Re: 타우린의 치매치료 기전 탐구 2020 nature!!!

[문형철]

칸슘항상성 조절

단백질 접힘의 안정화(소포체 기능부전 치료)

삼투압조절

--> 항산화, 항염증

--> 중추신경계에서 신경전달물질 역할(글루탐산 다음으로 많은 아미노산)

다른 논문

타우린 1/4는 담즙산과 conjugated되어 있음

--> 간담도 해독에 중요한 역할

https://www.mdpi.com/2218-1989/13/7/824#

https://kr.iherb.com/pr/life-extension-taurine-powder-10-58-oz-300-g/4900

1. nature  
2. scientific reports  
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4. article

Eval‎uation of the neuroprotective effect of taurine in Alzheimer’s disease using functional molecular imaging

• Article
• Open access
• Published: 23 September 2020

Eval‎uation of the neuroprotective effect of taurine in Alzheimer’s disease using functional molecular imaging

• Se Jong Oh, 
• Hae-June Lee, 
• Ye Ji Jeong, 
• Kyung Rok Nam, 
• Kyung Jun Kang, 
• Sang Jin Han, 
• Kyo Chul Lee, 
• Yong Jin Lee & 
• Jae Yong Choi 

Scientific Reports volume 10, Article number: 15551 (2020) Cite this article

•  
•  
•  
•  

Abstract

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder and the leading cause of dementia, but therapeutic treatment options are limited. Taurine has been reported to have neuroprotective properties against dementia, including AD. The present study aimed to investigate the treatment effect of taurine in AD mice by functional molecular imaging. To elucidate glutamate alterations by taurine, taurine was administered to 5xFAD transgenic mice from 2 months of age, known to apear amyloid deposition. Then, we performed glutamate positron emission tomography (PET) imaging studies for three groups (wild-type, AD, and taurine-treated AD, n = 5 in each group). As a result, brain uptake in the taurine-treated AD group was 31–40% higher than that in the AD group (cortex: 40%, p < 0.05; striatum: 32%, p < 0.01; hippocampus: 36%, p < 0.01; thalamus: 31%, p > 0.05) and 3–14% lower than that in the WT group (cortex: 10%, p > 0.05; striatum: 15%, p > 0.05; hippocampus: 14%, p > 0.05; thalamus: 3%, p > 0.05). However, we did not observe differences in Aβ pathology between the taurine-treated AD and AD groups in immunohistochemistry experiments. Our results reveal that although taurine treatment did not completely recover the glutamate system, it significantly increased metabolic glutamate receptor type 5 brain uptake. Therefore, taurine has therapeutic potential against AD.

요약
알츠하이머병(AD)은

만성 신경 퇴행성 질환이자 치매의 주요 원인이지만

치료 옵션은 제한적입니다.

타우린은 알츠하이머병을 포함한

치매에 대한 신경 보호 효과가 있는 것으로

보고되었습니다.

본 연구는 기능적 분자영상을 통해 타우린의 치매 쥐 치료 효과를 조사하는 것을 목표로 했습니다.

타우린에 의한 글루타메이트 변화를 규명하기 위해

아밀로이드 침착이 나타나는 것으로 알려진

생후 2개월부터 5xFAD 형질전환 생쥐에

타우린을 투여했습니다.

그런 다음 세 그룹(야생형, AD, 타우린 처리 AD, 각 그룹당 n = 5)을 대상으로

글루타메이트 양전자 방출 단층촬영(PET) 영상 연구를 수행했습니다.

그 결과,

타우린으로 치료한 AD 그룹의 뇌 흡수율은

야생형 그룹보다 31-40% 높았습니다(피질: 40%, p<0.05, 선조체: 32%, p<0.01, 해마: 36%, p< 0.01; 시상: 31%, p> 0.05), WT 그룹보다 3~14% 낮았습니다(피질: 10%, p> 0.05; 선조체: 15%, p> 0.05; 해마: 14%, p> 0.05; 시상: 3%, p> 0.05).

그러나

면역조직화학 실험에서는

타우린으로 치료한 AD 그룹과 그렇지 않은 그룹 간에

Aβ 병리의 차이를 관찰하지 못했습니다.

연구 결과에 따르면

타우린 치료가 글루타메이트 시스템을 완전히 회복시키지는 못했지만

대사성 글루타메이트 수용체 5형 뇌 흡수를 크게 증가시킨 것으로 나타났습니다.

따라서

타우린은

알츠하이머병에 대한 치료 잠재력을 가지고 있습니다.

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Introduction

Alzheimer’s disease (AD) is the most common cause of dementia (60–70%) in elderly individuals and leads to problems including memory loss, cognitive deficits, and intellectual disabilities1. Many studies have reported the deposition of senile plaques and neurofibrillary tangles as key pathological features in AD2. The global preval‎ence of AD is growing rapidly, highlighting the importance of early intervention, which may reduce the cost of medical support and improve patients’ quality of life3. According to a previous study, diagnosing people with mild cognitive impairment before dementia can save a total of 7–7.9 trillion dollars in the US4. AD significantly deteriorates patients’ quality of life, and a recent study reported that AD is closely related to circadian rhythm sleep disorders5. Therefore, extensive effort has been dedicated to the development of new drugs that reduce the amyloid burden and decelerate disease progression; however, effective therapeutic treatments have not yet been established.

Currently, two types of therapeutic drugs for AD have been approved by the US Food and Drug Administration (FDA), and these drugs exert their function via two mechanisms. Cholinesterase inhibitors (Donepezil (Pfizer, New York USA), rivastigmine (Novartis, Basel, Switzerland) and galantamine (Janssen, Beerse, Belgium)) increase the level of synaptic acetylcholine in the central nervous system (CNS), and additional studies on several cholinesterase inhibitors are ongoing6,7,8. N-methyl-D-aspartate (NMDA) receptor antagonists [i.e., memantine (Namenda, Forest Pharmaceuticals Inc, Missouri, USA)] slows the progression of AD by inhibiting glutamate excitotoxicity9. A recent study reported that NMDA receptor antagonists block NMDA-related ion channels and consequently reduce the influx of calcium ions into neurons10. Although these drugs are particularly effective in maintaining cognitive function, their disease-modifying efficacy remains controversial11. Therefore, developing therapeutic treatments for AD is essential.

Taurine, 2-aminoethanesulfonic acid, is the second most abundant endogenous amino acid after glutamate in the CNS12. The chemical plays multiple roles in the body, including thermoregulation, stabilization of protein folding, anti-inflammation, antioxidation, osmoregulation, calcium homeostasis and CNS development13,14,15. Previous reports in the literature have revealed a lack of taurine in the brains of AD patients16. Arai et al.17 reported that postmortem brain tissues of AD patients have low concentrations of taurine in the temporal cortex compared with control patients’ brain tissues. Multiple lines of evidence suggest taurine as a therapeutic agent for AD. Recently, taurine was reported to help improve cognitive function and protect against neuropathology in an animal model of AD18. Jakaria et al.19 reported that taurine displayed therapeutic potential against neurological disorders, including AD. Santa-Maria et al.20 reported that taurine binds to Aβ plaques with weak antifibrillogenic effects. In addition, intravenously administered taurine prevents Aβ neurotoxicity and cognitive impairment21. To date, no reports of the possible side effects of taurine have been documented, and due to its nontoxic properties in the body, taurine has been used in foods22,23,24.

To date, no studies have eval‎uated the effects of taurine on AD via functional molecular imaging. Therefore, the aim of the present study was to investigate the effect of taurine supplementation in AD mice by glutamate positron emission tomography (PET).

소개

알츠하이머병(AD)은

노인 치매의 가장 흔한 원인(60-70%)으로

기억 상실, 인지 결함, 지적 장애 등의 문제를 일으킵니다1.

많은 연구에서

노인성 플라크와 신경섬유 엉킴이

AD의 주요 병리학적 특징으로 보고되었습니다2.

전 세계적으로 알츠하이머병의 유병률이 빠르게 증가하면서

의료 지원 비용을 줄이고

환자의 삶의 질을 개선할 수 있는

조기 개입의 중요성이 강조되고 있습니다3.

이전 연구에 따르면

치매로 진행되기 전에 경도인지장애를 진단하면

미국에서 총 7조~7조 9천억 달러를 절약할 수 있다고 합니다4.

알츠하이머병은

환자의 삶의 질을 크게 악화시키며,

최근 연구에 따르면 알츠하이머병은

일주기 리듬 수면 장애와 밀접한 관련이 있는 것으로 보고되었습니다5.

따라서

아밀로이드 부담을 줄이고

질병 진행을 늦추는 신약 개발에 많은 노력을 기울여 왔지만

아직 효과적인 치료법은 확립되지 않았습니다.

현재 미국 식품의약국(FDA)에서 승인된 알츠하이머병 치료제는

두 가지 기전을 통해 그 기능을 발휘합니다.

1. 콜린에스테라제 억제제(도네페질(미국 화이자, 뉴욕),

리바스티그민(스위스 바젤, 노바티스),

갈란타민(벨기에 얀센, 비어스))는

중추신경계(CNS)에서 시냅스 아세틸콜린의 수준을 높이며

여러 콜린에스테라제 억제제에 대한 추가 연구가 진행 중입니다6,7,8.

2. N-메틸-D-아스파르트산염(NMDA) 수용체 길항제

[예: 메만틴(Namenda, 미국 미주리주 Forest Pharmaceuticals Inc)]는

글루타메이트 흥분 독성을 억제하여

AD의 진행을 늦춥니다9.

최근 연구에 따르면

NMDA 수용체 길항제는

NMDA 관련 이온 채널을 차단하여

결과적으로 칼슘 이온이 뉴런으로 유입되는 것을 감소시킨다고 합니다10.

이러한 약물은

인지 기능을 유지하는 데 특히 효과적이지만,

질병을 조절하는 효능은 여전히 논란의 여지가 있습니다11.

따라서

알츠하이머병 치료법 개발은

필수적입니다.

2- 아미노에탄설폰산인

타우린은

CNS에서 글루타메이트 다음으로 가장 풍부한

내인성 아미노산입니다12.

타우린은

체온 조절,

단백질 접힘의 안정화,

항염증,

항산화,

삼투압 조절 osmoregulation,

칼슘 항상성 및

CNS 발달13,14,15을 포함하여

신체에서 다양한 역할을 합니다.

타우린 기능

칼슘항상성 조절

단백질 접힘의 안정화(소포체 기능부전 치료)

삼투압조절

--> 항산화, 항염증

--> 중추신경계에서 신경전달물질 역할(글루탐산 다음으로 많은 아미노산)

The chemical plays multiple roles in the body, including

thermoregulation,

stabilization of protein folding,

anti-inflammation,

antioxidation,

osmoregulation,

calcium homeostasis and

CNS development

이전 문헌에 따르면

알츠하이머병 환자의 뇌에

타우린이 부족하다는 보고가 있었습니다16.

Arai등17은

알츠하이머 환자의 사후 뇌 조직이

대조군 환자의 뇌 조직에 비해

측두피질에 타우린 농도가 낮다고 보고했습니다.

타우린이

알츠하이머병 치료제로서 효과가 있다는

여러 증거가 있습니다.

최근 타우린은

알츠하이머병 동물 모델에서 인지 기능을 개선하고

신경 병리를 예방하는 데 도움이 되는 것으로

보고되었습니다18.

Jakaria등19은 타우린이 알츠하이머병을 포함한 신경 장애에 대한 치료 잠재력을 보인다고 보고했습니다. Santa-Maria등20은 타우린이 항섬유소생 효과가 약한 Aβ 플라크에 결합한다고 보고했습니다.

또한

타우린을 정맥으로 투여하면

Aβ 신경 독성과 인지 장애를 예방할 수 있다고 합니다21.

현재까지 타우린의 부작용에 대한 보고는 보고된 바 없으며,

타우린은 체내 무독성 특성으로 인해

식품22,23,24에 사용되어 왔습니다.

현재까지 기능적 분자 영상을 통해

타우린이 알츠하이머병에 미치는 영향을 평가한 연구는 없습니다.

따라서 본 연구의 목적은 글루타메이트 양전자 방출 단층촬영(PET)을 통해 AD 마우스에서 타우린 보충제의 효과를 조사하는 것이었습니다.

Results

PET images

The mean PET images (30–60 min) are shown in Fig. 1. By visual inspection, the AD group showed significantly lower striatal and hippocampal uptake than the wild-type (WT) group. The ADTaurine group showed relatively higher uptake than the AD group. The radioactivity of the olfactory bulb, which was due to spillover from the harderian gland, was also detected in the AD and ADTaurine groups.

Figure 1

Mean 18F-FPEB PET images (n = 5 for each group) between 30 and 60 min after injection in the three groups. All mean PET images were created using PMOD software (version 3.4). The AD group showed dramatically lower uptake than the WT group, and the ADTaurine group exhibited relatively higher uptake than the AD group. Images are shown scaled to the SUV.

세 그룹에서 주사 후 30분에서 60분 사이의 평균 18F-FPEB PET 이미지(각 그룹당 n = 5). 모든 평균 PET 이미지는 PMOD 소프트웨어(버전 3.4)를 사용하여 생성되었습니다. AD 그룹은 WT 그룹에 비해 현저히 낮은 흡수율을 보였고, AD타우린 그룹은 AD 그룹에 비해 상대적으로 높은 흡수율을 나타냈습니다. 이미지는 SUV에 맞게 조정되어 표시됩니다.

Time-activity curves (TACs)

Figure 2A–E shows the regional TACs for all groups. After approximately 10 min, the radioactivity of all target regions indicated lower uptake in the AD group than in the WT group. However, the ADTaurine group showed relatively higher uptake than the AD group. The uptake at 50 min post-injection (p.i.) for the target regions in the AD group was 25–36% lower than that in the WT group (Table 1). The radioactivity of the target regions was 31–40% higher in the ADTaurine group than in the AD group. The radioactivity in the cerebellum, as the reference region, was similar among all groups.

시간-활동 곡선(TAC)
그림 2A-E는 모든 그룹에 대한 지역별 TAC를 보여줍니다. 약 10분 후, 모든 표적 부위의 방사능은 AD 그룹에서 WT 그룹보다 낮은 흡수율을 보였습니다. 그러나 AD타우린 그룹은 AD 그룹보다 상대적으로 높은 흡수율을 보였습니다. AD 그룹의 표적 부위에 대한 주사 후 50분(p.i.)의 흡수율은 WT 그룹에 비해 25-36% 낮았습니다(표 1). 표적 부위의 방사능은 AD타우린 그룹이 AD 그룹보다 31~40% 더 높았습니다. 기준 부위인 소뇌의 방사능은 모든 그룹에서 비슷하게 나타났습니다.

Figure 2

Time-activity curves of the cortex, striatum, hippocampus, thalamus and cerebellum regions (A–E). Brain uptake in the taurine-treated AD group was higher than that in the AD group but lower than that in the WT group. AUC values for the target regions (F–J). AUC values in the AD group were lower than the corresponding values in the WT group, but the ADTaurine group showed higher AUC values than the AD group. Data represent the mean values ± SD (n = 5). *p < 0.05, **p < 0.01, ***p < 0.001, n.s. = statistically nonsignificant difference. Mean values were calculated and statistical analysis was performed using Prism software (version 8).

Full size image

Table 1 Comparison of SUVs for the target regions at 50 min p.i.

Full size table

These aspects are well represented in the pharmacokinetic (PK) parameters (Table 2). In the AD group, all area under the curve (AUC) values of the target regions were 27–38% lower than the corresponding values in WT mice (Fig. 2F–J). The taurine group showed a 37–46% higher AUC value than the AD group. The maximum concentration (Cmax) values of the target regions occurred between 1.95 and 2.48 min in the WT group, and the AD group exhibited comparable Cmax values (1.67–2.44). However, the Cmax values of the ADTaurine group increased compared to those of the other groups (2.41–3.30). According to the results of the peak arrival times (Tmax), 18F-FPEB reached a maximum concentration at 3.25 min p.i in the WT group. However, the Tmax values in the AD and ADTaurine groups were shorter than that in the WT group (AD: 1.55–2.34 min, ADTaurine: 1.35–1.45 min).

Table 2 Comparison of PK parameters for 18F-FPEB. The Cmax values of the ADTaurine group increased compared to those of the other groups.

Full size table

Distribution volume ratios (DVRs)

To elucidate the specific binding level for metabolic glutamate receptor type 5 (mGluR5), we calculated regional DVR values (Table 3). The mean DVR values for the AD group were 29–42% lower than those for the WT group. However, the ADTaurine group showed 15–20% higher DVR values than the AD group.

Table 3 Comparison of regional DVR values. The binding values in the ADTaurine group were significantly higher than those in the AD group.

Full size table

Immunoblotting

To determine whether the actual Aβ burden was affected by taurine, we performed immunohistochemistry (Fig. 3). As shown in Fig. 3A, Aβ deposition was not detected only in the WT mice. No morphological differences in Aβ were observed between the AD and ADTaurine groups. Additionally, no difference in Aβ deposition was observed between the two groups in the quantitative analysis (Fig. 3B, AD: 10.8 ± 2.8 vs ADTaurine: 10.8 ± 3.3, p > 0.05).

Figure 3

Immunohistochemical staining of Aβ in the brains of AD and ADTaurine mice (A). The insets represent high-magnification images of the hippocampus. No morphological difference in Aβ was observed between the AD and ADTaurine groups. Quantification of Aβ deposition in the hippocampus (B). No quantitative differences were observed between the AD and ADTaurine groups. Values are presented as the mean ± SD, n.s. = statistically nonsignificant difference, n.d. = not detected. All statistical analysis was performed using Prism software (version 8).

Full size image

Discussion

Early intervention for AD is known to have a greater positive effect than interventions during middle or late stages. Amyloid plaque deposition begins in mice of the 5xFAD strain at 2 months of age25. Therefore, in this study, taurine supplementation was started at 2 months of age to determine the therapeutic potential of taurine in the early stages of AD. Although taurine supplementation did not reduce amyloid pathology in the AD animal model, it significantly increased brain uptake of mGluR5. PK analysis also showed that the maximum concentration values were elevated by taurine, indicating that taurine may increase cerebral blood flow. Therefore, early treatment with taurine facilitated recovery of the glutamate system in AD. This is the first study to eval‎uate the therapeutic effect of taurine in AD using molecular imaging.

Many studies have reported that the glutamate system is associated with the progression of AD26,27,28. Caroline et al. reported that deregulation of glutamate-mediated excitatory signaling is a common mechanism in AD29. Renner et al.30 reported that the Aβ oligomer (AβO) directly causes deleterious effects in glutamate neurotransmission, leading to elevated intracellular calcium levels. In addition, Hamilton et al.31 showed that pathological glutamate signaling contributes to neuronal cell death. Glutamate receptor antagonists have been developed to treat AD, and their therapeutic efficiency has been verified. However, side effects, such as nausea, anorexia, dizziness and headache, which decrease the quality of life of patients, have been reported6, 7.

Taurine has not been reported to cause specific adverse events in clinical or preclinical cases. Previous clinical studies have reported that taurine does not induce genotoxic, carcinogenic or teratogenic effects in stroke or heart ischemia patients32,33,34. In Murakami et al.’s study35, no specific side effects were observed when C57BL/6J mice were treated with taurine for 6 months. Our study also revealed no severe side effects in rodents despite the long-term use of taurine for 7 months. We did not observe any changes in hair loss, water consumption or body weight in the mice throughout the experiment. In addition, no specific macroscopic changes were found upon autopsy. These results suggest that taurine has the potential to treat AD without side effects.

Biologically, taurine plays several crucial roles in the modulation of calcium signaling, osmoregulation, and membrane stabilization36, 37. The sulfonic acid group in taurine has been reported to bind to Aβ and prevent glycosaminoglycans (GAGs) from binding to Aβ. In AD patients, amyloid peptide binds to GAGs, causing plaques to accumulate in the brain and destroy neurons38. Another clinical study reported that 3-amino-1-propane sulfonic acid (3-APS) was designed as an anti-amyloid therapy and significantly reduces Aβ in the brain39. Taurine has structural similarity to 3-APS; therefore, we postulated that taurine would eventually bind Aβ directly to inhibit the interaction of GAGs with amyloid peptide20. This series of events is thought to eventually led to downregulation of mGluR5. Many studies in rodents also have demonstrated the effects of taurine on AD. Kim et al.40 reported that taurine significantly ameliorated hippocampus-related cognitive deficits in an AD mouse model. In another recent study, taurine was reported to bind directly to AβO and consequently ameliorated the behavioral deficiencies of AD, such as the loss of learning and memory18. Roberto et al.26 reported that taurine strongly protected neurons against the neurotoxicity of Aβ in vitro. Thy also demonstrated that taurine prevented neurotoxicity caused by Aβ and glutamate receptor agonists in an in vitro study. However, the studies referenced above were all performed based on ex vivo or behavioral observations rather than changes at the molecular level. The progression of AD begins preferentially with a change at the molecular level, and then clinical symptoms appear due to functional and structural changes in the brain. The novelty of the present study is that the therapeutic effects of taurine on AD were eval‎uated via functional PET.

Although the mechanism by which taurine regulates glutamatergic signaling is not yet clear, taurine may act as a modulator against AD in two manners. First, taurine is expected to play a role in facilitating the regulation of calcium signaling homeostasis in the brain, thereby leading to recovery of the glutamatergic system. Intracellular Ca2+ signaling is fundamental to neuronal physiology; therefore, disruptions in Ca2+ homeostasis are implicated in neuronal diseases, including AD41. Under physiological conditions, when calcium levels are increased in the mitochondria, Ca2+ is removed by a sodium-calcium exchanger. Such feedback helps maintain homeostasis of cellular calcium levels42. However, under pathological conditions, Aβ accumulation leads to upregulation of intracellular Ca2+ in mitochondria, which induces neuronal death43. Extensive evidence indicates that Aβ causes dysregulation of calcium signaling. Kim et al.44 reported that Aβ1–42 causes mitochondrial depolarization and increases dysregulated cellular Ca2+ levels. Weiss et al.45 showed that nimodipine, a Ca2+ channel blocker, reduced Aβ levels, implying that calcium homeostatic mechanisms are involved in Aβ neurotoxicity. Jakaria et al.46 also suggested that taurine reduced abnormal Ca2+ signaling in sensory neurons, which reduced glutamate-mediated toxicity. Second, taurine regulates AβO accumulation, eventually leading to upregulated glutamate. Previous studies showed that taurine inhibited the accumulation of amyloid plaques and prevented neurotoxicity in AD20, 26. However, in our immunohistochemistry analysis, no difference in Aβ plaque concentrations was found between the taurine-treated group and the AD group. The reason for this result is not obvious, but we hypothesize that taurine may be involved in a mechanism inhibiting the toxicity of AβO rather than Aβ plaques. Soluble AβO appears to be a more toxic and disease-relevant element in AD pathogenesis than plaques47,48,49. Jang et al.18 reported that taurine did not affect Aβ plaque levels in the APP/PS1 model but interacted directly with AβO, which led to enhanced memory function. Lesné et al.50 reported that Aβ plaques did not induce memory impairment in the absence of AβO in Tg2576 mice. Gandy et al.51 revealed that soluble AβO induced impaired cognitive function in an AD mouse model without Aβ plaques. Further investigation is required to address this issue.

The present study had some limitations. First, we did not perform glutamatergic signal measurements using nanomaterial-based biosensors. The level of glutamate was assessed only by PET images, and the exact molecular mechanism of taurine in AD cannot be determined from such images. Second, the number of animals included in the imaging and histological analyses was too few to derive solid support for the imaging findings (n = 5 for each group). Third, the most appropriate therapeutic intervention time could not be concluded from this study. We began treating AD mice with taurine at 2 months of age, representing an early therapeutic intervention. Therefore, the effects of administering taurine to aged mice remain unknown. Fourth, biochemical information supporting the effect of taurine on improving glutamatergic signaling is lacking, which needs to be addressed in a future study. Last, we did not include taurine-treated WT mice as a positive control group, which may have more clearly revealed the AD-specific treatment effects of taurine. In summary, although taurine treatment did not completely recover the glutamatergic system, it caused increased brain uptake of mGluR5 on PET and specific binding in the AD animal model. According to these results, taurine exerts a potential therapeutic effect in AD.

토론

알츠하이머병에 대한 조기 개입은

중기 또는 말기의 개입보다 긍정적인 효과가 더 큰 것으로 알려져 있습니다.

아밀로이드 플라크 침착은 생후 2개월에 5xFAD 균주 마우스에서 시작됩니다25.

따라서

이 연구에서는

알츠하이머 초기 단계에서 타우린의 치료 가능성을 확인하기 위해

생후 2개월에 타우린 보충제를 투여하기 시작했습니다.

타우린 보충제는

AD 동물 모델에서 아밀로이드 병리를 감소시키지는 못했지만,

mGluR5의 뇌 흡수를 유의하게 증가시켰습니다.

PK 분석에서도

타우린에 의해 최대 농도 값이 상승하는 것으로 나타나

타우린이 뇌 혈류를 증가시킬 수 있음을 시사했습니다.

따라서

타우린으로 조기에 치료하면

알츠하이머병에서

글루타메이트 시스템의 회복이 촉진되는 것으로

나타났습니다.

이 연구는 분자 이미징을 사용하여 알츠하이머병에서 타우린의 치료 효과를 평가한 최초의 연구입니다.

많은 연구에서

글루타메이트 시스템이

AD의 진행과 관련이 있다고 보고했습니다26,27,28.

Caroline 등은 글루타메이트 매개 흥분성 신호의 조절 완화가

AD의 일반적인 메커니즘이라고 보고했습니다29.

레너등30은

Aβ 올리고머(AβO)가

글루타메이트 신경전달에 직접적으로 해로운 효과를 일으켜

세포 내 칼슘 수치를 상승시킨다고 보고했습니다.

또한 해밀턴등31은

병적인 글루타메이트 신호가

신경세포 사멸에 기여한다는 사실을 보여주었습니다.

알츠하이머병 치료를 위해

글루타메이트 수용체 길항제가 개발되어

그 치료 효과가 검증되었습니다.

그러나

환자의 삶의 질을 떨어뜨리는

메스꺼움, 식욕부진, 어지럼증, 두통 등의 부작용이 보고되고 있습니다6, 7.

타우린은

임상 또는 전임상 사례에서 특정 부작용을 유발하는 것으로 보고되지 않았습니다. 이전의 임상 연구에 따르면 타우린은 뇌졸중이나 심장 허혈 환자에서 유전 독성, 발암성 또는 기형 유발 효과를 유발하지 않는 것으로 보고되었습니다32,33,34. Murakami 등의 연구35에서는 C57BL/6J 마우스를 6개월 동안 타우린으로 치료했을 때 특별한 부작용이 관찰되지 않았습니다. 저희 연구에서도 설치류에 타우린을 7개월간 장기간 투여했음에도 불구하고 심각한 부작용이 나타나지 않았습니다. 실험 기간 동안 쥐의 탈모, 수분 섭취량 또는 체중 변화는 관찰되지 않았습니다. 또한 부검 결과에서도 특별한 거시적 변화는 발견되지 않았습니다. 이러한 결과는 타우린이 부작용 없이 알츠하이머병을 치료할 수 있는 잠재력을 가지고 있음을 시사합니다.

생물학적으로 타우린은 칼슘 신호 조절, 삼투압 조절 및 막 안정화에 중요한 역할을 합니다36, 37. 타우린의 설폰산 그룹은 Aβ에 결합하여 글리코사미노글리칸(GAG)이 Aβ에 결합하는 것을 방지하는 것으로 보고되었습니다. 알츠하이머병 환자에서 아밀로이드 펩타이드는 GAG에 결합하여 플라크가 뇌에 축적되어 뉴런을 파괴합니다38. 또 다른 임상 연구에 따르면 3- 아미노 -1- 프로판 설폰산(3-APS)은 항 아밀로이드 치료제로 설계되었으며 뇌에서 Aβ를 크게 감소시킨다고 합니다39. 타우린은 3-APS와 구조적으로 유사하므로, 타우린이 결국 Aβ와 직접 결합하여 GAG와 아밀로이드 펩타이드의 상호작용을 억제할 것이라는 가설을 세웠습니다20. 이러한 일련의 사건은 결국 mGluR5의 하향 조절로 이어진다고 생각됩니다. 설치류를 대상으로 한 많은 연구에서도 타우린이 알츠하이머에 미치는 영향이 입증되었습니다. Kim등40은 타우린이 AD 마우스 모델에서 해마 관련 인지 결손을 유의미하게 개선했다고 보고했습니다. 최근의 또 다른 연구에서는 타우린이 AβO에 직접 결합하여 학습 및 기억력 상실과 같은 AD의 행동 결핍을 개선하는 것으로 보고되었습니다18. 로베르토등26은 타우린이 시험관 내에서 Aβ의 신경 독성으로부터 뉴런을 강력하게 보호한다고 보고했습니다. 또한 시험관 연구에서 타우린이 Aβ 및 글루타메이트 수용체 작용제로 인한 신경 독성을 예방한다는 사실을 입증했습니다. 그러나 위에 언급된 연구는 모두 분자 수준의 변화가 아닌 생체 외 또는 행동 관찰을 기반으로 수행되었습니다. 알츠하이머병의 진행은 우선적으로 분자 수준의 변화에서 시작되며, 이후 뇌의 기능적, 구조적 변화로 인해 임상 증상이 나타납니다. 본 연구의 참신함은 타우린이 알츠하이머병에 미치는 치료 효과를 기능성 PET를 통해 평가했다는 것입니다.

타우린이

글루탐산 신호 전달을 조절하는 메커니즘은 아직 명확하지 않지만,

타우린은 두 가지 방식으로 AD에 대한 조절제로 작용할 수 있습니다.

첫째, 타우린은 뇌의 칼슘 신호 항상성 조절을 촉진하여

글루탐산염 시스템의 회복을 유도하는 역할을 할 것으로 기대됩니다.

세포 내 Ca2+ 신호는 신경 세포 생리학의 기본이므로,

Ca2+ 항상성 장애는

알츠하이머병을 포함한 신경 질환과 관련이 있습니다41.

생리적 조건에서

미토콘드리아에서 칼슘 수치가 증가하면

나트륨-칼슘 교환기에 의해 Ca2+가 제거됩니다.

이러한 피드백은

세포 칼슘 수준의 항상성을 유지하는 데 도움이 됩니다42.

그러나

병리학적인 조건에서 Aβ 축적은

미토콘드리아에서 세포 내 Ca2+의 상향 조절로 이어져

신경 세포 사멸을 유도합니다43.

Aβ가 칼슘 신호의 조절 이상을 유발한다는 광범위한 증거가 있습니다. Kim등44은 Aβ1-42가 미토콘드리아 탈분극을 유발하고 조절 장애가 있는 세포 Ca2+ 수준을 증가시킨다고 보고했습니다. Weiss등45은 Ca2+ 채널 차단제인 니모디핀이 Aβ 수치를 감소시켜 칼슘 항상성 메커니즘이 Aβ 신경독성에 관여한다는 것을 보여주었습니다. Jakaria등46은 타우린이 감각 뉴런에서 비정상적인 Ca2+ 신호를 감소시켜 글루타메이트 매개 독성을 감소시킨다고 제안했습니다.

둘째, 타우린은 AβO 축적을 조절하여

결국 글루타메이트의 상향 조절을 유도합니다.

이전 연구에 따르면

타우린은 아밀로이드 플라크의 축적을 억제하고

AD에서 신경 독성을 예방하는 것으로 나타났습니다20, 26.

그러나 면역 조직 화학 분석에서 타우린 처리 그룹과 AD 그룹간에 Aβ 플라크 농도의 차이는 발견되지 않았습니다. 이 결과의 이유는 명확하지 않지만 타우린이 Aβ 플라크보다는 AβO의 독성을 억제하는 메커니즘에 관여할 수 있다는 가설을 세우고 있습니다. 수용성 AβO는 플라크47,48,49 보다 AD 발병 기전에서 더 독성이 강하고 질병과 관련된 요소로 보입니다. 장등18은 타우린이 APP/PS1 모델에서 Aβ 플라크 수치에 영향을 미치지 않고 AβO와 직접 상호 작용하여 기억 기능을 향상시킨다고 보고했습니다. Lesné등50은 Tg2576 마우스에서 Aβ 플라크가 없는 경우 기억력 손상을 유발하지 않는다고 보고했습니다. Gandy 등.51은 수용성 AβO가 Aβ 플라크가 없는 AD 마우스 모델에서 인지 기능 손상을 유발한다는 사실을 밝혀냈습니다. 이 문제를 해결하려면 추가 조사가 필요합니다.

본 연구에는 몇 가지 한계가 있었습니다. 첫째, 나노물질 기반 바이오센서를 사용하여 글루타메이트 신호 측정을 수행하지 않았습니다. 글루타메이트 수준은 PET 이미지로만 평가되었으며, 이러한 이미지로는 알츠하이머병에서 타우린의 정확한 분자 메커니즘을 확인할 수 없습니다. 둘째, 영상 및 조직학적 분석에 포함된 동물의 수가 너무 적어 영상 결과에 대한 확실한 근거를 도출할 수 없었습니다(각 그룹당 n = 5). 셋째, 이 연구에서 가장 적절한 치료 개입 시기를 결론 내릴 수 없었습니다. 우리는 생후 2개월에 타우린으로 AD 마우스를 치료하기 시작했는데, 이는 초기 치료 개입에 해당합니다. 따라서 노령 쥐에게 타우린을 투여했을 때의 효과는 아직 알려지지 않았습니다. 넷째, 타우린의 글루탐산 신호 개선 효과를 뒷받침하는 생화학적 정보가 부족하여 향후 연구에서 다뤄야 할 필요가 있습니다. 마지막으로, 타우린으로 치료한 WT 마우스를 양성 대조군으로 포함하지 않았기 때문에 타우린의 AD 특이적 치료 효과를 더 명확하게 밝힐 수 있었을 것입니다. 요약하면, 타우린 치료가 글루탐산 시스템을 완전히 회복시키지는 못했지만, 타우린은 PET에서 mGluR5의 뇌 흡수와 AD 동물 모델에서의 특이적 결합을 증가시켰습니다. 이러한 결과에 따르면 타우린은 알츠하이머병에서 잠재적인 치료 효과를 발휘합니다.

Methods

Animals

The care, maintenance, and treatment of animals in these studies followed protocols approved by the Institutional Animal Care and Use Committee of Korea Institute of Radiological & Medical Sciences (KIRAMS), and the experiments involving animals were performed according to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health. The animal housing chambers were automatically controlled at a temperature of 22 ± 3 °C and 55 ± 20% humidity under a 12-h light/dark cycle. A sterilized rodent diet and purified tap water were supplied ad libitum.

Drugs

Taurine was purchased from Sigma-Aldrich (St. Louis, Missouri, USA).

Study protocol

Three groups of mice were used for these studies: B6/SJL F1 hybrids (wild-type (WT), n = 5), 5xFAD mice (AD, n = 5), and 5xFAD mice treated with taurine by oral administration in drinking water from 2 to 9 months of age (ADTaurine, n = 5). Taurine was administered at a dose of 1000 mg/kg/day, which was reported to correspond to reduced hippocampal Aβ and behavioral improvements in AD mice in a previous study40. To calculate the taurine dose, the amount of water intake per mouse was calculated by measuring water consumption every week in each cage. The weight of each animal was also measured weekly to calculate the taurine dose. At 9 months of age, all groups underwent glutamate PET. After the imaging study was completed, the animals were sacrificed, and brain tissue samples were prepared. Immunohistochemistry experiments were performed to quantify mGluR5 in the target regions. A detailed study protocol is illustrated in Fig. 4.

Figure 4

Schematic of the study process.

Full size image

Preparation of 18F-FPEB

18F-FPEB was synthesized by nucleophilic substitution of F-18 on the precursor. The tracer was prepared according to a previously described procedure52. The mean radiochemical purity was 99%.

PET/CT scan

PET images of the mice were obtained using a small animal PET scanner (NanoScan, Mediso, Budapest, Hungary). The scanner has a peak absolute system sensitivity of > 9% in the 250–750 keV energy window, an axial field of view of 28 cm, a trans axial field of view of 35–120 mm and a trans axial resolution of 0.7 mm at 1 cm off center. Mice were anesthetized with 2.0% isoflurane, and 18F-FPEB (9.4 ± 1.2 MBq/200 µL) was injected through the tail vein with a syringe pump (KDS 210, KD scientific, Holliston, MA) for 1 min. Simultaneously, a dynamic PET scan was performed for 60 min, and images were reconstructed using the 3-dimensional ordered subset expectation maximization (3D-OSEM) algorithm with 4 iterations (14 × 30 s, 3 × 60 s, 4 × 300 s, 3 × 600 s, 24 frames in total). The imaging scans were acquired with an energy window of 400–600 keV. All images were reconstructed using the 3D-OSEM algorithm (4 iterations, 6 subsets). For attenuation correction and anatomical information, computed tomography (CT) scans were acquired immediately after PET (50 kVp of X-ray voltage with 0.16 mAs and a 520-µA anode current).

Image analysis

For the analysis of mouse brain data, a house-made brain MR template for 5xFAD was used53. For motion correction, all dynamic PET images were realigned to the mean PET images (0–24 frames) by the sum of the squared difference dissimilarity measure and the Powell algorithm (PMOD 3.4, PMOD Technologies Ltd, Switzerland). Considering that transient equilibrium for 18F-FPEB was reached after an average of 30 min, we used the mean PET images from the time windows of 30–60 min in dynamic PET. Then, each mean PET image was spatially normalized to the T2-weighted mouse brain MR template (M. Mirrione), which is embedded in PMOD software. Finally, individual dynamic PET images for all groups were spatially normalized to the MR template, masked to exclude extracerebral signals and smoothed with a 3D Gaussian filter (FWHM = 1.0 mm). The cortex, striatum, hippocampus, thalamus and cerebellum were selected as volumes of interest (VOIs) on the MR template (Fig. 5). Decay-corrected regional time-activity curves (TACs) were acquired from VOIs and normalized to account for differences in injected doses and body weights to yield units of the standardized uptake value (SUV). The SUV values obtained for each region of activity were multiplied by the body weight divided by the injected dose for each animal. PK parameters were estimated from TACs using Prism software (version 8, GraphPad Software, Inc., USA). AUC values were obtained from 10 to 60 min by the trapezoid rule. The Tmax and the Cmax were also compared between groups. In addition, the DVR was estimated using Logan graphical analysis to eval‎uate receptor binding density54. Using the Simplified Reference Tissue Model (SRTM), the individual clearance rate (k2′) was obtained from the TACs of target regions (t∗ = 10 min) and then applied to each DVR calculation.

Figure 5

Definition of VOIs in an AD mouse in the horizontal (A), coronal (B), and sagittal (C) planes. VOI applied PET images were produced using the PMOD fusion tool (version 3.4).

Full size image

Immunohistochemistry

After PET imaging studies, immunostaining experiments were performed. The test was performed as previously described25, 53. Two age-matched mice per group were sacrificed, and then their brains were extracted. Formalin-fixed mouse brains were first cranially divided into the hippocampal region (from − 1.94 to − 1.58 mm at the bregma) using disposable blades, embedded into paraffin and sectioned at 5-µm intervals. Immunohistochemistry was conducted using a Vectastain Elite ABC kit (Vector Laboratories Inc., Burlingame, CA, USA) following the manufacturer’s protocol. For antigen retrieval‎, the sections were placed in citrate buffer (pH 6.0) and heated in boiling water for 30 min. The sections were then placed in 0.3% H2O2 in absolute methanol for 15 min at room temperature to block endogenous peroxidase. The sections were incubated overnight at 4 °C with mouse anti-6E10 antibody (1:1000, SIG-39320, Covance, Emeryville, CA), washed and incubated with the corresponding secondary antibody. ImageJ was used to quantify the amount of Aβ in the hippocampus. As a control, the primary antibody was omitted from several test sections in each experiment. The sections were counterstained with Harris’ hematoxylin prior to mounting.

Statistical analysis

The quantitative results are expressed as the means ± SD. All statistical results were analyzed with Prism software. Student’s t-test was used to determine statistical significance at the 95% confidence level, and p < 0.05 was considered significantly different.

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