Abstract
HIV protease inhibitors are an important component of highly active antiretroviral therapy used to treat pregnant women infected with HIV. They have a low placental transfer and are highly plasma protein bound. This study was carried out to determine the unbound fraction of lopinavir in cord blood, and to characterize the binding of lopinavir to α1-acid glycoprotein (AAG) and human serum albumin (HSA), and displacement by ritonavir. Serum was obtained from cord blood from placentas obtained after cesarean section of healthy, non-HIV-infected women (n = 4). The unbound fraction of lopinavir in serum obtained from this cord blood was 0.022 ± 0.011%. The unbound fraction of lopinavir in separately obtained maternal serum samples (n = 4) was 0.89 ± 0.12%, which was not significantly different from that observed with cord serum samples. Varying concentrations of lopinavir, AAG, and HSA in buffer solutions were then used to characterize the lopinavir binding. The data were fit to obtain the number of binding sites (N) and equilibrium dissociation constant (KD). Binding of lopinavir to AAG (7–23 μM) was saturable with KD of 5.0 ± 1.1 μM and N of 1.2 ± 0.2. At low HSA concentrations (15–152 μM), lopinavir binding KD was 24.3 ± 8.7 μM and N was 1.1 ± 0.4; however, at 758 μM, lopinavir binding was essentially unsaturable. Lopinavir binding to AAG and HSA was not sensitive to ritonavir, and, thus, efforts to enhance fetal exposure to lopinavir should be focused on other issues such as efflux transporters.
Footnotes
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This work was supported in part by the National Institutes of Health National Center on Minority Health and Health Disparities [Grant 1P60-MD002256]; the Higher Education Equipment Trust Fund of Virginia; and the VCU School of Pharmacy, Department of Pharmaceutics.
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This work was previously presented as follows: Gulati A, Boudinot FD, and Gerk PM (2008) Binding of lopinavir to human serum albumin and alpha-1 acid glycoprotein. Annual Meeting of the American Association of Pharmaceutical Scientists; 2008 Nov 16–20; Atlanta, GA. Virginia Commonwealth University, Richmond, VA.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.109.026708.
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ABBREVIATIONS: AAG, α1-acid glycoprotein; HSA, human serum albumin; PBS, phosphate-buffered saline.
- Accepted May 12, 2009.
- Received January 13, 2009.
- The American Society for Pharmacology and Experimental Therapeutics
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