Correction: Epistasis of HTR1A and BDNF risk genes alters cortical 5-HT1A receptor binding: PET results link genotype to molecular phenotype in depression

In the original Article, co-author Professor Andreas Hahn was not included in the author list. This has been corrected in the XML, PDF and HTML versions of this Article.

Serotonin Transporter Binding in the Human Brain After Pharmacological Challenge Measured Using PET and PET/MR

Introduction: In-vivo quantification of the serotonin transporter (SERT) guided our understanding of many neuropsychiatric disorders. A recently introduced bolus plus constant infusion protocol has been shown to allow the reliable determination of SERT binding with reduced scan time. In this work, the outcomes of two methods, a bolus injection paradigm on a GE PET camera, and a bolus plus infusion paradigm on a combined Siemens PET/MR camera were compared. Methods: A total of seven healthy subjects underwent paired PET and paired PET/MR scans each with intravenous double-blind application of 7.5 mg citalopram or saline in a randomized cross-over study design. While PET scans were performed according to standard protocols and non-displaceable binding potentials (BP_ND) were calculated using the multi-linear reference tissue model, during PET/MR measurements [¹¹C]DASB was applied as bolus plus constant infusion, and BP_ND was calculated using the steady state method and data acquired at tracer equilibrium. Occupancies were calculated as the relative decrease in BP_ND between saline and citalopram scans. Results: During placebo scans, a mean difference in BP_ND of -0.08 (-11.71%) across all ROIs was found between methods. PET/MR scans resulted in higher BP_ND estimates than PET scans in all ROIs except the midbrain. A mean difference of -0.19 (-109.40%) across all ROIs between methods was observed for citalopram scans. PET/MR scans resulted in higher BP_ND estimates than PET scans in all ROIs. For occupancy, a mean difference of 23.12% (21.91%) was observed across all ROIs. PET/MR scans resulted in lower occupancy compared to PET scans in all ROIs except the temporal cortex. While for placebo, BP_ND of high-binding regions (thalamus and striatum) exhibited moderate reliability (ICC = 0.66), during citalopram scans ICC decreased (0.36-0.46). However, reliability for occupancy remained high (0.57-0.82). Conclusion: Here, we demonstrated the feasibility of reliable and non-invasive SERT quantification using a [¹¹C]DASB bolus plus constant infusion protocol at a hybrid PET/MR scanner, which might facilitate future pharmacological imaging studies. Highest agreement with established methods for quantification of occupancy and SERT BP_ND at baseline was observed in subcortical high-binding regions.

Epistasis of HTR1A and BDNF risk genes alters cortical 5-HT1A receptor binding: PET results link genotype to molecular phenotype in depression

Alterations of the 5-HT_1A receptor and BDNF have consistently been associated with affective disorders. Two functional single nucleotide polymorphisms (SNPs), rs6295 of the serotonin 1A receptor gene (HTR1A) and rs6265 of brain-derived neurotrophic factor gene (BDNF), may impact transcriptional regulation and expression of the 5-HT_1A receptor. Here we investigated interaction effects of rs6295 and rs6265 on 5-HT_1A receptor binding. Forty-six healthy subjects were scanned with PET using the radioligand [carbonyl-¹¹C]WAY-100635. Genotyping was performed for rs6265 and rs6295. Subjects showing a genotype with at least three risk alleles (G of rs6295 or A of rs6265) were compared to control genotypes. Cortical surface binding potential (BP_ND) was computed for 32 cortical regions of interest (ROI). Mixed model was applied to study main and interaction effects of ROI and genotype. ANOVA was used for post hoc analyses. Individuals with the risk genotypes exhibited an increase in 5-HT_1A receptor binding by an average of 17% (mean BP_ND 3.56 ± 0.74 vs. 2.96 ± 0.88). Mixed model produced an interaction effect of ROI and genotype on BP_ND and differences could be demonstrated in 10 ROI post hoc. The combination of disadvantageous allelic expression of rs6295 and rs6265 may result in a 5-HT_1A receptor profile comparable to affective disorders as increased 5-HT_1A receptor binding is a well published phenotype of depression. Thus, epistasis between BDNF and HTR1A may contribute to the multifactorial risk for affective disorders and our results strongly advocate further research on this genetic signature in affective disorders.

The effect of electroconvulsive therapy on cerebral monoamine oxidase A expression in treatment-resistant depression investigated using positron emission tomography

BACKGROUND

Electroconvulsive therapy (ECT) constitutes one of the most effective antidepressant treatment strategies in major depression (MDD). Despite its common use and uncontested efficacy, its mechanism of action is still insufficiently understood. Previously, we showed that ECT is accompanied by a global decrease of serotonin-1A receptors in MDD; however, further studies to investigate the involvement of the serotonergic system in the mechanism of action of ECT are warranted. The monoamine oxidase A (MAO-A) represents an important target for antidepressant treatments and was found to be increased in MDD. Here, we investigated whether ECT impacts on MAO-A levels in treatment-resistant patients (TRD).

METHODS

16 TRD patients (12 female, age 45.94 ± 9.68 years, HAMD 25.12 ± 3.16) with unipolar depression according to DSM-IV were scanned twice before (PET1 and PET2, to assess test-retest variability under constant psychopharmacotherapy) and once after (PET3) completing a minimum of eight unilateral ECT sessions using positron emission tomography and the radioligand [¹¹C]harmine to assess cerebral MAO-A distribution volumes (V_T). Age- and sex-matched healthy subjects (HC) were measured once.

RESULTS

Response rate to ECT was 87.5%. MAO-A V_T was found to be significantly reduced after ECT in TRD patients (-3.8%) when assessed in 27 a priori defined ROIs (p < 0.001). Test-retest variability between PET1 and PET2 was 3.1%. MAO-A V_T did not significantly differ between TRD patients and HC at baseline.

CONCLUSIONS

The small effect size of the significant reduction of MAO-A V_T after ECT in the range of test-retest variability does not support the hypothesis of a clinically relevant mechanism of action of ECT based on MAO-A. Furthermore, in contrast to studies reporting elevated MAO-A V_T in unmedicated depressed patients, MAO-A levels were found to be similar in TRD patients and HC which might be attributed to the continuous antidepressant pharmacotherapy in the present sample.

Parcellation of the Human Cerebral Cortex Based on Molecular Targets in the Serotonin System Quantified by Positron Emission Tomography In vivo

Parcellation of distinct areas in the cerebral cortex has a long history in neuroscience and is of great value for the study of brain function, specialization, and alterations in neuropsychiatric disorders. Analysis of cytoarchitectonical features has revealed their close association with molecular profiles based on protein density. This provides a rationale for the use of in vivo molecular imaging data for parcellation of the cortex with the advantage of whole-brain coverage. In the current work, parcellation was based on expression of key players of the serotonin neurotransmitter system. Positron emission tomography was carried out for the quantification of serotonin 1A (5-HT1A, n = 30) and 5-HT2A receptors (n = 22), the serotonin-degrading enzyme monoamine oxidase A (MAO-A, n = 32) and the serotonin transporter (5-HTT, n = 24) in healthy participants. Cortical protein distribution maps were obtained using surface-based quantification. Based on k-means clustering, silhouette criterion and bootstrapping, five distinct clusters were identified as the optimal solution. The defined clusters proved of high explanatory value for the effects of psychotropic drugs acting on the serotonin system, such as antidepressants and psychedelics. Therefore, the proposed method constitutes a sensible approach towards integration of multimodal imaging data for research and development in neuropharmacology and psychiatry.

Association of Protein Distribution and Gene Expression Revealed by PET and Post-Mortem Quantification in the Serotonergic System of the Human Brain

Regional differences in posttranscriptional mechanisms may influence in vivo protein densities. The association of positron emission tomography (PET) imaging data from 112 healthy controls and gene expression values from the Allen Human Brain Atlas, based on post-mortem brains, was investigated for key serotonergic proteins. PET binding values and gene expression intensities were correlated for the main inhibitory (5-HT1A) and excitatory (5-HT2A) serotonin receptor, the serotonin transporter (SERT) as well as monoamine oxidase-A (MAO-A), using Spearman's correlation coefficients (rs) in a voxel-wise and region-wise analysis. Correlations indicated a strong linear relationship between gene and protein expression for both the 5-HT1A (voxel-wise rs = 0.71; region-wise rs = 0.93) and the 5-HT2A receptor (rs = 0.66; 0.75), but only a weak association for MAO-A (rs = 0.26; 0.66) and no clear correlation for SERT (rs = 0.17; 0.29). Additionally, region-wise correlations were performed using mRNA expression from the HBT, yielding comparable results (5-HT1Ars = 0.82; 5-HT2Ars = 0.88; MAO-A rs = 0.50; SERT rs = -0.01). The SERT and MAO-A appear to be regulated in a region-specific manner across the whole brain. In contrast, the serotonin-1A and -2A receptors are presumably targeted by common posttranscriptional processes similar in all brain areas suggesting the applicability of mRNA expression as surrogate parameter for density of these proteins.

Assessment of Ketamine Binding of the Serotonin Transporter in Humans with Positron Emission Tomography

BACKGROUND

Comprehensive description of ketamine's molecular binding profile becomes increasingly pressing as use in real-life patient cohorts widens. Animal studies attribute a significant role in the substance's antidepressant effects to the serotonergic system. The serotonin transporter is a highly relevant target in this context, because it is central to depressive pathophysiology and treatment. This is, to our knowledge, the first study investigating ketamine's serotonin transporter binding in vivo in humans.

METHODS

Twelve healthy subjects were assessed twice using [11C]DASB positron emission tomography. A total of 0.50 mg/kg bodyweight ketamine was administered once i.v. prior to the second positron emission tomography scan. Ketamine plasma levels were determined during positron emission tomography. Serotonin transporter nondisplaceable binding potential was computed using a reference region model, and occupancy was calculated for 4 serotonin transporter-rich regions (caudate, putamen, thalamus, midbrain) and a whole-brain region of interest.

RESULTS

After administration of the routine antidepressant dose, ketamine showed <10% occupancy of the serotonin transporter, which is within the test-retest variability of [11C]DASB. A positive correlation between ketamine plasma levels and occupancy was shown.

CONCLUSIONS

Measurable occupancy of the serotonin transporter was not detectable after administration of an antidepressant dose of ketamine. This might suggest that ketamine binding of the serotonin transporter is unlikely to be a primary antidepressant mechanism at routine antidepressant doses, as substances that facilitate antidepressant effects via serotonin transporter binding (e.g., selective serotonin reuptake inhibitors) show 70% to 80% occupancy. Administration of high-dose ketamine is widening. Based on the positive relationship we find between ketamine plasma levels and occupancy, there is a need for investigation of ketamine's serotonin transporter binding at higher doses.

The influence of the rs6295 gene polymorphism on serotonin-1A receptor distribution investigated with PET in patients with major depression applying machine learning

Major depressive disorder (MDD) is the most common neuropsychiatric disease and despite extensive research, its genetic substrate is still not sufficiently understood. The common polymorphism rs6295 of the serotonin-1A receptor gene (HTR1A) is affecting the transcriptional regulation of the 5-HT_1A receptor and has been closely linked to MDD. Here, we used positron emission tomography (PET) exploiting advances in data mining and statistics by using machine learning in 62 healthy subjects and 19 patients with MDD, which were scanned with PET using the radioligand [carbonyl-¹¹C]WAY-100635. All the subjects were genotyped for rs6295 and genotype was grouped in GG vs C allele carriers. Mixed model was applied in a ROI-based (region of interest) approach. ROI binding potential (BP_ND) was divided by dorsal raphe BP_ND as a specific measure to highlight rs6295 effects (BP_Div). Mixed model produced an interaction effect of ROI and genotype in the patients' group but no effects in healthy controls. Differences of BP_Div was demonstrated in seven ROIs; parahippocampus, hippocampus, fusiform gyrus, gyrus rectus, supplementary motor area, inferior frontal occipital gyrus and lingual gyrus. For classification of genotype, 'RandomForest' and Support Vector Machines were used, however, no model with sufficient predictive capability could be computed. Our results are in line with preclinical data, mouse model knockout studies as well as previous clinical analyses, demonstrating the two-pronged effect of the G allele on 5-HT_1A BP_ND for, we believe, the first time. Future endeavors should address epigenetic effects and allosteric heteroreceptor complexes. Replication in larger samples of MDD patients is necessary to substantiate our findings.

Effects of Selective Serotonin Reuptake Inhibitors on Interregional Relation of Serotonin Transporter Availability in Major Depression

Selective serotonin reuptake inhibitors (SSRIs) modulate serotonergic neurotransmission by blocking reuptake of serotonin from the extracellular space. Up to now, it remains unclear how SSRIs achieve their antidepressant effect. However, task-based and resting state functional magnetic resonance imaging studies, have demonstrated connectivity changes between brain regions. Here, we use positron emission tomography (PET) to quantify SSRI's main target, the serotonin transporter (SERT), and assess treatment-induced molecular changes in the interregional relation of SERT binding potential (BP_ND). Nineteen out-patients with major depressive disorder (MDD) and 19 healthy controls (HC) were included in this study. Patients underwent three PET measurements with the radioligand [¹¹C]DASB: (1) at baseline, (2) after a first SSRI dose; and (3) following at least 3 weeks of daily intake. Controls were measured once with PET. Correlation analyses were restricted to brain regions repeatedly implicated in MDD pathophysiology. After 3 weeks of daily SSRI administration a significant increase in SERT BP_ND correlations of anterior cingulate cortex and insula with the amygdala, midbrain, hippocampus, pallidum and putamen (p < 0.05; false discovery rate, FDR corrected) was revealed. No significant differences were found when comparing MDD patients and HC at baseline. These findings are in line with the clinical observation that treatment response to SSRIs is often achieved only after a latency of several weeks. The elevated associations in interregional SERT associations may be more closely connected to clinical outcomes than regional SERT occupancy measures and could reflect a change in the regional interaction of serotonergic neurotransmission during antidepressant treatment.

Altered interregional molecular associations of the serotonin transporter in attention deficit/hyperactivity disorder assessed with PET

Altered serotonergic neurotransmission has been found to cause impulsive and aggressive behavior, as well as increased motor activity, all exemplifying key symptoms of ADHD. The main objectives of this positron emission tomography (PET) study were to investigate the serotonin transporter binding potential (SERT BP_ND ) in patients with ADHD and to assess associations of SERT BP_ND between the brain regions. 25 medication-free patients with ADHD (age ± SD; 32.39 ± 10.15; 10 females) without any psychiatric comorbidity and 25 age and sex matched healthy control subjects (33.74 ± 10.20) were measured once with PET and the highly selective and specific radioligand [¹¹ C]DASB. SERT BP_ND maps in nine a priori defined ROIs exhibiting high SERT binding were compared between groups by means of a linear mixed model. Finally, adopted from structural and functional connectivity analyses, we performed correlational analyses using regional SERT binding potentials to examine molecular interregional associations between all selected ROIs. We observed significant differences in the interregional correlations between the precuneus and the hippocampus in patients with ADHD compared to healthy controls, using SERT BP_ND of the investigated ROIs (P < 0.05; Bonferroni corrected). When correlating SERT BP_ND and age in the ADHD and the healthy control group, we confirmed an age-related decline in brain SERT binding in the thalamus and insula (R²  = 0.284, R²  = 0.167, Ps < 0.05; Bonferroni corrected). The results show significantly different interregional molecular associations of the SERT expression for the precuneus with hippocampus in patients with ADHD, indicating presumably altered functional coupling. Altered interregional coupling between brain regions might be a sensitive approach to demonstrate functional and molecular alterations in psychiatric conditions. Hum Brain Mapp 38:792-802, 2017. © 2016 Wiley Periodicals, Inc.

Modeling Strategies for Quantification of In Vivo 18F-AV-1451 Binding in Patients with Tau Pathology

Aggregation of hyperphosphorylated tau is a major hallmark of many neurodegenerative diseases, including Alzheimer disease (AD). In vivo imaging with PET may offer important insights into pathophysiologic mechanisms, diagnosis, and disease progression. We describe different strategies for quantification of ¹⁸F-AV-1451 (T807) tau binding, including models with blood sampling and noninvasive alternatives. Methods: Fifteen subjects (4 controls, 6 AD, 3 progressive supranuclear palsy, 2 cortico basal syndrome) underwent 180-min PET with ¹⁸F-AV-1451 and arterial blood sampling. Modeling with arterial input functions included 1-, 2-, and 3-tissue-compartment models and the Logan plot. Using the cerebellum as reference region, we applied the simplified reference tissue model 2 and Logan reference plot. Finally, simplified outcome measures were calculated as ratio, with reference to cerebellar concentrations (SUV ratio [SUVR]) and SUVs. Results: Tissue compartment models were not able to describe the kinetics of ¹⁸F-AV-1451, with poor fits in 33%-53% of cortical regions and 80% in subcortical areas. In contrast, the Logan plot showed excellent fits and parameter variance (total volume of distribution SE < 5%). Compared with the 180-min arterial-based Logan model, strong agreement was obtained for the Logan reference plot also for a reduced scan time of 100 min (R² = 0.91) and SUVR 100-120 min (R² = 0.94), with 80-100 min already representing a reasonable compromise between duration and accuracy (R² = 0.93). Time-activity curves and kinetic parameters were equal for cortical regions and the cerebellum in control subjects but different in the putamen. Cerebellar total volumes of distribution were higher in controls than patients. For these methods, increased cortical binding was observed for AD patients and to some extent for cortico basal syndrome, but not progressive supranuclear palsy. Conclusion: The Logan plot provided the best estimate of tau binding using arterial input functions. Assuming that the cerebellum is a valid reference region, simplified methods seem to provide robust alternatives for quantification, such as the Logan reference plot with 100-min scan time. Furthermore, SUVRs between target and cerebellar activities obtained from an 80- to 100-min static scan offer promising potential for clinical routine application.

Effects of norepinephrine transporter gene variants on NET binding in ADHD and healthy controls investigated by PET

Attention deficit hyperactivity disorder (ADHD) is a heterogeneous disorder with a strong genetic component. The norepinephrine transporter (NET) is a key target for ADHD treatment and the NET gene has been of high interest as a possible modulator of ADHD pathophysiology. Therefore, we conducted an imaging genetics study to examine possible effects of single nucleotide polymorphisms (SNPs) within the NET gene on NET nondisplaceable binding potential (BPND ) in patients with ADHD and healthy controls (HCs). Twenty adult patients with ADHD and 20 HCs underwent (S,S)-[18F]FMeNER-D2 positron emission tomography (PET) and were genotyped on a MassARRAY MALDI-TOF platform using the Sequenom iPLEX assay. Linear mixed models analyses revealed a genotype-dependent difference in NET BPND between groups in the thalamus and cerebellum. In the thalamus, a functional promoter SNP (-3081 A/T) and a 5'-untranslated region (5'UTR) SNP (-182 T/C), showed higher binding in ADHD patients compared to HCs depending on the major allele. Furthermore, we detected an effect of genotype in HCs, with major allele carriers having lower binding. In contrast, for two 3'UTR SNPs (*269 T/C, *417 A/T), ADHD subjects had lower binding in the cerebellum compared to HCs depending on the major allele. Additionally, symptoms of hyperactivity and impulsivity correlated with NET BPND in the cerebellum depending on genotype. Symptoms correlated positively with cerebellar NET BPND for the major allele, while symptoms correlated negatively to NET BPND in minor allele carriers. Our findings support the role of genetic influence of the NE system on NET binding to be pertubated in ADHD.

Value of three-dimensional US for optimizing guidance for ablating focal liver tumors

PURPOSE

To determine if three-dimensional ultrasound (3D US), by nature of its ability to simultaneously evaluate structures in three orthogonal planes and to study relationships of devices to tumor(s) and surrounding anatomic structures from any desired orientation, adds significant additional information to real-time 2D US used for placement of devices for ablation of focal liver tumors.

MATERIALS AND METHODS

Sixteen patients underwent focal ablation of 23 liver tumors during two intraoperative cryoablation (CA) procedures, three intraoperative radiofrequency ablation (RFA) procedures, 11 percutaneous ethanol injections (PEI) procedures, and six percutaneous RFA procedures. After satisfactory placement of the ablative device(s) with 2D US guidance, 3D US was used to reevaluate adequacy to device position. Information added by 3D US and resultant alterations in device deployment were tabulated.

RESULTS

3D US added information in 20 of 22 (91%) procedures and caused the operator to readjust the number or position of ablative devices in 10 of 22 (45%) of procedures. Specifically, 3D US improved visualization and confident localization of devices in 13 of 22 (59%) procedures, detected unacceptable device placement in 10 of 22 (45%), and determined that 2D US had incorrectly predicted device orientation to a tumor in three of 22 (14%).

CONCLUSIONS

Compared to conventional 2D US, 3D US provides additional relationship information for improved placement and optimal distribution of ablative agents for treatment of focal liver malignancy.

Fetal lip and primary palate: three-dimensional versus two-dimensional US

PURPOSE

To determine if three-dimensional (3D) ultrasonography (US) improves the ability to define the location and extent of facial clefting prenatally compared with two-dimensional (2D) US.

MATERIALS AND METHODS

Thirty-one fetuses suspected of having a facial cleft were examined prospectively with 2D and 3D US. Follow-up was performed in all fetuses.

RESULTS

Twenty-eight fetuses had a cleft lip at birth. The location of the cleft lip was correctly identified in all fetuses with 3D US and in 26 of 28 with 2D US. Twenty-two fetuses had a cleft primary palate. Nineteen and nine of 22 cleft palates were identified by using 3D and 2D US, respectively. Three fetuses suspected of having a facial cleft at 2D US had a normal palate at 3D US and at birth.

CONCLUSION

Three-dimensional US is useful to identify the location and extent of facial clefting. The advantages of 3D US are the following: (a) The face may be viewed in a standard orientation, (b) the defect may be viewed systematically by using an interactive display, and (c) the rendered image provides landmarks for the planar images. Patient decisions may be affected, since they can view the abnormality on a recognizable 3D rendered image.

Three-dimensional ultrasonographic imaging of the neonatal brain in high-risk neonates: preliminary study

The aim of this investigation was to compare the utility of three-dimensional ultrasonography versus two-dimensional ultrasonography in imaging the neonatal brain. Thirty patients in the neonatal intensive care unit underwent two-dimensional and three-dimensional ultrasonography. The resultant two- and three-dimensional images recorded on film and three-dimensional volumes (reviewed on a workstation) were evaluated independently. Comparable numbers of normal and abnormal studies were diagnosed by each modality. Axial images were considered useful in approximately 50% of three-dimensional cases. Image quality, overall and in the far-field, was rated higher on two-dimensional images. Three-dimensional sonographic acquisition time in the neonatal intensive care unit (1.7 min+/-0.7 standard deviation) was significantly shorter than that for two-dimensional sonography (9.0+/-4.5 min). The total time for evaluation on the three-dimensional workstation (4.4+/-1.1 min) was significantly less than that for two-dimensional images on film (10.6+/-4.7 min). In conclusion, three-dimensional ultrasonography is a promising, diagnostically accurate, and efficient imaging tool for evaluation of the neonatal brain; however, visualization must improve before it can replace two-dimensional ultrasonography.

Adjunctive 3D US for achieving portal vein access during transjugular intrahepatic portosystemic shunt procedures

PURPOSE

To evaluate the usefulness of information provided by three-dimensional ultrasound (3D US) and to determine whether 3D US decreased the number of passes required to obtain portal vein (PV) access during creation of transjugular intrahepatic portosystemic shunts (TIPS).

MATERIALS AND METHODS

Intermittent 3D US volume acquisitions were obtained during creation of TIPS in 20 patients. Useful information provided by 3D US was tabulated. The number of passes required to achieve PV access was recorded and results were compared retrospectively to 25 patients who underwent TIPS without 3D US.

RESULTS

3D US documented that the operator's opinion of which hepatic vein had been selected was incorrect in nine patients (45%), detected unfavorable PV anatomy that required modification of equipment or technique in seven patients (35%), permitted estimation of the trajectory required to access the targeted PV in all patients (100%), assisted in selecting the optimal point along the hepatic vein for origination of the needle pass in 11 patients (55%), allowed avoidance of a large hepatocellular carcinoma in one patient (5%), and confirmed that access into the main PV was intrahepatic in four patients (20%). The mean number of needle passes decreased from 10.4 in the historic control group to 4.6 in the 3D US group (P = .0001).

CONCLUSION

3D US provided imaging information that detected technical errors and altered anatomy, and provided positional and directional information to significantly improve needle pass efficiency.

Adjunctive 3D US for achieving portal vein access during transjugular intrahepatic portosystemic shunt procedures

PURPOSE

To evaluate the usefulness of information provided by three-dimensional ultrasound (3D US) and to determine whether 3D US decreased the number of passes required to obtain portal vein (PV) access during creation of transjugular intrahepatic portosystemic shunts (TIPS).

MATERIALS AND METHODS

Intermittent 3D US volume acquisitions were obtained during creation of TIPS in 20 patients. Useful information provided by 3D US was tabulated. The number of passes required to achieve PV access was recorded and results were compared retrospectively to 25 patients who underwent TIPS without 3D US.

RESULTS

3D US documented that the operator's opinion of which hepatic vein had been selected was incorrect in nine patients (45%), detected unfavorable PV anatomy that required modification of equipment or technique in seven patients (35%), permitted estimation of the trajectory required to access the targeted PV in all patients (100%), assisted in selecting the optimal point along the hepatic vein for origination of the needle pass in 11 patients (55%), allowed avoidance of a large hepatocellular carcinoma in one patient (5%), and confirmed that access into the main PV was intrahepatic in four patients (20%). The mean number of needle passes decreased from 10.4 in the historic control group to 4.6 in the 3D US group (P = .0001).

CONCLUSION

3D US provided imaging information that detected technical errors and altered anatomy, and provided positional and directional information to significantly improve needle pass efficiency.

Interaction between neutral endopeptidase and angiotensin converting enzyme inhibition in rats with myocardial infarction: effects on cardiac hypertrophy and angiotensin and bradykinin peptide levels

Combined inhibition of neutral endopeptidase 24.11 (NEP) and angiotensin converting enzyme (ACE) is a candidate therapy for hypertension and cardiac failure. Given that NEP and ACE metabolize angiotensin (Ang) and bradykinin (BK) peptides, we investigated the effects of NEP inhibition and combined NEP and ACE inhibition on Ang and BK levels in rats with myocardial infarction. We administered the NEP inhibitor ecadotril (0, 0.1, 1, 10, and 100 mg/kg/day), either alone or together with the ACE inhibitor perindopril (0.2 mg/kg/day) by 12-hourly gavage from day 2 to 28 after infarction. Ecadotril increased urine cyclic GMP and BK-(1-9) excretion. Perindopril potentiated the effect of ecadotril on urine cyclic GMP excretion. Neither perindopril nor ecadotril reduced cardiac hypertrophy when administered separately, whereas the combination of perindopril and 10 or 100 mg/kg/day ecadotril reduced heart weight/body weight ratio by 10%. Administration of ecadotril to perindopril-treated rats decreased plasma Ang-(1-7) levels, increased cardiac BK-(1-9) levels, and increased Ang II levels in plasma, kidney, aorta, and lung. These data demonstrate interactions between the effects of NEP and ACE inhibition on remodeling of the infarcted heart and on Ang and BK peptide levels. Whereas increased cardiac BK-(1-9) levels may contribute to the reduction of cardiac hypertrophy, the reduction in plasma Ang-(1-7) levels and increase in Ang II levels in plasma and tissues may compromise the therapeutic effects of combined NEP/ACE inhibition.

Effects of neutral endopeptidase inhibition and combined angiotensin converting enzyme and neutral endopeptidase inhibition on angiotensin and bradykinin peptides in rats

The combination of neutral endopeptidase 24.11 (NEP) and angiotensin converting enzyme (ACE) inhibition is a candidate therapy for hypertension and cardiac failure. Given that NEP and ACE metabolize angiotensin (Ang) and bradykinin (BK) peptides, we investigated the effects of NEP inhibition and combined NEP and ACE inhibition on the levels of these peptides. We administered the NEP inhibitor ecadotril (0, 0.1, 1, 10, 100 mg/kg per day), either alone or together with the ACE inhibitor perindopril (0.2 mg/kg per day), to rats by 12 hourly gavage for 7 days. Ecadotril produced diuresis, natriuresis, increased urine cyclic guanosine monophosphate and BK-(1-9) levels, increased Ang II and Ang I levels in plasma, and increased Ang I levels in heart. Perindopril reduced Ang II levels in kidney, and increased BK-(1-9) levels in blood, kidney and aorta. Combined NEP/ACE inhibition produced the summation of these effects of separate NEP and ACE inhibition. In addition, perindopril potentiated the ecadotril-mediated diuresis, natriuresis and decrease in urine BK-(1-7)/BK-(1-9) ratio, which is an index of BK-(1-9) metabolism. Moreover, combined NEP/ACE inhibition increased Ang II levels in plasma and lung. These data indicate that summation of the effects of separate NEP and ACE inhibition provides the basis for the therapeutic efficacy of their combination. Whereas potentiation by perindopril of the diuretic and natriuretic effects of ecadotril may contribute to the therapeutic effects, increased Ang II levels in plasma and lung may compromise the therapeutic effects of combined NEP/ACE inhibition.

Marked difference between angiotensin-converting enzyme and neutral endopeptidase inhibition in vivo by a dual inhibitor of both enzymes

Dual inhibition of neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE) offers the potential for improved therapy of hypertension and cardiac failure. S 21402-1 [(2S)-2-[(2S,3R)-2-thiomethyl-3-phenylbutanamido] propionic acid] is a sulfhydryl-containing potent inhibitor of both NEP (Ki = 1.7 nM) and ACE (Ki = 4.5 nM). S 21402-1 and the sulfhydryl-containing ACE inhibitor captopril were administered to rats by intraperitoneal injection (0, 0.3, 3, 30, 300 mg/kg). Urine was collected for 4 h; then plasma and kidneys were collected. The difference in NEP and ACE inhibition by S 21402-1 in vivo was greater than 1000-fold. All doses of S 21402-1 inhibited NEP, as indicated by plasma NEP activity, radioinhibitor binding to kidney sections, urinary sodium excretion and bradykinin-(1-7)/bradykinin-(1-9) ratio. However, only 300 mg/kg S 21402-1 inhibited ACE, as indicated by plasma angiotensin II/angiotensin I ratio, renin and angiotensinogen levels. Although S 21402-1 (30 and 300 mg/kg) inhibited renal NEP, as indicated by the bradykinin-(1-7)/bradykinin-(1-9) ratio in kidney, S 21402-1 had no effect on renal ACE, as indicated by the angiotensin II/angiotensin I ratio in kidney. Moreover, captopril was greater than 10-fold more potent than S 21402-1 as an ACE inhibitor in vivo. In separate experiments, the pressor response of anesthetized rats to angiotensin I showed more rapid decay in ACE inhibition by S 21402-1 than by captopril. These studies indicated that in vivo modification of S 21402-1 caused a much greater decrease in potency of ACE inhibition than NEP inhibition. Consequently, effective ACE inhibition by S 21402-1 required doses much higher than those required for NEP inhibition.

A role for protein kinase C in the attenuated response to 5-hydroxytryptamine in aortas from streptozotocin-diabetic rats

We investigated protein kinase C participation in the contractile response to 5-hydroxytryptamine (5-HT), and in the interaction between 5-HT and endothelin-1, in aortas from control and diabetic rats. Diabetic rats display attenuated reactivity to 5-HT (i.e., approximately 47% of control maximum). The protein kinase C inhibitor calphostin C (1 microM) significantly reduced responses to 5-HT only in aortas from control rats. In diabetic rats, maximum responses to 5-HT, in the presence of endothelin-1 (3 nM), were not significantly different to controls. The additional presence of calphostin C significantly reduced responses only in aortas from diabetic rats. These results may indicate an abnormality in the protein kinase C second messenger system during diabetes.

Attenuated 5-HT2 receptor-mediated responses in hindquarters of diabetic rats

Vasoconstrictor responses to 5-hydroxytryptamine (5-HT), alpha-methyl-5-HT, endothelin-1, arachidonic acid and the thromboxane A2-mimetic U46619 ((15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid) were obtained in blood-perfused hindquarters of 6-week streptozotocin-diabetic rats. When compared to responses obtained in hindquarters of control rats, responses to 5-HT, alpha-methyl-5-HT, and arachidonic acid were attenuated in hindquarters of diabetic rats. However, responses to endothelin-1 or U46619 were not significantly different between controls and diabetics. These results suggest that 5-HT2, but not endothelin ETA receptor-mediated responses are reduced in hindquarters of diabetic rats. The results utilising arachidonic acid and U46619 suggest that there may also be a defect in the cyclo-oxygenase cascade during diabetes.

Potentiation by endothelin-1 of 5-hydroxytryptamine responses in aortae from streptozotocin-diabetic rats: a role for thromboxane A2

1. We have previously reported maximum responses to 5-hydroxytryptamine (5-HT) are diminished in endothelium-intact and -denuded aortae from rats with streptozotocin-induced diabetes of 2-weeks duration. 2. In the present study, the thromboxane A2/prostaglandin H2 (TP) receptor antagonist GR32191B (1 microM) significantly reduced maximum responses to 5-HT in endothelium-intact aortae from both control and diabetic rats. In the presence of GR32191B, maximum responses to 5-HT, in endothelium-intact aortae from diabetic rats, were still significantly reduced compared to those obtained in aortae from controls. 3. GR32191B (1 microM) had no significant effect on maximum responses to 5-HT in endothelium-denuded aortae from either control or diabetic rats. 4. Interaction between 5-HT (0.1 microM-0.1 mM) and threshold concentrations of endothelin-1 (ET-1) or the thromboxane (Tx)A2-mimetic, U46619, were examined in endothelium-intact and -denuded aortae from control and 2-week streptozotocin-diabetic rats. 5. Maximum responses to 5-HT in the presence of a threshold concentration of ET-1 (3 nM), in endothelium-intact aortae from diabetic rats, were not significantly different from those of control rats. 6. Maximum responses to 5-HT in the combined presence of ET-1 (3 nM) and GR32191B (1 microM), in endothelium-intact aortae from diabetic rats, were significantly reduced compared to those obtained in aortae from controls. 7. Maximum responses to 5-HT in the presence of ET-1 (3 nM) in endothelium-denuded aortae from diabetic rats were significantly reduced compared to those from controls. 8. Maximum responses to 5-HT in the presence of a threshold concentration of U46619 (20 or 30 nM),in endothelium-intact aortae from diabetic rats, were not significantly different from responses of controls.9. Maximum responses to 5-HT in the presence of a threshold (5-20 nM) concentration of U46619, in endothelium-denuded aortae from diabetic rats, were not significantly different from responses of controls.10 The results of the present study indicate that endothelial-derived TxA2 contributes to the contractile response to 5-HT in aortae from control and diabetic rats. Endothelial-derived TxA2 also appears to play a role in the potentiation of 5-HT responses by ET-1 in aortae from diabetic rats.

Soluble plasma antigen in experimental Salmonella typhimurium infection in mice

To detect and characterize Salmonella antigen in blood, outbred CF-1 female mice were inoculated intraperitoneally with S. typhimurium LT-2 and blood was assayed by ELISA for Salmonella common structural antigen. Plasma antigen was detectable early in the course of infection and increased in quantity later in the course of illness when animals showed high grade bacteremia and high counts of splenic bacteria. Antigen was associated with a cell-free plasma fraction of blood, passed through filters with cut-offs of 0.2 mu and molecular mass of 1000 kDa, and was enhanced in detectability after heating to 100 degrees C for 15 min. Antigen was concentrated by diluting plasma 1:4 in 0.1 M EDTA, heating to 100 degrees C, and concentrating the supernate with an ultrafiltration membrane with a molecular mass cut-off of 15 kDa. By gel filtration, antigen was associated with a peak at about molecular mass 300 kDa in heated plasma and a peak at about 380 kDa in unheated plasma. These results indicate that murine typhoid infection results in circulating soluble plasma antigen, which is heat-stable with a molecular mass of approximately 300 kDa.

Attenuated 5-hydroxytryptamine receptor-mediated responses in aortae from streptozotocin-induced diabetic rats

1. This study was designed to examine further the attenuated contractile responses to 5-hydroxytryptamine (5-HT) previously observed in aortae from diabetic rats. 2. Cumulative concentration-response curves to 5-HT, and the 5-HT receptor agonists, alpha-methyl 5-HT (alpha-Me-5-HT, 5-HT2/1C agonist), (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2- aminopropane (DOI, 5-HT2/1C agonist) and 5-carboxamidotryptamine (5-CT, 5-HT1A/1B/1D agonist), were examined in endothelium-intact and -denuded aortae from 2-week streptozotocin (STZ)-diabetic and control rats. 3. In endothelium-intact and -denuded aortae from diabetic rats, maximum responses to 5-HT and alpha-Me-5-HT were significantly reduced compared to those of aortae from control rats. Responses to these agonists were inhibited by the 5-HT2/1C receptor antagonist, ketanserin (0.1 microM). 4. The attenuated responses to 5-HT of aortae from diabetic rats were normalized by chronic insulin treatment of the rats (5 units day-1, s.c.), but not by altering the glucose concentration of the bathing fluid. 5. The nitric oxide synthase inhibitor N-nitro-L-arginine (NOLA, 0.1 mM) significantly potentiated responses to both 5-HT and alpha-Me-5-HT in endothelium-intact aortae. However, the difference between maximum responses of aortae from diabetic and control rats was still evident in the presence of NOLA. 6. Endothelium-intact rings, in the presence of ketanserin (0.1 microM) and preconstricted with the thromboxane A2-mimetic, U46619 (0.1-0.3 microM), from control and diabetic rats, did not relax to cumulative additions of 5-HT (1 nM-30 microM). 7. Contractile responses to DOI were obtained only in endothelium-denuded aortae, and in endothelium-intact aortae in the presence of NOLA, from control rats.8. Contractile responses to 5-CT were obtained only in endothelium-denuded aortae from both control and diabetic rats, and in endothelium-intact aortae in the presence of NOLA, from control rats.9. [3H]-ketanserin binding studies showed that there was no significant change in the affinity or density of [3H]-ketanserin for binding sites in membrane preparations of aortae from control and diabetic rats.10. These results suggest that 5-HT contracts aortae from rats via 5-HT2/1c receptor activation.However, the simultaneous release of EDRF from endothelial cells in response to 5-HT does not appear to be receptor-mediated. The attenuated contractile responses observed to 5-HT in aortae from 2-week diabetic rats do not appear to be mediated by changes in either endothelial cell function or an alteration in 5-HT receptor affinity or density.

Effect of endothelium on diabetes-induced changes in constrictor responses mediated by 5-hydroxytryptamine in rat aorta

We investigated constrictor responses to 5-hydroxytryptamine (5-HT) and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI, a 5-HT2/5-HT1C receptor agonist) of aortic rings from 2- and 6-week streptozotocin-diabetic and vehicle control rats. At 10 g resting tension, maximum responses and -log EC50 values to 5-HT were significantly reduced in endothelium-intact and denuded aortas from 2- and 6-week diabetic rats relative to those from control rats (except for -log EC50 of endothelium-intact rings from 6-week diabetic rats). Removal of endothelium from aortas of 2- and 6-week diabetic and control rats caused significant increases both in -log EC50 values and in maximum responses to 5-HT. DOI caused marked contraction of endothelium-denuded aortas from control rats, but not of endothelium-intact aortas from control rats or aortas (either with or without endothelium) from diabetic rats. The nitric oxide (NO) synthase inhibitor N-nitro-L-arginine (NOLA) significantly potentiated constrictor responses to 5-HT in endothelium-intact aortas from control and diabetic rats. NOLA significantly potentiated constrictor responses to DOI in endothelium-intact aortas from control rats, but not in endothelium-intact aortas from diabetic rats. These results suggest that for aortas from 2- and 6-week diabetic rats, the diminished responses to 5-HT and DOI may be a result of reductions in 5-HT2-receptor-mediated responses of smooth muscle. The results also suggest that 5-HT and DOI can stimulate NO release from endothelial cells.