LEAD STUDIES : III. THE EFFECTS OF LEAD ON RED BLOOD CELLS. PART 1. CHANGES IN HEMOLYSIS

LEAD STUDIES : III. THE EFFECTS OF LEAD ON RED BLOOD CELLS. PART 3. A CHEMICAL EXPLANATION OF THE REACTION OF LEAD WITH RED BLOOD CELLS

These three papers have developed the following facts, which suffice to explain completely the anemia of lead poisoning. In vitro, the exposure to a very small amount of lead greatly changes the surface of the red blood cells. Their permeability to water is so altered that they shrink and are incapable of swelling as much as normal cells. With this is associated a marked increase in the resistance to different osmotic surroundings—demonstrated by far less hemolysis than normal in salt solution of very low concentrations. The "leaded" cells, however, are relatively short lived, and hemolyze readily as the result of slight trauma. These observations can also be demonstrated in vivo as experiments with rabbits with acute lead poisoning show. In addition to these effects on permeability, lead alters the physical properties of red blood cells so that they lose their normal stickiness and are no longer agglutinated by the sera of different isoagglutinating groups. All these changes are evidence of an effect on the surface of the cell; the interior of the cell does not undergo disturbances; at least, the physiological properties of the hemoglobin remain normal. The chemical reaction which causes these physical changes in the cell is a precipitation of insoluble lead phosphate and a formation of acid. This causes the "leaded" red blood cell to change from an elastic distensible sac, to one which is contracted, relatively inelastic and brittle. In such condition the cell can poorly withstand the trauma involved in circulation of the blood, and this lack of resistance probably explains the marked destruction of peripheral blood in lead poisoning.

Red blood cell osmotic fragility in Bufo arenarum exposed to lead

The effects on red blood cells of a single sublethal dose of Pb of 100 mg kg-1 administrated to adult Bufo arenarum were studied. The blood d-aminolevulinic acid dehydratase (d-ALAD) activity, the red blood cell (RBC) osmotic fragility (OF), and the hematocrit (Hct) were measured in control and lead poisoned toad. The enzyme d-ALAD is considered as a specific biomarker for human and animals lead exposure. In Bufo, lead also provoked a significant decrease in the d-ALAD activity without changes in the Hct. OF test was used to compare the impact of Pb on the extent of the RBC hemolysis produced by osmotic stress. Experimental data (absorbance of solubilized hemoglobin and [NaCl]) were fitted to the Orcutt et al. equation (1995) that allows a precise characterization of the parameters involved in OF. In blood from injected toads, the OF resulted significantly reduced. These changes were interpreted as a consequence of alterations in the composition and conformation of the RBC membrane due to Pb, as it was described for human erythrocytes.

Further observations on the mechanical fragility of the red cell in lead poisoning

Further experiments on the effects of lead on the mechanical fragility of the red cell confirm previous findings, that lead does not increase the mechanical fragility index of the red cell at the blood lead levels found in clinical plumbism.

Above these levels lead does increase the mechanical fragility index, reaching its maximum effect at about 50 μg. of lead/ml. blood.