環境因子以及藥物子結構影響二氧化錳氧化頭孢子類抗生素以及抗癌藥物的機制探討

Effect of environmental factors and the substructures reactivity on the oxidation of cephalosporin antibiotics and methotrexate by manganese dioxide

許明皓(Ming-Hao Hsu)

指導教授 ： 林郁真

國立臺灣大學/工學院/環境工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201901416

摘要

由於醫學科學的進步，現在已有成千數百種的藥物被使用。這些藥物常常以自身或者代謝產物形式的混合物釋放進環境中，且不能有效地透過傳統的廢水處理系統去除。頭孢子類抗生素（cephalosporin）是環境中第二常見的抗生素以及氨甲蝶呤（methotrexate, MTX）是一種化療和抗癌的藥物，這兩種藥物在環境水體之中都有被偵測到。因此，本文討論了頭孢子類抗生素氨甲蝶呤以及在二氧化錳和自然光光解這兩種重要的自然淨化的降解機理。
本研究旨在探討δ–二氧化錳（δ-MnO2）對不同環境因子中頭孢子類抗生素和氨甲蝶呤的氧化和轉化。結果表明，當二氧化錳負載量較高、初始藥物濃度較低以及溶液酸鹼值較低時會更加促進二氧化錳的氧化速率。而溶解的有機物質以及溶解的陽離子會抑制藥物的氧化（抑制能力：Mn2+ > Ca2+> Mg2+ > Fe3+）。選擇頭孢噻肟（CTX），頭孢氨芐（CFX），頭孢拉定（CFD），頭孢匹林（CFP）和頭孢唑啉（CFZ）作為目標頭孢子類抗生素並且研究δ-MnO2對於他們的氧化機制。雖然它們都具有相同的核心結構（core structure），但在pH4時觀察到非常不同的MnO2氧化速率 （初始反應速率常數kinit為0.014-2.6 h-1）。分析總有機碳顯示，頭孢子類抗生素以及氨甲蝶呤的轉化副產物在二氧化錳氧化下並不會被礦化並且會存留在水體之中。本研究鑑定了23種轉化副產物（5種核心結構副產物，6種CFX副產物，9種CFP副產物和3種CTX副產物）。對子結構和副產物分析的研究指出，氧化主要發生在核心結構的以下兩個位置：（1）頭孢子環上的硫原子和（2）碳–碳雙鍵（C = C）及其近端羧酸基團。當核心結構的C-3位置存在乙酰氧基甲基時，將會抑制酮-砜副產物的形成。總體結果表明，C-3位的取代基可以穩定核心結構，將導致氧化速率降低；此外，取決於子結構與二氧化錳的反應性，核心結構的碳–胺鍵上的子結構可能會影響頭孢子類抗生素的整體降解速率。因此造成反應速率的變化很大（CTX > CFP > CFD > 核心結構 ≈ CFX > CFZ）。本研究同時也可以幫助解釋頭孢子類抗生素在其他氧化過程中的降解機制。另一方面，本研究探討了太陽光對於二氧化錳氧化五種頭孢子類抗生素的影響，結果表明，在模擬光源下，二氧化錳藉由與CFP反應，初始還原速率比在暗反應中快8倍。
此外，本研究亦探討氨甲蝶呤照光之下影響二氧化錳氧化的特性，並發現氨甲蝶呤在水環境之中照光下會產生自身光敏降解。隨著初始濃度的增加，氨甲蝶呤不僅在去離子水中且在自然環境水體中都可增強其自身的直接光解反應。通過產生單線態氧 （1O2），氨甲蝶呤的三重激發態（3MTX*）和來自光轉化副產物的蝶啶結構的三重激發態（3PT*），使得氨甲蝶呤降解速率增加。在氨甲蝶呤低濃度（< 20 ppb）時，1O2扮演著重要角色，而在氨甲蝶呤濃度較高（> 2,000 ppb）時，氧氣的存在會抑制3MTX*和3PT*的生成進而降低氨甲蝶呤的總降解率。當氨甲蝶呤的C-N鍵斷裂時會產生大量的蝶啶衍生物（PT）和N-（4-氨基苯甲酰基）-L-谷氨酸（10ppm和500ppb MTX的產率分別為13.5 ± 0.6％和32.3 ± 2.2％）。本研究利用光轉化的副產物和氨甲蝶呤子結構的反應性，來了解其自身光敏的降解途徑。結果顯示氨甲蝶呤以及含有蝶啶結構的化合物在光降解過程中會產生蝶啶衍生物，而3PT*是可引起自身光降解的主要三重激發物質。由於氨甲蝶呤獨特的自身光敏特性並產生三重激發態或其誘發的活性物質，加速二氧化錳的光還原，在照射240分鐘後，二氧化錳會完全還原為二價錳離子。但是，詳細的機制還需要進一步探討與研究。

關鍵字

頭孢子類抗生素 ； 氨甲蝶呤 ； 二氧化錳 ； 光還原 ； 自身光敏 ； 三重激發態

並列摘要

As a result of advances in medical science, hundreds of pharmaceuticals are now widely used. Most of these pharmaceuticals are excreted as a mixture of their metabolized and unmetabolized forms and cannot be effectively removed by traditional wastewater treatment systems. Cephalosporin, the second most commonly used antibiotic class, and methotrexate, the chemotherapy and anticancer agent, can be detected in aquatic environments. Thus, the cephalosporin and methotrexate’s degradation mechanism of manganese dioxide and sunlight photolysis these two important natural attenuation process are discussed in this work.
This study aimed to explore the oxidation and transformation of the cephalosporins and methotrexate in the different environmental factors by δ-MnO2. The results showed that the MnO2 oxidation rate was promoted by environmental factors such as higher MnO2 loading, lower initial concentration and lower solution pH. The inhibitory effect occurred in the presence of dissolved organic matter and dissolved cations (inhibitory capacity: Mn2+ > Ca2+ > Mg2+ > Fe3+). Cefotaxime (CTX), cephalexin (CFX), cephradine (CFD), cephapirin (CFP), and cefazolin (CFZ), were selected as target cephalosporin antibiotics to study their oxidative transformation by δ-MnO2. Although they all have the same core structure (7-aminodesacetoxycephalosporanic acid), very different MnO¬2 oxidation rates were observed at pH 4 (the initial reaction rate constant kinit ranged from 0.014 to 2.6 h-1). Total organic carbon analysis indicated that the transformation byproducts of cephalosporins are less reactive and persistent under MnO2 oxidation. 23 transformation byproducts (5 core structure byproducts, 6 CFX byproducts, 9 CFP byproducts and 3 CTX byproducts) were identified. An extensive investigation of the substructure compounds and byproduct analysis revealed that the oxidation mainly occurred at the following two sites on the core structure: (1) the sulfur atom in the cephem ring and (2) the carbon-carbon double bond (C=C) and its proximal carboxylic acid group. When there is an acetyloxymethyl group at the C-3 position of the core structure, the formation of the keto-sulfone byproducts was inhibited. The overall results indicated that a substituent at the C-3 position could stabilize the core structure, which would result in a decrease in the oxidation rate; however, a substituent at the amine position of the core structure might affect the overall degradation rate of the cephalosporin, depending on its reactivity with MnO2. Thus, the apparent reaction rates varied widely in the trend of CTX > CFP > CFD > core structure ≈ CFX > CFZ. The mechanistic elucidation can also help explain the degradation rates of cephalosporin antibiotics in other oxidation processes. The effect of solar light on the oxidation of the five cephalosporin antibiotics by δ-MnO2 was also investigated, and the results indicated that the initial dissolution rate of δ-MnO2 under sunlight was approximately eight times faster than that in the dark in the presence of CFP.
The photo-assisted MnO2 oxidation is further investigated with methotrexate, found to undergo self-sensitized photodegradation in aqueous environments. As the initial concentration increased, methotrexate was able to enhance its own direct photolysis reaction not only in DI but also in natural waters. The methotrexate degradation rate increased through the production of singlet oxygen (1O2), the triplet excited state of methotrexate (3MTX*), and the triplet excited state of the pteridine structure (3PT*) from the phototransformation byproducts. At low methotrexate concentrations (<20 ppb), 1O2 played an important role, whereas at higher methotrexate concentrations (>2,000 ppb), the presence of oxygen decreased the overall methotrexate degradation rate by physically quenching 3MTX* and 3PT*. The cleavage of the C-N bond resulted in a significant amount of byproducts: pteridine derivatives and N-(4-aminobenzoyl)-L-glutamic acid (yields: 13.5 ± 0.6% and 32.3 ± 2.2% for 10 ppm and 500 ppb MTX, respectively). The reactivity of the phototransformation byproducts and the substructures of methotrexate were investigated to help elucidate the proposed self-sensitized pathways. The results indicated that methotrexate as well as compounds containing a pteridine structure will generate pteridine byproducts during photodegradation, and 3PT* is the primary triplet excited species that can cause self-sensitized photodegradation. Due to the unique self-photosensitive property, MTX can generate the triplet excited state species or reactive oxygen species to accelerate the photoreduction of δ-MnO2, which completely reduce to Mn2+ after 240 minutes of irradiation. However, the detailed mechanism needs further exploration.

並列關鍵字

Cephalosporin ； methotrexate ； manganese dioxide ； photoreduction ； self-photosensetization ； triplet excited state

參考文獻

Abolmaali, S.S., Tamaddon, A.M. and Dinarvand, R. (2013) A review of therapeutic challenges and achievements of methotrexate delivery systems for treatment of cancer and rheumatoid arthritis. Cancer Chemotherapy and Pharmacology 71(5), 1115-1130.

Andreozzi, R., Raffaele, M. and Nicklas, P. (2003) Pharmaceuticals in STP effluents and their solar photodegradation in aquatic environment. Chemosphere 50(10), 1319-1330.

Balgooyen, S., Alaimo, P.J., Remucal, C.K. and Ginder-Vogel, M. (2017) Structural transformation of MnO2 during the oxidation of bisphenol A. Environmental Science & Technology 51(11), 6053-6062.

Barrett, K.A. and McBride, M.B. (2005) Oxidative degradation of glyphosate and aminomethylphosphonate by manganese oxide. Environmental Science & Technology 39(23), 9223-9228.

Bertino, D.J. and Zepp, R.G. (1991) Effects of solar radiation on manganese oxide reactions with selected organic compounds. Environmental Science & Technology 25(7), 1267-1273.