Researchers at the University of Houston have found that the compound hydroxycitrate, HCA, a derivative of citric acid found in a variety of tropical plants, may be an effective inhibitor of calcium oxalate crystals, the most common component of kidney stones, and can actually dissolve the stones under certain conditions. The findings could produce one of the first advancements in treating kidney stones in 30 years.

Chemical Engineer Jeffrey Rimer. Source: University of HoustonKidney stones are small, hard mineral deposits that form inside the kidneys, affecting up to 12% of men and 7% of women. High blood pressure, diabetes and obesity can increase the risk, and the reported incidence is rising.

For decades, preventive treatment has been to drink plenty of water and avoid foods rich in oxalate, such as spinach, almonds and okra. Doctors often recommend that their patients take a potassium citrate supplement, which can slow the growth of oxalate crystals, or stones. However, some patients cannot tolerate common side effects that include nausea and diarrhea.

University of Houston researchers studied the effectiveness of both HCA and citrate, or CA, as remedies for kidney stones. While both compounds inhibited the growth of calcium oxalate crystals, HCA was more potent and displayed unique qualities advantageous to the development of new therapies.

Using atomic force microscopy, or AFM, to study interactions between the crystals, CA and HCA under realistic growth conditions, images showed the crystals shrinking when exposed to specific concentrations of HCA.

Researchers then turned to a computational method called density functional theory, or DFT, to study the structure and properties of the materials to learn how HCA and CA bind to calcium and to calcium oxalate crystals. They discovered HCA formed a stronger bond with crystal surfaces, inducing a strain that is seemingly relieved by the release of calcium and oxalate, leading to crystal dissolution.

They then tested HCA on seven human subjects who took the supplement for three days. This allowed researchers to determine that HCA is excreted through urine, a requirement for the supplement to work as a treatment.

“Our initial findings are very promising,” says Jeffrey Rimer, associate professor of chemical engineering at the University of Houston and lead author the study. “If it works in vivo, similar to our trials in the laboratory, HCA has the potential to reduce the incidence rate of people with chronic kidney stone disease.”