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Many mail filtering methods have been proposed, but they have not yet achieved perfect filtering. One of the reasons for this is the influence of modified words created by spammers to slip through the mail filtering, in which words are modified by insert symbols, spaces, HTML tags, etc. For example,“ price$ for be$t drug$! ”，“ priceC I A L I S ”， “ <font>se</font>xu<font>al</font> ”, etc. These are frequently replaced with new strings by changing the combination of symbols ,HTML tags etc. Mail filtering is a technique that captures trends in words in training mails (mails received in the past) and applies these trends to words in test mails (newly received emails). Some of the above modified words appear in both training and test mails, i.e., words that could be used as features of spam mail by using them unprocessed, while others appear only in test mails, i.e., words that have not been learned and require special processing (e.g., removal of symbols, search for similar words, etc.) for their use. However, existing methods do not make these distinctions and treat them in the same way. Therefore, in order to bring the filtering performance of the existing methods closer to perfect filtering, we developed a method in which the above modified words are separated into words that appear in both training and test mails and words that appear only in test mails, and each of these words is used for mail filtering. In this study, we treat the above modified words as ”strange words”. Typical examples of such strange words include, in addition to the above, new words included in ham mails, proper nouns used in close relationships, and abbreviations. The results of this study are as follows (1) In order to compare the filtering performance between strange words and other words, filtering experiments were conducted using existing methods with strange words, nouns, verbs, and adjectives. The results showed that the filtering performance of the strange words was the best. This means that strange words have a significant impact on the filtering performance, and we expect to improve the filtering performance of existing methods by developing a new method to utilize strange words. (2) In order to examine the breakdown of strange words, we counted the number of words that appeared in both training and test mails, and the number of words that appeared only in test mails. The results were compared with those obtained for nouns, verbs and adjectives. We found that there are a significant number of strange words that appear in both training and test mails, but only in one of the groups, i.e., ham or spam mail. Words with this appearance pattern are most useful for mail filtering. On the other hand, we found that there are many strange words that appear only in test mails, i.e., words that cannot be learned. We expect to improve the filtering performance by separating these strange words and developing a new method to use each of them. (3) For the use of strange words, we developed (A) a method for using words that appear in both training and test mails, and (B) a method for using words that appear only in test mails, respectively. (A) To examine the breakdown of strange words that appear in both training and test mails, we divided them into two categories: words that appear only in ham and spam mails, i.e., words with patterns that improve filtering performance, and words that do not, and examined their frequency of occurrence. The results showed that the words with appearance patterns that improve filtering performance tend to appear more frequently than those without such patterns. This means that by using words with a certain number of occurrences in filtering, it is possible to use more words that improve filtering performance. We developed a method to do this and conducted experiments with different threshold values to find the optimal value, and confirmed that setting the threshold around 7 improves filtering performance. (B) We compared the number of strange words that appear only in the test mails between ham and spam mails, and found that the number tends to be higher in spam mail than in ham mail. In order to utilize this difference for filtering, we proposed a method to set a uniform spam probability for strange words that appear only in the test mails, and attempted to find the optimal spam probability. As a result, setting the spam probability to 0.7 improved the filtering accuracy from 98.2% to 98.9%. By using (A) and (B) above together, both words that appear in both training and test mails and words that appear only in test mails can be used for mail filtering to increase accuracy. Mail filtering has been improved and its performance has reached its limit. In order to further improve accuracy, i.e., to approach perfect filtering, a new perspective is needed, and this paper provides one such perspective: the use of strange words. This paper is organized as follows. In Chapter 1, we review the background of mail filtering methods, discuss how spammers use strange words to slip through such filters. The purpose and structure of this paper are then presented. In Chapter 2, we will discuss related research on examples of filtering methods that have been proposed so far are given. In Chapter 3, we describe the mail datasets, word handling, and strange words used in the this paper. This is followed by an explanation of the ROC curve, which is the measure used to evaluate the filtering performance, and explanation of scatter plots and box-and-whisker plots. In Chapter 4, we compare the filtering performance between strange words and other words, and show that strange words have a significant impact on the filtering performance. Furthermore, based on the results of a breakdown of the number of strange words, we discuss the possibility of improving filtering performance by separating words that appear in both training and test mails from those that appear only in the test mails. We will work on this in the next chapters and report the results. In Chapter 5, we develop a method to use (A) above, i.e., strange words that appear in both training and test mails. From the results of counting the number of words used in the subject and body of each email, we show that the number tends to be smaller for words that degrade the filtering performance. Based on these results, we propose a method that sets a threshold for the number of words used in the subject and body of mails, and uses only those words that exceed the threshold for classification. Experiments are conducted to find the optimal value by varying the threshold, and the effect of this method on performance is reported. In Chapter 6, we develop a method to use (B) above, i.e., strange words that appear only in the test mails. We compare the number of types of these words in ham and spam mails, and show that the number tends to be larger in spam mails, and that this feature can be used as a bias for detecting spam mails. In this paper, we deal with experiments using bsfilter and develop a method to set spam probabilities uniformly for strange words that appear only in the test mails. After searching for the optimal spam probability, we report that a spam probability of 0.7 greatly improves the filtering performance. In Chapter 7, we describes the processing flow combining the methods developed in Chapter 5 and Chapter 6. The paper is then summarized, including future prospects.

Steel truss bridges, which are one of the bridge structures applicable to long spans, are widely used as marine bridges connecting mainland and remote island. Since such steel truss bridges are built on the sea, they are exposed to severe corrosive environment due to the influence of airborne salt. In addition, there are many parts where it is not easy to inspect to detect abnormalities, so it is more difficult to eliminate the risk of member damage in such steel truss bridges than in general bridges. On the other hand, once the marine bridges are built, they become an indispensable facility for the life of the island. Therefore, if there are no other traffic routes to access an island, the sustainability of the marine bridge is an important issue that is directly linked to the sustainability of the remote island life. When member damage occurs in a steel truss bridge, it depends on redundancy, which means the margin for the load-bearing capacity and load-bearing function, whether the damage develops into chain damage or remains limited damage. Bridges with redundancy could be restored by repairing even if the member damages occurred, because they did not develop into chain damages. In some cases, vehicles could pass through with traffic restrictions. Although redundancy is an important performance for maintaining life on remote islands that have no alternative traffic routes, there are few studies on evaluation and improvement methods of redundancy for long steel truss bridges used for marine bridges. The purpose of this study is to propose a method for improving the redundancy of long steel truss bridges, and three research subjects are set to achieve this purpose. The first study subject is the investigation of the effect of truss joint modeling on redundancy evaluation, and is the subject to appropriately evaluate the redundancy of steel truss bridges. The second is also the subject related to the redundancy evaluation of steel truss bridges, and is the development of dynamic response calculation method that considers the vibration characteristics of steel truss bridges, which are vibration systems with multiple degrees of freedom. The third study subject is a proposal for methods to improve the redundancy of long steel truss bridges. This paper consists of five chapters. Chapter 1 is an introduction, and describes the background of the research, the setting of the purpose and research subjects, and the previous studies. Chapter 2 describes the study on the modeling of the truss joint. In the analysis of healthy steel truss bridges with no member damage, the sectional forces can be calculated appropriately even with analysis modeling in which frame elements of truss members are rigidly connected at the truss joints, simply. On the other hand, in the redundancy analysis of steel truss bridges with member damages, it is shown that it is necessary to consider the shape of the gusset plates at the truss joints in analysis modeling. Chapter 3 describes the study on the calculation method of dynamic response caused by damage of truss members. There are cases where the dynamic response due to member damage is calculated in the same way as a single-degree-of-freedom vibration system. However, this study develops a dynamic response calculation method considering the vibration characteristics of long steel truss bridges by using the eigenvector of steel truss bridges with member damage. A method is proposed to set the magnitude of the eigenvector using balance equation of the work given to the steel truss bridge by the sectional force unloaded from damaged member and the strain energy stored in the steel truss bridge. In addition, a method is proposed to calculate the dynamic response by setting the range of vibration modes using the sum of effective mass ratio, and selecting the eigenvector that has the greatest effect on the dynamic response for each member. It is shown that the proposed calculation method gives redundancy evaluation closer to time-history-response analysis than the method that calculates the dynamic response in the same way as a single-degree-offreedom vibration system. Chapter 4 describes the study on redundancy improvement for a long steel truss bridge. A combination of the countermeasure against members that trigger chain damage and the countermeasure against members with insufficient load-bearing capacity is planned. Analysis clarifies that the X bracing, which is a reinforcing structure in X shape, is an efficient reinforcement that works against multiple member damage cases as the countermeasure against the trigger member of member chain damage. Also, the load-bearing capacity is verified by a loading test of specimens with reinforced structures. Since the subject bridge has 18 truss panels where X bracing can be installed, the placement patterns were examined by the optimization method. It is clarified that the weight of reinforcing material can be reduced by installing X-braces only at four truss panels in the alternating areas, rather than installing at all 18 truss panels. Chapter 5 describes the summary of this study and future developments.

In the dynamic global business landscape, finance and innovation stand as the twin pillars of corporate success. Both finance and innovation are vital for a company's long-term viability, demanding a harmonious interplay between prudent financial management and a culture that fosters innovation. Research in the field examining the relationship between a firm's finance and innovation is rapidly growing, offering profound insights into the dynamics shaping organizational success. While many empirical studies traditionally presumed that financial support drives innovative efforts, alternative perspectives support the reverse causation hypothesis, suggesting that innovation can stimulate financial performance. The current corporate management research often takes a segmented approach, focusing on either the signaling effect of innovation on financial performance or the influence of finance on innovation performance. While insightful, this segmented approach resembles examining separate puzzle pieces without considering the whole picture. We contend that finance and innovation are mutually interdependent, influencing each other. Our study uniquely explores both dimensions, investigating how financial resources stimulate innovation, and how innovation, primarily represented by patents, attracts investors and secures financial support. Focusing on Japanese corporations, our research provides a distinctive perspective due to Japan's diverse business landscape, strong patent system, and commitment to innovation. Japan's risk-averse market and global competition highlight the importance of innovation and the role of patents as signals for economic growth. The first study scrutinizes the intricate relationship between financial resources and firms' innovation outputs, exploring the influence of various financing sources, internal and external, inspired by the Pecking Order Theory. It involves a sample of 113 Japanese manufacturing firms listed on the JASDAQ market, using patent-based metrics to gauge technological innovation. The study highlights the crucial roles played by both internal and external financial resources in driving innovation outputs. Firms demonstrate a strong preference for self-generated financing, particularly internal funding. Additionally, the research unveils the complementary impact of debt financing, especially when internal resources are depleted, aligning with the Pecking Order Theory's risk principles. In our second study, we explore the reverse causation between innovation and finance, particularly during initial public offerings (IPOs). IPOs are pivotal, as they provide capital for growth and enhance a firm's reputation. However, information asymmetry poses a challenge, leading investors to rely on quality signals. We hypothesize that patents, as a proxy for innovation, mitigate information asymmetry because their information is verifiable, observable, and entails maintenance costs. Thus, a company with numerous patents before an IPO is likely to gain investor trust, leading to a more successful IPO. We analyze 338 newly listed Japanese firms across various industries, finding robust positive correlations between pre-IPO patent applications and IPO financial performance. This contribution enriches the literature on the impact of patents on IPO performance and illuminates the broader influence of innovation on finance. The third study delves into the dynamics of patent signaling within IPO firms, distinguishing between high-tech and low-tech sectors. High-tech firms often face more information asymmetry, with less transparency in R&D and patent disclosures, making them riskier for investors. Low- tech firms, with valuable patents and balanced resource allocation, are more accessible to investors. This raises the question of whether high-tech firms are less successful in using patent signals to raise total capital during the IPO process, as previous research has mainly focused on high-tech firms in technology-intensive markets. While prior studies often grouped all IPOs together or concentrated on specific industries, our study adds fresh insights to the entrepreneurship and innovation landscape by asserting that patents exert a more substantial influence on IPO success for low-tech companies in comparison to their high-tech counterparts. This observation underscores the necessity for an in-depth exploration of the patent signaling mechanism in IPOs, especially for low-tech firms characterized by simpler innovation portfolios and tangible assets appealing to risk-averse investors. Overall, our dissertation offers a comprehensive exploration of the interplay between finance and innovation in Japanese corporations, providing nuanced insights into the implications of this symbiotic relationship for businesses, policymakers, and scholars worldwide.

In Japan, China, and Singapore, several studies have reported increased incidences of peripheral venous catheter-related bloodstream infection by Bacillus cereus during the summer. Therefore, we hypothesized that bed bathing with a B. cereus-contaminated “clean” towels increases B. cereus contact with the catheter and increases the odds of contaminating the peripheral parenteral nutrition (PPN). We found that 1) professionally laundered “clean” towels used in hospitals have B. cereus (3.3×10^4 colony forming units (CFUs) / 25cm^2), 2) B. cereus is transferable onto the forearms of volunteers by wiping with the towels (n=9), and 3) B. cereus remain detectable (80∼660 CFUs /50cm^2) on the forearms of volunteers even with subsequent efforts of disinfection using alcohol wipes. We further confirmed that B. cereus grow robustly (10^2 CFUs /mL to more than 10^6 CFUs /mL) within 24hours at 30°C in PPN. Altogether we find that bed bathing with a towel contaminated with B. cereus leads to spore attachments to the skin, and that B. cereus can proliferate at an accelerated rate at 30°C compared to 20°C in PPN. We therefore highly recommend ensuring the use of sterile bed bath towels prior to PPN administration with catheter in patients requiring bed bathing.

【目的】代謝状態の朝晩の変化を理解することは、代謝障害を管理するためには重要である。我々は、インスリン分泌とインスリン感受性の観点からこの朝晩の変化を解析し、さらに概日リズムとの関連性を含めて検討することを目的とした。 【方法】非糖尿病成人男性14人と10人に対し、それぞれ75ｇ経口ブドウ糖負荷試験(OGTT)と高インスリン正常血糖（HE）クランプ実験を行った。各被験者に対し、午前8時と午後8時にOGTTまたはHEクランプを1回ずつ行った。ただし試験時間の順序は無作為とした。各試験直前に毛根を採取し、毛包における時計遺伝子発現量をリアルタイムPCR法で解析した。また、マウスの肝臓と筋肉でもAKTリン酸化をウエスタンブロット法により解析した。 【結果】OGTTの結果から、耐糖能は午前8時の方が良好であることがわかった。これは、OGTTにおける負荷後60分までのインスリン早期分泌とHEクランプで説明される骨格筋インスリン感受性の違いに起因すると考えられた。一方、OGTTにおける肝臓のインスリン抵抗性指数によって推定される肝インスリン感受性は、午後8時の方が良好であった。60分までのインスリン分泌量と肝臓のインスリン抵抗性指数の朝晩の差は、Per2のｍRNAの相対的発現量と有意に相関していた。ΔGIR（20時の値－8時の値）は、Δ非エステル化脂肪酸（NEFA）と有意に相関したが、時計遺伝子発現との相関は認められなかった。ΔNEFAは、E4bp4のmRNA発現量およびΔコルチゾールと有意に相関していた。マウスでは、ヒトの研究から予想されるように、AKTリン酸化は活動時間の初めに肝臓で減少し、筋肉で増加していた。 【結語】各組織の糖代謝は朝と晩で大きく異なっており、脂質代謝、時計遺伝子およびコルチゾールの影響を受けていることがわかった。この関連性についてのより深い知見が代謝障害の新たな改善法の開発に寄与する可能性がある。

Chromatography is considered as a key operation in the downstream process (DSP) of biopharmaceuticals, including proteins. Therapeutic proteins such as monoclonal antibodies (mAbs) with high economic values in the global market require immediate innovation in the purification step to adapt to the increased throughput from upstream. Authorities have also initiated changes toward a more modernized pharmaceutical manufacturing platform which is agile and flexible without extensive oversight. Instead of the conventional batch operation and empirical models, the design and application of in silico modeling and simulation for integrated multi-column processes to improve their performance in capture chromatography steps have been explored in the dissertation. Due to the fact that mechanistic models can reveal adsorption and mass transfer behaviors better in the chromatography compared to statistical models, mechanistic frameworks were applied in the study. Ion-exchange and protein A chromatography, the main categories of therapeutic protein chromatography were examined. With an example of oligonucleotides, the mass transfer phenomenon of biomolecules in different types of ion-exchange resins was explored by mechanistic models. The results demonstrate the effectiveness of modeling approaches to understand the chromatography process of biopharmaceuticals. By focusing on the DSP of mAbs, multi-column continuous chromatography was examined with IgG samples. The study covered the repeating batch to 4-column settings in the continuous periodic counter-current (PCC) chromatography, with development in modeling and simulation tools for process quantification and evaluation. Process performances including productivity, capacity utilization, and buffer consumption were investigated by simulations with the aim to increase productivities and lower buffer consumptions, which are the main bottleneck in the current DSP. The critical operation parameter, breakthrough percent (BT%) for column switching in PCC processes, requires the information from binding capacity, mass transfer, and non-loading operations. To obtain the optimal BT% under synchronized conditions, numerical solvers developed from mechanistic models were employed. It was found that over 20% improvement in buffer consumption and resin utilization can be observed in PCC processes while the same productivity as batch operation is maintained. Furthermore, regressive relations were developed for predictions of process performances and BT% based on the findings from PCC simulations. With high coherence in R2 over 0.95, the linear regression function can act as an accelerated method in the PCC process design. Finally, a new strategy of linear flow-velocity gradient (LFG) in the loading step was explored as a supplement to increase process efficiency. The method controls the total column capacity and the loaded amount as functions of time. Based on the relationship between the dynamic binding capacity and residence time, the gradient time of LFG was obtained. The optimal flow velocities and time gradients were examined by scanning through the range of applicable residence times. A case study of the 4-column PCC process is presented. By integrating a linear decreasing flow gradient in the PCC loading operation, the productivity has 1.4 times enhancement along with a 13% reduction in the cost of resin per amount of processed mAbs compared to constant flows. Undoubtedly, the next generation of DSP platform technology is directed toward continuous and integrated systems. Regarding the advantages in process performances and regulation perspectives, continuous manufacturing can advance development and manufacturing while assuring the product quality. The evolution in modeling and simulation enables faster development of in silico process prediction and evaluation. With the support from models, process design and optimization in chromatography can rise to the challenge.

Phosphorus is an indispensable nutrient to sustain the daily life of all living things on Earth. However, the over-enrichment of the aquatic ecosystem with phosphorus leads to eutrophication, which is still a global environmental problem. More stringent regulations have been put in place for the limit of phosphorus discharge to address this problem and resulted in the removal of phosphorus removal becomes exceptionally crucial. Furthermore, phosphorus deposits are a non-renewable resource and forecasted to deplete until 2170, given the current usage and global population growth. Thus, the removal of phosphorus coupled with the recovery and reuse of phosphorus offer the best strategies to meet the future phosphorus demand. Accordingly, adsorption represents a fascinating separation technique for phosphate from water because of the possibility of phosphorus recovery. Moreover, this approach has many advantages, such as efficient, easy operating conditions, low sludge production, and the possibility of regenerating the adsorbent. Numerous attractive low-cost adsorbents have been studied for phosphate removal, one of which is layered double hydroxides (LDH). Unfortunately, a high phosphate adsorption capacity of LDH can generally be achieved by calcination, which increases the preparation cost of LDH. In this study, LDH is functionalized with amorphous zirconium (hydr)oxide to obtain enhanced adsorption capacity and eliminate the high-temperature requirement during the synthesis process. Although different treatment techniques have been developed to eliminate phosphorus contamination, including for wastewater treatment, treated water often fails to meet quality regulations. Amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composites (am-Zr/MgFe-LDH) with different molar ratios (Zr/Fe = 1.5 2) were prepared in two-stage synthesis by the combination of coprecipitation and hydrothermal methods. The synthesis of the composite could eliminate the requirement of high-temperature calcination in the LDH for phosphate adsorption. Moreover, the phosphate adsorption ability of the composite was higher than that of the individual LDH and amorphous zirconium (hydr)oxide. The presence of amorphous zirconium (hydr)oxide increased the phosphate adsorption ability of composite at low pH. The adsorption capacity was increased by decreasing the pH and increasing the temperature (from 290 to 324 K). The bicarbonate (HCO3 ) was the most competitive anion for phosphate adsorption. The pseudo-secondorder model provided the best description of the kinetic adsorption data. Furthermore, the adsorbed phosphate was easily desorbed by 1 N and reused 2 N of NaOH solutions. The results suggest that the am-Zr/MgFe-LDH composite is a promising material for phosphate removal and recovery from wastewater. A Fixed-bed column has been considered an industrially feasible technique for phosphate removal from water. Besides the adsorption capacity, the effectiveness of an adsorbent is also determined by its reusability efficiency. In this study, phosphate removal by a synthesized am-Zr/MgFe-LDH in a fixed-bed column system was examined. The results showed that the increased bed height and phosphate concentration, and reduced flow rate, pH, and adsorbent particle size were found to increase the column adsorption capacity. The optimum adsorption capacity of 25.15 mg-P g^{-1} was obtained at pH 4. The coexistence of seawater ions had a positive effect on the phosphate adsorption capacity of the composite. Nearly complete phosphate desorption, with a desorption efficiency of 91.7%, could be effectively achieved by 0.1 N NaOH for an hour. Moreover, the initial adsorption capacity was maintained at approximately 83% even after eight adsorption-desorption cycles, indicating that the composite is economically feasible. The am-Zr/MgFe-LDH, with its high adsorption capacity and superior reusability, has the potential to be utilized as an adsorbent for phosphorus removal in practical wastewater treatment. The possible adsorption mechanisms of phosphate by am-Zr/MgFe-LDH were investigated via X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and pH at the point of zero charge (pHPZC) analyses. It was suggested that the high phosphate adsorption capacity of the composite involves three main adsorption mechanisms, which are the electrostatic attraction, inner-sphere complexation, and anion exchange, where the amorphous zirconium (hydr)oxide on the surface of the layered double hydroxides likely increased the number of active binding sites and surface area for adsorption. This study provides insights into the design of am-Zr/MgFe- LDH for phosphorus removal and recovery in a practical system.

The hippocampal dentate gyrus has been identified to play a critical role in maintaining contextual memory in many mammalian species. To evaluate learning-induced synaptic plasticity of granule cells, we subjected male rats to an inhibitory avoidance (IA) task and prepared acute hippocampal slices. In the presence of 0.5 µM tetrodotoxin, we recorded miniature EPSCs in male rats experiencing four groups: untrained, IA-trained, unpaired, and walk-through. Compared with the untrained, IA-trained, unpaired, and walk-through groups, the unpaired group significantly enhanced mean mEPSC amplitudes, suggesting the experience-induced plasticity at AMPA receptor-mediated excitatory synapses. For inhibitory synapses, both unpaired and walk-through groups significantly decreased mean mIPSC amplitudes, showing the experience-induced reduction of postsynaptic GABA_A receptor-mediated currents. Unlike the plasticity at CA1 synapses, it was difficult to explain the learning-specific plasticity at the synapses. However, overall multivariate analysis using four variables of mE(I)PSC responses revealed experience-specific changes in the diversity, suggesting that the diversity of excitatory/inhibitory synapses onto granule cells differs among the past experience of animals include the learning. In comparison with CA1 pyramidal neurons, granule cells consistently showed greater amplitude and frequency of mE(I)PSCs. Fluctuation analysis further revealed that granule cells provide more postsynaptic AMPA receptor channels and greater single-channel current of GABA_A receptors of than CA1 pyramidal neurons. These findings show functional differences between two types of principal cells in the hippocampus.

前身に投与された治療薬が脳組織実質に到達するには、神経組織の血管により形成される血液脳関門を通過する必要がある。そのため、組織への損傷を最小限に抑えて血液脳関門を開くことができれば、難治性神経疾患の治療法開発に大きな進展をもたらすことが期待される。本研究では、血液脳関門を形成する血管内皮細胞に発現するBasiginに着目し、その内因性リガンドであるCyclophilin A (CypA) を用いて、血液脳関門機能を人為的に制御することを目的とした。マウス脳血管内皮細胞株を用いたin vivo解析により、CypAの投与がBasiginを介して血液脳関門機能を低下させること、それにより脳実質へ効率的に薬物を送達できることを示した。単層培養された血管内皮細胞において、CypAはタイト結合構成分子の一つであるClaudin-5を一過性かつ可逆的に細胞膜から消失させて、バリアー機能を低下させることを見出した。また、マウスへのCypAの単回静脈内投与では血液脳関門が一定期間開いた後、自発的に元の状態へ回復することが示され、そしてその限定された機関において、全身投与された水溶性薬物Doxorubicinが脳組織実質へ送達されることが明らかとなった。本研究の結果は、CypAの静脈内投与によって、脳実質への薬物送達を自在にコントロールできることを示しており、難治性神経疾患に対する治療法確立に向けた重要な成果であると考えられる。

【背景】近年、歯周炎や歯肉炎に関連する嫌気性グラム桿菌であるFusobacterium nucleatum (F. nucleatum) は大腸がんの発生や進行に関与することが報告されている。この菌の制御が大腸がんの予防につながる可能性があると考え、深紫外線発光ダイオード (DUV-LED) によるF. nucleatumの殺菌効果を検討した。【方法】DUV-LEDのF. nucleatumに対する殺菌効果を定性的、定量的に評価した。ピーク波長が265nmと280nmの2種類のDUV-LEDを使用した。F. nucleatumのDNAに対するダメージは、シクロブタンピリミジン二量体(CPD)とピリミジンピリミドン光生成物 (6-4PP) の生成で評価した。【結果】DUV-LEDでの265nmまたは280nmの波長を3分間照射したところ、コロニーの成長は観察されなかった。265nmのDUV-LED光照射下におけるF. nucleatumの生存率は10秒照射で0.0014%、20秒照射で0%に低下した。同様に、280nmのDUV-LED光照射では，10秒照射で0.00044%、20秒照射で0%に低下した。DUV-LEDから35mmの距離での放射照度は、265nmのLEDで0.265mW/cm^2、280nmのLEDでは0.415mW/cm^2であった。従って、致死量を示す放射エネルギーは265nm LEDは5.3mJ/cm^2、280nm LEDは8.3mJ/cm^2であった。265nmと280nmのDUV-LED光をF. nucleatumに照射した際のCPDと6-4PPの量はそれぞれ6.548ng/μg、1.333ng/μgであった。【結論】DUV-LED光は、F. nucleatumに対して、ピリミジン二量体を形成することにより殺菌効果を発揮した。