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Updated: Aug 30, 2026
Human Liver Microphysiological System for Assessing Drug-Induced Liver Toxicity In Vitro
Published on: January 31, 2022
Effect of age on in vitro triazolam biotransformation in male human liver microsomes
Kiran C Patki1, Lisa L von Moltke, Jerold S Harmatz
1Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111, USA.
Abstract:
We studied age-related changes in enzyme kinetic parameters in human liver microsomes (HLMs) in vitro, using triazolam (TRZ), an index of CYP3A activity. HLMs were prepared from male livers from four age groups, n = 5 per group: A (14-20 years), B (21-40 years), C (41-60 years), and D (61-72 years). Mean V(max) values in groups B and C for both 1-hydroxytriazolam (1-OH-TRZ) and 4-hydroxy-triazolam (4-OH-TRZ) formation were significantly greater as compared with groups A and D individually, as well as the net intrinsic clearance (sum of the two pathways). The mean net intrinsic clearance (Cl(int)) values were 25.2, 89.8, 78, and 20.6 nl/min/mg protein in A, B, C, and D, respectively. TRZ Cl(int) correlated well with total CYP3A content (r(s) = 0.84; P < 0.0001). Testosterone (TST) inhibited 1-OH-TRZ formation and activated 4-OH-TRZ formation in all age groups, with no significant differences among the groups; this suggests that the drug-drug interaction potential using TRZ and TST as index CYP3A substrates may not change with age. Reduced V(max) and Cl(int) for TRZ hydroxylation and CYP3A protein in livers from elderly men suggest reduced CYP3A gene expression in this group.
Insights
Enzyme activity in human liver microsomes (HLMs) decreases in elderly men, indicating reduced CYP3A gene expression. This age-related decline in triazolam (TRZ) metabolism affects drug interactions.
Area of Science:
- Pharmacology
- Biochemistry
- Gerontology
Background:
- Human liver microsomes (HLMs) are crucial for drug metabolism.
- Cytochrome P450 3A (CYP3A) is a key enzyme in drug metabolism.
- Age-related changes in enzyme activity can impact drug efficacy and safety.
Purpose of the Study:
- To investigate age-related alterations in CYP3A enzyme kinetic parameters in human liver microsomes (HLMs).
- To assess the impact of aging on triazolam (TRZ) metabolism and its relationship with CYP3A content.
- To evaluate potential age-dependent changes in drug-drug interaction profiles using TRZ and testosterone (TST).
Main Methods:
- Human liver microsomes were prepared from male donors across four age groups (14-72 years).
- Enzyme kinetic parameters for triazolam (TRZ) hydroxylation (1-OH-TRZ and 4-OH-TRZ formation) were determined in vitro.
- Correlation between TRZ intrinsic clearance (Cl(int)) and total CYP3A content was analyzed.
- The effect of testosterone (TST) on TRZ metabolism was examined across age groups.
Main Results:
- Mean V(max) and net intrinsic clearance (Cl(int)) for TRZ hydroxylation were significantly lower in the youngest (14-20 years) and oldest (61-72 years) age groups compared to middle-aged groups (21-60 years).
- TRZ Cl(int) showed a strong positive correlation with total CYP3A content (r(s) = 0.84, P < 0.0001).
- Testosterone (TST) exhibited consistent inhibitory and activating effects on TRZ metabolism across all age groups, suggesting no significant age-related changes in this specific drug-drug interaction potential.
Conclusions:
- Reduced V(max) and Cl(int) for TRZ hydroxylation in elderly men suggest decreased CYP3A activity, likely due to reduced CYP3A gene expression.
- The findings indicate that while CYP3A activity declines with age, the potential for drug-drug interactions involving TRZ and TST may remain consistent.
- This study highlights the importance of considering age-related changes in drug metabolism for optimizing pharmacotherapy in elderly populations.
