Loss of serotonin 2A receptors exceeds loss of serotonergic projections in early Alzheimer's disease: a combined [C]DASB and [F]altanserin-PET study

In patients with Alzheimer's disease (AD), postmortem and imaging studies have revealed early and prominent reductions in cerebral serotonin 2A (5-HT_2A) receptors. To establish if this was due to a selective disease process of the serotonin system, we investigated the cerebral 5-HT_2A receptor and the serotonin transporter binding, the latter as a measure of serotonergic projections and neurons. Twelve patients with AD (average Mini Mental State Examination [MMSE]: 24) and 11 healthy age-matched subjects underwent positron emission tomography (PET) scanning with [¹⁸F]altanserin and [¹¹C]N,N-Dimethyl-2-(2-amino-4-cyanopheylthio)benzylamine ([¹¹C]DASB). Overall [¹⁸F]altanserin binding was markedly reduced in AD by 28%-39% (p = 0.02), whereas the reductions in [¹¹C]DASB binding were less prominent and mostly insignificant, except for a marked reduction of 33% in mesial temporal cortex (p = .0005). No change in [¹¹C]DASB binding was found in the midbrain. We conclude that the prominent reduction in neocortical 5-HT_2A receptor binding in early AD is not caused by a primary loss of serotonergic neurons or their projections.     

In vivo evaluation of amyloid deposition and brain glucose metabolism of 5XFAD mice using positron emission tomography

Positron emission tomography (PET) has been used extensively to evaluate the neuropathology of Alzheimer's disease (AD) in vivo. Radiotracers directed toward the amyloid deposition such as [¹⁸F]-FDDNP (2-(1-{6-[(2-[F]Fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile) and [¹¹C]-PIB (Pittsburg compound B) have shown exceptional value in animal models and AD patients. Previously, the glucose analogue [¹⁸F]-FDG (2-[(18)F]fluorodeoxyglucose) allowed researchers and clinicians to evaluate the brain glucose consumption and proved its utility for the early diagnosis and the monitoring of the progression of AD. Animal models of AD are based on the transgenic expression of different human mutant genes linked to familial AD. The novel transgenic 5XFAD mouse containing 5 mutated genes in its genome has been proposed as an AD model with rapid and massive cerebral amyloid deposition. PET studies performed with animal-dedicated scanners indicate that PET with amyloid-targeted radiotracers can detect the pathological amyloid deposition in transgenic mice and rats. However, in other studies no differences were found between transgenic mice and their wild type littermates. We sought to investigate in 5XFAD mice if the radiotracers [¹¹C]-PIB, and [¹⁸F]-Florbetapir could quantify the amyloid deposition in vivo and if [¹⁸F]-FDG could do so with regard to glucose consumption. We found that 5XFAD animals presented higher cerebral binding of [¹⁸F]-Florbetapir, [¹¹C]-PIB, and [¹⁸F]-FDG. These results support the use of amyloid PET radiotracers for the evaluation of AD animal models. Probably, the increased uptake observed with [¹⁸F]-FDG is a consequence of glial activation that occurs in 5XFAD mice.     

In vivo characterization of metabotropic glutamate receptor type 5 abnormalities in behavioral variant FTD

Although the pathogenesis underlying behavioral variant frontotemporal dementia (bvFTD) has yet to be fully understood, glutamatergic abnormalities have been hypothesized to play an important role. The aim of the present study was to determine the availability of the metabotropic glutamate receptor type 5 (mGluR5) using a novel positron emission tomography (PET) radiopharmaceutical with high selectivity for mGluR5 ([¹¹C]ABP688) in a sample of bvFTD patients. In addition, we sought to determine the overlap between availability of mGluR5 and neurodegeneration, as measured using [¹⁸F]FDG-PET and voxel-based morphometry (VBM). Availability of mGluR5 and glucose metabolism ([¹⁸F]FDG) were measured in bvFTD (n = 5) and cognitively normal (CN) subjects (n = 10). [¹¹C]ABP688 binding potential maps (BP_ND) were calculated using the cerebellum as a reference region, with [¹⁸F]FDG standardized uptake ratio maps (SUV_R) normalized to the pons. Grey matter (GM) concentrations were determined using VBM. Voxel-based group differences were obtained using RMINC. BvFTD patients showed widespread decrements in [¹¹C]ABP688 BP_ND throughout frontal, temporal and subcortical areas. These areas were likewise characterized by significant hypometabolism and GM loss, with overlap between reduced [¹¹C]ABP688 BP_ND and hypometabolism superior to that for GM atrophy. Several regions were characterized only by decreased binding of [¹¹C]ABP688. The present findings represent the first in vivo report of decreased availability of mGluR5 in bvFTD. This study suggests that glutamate excitotoxicity may play a role in the pathogenesis of bvFTD and that [¹¹C]ABP688 may prove a suitable marker of glutamatergic neurotransmission in vivo.     

Microglial activation in Alzheimer's disease: an (R)-[C]PK11195 positron emission tomography study

Inflammatory mechanisms, like microglial activation, could be involved in the pathogenesis of Alzheimer's disease (AD). (R)-[¹¹C]PK11195 (1-(2-chlorophenyl)-N-methyl-N-1(1-methylpropyl)-3-isoquinolinecarboxamide), a positron emission tomography (PET) ligand, can be used to quantify microglial activation in vivo. The purpose of this study was to assess whether increased (R)-[¹¹C]PK11195 binding is present in AD and mild cognitive impairment (MCI), currently also known as “prodromal AD.”     

Age-related reduction in dopamine D1 receptors in the human brain: from late childhood to adulthood,a positron emission tomography study

Age-dependent decrease in dopamine receptor density throughout adulthood is well described, meanwhile less is known about development of dopamine system in humans and in vivo it has not been investigated. We examined dopamine D1 receptor (D1DR) binding in the cerebral cortex and striatum of 12 adolescents (mean age 13.5±1.8 years) and 18 young adults (25±2.3 years) using positron emission tomography (PET) and radioligand [¹¹C]SCH23390. Over the age span of 10–30 years [¹¹C]SCH23390 binding (binding potential, BP) declined in all brain regions. The rate of BP decline was age-segment and brain region dependent. Most pronounced decline in BP was observed in the cortical regions during adolescence (mean BP in adults lower by 14–26% as compared to adolescents, P<0.0001). Significantly slower rate of decline in BP was observed in two cortical regions (orbitofrontal and posterior cingulate cortices) and striatal regions. The present PET-study provides new evidence on the development of D1DR in humans in vivo which is of critical importance for understanding of the biology of neurodevelopmental disorders.     

Imaging microglial activation and glucose consumption in a mouse model of Alzheimer's disease

In Alzheimer's disease (AD), persistent microglial activation as sign of chronic neuroinflammation contributes to disease progression. Our study aimed to in vivo visualize and quantify microglial activation in 13- to 15-month-old AD mice using [¹¹C]-(R)-PK11195 and positron emission tomography (PET). We attempted to modulate neuroinflammation by subjecting the animals to an anti-inflammatory treatment with pioglitazone (5-weeks' treatment, 5-week wash-out period). [¹¹C]-(R)-PK11195 distribution volume values in AD mice were significantly higher compared with control mice after the wash-out period at 15 months, which was supported by immunohistochemistry data. However, [¹¹C]-(R)-PK11195 μPET could not demonstrate genotype- or treatment-dependent differences in the 13- to 14-month-old animals, suggesting that microglial activation in AD mice at this age and disease stage is too mild to be detected by this imaging method.     

Imaging glial activation in patients with post-treatment Lyme disease symptoms: a pilot study using [<Superscript>11</Superscript>C]DPA-713 PET

The pathophysiology of post-treatment Lyme disease syndrome (PTLDS) may be linked to overactive immunity including aberrant activity of the brain’s resident immune cells, microglia. Here we used [¹¹C]DPA-713 and positron emission tomography to quantify the 18?kDa translocator protein, a marker of activated microglia or reactive astrocytes, in the brains of patients with post-treatment Lyme disease symptoms of any duration compared to healthy controls. Genotyping for the TSPO rs6971 polymorphism was completed, and individuals with the rare, low affinity binding genotype were excluded. Data from eight brain regions demonstrated higher [¹¹C]DPA-713 binding in 12 patients relative to 19 controls. [¹¹C]DPA-713 PET is a promising tool to study cerebral glial activation in PTLDS and its link to cognitive symptoms.     

Effects of amyloid-β peptides on the serotoninergic 5-HT1A receptors in the rat hippocampus

A recent [¹⁸F]MPPF-positron emission tomography study has highlighted an overexpression of 5-HT_1A receptors in the hippocampus of patients with mild cognitive impairment compared to a decrease in those with Alzheimer's disease (AD) [Truchot, L., Costes, S.N., Zimmer, L., Laurent, B., Le Bars, D., Thomas-Antérion, C., Croisile, B., Mercier, B., Hermier, M., Vighetto, A., Krolak-Salmon, P., 2007. Up-regulation of hippocampal serotonin metabolism in mild cognitive impairment. Neurology 69 (10), 1012-1017]. We used in vivo and in vitro neuroimaging to evaluate the longitudinal effects of injecting amyloid-β (Aβ) peptides (1-40) into the dorsal hippocampus of rats. In vivo microPET imaging showed no significant change in [¹⁸F]MPPF binding in the dorsal hippocampus over time, perhaps due to spatial resolution. However, in vitro autoradiography with [¹⁸F]MPPF (which is antagonist) displayed a transient increase in 5-HT_1A receptor density 7 days after Aβ injection, whereas [¹⁸F]F15599 (a radiolabelled 5-HT_1A agonist) binding was unchanged suggesting that the overexpressed 5-HT_1A receptors were in a non-functional state. Complementary histology revealed a loss of glutamatergic neurons and an intense astroglial reaction at the injection site. Although a neurogenesis process cannot be excluded, we propose that Aβ injection leads to a transient astroglial overexpression of 5-HT_1A receptors in compensation for the local neuronal loss. Exploration of the functional consequences of these serotoninergic modifications during the neurodegenerative process may have an impact on therapeutics targeting 5-HT_1A receptors in AD.     

Pyruvate‐lactate exchange and glucose uptake in human prostate cancer cell models. A study in xenografts and suspensions by hyperpolarized [1‐13C]pyruvate MRS and [18F]FDG‐PET

Reprogramming of energy metabolism in the development of prostate cancer can be exploited for a better diagnosis and treatment of the disease. The goal of this study was to determine whether differences in glucose and pyruvate metabolism of human prostate cancer cells with dissimilar aggressivenesses can be detected using hyperpolarized [1‐¹³C]pyruvate MRS and [¹⁸F]FDG‐PET imaging, and to evaluate whether these measures correlate. For this purpose, we compared murine xenografts of human prostate cancer LNCaP cells with those of more aggressive PC3 cells. [1‐¹³C]pyruvate was hyperpolarized by dissolution dynamic nuclear polarization (dDNP) and [1‐¹³C]pyruvate to lactate conversion was followed by ¹³C MRS. Subsequently [¹⁸F]FDG uptake was investigated by static and dynamic PET measurements. Standard uptake values (SUVs) for [¹⁸F]FDG were significantly higher for xenografts of PC3 compared with those of LNCaP. However, we did not observe a difference in the average apparent rate constant k_pl of ¹³C label exchange from pyruvate to lactate between the tumor variants. A significant negative correlation was found between SUVs from [¹⁸F]FDG PET measurements and k_pl values for the xenografts of both tumor types. The k_pl rate constant may be influenced by various factors, and studies with a range of prostate cancer cells in suspension suggest that LDH inhibition by pyruvate may be one of these. Our results indicate that glucose and pyruvate metabolism in the prostate cancer cell models differs from that in other tumor models and that [¹⁸F]FDG‐PET can serve as a valuable complementary tool in dDNP studies of aggressive prostate cancer with [1‐¹³C]pyruvate.     

Adrenocortical suppression by a single induction dose of etomidate

Summary In a prospective controlled trial we studied the effect of a single induction dose of etomidate or thiopentone on the adrenocortical function in 29 patients undergoing elective surgery. During anesthesia and in the recovery period serum cortisol rose significantly in the thiopentone group only. In contrast, after induction with etomidate serum cortisol decreased and remained below the starting values throughout the study period (5 h). The differences between the two groups were significant at 120, 150, 180, 210, and 240 min after induction (p<0.05). Moreover, plasma ACTH increased significantly more after etomidate than after thiopentone (p<0.02) indicating relative unresponsiveness of the adrenal cortex to stimulation by endogenous ACTH. We conclude that a single i.v. bolus of etomidate (0.26 mg/kg) leads to significant adrenal insufficiency in patients without preexisting endocrine abnormalities.Dedicated to Professor Dr. W. Kaufmann on the occasion of his 60th birthdaySupported by Landesamt fur Forschung, NRW     

Preclinical evaluation of 2-[18F]fluorodeoxysorbitol as a tracer for targeted imaging of Enterobacterales infection

Fluorine-18-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography (¹⁸F-FDG-PET) is widely used for the detection of inflammatory and infectious diseases. Although this modality has proven to be a useful diagnostic tool, reliable distinction of bacterial infection from sterile inflammation or even from a malignancy remains challenging. Therefore, there is a need for bacteria-specific tracers for PET imaging that facilitate a reliable distinction of bacterial infection from other pathology. The present study was aimed at exploring the potential of 2-[¹⁸F]-fluorodeoxysorbitol ([¹⁸F]FDS) as a tracer for detection of Enterobacterales infections. Sorbitol is a sugar alcohol that is commonly metabolized by bacteria of the Enterobacterales order, but not by mammalian cells, which makes it an attractive candidate for targeted bacterial imaging. The latter is important in view of the serious clinical implications of infections caused by Enterobacterales. Here we demonstrate that sorbitol-based PET can be applied to detect a broad range of clinical bacterial isolates not only in vitro, but also in blood and ascites samples from patients suffering from Enterobacterales infections. Notably, the possible application of [¹⁸F]FDS is not limited to Enterobacterales since Pseudomonas aeruginosa and Corynebacterium jeikeium also showed substantial uptake of this tracer. We conclude that [¹⁸F]FDS is a promising tracer for PET-imaging of infections caused by a group of bacteria that can cause serious invasive disease.     

Test-retest variability of high resolution positron emission tomography (PET) imaging of cortical serotonin (5HT2A) receptors in older, healthy adults

Background  

Position emission tomography (PET) imaging using [¹⁸F]-setoperone to quantify cortical 5-HT_2A receptors has the potential to inform pharmacological treatments for geriatric depression and dementia. Prior reports indicate a significant normal aging effect on serotonin 5HT_2A receptor (5HT_2AR) binding potential. The purpose of this study was to assess the test-retest variability of [¹⁸F]-setoperone PET with a high resolution scanner (HRRT) for measuring 5HT_2AR availability in subjects greater than 60 years old. Methods: Six healthy subjects (age range = 65–78 years) completed two [¹⁸F]-setoperone PET scans on two separate occasions 5–16 weeks apart.     

PET imaging of a collagen matrix reveals its effective injection and targeted retention in a mouse model of myocardial infarction

Injectable biomaterials have shown promise for cardiac regeneration therapy. However, little is known regarding their retention and distribution upon application in vivo. Matrix imaging would be useful for evaluating these important properties. Herein, hexadecyl-4-[¹⁸F]fluorobenzoate (¹⁸F-HFB) and Qdot labeling was used to evaluate collagen matrix delivery in a mouse model of myocardial infarction (MI). At 1wk post-MI, mice received myocardial injections of ¹⁸F-HFB- or Qdot-labeled matrix to assess its early retention and distribution (at 10 min and 2 h) by positron emission tomography (PET), or fluorescence imaging, respectively. PET imaging showed that the bolus of matrix at 10 min redistributed evenly within the ischemic territory by 2 h. Ex vivo biodistribution revealed myocardial matrix retention of ∼65%, which correlated with PET results, but may be an underestimate since ¹⁸F-HFB matrix labeling efficiency was ∼82%. For covalently linked Qdots, labeling efficiency was ∼96%. Ex vivo Qdot quantification showed that ∼84% of the injected matrix was retained in the myocardium. Serial non-invasive PET imaging and validation by fluorescence imaging confirmed the effectiveness of the collagen matrix to be retained and redistributed within the infarcted myocardium. This study identifies matrix-targeted imaging as a promising modality for assessing the biodistribution of injectable biomaterials for application in the heart.     

PET of Brain Prion Protein Amyloid in Gerstmann–Sträussler–Scheinker Disease

In vivo amyloid PET imaging was carried out on six symptomatic and asymptomatic carriers of PRNP mutations associated with the Gerstmann–Sträussler–Scheinker (GSS) disease, a rare familial neurodegenerative brain disorder demonstrating prion amyloid neuropathology, using 2-(1-{6-[(2-[F-18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile ([F-18]FDDNP). 2-Deoxy-2-[F-18]fluoro-d -glucose PET ([F-18]FDG) and magnetic resonance imaging (MRI) scans were also performed in each subject. Increased [F-18]FDDNP binding was detectable in cerebellum, neocortex and subcortical areas of all symptomatic gene carriers in close association with the experienced clinical symptoms. Parallel glucose metabolism ([F-18]FDG) reduction was observed in neocortex, basal ganglia and/or thalamus, which supports the close relationship between [F-18]FDDNP binding and neuronal dysfunction. Two asymptomatic gene carriers displayed no cortical [F-18]FDDNP binding, yet progressive [F-18]FDDNP retention in caudate nucleus and thalamus was seen at 1- and 2-year follow-up in the older asymptomatic subject. In vitro FDDNP labeling experiments on brain tissue specimens from deceased GSS subjects not participating in the in vivo studies indicated that in vivo accumulation of [F-18]FDDNP in subcortical structures, neocortices and cerebellum closely related to the distribution of prion protein pathology. These results demonstrate the feasibility of detecting prion protein accumulation in living patients with [F-18]FDDNP PET, and suggest an opportunity for its application to follow disease progression and monitor therapeutic interventions.     

Aluminium hydroxide stabilised MnFe2O4 and Fe3O4 nanoparticles as dual-modality contrasts agent for MRI and PET imaging

Magnetic nanoparticles (NPs) MnFe₂O₄ and Fe₃O₄ were stabilised by depositing an Al(OH)₃ layer via a hydrolysis process. The particles displayed excellent colloidal stability in water and a high affinity to [¹⁸F]-fluoride and bisphosphonate groups. A high radiolabeling efficiency, 97% for ¹⁸F-fluoride and 100% for ⁶⁴Cu-bisphosphonate conjugate, was achieved by simply incubating NPs with radioactivity solution at room temperature for 5 min. The properties of particles were strongly dependant on the thickness and hardness of the Al(OH)₃ layer which could in turn be controlled by the hydrolysis method. The application of these Al(OH)₃ coated magnetic NPs in molecular imaging has been further explored. The results demonstrated that these NPs are potential candidates as dual modal probes for MR and PET. In vivo PET imaging showed a slow release of ¹⁸F from NPs, but no sign of efflux of ⁶⁴Cu.     

Mechanism of renal necrosis induced by bromobenzene or chlorobenzene

Treatment of mice or rats with a single intraperitoneal dose of [¹⁴C]-bromobenzene or [¹⁴C]-chlorobenzene produced necrosis of the proximal convoluted renal tubules within 24–48 hr. The development of renal necrosis was associated with the covalent binding of substantial amounts of radiolabeled material to kidney proteins, and autoradiograms revealed that most of the covalently bound material was localized within the necrotic tubular cells. Prior inhibition of [¹⁴C]-bromobenzene metabolism in vivo with piperonyl butoxide blocked both the necrosis and the binding, suggesting that the necrosis and binding are caused by a toxic metabolite. Studies on the metabolism and covalent binding of [¹⁴C]-bromobenzene in hepatic and renal microsomes in vitro were compatible with the interpretation that the renal necrosis was caused by a metabolite formed in the liver and transported by the circulation to binding sites in the renal tubules.     

Etomidate: A selective adrenocortical 11β-hydroxylase inhibitor

Summary To investigate the adrenocortical suppression caused by the anesthetic etomidate, plasma levels of progesterone (P), 17-hydroxyprogesterone (17-OHP), 11-deoxycorticosterone (DOC), corticosterone (B), aldosterone (Aldo), 11-deoxycortisol (S), cortisol (F), and cortisone (E) were measured simultaneously before and after a short-term ACTH stimulation test in a 6.5-year-old boy whose convulsions could be kept under control only with constant etomidate infusions. During etomidate therapy, plasma levels of DOC and S were extremely elevated, the progestins P and 17-OHP were slightly elevated, whereas B and Aldo were in the lower normal range, and F and E were markedly decreased. A short-term ACTH stimulation test during etomidate infusion gave a blunted response of B, Aldo, F and E, whereas the level of DOC remained high and S even further increased. P and 17-OHP showed a positive response to ACTH. The ratios of B/DOC and F/S, which reflect adrenocortical 11-hydroxylase activity, were extremely decreased during etomidate and did not change after ACTH stimulation. In contrast, the ratios of DOC/P and S/17-OHP, which relect 21-hydroxylase activity, were elevated and remained elevated after ACTH stimulation. After discontinuation of etomidate therapy, all the baseline steroid levels were somewhat elevated, but responded normally to ACTH. These results demonstrate that etomidate causes a specific and reversible blockade of the 11-hydroxylation of adrenal steroid synthesis.Abbreviations P progesterone - DOC 11-deoxycorticosterone - B corticosterone - Aldo aldosterone - 170HP 17-hydroxyprogesterone - S 11-deoxycortisol - F cortisol - E cortisone - ACTH adrenocorticotrophic hormone Supported by a grant from the Deutsche Forschungsgemeinschaft     

Synthesis of two potential NK<Subscript>1</Subscript>-receptor ligands using [1-<Superscript>11</Superscript>C]ethyl iodide and [1-<Superscript>11</Superscript>C]propyl iodide and initial PET-imaging

Background

The previously validated NK₁-receptor ligand [O-methyl-¹¹C]GR205171 binds with a high affinity to the NK₁-receptor and displays a slow dissociation from the receptor. Hence, it cannot be used in vivo for detecting concentration changes in substance P, the endogenous ligand for the NK₁-receptor. A radioligand used for monitoring these changes has to enable displacement by the endogenous ligand and thus bind reversibly to the receptor. Small changes in the structure of a receptor ligand can lead to changes in binding characteristics and also in the ability to penetrate the blood-brain barrier. The aim of this study was to use carbon-11 labelled ethyl and propyl iodide with high specific radioactivity in the synthesis of two new and potentially reversible NK₁-receptor ligands with chemical structures based on [O-methyl-¹¹C]GR205171.

Methods

[1-¹¹C]Ethyl and [1-¹¹C]propyl iodide with specific radioactivities of 90 GBq/μmol and 270 GBq/μmol, respectively, were used in the synthesis of [O-methyl-¹¹C]GR205171 analogues by alkylation of O-desmethyl GR205171. The brain uptake of the obtained (2S,3S)-N-(1-(2- [1-¹¹C]ethoxy-5-(3-(trifluoromethyl)-4H-1,2,4-triazol-4-yl)phenyl)ethyl)-2-phenylpiperidin-3-amine (I) and (2S,3S)-2-phenyl-N-(1-(2- [1-¹¹C]propoxy-5-(3-(trifluoromethyl)-4H-1,2,4-triazol-4-yl)phenyl)ethyl)piperidin-3-amine (II) was studied with PET in guinea pigs and rhesus monkeys and compared to the uptake of [O-methyl-¹¹C]GR205171.

Results

All ligands had similar uptake distribution in the guinea pig brain. The PET-studies in rhesus monkeys showed that (II) had no specific binding in striatum. Ligand (I) had moderate specific binding compared to the [O-methyl-¹¹C]GR205171. The ethyl analogue (I) displayed reversible binding characteristics contrary to the slow dissociation rate shown by [O-methyl-¹¹C]GR205171.

Conclusion

The propyl-analogue (II) cannot be used for detecting changes in NK₁-ligand levels, while further studies should be performed with the ethyl-analogue (I).

     

Different inhibitory effect of etomidate and ketoconazole on the human adrenal steroid biosynthesis

Summary The narcotic agent etomidate and the antimycotic drug ketoconazole are known to block steroid biosynthesis in man. To study the different effects of these imidazole derivatives on human adrenal steroid biosynthesis we incubated slices of human adrenal glands with 3H-labeled precursors and increasing concentrations of etomidate or ketoconazole (0-2000 M). After extraction the labeled metabolites were separated by thin-layer chromatography and quantified by scintillation counting. Etomidate inhibited most potently 11-hydroxylase activity by suppressing the formation of corticosterone from 11-deoxycorticosterone to 1 % of control [50% inhibitory concentration (IC₅₀) 0.03 M] while ketoconazole suppressed 11-hy-droxylase to only 39% of control activity (IC₅₀ 15 M). Ketoconazole however, most potently blocked the conversion of 17-hydroxy-proges-terone to androstenedione by C17,20-desmolase to about 15% of control activity (IC₅₀ 1 M) while etomidate showed a much weaker effect on this enzyme with a suppression to 50% of C17,20-desmolase control activity at a concentration of 380 M. Both imidazole drugs showed a similar strong inhibitory effect on the activity of 17-hy-droxylase (IC₅₀ 6-18 M) and 16-hydroxylase (IC₅₀ 4–8 M) and did not affect 21-hydroxylase. These in vitro data indicate a predominant inhibitory effect of etomidate on corticosteroid biosynthesis by relative selective inhibition of 11-hydroxylase and of ketoconazole on the adrenal androgen biosynthesis by a predominant inhibition of C17,20-desmolase. This differential inhibitory effect of etomidate and ketoconazole on human steroid biosynthesis may be of clinical importance for a possible therapeutic use of these imidazole derivatives in endocrine disorders.Abbreviations IC₅₀ 50% inhibitory concentration Dedicated to Prof. Dr. G. Paumgartner on the occasion of his 60th birthday     

Early decrease of type 1 cannabinoid receptor binding and phosphodiesterase 10A activity in vivo in R6/2 Huntington mice

Several lines of evidence imply early alterations in endocannabinoid and phosphodiesterase 10A (PDE10A) signaling in Huntington disease (HD). Using [¹⁸F]MK-9470 and [¹⁸F]JNJ42259152 small-animal positron emission tomography (PET), we investigated for the first time cerebral changes in type 1 cannabinoid (CB1) receptor binding and PDE10A levels in vivo in presymptomatic, early symptomatic, and late symptomatic HD (R6/2) mice, in relation to glucose metabolism ([¹⁸F]FDG PET), brain morphology (magnetic resonance imaging) and motor function. Ten R6/2 and 16 wild-type (WT) mice were investigated at 3 different time points between the age of 4 and 13 weeks. Parametric CB1 receptor and PDE10A images were anatomically standardized to Paxinos space and analyzed voxelwise. Volumetric microMRI imaging was performed to assess HD pathology. In R6/2 mice, CB1 receptor binding was decreased in comparison with WT in a cluster comprising the bilateral caudate-putamen, globus pallidus, and thalamic nucleus at week 5 (−8.1% ± 2.6%, p = 1.7 × 10⁻⁵). Longitudinal follow-up showed further progressive decline compared with controls in a cluster comprising the bilateral hippocampus, caudate-putamen, globus pallidus, superior colliculus, thalamic nucleus, and cerebellum (late vs. presymptomatic age: −13.7% ± 3.1% for R6/2 and +1.5% ± 4.0% for WT, p = 1.9 × 10⁻⁵). In R6/2 mice, PDE10A binding potential also decreased over time to reach significance at early and late symptomatic HD (late vs. presymptomatic age: −79.1% ± 1.9% for R6/2 and +2.1% ± 2.7% for WT, p = 1.5 × 10⁻⁴). The observed changes in CB1 receptor and PDE10A binding were correlated to anomalies exhibited by R6/2 animals in motor function, whereas no correlation was found with magnetic resonance imaging-based striatal volume. Our findings point to early regional dysfunctions in endocannabinoid and PDE10A signaling, involving the caudate-putamen and lateral globus pallidus, which may play a role in the progression of the disease in R6/2 animals. PET quantification of in vivo CB1 and/or PDE10A binding may thus be useful early biomarkers for HD. Our results also provide evidence of subtle motor deficits at earlier stages than previously described.