Lazaroid therapy (methylaminochroman: U83836E) reduces vein graft intimal hyperplasia

Oral intake of hydrogen-rich water inhibits intimal hyperplasia in arterialized vein grafts in rats

AIMS

Arterialized vein grafts often fail due to intimal hyperplasia. Hydrogen potently protects organs and cells from many insults via its anti-inflammatory and antioxidant properties. We investigated the efficacy of oral administration of hydrogen-rich water (HW) for prevention of intimal hyperplasia.

METHODS AND RESULTS

The inferior vena cava was excised, stored in cold Ringer solution for 2 h, and placed as an interposition graft in the abdominal aorta of syngeneic Lewis rats. HW was generated by immersing a magnesium stick in tap water (Mg + 2H(2)O → Mg (OH)(2) + H(2)). Beginning on the day of graft implantation, recipients were given tap water [regular water (RW)], HW or HW that had been subsequently degassed water (DW). Six weeks after grafting, the grafts in the rats given RW or DW had developed intimal hyperplasia, accompanied by increased oxidative injury. HW significantly suppressed intimal hyperplasia. One week after grafting, the grafts in HW-treated rats exhibited improved endothelial integrity with less platelet and white blood cell aggregation. Up-regulation of the mRNAs for intracellular adhesion molecules was attenuated in the vein grafts of the rats receiving HW. Activation of p38 mitogen-activated protein kinase, matrix metalloproteinase (MMP)-2, and MMP-9 was also significantly inhibited in grafts receiving HW. In rat smooth muscle cell (A7r5) cultures, hydrogen treatment for 24 h reduced smooth muscle cell migration.

CONCLUSION

Drinking HW significantly reduced neointima formation after vein grafting in rats. Drinking HW may have therapeutic value as a novel therapy for intimal hyperplasia and could easily be incorporated into daily life.

Protandim attenuates intimal hyperplasia in human saphenous veins cultured ex vivo via a catalase-dependent pathway

Human saphenous veins (HSVs) are widely used for bypass grafts despite their relatively low long-term patency. To evaluate the role of reactive oxygen species (ROS) signaling in intima hyperplasia (IH), an early stage pathology of vein-graft disease, and to explore the potential therapeutic effects of up-regulating endogenous antioxidant enzymes, we studied segments of HSV cultured ex vivo in an established ex vivo model of HSV IH. Results showed that HSV cultured ex vivo exhibit an ~3-fold increase in proliferation and ~3.6-fold increase in intimal area relative to freshly isolated HSV. Treatment of HSV during culture with Protandim, a nutritional supplement known to activate Nrf2 and increase the expression of antioxidant enzymes in several in vitro and in vivo models, blocks IH and reduces cellular proliferation to that of freshly isolated HSV. Protandim treatment increased the activity of SOD, HO-1, and catalase 3-, 7-, and 12-fold, respectively, and decreased the levels of superoxide (O(2)(•-)) and the lipid peroxidation product 4-HNE. Blocking catalase activity by cotreating with 3-amino-1,2,4-triazole abrogated the protective effect of Protandim on IH and proliferation. In conclusion, these results suggest that ROS-sensitive signaling mediates the observed IH in cultured HSV and that up-regulation of endogenous antioxidant enzymes can have a protective effect.

U74389F, a 21-aminosteroid antioxidant, improves neoendothelial morphology, but not neointimal thickening after balloon catheter injury

U74389F is a compound in a family of 21-aminosteroids devoid of classical glucocorticoid action that inhibit lipid peroxidation. These compounds improve neurologic function and tissue survival after head or spinal cord injury. Dexamethasone inhibits development of intimal hyperplasia (IH) and improves attenuated nitric oxide (NO) production of the rabbit aorta subsequent to balloon catheter injury. We tested the hypothesis that U74389F is protective in a catheter-induced endothelial-denuded and arterial injury model. A 4-Fr Fogarty balloon (BALL) embolectomy catheter was passed through the thoracic aorta of New Zealand White rabbits treated with 15 mg/kg U74389F (LAZ) 2 days before and 1 week after injury. Animals were killed at 4 weeks after surgical intervention, and formation of IH was determined by calculating the intimal/medial ratio (I/M). The treatment groups of animals were injured untreated (BALL), injured treated (BALL/LAZ), uninjured treated (CONTROL/LAZ), and sham-operated treated (SHAM/LAZ). Scanning electron microscopy revealed that after injury lazaroid treatment produced an improvement of the neoendothelium (alignment in the direction of blood and fewer intercellular gaps) as compared with injured but untreated aortas. Relaxation to acetylcholine (NO formation) was impaired in aortic rings from catheterized animals; lazaroid treatment improved the relaxation to 10-6 mol/L acetylcholine but not to lower concentrations. I/M for SHAM/LAZ, BALL, and BALL/LAZ was 0.02 +/- 0.02, 21.6 +/- 1.6, and 17.2 +/- 2.5, respectively; BALL vs. BALL/LAZ, p < 0.06. An increased contractile response to 120 mmol/L KCl was observed after lazaroid treatment. This is the first report of lazaroid-mediated improvement in the neoendothelial morphology, improved neoendothelial NO generation, and augmented hypopolarizing contractile response, but no attenuation in the development of IH.

Pharmacologic inhibition of vein graft neointimal hyperplasia

Although arterial conduits are widely used and have improved the long-term results of coronary artery bypass grafting, vein grafts remain important additional conduits in coronary surgery. Newer studies show a saphenous vein graft patency of 60% or more at 10 years postoperatively. The pathology of vein graft disease consists of thrombosis, neointimal hyperplasia, and vein graft atherosclerosis, which limit graft longevity. Therapeutic strategies to prevent vein graft disease include external stenting, pharmacotherapy, and gene therapy. The potential benefits of a pharmacologic approach are as follows: (1) Drugs with a broad clinical experience can be used; (2) side effects of systemic application can be minimized by local therapy; and (3) no vascular injury, such as pressurizing the vein for a viral transfection approach, is necessary. The different sites for pharmacotherapy in vein graft disease are reviewed in this article.

Enhanced superoxide production in experimental venous bypass graft intimal hyperplasia: role of NAD(P)H oxidase

-Vein graft intimal hyperplasia, due to smooth muscle cell (SMC) proliferation, remains a limiting factor in long-term vein graft patency. Increased superoxide production regulates SMC mitogenesis and contributes to reduced NO bioactivity in systemic models of vascular disease. We compared superoxide production in experimental venous bypass grafts with ungrafted veins and determined its enzymatic sources and cellular localization. Vascular superoxide production was measured in vein grafts and control jugular veins obtained from normocholesterolemic rabbits undergoing jugular vein-carotid artery interposition bypass grafting. Surgical isolation of the contralateral jugular vein, without bypass grafting, provided an additional control for the effects of surgical manipulation. Superoxide production was increased 3-fold in vein grafts compared with control veins. Systematic stimulation and inhibition of specific oxidases revealed that the major source of increased vein graft superoxide production was a membrane-associated NAD(P)H-dependent oxidase. Western blotting of vascular homogenates demonstrated corresponding increases in NAD(P)H oxidase p22phox (membrane-associated) and p67phox (cytosolic) subunits in vein grafts compared with jugular veins. There was marked intimal hyperplasia in vein grafts, and immunohistochemical staining of vessel cryosections revealed increased p22phox-expressing cells in vein grafts that were predominantly intimal SMCs. Superoxide generation is increased in experimental vein grafts compared with ungrafted veins. The principal source of increased superoxide generation in vein grafts is an NAD(P)H oxidase, expressed by intimal SMCs. These findings suggest a role for NAD(P)H oxidase-mediated superoxide production in the proliferative response to vascular injury in vein grafts.

Combination therapy of cholesterol reduction and L-arginine supplementation controls accelerated vein graft atheroma

Hyperlipidemia contributes to the development of intimal hyperplasia and accelerated atheroma in vein bypass grafts. Dietary cholesterol reduction and oral supplementation with L-arginine have been shown to reduce accelerated atheroma in experimental vein grafts. This study extends these observations by examining the effect of the combination therapy of cholesterol reduction and L-arginine supplementation on the development of intimal hyperplasia in vein grafts in hypercholesterolemic animals. Thirty New Zealand White rabbits had a carotid vein bypass graft performed and were sacrificed at 28 days postoperatively either for morphology (light and electron microscopy) and videomorphometry, or for in vitro contractile studies. Twenty animals received a 1% cholesterol diet for 4 weeks prior to surgery. This diet was continued until harvest in ten animals. Ten cholesterol-fed animals received L-arginine supplementation (2 g/kg/day, p.o.) for 7 days preoperatively and thereafter until harvest and in addition were returned to a normal diet on the day of surgery. The last ten animals were controls (normal diet). Combined cholesterol reduction and L-arginine supplementation prevented accelerated atheroma in vein grafts, halted the change in enhanced smooth muscle cell contractility, and improved endothelial cell function. Early postoperative therapy targeting atheroma development in the high-risk patient could offer significant morphological and functional benefits.

A new animal model to study intimal hyperplasia in arteriovenous fistulas

BACKGROUND

Intimal hyperplasia (IH) plays a key role in the failure of arteriovenous (AV) fistulas. The animal models available to study IH in AV fistulas are expensive and do not mimic the development of truly stenotic IH. In this study we examined whether goats are a more suitable model to study IH in AV fistulas.

MATERIALS AND METHODS

Thirteen direct and four bridge graft AV fistulas between the carotid artery and the jugular vein of goats were explanted 10 to 195 days after creation. Immunohistochemical staining and morphometric measurements of intima and media were performed in the artery, the vein, the toe, and the heel of the venous anastomosis. Ratios of intimal to medial thickness (Ith/Mth) and area (Ia/Ma) were calculated.

RESULTS

IH developed in all goats, mainly at the anastomosis (Ia/Ma = 0.17) and the efferent vein (Ia/Ma = 0.31). The artery was almost free of lesions (Ia/Ma = 0.03). In the efferent vein, Ith/Mth varied between 0.59 and 0.68. In the anastomosis the largest value of Ith/Mth was measured at the suture lines (0.88 and 0.91). Absolute intimal area increased with time. IH contained many vascular smooth muscle cells with a patchy display of desmin positivity, an abundance of smooth muscle cell alpha-actin positivity, and almost complete endothelial cell coverage. Occlusion was due to thrombus formation on the IH.

CONCLUSION

A clear intimal hyperplasia developed in AV fistulas in goats at locations comparable to those in humans. Therefore, the AV fistula model in the goat may be seen as an effective model to study IH in hemodialysis AV fistulas.

Cardioprotective effects of pinacidil pretreatment and lazaroid (U74500A) preservation in isolated rat hearts after 12-hour hypothermic storage

BACKGROUND

Two important processes in the preservation of the function of donor hearts are the maintenance of ATP-sensitive potassium channel activity during myocardial ischemia and the scavenging of reactive oxygen species formed during reperfusion. The aim of this study was to compare the effect of three protocols on the preservation of hemodynamic function in isolated rat hearts after hypothermic storage. These protocols were: (1) pretreatment of the heart with a potassium channel opener (200 microM pinacidil); (2) storage of the heart in an aspartate-enriched extracellular cardioplegic solution containing the lazaroid antioxidant, U74500A (30 microM); and (3) a combination of protocols 1 and 2.

METHODS

Hearts from Wistar rats were perfused on a Langendorff apparatus. After stabilization in working mode, baseline measurements of heart rate, coronary and aortic flow, and cardiac output were performed. Hearts (n=6 in each group) were then randomized to protocols 1-3, untreated controls, or vehicle-treated controls. Hearts were stored in extracellular-based preservation solution for 12 hr at 2-3 degrees C, remounted on the perfusion apparatus, and stabilized as before; hemodynamic measurements were then repeated.

RESULTS

Recovery of hemodynamic function was enhanced by pinacidil pretreatment or incorporation of lazaroid in the storage solution, but the combination of these two treatments produced the best results.

CONCLUSIONS

Combined pharmacological activation of ATP-sensitive potassium channels before cardioplegia and the addition of U74500A to the preservation solution is associated with significantly enhanced hemodynamic function in the isolated rat heart after 12 hr of hypothermic storage. These data suggest a novel use for these agents in the transplantation context.

Local inhibition of tyrosine kinase activity markedly attenuates the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Intimal hyperplasia is due to the migration and proliferation of vascular smooth muscle cells after bypass surgery. Tyrosine kinases are involved in many signal transduction pathways including cell proliferation. This study examines the effects of local treatment with the tyrosine kinase inhibitor, tyrphostin AG-51, on the formation of intimal hyperplasia in vein grafts.

MATERIALS AND METHODS

Thirty-nine New Zealand White rabbits underwent interposition bypass grafting of the carotid artery using the jugular vein. In the first group (TKI), tyrphostin AG-51 (5 mg), dissolved in 600 microliter of dimethyl sulfoxide and Ringer's lactate (2:1, v:v), was used to incubate the veins ex vivo prior to grafting and delivered locally in 2.5 ml of 30% pluronic gel after grafting. The second group (DMSO) received the same treatment but without tyrphostin. In the third group (control), tyrphostin and DMSO were omitted from the incubation and gel delivery solutions. Postoperatively, vein grafts were harvested on Day 3 for Western analysis using an antiphosphotyrosine antibody (PY-20) to assess for tyrosine kinase activity, and on Day 28 for either morphologic or contractile function studies.

RESULTS

Local application of the TKI to vein grafts resulted in a 49% reduction in intimal hyperplasia compared to DMSO-treated vein grafts (31 +/- 4 micrometer vs. 61 +/- 5 micrometer, P < 0.01). Treatment with DMSO alone reduced intimal hyperplasia by 28% compared to control (85 +/- 4 micrometer, P < 0.05). The contractile responses in the DMSO and TKI-treated vein grafts were equivalent. Western analysis showed a 39-fold decrease in tyrosine phosphorylation with TKI treatment compared to control.

CONCLUSION

This study demonstrates that local short-term treatment with TKI produces a 49% reduction in intimal hyperplasia and suggests that phosphorylation of tyrosine residues is involved in the signaling pathways leading to the development of intimal hyperplasia in vein grafts.

Local effects of nitric oxide supplementation and suppression in the development of intimal hyperplasia in experimental vein grafts

OBJECTIVES

The universal response of vein grafts after insertion into the arterial circulation is the development of intimal hyperplasia; smooth muscle cell proliferation and connective tissue deposition, which may be modulated in part by dysfunctional endothelial nitric oxide (NO) metabolism. This study examines the effects of single dose, local application by pluronic gel of a NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and an NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME) on the formation of intimal hyperplasia.

MATERIALS

Forty New Zealand white rabbits underwent jugular vein interposition grafting of the common carotid artery.

DESIGN

Ten animals were controls, 10 animals had the outer surface of the vein graft coated with 30% pluronic gel (2.5 ml), and 10 each were immersed for 15 min prior to insertion in Ringer lactate containing 10(-3) M of SNAP or L-NAME and then had their vein grafts coated with 2.5 ml of gel containing either SNAP (10(-3) M) or L-NAME (10(-3) M), which allows for sustained delivery for up to 6 h. On the 28th post operative day, the animals were sacrificed and vein grafts were harvested for morphology by electron microscopy (SEM and TEM) and dimensional analysis by videomorphometry.

RESULTS

All vein grafts developed intimal hyperplasia. On SEM the vein grafts had a confluent layer of endothelial cells with multiple layers of smooth muscle cells representing intimal hyperplasia in TEM. There were no demonstrable morphological differences between the four groups. Local treatment with SNAP produced a significant 36% decrease in mean intimal thickness (72 +/- 4 microns vs. 45 +/- 4 microns; mean +/- S.E.M.; p < 0.01) without a change in medial thickness compared to gel-only treated groups (58 +/- 6 microns vs. 61 +/- 7 microns; p = ns). Inhibition of NO synthase by L-NAME had no effect on the development of intimal hyperplasia (72 +/- 4 microns vs. 79 +/- 10 microns; p = ns); medial thickness was also unchanged.

CONCLUSION

These data confirm the protective effect of NO in vascular injury and suggest that NO synthase activity is either absent or reduced to such a level that further inhibition in this short time course is not relevant to the pathophysiology of vein graft intimal hyperplasia.

Oral monoterpene therapy (perillyl alcohol) reduces vein graft intimal hyperplasia

The development of intimal hyperplasia is recognized as a major impediment to graft patency. D-Limonenes are monoterpenes with a recognized cytostatic effect on cell proliferation by inhibiting posttranslational isoprenylation of p21ras and other small G-proteins. This study examines the effect of perillyl alcohol, an oral hydroxylated D-limonene, on the development of intimal hyperplasia and its associated smooth muscle cell physiological responses in an experimental model of vein bypass grafting. Twenty New Zealand white rabbits had a right carotid interposition bypass graft using the ipsilateral external jugular vein. Ten animals received chronic oral therapy with a perillyl alcohol (200 mg/kg/day; begun 5 days before surgery and continued until harvest) and 10 control animals received vehicle only. All animals were sacrificed on the 28th postoperative day. Vein grafts were harvested either for morphology/videomorphometry (n = 6 per group) or for in vitro isometric tension studies (n = 4; four 5-mm rings per graft). The cell proliferation and incorporation of [3H]thymidine into the cellular DNA of serum-stimulated rabbit aortic smooth muscle cells was also assessed in the presence of increasing concentrations of perillyl alcohol (10(-9)-10(-4) M). Perillyl alcohol treated vein grafts showed a 22% reduction in overall mean intimal thickness (54 +/- 4 microns vs 69 +/- 3 microns; P = 0.006) but a 25% increase in overall mean medial thickness (86 +/- 4 microns vs 61 +/- 3 microns). The intimal ratio of the perillyl alcohol treated vein grafts decreased by 27% compared to controls. Perillyl alcohol induced norepinephrine and serotonin hypersensitivity in vein grafts compared to controls. The IC50 for perillyl alcohol was 176 nM with maximal inhibition at 5 microM. Incubation of smooth muscle cell cultures with increasing concentrations of perillyl alcohol showed a dose-dependent decrease in in vitro cellular proliferation, maximal at 1 microM. Therapy with perillyl alcohol alters the early development of intimal hyperplasia reducing the intimal response but increasing the medial response without significant changes in the physiological responses of the smooth muscle cells. Modulating G-proteins will affect the intimal hyperplastic response in vein grafts.

Functional and histological differences in autogenous and allogenic vein grafts: two different vasculopathies?

The long-term biological characteristics and the functional and morphological changes that occur in fresh allografts are poorly understood. This study tests the hypothesis that the development of intimal hyperplasia and its associated functional changes are accelerated in an allograft compared to an autograft due to the additional immunological stimuli. Common carotid vein bypass grafts were performed in 40 New Zealand White rabbits: 20 received their ipsilateral jugular veins (autologous) and 20 received the fresh contralateral jugular veins from the control rabbit (allogenic). Electron microscopy was performed and intimal and medial dimensions were determined by videoplanimetry at 7, 14, and 28 days. Contraction and relaxation studies to a panel of agonists were also performed. The EC50's (agonist concentration which produces 50% of the maximal response) were calculated. All grafts remained patent. Allografts showed a 51% decrease in overall mean intimal thickness (41 +/- 3 microns vs. 83 +/- 12 microns; P < 0.01) and a 97% increase in overall mean medial thickness (140 +/- 15 microns vs. 71 +/- 3 microns; P < 0.01) compared to the autografts. The lumen of the allogenic vein grafts was equivalent to the autologous vein grafts. Overall mean total wall thickness only increased by 17%, 181 microns vs. 154 microns for allo- and autografts, respectively. The EC50 for norepinephrine, histamine, and bradykinin were similar in the auto- and allografts, while the EC50 to serotonin was significantly less in the allografts than in the autografts. Neither the precontracted auto- or allografts relaxed to acetylcholine or serotonin (receptor mediated, endothelium dependent). The EC50 for calcium ionophore (nonreceptor mediated, endothelium dependent) was equivalent in the auto- and allografts. The EC50 for the sodium nitroprusside-induced relaxation (endothelium independent) was significantly higher in the allograft than in the autograft. This study demonstrates that there are two different vasculopathies occurring in autografts and allografts: intimal hyperplasia is predominant in the autograft while an exaggerated medial response is predominant in the allograft. Serotonin contractility and endothelial-independent relaxation are enhanced in the allograft compared to the autograft.