Liver transplantation in an adolescent with acute liver failure from acute lymphoblastic leukemia.

The most common identifiable causes of acute liver failure in pediatric patients are infection, drug toxicity, metabolic disease, and autoimmune processes. In many cases, the etiology of acute liver failure cannot be determined. Acute leukemia is an extremely rare cause of acute liver failure, and liver transplantation has traditionally been contraindicated in this setting. We report a case of acute liver failure in a previously healthy 15-yr-old male from pre-B-cell acute lymphoblastic leukemia. He underwent liver transplantation before the diagnosis was established, and has subsequently received chemotherapy for pre-B-cell acute lymphoblastic leukemia. He is currently alive 31 months post-transplantation. The published literature describing acute lymphoblastic leukemia as a cause of acute liver failure is reviewed.

Posterior reversible encephalopathy syndrome independently associated with tacrolimus and sirolimus after multivisceral transplantation.

Posterior reversible encephalopathy syndrome (PRES) is a small vessel microangiopathy of the cerebral vasculature that occurs in 0.5-5% of solid organ transplant recipients, most commonly associated with tacrolimus (Tac). Clinical manifestations include hypertension and neurologic symptoms. We report an adult multivisceral transplant recipient who experienced recurrent PRES initially associated with Tac and subsequently with sirolimus. A 49-year-old woman with short bowel syndrome underwent multivisceral transplantation due to total parenteral nutrition-related liver disease. She was initially maintained on Tac, mycophenalate mofetil (MMF) and prednisone. Three months after transplantation, she developed renal dysfunction, leading to a reduction in Tac and the addition of sirolimus. Eight months after transplantation, she developed PRES. Tac was discontinued and PRES resolved. Sirolimus was increased to maintain trough levels of 12-15 ng/mL. Fourteen months after transplant, she experienced recurrent PRES which resolved after discontinuing sirolimus. Currently 3 years posttransplant, she is maintained on cyclosporine, MMF and prednisone with no PRES recurrence. In addition to calcineurin inhibitors, sirolimus may also be associated with PRES after solid organ transplantation. Ours is the first report of sirolimus-associated PRES in the setting of multivisceral transplantation. Identifying a safe alternative immunosuppression regimen was challenging but ultimately successful.

Use of vascularized posterior rectus sheath allograft in pediatric multivisceral transplantation--report of two cases.

Restoring abdominal wall cover and contour in children undergoing bowel and multivisceral transplantation is often challenging due to discrepancy in size between donor and recipient, poor musculature related to birth defects and loss of abdominal wall integrity from multiple surgeries. A recent innovation is the use of vascularized posterior rectus sheath to enable closure of abdomen. We describe the application of this technique in two pediatric multivisceral transplant recipients--one to buttress a lax abdominal wall in a 22-month-old child with megacystis microcolon intestinal hypoperistalsis syndrome and another to accommodate transplanted viscera in a 10-month child with short bowel secondary to gastoschisis and loss of domain. This is the first successful report of this procedure with long-term survival. The procedure has potential application to facilitate difficult abdominal closure in both adults and pediatric liver and multivisceral transplantation.

Preferential priming of alloreactive T cells with indirect reactivity.

The relative contributions of the direct and indirect pathways in alloimmune responses have not been fully elucidated. We report a novel murine TCR transgenic system that can simultaneously track the CD4-direct (CD4-d), CD4-indirect (CD4-i) and CD8-direct (CD8-d) pathways after transplantation. Using this system, we have observed a profoundly greater proliferation of CD4-i T cells relative to CD4-d and CD8-d T cells after transplantation. Furthermore, a much larger proportion of CD4-i T cells attain an effector phenotype. We also analyzed endogenous, wild-type T cells using enzyme-linked immunospot analysis. In naïve mice, T cells with indirect reactivity were undetectable, but T cells with direct reactivity were abundant. However, 10 days after skin or heterotopic heart transplantation, CD4-i T cells comprised approximately 10% of the CD4+ response. Consistent with increased priming of the CD4-i pathway, we observed that the CD4-i T cells were further enriched in the effector cells migrating to the allograft and in memory-like T cells persisting after rejection. Thus, priming of the CD4-i pathway is favored after transplantation, allowing a rare population to rapidly become a major component of the CD4+ T-cell response in acute allograft rejection. The generalizability of this observation to other models remains to be determined.

Living donor kidney transplant recipients and clinical trials: participation profiles and impact on post-transplant care.

Many transplant physicians believe that transplant candidates who enroll in clinical trials may have better outcomes than those who do not enroll. We examined a 7-year cohort (1997-2003) of adult primary, non-HLA identical, living donor kidney transplant (LDKT) recipients to determine whether demographic characteristics predisposed to enrollment and whether participation affected posttransplant care intensity and/or allograft function. Overall, 146 of 512 (28.5%) LDKT recipients enrolled in clinical trials. LDKT recipients who were male and those who lived <100 miles from our transplant center were significantly more likely to participate. During the first post-transplant year, study patients (SPs) had more clinic visits (p < 0.0001) and more allograft biopsies (p = 0.024) compared to nonstudy patients (NSPs), but comparable numbers of hospital readmissions and allograft ultrasounds. SPs and NSPs did not differ in 1-year creatinine clearance, delta creatinine or rejection incidence. Overall graft and patient survival were comparable. We conclude that clinical trial participants were disproportionately male, had increased intensity of post-transplant care but comparable outcomes to nonparticipants.

Laparoscopic treatment of acute mesenteric torsion.

Acute torsion of the small bowel mesentery is a diagnostically challenging cause of acute abdominal pain, which most commonly afflicts pediatric patients with midgut malrotation. We describe a case of mesenteric torsion in an adult patient that had manifested as acute abdominal pain. The patient had a remote history of prior abdominal surgery, presenting on multiple occasions with undiagnosed acute intermittent abdominal pain. Diagnosis of mesenteric torsion was made by contrast enhanced CT and the ailment was successfully treated with laparoscopic surgery without recurrence.

Effect of adjacent histidine and cysteine residues on the spontaneous degradation of asparaginyl- and aspartyl-containing peptides.

Aspartate and asparagine residues in polypeptides are subject to nonenzymatic reactions that lead to deamidation, isomerization, peptide bond cleavage and racemization. Much of this reactivity is due to the propensity for the initial formation of a cyclic succinimide intermediate. We have been interested in determining the effect of the side chains of neighboring histidine and cysteine residues in facilitating these reactions, particularly in the possibility that they can act as general acids and bases. In this study, we found little or no effect of histidine residues preceding an asparagine residue in hexapeptides derived from the sequence of adrenocorticotropic hormone, while a histidine residue preceding an aspartic acid residue was found to increase the rate of succinimide formation 8- to 11-fold. The presence of a histidine residue following either an asparagine or aspartic acid residue did not effect the rate of succinimide formation by peptide-bond nitrogen attack, but did increase the rate of the competing side-chain nitrogen attack leading to cleavage in the asparaginyl-containing peptide. We found that the effect of a cysteine residue following an asparagine or aspartic acid residue was in general similar to that of a serine residue, although the cleavage reaction appeared to be enhanced. These results suggest that His-Asp sequences may be particularly labile to spontaneous degradation in proteins and peptides, possibly owing to the ability of the histidine residue to facilitate succinimide formation by protonating the OH- leaving group on the side chain carboxylic acid of the aspartic acid residue.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair of spontaneously deamidated HPr phosphocarrier protein catalyzed by the L-isoaspartate-(D-aspartate) O-methyltransferase.

The non-enzymatic deamidation at residues Asn-12 and Asn-38 of Escherichia coli phosphocarrier protein, HPr, and the repair of the resulting L-isoaspartyl (or beta-aspartyl) derivatives, HPr-1 and HPr-2, by recombinant human S-adenosylmethionine-dependent L-isoaspartate-(D-aspartate) O-methyltransferase (EC 2.1.1.77) were investigated. HPr is a component of the bacterial phosphoenolpyruvate:sugar phosphotransferase system that is involved in the concomitant translocation and phosphorylation of many hexose sugars. The major products of the deamidation reaction, L-isoaspartyl (or beta-aspartyl) residues at positions 12 and 38, were found to be substrates for the L-isoaspartate-(D-aspartate) O-methyltransferase, an enzyme active on a wide variety of peptides and proteins containing these abnormal residues. This enzyme has been shown to catalyze the first step in a process that can convert L-isoaspartyl residues in peptides to normal L-aspartyl residues. The affinity of a recombinant human methyltransferase for HPr-1, a form deamidated at Asn-38, was relatively poor (Km = 3.6 mM), while a greater affinity was found for HPr-2, a form deamidated at both Asn-12 and Asn-38 (Km = 197 microM). When HPr-2 was incubated with S-adenosylmethionine and the methyltransferase, the bulk of the L-isoaspartyl residues at position 12 was converted to L-aspartyl residues. The major-by-product was the D-isoaspartyl form. The conversion of L-isoaspartyl residues at position 38 to L-aspartyl residues was less complete, reflecting the lower affinity of the methyltransferase for this site. The phosphohydrolysis activity of the repaired form was found to be midway between the form containing only L-aspartyl residues at positions 12 and 38 and the deamidated HPr-2 form.

Mechanism of cleavage at Asn 148 during the maturation of jack bean concanavalin A.

The maturation of the lectin concanavalin A from the jack bean, Canavalia ensiformis, involves an unusual post-translational cleavage at three internal asparagine residues and the subsequent rearrangement and ligation of two of the resulting fragments. It is presently unclear whether these reactions are enzymatically catalyzed or occur autocatalytically. A specific model for non-enzymatic cleavage has been proposed where the attack of the side chain amide nitrogen atom of asparagine on its alpha-carbonyl carbon cleaves the peptide-bond and leaves a C-terminal succinimide residue. Spontaneous hydrolysis of the succinimide would result in the formation of both terminal asparagine and isoasparagine (aspartic acid alpha-amide) residues. We tested this model by chemically analyzing the C-terminal tryptic peptide of mature concanavalin A that contains the cleavage site residue Asn-148 as its C-terminal residue. We found that only free asparagine was released from this peptide with either elastase or leucine aminopeptidase digestion under conditions that released isoasparagine from a similar synthetic peptide. These results suggest that precursor processing in concanavalin A does not in fact follow a succinimide pathway, although other types of autocatalytic mechanisms remain possible.

Spontaneous degradation of polypeptides at aspartyl and asparaginyl residues: effects of the solvent dielectric.

We have investigated the spontaneous degradation of aspartate and asparagine residues via succinimide intermediates in model peptides in organic co-solvents. We find that the rate of deamidation at asparagine residues is markedly reduced in solvents of low dielectric strength. Theoretical considerations suggest that this decrease in rate is due to the destabilization of the deprotonated peptide bond nitrogen anion that is the postulated attacking species in succinimide formation. This result suggests that asparagine residues in regions with low dielectric constants, such as the interior of a protein or in a membrane bilayer, are protected from this type of degradation reaction. On the other hand, we found little or no effect on the rate of succinimide-mediated isomerization of aspartate residues when subjected to the same changes in dielectric constant. In this case, the destabilization of the attacking peptide bond nitrogen anion may be balanced by increased protonation of the aspartyl side chain carboxyl group, a reaction that results in a superior leaving group. Consequently, any protein structure or conformation that would increase the protonation of an aspartate side chain carboxyl group can be expected to render that residue more labile. These results may help explain why particular aspartate residues have been found to degrade in proteins at rates comparable to those of asparagine residues, even though aspartyl-containing peptides degrade more slowly than corresponding asparaginyl-containing peptides in aqueous solutions.