Hidden Plasmalogens Come Into View
Targeted nano-DESI tandem MSI separates low-abundance plasmalogens from more abundant near-isobaric lipids in mouse brain tissue.
Low-abundance plasmalogens can disappear beneath the signals of more abundant lipids with nearly identical masses, leaving their true tissue distributions unresolved. A workflow from Julia Laskin’s group at Purdue University uses targeted tandem mass spectrometry imaging to separate and map those hidden species in mouse brain tissue.
Rather than relying on precursor mass alone, the researchers used nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI), which extracts molecules directly from tissue through a flowing liquid junction. A targeted list of 165 multiple reaction monitoring transitions was then built from diagnostic fragments of sodium-adducted plasmalogens, LIPID MAPS entries, and data-dependent analysis of mouse brain extracts.
The resulting experiment resolved 38 plasmalogen species, including several absent from LIPID MAPS, and revealed distinct distributions across fiber tracts, the isocortex, and hippocampus. It also separated lipids that conventional MS1 imaging would merge into a single signal. At m/z 800.5, for example, a plasmalogen and a potassium-adducted phosphatidylcholine differed by only 0.1 millidalton yet showed clearly different spatial patterns. Distinguishing them by precursor mass would require resolving power above 8 million, whereas MRM separated them through diagnostic fragment ions.
By combining discovery-oriented bulk lipidomics with targeted imaging, the workflow preserves spatial information while reducing interference from higher-abundance isobars. The authors suggest that the same strategy could be adapted to other lipid classes and tissues where structurally distinct species overlap in mass.
Making Short Peptides Readable
A new workflow resolves a long-standing short-peptide problem by promoting stepwise fragmentation from the tagged N-terminus.
An N-terminal chemical tag has enabled accurate de novo sequencing of short peptides by directing tandem mass spectrometry fragmentation into a more complete and readable ion series.
Short peptides are difficult to sequence de novo because they generate few informative fragments, can undergo b-ion rearrangements, and may not match known database sequences. To address this, researchers at Kyushu University attached a coumarin-based tag, Me-Cou, to peptide N-termini before analysis by LC–trapped ion mobility–qTOF/MS.
The tag improved the retention of small peptides during liquid chromatography and promoted predictable fragmentation from the tagged N-terminus. Tests on model peptides containing four to ten amino acids produced complete b-ion ladders, providing the stepwise sequence information needed for de novo identification.
“Using our approach, the amino acid sequence of peptides can be determined step by step, starting from the tagged end, enabling highly accurate characterization of even the short ones,” said senior author Mitsuru Tanaka in a press release.
Across 86 dipeptide and 46 oligopeptide standards, conventional analysis correctly identified 67 of the 132 peptides and returned 32 incorrect assignments. Me-Cou-assisted sequencing correctly identified all 132 standards without misidentification after filtering candidates for complete b-ion coverage and precursor uniqueness.
Applied to casein peptone, the workflow reproducibly identified 328 peptides across triplicate analyses, compared with 262 using intact-peptide analysis. Gains were concentrated among peptides two to five residues long, with tripeptide identifications increasing approximately fivefold. Synthetic standards confirmed the selected candidate sequences, although derivatization efficiency was lower for oligopeptides than dipeptides.
The authors suggest that the controlled fragmentation could improve untargeted analysis of short endogenous peptides in protein hydrolysates, fermented foods, and biological fluids without restricting identification to existing sequence databases.
Redesigning the Fentanyl Vaccine
The preclinical vaccine challenges the idea that effective fentanyl immunization requires a close structural copy of the drug.
A fentanyl vaccine built around a chemically distinct scaffold has challenged the assumption that effective immunization requires a close structural copy of the target drug. Despite replacing fentanyl’s central piperidine ring, the vaccine generated broadly cross-reactive antibodies and preserved breathing in fentanyl-challenged mice.
“When we started testing this molecule as a vaccine component, we honestly didn’t know if it would work,” said first author Arran Stewart in a Scripps Research release. “The conventional wisdom says that to get the immune system to recognize fentanyl, you have to use something that looks like fentanyl. We were doing the opposite.”
The modified hapten was conjugated to a carrier protein, with MALDI–TOF mass spectrometry confirming loading comparable to a conventional fentanyl-derived vaccine. After four immunizations, both formulations produced sustained antibody titers and broad binding across a panel of fentanyl-class compounds, including carfentanil, acetylfentanyl, furanylfentanyl, and several fluorinated analogues. Binding remained minimal for morphine, oxycodone, methadone, naloxone, and naltrexone.
In fentanyl-challenged mice, the reconfigured vaccine shifted antinociceptive responses into substantially higher dose ranges and preserved ventilation near baseline, whereas control animals fell to roughly 30–40 percent of baseline ventilation. LC–MS measurements 15 minutes after dosing showed that brain fentanyl concentrations fell from 61.9 nanomolar in controls to 17.2 nanomolar in vaccinated mice, alongside increased concentrations in blood, consistent with antibody-mediated sequestration outside the brain.
“What this research shows us is that we don’t have to keep playing catch-up with every new synthetic designer drug that emerges,” said senior author Kim Janda. “By training the immune system to recognize the entire fentanyl class, not just individual structures, we can stay ahead of illicit drug traffickers.”
The vaccine remains preclinical, and broad analogue recognition was established primarily through binding assays rather than overdose challenges with each variant.
Portable Gas Profiling from a Single Sample
Combined miniRUEDI and GC-ECD extend portable dissolved-gas analysis from field measurements to stored gas samples.
Researchers have combined reusable passive samplers with miniRUEDI portable mass spectrometry and GC-ECD to measure major dissolved gases, noble gases, and transient tracers from a single small-volume sample.
The sampler transfers dissolved gases into a sealed gas phase before analysis, avoiding the need to transport water or extract gases in the laboratory. Gas-permeable silicone membranes allow the contents to equilibrate with the surrounding water, after which the valves are closed and the approximately 26 mL gas sample can be stored for later measurement.
The same sample was then interrogated by two complementary techniques. miniRUEDI portable mass spectrometry quantified nitrogen, oxygen, helium, argon, and krypton, before GC-ECD measured the lower-abundance anthropogenic tracers sulfur hexafluoride, CFC-12, and CFC-113. This sequential analysis extended portable MS beyond continuous field measurements to discrete samples while preserving enough material for trace-gas determination.
Equilibration was complete after approximately two days at 22 °C across the gases tested. Results from the passive samplers generally matched direct dissolved-gas measurements using the miniRUEDI membrane-inlet module, with argon the main exception at around 7 percent below the expected value. Repeated measurements produced standard deviations of approximately 0.15 percent for nitrogen and 0.8 percent for krypton, demonstrating sub-1 percent repeatability for the gases analyzed by miniRUEDI.
The authors highlight applications in groundwater dating, tracer-plume mapping, and studies of water transport and mixing, including age estimates for groundwater recharged within roughly the past 70 years using CFCs and sulfur hexafluoride.
(Mass) Spectacular and Strange
The Case of the Missing Curium
A lump of rock hauled from nearly five kilometers beneath the Pacific Ocean has preserved a record of events that took place far beyond Earth – including traces of a rare cosmic event more than 95 million years ago.
Ferromanganese crusts grow by only a few millimeters every million years, gradually collecting material from seawater and interstellar dust. In the new study, researchers divided one such crust into age-matched layers and used accelerator mass spectrometry to count individual atoms of iron-60, plutonium-244, and curium-247.
The iron-60 profile contained two distinct peaks, deposited around 2.4 million and 7.2 million years ago, consistent with nearby supernovae. Plutonium-244 told a different story: 77 interstellar atoms were distributed relatively evenly across layers spanning almost eight million years, suggesting a diffuse background left by a much older and rarer r-process event. The absence of interstellar curium-247, which is produced alongside plutonium-244 but decays much faster, pushed the estimated timing of that event back beyond 95 million years.
“Our results suggest that the plutonium originated from very rare cosmic explosions, such as those that would occur during the merger of two neutron stars or in extremely energetic supernovae,” said Anton Wallner in the team’s press release.
The team’s next target is the Moon, with lunar samples from NASA and the new HAMSTER facility intended to extend the search to other rare radionuclides.
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