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PubMed1978

Prevention and reversal of cholera enterotoxin effects in rabbit jejunum by nicotinic acid.

The cholera enterotoxin produces intestinal secretion associated with an elevation of tissue levels of cyclic adenosine 3',5'-monophosphate levels of cyclic adenosine 3',5'-monosphosphate (cAMP). The objectives of this study were to determine whether intestinal secretion and cAMP elevation induced by cholera toxin could be prevented, or once initiated, reversed by nicotinic acid, an agent known to lower tissue levels of cAMP. In rabbits, four jejunal loops were constructed as alternating control (3-ml isotonic electrolyte solution) and cholera toxin (same solution containing 50 mug purified cholera toxin) loops. Net intestinal secretion was determined by measuring fluid accumulation, after which intestinal biopsies were taken for cAMP assay. The animals were pretreated either subcutaneously with 50 mg/kg nicotinic acid in saline 3 h and 1 h before the introduction of cholera toxin, or intraluminally with 200 mg/kg nicotinic acid in Ringer's lactate solution 15 min before the instillation of cholera toxin. Under these conditions, nicotinic acid blocked the cholera toxin-induced secretion and the rise in cAMP measured 3 h after the loops were exposed to cholera toxin. The effect of the nicotinic acid administered within the lumen on net intestinal secretion was studied. Maximal inhibition of net intestinal secretion was achieved with an intraluminally administered dose of nicotinic acid of 100 mg/kg. This dose was chosen for testing the ability of nicotinic acid to reverse the effects of cholera toxin. When nicotinic acid was instilled into a fifth loop constructed distally to the four experimental loops 3 h after exposure of these loops to cholera toxin, both intestinal secretion and elevation of cAMP were reversed. These results suggest that nicotinic acid can prevent and reverse the secretory effects of cholera toxin and may have a role in the therapy of cholera and other cAMP-associated diarrheal diseases.

Animals↗
PubMed1979

Endemicity of cholera in Surabaya, Indonesia.

As the seventh pandemic of cholera is caused by V. cholerae biotype El Tor, the former criteria for endemicity of cholera need to be reconsidered as regards their applicability in areas that are infected with cholera. As the mortality rate of cholera nowadays can be reduced to a very low level due to modern methods of treatment, it is suggested that the infection rates of cholera should be taken into consideration as criteria of cholera endemicity, i.e. 1. Five years persistence of cholera cases in a given area. 2. Five percent infection rate among family contacts of cholera cases. 3. Minimum infection rate of 1% in a vicinity where cholera cases occur. It was also found that in such an endemic area it is very difficult to eliminate V. cholerae infection from a locality, even when all family contacts are treated with the full dose of tetracycline.

Adolescent↗
PubMed1975

Mechanism of action of Vibrio cholerae enterotoxin. Effects on adenylate cyclase of toad and rat erythrocyte plasma membranes.

The characteristics of the cholera toxin-stimulated adenylate cyclase of toad (Bufus marinus) and rat erythrocyte plasma membranes have been examined, with special emphasis on the response to purine nucleotides, fluoride, magnesium and catecholamine hormones. Toad erythrocytes briefly exposed to low concentrations of cholera toxin (40,000 to 60,000 molecules per cell) and incubated 2 to 4 hr at 30 degrees C exhibit dramatic alterations in the kinetic and regulatory properties of adenylate cyclase. The approximate Km for ATP, Mg++ increases from about 1.8 to 3.4 mMin the toxin-stimulated enzyme. The stimulation by cholera toxin increases with increasing ATP, Mg++ concentrations, from 20 percent at low levels (0.2 mM) to 500 percent at high concentrations (greater than 3 mM). Addition of GTP, Mg++ (0.2 mM) restores normal kinetic properties to the toxin-modified enzyme, such that stimulation is most simply explained by an elevation of Vmax. GTP enhances the toxin-treated enzyme activity two- to fourfold at low ATP concentrations, but this effect disappears at high levels of the substrate. At 0.6 mM ATP and 5 mM MgC12 the apparent K alpha for GTP, Mg++ is 5 to 10 muM. The control(unstimulated) enzyme demonstrates a very small response to the guanyl nucleotide, 5'-ITP also stimulates the toxin-treated enzyme but cGMP, guanine, and the pyrimidine nucleotides have no effect. Cholera toxin also alters the activation of adenylate cyclase by free Mg++, decreasing the apparent K alpha from about 25 to 5 mM. (minus)-Epinephrine sensitizes the toad erythrocyte adenylate cyclase to GTP and also decreases the apparent K alpha for free metal. Sodium fluoride, which causes a 70- to 100-fold activation of enzyme activity, has little effect on sensitivity to GTP, and does not change the apparent K alpha for Mg++; moreover,it prevents modulation of these parameters by cholera toxin. Conversely, cholera toxin severely inhibits NaF activation, and in the presence of fluoride ion the usual three to fivefold stimulation by toxin becomes a 30 to 60 percent inhibition of activity. The toxin-stimulated enzyme can be further activated by catecholamines; in the presence of GTP the (minus)-epinephrine stimulation is enhanced by two- to threefold. The increased catecholamine stimulation of toad erythrocyte adenylate cyclase induced by cholera toxin is explained primarily by an increase in the maximal extent of activation by the hormones. Rat erythrocyte adenylate cyclase is also modified by cholera toxin. In the mammalian system the apparent affinity for the hormone appears to be increased. Cholera toxin thus induces profound and nearly permanent changes in adenylate cyclase by a unique process which mimics the stimulation by hormones in important ways, and which also accentuates the normal hormonal response. The relevance of these findings to the mechanism of action of cholera toxin is considered.

Adenylyl Cyclases↗
PubMed1979

Action of cholera toxin on dispersed acini from guinea pig pancreas.

In dispersed acini from guinea pig pancreas cholera toxin bound reversibly to specific membrane binding sites to increase cellular cyclic AMP and amylase secretion. Cholera toxin did not alter outflux of 45Ca or cellular cyclic AMP. Binding of 125I-labeled cholera toxin could be detected within 5 min; however, cholera toxin did not increase cyclic AMP or amylase release until after 40 min of incubation. There was a close correlation between the dose vs. response curve for inhibition of binding of 125I-labeled cholera toxin by native toxin and the action of native toxin on cellular cyclic AMP. With different concentrations of cholera toxin, maximal stimulation of amylase release occurred when the increase in cellular cyclic AMP was approximately 35% of maximal. Cholera toxin did not alter the increase in 45Ca outflux or cellular cyclic GMP caused by cholecystokinin or carbachol but significantly augmented the increase in cellular cyclic AMP caused by secretin or vasoactive intestinal peptide. The increase in amylase secretion caused by cholera toxin plus secretin or vasoactive intestinal peptide was the same as that with cholera toxin alone. On the other hand, the increase in amylase secretion caused by cholera toxin plus cholecystokinin or carbachol was significantly greater than the sum of the increases caused by each agent alone.

Amylases↗
PubMed1976

Effect of aspirin on normal and cholera toxin-stimulated intestinal electrolyte transport.

The effect of aspirin on normal and cholera toxin-stimulated electrolyte transport has been investigated in vitro, because this drug appears to inhibit cholera toxin-induced intestinal secretion in in vivo animal models. In the Ussing chamber, 10 mM aspirin decreased the control rabbit ileal potential difference and short-circuit current by 50% and increased conductance by 28%. Bidirectional electrolyte flux determinations showed that aspirin significantly increased both Na and Cl absorption and reduced flux (which probably represents HCO3 secretion) to zero. This effect of aspirin appears to be identical to that reported to others with catecholamines as determined with similar techniques. However, alpha-adrenergic blockers did not prevent the electrical effects of aspirin, suggesting that aspirin does not have its effect through release of tissue stores of catecholamines. In the presence of aspirin, cholera toxin increased the potential difference and short-circuit current, and decreased the conductance of rabbit ileum in a fashion qualitatively similar to control tissues. However, aspirin reversed cholera toxin-stimulated Na transport from secretion to absorption, inhibited cholera toxin, induced Cl secretion by 58% and partially, but not significantly, inhibited HCO3 secretion. Thus, the inhibitory effect of aspirin on cholera toxin-induced electrolyte secretion appears to be due to aspirin-stimulated Na and Cl absorption. Although aspirin reduced tissue cyclic AMP concentrations in normal and cholera toxin-stimulated ileum, it also inhibited the electrolyte secretion induced by exogenous cyclic AMP. Thus, if aspirin's stimulatory effect on sodium and anion absorption in normal tissue and its inhibitory effect on cholera toxin-stimulated sodium and anion secretion involves a cyclic AMP-mediated system, the effect must be a step distal to cyclic AMP production or degradation. The exact mechanism of aspirin's effect on normal and cholera toxin-induced electrolyte transport, and its possible usefulness in the treatment of cholera diarrhea, remains to be determined.

Animals↗
PubMed1976

Possibilities of immunization against cholera and related enterotoxic enteropathies.

Scientifically controlled field studies have established that parenterally administered killed vibrio vaccines or somatic antigen preparations offer only limited degrees of protection in certain population groups and have made it obvious that new approaches to the immunoprophylaxis of cholera are needed. It has now also been established that the symptoms of cholera result from the action of the cholera enterotoxin (choleragen) on the epithelial cells of the small intestine. Immulogically related enterotoxins have been incriminated in other newly recognized diarrheal diseases (e.g., those caused by Escherichia coli and "non-agglutinable" (NAG)vibrios). Additionally, volunteer studies have shown that induced cholera results in rather solid and lasting immunity against homologous re-challenge thus proving that immunity against cholera is feasible. Although numerous studies have demonstrated the efficacy of purely antitoxic immunity in experimental animal models, the protective effect of parenterally administered glutaraldehyde treated toxoid in man has shown to be limited, at best. The protection attained following an attack of cholera suggests that local immune mechanism may be of predominant importance. Immunity has been stimulated, experimentally in mice, by toxin antigen administered per os on a single occasion. Choleragenoid, which is non-toxic but binds to the same receptors as cholera toxin, has been shown to provide immediate resistance as well as later immunity to toxin challenge. More ideal, however, would be a colonizing mutant of V. cholerae which elaborates a non-toxic cross-reactive material (CRM) like choleragenoid and which could stimulate local antitoxic as well as anti-vibrio immune mechanisms. A tox-mutant of V. cholerae which is avirulent for man has been shown to elicit substantial immunity in man but the ideal CRM-mutant has yet to be found.

Administration, Oral↗
PubMed1979

Antigenic specificity of neutralizing antibody to cholera toxin.

Selected rabbit antisera to cholera toxin antigens and convalescent cholera patient sera were analyzed using the permeability factor neutralization test and two sensitive in vitro serological assays specific for cholera toxin, cholera toxin A subunit, and cholera toxin B subunit. The results indicated that antisera to cholera toxin contained toxin-neutralizing activity as well as antibodies specific for both the A subunit and B subunit. It was clearly established that antisera to B subunit, devoid of significant anti-A subunit activity, neutralized the vascular permeability activity of cholera toxin. Antisera to A subunit contained neutralizing antibodies and antibodies to both A and B subunits. Absorption with B subunit removed both the toxin-neutralizing and anti-B subunit activities, while the anti-A activity was unaffected. Neutralizing antibody titers of rabbits immunized with B subunit were also observed to be significantly higher than neutralizing antibody titers of sera from A subunit-immunized rabbits, despite the overall similarity in anti-B subunit titers as determined by passive hemagglutination and radioimmunoassay of sera from the two groups of rabbits. Anti-alpha chain sera neither neutralized cholera toxin nor possessed significant antitoxin or anti-B subunit titers as determined by passive hemagglutination and radioimmunoassay. The anti-alpha chain sera contained high levels of antibody specific for A subunit, which is consistent with the hypothesis that the alpha chain is part of the A subunit structure. In contrast, the gamma chain was not shown to be antigenic. Sera from convalescent cholera patients possessed toxin-neutralizing antibody as well as passive hemagglutination and radioimmunoassay antibody against both A and B subunits.

Animals↗
PubMed1976

Properties of cholera toxin- and NaF-stimulated adenylate cyclase from mouse thymocytes.

Kinetic parameters of mouse thymocyte adenylate cyclase activity were determined. NaF and cholera toxin stimulated adenylate cyclase. Stimulation by either agent did not change the pH or Mg2+ optima relative to control (unstimulated cyclase). The Km value for ATP of adenylate cyclase stimulated by NaF was significantly reduced from control. By contrast, cholera toxin treatment did not change the Km relative to control. Adenylate cyclase, when stimulated by NaF, had an optimum for Mn2+ alone, or Mn2+ in combination with Mg2+, at least twice that of control. In contrast, cyclase activity prepared from cells treated with cholera toxin remained unchanged with regard to these divalent cations when compared to control. Addition of NaF to adenylate cyclase prepared from cells treated with cholera toxin resulted in a significant reduction (30%) in activity suggesting that both NaF and cholera toxin were acting on the same cyclase. NaF inhibition of cholera toxin-stimulated activity was shown to be a direct interaction of fluoride on the stimulated cyclase enzyme. This inhibition appeared to be immediate and independent on pH, Mg2+ or ATP concentrations. Although NaF inhibition was lost when Mn2+ was present in the reaction mixture, the activity expressed by addition of NaF to cyclase prepared from cholera toxin-treated cells was much less than by addition of NaF to control. As observed with cholera toxin stimulation alone, activity expressed by the inhibited enzyme (cholera toxin treated + NaF) exhibited a Km for ATP and an optimum for Mn2+ alone or in combination with Mg2+ similar to control.

Adenylyl Cyclases↗
PubMed1979

Ecology, serology, and enterotoxin production of Vibrio cholerae in Chesapeake Bay.

A total of 65 isolates of Vibrio cholerae, serotypes other than O--1, have been recovered from water, sediment, and shellfish samples from the Chesapeake Bay. Isolations were not random, but followed a distinct pattern in which salinity appeared to be a controlling factor in V. cholerae distribution. Water salinity at stations yielding V. cholerae (13 out of 21 stations) was 4 to 17 0/00, whereas the salinity of water at stations from which V. cholerae organisms were not isolated was less than 4 or greater than 17 0/00. From results of statistical analyses, no correlation between incidence of fecal coliforms and V. cholerae could be detected, whereas incidence of Salmonella species, measured concurrently, was clearly correlated with fecal coliforms, with Salmonella isolated only in areas of high fecal coliform levels. A seasonal cycle could not be determined since strains of V. cholerae were detectable at low levels (ca. 1 to 10 cells/liter) throughout the year. Although none of the Chesapeake Bay isolates was agglutinable in V. cholerae O group 1 antiserum, the majority for Y-1 adrenal cells. Furthermore, rabbit ileal loop and mouse lethality tests were also positive for the Chesapeake Bay isolates, with average fluid accumulation in positive ileal loops ranging from 0.21 to 2.11 ml/cm. Serotypes of the strains of V. cholerae recovered from Chesapeake Bay were those of wide geographic distribution. It is concluded from the data assembled to date, that V. cholerae is an autochthonous estuarine bacterial species resident in Chesapeake Bay.

Ecology↗
PubMedDate not supplied

[A comparison of the serological effects of classical cholera vaccine and of purified fraction vaccine, with or without simultaneous yellow fever vaccine (author's transl)].

In order to test whether simultaneously administered cholera vaccine has a depressive effect on yellow fever vaccine, a controlled trial was undertaken on school-age children in the South-Central Province of Cameroun. In addition to this principle objective, the study also permitted a comparison of the serological response in subjects vaccinated with classical cholera vaccine and in those vaccinated with a purified fraction vaccine, either with or without simultaneous yellow fever vaccine. The evaluation was measured by changes in vibriocidal antibodies and cholera agglutinins 30 days after vaccination. Only subjects without cholera antibodies prior to the study, were included. 1) Results obtained by assay of vibriocidal antibodies. It was confirmed that, no matter which cholera vaccine was used, the simultaneous administration of yellow fever vaccine had no influence on the percentage of subjects showing a significant rise in vibriocidal antibodies (4-fold increase in titre) following vaccination. In addition, in this study the purified fraction vaccine resulted in a significantly higher rate of seroconversion than did the classical vaccine. However, in comparison to other studies using classical cholera vaccine, our figures for seroconversion after purified fraction vaccine show very little, if any, differences. 2) Results obtained by assay of agglutinating antibodies. When measured by this method, there was a high frequency of non-reactors to the vaccines. This may be attributed to the date of the post vaccination blood speciment (30th day after vaccination). It has been shown that agglutinins decay rapidly after the 15th day following clinical cholera. Thus, the late date of the second speciment after vaccination could explain why we were unable to show any difference in the level of agglutinin after either classical or purified cholera vaccination. The simultaneous administration of the yellow fever vaccine did not influence the titre of agglutinins induced by the classic cholera vaccine. On the other hand, using the association, the seroconversion rate as observed on the 30th day post vaccination was significantly higher than that observed when the fraction was administered alone. If one accepts the generally admitted specificity of the agglutination reaction after clinical disease, two hypotheses can be considered: a) the yellow fever vaccine has an adjuvant effect for the production of antibodies induced by the purified fraction vaccine, or b) the addition of yellow fever vaccine has a retarding effect on the elimination of the agglutinins which, in the natural disease, are rapidly eliminated. Further studies to verify these hypothesis should be undertaken.

Adolescent↗
PubMed1979

Induction of refractoriness to isoproterenol by prior treatment of C6-2B rat astrocytoma cells with cholera toxin.

Rat C6-2B astrocytoma cells responded to cholera toxin treatment with an 8-fold increase in intracellular cyclic AMP concentrations. Cyclic AMP levels began to rise 60--90 minutes after addition of the toxin and reached maximal concentrations in 3 hours. Cells exposed to cholera toxin and the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX), displayed an increase in cyclic AMP of 15-fold. The peak isoproterenol response was reduced 80--90% in cells previously treated with cholera toxin. Cholera toxin-induced refractoriness was time dependent and was not altered by concurrent treatment with propranolol. Prolonged exposure of the cells to isoproterenol reduced the cyclic AMP response to cholera toxin by 80%. MIX augmented both cholera toxin-induced refractoriness and isoproterenol-induced refractoriness. Cycloheximide inhibited the full development of refractoriness to both cholera toxin and isoproterenol. These results indicate that C6-2B cell refractoriness to cholera toxin is mediated by cyclic AMP and requires new protein synthesis. Refractoriness in C6-2B cells does not appear to be agonist-specific and probably involves a common locus of action on adenylate cyclase beyond that of the membrane receptors for cholera toxin and isoproterenol.

1-Methyl-3-isobutylxanthine↗