Carbonyl (phenone) reductase in human liver: inter-individual variability

Area of Science:

• Biochemistry
• Pharmacology
• Human Physiology

Background:

• Carbonyl reductases are crucial enzymes involved in metabolizing xenobiotics and endogenous compounds.
• Their biological functions and structural aspects remain underexplored.
• Inter-individual variability in enzyme activity can impact drug metabolism and toxicity.

Purpose of the Study:

• To investigate the inter-individual variability of carbonyl reductase activity in human liver.
• To characterize the kinetic properties of carbonyl reductase using a prototype substrate.
• To assess the suitability of different human liver sources for carbonyl reductase studies.

Main Methods:

• In vitro metabolism assays using p-nitroacetophenone (PNAP) as a substrate.
• Enzyme activity screening across 17 kidney donor livers at varying PNAP concentrations (0.05 mM and 0.5 mM).
• Analysis of enzyme kinetic parameters and frequency distributions of activity ratios.

Main Results:

• Carbonyl reductase activity exhibited distinct high- and low-affinity enzyme sites.
• Activity rates at low substrate concentration (0.05 mM PNAP) showed a normal distribution.
• Activity rates at high substrate concentration (0.5 mM PNAP) indicated non-normal, potentially bi- or tri-modal distributions.
• Three out of 17 livers displayed atypical activity ratios, linked to reduced high-affinity enzyme function.
• Autopsy livers demonstrated approximately half the activity of kidney donor livers but are a more accessible tissue source.

Conclusions:

• Significant inter-individual variability exists in human liver carbonyl reductase activity.
• The high-affinity enzyme site appears to be a key determinant of this variability.
• Autopsy livers represent a practical and valuable resource for future research on human carbonyl reductases.