Endothelin system & its antagonism in chronic kidney disease

Since its discovery in 1988 the powerful vasoconstrictor endothelin-1 (ET-1) has been widely implicated in the pathophysiology of chronic kidney disease (CKD) as well as the cardiovascular disease with which it is associated. ET receptor antagonists have favourable effects in experimental models of these conditions and orally acting antagonists are now licensed for the treatment of pulmonary arterial hypertension. However, there is a paucity of human data regarding the role of ET-1 in CKD. In this thesis, I have therefore explored the utility of ET-1 as a biomarker in CKD, and, using selective ET receptor antagonists, the beneficial renal and cardiovascular effects of ET receptor antagonism in CKD. I have shown that as glomerular filtration rate (GFR) declines plasma ET-1 increases linearly whereas urinary ET-1 shows an exponential increase. Furthermore, urinary ET-1 may be a useful marker of disease activity in patients with lupus nephritis. Its levels are high in those with biopsy-proven active renal inflammation and these fall with treatment. I have shown that in subjects with stable non-diabetic proteinuric CKD, acute selective ETA receptor antagonism reduces blood pressure and arterial stiffness and that these systemic benefits are associated with an increase in renal blood flow and reduction in proteinuria. Importantly, these effects are seen on top of those achieved with maximal therapy with angiotensin converting enzyme inhibitors and/or angiotensin receptor blockers. Following a study confirming unchanged pharmacokinetics in CKD, I have used an oral selective ETA receptor antagonist to show that the reductions in BP, arterial stiffness and proteinuria seen in my acute studies are maintained longer term. This results of this study also suggest that the mechanism for the reduction in proteinuria is haemodynamic and relates to a reduction in GFR and filtration fraction. In summary, these studies suggest that ET-1 may act as a potential biomarker of renal inflammation, and confirm its role in the pathophysiology of the systemic and renal vasoconstriction seen in CKD. They also suggest that selective ETA receptor antagonism may provide a novel therapeutic approach in proteinuric CKD on top of standard therapies. Larger and longer term studies are now warranted to confirm this potential

TWEAK: a novel biomarker for lupus nephritis?

Renal involvement is common in systemic lupus erythematosus. Early diagnosis of lupus nephritis (LN), allowing the instigation of appropriate therapy, remains an important clinical challenge. Current biomarkers in clinical practice are less than ideal, lacking both sensitivity and specificity. In the previous issue of Arthritis Research & Therapy, Schwartz and colleagues demonstrated the potential value of urinary TNF-like weak inducer of apoptosis (uTWEAK) as a biomarker for LN. They showed that uTWEAK is elevated in subjects with LN at diagnosis compared with those with systemic lupus erythematosus but no renal disease, and correlates with the degree of clinical disease activity. These data are thought-provoking and provide the platform for future longer-term studies

Haemolytic anaemia complicating the concurrent use of allopurinol & azathioprine after kidney transplantation

Gout is a common problem in renal transplant recipients but often difficult to treat. Allopurinol can be combined with azathioprine but clinicians should be aware of the need for dose reduction, the potential to measure azathioprine breakdown products and the possible side effects of this combination. Leucopenia is a known side effect but this case report shows that haemolytic anaemia can also occur