Contribution of power Doppler sonography to the detection of renal allograft rejection in the cynomolgus monkey

Oral efficacy of the new immunomodulator FTY720 in cynomolgus monkey kidney allotransplantation, given alone or in combination with cyclosporine or RAD

BACKGROUND

FTY720 is a novel immunomodulator with a unique mechanism of action, i.e. chemokine-dependent lymphocyte homing into secondary lymphoid organs associated with profound lymphocyte depletion in blood. We investigated its efficacy, either FTY720 alone or together with cyclosporine or the rapamycin derivative rapamycin derivative (RAD), in cynomolgus monkey kidney allotransplantation.

METHODS

Life-supporting allotransplantation was performed in bilaterally nephrectomized hosts. Compounds were given once daily by oral gavage. Monitoring was done by serum creatinine and urea, and rejection was concluded when values exceeded 500 micromol/L and 50 mmol/L, respectively (5-6 times the upper limit of reference values). Rejection was confirmed by graft histology. The termination point was set to 100 days after transplantation. In addition, animals were monitored for 24 hr drug concentrations and thorough inspection of potential adverse side effects.

RESULTS

FTY720 given alone at 3.0 mg/kg per day prolonged rejection-free survival (33-85 days, mean 24 hr concentration between 54 and 66 ng/mL [n=3]), but it was not efficacious at a 0.3 mg/kg per day dose. For cyclosporine alone, 30 mg/kg per day during maintenance was efficacious (average concentration above 100 ng/mL, historical data from our group), and for RAD alone 0.75 mg/kg per day (concentration above 10 ng/mL). Efficacious FTY720-cyclosporine-A (CsA) or FTY720-RAD combinations were established using 0.1-0.3 mg/kg per day FTY720, 10-30 mg/kg per day cyclosporine, and/or 0.25-0.50 mg/kg per day RAD. Compared with single-compound treatment, FTY720 effective doses and 24 hr trough concentrations were at least tenfold lower in combination treatment and those of cyclosporine and RAD about twofold lower, indicative of effective synergy between the compounds. Already at the lowest FTY720 dose tested (0.03 mg/kg per day), there was a profound lymphocyte depletion down to about 30% of pretransplant values, which further increased at the highest dose (3.0 mg/kg per day, to about 14% of pretransplant values). Lymphocyte depletion was reflected by a decrease in T and B subpopulations.

CONCLUSION

FTY720 is an effective immunosuppressant in prevention of acute kidney allograft rejection in cynomolgus monkeys and synergizes with cyclosporine and/or RAD in yielding rejection-free allograft survival.

Ultrasound score is more predictive than serum creatinine in assessment of cellular rejection in cynomolgus monkey renal allografts

RATIONALE AND OBJECTIVES

To investigate whether ultrasound (US), in particular the use of an ultrasound scoring system, can provide more diagnostic information than clinical parameters, such as serum creatinine, for the diagnosis and determination of the degree of cellular rejection in renal allografts in the cynomolgus monkey (Macaca fascicularis).

METHODS

Sixty-eight cynomolgus monkeys with life-supporting renal allografts were examined with a 7.5MHz linear ultrasound transducer. One-hundred fifty two-dimensional, spectral, and power Doppler examinations were performed and four ultrasound parameters, percentage increase in graft volume, cortical thickness, resistive index (RI) of the renal arcuate artery, and power Doppler (PD) scores were recorded from serial examinations. An ultrasound score was assigned to each graft based on the number of those parameters that were abnormal; a score of 1 indicated that all four were normal, and a score of 5 that all four were abnormal. Each parameter and the combined score were compared with serum creatinine values and histology and evaluated statistically using Spearman rank correlation.

RESULTS

In animals with dysfunctioning allografts (serum creatinine elevations >200 micromol/L), Spearman rank correlation showed a significant correlation between the US score and the histology score: between 200 and 500 micromol/L, r = 0.309, P = 0.046, n = 31 and if > 500 micromol/L, r = 0.486, P = 0.005, n = 30. In those same animals, no correlation could be shown between serum creatinine values and the US score or between the serum creatinine values and the histologic diagnosis. In contrast to the US score, single ultrasound parameters were not found to correlate to histologic findings.

CONCLUSION

The application of ultrasound imaging in nonhuman primate renal transplant models provides valuable information concerning the presence and severity of cellular rejection in cases of graft dysfunction and the US score has a better predictive value of histology than serum creatinine values alone.

A straightforward algorithm for the quantification of power Doppler signals

RATIONALE AND OBJECTIVES

To document a simple algorithm that quantifies power Doppler signals by computer-based statistical image analysis.

METHODS

Personal computer-based software was developed. Color pixels representing power Doppler signals were separated from the background gray pixels in power Doppler images converted in BMP format. To avoid misregistration during this segmentation, a threshold value is required to adequately distinguish between gray and color pixels. Equating the intensity of each color pixel to a Power Value (PV), a histogram of Power Values in power Doppler images was obtained.

RESULTS

The software was designed to allow users to adjust two thresholds (Difference Threshold and Intensity Threshold) by observing the segmentation results in real time. The software calculates the following indexes within any region of interest as defined by the operator: mean PV, peak PV, standard deviation of PV, percentage power Doppler area, and integrated PV per unit area.

CONCLUSIONS

Power Doppler signals can be objectively quantified using this straightforward algorithm. This simple and practical method can be applied to comparative or longitudinal studies upon vascularity or blood flow.