Erythrocyte catechol-O-methyltransferase activity: genetic analysis in nuclear families with one child affected by Down syndrome

Aging rather than aneuploidy affects monoamine neurotransmitters in brain regions of Down syndrome mouse models

Altered concentrations of monoamine neurotransmitters and metabolites have been repeatedly found in people with Down syndrome (DS, trisomy 21). Because of the limited availability of human post-mortem tissue, DS mouse models are of great interest to study these changes and the underlying neurobiological mechanisms. Although previous studies have shown the potential of Ts65Dn mice – the most widely used mouse model of DS – to model noradrenergic changes, a comprehensive monoaminergic characterization in multiple brain regions has not been performed so far. Here, we used RP-HPLC with electrochemical detection to quantify (nor)adrenergic (NA, adrenaline and MHPG), dopaminergic (DA, HVA and DOPAC), and serotonergic compounds (tryptophan, 5-HT and 5-HIAA) in ten regionally dissected brain regions of Ts65Dn mice, as well as in Dp1Tyb mice – a novel DS mouse model. Comparing young adult aneuploid mice (2.5–5.5 months) with their euploid WT littermates did not reveal generalized monoaminergic dysregulation, indicating that the genetic overload in these mice barely affected the absolute concentrations at this age. Moreover, we studied the effect of aging in Ts65Dn mice: comparing aged animals (12–13 months) with their younger counterparts revealed a large number of significant changes. In general, the (nor)adrenergic system appeared to be reduced, while serotonergic compounds were increased with aging. Dopaminergic alterations were less consistent. These overall patterns appeared to be relatively similar for Ts65Dn and WT mice, though more observed changes were regarded significant for WT mice. Similar human post-mortem studies are necessary to validate the monoaminergic construct validity of the Ts65Dn and Dp1Typ mouse models.

•

Monoamine neurotransmitters and metabolites appear to be altered in Down syndrome.

•

The monoaminergic brain profile of two Down syndrome mouse models was examined.

•

Aneuploidy barely affected monoamines in Ts65Dn and Dp1Tyb mice vs. wild-type mice.

•

Aging to 12–13 months showed strong monoaminergic changes in the Ts65Dn mouse model.

•

Construct validity needs to be established by similar human post-mortem studies.

Ts1Cje Down syndrome model mice exhibit environmental stimuli-triggered locomotor hyperactivity and sociability concurrent with increased flux through central dopamine and serotonin metabolism

Ts1Cje mice have a segmental trisomy of chromosome 16 that is orthologous to human chromosome 21 and display Down syndrome-like cognitive impairments. Despite the occurrence of affective and emotional impairments in patients with Down syndrome, these parameters are poorly documented in Down syndrome mouse models, including Ts1Cje mice. Here, we conducted comprehensive behavioral analyses, including anxiety-, sociability-, and depression-related tasks, and biochemical analyses of monoamines and their metabolites in Ts1Cje mice. Ts1Cje mice showed enhanced locomotor activity in novel environments and increased social contact with unfamiliar partners when compared with wild-type littermates, but a significantly lower activity in familiar environments. Ts1Cje mice also exhibited some signs of decreased depression like-behavior. Furthermore, Ts1Cje mice showed monoamine abnormalities, including increased extracellular dopamine and serotonin, and enhanced catabolism in the striatum and ventral forebrain. This study constitutes the first report of deviated monoamine metabolism that may help explain the basis for abnormal behaviors, including the environmental stimuli-triggered hyperactivity, increased sociability and decreased depression-like behavior in Ts1Cje mice.

Rat liver and kidney catechol-O-methyltransferase activity measured by high-performance liquid chromatography with fluorescence detection

We have previously reported a highly sensitive method for the measurement of catechol-O-methyltransferase (COMT) activities in rat erythrocytes with norepinephrine (NE), an endogenous native substrate, using high-performance liquid chromatography (HPLC)-fluorescence or peroxyoxalate chemiluminescence reaction detection. Applying this method to COMT activities in rat liver and kidney, known to have the highest activities of all organs, the optimum reaction conditions were investigated. Under the optimum conditions, soluble (S)-COMT and membrane-bound (MB)-COMT activities in rat liver, with NE as a substrate, were 2.17 +/- 0.33 and 0.16 +/- 0.02 nmol/min/mg protein (n = 5), respectively. In rat kidney, S-COMT and MB-COMT activities were 1.81 +/- 0.20 and 0.079 +/- 0.009 nmol/min/mg protein (n = 5), respectively. Since liver and kidney play important roles in inactivating catecholamines, using the proposed method would yield critical information to delineate the role of metabolism of catecholamines in rat tissues.

Assessment of catechol-O-methyltransferase activity and its inhibition in erythrocytes of animals and humans

A non-radiometric method to measure the catechol-O-methyltransferase (COMT) activity in erythrocytes was modified to increase its sensitivity four-fold as well as its reproducibility and applicability. The method is based on the COMT-mediated O-methylation of 4-(naphtho [1,2-d] thiazol-2-yl) pyrocatechol, the product of which was determined fluorometrically. COMT activities down to less than 1% of those present at baseline could be measured precisely and accurately. The intra- and inter-assay coefficients were below 3 and 5.3%, respectively. Basal COMT activity and the distribution between soluble and membrane-bound COMT was shown to be variable among different species (ten species tested). The applicability of the method was demonstrated by the characterization of COMT activity-time courses in human erythrocytes after oral administration of the COMT inhibitor tolcapone. The assay developed will be useful in the rapid screening and clinical development of new COMT inhibitors.

Expression of functional membrane-bound and soluble catechol-O-methyltransferase in Escherichia coli and a mammalian cell line

Human catechol-O-methyltransferase (hCOMT) cDNA was used to express the recombinant hCOMT enzyme in sufficient quantities in prokaryotic as well as in eukaryotic cells to allow kinetic studies. When human membrane-bound catechol-O-methyltransferase (MB-COMT; amino acids 1-271) and the soluble catechol-O-methyltransferase COMT (S-COMT; delta membrane anchor hCOMT; amino acids 27-271), with the latter lacking the first 26 hydrophobic amino acids, were expressed in Escherichia coli, a relatively high-level synthesis of catalytically active enzymes was obtained. Insertion of the human MB-COMT-coding sequence into an eukaryotic expression vector under transcriptional control of the cytomegalovirus (CMV) promoter and enhancer yielded large quantities of hCOMT in human kidney 293 cells. Subcellular fractionation of 293 cells transfected with pBC12/CMV-hCOMT showed hCOMT to be located predominantly in the membrane fraction. The catechol-O-methyltransferase (COMT) activity was measured in cytosolic and membrane fractions at 37 degrees C, giving values of 33 and 114 units/mg of protein, respectively (1 unit produces 1 nmol of guaiacol/h). Km values were 10 microM for MB-COMT and 108 microM for S-COMT, indicating that recombinant MB-COMT exhibits a higher affinity for catechol as the substrate than the soluble form. RNA blot analysis of human hepatome cells (Hep G2), kidney, liver, and fetal brain revealed only one species of hCOMT mRNA of approximately 1.4 kb. Its level in these various tissues was similar to those of COMT protein in each tissue.(ABSTRACT TRUNCATED AT 250 WORDS)