Cervical and systemic concentrations of long acting hormonal contraceptive (LARC) progestins depend on delivery method: Implications for the study of HIV transmission.

Progestin-only long-acting reversible contraceptives (LARCs) are increasingly popular among women seeking contraception; however, recent epidemiological studies suggest that systemically administered medroxyprogesterone acetate (MPA) may increase HIV acquisition. In order to determine the exact mechanisms underlying increases in transmission specific to MPA use and to test safer, alternative contraceptive progestin types and delivery methods, in vitro modeling studies must be performed. To achieve this, it is imperative that accurate hormone concentrations be utilized when modeling progestin-mediated outcomes, as the down-stream effects are dose-dependent. The local concentrations of progestins to which the lower female genital tract tissues are exposed after initiation of LARCs are unknown, but they likely differ from peripheral concentrations, dependent upon the progestin type and delivery method. Here, we measured in vivo endocervical and plasma concentrations of (1) systemically-delivered depo MPA (DMPA), (2) levonorgestrel (LNG) delivered via intrauterine system (IUS) and (3) etonogestrel (ETG) delivered via vaginal ring in women who recently initiated contraception treatment. Levels of ETG and LNG in cervical secretions were 100-200 fold higher than plasma levels. In contrast, measurable MPA levels were approximately 10-fold higher in plasma compared to cervical secretions. These results will inform the design of accurate in vitro studies on the influence of progestins on epithelial cells, tissue explants, and peripheral blood cells, to be able to better predict in vivo outcomes. Subsequent observations will aid in determining how MPA might influence HIV acquisition and may facilitate identification of optimal progestin-containing LARC alternatives for women at high risk for HIV infection.

Measurement of arginine metabolites: regulators of nitric oxide metabolism.

Arginine is the substrate for nitric oxide synthases (NOS), and arginine availability regulates the production of nitric oxide. Through the activity of methyltransferases, arginine can be methylated to form monomethylarginine (NMMA), asymmetrical dimethylarginine (ADMA), and symmetrical dimethylarginine (SDMA). NMMA and ADMA directly inhibit NOS, whereas SDMA inhibits the cellular import of arginine through the cationic amino acid transporter. Increased levels of methylarginine compounds have been associated with many diseases including atherosclerosis, renal failure, pulmonary hypertension, and preeclampsia. Previous HPLC methods to measure these molecules rely on derivatization with ortho-phthalaldehyde, which is unstable and requires immediate pre- or post-column reactions. We have identified a new fluorometric agent that is stable for at least 1 week and provides chromatographic properties that facilitate separation of these chemically similar compounds by reverse phase chromatography.