Substrate-induced spectral changes in human normal and chronic myeloid leukemic granulocytes

Area of Science:

• Biochemistry
• Hematology
• Pharmacology

Background:

• The cytochrome P-450 mixed function oxidase system is crucial for drug metabolism.
• Granulocytes play a role in inflammatory and immune responses.
• Chronic myeloid leukemia (CML) is a hematological malignancy affecting myeloid cells.

Purpose of the Study:

• To investigate the interaction of drugs with the cytochrome P-450 system in human granulocytes.
• To compare the mixed function oxidase activity in normal versus CML granulocytes.
• To characterize substrate-induced spectral changes in granulocyte fractions.

Main Methods:

• Isolation of granulocytes from normal subjects and CML patients using Ficoll-Hypaque density gradient.
• Preparation of postmitochondrial supernatant fractions (S1).
• Spectrophotometric analysis of substrate-induced difference spectra following addition of various drugs (aminopyrine, phenobarbital, Tween 80, aniline, pyridine).

Main Results:

• Drug substrates induced reverse type I and modified type I (reverse type II) spectral changes in normal and CML granulocyte S1 fractions.
• Spectral changes were quantitatively proportional to substrate concentration.
• Leukemic granulocyte S1 fractions showed significantly smaller spectral changes and lower total heme content compared to normal granulocytes.

Conclusions:

• Human granulocyte cytochrome P-450 exhibits distinct spectral responses to drug substrates.
• The mixed function oxidase system in CML granulocytes is functionally impaired, evidenced by reduced spectral changes and decreased heme content.
• These findings suggest altered drug metabolism capabilities in leukemic granulocytes.