• A decrease in the coronary artery calcium score after 5 months of sodium thiosulfate treatment [ Time Frame: 5 months ] [ Designated as safety issue: Yes ]
  

• An decrease in pulse wave velocity, thoracic aorta and carotid artery calcification and correlation between these findings and changes in coronary artery calcification scores. [ Time Frame: 5 months ] [ Designated as safety issue: Yes ]
  

Hypothesis 1: The treatment of HD patients with high CAC scores with sodium thiosulfate for 5 months will decrease the amount of calcium in their coronary arteries.

Patients who are at high risk for having coronary calcification (history of MI, ischemic heart disease, peripheral or carotid artery disease) will be selected to undergo testing. We will recruit 52 HD patients receiving treatment in our units to undergo MDCT scanning along with non-invasive testing of PWV and CIMT. Assuming that 60% will have a CAC score of ≥50, 31 patients will be treated with sodium thiosulfate. We will administer 25% sodium thiosulfate solution (American Reagent Laboratories, Shirley, NY) at a dose of 12.5-25g/1.73m2 per over 15-30 minutes after each hemodialysis session for a total of 60 treatments (5 months). Assuming a 35% attrition rate, 20 patients will complete the entire protocol and undergo a repeat study of the initial battery of tests.

Rationale for treatment with sodium thiosulfate: Sodium thiosulfate, used as an antidote for cyanide poisoning for more than a century, is also an anti-oxidant, and binds with calcium to form a highly soluble calcium thiosulfate salt. The solubility of calcium thiosulfate salt is 250-100,000 fold higher than calcium oxalate or calcium phosphate salt. It has been used to treat recurrent calcium kidney stones and tumoral calcinosis (ectopic calcification usually around joints). It has also been used successfully in treating calcific uremic arteriopathy, a disease of small artery and soft tissue calcification, in several studies of dialysis patients and in our own experience of 5 patients. By 2 months there is radiological evidence of reduction in soft tissue calcification. Unpublished data also have demonstrated regression of established aortic calcification in uremic rats.

Sodium thiosulfate is a FDA approved medication for the treatment of cyanide poisoning. It is classified by the FDA as "generally recognized as safe". There are no known contraindications. The only side effects reported during intravenous (IV) administration in ESRD patients are nausea, vomiting and hyperosmia during the administration, which can be alleviated by pre-administration of anti-emetic medications. Sodium thiosulfate is slowly given through the dialysis venous line toward the end of HD treatments. The selected dose for this pilot study is the same as that used for the treatment of calcific uremic arteriopathy.

Hypothesis 2: Decreasing the CAC score will be associated with a decrease in the calcium content in other large arteries such as the thoracic aorta and carotid arteries.

Hypothesis 3: Decreasing the CAC score will be associated with a functional improvement of the vascular system (as assessed by pulse wave velocity).

Hypothesis 4: Decreasing the CAC score will be associated with a decrease in the severity of coronary artery stenoses.

Hypothesis 5: Decreasing the CAC will be associated with an increase in inhibitors of vascular calcification (such as fetuin-A) and/or decrease in promoters of vascular calcification (such as CRP).

We will freeze 10 ml of serum obtained prior to and then monthly during treatment for subsequent analyses. Included in the analysis will be Fetuin-A levels but other relevant markers will be considered. Blood will also be frozen for future genomic studies.