Antiapoptotic Effect Of Insulin Research Articles

Uncoupling protein 2 facilitates insulin-elicited protection against lipopolysaccharide-induced myocardial dysfunction

Sepsis-induced myocardial dysfunction is a critical cause of high mortality among patients with sepsis. Previously, insulin has been suggested to protect against lethal endotoxemia, while uncoupling protein 2 (UCP2) has been reported to exert beneficial effects against sepsis. Thus, this study aimed to investigate whether UCP2 is involved in insulin-elicited protection against myocardial dysfunction in lipopolysaccharide (LPS)-induced sepsis. Treatment of male SD rats with insulin for 30 min before LPS challenge improved the survival and cardiac function in endotoxemic rats, which was likely due to an insulin-dependent reduction of serum lactate dehydrogenase (LDH) activity and cardiac troponin T (cTn-T) levels, mitochondrial oxidative stress, and cardiomyocyte apoptosis. Insulin treatment also increased the Bcl-2/Bax ratio, prevented the release of cytochrome c into the cytosol, and reduced cleaved caspase-9 levels, which was determined by purifying the proteins using the His-tag Magnetic Bead Purification Kit (Fe3O4). Moreover, UCP2 was found to be upregulated in endotoxemic rats which were pretreated with insulin. To determine whether the apoptotic role of insulin is associated with UCP2 upregulation, we examined the effects of genipin, a UCP2 inhibitor, on insulin activity in LPS-treated H9c2 cells. Insulin strongly attenuated LPS-induced H9c2 cell apoptosis and stimulated UCP2 expression. However, genipin treatment eliminated the antiapoptotic effects of insulin. Thus, our results demonstrate that insulin-induced UCP2 upregulation plays a role in the protective effect of insulin against LPS-induced myocardial dysfunction.

Genetic Variants, Prediagnostic Circulating Levels of Insulin-like Growth Factors, Insulin, and Glucose and the Risk of Colorectal Cancer: The Multiethnic Cohort Study

Increased exposure of colonic and rectal epithelial cells to the promitotic and antiapoptotic effects of insulin and insulin-like growth factors (IGF) is hypothesized to increase colorectal cancer risk. In a case-control study nested within the Multiethnic Cohort, we attempted to replicate associations for five genetic variants associated with IGF system biomarkers, insulin, or glucose and to examine their association with the risk of colorectal cancer. In a subset of participants, the association between circulating biomarkers and colorectal cancer risk was examined. Unconditional logistic regression was used to calculate ORs and 95% confidence intervals (CI) for genetic variants (1,954 cases/2,587 controls) and serum biomarkers (258 cases/1,701 controls). Associations with circulating biomarkers were replicated in the Multiethnic Cohort for IGF1 rs35767 and for IGFBP3 rs2854744, rs2854746, and rs3110697 (P < 0.05). Homozygous carriers of the glucokinase regulator (GCKR) rs780094 variant T-allele were at a decreased risk of colorectal cancer (OR, 0.77; 95% CI, 0.64-0.92). In risk factor-adjusted models, participants with the highest prediagnostic IGF-II levels were at an increased risk [OR (T1 vs. T3), 1.58; 95% CI, 1.09-2.28; P(trend) = 0.011] and participants with the highest prediagnostic IGF-binding protein (IGFBP)-3 levels were at a decreased risk of colorectal cancer (OR, 0.53; 95% CI, 0.34-0.83; P(trend) = 0.003). These data provide further support for a role of prediagnostic IGF and insulin levels in the etiology of colorectal cancer. Future studies attempting to replicate the association between the GCKR rs780094 variant and the risk of colorectal cancer are warranted.

927 Antiapoptotic Effect of Insulin on Activated Hepatic Stellate Cells is Dependent on AKT and P70s6k

927 Antiapoptotic Effect of Insulin on Activated Hepatic Stellate Cells is Dependent on AKT and P70s6k

Mitogenic and anti-apoptotic effects of insulin in endometrial cancer are phosphatidylinositol 3-kinase/Akt dependent

ObjectiveTo determine serum insulin levels, expression and phosphorylation of InsR, IRS-1 and Akt in endometrial cancer (EC) tissues, and to explore the correlation between them. To investigate if insulin-induced mitogenic and anti-apoptotic effects are PI3K-dependent in EC cells. MethodsSerum insulin levels were measured by radioimmunoassay. We performed RT-PCR and western blotting to evaluate the expression and activation of key proteins of PI3K/Akt pathway in 63 EC tissues. The proliferation and apoptosis rates were determined with MTT, BrdU and annexin V/PI assays. ResultsSerum insulin levels and InsR, IRS-1 and Akt expression and phosphorylation were significantly elevated in patients with EC compared to those without EC. Additionally, levels of p-InsR, p-IRS-1, and p-Akt were significantly higher in patients with high-grade, advanced stage, deep myometrial invasion, and lymph-node metastasis. The expression and activation of InsR, IRS-1, and p-Akt were positively related with the levels of serum insulin. The insulin-induced mitogenic and anti-apoptotic effects in EC cells were blocked when cells were pre-incubated with LY294002. Ishikawa 3-H-12 cells showed increased p-Akt levels after treatment with insulin at 10−8M for 15min. The insulin-induced Akt activation was inhibited by LY294002 in a dose-dependent manner. ConclusionInsulin played an essential role in EC tumorigenesis. Activation of InsR, IRS-1, and Akt was associated with features of aggressive EC. Insulin was a mitogenic and anti-apoptotic agent for EC cells, and these effects were dependent on PI3K/Akt pathway. Decreasing insulin level and blocking the InsR-IRS-PI3K-Akt pathway could be viable preventive and therapeutic strategies for EC.

Effects of resveratrol on proliferation and apoptosis in rat ovarian theca-interstitial cells

Polycystic ovary syndrome (PCOS) is characterized by ovarian dysfunction and associated with ovarian theca-interstitial (T-I) cell hyperplasia, hyperinsulinemia, systemic inflammation and oxidative stress. This in vitro study tested whether rat T-I cell growth with or without insulin can be altered by resveratrol, a natural polyphenol with anti-carcinogenic, anti-inflammatory, anti-proliferative and antioxidant properties. Rat T-I cells were cultured with and without resveratrol and/or insulin, and the effects on DNA synthesis, number of viable cells and markers of apoptosis were evaluated. Resveratrol alone induced a potent concentration-dependent inhibition of cell growth by inhibiting DNA synthesis, decreasing the number of viable cells and increasing the activity of executioner caspases 3 and 7; these effects of resveratrol counteracted the pro-proliferative and anti-apoptotic effects of insulin. Immunofluorescence analysis of cells incubated with resveratrol showed concentration- and time-dependent morphological changes consistent with apoptosis. The present findings indicate that resveratrol promotes apoptosis to reduce rat T-I cell growth in vitro as well as inhibiting insulin-induced rat T-I cell growth. This suggests a possibility that resveratrol and/or mechanisms mediating its effect may be relevant to the development of novel treatments for PCOS, which is characterized by both excessive ovarian mesenchyma growth and hyperinsulinemia.

Abstract P125: A Novel Role for Survivin in Insulin-induced Inhibition of Myocardial Apoptosis in Ischemic/reperfused Heart

Objectives: Insulin reduces post-ischemic myocardial apoptotic death, but the mechanism remains unclear. Survivin, an anti-apoptotic protein has recently found participating in vascular repair. This study aimed to test the hypothesis that the up-regulation of survivin by insulin may play a role in the antiapoptotic and cardioprotective effects in the ischemic/reperfused (I/R) heart, and further investigate the signaling mechanism involved. Methods : Isolated adult Sprague-Dawley rat hearts were subjected to 30 min regional ischemia and 3 h of reperfusion. The hearts were randomized to receive insulin, insulin plus LY294002 (specific inhibitor of PI3K), or insulin plus rapamycin (specific inhibitor of mTOR) at the start of reperfusion. To further confirm the correlation between survivin and myocardial survival in vitro, cardiomyocytes were infected with adenovirus encoding survivin or transfected with siRNA targeting survivin. Phosphorylation of Akt, mTOR, p70S6K and the expression of protein survivin were determined and infarct size was assessed using TTC staining, cardiomyocytes apoptosis were evaluated after reperfusion by TUNEL staining and DNA laddering. Results: I/R increased myocardial survivin expression. Insulin reperfusion (10 −7 mol/L) resulted in a 4.2-fold increase in survivin expression (P&lt;0.01 vs. I/R alone), which was almost completely blocked by LY294002. Both of the mTOR phosphorylation and survivin expression were inhibited in the group of insulin reperfusion plus LY294002. Rapamycin reperfusion did not change Akt phosphorylation but partially inhibited survivin expression (16.7±1.2 vs. 9.8±1.6, P&lt;0.01 vs. I/R+Ins), which indicated a cardioprotective effect of survivin and a possible PI3K/Akt/mTOR/SVV signaling pathway during I/R. Moreover, over-expressed survivin provides protection against stimulated ischemia reperfusion induced cardiomyocyte apoptosis, while targeting survivin blunted the anti-apoptotic effect of insulin. Conclusion: This study demonstrates that insulin up-regulates myocardial survivin expression, partly at least, via PI3-kinase-mTOR mechanism, which contributes to the anti-apoptotic effect of insulin in the I/R heart.

Anti-Apoptotic Effect of Insulin in the Control of Cell Death and Neurologic Deficit after Acute Spinal Cord Injury in Rats

Recent studies confirmed that the new cell survival signal pathway of Insulin-PI3K-Akt exerted cyto-protective actions involving anti-apoptosis. This study was undertaken to investigate the potential neuroprotective effects of insulin in the pathogenesis of spinal cord injury (SCI) and evaluate its therapeutic effects in adult rats. SCI was produced by extradural compression using modified Allen's stall with damage energy of 40 g-cm force. One group of rats was subjected to SCI in combination with the administration of recombinant human insulin dissolved in 50% glucose solution at the dose of 1 IU/kg day, for 7 days. At the same time, another group of rats was subjected to SCI in combination with the administration of an equal volume of sterile saline solution. Functional recovery was evaluated using open-field walking, inclined plane tests, and motor evoked potentials (MEPs) during the first 14 days post-trauma. Levels of protein for B-cell lymphoma/leukemia-2 gene (Bcl-2), Caspase-3, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) were quantified in the injured spinal cord by Western blot analysis. Neuronal apoptosis was detected by TUNEL, and spinal cord blood flow (SCBF) was measured by laser-Doppler flowmetry (LDF). Ultimately, the data established the effectiveness of insulin treatment in improving neurologic recovery, increasing the expression of anti-apoptotic bcl-2 proteins, inhibiting caspase-3 expression decreasing neuronal apoptosis, reducing the expression of proinflammatory cytokines iNOS and COX-2, and ameliorating microcirculation of injured spinal cord after moderate contusive SCI in rats. In sum, this study reported the beneficial effects of insulin in the treatment of SCI, with the suggestion that insulin should be considered as a potential therapeutic agent.

Insulin Attenuates Apoptosis and Exerts Anti-Inflammatory Effects in Endotoxemic Human Macrophages

Insulin decreases the incidence of sepsis and improves mortality of critically ill patients. In endotoxemic as well as in thermally injured rats, insulin attenuates the systemic inflammatory response by decreasing the proinflammatory and increasing the antiinflammatory cascade. The aim of the present study was to determine the effects of insulin on cell survival, cell activity, apoptosis, and proinflammatory response in a human macrophage-like cell line (THP-1 cells) stressed with lipopolysaccharide (LPS). Human macrophages were stressed with LPS and received either saline or insulin. Cell viability was analyzed by MTS, apoptosis was detected using JC-1 and terminal deoxynucleotidyl transferase-mediated nick end labeling-staining, and to elucidate on the signaling pathway, we used wortmannin as a phosphatidylinositol-3-kinase inhibitor. Tumor necrosis factor (TNF) and interleukin-1beta (IL-1beta) were measured to determine the effect of insulin on proinflammatory cytokine expression. Insulin caused a significant increase in cell viability and significantly reduced apoptosis in LPS-stimulated human macrophages in a dose-dependent manner. The antiapoptotic effect of insulin could be completely blocked with the addition of wortmannin. Insulin significantly decreased TNF and IL-1beta in endotoxemic human macrophages. Our results indicate that insulin exerts antiapoptotic effects and reduces the expression of proinflammatory cytokines in endotoxemic human macrophages. The antiapoptotic effects are mediated via the phospatidylinositol-3-kinase-pathway.

Insulin and insulin-like growth factors inhibit and luteinizing hormone augments ovarian theca-interstitial cell apoptosis

Theca-interstitial (T-I) cells play a fundamental role in the control of ovarian function. Steroidogenic activity and growth of the T-I cells are regulated by many paracrine and endocrine factors. However, little is known about the mechanisms controlling T-I death. In an in vitro model of apoptosis, purified rat T-I cells were cultured for 24 h with serum and subsequently for up to an additional 24 h with serum or in serum-free medium with or without insulin, insulin-like growth factors (IGF-I and IGF-II) and LH or 8-bromo-cyclic AMP (8Br-cAMP). Apoptosis was identified by histological assessment of nuclear morphology and by detection of internucleosomal cleavage and quantified by determination of [alpha32P]-dideoxy-ATP 3'-end labeling of low molecular weight DNA. Serum withdrawal resulted in nuclear condensation and fragmentation into apoptotic bodies of T-I cells and led to pronounced DNA cleavage. Insulin (10 nM) protected T-I cells from apoptosis, reducing DNA fragmentation by 39 +/- 8% compared to serum-free controls. IGF-I (10 nM) and IGF-II (10 nM) had comparable antiapoptotic effects, decreasing DNA fragmentation by 55 +/- 9% and 37 +/- 14%, respectively. In contrast, LH (100 ng/ml) and 8Br-cAMP (1 mM) augmented the pro-apoptotic effect of serum withdrawal, increasing DNA fragmentation by 85 +/- 55% and 72 +/- 42%, respectively. The antiapoptotic effects of insulin and IGFs and the pro-apoptotic effect of LH, acting via the cAMP system, may be important in the maintenance of T-I homeostasis. Moreover, excessive levels of insulin and free IGFs may lead to T-I cell hyperplasia characteristic of conditions such as polycystic ovary syndrome.

Involvement of Adenylyl Cyclase Signaling Mechanism in Insulin and IGF‐I Coregulation of Fundamental Cell Processes

The discovery of the adenylyl cyclase signaling mechanism (ACSM) of insulin and related peptides allows for advancing the hypothesis of its participation in regulatory action on cell growth, apoptosis, and metabolism. The following evidences were obtained: (1) The order of efficiency of insulin and IGF-I growth-promoting action and their antiapoptotic effect coincides with that of the peptide-activating action on AC. (2) The growth-promoting and antiapoptotic effects of insulin and IGF-I are distinctly reproduced by cAMP. (3) The anabolic effects of insulin and IGF-I activation on glycogen synthesis and the pentosophosphate pathway are inhibited by cAMP.

Insulin Signaling in Arteries Prevents Smooth Muscle Apoptosis

Insulin is an antiapoptotic factor of cultured vascular cells, but it is not clear whether it also exerts antiapoptotic effects on vascular cells in vivo. We studied insulin receptor signaling in the arteries of normal and diabetic rats to establish whether insulin exhibits antiapoptotic activity toward vascular smooth muscle cells in vivo as well as in vitro. Western blot analysis and real-time polymerase chain reaction revealed alpha- and beta-subunits of the insulin receptor in association with insulin receptor substrate-1 and phosphatidylinositol 3-kinase in the media of the aorta and carotid artery. The insulin receptor signaling pathway was partially activated under physiological conditions, further activated by intravenous insulin injection, and was attenuated in streptozotocin-induced diabetic rats. Lipopolysaccharide injection induced more apoptosis of vascular smooth muscle cells in diabetic rats than in control rats, whereas insulin prevented apoptosis in the aortic wall. An in vitro study suggested that the antiapoptotic effect of insulin was mediated by phosphatidylinositol 3-kinase. Insulin is an antiapoptotic factor of vascular smooth muscle cells in vitro and in vivo. Decreased insulin activity on the artery may increase smooth muscle cell death and cause unstable plaque formation associated with diabetes.

Anti-apoptotic effect of insulin on normal hepatocytes in vitro and in vivo.

Liver growth factors are known to be anti-apoptotic for hepatocytes. The potential of insulin, a liver co-mitogen, has not been thoroughly evaluated. We studied the anti-apoptotic role of insulin on primary cultures of rat hepatocytes exposed to transforming growth factor-beta (TGF-beta) as the apoptotic agent and in the left portal vein ligation model (LVPL) of liver atrophy. Results show that insulin decreases apoptosis of TGF-beta-treated hepatocyte cultures by 43% (P < 0.002) and the alanine amino transferase (ALT) release by 49% (P < 0.001). Left lobes of LPVL animals displayed a significant increase in the levels of TGF-beta mRNA. In LPVL rats receiving continuous infusion of insulin in the left lobes, the weight of the atrophic lobes was higher over a 7-day period in comparison to control animals. This was associated with lower levels of serum ALT and with a five-fold decrease in the apoptotic index in the left lobes (P < 0.0001). Induction of Akt phosphorylation and increased expression of Bcl-xl were observed in the left lobes of insulin-treated animals. In conclusion, these results show that insulin is anti-apoptotic for normal hepatocytes both in vitro and in vivo and that the action of insulin is associated with increased Bcl-xl expression and Akt activation.

Insulin reduces apoptosis and increases DNA synthesis and cell size via distinct signalling pathways in Drosophila Kc cells.

During development of Drosophila, cell proliferation and size are known to be regulated by insulin. Here we use Drosophila Kc cells to examine the molecular basis for the control of cell growth by insulin. Growing cells in the presence of insulin increased cell number above control levels at 16, 24, 48 and 72 h. We have demonstrated a novel anti-apoptotic effect of insulin (approximately 50%) in these cells, measured by caspase 3-like activity, which contributed to the increase in cell number. The anti-apoptotic effect was observed both in control cells and those in which apoptosis was induced by ultraviolet irradiation. An approximately 2-fold stimulation of bromodeoxyuridine incorporation demonstrated that insulin also increased Kc cell proliferation by stimulating new DNA synthesis. The ability of insulin to increase cell number, stimulate bromodeoxyuridine incorporation and reduce caspase 3-like activity was prevented by PD98059, which inhibits activation of the Drosophila extracellular signal regulated kinase (DERK) pathway, and was unaffected by wortmannin, an inhibitor of Drosophila phosphatidylinositol 3-kinase (DPI3K). Insulin also increased cell size approximately 2-fold and this was prevented by wortmannin and rapamycin, an inhibitor of Drosphilia target of rapamycin (DTOR). In summary, we show that DERK plays an important role in mediating the effect of insulin to reduce apoptosis and increase DNA synthesis whereas the DPI3K/DTOR/Dp70S6 kinase pathway mediates effects of insulin on cell size in Drosophila Kc cells.

New insulin-competent adenylate cyclase signaling system as putative mechanism of antiapoptotic effect of insulin and insulin-like growth factor I.

New insulin-competent adenylate cyclase signaling system as putative mechanism of antiapoptotic effect of insulin and insulin-like growth factor I.

Mitogenic and anti-apoptotic activity of insulin on bovine embryos produced in vitro.

Insulin improves development of mammalian preimplantation embryos and, in addition to the regulation of glucose transport, it exerts mitogenic and anti-apoptotic activities. The expression of glucose transporters (Glut) mediating the uptake of this essential energy substrate is critical for embryo survival. An impaired expression of Glut leads to an increase in apoptosis at the blastocyst stage and involves Bax. The various effects of insulin were unravelled by supplementing the in vitro culture medium with insulin (1.7 micromol l(-1)) and (i) the rates of cleavage and blastocyst development were recorded; (ii) mitogenic activity was studied by determining the total number of blastocyst cells and the ratio between trophectoderm and inner cell mass (ICM) cells; (iii) the frequency of apoptosis in blastocysts was determined by the TdT-mediated duTP nick-end labelling (TUNEL) assay and by quantification of the relative amounts of mRNA for Bax and Bcl-XL; and (iv) expression for Glut1, Glut3 and Glut8 transcripts was compared between embryos cultured in the presence or absence of insulin. Insulin increased rates of cleavage (81.2+/-2.2 (control) to 86.0+/-2.5) and blastocyst development (24.7+/-1.9 to 31.3+/-1.2), and number of blastocyst cells (123.7+/-6.0 to 146.3+/-6.6); the increase in the number of blastocyst cells was due to a significantly higher number of trophectoderm cells (82.3+/-5.0 versus 100.3+/-5.5). Blastocysts derived from cultures supplemented with insulin showed a significant decrease in apoptosis as determined by the TUNEL assay (14.8+/-0.9 to 12.2+/-0.7). No effects of insulin on the mRNA expression of Glut isoforms and Bax and Bcl-XL were found. These results demonstrate that the mitogenic and anti-apoptotic effects of insulin on bovine preimplantation embryos did not correlate with changes in the amounts of mRNA for the glucose transporter isoforms Glut1, -3 and -8, or transcripts for Bax and Bcl-XL.

Mitogenic and anti-apoptotic activity of insulin on bovine embryos produced in vitro

Insulin improves development of mammalian preimplantation embryos and, in addition to the regulation of glucose transport, it exerts mitogenic and anti-apoptotic activities. The expression of glucose transporters (Glut) mediating the uptake of this essential energy substrate is critical for embryo survival. An impaired expression of Glut leads to an increase in apoptosis at the blastocyst stage and involves Bax. The various effects of insulin were unravelled by supplementing the in vitro culture medium with insulin (1.7 micromol l(-1)) and (i) the rates of cleavage and blastocyst development were recorded; (ii) mitogenic activity was studied by determining the total number of blastocyst cells and the ratio between trophectoderm and inner cell mass (ICM) cells; (iii) the frequency of apoptosis in blastocysts was determined by the TdT-mediated duTP nick-end labelling (TUNEL) assay and by quantification of the relative amounts of mRNA for Bax and Bcl-XL; and (iv) expression for Glut1, Glut3 and Glut8 transcripts was compared between embryos cultured in the presence or absence of insulin. Insulin increased rates of cleavage (81.2+/-2.2 (control) to 86.0+/-2.5) and blastocyst development (24.7+/-1.9 to 31.3+/-1.2), and number of blastocyst cells (123.7+/-6.0 to 146.3+/-6.6); the increase in the number of blastocyst cells was due to a significantly higher number of trophectoderm cells (82.3+/-5.0 versus 100.3+/-5.5). Blastocysts derived from cultures supplemented with insulin showed a significant decrease in apoptosis as determined by the TUNEL assay (14.8+/-0.9 to 12.2+/-0.7). No effects of insulin on the mRNA expression of Glut isoforms and Bax and Bcl-XL were found. These results demonstrate that the mitogenic and anti-apoptotic effects of insulin on bovine preimplantation embryos did not correlate with changes in the amounts of mRNA for the glucose transporter isoforms Glut1, -3 and -8, or transcripts for Bax and Bcl-XL.

Insulin is a potent survival factor in mesangial cells: Role of the PI3-kinase/Akt pathway

Elucidating the mechanisms of apoptosis is important for understanding the molecular mechanisms underlying glomerular disease. The phosphatidylinositol 3 kinase (PI3-kinase)/Akt pathway is essential for survival signaling in non-renal cells. However, little is known about the anti-apoptotic effect of insulin and the role of the PI3-kinase/Akt pathway in mesangial cells (MC) apoptosis. Apoptosis was induced in wild type, p27Kip1 (p27) -/- and p21Cip1/Waf1 (p21) -/- mouse MC by survival factor withdrawal, actinomycin D, ultraviolet (UV)-B irradiation and cycloheximide in the presence or absence of insulin (1 micromol/L) or insulin-like growth factor-I (IGF-I; 100 ng/mL). The activation and levels of Akt, extracellular signal regulated kinase (ERK) and specific cell cycle proteins were determined by Western blot analysis. Insulin and IGF-I inhibited wild-type MC apoptosis induced by survival factor withdrawal, actinomycin D, ultraviolet-B irradiation and cycloheximide and in p27 -/- MC when apoptosis was induced by survival factor withdrawal. Akt was activated by insulin and IGF-I during apoptosis. Blocking PI3-kinase with LY294002 reduced Akt activation and abrogated the anti-apoptotic effect of insulin. ERK was activated during apoptosis and blocking ERK activation with U0126 or PD98059 partially rescued MC from apoptosis. Moreover, insulin also suppressed ERK activation during apoptosis. Our results also showed that the CDK-inhibitor p21 was increased by insulin and that p21 up-regulation was PI3-kinase/Akt pathway dependent. Furthermore, p21 -/- MC apoptosis induced by survival factor withdrawal was not rescued by insulin in contrast to the wild-type and p27 -/- MC. These data suggest that p21 may have a critical role in the anti-apoptotic effect of insulin. Insulin is a potent survival factor for MC in response to a number of different apoptotic triggers, and this effect is mediated through the PI3-kinase/Akt pathway. Moreover, ERK and p21 may be involved in anti-apoptotic effect of insulin in MC.

Insulin inhibits apoptosis of macrophage cell line, THP-1 cells, via phosphatidylinositol-3-kinase-dependent pathway.

Hyperinsulinemia has recently been reported as a risk factor for atherosclerotic diseases such as coronary heart disease; however, its precise mechanism is not well understood. To elucidate the role of insulin in the development of atherogenesis, we have investigated the effect of insulin on cell survival in macrophages, which are known to be important in the atherosclerotic process. Apoptosis was induced in macrophage cell lines derived from human monocytes or murine macrophages by serum starvation. Insulin administration retarded macrophage apoptosis by means of DNA laddering, dimethylthiazol diphenyltetrazolium bromide assay, and annexin V binding assay. Insulin also enhanced mRNA expression and protein production of the antiapoptotic Bcl-XL gene in a dose-dependent manner within the range of physiological concentrations. In the exploration of the signaling pathway involved in these antiapoptotic effects of insulin, pretreatment of cells with a specific inhibitor of phosphatidylinositol-3-kinase significantly suppressed insulin-mediated cell survival and insulin-induced Bcl-XL expression in macrophages. These data indicate that the survival effect of insulin on the apoptosis of macrophages is associated with the upregulation of Bcl-XL expression, and it may be mediated through the phosphatidylinositol-3-kinase signaling pathway. These mechanisms could be involved in the possible role of insulin in the development of atherosclerosis.

Insulin Administered at Reoxygenation Exerts a Cardioprotective Effect in Myocytes by a Possible Anti-Apoptotic Mechanism

The metabolic cocktail of glucose-insulin-potassium (GIK) has been shown to reduce mortality in humans and reduce infarct size in the rat when administered from the onset of reperfusion following an ischemic insult. The mechanisms underlying GIK mediated cardioprotection are, however, still unclear. Recent data implicates insulin “alone” as the major protagonist of cardioprotection when administered at the time of reperfusion. We have therefore begun to investigate an insulin activated signalling pathway and the putative role of apoptosis in this insulin-induced cardioprotection. Simulated ischemia and reoxygenation were induced in rat neonatal cardiocyte experiments. The administration of insulin [0.3 mU/ml] at the moment of reoxygenation (InsR) enhanced myocardial cell viablility as assessed by trypan blue exclusion compared to vehicle alone treated control myocytes (InsR50±2%v controls 70±1%, P<0.001). This insulin-mediated cardioprotection was due, in part to a reduction in myocyte apoptosis as measured by TUNEL (InsR29±2%v controls 49±3%, P<0.001) and Annexin V staining (InsR34±2%v controls 65±3%, P<0.001). These cardioprotective and anti-apoptotic effects of insulin were completely abolished by the tyrosine kinase inhibitor lavendustin A and by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin. Thus, we conclude that the early administration of insulin appears to be an effective modality to reduce reoxgygenation injury in cardiocytes, in part, via the attenuation of ischemia/reoxygenation-induced apoptosis. Moreover, the cardioprotective and anti-apoptotic effects of insulin are mediated via tyrosine kinase and PI3-kinase signalling pathways.

Insulin-induced oxidative neuronal injury in cortical culture: mediation by induced N-methyl-D-aspartate receptors.

While effectively attenuating neuronal apoptosis in mouse cortical culture, insulin paradoxically induced neuronal necrosis with 48 h of exposure. The insulin neurotoxicity was blocked by an antioxidant but not by caspase inhibitors. Exposure to insulin led to tyrosine phosphorylation of the insulin receptor and the insulin-like growth factor-1 (IGF-1) receptor and activation of protein kinase C (PKC) and phosphoinositide 3-kinase (PI3-kinase). Inhibitors of tyrosine kinase and PKC, but not PI3-kinase, attenuated the insulin neurotoxicity. Conversely, the inhibitor of PI3-kinase but not PKC reversed the antiapoptotic effect of insulin. Suggesting that the gene activity-dependent emergence of excitotoxicity contributed to insulin neurotoxicity, macromolecule synthesis inhibitors and N-methyl-D-aspartate (NMDA) antagonists blocked it. Consistently, exposure to insulin increased the level of the NR2A subunit of the NMDA receptor without much altering NR1 or NR2B levels. The present study suggests that insulin can be both neuroprotective and neurotoxic in the same cell system but by way of different signaling cascades.