Mg, Mn, and Co ions enhance the formation of Entamoeba histolytica cyst-like structures resistant to sodium dodecyl sulfate

BACKGROUND

Entamoeba histolytica forms cyst-like structures (CLS) in PEHPS but not in TYS-33 medium. Sodium dodecyl sulfate [(SDS (0.1%)] dissolves most of them in 10 min, but not natural cysts. Chitin is responsible mainly for cyst wall resistance. Its synthesis depends on Mg(2)+, Mn(2)+, or Co(2)+, whose action is interactive. With the aid of the Simplex method, we analyzed the effect of 20 blends of these cations to find the one that, when added to PEHPS, produced the highest proportion of CLS resistant to 1% SDS (RCLS).

METHODS

The concentration of Mg(2)+, Mn(2)+, and Co(2)+ was determined in PEHPS and TYI-S-33 with a flame atomic absorption spectrometer. The proportion of RCLS produced in PEHPS with each ion blend was tested. The CLS and RCLS affinity to fluorescein wheat germ agglutinin (WGA/FITC), which binds chitin, was determined.

RESULTS

PEHPS contained a similar concentration of Co(2)+ (0.52 microM) and 3.4 and 1.6 times more Mg(2)+ (798 microM) and Mn(2)+ (3.15 microM) than TYI-S-33, respectively. The proportion of RCLS increased gradually in PEHPS until reaching 3.6 +/- 1.43% with MgCl(2) 1.22 mM, MnCl(2) 14.44 mM, and CoCl(2) 19.44 mM (ion blend No. 20). Both CLS and RCLS bound WGA/FITC. The RCLS formed in the presence of ion blend No. 20 appeared wrinkled.

CONCLUSIONS

Mg(2)+, Mn(2)+, and Co(2)+ enhanced the ability of PEHPS to form RCLS, possibly because these ions stimulated their chitin synthesis. Although ion blend No. 20 produced the highest proportion of RCLS, this high ion concentration may be toxic for encysting amebas.

Detection of a factor released by L5178Y lymphoblasts that inhibits mouse macrophage-activation induced by lipopolysaccharides

BACKGROUND

Several factors inhibit cellular immune response by deactivating macrophages, but very few, such as those described here, prevent macrophage activation.

METHODS

Ascites liquid from 12-day-old BALB/c mice bearing 5178Y lymphoma tumors was collected, and cell-free ascites liquid (CFAL) was separated from lymphoblasts. The supernatant (S1) was obtained from the homogenized and centrifuged lymphoblasts. Then, macrophage cultures containing 0.2 x 10(6) cells from lymphoma-bearing or healthy mice were added to 10 microL of CFAL or S1, plus 5 micrograms of lipopolysaccharides (LPS)/mL, 40 U interferon-gamma or a blend of both. Macrophages were incubated with CFAL or S1 prior to or after adding the activators to investigate whether any of the previously mentioned lymphoma fractions inhibited macrophage activation or whether they deactivated them. The effect of CFAL or S1 was estimated as the diminution of the amount of nitric oxide released by the experimental macrophage cultures with respect to controls (activated macrophages treated with none of the lymphoma fractions).

RESULTS

LPS, IFN-gamma, and the LPS/gamma blend activated macrophages from both lymphoma-bearing and healthy mice. None of the lymphoma fractions deactivated macrophages. CFAL, but not S1, inhibited the macrophage activation, i.e., the percentage of inhibition of nitric oxide releasing 76.7% and 78.1% in macrophages from healthy and lymphoma-bearing mice, respectively. In addition, CFAL was unable to inhibit the macrophage-activation effect of IFN-gamma or the LPS/IFN-gamma blend.

CONCLUSIONS

Mouse L5178Y lymphoma releases a factor that in vitro inhibits the macrophage activation induced by LPS, but not by IFN-gamma controls.

Axenic cultivation of Trichomonas vaginalis in a serum-free medium

Mammalian serum or bovine serum albumin are essential for Trichomonas vaginalis cultivated under axenic conditions. Unfortunately, these components inhibit several biological properties of these parasites. PACSR is a serum replacement, free of bovine serum albumin. used for axenic cultivation of Entamoeba histolytica. We show that PACSR is also useful for axenic cultivation of T. vaginalis. Tubes containing 5.5 ml PEHP, or TYI basal media, plus 8% PACSR (v/v), were inoculated with 10(3) trichomonads/ml from 3 strains (GT-3, GT-13, and GT-15) and incubated at 36.5 C for 72 hr. Depending on the strain, cultures grown in PEHP plus PACSR reached densities of 50% (GT-13), 63% (GT-3), or 82% (GT-15) as compared to controls grown in PEHPS. On the other hand, yields of GT-3, GT-13, and GT-15 maintained in TYI plus PACSR were, respectively, 53%, 57%, and 67% among those of cultures grown in TYI-S-33. In all experiments, PEHPS and TYI-S-33 contained 8% bovine serum. Yields reached in PEHPS were 2.07+/-0.275 to 4.83+/-4.41 x 10(6) trichomonads/ml, whereas in TYI-S-33, densities were 1.68+/-0.315 to 4.16+/-8.07 x 10(6) trichomonads/ml. In conclusion, PACSR added to PEHP or TYI media is useful for axenic cultivation of T. vaginalis in the absence of serum or bovine serum albumin. PACSR could be useful in performing analyses of biological properties that are inhibited by serum or any of its components.

Isolation of an Entamoeba histolytica intracellular alkaline phospholipase A2

The major hemolytic activity of Entamoeba histolytica is located in a subcellular fraction called P30. Its maximal effect is observed at pH 8.0 and 1 mM Ca2+ and is due to a phospholipase A (PLA). In the present study a membrane-associated phospholipase A2 was purified from P30 to homogeneity. P30 was fractionated with ethyl ether and the insoluble fraction was extracted with 1 M KCl. The KCl-soluble material was diluted ten times with 0.1 M TRIS-HCl (pH 9.5) and passed through a chromatofocusing column with a 9-4 pH gradient. Four peaks with PLA2 activity were obtained. By affinity chromatography, peak II, the one with the highest specific activity, was resolved in three more PLA2 peaks. Peak II.2 had the highest PLA2 specific activity. When analyzed by sodium dodecyl sulfate-polyacrylamide slab-gel electrophoresis under nonreducing conditions, peak II.2 yielded a single band with an apparent molecular mass of 30 kDa. Under reducing conditions the protein dissociated into two 15-kDa monomers. The purified PLA II.2 displayed its activity at the same conditions under which the P30 hemolytic activity was maximal. The isoelectric point of PLA II.2 was 7.0. The purification procedure described above provides sufficient material for determination of the relative importance of the enzyme in the E. histolytica pathogenic mechanisms.

Orally administered gossypol has no effect on eight hamster erythrocytic enzymes

The effectiveness of gossypol as an antifertilizing agent is due to the severe injuries or death that this drug produces on spermatozoa and spermatides. Several in vitro and in vivo studies have shown that spermatozoal lactic and malic dehydrogenases are inhibited by gossypol; and that these are more susceptible than the somatic enzymes. Notwithstanding, the in vivo effects on other somatic enzymes have been poorly analyzed. The present study shows that gossypol did not produce toxic effects on eight erythrocytic enzymes of male hamsters that were fed daily with 20 mg of gossypol/kg, for 1, 3, 5 or 10 days. The enzymatic activities analyzed were: adenylate kinase, hexokinase, glucose-6-phosphatase, glucose phosphoisomerase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglyceratokinase and pyruvate kinase.

Identification of Entamoeba histolytica intracellular phospholipase A and lysophospholipase L1 activities

Entamoeba histolytica phospholipase A and lysophospholipase activities from a vesicular subcellular fraction (P30) were analyzed. The products, obtained using specific substrates labeled with 14C or 3H, indicated the presence of phospholipase A1 and A2 as well as lysophospholipase L1 activities. The enzymes detected could participate in phospholipid metabolism and the alkaline phospholipase A2 may contribute to E. histolytica cytopathogenicity.

Differential effects of the (+)- and (-)-gossypol enantiomers upon Entamoeba histolytica axenic cultures

The in-vitro anti-amoebic effects of (+/-)-, (+)-, (-)-gossypol and emetine were tested against axenic trophozoites from five Entamoeba histolytica strains. The (-)-isomer was more active than the racemate and the (+)-isomer. These results indicate that the gossypol anti-amoebic activity is mainly due to its content of (-)-gossypol in all strains tested.

Entamoeba histolytica cysts with a defective wall formed under axenic conditions

Axenic HK9 Entamoeba histolytica strain amoebae, maintained in PEHS medium, displayed several cystic characteristics that involve an active process of cystic wall formation, cellular volume and density diminution, and one or two nuclear divisions. The differentiation process was asynchronic, beginning after the logarithmic growth phase. The axenic cysts, which were maintained in a 50 mOsm/kg medium at 4 degrees C for 72 h, produced growing trophozoites within 1-7 days of incubation at 36 degrees C in fresh medium. Negative results were obtained with trophozoites submitted to the above treatment, and with axenic cysts maintained in double-distilled water at 4 degrees C for 24 h, or in 0.1% sarkosyl, for 10 min at room temperature instead of 55 mosmol/kg medium. Thus, the HK9 E. histolytica strain, cultured in PEHPS, produced under axenic conditions a small proportion of mature, metabolically active cysts, but with an immature or abnormal wall.

A multipurpose solid-phase method for protein determination with Coomassie brilliant blue G-250

The multipurpose method for protein determination (MMPD) is based in the Coomassie brilliant blue G-250 binding to immobilized and washed proteins in paper filter disks, and the A600 measurement of the eluted protein-dye complexes. The analysis requires 5-microliters samples, put in 7-mm paper filter disks, which can be stored for up to 2 weeks, without sensible changes in their protein content. The A600 is a logarithmic function of the log of bovine serum albumin quantity, between 2.5 and 250 micrograms with two linear segments used as standard curves: one between 2.5 to 20 micrograms and the other between 20 and 80 micrograms. Results with the MMPD were quantitatively comparable with those obtained with the method of Lowry et al., and those reported by other workers, assaying the following material: (i) bovine serum albumin, in doubly distilled water or in presence of several substances that interfere with the current methods; and (ii) total homogenates and their respective trichloroacetic acid-insoluble extracts, which were obtained from several phenol-rich vegetal specimens and complex animal products. The MMPD is proposed as an alternative for protein determination for its versatility and reliability, in both vegetal or animal products, especially when the analysis with traditional methods is made difficult by the presence of natural or added interfering substances and the sample volume is too small to discard them, or when the material must be stored for relatively long periods of time, prior to its processing.

[Virulence factors of Entamoeba histolytica]

A panoramic view of the amebiasis concept, its pathogenesis and its epidemiologic importance is presented. Besides, a brief description of the characteristic lesions of the mainly affected organs is done. Then it is proposed a sequential relationship must occur in the amebic lesion production. Finally, the best characterized amoebal infective factors are analyzed. This paper does not pretend to be an exhaustive review, but to offer an image of the pathogenetic mechanisms of amebiasis.

[Development of a simplified method for the axenic culture of Entamoeba histolytica]

Since the TPS-1 medium description, by Diamond, for axenic cultivation of Entamoeba histolytica trophozoites, a spectacular advance in this parasite biology knowledge has been occurred. Recently we described a new medium, called PEHPS, which is as reliable as those of current use, and besides offers a more stable final density. From this latter, we developed, a new simpler medium, after being evaluated the specific contribution of several components of PEHPS. Yields as high as those obtained with the original medium were obtained after the following modifications, incorporated in the new medium formula: Osmolarity 318 +/- 6 mOsm/Kg, pH 6.8, redox potential -130 mV, regulated only with 1.0 g/l of ascorbic acid, glucose 3.75 g/l, instead of the original PEHPS characteristics, which are the following: Osmolarity 340 +/- 42 mOsm/KG, pH 7.0, regulated with both cysteine and ascorbic acid and 6.0 g/l of glucose. As the new medium supplementation with vitamins did not result in significative differences with respect to the non supplemented medium, we eliminated all of these from the final formula.

[Massive production of Entamoeba histolytica cysts under axenic conditions]

After an exponential phase of growth, HK9 strain amebas, kept in the axenic medium PEHPS, spontaneously acquire a form morphologically similar to various natural cysts, as well as a resistance to hypotonic shock, due to the effect of a wall, partially composed of polysaccharides. The number of differentiated amebas increases gradually, although their viability diminishes, in function of the incubation time. On the ninth day, 96% of the population is made up of these cells, although only 6% are viable. The ultramicroscopic structure of the great majority of differentiated amebas corresponds to that of immature cysts. These, and the PEHPS medium, constitute a good model for a characterization of the start of the differentiation of E. histolytica, and open the opportunity of obtaining in axenic conditions, massive cultures of mature cysts.

High susceptibility of five axenic Entamoeba histolytica strains to gossypol

The antiamoebic potency of gossypol was tested against 5 axenic Entamoeba histolytica strains, in logarithmic phase growth in PEHPS medium. All of the strains were moderately susceptible to this polyphenolic drug. The 50% inhibitory concentration (IC50) was of the same order of magnitude in all strains: 0.015 microM (for strain HM-1) to 0.067 microM (for HM-38). The difference between the IC50 of HM-1 and the remaining 4 strains (HM-38, HK-9, HM-2 and HM-3) was significant, although it was greater between HM-1 and HM-38 (P less than 0.005) than between HM-1 and the other 3 strains (P less than 0.05), for which the IC50 was 0.03 microM, 0.049 microM and 0.38 microM respectively. Gossypol is more toxic in vitro for amoebae than other drugs widely used clinically, its pharmacological effects and safe dosage in humans are well known because of its antifertilizing effect, and it is accumulated mainly in the liver and colon. Accordingly, this compound could be a good antiamoebic agent if it is as potent in vivo as it is in vitro.

[Reliability of the PEHPS culture medium for the in vitro evaluation of antiamebic drugs]

Monophasic liquid media for axenical cultivation of Entamoeba histolytica, have permitted to define diverse aspects of this parasite's biology, without associated organisms interference. In addition, these media have allowed the in vitro evaluation of new drugs with potential antiamebic properties. PEHPS, a new medium recently developed in our laboratory, was used in order to determine its usefulness in the searching for new antiamebic compounds. The antiamebic potency of currently employed drugs in clinical therapy: emetine, metronidazole and diiodohydroxyquinoline on E. histolytica, strain HM-1, trophozoites grown in PEHPS was tested. The IC50 for each drug was 0.082 microgram/ml, 0.10 micrograms/ml and 5.84 micrograms/ml respectively. Results obtained with each drug are statistically reliable and reproducible, and agree with the species sensibility reported by several other authors. Accordingly, we propose PEHPS as a useful medium for new antiamebic drug research.