Inheritance of low erythrocyte catechol-o-methyltransferase activity in man.

Catechol-O-methyltransferase activity was measured in blood obtained from 373 randomly selected subjects aged 16-18, 262 consecutive adult blood donors, and 201 first-degree relatives of subjects with RBC COMT activity of less than 8 U. The distribution of RBC COMT activity in a randoly selected populations was apparently bimodal with a nadir at approximately 8 U. Of a randomly selected population, 23% had low RBC COMT activity (less than 8 U), Because of previous reports of a significant sibling-sibling correlation of RBC COMT activity and because of the presence of a subgroup of subjects with low enzyme activity, RBC COMT activity was measured in blood from first-degree relatives of probands with low erythrocyte enzyme activity in 48 families. The results of segregation analyses of the data were compatible with autosomal recessive inheritence of an allele for low RBC COMT activity. RBC COMT in blood samples from siblings of probands inthese families also showed an apparent biomodal distribution.     

Human serum dopamine beta-hydroxylase: correlation of enzymatic activity with immunoreactive protein in genetically defined samples.

An antibody against human adrenal dopamine beta-hydroxylase (DBH) was used to quantitate immunoreactive DBH protein in human serum by an immunoprecipitation technique. A significant correlation was found between DBH enzyme activity and immunoreactive DBH protein in randomly selected serum samples (r = 0.94; N = 38; p less than .001). Studies of sera from obligate heterozygotes and individuals homozygous for the allele responsible for very low serum DBH enzymatic activity were compatible with a genetically mediated decrease in the quantity of circulating DBH protein in these subjects.     

Family studies of plasma dopamine-beta-hydroxylase thermal stability.

There are large individual variations in the thermal stability of human plasma dopamine-beta-hydroxylase (DBH). These variations are a characteristic of the DBH molecule itself. Individual subjects may be classified as those with thermolabile and those with thermostable plasma DBH. Of 362 randomly selected unrelated children, 8.01%, and of 238 randomly selected unrelated adult subjects, 5.46% had thermolabile plasma DBH. There was not a significant correlation of DBH thermolability with either sex or age on the basis of data from 230 adults and children in 53 randomly selected families. Subjects with thermolabile DBH had basal enzyme activity only about 55% of that in subjects with stable enzyme. There was not a direct relationship between DBH thermolability and the allele DBHL, the presence of which results in very low basal enzyme activity. There was a significant familial aggregation of the trait of DBH thermolability, but there was not a significant correlation of this trait among spouses. Although preliminary pedigree evaluation raised the possibility of monogenic inheritance of the trait of DBH thermolability by an autosomal recessive mechanism, three separate families in which both parents had thermolabile enzyme included offspring with thermostable DBH. All five of these offspring had very low basal plasma DBH and were presumed to be homozygous for the allele DBHL. These observations raised the possibility that the trait of plasma DBH thermolability may be inherited, and that there may be an interaction between the locus or loci responsible for thermal stability and the locus DBH.     

Dopamine-beta-hydroxylase activity in plasma obtained from the pulmonary artery and left ventricle of man

Dopamine-β-hydroxylase activity (DBH) has been measured in plasma obtained simultaneously from the pulmonary artery and left ventricle of fourteen patients who underwent diagnostic cardiac catheterisation. In the majority of these subjects the levels of enzyme activity in the arterial and venous blood were similar, indicating that inactivation of DBH had not occurred in its passage through the pulmonary circulation. One patient with pulmonary hypertension had a large a-v difference in enzyme activity that may have been caused by altered pulmonary haemodynamics. Three of the five subjects that undertook a standardised exercise test on a bicycle ergometer showed a significant increase in plasma DBH activity. There was no correlation between the increases in DBH activity and in cardiac index and heart rate.     

CHARACTERIZATION OF THE BASIS FOR DIFFERENCES IN SERUM DBH ACTIVITY IN IMMATURE AND ADULT RATS BY USE OF HOMOLOGOUS ANTIBODY

Abstract– Rat serum dopamine-β-hydroxylase (DBH) activity decreased 5-7-fold between 15 and 60 days of age. Immunoprecipitation performed with homologous antibody (guinea-pig anti-rat adrenal DBH) showed that during this time period the quantity of antibody necessary to precipitate 50% of the enzymatic activity (AD₅₀) decreased 5-fold from 0.25 to 0.05 μl/ml. The biochemical properties of rat serum DBH at 15 and 60 days of age were compared to test the hypothesis that there might be different biochemical forms of the enzyme in the blood of immature and adult rats. Thermal stability, apparent K_m for tyramine, electrophoretic mobility, pH optima and elution profile on gel filtratioh chromatography were all found to be similar for rat serum DBH at both ages. On the basis of homospecific activity and multiple similarities in biochemical characteristics, it appears that differences in serum activity at the two ages reflect differences in the steady-state levels of enzyme. To determine the turnover of serum DBH in the two age groups, the recovery of enzyme activity was monitored after acute clearance of the circulating pool of DBH by treatment with the homologous antiserum. Immunotitration of DBH activity in vivo indicated that the total pool of serum enzyme was 4-fold greater in the mature rat than in 4-day-olds. After treatment of adult rats with 2μl of homologous antiserum, serum DBH activity was reduced by 85% with a half-life of recovery of 3.0 ± 0.6 days; the estimated fractional rate of degradation was 0.23 ± 0.06 day^?1 and the rate of entrance was 2.3 ± 0.2 units/ml/day. After treatment of 4-day-old rats with 1 μl of homologous antiserum, serum DBH activity was reduced by 95% with a half-life of recovery of 3.3 ± 0.5 days: the estimated average fractional rate of degradation was 0.22 ± 0.06 day^?1 and the average rate of entrance was 10.7 ± 1.6 units/ml/day. Thus, the several-fold difference in steady-state levels of serum DBH in rat pups as compared to adult rats appears to be due to greatly increased rates of entrance of the enzyme in the immature rats.     

Serum dopamine-beta-hydroxylase: constancy of levels in normotensive adults and decreases with development of blood pressure elevation.

Dopamine-β-hydroxylase is stable in serum frozen for several years and in the same normotensive white males studied over 3–7 years, levels of this enzyme in serum usually remained relatively constant. In four of nine patients in whom there was an increase in blood pressure, serum DBH levels decreased to a greater extent than in any of the 13 subjects in whom there was no significant change in blood pressure. Normal blood donors with systolic blood pressures less than 110 had higher levels of serum DBH than did donors with blood pressures over 130. The relationship of serum DBH changes to sympathetic neuronal function in patients with elevated blood pressure is discussed.     

Blood dopamine beta-hydroxylase activity and noradrenaline levels in the developing white rat.

Dopamine beta-hydroxylase (DBH) (3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating) (EC 1.14.17.1) activity in serum of blood obtained by decapitation of white rats at 19, 20, and 21 days in utero, immediately after birth, and postnatally to 70 days, was measured. Noradrenaline (NA) and DBH in plasma from undisturbed, cannulated, postweaning rats were also assayed. During the last few days in utero and the first 2 postnatal days serum DBH activity tripled and then remained elevated during the suckling period. Upon weaning, serum DBH activity declined at first precipitously and then more slowly, until the adult level was reached around 70 days of age. This postweaning decrease in DBH activity was also observed with the cannulated animals. In contrast, plasma NA levels remained low and constant throughout the postweaning period. In suckling rats treated with 6-hydroxydopamine from 2 to 12 days of age, serum DBH activity decreased to less than half its initial value by day 8. It is suggested that the observed changes in serum DBH activity in fetal and postnatal rats reflect ontogenetic changes in sympathetic nerve terminals and that they are probably not correlated with release of NA.     

Serum dopamine beta-hydroxylase activity in non-human primates: phylogenetic and genetic implications

1. Serum dopamine beta-hydroxylase (DBH) activity is one to two orders of magnitude higher in man than in any other species previously studied. The high levels of human serum DBH are associated with the inherited allele DBHH. 2. DBH activity was measured in serum from gorillas, chimpanzees, orangutans, gibbons, rhesus monkeys and squirrel monkeys in an attempt to determine how recently in the course of evolution the allele DBHH had originated. 3. Of the non-human primates tested, only gorillas had high levels of serum DBH activity comparable to those found in man. 4. The genetic polymorphism responsible for evaluated serum DBH in man is probably of very recent evolutionary origin.     

Correlation of the fatty acid composition and fluid property of the cholesteryl esters in the serum of Nigerian children with sickle cell disease and healthy controls

In a previous study conducted in Nigeria, we found that children with sickle cell disease (SCD) had exceedingly low total serum cholesterol levels (mean=100-102mg/dl). The fact that significant reductions in the levels of certain polyunsaturated fatty acids (PUFA) have been documented in the serum phospholipids of these same SCD subjects led us to inquire as to the fatty acid composition of the cholesteryl esters (CE) in their serum. Lecithin:cholesterol acyl transferase (LCAT), the enzyme in blood that catalyzes the reaction in which tissue cholesterol is acylated prior to its removal from cell membranes, is relatively specific for certain PUFA. CE in blood serum from 43 male and 42 female children with SCD, ages 4-18 years, and equal numbers of age- and gender-matched controls were analyzed for their fatty acid composition. Relative to the non-SCD controls, the CE of the SCD subjects contained 9% less linoleic acid, 16% less arachidonic acid, 40% less alpha-linolenic acid, 50% less eicosapentaenoic acid, and 36% less docosahexaenoic acid, but 15% more palmitic acid and 10% more oleic acid. Overall, the acyl chains of the CE of the SCD subjects were less fluid than those of the controls, as determined by comparison of their mean melting points (MMP) and double bond indices (DBI). MMP and DBI were both estimated from the individual constituent fatty acids comprising the CE acyl chains. The strongest correlations between MMP and fatty acid mole percent were seen with palmitic acid and linoleic acid. These results show that the fatty acid composition of the serum CE of children with SCD is abnormal relative to controls who do not have this hematologic disorder. We speculate that suboptimal fatty acid nutrition in Nigerian children with SCD compromises their ability to remove cholesterol from their tissues due to preference of the LCAT enzyme for PUFA, thereby accounting, in part at least, for the low total serum cholesterol levels one finds in children with SCD.     

Polymorphisms and low plasma activity of dopamine-beta-hydroxylase in ADHD children

Attention-deficit Hyperactivity disorder (ADHD) is a multifactorial disorder clinically characterized by inattentiveness, impulsivity and hyperactivity. The occurrence of this disorder is between 3 and 6% of the children population, with boys predominating over girls at a ratio of 3:1 or more. The research of some candidate genes (DRD4, DAT, DRD5, DBH, 5HTT, HTR1B and SNAP25) brought consistent results confirming the heredity of ADHD syndromes. Dopamine-beta-hydroxylase (DBH) is an enzyme responsible for the conversion of dopamine into noradrenaline. Alteration of the dopamine/noradrenaline levels can result in hyperactivity. The DBH protein is released in response to stimulation. DBH activity, derived largely from sympathetic nerves, can be measured in human plasma. Patients with ADHD showed decreased activities of DBH in serum and urine. Low DBH levels correlate indirectly with the seriousness of the hyperkinetic syndrome in children [19,20]. In the DBH gene, the G444A, G910T, C1603T, C1912T, C-1021T, 5 -ins/del and TaqI polymorphisms occur frequently and may affect the function of gene products or modify gene expression and thus influence the progression of ADHD. This article reviews the DBH itself and polymorphisms in the DBH gene that influence the DBH activity in the serum and the CSF level of DBH. All those are evaluated in connection with ADHD.     

Segregation and linkage analyses of dopamine-beta-hydroxylase activity.

Dopamine-beta-hydroxylase (DBH) activity in serum was measured by spectrophotometric methods in 95 persons of a large family (HGAR 2), along with 27 polymorphic markers from blood, urine and saliva. The distribution of DBH activity, after appropriate transformation and age adjustment, showed a significantly better fit to a mixture of two normal distributions than a single normal distribution. Pedigree segregation analyses showed evidence of a possible major gene governing low levels of DBH activity, segregating in this family in a recessive fashion. Linkage analyses between that major locus and the 27 polymorphic markers showed no significant lod scores favoring linkage. The highest lod score obtained was 0.81 with Lp at zero recombination fraction. In addition, published data on DBH activity measured by radiochemical assays on 22 families with 161 members were reanalyzed as a quantitative trait, with appropriate correction for ascertainment bias. The results were similar to that of HGAR 2, corroborating the existence of a major locus for DBH activity.     

Dopamine-Beta-Hydroxylase: An Index of Adrenergic Function in Hypertensive Patients

Previous attempts to assess sympathetic nervous system activity in patients with hypertension have used a variety of physiologic, pharmacologic and biochemical techniques. Results have been conflicting and confusing. Recently, the activity in plasma of the catecholamine synthesizing enzyme, dopamine-beta-hydroxylase (DBH), has been proposed as an index of sympathetic nervous system activity. Studies of apparently healthy subjects show that high values (greater than 60 units per liter) for plasma DBH activity correlate with pronounced daily lability of blood pressure and frequent readings greater than 130/85 mm of mercury. Studies of patients referred for evaluation of established hypertension show significantly higher values for plasma DBH activity in patients with primary hypertension than in those with commonly recognized forms of secondary hypertension—that is, renovascular, renal parenchymal and adrenocortical. Therefore, the measurement of plasma DBH activity may be helpful in the study and differential diagnosis of hypertensive diseases. Measurement of DBH in plasma is inexpensive, reproducible and relatively easy to do.     

Study on DBH Genetic Polymorphisms and Plasma Activity in Attention Deficit Hyperactivity Disorder Patients from Eastern India

Dysfunctions in the norepinephric pathway have been speculated in the etiology of attention deficit hyperactivity disorder (ADHD), a common problem for children. Synthesis of norepinephrine from dopamine is catalyzed by the enzyme dopamine β-hydroxylase and numerous polymorphisms in the DBH gene have been found to exert their direct influence on the enzyme activity independently. In the present study association of ADHD with four genetic polymorphisms, DBH-STR, rs1611115, rs1108580, and rs2519152, was examined in subjects belonging to eastern India. ADHD subjects (n = 111) were recruited following DSM-IV criteria. Peripheral blood samples were collected from nuclear families with ADHD probands. A group of ethnically matched healthy volunteers (n = 130) was also recruited. Genomic DNA was analyzed by PCR amplification followed by restriction digestion and genotyping. Data obtained were subjected to both family-based as well as population-based statistical analyses. Plasma DβH activity was measured using a photometric assay and its correlation with the genetic polymorphisms was analyzed using analysis of variance. Case–control analysis revealed no significant differences in allelic frequencies; however, significant paternal over-transmission (P = 0.02) of the rs2519152 ‘G’ allele to ADHD probands was noticed. A haplotype, composed of 12R-C-G-G, also showed biased transmission. Strong correlation was observed between enzyme activity and rs1611115, rs1108580, and rs2519152 (P = 1.51E-6, 0.04, and 0.003, respectively). The present study hints toward the fact that DBH gene polymorphisms have some role in the etiology of ADHD in eastern Indian population and their study could be useful for therapeutic intervention.     

Heat stability and pH activity data of alpha-L-fucosidase in human serum vary with enzyme concentration

alpha-L-Fucosidase from serum of humans with either high or low enzyme activity was separately purified. the enzyme from either source had virtually the same heat stability and pH activity profile. It has been widely reported that alpha-L-fucosidase in crude sera from individuals with high and low enzyme activity differed with respect to heat stability and activity at pH 4 relative to activity at pH 5, the pH optimum of the enzyme. We investigated this discrepancy and found that both the heat stability and relative activity at pH 4 of alpha-L-fucosidase from sera with either high or low enzyme activity was dependent upon enzyme concentration. With decreasing enzyme concentration, the enzyme was more heat labile and had less relative activity at pH 4. Consequently, if the data obtained using high and low enzyme activity sera are compared on the basis of equivalent amounts of serum instead of equivalent amounts of enzyme activity, differences between the enzyme from high and low activity serum would be erroneously inferred. Apparently, this is what other investigators have done. Moreover, we found that alpha-L-fucosidase can exist in heat-stable or labile species with sedimentation coefficients of 9.8 S and 4.8 S, respectively. The interconversion and relative proportion of these species is dependent upon enzyme concentration and pH.     

Angiotensin-converting enzyme and anorexia nervosa

Angiotensin-converting enzyme (ACE) activity was measured in 10 patients with anorexia nervosa, 6 with hyperthyroid Graves' disease, and 7 with primary hypothyroidism. Patients with anorexia nervosa had a low serum ACE activity (9.8 +/- 2.2 IU/l), as compared to findings in normal subjects (13.4 +/- 3.5 IU/l) (P less than 0.05). Patients with hyperthyroid Graves' disease had high serum ACE activity (23.7 +/- 5.8 IU/l), as compared to levels in normal subjects (P less than 0.01), and patients with primary hypothyroidism tended to have low serum ACE activity (10.1 +/- 1.8 IU/l), compared to the normal subjects (P less than 0.1). Following weight gain (before; 71.3 +/- 10.2% of ideal body weight, after; 88.7 +/- 5.6% of ideal body weight), serum ACE activity in patients with anorexia nervosa reverted to within the normal range (13.8 +/- 3.5 IU/l), and serum T3 concentration was restored to the normal range (before; 0.7 +/- 0.2 ng/ml, after; 1.1 +/- 0.3 ng/ml). In these patients, ACE activity correlated with the per cent of ideal body weight (P less than 0.05). These data suggest that, in underweight subjects with anorexia nervosa, decreased serum ACE activities may relate to emaciation.     

Variations in serum dopamine beta-hydroxylase in normal subjects and chronic alcoholics

Serum dopamine beta-hydroxylase (DBH) activity varies greatly between individuals but is usually relatively constant within individuals. DBH activity was determined in 20 normal subjects and 6 chronic alcoholics during alcohol ingestion and withdrawal, under controlled and standardized conditions. For all subjects mean random DBH was 423 +/- 249 (mean +/- SD) nmol phenylethanolamine/h per millilitre serum. Between-day serum DBH values vary more than within-day values (21.1% vs 15.1%). Cold-pressor testing or sudden standing does not increase mean DBH; however, some individuals show a significant increase which cannot be elicited on repeat testing. Mean DBH activity did not vary significantly over 24 h. Clinically useful correlations between single random DBH and blood pressure or 24-h urine catechols should not be expected.     

Dopamine beta-hydroxylase in rat serum and lymph: changes with age and effect of cold exposure.

The pH optimum for rat serum dopamine beta-hydroxylase (DBH) (3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating)(EC 1.14.17.1) was 4.0 in acetate buffer; other requirements were as reported by others. DBH activity in serum of 20-day-old fetuses is slightly higher than in that of their mothers. Levels of the enzyme in blood a few hours after birth are almost five times greater than in the adult, remain high during the suckling period, then drop rapidly during the 4th week after birth to about three times the adult level, which is then slowly reached over the next few weeks. These fluctuations in serum DBH activity coincide with the period of intense development and maturation of the sympathetic nervous system. There was not significant effect of cold exposure on blood DBH activity when newborn, suckling, weanling or adult warm- and cold-acclimated rats were exposed to cold. Similarly, exposure to cold that elicited two- to three-fold increases in O2 consumption failed to increase DBH activity in thoracic duct lymph. Therefore serum and lymph DBH activities are not sensitive indices of sympathetic secretory activity in the intact rat.     

Mercaptopurine pharmacogenetics: Monogenic inheritance of erythrocyte thiopurine methyltransferase activity

Thiopurine methyltransferase (TPMT) catalyzes thiopurine S-methylation, an important metabolic pathway for drugs such as 6-mercaptopurine. Erythrocyte (RBC) TPMT activity was measured in blood samples from 298 randomly selected subjects. Of the subjects, 88.6% were included in a subgroup with high enzyme activity (13.50 ± 1.86 U, mean ± SD), 11.1% were included in a subgroup with intermediate activity (7.20 ± 1.08 U), and 0.3% had undetectable activity. This distribution conforms to Hardy-Weinberg predictions for the autosomal codominant inheritance of a pair of alleles for low and high TPMT activity, TPMT^L and TPMT^H, with gene frequencies of .059 and .941, respectively. If RBC TPMT activity is inherited in an autosomal codominant fashion, then subjects homozygous for TPMT^H would have high enzyme activity, subjects heterozygous for the two alleles would have intermediate activity, and subjects homozygous for TPMT^L would have undetectable activity. The segregation of RBC TPMT activity among 215 first-degree relatives in 50 randomly selected families and among 35 members of two kindreds and one family selected because they included probands with undetectable RBC enzyme activity were also compatible with the autosomal codominant inheritance of RBC TPMT. For example, in eight matings between subjects with intermediate activity (presumed genotype TPMT^L TPMT^H) and subjects with high activity (presumed genotype TPMT^H TPMT^H), 47% (8/17) of the offspring had intermediate activity. This value is very similar to the 50% figure expected on the basis of autosomal codominant inheritance (χ²_[1] = .059). Further experiments are required to determine whether this genetic polymorphism for an important drug metabolizing enzyme may represent one factor in individual variations in sensitivity to thiopurines.     

Dopamine-beta-hydroxylase inhibition acutely stimulates rats hypothalamic noradrenaline and dopamine neuronal activity as assessed from metabolic ratios and circulating glucose and ACTH responses

Because central noradrenaline neuronal activity is tonically inhibited by noradrenaline (NA) itself via an action at prejunctional alpha 2-adrenoceptors, it was hypothesised that the blockade of central NA synthesis following acute dopamine-beta -hydroxylase (DBH) inhibition might primarily deplete prejunctional NA levels and result in an increase in central NA neuronal activity through reduced NA autoinhibition. This hypothesis was tested in the rat following the acute administration of the DBH inhibitors diethyldithiocarbamate (DDC) and cysteamine (CSH). Computerised gas chromatography/mass spectrometry was used to precisely measure the hypothalamic levels of NA and dopamine (DA) together with those of their primary neuronal metabolites dihydroxyphenylethyleneglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC), respectively. Both DDC (at 4 h) and CSH (at 30 min.) caused approximately a 50% reduction of hypothalamic NA concentrations. However this was associated with marked and highly significant increases in hypothalamic DHPG levels (by 50-100%) and in the hypothalamic ratio DHPG/NA. Also, when measured after CSH, the hypothalamic levels of the DHPG metabolite 3-methoxy-4-hydroxyphenylethyleneglycol were highly significantly increased. Consistent with increased DA neuronal activity, both DBH inhibitors raised DA and DOPAC levels and also the ratio DOPAC/DA in the hypothalami of treated rats and markedly suppressed serum prolactin levels (all p less than 0.01). The rise in hypothalamic concentrations of DHPG indicates that an increase in hypothalamic NA neuronal activity occurs following DBH inhibition. Significant elevations of blood glucose, corticosterone and ACTH were also observed after DBH inhibition. As we have previously demonstrated that increased central NA activity is associated with elevations of blood glucose, corticosterone and ACTH, these data provide further evidence for a functional increase in central NA activity caused by acute DBH inhibition. It is proposed that the increase in hypothalamic NA activity after DBH inhibition results from a primary depletion of the prejunctional alpha 2-active autoregulatory pool of NA.     

Quantitative variations of red-cell cytochrome b5 reductase (NADH-methemoglobin-reductase) in the Algerian population

Summary A striking proportion of Algerian subjects was reported among patients with congenital recessive methemoglobinemia due to cytochrome b₅ reductase deficiency (Kaplan et al. 1979).A population survery was carried out in red blood cells from 1000 algerian subjects. In 16 subjects, the cytochrome b₅ reductase activity was diminished by 50%. Family studies indicated the presence of a defective allele with an overall gene frequency of 0.008. Immunologically cross-reacting material was found in red cells with low cytochrome b₅ reductase activity. Leukocytes exhibited normal levels of enzyme in some families and low levels in others suggesting that at least two different deficient alleles at the DIA₁ locus were present in the Algerian population. A higher prevalence of the deficient allele(s) was found in subjects of Kabyle origin.