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Potential role of middle molecular compounds in the development of uremic anemia
Abstract:
In preceding papers it was demonstrated that middle molecular fractions isolated from uremic patients (MM) impair hemoglobin synthesis by inhibiting the enzyme Delta-aminolevulinic acid dehydrase (D-ALA-D) and by diminishing the globin synthesis in reticulocytes from healthy subjects. Additionally, the susceptibility to oxidative damage of erythrocytes is increased in the presence of MM. Studies were undertaken to elucidate the underlying mechanisms. It was found that the MM induced D-ALA-D inhibition is reversed both by Zn and by GSH in vitro indicating that MM exert their effect on the enzyme either by affecting essential SH-groups within the enzyme molecule or by altering the enzyme configuration by interaction with the Zn atom. MM causing an increased oxidative hemolysis rate (OHR) also inhibit the catalase activity and the glucose consumption of normal and uremic erythrocytes. It is concluded that the augmented OHR in uremia is induced by accumulating hydrogen peroxide which cannot be sufficiently removed due to the MM mediated catalase inhibition and the concomitant impairment of the glucose utilisation.
Insights
Middle molecular fractions (MM) from uremic patients impair hemoglobin synthesis and increase erythrocyte oxidative damage. MM inhibit key enzymes and glucose utilization, leading to harmful hydrogen peroxide accumulation in uremia.
Area of Science:
- Biochemistry
- Hematology
- Uremia Pathophysiology
Background:
- Uremic toxins, specifically middle molecular fractions (MM), are known to negatively impact red blood cell function.
- Previous studies indicated MM interfere with hemoglobin and globin synthesis and increase oxidative stress in erythrocytes.
Purpose of the Study:
- To elucidate the mechanisms by which MM impair red blood cell function in uremia.
- To investigate the effects of MM on Delta-aminolevulinic acid dehydrase (D-ALA-D) activity, oxidative hemolysis, catalase activity, and glucose metabolism.
Main Methods:
- In vitro studies using isolated middle molecular fractions (MM) from uremic patients.
- Assays for D-ALA-D inhibition, globin synthesis, oxidative hemolysis rate (OHR), catalase activity, and glucose consumption in erythrocytes.
- Investigated the effects of Zinc (Zn) and glutathione (GSH) on MM-induced D-ALA-D inhibition.
Main Results:
- MM inhibited D-ALA-D and globin synthesis, and increased erythrocyte susceptibility to oxidative damage.
- D-ALA-D inhibition by MM was reversible with Zn and GSH, suggesting interference with enzyme's SH-groups or Zn binding.
- MM increased OHR by inhibiting catalase activity and impairing glucose utilization in erythrocytes, leading to hydrogen peroxide accumulation.
Conclusions:
- MM contribute to impaired hemoglobin synthesis and increased oxidative hemolysis in uremia.
- MM-induced D-ALA-D inhibition is linked to alterations in enzyme structure or essential cofactors.
- Accumulation of hydrogen peroxide, due to inhibited catalase and reduced glucose metabolism by MM, drives augmented oxidative hemolysis in uremia.