Remote Surveillance Technology of Dialysis Arteriovenous Access: Retrospective Evaluation in a UK Renal Centre.

BACKGROUND: Early identification of dysfunctional arteriovenous haemodialysis (HD) vascular access (VA) is important for timely referral and intervention. METHOD: We retrospectively calculated VA risk score using Vasc-Alert surveillance software technology from HD treatment sessions in 2 satellite HD units over 18 months. We included in the analysis HD patients dialysing with arteriovenous fistula or graft (AVF/G) with available Vasc-Alert data for≥ 2 months. For group one (eventful) that included patients who developed vascular access thrombosis or stenosis over the study period, we collected Vasc-Alert risk score 2 months prior to the event and, for group two (uneventful), over 5 consecutive months. Vasc-Alert technology utilises routinely collected data during HD to calculate VA risk score and triggers an alert if the score is ≥7 in 3 consecutive dialysis sessions. Patients with >2 alerts (vascular access score ≥7) per month were considered to have positive alerts. RESULTS: From 140 HD patients, 81 patients dialysed via AVF/G. 77/81 had available Vasc-Alert data and were included in the final analysis. Out of 17 eventful patients, 11 (64.7%) had positive alerts 2 months prior to the vascular event. Out of the 60 patients without vascular events, 20 patients (33.3%) had positive alert. Vasc-Alert's sensitivity and specificity for vascular events were 64.7% and 66.6%, respectively. Within the 6 patients with thrombosed access, 2 patients (33.3%) detected by Vasc-Alert were not detected with clinical monitoring. CONCLUSION: Vascular access risk score can be a useful non-invasive vascular access surveillance method to assist clinical decision making.

Different transition-state structures for the reactions of beta-lactams and analogous beta-sultams with serine beta-lactamases.

Beta-sultams are the sulfonyl analogues of beta-lactams, and N-acyl beta-sultams are novel inactivators of the class C beta-lactamase of Enterobacter cloacae P99. They sulfonylate the active site serine residue to form a sulfonate ester which subsequently undergoes C-O bond fission and formation of a dehydroalanine residue by elimination of the sulfonate anion as shown by electrospray ionization mass spectroscopy. The analogous N-acyl beta-lactams are substrates for beta-lactamase and undergo enzyme-catalyzed hydrolysis presumably by the normal acylation-deacylation process. The rates of acylation of the enzyme by the beta-lactams, measured by the second-order rate constant for hydrolysis, kcat/K(m), and those of sulfonylation by the beta-sultams, measured by the second-order rate constant for inactivation, k(i), both show a similar pH dependence to that exhibited by the beta-lactamase-catalyzed hydrolysis of beta-lactam antibiotics. Electron-withdrawing groups in the aryl residue of the leaving group of N-aroyl beta-lactams increase the rate of alkaline hydrolysis and give a Bronsted beta(lg) of -0.55, indicative of a late transition state for rate-limiting formation of the tetrahedral intermediate. Interestingly, the corresponding Bronsted beta(lg) for the beta-lactamase-catalyzed hydrolysis of the same substrates is -0.06, indicative of an earlier transition state for the enzyme-catalyzed reaction. By contrast, although the Bronsted beta(lg) for the alkaline hydrolysis of N-aroyl beta-sultams is -0.73, similar to that for the beta-lactams, that for the sulfonylation of beta-lactamase by these compounds is -1.46, compatible with significant amide anion expulsion/S-N fission in the transition state. In this case, the enzyme reaction displays a later transition state compared with hydroxide-ion-catalyzed hydrolysis of the beta-sultam.

Novel mechanism of inhibiting beta-lactamases by sulfonylation using beta-sultams.

Beta-sultams are the sulfonyl analogues of beta-lactams and N-acyl beta-sultams are novel inactivators of the class C beta-lactamase of Enterobacter cloacae P99. The rates of inactivation show a similar pH-rate dependence as that exhibited by the beta-lactam antibiotics and with ESIMS data it is suggested that beta-sultams sulfonylate the active site serine residue to form a sulfonate ester.

Structure-reactivity relationships in the inactivation of elastase by beta-sultams.

N-Acyl-beta-sultams are time dependent irreversible active site directed inhibitors of elastase. The rate of inactivation is first order with respect to beta-sultam concentration and the second order rate constants show a similar dependence on pH to that for the hydrolysis of a peptide substrate. Inactivation is due to the formation of a stable 1:1 enzyme inhibitor complex as a result of the active site serine being sulfonylated by the beta-sultam. Ring opening of the beta-sultam occurs by S-N fission in contrast to the C-N fission observed in the acylation of elastase by N-acylsulfonamides. Structure-activity effects are compared between sulfonylation of the enzyme and alkaline hydrolysis. Variation in 4-alkyl and N-substituted beta-sultams causes differences in the rates of inactivation by 4 orders of magnitude.

Hydrolysis of a sulfonamide by a novel elimination mechanism generated by carbanion formation in the leaving group.

The alkaline hydrolysis of N-alpha-methoxycarbonyl benzyl-beta-sultam occurs 10(3) times faster than the corresponding carboxylate and with rapid D-exchange at the alpha-carbon: the pH rate profile indicates pre-equilibirum CH ionisation and together with formation of benzoyl formate as a product this suggests a novel mechanism for hydrolysis.