Possible contribution of indomethacin to the carcinogenicity of nongenotoxic bladder carcinogens that cause bladder calculi.

Nongenotoxic bladder carcinogens that form bladder calculi have been concluded to be of low carcinogenic risk to humans because bladder stones would be expelled or surgically removed before they had a chance to exert their carcinogenic effect. It is the aim of this report to examine the possible contribution of indomethacin to the carcinogenic risk posed by nongenotoxic bladder carcinogens that cause bladder stones. Indomethacin may act as a tumor promoter in the bladder by interfering with the synthesis of prostaglandins. Prostaglandins have a cytoprotective function in the gastric mucosa and possibly also in the urinary bladder. Diminished cytoprotection may be implicated in bladder carcinogenesis as beta-naphthylamine, a human bladder carcinogen, also inhibits prostaglandin synthesis in vitro. The presence of other tumor promoters in the bladder may further ensure that tumors would be formed even if bladder stones were expelled. People who are exposed to nongenotoxic bladder carcinogens that are present in the environment and that form bladder stones, therefore, may be at an increased risk for developing bladder cancer if they are also exposed to tumor promoters, such as indomethacin.

Aggressive behavior increases after termination of chronic sildenafil treatment in mice.

Recent reports to the U.S. Food and Drug Administration Adverse Event Reporting System implicate sildenafil citrate in adverse emotional and aggressive behaviors. Sildenafil citrate (Viagra) is widely prescribed for erectile dysfunction and acts by inhibiting phosphodiesterase Type-5, resulting in accumulation of cyclic-guanosine monophosphate (cGMP). Cyclic-GMP is synthesized by guanylyl cyclase that is directly activated by the messenger molecule, nitric oxide (NO), formed throughout the CNS by the enzyme nitric oxide synthase (NOS). Elevated concentrations of cGMP have been associated with increased aggressive behavior. In addition, the potential effect of cGMP accumulation on NO-mediated behavioral and neuroendocrine function through possible feedback mechanisms remains unspecified; however, neuronal NOS (nNOS) inhibition by pharmacologic agents or ablation of the gene encoding nNOS increases aggressive behavior in male mice. We tested the hypothesis that sildenafil citrate may increase aggression via its actions on cGMP and potential feedback inhibition of NO concentrations. Male C57BL/6 mice were injected with saline vehicle (0), 2, 5, 8, or 10 mg/kg of sildenafil citrate thrice weekly for 4 weeks. Latency to display aggressive behavior, frequency, and duration of aggressive behavior were recorded during neutral-arena aggression tests. No change in agonistic behavior was observed in mice during treatment with sildenafil citrate. However, sildenafil-treated mice given the highest dose were generally more aggressive 1 week post-cessation of drug treatment as compared to vehicle-treated mice. Additional investigation into potential withdrawal effects or abuse doses seems warranted.

Evaluation of the adequacy of published studies of low-dose effects of bisphenol A on the rodent prostate for use in human risk assessment.

Studies conducted in our laboratories and by others found no consistent correlation between prostate size, prostate pathology, or the development of prostate cancer under a variety of experimental conditions. Furthermore, an evaluation of eight published studies that were conducted in mice and rats following in utero exposure by oral treatment of dams with low levels of bisphenol A (BPA) and that focused on the prostate identified several discrepancies that affect their adequacy for use in human risk assessment. For example, there was inadequate reporting of the purity of BPA and the animal supplier used, and housing of offspring was not the same among the studies. In addition, there were differences between studies with mice and rats in exposure regimen, route of exposure, and numbers of dams or pups used per BPA dose group. Poor inter- and intraspecies correlation (i.e., mouse to rat or between mouse or rat strains) further complicates the ability to use results from these studies to predict potential prostate effects in humans. Thus, we conclude that a finding of increased prostate weight in rodent studies with perinatal exposure in the absence of associated pathologic and/or functional changes is meaningless and not indicative of a potential adverse effect in humans.

Neurologic, psychological, and aggressive disturbances with sildenafil.

BACKGROUND: Anecdotal reports and case studies have described psychological disturbances and aggressive behavior in some men taking sildenafil. In the course of assisting the defense in a trial in which a man was alleged to have committed rape and in which sildenafil was implicated, a mechanistic hypothesis was formulated by the first author for central nervous system (CNS) adverse effects associated with the use of sildenafil. OBJECTIVE: To examine whether there was any scientific information available to suggest a possible mechanism for or an association between exposure to sildenafil and aggressive behavior. METHODS: The scientific literature on sildenafil, nitric oxide (NO), and the NO-cyclic-guanosine monophosphate (cyclic-GMP) signaling pathway was reviewed. Adverse event reports that referenced sildenafil and were filed with the Food and Drug Administration Adverse Event Reporting System between January 4, 1998, and February 21, 2001, also were examined. RESULTS: Published studies reported that sildenafil crosses the blood-brain barrier, that it exerts various biochemical and physiologic effects in the brain, and that it affects information processing. Other published reports indicated that phosphodiesterase type 5 (PDE-5), NO synthase, and guanylyl cyclase are present at highest activities in areas of the brain responsible for behavior, sexual drive, and emotion, and that NO modulates aggression and sexual behavior in male mice. In addition, 274 adverse event reports designated sildenafil as the primary suspect of various neurologic disturbances, amnesia, and aggressive behavior. DISCUSSION: Evidence has been presented for an association between sildenafil and various CNS adverse effects, including aggressive behavior. Whether sildenafil causes these effects by inhibiting PDE-5 in the brain, accumulating cyclic-GMP, decreasing NO, and affecting cell-cell signaling and modulation of aggressive behavior requires further investigation. CONCLUSIONS: It is recommended that, before prescribing sildenafil for erectile dysfunction, clinicians should caution their patients and their partners on the possibility of neurologic, emotional, or psychological disturbances; amnesia or loss of consciousness; or aggressive behavior.