The uses and abuses of Vitamin D compounds in chronic kidney disease-mineral bone disease (CKD-MBD)

Vitamin D is of paramount importance to skeletal development, integrity and health. Vitamin D homeostatis is typically deranged in a number of chronic conditions, of which chronic kidney disease is one of the most important. The use of vitamin D based therapy to target secondary hyperparathyroidism is now several decades old, and there is a large body of clinical practice, experience, guidelines and research to underpin this. However, there are many unknowns, of significant clinical relevance. Amongst which is what "species" of vitamin D we should be using, in what patient, and, under what conditions. Sadly, there has been a real dearth of randomised controlled trials, and trials with outputs of clinical relevance, which means our clinical practice has not developed and refined adequately ove the last 4 decades. This article will discuss the vexed but critical questions of which vitamin D therapies might suit which kidney patients, and will high-light the many important clinical questions which urgently require answering.

Uric acid as a cardiorenal risk factor - ready for prime-time?

Patients with cardiac morbidity are known to have increased risk of developing renal disease, and vice versa. Cardiorenal syndrome is a general term describing concomitant cardiac and renal dysfunction, and recently there has been renewed interest in the role of uric acid (UA) in its pathophysiology and management. There is evidence to suggest that UA-lowering drugs, such as the xanthine oxidase (XO) inhibitors allopurinol and Febuxostat, may not only retard deteriorating renal function in the context of chronic kidney disease (CKD) but also confer protective cardiovascular effects. As these diseases represent considerable health burdens, this evidence merits evaluation to determine whether or not hyperuricaemia is a cardiorenal risk factor that necessitates intervention and if existing pharmacological agents are sufficiently efficacious.

Prevalence and predictors of abdominal aortic calcification in healthy living kidney donors

BACKGROUND

Vascular calcification (VC) is common and is both a marker and a cause of increased cardiovascular morbidity and mortality, especially so in chronic kidney disease (CKD) patients. Renal transplantation is the cornerstone of the successful long-term management of CKD, and in order to satisfy transplantation needs, more use is made now of living kidney donors (LKD). Prior to selection for transplantation, much screening of potential LKD takes place, including for cardiovascular issues. It is not known; however, how much these potentially healthy LKD may be prone to clinically silent VC.

METHODS

We identified 103 living kidney donors from 2011 renal transplant records. Abdominal aortic calcification (AAC) was assessed using existing abdominal CT imaging using multi-channel CT aortograms (used primarily to assess renal vascular anatomy). Using these CT scans, manual calcium scoring was undertaken to calculate total aortic calcium load (AAC severity score). The prevalence, severity and associations of AAC between calcified and non-calcified donors were then compared.

RESULTS

A total of 103 donors were identified from records. Ninety three of these had detailed clinical records to complement their CT scans. Fifty of ninety-three donors were male, and the mean age was 45.9 ± 1.8 years. Mean MDRD eGFR was 88.73 ± 2.97 ml/min/1.73 m(2). 7.14 ± 3.07 % of the aorta in these donors was calcified with a mean AAC severity score of 0.98 ± 0.56. In kidney donors >50 years of age, there was significantly more AAC than in those <50: 2.47 ± 1.56 versus 0.31 ± 0.29, p < 0.001. There was no relationship between the presence or severity of aortic VC and donor GFR, systolic blood pressure, pulse pressure, calcium-phosphate product or smoking.

CONCLUSIONS

AAC prevalence, patterns and severity in this important donor population have not previously been described in the literature. There was relatively little VC in what would be regarded as a "healthy" donor population. VC was more common with age, but the other possible risk factors for the presence or severity of VC did not impact on overall AAC scores. VC did not influence vascular stiffness as represented by pulse pressure. Following the evolution of AAC over time in those who have donated a kidney, and lost some global renal function as a consequence, would be of considerable interest.

4-pyridone-3-carboxamide ribonucleoside triphosphate accumulating in erythrocytes in end stage renal failure originates from tryptophan metabolism

We recently identified an erythrocyte nucleotide accumulating in end-stage renal disease as 4-pyridone-3-carboxamide ribonucleotide triphosphate (4PYTP), a nucleotide never described previously. Plasma tryptophan concentration has been previously reported to be reduced in patients in chronic renal failure that is in turn associated with elevated precursors of tryptophan metabolism, including L -kynurenine and quinolinic acid, both of which have been implicated in the neurotoxic manifestations of chronic renal failure. Here we compare mean erythrocyte 4PYTP, and plasma tryptophan concentrations, in controls and four patient groups with renal impairment (10 per group) and confirmed a reduction in plasma tryptophan in patients on dialysis that corrected with renal transplantation. We found: An inverse correlation between plasma tryptophan and red cell 4PYTP concentrations (R(2)=0.44, P<0.001) when all patients were grouped together. Restoration of both tryptophan and 4PYTP concentrations to control values was only achieved following renal transplantation. 4PYTP was absent from erythrocytes in Molybdenum cofactor (MoCF) deficiency implicating aldehyde oxidase/dehydrogenase, a Molybdenum requiring enzyme. High 4PYTP erythrocyte concentrations in adenine or hypoxanthine-phosphoribosyltransferase deficient patients in severe uremia (113 microM and 103 microM), confirmed the lack of involvement of either enzyme in 4PYTP formation. We propose that 4PYTP is formed by a novel route involving the oxidation of the intermediates of NAD turnover from quinolinic acid by aldehyde oxidase.

Transmission of syphilis by solid organ transplantation

Two organ recipients developed serologic evidence of syphilis infection after renal transplantation from a common deceased donor with a history of treated syphilis. Testing of donor serum for syphilis, which occurred after transplantation, gave results interpreted as consistent with past infection. However, subsequent serologic results in the recipients suggested transmission of infection at transplantation due to active infection of the donor. This may be explained by recent donor re-infection in view of the current syphilis epidemic in the United Kingdom. An initial error in the treatment of recipients further served to highlight unfamiliarity in managing this resurgent infection in the context of organ transplantation.

Chronic renal allograft dysfunction: the evidence for a change in immunosuppression

In renal transplantation the calcineurin inhibitors (CNIs) have played a crucial role in the reduction in acute rejection rates. Unfortunately this has not been matched by an improvement in long-term graft survival rate. The development of chronic allograft nephropathy (CAN) is the second most common cause of graft loss, after death from cardiovascular causes. CAN has a multifactorial aetiology that includes immunological and nonimmunological factors relating to both donor and recipient. The use of CNIs has been strongly implicated as a risk factor for the development of CAN. With the ongoing development of new immunosuppressant agents the possibility of avoiding the CNIs now exists. Many studies have been designed to investigate strategies to minimise or avoid CNI exposure and to prolong graft survival. To achieve CNI withdrawal whilst avoiding rejection, additional immunosuppressants need to be substituted into the drug regimen. Long-term side effects of the immunosuppressant used need to be taken into account when drug changes are being considered. In light of current evidence, CNI reduction with optimal use of mycophenolate mofetil appears to be the most effective strategy in managing the patient with CAN.

An unusual pyridine nucleotide accumulating in erythrocytes: its identity and positive correlation with degree of renal failure

We have investigated an unusual nucleotide that accumulates, with precursors, in the erythrocytes of patients in uraemia. This nucleotide is related chemically to the NAD breakdown product, N1-methyl-2-pyridone-5-carboxamide (Me2Py), found in high concentrations in the plasma of uraemic patients. Both Me2Py and the nucleotide accumulate to high concentrations in the blood during uraemia: our investigations of samples from renal out-patients have provided information on a plausible link between the two compounds.

GTP concentrations are elevated in erythrocytes of renal transplant recipients when conventional immunosuppression is replaced by the inosine monophosphate dehydrogenase inhibitor mycophenolic acid mofetil (MMF)

We show that GTP concentrations rise in the erythrocytes of renal transplant recipients receiving the immunosuppressant MMF, and demonstrate that this effect is not caused by poor renal function after engraftment. We propose a model that is consistent with our observations.

Eosinophilia and symptomatic pulmonary amyloidosis

The case of a man with progressive breathlessness and pulmonary infiltration caused by AL amyloidosis associated with multiple myeloma is presented. There was a marked peripheral eosinophilia, which has not previously been described with amyloidosis.

Symptomatic cytomegalovirus infection complicating treatment of acute systemic vasculitis

Cytomegalovirus (CMV) is usually a complication of renal/solid organ or bone marrow transplantation. We describe three cases of severe CMV in the context of vasculitis immunosuppression.

Aspergillus endophthalmitis: an unusual complication of disseminated infection in renal transplant patients

Endogenous Aspergillus endophthalmitis (AE) is a rare complication of invasive aspergillosis (IA) in transplant patients. In this report, we describe two patients with polycystic kidney disease, who developed AE with cerebral involvement after renal transplantation. Both patients received intense immunosuppression with methyl prednisolone and mycophenolate mofitil (MMF) because of persistent rejection, which rendered them diabetic and vulnerable to opportunistic infections. Endophthalmitis developed within six months of transplantation and was confirmed by microscopy and culture of the vitreous fluid. Patients were treated with combinations of different anti-fungal agents including liposomal amphotericin B, 5-flucytosine, itraconazole, voriconazole and terbinafine. In an electronic MEDLINE review, we found eight further cases of AE in renal transplant patients between 1959 and September 2002. Based on this review, we identified possible risk factors including CMV infection, diabetes mellitus and treatment for rejection with agents such as methyl prednisolone and MMF. In 70% of cases the histology, microscopy or culture of vitreous fluid confirmed the diagnosis. The outcome of AE in renal transplant patients was poor with 70-100% mortality. The review of reported cases and current practice guidelines suggests that vitrectomy and intravitreal amphoterecin B is the treatment of choice. In addition, new antifungal agents with good CSF and ocular penetration such as voriconalzole should be considered for the treatment of invasive cerebral/ocular aspergillosis.

A clinical description of rifampicin-induced acute renal failure in 170 consecutive cases

Rifampicin re-administration may cause immunologically mediated acute tubulo-interstitial injury. Retrospectively, 170 consecutive cases with acute renal failure (ARF) following re-treatment with rifampicin (71% males, 29% females, age 21 to 68 years) were analysed, which accounted for 12% of all ARF patients treated by two large dialysis referral centres in Romania, Timisoara and Iasi, between 1974-2001 and 1988-2001, respectively. The most frequent clinical features of rifampicin-induced ARF were: Anuria, gastro-intestinal (abdominal pain, nausea, vomiting and diarrhoea) and "flu-like" symptoms. Urine analysis revealed sterile leucocyturia in 54%, proteinuria in 31%, haematuria in 26% and haemoglobinuria in 7% of cases. Haemolytic anaemia was frequent, found in 66% of the patients; half of these had Hct values of < 30%, thrombocytopenia and also more severe renal damage (a longer anuric phase and a slower recovery of the renal function), thus suggesting a severe multi-target autoimmune aggression. The association of hepatic injury--not explained by prior hepatic disease, B or C hepatitis virus infection or history of alcohol abuse--was encountered in 17% of the cases, without a significant influence on the renal and the general outcome. The outcome of rifampicin-induced ARF is generally favourable, with complete recovery of the renal function within 30 days in 52% of the cases and within 90 days in 92% of the cases. The mortality rate was 3.5%, compared to 21% for the overall ARF population treated during the same period (p < 0.05).

Successful renal transplantation decreases aortic stiffness and increases vascular reactivity in dialysis patients

BACKGROUND

Patients with end-stage renal disease on dialysis have among the highest cardiovascular event rates documented. Abnormal nitric oxide (NO)-dependent endothelial reactivity and increased arterial stiffness are commonly described in hemodialysis (HD) patients. Measures of aortic stiffness--aortic pulse wave velocity (PWV) and augmentation index (AGI)--have been shown to be powerful predictors of survival on hemodialysis. It is not known how these parameters interfere with successful renal transplantation.

METHODS

PWV and aortic AGI (difference between the first and second systolic peak on the aortic pressure waveform divided by the pulse wave height) were determined from contour analysis of arterial waveforms recorded by applanation tonometry using a SphygmoCor device in 41 HD patients (20 men; age, 41.8 years) and in a control group of 20 patients with essential hypertension (HTA) (10 men; age, 43.6 years). Twenty of the HD patients (10 men; age, 39.7 years) received live-related renal transplants (RTx) and were restudied (3 months after RTx, normal serum creatinine). NO-dependent and NO-independent vascular reactivity were assessed by changes in AGI after challenges with inhaled salbutamol (SAL) and sublingual nitroglycerin (NTG), respectively.

RESULTS

AGI values were significantly lower in RTx patients compared with subjects on hemodialysis (15.9 +/- 13.9% vs. 27.9 +/- 11.9%, P<0.05), but similar to essential HTA controls (16.5 +/- 17%). Serial AGI measurements showed that successful renal transplantation is associated with a decrease in AGI in all cases, from a mean of 25.1 +/- 7.8% while on dialysis to 15.9 +/- 7.0% 3 months after transplantation (P<0.0001). The responsiveness to both endothelium-dependent stimuli (inhaled SAL) and endothelium-independent stimuli (sublingual NTG) was greater in transplant patients than in hemodialysis patients (SAL-induced decrease in AGI -82.3 +/- 65.7% vs. 45 +/- 72.3%, P<0.01; and NTG-induced decrease in AGI 197 +/- 108 vs. -129.0 +/- 215.5%, P<0.01). PWV values in dialysis patients (7.19 +/- 1.88 m/sec) were significantly higher than those measured in essential HTA patients (6.34 +/- 1.32 m/sec, P<0.05) with normal renal function (despite similar blood pressure levels). PWV after RTx was 6.59 +/- 1.62 m/sec, significantly different from pretransplantation (dialysis) values (P<0.05 for comparison) but similar to the control group of essential HTA patients.

CONCLUSIONS

Renal transplantation is associated with marked improvements in vascular structure and function to a profile comparable to essential HTA patients.

Bilateral popliteal aneurysms complicating adult polycystic kidney disease in a patient with a marfanoid habitus

A man born in 1944 presented with an episode of macroscopic haematuria during a urinary tract infection in 1988. He was unusually tall at 2 metres. An intravenous pyelogram and an abdominal ultrasound disclosed the presence of bilaterally enlarged polycystic kidneys and a polycystic liver. There was a family history of renal disease. Plasma creatinine (180 micro mol/l) and blood pressure (150/100 mm Hg) were both raised. Despite good blood pressure control his renal function declined progressively and he started renal dialysis treatment in 1995. He received a renal allograft in 1996. In 1994 he had noticed a painful swelling behind his left knee. Computed tomography with contrast showed a large popliteal aneurysm. This was replaced with a vein graft. The right popliteal artery showed milder changes, and this was repaired in 1999. Popliteal aneurysms develop most often in older vasculopaths with multiple risk factors; connective tissue disorders have rarely been associated with their presence in younger patients. Polycystic kidney disease has been associated with several aneurysms, most notably cerebral, but not popliteal. The patient's marfanoid habitus also may have played a part. This case emphasises the mixed aetiology of popliteal aneurysms.

Sarcoidosis emerging after adrenalectomy for Cushing's syndrome

Cushing's syndrome is characterised by circulating steroid excess; the mainstay of treatment of systemic sarcoidosis is steroid therapy. We describe a case of sarcoidosis emerging after treatment for Cushing's syndrome.

Staghorn calculi complicating renal transplantation in patients with persistent post-transplantation hyperparathyroidism

Renal stones rarely complicate renal transplants. Their causation is diverse. We describe 2 patients with significant staghorn calculi caused by metabolic factors.

Successful retransplantation using rapamycin in a patient with previous calcineurin inhibitor-induced posterior leukoencephalopathy syndrome

Posterior Leukoencephalopathy Syndrome (PLES) is a rare but serious neurological condition with many aetiologies. In the era of organ transplantation there have been sporadic reports of calcineurin-inhibitor associated PLES. We describe a case, with subsequent uneventful retransplantation using sirolimus.

New markers and therapies for coronary artery disease in renal patients

Coronary artery disease is very frequent in dialysis patients, and influences their survival while on dialysis and even after renal transplantation. There are problems with screening tools in that they have reduced sensitivity and specificity in the uraemic individual. There is a real need for additional and complementary markers of coronary disease in these patients. We discuss some novel ideas for screening and for intervention in this most challenging clinical setting.

Early treatment with allopurinol in familial juvenile hyerpuricaemic nephropathy (FJHN) ameliorates the long-term progression of renal disease

BACKGROUND

The efficacy of allopurinol in autosomal dominant familial juvenile hyperuricaemic nephropathy (FJHN) has been disputed.

AIM

To address this question, in the absence of controlled trials.

DESIGN

Retrospective long-term follow-up study.

METHODS

All kindreds were biochemically screened. Measurements included uric acid clearance, creatinine clearance, serum creatinine, and glomerular filtration rate (GFR). We used five siblings who had died or progressed to transplantation, ten other deceased relatives, and two index cases (one untreated, one non-compliant) as controls to assess the effects of allopurinol.

RESULTS

Of eight families with FJHN, six had a strong history of renal disease and early parental death (mean age 41 years, n=10). Of 27 patients started immediately on allopurinol and treated uninterruptedly, 21 responded well, including three children born subsequently. Eight siblings (mean age 19 years) with a normal plasma creatinine at start (<120 micromol/l, mean GFR 80 ml/min/1.73 m(2)) retained stable renal function (mean 14.5 years, mean age 34 years, GFR 85 ml/min/1.73 m(2)). Of the 13 other responders, treated for up to 34 years, 10 with a creatinine <200 micromol/l at diagnosis (mean age 28 years, mean creatinine 137 micromol/l at start) now have a mean creatinine of 210 micromol/l. In contrast, five patients (mean age 26 years) with a creatinine >200 micromol/l (GFR <35 ml/min/1.73 m(2)) when allopurinol commenced, plus one untreated index case, all progressed rapidly (mean 6 years) to end-stage renal failure. In two others (one non-compliant, one initially untreated), GFR fell by >50% in 7 years. Introduction of allopurinol in the latter has stabilized GFR.

DISCUSSION

Allopurinol reduced the morbidity and mortality from renal failure seen in untreated siblings and previous generations of these families. Early diagnosis of FJHN is important, so that treatment can begin before irreversible renal damage has developed.

Laudable pus - lardaceous kidneys

Amyloidosis frequently affects the kidney leading to proteinuria and loss of function. In cases of AA (reactive/inflammatory) amyloidosis, it is sometimes possible to quench the stimulus to chronic inflammation and by so doing stop further elaboration and deposition of amyloid fibrils. We describe the case of a man with a long-standing empyema who developed nephrotic syndrome and renal impairment. The empyema was resected and shortly afterwards proteinuria disappeared and renal function improved. Strenuous efforts are mandatory to locate and definitively treat underlying inflammatory foci in AA amyloidosis.

Nephrotic syndrome: more than just oedema

Oedema is the commonest presenting symptom and sign in nephrotic syndrome. Hypercholesterolaemia, thromboembolic events, and infectious complications may also be features. Three patients are described, each of whose nephrotic syndrome presented with a less common symptom or sign--recurrent pleural effusion, hypercholesterolaemia and oedema, pulmonary embolism--and, as a result, experienced some diagnostic delay. By forgetting to consider nephrotic syndrome, and its underlying causes, there may be inappropriate investigations and treatment for the patient.