- 學位論文
Nicotinic acid延長壽命的能力取決於細胞內NAD+是否低於sirtuins的受質飽和濃度
The lifespan-extension ability of nicotinic acid depends on whether the intracellular NAD+ level is lower than the saturated concentration of sirtuins
摘要
Nicotinic Acid (菸鹼酸，NA)是維生素B3（亦稱為菸鹼素niacin）主要的形式之一，具有良好的降血脂功效。研究指出熱量限制能經由增加細胞內的NAD+濃度，進而活化sirtuins蛋白（在線蟲主要是Sir2.1；人類是SIRT1）的活性而能延長壽命。NA在體內能代謝生成NAD+，理論上能作為熱量限制模仿劑，延長細胞和線蟲的壽命，然而，研究卻指出NA可以延長線蟲的壽命，但無法延長細胞的壽命，因此本研究擬以Hs68細胞與N2線蟲兩種模式探討NA延長壽命的能力和機制，以評估其作為熱量限制模仿劑的潛力，並解答NA對細胞和線蟲作用不一致的原因。結果顯示，NA 73.9μg/plate能延長線蟲的平均壽命約17% (P < 0.05)，並有效改善線蟲活動力與降低autofluorescence等衰老標記，然而，NA對細胞壽命與SA-βG衰老標記則無顯著影響。無論對細胞和線蟲NA皆可有效提升細胞內或體內的NAD+濃度。進一步研究發現SIRT1所需NAD+之飽和濃度約為200μM，正常細胞中NAD+濃度約為460μM，而N2線蟲體內之NAD+濃度則約為55μM，當線蟲培養在外加NAD+培養基，使體內NAD+濃度達到約150μM時，NA即失去顯著延長線蟲壽命及改善衰老輔助指標的能力。因此，Hs68細胞可能因為NAD+濃度已超過SIRT1所需受質的飽和濃度，造成NA延長細胞壽命的能力並不顯著，而由於線蟲本身NAD+含量較低，因此NA延長線蟲壽命的能力較為顯著。由此推論，補充NA具有模仿熱量限制作用應該只限於體內NAD+濃度較低的生命體或維生素B3缺乏的個體。
並列摘要
Nicotinic Acid (NA) is one of the major forms of vitamin B3 (also known as niacin) and has good hypolipidemic effects. Studies have shown that calorie restriction can extend lifespan by increasing the concentration of NAD+ in cells, thereby upregulating the activity of the sirtuins protein (Caenorhabditis elegans is Sir2.1; human is SIRT1). NA can be metabolized in the body to produce NAD+, which can theoretically act as a calorie restriction mimetic (CRM) to extend the lifespan of cells and C. elegans. However, studies have pointed out that NA has an inconsistent effect on C. elegans and cells lifespan. Therefore, this study explored the ability and mechanism of NA to extend lifespan in both Hs68 cells and C. elegans models to assess its potential as a CRM and to answer the inconsistent effect on cells and C. elegans. The results showed that NA could effectively increase the concentration of NAD+ in both Hs68 cells and C. elegans. In addition, NA 73.9μg/plate could elevate the average lifespan of C. elegans by about 17% (P < 0.05) and effectively improve aging markers such as autofluorescence and motility of C. elegans . However, NA has no significant effect on Hs68 cells lifespan and aging markers SA-βG. Further studies indicated that the saturated NAD+ required by SIRT1 was about 200μM, and the concentration of NAD+ in normal cells was about 460μM. The concentration of NAD+ in N2 C. elegans was about 55μM. When the C. elegans were cultured in Nematode Growth Media (NGM) containing 100μM NAD+, the concentration of NAD+ in C. elegans could reach about 150 μM, and NA lost the ability to further significantly extend the lifespan and improve the aging markers of C. elegans. Thus, NA may not have a significant ability to extend the lifespan of Hs68 cells because the concentration of NAD+ exceeds the saturated concentration of SIRT1. However, due to the lower NAD+ levels in C. elegans, the ability of NA to extend the lifespan of C. elegans is significant. It is inferred that the supplementation of NA for an calorie restriction-mimicking effect should be limited to individuals with lower NAD+ concentrations in vivo or vitamin B3 deficient individuals.