Aberrant S-nitrosylation mediates calcium-triggered ventricular arrhythmia in the intact heart

Nitric oxide (NO) derived from the activity of neuronal nitric oxide synthase (NOS1) is involved in S-nitrosylation of key sarcoplasmic reticulum (SR) Ca²⁺ handling proteins. Deficient S-nitrosylation of the cardiac ryanodine receptor (RyR2) has a variable effect on SR Ca²⁺ leak/sparks in isolated myocytes, likely dependent on the underlying physiological state. It remains unknown, however, whether such molecular aberrancies are causally related to arrhythmogenesis in the intact heart. Here we show in the intact heart, reduced NOS1 activity increased Ca²⁺-mediated ventricular arrhythmias only in the setting of elevated myocardial [Ca²⁺]_i. These arrhythmias arose from increased spontaneous SR Ca²⁺ release, resulting from a combination of decreased RyR2 S-nitrosylation (RyR2-SNO) and increased RyR2 oxidation (RyR-SOx) (i.e., increased reactive oxygen species (ROS) from xanthine oxidoreductase activity) and could be suppressed with xanthine oxidoreductase (XOR) inhibition (i.e., allopurinol) or nitric oxide donors (i.e., S-nitrosoglutathione, GSNO). Surprisingly, we found evidence of NOS1 down-regulation of RyR2 phosphorylation at the Ca²⁺/calmodulin-dependent protein kinase (CaMKII) site (S2814), suggesting molecular cross-talk between nitrosylation and phosphorylation of RyR2. Finally, we show that nitroso–redox imbalance due to decreased NOS1 activity sensitizes RyR2 to a severe arrhythmic phenotype by oxidative stress. Our findings suggest that nitroso–redox imbalance is an important mechanism of ventricular arrhythmias in the intact heart under disease conditions (i.e., elevated [Ca²⁺]_i and oxidative stress), and that therapies restoring nitroso–redox balance in the heart could prevent sudden arrhythmic death.Nitric oxide (NO) is an important regulator of cardiac function via both the activation of cyclic guanosine monophosphate-dependent signaling pathways and direct posttranslational modification of protein thiols (S-nitrosylation) (1). NO derived from the activity of neuronal nitric oxide synthase (NOS1) is involved in S-nitrosylation of key sarcoplasmic reticulum (SR) Ca²⁺ handling proteins (2). In particular, nitrosylation of both skeletal and cardiac muscle ryanodine receptors (RyR1 and RyR2, respectively) alters their release properties, favoring activation (3, 4). Notably, an increase in RyR2 open probability can cause spontaneous SR Ca²⁺ release, which may cause arrhythmias. Recently, it was shown that decreased RyR2 S-nitrosylation (RyR2-SNO) through loss of NOS1, was associated with increased spontaneous SR Ca²⁺ release events in isolated cardiomyocytes, following rapid pacing (5). In a separate study, NOS1 deficiency was shown to decrease spontaneous SR Ca²⁺ sparks and the open probability of RyR2 under resting conditions in cardiomyocytes and lipid bilayers, respectively (6). These studies suggest that NOS1 deficiency has a variable effect on RyR2 function, likely dependent on the underlying physiological state (i.e., rapid heart rate versus quiescence). It remains unknown, however, whether these changes create a substrate for arrhythmogenesis in the intact heart.It is increasingly evident that activities of nitric oxide and reactive oxygen species (ROS) are tightly coupled in cardiomyocytes producing nitroso–redox balance. Elevated ROS production (oxidative stress) is a hallmark of several cardiovascular diseases associated with increased risk of fatal ventricular arrhythmias [e.g., myocardial infarction (MI) and heart failure]. Burger et al. (7) recently demonstrated an increased incidence of ventricular arrhythmias following MI in NOS1-deficient mice. These data suggest that a nitroso–redox imbalance may be arrhythmogenic in the setting of MI. However, the molecular basis of the increased arrhythmogenesis is not known.In the current study, we found that decreased NOS1 activity increased Ca²⁺-mediated ventricular arrhythmias only in the setting of elevated myocardial [Ca²⁺]_i. These arrhythmias arose from increased spontaneous SR Ca²⁺ release resulting from a combination of decreased RyR2-SNO and increased RyR2 oxidation (RyR2-SOx) [i.e., increased ROS from xanthine oxidoreductase (XOR) activity] and could be suppressed with xanthine oxidoreductase inhibition (i.e., allopurinol) or nitric oxide donors (i.e., GSNO). Notably, we found evidence of NOS1 regulation of RyR2 phosphorylation at the Ca²⁺/calmodulin-dependent protein kinase (CaMKII) site (S2814), suggesting molecular cross-talk between the nitrosylation and phosphorylation states of RyR2. Finally, we show that nitroso–redox imbalance due to decreased NOS1 activity sensitizes RyR2 to a severe arrhythmic phenotype under oxidative stress.     

Improving outcomes in umbilical cord blood transplantation: State of the art

Only 30% of patients who require an allogeneic hematopoietic cell transplant will have a HLA matched sibling donor. Many patients, particularly those patients with diverse racial and ethnic backgrounds, may not be able to identify a suitably matched unrelated donor. Over 25,000 umbilical cord blood transplant procedures have been performed in the last 25 years. Considerable challenges exist in defining the appropriate conditioning regimen and graft vs host disease prophylaxis, surmounting issues of cell dose and delayed engraftment, and improving immune recovery. In this review, we discuss strategies to improve umbilical cord blood transplant outcomes, focusing on cord blood unit selection, expansion, and homing efficiency.     

A structured interview guide for global impressions: increasing reliability and scoring accuracy for CNS trials

Background

The clinical global impression of severity (CGI-S) scale is a frequently used rating instrument for the assessment of global severity of illness in Central Nervous System (CNS) trials. Although scoring guidelines have been proposed to anchor these scores, the collection of sufficient documentation to support the derived score is not part of any standardized interview procedure. It is self evident that the absence of a standardized, documentary format can affect inter-rater reliability and may adversely affect the accuracy of the resulting data.

Method

We developed a structured interview guide for global impressions (SIGGI) and evaluated the instrument in a 2-visit study of ambulatory patients with Major Depressive Disorder (MDD) or schizophrenia. Blinded, site-independent raters listened to audio recorded SIGGI interviews administered by site-based CGI raters. We compared SIGGI-derived CGI-S scores between the two separate site-based raters and the site-independent raters.

Results

We found significant intraclass correlations (p = 0.001) on all SIGGI-derived CGI-S scores between two separate site-based CGI raters with each other (r = 0.768) and with a blinded, site-independent rater (r = 0.748 and r = 0.706 respectively) and significant Pearson’s correlations between CGI-S scores with all MADRS validity comparisons for MDD and PANSS comparisons for schizophrenia (p- 0.001 in all cases). Compared to site-based raters, the site-independent raters gave identical “dual” CGI-S scores to 67.6% and 68.2% of subjects at visit 1 and 77.1% at visit 2.

Conclusion

We suggest that the SIGGI may improve the inter-rater reliability and scoring precision of the CGI-S and have broad applicability in CNS clinical trials.     

Concomitant dysregulation of androgen secretion and dysfunction of adipose tissue induced insulin resistance

Hyperandrogenism and hyperinsulinemia have resulted from dysfunction of the theca cell of the ovary and adipose tissue and each one potentiates the other in patients with androgen excess disorders e.g., polycystic ovary disease and idiopathic hirsutism. Possible external and/or internal triggers can produce such cellular dysfunction. There is evidence that sodium valproate acts as a trigger of cellular dysfunction and produces both hyperinsulinemia and hyperandrogenism. Therefore, the elimination of these triggers can help the patients to recover from hyperinsulinemia, insulin resistance and hyperandrogenism.