Cross-Species Molecular Imaging of Bile Salts and Lipids in Liver: Identification of Molecular Structural Markers in Health and Disease

Abstract

The liver is the primary organ involved in handling of bile salts, a class of amphipathic molecules with signaling activities as well as desired and detrimental detergent actions. To allow in-depth investigation of functions of bile salts in healthy and diseased liver, the spatial distribution of bile salt species within the liver needs to be studied. Therefore, the aim of our study was to determine hepatic bile salt distribution and identify specific lipid markers that define the structural elements of the liver. Matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) was used to monitor the spatial distribution of bile salts and lipids in liver sections of rat, dog, and patients with unaffected and cholestatic parenchyma. MALDI-MSI in negative ion mode showed the local presence of a variety of bile salts, predominantly taurine-conjugates, as localized patches of varying sizes (representing the bile ducts) throughout the liver tissue. Specific molecular markers were identified for the connective tissue (phosphatidic acids, e.g., [PA (18:0_18:1)–H]−), the liver parenchyma (phosphatidylinositols, e.g., [PI (18:0_20:4)-H]−), and the bile ducts (hydroxylated-sulfatides, e.g., [ST–OH (18:1_24:0)-H]−). One of these sulfatides (at m/z 906.6339) was found to be uniquely localized in a thin lining on the inside of the bile duct, colocalized with cytokeratins, and encased luminal bile salts. A similar distribution of the aforementioned sulfatide was observed, albeit in constricted ductular structures, in the liver of a patient with a mild clinical phenotype of primary sclerosing cholangitis (PSC). In contrast, sulfatides were virtually absent in the liver of patients with PSC and a severe clinical phenotype, with (atypical) cholanoids (e.g., the bile alcohol 5-cyprinolsulfate) abundant in the extra-ductular space and glyco(cheno)deoxycholic acid-3-sulfate localized to fibrotic connective tissue. The latter two molecular species were able to discriminate between healthy liver tissue (n = 3) and tissue from PSC patients with a severe clinical phenotype (n = 3). In conclusion, the distinct structural elements of the mammalian liver are characterized by specific classes of lipids. We propose that (hydroxylated-)sulfatides are specific molecular markers of the bile duct.

Metabolites and Lipids Associated with Fetal Swine Anatomy via Desorption Electrospray Ionization – Mass Spectrometry Imaging

“…PI(34:1), PI(38:4) and PA(36:2) were detected in the pig fetuses liver and also were reported in pig oocytes by DESI-MS 23,28 . In addition, PI(38:4) and PA(36:2) are considered biomarkers of connective tissue and hepatic parenchyma respectively, being identified in dogs and human liver by MALDI-MS imaging 58 .…”

Evaluation of lipid coverage and high spatial resolution MALDI-imaging capabilities of oversampling combined with laser post-ionisation

“…Healthy rat liver was obtained from Maastricht University in accordance with protocols approved by the Animal Care and Use Committee (DEC number 2014-120) and was from the same animal used in a recent study [29]. Rats were provided ad libitum access to water and regular chow.…”

MALDI-Mass Spectrometry Imaging to Investigate Lipid and Bile Acid Modifications Caused by Lentil Extract Used as a Potential Hypocholesterolemic Treatment

“…Additionally, we speculated that the gut–brain connection and the hypercholesterolemia altered the expression of lipids and cholesterol levels in the brain. Here, we employed the matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to analyze organs harvested from the same animals sacrificed in the paper from Micioni Di Bonaventura et al [5] (Figure 1), and investigate whether LE food supplementation affects cholesterol and lipid levels of the brain, intestines, and liver, and bile acid levels in the intestines and liver [14–17]. MALDI-MSI has been proven to be an extremely valuable tool able to study the spatial distribution of a wide variety of analytes (e.g., lipid, protein, peptide, metabolites) with high sensitivity [18–20].…”