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Metformin attenuates palmitate-induced endoplasmic reticulum stress, serine phosphorylation of IRS-1 and apoptosis in rat insulinoma cells.

Simon-Szabó L, Kokas M, Mandl J, Kéri G, Csala M - PLoS ONE (2014)

Bottom Line: The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis).Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells.Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary; MTA-SE Pathobiochemistry Research Group, Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary.

ABSTRACT
Lipotoxicity refers to cellular dysfunctions caused by elevated free fatty acid levels playing a central role in the development and progression of obesity related diseases. Saturated fatty acids cause insulin resistance and reduce insulin production in the pancreatic islets, thereby generating a vicious cycle, which potentially culminates in type 2 diabetes. The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis). Since improvement of β-cell viability is a promising anti-diabetic strategy, the protective effect of metformin, a known insulin sensitizer was studied in rat insulinoma cells. Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells. Attenuation of β-cell lipotoxicity was also revealed by lower induction/activation of various ER stress markers, e.g. phosphorylation of eukaryotic initiation factor 2α (eIF2α), c-Jun N-terminal kinase (JNK), insulin receptor substrate-1 (IRS-1) and induction of CCAAT/enhancer binding protein homologous protein (CHOP). Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

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Cell viability.RINm5F rat insulinoma cells were treated with palmitate (500 µM) or vehicle at 70–80% confluence and incubated for various time periods up to 24 h as indicated. Cell viability was assessed by trypan blue exclusion and expressed as the percentage of live cells in the total cell population. Data are presented as mean values ± S.D. of three experiments; aP<0.05, bP<0.01, cP<0.001 v.s. untreated control.
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pone-0097868-g001: Cell viability.RINm5F rat insulinoma cells were treated with palmitate (500 µM) or vehicle at 70–80% confluence and incubated for various time periods up to 24 h as indicated. Cell viability was assessed by trypan blue exclusion and expressed as the percentage of live cells in the total cell population. Data are presented as mean values ± S.D. of three experiments; aP<0.05, bP<0.01, cP<0.001 v.s. untreated control.

Mentions: β-Cell protective effect of metformin was tested by assessing lipoapoptosis in RINm5F rat insulinoma cells. Cell death was provoked by the addition of albumin-conjugated palmitate at 500 µM concentration, according to previous studies using the same cell line [15]. Palmitate treatment did not cause a significant change in β-cell viability within the first 6 h; however an accelerating decrease in the number of viable cells was observed in longer incubations and approximately 75% of palmitate-treated cells died within 24 h (Fig. 1). This time course and several previous findings in β-cells [18]–[20] or other cell types [21]–[23] indicated that early lipoapoptosis and the underlying mechanisms could be best investigated at 6–8 h.


Metformin attenuates palmitate-induced endoplasmic reticulum stress, serine phosphorylation of IRS-1 and apoptosis in rat insulinoma cells.

Simon-Szabó L, Kokas M, Mandl J, Kéri G, Csala M - PLoS ONE (2014)

Cell viability.RINm5F rat insulinoma cells were treated with palmitate (500 µM) or vehicle at 70–80% confluence and incubated for various time periods up to 24 h as indicated. Cell viability was assessed by trypan blue exclusion and expressed as the percentage of live cells in the total cell population. Data are presented as mean values ± S.D. of three experiments; aP<0.05, bP<0.01, cP<0.001 v.s. untreated control.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4045581&req=5

pone-0097868-g001: Cell viability.RINm5F rat insulinoma cells were treated with palmitate (500 µM) or vehicle at 70–80% confluence and incubated for various time periods up to 24 h as indicated. Cell viability was assessed by trypan blue exclusion and expressed as the percentage of live cells in the total cell population. Data are presented as mean values ± S.D. of three experiments; aP<0.05, bP<0.01, cP<0.001 v.s. untreated control.
Mentions: β-Cell protective effect of metformin was tested by assessing lipoapoptosis in RINm5F rat insulinoma cells. Cell death was provoked by the addition of albumin-conjugated palmitate at 500 µM concentration, according to previous studies using the same cell line [15]. Palmitate treatment did not cause a significant change in β-cell viability within the first 6 h; however an accelerating decrease in the number of viable cells was observed in longer incubations and approximately 75% of palmitate-treated cells died within 24 h (Fig. 1). This time course and several previous findings in β-cells [18]–[20] or other cell types [21]–[23] indicated that early lipoapoptosis and the underlying mechanisms could be best investigated at 6–8 h.

Bottom Line: The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis).Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells.Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary; MTA-SE Pathobiochemistry Research Group, Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary.

ABSTRACT
Lipotoxicity refers to cellular dysfunctions caused by elevated free fatty acid levels playing a central role in the development and progression of obesity related diseases. Saturated fatty acids cause insulin resistance and reduce insulin production in the pancreatic islets, thereby generating a vicious cycle, which potentially culminates in type 2 diabetes. The underlying endoplasmic reticulum (ER) stress response can lead to even β-cell death (lipoapoptosis). Since improvement of β-cell viability is a promising anti-diabetic strategy, the protective effect of metformin, a known insulin sensitizer was studied in rat insulinoma cells. Assessment of palmitate-induced lipoapoptosis by fluorescent microscopy and by detection of caspase-3 showed a significant decrease in metformin treated cells. Attenuation of β-cell lipotoxicity was also revealed by lower induction/activation of various ER stress markers, e.g. phosphorylation of eukaryotic initiation factor 2α (eIF2α), c-Jun N-terminal kinase (JNK), insulin receptor substrate-1 (IRS-1) and induction of CCAAT/enhancer binding protein homologous protein (CHOP). Our results indicate that the β-cell protective activity of metformin in lipotoxicity can be at least partly attributed to suppression of ER stress.

Show MeSH
Related in: MedlinePlus