TIME‐DEPENDENT TRANSITION FROM H₂O₂–EXTRACELLULAR SIGNAL‐REGULATED KINASE‐ TO O₂⁻–NITRIC OXIDE‐DEPENDENT MECHANISMS IN THE STIMULATORY EFFECT OF LEPTIN ON RENAL Na⁺/K⁺‐ATPase IN THE RAT

Abstract

1. Recent studies suggest that leptin, a peptide hormone secreted by white adipose tissue, is involved in the pathogenesis of arterial hypertension, in part by regulating renal sodium handling. Previously, we have demonstrated that in normal rats leptin has a time-dependent effect on renal Na(+)/K(+)-ATPase that drives tubular sodium reabsorption. Short-term leptin infusion results in a transient decrease in Na(+)/K(+)-ATPase activity, whereas prolonged administration stimulates the enzyme. 2. In the present study, we investigated whether these acute effects of leptin are preserved in rats with experimentally induced chronic hyperleptinaemia. 3. Hyperleptinaemia was induced by administration of exogenous leptin (0.25 mg/kg twice daily, s.c., for 7 days). Acute effects of leptin in anaesthetized control (normoleptinaemic) and hyperleptinaemic animals was investigated. Leptin was infused into the abdominal aorta proximally to the renal arteries for 0.5, 1, 2 or 3 h. 4. Leptin (1 microg/min per kg) had a time-dependent effect on renal Na(+)/K(+)-ATPase in both the control and hyperleptinaemic groups. The inhibitory effect observed after 0.5 h infusion was impaired in the hyperleptinaemic group. However, in both groups this effect was abolished by the Janus kinase inhibitor tyrphostin AG490 (100 nmol/min per kg), as well as by the phosphatidylinositol 3-kinase inhibitors wortmannin (10 nmol/min per kg) and LY294002 (1 micromol/min per kg). 5. The stimulatory effect of leptin on Na(+)/K(+)-ATPase activity was observed after 3 h of infusion and was of similar magnitude in control and hyperleptinaemic groups. In the control group, the stimulatory effect of leptin was abolished by the NADPH oxidase inhibitor apocynin (1 micromol/min per kg), the H(2)O(2) scavenger catalase (1 mg/min per kg) and the extracellular signal-regulated kinase (ERK) inhibitor PD98059 (100 nmol/min per kg). In contrast, in the hyperleptinaemic group, the stimulatory effect of leptin was abolished by the cGMP analogue 8-bromo-cGMP (100 nmol/min per kg) and by the superoxide dismutase mimetic tempol (100 micromol/min per kg) but was not affected by catalase or PD98059. 6. Leptin increased urinary H(2)O(2) excretion and ERK phosphorylation in the renal tissue only in the control group. 7. The results suggest that the acute stimulatory effect of leptin on renal Na(+)/K(+)-ATPase is mediated by divergent mechanisms depending on the chronic leptin level (i.e. by H(2)O(2)-dependent stimulation of ERK in normoleptinaemic animals and by superoxide-dependent impairment of the nitric oxide-cGMP pathway in hyperleptinaemic rats).

NOX in liver fibrosis

“…The results demonstrate that NADPH oxidase in HSCs regulates their activation process, so that the NADPH oxidase complex regulates liver fibrogenesis in response to Ang II, PDGF or apoptotic bodies. Since NADPH oxidase mediates the effects of several other agonists in extra-hepatic cells [89][90][91] (leptin, endothelin, homocystein), these potentially interesting agonists need to be assessed in HSC activation. Secondarily, two different NADPH oxidase forms, the phagocytic and the nonphagocytic form, are apparently both actively operating in liver fibrogenesis.…”

Reduced nicotinamide adenine dinucleotide phosphate oxidase mediates fibrotic and inflammatory effects of leptin on hepatic stellate cells

“…Recently, not only angiotensin II but also platelet‐derived growth factor (PDGF) and apoptotic bodies have been recognized as NADPH‐dependent agonists in HSCs 23. In addition, leptin‐induced ROS production in kidney and in smooth muscle cells is blocked by the NADPH oxidase inhibitor diphenylene‐iodonium (DPI) 24–26. In the liver, leptin is a fibrogenic agonist that may activate HSCs through H 2 O 2 production, but its relationship with NADPH oxidase has not been investigated 27…”

Leptin and the Regulation of Renal Sodium Handling and Renal Na+- Transporting ATPases: Role in the Pathogenesis of Arterial Hypertension

“…To resolve why O 2 -• -NO mechanism predominates after 7-day systemic leptin administration [57] and H 2 O 2 -ERK dependent one after local 3-hour hormone infusion [63], we examined the effect of locally infused leptin in control animals as well as in rats made hyperleptinemic by preceding 7-day systemic leptin treatment [64]. Using combined biochemical and pharmacological approaches, we demonstrated that leptin infused locally to the renal artery stimulated cortical and medullary Na + ,K + -ATPase through the H 2 O 2 -ERK dependent mechanism in normal rats but through the O 2 -• -NO mechanism in previously hyperleptinemic rats, which suggests that the mechanism of antinatriuretic effect of leptin changes time-dependently when hormone is administered for prolonged time period.…”