Abstract
Background:
Detoxification enzymes, including cytochrome P450 isoforms (CYP1A2 and CYP2E1) and glutathione-S-transferase (GST), play key roles in xenobiotic metabolism and organ protection. Although crocodile-derived bioactive compounds have gained biomedical interest, the in vivo effects of C. siamensis liver extract on mammalian detoxification pathways remain largely unexplored.

Aim:
To evaluate the effects of oral administration of C. siamensis liver extract on phase I (CYP1A2, CYP2E1) and phase II (GST) detoxification enzyme activities, kinetic parameters (Vmax, Km, catalytic efficiency), and selected blood biochemical profiles in rat liver and kidneys.

Methods:
Male Wistar rats (n = 5) were orally administered freeze-dried C. siamensis liver extract at 0, 50, 100, 200, 400, or 800 mg/kg for seven days. Liver and kidney tissues were collected for microsomal and cytosolic fractionation. Enzyme activities were quantified using specific substrates (CEC for CYP1A2, 7-MFC for CYP2E1, CDNB for GST), and kinetic parameters were calculated by Michaelis–Menten modelling. Serum albumin, total protein, cholesterol, and glucose were analyzed using automated clinical assays. Data were assessed by one-way ANOVA with Tukey’s post hoc test for variables that met parametric assumptions, whereas non-parametric data were analyzed using the Kruskal–Wallis test.

Results:
Crocodile liver extract produced dose-dependent and tissue-specific modulation of detoxification enzymes. Hepatic CYP1A2 showed a biphasic response, with catalytic efficiency increasing markedly at 400–800 mg/kg. Hepatic CYP2E1 activity increased toward 400 mg/kg before stabilizing. In kidneys, CYP1A2, CYP2E1, and GST activities were consistently elevated, with GST showing the strongest induction; Vmax increased from 0.16 to 0.59 µmol/min/mg at 800 mg/kg. Several groups exhibited enhanced catalytic efficiency despite reduced Vmax, indicating improved substrate affinity. Blood analyses showed increased serum albumin and total protein, while cholesterol and glucose were reduced, ssuggesting metabolic benefits associated with liver-related biochemical changes.

Conclusion:
Oral supplementation with C. siamensis liver extract modulates phase I and phase II detoxification pathways in rats, with pronounced induction in renal tissues and high-dose enhancement in hepatic enzymes. These findings provide the first in vivo evidence that reptile-derived liver extract can enhance xenobiotic metabolism and support metabolic homeostasis, highlighting its potential as a natural bioactive supplement in veterinary applications.

Key words: Crocodylus siamensis; Detoxification enzymes; CYP; GST; Biotransformation.