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腦神經膠質瘤是人類中最常見及最惡性的腦瘤。其癌化的機制迄今尚未明
瞭。在中樞神經內, 胰島素會促進腦神經細胞的生長與發育, 並可充當腦
細胞的調節因子。而本研究主要是探討經過血清饑餓過的腦膠質瘤, 胰島
素對其早期細胞生長的影響。在我們的細胞培養系統中, 腦膠質瘤養在額
外添加胰島素的培養液中, 的確會生長得較快。然而, 當細胞經過血清饑
餓的處理後, 胰島素則會減緩細胞早期 12 至 24 小時內的生長速率。而
且血清饑餓的處理時間愈久, 細胞生長速率愈遲緩。本論文藉由分析細胞
週期, 細胞的存活及細胞漂浮等方法逐一探究胰島素造成細胞生長受阻滯
的原因。當血清饑餓處理過的細胞被添加胰島素後,會增加 trypan blue-
positive 的死亡細胞, 而且也會造成部分細胞的漂浮, 但這些細胞的數
目並不足以解釋受胰島素作用後, 所產生生長速率降低的現象。當胰島素
作用六小時後, 外觀上呈現計劃性死亡的細胞有增多( 多達 12% ) 的趨
勢, 與 Histone 有聯結的 DNA片斷, 也比較多。在胰島素存在下,可加速
細胞週期的進程,同時伴隨 DNA 合成的能力增加; 而且以 Okadaic acid
作為細胞週期的抑制因子, 也證實細胞會比對照組較快達到 G2/M 期; 胰
島素相似生長因子與胰島素具有類似的作用, 會延滯細胞生長速率, 而細
胞轉型因子 -beta 及表皮細胞生長因子則不會。綜合這些結果所示, 被
血清饑餓過的細胞中, 有某些次族群的細胞,受胰島素作用後, 引發計劃
性死亡, 而造成早期細胞生長的降緩。
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Glioblastoma is the most common and malignant brain tumors in
the human central nervous system (CNS). As yet, the mechanism
of tumor progression is not well understood. In the CNS,
insulin promotes the growth and development of neuron and acts
as a neuronmodulator. The objective of this study was to
examine the influence on the early growth phase of gliomas
after serum starvation. In our culture system, glioma U-373MG
cells grew as reported more faster in medium containing
additional insulin. Yet, insulin decreased the growth rate in
the period of early 12-24h when cells were serum-starved
previously.The longer the cells were starved, the lower the
growth rate was. The possible causes for this suppression of
growth rate were approached by analyzing parameters of cell
cycle, cell viability and cell detachment.The trypan blue-
positive death cells and floated cells were increased in
cultures with lower growth rate, but that were not sufficient
to explain the insulin-induced suppression. At 6 h after
insulin treatment,cells with apoptotic nuclei, histone-
associated DNA fragments were increased.Accelerated cell cycle
in company with an increase of the [3H]-thymindine
incorporation was seen among cells in the presence of insulin.
Besides, the promotion of cell cycle by insulin was confirmed
by using okadaic acid as cell cycle blocker. Thus, the
decreased growth rate upon insulin stimulation was not due to
retarded cell cycle progression. The IGF-I,but not EGF and TGF-
beta, could also suppress cell growth as the insulin did. In
conclusion, these data indicated that programmed cell death was
triggered by insulin and IGF-I in a subpopulation of serum-
starved cells and that might be the main cause for the observed
growth suppression in glioma U-373MG.
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