Multiplexed Targeted Spatial Mass Spectrometry Imaging Assays to monitor lipids and NAD ⁺ metabolites in male CD38 knockout mice exhibiting improved metabolism

Mass spectrometry imaging (MSI) is a rapidly advancing technology that provides mapping of the spatial molecular landscape of tissues for a variety of analytes. Matrix-assisted laser desorption/ionization (MALDI)-MSI is commonly employed, however, confident in situ identification and accurate quantification of analytes remain challenging. We present a novel imaging methodology combining trapped ion mobility spectrometry (TIMS)-based parallel accumulation-serial fragmentation (PASEF) with MALDI ionization for targeted imaging parallel reaction monitoring (iprm-PASEF). We investigated the spatial distribution of lipids and metabolites in liver tissues from male wild-type and CD38 knockout mice (CD38 ^-/- ). CD38, an enzyme involved in nicotinamide adenine dinucleotide (NAD⁺) metabolism, significantly influences liver metabolic function and contributes to age-related NAD⁺ decline. Although CD38 deletion previously was linked to improved metabolic phenotypes, the underlying spatial metabolic mechanisms are poorly understood. The spatial iprm-PASEF workflow enabled confident identification and differentiation of lipid isomers at the MS2 fragment ion level and confirmed increased NAD ⁺ and decreased adenosine diphosphate ribose (ADPR), a by-product of NAD ⁺ hydrolysis, in CD38 ^-/- livers. This approach provided confident, specific, and robust MS2-based identification and quantification of fragment ions in spatial MSI experiments. Additionally, the innovative iprm-PASEF opens unprecedented opportunities for spatial metabolomics and lipidomics, offering spatially resolved insights into molecular mechanisms.