Experimental cystitis has been induced by intravesical instillation of a variety of irritants, including bacterial lipopolysaccharide (LPS), acid, turpentine, mustard oil, croton oil, and acrolein. Systemic treatment of rodents with cyclophosphamide is one of the most common methods used to initiate cystitis. Cyclophosphamide is an antineoplastic agent, and hemorrhagic cystitis is a common complication observed in patients treated with this drug. Cyclophosphamide is metabolized by the liver to acrolein, and the presence of acrolein within the bladder is thought to be the cause of cystitis in patients or animals that receive cyclophosphamide (104
). Chemical irritants, including cyclophosphamide or acrolein, directly damage the urothelium and other cells of the bladder, resulting in varying degrees of erosion of the mucosa, edema, hemorrhage, and leukocytic infiltration of the bladder wall.
Exogenous irritants have been used to induce inflammation of the bladder in rats and mice to create cystitis to investigate mechanisms underlying pain and inflammation associated with cystitis. The advantage of these models is that they allow control of the timing, duration, and severity of inflammation. It is also possible to investigate various strategies intended to diminish the severity of pain and inflammation in these controlled models. Unfortunately, studies that investigate treatment options are typically designed to administer the particular intervention being evaluated prior to initiation of bladder inflammation. While this may imply efficacy in patients that have intermittent cystitis, these results may or may not be applicable to patients who have established inflammation at the time of examination and treatment. Other disadvantages of these models primarily relate to whether or not the mechanisms that underlie the response of the bladder and nervous system to these compounds are relevant to those that result in inflammation and associated pain in patients with cystitis.
E. coli LPS is the bacterial product most commonly instilled into the bladder to initiate cystitis. Instillation of E. coli LPS alone into the bladders of mice stimulates cystitis characterized by edema, hemorrhage, and infiltration of neutrophils into the bladder wall (106
), and there is evidence that LPS may cross the bladder wall, enter lymphatics or blood vessels, and ultimately be deposited in other organs, including the lungs and rectum (107
). In rats, protamine sulfate is typically instilled into the bladder to destroy the glycosaminoglycan layer prior to infusion of LPS to induce cystitis (108
). Interestingly, systemic administration of E. coli LPS by intraperitoneal or intravenous injection also stimulates inflammation of the bladder in rats and mice characterized primarily by edema within the bladder wall (71
). The toll-like receptor 4 (TLR4) is thought to be the transmembrane receptor responsible for cellular response to LPS (113
), and instillation of uropathogenic E. coli into the bladders of mice that spontaneously express dominant negative TLR4 (C3H/HeJ mice) resulted in bacterial colonization of the bladder wall in the absence of inflammation (115
Bacillus Calmette-Gueirin (BCG), prepared from an attenuated strain of Mycobacterium bovis, was initially used as a vaccine against tuberculosis (116
). BGG is now commonly instilled into the bladder to treat superficial, noninvasive cancer (117
). It has recently been reported that instillation of BCG into the bladders of mice stimulates profound inflammation (118
A survey of relevant literature suggests that the vast majority of experimental studies of the onset and sequela of cystitis utilize exposure of the bladder to irritant chemicals. It was reported over 20 years ago that intravesical instillation of turpentine, mustard oil, or croton oil stimulated cystitis characterized by edema, hemorrhage and leukocytic infiltration of the bladder wall (119
). Bladder inflammation has also been induced by intravesical administration of hydrochloric (120
) or acetic (122
) acid in rats and mice. These models consistently produce cystitis and damage to the urothelium that is accompanied by activation of a variety of signaling pathways too numerous to summarize in this review (29
Hemorrhagic cystitis has been reported as a complication of treatment of patients with cyclophosphamide since the mid-1960’s (130
). Systemic treatment of rodents with cyclophosphamide as a model to induce cystitis has been used for at least 40 years (131
) and is one of the most common experimental models of bladder inflammation. Cyclophosphamide has not been reported to stimulate inflammation of other organs of the urinary tract (132
), and, as mentioned previously, its irritant effects on the bladder have been attributed to contact of the bladder surface with acrolein.
Direct instillation of acrolein into the bladder has been shown to induce cystitis (133
). This model has the potential advantage relative to systemic administration of cyclophosphamide of not requiring hepatic metabolism of cyclophosphamide to acrolein, and at least one study reported differential rates of metabolism of cyclophosphamide and subsequent excretion of acrolein into the urine by two strains of mice (135
). We investigated cystitis induced by intravesical instillation of acrolein in mice to determine whether or not the severity of cystitis could be more tightly controlled and also whether or not differences in response to acrolein could be detected among strains of mice () (136
). We found that the intensity of inflammation could be varied in direct proportion to the concentration of acrolein instilled, and we also observed that, when identical volumes and concentrations were administered intravesically, acrolein-induced cystitis was more severe in C57bl/6n and C3H/OuJ mice than in C3H/HeJ mice. Part of the motivation for performing this study was the concern that the severity of cystitis induced by some models could be so severe that subtle differences in signaling or response to potential therapeutic interventions could be overwhelmed by massive tissue damage and inflammation. The results of this study indicate that strains of rats and mice, as well as the intensity of inflammation induced, should be considered when selecting models of cystitis to investigate mechanisms underlying bladder inflammation or response to various interventions.
Figure 1 Four (A) and 24 hours (B) after instillation of acrolein (6, 10, or 100 μg; 15 μl total volume) or 15 μl phosphate buffered saline (PBS; control) into the bladders of female C57BL6N mice, it was observed that the severity of inflammation (more ...)