Gender Modifies the Effect of Ursodeoxycholic Acid in a Randomized Controlled Trial in Colorectal Adenoma Patients

Purpose: Ursodeoxycholic acid (UDCA) was one of the earliest agents investigated as a drug for colorectal cancer prevention. However, UDCA failed to show efficacy to prevent the development of colorectal adenomas in a large, phase III, randomized, placebo-controlled trial. We re-evaluated the effect of UDCA in men and women separately, based on sex-specific differences in bile acid metabolism and suspected variation in etiologic factors contributing to colorectal cancer risk.

Experimental Design: We conducted a secondary analysis of the efficacy of UDCA to prevent colorectal adenoma in men (n = 804) and women (n = 388).

Results: We found no reduction in risk of any metachronous adenoma with UDCA treatment in men or women. However, UDCA treatment significantly lowered the odds of advanced lesions [odds ratio (OR), 0.62; 95% confidence interval (CI), 0.43-0.89] in men, but not women. We also observed significantly higher odds of advanced lesions with UDCA treatment in women who were younger (age, <65 years; OR, 3.24; 95% CI, 1.10-9.56), obese (body mass index, ≥30 kg/m²; OR, 5.45; 95% CI, 1.42-20.9), or in the highest tertile of total dietary fat (≥56.2 g/day; OR, 3.48; 95% CI, 1.35-8.95). In a multivariate model, the interactive effect of fat intake accounted for the modulating effects of age and body mass index in women.

Conclusion: Our findings support the use of UDCA for preventing advanced colorectal adenomas in men. The increased odds of adenoma among women with high fat intake suggest a previously unrecognized harm that warrants further study, especially given the chronic exposure to UDCA in patients with primary biliary cirrhosis and the increasing investigational use of UDCA for several other conditions.

Bile acids are a group of acidic steroids produced in the liver, stored in the gall bladder, and secreted into the intestine to aid in the digestion of dietary lipids, where 90% to 95% are reabsorbed through enterohepatic recirculation (1). Secondary bile acids have long been implicated in the etiology of colorectal cancer (CRC), particularly those arising in the proximal colon (2), for which women are at higher risk than men (3, 4). Ecological (5–8) and case-control studies (9–11), including a meta-analysis (12), support a positive association between fecal bile acid levels and colorectal neoplasia. Secondary bile acids, including the hydrophobic deoxycholic acid (DCA), exhibit a spectrum of chemical and biological properties including protumorigenic effects, for which the exact mechanism of action is unknown (13). One proposed mechanism is bile acid–induced DNA damage, which results in mutations and tumor initiation; alternatively, bile acid effects on cell signaling, including activation of β-catenin, and selection pressure for apoptosis resistance have been shown to promote tumor development in a cancer-prone epithelium (14, 15).

One of the early, high-interest pharmacologic agents for chemoprevention of CRC was ursodeoxycholic acid (UDCA), a tertiary bile acid found naturally in low concentrations in humans (16). Early work suggested that long-term use of UDCA in patients with ulcerative colitis and primary sclerosing cholangitis reduced the risk of colonic neoplasia (17, 18). UDCA has been shown to prevent colorectal carcinogenesis in male Fisher rats receiving azoxymethane (19) and to counter the carcinogenic effects of secondary bile acids, particularly DCA (4). UDCA also affects fecal bile acid levels, resulting in proportionally lower concentrations of DCA relative to UDCA (20). In addition, a number of antitumor effects have been attributed to UDCA, including inhibitory activity for many of the same regulatory pathways activated by DCA, such as the mitogen-activated protein kinase pathway (21, 22). Furthermore, UDCA exhibits suppressive activity on arachidonic acid metabolism, including inhibition of cyclooxygenase-2 and inducible nitric oxide synthase (23, 24). These mechanistic actions made UDCA an attractive chemopreventive agent, particularly given its low toxicity (25).

In 2005, we reported the results of a large, phase III, double-blinded, placebo-controlled chemoprevention trial, which tested the efficacy of UDCA in persons with a history of colorectal adenoma (26). We did not detect a significant difference for the incidence of any metachronous adenoma between UDCA (daily 8-10 mg/kg of body weight) and placebo arms over 3 years. However, we observed a significant 39% reduction in colorectal adenoma with high-grade dysplasia in the treatment group. This result is consistent with previous studies that found decreased risk of CRC and high-grade dysplasia with UDCA use in patients with ulcerative colitis (18).

CRCs evolve through multiple (and possibly distinct) precursor pathways that manifest as differences in microsatellite stability, the degree of chromosomal instability, the extent of methylation in the CpG island of specific genes, and the presence and type of mutations in BRAF, KRAS, β-catenin, APC, and p53 (27). Differences in incidence rates, anatomic location (e.g., proximal versus distal), and risk factor profiles (e.g., bile acid exposure) for CRC subtypes in men and women suggest important sex-specific susceptibilities for the development of distinct morphologic and molecular subtypes (28). Thus, we reanalyzed data from the phase III UDCA chemoprevention trial to assess potential differences in efficacy by sex.

A phase III clinical trial of UDCA to prevent metachronous adenomas was conducted at the Arizona Cancer Center, the details of which have been reported previously (26). Briefly, this double-blinded, placebo-controlled, randomized trial tested the efficacy of UDCA on preventing metachronous adenoma among patients who had at least one colorectal adenoma removed during a prestudy colonoscopy. A total of 1,285 participants were randomized to daily UDCA or placebo, of which 1,192 (804 men and 388 women) had at least one follow-up colonoscopy.

As reported previously (26), participants were classified as having a metachronous adenoma if one or more colorectal adenomas or adenocarcinomas were discovered at least 6 mo after the qualifying colonoscopy. Advanced adenomas were defined as those with adenocarcinoma, high-grade dysplasia, villous/tubulovillous histology, or a diameter of ≥1 cm. Participants were classified as having a proximal adenoma if any of their metachronous adenomas occurred in the proximal colon. Multiplicity was defined as three or more metachronous adenomas.

Study participants self-administered the Arizona Food Frequency Questionnaire at baseline (29). The questionnaire asked respondents to report how often they usually consumed each listed food item over the previous 12-mo period. Subsequent nutrient calculations used age- and sex-specific portion size estimates.

The association between UDCA treatment and any metachronous adenoma was assessed using logistic regression modeling, stratified by sex. For specific adenoma types, participants with a particular kind of lesion were compared with the combined group of those without any metachronous adenoma plus those with an adenoma that lacked the characteristic in question (e.g., participants with advanced lesion versus those without any metachronous adenoma plus those with nonadvanced adenomas). Potential treatment-by-X [e.g., sex, age, body mass index (BMI), and dietary fat] interactions were assessed with likelihood ratio tests, using both continuous and categorical versions of these variables in alternating models.

To investigate the potential relationship between multiple modulating factors, sex-stratified multivariate models testing the effect of treatment were generated for each of the adenoma-related end points. These models were adjusted for age, BMI, and dietary fat, allowing for the potential of two-way interactions between treatment and these three covariates. Manual backwards elimination variable selection started with all two-way interaction terms in the models and removed the interaction terms and covariates with Wald statistics P > 0.05 in a hierarchical manner. All statistical analyses were done using Stata 10.1 (StataCorp), all reported P values are two-sided, and no adjustments were made for multiple comparisons.

Two-thirds of the trial's participants were male (n = 804, 67%; Table 1). Compared with women, male participants consumed more dietary calcium (1,066 versus 889 mg/day), had a higher BMI (28.5 versus 27.5 kg/m²), and had a higher waist-to-hip ratio (0.96 versus 0.81). Women were more likely than men to report a family history of CRC (34% versus 24%), but they were less likely to report use of bile acid sequestrants (29% versus 37%). The proportion of White subjects (95%) did not differ by sex, and neither did the mean age (66 years) nor mean level of serum triglycerides (157 mg/dL). Half (51%) of the women reported using hormone replacement therapy. There were no substantial differences in the levels of any of these variables between the two treatment arms for either sex.

Consistent with the original findings (26), we found no significant reduction in any metachronous adenoma among men nor women taking UDCA (Table 2). However, we detected effect modification by sex when examining specific types of adenomas. Men in the treatment group experienced a significant 57% reduction in the odds of high-grade dysplastic adenomas [odds ratio (OR), 0.43; 95% confidence interval (95% CI), 0.24-0.76), but there was no effect on such lesions among women (P_interaction = 0.033). We also found a significant 39% reduction in the odds of large adenomas for men in the treatment group (OR, 0.61; 95% CI, 0.38-0.96), but there was no effect on large lesions among women (P_interaction = 0.013). Furthermore, we detected a significant 38% reduction in the odds of advanced adenomas for men in the treatment group (OR, 0.62; 95% CI, 0.43-0.89), but there was no effect on advanced lesions among women (P_interaction = 0.006). There were no significant treatment effects for adenomas defined by villous/tubulovillous histology, proximal location, or multiplicity (three or more adenomas) for men or women.

Given the benefit of UDCA in men and not women for colorectal adenoma prevention, we hypothesized that factors that influence bile acid metabolism and secretion (30) may explain our gender-specific results. Therefore, we further investigated male-female differences by examining whether age, BMI, or total dietary fat modified the effect of UDCA treatment on metachronous adenoma. For men, there were no significant treatment-by-age interactions for any type of metachronous adenoma (Table 3). For women, however, we detected significantly increased odds of advanced lesions with UDCA treatment among women under age 65 years (OR, 3.24; 95% CI, 1.10-9.56; P_interaction = 0.015). Similarly, there were no significant treatment-by-BMI interactions for any type of metachronous adenoma for men (Table 4). In contrast, we detected significantly increased odds of advanced lesions with UDCA treatment among obese women (BMI, ≥30 kg/m²; OR, 5.45; 95% CI, 1.42-20.9; P_interaction = 0.013).

We also found significant treatment-by-fat interactions in women for any metachronous adenoma (P_interaction = 0.001), advanced lesions (P_interaction = 0.028), proximal location (P_interaction = 0.006), and multiplicity (P_interaction = 0.030), but not for men (Table 5). The adverse effect of UDCA in women was restricted to those in the highest tertile of total dietary fat (≥52.6 g/day). Women in the lowest tertile (<35.5 g/day) showed borderline significant protection against any adenoma with UDCA treatment (OR, 0.51; 95% CI, 0.25-1.03), compared with significantly increased odds in the highest tertile (OR, 2.50; 95% CI, 1.21-5.18). Furthermore, we found significantly increased odds of advanced lesions for women in the highest tertile of total dietary fat (OR, 3.48; 95% CI, 1.35-8.95).

When examined separately, age, BMI, and total dietary fat each modified the effect of UDCA treatment in women. Age and BMI were both significantly correlated with total dietary fat (ρ = −0.18 and 0.20, respectively; both P < 0.001), but not with each other (P = 0.594), in women. Thus, we sought to determine whether or not the modulating effects of age and BMI were explained by fat intake, using sex-stratified multivariate models. For any adenoma, proximal location, and multiplicity, only the treatment-by-fat interaction remained significant (P < 0.05), whereas both the treatment-by-age and treatment-by-BMI interactions were not (P > 0.05). Age continued to be significantly associated with all of these outcomes, and BMI remained significantly associated with only proximal location. Thus, for these outcomes, the modulating effects of age and BMI were explained by the interaction of treatment with fat intake. For men, in contrast, all three interaction terms were removed from the multivariate models for all adenoma-related outcomes (P > 0.05).

Our results were not substantially different when we used saturated fat intake in these multivariate models instead of total dietary fat; the one exception was for the proximal location outcome in women, in which the treatment-by-fat interaction was no longer significant. We did not model both fat variables simultaneously due to their extremely high correlation (ρ = 0.96, P < 0.001). Furthermore, we explored other treatment-by-X interactions for family history of CRC, aspirin use, bile acid sequestrants, and hormone replacement therapy; we found no significant interactions with any of these variables (data not shown).

In a secondary analysis of a randomized UDCA trial, we found that sex significantly modified the effect of UDCA treatment on certain subtypes of metachronous colorectal adenomas. UDCA significantly reduced the odds of large, high-grade dysplastic, and advanced adenomas for men, but not women. We also observed significantly increased odds of advanced lesions among women in the treatment group who were young (age, <65 years), obese (BMI, ≥30 kg/m²), or in the highest tertile of total dietary fat (≥52.5 g/day). Multivariate modeling showed that the modulating effects of age and BMI in women could be explained by total dietary fat, as these variables were strongly correlated. To our knowledge, no previous studies have evaluated sex-specific benefit or risk of UDCA in any setting, including use in patients with ulcerative colitis who were receiving UDCA for the treatment of primary sclerosing cholangitis (17, 18, 31). These studies, however, are limited by small sample sizes.

Recent advances in the molecular classification of CRCs have shown that colorectal tumors comprise a heterogeneous group of diseases. These tumors are thought to arise through molecularly distinct precursors that exhibit anatomic preference in the colon (i.e., proximal versus distal) and for which men and women experience differential risk (27). Thus, UDCA may act in only a subgroup of adenoma formers, which led us to re-evaluate UDCA benefit in our trial using existing information on factors that may influence subtype-specific risk (e.g., sex, age, anatomic location, development of multiple lesions, and family history of CRC). Our finding that the odds of advanced adenomas were reduced by 38% in men receiving UDCA supports our a priori hypothesis that UDCA acts as a chemopreventive agent for CRC in humans. We found no evidence of a differential effect by anatomic location or the development of multiple adenomas.

UDCA was originally introduced as a drug for gallstone dissolution, acting to reduce stone formation by lowering the cholesterol saturation index of bile, protecting against cholesterol nucleation, and possibly by increasing gallbladder volume and prolonging emptying (32). Female sex hormones and obesity are two of the best-recognized risk factors for gallstone formation (33). Our observation of an adverse effect of UDCA in the same subgroup as those at highest risk for gallstones leads us to hypothesize that UDCA may increase exposure of the intestinal tract to lithogenic and potentially protumorigenic and/or proinflammatory bile acids, which may derive from small, asymptomatic gallstones. Alternatively, in persons at high risk for gallstones, UDCA might have a differential adverse effect on the composition of secondary and tertiary bile acids in the colon. Examples of gender differences influencing composition, conjugation, and transport/uptake of bile acids have been described in animal models (34, 35) and humans (36, 37), although sex-specific analyses are limited.

We attempted to address the potential contribution of existing gall bladder disease as a risk factor in our study by assessing participant use of bile acid sequestrants, but we found no supportive evidence of an interaction with UDCA (data not shown). Data on cholecystectomy were not available, so we were unable to assess the potential role of gall bladder removal. Of the other putative modifiers of bile acid exposure for which we had data (e.g., dietary calcium, serum cholesterol, and serum triglycerides), only dietary fat modified the effect of UDCA among women; furthermore, it appeared to account for the observed treatment interactions with age and BMI. Thus, the observed modulating effects of younger age and BMI in women are likely related to their association with higher intakes of dietary fat, which have been suggested to be associated with more lithogenic bile in animal models (38). Results from studies in humans are equivocal, where recognized gender differences and broad interindividual variability limit interpretation of association studies and small feeding trials (39, 40).

The exact mechanism of action of UDCA for the prevention of high-grade dysplasia observed in our study (26) and others (17, 18) is unknown. Biological differences between protumorigenic and antitumorigenic bile acids are subtle (41). Extensive overlap in the chemical and signaling properties of protumorigenic hydrophobic (e.g., DCA) and antitumorigenic hydrophilic (e.g., UDCA) bile acids and effects on nuclear receptors, such as the nuclear bile acid receptor farnesoid X receptor (15), challenge our understanding of the opposing effects of these molecules. UDCA has potent cytoprotective effects in hepatocytes and cholangiocytes, as well as colon cancer cell lines, which is counterintuitive for an inherent anticancer activity (15, 22). Antiapoptotic effects that have been attributed to UDCA include inhibition of p53 transcription, resulting in suppression of Bax translocation from the cytosol to the mitochondrial membrane, cytochrome c release, caspase activation, mitochondrial membrane perturbation, and pore formation (14, 15, 42). Under certain circumstances, UDCA may offer a survival advantage to premalignant lesions, as observed here, thereby countering any antitumor activity. This protumorigenic effect might occur through effects of sex on the metabolism and/or transport of UDCA and its conjugated forms; alternatively, the interaction of cofactors (e.g., steroid hormones or dietary fat) on signaling pathways could modulate the effect of UDCA. Additional studies are needed to separate the antitumor action of UDCA from possible protumorigenic activities and to understand their relationship to sex and potential signaling cofactors, like dietary fat.

Regardless of the biological mechanism, our finding of a potential adverse effect of UDCA on colorectal adenoma in women is important because UDCA is already approved for a number of uses. Most commonly, UDCA is prescribed for the treatment of primary bile duct disease, particularly primary biliary cirrhosis, which is substantially more common in women than men (43). Beneficial effects of UDCA for the treatment of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis have also been reported (44). In addition, the potent antiapoptotic activities of taurine-conjugated UDCA (tauroursodeoxycholic acid) have prompted its study for the prevention of apoptotic-mediated disease, including amyotrophic lateral sclerosis⁴

and Alzheimer's disease (45), the latter of which represents a sizable patient population that might be exposed. Furthermore, tauroursodeoxycholic acid has been shown to alleviate endoplasmic reticulum stress and restore glucose homeostasis in a mouse model of type 2 diabetes (46). The fact that patients are already using UDCA, with increasing clinical uses on the horizon, highlights the necessity of understanding whether or not this agent exhibits protumorigenic effects.

To our knowledge, no previous studies have reported any serious adverse effects of UDCA in the clinical setting; however, the evaluable data come from studies with limited use for cancer (or adenoma) end points, and the sample sizes are generally too small for stratification by age or sex. Our findings are the first to show a potential adverse effect of UDCA for adenoma development in the colorectum. Although the trial was not powered for sex stratification, we were able to detect significantly increased odds of advanced lesions in young and obese women and in women consuming fat in the upper tertile of intake. Due to our limited sample size, however, we were not able to stratify by age, BMI, and dietary fat simultaneously. Additionally, we chose not to adjust for multiple comparisons, as we envisioned these analyses as hypothesis generating and not hypothesis testing. We were also unable to investigate the potential role of gall bladder removal, as this information was not available for our study. Furthermore, the 3-year trial duration may be too short to capture the important effects of UDCA on various types of colorectal adenomas, let alone cancer.

Although additional studies are certainly needed, the significantly higher odds of adenoma in women with the highest dietary fat intake with UDCA exposure suggest the potential for a proneoplasia effect of UDCA in women. However, UDCA treatment may protect low fat-intake women against metachronous adenomas. Furthermore, UDCA seems protective in men for advanced adenomas. Although these results support a chemopreventive effect of UDCA for colorectal adenoma, they highlight a need for additional efforts to separate the antitumor properties of UDCA from potential proneoplasia effects. Further investigation is needed to confirm our results before recommending any change in the clinical use of UDCA. In the interim, female patients taking UDCA for primary biliary cirrhosis—women suffer from this condition far more frequently than do men and generally take UDCA for the rest of their lives—and participants in clinical trials of UDCA for other conditions should follow current CRC screening recommendations to detect advanced adenomas and possible cancers early and, thus, mitigate any potential harm from UDCA.

No potential conflicts of interest were disclosed.