The St. Jude "Silzone" valve: midterm results in treatment of active endocarditis.

BACKGROUND: The Silzone-coated St. Jude Medical valve (SJM "Silzone" valve), developed to reduce prosthetic valve endocarditis (PVE), was recalled by SJM due to a higher rate of paravalvular leaks. The aim of this study was to determine the efficacy of the SJM "Silzone" valve in avoiding PVE and to evaluate the frequency of paravalvular leaks, when the valve was used exclusively for active bacterial endocarditis. METHODS: From January 1998 to December 1999, the SJM "Silzone" valve was implanted in 40 consecutive patients with active endocarditis (20 aortic, 14 mitral, and 6 both valves). Late transesophageal echocardiography was performed in 87% of survivors, and transthoracic echocardiography in the remaining 13%. Follow-up was 100%. RESULTS: Hospital mortality was 17.5%. Early PVE occurred in 2 of 40 patients (5%). There were two late deaths without signs of recurrent PVE. A hemodynamic relevant paravalvular leak necessitating reoperation was seen in 2 patients within 6 months after operation. The rate of a minor paravalvular leak was 13% (4 of 31 patients). CONCLUSIONS: The SJM "Silzone" valve when implanted for active bacterial endocarditis does not give better results than other mechanical prostheses with regard to early recurrence of endocarditis. The rate of a hemodynamic relevant paravalvular leak requiring reoperation seems rather high during the early postoperative period, whereas the occurrence of minor paravalvular leaks is comparable with that of other mechanical prostheses. Routine observation, recommended for all patients with mechanical heart valves, is also sufficient for patients with the SJM "Silzone" valve.

Fulminant toxoplasmosis in a heart transplant recipient.

Toxoplasma gondii infections in heart transplant recipients emerge in most cases as newly acquired infections of the immunocompromised sero-negative patient from an exogenous source, usually the donor organ. We report on a 64-year-old heart transplant recipient who developed pneumonitis, myocarditis, and hyperacute encephalitis three weeks after transplantation. Histopathological examination of an endomyocardial biopsy revealed fulminant T. gondii infection. Although appropriate chemotherapy was administered immediately, the patient died the next day. Our case demonstrates that if a histological diagnosis is not rendered in time, fulminant toxoplasmosis may lead to a fatal outcome. In conclusion, a general screening of the donors and recipients for opportunistic infections, including toxoplasmosis, and an appropriate prophylaxis should always be considered.

Isolation and refolding of a mutant methionine-free interleukin-2-receptor alpha chain synthesized as a fusion protein in Escherichia coli.

A soluble domain of the interleukin(IL)-2 receptor, the alpha chain synthesized in Escherichia coli, was employed to study expression and refolding of the protein. The results showed that it is possible to obtain biologically active synthetic methionine-free IL-2 receptor alpha chain (synIL-2R alpha) after BrCN cleavage and renaturation of the crude cleavage material, although the alpha chain is expressed as a deglycosylated, methionine-free protein. The soluble receptor comprises amino acids 1-219 and forms 5 disulfide bonds in its biologically active state. Biological activity has been analysed by affinity chromatography and ELISA with mutant [Ala125]IL-2 and monoclonal antibodies as ligands. Renaturation yield is limited mainly by the high aggregation rate of incorrectly folded protein. Aggregation could be limited by varying the oxidation conditions. The deletion of a non-bridging cysteine at position 192 in the synIL-2R alpha did not affect the renaturation yield of the receptor protein. Additionally a cysteine-free and methionine-free beta-galactosidase derivative was fused to the soluble synIL-2R alpha derivatives to prevent reoxidation of incorrect disulfide bonds in the crude BrCN-cleavage material. It is suggested that cysteine impurities from cyanogen-bromide-cleaved peptides might interfere seriously with the refolding process of the synthetic IL-2 receptor alpha-subunit.

Overexpression, purification, and use of a soluble human interleukin-4 receptor alpha-chain/Ig gamma 1 fusion protein for ligand binding studies. Characterization of ligand binding to soluble IL-4 receptor alpha-chain by surface plasmon resonance measurements and by microtiter-plate-based ELISA with biotinylated IL-4.

The pleiotropic cytokine IL-4 transmits cellular signals mainly via the IL-4 receptor complex, with the alpha-chain as the high affinity binding subunit. Here we describe the overexpression of a soluble IL-4R alpha-chain (sIL-4R) as a fusion to immunoglobulin gamma 1 heavy chain, consisting of the H-CH2-CH3 domains, in baby hamster kidney cells. The dimeric fusion protein named sIL-4R:E gamma 1 was purified from culture supernatant by protein-A affinity chromatography, yielding up to 10 mg/l homogenous protein which was highly stable. The antibody-like features of the sIL-4R:E gamma 1 fusion protein allowed immobilization on a biosensor matrix for surface plasmon resonance measurements by direct amine coupling as well as immobilization on microtiter plates coated with protein A for displacement binding. Kinetic parameters (kon and koff) for binding of IL-4 or the antagonistic mutant IL-4(Y124D) to the sIL-4R:E gamma 1 fusion protein on the chip as determined with the BIAcore instrument showed a high affinity binding with KD = 239 +/- 35 pM and KD=148 +/- 33 pM, respectively. The extremely high kon rate and the relatively slow koff rate for both ligands highlighted the limits of the BIAcore technology. The binding affinity as calculated in displacement binding studies with biotinylated IL-4 was similar for IL-4 and IL-4(Y124D) (IC50=1.1nM), thus offering a simple alternative for initial characterization of IL-4 mutants.