Quantitative and qualitative differences in thrombopoietin-dependent hematopoietic progenitor development between cord blood and bone marrow

BACKGROUND: To assess the clinical application of thrombopoietin (TPO) for thrombocytopenia of patients receiving cord blood (CB) or bone marrow (BM) transplants, we examined whether various types of hematopoietic progenitors including megakaryocyte (MK) progenitors from CB and BM exerted different proliferative and differentiative potential in the presence of TPO. METHODS: The development of MK, granulocyte-macrophage, and erythroid/mixed erythroid (E/Mix) progenitors in a serum-deprived liquid culture medium supplemented with TPO was compared between CD34+ CB and BM cells. RESULTS: The CD34+ CB cells generated 30-fold more MKs than the CD34+ BM cells, but the CB-derived MKs were more immature. A single-cell culture study showed that CB CD34+CD38- cells as well as CD34+CD38+ cells proliferated in response to TPO, whereas the two subpopulations of CD34+ BM cells showed little multiplication. In short-term liquid cultures containing CD34+ CB or BM cells, TPO significantly increased the absolute numbers of various types of colony-forming cells, compared with the input values. In particular, MK progenitors and E/Mix progenitors in CB were amplified to a substantially greater extent than in BM. The superior response of CD34+ CB cells to TPO observed in this study may be due in part to the use of cryopreserved cells. CONCLUSIONS: Our results suggest that TPO alone cannot only stimulate megakaryocytopoiesis but also increase the numbers of various types of hematopoietic progenitors, and that quantitative and qualitative differences in TPO-dependent hematopoietic progenitor development exist between CB and BM.     

Erythropoietin protects the kidney against the injury and dysfunction caused by ischemia-reperfusion

Erythropoietin (EPO) is upregulated by hypoxia and causes proliferation and differentiation of erythroid progenitors in the bone marrow through inhibition of apoptosis. EPO receptors are expressed in many tissues, including the kidney. Here it is shown that a single systemic administration of EPO either preischemia or just before reperfusion prevents ischemia-reperfusion injury in the rat kidney. Specifically, EPO (300 U/kg) reduced glomerular dysfunction and tubular injury (biochemical and histologic assessment) and prevented caspase-3, -8, and -9 activation in vivo and reduced apoptotic cell death. In human (HK-2) proximal tubule epithelial cells, EPO attenuated cell death in response to oxidative stress and serum starvation. EPO reduced DNA fragmentation and prevented caspase-3 activation, with upregulation of Bcl-X(L) and XIAP. The antiapoptotic effects of EPO were dependent on JAK2 signaling and the phosphorylation of Akt by phosphatidylinositol 3-kinase. These findings may have major implications in the treatment of acute renal tubular damage.     

Involvement of peripheral benzodiazepine receptor in the oxidative stress, death-signaling pathways, and renal injury induced by ischemia-reperfusion

The peripheral benzodiazepine receptor (PBR) is a critical component of the mitochondrial permeability transition pore, which is involved in the regulation of cell death. In the present study we investigated the role of PBR in the regulation of signaling pathways leading to apoptotic and necrotic damage and renal dysfunction in a rat model of ischemia-reperfusion. Renal ischemia-reperfusion led to extended tubular apoptosis and necrosis that were associated with peroxidative damage, high levels of proapoptotic Bax expression, and low levels of antiapoptotic Bcl-2 expression, cleavage of death substrate, poly(ADP-ribose) polymerase (PARP), and activation of a key effector of apoptosis, caspase-3. Rat pretreatment with a novel PBR antagonist, SSR180575, significantly decreased postreperfusion oxidative stress and tubular apoptosis and necrosis. This effect was associated with inhibition of caspase-3 activation and PARP cleavage, upregulation of Bcl-2, and downregulation of Bax. Furthermore, inhibition of PBR accelerated the recovery of normal renal function, as assessed by measurement of levels of plasma creatinine and blood urea nitrogen. These findings reveal a role for PBR as a modulator of necrotic and apoptotic cell death induced by ischemia-reperfusion and suggest that regulation of PBR may provide new therapeutic implications for the prevention of acute renal failure.     

Nonerythropoietic derivative of erythropoietin protects against tubulointerstitial injury in a unilateral ureteral obstruction model.

BACKGROUND: Erythropoietin (EPO), a member of the cytokine type I superfamily, acts to increase circulating erythrocytes primarily by preventing apoptosis of erythroid progenitors, is known to protect tissues and can raise haemoglobin (Hb) concentrations. Recently, a second receptor for EPO comprising the EPO receptor and beta-common receptor has been reported to mediate EPO-induced tissue protection. EPO modified by carbamylation (CEPO) only signals through this second receptor. Accordingly, we hypothesized that treatment with CEPO, which would not increase Hb concentrations, would protect against tubular damage and thereby inhibit tubulointerstitial injuries. METHODS: We evaluated therapeutic effects of CEPO using a rat unilateral ureteral obstruction model. RESULTS: CEPO decreased tubular apoptosis and alpha-smooth muscle actin (alphaSMA) expression in the absence of polycythaemia, while the untreated obstructed kidneys exhibited increased tubular apoptosis with expanded (alphaSMA) expression. While EPO treatment similarly inhibited tubular apoptosis and alphaSMA expression, EPO treatment increased Hb concentrations and induced a wedge-shaped infarction. CONCLUSION: We established a therapeutic approach using CEPO to protect against tubulointerstitial injury. The therapeutic value of this approach warrants further attention and preclinical studies.     

肥厚性瘢痕细胞凋亡检测及其相关调控因素的研究

目的　探讨肥厚性瘢痕的发生与成纤维细胞和血管内皮细胞凋亡的关系，以及有关调控因素的影响。　方法　应用原位末端标记和免疫组织化学染色等技术，对61例烧伤后整形患者肥厚性瘢痕和20例其他手术患者非肥厚性瘢痕进行了细胞凋亡以及ICE、Bcl-2表达的检测。　结果肥厚性瘢痕增厚期、成熟期成纤维细胞以及血管内皮细胞凋亡阳性细胞指数分别为6.60±4.43和8.90±6.01，成熟期分别为25.60±5.70和26.60±6.02，两期同种细胞间相比，凋亡阳性细胞指数均有非常显著性差异（P＜0.01）。增厚期ICE阳性表达率较成熟期显著降低（P＜0.01），而Bcl-2阳性率却显著高于成熟期组（P＜0.01）。　结论　细胞凋亡减少可能与肥厚性瘢痕的形成有关，ICE和Bcl-2可能参与了肥厚性瘢痕成纤维细胞和血管内皮细胞凋亡的调控。     

RANK Expression as a cell surface marker of human osteoclast precursors in peripheral blood, bone marrow, and giant cell tumors of bone.

RANK expression in vivo on hematopoietic subsets including pre-osteoclasts, identified by monoclonal antibodies, has not been described. We describe the lineages that express RANK in bone marrow, peripheral blood, and GCTs. We show that CD14(+)RANK(high) cells constitute a circulating pre-osteoclast pool. INTRODUCTION: The expression of RANK by subsets of hematopoietic cells has not been adequately studied in humans. While attributed to the monocytoid lineage, the phenotype of the pre-osteoclast (pre-OC) with respect to RANK expression in vivo remains unclear. We tested monoclonal antibodies (MAbs) raised against the extracellular domain of recombinant human RANK for reactivity with normal peripheral blood (PB) and bone marrow (BM) mononuclear cells (PBMNCs and BMMNCs, respectively). We also tested reactivity with giant cell tumor cells (GCT), a confirmed source of pre-OC and mature OCs. MATERIALS AND METHODS: Human PBMNCs, BMMNCs, and GCT cells were analyzed for reactivity with anti-RANK MAbs by flow cytometry in combination with hematopoietic lineage restricted markers. GCTs were also analyzed by immunofluorescence. CD14+ monocytoid cells were sorted by fluorescence-activated cell sorting (FACS) based on their relative RANK expression and cultured under OC-forming conditions. RESULTS: RANK+ cells were detected similarly by three independent anti-RANK MAbs. One MAb (80736) immunoprecipitated RANK-RANKL complexes from surface-biotinylated GCT lysates. Using dual-color flow cytometry, RANK was detected on CD14+ (monocytoid), CD19+ (B-lymphoid), CD56+ (NK cell), and glycophorin A+ erythroid progenitors. Minor populations of both CD3+ T lymphocytes and BM CD34+ hematopoietic progenitors also expressed cell surface RANK. In GCTs, RANK expression was identified on mononuclear CD45(+)CD14(+)alphaVbeta3(+)c-Fms+ cells, likely to be committed pre-OC, and on multinucleated CD45(+)alphaVbeta3(+)TRACP(+) OCs. Importantly, sorted CD14(+)RANK(high) PBMNCs treated with recombinant RANKL and macrophage-colony stimulating factor (M-CSF) gave rise to approximately twice the number of osteoclasts than RANK(mid) or RANK(low) cells. CONCLUSIONS: These results suggest that committed monocytoid RANK+ pre-OCs are represented in the marrow and circulate in the periphery, forming a pool of cells capable of responding rapidly to RANKL. The ability to reliably detect committed pre-OC in peripheral blood could have important clinical applications in the management of diseases characterized by abnormal osteoclastic activity.     

Apigenin drives the production of reactive oxygen species and initiates a mitochondrial mediated cell death pathway in prostate epithelial cells

BACKGROUND: Phytoestrogens may reduce tumorigenesis in prostate cancer. We screened five phytoestrogens for their effect on cell growth and apoptosis in PWR-1E, LNCaP, PC-3, and DU145 prostate epithelial cells in vitro. METHODS: We assessed cell number, proliferation, and apoptosis using crystal violet assays, flow cytometric analysis, and TUNEL. Focusing specifically on apigenin we assessed the ability of calpain, serine protease, caspase, estrogen receptor, and ceramide synthase inhibitors to block apigenin induced apoptosis. We also analyzed caspase 3, 7, 8, 9, Bcl-2, Bax, Bid, and cytochrome C by Western analysis, and mitochondrial permeability and reactive oxygen species production by flow cytometry using mitosensor(TM) and DCFH-DA, respectively. RESULTS: Apigenin and silybinin significantly reduced cell number, with apigenin inducing apoptosis in PWR-1E, LNCaP, PC-3, and DU145 cells. The PC-3 and DU145 cells were less susceptible to apigenin induced apoptosis then LNCaP and PWR-1E cells. The induction of apoptosis by apigenin was caspase dependent. Apigenin generated reactive oxygen species, a loss of mitochondrial Bcl-2 expression, mitochondrial permeability, cytochrome C release, and the cleavage of caspase 3, 7, 8, and 9 and the concomitant cleavage of the inhibitor of apoptosis protein, cIAP-2. The overexpression of Bcl-2 in LNCaP B10 cells reduced the apoptotic effects of apigenin. CONCLUSIONS: Apigenin induces cell death in prostate epithelial cells using a mitochondrial mediated cell death pathway. Bcl-2 has a role in inhibiting apigenin induced cell death in prostate epithelial cells.     

尼莫地平复合7.5%高渗盐水对七氟醚诱导老龄大鼠海马神经元凋亡的影响

目的探讨尼莫地平复合7.5%高渗盐水对七氟醚诱导老龄大鼠海马神经元凋亡的影响。方法健康雄性Wistar大鼠96只,18月龄,体重450~500g,采用随机数字表法将其分为四组(n=24):对照组(C组)、尼莫地平组(N组)、高渗盐水组(HS组)和尼莫地平+高渗盐水组(NHS组)。C组腹腔和尾静脉注射生理盐水;N组腹腔注射尼莫地平1 mg/kg,尾静脉注射生理盐水;HS组尾静脉注射7.5%高渗盐水4 ml/kg,腹腔注射生理盐水;NHS组腹腔注射尼莫地平1mg/kg,尾静脉注射7.5%高渗盐水4ml/kg。30min后四组大鼠吸入3%七氟醚2h。于麻醉前1d、麻醉后1、3、7d行Morris水迷宫实验,实验结束后每组随机处死8只大鼠,取海马组织,采用流式细胞术测定海马神经元凋亡率和胞浆钙离子浓度;采用RT-PCR法测定海马Bcl-2、Bax的mRNA表达量。结果与C组比较,N、HS、NHS组大鼠麻醉后1、3、7d逃避潜伏期明显缩短,穿越原平台次数明显增加,麻醉后1、7d海马神经元凋亡率和胞浆钙离子浓度明显减低,Bcl-2 mRNA表达量明显上调,Bax mRNA表达量明显下调,Bax/Bcl-2比值明显降低(P0.05);与NHS组比较,N和HS组大鼠麻醉后1、3、7d逃避潜伏期明显延长,穿越原平台次数明显减少,麻醉后1、7d海马神经元凋亡率和胞浆钙离子浓度明显增高,Bcl-2 mRNA表达量明显下调,Bax mRNA表达量明显上调,Bax/Bcl-2比值明显升高(P0.05)。结论尼莫地平复合7.5%高渗盐水可抑制钙超载,降低七氟醚诱导老龄大鼠海马神经元凋亡率,且其作用优于单独给药。     

Hydrogen peroxide-dependent declines in Bcl-2 induces apoptosis in hypoxic liver

BACKGROUND: Low-flow hypoxia induces xanthine oxidase-dependent hydrogen peroxide production by hepatocytes in the midzone of blood-perfused rat livers and apoptosis in sinusoidal endothelial cells (SECs). As Bcl-2 is a potent inhibitor of apoptotic cell death and is localized mainly in the inner mitochondrial membrane and crista, the purpose of this study was to determine whether cell-specific changes in mitochondrial Bcl-2 levels could account for the hypoxia-induced apoptosis in SECs. MATERIALS AND METHODS: A low-flow hypoxia model was generated in isolated rat livers by reducing perfusate inflow pressure from 10 to 2.5 cmH2O for 2 h. Apoptosis was then evaluated using the TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) method. Mitochondrial Bcl-2 protein levels were determined in hepatocytes and SECs using cryosectioning immunogold labeling electron microscopy.Results. TUNEL-positive nonparenchymal cells, identified as SECs, were observed predominantly in the midzone of low-flow hypoxic rat livers, whereas few parenchymal cells were stained. Mitochondrial Bcl-2 levels were higher in SECs than in hepatocytes under control conditions, but they declined significantly during hypoxia, though no morphological signs of apoptosis were apparent. In hepatocytes, by contrast, Bcl-2 levels were unaffected by hypoxia. Pretreatment with a specific xanthine oxidase inhibitor, sodium (-)-8-(3-methoxy-4-phenylsulfinylphenyl) pyrazolo [1,5-a]-1,3,5-triazine-4-olate monohydrate, which blocks production of hydrogen peroxide, also blocked both the hypoxia-induced apoptosis and the decline in mitochondrial Bcl-2 in SECs. CONCLUSION: Hydrogen peroxide-dependent declines in Bcl-2 induce apoptosis in SECs in the hypoxic rat liver.     

Erythropoietin Signaling: A Novel Regulator of White Adipose Tissue Inflammation During Diet-Induced Obesity

Obesity-induced white adipose tissue (WAT) inflammation and insulin resistance are associated with macrophage (Mф) infiltration and phenotypic shift from “anti-inflammatory” M2-like to predominantly “proinflammatory” M1-like cells. Erythropoietin (EPO), a glycoprotein hormone indispensable for erythropoiesis, has biological activities that extend to nonerythroid tissues, including antiapoptotic and anti-inflammatory effects. Using comprehensive in vivo and in vitro analyses in mice, EPO treatment inhibited WAT inflammation, normalized insulin sensitivity, and reduced glucose intolerance. We investigated EPO receptor (EPO-R) expression in WAT and characterized the role of its signaling during obesity-induced inflammation. Remarkably, and prior to any detectable changes in body weight or composition, EPO treatment reduced M1-like Mф and increased M2-like Mф in WAT, while decreasing inflammatory monocytes. These anti-inflammatory effects were found to be driven, at least in part, by direct EPO-R response in Mф via Stat3 activation, where EPO effects on M2 but not M1 Mф required interleukin-4 receptor/Stat6. Using obese ∆EpoR mice with EPO-R restricted to erythroid cells, we demonstrated an anti-inflammatory role for endogenous EPO. Collectively, our findings identify EPO-R signaling as a novel regulator of WAT inflammation, extending its nonerythroid activity to encompass effects on both Mф infiltration and subset composition in WAT.     

Apoptosis and surgical trauma: dysregulated expression of death and survival factors on peripheral lymphocytes

BACKGROUND: Surgery and anesthesia cause depression of cell-mediated immunity in the postoperative period, including a reduction in the numbers of circulating lymphocytes. It has been claimed that this immunosuppression is associated with an increased incidence of postoperative infections. HYPOTHESIS: Lymphocytopenia following surgical trauma depends on a dysregulated expression of death/and survival factors associated with apoptosis that, in turn, interferes with the occurrence of postsurgical infections. DESIGN: Fifteen subjects undergoing elective surgery under general anesthesia entered the study. The data of the patients who had infections during the postoperative outcome were compared with the data of those who did not. The data were collected prospectively. MAIN OUTCOME MEASURES: Peripheral blood samples were drawn before the operation, and 24 hours and 96 hours after the operation. Lymphocytes were isolated and examined for quantification and phenotypic analysis of apoptosis using the 7-amino-actinomycin D method, as well as for Fas and Fas ligand, interleukin 1-converting enzyme p20/caspase-1, Bcl-2, and p35 expression. The rate of apoptotic cells was correlated with the incidence of postoperative infections. SETTING: University hospital. RESULTS: Twenty-four hours after surgery, CD4(+) and CD8(+) cells exhibited a significantly higher frequency of apoptosis as well as of Fas and Fas ligand and interleukin 1-converting enzyme p20/caspase-1 expressions than preoperatively. This increase was paralleled by a significant down-regulation of antiapoptotic factors such as Bcl-2. However, the expression of the proapoptotic factor p35 was reduced. In addition, we found a relationship between the rate of the apoptotic CD8(+) subset and the occurrence of infectious complications during the postoperative course. At 96 hours after surgery, the variables studied returned to the baseline levels. CONCLUSIONS: In the early postoperative period, surgical trauma under general anesthesia induces an intracellular perturbation on peripheral lymphocytes, resulting in both up-regulation of death-signaling factors and down-regulation of survival-signaling factors. The increased apoptosis of CD8(+) lymphocytes, but not of CD4(+) cells, seemed to be associated with a greater risk of postsurgical infections.     

前列腺移行带及外周带细胞增殖和凋亡的研究

目的:研究前列腺不同区带间细胞的增殖和凋亡,并比较其差异。方法:应用末端脱氧核苷酸转移酶介导的dUTP缺口末端标记法(TUNEL)检测17例正常前列腺移行带和外周带、20例良性前列腺增生(BPH)移行带上皮细胞凋亡率,免疫组化法检测细胞增殖核抗原(PCNA)及Bcl-2表达。RT-PCR法半定量验证Bcl-2 mRNA表达。结果:①正常前列腺移行带上皮细胞凋亡率和增殖率均显著低于外周带[(13.7±4.32%)vs(20.9±6.44)%和(14.6±4.34)%vs(25.6±6.35)%,P<0.01],增生的移行带上皮细胞凋亡减少,同时细胞增殖增加。②正常前列腺外周带上皮细胞Bcl-2表达率低于移行带,后者又显著低于BPH移行带(P<0.01)。增生的移行带中Bcl-2表达率与上皮细胞凋亡率呈显著负相关(rs=-0.867,P<0.01)。结论:移行带和外周带存在细胞增殖和凋亡率差异。增生的移行带上皮细胞凋亡减少,同时细胞增殖增加,这可能是BPH的重要病理基础。Bcl-2在移行带高表达参与了BPH病理过程。     

Induction and mechanism of apoptotic cell death by propofol in HL-60 cells

BACKGROUND: Apoptosis (programmed cell death) occurs in various physiological and pathological conditions, exhibits a characteristic mechanism of intracellular sequential reaction and may be involved in determining clinical outcome. The antioxidant activity of propofol (2,6-diisopropylphenol) together with the stimulating effect of protein kinase C suggests that propofol might have the potential to modulate apoptosis. Thus, it is of both clinical interest and biomedical importance to investigate and clarify the effect and mechanism of propofol upon the intracellular reactions underlying apoptotic cell death. METHODS: The effect of propofol on apoptosis was investigated using cultured human promyelocytic leukemia HL-60 cells. This well-characterized cell line is useful for the study of apoptosis because the various biochemical steps occurring during apoptosis have been well documented. RESULTS: Treatment of HL-60 cells with propofol resulted in growth inhibition with the formation of apoptotic bodies in a concentration-dependent manner. DNA fragmentation and ladder formation was also observed in a concentration-dependent manner. Propofol treatment resulted in activation of caspase-3, -6, -8 and -9, thereby suggesting that cell surface death receptor activation of the caspase cascade mediates propofol-induced apoptosis with consequent formation of the cleaved product of Bid (a pro-apoptotic Bcl-2 family member protein) and activation of the mitochondrial pathway with cytosolic release of cytochrome c. CONCLUSION: Propofol may induce apoptosis, which is dependent on the mechanism that activates both the cell surface death receptor pathway and the mitochondrial pathway.     

Antioxidative effects of erythropoietin

Erythropoietin (EPO) has been shown to exert cytoprotective effects on erythroid progenitor cells as well as various non-erythroid cells. Experimental studies have demonstrated the renoprotective effects of EPO in various acute and chronic renal injury models. These protective effects have been largely attributed to antiapoptotic signalings of EPO. However, injured cells undergoing apoptosis are generally too severely damaged to function properly. Therefore, simply corrupting apoptotic pathway is unlikely to be an effective strategy, because the remaining damaged cells may not function appropriately, or they may eventually undergo necrotic cell death. Recent evidences suggest that EPO also provides cytoprotection by ameliorating oxidative stress, the principal cellular insult. EPO may exert its antioxidative effects directly by exploiting intracellular antioxidative mechanisms such as heme oxygenase-1 and glutathione peroxidase. In addition, EPO may act indirectly by inducing iron depletion and thereby inhibiting iron-dependent oxidative injury. Increasing red blood cells by EPO may also indirectly reduce cellular oxidative stress, as red blood cells are loaded with a substantial amount of antioxidative enzymes. Further investigation regarding the mechanisms of cellular antioxidative responses to EPO would provide a better insight to cytoprotective action of EPO, and would support the development of better cytoprotective drugs in the near future.     

The phenotypical and functional characteristics of cord blood monocytes and CD14(-/low)/CD16(+) dendritic cells can be relevant to the development of cellular immune responses after transplantation

Umbilical cord blood (UCB) has been used as an alternative source of haematopoietic progenitors for transplantation presenting advantages over bone marrow (BM) that are related with known shortages of newborns' immune system at adaptive and innate levels. Using flow cytometry, we studied the expression of Toll-like receptors (TLRs) and chemokine receptors (CKRs) and the production of pro-inflammatory cytokines by monocytes and CD14(-/low)/CD16(+)DCs from peripheral blood (PB; n=10), and umbilical cord blood (UCB; n=10). CKRs and cytokines were studied before and after stimulation of cells with LPS plus IFN-gamma. We also identified the two populations in normal bone marrow samples (BM; n=5). BM presented lower frequencies of both studied populations when compared to UCB and PB. CD14(-/low)/CD16(+)DCs presented a pattern of TLR expression different from mature monocytes reflecting distinct functions for these two populations. UCB cells presented reduced expression of TLR-4 and lower capability to produce cytokines prior stimulation. The populations studied presented different patterns of CKR expression reflecting distinct migratory pathways. Moreover, UCB cells presented higher expressions of CXCR4 and CCR7 that may be involved in immune system maturation and stem cell homing. Monocytes and CD14(-/low)/CD16(+)DCs present functional and phenotypical characteristics that may contribute to the lower incidence and severity of GVHD.     

Proapoptotic Bax is hyperexpressed in isolated human islets compared with antiapoptotic Bcl-2

BACKGROUND: Apoptosis is a well-documented pathway for islet cell death. One potential mechanism is overexpression of death-promoting Bax compared with antiapoptotic Bcl-2 in islets. METHODS: We isolated islets from 10 human pancreata and measured the expression of Bax mRNA and Bcl-2 mRNA by real-time quantitative polymerase chain reaction; islet and pancreas expression of Bax, Bcl-2, activated caspase-3, and cleaved poly (ADP-ribose) polymerase were also assessed by immunohistochemistry. Islet cell apoptosis was evaluated by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) assay and by flow cytometry. RESULTS: The mean (+/-SE) level of Bax mRNA was 336+/-79 copies per nanogram of total RNA, and the level of Bcl-2 mRNA was 36+/-10 (P=0.001). A positive correlation existed between islet expression of Bax mRNA and Bcl-2 mRNA (P=0.001). The islet Bax to Bcl-2 ratio was 10.8+/-1.3 and 1.71+/-0.3 for the spleens (P=0.0001). Bax mRNA (P=0.04), but not Bcl-2 mRNA, was expressed at a higher level in islets compared with spleens. Human islets contained large numbers of cells expressing Bax protein, whereas only infrequent islet cells expressed Bcl-2 protein, activated caspase-3, and poly (ADP-ribose) polymerase. The apoptotic index was 5% by TUNEL assay, and the percentage of apoptotic islet cells was 9.7+/-2.5% by flow cytometry. Sections of human pancreas before islet isolation showed islet staining for Bax but not Bcl-2. CONCLUSIONS: Our finding that isolated human islets express Bax at a higher level compared with Bcl-2 suggests a molecular mechanism for islet cell death by apoptosis. We hypothesize that reducing islet expression of Bax, or regulating its activation, will help preserve islet cell mass after islet transplantation.