Response to Transdermal Selegiline Smoking Cessation Therapy and Markers in the 15q24 Chromosomal Region.

INTRODUCTION: Current treatments for smoking cessation have limited efficacy. A potential pharmaceutical treatment for smoking cessation is selegiline, a selective and irreversible monoamine oxidase B inhibitor. A few clinical trials have been carried out using selegiline but the results have been mixed. We sought to determine if genetic markers in cholinergic loci in the 15q24 chromosomal region predict response to smoking cessation therapy with selegiline. METHODS: We performed an 8-week double-blind, placebo-controlled clinical trial of the selegiline transdermal system in heavy smokers, with follow-up at weeks 25 and 52. Eight single nucleotide polymorphisms (SNPs) in the 15q24 region, which contains the genes for the nicotinic acetylcholine receptor subunits CHRNA5, CHRNA3, and CHRNB4, were investigated for association with treatment response. RESULTS: The CHRNB4 promoter SNP rs3813567 was associated with both point prevalence abstinence and post-quit craving. Carriers of the minor C allele treated with selegiline showed lower rates of abstinence and higher levels of craving than selegiline-treated non-carriers, indicating that the rs3813567 C allele adversely affects abstinence in selegiline-treated smokers. This effect was not present among placebo-treated smokers. Selegiline-treated smokers with the CHRNA5 rs680244 GG genotype had lower post-quit craving, and unlike placebo-treated GG-carrying smokers, did not experience a post-quit increase in depressive symptoms. CONCLUSIONS: Variants in genes encoding cholinergic receptors affect abstinence, craving and mood in selegiline-treated smokers. Selegiline primarily affects dopamine levels in the brain, but cholinergic input affects nicotine-induced dopaminergic activity. These markers may have value in identifying those likely to respond to selegiline for smoking cessation.

BDNF and CREB1 genetic variants interact to affect antidepressant treatment outcomes in geriatric depression.

AIM: Brain-derived neurotrophic factor (BDNF) is associated with antidepressant response on the cellular level, in animal models, and in clinical studies. A common variant in the BDNF gene results in a substitution of a methionine (Met) for a valine at the amino acid position 66. Previous studies reported that the Met variant results in enhanced response to antidepressant medications. These findings may be at odds with studies indicating that on a cellular level the Met variant impairs the secretion of BDNF. MATERIALS AND METHODS: We examined the effects of BDNF single nucleotide polymorphisms (SNPs) in response to the antidepressants paroxetine and mirtazapine in a sample of 246 geriatric patients with major depression, treated in a double-blind, randomized, 8-week clinical trial. We also examined the effects of genetic variation at the BDNF-related loci neurotrophic tyrosine kinase receptor 2, cyclic AMP responsive element binding protein 1 (CREB1), and CREB binding protein. A total of 53 SNPs were genotyped. RESULTS: BDNF genetic variation had a significant effect on the efficacy of paroxetine, with patients carrying the Met allele showing impaired response. SNPs at the CREB1 locus, which encodes a transcription factor important in BDNF signaling, also predicted response to paroxetine. Furthermore, we found a significant gene-gene interaction between BDNF and CREB1 that affected response to paroxetine. Because BDNF has been associated with cognitive function, we tested the effects of BDNF SNPs on change in a wide variety of cognitive tests over the 8-week trial, but there were no significant effects of genotype on cognition. CONCLUSION: These results provide new evidence for the importance of the BDNF pathway in antidepressant response in geriatric patients. The negative effect of the Met66 allele on antidepressant outcomes is consistent with basic science findings indicating a negative effect of this variant on BDNF activity in the brain. Further, the effect of BDNF genetic variation on antidepressant treatment is modified by variation in the gene encoding the downstream effector CREB1.

Markers in the 15q24 nicotinic receptor subunit gene cluster (CHRNA5-A3-B4) predict severity of nicotine addiction and response to smoking cessation therapy.

Stopping smoking is difficult even with treatment. Many patients prescribed pharmacologic treatments for smoking cessation experience side effects or lack of efficacy. We performed a pharmacogenetic study of the efficacy and tolerability of bupropion and transdermal nicotine (TN), two treatments for smoking cessation. Samples were drawn from two studies. In the first study (Maintenance 1, MT1), 301 smokers received bupropion plus TN for 11 weeks, followed by 14 weeks of placebo or bupropion. In the second study (MT2), 276 smokers received bupropion and TN for 8 weeks. We focused on eight SNPs in the 15q24 region, which contains the genes for the nicotinic cholinergic receptor subunits CHRNA5, CHRNA3, and CHRNB4, and has previously been implicated in nicotine addiction and smoking cessation. Analyses of baseline smoking quantity (SQ) identified an association between SQ and both the functional CHRNA5 SNP rs16969968 (D398N) and the CHRNA3 SNP rs1051730 (Y215Y) in a combined cohort containing MT1 and MT2. An association between SQ and ethnicity was also identified in the combined cohort. Pharmacogenetic analysis showed a significant association between rs8192475 (R37H) in CHRNA3 and both higher craving after quitting and increased withdrawal symptoms over time in MT2. Two markers for point prevalence abstinence, CHRNA5 SNP rs680244 and CHRNB4 SNP rs12914008, were also identified in MT2, with the strongest findings at week 52. These results provide further support for the role of the CHRNA5/A3/B4 subunits in determining number of cigarettes smoked and response to smoking cessation therapy.

ABCB1 (MDR1) polymorphisms and antidepressant response in geriatric depression.

OBJECTIVE: Variation in the ATP-binding cassette, subfamily B, member 1 transporter (ABCB1) (multidrug-resistance gene 1) gene has been investigated as a predictor of response to treatment with a variety of medications such as antiarrhythmics, chemotherapeutic agents, anti-HIV medications, and some psychotropics. The ABCB1 gene product, P-glycoprotein, affects the transport of drugs out of many cell types, including endothelial cells at the blood-brain barrier. We sought to determine if ABCB1 polymorphisms predict response to antidepressant treatment in geriatric patients. METHODS: We compared the effects of ABCB1 genetic variation on the therapeutic response to paroxetine, a P-glycoprotein substrate, and to mirtazapine, which is not thought to be transported by ABCB1, in a sample of 246 elderly patients with major depression treated in a clinical trial setting. A total of 15 single nucleotide polymorphisms in the ABCB1 gene were assessed in each patient. Two of these ABCB1 single nucleotide polymorphisms were earlier reported to predict treatment response in patients prescribed with P-glycoprotein substrate antidepressants. RESULTS: The two earlier identified ABCB1 markers for antidepressant response predicted time to remission in our paroxetine-treated patients, but not in the mirtazapine-treated patients. These results replicate the published findings of others. If a Bonferroni correction for type I error is made, our results do not reach the criteria for statistical significance. However, the Bonferroni correction may be too conservative given the strong linkage disequilibrium among some of the markers and our aim to replicate the earlier published findings. CONCLUSION: Our study provides confirmation that certain ABCB1 polymorphisms predict response to substrate medications in geriatric patients.

FKBP5 polymorphisms and antidepressant response in geriatric depression.

Genetic variation at the FKBP5 locus has been reported to affect clinical outcomes in patients treated with antidepressant medications in several studies. However, other reports have not confirmed this association. FKBP5 may regulate the sensitivity of the hypothalamic-pituitary-adrenal axis. We tested two FKBP5 single nucleotide polymorphisms (rs1360780 and rs3800373) in a sample of 246 geriatric patients treated for 8 weeks in a double-blind randomized comparison trial of paroxetine and mirtazapine. These two polymorphisms had previously been reported to predict efficacy in depressed patients treated with selective serotonin reuptake inhibitors such as paroxetine, and those treated with mirtazapine, an agent with both serotonergic and noradrenergic actions. However, we found no significant associations between these FKBP5 genetic variants and clinical outcomes. Neither mean Hamilton Depression Rating Scale scores nor time to remission or response were predicted by FKBP5 genetic variation. These results suggest that FKBP5 is unlikely to play a major role in determining antidepressant treatment outcomes in geriatric patients.

Gene expression profile of the PDAPP mouse model for Alzheimer's disease with and without Apolipoprotein E.

The APOE epsilon 4 allele is a strong risk factor for Alzheimer's disease (AD). However, the molecular basis for this effect remains unclear. We examined expression of approximately 12,000 genes and expressed sequence tags in the hippocampus and cortex of PDAPP (APP(V717)) mice modeling AD that show extensive amyloid beta (A beta) deposition, and in PDAPP mice lacking murine APOE expression, which show marked attenuation of A beta deposition in the brain. Wild type and APOE knockout animals were also examined. Expression levels were determined at the initial stage of A beta deposition, as well as in older animals showing extensive neuropathological changes. Fifty-four transcripts were identified using our statistical analysis as differentially regulated between the PDAPP and PDAPP/APOE ko mice, whereas 31 transcripts were classified as differentially regulated among PDAPP mice and WT animals, and seven transcripts were identified as regulated between the PDAPP/APOE ko animals and the APOE ko animals. Interestingly, many of the differentially regulated genes we detected can be related to biological processes previously shown to be important in AD pathophysiology, including inflammation, calcium homeostasis, cholesterol transport and uptake, kinases and phosphatases involved in tau phosphorylation and dephosphorylation, mitochondrial energy metabolism, protein degradation, neuronal growth, endoplasmic reticulum (ER) stress related proteins, antioxidant activity, cytoskeletal organization, and presenilin binding proteins. Regulated genes also included some not directly associated with AD in the past but likely to be involved in known AD pathophysiologic mechanisms, and others that may represent completely novel factors in the pathogenesis of AD. These results provide a global molecular profile of hippocampal and cortical gene expression during the initial and intermediate stages Abeta deposition, and the effects of APOE deletion on this process.

Utilization of diagnostic medical imaging: comparison of radiologist referral versus same-specialty referral.

PURPOSE: To retrospectively compare the frequency with which patients underwent diagnostic medical imaging procedures during episodes of outpatient medical care according to whether their physicians referred patients for imaging to themselves and/or physicians in their same specialty or to radiologists. MATERIALS AND METHODS: Institutional review board approval was not necessary for this HIPAA-compliant study. An insurance claims database from a large national employer-based health plan was obtained. Claims data from 1999-2003 were grouped into episodes of care for six conditions: cardiopulmonary disease, coronary and/or cardiac disease, extremity fracture, knee pain, intraabdominal malignancy, and stroke. For each condition, each referring physician's behavior was categorized as either "same-specialty referral" or "radiologist referral" on the basis of that physician's entire history of imaging referrals for the condition. The frequency with which patients underwent diagnostic medical imaging procedures during episodes of care was compared according to whether their physicians referred patients for imaging to themselves and/or same-specialty physicians or to radiologists. Rates were compared by using chi(2) tests, and logistic regression was used to compare utilization rates, with patient age and number of comorbidities as covariates. RESULTS: For the conditions evaluated, physicians who referred patients to themselves or to other same-specialty physicians for diagnostic imaging used imaging between 1.12 and 2.29 times as often, per episode of care, as physicians who referred patients to radiologists (P < .005 for all comparisons). Adjusting for patient age and comorbidity, the likelihood of imaging was 1.196-3.228 times greater for patients cared forby same-specialty-referring physicians. CONCLUSION: Same-specialty-referring physicians tend to utilize imaging more frequently than do physicians who refer their patients to radiologists. These results cannot be explained by differences in case mix (because analyses were performed within six specific conditions of interest), patient age, or comorbidity.

Analysis of neuronal gene expression with laser capture microdissection.

The brain is a heterogeneous tissue in which the numbers of neurons, glia, and other cell types vary among anatomic regions. Gene expression studies performed on brain homogenates yield results reflecting mRNA abundance in a mixture of cell types. Therefore, a method for quantifying gene expression in individual cell populations would be useful. Laser capture microdissection (LCM) is a new technique for obtaining pure populations of cells from heterogeneous tissues. Most studies thus far have used LCM to detect DNA sequences. We developed a method to quantify gene expression in hippocampal neurons from mouse brain using LCM and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). This method was optimized to permit histochemical or immunocytochemical visualization of nerve cells during LCM while minimizing RNA degradation. As an example, gene expression was quantified in hippocampal neurons from the Tg2576 mouse model for Alzheimer's disease.