Philip D. Acott

BK virus infection, replication, and diseases in pediatric kidney transplantation

Polyomavirus-associated nephropathy is diagnosed in 2–8% of pediatric renal transplants and often precedes renal allograft dysfunction. Without intervention, however, significant graft dysfunction is observed in more than 50% of cases, although progressive early graft loss is reported in only three of 32 (9%) of cases. No specific treatment is available, but early decrease in immunosuppression is followed by declining human polyomavirus type 1 (BK virus) replication and improved outcome. The data suggest differences between pediatric and adult kidney transplantation. Possibly, pediatric patients might be able to mount a more vigorous BK virus-specific immune response than adult patients under similar modulation of immunosuppression. Also the role of cidofovir and leflunomide is still unresolved in pediatric patients. Larger prospective trials are needed to better define the impact of BK virus immunity for replication and disease as well as the role of reducing immunosuppression with or without cidofovir or leflunomide in pediatric transplant patients.

Extravesical ureteroneocystostomy with and without internalized ureteric stents in pediatric renal transplantation

Abstract: The use of ureteric double‐J stents and the Lich‐Gregoir (extravesical) technique of ureteroneocystotomy have both been shown to decrease the rate of urologic complications in adult kidney transplantation (Tx). There are, however, few studies of the systematic use of stents in pediatric renal Tx. Between 1991 and 1997, 32 consecutive pediatric renal transplant recipients routinely received a 6F‐12 cm indwelling double‐J stent and were studied prospectively. These patients were compared with 32 consecutive pediatric recipients in whom a stent was not used. The latter were transplanted between 1987 and 1991 and formed the control group. All patients had a Lich‐Gregoir ureteroneocystotomy. Stents were removed under general‐anesthetic cystoscopy 2–3 weeks after Tx. Immunosuppression for stented patients was polyclonal antibody induction, delayed (7–10 days) cyclosporin A, azathioprine, and prednisone. The control group received the same triple drug regimen but with no induction in 29 of the 32 patients. All patients were followed‐up with at least one ultrasound evaluation in the first month, and a renal scan and repeat ultrasound were performed if there was any rise in serum creatinine. In the stented group there were two patients with urinary leak and no obstructions. In the non‐stented group there were no leaks and one obstruction. There was no graft loss owing to urologic complications in either group. There were three cases of stent expulsion (all in girls) and one case of stent migration in the posterior urethra (a boy). The 1‐yr graft survival rate was 90.6% in the stented group and 65.6% in the non‐stented group. The prophylactic use of an indwelling ureteral stent in pediatric renal Tx did not reduce the risk of urinary leakage or obstruction. Stent migration is a common phenomenon and, while not a serious complication, is traumatic to children. Furthermore, removal of an internalized double‐J stent requires a general anesthetic. We recommend using a stent for selected patients only.

Effects of chronic phthalate exposure on the kidney

Several investigators have reported the finding of polycystic kidney disease (PKD) at autopsy in patients who had undergone long-term hemodialysis for renal failure due to causes other than PKD. We initiated studies to determine whether the drugs or chemicals to which patients on dialysis are exposed could be responsible for these cystic changes. Adult rats were tube fed chemical residues from an artificial kidney or phthalate esters [di(2-ethylhexyl) phthalate, DEHP], which are a main component of these plastic kidneys or a control solution. Rats receiving DEHP or residues showed a significantly higher incidence of focal cysts when compared to controls. Rats receiving DEHP developed a significant decrease in kidney function as demonstrated by creatinine clearance, and these animals had the highest tissue levels of measureable DEHP. We postulate that patients receiving long-term dialysis may acquire PKD secondary to their exposure to chemicals leached from artificial kidneys.

Brain cyclosporin A levels are determined by ontogenic regulation of mdr1a expression.

Cyclosporin A (CyA) toxicity is a common occurrence in pediatric organ transplant patients. We hypothesized that reduced mdr1a expression in newborn and developing mice would affect CyA accumulation within organs and/or toxicity. For functional studies, CyA was administered (5 mg kg–1 i.p.) to 1-, 12-, and 19-day, and adult male and female mdr1a+/+ and mdr1a–/– mice. Peak blood CyA was lower in 1-, 12-, and 19-day-old (1000 ng ml–1) versus adult (1500 ng ml–1) mice but was similar in mdr1a+/+ and mdr1a–/– mice. Kidney mdr1a expression (measured by quantitative polymerase chain reaction) increased 2.5-fold in 19-day-old male and female mice and increased another 4-fold in adult females compared with adult males. Liver mdr1a expression increased 6-fold by day 12 compared with neonatal mice. Thereafter, maintenance of hepatic mdr1a expression in females and a reduction to neonatal levels in males was observed. Kidney/blood (8- to 9-fold) and liver/blood (12- to 15-fold) CyA levels were highest on days 12 and 19 and were not dependent on maturational changes in mdr1a mRNA levels. Adults had higher brain expression of mdr1a mRNA (3-fold), a corresponding 5-fold increase in immunodetectable P-glycoprotein, and 80% lower brain accumulation of CyA compared with 1-day-old mice. Conversely, in mdr1a-null mice, brain/blood CyA was similar in newborn and adult mice. A similar pattern was observed for the brain accumulation of the mdr1a substrate 3H-digoxin. We conclude that the risk for central nervous system drug toxicity could be higher in neonates or young children as a consequence of underdeveloped P-glycoprotein.

In vitro effect of cyclosporin A on primary and chronic BK polyoma virus infection in Vero E6 cells

Abstract: Cyclosporin A (CsA) is known to possess antiviral activity against several viruses in vitro, but the effect of CsA on BK polyoma virus (BKV) replication has not been examined. We investigated the impact of CsA on primary, chronic, and high‐level BKV infection using a cell system of kidney cell origin (Vero E6 cells). During the first 2 h post infection, cells treated with CsA up to 3200 μg/L showed a near‐identical BK viral load to untreated cells, with only a very minor reduction in the CsA‐treated cells observed at 4 h. In chronic culture, CsA completely suppressed the primary BKV infection peak in a non‐dose‐dependent manner within the dose range of 200–12,800 μg/L (P<0.05). BKV reactivation was also inhibited in the presence of CsA at doses of 200–3200 μg/L: the mean number of BKV DNA copies/mL remained stable or even decreased slightly compared with a 7‐log increase in the non‐CsA group (P<0.01). CsA did not influence BKV DNA copies/mL in Vero E6 cells with high‐level infection (>109 copies/mL). Cellular protein measurements indicated that the antiviral effect of CsA was not a result of cytotoxicity. These findings from a relevant in vitro kidney cell system indicate that CsA suppresses the primary BKV infection peak and inhibits escape to BKV reactivation; these effects are dose independent and not related to cytotoxicity. The intracellular antiviral mode of action of CsA against BKV does not appear to be via inhibition of viral cell entry pathways.

Infection concomitant with pediatric renal allograft rejection.

Renal allograft rejection episodes are frequent in children and often lead to allograft failure. Frequent association of fever with rejection in our transplant program provoked a prospective evaluation of concurrent infection during rejection episodes. Because cytomegalovirus has an established role in rejection and allograft survival, evaluation of cytomegalovirus and other herpes viruses (human simplex virus type 1, varicella, Epstein-Barr virus, and human herpes virus type 6 [HHV-6]) was undertaken in addition to standard bacterial investigation. A total of 37 patients were followed over a 30-month period. Six of eight rejection episodes were associated with herpes viruses (HHV-6, n = 6, and Epstein-Barr virus, n = 1). Three of the herpes-group-associated rejection episodes were treated with antiviral therapy in addition to pulse steroid treatment, with full recovery. The three patients with HHV-6-associated rejection episodes who were treated with pulse steroids, but no antiviral therapy, developed chronic allograft rejection. The recipients response to allograft antigens may be influenced by concomitant herpes infection, and specific antiviral therapy appears to be indicated when infection is confirmed in association with rejection. An antiviral treatment program coupled with modulation of standard antirejection immunotherapy has the potential to improve morbidity and mortality in the pediatric renal transplant population.

Decreased bone mineral density in the pediatric renal transplant population

Abstract: All renal transplant recipients at our centre have had bone mineral density assessment (BMD) by DEXA scans of their lumbar spine while on the transplant waitlist and at 6‐month intervals post‐transplant over the past 7 yr. Risk factors for osteopenia and osteoporosis including donor source, dialysis status prior to transplantation, prior renal disease, and biopsy confirmed rejection events and their relationship to BMD of the lumbar spine were assessed.

Norfloxacin interferes with cyclosporine disposition in pediatric patients undergoing renal transplantation

Prophylactic treatment with norfloxacin was initiated in a group of pediatric patients undergoing renal transplantation who were receiving cyclosporine and were susceptible to recurrent urinary tract infections. At discharge from the hospital, the mean daily dose of cyclosporine needed to maintain trough cyclosporine blood levels of 150 to 400 ng/ml was 4.5 mg/kg/day for the patients who received norfloxacin compared with 7.4 mg/kg/day for patients who did not receive the antibiotic. This observation suggested that the clearance of cyclosporine was decreased by the concomitant use of norfloxacin. The effect of norfloxacin on specific drug‐metabolizing cytochrome P450 isozymes in vitro was examined to determine if the metabolism and subsequent clearance of cyclosporine and possibly other drugs are altered through a metabolic interaction with norfloxacin. In human liver microsomes, the activity of cytochrome P4503A4, the isozyme that metabolizes cyclosporine in humans, was inhibited by norfloxacin. In rat liver microsomes, norfloxacin inhibited the activity of cytochrome P4503A2, the isozyme responsible for cyclosporine metabolism in this species, but did not alter the activity of the rat cytochrome P450 isozymes 1A, 2E1, and 4A1. The in vitro studies suggest that the lower cyclosporine dose required by pediatric patients who were given norfloxacin was caused by inhibition of the metabolism of cyclosporine.

Suppression of early and chronic BK polyoma virus replication by mycophenolic acid in Vero cells

Consensus is lacking about which immunosuppressant agents potentiate BK virus infection. The effects of mycophenolic acid (MPA) were investigated in BK virus (BKV)‐infected Vero E6 cells. MPA (1–16 mg/l) exhibited a dose‐dependent anti‐viral effect (101–104 fold reduction in BKV DNA copies/ml) in supernatant, similar to cidofovir (2.5–25 mg/l). This effect was observed for early and persistent infection, and infection with noncoding control region (NCCR) rearranged BKV. MPA reduced BKV DNA copies/ml by >1 log after day 14 in three patient isolates before and after NCCR rearrangement, and in cells. MPA reduced total cellular protein levels, consistent with an anti‐metabolite effect without increased cytopathic activity. BKV infection was associated with a transient, significant reduction of collagen 1A1 on day 7 but not on days 14, 21, and 28 or in the presence of MPA. Reduction of alpha smooth muscle actin mRNA was observed only in the BKV + MPA group, and only on day 7. There was no significant alteration of heat shock protein 47 or transforming growth factor‐β mRNA expression. These in vitro data suggest that MPA may have a protective, anti‐viral effect in BKV‐infected renal tubular cells with an anti‐viral response. Maintaining, or even increasing, the MPA dose should be evaluated for reduction of BKV viremia levels.

Acadian variant of Fanconi syndrome is caused by mitochondrial respiratory chain complex I deficiency due to a non-coding mutation in complex I assembly factor NDUFAF6.

The Acadian variant of Fanconi Syndrome refers to a specific condition characterized by generalized proximal tubular dysfunction from birth, slowly progressive chronic kidney disease and pulmonary interstitial fibrosis. This condition occurs only in Acadians, a founder population in Nova Scotia, Canada. The genetic and molecular basis of this disease is unknown. We carried out whole exome and genome sequencing and found that nine affected individuals were homozygous for the ultra-rare non-coding variant chr8:96046914 T > C; rs575462405, whereas 13 healthy siblings were either heterozygotes or lacked the mutant allele. This variant is located in intron 2 of NDUFAF6 (NM_152416.3; c.298-768 T > C), 37 base pairs upstream from an alternative splicing variant in NDUFAF6 chr8:96046951 A > G; rs74395342 (c.298-731 A > G). NDUFAF6 encodes NADH:ubiquinone oxidoreductase complex assembly factor 6, also known as C8ORF38. We found that rs575462405-either alone or in combination with rs74395342-affects splicing and synthesis of NDUFAF6 isoforms. Affected kidney and lung showed specific loss of the mitochondria-located NDUFAF6 isoform and ultrastructural characteristics of mitochondrial dysfunction. Accordingly, affected tissues had defects in mitochondrial respiration and complex I biogenesis that were corrected with NDUFAF6 cDNA transfection. Our results demonstrate that the Acadian variant of Fanconi Syndrome results from mitochondrial respiratory chain complex I deficiency. This information may be used in the diagnosis and prevention of this disease in individuals and families of Acadian descent and broadens the spectrum of the clinical presentation of mitochondrial diseases, respiratory chain defects and defects of complex I specifically.