Nifedipine treatment reduces resting calcium concentration, oxidative and apoptotic gene expression, and improves muscle function in dystrophic mdx mice

Duchenne Muscular Dystrophy (DMD) is a recessive X-linked genetic disease, caused by mutations in the gene encoding dystrophin. DMD is characterized in humans and in mdx mice by a severe and progressive destruction of muscle fibers, inflammation, oxidative/nitrosative stress, and cell death. In mdx muscle fibers, we have shown that basal ATP release is increased and that extracellular ATP stimulation is pro-apoptotic. In normal fibers, depolarization-induced ATP release is blocked by nifedipine, leading us to study the potential therapeutic effect of nifedipine in mdx muscles and its relation with extracellular ATP signaling. Acute exposure to nifedipine (10 µM) decreased [Ca(2+)]r, NF-κB activity and iNOS expression in mdx myotubes. In addition, 6-week-old mdx mice were treated with daily intraperitoneal injections of nifedipine, 1 mg/Kg for 1 week. This treatment lowered the [Ca(2+)]r measured in vivo in the mdx vastus lateralis. We demonstrated that extracellular ATP levels were higher in adult mdx flexor digitorum brevis (FDB) fibers and can be significantly reduced after 1 week of treatment with nifedipine. Interestingly, acute treatment of mdx FDB fibers with apyrase, an enzyme that completely degrades extracellular ATP to AMP, reduced [Ca(2+)]r to a similar extent as was seen in FDB fibers after 1-week of nifedipine treatment. Moreover, we demonstrated that nifedipine treatment reduced mRNA levels of pro-oxidative/nitrosative (iNOS and gp91(phox)/p47(phox) NOX2 subunits) and pro-apoptotic (Bax) genes in mdx diaphragm muscles and lowered serum creatine kinase (CK) levels. In addition, nifedipine treatment increased muscle strength assessed by the inverted grip-hanging test and exercise tolerance measured with forced swimming test in mdx mice. We hypothesize that nifedipine reduces basal ATP release, thereby decreasing purinergic receptor activation, which in turn reduces [Ca(2+)]r in mdx skeletal muscle cells. The results in this work open new perspectives towards possible targets for pharmacological approaches to treat DMD.

Electrical stimuli are anti-apoptotic in skeletal muscle via extracellular ATP. Alteration of this signal in Mdx mice is a likely cause of dystrophy

ATP signaling has been shown to regulate gene expression in skeletal muscle and to be altered in models of muscular dystrophy. We have previously shown that in normal muscle fibers, ATP released through Pannexin1 (Panx1) channels after electrical stimulation plays a role in activating some signaling pathways related to gene expression. We searched for a possible role of ATP signaling in the dystrophy phenotype. We used muscle fibers from flexor digitorum brevis isolated from normal and mdx mice. We demonstrated that low frequency electrical stimulation has an anti-apoptotic effect in normal muscle fibers repressing the expression of Bax, Bim and PUMA. Addition of exogenous ATP to the medium has a similar effect. In dystrophic fibers, the basal levels of extracellular ATP were higher compared to normal fibers, but unlike control fibers, they do not present any ATP release after low frequency electrical stimulation, suggesting an uncoupling between electrical stimulation and ATP release in this condition. Elevated levels of Panx1 and decreased levels of Cav1.1 (dihydropyridine receptors) were found in triads fractions prepared from mdx muscles. Moreover, decreased immunoprecipitation of Cav1.1 and Panx1, suggest uncoupling of the signaling machinery. Importantly, in dystrophic fibers, exogenous ATP was pro-apoptotic, inducing the transcription of Bax, Bim and PUMA and increasing the levels of activated Bax and cytosolic cytochrome c. These evidence points to an involvement of the ATP pathway in the activation of mechanisms related with cell death in muscular dystrophy, opening new perspectives towards possible targets for pharmacological therapies.

Exercise sensitizes skeletal muscle to extracellular ATP for IL-6 expression in mice

Active skeletal muscle synthesizes and releases interleukin-6 (IL-6), which plays important roles in the organism's adaptation to exercise. Autocrine/paracrine ATP signaling has been shown to modulate IL-6 expression. The aim of this study was to determine whether a period of physical activity modifies the ATP-induced IL-6 expression. BalbC mice were either subject to 5 weeks voluntary wheel running (VA) or kept sedentary (SED). Flexor digitorum brevis muscles were dissected, stimulated with different ATP concentrations (0-100 μM) and IL-6 mRNA levels were measured using qPCR. ATP evoked a concentration-dependent rise in IL-6 mRNA in both SED and VA mice. VA mice however, had significantly higher ATP sensitivity (pD2 pharmacological values: VA=5.58±0.02 vs. SED=4.95±0.04, p<0.05). Interestingly, in VA mice we observed a positive correlation between the level of physical activity and the IL-6 mRNA increase following fiber stimulation with 10 μM ATP. In addition, there were lower P2Y2- and higher P2Y14-receptor mRNA levels in skeletal muscles of VA compared to SED mice, showing plasticity of nucleotide receptors with exercise. These results suggest that exercise increases skeletal muscle ATP sensitivity, a response dependent on the level of physical activity performed. This could have an important role in the mechanisms controlling skeletal muscle adaptation to exercise and training.

Cav1.1 controls frequency-dependent events regulating adult skeletal muscle plasticity

An important pending question in neuromuscular biology is how skeletal muscle cells decipher the stimulation pattern coming from motoneurons to define their phenotype as slow or fast twitch muscle fibers. We have previously shown that voltage-gated L-type calcium channel (Cav1.1) acts as a voltage sensor for activation of inositol (1,4,5)-trisphosphate [Ins(1,4,5)P₃]-dependent Ca(2+) signals that regulates gene expression. ATP released by muscle cells after electrical stimulation through pannexin-1 channels plays a key role in this process. We show now that stimulation frequency determines both ATP release and Ins(1,4,5)P₃ production in adult skeletal muscle and that Cav1.1 and pannexin-1 colocalize in the transverse tubules. Both ATP release and increased Ins(1,4,5)P₃ was seen in flexor digitorum brevis fibers stimulated with 270 pulses at 20 Hz, but not at 90 Hz. 20 Hz stimulation induced transcriptional changes related to fast-to-slow muscle fiber phenotype transition that required ATP release. Addition of 30 µM ATP to fibers induced the same transcriptional changes observed after 20 Hz stimulation. Myotubes lacking the Cav1.1-α1 subunit released almost no ATP after electrical stimulation, showing that Cav1.1 has a central role in this process. In adult muscle fibers, ATP release and the transcriptional changes produced by 20 Hz stimulation were blocked by both the Cav1.1 antagonist nifedipine (25 µM) and by the Cav1.1 agonist (-)S-BayK 8644 (10 µM). We propose a new role for Cav1.1, independent of its calcium channel activity, in the activation of signaling pathways allowing muscle fibers to decipher the frequency of electrical stimulation and to activate specific transcriptional programs that define their phenotype.

Abstract P4-09-10: Prospective Analysis of Fatty Acid Synthase (FASN) in Breast Cancer Tissue of Early-Stage Breast Cancer Patients

Background: Cancer cells require nutrients to survive in the unfavorable microenvironment of primary solid tumors or metastases before angiogenesis development. Fatty acid synthase (FASN) is a multi-enzyme protein that catalyzes fatty acid synthesis. Expression levels of FASN are low or undetectable in normal human tissues except for the liver and the adipose tissue. In contrast, high levels of FASN expression have been detected in breast cancer tumors and other human carcinomas. Several reports highlight that FASN overexpression in tumor samples correlates with progression, aggressiveness and metastatic potential of the disease. In adition, some studies have suggested the same correlation with serum levels of FASN. Our aim was to analyze the association between the expression of tumor and serum levels of FASN with clinical and pathological prognostic factors in early-stage breast cancer patients.

Methods: Fifty-five patients with early-stage breast cancer treated with surgery and post-operative chemotherapy were included in the study. We prospectively measured the levels of FASN in tumor and serum samples. Clinical data included demographic characteristics, menarche, pregnancy, breast feeding, menopausal status and body mass index (BMI). Pathological and molecular data included: pathological state, histological grade, estrogen and progesterone receptors, HER2 status, p53 mutation and Ki 67 levels. FASN tissue expression levels were determined by IHC and circulating FASN levels were determined by ELISA. FASN expression was graded from 0 to 3+, meaning 0–1+ normal amounts of FASN protein compared to non-tumor breast tissue, 2+ moderate amounts and 3+ the highest levels of FASN expression. Baseline characteristics were summarized descriptively. Categorical variables were compared by c2 or Fisher's exact. For continuous variables, if the data are approximately normal, the two groups were compared using ANOVA. If the normality assumption is not warranted, then the Kruskall-Wallis test has been used.

Results: Median age was 49 (rage 33–77). 51% of the patients were menopausal and median BMI was 24,75. Thirty-four percent of the patients had stage I, 51% stage II and 15% stage III. We observed a statistically significant association between FASN over expression and the lack of progesterone receptors (p = 0.027) in tumor samples. In contrast, we found no relation between FASN and estrogen receptor nor between FASN and HER2 tumor expression in this setting. Menopause and age were strongly related to higher levels of FASN tumor expression (p &lt; 0.001). Patients with higher BMI had higher levels of FASN in tumor tissue although this association was not statistically significant (p = 0.07). Finally, we observed a positive relation between breast cancer stage and the levels of FASN tumor (p = 0.05). In contrast, circulating FASN levels were not associated with any pathological or clinical prognostic factor.

Conclusions: Our study suggests that FASN overexpression is significantly related to age, menopausal status, more advanced stages and lack of progesterone receptor expression in early-stage breast cancer patients. However, no relation between serum levels of FASN and the clinical or molecular prognostic factors have been observed.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-09-10.

[Genetic bases of attention deficit hyperactivity disorder]

AIMS

The purpose of this study is to update the information available on the main group of genes that have been related with a susceptibility to attention deficit hyperactivity disorder (ADHD) or with the pharmacological response to different drugs used in the treatment of ADHD, in a number of different association and meta-analysis studies.

DEVELOPMENT

Different studies have provided evidence of the importance of the genetic load in the susceptibility to ADHD. The work carried out to date point to genes in the dopaminergic system, such as the gene that codes for the dopamine transporter (DAT1 or SLC6A3) and for the dopamine receptor D4 (DRD4); in the noradrenergic system, like the gene coding for the adrenergic alpha-2A receptor (ADRA2A), the COMT gene, which codes for the enzyme catechol-O-methyltransferase and the gene that codes for latrophilin 3 (LPHN3), as genes that are candidates for playing a part in the susceptibility to ADHD, and being involved in the pharmacological response as well as in the risk of presenting associated behavioural disorders. On the other hand, the genes involved in regulating the metabolism of the drugs used in the treatment of ADHD, such as the gene CYP2D6 and gene CES1, play a role in the efficiency and tolerance of these psycho-pharmaceuticals.

CONCLUSIONS

Although in recent years there has been an increase in the number of pharmacogenetic studies conducted on ADHD, findings differ significantly from one study to another. Integrating and meta-analytical studies are needed to be able to develop a more personalised treatment for ADHD.

Association of neurexin 3 polymorphisms with smoking behavior

The Neurexin 3 gene (NRXN3) has been associated with dependence on various addictive substances, as well as with the degree of smoking in schizophrenic patients and impulsivity among tobacco abusers. To further evaluate the role of NRXN3 in nicotine addiction, we analyzed single nucleotide polymorphisms (SNPs) and a copy number variant (CNV) within the NRXN3 genomic region. An initial study was carried out on 157 smokers and 595 controls, all of Spanish Caucasian origin. Nicotine dependence was assessed using the Fagerström index and the number of cigarettes smoked per day. The 45 NRXN3 SNPs genotyped included all the SNPs previously associated with disease, and a previously described deletion within NRXN3. This analysis was replicated in 276 additional independent smokers and 568 controls. Case-control association analyses were performed at the allele, genotype and haplotype levels. Allelic and genotypic association tests showed that three NRXN3 SNPs were associated with a lower risk of being a smoker. The haplotype analysis showed that one block of 16 Kb, consisting of two of the significant SNPs (rs221473 and rs221497), was also associated with lower risk of being a smoker in both the discovery and the replication cohorts, reaching a higher level of significance when the whole sample was considered [odds ratio = 0.57 (0.42-0.77), permuted P = 0.0075]. By contrast, the NRXN3 CNV was not associated with smoking behavior. Taken together, our results confirm a role for NRXN3 in susceptibility to smoking behavior, and strongly implicate this gene in genetic vulnerability to addictive behaviors.

Cortisol responses in children and adults with attention deficit hyperactivity disorder (ADHD): a possible marker of inhibition deficits

Attention deficit hyperactivity disorder (ADHD) is a heterogeneous disease whose neurobiological background is not completely understood. It has been proposed that deficits of the inhibitory function with an underactive behavioral inhibition system (BIS) may be in the core of ADHD. In this regard, this review summarizes all studies that examine the involvement of cortisol in ADHD. Differences in cortisol responses from different ADHD subtypes, hyperactive/impulsive, inattentive, and combined, are analyzed. In addition, we examine the role of comorbidities as confounding factors in the study of cortisol in ADHD, including comorbid disruptive behavioral disorder (DBD), as well as anxiety and depressive disorders. Because ADHD is a neurodevelopmental condition and approximately half of the children enter adulthood with the disorder, we review cortisol studies in adults and children separately. Two diverse patterns of cortisol have been reported both in children and adults with ADHD. Blunted cortisol responses to stress are associated with comorbid DBD, whereas high cortisol responses are associated to comorbid anxiety disorders. Nevertheless, the inhibitory deficits in ADHD do not appear to be related directly to cortisol deficits in either children or adults. This review increases our understanding of the heterogeneity of ADHD and could help in determining new strategies for the treatment of these patients. Future studies including gender and a more systematic methodology to study the cortisol response are needed.

Functional improvement and correlations with symptomatic improvement in adults with attention deficit hyperactivity disorder receiving long-acting methylphenidate

BACKGROUND

Data on the relationship between core symptoms and daily functioning in adults with attention deficit hyperactivity disorder (ADHD) are limited. Daily functioning was assessed as part of an open-label extension, and associations with symptom scores were evaluated.

METHOD

After a 5-week double-blind study with adults with ADHD receiving osmotic-controlled release oral delivery system (OROS) methylphenidate (MPH) 18, 36 or 72 mg/day, or placebo, participants were eligible for a 7-week open-label extension in which all patients received OROS MPH. Data for the Conners' Adult ADHD Rating Scale - Observer: Screening Version (CAARS-O:SV) (primary endpoint) have been presented previously. Secondary endpoints included the observer self-reported short version of the CAARS (CAARS-S:S) and the Clinical Global Impressions - Severity Scale (CGI-S). Daily functioning and quality of life were assessed using the Sheehan Disability Scale (SDS) and the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q) respectively. In post-hoc analyses, changes in CAARS-O:SV were evaluated in subgroups. Relationships between symptom and functional outcomes were evaluated in a multivariate regression analysis.

RESULTS

A total of 370 patients entered the open-label extension. Significant improvements from baseline in CAARS-O:SV were similar regardless of sex, ADHD subtype, prior treatment or psychiatric co-morbidity. Significant improvements from double-blind baseline were also seen for the CAARS-S:S, CGI-S, SDS and Q-LES-Q. Improvements in the CAARS-O:SV Hyperactivity/Impulsivity subscale were associated with improvements in SDS total and subscale scores, and in the Q-LES-Q score at open-label endpoint. Improvements in CAARS-O:SV Inattention subscale and CGI-S scores were not significantly associated with functional changes.

CONCLUSIONS

Improvements in ADHD symptoms relating to hyperactivity and impulsivity in adults receiving OROS MPH are associated with improvements in daily functioning and quality of life.

Risk factors for cocaine-induced psychosis in cocaine-dependent patients

Cocaine consumption can induce transient psychotic symptoms, expressed as paranoia or hallucinations. Cocaine induced psychosis (CIP) is common but not developed in all cases. This is the first European study on the relationship between CIP, consumption pattern variables and personality disorders. We evaluated 173 cocaine-dependent patients over 18 years; mostly males, whose average age was 33.6 years (SD = 7.8). Patients attending an outpatient addictions department were enrolled in the study and subsequently systematically evaluated using SCID I and SCID II interviews for comorbid disorders, a clinical interview for psychotic symptoms and EuropASI for severity of addiction. A high proportion of cocaine dependent patients reported psychotic symptoms under the influence of cocaine (53.8%), the most frequently reported being paranoid beliefs and suspiciousness (43.9%). A logistic regression analysis was performed, finding that a model consisting of amount of cocaine consumption, presence of an antisocial personality disorder and cannabis dependence history had 66.2% sensitivity 75.8% specificity predicting the presence of CIP. In our conclusions, we discuss the relevance of evaluating CIP in all cocaine dependent-patients, and particularly in those fulfilling the clinical profile derived from our results. These findings could be useful for a clinical approach to the risks of psychotic states in cocaine-dependent patients.