Protective effect of dietary potassium against vascular injury in salt-sensitive hypertension.

Hypertensive cardiovascular damage is accelerated by salt loading but counteracted by dietary potassium supplementation. We suggested recently that antioxidant actions of potassium contribute to protection against salt-induced cardiac dysfunction. Therefore, we examined whether potassium supplementation ameliorated cuff-induced vascular injury in salt-sensitive hypertension via suppression of oxidative stress. Four-week-old Dahl salt-sensitive rats were fed a normal-salt (0.3% NaCl), high-salt (8% NaCl), or high-salt plus high-potassium (8% KCl) diet for 5 weeks, and some of the rats fed a high-salt diet were also given antioxidants. One week after the start of the treatments, a silicone cuff was implanted around the femoral artery. Examination revealed increased cuff-induced neointimal proliferation with adventitial macrophage infiltration in arteries from salt-loaded Dahl salt-sensitive rats compared with that in arteries from non-salt-loaded animals (intima/media ratio: 0.471+/-0.070 versus 0.302+/-0.037; P<0.05), associated with regional superoxide overproduction and reduced nicotinamide-adenine dinucleotide phosphate oxidase activation and mRNA overexpression. On the other hand, simultaneous potassium supplementation attenuated salt-induced neointimal hyperplasia (intima/media ratio: 0.205+/-0.012; P<0.001), adventitial macrophage infiltration, superoxide overproduction, and reduced nicotinamide-adenine dinucleotide phosphate oxidase activation and overexpression. Antioxidants, which decrease vascular oxidative stress, also reduced neointima formation induced by salt excess. In conclusion, high-potassium diets seems to have a protective effect against the development of vascular damage induced by salt loading mediated, at least in part, through suppression of the production of reactive oxygen species probably generated by reduced nicotinamide-adenine dinucleotide phosphate oxidase.

Endogenous adrenomedullin protects against vascular response to injury in mice.

BACKGROUND: In our previous study, adrenomedullin (AM) overexpression could limit the arterial intimal hyperplasia induced by cuff injury in rats. However, it remains to be elucidated whether endogenous AM plays a role against vascular injury. METHODS AND RESULTS: We used the AM knockout mice to investigate the effect of endogenous AM. Compared with wild-type (AM+/+) mice, heterozygous AM knockout (AM+/-) mice had the increased intimal thickening of the cuff-injured femoral artery, concomitantly with lesser AM staining. In AM+/- mice, cuff placement increased both the production of superoxide anions (O2-) measured by coelentarazine chemiluminescence and the immunostaining of p67phox and gp91phox, subunits of NAD(P)H oxidase in the adventitia, associated with the increment of CD45-positive leukocytes, suggesting that the stimulated formation of radical oxygen species accompanied chronic adventitial inflammation. Not only the AM gene transfection but also the treatment of NAD(P)H oxidase inhibitor apocynin and membrane-permeable superoxide dismutase mimetic tempol could limit cuff-induced intimal hyperplasia in AM+/- mice, associated with the inhibition of O2- formation in cuff-injured artery. CONCLUSIONS: The overproduction of oxidative stress induced by the increased NAD(P)H oxidase activity might be involved in cuff-injured arterial intimal hyperplasia in AM+/- mice. Thus, it is suggested that endogenous AM possesses a protective action against the vascular response to injury, possibly through the inhibition of oxidative stress production.

Estrogen receptor beta mediates the inhibitory effect of estradiol on vascular smooth muscle cell proliferation.

OBJECTIVES: It has been demonstrated that 17beta-estradiol (E2) has an inhibitory effect on the proliferation of vascular smooth muscle cells (VSMCs) through an estrogen receptor (ER)-dependent pathway. Both ER subtypes, classical ER (ERalpha) and the newly identified ER subtype (ERbeta), are expressed in VSMCs. However, it remains unknown which receptor plays the critical role in the inhibitory effect on VSMC proliferation. METHODS AND RESULTS: We constructed replication-deficient adenoviruses bearing the coding region of human ERalpha, ERbeta, and the dominant-negative form of ERbeta (designated AxCAERalpha, AxCAERbeta, and AxCADNERbeta, respectively). Prior to infection with the adenoviruses, 100 nmol/l E2 attenuated DNA synthesis by up to 14% and transactivated the estrogen-induced expression of the desired mRNA in rat VSMCs. This was accompanied by increased transcriptional activity of estrogen responsive element in response to E2, and the increase was comparable between AxCAERalpha and AxCAERbeta. When VSMCs were infected with AxCAERbeta at a multiplicity of infection of 5 or higher, DNA synthesis as well as cell number decreased by 50% in response to E2, and the effect was abolished by co-infection with AxCADNERbeta. In contrast, when VSMCs were infected with AxCAERalpha, the reduction in DNA synthesis was minimal. CONCLUSIONS: Our results indicate that ERbeta is more potent than ERalpha in the inhibitory effect on VSMC proliferation.

Adrenomedullin overexpression to inhibit cuff-induced arterial intimal formation.

Adrenomedullin (AM) inhibits vascular smooth muscle cell proliferation stimulated by fetal calf serum and platelet-derived growth factor in vitro. In this study, an adenovirus expressing AM (AxCAAM) was created to examine the in vivo action of AM. Femoral arteries of Wistar rats were wrapped with a silicone cuff and treated with adenovirus expressing Escherichia coli beta-galactosidase (AxCALacZ) or AxCAAM. Immunoreactivity for endothelial nitric oxide synthase (eNOS) was reduced in the endothelium of cuff-injured arteries and was associated with increased local DNA synthesis. Consequently, the intimal formation measured by the intimal-to-medial ratio was significantly increased at 14 and 28 days after the cuff placement. AxCAAM-infected arteries increased the expression of eNOS in the endothelium and inducible NOS in the media and the adventitia. AxCAAM significantly decreased the intimal-to-medial ratio by 40% at 14 days and 51% at 28 days, whereas AxCALacZ showed no changes compared with cuff-injured control arteries. AM overexpression effectively limits intimal hyperplasia by reducing cell proliferation through a nitric oxide-dependent pathway of eNOS. Our findings suggest the possibility of a therapeutic use of the AM gene for the prevention of vascular proliferative disorders.