Longitudinal study of a mouse model of familial porphyria cutanea tarda

Most rodent models of porphyria cutanea tarda (PCT) share in common the administration of iron and agents that induce transcription of cytochrome P450s. Dissection of changes related to porphyrin accumulation required generation of a genetic model free from exogenous precipitants. Mice heterozygous for a null Urod mutation and homozygous for null Hfe alleles spontaneously develop major increases in hepatic and urinary porphyrins several months after weaning but the high % uroporphyrin signature of PCT is established earlier, before total hepatic and urinary porphyrins rise. Total porphyrin levels eventually plateau at higher levels in females than in males. Porphyrinogens were the dominant tetrapyrroles accumulating in hepatocytes. Hepatic Urod activity is markedly reduced but total hepatic heme content does not diminish. Microsomal heme, however, is reduced and in vitro metabolism of prototype substrates showed that some but not all cytochrome P450 activities are reduced. High hepatic levels of uroporphyrinogen are also associated with increased glutathione S-transferase activity and elevated mRNA of 2 transporters, Abcc1 and Abcc4. This murine model of familial PCT affords the opportunity to study changes in porphyrinogen and porphyrin accumulation and transport in the absence of exogenous factors that alter P450 activity and transmembrane transporters.

Oral L-arginine in patients with coronary artery disease on medical management

BACKGROUND

Vascular nitric oxide (NO) bioavailability is reduced in patients with coronary artery disease (CAD). We investigated whether oral L-arginine, the substrate for NO synthesis, improves homeostatic functions of the vascular endothelium in patients maintained on appropriate medical therapy and thus might be useful as adjunctive therapy.

METHODS AND RESULTS

Thirty CAD patients (29 men; age, 67+/-8 years) on appropriate medical management were randomly assigned to L-arginine (9 g) or placebo daily for 1 month, with crossover to the alternate therapy after 1 month off therapy, in a double-blind study. Nitrogen oxides in serum (as an index of endothelial NO release), flow-mediated brachial artery dilation (as an index of vascular NO bioactivity), and serum cell adhesion molecules (as an index of NO-regulated markers of inflammation) were measured at the end of each treatment period. L-Arginine significantly increased arginine levels in plasma (130+/-53 versus 70+/-17 micromol/L, P<0.001) compared with placebo. However, there was no effect of L-arginine on nitrogen oxides (19.3+/-7.9 versus 18. 6+/-6.7 micromol/L, P=0.546), on flow-mediated dilation of the brachial artery (11.9+/-6.3% versus 11.4+/-7.9%, P=0.742), or on the cell adhesion molecules E-selectin (47.8+/-15.2 versus 47.2+/-14.4 ng/mL, P=0.601), intercellular adhesion molecule-1 (250+/-57 versus 249+/-57 ng/mL, P=0.862), and vascular cell adhesion molecule-1 (567+/-124 versus 574+/-135 ng/mL, P=0.473).

CONCLUSIONS

Oral L-arginine therapy does not improve NO bioavailability in CAD patients on appropriate medical management and thus may not benefit this group of patients.

Effects of oral L-arginine on endothelium-dependent vasodilation and markers of inflammation in healthy postmenopausal women

OBJECTIVES

We examined whether oral administration of L-arginine, the substrate for nitric oxide (NO) synthesis, increases NO bioactivity in healthy postmenopausal women.

BACKGROUND

Nitric oxide may protect arteries against atherosclerosis, as suggested by experimental studies in animals. Estrogen therapy, which has been shown to increase NO bioactivity in the vasculature of healthy postmenopausal women, is not acceptable for long-term use by many women.

METHODS

In a randomized, double-blind, crossover study, 10 postmenopausal women without additional risk factors for atherosclerosis received L-arginine 9 g or placebo daily for one month, with treatment periods separated by one month. Nitric oxide levels in serum (as an index of endothelial NO release), brachial artery endothelium-dependent dilator responses to hyperemia by ultrasonography (as an index of vascular NO bioactivity) and markers of inflammation in blood that are inhibited by NO in cell culture experiments were measured at the end of each treatment period.

RESULTS

L-arginine levels in plasma were increased in all women during L-arginine treatment compared with placebo (136.8 +/- 63.1 vs. 75.2 +/- 16.2 micromol/liter, p = 0.009). However, there was no change in serum nitrogen oxide levels (42.1 +/- 24.5 vs. 39.1 +/- 16.6 micromol/liter, p = 0.61), nor was there an effect of L-arginine on flow-mediated dilation during hyperemia (3.8 +/- 3.0% vs. 4.9 +/- 4.8%, p = 0.53) compared with placebo. Our study had sufficient power (beta = 0.80) to detect a true absolute treatment difference in flow-mediated brachial artery dilation of 1.7% or larger as statistically significant at alpha = 0.05. There was no effect of L-arginine on serum levels of soluble cell adhesion molecules compared with placebo: E-selectin (50.6 +/- 14.8 vs. 52.1 +/- 17.0 ng/ml, p = 0.45), intercellular adhesion molecule-1 (230 +/- 51 vs. 230 +/- 52 ng/ml, p = 0.97) and vascular cell adhesion molecule-1 (456 +/- 62 vs. 469 +/- 91 ng/ml, p = 0.53).

CONCLUSIONS

Oral administration of L-arginine may not augment endothelial NO synthesis and release in postmenopausal women and is thus unlikely to be of general benefit to healthy postmenopausal women in protection from the development of atherosclerosis.

Vascular effects of estrogen and vitamin E therapies in postmenopausal women

BACKGROUND

Estrogen and vitamin E therapies have been suggested to reduce cardiovascular risk, but comparison of the vascular effects of these therapies to determine mechanisms of potential benefit has not been performed in postmenopausal women.

METHODS AND RESULTS

In a double-blind, 3-period crossover study, we randomly assigned 28 healthy postmenopausal women to conjugated equine estrogens (CE) 0. 625 mg/d, vitamin E 800 IU/d, and their combination, with measurements made before and after each 6-week treatment period. The ratio of LDL to HDL cholesterol and lipoprotein(a) decreased on therapies including CE but increased on vitamin E alone (P<0.001 and P=0.002, respectively, by ANOVA). Brachial artery flow-mediated dilation improved on all therapies (all P<0.001 versus pretreatment values) and to a similar degree (P=0.267 by ANOVA). No therapy improved the dilator response to nitroglycerin. CE lowered serum levels of cell adhesion molecules E-selectin, ICAM-1, and VCAM-1 (all P<0.05 versus pretreatment values). Vitamin E had no significant effect on levels of these markers of inflammation (P<0. 001 by ANOVA for E-selectin). CE alone or combined with vitamin E but not vitamin E alone lowered or showed a trend for lowering plasma levels of plasminogen activator inhibitor type-1 (P=0.069 by ANOVA).

CONCLUSIONS

Estrogen and vitamin E therapies similarly improved arterial endothelium-dependent vasodilator responsiveness consistent with increased nitric oxide in healthy postmenopausal women, despite divergent effects on atherogenic lipoproteins. However, only estrogen reduced markers of vascular disease.

Mechanism by which quinapril improves vascular function in coronary artery disease

Angiotensin-converting enzyme (ACE) inhibition has been shown to improve endothelium-dependent vasodilator responsiveness, but the contribution and mechanism of enhanced nitric oxide (NO) bioactivity to this effect in patients with coronary artery disease are unknown. We investigated the effect of ACE inhibition on brachial artery dilator responsiveness to increased shear stress after forearm ischemia by ultrasonography as a bioassay for endothelial NO available to vascular smooth muscle in 9 men with coronary artery disease. Serum nitrogen oxides were measured after 3 days of nitrate-restricted diet as an index of endothelial NO release. Patients received quinapril 20 to 40 mg/day for 8 weeks. Relative to pretreatment measurements, quinapril increased flow-mediated dilation (from 2.4+/-0.4 to 10.8+/-2.2, p <0.001), with significant improvement persisting 1 week after discontinuation of therapy (6.7+/-2.5%, p <0.01). However, quinapril decreased serum nitrogen oxide levels by 19+/-17% compared with pretreatment values (from 58.2+/-19.0 to 46.0+/-13.3 micromol/L, p <0.01). Thus, ACE inhibitor therapy with quinapril selectively improves endothelium-dependent vasodilator responsiveness by increased NO bioactivity in relation to vascular smooth muscle in patients with coronary artery disease, an effect achieved at a lower rate of NO release from the endothelium. These findings suggest that ACE inhibitors may reduce angiotensin II-induced oxidant stress within the vessel wall and protect NO from oxidative inactivation. This effect may reduce endothelial NO synthesis required for vasomotor regulation.

Vascular effects of estrogen and cholesterol-lowering therapies in hypercholesterolemic postmenopausal women

BACKGROUND

Lipoproteins affect endothelium-dependent vasomotor responsiveness. Because lipoprotein effects of estrogen and cholesterol-lowering therapies differ, we studied the vascular responses to these therapies in hypercholesterolemic postmenopausal women.

METHODS AND RESULTS

We randomly assigned 28 women to conjugated equine estrogen (CE) 0.625 mg, simvastatin 10 mg, and their combination daily for 6 weeks. Compared with respective baseline values, simvastatin alone and combined with CE reduced LDL cholesterol to a greater extent than CE alone (both P<0.05). CE alone and combined with simvastatin raised HDL cholesterol and lowered lipoprotein(a) to a greater extent than simvastatin alone (all P<0.05). Flow-mediated dilation of the brachial artery (by ultrasonography) improved (all P<0.001 versus baseline values) on CE (4.0+/-2.6% to 10.2+/-3.9%), simvastatin (4.3+/-2.4% to 10.0+/-3.9%), and CE combined with simvastatin (4.6+/-2.0% to 9.8+/-2.6%), but similarly among therapies (P=0.507 by ANOVA). None of the therapies improved the dilator response to nitroglycerin (all P>/=0.184). Only therapies including CE lowered levels of plasminogen activator inhibitor type 1 and the cell adhesion molecule E-selectin (all P<0. 05 versus simvastatin).

CONCLUSIONS

Although estrogen and statin therapies have differing effects on lipoprotein levels, specific improvement in endothelium-dependent vasodilator responsiveness is similar. However, only therapies including estrogen improved markers of fibrinolysis and vascular inflammation. Thus, estrogen therapy appears to have unique properties that may benefit the vasculature of hypercholesterolemic postmenopausal women, even if they are already on cholesterol-lowering therapy.