利用水凝膠微貼片取樣及質譜方法偵測皮膚代謝物

Abstract

質譜學於 20 世紀中的後數十年以及21 世紀初期之創新與演進使其成為多方適用而且普遍的一門技術。質譜是一項非常優越的分析技術，因為它可以準確的定性及定量各種不同的化學分子。質譜在各不同研究領域的應用發展得非常快速，並且已進入臨床實驗室中，其中又以利用和液相、氣相層析儀連用的質譜作為醫療診斷及尋找生物標記物的方法最為有用。現代質譜方法讓存在於各類生物樣品中的低分子量分子之測量變得更加容易。這個結果促成了系統生物學其中一項的發展─代謝體學。 在大多數臨床分析的標準流程中，通常以血液及尿液作為分析樣本。在此論文中, 我著重在非傳統生物樣品之分析，並特別注重在皮膚代謝物的取樣及分析，其樣品之蒐集為非侵入性且不需要額外的樣品前處理即可以進行質譜分析。本論文第一章為研究背景的簡要介紹，其中包含代謝物組學的定義、質譜的基本原理、質譜在非傳統生物樣品定量分析的應用以及概述目前皮膚代謝物的研究現況。

本於將皮膚代謝物分析的實用性納入考量，我們提出一個快速、非侵入性取樣皮膚代謝物且可直接被質譜篩選的簡單工具(第二章)。我們所發明的簡單工具為由具化學惰性之鐵氟龍及鑲嵌於其上之生物相容性水凝膠微貼片組成的探針。探針和代謝物游離源技術─奈米噴霧脫附電噴灑游離(nanoDESI) 線上結合，所收集到之微量皮膚代謝物樣品已足夠進行化學指紋的鑑定。利用MS/MS 及高解析度質譜分析，二十四種低分子量皮膚代謝物已經能夠被鑑定出來(第二-四章)。

在水凝膠微貼片中，每個大貼片上有由微貼片排列成之5 × 5 點狀陣列。此陣列式微貼片(micropatch-arrayed pads; MAPAs) 用於取得皮膚表面之化學物質於空間上的分布(第三章)。取樣貼片的質譜掃描是自動化的。另外實驗系統中含有一3D 印製的溼度室，用以避免水凝膠的風乾。MAPAs 應用於追蹤施加在人類皮膚 (體內試驗) 及豬隻皮膚 (體外試驗) 的局部性藥物之分布情形。體內和體外試驗的藥物分布 之差異可以使用此方法觀察到。

此外，兩項皮膚代謝物的研究能夠藉由水凝膠微貼片的取樣來進行質譜分析。在這些研究當中，我們選定受乾癬之苦之患者的皮膚代謝物(第四、五章)，實驗所 獲得乾癬之代謝體組學的相關訊息或許能夠為乾癬複雜的病理生理學帶來新的洞見。在第一個代謝體學研究中，總共收集了一百個患者及一百個健康個體的皮膚代謝物 樣品(第四章)。本實驗以客製化的演算法自動處理研究中的大量資料。除此之外，化學計量分析可分辨出乾癬皮膚與健康皮膚間代謝體的主要差異。本實驗顯示數種極性代謝物和乾癬患部的嚴重程度分數呈現正相關(choline 和 glutamic acid) 或負相關(urocanic acid 和citrulline)，這些代謝物被視為疾病演變過程的生物標記物。在第 二個代謝體學的研究中，我們研究乾癬患者在接受最新療法─生物製劑後，其血清及乾癬患部皮膚上代謝物組成之動態改變(第五章)。在接受療程後的五到七個月間多次收集十九位患者的皮膚代謝物及血液樣品。如同預期，並非每位患者對於生物製劑療法都有相同的反應及結果，且在療程中期間觀察到皮膚代謝物組成的改變。

Innovation in mass spectrometry (MS) in the last decade of the 20th century and in the beginning of the 21st century made it a versatile and accessible technique. MS is a very powerful analytical technique because it can accurately identify and quantify various types of chemicals. The applications of MS in different research areas develop rapidly. MS has already entered clinical laboratories. In particular, hyphenating liquid and gas chromatography with MS is useful in medical diagnostics and biomarker discovery. Modern MS methods facilitated measurements of low-molecular-weight molecules present in various biological samples. This resulted in the development of a new subdivision of systems biology – metabolomics. In most standard protocols in clinical analysis, blood and urine specimens are analyzed. In this thesis, I highlight analysis of unconventional biological specimens. In particular, I focus on sampling and analysis of skin excretions, which could be collected in totally non-invasive manner, and analyzed by MS without extensive sample preparation. A brief introduction of the background of my research, including definition of metabolomics, basic principles of MS, application of MS for quantitative analysis of unconventional biological specimens and a summary of current status of skin excretions testing, are presented in Chapter 1 of this thesis.

Taking into account the usefulness of skin excretion analysis, we proposed a simple tool for fast and non-invasive collection of minute quantities of skin excretions that could directly be screened by MS (Chapter 2). A simple probe composed of biocompatible agarose hydrogel micropatches embedded within chemically inert probes was invented. The probe was combined on-line with an extraction-ionization technique – nanospray desorption electrospray ionization (nanoDESI). Tiny amounts of the collected skin specimens were found to be sufficient to perform chemical fingerprinting. Twenty four low-molecular-weight skin metabolites have been putatively identified based on MS/MS and high-resolution MS analysis (Chapter 2-4).

In one variant of the hydrogel micropatch probe, the micropatches were arranged in an array of spots (5 × 5) within a larger chip. So-called micropatch-arrayed pads (MAPAs) were used to acquire spatial distribution of chemicals on skin surface (Chapter 3). MS scanning of the probe was automated and a 3D-printed humidity chamber, preventing hydrogel from drying, was incorporated into the experimental system. MAPAs were applied to follow dispersion of topical drugs applied to human skin in vivo and to porcine skin ex vivo. Differences between drug dispersion in vivo and ex vivo were observed.

Furthermore, two skin metabolomic studies were conducted using hydrogel micropatch sampling and MS. In these studies, we investigated the skin metabolomes of patients suffering from a common skin disease – psoriasis (Chapters 4 and 5). Obtaining information about the metabolomes of psoriatic skin may bring new insights into the complex pathophysiology of this disease. In the first metabolomic study, skin excretion specimens from 100 patients and 100 healthy individuals were collected (Chapter 4). A custom-developed algorithm automated processing of the large data sets obtained in the course of this study. Further chemometric analysis revealed major differences between the metabolomes of psoriatic and healthy skin. Several polar metabolites correlated positively (choline and glutamic acid) or negatively (urocanic acid and citrulline) with the severity score values characterizing psoriatic plaques. Those metabolites are considered as biomarkers of the disease progression. In the second metabolomic study, we investigated dynamic changes of metabolic profiles of psoriatic skin and blood plasma of patients treated with the newest type of therapy – biologics (Chapter 5). Skin excretion and blood specimens were collected multiple times from 19 patients during the first 5-7 months of therapy. As expected, not every patient reacted to the biologic therapy in the same way. Alterations to the metabolic skin profiles were observed in the course of the treatment.