Applying secondary ion mass spectrometry to the analysis of elements in goblet cells of conjunctiva

The subcellular distribution of small molecules: from pharmacokinetics to synthetic biology

The systemic pharmacokinetics and pharmacodynamics of small molecules are determined by subcellular transport phenomena. Although approaches used to study the subcellular distribution of small molecules have gradually evolved over the past several decades, experimental analysis and prediction of cellular pharmacokinetics remains a challenge. In this review, we survey the progress of subcellular distribution research since the 1960s, with a focus on the advantages, disadvantages and limitations of the various experimental techniques. Critical review of the existing body of knowledge points to many opportunities to advance the rational design of organelle-targeted chemical agents. These opportunities include (1) development of quantitative, non-fluorescence-based, whole cell methods and techniques to measure the subcellular distribution of chemical agents in multiple compartments; (2) exploratory experimentation with nonspecific transport probes that have not been enriched with putative, organelle-targeting features; (3) elaboration of hypothesis-driven, mechanistic and modeling-based approaches to guide experiments aimed at elucidating subcellular distribution and transport; and (4) introduction of revolutionary conceptual approaches borrowed from the field of synthetic biology combined with cutting edge experimental strategies. In our laboratory, state-of-the-art subcellular transport studies are now being aimed at understanding the formation of new intracellular membrane structures in response to drug therapy, exploring the function of drug-membrane complexes as intracellular drug depots, and synthesizing new organelles with extraordinary physical and chemical properties.

Mass microscopy: high-resolution imaging mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) is a technique that localizes the spatial distribution of molecules and identifies structures by their molecular mass signatures. Recently, the resolution of MALDI-IMS has been up to microscopic level. MALDI-IMS does not need either separation or purification procedures of target molecules and enables us to observe the localization of numerous molecules simultaneously. In particular, MALDI-MS time-of-flight/time-of-flight (TOF/TOF) is one of the instruments widely adopted for IMS, which allows the analysis of numerous biomolecules ranging over wide molecular weights. Even in a single data point, hundreds and thousands of mass peaks can be detected, and this makes the resulting mass spectrum extremely complex. This enormous volume of IMS data has driven the development of statistical approaches, especially multivariate analyses. By employing these approaches, researchers can figure out the important characteristics of their IMS data sets. The establishment of automatic molecular identification procedures involving MS(2) analysis, also known as MS/MS, performed by tandem mass spectrometry to obtain the information about molecular structure and composition, and database search available on the web is an important task for the near future. In this review, we introduce IMS-especially MALDI-IMS-with reference to its applications in biomolecular analyses, the workflow of IMS, the principle of IMS and other related technologies.

Ocular surface in Zn-deficient rats

PURPOSE

We studied the cornea and conjunctiva of Zn-deficient rats with an electron microscope and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to elucidate the role of trace elements in the cornea and conjunctiva.

MATERIALS AND METHODS

Twenty-one-day-old Wistar Kyoto rats were fed a Zn-deficient diet and deionized water for 7 weeks and then killed. The control rats were fed a Zn-deficient diet and deionized water supplemented with 3 mg Zn/100 ml. After 7 weeks on the deficient diet, another group of rats was given drinking water containing 3 mg Zn/100 ml and the usual diet containing 4.7 mg Zn/100 g for 8 weeks for recovery. The cornea and conjunctiva were examined by electron microscopy and TOF-SIMS.

RESULTS

Microvilli and microplicae in the most superficial layer of the epithelium of the Zn-deficient rat conjunctiva and cornea were prominently reduced, and dark cells were significantly increased. The numbers of goblet cells were decreased in the conjunctiva of the Zn-deficient group. Zn, Ca and Al ions were significantly fewer, but K, Fe, Cl and S ions were significantly more numerous in the Zn-deficient group than in the control group. In the cornea of the Zn-deficient group, there was significantly more Cl but less Ca and vitamin C than in the controls.

DISCUSSION

Zn deficiency may interfere with protein, nucleic acid and collagen synthesis through the reduction of Zn-containing enzymes. Myosin-like substance, actin filaments and tonofibrils are important structural components for microvilli and microplicae in the epithelium. Maldevelopment of these structural components may be related to disturbed activities of Zn-containing enzymes in protein and collagen synthesis because of Zn deficiency. In addition, Zn deficiency caused changes in the levels of Zn and other trace elements such as Ca, Al, S, Fe, and Cl and vitamin C.

CONCLUSION

Zn deficiency resulted in poorly developed microvilli and microplicae on the ocular surface tissues, reduced the number of goblet cells and changed the quantity of trace elements and vitamin C.

Bioimaging TOF-SIMS: localization of cholesterol in rat kidney sections

Here, we show the localization of a whole organic molecule in biological tissue using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Rat kidneys were sectioned by cryoultramicrotomy and dried at room temperature. The samples were covered with a thin silver layer and analyzed in an imaging TOF-SIMS instrument equipped with a Ga(+)-source. The cholesterol signal showed a high concentration in the nuclear areas of the epithelial cells and a lower concentration over areas representing the basal lamina of renal tubules. A more diffuse distribution of cholesterol was also found over areas representing the cytoplasm or plasma membrane of the epithelial cells.