Protective effect of taurine on hypochlorous acid toxicity to nuclear nucleoside triphosphatase in isolated nuclei from rat liver

Abstract

Aim: Taurine has been shown to be an effective scavenger of hypochlorous acid (HOCl). The role of HOCl is well established in tissue damage associated with inflammation and injury. In the present study, the effect of HOCl on nuclear nucleoside triphosphatase of hepatocytes and the ability of taurine to prevent this effect were investigated.

Methods: Isolated hepatic nuclei from rat liver were exposed to HOCl with or without taurine. The NTPase activity on nuclear envelope was assayed using ATP and GTP as substrates, respectively.

Results: The first series of experiments evaluated the toxicity of HOCl and the efficacy of taurine to protect NTPase. HOCl at 10(-9)-5 x 10(-6) mol/L reduced nuclear NTPase activities in a concentration dependent manner (ATP and GTP as substrates) (P<0.01). HOCl at 10(-6) mol/L reduced the NTPase activity by 65% (ATP as substrate) and 76% (GTP as substrate). Taurine (10(-7) to 10(-4) mol/L) was tested for protection against HOCl at 10(-6) mol/L and the nuclei treated with 5 x 10(-4) mol/L taurine exhibited only 20% and 12% reduction in NTPase activities compared to untreated controls. A second study was performed comparing taurine to glutathione (GSH). GSH and HOCl at 10(-6) mol/L exhibited 46% and 67.4% reduction in NTPase activities compared with control. GSH (10(-4) mol/L) which was incubated with the nuclei and HOCl still exhibited 44.2% and 44.8% reduction in NTPase activities of untreated control. Taurine with HOCl only exhibited 15.2% and 17.1% reduction in NTPase activities, which provided more powerful protection against HOCl than GSH. The third experiment was undertaken to evaluate the specificity of taurine against HOCl. Incubation of rat hepatic nuclei with Fe(3+)/H(2)O(2) (1 m mol/L vs 5 micromol/L) resulted in a decrease in nuclear NTPase activities (P<0.01). When hepatic nuclei were incubated with Tau (10(-4) mol/L) and Fe(3+)/H(2)O(2) (1m mol/L vs 5 micromol/L), nuclear NTPase activities were only slightly increased as compared with that of incubation with Fe(3+)/H(2)O(2) alone. However, GSH failed to alter the NTPase activities induced by Fe(3+)/H(2)O(2).

Conclusion: The present findings indicate that HOCl can act as an inhibitor of nuclear NTPase. Taurine can antagonistically reduce the toxicity of HOCl to NTPase.

Figure 1

Inhibitory effect of hypochlorous acid on hepatic nuclear NTPase activity. ATP and GTP were used as reaction substrates, respectively. Mean ± SD, n = 6. ^aP < 0.05, ^bP < 0.01 com-pared with control.

Figure 2

Effect of taurine on OCl^--induced inhibition of NTPase activity in hepatic nuclei. ATP and GTP were used as reaction substrates, respectively. Mean ± SD, n = 6. ^aP < 0.05, ^bP < 0.01 com-pared with OCl (10^-6 mol/L) group. ^cP < 0.05, ^dP < 0.01 compared with control.

Figure 3

Effects of glutathione on OCl^--induced inhibition of NTPase activity in hepatic nuclei. ATP and GTP were used as reaction substrates, respectively. Mean ± SD, n = 6. ^bP < 0.01 com-pared with control group (OCl^-1 10^-6 mol/L). ^aP < 0.05, ^cP < 0.01 compared with (10^-6 mol/L OCl^-1 + 10^-4 mol/L taurine).