Risk factors for bacterial catheter colonization in regional anaesthesia

BACKGROUND: Although several potential risk factors have been discussed, risk factors associated with bacterial colonization or even infection of catheters used for regional anaesthesia are not very well investigated. METHODS: In this prospective observational trial, 198 catheters at several anatomical sites where placed using a standardized technique. The site of insertion was then monitored daily for signs of infection (secretion at the insertion site, redness, swelling, or local pain). The catheters were removed when clinically indicated (no or moderate postoperative pain) or when signs of potential infection occurred. After sterile removal they were prospectively analyzed for colonization, defined as > 15 colony forming units. RESULTS: 33 (16.7%) of all catheters were colonized, and 18 (9.1%) of these with additional signs of local inflammation. Two of these patients required antibiotic treatment due to superficial infections. Stepwise logistic regression analysis was used to identify factors associated with catheter colonization. Out of 26 potential factors, three came out as statistically significant. Catheter placement in the groin (odds-ratio and 95%-confidence interval: 3.4; 1.5-7.8), and repeated changing of the catheter dressing (odds-ratio: 2.1; 1.4-3.3 per removal) increased the risk for colonization, whereas systemic antibiotics administered postoperatively decreased it (odds ratio: 0.41; 0.12-1.0). CONCLUSION: Colonization of peripheral and epidural nerve catheter can only in part be predicted at the time of catheter insertion since two out of three relevant variables that significantly influence the risk can only be recorded postoperatively. Catheter localisation in the groin, removal of the dressing and omission of postoperative antibiotics were associated with, but were not necessarily causal for bacterial colonization. These factors might help to identify patients who are at increased risk for catheter colonization.     

Identification of a hepatic factor capable of supporting hepatitis C virus replication in a nonpermissive cell line

Although hepatitis C virus E2 protein can bind to human cells by interacting with a putative viral receptor, CD81, the interaction alone is not sufficient to establish permissiveness for hepatitis C virus infection. Using an Epstein-Barr virus-based extrachromosomal replication system, we have screened through a human liver cDNA library and successfully identified a cDNA capable of supporting hepatitis C virus replication in an otherwise nonpermissive cell line. This cDNA encodes a protein exhibiting homology to a group of proteins derived from various evolutionarily distant species, including Oryza sativa submergence-induced protein 2A. The mRNAs encoding this factor are heterogeneous at the 5' ends and are ubiquitously expressed in multiple tissues, albeit in a very small amount. The longest mRNA contains an in-frame and upstream initiation codon and codes for a larger protein. This 5'-extended form of mRNA was detected in hepatocellular carcinoma, but not in normal liver tissue. Immunofluorescence analysis demonstrated that the hepatic factor was distributed evenly in cells, but occasionally formed aggregations in the peri- or intranuclear areas. In summary, we have identified a hepatic factor capable of supporting hepatitis C virus replication in an otherwise nonpermissive cell line. This factor belongs to a previously uncharacterized protein family. The physiological function of this protein awaits further study.     

Factors influencing preoperative stress response in coronary artery bypass graft patients

BACKGROUND: In many studies investigating measures to attenuate the hemodynamic and humoral stress response during induction of anaesthesia, primary attention was paid to the period of endotracheal intubation since it has been shown that even short-lasting sympathetic cardiovascular stimulation may have detrimental effects on patients with coronary artery disease. The aim of this analysis was, however, to identify the influencing factors on high catecholamine levels before induction of anaesthesia. METHODS: Various potential risk factors that could impact the humoral stress response before induction of anaesthesia were recorded in 84 males undergoing coronary aortic bypass surgery, and were entered into a stepwise linear regression analysis. The plasma level of norepinephrine measured immediately after radial artery canulation was chosen as a surrogate marker for the humoral stress response, and it was used as the dependent variable in the regression model. Accordingly, the mean arterial blood pressure, heart rate and the calculated pressure-rate product were taken as parameters of the hemodynamic situation. RESULTS: Stepwise regression analysis revealed that the oral administration of low-dose clonidine (mean dose 1.75 μg.kg-1) on the morning of surgery was the only significant predictor (p = 0.004) of the high variation in preoperative norepinephrine plasma levels. This intervention decreased norepinephrine levels by more than 40% compared to no clonidine administration, from 1.26 to 0.75 nmol.l-1. There was no evidence for dose-responsiveness of clonidine. All other potential predictors were removed from the model as insignificant (p > 0.05). The use of beta-blocker, ace-inhibitors, ejection fraction, and body mass index were significant determinants for the hemodynamic situation (heart rate, mean arterial pressure, pressure rate product) of the patient during the pre-induction period. CONCLUSION: The oral administration of clonidine is the only significant predictor for the observed variation of norepinephrine levels during the preoperative period. Lack of significant dose responsiveness suggests that even a low dose of the drug can attenuate the preoperative stress response and thus is recommended in cardiovascular high risk patients.     

Mutational analysis of the autoprocessing site of subtilisin YaB-G124A

The potential residue at the autoprocessing site for improving processing efficiency was evaluated from hydrolysis of 19 cleavage-site-mimicking octapeptides, VTTXQTVP (-4 to +4), by the mature subtilisin YaB and YaB-G124A mutants. Both enzymes cleaved the octapeptides mainly at two sites, X-Q (A-site) and Q-T (B-site), at varied preferences. Based on the results above, Met(-1) of YaB-G124A was mutated and, as expected, extracellular enzyme production increased with Gln or Ala replacement, but decreased with Ile or Asp substitution. Together with previous structural studies, our results suggest that autoprocessing is dependent on not only the primary structure, but also the peptide flexibility around the processing site. Cleavage at the B-site resulted in a novel YaB mutant lacking the N-terminus Gln 1, which led the mutant enzyme to less enzymatic activity by 80% and less thermal stability by 20 degrees C, perhaps due to its ligation to the high-affinity calcium ion.     

Molecular basis for the susceptibility of fibrin-bound thrombin to inactivation by heparin cofactor ii in the presence of dermatan sulfate but not heparin

Although fibrin-bound thrombin is resistant to inactivation by heparin.antithrombin and heparin.heparin cofactor II complexes, indirect studies in plasma systems suggest that the dermatan sulfate.heparin cofactor II complex can inhibit fibrin-bound thrombin. Herein we demonstrate that fibrin monomer produces a 240-fold decrease in the heparin-catalyzed rate of thrombin inhibition by heparin cofactor II but reduces the dermatan sulfate-catalyzed rate only 3-fold. The protection of fibrin-bound thrombin from inhibition by heparin.heparin cofactor II reflects heparin-mediated bridging of thrombin to fibrin that results in the formation of a ternary heparin.thrombin.fibrin complex. This complex, formed as a result of three binary interactions (thrombin.fibrin, thrombin.heparin, and heparin.fibrin), limits accessibility of heparin-catalyzed inhibitors to thrombin and induces conformational changes at the active site of the enzyme. In contrast, dermatan sulfate binds to thrombin but does not bind to fibrin. Although a ternary dermatan sulfate. thrombin.fibrin complex forms, without dermatan sulfate-mediated bridging of thrombin to fibrin, only two binary interactions exist (thrombin.fibrin and thrombin. dermatan sulfate). Consequently, thrombin remains susceptible to inactivation by heparin cofactor II. This study explains why fibrin-bound thrombin is susceptible to inactivation by heparin cofactor II in the presence of dermatan sulfate but not heparin.     

Coronary pressure and FFR predict long-term outcome after PTCA

Although coronary stents have been the most important improvement in percutaneous coronary interventions in the last 10 years, it is well known to interventionalists that many patients after percutaneous transluminal coronary angioplasty (PTCA) have a favourable outcome without stenting. Coronary angiography, however, is not sensitive enough to identify those particular patients and it has been suggested that a combination of angiographic and functional criteria would be more suitable to distinguish patients with a low restenosis chance after plain balloon angioplasty. In the present study, the authors investigated the value of coronary pressure measurement for conditional stenting in 85 patients. It was demonstrated that in patients in whom a high fractional flow reserve (FFR) was present (> 0.90), the incidence of coronary events at two-year follow-up was almost three times lower than in those patients with an FFR below 0.90. Such high FFRs could be obtained in approximately 45% of all patients. In an additional group of patients, it was demonstrated by intravascular ultrasound (IVUS) studies that the mechanism of a high FFR after plain balloon angioplasty is most likely the result of a larger lumen compared with patients with a suboptimal FFR. This means that, in patients in whom both the angiographic and the functional result after PTCA is optimal, a restenosis rate is achieved similar to that achieved by stenting. Obviously, in such patients, additional stenting and a number of problems in the long-term possibly related to stenting can be avoided. Therefore, coronary angiography and coronary pressure measurement have a complementary value in the evaluation of PTCA results and such information can be easily obtained by using a pressure wire instead of a regular guidewire.     

Design of reference populations for genomic selection in crossbreeding programs

Background

In crossbreeding programs, genomic selection offers the opportunity to make efficient use of information on crossbred (CB) individuals in the selection of purebred (PB) candidates. In such programs, reference populations often contain genotyped PB animals, although the breeding objective is usually more focused on CB performance. The question is what would be the benefit of including a larger proportion of CB individuals in the reference population.

Methods

In a deterministic simulation study, we evaluated the benefit of including various proportions of CB animals in a reference population for genomic selection of PB animals in a crossbreeding program. We used a pig breeding scheme with selection for a moderately heritable trait and a size of 6000 for the reference population.

Results

Applying genomic selection to improve the performance of CB individuals, with a genetic correlation between PB and CB performance (r_PC) of 0.7, selection accuracy of PB candidates increased from 0.49 to 0.52 if the reference population consisted of PB individuals, it increased to 0.55 if the reference population consisted of the same number of CB individuals, and to 0.60 if the size of the CB reference population was twice that of the reference population for each PB line. The advantage of using CB rather than PB individuals increased linearly with the proportion of CB individuals in the reference population. This advantage disappeared quickly if r_PC was higher or if the breeding objective put some emphasis on PB performance. The benefit of adding CB individuals to an existing PB reference population was limited for high r_PC.

Conclusions

Using CB rather than PB individuals in a reference population for genomic selection can provide substantial advantages, but only when correlations between PB and CB performances are not high and PB performance is not part of the breeding objective.     

Differential tissue and ligand-dependent signaling of GPR109A receptor: Implications for anti-atherosclerotic therapeutic potential

Until recently, the anti-atherosclerotic effects of niacin were attributed primarily to its lipid modification properties mediated by adipocyte G-protein coupled receptor GPR109A, though recent studies have raised significant doubts about this mechanism. In fact, in rodents it has recently been demonstrated that niacin inhibits progression of atherosclerosis through actions on immune cells, particularly via macrophage-expressed GPR109A, independent of lipid-modifying properties. Here, we studied GPR109A signal transduction in human Langerhans cells, macrophages and adipocytes. We find that the consequences of receptor activation are profoundly influenced by cellular context and that ligand-biased signaling significantly impacts functionally relevant signaling. In Langerhans cells, niacin initiates GPR109A-mediated signaling pathways (Erk1/2 and Ca^2 +) responsible for the release of vasodilatory prostanoids, while the synthetic GPR109A agonist MK-0354 fails to elicit any signaling, providing a mechanistic basis for the latter compound's inability to cause flushing. While GPR109A mediates inhibition of cAMP in adipocytes, in macrophages GPR109A signaling via G_βγ subunits results in paradoxical augmentation of intracellular cAMP levels. Also, in macrophages niacin and GPR109A full agonists induce Erk1/2 and Ca^2 + signaling, release of prostanoids, upregulation of cholesterol transporters ABCA1 and ABCG1 and stimulation of reverse cholesterol transport in GPR109A dependent manner. A mechanism is presented in which signals from the autocrine action of released prostanoids and G_i protein mediated cAMP augmentation are integrated leading to modulation of reverse cholesterol transport regulatory components. These studies provide key insights into mechanisms by which GPR109A may influence cholesterol efflux in macrophages; a process that may be at least partially responsible for niacin's anti-atherosclerotic activity. MK-0354 does not induce niacin-like GPR109A signaling in macrophages, suggesting that biased agonists devoid of the flushing side-effect may also lack properties required for macrophage-mediated anti-atherosclerotic effects.