Basic and Translational Science Lipid Peroxidation Product 4-Hydroxynonenal Contributes to Bladder Smooth Muscle Damage Rik de Jongh, Guido R. M. M. Haenen, Gommert A. van Koeveringe, Miriam Dambros, and Philip E. V. van Kerrebroeck OBJECTIVES Bladder outlet obstruction is correlated with an increased peroxidation of lipids. The aldehyde 4-hydroxynonenal (HNE) is produced in relative large amounts during lipid peroxidation. The aim of this study was to investigate the effect of HNE on excitation-contraction coupling of detrusor smooth muscle. METHODS We used smooth muscle strips from pig urinary bladder. Contractile responses to electrical field stimulation (EFS) (4 to 32 Hz), carbachol (10 -8 to 3.10 –5 M), and potassium (65.3 mM) were monitored before and after the addition of HNE. We investigated the effect of the synthetic thiol inactivator N-ethylmaleimide (NEM) on the stimulation pathways and compared it with the HNE-mediated effect. RESULTS Responses of detrusor strips to EFS were for the greater part based on neurogenic stimulation and the release of acetylcholine. HNE (100 M) diminished contractile responses to EFS and carbachol to the same extent. The pD 2 value of the carbachol concentration response curve did not decrease after exposure to HNE. The maximal effect obtained with carbachol was signifi- cantly reduced after 100 M HNE treatment. Contractions induced by potassium were affected in a similar degree by HNE compared with EFS- and carbachol-induced responses of comparable amplitude. Incubation of bladder strips with NEM had similar effects on pharmacological responses compared with HNE exposure. CONCLUSIONS 4-Hydroxynonenal affects pig bladder contractility. L-type calcium channels and or the contractile system of the bladder muscle are susceptible to HNE-mediated damage. The cholinergic nerves and the muscarinic receptor signaling system remain largely unaffected. The effects of HNE are most likely mediated via alkylation of sulfhydryl groups. UROLOGY 71: 974 –978, 2008. © 2008 Elsevier Inc. B ladder outlet obstruction and acute urinary reten- tion followed by bladder decompression are corre- lated with an increased peroxidation of lipids. 1–3 Animal models of bladder outlet obstruction indicate that ischemia/reperfusion injury is an important etiolog- ical factor in deteriorating bladder function. 4–6 Reperfu- sion injury of the bladder seems to be more detrimental than ischemia alone. 7 Especially during the reperfusion period, reactive oxygen species (ROS) are formed. Be- sides ischemia/reperfusion, inflammatory processes in the bladder wall are likely to contribute to the smooth muscle dysfunction associated with bladder outflow obstruc- tion. 8 –10 Bladder inflammation is characterized by infil- tration of neutrophils, macrophages, mast cells, and lym- phocytes in the bladder wall. 11,12 In particular, the activation of phagocytic leukocytes results in the forma- tion of ROS. 13 Antioxidants and nitric oxide synthase inhibitors can protect the bladder against functional damage resulting from outlet obstruction, furthermore confirming that bladder outlet obstruction is associated with nitric oxide and the generation of ROS. 14 –17 ROS can damage various cellular components such as proteins, lipids, and DNA, and consequently contribute to smooth muscle dysfunction. Oxidative damage to lipids is known as lipid peroxidation. Peroxidation of fatty acids gives rise to various reactive aldehydes such as malondialdehyde (MDA) and 4-hydroxynonenal (HNE). HNE is highly reactive and produced in relative large amounts during lipid peroxidation. Concentrations of HNE in the mem- brane can reach 4 to 10 mM in vivo. This reactive aldehyde is an important mediator of free radical damage and contributes to smooth muscle dysfunction. 18,19 This study was supported by the WAMU Foundation, Maastricht, The Netherlands. From the Department of Urology, University Hospital Maastricht, Maastricht; and the Department of Pharmacology and Toxicology, Faculty of Medicine, Maastricht University, Maastricht, The Netherlands; and the Department of Urology, São Fran- cisco University, Sao Paulo, Brazil Reprint requests: Rik de Jongh, Department of Urology, University Hospital Maas- tricht, P. Debyelaan 25, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. E-mail: r.dejongh@mmc.nl Submitted: June 24, 2007, accepted (with revisions): November 7, 2007 974 © 2008 Elsevier Inc. 0090-4295/08/$34.00 All Rights Reserved doi:10.1016/j.urology.2007.11.014