Arterial stiffness and functional properties in chronic kidney disease patients on different dialysis modalities: an exploratory study.

BACKGROUND: Abnormalities of vascular function and accumulation of oxidative stress have been associated with chronic kidney disease (CKD). Dialysis modalities, peritoneal dialysis (PD) and haemodialysis (HD) may differentially impact on vascular function and oxidative stress. METHODS: Patients undergoing living donor transplantation were studied for vascular stiffness using pulse wave velocity measurements, and inferior epigastric arteries were harvested to examine in vitro stiffness and functional properties and evidence of oxidative stress. Forty-one patients were studied representing PD (n = 12), HD (n = 14) and non-dialysed recipients (n = 15). RESULTS: We demonstrated differences in stiffness from in vivo and in vitro measurements such that non-dialysis < HD < PD groups. The stiffness measurements did not correlate with duration of CKD nor dialysis duration, but did so with phosphate levels (r = 0.356, P = 0.02). From the in vitro isometric force experiments, HD arteries demonstrated decreased contractility and endothelium-dependent relaxation compared with PD and non-dialysis vessels. Level of oxidative stress (as indicated by the 8-isoprostane level) was 30% higher in HD arteries than in PD arteries. Protein expression of inducible nitric oxide synthase, NADPH subunits and xanthine oxidase was upregulated in HD arteries, while superoxide dismutase was downregulated. The compromised vascular function in HD arteries was improved by pharmacological means that eliminated oxidative stress. CONCLUSIONS: We report associations between vasomotor function and oxidative stress in the vasculature of patients receiving different dialysis therapies. Oxidative stress, which may be differentially augmented during PD and HD, may play an important role in the vascular dysfunction in dialysis populations.

Effectiveness of combination of losartan potassium and doxycycline versus single-drug treatments in the secondary prevention of thoracic aortic aneurysm in Marfan syndrome.

OBJECTIVE: Losartan potassium (INN losartan), an antihypertensive drug, has been shown to prevent thoracic aortic aneurysm in Marfan syndrome through the inhibition of transforming growth factor beta. Recently we reported that doxycycline, a nonspecific inhibitor of matrix metalloproteinases 2 and 9, normalized aortic vasomotor function and suppressed aneurysm growth. We hypothesized that a combination of losartan potassium and doxycycline would offer better secondary prevention treatment than would single-drug therapy to manage thoracic aortic aneurysm. METHODS: A well-characterized mouse model of Marfan syndrome (Fbn1(C1039G/+)) was used. At 4 months of age, when aneurysm had established, mice (n = 15/group) were given doxycycline alone (0.24 g/L), losartan potassium alone (0.6 g/L), or combined (0.12-g/L doxycycline and 0.3-g/L losartan potassium) in drinking water. Littermate Fbn1(+/+) mice served as control. Thoracic aortas at 6 and 9 months were studied. RESULTS: At 9 months, aortic diameter in untreated group was increased by 40% relative to control. Losartan potassium or doxycycline reduced aortic diameter by 10% to 16% versus untreated aortas. Losartan potassium and doxycycline combined completely prevented thoracic aortic aneurysm and improved elastic fiber organization, also downregulating matrix metalloproteinases 2 and 9 and transforming growth factor beta and normalizing aortic contractile and relaxation functions to control values. CONCLUSIONS: Neither losartan potassium nor doxycycline alone completely restored vascular integrity and cell function when given during delayed treatment, indicating the importance of timed pharmacologic intervention. Combined, however, they synergistically offered better aneurysm-suppressing effects than did single-drug medication in the secondary prevention of thoracic aortic aneurysm.

Differential microvasculature dysfunction in living kidney donor transplant recipients: nondialyzed versus dialyzed chronic kidney disease patients.

We hypothesized that there was differential vasomotor dysfunction in the microcirculation between nondialyzed and dialyzed chronic kidney disease (CKD) patients. During live donor kidney transplantation procedures, skin arterioles (SkA; internal diameter = 120 +/- 5 microm) from donors (n = 27) and recipients (nondialysis = 15; dialysis = 20) were dissected from the abdominal wall at the incision site. In vivo aortic pulse wave velocity (PWV) was also measured. In the in vitro isometric force measurement, nondialyzed SkA exhibited comparable contraction to donor SkA, whereas dialyzed SkA had 60 and 40-50% increase in contraction in response to depolarization and agonist (that is, phenylephrine, serotonin and endothelin-1) stimulation, respectively. The acetylcholine-induced relaxation in the nondialyzed SkA was decreased by 50% compared with dialyzed SkA. However, pre-incubation with superoxide dismutase greatly enhanced the relaxation response in the nondialyzed, but not in the dialyzed SkA and donor SkA. Pre-incubation with N(G)-nitro-L-arginine methyl ester (L-NAME) elevated the resting tension and left-shifted the concentration response curve of phenylephrine-stimulated contraction in the donor-SkA. L-NAME only increased the resting tension in the nondialyzed vessel. In vitro stiffness positively correlated with PWV (R(2) = 0.302, p = 0.001), and dialyzed SkA was 60% stiffer than nondialyzed and donor SkA. The acetylcholine relaxation was negatively correlated with PWV in donors and recipients (R(2) = 0.282, p = 0.01). In conclusion, we have uniquely demonstrated differential microvasculature dysfunction between nondialyzed and dialyzed CKD patients.

Vasomotor dysfunction in the thoracic aorta of Marfan syndrome is associated with accumulation of oxidative stress.

We have described that the progression of thoracic aortic aneurysm in Marfan syndrome is accompanied with aortic vascular dysfunction. In the present study, we hypothesized that the impaired contractile function and endothelial-dependent relaxation could be resulted from oxidative stress in the thoracic aorta. Adrenergic contraction and cholinergic relaxation of thoracic aortae from mice (n=40; age=3, 6, 9 months) heterozygous for FBN1 allele (Fbn1(C1039G/+)), a well-defined model of Marfan syndrome, were compared with those from control (n=40). The aortic 8-isoprostane level, an oxidative stress marker, was 32-50% greater in the Marfan group than in the control. Pre-incubation with superoxide dismutase (SOD) improved the phenylephrine-induced contraction and the sensitivity to acetylcholine in Marfan aortae, but not in controls. The phenylephrine-contraction in Marfan aortae was potentiated by 1400 W, an inducible nitric oxide synthase (iNOS) inhibitor, and allopurinol, a xanthine oxidase inhibitor. Acetylcholine-induced relaxation was restored by apocynin, an inhibitor of NAD(P)H oxidase. Protein expression of SOD-1 and SOD-2 was decreased in Marfan aortae, whereas that of xanthine oxidase, iNOS, and the enzymatic subunits of NAD(P)H oxidase was increased. The vasomotor dysfunction in Marfan thoracic aortae could be associated with accumulation of oxidative stress due to unbalanced protein expression of superoxide-producing and superoxide-eliminating enzymes.

Long-term effects of losartan on structure and function of the thoracic aorta in a mouse model of Marfan syndrome.

BACKGROUND AND PURPOSE: During development of thoracic aortic aneurysms in a mouse model of Marfan syndrome, upregulation of matrix metalloproteinase (MMP)-2 and -9 was accompanied by compromised aortic constriction and endothelium-dependent relaxation. Losartan has been proposed for the prevention of thoracic aortic aneurysm. We hypothesized that losartan would suppress MMP-2/-9 activation and improve aortic vasomotor function in this model. EXPERIMENTAL APPROACH: A well-characterized mouse model of Marfan syndrome (Fbn1(C1039G/+)) was used. Starting at 6 weeks old, Marfan mice were untreated or given losartan (0.6 g.L(-1) in drinking water, n= 30). The littermate Fbn1(+/+) mice served as control. Thoracic aortas were studied at 3, 6 and 9 months by histology and by contractility assays in isolated segments in vitro. KEY RESULTS: Losartan improved elastic fibre organization and increased aortic breaking stress. Losartan reduced the activity and protein expression of MMP-2 and MMP-9 at all ages. Aortic constriction in response to membrane depolarization or phenylephrine was increased by losartan at 3 and 9 months by 100-200%. Active force of aortic smooth muscle was also increased at 6 and 9 months. Acetylcholine-induced endothelium-dependent relaxation was improved by 30% after 3 months of losartan treatment, but such improvement disappeared with longer duration of treatment, accompanied by reduced phosphorylation of endothelial nitric oxide (NO) synthase(Ser1177), Akt(Thr308) and Akt(Ser473), compared with the control. CONCLUSIONS AND IMPLICATIONS: Losartan improved the contractile function of aorta and reduced MMP activation. However, the endothelial NO pathway remained suppressed in the thoracic aorta during losartan treatment, which might limit its long-term benefits in Marfan syndrome.

Upregulation of matrix metalloproteinase-2 in the arterial vasculature contributes to stiffening and vasomotor dysfunction in patients with chronic kidney disease.

BACKGROUND: Cardiovascular disease is the leading cause of mortality in chronic kidney disease patients on maintenance dialysis. Given the importance of matrix metalloproteinase-2 (MMP-2) in matrix integrity, vascular cell function, and structural stability, we hypothesized that MMP-2 was elevated in the macrovasculature in dialyzed chronic kidney disease patients compared with chronic kidney disease patients not on dialysis and kidney donors. METHODS AND RESULTS: Arteries from live kidney donors (A(donor); n=30) and recipients (nondialysis [A(nondialyzed)], n=17; dialysis [A(dialyzed)], n=23 [peritoneal dialysis, n=10; hemodialysis, n=13]) were harvested during the transplantation procedure. Compared with A(donor), MMP-2 upregulation was evident in both recipient groups. Protein expression of latent plus active MMP-2 in A(dialyzed) was 2-fold that in A(nondialyzed). MMP-2 activity increased with length of dialysis (r=0.573, P=0.004). In A(dialyzed), medial elastic fiber fragmentation was pronounced, and the ratio of external elastic lamina to media was negatively correlated with MMP-2 activity (r=-0.638, P=0.001). A(dialyzed) was 25% stiffer than A(nondialyzed); this increased stiffness correlated with MMP-2 activity (r=0.728, P<0.0001) and the severity of medial calcium deposition (r=0.748, P=0.001). The contractile function and endothelium-dependent relaxation were reduced by 35% to 55% in A(dialyzed) and were negatively associated with MMP-2 activity (r=-0.608, P=0.002; r=-0.520, P=0.019, respectively). Preincubation with MMP-2 inhibitor significantly improved contractility and relaxation in A(dialyzed). CONCLUSIONS: We describe a strong correlation between MMP-2 activation and elastic fiber disorganization, stiffness, calcification, and vasomotor dysfunction in the arterial vasculature in dialyzed chronic kidney disease patients. These findings may contribute to an improved understanding of mechanisms important in vascular health in chronic kidney disease patients.

Matrix metalloproteinase-2 and -9 exacerbate arterial stiffening and angiogenesis in diabetes and chronic kidney disease.

AIMS: Chronic kidney disease (CKD) and diabetes are the prominent risk factors of cardiovascular disease (CVD). Matrix metalloproteinase (MMP)-2 and -9 regulate vascular structure by degrading elastic fibre and inhibit angiogenesis by generating angiostatin. We hypothesized that MMP-2 and -9 were up-regulated in the arterial vasculature from CKD patients with diabetes, compared with those without diabetes. METHODS AND RESULTS: During living donor transplantation procedures, arteries from donors (n = 8) and recipients (non-diabetic, n = 8; diabetic, n = 8; matched in age, gender, and dialysis treatments) were harvested. Diabetic arteries had increased MMP-2 and -9 activities by 42 and 116% compared with non-diabetic ones. Diabetic arteries were the stiffest, and the stiffness measurement was highly correlated with the summation of MMP-2 + MMP-9 activities (r = 0.738, P = 0.0002). Pulse wave velocity measurements correlated with MMP activity (r = 0.683, P = 0.005). Elastic fibre degradation and calcification were worst in diabetic vessels. The phosphate level, which was 25% higher in diabetic patients, correlated with MMP activity (r = 0.513, P = 0.04) and in vitro stiffness (r = 0.545, P = 0.03), respectively. Angiostatin expression was doubled, whereas vascular endothelial growth factor was 50% reduced in diabetic compared with non-diabetic vessels. Microvascular density in diabetic vessels was 48% of that in non-diabetic ones, and it was strongly associated with MMP activity (r = -0.792, P < 0.0001) and vasorelaxation (r = 0.685, P = 0.0009). CONCLUSION: Using a matched case-control design, we report up-regulation of MMP-2 and -9 in diabetic CKD arteries and correlate those with stiffening, impaired angiogenesis, and endothelial dysfunction. These findings may help to explain the high susceptibility of CVD in diabetic and non-diabetic CKD patients.

Long-term doxycycline is more effective than atenolol to prevent thoracic aortic aneurysm in marfan syndrome through the inhibition of matrix metalloproteinase-2 and -9.

Beta-blockers, eg, atenolol, are the cornerstone therapy for thoracic aortic aneurysm (TAA) in patients with Marfan syndrome; however, continued aortic dilatation has been reported. We have demonstrated that matrix metalloproteinase (MMP)-2 and -9 were upregulated during progression of TAA in Marfan syndrome, accompanied with degenerated elastic fibers and vasomotor dysfunction. We hypothesized that doxycycline, a nonspecific inhibitor of MMPs, would ameliorate TAA by attenuating elastic fiber degeneration and improving vasomotor function. A well-characterized mouse model of Marfan syndrome (Fbn1(C1039G/+)) was used. Mice were untreated (n=40), given doxycycline (0.24 g/L, n=30), or given atenolol (0.5 g/L, n=30) in drinking water at 6 weeks of age. The Fbn1(+/+) mice served as control (n=40). At 3, 6, and 9 months, aortic segments from the ascending, arch, and descending portions were used to obtain the "average" value of the whole thoracic aorta. TAA was prevented in the doxycycline group, whereas mild aneurysm was evident in the atenolol group. Doxycycline improved elastic fiber integrity, normalized aortic stiffness, and prevented vessel weakening. The impairment of vasocontraction and endothelium-dependent relaxation in the untreated and atenolol groups were improved by doxycycline. The upregulation of transforming growth factor-beta in the Marfan aorta was suppressed by doxycycline. Doxycycline augmented expression ratios of tissue inhibitors of MMP to MMPs. Intraperitoneally injected neutralizing antibodies against MMP-2 and -9 yielded similar effects to doxycycline. We concluded that long-term treatment with doxycycline, through the inhibition of MMP-2 and -9, is more effective than atenolol in preventing TAA in Marfan syndrome by preserving elastic fiber integrity, normalizing vasomotor function, and reducing transforming growth factor-beta activation.

Mechanical and pharmacological approaches to investigate the pathogenesis of Marfan syndrome in the abdominal aorta.

BACKGROUND: Occurrence of disease complications in the abdominal aorta in Marfan syndrome, a connective tissue disorder caused by mutations in the gene encoding fibrillin-1, is relatively rare. We hypothesized that Marfan syndrome could affect the structure, vasomotor function and mechanical property of the abdominal aorta. METHODS AND RESULTS: Abdominal aorta from mice at 3, 6, 9 and 12 months of age, heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1(C1039G/+), Marfan mice, n = 50), were compared with those from age-matched control littermates (n = 50). Marfan abdominal aorta demonstrated pronounced elastic fiber degradation and disorganization, concomitant with an increased aortic stiffness during aging. In the isometric force measurement, vasoconstriction in response to membrane depolarization or phenylephrine stimulation was similar in both Marfan and control abdominal aorta. However, Marfan abdominal aorta was less sensitive to the inhibition of the phenylephrine-induced contraction by indomethacin and SQ-29548, during which the release of thromboxane A(2) was one half of that of the controls. Nevertheless, the protein expression of cyclooxygenase-1 and cyclooxygenase-2 detected by Western immunoblotting was not different between the 2 strains. CONCLUSIONS: We demonstrated that Marfan syndrome affected abdominal aorta with respect to matrix elastic fiber organization, aortic stiffness and release of thromboxane A(2).