Selection of viable cardiomyocytes for cell transplantation using three-dimensional tissue culture

BACKGROUND

We developed a three-dimensional cardiac tissue culture system to select viable and contractile cells for the purpose of cardiomyocyte transplantation. In this study we will show that reaggregation of cardiomyocytes in culture is an active process indicative of cardiomyocyte viability and functionality.

METHODS

Myocardial tissue from newborn mice has been enzymatically digested, incubated in culture inserts, and studied by phase contrast microscopy, conventional histology, immunohistochemistry, electron microscopy, and TUNEL assay.

RESULTS

Cells that are plated on nonadhesive surfaces, reaggregate to spontaneously contracting cell aggregates. The capacity to reaggregate was significantly dependent from the age of the tissue donor (P<0.0001) and on the method of enzymatic dissociation (P<0.0001). The majority of cells within the aggregates consisted of cardiomyocytes. After 24 hr incubation, significant amounts of laminin and fibronectin had been deposited between the cells. Ultrastructural analysis revealed viable cardiomyocytes attached to each other by tight junctions. The apoptotic rate within the aggregates was 11.4+/-4.6 vs. 44.5+/-10.5% immediately after dissociation (P<0.05).

CONCLUSIONS

The capacity to form spontaneously contracting aggregates is an inherent characteristic of viable cardiomyocytes in 3-dimensional cultures, which could be successfully exploited for cellular cardiomyocyte transplantation.

Human serum induces apoptosis of xenogenic cardiomyocytes in vivo and in vitro

Discordant xenotransplantation is complicated by delayed xenograft rejection (DXR). Previous studies have demonstrated that anti-apoptotic genes are protective against DXR. This study examines the hypothesis that apoptosis plays a role in human anti-xenograft responses. C57BL/6 mice and NOD SCID mice were given a single intravenous injection of either a lethal dose (LD, survival < 30 min) or a sublethal dose (SLD) of human serum, and isolated pig and mouse rod-shaped cardiomyocytes were exposed to human serum in vitro. In situ detection of apoptotic cells in mouse hearts was assessed using a terminal deoxynucleotidyl transferase-mediated dUTP nicked-end labeling assay. Mice transfused with human serum had approximately a 10-fold increased percentage of apoptotic cells after SLD 18 h post-injection compared with animals given saline, and a fourfold increase over LD. Administration of cobra venom factor (CVF) decomplemented SLD 18 h did not significantly (P > 0.05) alter the percentage apoptosis. The addition of 20 mM Gal-alpha-1,3-Gal to SLD 18 h significantly (P < 0.05) reduced percentage apoptosis to levels comparable to saline treated control animals. In vitro using mouse and pig cardiomyocytes demonstrated parallel results as in vivo experiments. Human serum induces apoptosis of cardiomyocytes in immunocompetent and immunoincompetent mice in vivo, as well as mouse and pig cardiomyocytes in vitro. Further, this apoptotic response can be inhibited by the addition of Gal-alpha-1,3-Gal without affecting the capacity of the serum to cause HAR. These results demonstrate that a putative human serum factor induces a delayed apoptotic injury of xenograft tissues, and supports the hypothesis that apoptosis may be an important mediator of DXR.

Blood distribution and single-dose pharmacokinetics of leflunomide

Leflunomide (HWA 486, LEF) is a novel isoxazole derivative with potent immunosuppressive properties. LEF is converted to its active metabolite (A77 1726) after absorption. Presently, the blood distribution and pharmacokinetics of LEF have not been reported. Such information would prove invaluable in determining the appropriate medium for analysis and optimal immunosuppressive dosing regimes. In this study, A77 1726 was found to be primarily associated (> 95%) with the lipoprotein free fraction of plasma at all tested concentrations ranging from 0.4 to 100 mg/L. Detectable levels of A77 1726 (0.34 +/- 0.18 mg/L), analyzed by HPLC, were found in the plasma free fraction only at the highest tested concentration (100 mg/L). Single-dose pharmacokinetics of A77 1726 (i.v.) and HWA 486 (p.o.) were investigated in five healthy New Zealand white rabbits. The half-lives (t1/2) of A77 1726 i.v. and HWA 486 p.o. administration were 3.88 +/- 2.3 and 3.18 +/- 1.6 h, respectively. The volume of distribution by both routes of administration indicates minimal distribution into tissues (Vdss p.o. = 0.14 +/- 0.03 L/kg and Vdssi.v. = 0.09 +/- 0.02 L/kg). The mean residence time of A77 1726 was greater after oral administration of LEF (MRTp.o. = 10.54 +/- 2.6 h and MRTi.v. = 6.76 +/- 1.0 h). Identical areas under the curve suggest bioavailability was 100% (AUCp.o. = 421.16 +/- 204.5 mg.h/L and AUCi.v. = 399.75 +/- 126.9 mg.h/L).

Measurement of the active leflunomide metabolite (A77 1726) by reverse-phase high-performance liquid chromatography

The immunosuppressive activity of leflunomide is expressed after conversion to its pharmacologically active metabolite A77 1726. Leflunomide is a potent immunosuppressant that inhibits both T-cell and B-cell activity. To date, no pharmacokinetic data have been reported on leflunomide or A77 1726, primarily because of lack of a suitable method for its analysis. We describe here the development and evaluation of a reverse-phase high-performance liquid chromatographic (HPLC) method for the analysis of A77 1726 in whole blood or plasma from humans or rabbits. In human blood, the method exhibited good analytic recoveries from 78 +/- 13.5% to 108 +/- 4.8% (mean +/- SD) for drug concentrations ranging from 400 to 100,000 micrograms/L. When using a sample volume of 0.25 ml the sensitivity of the method was found to be 400 micrograms/L, with a working standard range of up to 200,000 micrograms/L. The sensitivity of the method can be increased to 40 micrograms/L when 1.0 ml of sample is used. Between-run coefficients of variation of 12.2 and 14.7% at A77 1726 mean concentrations of 1,006 and 8,146 micrograms/L were found for this method. No significant differences in recovery of drug were noted when either human or rabbit plasma or whole blood was used as the medium of analysis. In whole-blood specimens, A77 1726 was found to be stable for up to 10 days at -20 or -70 degrees C.