Alpha-1 Acid Glycoprotein as a Biomarker for Subclinical Illness and Altered Drug Binding in Rats

Alpha-1 acid glycoprotein (AGP) is a significant drug binding acute phase protein that is present in rats. AGP levels are known to increase during tissue injury, cancer and infection. Accordingly, when determining effective drug ranges and toxicity limits, consideration of drug binding to AGP is essential. However, AGP levels have not been well established during subclinical infections. The goal of this study was to establish a subclinical infection model in rats using AGP as a biomarker. This information could enhance health surveillance, aid in outlier identification, and provide more informed characterization of drug candidates. An initial study (n = 57) was conducted to evaluate AGP in response to various concentrations of Staphylococcus aureus (S. aureus) in Sprague-Dawley rats with or without implants of catheter material. A model validation study (n = 16) was then conducted using propranolol. Rats received vehicle control or S. aureus and when indicated, received oral propranolol (10 mg/kg). Health assessment and blood collection for measurement of plasma AGP or propranolol were performed over time (days). A dose response study showed that plasma AGP was elevated on day 2 in rats inoculated with S. aureus at 106, 107 or, 108 CFU regardless of implant status. Furthermore, AGP levels remained elevated on day 4 in rats inoculated with 107 or 108 CFUs of S. aureus. In contrast, significant increases in AGP were not detected in rats treated with vehicle or 103 CFU S. aureus. In the validation study, robust elevations in plasma AGP were detected on days 2 and 4 in S. aureus infected rats with or without propranolol. The AUC levels for propranolol on days 2 and 4 were 493 ± 44 h × ng/mL and 334 ± 54 h × ng/mL, respectively), whereas in noninfected rats that received only propranolol, levels were 38 ± 11 h × ng/mL and 76 ± 16. h × ng/mL, respectively. The high correlation between plasma propranolol and AGP demonstrated a direct impact of AGP on drug pharmacokinetics and pharmacodynamics. The results indicate that AGP is a reliable biomarker in this model of subclinical infection and should be considered for accurate data interpretation.