The role of Urinary Cations in the etiology of interstitial cystitis: A Multisite Study
To determine if patients with interstitial cystitis (IC) had elevated levels of toxic urinary cations compared to controls. To identify and quantify these cationic metabolites in patients with IC vs control subjects and determine their cytotoxicity to cultured urothelial cells.
Isolation of cationic fraction (CFs) was achieved by solid phase extraction using an Oasis® MCX cartridge on urine specimens of patients and control subjects. C18 reverse-phase high performance liquid chromatography (RP-HPLC) with UV detection was used to profile cationic metabolites and they were quantified by area under the peaks and normalized to creatinine. Major CF peaks were identified by RP-HPLC and liquid chromatography-tandem mass spectrometry (LC-MS and LC-MS/MS). HTB-4 urothelial cells were used to determine the cytotoxicity of CF and of individual metabolites. All specimens were received blinded for processing.
The C18 RP-HPLC analysis was performed on MCX CFs metabolites isolated from urine samples of 70 IC patients and 34 control subjects. The mean (SEM) for control vs patient was 3.84 (0.20) vs 6.71 (0.37) mAU*min/µg creatinine, respectively (p = 0.0001). The MCX CF cytotoxicity normalized to creatinine for control vs patient in mean (SEM) percent was -7.79 (3.32)% vs 20.03 (2.75)% (p < 0.0005). Negative number for control group reflects cell growth. The major toxic cations were 1-methyladenosine (1-MEA), 1-methylguanine (1-MEG), N2, N2-dimethyl guanosine (N2, N2-DMEG) and L-tryptophan (L-Trp)
These data confirm a single site report on the elevation of toxic cations in the urine of IC patients compared to normal subjects. This is an important piece of the IC puzzle because the toxic cations injure bladder mucus and initiate the epithelial leak and may be the primary cause of IC.