Gas chromatography/mass spectrometry measurement of xenon in gas‐loaded liposomes for neuroprotective applications

Abstract

Rationale We have produced a liposomal formulation of xenon (Xe-ELIP) as a neuroprotectant for inhibition of brain damage in stroke patients. This mandates development of a reliable assay to measure the amount of dissolved xenon released from Xe-ELIP in water and blood samples. Methods Gas chromatography-Mass Spectrometry (GC-MS) was used to quantify xenon gas released into the headspace of vials containing Xe-ELIP samples in water or blood. In order to determine blood concentration of xenon in vivo after Xe-ELIP administration, 6 mg Xe-ELIP lipid was infused intravenously into rats. Blood samples were drawn directly from a catheterized right carotid artery. After introduction of the samples, each vial was allowed to equilibrate to 37° C in a water bath, followed by 20 minutes of sonication prior to headspace sampling. Xenon concentrations were calculated from a gas dose-response curve and normalized using the published xenon water-gas solubility coefficient. Results The mean corrected percent of xenon from Xe-ELIP released into water was 3.87 ± 0.56% (SD, n = 8), corresponding to 19.3 ± 2.8 μl/mg lipid, which is consistent with previous independent Xe-ELIP measurements. The corresponding xenon content of Xe-ELIP in rat blood was 23.38 ± 7.36 μl/mg lipid (n = 8). Mean rat blood xenon concentration after IV administration of Xe-ELIP was 14 ± 10 μM, which is approximately 15% of the estimated neuroprotective level. Conclusions Using this approach, we have established a reproducible method for measuring dissolved xenon in fluids. These measurements have established that neuroprotective effects can be elicited by less than 20% of the calculated neuroprotective xenon blood concentration. More work will have to be done to establish the protective xenon pharmacokinetic range.

Characterization and Imaging of Lipid-Shelled Microbubbles for Ultrasound-Triggered Release of Xenon

“…The GC/MS measurement underestimation may have been due to loss of gas during sample transfer and injection. These observations are consistent with a previous study [38], which reported that GC/MS measurements of Xe-saturated water were able to measure only 64% of the total Xe dose (volume of gas released into the headspace plus that retained in the Xe-saturated solution).…”

“…Xe-ELIP have also been shown to adhere to damaged endothelium, which could improve targeting of Xe to ischemic areas [17]. The total Xe dose in Xe-OFP-MB per milliliter of solution was 1.7-fold lower than in Xe-ELIP [17,38]. The lipid concentration per milliliter of solution in Xe-OFP-MB and Xe-ELIP was 1 and 10 mg/ml, after formation (MB) or reconstitution (ELIP), respectively.…”

“…The quantification of Xe and OFP dose in the microbubbles was performed using GC/MS [38]. The Xe-MB and Xe-OFP-MB vials were shipped on ice overnight to the University of Texas Health Science Center at Houston, and GC/MS was performed on the second day after adding xenon or xenon and OFP gas to the vials through the septum.…”

Oral delivery of xenon for cardiovascular protection

“…Xe concentration was measured using GC-MS (HP 6890-HP 5973A) interfaced with a G1512 controller, a GC injector (tower and tray), and an Edwards E2M2 rough pump (Agilent Technologies, Santa Clara, CA, USA)] as previously described 37 .…”

“…Animals were fed with Xe-enriched solution (200 µl administrated by gavage), and blood was taken from the heart 10 minutes after administration of Xe-enriched solution. Xe concentration was measured by GC-MS as previously described 37 .…”