Introduction

The prolonged and high-dose use of synthetic glucocorticoids is known to be associated with hyperglycemia, which, in turn, contributes to the development of new-onset steroid-induced diabetes (NOSID)1,2. These drugs are commonly prescribed for the treatment of various medical conditions3. Researchers have been investigating the pathophysiology of NOSID4. Studies indicate that glucocorticoids not only induce insulin resistance but also impact pancreatic β-cell mass and function4. The complex relationship between glucocorticoids and pancreatic β-cells remains a subject of ongoing research due to the pivotal role of impaired β-cell function in the diabetes pathogenesis. Experimental studies have consistently shown that chronic exposure of both pancreatic β-cell lines and mouse pancreatic islets to glucocorticoids leads to a reduction in pancreatic β-cell mass and insulin secretion. Furthermore, prior research has uncovered several mechanisms through which glucocorticoids exert their inhibitory effects on insulin secretion, including reduced glucose uptake and oxidation, membrane depolarization, and modulation of calcium-mediated insulin exocytosis5,6. It is noteworthy that oxidative stress has been proposed as a contributing factor in the induction of apoptosis in pancreatic β-cells7.

A previous study by our research group demonstrated that dexamethasone decreased glutathione S-transferase P 1 (GSTP1) protein expression in mouse pancreas8. GSTP1 is an enzyme that belongs to the supergene family of glutathione S-transferases (GSTs)9. GSTP1 plays a pivotal role in the detoxification of oxidative stress9, and GSTP1 inactivation may result in increased cell susceptibility to oxidative DNA damage10. GSTP1 polymorphism was found to be associated with several cancers, including hepatocellular cancer and chronic myeloid leukemia (CML)11,12,13. Loss of GSTP1 causes an accumulation of oxidative stress in prostate cancer cells10. GSTP1 was also reported to exert a protective effect against oxidative stress in cancer cells14. GSTP1 prevents cancer cell apoptosis by inhibiting c-Jun NH2-terminal kinase (JNK) activation15.

Imatinib mesylate (Gleevec; Novartis AG, Basel, Switzerland) is a selective tyrosine kinase inhibitor16. Several studies reported that treatment with imatinib could cure both malignancies and diabetes in diabetic cancer patients [in both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM)], and could also cure malignancies in nondiabetic cancer patients17,18,19. Imatinib was also reported to reverse diabetes in new-onset nonobese diabetic (NOD) mice20. Tyrosine kinase inhibitors were shown to aggressively promote the expression of glucose transporter 2 (GLUT2) and NK2 homeobox 2 (NKX2-2), which are both positive regulators of insulin gene expression, on β-cells21. Imatinib also decreased reactive oxygen species (ROS) production via increased degradation of the α-subunit of the flavocytochrome b558 (p22phox), which is a subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase22.

The aim of this study was to test our hypothesis that imatinib would protect against dexamethasone-induced pancreatic β-cell apoptosis via increased GSTP1 expression and reduced oxidative stress.

Materials and methods

Animal studies

Institutional Animal Care and Use Committee of the Faculty of Medicine Siriraj Hospital, Mahidol University approved the animal experimentation protocol COA number SI-ACUP 004/2559). All the experiment followed the arrive guidelines. In this study, 8-week-old male ICR mice were obtained from the National Laboratory Animal Center at Mahidol University in Nakhon Pathom, Thailand. Upon their arrival at the animal center, these mice were randomly kept in groups of 5–6 animals per cage and allowed one week of acclimatization. These mice were housed in a controlled environment replicating a natural day-night cycle, which consisted of a 12 h light/dark cycle and were fed ad libitum.

Mouse pancreatic islet isolation and culture

Pancreatic islets were obtained via collagenase digestion. Briefly, mice were sacrificed in a carbon dioxide chamber for 2 min. After sacrifice, collagenase-P was infused into the pancreas and placed in a conical tube. Subsequently, the tube was immersed in a water bath at 37℃ for digestion. Histopaque gradient were used for islet separation. After the separation, islets were hand-picked under a stereomicroscope. A total of 300–500 islets were cultured in RPMI 1640 medium supplemented with heat-activated fetal bovine serum (FBS). The islets were maintained under experimental conditions for 7 days, with the culture medium being changed every 2 days.

Insulin (INS-1) cell culture

The INS-1 cell line was procured from Merck Life Science in Darmstadt, Germany. These cells were cultured in RPMI 1640 Medium, which was supplemented with heat-inactivated FBS, penicillin, and streptomycin. They were maintained at a constant temperature of 37℃ in a cell culture incubator. To ensure their vitality, the medium was refreshed every other day. INS-1 was exposed to a medium containing experimental conditions depicted in the figures. All experimental procedures strictly adhered to relevant guidelines and regulations.

Measurement of intracellular superoxide generation

To assess superoxide production, we employed a nitro blue tetrazolium chloride (NBT) assay. INS-1 cells were treated with experimental conditions as depicted in the Fig. 2A,B for 48 h. Following this incubation, the cells underwent an additional 90 min treatment with NBT. Subsequently, cells were lysed in potassium hydroxide (KOH), and the insoluble formazan crystals released were dissolved in dimethyl sulfoxide (DMSO). Superoxide production was quantified by measuring the optical density (OD) at a wavelength of 630 nm. Optical density measurements were performed using a PowerWave microplate scanning spectrophotometer (BioTek Instruments, Inc., Winooski, VT, USA).

Analysis of cell apoptosis via Annexin V-fluorescein isothiocyanate/propidium iodide (Annexin V-FITC/PI) staining

In this study, the Annexin V/PI assay was performed to investigate apoptosis. INS-1 cells were treated with the conditions shown in Fig. 1B for 72 h. Following the treatment, the cells were suspended in PBS. Annexin V-FITC (BD Biosciences, San Jose, CA, USA) was added to the cells and incubated for 15 min. After this incubation, PI (BD Biosciences, San Jose, CA, USA) was added to the cells and further incubated for 15 min. Subsequently, the number of apoptotic cells was assessed using a FACSort Flow Cytometer (Becton, Dickinson and Company, Franklin Lakes, NJ, USA).

Figure 1
figure 1

The effect of dexamethasone and RU486 on pancreatic β-cell apoptosis and GSTP1 protein expression. (A) Percent apoptosis in INS-1 cells at 72 h was evaluated by Annexin V-FITC/PI staining. (B) Representative Western blot analysis of GSTP1 and β-actin from INS-1 cells. The bar graph shows the GSTP1 protein level normalized to the β-actin protein. (C) Representative Western blot analysis of GSTP1 and β-actin from mouse islets. The bar graph shows the GSTP1 protein level normalized to the β-actin protein. (D) Representative Western blot analysis of GSTP1 and β-actin from INS-1 cells cultured with or without dexamethasone in the presence or absence of RU486. The bar graph shows the GSTP1 protein level normalized to the β-actin protein. Data are expressed as the mean ± SEM of at least 3 independent experiments, and a p-value less than 0.05 indicates statistical significance. (*p < 0.05 vs. dexamethasone; **p < 0.01 vs. dexamethasone; ***p < 0.001 vs. dexamethasone; ##p < 0.01 vs. control; and, ###p < 0.001 vs. control).

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Western blot analysis

In this study, protein expression levels were evaluated using Western blot analysis.

Lysis of both INS-1 cells and mouse pancreatic islets was conducted using RIPA buffer, which was sourced from Pierce Biotechnology (Rockford, IL, USA) and was supplemented with protease inhibitors. The protein concentrations were determined using a Micro BCA Protein Assay Kit from Pierce Biotechnology. Equal amounts of proteins were separated in SDS-polyacrylamide gels. A semi-dry transfer system was used to transfer the proteins onto PVDF membranes (Bio-Rad Laboratories, Hercules, CA, USA). After the transfer, the membranes were cut in the areas of the target bands, and 5% non-fat milk in TBST was applied to block non-specific proteins. The membranes were incubated with this blocking solution at room temperature for 1 h. Subsequently, the membranes were incubated 16–18 h at 4℃ with primary antibodies. These antibodies included mouse monoclonal anti-GSTP1, mouse monoclonal anti-phosphorylated (p)-p38 mitogen-activated protein kinase (p-p38), mouse monoclonal anti-p-c-Jun NH2-terminal kinase (anti-p-JNK), mouse monoclonal anti-JNK, mouse monoclonal anti-p-extracellular signal-regulated kinase 1/2 (anti-p-ERK1/2), mouse monoclonal anti-ERK, rabbit polyclonal anti-β-cell lymphoma-2 associated X (anti-BAX), mouse monoclonal anti-β-cell lymphoma-2 (anti-BCL2), mouse monoclonal anti-β-actin (all from Santa Cruz Biotechnology, Dallas, TX, USA), or rabbit polyclonal anti-GSTP1 (Abnova, Taipei, Taiwan). After the primary antibody incubation, the membranes were washed three times with TBST and then incubated with HRP-conjugated secondary antibodies. Following another set of TBST washes, chemiluminescent detection was performed using enhanced chemiluminescence (Pierce Biotechnology). Quantification of protein expression levels was analyzed using ImageJ densitometry software (version 1.43; National Institutes of Health, Bethesda, MD, USA).

Measurement of cell viability

The PrestoBlue assay was conducted to assess cell viability in a 96-well plate. In brief, INS-1 cells were subjected to the experimental conditions depicted in the Fig. 2C for 72 h. After the incubation, PrestoBlue reagent was added to the cells and further incubated for 2 h. Cell viability was measured using a PowerWave microplate scanning spectrophotometer (BioTek Instruments) by recording the optical density (OD) at a wavelength of 570 nm (with a reference wavelength of 600 nm).

Figure 2
figure 2

The effect of dexamethasone and NBDHEX on superoxide production and cell viability in INS-1 cells. (A) Cellular superoxide production was determined by NBT assay. (B) The effect of NBDHEX on cellular superoxide production was determined by NBT assay. (C) Cell viability was assessed by PrestoBlue assay. Data are expressed as the mean ± SEM of at least 3 independent experiments, and a p-value less than 0.05 indicates statistical significance. (**p < 0.01 vs. dexamethasone; ##p < 0.01 vs. control; *p < 0.05 vs. dexamethasone; and, #p < 0.05 vs. control).

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Statistical analysis

Results are presented as the mean ± standard error of the mean (SEM). One-way analysis of variance (ANOVA), followed by Tukey’s post hoc test, was performed to determine the differences between groups. Statistical analysis was conducted using GraphPad Prism 5.01 software (GraphPad, San Diego, CA, United States).

Results

Imatinib demonstrates a protective effect against pancreatic β-cell apoptosis induced by dexamethasone

To investigate the impact of imatinib on dexamethasone-induced apoptosis in pancreatic β-cells, INS-1 cells were cultured in the presence or absence of 10 μM imatinib while exposing them to 0.1 μM dexamethasone. Subsequently, Annexin V-FITC/PI assay were performed to assess apoptosis. The results showed that dexamethasone markedly increased INS-1 cell apoptosis. In the presence of imatinib, dexamethasone-induced apoptosis in INS-1 cells significantly decreased compared to cells exposed to dexamethasone alone (Fig. 1A). However, imatinib alone had no significant impact on INS-1 cell apoptosis compared to the untreated control. These results demonstrate that 10 μM imatinib effectively prevents dexamethasone-induced apoptosis in pancreatic β-cells.

Imatinib upregulates GSTP1 expression in INS-1 cells treated with dexamethasone

The impact of dexamethasone and imatinib on GSTP1 protein expression in INS-1 cells was evaluated through an immunoblotting approach (Fig. 1B). Dexamethasone significantly reduced GSTP1 protein expression compared to the levels observed in the untreated control group. In contrast, the co-administration of dexamethasone and imatinib resulted in an increase in GSTP1 protein expression compared to the levels observed in INS-1 cells cultured with dexamethasone alone. When administered alone, imatinib did not significantly alter GSTP1 protein expression compared to the control group. These findings suggest that imatinib significantly enhances GSTP1 expression in dexamethasone-treated INS-1 cells.

Imatinib increases GSTP1 expression in dexamethasone-treated mouse islets

To investigate the influence of dexamethasone and imatinib on GSTP1 protein expression in isolated mouse islets, the islets were cultured with or without 0.1 µM dexamethasone and with or without the addition of 10 µM imatinib, and subsequently analyzed using the immunoblot method (Fig. 1C). In the presence of dexamethasone, GSTP1 protein expression exhibited a significant reduction compared to the untreated control in isolated mouse islets. In contrast, GSTP1 protein expression significantly increased in isolated mouse islets cultured with both 0.1 µM dexamethasone and 10 μM imatinib, compared to those cultured with dexamethasone alone. Imatinib, when administered alone, did not significantly affect GSTP1 protein expression in isolated mouse islets compared to the untreated controls.

Dexamethasone decreases GSTP1 via the glucocorticoid receptor

To investigate whether dexamethasone reduces GSTP1 expression through the glucocorticoid receptor (GR), INS-1 cells were cultured with or without dexamethasone, in addition to co-treatment with RU486, a GR inhibitor. Subsequently, GSTP1 protein levels were assessed using Western blot analysis. Dexamethasone significantly reduced GSTP1 protein levels, but co-administration with RU486 restored them to levels comparable to the control condition. Notably, RU486 alone had no significant impact on GSTP1 expression (Fig. 1D). These results provide evidence that dexamethasone diminishes GSTP1 expression through the GR.

Imatinib alleviates oxidative stress induced by dexamethasone in pancreatic β-cells

Previous research from our group revealed that dexamethasone decreases GSTP1, an enzyme responsible for detoxifying and reducing oxidative damage. Accumulation of reactive oxygen species (ROS) can trigger cell death. To investigate whether imatinib can prevent dexamethasone-induced apoptosis in pancreatic β-cells by reducing ROS, we measured intracellular superoxide production using the NBT assay. Dexamethasone significantly elevated superoxide production compared to the control condition. However, co-administration of imatinib with dexamethasone reduced superoxide production to levels similar to those in the control condition. Imatinib alone did not exert a significant effect on superoxide levels (Fig. 2A). These results indicate that imatinib alleviates oxidative stress induced by dexamethasone in pancreatic β-cells.

NBDHEX, which is a GSTP1 inhibitor, neutralized the effect of combined imatinib and dexamethasone on superoxide production and cell viability

To determine whether NBDHEX, which is a GSTP1 inhibitor, can neutralize the ability of imatinib to inhibit dexamethasone-induced superoxide production, INS-1 cells were cultured in 0.1 µM dexamethasone with or without 10 µM imatinib in addition to co-treatment with or without 0.4 µM NBDHEX before measuring superoxide production by NBT assay. The result showed that 0.4 µM NBDHEX significantly decreased the ability of imatinib to inhibit superoxide production when co-cultured with 0.1 µM dexamethasone with 10 µM imatinib (Fig. 2B).

To confirm whether imatinib prevents pancreatic β-cell apoptosis induced by dexamethasone via GSTP1, INS-1 cells were cultured in 0.1 µM dexamethasone with or without 10 µM imatinib, in addition to co-treatment with or without 0.4 µM NBDHEX, before measuring cell viability using the PrestoBlue assay. Dexamethasone significantly increased cell apoptosis, while the combination treatment with dexamethasone and imatinib significantly decreased cell apoptosis. The combination treatment with dexamethasone, imatinib, and NBDHEX resulted in levels of cell apoptosis similar to those observed with treatment using dexamethasone alone (Fig. 2C).

Imatinib decreases pancreatic β-cell apoptosis induced by dexamethasone via a reduction of p-JNK

Previous studies reported reduced GSTP1-induced apoptosis via activation of JNK [23-25]. We utilized Western blot analysis to investigate how the combination of imatinib and dexamethasone affects p-JNK. Dexamethasone elevated the expression of p-JNK in comparison to the protein levels observed in the control condition (Fig. 3A). The combination of dexamethasone and imatinib significantly reduced p-JNK expression compared to the condition with dexamethasone alone. Imatinib alone did not significantly change p-JNK expression compared to those observed in control conditions. These findings suggest that dexamethasone stimulated the expression of p-JNK.

Figure 3
figure 3

The effect of dexamethasone and imatinib on p-JNK, p-p38, and p-ERK1/2 protein expression. (A) Representative Western blot analysis of p-JNK normalized to the JNK protein. (B) Representative Western blot analysis of p-p38 normalized to the p38 protein. (C) Representative Western blot analysis of p-ERK1/2 normalized to the ERK1/2 protein. Data are expressed as the mean ± SEM of at least 3 independent experiments, and a p-value less than 0.05 indicates statistical significance. (#p < 0.05 vs. control; *p < 0.05 vs. dexamethasone; and, **p < 0.01 vs. dexamethasone).

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Imatinib decreases pancreatic β-cell apoptosis induced by dexamethasone via reduction of p-p38

Decreased GSTP1 was reported to induce apoptosis via p-p38 [24, 25]. Western blot analysis was employed to investigate how the combination of imatinib and dexamethasone affected p-p38 levels. Dexamethasone markedly increased the expression of p-p38 in comparison to the protein levels observed under control conditions (Fig. 3B). Conversely, co-administration of dexamethasone and imatinib resulted in a significant reduction in p-p38 expression compared to the effects of dexamethasone alone. Interestingly, imatinib by itself did not lead to a statistically significant alteration in p-p38 expression when contrasted with the control conditions. These findings suggest that dexamethasone stimulates p-p38 expression.

Imatinib increases dexamethasone-induced pancreatic β-cell apoptosis via increased expression of ERK1/2

Loss of GSTP1 was reported to induce apoptosis via decreased ERK1/2 expression23. To assess the impact of combining imatinib with dexamethasone on ERK1/2, we conducted Western blot analysis to evaluate the levels of phosphorylated ERK1/2 (p-ERK1/2). Dexamethasone significantly reduced the p-ERK1/2 compared to that of the control condition (Fig. 3C). The effect of dexamethasone on p-ERK1/2 expression was significantly increased in the dexamethasone plus imatinib condition compared to that of the dexamethasone alone condition. On the other hand, there was no noteworthy change in p-ERK1/2 expression in the imatinib-only condition when compared to the control condition. These findings suggest that dexamethasone induces the expression of p-ERK1/2.

Imatinib suppresses dexamethasone-induced BAX, but activates BCL-2 expression

Oxidative stress is known to activate the mitochondrial apoptotic pathway [27]. To investigate whether imatinib can protect pancreatic β-cells from dexamethasone-induced cell death via this pathway, Western blot analysis was performed to assess the expression levels of BAX, a proapoptotic protein, and BCL-2, an antiapoptotic protein. Our findings revealed that dexamethasone increased the expression of the BAX protein when compared to the control condition. However, the presence of imatinib in cells treated with dexamethasone effectively reduced the upregulation of BAX protein levels (Fig. 4A). Conversely, dexamethasone significantly reduced the expression of the BCL-2 protein compared to the control condition. This decrease was counteracted when imatinib was introduced together with dexamethasone. Importantly, imatinib alone did not produce substantial changes in the expression levels of BAX and BCL-2 proteins (Fig. 4B). These findings indicate that imatinib has a protective factor against dexamethasone-induced apoptosis in pancreatic β-cells by suppressing the mitochondrial apoptotic pathway.

Figure 4
figure 4

The effect of dexamethasone and imatinib on BAX and BCL2 protein expression. (A) Representative Western blot analysis of the proapoptotic protein BAX normalized to the β-actin protein in INS-1 cells at 48 h. (B) Representative Western blot analysis of BCL2 normalized to the β-actin protein in INS-1 cells at 48 h. Data are expressed as the mean ± SEM of at least 3 independent experiments, and a p-value less than 0.05 indicates statistical significance. (##p < 0.01 vs. control; ####p < 0.0001 vs. control; and, *p < 0.05 vs. dexamethasone) (C) The pictorially demonstrated proposed effect of imatinib is decreased dexamethasone-induced pancreatic β-cell apoptosis via the induction of GSTP1. Dexamethasone suppresses GSTP1 expression, which increases ROS and p-JNK. ROS also induces p-p38, but decreases p-ERK1/2, which causes apoptosis. Imatinib ameliorates the suppression of GSTP1, which results in a decrease in ROS, p-JNK, and p-p38 expression to control levels. These data strongly suggest that imatinib can protect against dexamethasone-induced pancreatic β-cell apoptosis in mouse INS-1 cells.

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Discussion

In the present study, we demonstrated that imatinib protects against dexamethasone-induced pancreatic β-cell apoptosis via increased GSTP1 in mouse INS-1 cells. GCs were previously reported to increase cell apoptosis in INS-1 cells and mouse islets5,24. GCs induced pancreatic β-cell apoptosis via several pathways, including oxidative stress4. Previous study found that dexamethasone decreased GSTP1, which is a detoxifying enzyme9. The present study further demonstrated that RU486, which is a GR inhibitor, is able to prevent dexamethasone-reduced GSTP1 expression. This result is consistent with that from a previous study that reported that GSTP1 suppressed lung cell apoptosis caused by radiation25. GSTP1 was also reported to play a role in inhibiting several types of tumor cell apoptosis10,11,14,26. Moreover, GSTP1 polymorphism was found to increase the risk of developing type 2 diabetes at an early age27. Taken together, this evidence strongly suggests that dexamethasone induces pancreatic β-cell apoptosis via a reduction of GSTP1.

Our results showed that imatinib effectively restored the level of GSTP1 expression back to control condition level from the decreased level of GSTP1 expression after dexamethasone treatment. Dexamethasone increased oxidative stress compared to control, whereas imatinib significantly reduced oxidative stress compared to dexamethasone alone. Dexamethasone was reported to induce oxidative stress in neuron cells, skeletal muscle, and pancreatic β-cells24,28,29. Imatinib was shown to have antioxidant effect in spinal cord injury rat model via increased Nrf2 and HO-130. Imatinib also exerted protective effect against ischemia and reperfusion of the lung via increased catalase enzyme level31. In contrast, imatinib was reported to increase ROS in the liver and kidney22,32. It is, therefore, possible that imatinib influences oxidative stress differently in different tissues. Our result demonstrated that NBDHEX, which is a GSTP1 inhibitor, neutralized the protective effect of imatinib against oxidative stress. This suggests that the protective effect of imatinib against dexamethasone is via GSTP1. Previous study suggested a correlation between imatinib and GSTP1 based on their finding of a GSTP1 polymorphism being significantly associated with imatinib resistance in a CML patient26. However, the mechanism that associates GSTP1 polymorphism and imatinib resistance remains unknown.

Our previous study showed that dexamethasone induced pancreatic β-cell apoptosis via the GR33. That same study also revealed that RU486, which is a GR inhibitor, is able to significantly reduce dexamethasone-induced pancreatic β-cell apoptosis in INS-1 cells. The present study showed that RU486 ameliorated dexamethasone-reduced GSTP1 expression. This result confirms that dexamethasone decreased GSTP1 expression via the GR. Previous study suggested that reduction of GSTP1 might increase JNK expression and apoptosis34. Our result demonstrated that dexamethasone decreased GSTP1, but increased JNK and cell apoptosis. Our result is consistent with those from two previous studies that suggested that GSTP1 binds to JNK and inhibits JNK activity35,36. When GSTP1 decreases, the disassociation complex between GSTP1-JNK also decreases, which is then followed by increased activation of JNK. JNK also promotes mitochondrial apoptosis37. This is consistent with our finding that dexamethasone increased BAX, but decreased BCL2. Combination imatinib and dexamethasone reversed GSTP1, JNK, Bax, and BCL2 expression. Our data is also supported by data from a recent study that reported that imatinib decreased the respiratory chain in mitochondria, and increased AMPK and β-cell survival in NOD mice38. Thus, the results of our study strongly suggest that imatinib ameliorates dexamethasone-induced pancreatic β-cell apoptosis via a reduction of GSTP1 and reduced oxidative stress.

Our study also showed that dexamethasone decreased GSTP1 and increased ROS. ROS was reported to both increase p38 expression and induce cell apoptosis39. It was also reported that increased ROS inhibited ERK1/2 protein expression40. Reduction of ERK1/2 was shown to decrease insulin production via reduced β-cell proliferation and lower β-cell mass41. This corresponds with our finding that dexamethasone increased p38, but decreased ERK1/2 expression. Combination imatinib and dexamethasone reversed ROS, p38, and ERK1/2 expression in our study, and this is consistent with previous studies that reported that imatinib decreases oxidative stress30,32. There is no direct evidence that establishes a confirmed relationship between imatinib and GSTP1; however, CML patients with a GSTP1 polymorphism had a poor response to imatinib42. This educated suspicion was further supported by the use of NDHEX, which is a GSTP1 inhibitor, in the present study. More specifically, we found that NBDHEX treatment was able to neutralize the protective effect of imatinib against dexamethasone (Supplementary Figure 2C).

Conclusion

The results of this study demonstrated that dexamethasone decreases GSTP1 and increases pancreatic β-cell apoptosis. However, combination treatment with dexamethasone and imatinib significantly increased both GSTP1 expression and pancreatic β-cell viability. The effect of imatinib on GSTP1 was confirmed by NBDHEX, which is a GSTP1 inhibitor. NDHEX reversed superoxide production and cell viability, which together comprise the protective effect of imatinib against dexamethasone. Taken together, the data from this study indicates that imatinib prevents dexamethasone-induced pancreatic β-cell apoptosis via increased GSTP1 and reduced oxidative stress. It is noteworthy that dexamethasone induces pancreatic β-cell apoptosis through several pathways. Our group previously reported that dexamethasone increases DR5, a death receptor for TRAIL33. Oxidative stress can induce inflammation43, and inflammation can, in turn, increase oxidative stress44. Imatinib has been shown to inhibit both oxidative stress38 and inflammation signaling33. Thus, imatinib protects against dexamethasone-induced pancreatic β-cell apoptosis by inhibiting both oxidative stress and inflammation signaling.