Karkouti and colleagues [1Karkouti K. Djaini G. Borger M. et al.Low hematocrit during cardiopulmonary bypass is associated with increased risk of preoperative stroke in cardiac surgery.Ann Thorac Surg. 2005; 80: 1381-1387Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar] have recently reported a positive association between the nadir of operative hematocrit (Hct) during coronary artery bypass surgery (CABS), and the risk of perioperative stroke. A survey of 5,000 consecutive operations by Habib and colleagues [2Habib R.H. Zacharias A. Schwann T.A. Riordan C.J. Durham S.J. Shah A. Adverse effects of low hematocrit during cardiopulmonary bypass in the adult should current practice be changed?.J Thorac Cardiovascular Surg. 2003; 125: 1438-1450Abstract Full Text Full Text PDF PubMed Scopus (328) Google Scholar] found the lowest quintile of Hct was also linked to vital organ dysfunction, morbidity, and 6-year survival. We sought evidence of whether a low operative Hct was a risk factor for the development of cognitive disturbance in the aftermath of CABS. This analysis was performed in a cohort of patients recruited into a study that examined the impact of leukocyte depleting filter in CABS [3Whitaker D.C. Newman S.P. Stygall J. Hope-Wynne C. Harrison M.J.G. Walesby R.K. The effect of leucocyte-depleting arterial line filters on cerebral microemboli and neuropsychological outcome following coronary artery bypass surgery.Eur J Cardiothorac Surg. 2004; 25: 267-274Crossref PubMed Scopus (74) Google Scholar]. The details of recruitment of the operative technique and the neuropsychological assessment preoperatively and 6 to 8 weeks after elective CABS are described in the full report of the interventional study [3Whitaker D.C. Newman S.P. Stygall J. Hope-Wynne C. Harrison M.J.G. Walesby R.K. The effect of leucocyte-depleting arterial line filters on cerebral microemboli and neuropsychological outcome following coronary artery bypass surgery.Eur J Cardiothorac Surg. 2004; 25: 267-274Crossref PubMed Scopus (74) Google Scholar]. Here we set out the results of venous Hct measured preoperatively (42.7%; standard deviation [SD], 4.6%) 30 minutes after initiation of bypass (27.4%; SD, 4.9%) 10 minutes after the end of bypass (29.5%; SD, 3.4) and on the first postoperative day (32.1%; SD, 3.9%) in the 111 patients with full data at the time points. The Z change scores were calculated for each of the 10 tests in the neuropsychological test battery between individuals performances 6 to 8 weeks postoperatively compared with the preoperative score. A global Z change score was also calculated for each patient’s performances in the test battery as a whole. No correlation was found (Pearson) between Hct levels of any time point including the nadir, and Z change scores of neuropsychological performance using either the global or individual test data. The subset of patients who were older than 65 years of age showed no association between Hct level and cognitive outcome. This absence of an effect may relate to the success of the operative strategy of restricting falls of Hct below 20 (only 1 patient had a hematocrit during bypass below this level of 19.4%). By contrast Karkouti and colleagues [1Karkouti K. Djaini G. Borger M. et al.Low hematocrit during cardiopulmonary bypass is associated with increased risk of preoperative stroke in cardiac surgery.Ann Thorac Surg. 2005; 80: 1381-1387Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar] reported that 25% of their cases had levels below 20. Although the optimal Hct for cerebral oxygen delivery in humans is held to be 35.2% from positron emission tomography, in animal studies the compensation for loss of oxygen carrying capacity at low Hct is not obvious until 19%. Also, a better than expected compensation has been reported for the special circumstances of hypothermic bypass. The lack of evidence for a low Hct contributing to the cognitive disturbance after CPB does not of course mean that the ongoing debate about the optimal Hct during bypass for other organs and other outcomes should be neglected. It may however provide a further pointer to what the target level should be. ReplyThe Annals of Thoracic SurgeryVol. 82Issue 3PreviewWe would like to thank Drs Harrison and colleagues [1] for their interest in our study [2], and we appreciate this opportunity to comment on their interesting results. In their exploratory analysis of 111 patients enrolled in a previous study, Harrison and colleagues [1] did not find an association between nadir hematocrit during cardiopulmonary bypass (CPB) and neurocognitive dysfunction after coronary artery bypass surgery (CABS). We agree that the absence of an association may be due to the higher average nadir hematocrit concentrations in their sample relative to ours (27% vs 23%, respectively). Full-Text PDF

S-Glutathionylation (thiolation) is a ubiquitous redox-sensitive and reversible modification of protein cysteinyl residues that can directly regulate their activity. While well established in animals, little is known about the formation and function of these mixed disulfides in plants. After labeling the intracellular glutathione pool with [35S]cysteine, suspension cultures of Arabidopsis (Arabidopsis thaliana ecotype Columbia) were shown to undergo a large increase in protein thiolation following treatment with the oxidant tert-butylhydroperoxide. To identify proteins undergoing thiolation, a combination of in vivo and in vitro labeling methods utilizing biotinylated, oxidized glutathione (GSSG-biotin) was developed to isolate Arabidopsis proteins/protein complexes that can be reversibly glutathionylated. Following two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry proteomics, a total of 79 polypeptides were identified, representing a mixture of proteins that underwent direct thiolation as well as proteins complexed with thiolated polypeptides. The mechanism of thiolation of five proteins, dehydroascorbate reductase (AtDHAR1), zeta-class glutathione transferase (AtGSTZ1), nitrilase (AtNit1), alcohol dehydrogenase (AtADH1), and methionine synthase (AtMetS), was studied using the respective purified recombinant proteins. AtDHAR1, AtGSTZ1, and to a lesser degree AtNit1 underwent spontaneous thiolation with GSSG-biotin through modification of active-site cysteines. The thiolation of AtADH1 and AtMetS required the presence of unidentified Arabidopsis proteins, with this activity being inhibited by S-modifying agents. The potential role of thiolation in regulating metabolism in Arabidopsis is discussed and compared with other known redox regulatory systems operating in plants.

Glutathione transferases in soybean (GmGSTs) involved in herbicide detoxification in cell suspension cultures were purified by S-hexylglutathione affinity chromatography and resolved by a combination of HPLC and SDS–PAGE into 11 polypeptides. Analysis by Western blotting using antisera raised to three previously characterised tau (GmGSTU) class subunits demonstrated that five polypeptides were related to GmGSTU1, three to GmGSTU2, and one to Gm GSTU3. Plants contained a simpler profile of polypeptides, with a single GmGSTU2-like polypeptide predominating. With respect to herbicide detoxification, two GmGSTU2-related polypeptides dominated the activity toward the chloroacetanilide acetochlor, while an unclassified subunit was uniquely associated with the detoxification of diphenyl ethers (acifluorfen, fomesafen). The inducibility of the different GST subunits was determined in soybean plants exposed to photobleaching diphenyl ethers and the safeners naphthalic anhydride and dichlormid. GmGSTU3, a GmGSTU1-like polypeptide, and thiol (homoglutathione) content were induced by all chemical treatments, while two uncharacterised subunits were only induced in plants showing photobleaching.