Effect of Ramipril on Urinary Protein Excretion in Maintenance Renal Transplant Patients Converted to Sirolimus

This prospective, randomized, double-blind, placebo-controlled study evaluated the effects of ramipril on urinary protein excretion in renal transplant patients treated with sirolimus following conversion from a calcineurin inhibitor. Patients received ramipril or placebo for up to 6 weeks before conversion and 52 weeks thereafter. Doses were increased if patients developed proteinuria (urinary protein/creatinine ratio ≥0.5); losartan was given as rescue therapy for persistent proteinuria. The primary end point was time to losartan initiation. Of 295 patients randomized, 264 met the criteria for sirolimus conversion (ramipril, 138; placebo, 126). At 52 weeks, the cumulative rate of losartan initiation was significantly lower with ramipril (6.2%) versus placebo (23.2%) (p < 0.001). No significant differences were observed between ramipril and placebo for change in glomerular filtration rate from baseline (p = 0.148) or in the number of patients with biopsy-confirmed acute rejection (13 vs. 5, respectively; p = 0.073). One patient in the placebo group died due to cerebrovascular accident. Treatment-emergent adverse events were consistent with the known safety profile of sirolimus and were not potentiated by ramipril co-administration. Ramipril was effective in reducing the incidence of proteinuria for up to 1 year following conversion to sirolimus in maintenance renal transplant patients.

Immunosuppression with belatacept-based, corticosteroid-avoiding regimens in de novo kidney transplant recipients

Current immunosuppressive regimens in renal transplantation typically include calcineurin inhibitors (CNIs) and corticosteroids, both of which have toxicities that can impair recipient and allograft health. This 1-year, randomized, controlled, open-label, exploratory study assessed two belatacept-based regimens compared to a tacrolimus (TAC)-based, steroid-avoiding regimen. Recipients of living and deceased donor renal allografts were randomized 1:1:1 to receive belatacept-mycophenolate mofetil (MMF), belatacept-sirolimus (SRL), or TAC-MMF. All patients received induction with 4 doses of Thymoglobulin (6 mg/kg maximum) and an associated short course of corticosteroids. Eighty-nine patients were randomized and transplanted. Acute rejection occurred in 4, 1 and 1 patient in the belatacept-MMF, belatacept-SRL and TAC-MMF groups, respectively, by Month 6; most acute rejection occurred in the first 3 months. More than two-thirds of patients in the belatacept groups remained on CNI- and steroid-free regimens at 12 months and the calculated glomerular filtration rate was 8-10 mL/min higher with either belatacept regimen than with TAC-MMF. Overall safety was comparable between groups. In conclusion, primary immunosuppression with belatacept may enable the simultaneous avoidance of both CNIs and corticosteroids in recipients of living and deceased standard criteria donor kidneys, with acceptable rates of acute rejection and improved renal function relative to a TAC-based regimen.

Telomere dynamics in an immortal human cell line

The integration of transfected plasmid DNA at the telomere of chromosome 13 in an immortalized simian virus 40-transformed human cell line provided the first opportunity to study polymorphism in the number of telomeric repeat sequences on the end of a single chromosome. Three subclones of this cell line were selected for analysis: one with a long telomere on chromosome 13, one with a short telomere, and one with such extreme polymorphism that no distinct band was discernible. Further subcloning demonstrated that telomere polymorphism resulted from both gradual changes and rapid changes that sometimes involved many kilobases. The gradual changes were due to the shortening of telomeres at a rate similar to that reported for telomeres of somatic cells without telomerase, eventually resulting in the loss of nearly all of the telomere. However, telomeres were not generally lost completely, as shown by the absence of polymorphism in the subtelomeric plasmid sequences. Instead, telomeres that were less than a few hundred base pairs in length showed a rapid, highly heterogeneous increase in size. Rapid changes in telomere length also occurred on longer telomeres. The frequency of this type of change in telomere length varied among the subclones and correlated with chromosome fusion. Therefore, the rapid changes in telomere length appeared occasionally to result in the complete loss of telomeric repeat sequences. Rapid changes in telomere length have been associated with telomere loss and chromosome instability in yeast and could be responsible for the high rate of chromosome fusion observed in many human tumor cell lines.

Delayed chromosomal instability induced by DNA damage

DNA damage induced by ionizing radiation can result in gene mutation, gene amplification, chromosome rearrangements, cellular transformation, and cell death. Although many of these changes may be induced directly by the radiation, there is accumulating evidence for delayed genomic instability following X-ray exposure. We have investigated this phenomenon by studying delayed chromosomal instability in a hamster-human hybrid cell line by means of fluorescence in situ hybridization. We examined populations of metaphase cells several generations after expanding single-cell colonies that had survived 5 or 10 Gy of X rays. Delayed chromosomal instability, manifested as multiple rearrangements of human chromosome 4 in a background of hamster chromosomes, was observed in 29% of colonies surviving 5 Gy and in 62% of colonies surviving 10 Gy. A correlation of delayed chromosomal instability with delayed reproductive cell death, manifested as reduced plating efficiency in surviving clones, suggests a role for chromosome rearrangements in cytotoxicity. There were small differences in chromosome destabilization and plating efficiencies between cells irradiated with 5 or 10 Gy of X rays after a previous exposure to 10 Gy and cells irradiated only once. Cell clones showing delayed chromosomal instability had normal frequencies of sister chromatid exchange formation, indicating that at this cytogenetic endpoint the chromosomal instability was not apparent. The types of chromosomal rearrangements observed suggest that chromosome fusion, followed by bridge breakage and refusion, contributes to the observed delayed chromosomal instability.

Telomeres and their possible role in chromosome stabilization

The evidence to date generally supports the hypothesis that telomere capping makes chromosome fragments refractory to subsequent rejoining events, but this control may be somewhat relaxed after chromosome breakage. Cell survival requires that the fragments rejoin before metaphase. Unprotected ends such as those produced by DNA damage are subject to degradation, presumably by endogenous cellular exo- and endonucleases. Telomere repeat sequences may be added to broken chromosome ends to protect the ends from further degradation. That telomeric DNA does not always prevent rejoining raises interesting questions as to what constitutes capping, and how rapidly it occurs after DNA damage in relation to chromosome break rejoining. The prevention of degradation and control of rejoining may be mediated by telomere-specific binding proteins, especially the telomere terminal binding protein [Gualberto et al., 1992; Longtine et al., 1989; Price, 1990; Price and Cech, 1989]. Some of these proteins may be involved in scavenging telomeric DNA when the cell senses that chromosomal breaks have occurred. This mechanism is consistent with the observations of Murnane and Yu [1993], who found that a plasmid with telomere sequences was stably integrated in vivo into a chromosome terminal breakpoint lacking telomere repeats. It is also consistent with the high frequency of interstitial telomere sequences observed in normal cells; a history of DNA damage and repair may be recorded by these sequences (Ijdo et al., 1991]. Although chromosome break rejoining is an efficient process in eukaryotic cells, some breaks are never rejoined and can result in terminal deletions and chromatid and isochromatid deletions at metaphase. It is unclear why these breaks are not rejoined, but it may be due to one or more of the following: 1) chance: broken chromosomes are separated, do not approach sufficiently close to one another, and are consequently physically unable to rejoin; 2) a large number of added telomere repeat sequences indicating to the cell that the chromosome has an authentic telomere; 3) some other DNA modification event that protects DNA ends from degradation, e.g., folding back of DNA ends to form a hairpin, as has been implicated in VDJ recombination [Lieber, 1993].