S Zaslau, A Luchey, D Riggs, B Jackson
experimental model, interstitial cystitis, pathogenesis, urinary markers
S Zaslau, A Luchey, D Riggs, B Jackson. Interstitial Cystitis: Pathogenesis, Urinary Markers, and Experimental Models. The Internet Journal of Urology. 2009 Volume 7 Number 1.
Interstitial Cystitis (IC) is a chronic and painful inflammation of the bladder wall that most often causes frequency and urgency to urinate. Interstitial cystitis (IC) affects at least 20,000 to 90,000 women in the United States
The NIH-NIDDK established a set of inclusion and exclusion criteria, originally meant to be for research protocols
A periodical search was performed using PubMed to identify references pertaining to etiologies of IC, with a focus on the use of in vitro models. Search terms included cystitis, in vitro, model, interstitial cystitis and etiology. Articles published from 1980 to August of 2003 were included, with an emphasis placed on the more recent literature. The leading etiological hypotheses were identified as urine toxicity, occult infection, defective urothelium, neurogenic inflammation, mast cell activation and autoimmunity. These theories of pathogenesis are detailed below.
THEORIES OF PATHOGENESIS
Toxic Substances in the Urine
One of the leading theories of pathogenesis is that the urine of IC patients is itself carrying a toxic substance accounting for the disorder. This may be an abnormal substance, uniquely present in the urine of IC patients, or a normal constituent present at an abnormal concentration. This hypothesis is usually tested by exposing normal adult urothelial cells to samples of urine from IC and control patients. The proliferation of the cells is then assessed by measuring the uptake of 3H-thymidine.
Studies of this type have yielded conflicting results. In one report, inhibition of colony formation by urine from healthy volunteers or women with IC was not significantly different
Other studies have shown the presence of antiproliferative factor (APF), in the urine of IC patients that inhibits the proliferation of normal human bladder epithelial cells in vitro
The theory that IC urine contains toxic factors is also supported by the fact that bladder tissues treated with urine from IC patients showed increased expression of a stress protein (heat shock protein, 72 kDa HSP). Increases in this stress protein have also been observed after exposure to known harmful environmental stimuli. The precise role of stress proteins is unknown, but there appears to be a direct relationship between the induction of HSP and thermotolerance, suggesting a cytoprotective function
In another study, fractions of normal urine were examined for toxic effects on bladder tissue in vitro. In the same system, the effects of Tamm-Horsfall protein (THP) were measured. THP, the most abundant protein in normal urine, is thought to be a cytoprotective factor that acts as a scavenger of cationic substances that have potential to injure bladder mucosa. Normal human urine contains cationic, low molecular weight components that, when separated from the bulk of urinary wastes, are cytotoxic to urothelial cells. This cytotoxicity can be blocked by pre-incubation with THP
Another cytoprotective factor in the bladder is the glycocalyx. This layer of glycoproteins and glycosaminoglycans
Although the symptoms of interstitial cystitis are similar to those of bacterial cystitis, urinalysis and urine cultures routinely demonstrate no evidence of infection. Even more sensitive examinations (nested PCR assays for bacterial DNA) of bladder tissue from IC patients and healthy women have failed to demonstrate a specific bacterial or viral cause
Histopathologic changes evident in IC include submucosal inflammation along with thinning or ulceration of bladder epithelium
Mast Cell Activation
Substance P and Bradykinin are also powerful activators of mast cells. Increased numbers of mast cells have been demonstrated within the detrusor layer of the bladder in IC patients
Many of the clinical features of IC suggest that autoimmunity may play a role in the chronic inflammatory component of the disease. The symptoms are chronic, with exacerbations and remissions. Autoantibodies have been detected in the sera of IC patients to a greater extent than in controls
The development of new and more effective treatments modalities for IC has been severely hampered by the lack of experimental models. Several
The reduction in cell proliferation was pH dependent, however it was not time dependent. No increase in response was observed among the 3 time-points tested (24, 48, and 72 hours, Figure 1).
The statistically significant anti-proliferative effects of pH exhibited here suggest that urine pH could be a contributing cause of or product of Interstitial Cystitis. Further research is needed, but these results suggest that reduction of media pH in vitro could provide a model of IC that could prove to be invaluable for the investigation of new and improved treatment modalities
Potential areas of further research involve mapping out the complex interaction of inflammatory mediators in the IC microenvironment. Urothelial cells in IC express different surface proteins than do healthy cells exposed to cytokines
The etiology of IC remains elusive. The use of in vitro models examine various elements of the disease has been quite useful, although they do have some inherent limitations. In particular, they cannot address certain issues involving anatomic location or patient sensitivity. Another limitation is that most in vitro models require the use of serum-supplemented culture media, which may influence the data. The use of growth inhibition and cytotoxicity, may not be appropriate endpoints for assessing the disease. Techniques of re-creating disease conditions are becoming more and more realistic however, and with each new study, our etiological picture becomes more clear. What are now separate theories will likely begin to blend together into one model explaining the symptomatology, histopathological findings and unique characteristics of IC described in the literature.