Effects of tempol and redox-cycling nitroxides in models of oxidative stress

Abstract

Tempol is a redox-cycling nitroxide that promotes the metabolism of many reactive oxygen species (ROS) and improves nitric oxide bioavailability. It has been studied extensively in animal models of oxidative stress. Tempol has been shown to preserve mitochondria against oxidative damage and improve tissue oxygenation. Tempol improved insulin responsiveness in models of diabetes mellitus and improved the dyslipidemia, reduced the weight gain and prevented diastolic dysfunction and heart failure in fat-fed models of the metabolic syndrome. Tempol protected many organs, including the heart and brain, from ischemia/reperfusion damage. Tempol prevented podocyte damage, glomerulosclerosis, proteinuria and progressive loss of renal function in models of salt and mineralocorticosteroid excess. It reduced brain or spinal cord damage after ischemia or trauma and exerted a spinal analgesic action. Tempol improved survival in several models of shock. It protected normal cells from radiation while maintaining radiation sensitivity of tumor cells. Its paradoxical pro-oxidant action in tumor cells accounted for a reduction in spontaneous tumor formation. Tempol was effective in some models of neurodegeneration. Thus, tempol has been effective in preventing several of the adverse consequences of oxidative stress and inflammation that underlie radiation damage and many of the diseases associated with aging. Indeed, tempol given from birth prolonged the life span of normal mice. However, presently tempol has been used only in human subjects as a topical agent to prevent radiation-induced alopecia.

Figure 1

Redox cycling reactions of tempol involving the nitroxide radical (Panel A) or the 4-position of the piperidine ring (Panel B). Panel A: Reprinted from Soule, B. P., Hyodo, F., Matsumoto, K., Simone, N. L., Cook, J. A., Krishna, M. C., et al. (2007). The chemistry and biology of nitroxide compounds. Free Radic Biol Med 42, 1632-1650. Copyright 2007 Elsevier Limited. Used with permission. Panel B: Reprinted from Saito, K., Takeshita, K., Ueda, J., & Ozawa, T. (2003). Two reaction sites of a spin label, TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), with hydroxyl radical. J Pharm Sci 92, 275-280. Copyright John Wiley & Sons Inc. Used with permission.

Figure 2

Mean ± SEM values for percentage inhibition of cellular superoxide formation in cultured preglomerular vascular smooth muscle cells stimulated with angiotensin II and detected by low concentration lucigenin chemiluminence by maximum effective concentrations (10^-3M or 10^-4M) of drugs. PEG, pegolated; SOD, Cu/Zn superoxide dismutase; tempol, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl; NAC, N-acetyl-L-cysteine; EPC, (-)epicatechin; NTB, nitroblue tetrozolium; Fe-TTPS, 5,10,15,20-tetrakis (4 sulphonatophenyl) porphyronate iron; Tr, trolox; Toc, α-tocopherol; Asc, ascorbate. Compared to SOD: *, p<0.0125; a, generation of O₂^{. −} increased at lower drug concentration. Data drawn from Luo, Z., Chen, Y., Chen, S., Welch, W. J., Andresen, B. T., Jose, P. A., et al. (2009). Comparison of inhibitors of superoxide generation in vascular smooth muscle cells. Br J Pharmacol 157, 935-943.

Figure 3

Panel A depicts the relationship between renal oxygen usage (Q_O2) and tubular sodium transport (T_Na) in normal rats. It shows the effects of increases in an angiotensin II, reactive oxygen species or reduction in nitric oxide to increase the slope of the line (and decrease the efficacy of renal O₂ usage for chemical work) or tempol or an angiotensin receptor blocker given to these models to reduce the slope of the line. Panel B shows mean ± SEM values for PO₂ measured with an ultramico, coaxial electrode placed within the renal tubule by micropuncture. Rats received vehicle (open boxes) or angiotensin II at 200 ng · kg^-1 · min by osmotic minipump (closed boxes) given with vehicle or tempol at 200 nmol · kg^-1 · min sc for two weeks. Panel A, data drawn from: Welch, W. J., Blau, J., Xie, H., Chabrashvili, T., & Wilcox, C. S. (2005). Angiotensin-induced defects in renal oxygenation: role of oxidative stress. Am J Physiol 288, H22-H28. Welch, W. J., Mendonca, M., Aslam, S., & Wilcox, C. S. (2003). Roles of oxidative stress and AT₁ receptors in renal hemodynamics and oxygenation in the post-clipped 2K,1C kidney. Hypertens 41, 692-696. Welch, W. J., Baumgärtl, H., Lübbers, D., & Wilcox, C. S. (2003). Renal oxygenation defects in the spontaneously hypertensive rat: role of AT₁ receptors. Kidney Int 63, 202-208. Welch, W. J., Baumgärtl, H., Lübbers, D., & Wilcox, C. S. (2001). Nephron PO₂ and renal oxygen usage in the hypertensive rat kidney. Kidney Int 59, 230-237. Panel B, data drawn from: Welch, W. J., Blau, J., Xie, H., Chabrashvili, T., & Wilcox, C. S. (2005). Angiotensin-induced defects in renal oxygenation: role of oxidative stress. Am J Physiol 288, H22-H28.

Figure 4

Mean ± SEM values from obese Zucker rats fed for 10 weeks a reduced fat diet (14%; open boxes), a high fat diet (35%, cross-hatched boxes) as a model of the human metabolic syndrome, or a high fat diet and given tempol (1 mmol · l^-1) in the drinking water (closed boxes). In addition to the effects shown, tempol lowered the mean arterial pressure and renal NADPH oxidase activity and corrected albuminuria but did not modify food intake. Data drawn from Ebenezer, P. J., Mariappan, N., Elks, C. M., Haque, M., & Francis, J. (2009). Diet-Induced Renal Changes in Zucker Rats Are Ameliorated by the Superoxide Dismutase Mimetic TEMPOL. Obesity (Silver Spring) 17, 1994-2002.

Figure 5

Mean ± SEM values from rat studies of the two kidney, one clip (2K,1C) model of Goldblatt hypertension. Rats were studied after 3 weeks (Panel A-C) or 10 weeks (Panel D) of sham operation (open boxes) or 2K,1C hypertension and given a vehicle (grey boxes), the angiotensin receptor blocker candesartan (10 mg · kg^-1 · day^-1 × 14 days; solid boxes), tempol (200 nmol · kg^-1 · min^-1 sc × 14 days; cross-hatched boxes). Compared to 2K,1C + vehicle: *, p<0.05; **, p<0.01. Panel A to C, data drawn from Welch, W. J., Mendonca, M., Aslam, S., & Wilcox, C. S. (2003). Roles of oxidative stress and AT₁ receptors in renal hemodynamics and oxygenation in the post-clipped 2K,1C kidney. Hypertens 41, 692-696. Panel D, data drawn from Castro, M. M., Rizzi, E., Rodrigues, G. J., Ceron, C. S., Bendhack, L. M., Gerlach, R. F., et al. (2009). Antioxidant treatment reduces matrix metalloproteinase-2-induced vascular changes in renovascular hypertension. Free Radic Biol Med 46, 1298-1307.

Figure 6

Mean ± SEM values in salt-loaded spontaneously hypertensive rats with leptin receptor deficiency as a model of the metabolic syndrome. Rats were given normal salt diet (open bars), high salt diet (8% salt: grey bars) or high salt diet and oral tempol (1 mmol · l^-1) for four weeks (solid bars). There were no significant differences for the variables shown between the normal salt and the high salt plus tempol groups. Data drawn from Matsui, H., Ando, K., Kawarazaki, H., Nagae, A., Fujita, M., Shimosawa, T., et al. (2008). Salt excess causes left ventricular diastolic dysfunction in rats with metabolic disorder. Hypertens 52, 287-294.