The integration of pharmacophore-based 3D QSAR modeling and virtual screening in safety profiling: A case study to identify antagonistic activities against adenosine receptor, A2A, using 1,897 known drugs.

Safety pharmacology screening against a wide range of unintended vital targets using in vitro assays is crucial to understand off-target interactions with drug candidates. With the increasing demand for in vitro assays, ligand- and structure-based virtual screening approaches have been evaluated for potential utilization in safety profiling. Although ligand based approaches have been actively applied in retrospective analysis or prospectively within well-defined chemical space during the early discovery stage (i.e., HTS screening and lead optimization), virtual screening is rarely implemented in later stage of drug discovery (i.e., safety). Here we present a case study to evaluate ligand-based 3D QSAR models built based on in vitro antagonistic activity data against adenosine receptor 2A (A2A). The resulting models, obtained from 268 chemically diverse compounds, were used to test a set of 1,897 chemically distinct drugs, simulating the real-world challenge of safety screening when presented with novel chemistry and a limited training set. Due to the unique requirements of safety screening versus discovery screening, the limitations of 3D QSAR methods (i.e., chemotypes, dependence on large training set, and prone to false positives) are less critical than early discovery screen. We demonstrated that 3D QSAR modeling can be effectively applied in safety assessment prior to in vitro assays, even with chemotypes that are drastically different from training compounds. It is also worth noting that our model is able to adequately make the mechanistic distinction between agonists and antagonists, which is important to inform subsequent in vivo studies. Overall, we present an in-depth analysis of the appropriate utilization and interpretation of pharmacophore-based 3D QSAR models for safety screening.

Intravital Multiphoton Microscopy with Fluorescent Bile Salts in Rats as an In Vivo Biomarker for Hepatobiliary Transport Inhibition.

The bile salt export pump (BSEP) is expressed at the canalicular domain of hepatocytes, where it mediates the elimination of monovalent bile salts into the bile. Inhibition of BSEP is considered a susceptibility factor for drug-induced liver injury that often goes undetected during nonclinical testing. Although in vitro assays exist for screening BSEP inhibition, a reliable and specific method for confirming Bsep inhibition in vivo would be a valuable follow up to a BSEP screening strategy, helping to put a translatable context around in vitro inhibition data, incorporating processes such as metabolism, protein binding, and other exposure properties that are lacking in most in vitro BSEP models. Here, we describe studies in which methods of quantitative intravital microscopy were used to identify dose-dependent effects of two known BSEP/Bsep inhibitors, 2-[4-[4-(butylcarbamoyl)-2-[(2,4-dichlorophenyl)sulfonylamino]phenoxy]-3-methoxyphenyl]acetic acid (AMG-009) and bosentan, on hepatocellular transport of the fluorescent bile salts cholylglycyl amidofluorescein and cholyl-lysyl-fluorescein in rats. Results of these studies demonstrate that the intravital microscopy approach is capable of detecting Bsep inhibition at drug doses well below those found to increase serum bile acid levels, and also indicate that basolateral efflux transporters play a significant role in preventing cytosolic accumulation of bile acids under conditions of Bsep inhibition in rats. Studies of this kind can both improve our understanding of exposures needed to inhibit Bsep in vivo and provide unique insights into drug effects in ways that can improve our ability interpret animal studies for the prediction of human drug hepatotoxicity.

Modeling Therapeutic Antibody-Small Molecule Drug-Drug Interactions Using a Three-Dimensional Perfusable Human Liver Coculture Platform.

Traditional in vitro human liver cell culture models lose key hepatic functions such as metabolic activity during short-term culture. Advanced three-dimensional (3D) liver coculture platforms offer the potential for extended hepatocyte functionality and allow for the study of more complex biologic interactions, which can improve and refine human drug safety evaluations. Here, we use a perfusion flow 3D microreactor platform for the coculture of cryopreserved primary human hepatocytes and Kupffer cells to study the regulation of cytochrome P450 3A4 isoform (CYP3A4) activity by chronic interleukin 6 (IL-6)-mediated inflammation over 2 weeks. Hepatocyte cultures remained stable over 2 weeks, with consistent albumin production and basal IL-6 levels. Direct IL-6 stimulation that mimics an inflammatory state induced a dose-dependent suppression of CYP3A4 activity, an increase in C-reactive protein (CRP) secretion, and a decrease in shed soluble interleukin-6 receptor (IL-6R) levels, indicating expected hepatic IL-6 bioactivity. Tocilizumab, an anti-IL-6R monoclonal antibody used to treat rheumatoid arthritis, has been demonstrated clinically to impact small molecule drug pharmacokinetics by modulating cytochrome P450 enzyme activities, an effect not observed in traditional hepatic cultures. We have now recapitulated the clinical observation in a 3D bioreactor system. Tocilizumab was shown to desuppress CYP3A4 activity while reducing the CRP concentration after 72 hours in the continued presence of IL-6. This change in CYP3A4 activity decreased the half-life and area under the curve up to the last measurable concentration (AUClast) of the small molecule CYP3A4 substrate simvastatin hydroxy acid, measured before and after tocilizumab treatment. We conclude that next-generation in vitro liver culture platforms are well suited for these types of long-term treatment studies and show promise for improved drug safety assessment.

Utilization of human nuclear receptors as an early counter screen for off-target activity: a case study with a compendium of 615 known drugs.

Off-target effects of drugs on nuclear hormone receptors (NHRs) may result in adverse effects in multiple organs/physiological processes. Reliable assessments of the NHR activities for drug candidates are therefore crucial for drug development. However, the highly permissive structures of NHRs for vastly different ligands make it challenging to predict interactions by examining the chemical structures of the ligands. Here, we report a detailed investigation on the agonistic and antagonistic activities of 615 known drugs or drug candidates against a panel of 6 NHRs: androgen, progesterone, estrogen α/ß, and thyroid hormone α/ß receptors. Our study revealed that 4.7 and 12.4% compounds have agonistic and antagonistic activities, respectively, against this panel of NHRs. Nonetheless, potent, unintended NHR hits are relatively rare among the known drugs, indicating that such interactions are perhaps not tolerated during drug development. However, we uncovered examples of compounds that unintentionally agonize or antagonize NHRs. In addition, a number of compounds showed multi-NHR activities, suggesting that the cross-talk between multiple NHRs co-operate to elicit in vivo effects. These data highlight the merits of counter screening drug candidate against NHRs during drug discovery/development.

An Orally Available BACE1 Inhibitor That Affords Robust CNS Aß Reduction without Cardiovascular Liabilities.

BACE1 inhibition to prevent Aß peptide formation is considered to be a potential route to a disease-modifying treatment for Alzheimer's disease. Previous efforts in our laboratory using a combined structure- and property-based approach have resulted in the identification of aminooxazoline xanthenes as potent BACE1 inhibitors. Herein, we report further optimization leading to the discovery of inhibitor 15 as an orally available and highly efficacious BACE1 inhibitor that robustly reduces CSF and brain Aß levels in both rats and nonhuman primates. In addition, compound 15 exhibited low activity on the hERG ion channel and was well tolerated in an integrated cardiovascular safety model.

Development of 2-aminooxazoline 3-azaxanthenes as orally efficacious ß-secretase inhibitors for the potential treatment of Alzheimer's disease.

The ß-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is one of the most hotly pursued targets for the treatment of Alzheimer's disease. We used a structure- and property-based drug design approach to identify 2-aminooxazoline 3-azaxanthenes as potent BACE1 inhibitors which significantly reduced CSF and brain Aß levels in a rat pharmacodynamic model. Compared to the initial lead 2, compound 28 exhibited reduced potential for QTc prolongation in a non-human primate cardiovascular safety model.

Retinal Toxicity Induced by a Novel ß-secretase Inhibitor in the Sprague-Dawley Rat.

ß-Secretase 1 (BACE1) represents an attractive target for the treatment of Alzheimer's disease. In the course of development of a novel small molecule BACE1 inhibitor (AMG-8718), retinal thinning was observed in a 1-month toxicity study in the rat. To further understand the lesion, an investigational study was conducted whereby rats were treated daily with AMG-8718 for 1 month followed by a 2-month treatment-free phase. The earliest detectable change in the retina was an increase in autofluorescent granules in the retinal pigment epithelium (RPE) on day 5; however, there were no treatment-related light microscopic changes observed in the neuroretina and no changes observed by fundus autofluorescence or routine ophthalmoscopic examination after 28 days of dosing. Following 2 months of recovery, there was significant retinal thinning attributed to loss of photoreceptor nuclei from the outer nuclear layer. Electroretinographic changes were observed as early as day 14, before any microscopic evidence of photoreceptor loss. BACE1 knockout rats were generated and found to have normal retinal morphology indicating that the retinal toxicity induced by AMG-8718 was likely off-target. These results suggest that AMG-8718 impairs phagolysosomal function in the rat RPE, which leads to photoreceptor dysfunction and ultimately loss of photoreceptors.

A multifactorial approach to hepatobiliary transporter assessment enables improved therapeutic compound development.

The bile salt export pump (BSEP) is expressed at the canalicular domain of hepatocytes, where it serves as the primary route of elimination for monovalent bile acids (BAs) into the bile canaliculi. The most compelling evidence linking dysfunction in BA transport with liver injury in humans is found with carriers of mutations that render BSEP nonfunctional. Based on mounting evidence, there appears to be a strong association between drug-induced BSEP interference and liver injury in humans; however, causality has not been established. For this reason, drug-induced BSEP interference is best considered a susceptibility factor for liver injury as other host- or drug-related properties may contribute to the development of hepatotoxicity. To better understand the association between BSEP interference and liver injury in humans, over 600 marketed or withdrawn drugs were evaluated in BSEP expressing membrane vesicles. The example of a compound that failed during phase 1 human trials is also described, AMG 009. AMG 009 showed evidence of liver injury in humans that was not predicted by preclinical safety studies, and BSEP inhibition was implicated. For 109 of the drugs with some effect on in vitro BSEP function, clinical use, associations with hepatotoxicity, pharmacokinetic data, and other information were annotated. A steady state concentration (C(ss)) for each of these annotated drugs was estimated, and a ratio between this value and measured IC50 potency values were calculated in an attempt to relate exposure to in vitro potencies. When factoring for exposure, 95% of the annotated compounds with a C(ss)/BSEP IC50 ratio ≥ 0.1 were associated with some form of liver injury. We then investigated the relationship between clinical evidence of liver injury and effects to multidrug resistance-associated proteins (MRPs) believed to play a role in BA homeostasis. The effect of 600+ drugs on MRP2, MRP3, and MRP4 function was also evaluated in membrane vesicle assays. Drugs with a C(ss)/BSEP IC50 ratio ≥ 0.1 and a C(ss)/MRP IC50 ratio ≥ 0.1 had almost a 100% correlation with some evidence of liver injury in humans. These data suggest that integration of exposure data, and knowledge of an effect to not only BSEP but also one or more of the MRPs, is a useful tool for informing the potential for liver injury due to altered BA transport.

Design and synthesis of potent, orally efficacious hydroxyethylamine derived ß-site amyloid precursor protein cleaving enzyme (BACE1) inhibitors.

We have previously shown that hydroxyethylamines can be potent inhibitors of the BACE1 enzyme and that the generation of BACE1 inhibitors with CYP 3A4 inhibitory activities in this scaffold affords compounds (e.g., 1) with sufficient bioavailability and pharmacokinetic profiles to reduce central amyloid-ß peptide (Aß) levels in wild-type rats following oral dosing. In this article, we describe further modifications of the P1-phenyl ring of the hydroxyethylamine series to afford potent, dual BACE1/CYP 3A4 inhibitors which demonstrate improved penetration into the CNS. Several of these compounds caused robust reduction of Aß levels in rat CSF and brain following oral dosing, and compound 37 exhibited an improved cardiovascular safety profile relative to 1.

Development and evaluation of a genomic signature for the prediction and mechanistic assessment of nongenotoxic hepatocarcinogens in the rat.

Evaluating the risk of chemical carcinogenesis has long been a challenge owing to the protracted nature of the pathology and the limited translatability of animal models. Although numerous short-term in vitro and in vivo assays have been developed, they have failed to reliably predict the carcinogenicity of nongenotoxic compounds. Extending upon previous microarray work (Fielden, M. R., Nie, A., McMillian, M., Elangbam, C. S., Trela, B. A., Yang, Y., Dunn, R. T., II, Dragan, Y., Fransson-Stehen, R., Bogdanffy, M., et al. (2008). Interlaboratory evaluation of genomic signatures for predicting carcinogenicity in the rat. Toxicol. Sci. 103, 28-34), we have developed and extensively evaluated a quantitative PCR-based signature to predict the potential for nongenotoxic compounds to induce liver tumors in the rat as a first step in the safety assessment of potential nongenotoxic carcinogens. The training set was derived from liver RNA from rats treated with 72 compounds and used to develop a 22-gene signature on the TaqMan array platform, providing an economical and standardized assay protocol. Independent testing on over 900 diverse samples (66 compounds) confirmed the interlaboratory precision of the assay and its ability to predict known nongenotoxic hepatocarcinogens (NGHCs). When tested under different experimental designs, strains, time points, dose setting criteria, and other preanalytical processes, the signature sensitivity and specificity was estimated to be 67% (95% confidence interval [CI] = 38-88%) and 59% (95% CI = 44-72%), respectively, with an area under the receiver operating characteristic curve of 0.65 (95% CI = 0.46-0.83%). Compounds were best classified using expression data from short-term repeat dose studies; however, the prognostic expression changes appeared to be preserved after longer term treatment. Exploratory evaluations also revealed that different modes of action for nongenotoxic and genotoxic compounds can be discriminated based on the expression of specific genes. These results support a potential early preclinical testing paradigm to catalyze broader understanding of putative NGHCs.

Current and future applications of toxicogenomics: Results summary of a survey from the HESI Genomics State of Science Subcommittee.

BACKGROUND: In spite of the application of toxicogenomic (TGx) data to the field of toxicology for the past 10 years, the broad implementation and full impact of TGx for chemical and drug evaluation to improve decision making within organizations and by policy makers has not been achieved. OBJECTIVES: The goal of the Health and Environmental Sciences Institute (HESI) Committee on the Application of Genomics to Mechanism-based Risk Assessment was to construct and summarize a multisector survey, addressing key issues and perspectives on the current and future practical uses and challenges of implementing TGx data to facilitate discussions for decision making within organizations and by policy makers. METHODS: An online survey to probe the current status and future challenges facing the field of TGx for drug and chemical evaluation in experimental and nonclinical models was taken by scientists and scientific decision/policy makers actively engaged in the field of TGx within industrial, academic, and regulatory sectors of the United States, Europe, and Japan. For this survey, TGx refers specifically to the analysis of gene expression responses to evaluate xenobiotic exposure in experimental and preclinical models. RESULTS: The survey results are summarized from questions covering broad areas including technology used, organizational capacity and resource allocation, experimental approaches, data storage and exchange, perceptions of benefits and hurdles, and future expectations. CONCLUSIONS: The survey findings provide valuable information on the current state of the science of TGx applications and identify key areas in which TGx will have an impact as well as the key hurdles in applying TGx data to address issues. The findings serve as a public resource to facilitate discussions on the focus of future TGx efforts to ensure that a maximal benefit can be obtained from toxicogenomic studies.

A novel statistical algorithm for gene expression analysis helps differentiate pregnane X receptor-dependent and independent mechanisms of toxicity.

Genome-wide gene expression profiling has become standard for assessing potential liabilities as well as for elucidating mechanisms of toxicity of drug candidates under development. Analysis of microarray data is often challenging due to the lack of a statistical model that is amenable to biological variation in a small number of samples. Here we present a novel non-parametric algorithm that requires minimal assumptions about the data distribution. Our method for determining differential expression consists of two steps: 1) We apply a nominal threshold on fold change and platform p-value to designate whether a gene is differentially expressed in each treated and control sample relative to the averaged control pool, and 2) We compared the number of samples satisfying criteria in step 1 between the treated and control groups to estimate the statistical significance based on a null distribution established by sample permutations. The method captures group effect without being too sensitive to anomalies as it allows tolerance for potential non-responders in the treatment group and outliers in the control group. Performance and results of this method were compared with the Significant Analysis of Microarrays (SAM) method. These two methods were applied to investigate hepatic transcriptional responses of wild-type (PXR(+/+)) and pregnane X receptor-knockout (PXR(-/-)) mice after 96 h exposure to CMP013, an inhibitor of ß-secretase (ß-site of amyloid precursor protein cleaving enzyme 1 or BACE1). Our results showed that CMP013 led to transcriptional changes in hallmark PXR-regulated genes and induced a cascade of gene expression changes that explained the hepatomegaly observed only in PXR(+/+) animals. Comparison of concordant expression changes between PXR(+/+) and PXR(-/-) mice also suggested a PXR-independent association between CMP013 and perturbations to cellular stress, lipid metabolism, and biliary transport.

A double-blind, placebo-controlled pilot study of galantamine to improve cognitive dysfunction in minimally symptomatic bipolar disorder.

OBJECTIVE: There is increasing evidence that cognitive impairment is common in patients with bipolar disorder. The purpose of this study was to determine whether galantamine augmentation improved cognition in patients with euthymic bipolar disorder. In addition, the effect of galantamine on clinical measures of functioning and psychopathology was assessed. METHOD: This study was a randomized double-blind, placebo-controlled, parallel design examining the impact of galantamine augmentation on cognition and other clinical measures in 30 patients during the course of 3 months. Sixteen subjects who completed baseline and follow-up second neuropsychological testing were evaluable (10 with galantamine and 6 with placebo). RESULTS: The galantamine group showed improved performance on the California Verbal Learning Test total learning and the placebo group showed improved performance on the 2 Delis-Kaplan Executive Functioning System trail-making conditions and category fluency. CONCLUSIONS: Episodic memory performance was improved in the galantamine treatment group but did not improve in the placebo group. In contrast, performance on 2 of the processing speed measures showed significant improvement in the placebo condition, whereas that of the patients treated with galantamine did not improve. Galantamine may thus have specific benefits for episodic memory, but not processing speed, in patients with cognitive impairment as part of bipolar disorder.

A prospective, open-label study of Aripiprazole mono- and adjunctive treatment in acute bipolar depression.

OBJECTIVE: To examine the efficacy and tolerability of aripiprazole treatment for acute bipolar depression. METHODS: A six-week prospective, nonrandomized, open label study was conducted in depressed bipolar outpatients (types I, II, and NOS), as diagnosed by DSM-IV criteria. Previous treatments were continued unchanged, and new treatments not permitted, except lorazepam up to 2 mg daily. Aripiprazole was dosed flexibly up to a maximum of 30 mg daily, based on tolerability and efficacy. Montgomery-Asberg Depression Rating Scale (MADRS) and Mania Rating Scale (MRS) scores were used to assess changes in mood symptoms. Side effect outcomes were measured. Data was analyzed using last observation carried forward methodology and Analysis of Variance. RESULTS: Twenty patients (15 men, 5 women) with bipolar disorder (10 type I, 7 type II, 3 type NOS) enrolled in the study. Mean endpoint dose was 13.6 mg/d+/-10.0 mg/d. Thirteen (65%) patients completed 6 weeks of treatment. MADRS and MRS scores significantly improved during treatment. 44% of patients who completed at least one week of treatment were considered responders, based on > or =50% decrease in MADRS scores from baseline. Side effect measures were mostly unchanged during treatment. CONCLUSION: Depressive symptoms improved in bipolar patients treated with open-label aripiprazole.

Interlaboratory evaluation of genomic signatures for predicting carcinogenicity in the rat.

The Critical Path Institute recently established the Predictive Safety Testing Consortium, a collaboration between several companies and the U.S. Food and Drug Administration, aimed at evaluating and qualifying biomarkers for a variety of toxicological endpoints. The Carcinogenicity Working Group of the Predictive Safety Testing Consortium has concentrated on sharing data to test the predictivity of two published hepatic gene expression signatures, including the signature by Fielden et al. (2007, Toxicol. Sci. 99, 90-100) for predicting nongenotoxic hepatocarcinogens, and the signature by Nie et al. (2006, Mol. Carcinog. 45, 914-933) for predicting nongenotoxic carcinogens. Although not a rigorous prospective validation exercise, the consortium approach created an opportunity to perform a meta-analysis to evaluate microarray data from short-term rat studies on over 150 compounds. Despite significant differences in study designs and microarray platforms between laboratories, the signatures proved to be relatively robust and more accurate than expected by chance. The accuracy of the Fielden et al. signature was between 63 and 69%, whereas the accuracy of the Nie et al. signature was between 55 and 64%. As expected, the predictivity was reduced relative to internal validation estimates reported under identical test conditions. Although the signatures were not deemed suitable for use in regulatory decision making, they were deemed worthwhile in the early assessment of drugs to aid decision making in drug development. These results have prompted additional efforts to rederive and evaluate a QPCR-based signature using these samples. When combined with a standardized test procedure and prospective interlaboratory validation, the accuracy and potential utility in preclinical applications can be ascertained.

Divalproex in the treatment of acute bipolar depression: a preliminary double-blind, randomized, placebo-controlled pilot study.

OBJECTIVE: To determine the efficacy of divalproex (extended release) in the treatment of acute nonrefractory bipolar depression. METHOD: In a stratified, double-blind, randomized, placebo-controlled trial, 18 acutely depressed bipolar outpatients (DSM-IV criteria) received either divalproex monotherapy (target dose level, 70-90 ng/dL) (N = 9) or placebo (N = 9) for 6 weeks. Patients were recruited between January 2004 and May 2005. Clinical assessment on the Montgomery-Asberg Depression Rating Scale (MADRS) determined primary efficacy. RESULTS: The divalproex treatment group showed significantly greater reduction in MADRS scores compared to placebo (group x time interaction, p = .0078). Absolute effect size of estimated MADRS total score reduction over time was 13.6 points with divalproex versus 1.4 points with placebo (p = .003, linear growth curve model). Standardized effect size was large (Cohen d = 0.81). MADRS item analyses demonstrated improvement in core mood symptoms more than in anxiety or insomnia symptoms. There was also a modest but significant association between MADRS and Mania Rating Scale scores in the divalproex group (r = 0.29, df = 51, p = .03), but not in the placebo group (r = -0.15, df = 35, p = .36). CONCLUSIONS: Divalproex appeared to be an effective treatment for acute nonrefractory bipolar depression, which is consistent with previous small randomized studies. Some evidence of benefit in the depressive mixed state was observed. Confirmation or refutation with larger randomized clinical trials is warranted. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT00226343.

An open prospective study of zonisamide in acute bipolar depression.

OBJECTIVE: To examine the effectiveness and safety of zonisamide in the treatment of acute bipolar depression. METHODS: An open-label, prospective, nonrandomized, 8-week study conducted in bipolar outpatients (type I, type II, or not otherwise specified) with depressive symptoms. No patient was manic or mixed at study entry. Previous treatments were continued unchanged, but no new treatments were allowed. Montgomery Asberg Depression Rating Scale and the Mania Rating Scale from the Schedule of Affective Disorders and Schizophrenia-Change Version were used. RESULTS: Twenty patients (10 men, 10 women) with bipolar disorder (17 type I, 2 type II, 1 NOS), aged 38.1 +/- 8.81 years, received zonisamide at mean dose of 222.5 +/- 85.1 mg/d. Mean Montgomery Asberg Depression Rating Scale scores improved significantly from baseline to endpoint (mean difference = -8.4, 95% confidence interval [4.1, 12.6], P = 0.001). Ten patients (50%) terminated early due to adverse effects, mostly side effects including nausea/vomiting, cognitive impairment, and sedation. One patient experienced increased suicidal ideation, and one patient experienced hypomania. CONCLUSIONS: This study suggests improvement of depressive symptoms in this sample with 8 weeks of open-label zonisamide treatment.

Preliminary findings of uncoupling of flow and metabolism in unipolar compared with bipolar affective illness and normal controls.

Cerebral metabolism (CMR for glucose or oxygen) and blood flow (CBF) have been reported to be closely correlated in healthy controls. Altered relationships between CMR and CBF have been reported in some brain disease states, but not others. This study examined relationships between global and regional CMRglu vs. CBF in controls and medication-free primary affective disorder patients. Nine bipolars, eight unipolars, and nine healthy controls had [15O]-water positron emission tomography (PET) scans at rest, and [18F]-fluorodeoxyglucose PET scans during an auditory continuous performance task. Patients had [15O]-water and FDG PET scans in tandem the same day; controls had an average of 45+/-27 days between scans. Maps of regional coupling were constructed for each subject group. In controls and bipolars, global and virtually all regional correlation coefficients for CMRglu and CBF were positive, albeit more robustly so in controls. However, correlative relationships in unipolars were qualitatively different, such that global and most regional measures of flow and metabolism were not positively related. Unipolars had significantly fewer positive regional correlation coefficients than healthy controls and bipolars. These were significantly different from controls in orbital cortex, anterior cingulate, posterior cingulate, and posterior temporal cortex, and different from bipolars in pregenual anterior cingulate. In unipolars, the degree of flow-metabolism uncoupling was inversely correlated with Hamilton depression scores, indicating the severity of uncoupling was directly related to the severity of depression. These preliminary data suggest abnormal relationships between cerebral metabolism and blood flow globally and regionally in patients with unipolar depression that warrant replication and extension to potential pathophysiological implications.

Bupropion and venlafaxine responders differ in pretreatment regional cerebral metabolism in unipolar depression.

BACKGROUND: Pretreatment functional brain imaging was examined for never-hospitalized outpatients with unipolar depression compared with control subjects in a crossover treatment trial involving bupropion or venlafaxine monotherapy. METHODS: Patients (n = 20) with unipolar depression received baseline (medication-free) fluorine-18 deoxyglucose (FDG) positron emission tomography (PET) scan and then at least 6 weeks of bupropion or venlafaxine monotherapy in a single-blind crossover trial. Age-matched healthy control subjects (n = 20) also received baseline FDG PET scans. For each medication PET data from patients compared with control subjects was analyzed as a function of treatment response (defined as moderate to marked improvement on the Clinical Global Impression Scale). RESULTS: Treatment response rates were similar for buproprion (32%) and venlafaxine (33%). Compared with control subjects, responders but not nonresponders, to both drugs demonstrated frontal and left temporal hypometabolism. Selectively, compared with control subjects bupropion responders (n = 6) also had cerebellar hypermetabolism, whereas venlafaxine responders (n = 7) showed bilateral temporal and basal ganglia hypometabolism. CONCLUSIONS: These data suggest that pretreatment frontal and left temporal hypometabolism in never-hospitalized depressed outpatients compared with control subjects is linked to positive antidepressant response and that additional alterations in regional metabolism may be linked to differential responsivity to bupropion and venlafaxine monotherapy.

Left prefrontal-repetitive transcranial magnetic stimulation (rTMS) and regional cerebral glucose metabolism in normal volunteers.

Repetitive transcranial magnetic stimulation (rTMS) holds promise as a probe into the pathophysiology and possible treatment of neuropsychiatric disorders. To explore its regional effects, we combined rTMS with positron emission tomography (PET). Fourteen healthy volunteers participated in a baseline 18-fluorodeoxyglucose (FDG) PET scan. During a second FDG infusion on the same day, seven subjects received 30 min of 1 Hz rTMS at 80% of motor threshold to left prefrontal cortex, and seven other subjects received sham rTMS under identical conditions. Global and normalized regional cerebral glucose metabolic rates (rCMRglu) from the active and sham conditions were compared to baseline and then to each other. Sham, but not active 1 Hz rTMS, was associated with significantly increased global CMRglu. Compared to baseline, active rTMS induced normalized decreases in rCMRglu in right prefrontal cortex, bilateral anterior cingulate, basal ganglia (L>R), hypothalamus, midbrain, and cerebellum. Increases in rCMRglu were seen in bilateral posterior temporal and occipital cortices. Sham rTMS compared to baseline resulted in isolated normalized decreases in rCMRglu in left dorsal anterior cingulate and left basal ganglia, and increases in posterior association and occiptal regions. Differences between the 1 Hz active versus sham changes from baseline revealed that active rTMS induced relative decrements in rCMRglu in the left superior frontal gyrus and increases in the cuneus (L>R). One Hertz rTMS at 80% motor threshold over the left prefrontal cortex in healthy subjects compared to sham rTMS in another group (each compared to baseline) induced an area of decreased normalized left prefrontal rCMRglu not directly under the stimulation site, as well as increases in occipital cortex. While these results are in the predicted direction, further studies using other designs and higher intensities and frequencies of rTMS are indicated to better describe the local and distant changes induced by rTMS.