Laura Olivi

Pathophysiology of calcium and phosphate metabolism impairment in Chronic Kidney Disease

Secondary hyperparathyroidism (SHPT) is a classical feature of chronic kidney disease (CKD). Commonly, hypocalcemia, hyperphosphatemia, and vitamin D deficiency are involved into the pathogenesis of SHPT. Parathyroid (PT) glands are characterized by a low turnover and rarely undergo mitoses. However, in the presence of low calcium, high phosphorus, vitamin D deficiency, and uremia, PT cells leave quiescence. In the last decade, both new molecular and cellular mechanisms have been investigated in the pathophysiology of SHPT, between them the emerging role of the PT vitamin D receptor and calcium-sensing receptor. Furthermore, recent studies indicate that the fibroblast growth factor-23 may play a central role in the regulation of phosphate-vitamin D metabolism in CKD. Certainly, in the next future, these new insights into the pathogenesis of SHPT will give the possibility to improve the treatment of this condition in the CKD population.

The -665 C>T polymorphism in the eNOS gene predicts cardiovascular mortality and morbidity in white Europeans.

We recently identified rs3918226 as a hypertension susceptibility locus (−665 C>T), TT homozygosity being associated with higher hypertension risk. T compared with C allele transfected cells had lower endothelial nitric oxide synthase (eNOS) expression. In the family-based Flemish Study on Environment, Genes and Health Outcomes (50.9% women; mean age 40.3 years), we investigated whether 32 TT homozygotes had worse outcomes than 2787 C allele carriers. Over 15 years (median), total and cardiovascular mortality and cardiovascular and coronary events amounted to 269 (9.5%), 98 (3.5%), 247 (8.8%) and 120 (4.3%), respectively. While accounting for family clusters, the hazard ratios associated with TT homozygosity were 4.11 (P=0.0052) for cardiovascular mortality (4 deaths), 2.75 (P=0.0067) for cardiovascular events (7 endpoints) and 3.10 (P=0.022) for coronary events (4 endpoints). With adjustment for cardiovascular risk factors, these hazard ratios were 6.01 (P=0.0003), 2.64 (P=0.0091) and 2.89 (P=0.010), respectively. Analyses unadjusted for blood pressure and antihypertensive treatment produced consistent results. For all fatal plus nonfatal cardiovascular events, the positive predictive value, attributable risk and population-attributable risk associated with TT homozygosity were 21.9, 61.5 and 2.0%, respectively. In conclusion, TT homozygosity at the position −665 in the eNOS promoter predicts adverse outcomes, independent of blood pressure and other risk factors.

Unsuccessful application of taurolidine in the treatment of fungal peritonitis in peritoneal dialysis

Fungal peritonitis (FP) is a serious complication for peritoneal dialysis (PD) patients, determining hospitalization, technique failure, catheter loss and death. In the 2005 update, treatment recommendations for FP from the International Society of Peritoneal Dialysis (ISPD) advocate catheter removal immediately after fungi are identified by microscopy or culture. The availability of more effective medical treatments could therefore be of great importance. The aim of this report is to describe a case of a 43-year-old, diabetic, HIV positive PD patient with fluconazole resistant Candida peritonitis, who was treated with an i.p. taurolidine solution. Taurolidine is a non-antibiotic antimicrobial, with broad bactericidal and fungicidal properties. It has been used during surgery for lavage of the peritoneum in cases of peritonitis. Its mechanism of action is related to direct toxic action on micro-organisms, through a chemical reaction between active taurolidine derivatives and structures on the cell wall. Treatment failed because the patient had severe burning pain during i.p. administration of the drug, limiting its dose. PD catheter removal allowed complete recovery. It remains undetermined if, with different doses and methodology, taurolidine could be more effective in treating bacterial and/or fungal peritonitis. Currently, catheter removal remains the most effective therapy of fungal peritonitis.

Management of secondary hyperparathyroidism in the elderly patient with chronic kidney disease.

Patients with chronic kidney disease (CKD) are generally affected by secondary hyperparathyroidism (SHPT). High phosphate, low calcium and vitamin D deficiency represent the classical ‘triad’ involved into the pathogenesis of SHPT in renal insufficiency, in which downregulation of the parathyroid vitamin D receptor and calcium-sensing receptor represents a critical step. Recently, new studies indicate that fibroblast growth factor 23 may play a central role in the regulation of phosphate-vitamin D metabolism in patients with CKD.These new insights into the pathogenesis of SHPT will possibly improve the treatment of this condition in patients with CKD. The ‘modern’ treatment of SHPT in CKD patients consists of free-calcium and aluminium phosphate binders, vitamin D receptor activators and calcimimetics. However, calcium- and aluminium-based phosphate binders and calcitriol are therapeutic tools that are not without complications, including increasing the risk of cardiovascular calcification in patients with CKD. This review summarizes the current understanding and evidence supporting strategies for SHPT treatment in CKD patients, with particular focus on the elderly, although specific guidelines for control of this disorder in this age group are lacking.

New acquisitions in therapy of secondary hyperparathyroidism in chronic kidney disease and peritoneal dialysis patients: role of vitamin D receptor activators.

Secondary hyperparathyroidism is a serious complication of chronic renal disease when function decline and is characterized by abnormalities in serum calcium and phosphate profile, along with a decline in calcitriol synthesis. A reduced density of specific receptors for vitamin D and calcium in several tissues and organs are also present, thus contributing to parathyroid hyperplasia and abnormal parathyroid hormone synthesis and secretion. This metabolic derangement is observable early in the course of chronic renal failure (stages 3 and 4) and on this basis it should also be treated early in order to avoid important clinical consequences. To afford secondary hyperparathyroidism, several strategies should be considered: phosphate oral intake control (diet and phosphate binders), adequate calcium oral intake, vitamin D receptor activation. More specifically, the concept of selective vitamin D receptor activation will be considered as well as its biological effects, the use of paricalcitol (a selective vitamin D receptor activator) given orally to patients on peritoneal dialysis, and stages 3 and 4 of chronic renal failure. Finally, we will consider a series of nonclassical interesting potential mechanisms of selective vitamin D receptor activation leading to reduced cardiovascular and all-cause mortality.