Recanalization after intravenous thrombolysis: Does a recanalization time window exist?

BACKGROUND

To evaluate the time course of major vessel recanalization under IV thrombolysis in relation to functional outcome in acute ischemic stroke.

METHODS

A total of 99 patients with an acute anterior circulation vessel occlusion who underwent IV thrombolysis were included. All patients had a standardized admission and follow-up procedure. Color-coded duplex sonography was performed on admission, 30 minutes after thrombolysis, and at 6 and 24 hours after onset of symptoms. Recanalization was classified as complete, partial, and absent. Functional outcome was rated with the modified Rankin Scale on day 30.

RESULTS

Complete recanalization occurred significantly more frequently in patients with multiple branch occlusions compared to those with mainstem occlusion (OR 5.33; 95% CI, 2.18 to 13.05; p < 0.0001) and was associated with lower NIH Stroke Scale (NIHSS) scores (p < 0.001). Not the specific time point of recanalization at 6 or 24 hours after stroke onset, but recanalization per se within 24 hours (OR 7.8; 95% CI 2.2 to 28.2; p = 0.002) was significantly associated with a favorable outcome. Multivariate analysis revealed recanalization at any time within 24 hours and NIHSS scores on days 1 and 7 together explaining 75% of the functional outcome variance 30 days after stroke.

CONCLUSIONS

Complete recanalization up to 24 hours after stroke onset is significantly associated with the short-term clinical course and functional outcome 30 days after acute stroke.

Structural mechanism for the fine-tuning of CcpA function by the small molecule effectors glucose 6-phosphate and fructose 1,6-bisphosphate

In Gram-positive bacteria, carbon catabolite regulation (CCR) is mediated by the carbon catabolite control protein A (CcpA), a member of the LacI-GalR family of transcription regulators. Unlike other LacI-GalR proteins, CcpA is activated to bind DNA by binding the phosphoproteins HPr-Ser46-P or Crh-Ser46-P. However, fine regulation of CCR is accomplished by the small molecule effectors, glucose 6-phosphate (G6P) and fructose 1,6-bisphosphate (FBP), which somehow enhance CcpA-(HPr-Ser46-P) binding to DNA. Unlike the CcpA-(HPr-Ser46-P) complex, DNA binding by CcpA-(Crh-Ser46-P) is not stimulated by G6P or FBP. To understand the fine-tuning mechanism of these effectors, we solved the structures of the CcpA core, DeltaCcpA, which lacks the N-terminal DNA-binding domain, in complex with HPr-Ser46-P and G6P or FBP. G6P and FBP bind in a deep cleft, between the N and C subdomains of CcpA. Neither interacts with HPr-Ser46-P. This suggests that one role of the adjunct corepressors is to buttress the DNA-binding conformation effected by the binding of HPr-Ser46-P to the CcpA dimer N subdomains. However, the structures reveal that an unexpected function of adjunct corepressor binding is to bolster cross interactions between HPr-Ser46-P residue Arg17 and residues Asp69 and Asp99 of the other CcpA subunit. These cross contacts, which are weak or not present in the CcpA-(Crh-Ser46-P) complex, stimulate the CcpA-(HPr-Ser46-P)-DNA interaction specifically. Thus, stabilization of the closed conformation and bolstering of cross contacts between CcpA and its other corepressor, HPr-Ser46-P, provide a molecular explanation for how adjunct corepressors G6P and FBP enhance the interaction between CcpA-(HPr-Ser46-P) and cognate DNA.

On the ability of ultrasound parametric perfusion imaging to predict the area of infarction in acute ischemic stroke

PURPOSE

Cerebral perfusion deficits in acute ischemic stroke can be detected by means of transcranial harmonic imaging after ultrasound contrast agent bolus injection. We evaluated five different parameters of the bolus kinetics as parametric images and correlated areas of disturbed perfusion with the area of definite infarction.

MATERIALS AND METHODS

Perfusion harmonic imaging after SonoVue bolus injection (BHI) was used to investigate 22 patients suffering from acute internal carotid artery infarction. For each subject, we calculated five different images based on the following parameters from the time-intensity curve in each pixel: pixelwise peak intensity (PPI), area under the curve (AUC), positive gradient (PG), time to peak (TTP), and a three factor image from the factor analysis of medical image sequences (FAMIS). The findings in the diencephalic imaging plane were compared with the definite area of infarction, as diagnosed by cranial CT.

RESULTS

In predicting the definite area of infarction in follow-up CT, we found the following sensitivities and positive predictive values (PPV): PPI (100 %/95 %), AUC (100 %/90 %), FAMIS (89 %/89 %), PG (84 %/94 %) and TTP (47 %/100 %). The areas of disturbed perfusion in all five types of parametric images correlated significantly with the area of infarction in CT. Images from the FAMIS algorithm and PPI images showed the highest Spearman rank correlation with the area of definite infarction as displayed in CT (both r = 0.76, p < 0.001). Images from the other parameters correlated as follows: PG: r = 0.62 (p = 0.003), AUC: r = 0.53 (p = 0.014), TTP: r = 0.50 (p = 0.021).

CONCLUSION

BHI can detect disturbed perfusion in acute hemispheric stroke. In their ability to predict the development of an infarction, intensity-based parameters and FAMIS were determined to have a high sensitivity, and TTP was found to have a high PPV and specificity.

Interference of components of the phosphoenolpyruvate phosphotransferase system with the central virulence gene regulator PrfA of Listeria monocytogenes

Analysis of Listeria monocytogenes ptsH, hprK, and ccpA mutants defective in carbon catabolite repression (CCR) control revealed significant alterations in the expression of PrfA-dependent genes. The hprK mutant showed high up-regulation of PrfA-dependent virulence genes upon growth in glucose-containing medium whereas expression of these genes was even slightly down-regulated in the ccpA mutant compared to the wild-type strain. The ptsH mutant could only grow in a rich culture medium, and here the PrfA-dependent genes were up-regulated as in the hprK mutant. As expected, HPr-Ser-P was not produced in the hprK and ptsH mutants and synthesized at a similar level in the ccpA mutant as in the wild-type strain. However, no direct correlation was found between the level of HPr-Ser-P or HPr-His-P and PrfA activity when L. monocytogenes was grown in minimal medium with different phosphotransferase system (PTS) carbohydrates. Comparison of the transcript profiles of the hprK and ccpA mutants with that of the wild-type strain indicates that the up-regulation of the PrfA-dependent virulence genes in the hprK mutant correlates with the down-regulation of genes known to be controlled by the efficiency of PTS-mediated glucose transport. Furthermore, growth in the presence of the non-PTS substrate glycerol results in high PrfA activity. These data suggest that it is not the component(s) of the CCR or the common PTS pathway but, rather, the component(s) of subsequent steps that seem to be involved in the modulation of PrfA activity.

Residues His-15 and Arg-17 of HPr participate differently in catabolite signal processing via CcpA

The carbon catabolite control protein A (CcpA) senses the physiological state of the cell by binding several effectors and responds with differential regulation of many genes in Bacilli. HPr-Ser46-P or Crh-Ser46-P interact with CcpA and stimulate binding to catabolite responsive elements. In addition, the glycolytic intermediates fructose 1,6-bisphosphate (FBP) and glucose 6-phosphate (Glc-6-P) stimulate HPr-Ser46-P but not Crh-Ser46-P binding to CcpA. The mechanisms by which coeffector binding to CcpA is linked to differential gene expression are unclear. To address this question we mutated residues participating in the interaction between HPr-Ser46-P or Crh-Ser46-P and CcpA and analyzed their effects on CcpA binding and stimulation of cre binding by surface plasmon resonance. The HPrH15A and CcpAD297A mutations do not affect complex formation but abolish FBP and Glc-6-P stimulation. Likewise, the CrhQ15H mutant becomes sensitive to these glycolytic intermediates. Hence, the contact of HPrHis-15 to Asp-297 in CcpA is a determinant for HPr specific FBP and Glc-6-P stimulation. The HPrR17A and -K mutants are both strongly impaired in stimulation of CcpA binding to cre, but only HPrR17A is defect in binding to CcpA indicating that these residues affect allostery of CcpA. Mutations of the residues of CcpA, which contact Arg-17 of HPr, exhibit differential effects on regulation of catabolic genes. Taken together, His-15 of HPr processes sensing information, while Arg-17 is involved in determining the genetic output.

Species-specific differences in the activity of PrfA, the key regulator of listerial virulence genes

PrfA, the master regulator of LIPI-1, is indispensable for the pathogenesis of the human pathogen Listeria monocytogenes and the animal pathogen Listeria ivanovii. PrfA is also present in the apathogenic species Listeria seeligeri, and in this study, we elucidate the differences between PrfA proteins from the pathogenic and apathogenic species of the genus Listeria. PrfA proteins of L. monocytogenes (PrfA(Lm) and PrfA*(Lm)), L. ivanovii (PrfA(Li)), and L. seeligeri (PrfA(Ls)) were purified, and their equilibrium constants for binding to the PrfA box of the hly promoter (Phly(Lm)) were determined by surface plasmon resonance. In addition, the capacities of these PrfA proteins to bind to the PrfA-dependent promoters Phly and PactA and to form ternary complexes together with RNA polymerase were analyzed in electrophoretic mobility shift assays, and their abilities to initiate transcription in vitro starting at these promoters were compared. The results show that PrfA(Li) resembled the constitutively active mutant PrfA*(Lm) more than the wild-type PrfA(Lm), whereas PrfA(Ls) showed a drastically reduced capacity to bind to the PrfA-dependent promoters Phly and PactA. In contrast, the efficiencies of PrfA(Lm), PrfA*(Lm), and PrfA(Li) forming ternary complexes and initiating transcription at Phly and PactA were rather similar, while those of PrfA(Ls) were also much lower. The low binding and transcriptional activation capacities of PrfA(Ls) seem to be in part due to amino acid exchanges in its C-terminal domain (compared to PrfA(Lm) and PrfA(Li)). In contrast to the significant differences in the biochemical properties of PrfA(Lm), PrfA(Li), and PrfA(Ls), the PrfA-dependent promoters of hly (Phly(Lm), Phly(L)(i), and Phly(L)(s)) and actA (PactA(Lm), PactA(L)(i), and PactA(L)(s)) of the three Listeria species did not significantly differ in their binding affinities to the various PrfA proteins and in their strengths to promote transcription in vitro. The allelic replacement of prfA(Lm) with prfA(Ls) in L. monocytogenes leads to low expression of PrfA-dependent genes and to reduced in vivo virulence of L. monocytogenes, suggesting that the altered properties of PrfA(Ls) protein are a major cause for the low virulence of L. seeligeri.

Phosphoprotein Crh-Ser46-P displays altered binding to CcpA to effect carbon catabolite regulation

In Gram-positive bacteria, the catabolite control protein A (CcpA) functions as the master transcriptional regulator of carbon catabolite repression/regulation (CCR). To effect CCR, CcpA binds a phosphoprotein, either HPr-Ser46-P or Crh-Ser46-P. Although Crh and histidine-containing protein (HPr) are structurally homologous, CcpA binds Crh-Ser46-P more weakly than HPr-Ser46-P. Moreover, Crh can form domain-swapped dimers, which have been hypothesized to be functionally relevant in CCR. To understand the molecular mechanism of Crh-Ser46-P regulation of CCR, we determined the structure of a CcpA-(Crh-Ser46-P)-DNA complex. The structure reveals that Crh-Ser46-P does not bind CcpA as a dimer but rather interacts with CcpA as a monomer in a manner similar to that of HPr-Ser46-P. The reduced affinity of Crh-Ser46-P for CcpA as compared with that of HPr-Ser46 P is explained by weaker Crh-Ser46-P interactions in its contact region I to CcpA, which causes this region to shift away from CcpA. Nonetheless, the interface between CcpA and helix alpha 2 of the second contact region (contact region II) of Crh-Ser46-P is maintained. This latter finding demonstrates that this contact region is necessary and sufficient to throw the allosteric switch to activate cre binding by CcpA.