Free fatty acids released from phospholipids are the major heat-stable hemolytic factor of Entamoeba histolytica trophozoites

The major hemolytic activity of Entamoeba histolytica trophozoites is located in a vesicular fraction called P30 and known to be due to heat-labile and heat-stable hemolytic components whose effect increases up to 100 times during preincubation at 36 degrees C. The heat-stable hemolytic activity (HSHA) was found in the chloroform-methanol extract of preincubated P30, whose partition with 2 M KCl yielded a lipid fraction, an interphase, and an aqueous phase. HSHA was detected only in the lipid fraction, where it amounted to 59% of the chloroform-methanol extract activity and increased 50% when supplemented with the interphase material; it was accounted for by the free fatty acids, whose potency increased 33% with the interphase material, and was blocked by delipidated bovine serum albumin. A parallel increase in free fatty acids and lysophospholipids and a corresponding decrease in phospholipids were observed during P30 preincubation. Most of the phospholipase activity of trophozoite homogenates was also found in P30. Therefore, most of the HSHA generated during preincubation was due to free fatty acids released from phospholipids by a P30 phospholipase that may contribute significantly to E. histolytica cytopathogenicity and virulence.

PEHPS medium: an alternative for axenic cultivation of Entamoeba histolytica and E. invadens

Knowledge of Entamoeba histolytica biology in the last 17 years has been acquired largely as a consequence of this parasite's axenic cultivation in TPS-1 or TYI-S-33 media. Unfortunately, there are often low yields in these media, due to variability of their main components, Panmede and yeast extract. We describe a medium, PEHPS, of which the main components are extracts of ox liver, and ox and swine pancreas (EHP). 5 strains of E. histolytica and 2 of E. invadens were quickly and easily adapted to PEHPS and serially cultivated for 3 years. Yields progressively rose initially, and then became stable. Depending on the strain, average yields in the last 6 months of this study were 1.3 to 3.1 x 10(5) amoebae/ml for E. histolytica and 5.5 to 5.7 x 10(5) for E. invadens. All the 18 EHP batches tested supported vigorous amoebal growth. PEHPS had 2 additional advantages: (a) it was stable at 4 degrees C or 25 degrees C for 9 months, and at -10 degrees C for at least 2 years, and (b) it supported amoebal growth with inocula as low as one trophozoite/ml. PEHPS avoids the variability shown by TPS-1 and TYI-S-33, and could therefore be a good alternative for axenic amoebal cultivation.

Latency and heterogeneity of Entamoeba histolytica hemolysins

We have found that the hemolytic potency of P30 - a subcellular fraction that contains most of the hemolytic activity of Entamoeba histolytica trophozoites--increased up to 100 times by preincubation for 36 h at 36 degrees C. This remarkable increase in potency was due to the in vitro generation of heat-labile as well as heat-stable hemolytic components and could be prevented if P30 was preincubated at 4 degrees C or subjected to either heating at 90 degrees C or to repeated freeze-thawing cycles before preincubation at 36 degrees C. The major hemolytic activity of E. histolytica thus appears to depend on latent, heat-labile and heat-stable hemolysins that are probably unmasked through the action of endogenous amebal enzymes.

Subcellular distribution and stability of the major hemolytic activity of Entamoeba histolytica trophozoites

Since the hemolytic activity of extracts from Entamoeba histolytica trophozoites previously described by us might determine at least partially the necrotic lesions of amebiasis, we have continued its characterization in vitro. Using rat erythrocytes as target cells, we have found that cytolysis by E. histolytica trophozoite extracts was (1) dose dependent, (2) localized mainly in a vesicular fraction whose absolute and specific activities were respectively 1.9 and 4.0 times higher than those of total extracts, (3) maximal at pH 8 in the presence of 1 mM Ca++, and (4) progressively lost by heating at 90 degrees C or repeated freezing and thawing. From these results we infer that the major hemolytic factor of E. histolytica may be a protein normally neutralized by an intracellular inhibitor or activated during fractionation.

Cytopathogenicity of Entamoeba histolytica: trophozoite homogenates modulate DNA synthesis in a mammalian cell line

We examined the effect of total trophozoite homogenates from four axenized strains of Entamoeba histolytica (HK9, HM1, HM2, and HM3) on the DNA synthesis of subconfluent cultures of Chinese hamster ovary (CHO) cells incubated at low (0.1%) serum concentration. HM1, HM2, and HM3 extracts increased [3H]thymidine incorporation to acid-insoluble material in CHO cells up to a maximum of 2.5, 1.5, and 1.5 times respectively, at doses of amebal protein ranging from 16 to 125 micron/ml. HM1 and HM2 extracts at doses higher than those causing maximal stimulation, and HM3 and HK9 extracts above 250 micron protein per ml, progressively inhibited [3H]thymidine incorporation by CHO cells at a strain-specific rate. The extracts with both the most potent stimulatory and inhibitory effects were those from HM1 and HM2, also the most virulent strains. This strain-specific ability of amebal products to modulate cell DNA synthesis may play a significant role in amebal virulence.

Cytopathogenicity of Entamoeba histolytica: hemolytic activity of trophozoite homogenates

In in vitro assays the hemolytic activity of total homogenates of trophozoites of seven strains of amebae were tested for specificity and potency against the erythrocytes of eight mammalian species. The species of Entamoeba included in the tests were E. histolytica, E. invadens, E. moshkovskii, and the Laredo type of E. histolytica. The hemolytic activity was found to be dose-dependent and strain-specific, with E. histolytica being generally the species having the highest hemolytic potency.