Hope for vascular cognitive impairment: Ac-YVAD-cmk as a novel treatment against white matter rarefaction

Vascular cognitive impairment (VCI) is the second leading cause of dementia with limited treatment options, characterised by cerebral hypoperfusion-induced white matter rarefaction (WMR). Subcortical VCI is the most common form of VCI, but the underlying reasons for region susceptibility remain elusive. Recent studies employing the bilateral cortical artery stenosis (BCAS) method demonstrate that various inflammasomes regulate white matter injury and blood-brain barrier dysfunction but whether caspase-1 inhibition will be beneficial remains unclear. To address this, we performed BCAS on C57/BL6 mice to study the effects of Ac-YVAD-cmk, a caspase-1 inhibitor, on the subcortical and cortical regions. Cerebral blood flow (CBF), WMR, neuroinflammation and the expression of tight junction-related proteins associated with blood-brain barrier integrity were assessed 15 days post BCAS. We observed that Ac-YVAD-cmk restored CBF, attenuated BCAS-induced WMR and restored subcortical myelin expression. Within the subcortical region, BCAS activated the NLRP3/caspase-1/interleukin-1beta axis only within the subcortical region, which was attenuated by Ac-YVAD-cmk. Although we observed that BCAS induced significant increases in VCAM-1 expression in both brain regions that were attenuated with Ac-YVAD-cmk, only ZO-1 and occludin were observed to be significantly altered in the subcortical region. Here we show that caspase-1 may contribute to subcortical regional susceptibility in a mouse model of VCI. In addition, our results support further investigations into the potential of Ac-YVAD-cmk as a novel treatment strategy against subcortical VCI and other conditions exhibiting cerebral hypoperfusion-induced WMR.

Sarin-Induced Neuroinflammation in Mouse Brain Is Attenuated by the Caspase Inhibitor Q-VD-OPh

Organophosphates cause hyperstimulation of the central nervous system, leading to extended seizures, convulsions, and brain damage. Sarin is a highly toxic organophosphate nerve agent that has been employed in several terrorist attacks. The prolonged toxicity of sarin may be enhanced by the neuroinflammatory response initiated by the inflammasome, caspase involvement, and generation/release of proinflammatory cytokines. Since neurodegeneration and neuroinflammation are prevalent in sarin-exposed animals, we were interested in evaluating the capacity of quinolyl-valyl-O-methylaspartyl-[-2,6-difluorophenoxy]-methyl ketone (Q-VD-OPh), a pan caspase inhibitor to attenuate neuroinflammation following sarin exposure. To test this hypothesis, sarin-exposed C57BL/6 mice were treated with Q-VD-OPh or negative control quinolyl-valyl-O-methylglutamyl-[-2,6-difluorophenoxy]-methyl ketone, sacrificed at 2- and 14-day time points, followed by removal of the amygdala and hippocampus. A Bio-Rad 23-Plex cytokine analysis was completed on each tissue. The results suggest that exposure to sarin induced a dramatic increase in interleukin-1β and 6 other cytokines and a decrease in 2 of the 23 cytokines at 2 days in the amygdala compared with controls. Q-VD-OPh attenuated these changes at the 2-day time point. At 14 days, six of these cytokines were still significantly different from controls. Hippocampus was less affected at both time points. Diazepam, a neuroprotective drug against nerve agents, caused an increase in several cytokines but did not have a synergistic effect with Q-VD-OPh. Treatment of sarin exposure with apoptosis inhibitors appears to be a worthwhile approach for further testing as a comprehensive counteragent against organophosphate exposure. SIGNIFICANCE STATEMENT: A pan inhibitor of caspases (Q-VD-OPh) was proposed as a potential antidote for sarin-induced neuroinflammation by reducing the level of inflammation via inflammasome caspase inhibition. Q-VD-OPh added at 30 minutes post-sarin exposure attenuated the inflammatory response of a number of cytokines and chemokines in the amygdala and hippocampus, two brain regions sensitive to organophosphate exposure. Apoptotic marker reduction at 2 and 14 days further supports further testing of inhibitors of apoptosis as a means to lessen extended organophosphate toxicity in the brain.

Perkinsus marinus suppresses in vitro eastern oyster apoptosis via IAP-dependent and caspase-independent pathways involving TNFR, NF-kB, and oxidative pathway crosstalk

The protozoan parasite Perkinsus marinus causes Dermo disease in eastern oysters, Crassostrea virginica, and can suppress apoptosis of infected hemocytes using incompletely understood mechanisms. This study challenged hemocytes in vitro with P. marinus for 1 h in the presence or absence of caspase inhibitor Z-VAD-FMK or Inhibitor of Apoptosis protein (IAP) inhibitor GDC-0152. Hemocytes exposure to P. marinus significantly reduced granulocyte apoptosis, and pre-incubation with Z-VAD-FMK did not affect P. marinus-induced apoptosis suppression. Hemocyte pre-incubation with GDC-0152 prior to P. marinus challenge further reduced apoptosis of granulocytes with engulfed parasite, but not mitochondrial permeabilization. This suggests P. marinus-induced apoptosis suppression may be caspase-independent, affect an IAP-involved pathway, and occur downstream of mitochondrial permeabilization. P. marinus challenge stimulated hemocyte differential expression of oxidation-reduction, TNFR, and NF-kB pathways. WGCNA analysis of P. marinus expression in response to hemocyte exposure revealed correlated protease, kinase, and hydrolase expression that could contribute to P. marinus-induced apoptosis suppression.

The Smac mimetic BV6 cooperates with STING to induce necroptosis in apoptosis-resistant pancreatic carcinoma cells

Pancreatic cancer (PC) still remains a major cause of cancer-related death worldwide and alternative treatments are urgently required. A common problem of PC is the development of resistance against apoptosis that limits therapeutic success. Here we demonstrate that the prototypical Smac mimetic BV6 cooperates with the stimulator of interferon (IFN) genes (STING) ligand 2',3'-cyclic guanosine monophosphate-adenosine monophosphate (2'3'-cGAMP) to trigger necroptosis in apoptosis-deficient PC cells. Pharmacological inhibition of key components of necroptosis signaling, such as receptor-interacting protein 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL), significantly rescues PC cells from 2'3'-cGAMP/BV6/zVAD.fmk-mediated cell death, suggesting the induction of necroptosis. Consistently, 2'3'-cGAMP/BV6 co-treatment promotes phosphorylation of MLKL. Furthermore, we show that 2'3'-cGAMP stimulates the production of type I IFNs, which cooperate with BV6 to trigger necroptosis in apoptosis-deficient settings. STING silencing via siRNA or CRISPR/Cas9-mediated gene knockout protects PC cells from 2'3'-cGAMP/BV6/zVAD.fmk-mediated cell death. Interestingly, we demonstrate that nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNFα), and IFN-regulatory factor 1 (IRF1) signaling are involved in triggering 2'3'-cGAMP/BV6/zVAD.fmk-induced necroptosis. In conclusion, we show that activated STING and BV6 act together to exert antitumor effects on PC cells with important implications for the design of new PC treatment concepts.

Necrostatin-1 Synergizes the Pan Caspase Inhibitor to Attenuate Lung Injury Induced by Ischemia Reperfusion in Rats

BACKGROUND

Both apoptosis and necroptosis have been recognized to be involved in ischemia reperfusion-induced lung injury. We aimed to compare the efficacies of therapies targeting necroptosis and apoptosis and to determine if there is a synergistic effect between the two therapies in reducing lung ischemia reperfusion injury.

METHODS

Forty Sprague-Dawley rats were randomized into 5 groups: sham (SM) group, ischemia reperfusion (IR) group, necrostatin-1+ischemia reperfusion (NI) group, carbobenzoxy-Val-Ala-Asp-fluoromethylketone+ischemia reperfusion (ZI) group, and necrostatin-1+carbobenzoxy-Val-Ala-Asp-fluoromethylketone+ischemia reperfusion (NZ) group. The left lung hilum was exposed without being clamped in rats from the SM group, whereas the rats were subjected to lung ischemia reperfusion by clamping the left lung hilum for 1 hour, followed by reperfusion for 3 hours in the IR group. 1 mg/kg necrostatin-1 (Nec-1: a specific necroptosis inhibitor) and 3 mg/kg carbobenzoxy-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk: a pan caspase inhibitor) were intraperitoneally administrated prior to ischemia in NI and ZI groups, respectively, and the rats received combined administration of Nec-1 and z-VAD-fmk in the NZ group. Upon reperfusion, expressions of receptor-interacting protein 1 (RIP1), receptor-interacting protein 3 (RIP3), and caspase-8 were measured, and the flow cytometry analysis was used to assess the cell death patterns in the lung tissue. Moreover, inflammatory marker levels in the bronchoalveolar lavage fluid and pulmonary edema were evaluated.

RESULTS

Both Nec-1 and z-VAD-fmk, either alone or in combination, significantly reduced morphological damage, inflammatory markers, and edema in lung tissues following reperfusion, and cotreatment of z-VAD-fmk with Nec-1 produced the optimal effect. The rats treated with Nec-1 had lower levels of inflammatory markers in the bronchoalveolar lavage fluid than those receiving z-VAD-fmk alone (P < 0.05). Interestingly, the z-VAD-fmk administration upregulated RIP1 and RIP3 expressions in the lung tissue from the ZI group compared to those in the IR group (P < 0.05). Reperfusion significantly increased the percentages of necrotic and apoptotic cells in lung tissue single-cell suspension, which could be decreased by Nec-1 and z-VAD-fmk, respectively (P < 0.05).

CONCLUSIONS

Nec-1 synergizes the pan caspase inhibitor to attenuate lung ischemia reperfusion injury in rats. Our data support the potential use of Nec-1 in lung transplantation-related disorders.

[MAPK signaling pathways involved in aluminum-induced apoptosis and necroptosis in SH-SY5Y cells]

OBJECTIVE

To explore the role of MAPK signaling pathway in apoptosis and necroptosis induced by aluminum in SH-SY5Y cells.

METHODS

To imitate neural cell death induced by aluminium, AlCl3 x 6H2O (4 mmol/L) was used to treat SH-SY5Y cells. Necrostatin-1 (Nec-1,60 μmol/L), the specific inhibitor for necroptosis, and zVAD-fmk (20 μmol/L), the specific inhibitor for apoptosis, were added into cultures for inhibiting the occurrence of necroptosis and apoptosis. CCK-8 was performed to measure cell viability, flow cytometry was used to test the difference of apoptosis rate and necrosis rate between groups, and western-blot was used to detect the change of MAPK protein.

RESULTS

Compared with blank control group, solvent control group, Nec-1 control group and zVAD-fmk control group, cell viabiligy of Al(3+) exposed group, Al(3+) plus Nec-1 group and Al(3+) plus zVAD-fmk group decreaced (P < 0.05). Compared with Al(3+) exposed group, cell viability of Al(3+) plus Nec-1 group and Al(3+) plus zVAD-fmk group increased (P < 0.05). Necrotic rate and apoptotic rate in Al(3+) exposed group, Al(3+) plus Nec-1 group and Al(3+) plus zVAD-fmk group obviously increased compared with blank control group, solvent control group, Nec-1 control group and zVAD-fmk control group (P < 0.05). Compared with Al(3+) exposed group, necrotic and apaptotic rate of Al(3+) plus zVAD-fmk group and Al(3+) plus Nec-1 group were statistically significant decreased (P < 0.05). Compared with blank control group, solvent control group, Nec-1 control group and zVAD-fmk control group, expression of p-p38 in Al(3+) exposed group, Al(3+) plus Nec-1 group and Al(3+) plus zVAD-fmk group increased obviously (P < 0.05), and expression of p-ERK decreased significantly (P < 0.05). Compared with Al(3+) exposed group, expression of p-p38 decreased (P < 0.05), but p-ERK increased in Al(3+) plus Nec-1 group (P < 0.05).

CONCLUSION

The ERK and p38 MAPK signaling pathways are involved in aluminum-induced necroptosis in SH-SY5Y cells, but only ERK signaling pathway is involved in aluminum-induced apoptosis, and JNK signaling pathway is not involved in aluminum-induced cell death.

[Gleevec induces apoptosis in K562 cells through activating caspase-3]

The present study is to elucidate the mechanisms underlying Gleevec-induced apoptosis of chronic myeloid leukemia (CML) K562 cells in vitro. The apoptotic cell death and cell cycle distribution after Gleevec treatment and the effect of PDCD4 siRNA on Gleevec-induced apoptosis of K562 cells were analyzed by flow cytometry. The effect of Gleevec on p-Crkl, caspase-3, PARP and PDCD4 protein levels, and the knockdown efficacy of PDCD4 siRNA were detected by Western blotting. The results showed that Gleevec dramatically suppressed the phosphorylation level of Crkl in a dose-dependent manner and induced significant apoptosis and G0/G1 cell cycle arrest of K562 cells in time- and dose-dependent manners. In addition, Gleevec activated caspase-3 and its downstream substrates PARP, and the caspase pan inhibitor Z-VAD-FMK (50 micromol x L(-1)) markedly reduced Gleevec-induced apoptosis from 47.97% +/- 10.56% to 31.05% +/- 9.206% (P < 0.05). Moreover, Gleevec significantly increased the protein expression of programmed cell death 4 (PDCD4). PDCD4 knockdown by siRNA reduced Gleevec-induced apoptosis from 46.97% +/- 14.32% to 42.8% +/- 11.43%. In summary, Gleevec induced apoptosis in K562 cells via caspase-3 activation.

Thymoquinone induces apoptosis in malignant T-cells via generation of ROS

We show that HTLV-1 negative leukemia cells are more sensitive to TQ due to higher levels of drug-induced reactive oxygen species (ROS). PreG1 population in HTLV-1 negative Jurkat and CEM was higher than HTLV-1 transformed HuT-102 and MT-2 cells. Peripheral blood mononuclear cells were more resistant. Hoechst staining indicated more features of apoptosis, namely nuclear blebs and shrunken nuclei in HuT-102 than Jurkat. A greater depletion of the antioxidant enzyme glutathione occurred in Jurkat, which consequently led to an increase in ROS, loss of mitochondrial membrane potential, cytochrome c release, activation of caspases 3 and 9, and cleavage of PARP. Treatment with z-VAD-fmk partially reversed TQ-induced apoptosis, suggesting a caspase-dependent mechanism. N-acetyl cysteine prevented apoptosis providing evidence that cell death is ROS-dependent. Catalase prevented apoptosis to a lesser extent than NAC. In summary, TQ induces apoptosis in adult T cell leukemia/lymphoma by decreasing glutathione and increasing ROS, and levels of ROS underlie the differential cellular response to TQ. Our data suggest a potential therapeutic role for TQ in sensitizing HTLV-I-negative T-cell lymphomas.

Na+ binding to meizothrombin desF1

Meizothrombin is the physiologically active intermediate generated by a single cleavage of prothrombin at R320 to separate the A and B chains. Recent evidence has suggested that meizothrombin, like thrombin, is a Na(+)-activated enzyme. In this study we present the first X-ray crystal structure of human meizothrombin desF1 solved in the presence of the active site inhibitor PPACK at 2.1 A resolution. The structure reveals a Na(+) binding site whose architecture is practically identical to that of human thrombin. Stopped-flow measurements of Na(+) binding to meizothrombin desF1 document a slow phase of fluorescence change with a k(obs) decreasing hyperbolically with increasing [Na(+)], consistent with the existence of three conformations in equilibrium, E*, E and E:Na(+), as for human thrombin. Evidence that meizothrombin exists in multiple conformations provides valuable new information for studies of the mechanism of prothrombin activation.

Mechanism and significance of specific proteolytic cleavage of Reelin

Reelin is a secreted glycoprotein essential for normal brain development and function. In the extracellular milieu, Reelin is subject to specific cleavage at two (N-t and C-t) sites. The N-t cleavage of Reelin is implicated in psychiatric and Alzheimer's diseases, but the molecular mechanism and physiological significance of this cleavage are not completely understood. Particularly, whether the N-t cleavage affects the signaling activity of Reelin remains controversial. Here, we show that the protease in charge of the N-t cleavage of Reelin requires the activity of certain proprotein convertase family for maturation and has strong affinity for heparin. By taking advantage of these observations, we for the first time succeeded in obtaining "Uncleaved" and "Completely Cleaved" Reelin proteins. The N-t cleavage splits Reelin into two distinct fragments and virtually abolishes its signaling activity. These findings provide an important biochemical basis for the function of Reelin proteolysis in brain development and function.

Contributions of autophagic and apoptotic mechanisms to CrTX-induced death of K562 cells

Previous studies reported that the neurotoxin, Crotoxin, isolated from the venom of South American rattlesnake had potent anti-tumor activity. Here, we investigated the involvement of autophagy and apoptosis in the Crotoxin-induced death of chronic myeloid leukemia cell line K562 cells. The neurotoxin dose dependently inhibited the viability of K562 cells. Crotoxin stimulated the autophagic activity as evidenced by the appearance of punctuate monodansylcadaverine (MDC) fluorescence staining in the cytoplasm and increased the formation of autophagosomes. Crotoxin caused the collapse of the mitochondrial membrane potential, release of cytochrome c and activation of caspase-3. Caspase inhibitors attenuated Crotoxin-induced K562 cell death, while blockage of autophagy maturation with 3-methyladenine (3-MA) and NH4Cl potentiated the neurotoxin's cytotoxicity. These results suggest that an apoptotic mechanism contributes to the Crotoxin-induced death of K562 cells, while the activation of autophagy delays neurotoxin-induced apoptosis.

Local thymic caspase-9 inhibition improves survival during polymicrobial sepsis in mice

Caspase-9 is believed to play an essential role in sepsis-induced lymphocyte apoptosis. The aim of this study was therefore to evaluate its contribution within the caspase-dependent apoptosis pathway in a murine model of polymicrobial sepsis. Local injections of Z-LEHD-fmk, a specific caspase-9 inhibitor, into thymi of septic mice led to the complete inhibition of caspase-9, decreased apoptosis of resident tissue cells, and, in addition, reduced further downstream caspase-3 activity. In contrast to its systemic administration, only local injections improved the overall survival of septic mice. However, local injections of a pancaspase inhibitor (Z-VAD-fmk) did not improve survival, although caspase-3 activity was reduced to a similar degree as by the administration of Z-LEHD-fmk. These results indicate that local apoptosis of lymphatic tissue in polymicrobial sepsis is processed dependent of caspase-9 and suggests alternative caspase-dependent beneficial effects, which may determine a positive outcome.

Caspase-3 is required in the apoptotic disintegration of the nuclear matrix

Apoptotic breakdown of cellular structures is largely mediated by caspases. One target of degradation is a proteinaceous framework of the nucleus termed the nuclear matrix. We compared the apoptotic changes of the nuclear matrix in staurosporine-treated caspase-3-deficient MCF-7 cells transfected with intact CASP-3 gene (MCF-7c3) or an empty vector (MCF-7v) as a control. Nuclear Mitotic Apparatus protein (NuMA), lamin A/C and lamin B were used as markers for internal nuclear matrix and peripheral nuclear lamina, respectively. In both cell lines, staurosporine induced rapid cytoplasmic shrinkage and partial chromatin condensation. MCF-7c3 cells formed apoptotic bodies, whereas MCF-7v cells did not. NuMA and lamins were actively cleaved in MCF-7c3 cells following caspase-3 activation, but only minimal or no cleavage was detected in MCF-7v cells. Interestingly, lamin B but not lamin A/C was relocated into cytoplasmic granules in apoptotic MCF-7v cells. Pancaspase inhibitor, z-VAD-fmk, prevented the apoptotic changes, while caspase-3 inhibitor, z-DEVD-fmk, induced lamin B granules in both cell lines. These results show that caspase-3 is involved in the cleavage of NuMA and lamins either directly or by activating other proteases. This may be essential for disintegration of the nuclear structure during apoptosis.

Induction of apoptosis in macrophages by air oxidation of dioleoylphosphatidylglycerol

Dioleoylphosphatidylglycerol (DOPG) containing unsaturated sites is the target of oxidation during preparation, storage, or in vivo use of anionic liposomes. We investigated the biological effect of air oxidation of DOPG on RAW 264.7 murine macrophage-like cells. Oxidation was induced by exposing DOPG to air for 24-72 h. The extent of air oxidation was confirmed using Matrix-Assisted Laser Desorption and Ionization with Time-of-Flight (MALDI-TOF) mass spectrometry. The product of the air oxidation of DOPG was identified as the addition of one oxygen atom to one of the symmetrical fatty moieties of DOPG at m/z 814.77. The treatment of DOPG with air oxidation produced dose-dependent cytotoxicity in macrophages. RAW 264.7 cells exposed to oxidized DOPG exhibited morphological features of apoptosis, such as chromatin condensation and cell shrinkage. Typical apoptotic ladders were observed in DNA extracted from RAW 264.7 cells treated with oxidized DOPG. Flow cytometric analysis demonstrated an increase in the hypodiploid DNA population (sub-G1), indicating that DNA cleavage occurred after treatment with oxidized DOPG. In addition, we showed that pretreating RAW 264.7 cells with zVAD-fmk, a general caspase inhibitor, did not prevent apoptosis induced by oxidized DOPG, suggesting that apoptosis in macrophage cells follows a caspase-independent pathway. These results point to a need for precaution in formulating DOPG liposomes for drug delivery and therapeutic purposes.

Recent advances in the imaging of programmed cell death

A deficiency or an excess of programmed cell death (apoptosis) is an integral component of autoimmune disorders, organ and bone marrow transplant rejection, and cancer. A technique to image programmed cell death would be useful in the development of drugs to treat these and others diseases, and to monitor the effectiveness of therapy. The most widely studied agent for the in vivo study of apoptosis is radiolabeled annexin V, an endogenous protein labeled with technectium-99m, now undergoing clinical trials in both Europe and the United States. While annexin V has been studied extensively in humans the precise mechanism(s) of uptake of this agent in vivo is unclear and needs further study. Other agents are also underdevelopment including radiolabeled forms of Z-VAD.fmk, a potent inhibitor of the enzymatic cascade intimately associated with apoptosis. MR imaging techniques and tracers also hold promise as methods to monitor apoptotic cell death. In this article we will review these and other imaging technologies for the non-invasive imaging of cell death. The mechanism(s) and latest data on the conditions in which cellular stress and early apoptosis occur will also be discussed in detail including potential new strategies for the targeting and novel therapeutic interventions of tissues and organs undergoing stress or apoptosis when cell salvage is still possible.

Staining of human sperm with fluorochrome-labeled inhibitor of caspases to detect activated caspases: correlation with apoptosis and sperm parameters

BACKGROUND

Detection of apoptosis in sperm samples may help evaluate sperm quality. Recently, it has been suggested that in some ejaculated sperm populations, apoptosis is caspase dependent. The aim of this study was to investigate the presence of activated caspases and examine possible correlations with apoptosis and sperm parameters in semen samples prepared for IVF.

METHODS

To detect activated caspases, neat semen from infertile patients and sperm prepared by PureSperm gradient were stained with the fluorescein isothyocyanate-Val-Ala-Asp-fluoromethylketone (FITC-VAD-fmk) and analysed by flow cytometry. Cell death was determined by DNA fragmentation (TUNEL) and mitochondrial membrane potential. Sperm parameters were studied by conventional microscopy.

RESULTS

FITC-VAD-fmk stained sperm cells in situ and the subcellular labeling pattern was compatible with the known localization of caspases. A significant correlation was found between the frequency of FITC-VAD-fmk stained cells and cell death markers. In both prepared sperm and neat semen a negative correlation was found between the percentage of FITC-VAD-fmk positive cells and standard parameters (concentration/motility). FITC-VAD-fmk positive cells negatively correlated with high fertilization rates after IVF.

CONCLUSIONS

Labelling of sperm cells with the activated caspases-reacting fluorochrome provides a sensitive assay for detection of sperm apoptosis. This cytometric assay can be helpful to test sperm before IVF.

Palmitic and stearic fatty acids induce caspase-dependent and -independent cell death in nerve growth factor differentiated PC12 cells

Apoptotic cell death has been proposed to play a role in the neuronal loss observed following traumatic injury in the CNS and PNS. The present study uses an in vitro tissue culture model to investigate whether free fatty acids (FFAs), at concentrations comparable to those found following traumatic brain injury, trigger cell death. Nerve growth factor (NGF)-differentiated PC12 cells exposed to oleic and arachidonic acids (2 : 1 ratio FFA/BSA) showed normal cell survival. However, when cells were exposed to stearic and palmitic acids, there was a dramatic loss of cell viability after 24 h of treatment. The cell death induced by stearic acid and palmitic acid was apoptotic as assessed by morphological analysis, and activation of caspase-8 and caspase-3-like activities. Western blotting showed that differentiated PC12 cells exposed to stearic and palmitic acids exhibited the signature apoptotic cleavage fragment of poly (ADP-ribose) polymerase (PARP). Interestingly, blockade of caspase activities with the pan-caspase inhibitor z-VAD-fmk failed to prevent the cell death observed induced by palmitic or stearic acid. RT-PCR and RNA blot experiments showed an up-regulation of the Fas receptor and ligand mRNA. These findings are consistent with our hypothesis that FFAs may play a role in the cell death associated with trauma in the CNS and PNS.

Apoptotic mechanisms in T47D and MCF-7 human breast cancer cells

To investigate the mechanisms underlying apoptosis in breast cancer cells, staurosporine was used as an apoptotic stimulus in the human breast cancer cell lines MCF-7 and T47D. Staurosporine induced dose and time dependent increases in DNA fragmentation which was abrogated by z-VAD-fmk. MCF-7 cells did not express caspase-3, suggesting that DNA fragmentation occurred in the absence of caspase-3 and that other caspases may be involved. Staurosporine induced DEVDase activity in T47D cells suggesting the involvement of caspase-3 and/or caspase-7, yet there was no DEVDase activity in MCF-7 cells, probably ruling out the involvement caspase-7. However, staurosporine induced the cleavage of pro-caspase-6 in MCF-7 cells, but not in T47D cells. Caspase dependent PARP cleavage was detected in MCF-7 cells at 3 h, whereas only partial PARP cleavage was detected in T47D cells and then only after 24 h. Moreover, staurosporine led to cytochrome c release at 2 h in MCF-7 cells and 6 h in T47D cells. In addition, a time dependent and caspase-independent reduction of the mitochondrial transmembrane potential was observed; which appeared to occur after the release of cytochrome c. Translocation of Bax from the cytosol to mitochondria was observed in both cell types, and this preceded cytochrome c release in both T47D and MCF-7 cells. Apoptotic events in both cell types differ temporally, involving activation of different caspases and mitochondrial changes.

Inhibition of HIV-2(ROD) replication in a lymphoblastoid cell line by the alpha1-antitrypsin Portland variant (alpha1-PDX) and the decRVKRcmk peptide: comparison with HIV-1(LAI)

We investigated the effects of alpha1-antitrypsine Portland variant (alpha1-PDX) and decanoylRVKRchloromethylketone (decRVKRcmk) on HIV-2(ROD) replication in the Jurkat lymphoblastoid cell line. To this end, cells were stably transfected with the alpha1-PDX (J-PDX) and used as targets for HIV-2(ROD) infection. Controls were prepared with the empty vector (J-pcDNA3). HIV-2(ROD) and HIV-1(LAI) replications were significantly inhibited and delayed in the presence of the alpha1-PDX protein. When decRVKRcmk was used at 35 microM, inhibition rates were 70-80% for HIV-2(ROD) and HIV-1(LAI), while total inhibition occurred at 70 microM. Control peptides consisting of decanoylRVKR and acetylYVADcmk had no effect. In the presence of the alpha1-PDX or the decRVKRcmk at 35 microM, the infectivity of HIV-2(ROD) and HIV-1(LAI) produced was 3-4-fold lower. Both molecules inhibited syncytium formation by HIV-2(ROD) and HIV-1(LAI) to a considerable extent. Finally, the inhibition of viral replication was correlated with the ability of the decRVKRcmk at 35 and 70 microM and of the alpha1-PDX, to inhibit the processing of envelope glycoprotein precursors. The alpha1-PDX protein and the decRVKRcmk peptide at 35 microM inhibited HIV-2 and HIV-1 to a similar level suggesting that identical or closely related endoproteases are involved in the maturation of their envelope glycoprotein precursors into surface and transmembrane glycoproteins. The significant inhibition observed with alpha1-PDX indicates that furin or furin-like endoproteases appear to play a major role in the maturation process.

Detection of caspase activation in situ by fluorochrome-labeled caspase inhibitors

Apoptosis is dependent on the activation of a group of proteolytic enzymes called caspases. Caspase activation can be detected by immunoblotting using caspase-specific antibodies or by caspase activity measurement employing pro-fluorescent substrates that become fluorescent upon cleavage by the caspase. Most of these methods require the preparation of cell extracts and, therefore, are not suitable for the detection of active caspases within the living cell. Using FAM-VAD-FMK, we have developed a simple and sensitive assay for the detection of caspase activity in living cells. FAM-VAD-FMK is a carboxyfluorescein (FAM) derivative of benzyloxycarbonyl-valine-alanine-aspartic acid-fluoromethyl ketone (zVAD-FMK), which is a potent broad-spectrum inhibitor of caspases. FAM-VAD-FMK enters the cell and irreversibly binds to activated caspases. Cells containing bound FAM-VAD-FMK can be analyzed by flow cytometry, fluorescence microscopy, or a fluorescence plate reader. Using FAM-VAD-FMK, we have measured caspase activation in live non-adherent and adherent cells. We show that FAM-VAD-FMK labeled Jurkat and HeLa cells that had undergone apoptosis following treatment with camptothecin or staurosporine. Non-stimulated negative control cells were not stained. Pretreatment with the general caspase inhibitor zVAD-FMK blocked caspase-specific staining in induced Jurkat and HeLa cells. Pretreatment of staurosporine-induced Jurkat cells with FAM-VAD-FMK inhibited affinity labeling of caspase-3, -6, and -7, blocked caspase-specific cell staining, and led to the inhibition of apoptosis. In contrast, the fluorescent control inhibitor FAM-FA-FMK had no effect. Measurement of caspase activation in 96-well plates showed a 3- to 5-fold increase in FAM-fluorescence in staurosporine-treated cells compared to control cells. In summary, we show that FAM-VAD-FMK is a versatile and specific tool for detecting activated caspases in living cells.

Detection of caspases activation by fluorochrome-labeled inhibitors: Multiparameter analysis by laser scanning cytometry

BACKGROUND

The fluorochrome-labeled inhibitors of caspases (FLICA) were recently used as markers of activation of these enzymes in live cells during apoptosis (Bedner et al.: Exp Cell Res 259:308-313, 2000). The aims of this study were to (a) explore if FLICA can be used to study intracellular localization of caspases; (b) combine the detection of caspase activation with analysis of the changes with cell morphology detected by microscopy and laser scanning cytometry (LSC); and (c) adapt the assay to fixed cells that would enable correlation, by multiparameter analysis, of caspase activation with the cell attributes that require cell permeabilization in order to be measured.

METHODS

Apoptosis of human MCF-7, U-937, or HL-60 cells was induced by camptothecin (CPT) or tumor necrosis factor-alpha (TNF-alpha) combined with cycloheximide (CHX). Binding of FLICA to apoptotic versus nonapoptotic cells was studied in live cells as well as following their fixation and counterstaining of DNA. Intensity of cell labeling with FLICA and DNA-specific fluorochromes was measured by LSC.

RESULTS

Exposure of live cells to FLICA led to selective labeling of cells that had morphological changes characteristic of apoptosis. The FLICA labeling withstood cell fixation and permeabilization, which made it possible to stain DNA and measure its content for identification of the cell cycle position of labeled cells. When fixed cells were treated with FLICA, both apoptotic and nonapoptotic cells became strongly labeled and the labeling pattern was consistent with the localization of caspases as reported in the literature. A translocation of the FLICA binding targets from mitochondria to cytosol was seen in the MCF-7 cells treated with CPT. FLICA binding was largely (> 90%) prevented by the substrates of the caspases or by the unlabeled caspase inhibitors having the same peptide moiety as the respective FLICA.

CONCLUSIONS

The detection of caspase activation combined with cell permeabilization requires exposure of live cells to FLICA followed by their fixation. Cell reactivity with the respective FLICA, under these conditions, identifies the activated caspases and makes it possible to correlate their activation with the cell cycle position and other cell attributes that can be measured only after cell fixation/permeabilization. FLICA can also be used to study intracellular localization of caspases, including their translocation.

Crystal structure of delta-chymotrypsin bound to a peptidyl chloromethyl ketone inhibitor

Chymotrypsin is a member of the trypsin family of serine proteases and is one of the first proteins successfully studied by X-ray crystallography. It is secreted into the intestine as the inactive precursor chymotrypsinogen; four sequential cleavages of the peptide bonds following residues 13, 15, 146 and 148 occur to generate the active pi, delta, kappa and alpha forms of chymotrypsin. (13)C NMR has shown [O'Connell & Malthouse (1995). Biochem. J. 307, 353-359] that when the delta form of chymotrypsin is inhibited by 2-(13)C-enriched benzyloxycarbonylglycylglycylphenylalanyl chloromethane, a tetrahedral adduct is formed which is thought to be analogous to the tetrahedral intermediate formed during catalysis. This inhibitor complex has been crystallized as a dimer in space group P4(1)2(1)2. The structure has been refined at 2.14 A resolution to an R value of 21.2% (free R = 25.2%). Conformational differences between delta-chymotrypsin and chymotrypsinogen in the region of the flexible autolysis loop (residues 145-150) were observed. This is the first crystal structure of delta-chymotrypsin and includes two residues which are disordered in previous crystal structures of active chymotrypsin. A difference of 11.3 A(2) between the average B values of the monomers within the asymmetric unit is caused by lattice-disordering effects approximating to rotation of the molecules about a crystallographic screw axis. The substrate-binding mode of the inhibitor was similar to other chymotrypsin peptidyl inhibitor complexes, but this is the first published chymotrypsin structure in which the tetrahedral chloromethyl ketone transition-state analogue is observed. This structure is compared with that of a similar tetrahedral transition-state analogue which does not alkylate the active-site histidine residue.

Validation of an ELISA for the quantitation of lanoteplase, a novel plasminogen activator

An ELISA was developed and validated for the quantitation of lanoteplase in human citrated plasma. The ELISA employed a monoclonal anti-lanoteplase antibody absorbed onto 96-well microtiter plates to capture lanoteplase in citrated human plasma samples containing PPACK, a protease inhibitor. The captured lanoteplase was detected using a biotinylated rabbit anti-lanoteplase polyclonal antibody. The standard curve range in human plasma for the ELISA was 7-100 ng/ml. Assessment of individual standard curve variability indicated reproducible responses with r2 values of > or = 0.985. The accuracy (% DEV) and precision (%RSD) estimates for the ELISA based on the predicted values from quality control (QC) samples were within 7.3% and 11%, respectively. Cross-reactivity with t-PA was determined to be less than 11% by ELISA. The stability of lanoteplase was established in human citrated PPACK plasma for 24 hours at 4 degrees C, for 2 months at -20 degrees C, for 22 months at -70 degrees C, three weeks at room temperature, and through four freeze/thaw cycles. To quantify lanoteplase plasminogen activator (PA) activity, a commercially available chromogenic activity assay was also validated. This method and its application is described briefly here. The lanoteplase ELISA as well as the commercial activity method were successfully employed to evaluate the pharmacokinetic parameters of lanoteplase in support of clinical Phase II/III studies.

Caspase-1-independent, Fas/Fas ligand-mediated IL-18 secretion from macrophages causes acute liver injury in mice

IL-18, produced as a biologically inactive precursor, is processed by caspase-1 in LPS-activated macrophages. Here, we investigated caspase-1-independent processing of IL-18 in Fas ligand (FasL)-stimulated macrophages and its involvement in liver injury. Administration of Propionibacterium acnes (P. acnes) upregulated functional Fas expression on macrophages in an IFNgamma-dependent manner, and these macrophages became competent to secrete mature IL-18 upon stimulation with FasL. This was also the case for caspase-1-deficient mice. Administration of recombinant soluble FasL (rFasL) after P. acnes priming induced comparable elevation of serum IL-18 in parallel with elevated serum liver enzyme levels. However, liver injury was not induced in IL-18-deficient mice after rFasL administration. These results indicate a caspase-1-independent pathway of IL-18 secretion from FasL-stimulated macrophages and its critical involvement in FasL-induced liver injury.

Caspases disrupt mitochondrial membrane barrier function

Mitochondrial intermembrane proteins including cytochrome c are known to activate caspases. Accordingly, a disruption of the mitochondrial membrane barrier function with release of cytochrome into the cytosol has been shown to precede caspase activation in a number of different models of apoptosis. Here, we addressed the question of whether caspases themselves can affect mitochondrial membrane function. Recombinant caspases were added to purified mitochondria and were found to affect the permeability of both mitochondrial membranes. Thus, caspases cause a dissipation of the mitochondrial inner transmembrane potential. In addition, caspases cause intermembrane proteins including cytochrome c and AIF (apoptosis-inducing factor) to be released through the outer mitochondrial membrane. These observations suggest that caspases and mitochondria can engage in a circular self-amplification loop. An increase in mitochondrial membrane permeability would cause the release of caspase activators, and caspases, once activated, would in turn increase the mitochondrial membrane permeability. Such a self-amplifying system could accelerate the apoptotic process and/or coordinate the apoptotic response between different mitochondria within the same cell.

Use of thrombin inhibitors ex vivo allows critical care clinical chemistry and hematology testing on common specimens

OBJECTIVE

To evaluate the suitability of the thrombin inhibitors PPACK (D-phenylalanyl-L-prolyl-L-arginine chloromethylketone) or Argatroban for anticoagulation of blood prior to critical care testing of whole blood or plasma.

DESIGN AND METHODS

Initially we evaluated the effect of PPACK (0-200 microM) or Argatroban (0-590 microM) on serum glucose, urea, creatinine, calcium and electrolyte tests on two chemistry analyzers (Hitachi 717 and Ektachem 700XR). Subsequently plasma and serum from whole blood samples containing either heparin 15,000 IU/L or PPACK 75 microM or Argatroban 245 microM or no anticoagulant were tested and compared. We analysed and compared whole blood containing either PPACK 75 microM or Argatroban 245 microM or ethylenediaminetetraacetic acid (EDTA) using a Coulter STK-R hematology analyzer at intervals for 90 minutes.

RESULTS

The measurement of electrolytes, urea, creatinine, calcium or glucose was unaffected by either Argatroban or PPACK in either serum or anticoagulant-specific plasmas (p > 0.05). For specimens from individual donors, serum potassium was higher than plasma potassium, irrespective of anticoagulant used. Clinically equivalent complete blood counts were achieved for 60 minutes using EDTA-whole blood, or whole blood containing 245 microM Argatroban or 75 microM PPACK. However automated differential white cell counting was not reliable with either form of thrombin inhibitor-whole blood. Argatroban-anticoagulated blood demonstrated concentration and time dependent changes in platelet counts, whereas platelet counts were stable in blood containing 75 microM PPACK for up to 90 minutes.

CONCLUSION

Specimens of blood anticoagulated with either 75 microM PPACK or 245 microM Argatroban can be used for either critical care chemistry or hematology testing.

Determination of the ionization state of the active-site histidine in a subtilisin-(chloromethane inhibitor) derivative by 13C-NMR

Subtilisin BPN' has been alkylated using benzyloxycarbonyl-glycylglycyl[1-13C]phenylalanylchloromethane+ ++. Using difference 13C-NMR spectroscopy a single signal due to the 13C-enriched alpha-methylene carbon of the subtilisin-(chloromethane inhibitor) derivative was detected. No evidence for the denaturation/ autolysis of this derivative was obtained from pH 3.5 to 11.5. However, incubating at pH 12.75 or heating in the presence of SDS at pH 6.9 did denature this derivative. The negative titration shift of the alpha-methylene carbon of the denatured derivatives confirmed that the inhibitor had alkylated N-3 of the imidazole ring of the active-site histidine. The positive titration shift of 3.96 p.p.m. and the pKa of 7.04 obtained from studying the native subtilisin-(chloromethane inhibitor) derivative are assigned to oxyanion formation. We conclude that the pKa of the alkylated histidine residue in the native subtilisin-(chloromethane inhibitor) derivative must be > 12 and that subtilisin preferentially stabilizes the zwitterionic tetrahedral adduct consisting of the oxyanion and the imidazolium ion of the active-site histidine residue. We show that even before the oxyanion is formed the pKa of the active-site histidine must be much greater than that of the oxyanion in the zwitterionic tetrahedral adduct. We discuss the significance of our results for the catalytic mechanism of the serine proteinases.

Visualization of thrombi in pulmonary arteries with radiolabeled, enzymatically inactivated tissue-type plasminogen activator

BACKGROUND

Despite the high frequency of pulmonary thromboembolism and its significant morbidity and mortality, diagnosis remains suboptimal. We have been developing a method for prompt detection with the use of radiolabeled, inactivated tissue-type plasminogen activator (TPA) and performed the present study to determine whether its use permits rapid scintigraphic visualization of pulmonary thrombi in vivo.

METHODS AND RESULTS

The thrombolytic, but not fibrin-binding, property of TPA was inactivated with a tripeptide chloromethyl ketone (YPACK) that had already been iodinated with 123I to radiolabel the TPA. Pulmonary arterial thrombosis was induced in nine dogs with the use of guide wires modified to provide thrombogenic tips. 123I-YPACK-TPA (1.1 to 7.8 mCi, 0.5 to 7.8 mg) was infused for 5 minutes into either the systemic or the pulmonary circulation. Clearance of radioactivity from the blood was rapid and indistinguishable from that of unlabeled, thrombolytically active TPA, with only 6.7 +/- 1.0% (mean +/- SEM) of peak radioactivity remaining after 60 minutes and minimal release of labeled fragments from the liver during this interval. Thrombi were visualized with single photon emission computed tomography and/or planar imaging 40 to 120 minutes after infusion of tracer in all seven animals given at least 3.7 mCi of 123I-YPACK-TPA. Ratios of radioactivity in thrombus (wet mass, 610 +/- 64 mg) to blood were high (14 +/- 3:1).

CONCLUSIONS

The use of radiolabeled TPA in which thrombolytic activity is inactivated permits prompt scintigraphic detection of thrombi in pulmonary arteries in vivo.

Scintigraphic visualization of pulmonary thrombi with 123I-YPACK-TNK-tPA

BACKGROUND

We have previously demonstrated that radiolabeled tissue-type plasminogen activation (tPA) in which the plasminogen-activating catalytic site has been inactivated binds avidly to thrombi and can be used for scintigraphic detection of pulmonary thrombi in vivo. The present study was performed to overcome identified limitations of the initially developed approach and to determine whether a tracer made with a molecular variant of tPA, TNK-tPA, would provide superior images of pulmonary thrombi and hence facilitate differential diagnosis of pulmonary embolism from acute myocardial infarction. It was thought that TNK-tPA may be superior in view of its longer biological half-life and less avid uptake by macrophages that would otherwise contribute to high background because of non-clot-selective uptake of the tracer.

METHODS

123I-tyrosylprolylarginyl chloromethyl ketone (123I-YPACK-TNK-tPA) was infused into the systemic circulation of dogs with either pulmonary or right ventricular thrombi induced with thrombogenic tips of modified guide wires. Planar and single-photon emission computed tomography (SPECT) scintigraphic data were obtained, and blood and tissue samples were acquired for analysis of the distribution of the radiotracer over time.

RESULTS

Tracer cleared from blood with an alpha phase half-life of 10 +/- 1 min, paralleling the clearance of unlabeled TNK-tPA. Only minimal release of labeled fragments from liver into blood occurred during the entire time course of the imaging studies. Pulmonary thrombi were visualized with SPECT within 30-120 min in all dogs. Images were superior to those obtained after infusion of labeled wild-type tPA, primarily because of diminished background radioactivity and consequently increased scintigraphic contrast. In one dog which had a right ventricular thrombus, the thrombus was readily detectable in both planar and SPECT images.

CONCLUSIONS

Radiolabeled TNK-tPA in which plasminogen-activating activity has been inhibited biochemically is an excellent radiopharmaceutical for prompt scintigraphic detection of pulmonary and ventricular thrombi in vivo, and an attractive candidate for rapid, sensitive and non-invasive diagnosis of pulmonary thromboembolic disease in patients.

D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK): alternative anticoagulant to heparin salts for blood gas and electrolyte specimens

D-Phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK), a selective thrombin inhibitor, was evaluated as an alternative anticoagulant to lithium heparin (LiHep) for blood gas and whole-blood electrolyte analyses. Initial studies in serum revealed a negative proportional bias for ionized calcium (iCa) concentration measured in the range of increasing concentrations of LiHep (-0.02 mmol/L iCa per 33 kIU/L), whereas no bias in iCa concentration was detected with increasing concentrations of PPACK. No anticoagulant-dependent changes in serum sodium, potassium, chloride, glucose, lactate, ionized magnesium, or pH were detected with either PPACK or LiHep. Similarly, no bias was observed in the measurement of whole-blood PO2, PCO2, pH, or sodium or potassium concentrations with either anticoagulant. Whole blood anticoagulated with LiHep (33 kIU/L) demonstrated a consistent -0.06 +/- 0.01 mmol/L bias for iCa compared with a nonanticoagulated whole-blood control. In comparison, no iCa bias was observed with PPACK-anticoagulated whole blood. We conclude that PPACK has ideal bias-free properties as an anticoagulant in analyses for blood gases, electrolytes, and iCa.

In situ characterization of antigenic and functional tissue factor expression in human tumors utilizing monoclonal antibodies and recombinant factor VIIa as probes

Tissue factor (TF), the primary initiator of blood coagulation in vivo, is expressed in vitro by a variety of cells. Previous efforts to localize TF in tissue and cells have been limited principally to the use of immunological techniques. In the present study, we describe a novel functional probe for TF expression, which can be utilized to localize functional TF in situ in human cells and tissues. This probe, a biotinylated phe-pro-arg-chloro-methyl-ketone-labeled rVIIa (FPR-ck-VIIa), interacts with TF via high-affinity binding sites. The binding of FPR-ck-VIIa, therefore, can be correlated with the ability of TF to activate clotting. In the described studies, TF antigen (TF:Ag) expression was examined immunohistochemically with various TF-specific monoclonal antibodies (MAbs) and was correlated with functional TF expression using our novel TF-binding probe (eg, FPR-ck-VIIa). Initial results indicate that TF:Ag expression correlates with the expression of functional TF (TF:VIIa), and the specificity of both types of probes was confirmed. Parallel antigenic and functional TF expression in situ was demonstrated in various human tumors. We believe this to be the first demonstration of functional TF in situ in human cells and tissues. We suggest that FPR-ck-VIIa should prove a useful reagent for studying the role of TF in the pathogenesis of clotting complications of human disease.

Binding of alpha-thrombin to fibrin depends on the quality of the fibrin network

Binding of human alpha-thrombin to fibrin was studied in a purified system at pH 7.35, I 0.08 and 37 degrees C. Binding experiments with active thrombin resulted in fibrin clots of variable quality, depending on the thrombin concentration: opaque gels composed of 'coarse' network were produced at low thrombin concentrations, while increasing concentrations of thrombin led to more translucent 'fine' gels. Scatchard analysis showed a non-linear dependence of thrombin binding to fibrin, suggesting the existence in fibrin(ogen) of multiple classes of binding sites for thrombin. Binding of catalytic-site-inhibited thrombin was investigated in clots of defined quality produced with three different concentrations of a thrombin-like enzyme, batroxobin (EC 3.4.21.29). Straight lines of different slopes were established by Scatchard analysis of binding data at each fixed batroxobin concentration. These results favour a model according to which binding affinity for thrombin depends on the thickness of fibrin bundles. Labelled active-site-inactivated thrombin incorporated in batroxobin-induced clots was only sparingly released during incubation for 24 h in the presence of a 200-fold excess of unlabelled thrombin, indicating that thrombin binding to fibrin is not reversible and that Scatchard analysis is not appropriate for quantification of binding parameters. Irreversible binding of thrombin appears to reflect trapping of thrombin molecules within fibrin fibres. The amount of trapped thrombin depends on the quality of the fibrin fibres, which in turn is determined by the concentration of the clotting enzyme.

Binding of a substrate analogue can induce co-operative structure in the plasmin serine-proteinase domain

Human miniplasminogen and miniplasmin were studied by n.m.r. spectroscopy and differential scanning calorimetry (d.s.c.) in order to investigate the structural properties of the serine-proteinase domain. The d.s.c. thermograms of both miniplasminogen and non-inactivated miniplasmin at pH 4.0 can be closely fitted to two transitions, at 62 +/- 2 and 72 +/- 2 degrees C, corresponding to unfolding of the kringle 5 and proteinase domains respectively. No evidence was found, under these conditions, for non-co-operative unfolding of the proteinase domain. On inactivation of miniplasmin with an affinity label, a number of additional resonances arising from residues of the proteinase domain are observed in resolved regions of the n.m.r. spectrum. A combination of variable-temperature n.m.r. and d.s.c. has shown that part of the proteinase domain undergoes a major conformational transition on heating which is distinct from the unfolding of the remainder of the proteinase domain or the kringle 5 domain. This additional transition occurs at a temperature that depends on the nature of the affinity label present and is not observed in the absence of an inactivating agent. These results provide direct evidence for the existence of a region of the proteinase domain which, under these conditions, becomes structured only in the presence of a bound substrate.

Affinity chromatography of platelets on immobilized thrombin: retention of catalytic activity by platelet-bound thrombin

Radioactivity from I125-labeled human platelets was measured to estimate the extent of binding of platelet surface proteins to immobilized thrombin. 1-3% of the radioactivity was bound with 10-20% of this amount apparently irreversibly bound to the thrombin matrix. Site-specific chemical modification of thrombin with pyridoxal-5'-phosphate, N-bromosuccinimide or tetranitromethane resulted in a variable reduction of the amount of radiolabel bound. When thrombin modified with H-D-PheProArg-chloromethyl ketone (PPACK) was coupled to the matrix, there was no difference in the binding of platelet membrane proteins when compared to a control thrombin preparation while thrombin modified with tosyl-Lys-chloromethyl ketone (TLCK) coupled to the matrix did not bind radiolabel any more effectively than albumin which served as the control. However, when thrombin was modified with PPACK after coupling to the agarose matrix, ability to bind radiolabel was lost. Thrombin bound to platelets remained catalytically active when assayed with a peptide nitroanilide substrate. These results suggest tight binding between thrombin and platelets that is not only not dependent on active site integrity but leaves the bound thrombin catalytically competent.

[A substrate inhibitor analysis of the urinary excretion of tissue and plasma kallikreins in patients with chronic glomerulonephritis]

The usage of substrate inhibitor analysis made it possible to estimate the levels of excretion of plasma proteinases, including plasma kallikrein in the urinary DValLeuArgpNA (S-2266)- and DProPheArgpNA (S-2302)-amidase activity in patients with latent and nephrotic types of chronic glomerulonephritis (CGN). The soya bean trypsin inhibitor, an inhibitor of plasma kallikrein and other plasma proteinases, such as that of the blood coagulative factors XIa and XIIa, and the high selective plasma kallikrein inhibitor DPhePheArgCH2Cl were used as those differentiating kallikreins of tissue and plasma origin. The S-2266 and S-2302-amidase activity of the urine from healthy subjects was shown to be determined by only tissue (renal) kallikrein. The urine from the patients with a latent CGN type displayed the activity of plasma proteinases, but plasma kallikrein made no significant contribution to the urine amidase activity in these patients. With a nephrotic CGN type, great quantities of trypsin-like proteinases were secreted from the plasma through the glomerular filter into the urine, the proportion of plasma kallikrein in the urinary S-2266 and S-2302-amidase activities being approximately 27%. The compensatory and pathogenetic role of plasma kallikrein is discussed if there is lower excretion of tissue (renal) kallikrein in CGN with the nephrotic syndrome.

Synthesis, purification, and characterization of an Arg152----Glu site-directed mutant of recombinant human blood clotting factor VII

Coagulation factor VII circulates in blood as a single-chain zymogen of a serine protease and is converted to its activated two-chain form, factor VIIa, by cleavage of an internal peptide bond located at Arg152-Ile153. Previous studies using serine protease active-site inhibitors suggest that zymogen factor VII may possess sufficient proteolytic activity to initiate the extrinsic pathway of blood coagulation. In order to assess the putative intrinsic proteolytic activity of single-chain factor VII, we have constructed a site-specific mutant of recombinant human factor VII in which arginine-152 has been replaced with a glutamic acid residue. Mutant factor VII was purified in a single step from culture supernatants of baby hamster kidney cells transfected with a plasmid containing the sequence for Arg152----Glu factor VII using a calcium-dependent, murine anti-factor VII monoclonal antibody column. Purified mutant factor VII was indistinguishable from plasma-derived or recombinant wild-type factor VII by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and migrated as a single band with an apparent molecular weight of 50,000. The average specific activity of several mutant factor VII preparations was 0.00025 unit/micrograms, or 0.01% of that observed for recombinant wild-type factor VII preparations. The clotting activity of mutant factor VII was, however, completely inhibited following incubation with dansyl-Glu-Gly-Arg chloromethyl ketone, suggesting that the apparent clotting activity of mutant factor VII was due to a contaminating serine protease.(ABSTRACT TRUNCATED AT 250 WORDS)

The refined 1.9 A crystal structure of human alpha-thrombin: interaction with D-Phe-Pro-Arg chloromethylketone and significance of the Tyr-Pro-Pro-Trp insertion segment

A stoichiometric complex formed between human alpha-thrombin and D-Phe-Pro-Arg chloromethylketone was crystallized in an orthorhombic crystal form. Orientation and position of a starting model derived from homologous modelling were determined by Patterson search methods. The thrombin model was completed in a cyclic modelling-crystallographic refinement procedure to a final R-value of 0.171 for X-ray data to 1.92 A. The structure is in full agreement with published cDNA sequence data. The A-chain, ordered only in its central part, is positioned along the molecular surface opposite to the active site. The B-chain exhibits the characteristic polypeptide fold of trypsin-like proteinases. Several extended insertions form, however, large protuberances; most important for interaction with macromolecular substrates is the characteristic thrombin loop around Tyr60A-Pro60B-Pro60C-Trp60D (chymotrypsinogen numbering) and the enlarged loop around the unique Trp148. The former considerably restricts the active site cleft and seems likely to be responsible for poor binding of most natural proteinase inhibitors to thrombin. The exceptional specificity of D-Phe-Pro-Arg chloromethylketone can be explained by a hydrophobic cage formed by Ile174, Trp215, Leu99, His57, Tyr60A and Trp60D. The narrow active site cleft, with a more polar base and hydrophobic rims, extends towards the arginine-rich surface of loop Lys70-Glu80 that probably represents part of the anionic binding region for hirudin and fibrinogen.

Human D-Phe-Pro-Arg-CH2-alpha-thrombin crystallization and diffraction data

Human alpha-thrombin, inhibited with the high-affinity irreversible inhibitor D-Phe-Pro-Arg-chloromethylketone, has been crystallized from polyethylene glycol 8000 solutions buffered with 0.1 M-sodium phosphate. The crystals are: orthorhombic, a = 67.9(1) A, b = 87.9(1) A, c = 61.0(1) A, space group P2(1)2(1)2(1) with four molecules per unit cell. This gives a protein fraction of 58% consistent with the excellent X-ray diffraction quality of the crystals. A mercury heavy-atom derivative is being prepared from a thioester analogue of D-Phe-Pro-Arg-CH2-alpha-thrombin in anticipation of a complete crystallographic structure determination.

Monitoring of hemostasis parameters during coronary thrombolysis with recombinant tissue-type plasminogen activator

The monitoring of changes in the blood coagulation and fibrinolytic systems during thrombolytic therapy with recombinant tissue-type plasminogen activator (rt-PA) may be complicated by artifacts due to in vitro activation after blood collection and to interference of other agents (e.g., heparin) in the assays. In 106 patients with early acute myocardial infarction, infused with 150 mg of rt-PA (G11044) intravenously over 5 to 8 hours, blood samples were collected into liquid citrate supplemented with the plasmin inhibitor aprotinin (200 KIU/ml plasma) or on a lyophilized mixture of acidified citrate and the synthetic t-PA inhibitor D-Phe-Pro-Arg-CH2Cl (PPACK). A good correlation between precipitable (sulphite) and functional (clotting rate) fibrinogen levels was observed in plasma collected on citrate before therapy (r = 0.76) and in samples collected after 3 hours on either aprotinin (r = 0.87) or PPACK (r = 0.82). Precipitable fibrinogen levels were approximately 10% higher than functional level, in baseline samples collected on citrate alone and approximately 20% higher in 3 hour samples collected on either PPACK or aprotinin. Fibrinogen levels measured with both assays correlated well, but were somewhat higher in samples collected on PPACK than on aprotinin. rt-PA antigen levels assayed in plasma collected in either inhibitor correlated well (r = 0.90) but were 10-20% higher in PPACK containing samples. Addition of heparin up to 9 units/ml to plasma had no effect on the functional fibrinogen assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Iodination of peptidyl chloromethyl ketones for protease affinity labels

The specificity of peptidyl chloromethyl ketones has been used to label proteases in complex biological systems by incorporating tyrosine into the structure for eventual radioiodination. Contrary to results with iodination of proteins, a mild reagent, that is, one which iodinates at neutrality, was unsuitable, giving complex mixtures with poor reproducibility, apparently because of side reactions at the chloromethyl ketone group. On the other hand, iodine monochloride in acetic acid provided clean products. In the cases examined where a tyrosine residue was not appropriate for the specificity of the target protease, this residue was located well displaced from the primary specificity site. The resultant diiodotyrosine-containing derivatives were generally highly active as protease inhibitors. The p-aminobenzoyl group was used as an alternative to tyrosine as an iodinatable component.

The incorporation of a fluorescent probe into the active sites of one- and two-chain tissue-type plasminogen activator

Dansyl-glutamyl-glycyl-arginyl chloromethyl ketone (DEGR-CK) was shown to inactivate both one- and two-chain human, recombinant tissue-type plasminogen activator (t-PA). The interaction of DEGR-CK with both forms of t-PA was accompanied by an identical increase in the fluorescence intensity and a blue shift in the wavelength of maximum emission, which suggests that the environment of the incorporated DEGR is similar in both one- and two-chain t-PA. The kinetics of the interaction of t-PA with DEGR-CK could be followed by both loss of activity and increase in fluorescence. The second order rate constants (k2/Ki) obtained with these two methods agreed quite well. With two-chain t-PA the values were 42 X 10(4) M-1 min-1 and 46 X 10(4) M-1 min-1 by the activity loss and fluorescence methods, respectively. With one-chain t-PA the results were 2.5 X 10(4) M-1 min-1 and 3.1 X 10(4) M-1 min-1. The rate at which one-chain t-PA is inactivated by DEGR-CK is 15 times lower than the rate with two-chain t-PA. The results demonstrated, however, that the cleavage of the one-chain protein to the two-chain form is not required for reactivity with DEGR-CK. This fluorescently labeled t-PA should be useful in probing the interactions of one- and two-chain t-PA with other proteins.

Inhibition of trypsin-like serine proteinases by tripeptide arginyl and lysyl chloromethylketones

Tripeptide derivatives of lysyl or arginyl chloromethylketone inhibit the trypsin-like serine proteases trypsin, thrombin, plasmin, Factor Xa, urokinase, tissue-type plasminogen activator and protein Ca following the reaction scheme: (formula; see text) Extremely potent tripeptide inhibitors were obtained for thrombin and trypsin (k2/Ki greater than 10(6) M-1s-1), moderate inhibitors for plasmin and Factor Xa (10(6) M-1s-1 greater than k2/Ki greater than 10(4) M-1s-1) and only weak inhibitors for urokinase, tissue-type plasminogen activator and protein Ca (k2/Ki less than 10(4) M-1s-1). Thrombin and Factor Xa as well as urokinase and tissue-type plasminogen activator can be discriminated on the basis of their inhibitory spectrum towards some of these inhibitors.

Dansylalanyllysylchloromethyl ketone as a fluorescent probe for localization of acrosin activity in boar and human spermatozoa

The localization of acrosin (EC 3.4.21.10) activity in mammalian spermatozoa was investigated by use of the fluorescent site-directed acrosin inhibitor, dansylalanyllysylchloromethyl ketone (DALCK). Fluorescence microscope preparations revealed, after the spermatozoa were subjected to a specific treatment, that acrosin activity is confined specifically to the inner acrosomal membrane (IAM). Spectrofluorometric and fluorescence polarization investigations verified that the fluorescent probe, once it is specifically bound to the treated spermatozoa, lies in a very hydrophobic environment and shows a remarkable reduction of rotational freedom. These results are compatible with the hypothesis that, under the experimental conditions used, active acrosin is tightly bound to the IAM and that the "specificity site" of the acrosin-active center is probably of a highly hydrophobic nature.

A study of the alkaline mesentericopeptidase active site by means of peptide chloromethyl ketones

The kinetics of inactivation of alkaline mesentericopeptidase was studied using chloromethyl ketone derivatives of amino acids and peptides. It was shown that Tos-LysCH2Cl and Tos-PheCH2Cl did not influence the enzyme activity, while the inhibitory effect of Cbz-Ala-Gly-PheCH2Cl was 35 times that of Cbz-Ala-PheCH2Cl. The dependence of the pseudo-first order rate constant of the enzyme inactivation by Cbz-Ala-Gly-PheCH2Cl on pH and temperature indicated that a group with a pK of 6.59 and deltaHi of 7.7 kcal/mol was the site of the inhibitor's attack. Amino acid analysis of the modified totally inactive enzyme revealed a definite loss of histidine and after performic acid oxidation a recovery of 3-carboxymethyl histidine. The whole set of experimental data is convincing evidence on behalf of a selective alkylation of the N-3 of the active site histidine after treatment with Cbz-Ala-PheCH2Cl and Cbz-Ala-Gly-PheCH2Cl. Alkaline mesenteriocopeptidase possesses an extended active site and only a peptide chloromethyl ketone, covering a determined sequence of theenzyme molecule (S3, S2, S1, S'1, S'2, S'3 ...) is able to provide effective inhibition. The values of the inactivation constant (kinact) for Cbz-Ala-PheCH2Cl and Cbz-Ala-Gly-PheCH2Cl are close to the corresponding values reported for subtilisin Amylosacchariticus.

The reaction of aminoacylase with chloromethylketone analogs of amino acids

1. Aminoacylase is irreversibly inactivated by the chloromethylketone analogs of benzyloxy-carobonyl-L-alanine, L-alanine, L-leucine, L-aspartic acid (beta), tosyl-L-phenylalanine and L-leucyl-L-alanine. The kinetics of the inactivation of the enzyme by the halo-methylketones were investigated. 2. Leucyl-and alanyl chloromethylketone inactivate the enzyme by blocking of 4 SH groups. Experiments with [U-14C]leucyl chloromethylketone confirm that maximal 4 residues are covalently bound to be protein. 3. Inactivation of the enzyme by benzyloxycarbonylalanyl and tosylphenylalanyl chloromethylketone is the result of the substitution of the epsilon-amino group of one lysine resine residue per active site and not of SH groups. However, in the presence of competitive inhibitors these halomethylketones react only with the SH groups of the enzyme, too.

Affinity labelling of proteinases with tryptic specificity by peptides with C-terminal lysine chloromethyl ketone

Methods are described for the synthesis of peptides terminating in Lys-CH(2)Cl. The products were examined as affinity labels for several enzymes of trypsin-like specificity which are resistant to Tos-Lys-CH(2)Cl. In part, the inertness of the latter may be due to the sulphonamide group, since Z-Lys-CH(2)Cl was more effective. However, a number of tripeptides with C-terminal Lys-CH(2)Cl were superior in their ability to inactivate subtilisin, thrombin and plasma kallikrein. The possibility of developing enzyme-specific reagents selective for members within the trypsin-like group is demonstrated by Ala-Phe-Lys-CH(2)Cl, which readily inactivates plasma kallikrein but not thrombin.