The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP.

The spinocerebellar ataxias (SCAs) are a class of incurable diseases characterized by degeneration of the cerebellum that results in movement disorder. Recently, a new heritable form of SCA, spinocerebellar ataxia type 48 (SCA48), was attributed to dominant mutations in STIP1 homology and U box-containing 1 (STUB1); however, little is known about how these mutations cause SCA48. STUB1 encodes for the protein C terminus of Hsc70 interacting protein (CHIP), an E3 ubiquitin ligase. CHIP is known to regulate proteostasis by recruiting chaperones via a N-terminal tetratricopeptide repeat domain and recruiting E2 ubiquitin-conjugating enzymes via a C-terminal U-box domain. These interactions allow CHIP to mediate the ubiquitination of chaperone-bound, misfolded proteins to promote their degradation via the proteasome. Here we have identified a novel, de novo mutation in STUB1 in a patient with SCA48 encoding for an A52G point mutation in the tetratricopeptide repeat domain of CHIP. Utilizing an array of biophysical, biochemical, and cellular assays, we demonstrate that the CHIPA52G point mutant retains E3-ligase activity but has decreased affinity for chaperones. We further show that this mutant decreases cellular fitness in response to certain cellular stressors and induces neurodegeneration in a transgenic Caenorhabditis elegans model of SCA48. Together, our data identify the A52G mutant as a cause of SCA48 and provide molecular insight into how mutations in STUB1 cause SCA48.

Effect of scheduling tramadol as a controlled substance on poison center exposures to tramadol.

BACKGROUND: There is limited information on the effect of scheduling a drug as a controlled substance with comparable data from both a pre-scheduling and post-scheduling time period. OBJECTIVE: To investigate the temporal changes on poisoning cases involving tramadol in 4 states: 2 states where it has been scheduled and 2 where it is not scheduled. METHODS: Databases were searched for all cases involving tramadol reported from 2003 through 2009 at 6 regional poison centers that served Arkansas, Kentucky, Ohio, and West Virginia. To allow for comparison based on population, state population estimates were obtained from the US Census Bureau. RESULTS: Over the 7-year study period, the number of tramadol cases increased from 401 per year to 1009 cases per year. The mean annual increase in tramadol cases for all 4 states ranged from 8.8% to 14.1%. Post-scheduling in Arkansas and Kentucky, there was a mean decrease in cases of 4% and 31%, respectively. During this same period, the comparison states of West Virginia and Ohio showed a continued increase of 14% and 23%, respectively. The mean annual increase in tramadol cases per 100,000 population for all 4 states ranged from 16% to 31%. Post-scheduling of tramadol, there was an annual decrease in tramadol human exposures of 5% to 31% in Arkansas and Kentucky, respectively. During this same period, West Virginia and Ohio showed a continued annual increase of 14%. CONCLUSIONS: The decrease in the number of cases of tramadol exposure following its addition to the schedule of controlled substances in Kentucky and Arkansas suggests that adding a drug to the schedule of controlled substances may result in a decrease in poisoning exposures related to that drug.

Antibodies against the carboxyl-terminal end of the Trypanosoma cruzi ribosomal P proteins are pathogenic.

Sera from patients with chronic Chagas heart disease recognize the carboxyl-terminal regions of the Trypanosoma cruzi ribosomal P proteins defined by B cell epitopes P013 (EDDDDDFGMGALF) and R13 (EEEDDDMGFGLFD) corresponding to the T. cruzi ribosomal P0 (TcP0) and P2beta (TcP2beta) proteins, respectively. It has been hypothesized that both epitopes may induce antibodies that cross-react and stimulate the beta1-adrenoreceptor. However, no proof as to their pathogenicity has been obtained. We investigated the consequences of immunizing mice with either TcP0 or TcP2beta proteins. Of 24 immunized animals, 16 generated antibodies against the carboxyl-terminal end of the corresponding protein, 13 of which showed an altered ECG (P<0.001, 81%). Immunization with TcP0 induced anti-P013 antibodies that bind to and stimulate cardiac G-protein-coupled receptors and are linked to the induction of supraventricular arrhythmia, repolarization, and conduction abnormalities as monitored by serial electrocardiographic analysis. In contrast, immunization with TcP2beta generated anti-R13 antibodies with an exclusive beta1-adrenergic-stimulating activity whose appearance strictly correlated with the recording of supraventricular tachycardia and death. These findings demonstrate that anti-P antibodies are arrhythmogenic in the setting of a normal heart, since no inflammatory lesions or fibrosis were evident to light microscopic examination.

Behavior of atrial natriuretic factor in an experimental model of Trypanosoma cruzi infection in rats.

Enhanced atrial natriuretic factor (ANF) production by the heart is related to hemodynamic overload, cardiac growth, and hypertrophy. The heart is one of the most affected organs during Trypanosoma cruzi infection. We tested the hypothesis that myocarditis produced by parasite infection alters the natriuretic peptide system by investigating the behavior of plasma ANF during the acute and chronic stages of T. cruzi infection in rats. Sprague-Dawley rats were infected with T. cruzi clone Sylvio-X10/7. Cardiac morphology showed damage to myocardial cells and lymphocyte infiltration in the acute phase; and fibrosis and cell atrophy in the chronic period. Plasma ANF levels (radioimmunoassay) were significantly higher in acute (348 +/- 40 vs. 195 +/- 36 pg/ml, P < 0.05, n = 17) and chronic T. cruzi myocarditis (545 +/- 81 vs. 229 +/- 38 pg/ml, P < 0.001, n = 11) than in their respective controls (n = 10 and 14). Rats in the chronic phase also showed higher levels than rats in the acute phase (P < 0.01). The damage of myocardial cells produced by the parasite and the subsequent inflammatory response could be responsible for the elevation of plasma ANF during the acute period of T. cruzi infection. The highest plasma ANF levels found in chronically infected rats could be derived from the progressive failure of cardiac function.

Antibodies against myosin in sera of patients with idiopathic paroxysmal atrial fibrillation.

INTRODUCTION: Circulating autoantibodies against myosin heavy chain have been detected in patients with ventricular myocarditis and in patients with dilated cardiomyopathy. This study investigated the presence of antibodies against myosin in sera of healthy control persons as compared with patients with idiopathic paroxysmal atrial fibrillation refractory to antiarrhythmic therapy. METHODS AND RESULTS: An SDS-PAGE (sodium dodecylsulfate polyacrylamide gel electrophoresis) procedure, followed by Western blotting with homogenates and membrane fractions of human left ventricular and atrial specimen as antigens, was used to analyze sera of 10 patients with idiopathic paroxysmal atrial fibrillation and 10 age-matched healthy control subjects. Circulating immunoglobulin G reactivity against cardiac myosin heavy chain was detected in 6 patients (60%) as compared with 1 control subject (10%). This difference was statistically significant (P < 0.05). All patients with idiopathic paroxysmal atrial fibrillation who showed reactivity against myosin heavy chain also had specific reactivity in their sera that exhibited reactivities to both ventricular and atrial cardiac myosin heavy chain isoforms. CONCLUSION: This study demonstrates the presence of circulating autoantibodies against myosin heavy chain in a significant percentage of patients with idiopathic paroxysmal atrial fibrillation and raises the possibility of an autoimmune process in some patients with paroxysmal atrial fibrillation.

Tolerance to lower body negative pressure exposure: comparison between patients with neurocardiogenic syncope and controls.

Lower body negative pressure exposure (LBNPE) produces hemodynamic modifications similar to those produced by head-up tilt test (HUT). Patients with vasovagal syncope are more susceptible to HUT than healthy persons. The supine position during LBNPE would facilitate the simultaneous performance of complementary methods. The aim of this study was to compare tolerance to LBNPE between a group of patients with vasovagal syncope and a group of healthy volunteers. Eleven patients with vasovagal syncope and positive HUT and 13 healthy volunteers without prior history of syncope and negative HUT were included. The following protocol was used: -10 mmHg, 1 minute; -20 mmHg, 1 minute; -30 mmHg, 3 minutes, and -40, -50, -60, and -70 mmHg, 5 minutes for each stage. Tolerance was expressed as: maximum tolerated negative pressure (Max NP), maximum tolerated time (Max T), and sigma P x T, where P = pressure and T = time. Syncope or presyncope during the test was considered positive LBNPE. LBNPE was positive at -50 or -60 mmHg in 8 of 11 patients (73%). One healthy volunteer had presyncope after 5 minutes at -70 mmHg. Tolerance, as expressed by any of the three parameters, was significantly higher for the healthy volunteers (Max NP: -59.1 +/- 7.9 vs -70, P < 0.01; Max T: 19.1 +/- 4.2 vs 24.4 +/- 0.3, P < 0.01; sigma P x T: 836.3 +/- 269.5 vs 1214.6 +/- 18, P < 0.01). We conclude that patients with neurocardiogenic syncope have a significantly lower tolerance to LBNPE than subjects with no previous history of syncope.

Reproducibility of head-up tilt test in patients with syncope.

As the head-up tilt test (HUT) is employed to verify the efficacy of undertaking a treatment, we prospectively evaluated the reproducibility of positive and negative results, as well as that of the response type in 64 consecutive patients (mean age 34.6 +/- 22.9 years) with syncope of unknown cause. Two HUTs (60 min, 75 degrees), separated by an interval of 9.77 +/- 8.21 days, were performed on each patient. Positive responses were reproduced in the second HUT in 54.5% of the patients. A greater reproducibility (84.3%) was observed for negative responses. Of the 31 patients with a negative first test, 5 had a positive response during the second HUT. Using a multivariate analysis, no clinical variable correlated with the reproducibility of positive or negative results. Likewise, neither arterial pressure nor heart rate observed during the test were correlated with reproducibility. Of 18 patients who reproduced positive responses, 12 (66.6%) did so with the same response modality. In three patients with documented monomorphic sustained ventricular tachycardia, which was hemodynamically well tolerated, and in one patient with temporal spike wave activity in the electroencephalogram, HUT was also positive. It was concluded that the low reproducibility of HUT limits its usefulness as a tool for evaluating treatment efficacy. The variability of the type of response suggests a common mechanism leading to cardioinhibitory and vasodepressor reactions. A positive result in only the second study shows the rationale of performing two tests when the first one is negative.