Molecular mechanisms of myocardial nitroso-redox imbalance during on-pump cardiac surgery.

BACKGROUND: The mechanism responsible for left ventricular dysfunction after cardiac surgery is only partly understood. In isolated rat hearts subjected to an ischaemia-reperfusion protocol, left ventricular dysfunction was associated with uncoupling of endothelial nitric oxide synthase (NOS) activity secondary to oxidation of the NOS cofactor, tetrahydrobiopterin (BH4). Here we investigated the effect of cardiopulmonary bypass and reperfusion on myocardial nitroso-redox balance in patients undergoing cardiac surgery. METHODS: From 116 patients who underwent elective cardiac surgery on cardiopulmonary bypass, paired samples of the right atrial appendages were obtained before venous cannulation of the right atrium and after myocardial reperfusion. Superoxide production from atrial samples was measured by lucigenin (5 µmol/L) enhanced chemiluminescence and 2-hydroxyethidium (2-OHE) detection by high-performance liquid chromatography (HPLC). BH4, oxidised biopterins, GTP-cyclohydrolase 1 (GTPCH-1, the rate-limiting enzyme in BH4 synthesis), and NOS activity ((14)C L-arginine to L-citrulline conversion) were measured by HPLC. FINDINGS: Atrial superoxide production increased significantly after reperfusion (from mean 37·83 relative light units per s per mg [SE 3·71] before cannulation to 65·02 [6·01] after reperfusion, p<0·0001; n=46 samples from 23 patients) due to increased mitochondrial and NOX2 oxidase activity (by 309% and 149%; p=0·002 and p=0·0002, respectively) and uncoupling of NOS activity. Atrial content of BH4 after perfusion was reduced (by 32%, p=0·001), as was activity of GTPCH1 (50%, p<0·0001). NOS activity decreased significantly after reperfusion (60%, p=0·0005) and this reduction was not affected by BH4 supplementation (10 µM) or NOX2 inhibition ex vivo. Instead, we identified increased endothelial NOS s-glutathionylation as the main mechanism for NOS uncoupling after reperfusion. Reversing NOS s-glutathionylation with dithiothreitol (100 µmol/L) completely restored NOS activity after reperfusion (p=0·34). INTERPRETATION: Our findings suggest that NOS s-glutathionylation, rather than BH4 depletion, accounts for NOS dysfunction in patients after cardiac surgery and cardiopulmonary bypass. FUNDING: British Heart Foundation.

Cardiomyocyte GTP cyclohydrolase 1 and tetrahydrobiopterin increase NOS1 activity and accelerate myocardial relaxation.

RATIONALE: Tetrahydrobiopterin (BH4) is an essential cofactor of nitric oxide synthases (NOS). Oral BH4 supplementation preserves cardiac function in animal models of cardiac disease; however, the mechanisms underlying these findings are not completely understood. OBJECTIVE: To study the effect of myocardial transgenic overexpression of the rate-limiting enzyme in BH4 biosynthesis, GTP cyclohydrolase 1 (GCH1), on NOS activity, myocardial function, and Ca2+ handling. METHODS AND RESULTS: GCH1overexpression significantly increased the biopterins level in left ventricular (LV) myocytes but not in the nonmyocyte component of the LV myocardium or in plasma. The ratio between BH4 and its oxidized products was lower in mGCH1-Tg, indicating that a large proportion of the myocardial biopterin pool was oxidized; nevertheless, myocardial NOS1 activity was increased in mGCH1-Tg, and superoxide release was significantly reduced. Isolated hearts and field-stimulated LV myocytes (3 Hz, 35°C) overexpressing GCH1 showed a faster relaxation and a PKA-mediated increase in the PLB Ser16 phosphorylated fraction and in the rate of decay of the [Ca2+]i transient. RyR2 S-nitrosylation and diastolic Ca2+ leak were larger in mGCH1-Tg and ICa density was lower; nevertheless the amplitude of the [Ca2+]i transient and contraction did not differ between genotypes, because of an increase in the SR fractional release of Ca2+ in mGCH1-Tg myocytes. Xanthine oxidoreductase inhibition abolished the difference in superoxide production but did not affect myocardial function in either group. By contrast, NOS1 inhibition abolished the differences in ICa density, Ser16 PLB phosphorylation, [Ca2+]i decay, and myocardial relaxation between genotypes. CONCLUSIONS: Myocardial GCH1 activity and intracellular BH4 are a limiting factor for constitutive NOS1 and SERCA2A activity in the healthy myocardium. Our findings suggest that GCH1 may be a valuable target for the treatment of LV diastolic dysfunction.

Effects of the crude extract of Polygala tenuifolia Willd on human sperm in vitro.

The aim of the present study is to analyze sperm membrane changes and the spermicidal effect in treatment with the crude extract from Polygala tenuifolia Willd (PTW) in vitro. The root of PTW was extracted in distilled water. Normal human spermatozoa were used to assess the spermicidal activity (Sander-Cramer assay) of the extract from the PTW root. The hypo-osmotic swelling (HOS) test and the eosin Y (EY) staining were used to detect the integrity of sperm membrane and vitality. The sperm chromatin dispersion (SCD) test was performed to determine sperm DNA integrity. N-9 was used as a reference standard and semen added to physiological saline was used as the control. Semen samples were donated by 42 healthy fertile men. The crude extract from the root of PTW could immobilize and kill 100% spermatozoa within 20 s in vitro at the concentrations of 20.0 and 10.0 mg/ml; at the concentration of 5.0 mg/ml, spermatozoa were immobilized in (39.5±3.2) s. In the groups of the crude extract from the root of PTW and N-9 solution, the rate of the normal HOS (tails swollen) and the white head (unstained) was 0%, and the rate of the abnormal HOS (tails unswollen) and red head (stained) was 100%. Sperm DNA fragmentation showed no change in exposure to the crude extract from the root of PTW and N-9 solution. The sperm revival test did not show any spermatozoa that recovered their motilities. The rapid spermicidal activity of the crude extract from the root of PTW in vitro may occur by the disruption of the sperm membrane integrity.

Antiangiogenic therapy for human pancreatic carcinoma xenografts in nude mice.

AIM: To investigate the anti-tumor effects of antiangiogenic therapy (a combination of TNP-470, an antiangiogenic compound, with gemcitabine, an antimetabolite) on human pancreatic carcinoma xenografts and its mechanism. METHODS: A surgical orthotopic implantation (SOI) model was established by suturing small pieces of SW1990 pancreatic carcinoma into the tail of pancreas in nude male mice. Mice then received either single therapy (n = 24) or combined therapy (n = 32). Mice receiving single therapy were randomly divided into control group, G100 group receiving 100 mg/kg gemcitabine IP on d 0, 3, 6 and 9 after transplantation, and T30 group receiving 30 mg/kg TNP-470 s.c on alternate days for 8 wk. Mice receiving combined therapy were randomly divided into control group, T15 group, G50 group and combination group (TNP-470 30 mg/kg and gemcitabine 50 mg/kg). Animals were killed 8 wk after transplantation. Transplanted tumors, liver, lymph node and peritoneum were removed. Weight of transplanted tumors, the T/C rate (the rate of mean treated tumor weight to mean control tumor weight), change of body weight, metastasis rate, and 9-wk survival rate were investigated. Tumor samples were taken from the control group, T30 group, G100 group and combination group. PCNA index (PI) and microvessel density (MVD) were investigated by immunohistochemical staining for PCNA and factor VIII, respectively. RESULTS: There was a significant inhibitory effect on primary tumor growth of pancreatic carcinoma in G100 group, compared to T30 group, whereas tumor metastasis was significantly inhibited in T30 group compared to G100 group. There was no significant improvement in survival rate in these two groups. No significant inhibitory effect on tumor growth and metastasis in T15 group and G50 group. However, significant anti-tumor and anti-metastatic effects were observed in the combination group with a significant improvement in survival rate. The inhibitory effect on tumor growth in combination group enhanced 2 times in comparison with G50 group and 5 times in comparison with T15 group. Moreover, 25% of the animals bearing tumors were cured by the combination therapy. The levels of MVD and PI were 14.50+/-5.93 and 0.41+/-0.02, 12.38+/-1.60 and 0.30+/-0.07, 7.13+/-2.99 and 0.37+/-0.03, and 5.21+/-1.23 and 0.23+/-0.02 respectively in the control group, G100 group, T30 group and combination group. A significant inhibitory effect on PI level and MVD level was observed in G100 group and T30 group respectively whereas both MVD and PI levels were significantly inhibited in the combination group (P<0.05). CONCLUSION: Antiangiogenic therapy shows significant anti-tumor and anti-metastatic effects, and is helpful to reduce the dosage of cytotoxic drugs and the side effects. These effects are related to the antiangiogenic effect of TNP-470 and cytotoxic effect of gemcitabine.