A robust strategy for proteomic identification of biomarkers of invasive phenotype complexed with extracellular heat shock proteins

As an extension of their orchestration of intracellular pathways, secretion of extracellular heat shock proteins (HSPs) is an emerging paradigm of homeostasis imperative to multicellular organization. Extracellular HSP is axiomatic to the survival of cells during tumorigenesis; proportional representation of specific HSP family members is indicative of invasive potential and prognosis. Further significance has been added by the knowledge that all cancer-derived exosomes have surface-exposed HSPs that reflect the membrane topology of cells that secrete them. Extracellular HSPs are also characteristic of chronic inflammation and sepsis. Accordingly, interrogation of extracellular HSPs secreted from cell culture models may represent a facile means of identifying translational biomarker signatures for targeting in situ. In the current study, we evaluated a simple peptide-based multivalent HSP affinity approach using the Vn96 peptide for low speed pelleting of HSP complexes from bioreactor cultures of cell lines with varying invasive phenotype in xenotransplant models: U87 (glioblastoma multiforme; invasive); HELA (choriocarcinoma; minimally invasive); HEK293T (virally transformed immortalized; embryonic). Proteomic profiling by bottom-up mass spectrometry revealed a comprehensive range of candidate biomarkers including primary HSP ligands. HSP complexes were associated with additional chaperones of prognostic significance such as protein disulfide isomerases, as well as pleiotropic metabolic enzymes, established as proportionally reflective of invasive phenotype. Biomarkers of inflammatory and mechanotransductive phenotype were restricted to the most invasive cell model U87, including chitinase CHI3L1, lamin C, amyloid derivatives, and histone isoforms.

Meeting report: discussions and preliminary findings on extracellular RNA measurement methods from laboratories in the NIH Extracellular RNA Communication Consortium

Extracellular RNAs (exRNAs) have been identified in all tested biofluids and have been associated with a variety of extracellular vesicles, ribonucleoprotein complexes and lipoprotein complexes. Much of the interest in exRNAs lies in the fact that they may serve as signalling molecules between cells, their potential to serve as biomarkers for prediction and diagnosis of disease and the possibility that exRNAs or the extracellular particles that carry them might be used for therapeutic purposes. Among the most significant bottlenecks to progress in this field is the lack of robust and standardized methods for collection and processing of biofluids, separation of different types of exRNA-containing particles and isolation and analysis of exRNAs. The Sample and Assay Standards Working Group of the Extracellular RNA Communication Consortium is a group of laboratories funded by the U.S. National Institutes of Health to develop such methods. In our first joint endeavour, we held a series of conference calls and in-person meetings to survey the methods used among our members, placed them in the context of the current literature and used our findings to identify areas in which the identification of robust methodologies would promote rapid advancements in the exRNA field.

Small extracellular vesicles as tumor biomarkers for glioblastoma

Small extracellular organelles such as exosomes and microvesicles are currently being studied as a novel way to track tumor progression, pseudoprogression, and treatment monitoring. Their role in intercellular communication shows potential in the treatment of even the most formidable cancers. Glioblastoma (GBM) is the most common malignancy of the brain and has no known cure. A large emphasis has been placed on trying to improve the prognosis of this aggressive primary brain tumor. It has recently been discovered that small extracellular vesicles, mainly exosomes and microvesicles, play a role in the cell signaling process that leads to uncontrollable cell growth indicative of a tumor state. Here we describe the role of exosomes and microvesicles as a tumor biomarker for tracking the progression of different types of cancer, with an emphasis on GBM.

The molecular basis of high-affinity binding of the antiarrhythmic compound vernakalant (RSD1235) to Kv1.5 channels

Vernakalant (RSD1235) is an investigational drug recently shown to convert atrial fibrillation rapidly and safely in patients (J Am Coll Cardiol 44:2355-2361, 2004). Here, the molecular mechanisms of interaction of vernakalant with the inner pore of the Kv1.5 channel are compared with those of the class IC agent flecainide. Initial experiments showed that vernakalant blocks activated channels and vacates the inner vestibule as the channel closes, and thus mutations were made, targeting residues at the base of the selectivity filter and in S6, by drawing on studies of other Kv1.5-selective blocking agents. Block by vernakalant or flecainide of Kv1.5 wild type and mutants was assessed by whole-cell patch-clamp experiments in transiently transfected human embryonic kidney 293 cells. The mutational scan identified several highly conserved amino acids, Thr479, Thr480, Ile502, Val505, and Val508, as important residues for affecting block by both compounds. In general, mutations in S6 increased the IC50 for block by vernakalant; I502A caused an extremely local 25-fold decrease in potency. Specific changes in the voltage-dependence of block with I502A supported the crucial role of this position. A homology model of the pore region of Kv1.5 predicted that, of these residues, only Thr479, Thr480, Val505, and Val508 are potentially accessible for direct interaction, and that mutation at additional sites studied may therefore affect block through allosteric mechanisms. For some of the mutations, the direction of changes in IC50 were opposite for vernakalant and flecainide, highlighting differences in the forces that drive drug-channel interactions.

Sulfo-Lewis(x) diminishes neutrophil infiltration and free radicals with minimal effect on serum cytokines after liver ischemia and reperfusion

BACKGROUND

Cell adhesion plays a central role in the pathogenesis of neutrophil-induced hepatic injury after ischemia and reperfusion. Sialyl Lewis(x) binds to selectins mediating neutrophil adherence to endothelium, thereby facilitating subsequent migration and tissue damage.

AIM

We studied the effect of a novel sulfo-derivative of sialyl Lewis(x), GM-1998, on the liver inflammatory response after ischemia and reperfusion. Specifically, we evaluated its impact on three key inflammatory mediators: neutrophil migration, free radicals, and serum cytokines.

MATERIAL AND METHODS

Rats were subjected to total hepatic ischemia for 90 min using an extracorporeal portosystemic shunt to avoid splanchnic congestion. GM-1998 was given at a total dose of 20 mg/kg both prior to and after reperfusion. Liver function tests, liver tissue free radicals, and myeloperoxidase (MPO), serum cytokines (IL-1, TNF-alpha), and liver histology were analyzed 4 hr after reperfusion. Additionally, survival was followed for up to 7 days.

RESULTS

Seven-day survival significantly increased from 20% in the control group to 65% in the sulfo-Lewis(x) treated group. Liver function tests and histological damage scores were improved in comparison to controls. We observed significant downregulation of free radicals and neutrophil migration. This compound did not significantly affect serum cytokine levels.

CONCLUSIONS

GM-1998 showed a protective effect in an in vivo model of severe liver ischemia and reperfusion by decreasing tissue free radical levels and selectin-mediated neutrophil migration. This protective effect was also reflected in improved liver function tests and histological response leading to better survival. We confirmed the beneficial effect of neutrophil blockade as a key target to prevent damage after the reperfusion phenomenon by using a glycomimetic sulfo-Lewis(x).

Characterization of renal ischemia-reperfusion injury in rats

The purpose of this study was to characterize the time course of renal ischemia-reperfusion injury in the rat. Male Sprague-Dawley rats were subjected to bilateral renal clamping for 45 min. At reestablishment of blood flow, the rats were divided into nine groups (representing 0, 0.5, 1, 2, 4, 6, 9, and 24 h, and 1 week post-ischemia). At each time point, blood samples were taken for analysis of blood urea nitrogen (BUN) and creatinine, and both kidneys were harvested for histopathology and myeloperoxidase activity (MPO) assays. An intracellular adhesion molecular (ICAM-1) monoclonal antibody (IMAb) was tested in a separate group of animals (1 mg/rat) to confirm that it may provide renal protection previously reported by Kelly et al. (1994). Following renal ischemia, significant increases in serum BUN and creatinine were observed compared to levels in normal animals. Serum BUN and creatinine increased 2, 4, and 6 h post-ischemia leading to peak elevations 24 h post-ischemia. Values returned to normal at the 1 week time point. MPO activity was slightly increased 2 and 4 h following ischemia, with peak elevations occurring at the 6-h and 9-h time points. Histopathologic examination of kidneys revealed that the most severe damage occurred at the 24-h time point, which correlated with the peak elevations in serum BUN and creatinine. Evidence of renal injury was still evident histologically 1 week following ischemia, although renal function tests (BUN and creatinine) had returned to normal. In summary, renal injury following ischemia may be demonstrated as early as 4 h post-ischemia as judged by changes in renal function, MPO levels, and renal histopathology. However, based upon renal function tests and histology, peak injury is observed approximately 24 h following ischemia. The ICAM-1 monoclonal antibody, ICAM-Ab, provided some renal protection against ischemia-reperfusion injury in this study as measured by serum creatinine, BUN and renal histopathology. However, in contrast to the results reported by Kelly et al., the magnitude of the protective effects was not as dramatic in the present study, and furthermore, no reductions in renal MPO activity were observed.

Polyethylene glycol-conjugated superoxide dismutase attenuates reperfusion injury when administered twenty-four hours before ischemia

Covalent linkage of polyethylene glycol to superoxide dismutase prolongs the serum half-life of the enzyme and may facilitate intracellular access. We tested the myocardial protective effect of polyethylene glycol superoxide dismutase administered once, 24 hours before ischemia. Because hearts were studied ex vivo in a crystalloid perfused system, cardioprotection could be ascribed to intramyocardial or membrane-bound polyethylene glycol superoxide dismutase accumulation. Thirty isolated rabbit hearts from the four following groups were studied: (1) control: untreated rabbits (n = 7); (2) PEG-control: 24-hour intravenous preinfusion of methoxypolyethylene glycol 5000 (5 mg/kg) to examine the effect of polyethylene glycol alone, without conjugation to superoxide dismutase (n = 8); (3) PEG-SOD 10,000: 24-hour preinfusion of polyethylene glycol superoxide dismutase (10,000 U/kg) (n = 8); (4) PEG-SOD 30,000: 24-hour preinfusion of polyethylene glycol superoxide dismutase (30,000 U/kg) (n = 7). After measurement of baseline function with use of an intraventricular balloon, hearts were subjected to normothermic ischemia until a 4 mm Hg rise in intracavitary pressure was observed. Function was assessed at 15-minute intervals throughout reperfusion and expressed as percent return of developed pressure. After 60 minutes of reperfusion, recovery of function was greater for the PEG-SOD 30,000 group (85.6% +/- 2.6%) when compared with either the untreated or PEG-control group (68.9% +/- 2.3% and 71.4% +/- 2.0%, respectively). A similar difference was seen throughout reperfusion. Although an improved return of function was shown in the lower dose PEG-SOD 10,000 group, the margin of difference when compared with any of the control groups was determined to be insignificant at all times of reperfusion and at 60 minutes (75.9% +/- 3.2%). These data demonstrate that high, but not low, doses of polyethylene glycol superoxide dismutase significantly reduce reperfusion injury when administered 24 hours before initiation of global ischemia. Moreover, since the perfusate was superoxide dismutase free, this effect was most likely intramyocardial or membrane bound and therefore might be added to protection afforded by circulating superoxide dismutase.

PEG-SOD improves postischemic functional recovery and antioxidant status in blood-perfused rabbit hearts

The isolated blood-perfused rabbit heart, subjected to 60 min of cardioplegic arrest and 60 min of reperfusion, was used to assess the effects of polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) on postischemic recovery of left ventricular developed pressure (LVDP), the tissue activity of SOD, and tissue redox state. The five groups studied were the following: PEG-SOD-free control (group A), PEG-SOD as a pretreatment and as an additive during cardioplegia and reperfusion (group B), PEG-SOD as a pretreatment and a cardioplegic additive (group C), PEG-SOD in cardioplegia alone (group D), and PEG-SOD in reperfusion alone (group E). The results show that pretreatment with PEG-SOD improves postischemic recovery of LVDP (72 +/- 2% and 66 +/- 7 vs. 47 +/- 4% in groups B, C, and A, respectively). This protection was associated with an improved tissue redox state. Thus the ischemia-induced rise in oxidized glutathione was reduced from 313 +/- 26% (group A) to 162 +/- 15 and 138 +/- 14% (groups B and C, respectively), and the fall in reduced glutathione was attenuated from 51 +/- 5% to 35 +/- 6 and 13 +/- 5%, respectively. Tissue Mn-SOD activity was also conserved from 36 +/- 4% (group A) to 71 +/- 6 and 94 +/- 4% (groups B and C, respectively). No significant effect was seen when PEG-SOD was applied in cardioplegia or during reperfusion alone.

PEG-SOD and myocardial antioxidant status during ischaemia and reperfusion: dose-response studies in the isolated blood perfused rabbit heart

We have previously shown that the polyethylene glycol conjugated superoxide dismutase (SOD), which has a plasma half-life of more than 24 h, protects the blood perfused rabbit heart against injury during ischaemia and reperfusion. However, the profile for the dose-dependency of protection was bell-shaped with loss of efficacy below 6000 and above 30,000 U/kg. In the present study, isolated rabbit hearts, perfused with blood from support rabbits, were subjected to a 2 min infusion with St Thomas' Hospital cardioplegic solution followed by 60 min of global ischaemia (37 degrees C) and 60 min of reperfusion. PEG-SOD was administered 1 h or 12-24 h before ischaemia. We assessed the effect of PEG-SOD on ischaemia- and reperfusion-induced changes in: (i) the tissue content of reduced glutathione (GSH), oxidized glutathione (GSSG) and malondialdehyde (MDA) and (ii) the activity of CuZn-SOD, Mn-SOD and glutathione peroxidase and reductase (GPD and GRD). Ischaemia and reperfusion reduced tissue GSH content by 70% and increased GSSG content by 400% (from their fresh aerobic values of 13.1.9 and 0.09 +/- 0.01 nmol/mg protein, respectively). PEG-SOD, given intravenously at various doses to donor and support rabbits 1 h or 12-24 h before ischaemia, protected against these changes with a bell-shaped dose-response relationship. Thus, with 0, 3000, 6000, 12,000, 30,000 and 60,000 U/kg, GSH content was 4.1 +/- 0.4, 4.8 +/- 0.4, 8.5 +/- 0.5, 12.3 +/- 1.6, 12.3 +/- 1.6 and 5.0 +/- 0.5 nmol/mg protein in the 1 h pretreatment group and 4.1 +/- 0.4, 4.2 +/- 0.5, 10.4 +/- 1.5, 11.2 +/- 1.1, 11.4 +/- 0.7 and 4.7 +/- 0.6 nmol/mg protein in the 12-24 h pretreatment group (means +/- S.E.M.). For GSSG the corresponding values were 0.36 +/- 0.04, 0.34 +/- 0.03, 0.12 +/- 0.01, 0.12 +/- 0.01, 0.11 +/- 0.01 and 0.41 +/- 0.03 nmol/mg protein for the 1 h group and 0.36 +/- 0.04, 0.35 +/- 0.02, 0.15 +/- 0.01, 0.12 +/- 0.01, 0.11 +/- 0.01 and 0.34 +/- 0.02 nmol/mg protein for the 12-24 h group. Ischaemia and reperfusion had no effect on tissue MDA content or CuZn-SOD, GDP and GRD activity, and in general, PEG-SOD also lacked significant effect on any of these variables at any dose studied. However, Mn-SOD activity was severely reduced by ischaemia and reperfusion (from 42 +/- 7 U/mg protein in fresh aerobic controls to 6 +/- 1 U/mg protein at the end of reperfusion).(ABSTRACT TRUNCATED AT 400 WORDS)

PEG-SOD and myocardial protection. Studies in the blood- and crystalloid-perfused rabbit and rat hearts

BACKGROUND

Polyethylene glycol, covalently linked to superoxide dismutase (PEG-SOD), has a long plasma half-life (greater than 30 hours) and has been proposed as an effective agent for reducing free radical-mediated injury ischemia and reperfusion.

METHODS AND RESULTS

Using an isolated rabbit heart perfused with arterial blood from a support rabbit, we have demonstrated that pretreatment with PEG-SOD (30,000 units/kg, intravenous bolus, 12-24 hours before 60 minutes of normothermic global ischemia), combined with addition of PEG-SOD to the blood perfusion circuit (30,000 units/kg to the support rabbit) and inclusion of PEG-SOD (150 micrograms/ml) in a cardioplegic solution, enhanced the postischemic recovery of left ventricular developed pressure (LVDP) from 51 +/- 6 to 74 +/- 9 mm Hg (p less than 0.05; n = 9 per group). In further studies we showed that, whereas maximum protection was obtained when PEG-SOD was given as a combined pretreatment and additive to both the cardioplegic and the reperfusate solutions (postischemic LVDP recovery increased from 44 +/- 4% in the control group to 70 +/- 3% in the PEG-SOD group), the administration of PEG-SOD during pretreatment plus cardioplegia or during reperfusion alone also resulted in a significant improvement in postischemic function (62 +/- 7% and 60 +/- 3%, respectively). However, the use of PEG-SOD as a cardioplegic additive alone failed to afford protection (47 +/- 4% recovery of LVDP). In dose-response studies (with 0, 3,000, 6,000, 12,000, 30,000, or 60,000 units/kg; n = 8 per group), maximum recovery of LVDP was obtained with the administration of 12,000 units/kg of PEG-SOD. Studies of the plasma activity of PEG-SOD confirmed its long half-life and showed that the treatment with PEG-SOD either 1 hour or 12-24 hours before the study resulted in similar levels of plasma activity. In an attempt to assess any involvement of blood-borne elements in the protection afforded by PEG-SOD, studies were also carried out in the crystalloid-perfused rabbit heart, and no protection was observed. Similarly, no protection was observed at any one of a variety of doses in the crystalloid-perfused rat heart.

CONCLUSIONS

PEG-SOD can afford protection in the blood-perfused rabbit heart; this protection is dose dependent and probably involves some action of PEG-SOD on blood-borne elements, possibly leukocytes.