Salt Intake and Antiproteinuric Effect of Paricalcitol in Type 2 Diabetes

Proteinuria is an independent risk factor for cardiovascular morbidity and mortality and for renal disease progression. More proteinuria is associated with faster progression, whereas treatments that reduce proteinuria are renoprotective in both diabetic and non diabetic chronic kidney disease. Of note, lower the residual proteinuria achieved by treatment slower is the disease progression in the long term. On the basis of the above findings, proteinuria has become a target of renoprotective therapy.

Among different antihypertensive medications, those that inhibit the Renin Angiotensin System, such as angiotensin converting enzyme (ACE)inhibitors and angiotensin receptor blockers (ARBs), are those that at comparable blood pressure control, more effectively reduce proteinuria and slow renal disease progression. Thus they have become the key component of renoprotective therapy in patients with proteinuric chronic kidney disease. Observational studies found that their effectiveness, however, is limited or even fully blunted in patients who eat large amount of salt.

Experimental evidence indicates a renoprotective role of the vitamin D system in chronic renal disease. A recent randomized, controlled trial, add-on therapy with selective Vitamin D receptor activator paricalcitol showed an additive antiproteinuric effect in subjects with type 2 diabetes and chronic kidney disease on background Renin-angiotensin-system inhibitor therapy. This effect, however, was largely restricted to subjects with daily sodium intake exceeding 12 grams and was negligible in those with lower sodium intake. Thus, treatment with paricalcitol appears to be effective in particular in those patients who do not appreciably benefit of renin angiotensin system (RAS) inhibitors therapy because of high salt intake. Thus, whether the antiproteinuric effect of paricalcitol is modified by concomitant salt intake in patients with chronic kidney disease (CKD) on background RAS inhibitors therapy, is worth investigating.

The broad aim of this study is to evaluate the interaction between paricalcitol therapy and sodium intake in type 2 diabetes patients with proteinuric kidney disease on stable background RAS inhibitor therapy.