Versican Secreted by Cancer-Associated Fibroblasts is a Poor Prognostic Factor in Hepatocellular Carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is highly recurrent. Cancer-associated fibroblasts (CAFs), a major component of the tumor microenvironment, promote malignancy; however, the mechanisms underlying their actions are obscure. We aimed to identify CAF-specific proteins in HCC and determine whether they could be potential therapeutic targets. METHODS: Using comprehensive proteomic analysis of CAFs and noncancerous fibroblasts (NFs) primary-cultured from resected HCC specimens from the same patients, CAF-specific proteins were identified. Immunohistochemistry for versican (VCAN) was performed on cancerous tissues obtained from 239 patients with HCC. Conditioned medium from CAFs transfected with siRNA for VCAN was analyzed in vitro. RESULTS: CAFs significantly promoted HCC cell proliferation, migration, and invasion (p < 0.01, 0.01, and 0.01, respectively) compared with NFs. VCAN was upregulated in CAFs, and its stromal level correlated with poor differentiation (p = 0.009) and positive vascular invasion (p = 0.003). Stromal VCAN level was also associated with significantly lower overall (p = 0.002) and relapse-free (p < 0.001) survival rates. It also independently predicted prognosis and recurrence. VCAN-knockdown CAFs significantly suppressed HCC cell migration and invasion compared with negative control. CONCLUSIONS: VCAN secreted from CAFs promoted malignant transformation of HCC cells and has potential as a new therapeutic target in HCC.

A mouse model of short-term, diet-induced fatty liver with abnormal cardiolipin remodeling via downregulated Tafazzin gene expression.

BACKGROUND: Cardiolipin (CL) helps maintain mitochondrial structure and function. Here we investigated whether a high carbohydrate diet (HCD) fed to mice for a short period (5 days) could modulate the CL level, including that of monolysoCL (MLCL) in the liver. RESULTS: Total CL in the HCD group was 22% lower than that in the normal chow diet (NCD) group (P < 0.05). The CL72:8 level strikingly decreased by 93% (P < 0.0001), whereas total nascent CLs (CLs other than CL72:8) increased (P < 0.01) in the HCD group. The total MLCL in the HCD group increased by 2.4-fold compared with that in the NCD group (P < 0.05). Tafazzin expression in the HCD group was significantly downregulated compared with that in the NCD group (P < 0.05). A strong positive correlation between nascent CL and total MLCL (r = 0.955, P < 0.0001), and a negative correlation between MLCL and Tafazzin expression (r = -0.593, P = 0.0883) were observed. CONCLUSION: A HCD modulated the fatty acid composition of CL and MLCL via Tafazzin in the liver, which could lead to mitochondrial dysfunction. This model may be useful for elucidating the relationship between fatty liver and mitochondrial dysfunction. © 2021 Society of Chemical Industry.

Identification of Coiled-Coil Domain-Containing Protein 180 and Leucine-Rich Repeat-Containing Protein 4 as Potential Immunohistochemical Markers for Liposarcoma Based on Proteomic Analysis Using Formalin-Fixed, Paraffin-Embedded Tissue.

Recent technical improvements in both mass spectrometry and protein extraction have made it possible to use formalin-fixed, paraffin-embedded (FFPE) tissues for proteome analysis. In this study, comparable proteome analysis of FFPE tissues revealed multiple candidate marker molecules for differentiating atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) from lipoma. A total of 181 unique proteins were identified for ALT/WDL. Of the identified proteins, coiled-coil domain-containing protein 180 (CCDC180) and leucine-rich repeat-containing protein 4 (LRRC4) were studied as candidate markers of ALT/WDL. CCDC180 and LRRC4 immunohistochemistry clearly stained tumor cells of ALT/WDL and dedifferentiated liposarcoma and could differentiate them from lipoma with high accuracy. Cell biological methods were used to further examine the expression of the candidate marker molecules in liposarcoma cells. In liposarcoma cells, knockdown of CCDC180 and LRRC4 inhibited cell proliferation. CCDC180 inhibited cell migration, invasion, and apoptosis resistance in WDL cells. Adipogenic differentiation suppressed the expression of CCDC180 and LRRC4 in WDL cells. These results indicated that LRRC4 and CCDC180 are novel immunohistochemical markers for differentiating ALT/WDLs. Their expression was associated with adipocyte differentiation and contributed to malignant potentials of WDL cells. Proteome analysis using a standard stock of FFPE tissues can reveal novel biomarkers for various diseases, which contributes to the progress of molecular pathology.

Dietary salmon milt extracts attenuate hepatosteatosis and liver dysfunction in diet-induced fatty liver model.

BACKGROUND: Dietary nucleotides have several reported beneficial effects. Here, we report on a proteomic analysis of the effect of dietary nucleotides-rich salmon milt extract (SME) on the liver in a diet-induced fatty liver model. RESULTS: Young male normal ddY mice were fed a normal chow diet, high carbohydrate diet (HCD), HCD containing 1% SME, or HCD containing 10% SME for 5 days following by a 2-day fast. Increased serum alanine transferase and aspartate transferase activities were observed in the HCD group and were significantly attenuated in the SME groups (P < 0.05). Hepatic steatosis was observed in all the HCD groups. Hepatic expression of Tnfα was significantly suppressed in the 10% SME group (P < 0.05). Comprehensive proteomic analysis of the liver in the SME groups revealed an increase in the levels of major proteins involved in mitochondrial bioenergetics, including peroxisome proliferator-activated receptor gamma co-activator 1 alpha, mitochondrial thioredoxin, cardiolipin synthase, peroxisome proliferator-activated receptor alpha, and carnitine palmitoyltransferase I. CONCLUSION: Dietary SME improved liver function in the diet-induced fatty liver model. Activation of mitochondrial biogenetic function might be involved in this process. © 2018 Society of Chemical Industry.

Post-reperfusion hydrogen gas treatment ameliorates ischemia reperfusion injury in rat livers from donors after cardiac death: a preliminary study.

BACKGROUND AND PURPOSE: We reported previously that hydrogen gas (H2) reduced hepatic ischemia and reperfusion injury (IRI) after prolonged cold storage (CS) of livers retrieved from heart-beating donors. The present study was designed to assess whether H2 reduced hepatic IRI during donation of a cardiac death (DCD) graft with subsequent CS. METHODS: Rat livers were harvested after 30-min cardiac arrest and stored for 4 h in University of Wisconsin solution. The graft was reperfused with oxygenated buffer, with or without H2 (H2 or NT groups, respectively), at 37° for 90 min on isolated perfused rat liver apparatus. RESULTS: In the NT group, liver enzyme leakage, apoptosis, necrosis, energy depletion, redox status, impaired microcirculation, and bile production were indicative of severe IRI, whereas in the H2 group these impairments were significantly suppressed. The phosphorylation of cytoplasmic MKK4 and JNK were enhanced in the NT group and suppressed in the H2 group. NFkB-p65 and c-Fos in the nucleus were unexpectedly unchanged by IRI regardless of H2 treatment, indicating the absence of inflammation in this model. CONCLUSION: H2 was observed to ameliorate IRI in the DCD liver by maintaining microcirculation, mitochondrial functions, and redox status, as well as suppressing the cytoplasmic MKK4-JNK-mediated cellular death pathway.

Different desmin peptides are distinctly deposited in cytoplasmic aggregations and cytoplasm of desmin-related cardiomyopathy patients.

Desmin-related cardiomyopathy is a heterogeneous group of myofibrillar myopathies characterized by aggregates of desmin and related proteins in myocytes. It has been debated how the expression and protein structure are altered in the aggregates and other parts of myocytes in patients. To address this question, we investigated the proteome quantification as well as localization in formalin-fixed and paraffin-embedded specimens of the heart of patients by imaging mass spectrometry and liquid chromatography-mass spectrometry analyses. Fifteen tryptic peptide signals were enriched in the desmin-related cardiomyopathy myocardium, twelve of which were identified as desmin peptides with 14.3- to 27.3-fold increase compared to normal hearts. High-intensity signals at m/z 1032.5 and 1002.5, which were desmin peptides 59-70 at the head portion and 213-222 at the 1B domain, were with infrequent colocalization distributed not only in desmin-positive intracytoplasmic aggregates but also in histologically normal cytoplasm, indicating that desmin protein is fragmented and different types of naturally-occurring truncated proteins ectopically assemble throughout the heart of patients. Thus, in addition to conventional histological identification of protein aggregates, specific desmin peptides show a marked difference in quantity and localization in a tissue section of desmin-related cardiomyopathy and differentiate from other cardiomyopathies. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

Selective improvement of peptides imaging on tissue by supercritical fluid wash of lipids for matrix-assisted laser desorption/ionization mass spectrometry.

There is a high analytical demand for improving the detection sensitivity for various peptides in matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) because exhaustive distribution analyses of various peptides could help to reveal the function of peptides in vivo. To improve the sensitivity of peptide detection, we used supercritical fluid of CO2 (scCO2) as washing solvent for a pretreatment to remove lipids. We evaluated whether our wash method using scCO2 with an entrainer improved the detection of peptides and suppressed lipid detection in MALDI-IMS. Our analysis revealed that the signal intensities of peptides such as m/z 3339.8, 3530.9, 4233.3, 4936.7, and 4963.7 were increased in scCO2-washed samples. The greatest improvement in the signal-to-noise ratio (S/N) was found at m/z 4963.7, which was identified as thymosin ß4, with the S/N reaching almost 190-fold higher than the control. Additionally, all of the improved signals were associated with the morphologic structure. Our method allows us to analyze the distribution of molecules, especially in the region of m/z 3000-5200. For these improvements, the polarity difference between scCO2 and the matrix solution used was considered as a key. A wider variety of molecules can be analyzed in the future due to this improvement of the detection sensitivity by optimizing the polarity of scCO2 with various entrainers. Graphical Abstract Mass spectra of m/z 4900-5000 obtained from a scCO2-washed tissue (upper, blue) and a control tissue (lower, red). Ion distribution of the signals at m/z 4936.7 and m/z 4963.7 specifically ditected from scCO2-washed samples.

Overexpression of Lysophosphatidylcholine Acyltransferase 1 and Concomitant Lipid Alterations in Gastric Cancer.

BACKGROUND: The involvement of lipids in carcinogenic and developmental processes has been reported in some malignancies, but their roles in gastric cancer remain to be analyzed. In this study, we compared the lipid content of gastric cancer tissue and adjacent nonneoplastic mucosa using imaging mass spectrometry. METHODS: Mass spectra were acquired from 12 sections of human gastric cancer tissue and adjacent nonneoplastic mucosa using a matrix-assisted laser desorption-ionization time-of-flight tandem mass spectrometry type mass spectrometer equipped with a 355 nm Nd:YAG laser. Protein expression of lysophosphatidylcholine acyltransferase 1 (LPCAT1), which converts lysophosphatidylcholine (LPC) to phosphatidylcholine (PC) in the presence of acyl-CoA in Lands' cycle, was immunohistochemically analyzed in 182 gastric cancer specimens. RESULTS: The averaged mass spectra from the cancer tissue and nonneoplastic mucosa were identical. Most of the signals that differed between cancer tissue and nonneoplastic mucosa corresponded to phospholipids, the majority of which were PC and LPC. Two signals, m/z 798.5 and 496.3, were higher and lower, respectively, in cancer tissues, predominantly in differentiated adenocarcinoma. A database search enabled identification of the ions at m/z 798.5 and m/z 496.3 as potassium-adducted PC (16:0/18:1) and proton-adducted LPC (16:0), respectively. Immunohistochemical analysis revealed that LPCAT1 was highly expressed in cancer lesions compared to nonneoplastic mucosa, predominantly in differentiated adenocarcinoma. LPCAT1 expression levels correlated positively with tumor differentiation and negatively with tumor depth, lymph node metastasis, and tumor stage. CONCLUSIONS: Overexpressed LPCAT1 protein in gastric mucosa appears to play important roles in the tumorigenic process of gastric cancer by converting LPC to PC.

Imaging Mass Spectrometry Reveals a Unique Distribution of Triglycerides in the Abdominal Aortic Aneurysmal Wall.

The pathophysiology underlying abdominal aortic aneurysms (AAAs) remains unknown. In this study, we applied imaging mass spectrometry (IMS) to analyze the pathophysiology of the aneurysmal wall. Comparisons were performed between the tissue samples from the neck and the sac of the AAA, at a single time point, in 30 patients who underwent elective surgery of their AAAs. The localization of each lipid molecule in the aortic wall was assessed by IMS. Histopathological examination and IMS revealed a characteristic distribution of triglycerides (TGs) specifically in the aneurismal adventitia of the sac. This characteristic TG distribution was derived from an ectopic appearance of adipocytes in the adventitia. Furthermore, ectopic adipocyte accumulation in the aortic wall leads to the loss of the collagen fiber network subsequent to the wall rupture. The underlying mechanism of adipocyte accumulation involves the presence of adipose-derived stem cells (ADSCs) in the aneurismal adventitia and the expression of peroxisome proliferator-activated receptor gamma 2, a master regulator of adipocyte differentiation by some ADSCs. This study reveals new, previously overlooked aspects of AAA pathology.

Direct profiling of the phospholipid composition of adult Caenorhabditis elegans using whole-body imaging mass spectrometry.

A protocol for the direct analysis of the phospholipid composition in the whole body of adult soil nematode, Caenorhabditis elegans (C. elegans), was developed, which combined freeze-cracking of the exoskeletal cuticle and matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS). Biomolecules in the m/z range from 700 to 900 were more effectively detected in the freeze-cracked than from simple frozen adult nematode bodies. Different distribution of biomolecules was observed in a nematode body when the matrix was applied with a sublimation deposition method. The whole-body IMS technique was applied on genetically deficient mutant C. elegans to combine whole-body lipidomics and genetics, by comparing the fatty acid compositions, especially of the phosphatidylcholine (PC) species, between the wild-type and fat-1 mutants, which lack the gene encoding an n-3 fatty acid desaturase. A significant reduction of PC(20:5/20:5) and PC(20:4/20:5) and a marked increase of PC(20:4/20:4), PC(20:3/20:4), and PC(20:3/20:3) were detected in the fat-1 mutants in positive ion mode. In addition, phospholipid compositions other than PCs were analyzed in negative ion mode. A loss of a possible phosphatidylinositol (PI) with 18:0/20:5 and a compensative accumulation of putative PI(18:0/20:4) were detected in the fat-1 mutants. In conclusion, the whole-body MALDI-IMS technique is useful for the profiling of multiple biomolecules in C. elegans in both intra- and inter-individual levels.

Matrix-assisted laser desorption/ionization imaging mass spectrometry revealed traces of dental problem associated with dental structure.

Periodontal disease is a serious dental problem because it does not heal naturally and leads to tooth loss. In periodontal disease, inflammation at periodontal tissue is thought as predominant, and its effect against tooth itself remains unclear. In this study, we applied matrix-assisted laser desorption/ionization imaging mass spectrometry (IMS) to teeth for the first time. By comparing anatomical structure of tooth affected with periodontal disease with normal ones, we analyzed traces of the disease on tooth. We found signals characteristic of enamel, dentin, and dental pulp, respectively, in mass spectra obtained from normal teeth. Ion images reconstructed using these signals showed anatomical structures of the tooth clearly. Next, we performed IMS upon teeth of periodontal disease. Overall characteristic of the mass spectrum appeared similar to normal ones. However, ion images reconstructed using signals from the tooth of periodontal disease revealed loss of periodontal ligament visualized together with dental pulp in normal teeth. Moreover, ion image clearly depicted an accumulation of signal at m/z 496.3 at root surface. Such an accumulation that cannot be examined only from mass spectrum was revealed by utilization of IMS. Recent studies about inflammation revealed that the signal at m/z 496.3 reflects lyso-phosphatidylcholine (LPC). Infiltration of the signal is statistically significant, and its intensity profile exhibited the influence has reached deeply into the tooth. This suggests that influence of periodontal disease is not only inflammation of periodontal tissue but also infiltration of LPC to root surface, and therefore, anti-inflammatory treatment is required besides conventional treatments.

Imaging mass spectrometry distinguished the cancer and stromal regions of oral squamous cell carcinoma by visualizing phosphatidylcholine (16:0/16:1) and phosphatidylcholine (18:1/20:4).

Most oral cancers are oral squamous cell carcinoma (OSCC). The anatomical features of OSCC have been histochemically evaluated with hematoxylin and eosin. However, the border between the cancer and stromal regions is unclear and large portions of the cancer and stromal regions are resected in surgery. To reduce the resected area and maintain oral function, a new method of diagnosis is needed. In this study, we tried to clearly distinguish the border on the basis of biomolecule distributions visualized by imaging mass spectrometry (IMS). In the IMS dataset, eleven signals were significantly different in intensity (p < 0.01) between the cancer and stromal regions. Two signals at m/z 770.5 and m/z 846.6 were distributed in each region, and a clear border was revealed. Tandem mass spectrometric (MS/MS) analysis identified these signals as phosphatidylcholine (PC) (16:0/16:1) at m/z 770.5 in the cancer region and PC (18:1/20:4) at m/z 846.6 in the stromal region. Moreover, the distribution of PC species containing arachidonic acid in the stromal region suggests that lymphocytes accumulated in response to the inflammation caused by cancer invasion. In conclusion, the cancer and stromal regions of OSCCs were clearly distinguished by use of these PC species and IMS analysis, and this molecular identification can provide important information to elucidate the mechanism of cancer invasion.

Increased phosphatidylcholine (16:0/16:0) in the folliculus lymphaticus of Warthin tumor.

Warthin tumor (War-T), the second most common benign salivary gland tumor, consists mainly of neoplastic epithelium and lymphoid stroma. Some proteins and genes thought to be involved in War-T were evaluated by molecular biology and immunology. However, lipids as an important component of many tumor cells have not been well studied in War-T. To elucidate the molecular biology and pathogenesis of War-T, we investigated the visualized distribution of phosphatidylcholines (PCs) by imaging mass spectrometry (IMS). In our IMS analysis of a typical case, 10 signals were significantly different in intensity (p < 0.01) between the War-T and non-tumor (Non-T) regions. Five specific PCs were frequently found in the War-T regions of all of the samples: [PC (16:0/16:0) + K](+) (m/z 772.5), [PC (16:0/20:4) + K](+) (m/z 820.5), [PC (16:0/20:3) + K](+) (m/z 822.5), [PC (18:2/20:4) + K](+) (m/z 844.5), and [PC (18:0/20:5) + K](+) (m/z 846.5). PC (16:0/16:0) was increased specifically in the folliculus lymphaticus of War-T lymphoid stroma, suggesting a different metabolism. Localization of PC (16:0/16:0) might reflect inflammation activity participating in the pathogenesis of War-T. Thus, our IMS analysis revealed the profile of PCs specific to the War-T region. The molecules identified in our study provide important information for further studies of War-T pathogenesis.

Accumulated phosphatidylcholine (16:0/16:1) in human colorectal cancer; possible involvement of LPCAT4.

The identification of cancer biomarkers is critical for target-linked cancer therapy. The overall level of phosphatidylcholine (PC) is elevated in colorectal cancer (CRC). To investigate which species of PC is overexpressed in colorectal cancer, an imaging mass spectrometry was performed using a panel of non-neoplastic mucosal and CRC tissues. In the present study, we identified a novel biomarker, PC(16:0/16:1), in CRC using imaging mass spectrometry. Specifically, elevated levels of PC(16:0/16:1) expression were observed in the more advanced stage of CRC. Our data further showed that PC(16:0/16:1) was specifically localized in the cancer region when examined using imaging mass spectrometry. Notably, because the ratio of PC(16:0/16:1) to lyso-PC(16:0) was higher in CRC, we postulated that lyso-PC acyltransferase (LPCAT) activity is elevated in CRC. In an in vitro analysis, we showed that LPCAT4 is involved in the deregulation of PC(16:0/16:1) in CRC. In an immunohistochemical analysis, LPCAT4 was shown to be overexpressed in CRC. These data indicate the potential usefulness of PC(16:0/16:1) for the clinical diagnosis of CRC and implicate LPCAT4 in the elevated expression of PC(16:0/16:1) in CRC.

Lysophosphatidylcholine acyltransferase 1 altered phospholipid composition and regulated hepatoma progression.

BACKGROUND & AIMS: Several lipid synthesis pathways play important roles in the development and progression of hepatocellular carcinoma (HCC), although the precise molecular mechanisms remain to be elucidated. Here, we show the relationship between HCC progression and alteration of phospholipid composition regulated by lysophosphatidylcholine acyltransferase (LPCAT). METHODS: Molecular lipidomic screening was performed by imaging mass spectrometry (IMS) in 37 resected HCC specimens. RT-PCR and Western blotting were carried out to examine the mRNA and protein levels of LPCATs, which catalyze the conversion of lysophosphatidylcholine (LPC) into phosphatidylcholine (PC) and have substrate specificity for some kinds of fatty acids. We examined the effect of LPCAT1 overexpression or knockdown on cell proliferation, migration, and invasion in HCC cell lines. RESULTS: IMS revealed the increase of PC species with palmitoleic acid or oleic acid at the sn-2-position and the reduction of LPC with palmitic acid at the sn-1-position in HCC tissues. mRNA and protein of LPCAT1, responsible for LPC to PC conversion, were more abundant in HCCs than in the surrounding parenchyma. In cell line experiments, LPCAT1 overexpression enriched PCs observed in IMS and promoted cell proliferation, migration, and invasion. LPCAT1 knockdown did viceversa. CONCLUSIONS: Enrichment or depletion of some specific PCs, was found in HCC by IMS. Alteration of phospholipid composition in HCC would affect tumor character. LPCAT1 modulates phospholipid composition to create favorable conditions to HCC cells. LPCAT1 is a potent target molecule to inhibit HCC progression.

Visualization of phosphatidylcholine (16:0/16:0) in type II alveolar epithelial cells in the human lung using imaging mass spectrometry.

Imaging mass spectrometry (MS) is an emerging technique that can detect numerous biomolecular distributions in a non-targeting manner. In the present study, we applied a mass imaging modality, mass microscopy, to human lung tissue and identified several molecules including surfactant constituents in a specific structure of the lung alveoli. Four peaks were identified using imaging MS, and the ion at m/z 772.5, in particular, was localized at some spots in the alveolar walls. Using an MS/MS analysis, the ion was identified as phosphatidylcholine (PC)(16:0/16:0), which is the main component of lung surfactant. In a larger magnification of the lung specimen, PC (16:0/16:0) was distributed in a mottled fashion in a section of the lung. Importantly, the distribution of PC (16:0/16:0) was identical to that of anti-SLC34A2 antibody immunoreactivity, which is known to be a specific marker of type II alveolar epithelial cells, in the same section. Our experience suggests that imaging MS has excellent potential in human pathology research.

Warm Ischemia Induces Spatiotemporal Changes in Lysophosphatidylinositol That Affect Post-Reperfusion Injury in Normal and Steatotic Rat Livers.

Warm ischemia-reperfusion injury is a prognostic factor for hepatectomy and liver transplantation. However, its underlying molecular mechanisms are unknown. This study aimed to elucidate these mechanisms and identify the predictive markers of post-reperfusion injury. Rats with normal livers were subjected to 70% hepatic warm ischemia for 15, 30, or 90 min, while those with steatotic livers were subjected to 70% hepatic warm ischemia for only 30 min. The liver and blood were sampled at the end of ischemia and 1, 6, and 24 h after reperfusion. The serum alanine aminotransferase (ALT) activity, Suzuki injury scores, and lipid peroxidation (LPO) products were evaluated. The ALT activity and Suzuki scores increased with ischemic duration and peaked at 1 and 6 h after reperfusion, respectively. Steatotic livers subjected to 30 min ischemia and normal livers subjected to 90 min ischemia showed comparable injury. A similar trend was observed for LPO products. Imaging mass spectrometry of normal livers revealed an increase in lysophosphatidylinositol (LPI (18:0)) and a concomitant decrease in phosphatidylinositol (PI (18:0/20:4)) in Zone 1 (central venous region) with increasing ischemic duration; they returned to their basal values after reperfusion. Similar changes were observed in steatotic livers. Hepatic warm ischemia time-dependent acceleration of PI (18:0/20:4) to LPI (18:0) conversion occurs initially in Zone 1 and is more pronounced in fatty livers. Thus, the LPI (18:0)/PI (18:0/20:4) ratio is a potential predictor of post-reperfusion injury.

Imaging mass spectrometry for lipidomics.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful tool that enables the simultaneous detection and identification of biomolecules in analytes. MALDI-imaging mass spectrometry (MALDI-IMS) is a two-dimensional MALDI-MS technique used to visualize the spatial distribution of biomolecules without extraction, purification, separation, or labeling of biological samples. This technique can reveal the distribution of hundreds of ion signals in a single measurement and also helps in understanding the cellular profile of the biological system. MALDI-IMS has already revealed the characteristic distribution of several kinds of lipids in various tissues. The versatility of MALDI-IMS has opened a new frontier in several fields, especially in lipidomics. In this review, we describe the methodology and applications of MALDI-IMS to biological samples.

Visualization of dynamic change in contraction-induced lipid composition in mouse skeletal muscle by matrix-assisted laser desorption/ionization imaging mass spectrometry.

Lipids in skeletal muscle play a fundamental role both in normal muscle metabolism and in disease states. Skeletal muscle lipid accumulation is associated with several chronic metabolic disorders, including obesity, insulin resistance, and type 2 diabetes. However, it is poorly understood whether the lipid composition of skeletal muscle changes by contraction, due to the complexity of lipid molecular species. In this study, we used matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) to investigate changes in skeletal muscle lipid composition induced by contraction. We successfully observed the reduction of diacylglycerol and triacylglycerol, which are generally associated with muscle contraction. Interestingly, we found the accumulation of some saturated and mono-unsaturated fatty acids and poly-unsaturated fatty acids containing phosphatidylcholine in contracted muscles. Moreover, the distributions of several types of lipid were changed by contraction. Our results show that changes in the lipid amount, lipid composition, and energy metabolic activity can be evaluated in each local spot of cells and tissues at the same time using MALDI-IMS. In conclusion, MALDI-IMS is a powerful tool for studying lipid changes associated with contractions.