding drug BTO-956 inhibits R3230AC mammary carcinoma growth and angiogenesis in Fischer 344 rats

BTO-956 [methyl-3,5-diiodo-4-(4'-methoxyphenoxy)benzoate], a novel tubulin-binding drug and thyroid hormone analogue, was originally found to inhibit human carcinoma cell proliferation in vitro and to have potent growth delay activity in human breast and ovarian carcinoma xenografts in nude mice. Here we report that BTO-956 given to Fischer 344 rats also inhibits corneal angiogenesis and the growth and neovascularization of the R3230Ac rat mammary carcinoma tumor implanted in skin-fold window chambers. Hydron pellets containing recombinant human basic fibroblast growth factor (50 ng) and Sucralfate (20 microg) were implanted into surgically created corneal micropockets (day 0). BTO-956 was administrated by oral gavage (500 mg/kg, twice a day for 6 days) on days 1-6 (controls received vehicle alone). On day 7, rats received retrograde infusions of India ink via the thoracic aorta to visualize the corneal vasculature. Digitized images of slide-mounted corneas from control and treated animals were taken with a microscope. For the tumor growth and angiogenesis study, small pieces of R3230Ac tumor from a donor rat were implanted into surgically prepared window chambers (day 0). BTO-956 was given during days 5-11, and images of the tumors and their vasculature were recorded on day 12. No body weight loss was observed in either study. BTO-956 significantly inhibited corneal angiogenesis (by 50-80%), as assessed by measurements of limbal circumference displaying neovascularization, vessel length, vascularized area, and vascular area density. In the window chamber assay, tumors from treated animals were >50% smaller than tumors in control animals. In addition, vascular length densities in peripheral tumor zones were 30% less in treated compared with control animals. Together, these findings demonstrate that BTO-956 can inhibit angiogenesis induced by a growth factor in the rat cornea and in the peripheral area of implanted tumors, where tumor angiogenesis is most active.

m-Iodobenzoic acid complexes with selected metals: molecular structure and antimicrobial activity

Complexes of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, manganese, and zinc with m-iodobenzoic acid were studied. The FT-IR and FT-Raman spectra of the mentioned compounds in the solid state and water solutions were recorded and analyzed. Principal component analysis (PCA) was performed on the wavenumbers of selected bands (eight bands) occurring in the vibrational spectra. The numbers obtained as a result of this procedure characterize the electronic properties of the molecule of each complex. The antimicrobial activity of the studied compounds against selected bacteria (Escherichia coli and Bacillus subtilis) and yeast (Saccharomyces cerevisiae and Hansenula anomala) was estimated. The relationship between the chemical properties (as characterized by PCA of the IR spectra) and antimicrobial properties of the compounds was examined, and a good correlation between the two factors was found.

Cancer cell selectivity of 5-iodo-6-aminobenzopyrone (INH2BP) and methyl-3,5-diiodo-4(4'-methoxyphenoxy) benzoate (DIME)

The cellular pharmacologic actions, as measured by cell killing, of INH2BP, DIME and INO2BA (+ BSO) were determined in three types of cancer cells and compared to their action on quiescent confluent human foreskin fibroblast (HSF) and pre-confluent growing fibroblasts. The confluent HSF cells were completely refractory to the action of INH2BP and DIME, but were killed by INO2BA (+ BSO). Proliferating HSF and all three tumor cell types were killed by all three drugs. The apparent in vivo tumor specificity of INH2BP and DIME is explained by preferential cell cycle dependent selective drug uptake into tumor cells and by drug metabolism that reverses drug action in less vigorously cycling normal cells. The covalent binding of iodonitrosobenzamide (formed from INO2BA) and its toxicity are regulated by the concentration of GSH, and exhibit no cell cycle selectivity.

Glyceraldehyde-3-phosphate dehydrogenase inactivation by peroxynitrite

Rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was inactivated by peroxynitrite under biologically relevant conditions. The decrease of enzymatic activity followed an exponential function, and the concentration of peroxynitrite needed to inactivate 50% of 7 microM GAPDH (IC50) was 17 microM. Hydroxyl radical scavengers did not protect GAPDH from inactivation, but molecules that react directly with peroxynitrite such as cysteine, glutathione, or methionine and the substrate, glyceraldehyde 3-phosphate, afforded significant protection. Assuming simple competition kinetics between scavengers and the enzyme, we estimated a second-order rate constant of (2.5 +/- 0.5) x 10(5) M-1 s-1 at 25 degreesC and pH 7.4 for the GAPDH tetramer. The loss of enzyme activity was accompanied by protein thiol oxidation (two thiols oxidized per subunit) with only one critical thiol responsible of enzyme inactivation. Indeed, the pH profile of inactivation was consistent with the reaction of GAPDH sulfhydryls (GAPDH-SH) with peroxynitrite. Peroxynitrite-inactivated GAPDH was resistant to arsenite reduction and only 15% recovered by 20 mM dithiothreitol, suggesting that GAPDH-SH has been mainly oxidized to sulfinic or sulfonic acid, with a minor proportion yielding a disulfide. On the other hand, under anaerobic conditions the peroxynitrite precursor, nitric oxide (*NO), only slowly inactivated GAPDH with a rate constant of 11 M-1 s-1. The remarkable reactivity of the critical thiol group in GAPDH (Cys-149) toward peroxynitrite, which is one order of magnitude higher than that of previously studied sulfhydryls, indicate that it may constitute a preferential intracellular target for peroxynitrite.

Molecular pharmacology of methyl-3,5-diiodo-4 (4'methoxyphenoxy) benzoate (DIME) and its non-hydrolyzible ethanone analog (DIPE) (Review)

A molecular structural relationship of thyroid hormones to methyl-3,5-diiodo-4-(4'-methoxy-phenoxy) benzoate (DIME) and 1-[3,5-diiodo-4-(4'-methoxyphenoxy)-phenyl]-ethanone) (DIPE) and to apoptosis-mediated metamorphogenic mechanisms is postulated. DIME disrupts microtubule assembly already in anaphase, preparing cells for G2/M block, chromosome aggregation and caspase-3 mediated apoptosis. Cooperative action of DIME and vincristine, defining mutually exclusive cellular sites, identifies microtubules as primary drug targets followed by downstream cellular consequences, leading to cell death. Absence of in vivo toxicity of DIME appears to be related to impermeability to DIME of normal cells, but not of tumor cells in vivo. Normal tissue cells hydrolyze DIME but most tumor cells, except lung cancer cells, do not. DIPE, being resistant to enzymatic hydrolysis, is equally effective in all tumor cells.

Unusual potentiation by vinca alkaloids of the cytostatic and cytocidal action of methyl-3,5-diiodo-4-(4'-methoxyphenoxy) benzoate (DIME) and its nonhydrolyzable ethanone analog (DIPE) on MDA-MB-231 human mammary cancer cells

Drug interaction between DIME or DIPE ¿1-[3, 5-diiodo-4-(4'-methoxyphenoxy)-phenyl]-ethanone¿ with vincristine and vinblastine on the growth rate of MDA-MB-231 human mammary cancer cells was determined by the median effect kinetic method. Mutually exclusive cellular binding sites were identified kinetically and isobologram analyses showed potentiation. The combind effect of 0.75 MICROM DIME and 2 nM vincristine demonstrated a nearly type of mutual activation. It was shown that the nonhydrolyzable DIME derivative DIPE is equivalent to DIME, but because of its biological stability is a preferred drug candidate. Vinblastine-DIME cooperative action is similar to that of vincristine-DIME (or DIPE). Activation of caspase 3 by both DIME and vincristine is greatly potentiated when both drugs are added simultaneously in a given proportion. We propose that following a primary binding of DIME and vinca alkaloids to microtubules, an as yet unrecognized mutual activation of caspase 3 apoptotic path is initiated, explaining DNA fragmentation and cell death. A subpopulation of cancer cells, capable of slow growth at 1.5 microM DIME was identified. This cell type was also killed by the DIME-vincristine drug combination.

Nitric oxide and thiol redox regulation of Janus kinase activity

The activation of Janus kinases (JAKs) is crucial for propagation of the proliferative response initiated by many cytokines. The proliferation of various cell lines, particularly those of hematopoietic origin, is also modulated by mediators of oxidative stress such as nitric oxide and thiol redox reagents. Herein we demonstrate that nitric oxide and other thiol oxidants can inhibit the autokinase activity of rat JAK2 in vitro, presumably through oxidation of crucial dithiols to disulfides within JAK2. The reduced form of JAK2 is the most active form, and the oxidized JAK2 form is inactive. Nitric oxide pretreatment of quiescent Ba/F3 cells also inhibits the interleukin 3-triggered in vivo activation of JAK2, a phenomenon that correlates with inhibited proliferation. Furthermore, we observed that the autokinase activity of JAK3 responds in a similar fashion to thiol redox reagents in vitro and to nitric oxide donors in vivo. We suggest that the thiol redox regulation of JAKs may partially explain the generally immunosuppressive effects of nitric oxide and of other thiol oxidants.

In vivo tissue compatibility of two radio-opaque polymeric biomaterials

Polymeric biomaterials featuring intrinsic radio-opacity continue to attract considerable scientific attention. This work focusses on two polymers that contain covalently bound iodine, rendering the materials radio-opaque. The first material is hard, transparent and glass-like, and consists of methyl methacrylate, 2-(2'-iodobenzoyl)-ethyl methacrylate (1) and 2-hydroxyethyl methacrylate (HEMA), in the molar ratio 65:20:15, respectively. The second material is a cross-linked hydrophilic network, consisting of HEMA and 1, in the molar ratio 80:20, respectively. Both materials were characterized by means of different physico-chemical techniques, including magic-angle-spinning solid state NMR spectroscopy, infrared spectroscopy and differential scanning calorimetry. Moreover, both materials were implanted subcutaneously in rats for 24 days. Upon explanation and histological examination, it appeared that both materials were well tolerated. No tissue necrosis, abscess formation or inflammation were observed. The samples were found to be surrounded by a vascularized capsule consisting of connective tissue cells. The results reveal excellent tissue compatibility for both materials. This is an important observation, since tissue compatibility is absolutely necessary for the applications which are foreseen for this type of radio-opaque biomaterials.

Redox regulation of maize NADP-malic enzyme by thiol-disulfide interchange: effect of reduced thioredoxin on activity

Incubation of C4 NADP-malic enzyme from maize leaves with the oxidant o-iodosobenzoate leads to the reversible and complete inactivation of the enzyme. The time-course of inactivation is biphasic with the rate depending on the o-iodosobenzoate concentration. The inactivation is partially prevented by L-malate, NADP and Mg2+ alone, while NADP plus Mg2+ afford total protection. The complete reversal of the inactivation by the reductive agents dithiothreitol and 2-mercaptoethanol suggests that the modification of the enzyme by o-iodosobenzoate occurs concomitant with the oxidation of one or more pairs of sulfhydryl groups to the disulfide state, producing a conformationally altered form of the protein or directly modifying the active site. Titration of free thiol groups before and after inactivation of maize malic enzyme by o-iodosobenzoate shows a decrease in the accessible groups from 7 to 5, suggesting inactivation is accompanied by oxidation of two vicinal thiols. The oxidized form of the enzyme is rapidly reactivated by incubation with chemical and photochemically reduced thioredoxin in vitro, while the 'dark' activity of the enzyme is enhanced to the level of the 'light' activity by dithiothreitol. This evidence suggests that a reversible reduction and oxidation of disulfide bonds may take place during the regulation of the enzyme, indicating that the redox state of the disulfide bonds of C4 NADP-malic enzyme from maize leaves is important for the expression of maximal catalytic activity.

o-Iodosobenzoic oxidation and cleavage of myosin subfragment 1

1. o-Iodosobenzoic acid (IOB) caused the formation of a disulfide bridge between SH1 and SH2 groups of myosin SF1 rendering inactive its ATPase activity. 2. IOB at high concentrations provoked fragmentation of SF1 at its tryptophan residues. 3. The main fragmentation point was located at 15 K from the amino terminus of the myosin heavy chain. 4. Actin was not fragmented by IOB. It protected SF1 tryptophans from IOB attack. 5. These results suggest a possible use of IOB as a reagent to study protein tryptophan under nondenaturing conditions.

Reduction of nitroaromatic compounds by anaerobic bacteria isolated from the human gastrointestinal tract

Human intestinal microbial flora were screened for their abilities to reduce nitroaromatic compounds by growing them on brain heart infusion agar plates containing 1-nitropyrene. Bacteria metabolizing 1-nitropyrene, detected by the appearance of clear zones around the colonies, were identified as Clostridium leptum, Clostridium paraputrificum, Clostridium clostridiiforme, another Clostridium sp., and a Eubacterium sp. These bacteria produced aromatic amines from nitroaromatic compounds, as shown by thin-layer chromatography, high-pressure liquid chromatography, and biochemical tests. Incubation of three of these bacteria with 1-nitropyrene, 1,3-dinitropyrene, and 1,6-dinitropyrene inactivated the direct-acting mutagenicity associated with these compounds. Menadione and o-iodosobenzoic acid inhibited nitroreductase activity in all of the isolates, indicating the involvement of sulfhydryl groups in the active site of the enzyme. The optimum pH for nitroreductase activity was 8.0. Only the Clostridium sp. required added flavin adenine dinucleotide for nitroreductase activity. The nitroreductases were constitutive and extracellular. An activity stain for the detection of nitroreductase on anaerobic native polyacrylamide gels was developed. This activity stain revealed only one isozyme in each bacterium but showed that the nitroreductases from different bacteria had distinct electrophoretic mobilities.

Protein radiohalogenation: observations on the design of N-succinimidyl ester acylation agents

In previous studies we have demonstrated that antibodies radioiodinated with N-succinimidyl 3-iodobenzoate (SIB) are less susceptible to loss of radioiodine in vivo than antibodies iodinated directly by electrophilic substitution on their tyrosine residues with Iodogen. Since the Bolton-Hunter reagent, N-succinimidyl 3-(4-hydroxy-3-iodophenyl)propionate, is identical with SIB except that it contains a hydroxyl group on the aromatic ring and a two-methylene spacer, a comparison of their coupling chemistry and in vivo behavior was performed to better understand the structural requirements for a useful iodinated acylation agent. Protein concentration and pH had a significant effect on the coupling efficiency of both SIB and the Bolton-Hunter reagent; however, protein-labeling yields with SIB were generally higher by a factor of 2. Paired-label biodistribution studies in mice demonstrated that thyroid uptake (a monitor of dehalogenation) of antibody labeled by the Bolton-Hunter method was twice that of antibody labeled with SIB but only 7% of that observed for antibody labeled with Iodogen. These results suggest that even minor differences in iodination site can profoundly alter the retention of label on a protein in vivo.

The dithiothreitol-stimulated dissociation of the chloroplast coupling factor 1 epsilon-subunit is reversible

The chloroplast coupling factor 1 complex (CF1) contains an epsilon-subunit which inhibits the CF1 ATPase activity. Chloroform treatment of Chlamydomonas reinhardtii thylakoid membranes solubilizes only forms of the enzyme which apparently lack the delta-subunit. Four interrelated observations are described in this paper. (1) The dithiothreitol- (DTT) induced ATPase activation of CF1(-delta) and the DTT-induced formation of a physically resolvable CF1(-delta,epsilon) from the CF1(-delta) precursor are compared. The similar time-courses of these two phenomena suggest that the dissociation of the epsilon-subunit is an obligatory process in the DTT-induced ATPase activation of soluble CF1. (2) The reversible dissociation of the epsilon-subunit of the CF1 is demonstrated by the exchange of subunits between distinguishable oligomers. 35S-labelled chloroplast coupling factor 1 lacking the delta and epsilon subunits [CF1(-delta,epsilon)] was added to a solution of non-radioactive coupling factor 1 lacking only the delta subunit [CF1(-delta)]. After separation of the two enzyme forms, via high resolution anion-exchange chromatography, radioactivity was detected in the chromatographic fractions containing CF1(-delta). (3) epsilon-deficient CF1 can be resolved from DTT pretreated epsilon-containing CF1 for several days after the removal of DTT. On the other hand, brief incubation of the DTT pretreated epsilon-containing CF1 with low concentrations of o-iodosobenzoate results in chromatographs containing only the peak of epsilon-containing CF1. A simple explanation for this phenomenon is that reduction of CF1 with DTT increases the apparent dissociation constant for the epsilon-subunit to an estimated 3.5 x 10(-8) M (+/- 1.0 x 10(-8) M) from a value of less than or equal to 5 x 10(-11) M for the oxidized enzyme. (4) ATPase activity data show that oxidation of the epsilon-deficient enzyme does not completely inhibit its manifest activity, but oxidation of DTT pre-treated CF1 which contains the epsilon-subunit completely inhibits manifest activity. A simple model is proposed for the influence of the oxidation state of the soluble enzyme on the distribution of ATPase-inactive and ATPase-active subunit configurations.

High valent iron oxo intermediates might be involved during activation of ribonucleotide reductase: single oxygen atom donors generate the tyrosyl radical

The active form of protein B2, the small subunit of ribonucleotide reductase from E. Coli, contains a binuclear non heme iron center and a tyrosyl radical. MetB2 is an inactive form that lacks the radical but retains the Fe(III) center. We earlier proposed that the function of the iron center was to catalyze the one-electron oxidation of the tyrosine residue from metB2 by dioxygen. We now report that incubation of metB2 with single oxygen atom donors, hydrogen peroxide, 3-chloroperoxybenzoic acid, monoperoxophtalate and 2-iodosobenzoate, also results in the formation of the tyrosyl radical, as monitored by UV-visible and EPR spectroscopy. A mechanism of reductive activation of dioxygen by the binuclear non heme iron center involving iron-oxo intermediates is proposed.

Thrombin generation in nonclottable mixtures of blood and nonionic contrast agents

The four newly introduced contrast agents--iopamidol, iohexol, ioversol, and ioxaglate--are of much lower osmolality than conventional agents, and claims have been made that they are substantially safer. A chromogenic assay for thrombin was applied to 1:1 (50%), 2:1 (67%), and 4:1 (80%) contrast agent-whole blood mixtures, each containing enough contrast agent to render them unclottable. Thrombin generation occurred in the nonionic-whole blood mixtures and increased with time. No thrombin could be detected in any ioxaglate-whole blood mixtures. The authors conclude that this difference presents a novel hazard in that iopamidol, iohexol, and ioversol permit thrombin generation to occur while inhibiting the fibrin polymerization step of blood coagulation, thus posing a significant, albeit theoretical, threat to patient well-being.

Renal effects of the non-ionic contrast medium iopentol after intravenous injection in healthy volunteers

Renal effects of the new non-ionic contrast medium iopentol in increasing doses were assessed and compared with the effects of physiologic saline. Twenty-four healthy male volunteers, allocated to three dose groups, were given iopentol intravenously in doses of 0.3, 0.6, and 1.2 g I/kg body weight, respectively. The highest dose group was also given physiologic saline separately as a control. The diuresis increased in all groups, most in the highest dose group, and with a concomitant fall of urine osmolality and increase in osmolar clearance. A slight decrease of serum osmolality, creatinine and urea occurred at 3 hours due to hemodilution. The glomerular filtration rate was unaffected by iopentol. The urinary excretion of albumin and beta 2-microglobulin was unchanged. However, urinary N-acetyl-beta-glucosaminidase and alkaline phosphatase increased significantly, most in the highest dose group. All changes were reversible.

Metabolic myopathy produced by acute inhibition of glyceraldehyde-3-phosphate dehydrogenase with ortho-iodosobenzoic acid

A previously developed model of exercise-induced muscle contracture using iodoacetate to inhibit glyceraldehyde-3-phosphate dehydrogenase in rat hindlimb muscles produced selective type II myofiber damage. Utilizing a modification of the same model system, rats were given intra-aortic ortho-iodosobenzoic acid (700 nmol/kg body weight), which cleaves tryptophanyl peptides from glyceraldehyde-3-phosphate dehydrogenase. Within 2-4 h, spontaneous electrically-silent contracture developed in the injected musculature resulting in a plantar-flexed position of the hindlimb. After 24 h, the extensor digitorum longus and tibialis anterior muscles appeared grossly swollen (edematous) and discolored. Microscopically, the extensor digitorum longus (composed predominantly of type II myofibers) contained many randomly scattered, damaged myofibers, reduced glycogen content, absent glyceraldehyde-3-phosphate dehydrogenase activity, interstitial edema and focal collections of mononuclear phagocytes. Damaged fibers showed degenerative changes and contained stainable intracellular calcium. On modified trichrome-stained sections, an outer red staining rim of material was identifiable in many fibers. The fibers of the soleus muscle (composed predominantly of type I myofibers) were not damaged, indicating a preferential ortho-iodosobenzoic acid effect on type II myofibers.

Safety and pharmacokinetics of ioversol in healthy volunteers

Ioversol 320, a new nonionic iodinated contrast medium, was injected intravenously into 24 healthy male volunteers using saline as a control. Physical examination, vital signs, electrocardiogram, biochemical and hematological data were recorded before and at intervals after injection. No significant changes were observed. Seventeen volunteers reported no side effects; six volunteers had mild transitory symptoms considered to be related to the contrast medium. The authors conclude that broader clinical trials can be safely conducted to determine safety and tolerability of ioversol.

Hemodynamic effects of ioversol in the dog and rat

The hemodynamic effects of selectively administered ioversol were examined in the dog and rat. At concentrations ranging from 32% to 37% I, wt/vol, ioversol was compared with nonionic (iohexol, iopamidol) and ionic (diatrizoate) contrast media for cardiovascular responses following injections into the femoral vein, right and left coronary arteries, left ventricle, and the pulmonary and femoral arteries of the dog, and into the carotid artery of the rat. Regardless of the intravascular route of injection, ioversol generally caused minimal effects on the heart rate, minimal to moderate decreases in myocardial contractility, left ventricular pressure, mean arterial pressure, pulmonary vascular resistance, and systemic vascular resistance. These effects of ioversol were comparable to those of iohexol and iopamidol, and were relatively less profound than those of diatrizoate. Under experimental conditions injections of ioversol exerted hemodynamic effects comparable to those of other nonionic agents, yet relatively diminished as compared with a representative high-osmolality ionic contrast agent. These results suggest that the nonionic contrast agent, ioversol, should be well tolerated in patients following injections via similar intravascular routes.

Hemodynamic and electrocardiographic effects of ioversol during cardiac angiography. Comparison with iopamidol and diatrizoate

We studied the hemodynamic and electrocardiographic responses to left ventriculography and coronary arteriography with three angiographic contrast agents. Two were nonionic agents (ioversol 32% iodine, 60 patients, and iopamidol 37% iodine, 30 patients). The third was a conventional ionic agent (diatrizoate 37% iodine, 30 patients). Cardiovascular hemodynamics and the electrocardiogram were recorded for 5 minutes after left ventricular injection and for 2 minutes after coronary injections. Following left ventriculography, diatrizoate caused a greater increase in cardiac output, left ventricular end diastolic pressure, and corrected QT interval while causing a greater decrease in arterial pressure than did either ioversol or iopamidol, which were indistinguishable from each other. Following left coronary arteriography, diatrizoate caused a significant decrease in heart rate, prolongation of the corrected QT interval, and increase in T wave amplitude. In contrast, neither ioversol nor iopamidol caused significant changes in any electrocardiographic parameters. Adverse reactions were more common with diatrizoate than with either ioversol or iopamidol. There were no recognizable differences in angiographic image quality among the three agents. We conclude that the angiographic performance of ioversol is equivalent to that of iopamidol and that both cause less hemodynamic and electrocardiographic disturbance than diatrizoate.

Iotrol, iodixanol, and 2-deoxy-D-glucose effects on neural tissue CO2 production

In vivo and in vitro experiments have demonstrated that the myelographic agent metrizamide decreases neural tissue glucose metabolism whereas iohexol and iopamidol do not. This study compares the changes in slices of rat hippocampus CO2 production caused by the nonionic dimers iotrol and iodixanol with the effects of metrizamide and 2-deoxy-D-glucose. After 6-hr incubations, 70-mmol/l concentrations of iotrol and iodixanol increased CO2 production by 11 +/- 20% and 31 +/- 35%, respectively, as compared with the artificial CSF control medium. Metrizamide at 70 mmol/l and 2-deoxy-D-glucose at 35 mmol/l decreased CO2 production by 32 +/- 13% and 96 +/- 1%, respectively. The increases in CO2 production with iotrol and iodixanol appear to indicate that these molecules have some effect on cell metabolism. The mechanism for the increase in CO2 production could involve an effect on the glucose metabolic pathway or could be indirect via a mechanism that increases cell energy utilization. These in vitro effects have not been verified with in vivo experiments.

Tryptic digestion of bovine secretory IgA at elevated temperature and in urea. Isolation of SC domain 1 which is covalently bound to IgA dimer and binds non-covalently to IgM

1. Tryptic cleavage sites in bovine secretory component (SC) which become inaccessible when SC is bound to IgA dimer remained inaccessible at 60 degrees C and in 4 M urea at 37 degrees C. 2. This suggests the presence of strong interactions compatible with published affinity constants of ca 10(8) M-1. 3. In 5 M urea at 37 degrees C further cleavage of bound SC did occur to produce a fragment consisting of domain 1 which was disulphide bridged to the IgA dimer. 4. Binding studies on the isolated fragment showed that domain 1 did not account for all the binding by SC. 5. Cleavage of the isolated fragment with iodosobenzoic produced a smaller fragment consisting of the n-terminal third of domain 1 (residues 1-35). This N-terminal fragment showed significant binding.

The reversible oxidation of vicinal SH groups in 4-aminobutyrate aminotransferase. Probes of conformational changes

4-Aminobutyrate aminotransferase is inactivated by preincubation with iodosobenzoate at pH 7. The reaction of 2 SH residues/dimer resulted in formation of an oligomeric species of Mr = 100,000 detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The subunits cross-linked via a disulfide bond are dissociated by addition of 2-mercaptoethanol which also restores full catalytic activity (Choi, S. Y., and Churchich, J.E. (1985) J. Biol. Chem. 260, 993-997). The substrate 2-oxoglutarate prevents inactivation of the enzyme by iodosobenzoate and the subsequent formation of one disulfide bond, whereas 4-aminobutyrate has no effect on the reactivity of SH groups with iodosobenzoate. Modified 4-aminobutyrate aminotransferase (containing 1 disulfide bond) catalyzes a half-transamination reaction; but it is unable to react with 2-oxoglutarate to generate the aldimine form of the enzyme. The spectroscopic properties (fluorescence yield and polarization of fluorescence) of PMP bound to the modified enzyme are different from those of pyridoxamine phosphate (PMP) bound to the native enzyme. The polarization of fluorescence values of PMP bound to the cross-linked enzyme, excited over the spectral range 310-370 nm, are greater (25%) than those of the cofactor of the native enzyme. An increase in the polarization values implies that the motion of PMP is restricted when the subunits are cross-linked via a disulfide bond.

Nucleolysis and diskography--an experimental study on interaction of chymopapain and contrast medium

A test was carried out on 11 young, full sized mongrels to determine whether there is an interaction between chymopapain and the contrast agents iotrolan and iopamidol. A total of 75 intervertebral disks were punctured: nucleolysis alone was performed on 20, diskography with iotrolan and subsequent nucleolysis on 20, and diskography with iopamidol and subsequent nucleolysis on 10. Diskography alone was performed 10 times with iotrolan and 5 times with iopamidol. Aqua dest. was given intradiskally 5 times, and puncture was carried out 5 times without the administration of any substance. Following puncture, x-rays of the lumbar vertebral column were taken laterally: daily for the first 10 days, then weekly. Disk space narrowing typical of nucleolysis with chymopapain was found among the disks that were nucleolyzed only to the same extent as among those that had undergone diskography previously. There was no evidence of narrowing of the other disk spaces which had been punctured but not treated with chymopapain. On some of the dogs, CT and MRI examinations were carried out. The CTs showed a homogenous hypodensity in all of the disks, in which chymopapain had been injected. The MRI revealed a signal loss in all of the nucleolyzed disks. The results of short and long term follow up demonstrate that inhibition of chymopapain by iotrolan or iopamidol is not to be expected and therefore diskography prior to chemonucleolysis can be performed without danger of enzyme inactivation.

Rat liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Identification of essential sulfhydryl residues in the primary sequence of the enzyme

The kinase and sugar phosphate exchange reactions of rat liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase were inactivated by treatment with 5'-p-fluorosulfonylbenzoyladenosine or 8-azido-ATP, but activity could be restored by the addition of dithiothreitol. This inactivation was accompanied by incorporation of 5'-p-sulfonylbenzoyl[8-14C]adenosine into the enzyme that was not released by the addition of dithiothreitol. The lack of effect of ATP analogs on the ATP/ADP exchange or on bisphosphatase activity and reversal of their effects on the kinase and sugar phosphate reactions by dithiothreitol suggest that 1) they reacted with sulfhydryl groups important for sugar phosphate binding in the kinase reaction, and 2) the inactivation of the kinase by these analogs involves a specific reaction that is not related to their general mechanism of attacking nucleotide-binding sites. In addition, alkylation of the enzymes' sulfhydryls with iodoacetamide prevented inactivation by 5'-p-fluorosulfonylbenzoyladenosine, suggesting that the same thiols were involved. o-Iodosobenzoate inactivated the kinase and sugar phosphate exchange; the inactivation was reversed by dithiothreitol; but there was no effect on the bisphosphatase or nucleotide exchange, indicating that oxidation occurred at the same sulfhydryl that are associated with sugar phosphate binding. ATP or ADP, but not fructose 6-phosphate, protected these groups from modification by 5'-p-fluorosulfonylbenzoyladenosine, 8-azido-ATP, and o-iodosobenzoate. ATP also induced dramatic changes in the circular dichroism spectrum of the enzyme, suggesting that adenine nucleotide protection of thiol groups resulted from changes in enzyme secondary structure. Analysis of cyanogen bromide fragments of 14C-carboxamidomethylated enzyme showed that all radioactivity was associated with cysteinyl residues in a single cyanogen bromide fragment. Three of these cysteinyl residues are clustered in a 38-residue region, which probably plays a role in maintaining the conformation of the kinase sugar phosphate-binding site.

Reaction of liver pyruvate kinase with sulfhydryl reagents: effect on its activity

Homogeneous liver pyruvate kinase was reacted with different sulfhydryl reagents, which included o-iodosobenzoate, 5',5'-dithiobis(2-nitrobenzoic acid) and N-ethylmaleimide. Activity determinations of the treated enzyme made with and without Fru(1,6)P2 indicate that the protein contains two sulfhydryl groups per subunit important to its properties, one more accessible than the other. Fru(1,6)P2 added to mixtures prevented loss of activity obtained with o-iodosobenzoate and 5',5'-dithiobis(2-nitrobenzoic acid). It appears that Fru(1,6)P2 does not interfere with the reaction of the reagent with the sulfhydryl group, but prevents an ensuing conformational change, which leads to changes in the enzyme's properties.

A comparison of blood-brain barrier disruption by intracarotid iohexol and iodixanol in the rabbit

A rabbit model was used to compare the effect on the blood-brain barrier of the intracarotid injection of two new contrast media: iohexol, a nonionic monomer, and iodixanol, a nonionic dimer. It was hypothesized that the low osmolality of iodixanol (272 mOsm/kg at 300 mgl/ml) would cause less disruption of the blood-brain barrier than the relatively higher osmolality of iohexol (690 mOsm/kg at 300 mgl/ml). The degree of blood-brain barrier disruption was assessed qualitatively, by observing the degree of cortical staining with Evans' Blue dye, and quantitatively, by calculating the difference in uptake of 99mTc-pertechnetate between injected and noninjected hemispheres. Statistical analysis of the results showed that both iodixanol and iohexol had a significantly greater effect on blood-brain barrier disruption than did isotonic saline (0.005 greater than p greater than .001), but that the effect of iodixanol was not significantly different from that of iohexol with respect to either Evans' Blue staining (p greater than .05) or pertechnetate uptake (.75 less than p less than .90). Thus, the low-osmolality iodixanol has no significant advantage over iohexol in terms of blood-brain barrier disruption after experimental carotid angiography.

3,4,5-Triiodobenzoic acid affects [3H]verapamil binding to plant and animal membrane fractions and smooth muscle contraction

3,4,5-Triiodobenzoic acid, known as auxin transport inhibitor, stimulates specific [3H]verapamil binding to zucchini microsomes by 100% (EC50 = 1 microM). This stimulatory effect is due to a decrease of the apparent equilibrium dissociation constant KD for verapamil from 60 nM to 33 nM without significantly changing the maximum number of binding sites. 3,4,5-Triiodobenzoic acid also increases specific [3H]verapamil binding to rabbit skeletal muscle membranes (EC50 greater than or equal to 20 microM) without affecting [3H]nitrendipine and [3H]-d-cis-diltiazem binding. If 3,4,5-triiodobenzoic acid is added to isolated rings of rabbit A. saphena contracted by potassium depolarization, a dose-dependent relaxation is observed with an IC50 value of about 8 microM. Contractions initiated by the addition of 3 microM norepinephrine can also be abolished by 3,4,5-triiodobenzoic acid with half maximal inhibition at 40 microM.

Effects of contrast media on cultured myocardial cells

To quantify and characterize mechanisms of negative inotropic effects of ionic and nonionic angiographic contrast media, spontaneously contracting monolayers of cultured chick ventricular cells were studied using the Renografin-76 and iohexol as characteristic ionic and nonionic contrast agents. Utilizing microscopic video-motion detector techniques the effect of each contrast agent on contraction amplitude was measured. Also, the effect of changes in the ionized calcium concentration and osmolality induced by the contrast agents was evaluated. The study demonstrated a linear depression of contractility by increasing contrast concentrations. The negative inotropic effect of Renografin-76 was significantly greater than that of iohexol. Renografin-76 demonstrated significant calcium binding, whereas iohexol had none. Correction for calcium binding by Renografin-76 partially reversed the negative inotropic effect of this agent. Hypertonic sugar solutions of equivalent osmolality to the contrast agents demonstrated dose-related negative inotropic effects such that, in this preparation, calcium binding by Renografin-76 and its high osmolality accounted for all its negative inotropic effect. In contrast, iohexol demonstrated an intrinsic negative inotropic effect not completely explained by its osmolality.

Effects of ioglycamide on the hepatic transport of bilirubin and its mono- and diconjugates in the rat

Bilirubin seems to share the biliary excretion pathway with other organic anions, but not with bile acids. We studied the effects of the organic anion ioglycamide, an iodinated contrast agent, on bilirubin metabolism in Wistar rats. This compound does not undergo conjugation and is characterized by a maximal biliary secretory rate (Tm). The results show that in spite of producing a 3-fold increase in bile flow, ioglycamide excretion under Tm conditions decreased the output of unconjugated bilirubin and its monoconjugate by approximately 90%. Diconjugated bilirubin decreased by only 50% and became by far the predominant pigment in bile (86.5 +/- 6.0% of total pigment vs. 61.0 +/- 4.0% in basal conditions, n = 12). Unconjugated and monoconjugated bilirubins changed in parallel suggesting that the former arises from the monoconjugates. In serum, diconjugated bilirubin augmented from trace amounts to 1.15 +/- 0.17 mumole per liter. Total conjugated pigments in serum increased from 5 to 85% of total bilirubin. Bile acid output remained unchanged. Pretreatment of rats with ioglycamide altered neither the activity of bilirubin UDP-glucuronyltransferase nor the ratio of diconjugate to monoconjugate formed at both low (25 microM) and high (164 microM) bilirubin concentrations. The observed biological effects of ioglycamide were dose-dependent and fully reversible. We suggest that ioglycamide interferes with the excretion of conjugated bilirubins ("bilirubinostasis"). The monoconjugates retained in the hepatocyte might then undergo more efficient transformation to diconjugates, the latter thus becoming the most important bile pigments in serum and bile.

In vivo catabolism of human low density lipoprotein in the rat is mediated by a nonsaturable, low-affinity mechanism

The degradation of human low density lipoprotein (LDL) was analyzed in fasted rats treated for 3 days with either 4-aminopyrazolo-(3,4-d)pyrimidine (4APP) or saline. Treatment with 4APP caused an 80% decrease in serum cholesterol concentration. The mono-exponential serum decay of a tracer amount of labelled LDL was changed neither by 4APP treatment, nor by the simultaneous injection of a bolus of unlabelled LDL. The sites of degradation of human LDL were determined using the nondegradable labelling compound O-(4-diazo-3-[125I]iodobenzoyl)sucrose (D125IBS). The sites of degradation and the rate of degradation of D125IBS labelled LDL were also not affected by 4APP treatment or by injection of a bolus of unlabelled LDL. It is concluded that human LDL is catabolised in the rat by way of a nonsaturable, low-affinity mechanism.

Transport of beta-globin mRNA from nuclei of murine Friend erythroleukemia cells. Reversible inhibition of transport by the oxidizing sulfhydryl reagent o-iodosobenzoate

An in vitro assay system for analysis of beta-globin mRNA transport is described. Nuclei isolated from murine Friend erythroleukemia cells induced to synthesize globin mRNA, were incubated in micro-assays. By electrophoresis and hybridization analysis, released 9-S beta-globin mRNA was shown to be undegraded. After direct blotting, the released mRNA was quantified by hybridization with a labeled plasmid containing a beta-globin DNA restriction fragment. The inducibility of beta-globin mRNA transport corresponded to that previously reported for the release of rapidly labeled RNA in other assay systems. In contrast to the ineffectiveness of high concentrations of the sulfhydryl reagent iodoacetate, low concentrations of the oxidizing sulfhydryl reagent, o-iodosobenzoate, inhibited the release of beta-globin mRNA from nuclei of erythroleukemia cells, as well as the release of rapidly labeled RNA from rat liver nuclei. The inhibitory effect of the oxidizing agent on beta-globin mRNA transport could be reversed by postincubation of the nuclei with the reducing agent, dithiothreitol. The potential role of disulfide bond formation on RNA transport is discussed.

Omnipaque and Urografin in left ventriculography and coronary arteriography. A randomised, double blind study

In order to compare tolerability and radiographic properties of Omnipaque (iohexol) 350 mg I/ml and Urografin (sodium meglumine diatrizoate) 76% (370 mg I/ml) in left ventriculography and coronary arteriography, a randomised, double-blind parallel study was conducted. ECG, heart rate, blood pressure, cardiac output, oxygen saturation, CK-MB, adverse reactions and opacification were recorded. Twenty-five patients received Omnipaque and 24 Urografin and all patients were included in the final material. Omnipaque was found to have less influence on haemodynamics than Urografin. Few adverse reactions were encountered in the entire study, but fewer after injections of Omnipaque than after Urografin. Equally good opacification was demonstrated for both media. Omnipaque was found well suited for cardioangiography and superior to standard ionic media.

Differential effect of thiol oxidants on the chloroplast H+-ATPase in the light and in the dark

The effect of thiol oxidants on the light-activated H+-ATPase has been studied in freshly broken and intact chloroplasts. The following observations were made: (i) in chloroplasts which are osmotically shocked after light activation, ferricyanide stimulates the deactivation of the enzyme in the dark, but has little effect in the light; (ii) similarly, o-iodosobenzoate is a most efficient deactivator of the ATPase in intact chloroplasts in the dark but not in the light; (iii) the activated ATPase becomes sensitive to oxidants in the light upon the addition of an uncoupler; (iv) the oxidant-induced deactivation in the dark dominates the stabilizing effect of pyrophosphate or ADP plus Mg2+; (v) full deactivation of the ATPase by dark adaptation or by oxidants does not affect the rate of photophosphorylation under saturating conditions. A model is suggested in which two kinds of conformational changes are involved in the regulation of the ATPase: those induced by the trans-membrane-proton gradient and those by oxidation-reduction of the enzyme. These changes result in the preferential interaction with thiol reductants in the light but with thiol oxidants in the dark.

4-Aminobutyrate aminotransferase reaction of sulfhydryl residues connected with catalytic activity

4-Aminobutyrate aminotransferase is inactivated by preincubation with N-(1-pyrene)maleimide (mixing molar ratio 10:1) at pH 7. The reaction with N-(1-pyrene)maleimide was monitored by fluorescence spectroscopy and the degree of labeling of the enzyme determined by absorption spectroscopy. The blocking of 2 cysteinyl residues/enzyme dimer is needed for inactivation of the aminotransferase. The time course of the reaction is significantly affected by the substrate alpha-ketoglutarate, which afforded complete protection against the loss of catalytic activity. Trypsin digestion of pyrene-labeled aminotransferase, followed by gel filtration and "fingerprint" analysis, revealed the presence of only one peptide tagged with the fluorescent probe. The reaction of approximately 1.9 SH residues/dimer with iodosobenzoate resulted in enzyme inactivation together with a formation of an oligomeric species of Mr = 100,000 detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The cross-linked subunits are dissociated by addition of 2-mercaptoethanol which also restores full catalytic activity. Altogether, these observations are consistent with the concept that inactivation of 4-aminobutyrate aminotransferase by iodosobenzoate proceeds through disulfide bond formation between vicinal cysteinyl residues of the protein. It is postulated that the critical sulfhydryl groups of the enzyme are situated on opposite sides of the dimeric structure at the subunit interfaces.

Pharmacological action of radiographic contrast media reduced cerebrospinal fluid production in the dog

Intravenous administration of radiographic contrast media (CM) significantly decreases cerebrospinal fluid (CSF) production as measured by negative pressure collection from a lateral ventricle of the anesthetized dog. This effect has been shown with the conventional ionic CM, sodium diatrizoate, and is now reported for the new nonionic agent, iohexol. Continuous infusion of either agent maintains the decrease. The magnitude of the CM-induced decreased CSF production is proportional to the dose in the range of 1 to 4 ml/kg. This action of CM cannot be explained by an osmotic mechanism. Two enzymes involved in the elaboration of CSF, carbonic anhydrase and sodium, potassium-adenosine triphosphatase, are not inhibited by sodium diatrizoate sufficiently in vitro to explain this action of CM. These results indicate a pharmacological action by i.v. CM that may require special attention when reduced CSF production would be deleterious.

Iohexol vs. metrizamide in studies of glucose metabolism. A survey

Nonionic contrast media represent a significant advance for myelography due to their substantially lower neurotoxicity. Some side effects have been noted with metrizamide, however. Origins of adverse effects have not been clearly defined. Studies reviewed here investigated the effects of two nonionic contrast media, metrizamide and iohexol, on glucose metabolism in neural tissue cells in vitro using rat hippocampal tissue slices. Isotonic metrizamide produced metabolic disturbances that may partially explain some clinical adverse effects. It was hypothesized that iohexol, which, unlike metrizamide, does not contain a 2-deoxy-D-glucose component, would not have this effect. A series of in vitro experiments compared the two media. Results showed no evidence that iohexol caused metabolic disturbances, but in vitro there was a depressive effect on metabolism from hypertonicity. In vivo water will rapidly diffuse toward hypertonic areas, thus neutralizing the osmotic effect. The lesser metabolic effect suggests that iohexol would be safer than metrizamide for subarachnoid examinations.

Clinical experience with ioxaglate (Hexabrix) in selective coronary arteriography

This prospective nonrandomized study was performed to evaluate the safety and efficacy of, as well as patient tolerance for, a new low osmolality contrast medium, ioxaglate (Hexabrix), in 90 adult patients of both sexes who were referred to our cardiac catheterization laboratory for angiocardiography including selective coronary arteriography. Ioxaglate did not cause any major adverse effects; side effects were rare and mild. Hemodynamic changes were minimal, even in patients with severe coronary artery disease, and no arrhythmias were seen. The radiographic quality of angiograms was scored as good to excellent for each examination, and was equal to that of films performed using a conventional contrast medium. Ioxaglate may be the contrast medium of choice for angiocardiography, especially in patients at high risk, i.e., those with severe coronary artery disease or severe left ventricular dysfunction.

Contrast agents for cardiac angiography: effects of a nonionic agent vs. a standard ionic agent

The effects on cardiac hemodynamics and serum parameters of a standard contrast agent (sodium methylglucamine diatrizoate [Renografin 76]) were compared with the effects of a new nonionic agent (iohexol) in a double-blind study in 51 patients undergoing coronary angiography and left ventriculography. No significant alteration in measured blood parameters occurred with either contrast agent. Hemodynamic changes occurred with both, but were significantly greater with the standard Renografin than with the low-osmolality, nonionic iohexol. After left ventriculography, heart rate increased and peripheral arterial pressure fell with both agents, but less with iohexol. Following coronary artery injections, heart rate and arterial pressure decreased with both agents, but the changes were more marked and occurred earlier with the standard contrast material. It is concluded that iohexol causes less alteration in cardiac function than does the agent currently most widely used. Nonionic contrast material is likely to improve the safety of coronary angiography, particularly in those patients at greatest risk.

Effects of drug-induced reduction in oxyhemoglobin affinity on survival time of mice in severe hypoxic conditions

We studied the effect of ortho-iodo sodium benzoate (OISB) given intraperitoneally to mice. 300 and 600 mg/kg of OISB increased P50 from the control value of 41.2 mmHg to 42.7 mmHg and 45.7 mmHg, respectively. The mice were then exposed to two experimental hypoxias, namely, hypobaric hypoxia and carbon monoxide hypoxia. Mean survival time was prolonged from 67.8 (control saline) to 94.8 sec (OISB 300 mg/kg) and 112.2 sec (OISB 600 mg/kg) in the hypobaric hypoxia, and from 201.3 sec (control saline) to 329.7 sec (OISB 300 mg/kg) and 407.7 sec (OISB 600 mg/kg) in the carbon monoxide hypoxia. We concluded that OISB had prolonged survival time by reducing oxyhemoglobin affinity, thus facilitating oxygen release in severe hypoxic conditions.

The effect of iohexol on glucose metabolism compared with metrizamide

In a previous in vitro study we demonstrated reduced CO2 production in rat hippocampal tissue when metrizamide was added. This metabolic depression is believed to be a result of the 2-deoxy-D-glucose (2-DG) portion of the metrizamide molecule since 2-DG is a known competitive inhibitor of glucose metabolism. This competitive inhibition probably occurs at the cell membrane since it has never been shown that metrizamide penetrates neural cells. Further the inhibition is most likely related to competition for the membrane glucose carrier. A new nonionic contrast medium, iohexol, does not contain a 2-DG component and if the hypothesis for the metabolic inhibition is valid we should not expect metabolic inhibition with iohexol. This hypothesis was tested using the rat hippocampus model previously used for metrizamide. We compared iohexol with metrizamide in isotonic concentrations and also examined the effect of hypertonicity. These experiments did not demonstrate inhibition of CO2 production with iohexol at near physiologic osmolalities, however, there was a marked depressive effect with increasing osmolality. This effect from hypertonicity is, however, probably of less importance in vivo where water will rapidly diffuse toward the hypertonic areas. The apparent lack of interference of the iohexol molecule on glucose metabolism should therefore make iohexol a more suitable contrast medium, for subarachnoid investigations than metrizamide.

Tolerance and biochemical effects from intravenous injection of ioxaglate in healthy volunteers

The influence of intravenous injection of ioxaglate (Hexabrix, 320 mg I/ml) on various biochemical, coagulation and fibrinolytic parameters, fractionated plasma proteins, precordial ECG and blood pressure was prospectively and sequentially studied in 9 healthy volunteers. One ml/kg body weight of the contrast medium was injected within one minute into an antecubital vein. Small, but statistically significant, changes in some of the biochemical parameters were found during the observation period, 2 to 4 days. All values of the biochemical parameters were, however, within the normal reference range for each parameter. No significant alterations were seen in the coagulation parameters. Increased fibrinolysis was recorded in some subjects both before and after the injection. No fibrinolytic degradation products were found indicating that the fibrinolysis was nominal. No significant changes were observed in the fractionated plasma proteins. The heart rate decreased significantly 15 seconds after commencing the injection. No significant changes in blood pressure were recorded. Two participants became nauseated and one of them vomited during the injection. Apart from this, no adverse effects were noted. No clinically significant changes following the injections were found.