Molecular Basis of Human Salt Sensitivity: The Role of the 11β-Hydroxysteroid Dehydrogenase Type 2*
Abstract Salt-sensitive subjects (SS) increase their blood pressure with increasing salt intake. Because steroid hormones modulate renal sodium retention, we hypothesize that the activity of the 11β-hydroxy-steroid dehydrogenase type 2 (11βHSD2) enzyme is impaired in SS subjects as compared with salt-resistant (SR) subjects. The 11βHSD2 enzyme inactivates 11-hydroxy steroids in the kidney, thus protecting the nonselective mineralocorticoid receptor from occupation by glucocorticoids. We performed an association study using a recently identified single AluI polymorphism in exon 3 and a polymorphic microsatellite marker of the HSD11B2 gene in 149 normotensive white males (37 SS and 112 SR). The activity of the enzyme 11βHSD2 was assessed by determining the urinary ratio of cortisol (THF+5αTHF) to cortisone (THE) metabolites by gas chromatography in all the 37 SS subjects and in 37 age- and body habitus-matched SR volunteers. Mean (THF+5αTHF)/THE ratio was markedly elevated in SS subjects compared with SR subjects (1.51 ± 0.34 vs. 1.08 ± 0.26, P < 0.00001), indicating enhanced access of glucocorticoids to the mineralocorticoid receptor in SS subjects. In 58% of SS subjects this ratio was higher than the maximum levels in SR subjects. The salt-induced elevation in arterial pressure increased with increasing (THF+5αTHF)/THE ratio (r2 = 0.51, P < 0.0001). A total of 12 alleles of the polymorphic microsatellite marker were detected. Homozygosity for the allele A7 was higher in SS subjects than in SR subjects (41 vs. 28%, P < 0.005), whereas the occurrence of the allele A7 with allele A8 was lower in SS subjects than in SR subjects (8 vs. 15%, P< 0.03). The prevalence of salt sensitivity was 35% in subjects with allele A7/A7, whereas salt sensitivity was present in only 9% of the subjects with allele A7/A8. The (THF+5αTHF)/THE ratio was higher in subjects homozygous for the A7 microsatellite allele as compared with the corresponding control subjects. The prevalence of the AluI allele was 8.0% in SR subjects and 5.4% in SS subjects and did not correlate with blood pressure. The decreased activity of the 11βHSD2 in SS subjects indicates that this enzyme is involved in salt-sensitive blood pressure response in humans. The association of a polymorphic microsatellite marker of the gene with a reduced 11βHSD2 activity suggests that variants of the HSD11B2 gene contribute to enhanced blood pressure response to salt in humans.
