Renal and adrenal mechanisms in cyclosporine-induced hyperkalaemia after renal transplantation

A physiology-based approach to a patient with hyperkalemic renal tubular acidosis

Hyperkalemic renal tubular acidosis is a non-anion gap metabolic acidosis that invariably indicates an abnormality in potassium, ammonium, and hydrogen ion secretion. In clinical practice, it is usually attributed to real or apparent hypoaldosteronism caused by diseases or drug toxicity. We describe a 54-year-old liver transplant patient that was admitted with flaccid muscle weakness associated with plasma potassium level of 9.25 mEq/L. Additional investigation revealed type 4 renal tubular acidosis and marked hypomagnesemia with high fractional excretion of magnesium. Relevant past medical history included a recent diagnosis of Paracoccidioidomycosis, a systemic fungal infection that is endemic in some parts of South America, and his outpatient medications contained trimethoprim-sulfamethoxazole, tacrolimus, and propranolol. In the present acid-base and electrolyte case study, we discuss a clinical approach for the diagnosis of hyperkalemic renal tubular acidosis and review the pathophysiology of this disorder.

Management of Hyperkalemia: An Update for the Internist

Hyperkalemia is a clinically important electrolyte abnormality that occurs most commonly in patients with chronic kidney disease. Due to its propensity to induce electrophysiological disturbances, severe hyperkalemia is considered a medical emergency. The management of acute and chronic hyperkalemia can be achieved through the implementation of various interventions, one of which is the elimination of medications that can raise serum potassium levels. Because many such medications (especially inhibitors of the renin-angiotensin aldosterone system) have shown beneficial effects in patients with cardiovascular and renal disease, their discontinuation for reasons of hyperkalemia represent an undesirable clinical compromise. The emergence of 2 new potassium-binding medications for acute and chronic therapy of hyperkalemia may soon allow the continued use of medications such as renin-angiotensin-aldosterone system inhibitors even in patients who are prone to hyperkalemia. This review article provides an overview of the physiology and the pathophysiology of potassium metabolism and hyperkalemia, the epidemiology of hyperkalemia, and its acute and chronic management. We discuss in detail emerging data about new potassium-lowering therapies, and their potential future role in clinical practice.

Aldosterone resistance in kidney transplantation is in part induced by a down-regulation of mineralocorticoid receptor expression1

BACKGROUND

After renal transplantation immunosuppressive drugs-like cyclosporin A (CsA) and FK506 induce either hypoaldosteronism or pseudo-hypoaldosteronism presenting with hyperkalemia and metabolic acidosis. We investigated the relationship between renal allograft function under CsA therapy and plasma aldosterone concentration, potassium- and water homeostasis and mineralocorticoid receptor (MR) expression level in peripheral leukocytes.

METHODS

We studied 21 renal transplant patients under CsA therapy and 12 healthy controls. Transplant recipients were studied before and under fludrocortisone treatment. Using quantitative reverse-phase polymerase chain reaction (RT-PCR) specific for the MR, we analyzed the level of expression of MR in peripheral leukocytes.

RESULTS

In acidotic transplant recipients (HCO(3) 18.5 +/- 1.2 mM) renal function was only slightly impaired with 2.0 +/- 0.2 mg creatinine/dL when compared with 1.8 +/- 0.3 mg/dL (ns) in non-acidotic patients (HCO(3) 23.0 +/- 2.8 mM). Mean plasma aldosterone levels in renal transplant recipients did not differ from control levels (150 +/- 33 pg/mL vs. 148 +/- 33 pg/mL, ns). In contrast, the expression level of MR in peripheral leukocytes of renal transplant recipients treated with CsA was significantly decreased when compared with healthy controls without renal disease (120 +/- 78 vs. 423 +/- 73 RNA molecules/0.5 microg total RNA, p < 0.01). The level of expression of MR in renal transplant recipients did not differ between acidotic patients and non-acidotic patients (ns). The application of fludrocortisone reversed hyperkalemia and metabolic acidosis without significant effect on MR expression.

CONCLUSIONS

The present data demonstrate that hyperkalemia and metabolic acidosis following CsA treatment in kidney transplantation might be associated with a down-regulation of MR expression on peripheral leukocytes. Electrolyte imbalance is reversible on application of fludrocortisone. This observation supports fludrocortisone treatment in transplant patients with severe electrolyte disturbances.

Course of renal allograft histopathology after transplantation in early childhood

BACKGROUND

We report a long-term prospective follow-up of renal allograft histology in children <5 years of age at transplantation (Tx).

METHODS

Fifty-one kidney allograft recipients were prospectively followed for renal allograft histology and function up to 7 years after Tx. Twenty patients were recipients of kidneys from living related donors, and 31 were cadaveric kidney recipients. All patients received triple immunosuppression. Biopsies were analyzed according to the Banff classification and scored semiquantitatively. The "chronic allograft damage index" (CADI) was calculated.

RESULTS

Five of seven grafts were lost because of nephrosis in patients with congenital nephrotic syndrome of the Finnish type. Most of the biopsies (52-69%) were considered normal (Banff classification), and the proportion with chronic allograft nephropathy did not increase with time. The median CADI score was 2.5 (scale: 0-36) at 1.5 years and 3.5 at 7 years. Recipients with an acute rejection episode had higher CADI scores than recipients without acute rejection episode. Patients with a high CADI score at 3 years had inferior graft function at 5 years. Recipients <2 years of age had CADI scores and numbers of acute rejection episode similar to recipients between 2 and 5 years of age. However, in contrast to the older recipients, the younger recipients did not improve their absolute glomerular filtration rate with time.

CONCLUSIONS

The long-term histopathological findings were mostly mild and stable with time. Acute rejection episode had an impact on these changes and CADI predicted later graft function. Nonimmunological risk factors seem to be more important in the youngest recipients.

Graft function 5-7 years after renal transplantation in early childhood

BACKGROUND

Low recipient age is still a risk factor for graft failure after kidney transplantation (Tx). Detailed prospective reports on long-term graft function in small children after renal Tx are still lacking.

METHODS

Forty-nine kidney allograft recipients who received transplants before the age of 5 years were followed prospectively. The most common disease was congenital nephrotic syndrome of the Finnish type. Twenty patients were recipients of living related donors (LRD), and 29 were cadaveric kidney (CAD) recipients. All patients received triple immunosuppression. Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), sodium, urate, and potassium handling, and concentrating capacity were studied for up to 7 years after Tx.

RESULTS

Patient survival 7 years after Tx was 100% for LRD and 96% for CAD recipients. Graft survival was 94% for LRD and 79% for CAD recipients (P=NS) and 89% and 83% for children >2 years and <2 years of age at Tx, respectively (P=NS). Five years after Tx, GFR was 70 vs. 64 and ERPF was 380 vs. 310 ml/min/1.73 m2 for LRD and CAD recipients, respectively (P=NS). Mean absolute GFR remained stable. GFR was lower in children who received transplants at <2 years than in children who received transplants at >2 years of age, 54 vs. 75 ml/min/1.73 m2 (P=0.02). Sodium handling remained intact, but hyperuricemia was seen in 43-67%; 17-33% showed abnormal handling of potassium; and most patients had a subnormal concentrating capacity.

CONCLUSIONS

Excellent long-term graft survival and good graft function can be achieved with triple immunosuppression, even in young CAD kidney recipients.

Paediatric kidney transplantation

Renal transplantation is the optimal form of renal replacement therapy leading to substantial improvement in the quality of life. It has rapidly become the standard treatment for end-stage renal disease in children. However, despite impressive short-term results significant long-term problems remain unsolved. Because of the lack of effective treatment for chronic rejection and common recipient noncompliance, allograft half-life has not improved significantly during the last decade. A paediatric recipient is likely to need several retransplantations in adulthood. Moreover, the immunosuppressive drugs used today have potentially serious side-effects including nephrotoxicity and de novo malignancy. These are especially relevant for paediatric recipients who will continue to receive therapy for several decades. Most therapeutic protocols used for children are derived from those used for adults. However, the metabolic differences between an adult and a growing and developing paediatric transplant recipient are not always adequately appreciated before these new therapies are initiated. In the near future, we are likely to see new and more efficient drugs become available. It is important that we try to understand their properties in children and use them and our current arsenal on an individual basis aiming at optimal graft survival but also at avoiding unnecessary adverse effects.