Genetic impact of blood C-reactive protein levels on chronic spinal & widespread pain

PURPOSE

Causal mechanisms underlying systemic inflammation in spinal & widespread pain remain an intractable experimental challenge. Here we examined whether: (i) associations between blood C-reactive protein (CRP) and chronic back, neck/shoulder & widespread pain can be explained by shared underlying genetic variants; and (ii) higher CRP levels causally contribute to these conditions.

METHODS

Using genome-wide association studies (GWAS) of chronic back, neck/shoulder & widespread pain (N = 6063-79,089 cases; N = 239,125 controls) and GWAS summary statistics for blood CRP (Pan-UK Biobank N = 400,094 & PAGE consortium N = 28,520), we employed cross-trait bivariate linkage disequilibrium score regression to determine genetic correlations (rG) between these chronic pain phenotypes and CRP levels (FDR < 5%). Latent causal variable (LCV) and generalised summary data-based Mendelian randomisation (GSMR) analyses examined putative causal associations between chronic pain & CRP (FDR < 5%).

RESULTS

Higher CRP levels were genetically correlated with chronic back, neck/shoulder & widespread pain (rG range 0.26-0.36; P ≤ 8.07E-9; 3/6 trait pairs). Although genetic causal proportions (GCP) did not explain this finding (GCP range - 0.32-0.08; P ≥ 0.02), GSMR demonstrated putative causal effects of higher CRP levels contributing to each pain type (beta range 0.027-0.166; P ≤ 9.82E-03; 3 trait pairs) as well as neck/shoulder pain effects on CRP levels (beta [S.E.] 0.030 [0.021]; P = 6.97E-04).

CONCLUSION

This genetic evidence for higher CRP levels in chronic spinal (back, neck/shoulder) & widespread pain warrants further large-scale multimodal & prospective longitudinal studies to accelerate the identification of novel translational targets and more effective therapeutic strategies.

A Shared Genetic Signature for Common Chronic Pain Conditions and its Impact on Biopsychosocial Traits

The multiple comorbidities & dimensions of chronic pain present a formidable challenge in disentangling its aetiology. Here, we performed genome-wide association studies of 8 chronic pain types using UK Biobank data (N =4,037-79,089 cases; N = 239,125 controls), followed by bivariate linkage disequilibrium-score regression and latent causal variable analyses to determine (respectively) their genetic correlations and genetic causal proportion (GCP) parameters with 1,492 other complex traits. We report evidence of a shared genetic signature across chronic pain types as their genetic correlations and GCP directions were broadly consistent across an array of biopsychosocial traits. Across 5,942 significant genetic correlations, 570 trait pairs could be explained by a causal association (|GCP| >0.6; 5% false discovery rate), including 82 traits affected by pain while 410 contributed to an increased risk of chronic pain (cf. 78 with a decreased risk) such as certain somatic pathologies (eg, musculoskeletal), psychiatric traits (eg, depression), socioeconomic factors (eg, occupation) and medical comorbidities (eg, cardiovascular disease). This data-driven phenome-wide association analysis has demonstrated a novel and efficient strategy for identifying genetically supported risk & protective traits to enhance the design of interventional trials targeting underlying causal factors and accelerate the development of more effective treatments with broader clinical utility. PERSPECTIVE: Through large-scale phenome-wide association analyses of >1,400 biopsychosocial traits, this article provides evidence for a shared genetic signature across 8 common chronic pain types. It lays the foundation for further translational studies focused on identifying causal genetic variants and pathophysiological pathways to develop novel diagnostic & therapeutic technologies and strategies.

Surface Normals and Light Directions From Shading and Polarization

We introduce a method of recovering the shape of a smooth dielectric object using diffuse polarization images taken with different directional light sources. We present two constraints on shading and polarization and use both in a single optimization scheme. This integration is motivated by photometric stereo and polarization-based methods having complementary abilities. Polarization gives strong cues for the surface orientation and refractive index, which are independent of the light direction. However, employing polarization leads to ambiguities in selecting between two ambiguous choices of the surface orientation, in the relationship between the refractive index and zenith angle (observing angle). Moreover, polarization-based methods for surface points with small zenith angles perform poorly owing to the weak polarization. In contrast, the photometric stereo method with multiple light sources disambiguates the surface normals and gives a strong relationship between surface normals and light directions. However, the method has limited performance for large zenith angles and refractive index estimation and faces strong ambiguity when light directions are unknown. Taking the advantages of these methods, our proposed method recovers surface normals for small and large zenith angles, light directions, and refractive indexes of the object. The proposed method is positively evaluated in simulations and real-world experiments.

Genetic risk for chronic pain is associated with lower antidepressant effectiveness: Converging evidence for a depression subtype

INTRODUCTION

Chronic pain and depression are highly comorbid and difficult-to-treat disorders. We previously showed this comorbidity is associated with higher depression severity, lower antidepressant treatment effectiveness and poorer prognosis in the Australian Genetics of Depression Study.

OBJECTIVE

The current study aimed to assess whether a genetic liability to chronic pain is associated with antidepressant effectiveness over and above the effect of genetic factors for depression in a sample of 12,863 Australian Genetics of Depression Study participants.

METHODS

Polygenic risk scores were calculated using summary statistics from genome-wide association studies of multisite chronic pain and major depression. Cumulative linked regressions were employed to assess the association between polygenic risk scores and antidepressant treatment effectiveness across 10 different medications.

RESULTS

Mixed-effects logistic regressions showed that individual genetic propensity for chronic pain, but not major depression, was significantly associated with patient-reported chronic pain (Pain^PRS OR = 1.17 [1.12, 1.22]; MD^PRS OR = 1.01 [0.98, 1.06]). Significant associations were also found between lower antidepressant effectiveness and genetic risk for chronic pain or for major depression. However, a fully adjusted model showed the effect of Pain^PRS (adjOR = 0.93 [0.90, 0.96]) was independent of MD^PRS (adjOR = 0.96 [0.93, 0.99]). Sensitivity analyses were performed to assess the robustness of these results. After adjusting for depression severity measures (i.e. age of onset; number of depressive episodes; interval between age at study participation and at depression onset), the associations between Pain^PRS and patient-reported chronic pain with lower antidepressant effectiveness remained significant (0.95 [0.92, 0.98] and 0.84 [0.78, 0.90], respectively).

CONCLUSION

These results suggest genetic risk for chronic pain accounted for poorer antidepressant effectiveness, independent of the genetic risk for major depression. Our results, along with independent converging evidence from other studies, point towards a difficult-to-treat depression subtype characterised by comorbid chronic pain. This finding warrants further investigation into the implications for biologically based nosology frameworks in pain medicine and psychiatry.

Genetic basis to structural grey matter associations with chronic pain

Structural neuroimaging studies of individuals with chronic pain conditions have often observed decreased regional grey matter at a phenotypic level. However, it is not known if this association can be attributed to genetic factors. Here we employed a novel integrative data-driven and hypothesis-testing approach to determine whether there is a genetic basis to grey matter morphology differences in chronic pain. Using publicly available genome-wide association study summary statistics for regional chronic pain conditions (n = 196 963) and structural neuroimaging measures (n = 19 629-34 000), we applied bivariate linkage disequilibrium-score regression and latent causal variable analyses to determine the genetic correlations (rG) and genetic causal proportion (GCP) between these complex traits, respectively. Five a priori brain regions (i.e. prefrontal cortex, cingulate cortex, insula, thalamus and superior temporal gyrus) were selected based on systematic reviews of grey matter morphology studies in chronic pain. Across this evidence-based selection of five brain regions, 10 significant negative genetic correlations (out of 369) were found (false discovery rate < 5%), suggesting a shared genetic basis to both reduced regional grey matter morphology and the presence of chronic pain. Specifically, negative genetic correlations were observed between reduced insula grey matter morphology and chronic pain in the abdomen (mean insula cortical thickness), hips (left insula volume) and neck/shoulders (left and right insula volume). Similarly, a shared genetic basis was found for reduced posterior cingulate cortex volume in chronic pain of the hip (left and right posterior cingulate), neck/shoulder (left posterior cingulate) and chronic pain at any site (left posterior cingulate); and for reduced pars triangularis volume in chronic neck/shoulder (left pars triangularis) and widespread pain (right pars triangularis). Across these negative genetic correlations, a significant genetic causal proportion was only found between mean insula thickness and chronic abdominal pain [rG (standard error, SE) = -0.25 (0.08), P = 1.06 × 10-3; GCP (SE) = -0.69 (0.20), P = 4.96 × 10-4]. This finding suggests that the genes underlying reduced cortical thickness of the insula causally contribute to an increased risk of chronic abdominal pain. Altogether, these results provide independent corroborating evidence for observational reports of decreased grey matter of particular brain regions in chronic pain. Further, we show for the first time that this association is mediated (in part) by genetic factors. These novel findings warrant further investigation into the neurogenetic pathways that underlie the development and prolongation of chronic pain conditions.

Comorbid Chronic Pain and Depression: Shared Risk Factors and Differential Antidepressant Effectiveness

The bidirectional relationship between depression and chronic pain is well-recognized, but their clinical management remains challenging. Here we characterize the shared risk factors and outcomes for their comorbidity in the Australian Genetics of Depression cohort study (N = 13,839). Participants completed online questionnaires about chronic pain, psychiatric symptoms, comorbidities, treatment response and general health. Logistic regression models were used to examine the relationship between chronic pain and clinical and demographic factors. Cumulative linked logistic regressions assessed the effect of chronic pain on treatment response for 10 different antidepressants. Chronic pain was associated with an increased risk of depression (OR = 1.86 [1.37-2.54]), recent suicide attempt (OR = 1.88 [1.14-3.09]), higher use of tobacco (OR = 1.05 [1.02-1.09]) and misuse of painkillers (e.g., opioids; OR = 1.31 [1.06-1.62]). Participants with comorbid chronic pain and depression reported fewer functional benefits from antidepressant use and lower benefits from sertraline (OR = 0.75 [0.68-0.83]), escitalopram (OR = 0.75 [0.67-0.85]) and venlafaxine (OR = 0.78 [0.68-0.88]) when compared to participants without chronic pain. Furthermore, participants taking sertraline (OR = 0.45 [0.30-0.67]), escitalopram (OR = 0.45 [0.27-0.74]) and citalopram (OR = 0.32 [0.15-0.67]) specifically for chronic pain (among other indications) reported lower benefits compared to other participants taking these same medications but not for chronic pain. These findings reveal novel insights into the complex relationship between chronic pain and depression. Treatment response analyses indicate differential effectiveness between particular antidepressants and poorer functional outcomes for these comorbid conditions. Further examination is warranted in targeted interventional clinical trials, which also include neuroimaging genetics and pharmacogenomics protocols. This work will advance the delineation of disease risk indicators and novel aetiological pathways for therapeutic intervention in comorbid pain and depression as well as other psychiatric comorbidities.

Centrifugation stress reduces the responsiveness of spermatozoa to a capacitation stimulus in in vitro-aged semen

Density gradient centrifugation of semen is commonly used in many assisted reproduction techniques. Although gradients have the potential to isolate and enrich motile and viable spermatozoa, the centrifugation force presents a stress factor to cell organelles and membranes. The objective of the study was to evaluate the impact of density gradient centrifugation stress on sperm capacitation dynamics, cell stability and the ability of spermatozoa to specifically respond to bicarbonate in extended semen undergoing in vitro ageing. Extended boar semen (n = 7) was stored for 12, 24, 72 and 120 h respectively at 17 °C before centrifugation and incubation in variations of an in vitro capacitation medium. The number of viable, acrosome intact sperm and motility parameters as assessed by computer-assisted semen analysis did not change during storage. Kinetic changes in viability (plasma membrane integrity) and intracellular calcium levels (calcium influx) during in vitro capacitation were assessed after preparation of semen samples with both, a Percoll and a sucrose gradient centrifugation, either only Percoll, only sucrose centrifugation or no centrifugation. Changes in the viable sperm population that could be specifically attributed as a response to either bicarbonate or calcium were determined. In in vitro-aged (>12 h stored) spermatozoa, centrifugation reduced the proportion of spermatozoa which specifically responded to the capacitating stimulus bicarbonate. Concomitantly, centrifugation increased the proportion of spermatozoa responding to calcium in absence of bicarbonate, thus indicating an increased sensitivity to incubation per se. Absence of centrifugation steps during semen preparation, revealed a highly conserved ability of in vitro-aged spermatozoa to specifically respond to bicarbonate. In conclusion, density gradient centrifugation alters the physiological property of spermatozoa for controlled capacitation, which may influence the success rates of centrifuged semen in assisted reproductive technologies and confound interpretation of capacitation assays.

Attentional switching in humans and flies: rivalry in large and miniature brains

Human perception, and consequently behavior, is driven by attention dynamics. In the special case of rivalry, where attention alternates between competing percepts, such dynamics can be measured and their determinants investigated. A recent study in the fruit fly, Drosophila melanogaster, now shows that the origins of attentional rivalry may be quite ancient. Furthermore, individual variation exists in the rate of attentional rivalry in both humans and flies, and in humans this is under substantial genetic influence. In the pathophysiological realm, slowing of rivalry rate is associated with the heritable psychiatric condition, bipolar disorder. Fly rivalry may therefore prove a powerful model to examine genetic and molecular influences on rivalry rate, and may even shed light on human cognitive and behavioral dysfunction.

Slow binocular rivalry in bipolar disorder

BACKGROUND

The rate of binocular rivalry has been reported to be slower in subjects with bipolar disorder than in controls when tested with drifting, vertical and horizontal gratings of high spatial frequency.

METHOD

Here we assess the rate of binocular rivalry with stationary, vertical and horizontal gratings of low spatial frequency in 30 subjects with bipolar disorder, 30 age- and sex-matched controls, 18 subjects with schizophrenia and 18 subjects with major depression. Along with rivalry rate, the predominance of each of the rivaling images was assessed, as was the distribution of normalized rivalry intervals.

RESULTS

The bipolar group demonstrated significantly slower rivalry than the control, schizophrenia and major depression groups. The schizophrenia and major depression groups did not differ significantly from the control group. Predominance values did not differ according to diagnosis and the distribution of normalized rivalry intervals was well described by a gamma function in all groups.

CONCLUSIONS

The results provide further evidence that binocular rivalry is slow in bipolar disorder and demonstrate that rivalry predominance and the distribution of normalized rivalry intervals are not abnormal in bipolar disorder. It is also shown by comparison with previous work, that high strength stimuli more effectively distinguish bipolar from control subjects than low strength stimuli. The data on schizophrenia and major depression suggest the need for large-scale specificity trials. Further study is also required to assess genetic and pathophysiological factors as well as the potential effects of state, medication, and clinical and biological subtypes.

Raf-induced transformation requires an interleukin 1 autocrine loop

The c-Raf-1 serine/threonine protein kinase plays a critical role in the proliferation of most cell types that have been examined. As such, the Raf proto-oncogene is thought to play a central role in the development of human tumors. Although the c-raf-1 gene itself rarely appears to be mutated in human tumors, the kinase activity of Raf is frequently found to be more active in tumor cells, likely through constitutive activation of upstream activators of Raf. The downstream events triggered by Raf that are involved in transformation have been studied less extensively. We show in this study that Raf-induced transformation of NIH 3T3 cells requires the activation of the ubiquitously expressed transcription factor, nuclear factor-kappaB, by Raf. Furthermore, through the use of CrmA, interleukin 1 (IL-1) receptor antagonist, and a dominant-negative form of TRAF6, we demonstrate a requirement for IL-1 production and signaling from the IL-1 receptor as necessary components of Raf-induced transformation. These results indicate that IL-1 may be used as an autocrine growth factor by a number of tumors in which activation of Raf plays an important role in transformation and suggest that blockade of IL-1 signaling may be an approach to limiting the growth of certain tumors.

Rapid streptococcal testing in Vietnamese children with pharyngitis

Streptococcal pharyngitis has been a significant public health problem in Vietnam for many years. Accurate diagnosis of the infection, however, has been difficult. We carried out a clinical trial of a rapid streptococcal antigen detection test (Quick-Vue (R) Flex Strep A) on a population of 777 children with pharyngitis seen at the Institute for the Protection of Children's Health (Children's Hospital) in Hanoi, Vietnam. Bacterial culture was performed in parallel with the rapid test on simultaneously obtained throat swab specimens. The rapid test was found to be 89% sensitive and 92% specific (96% in children not on prior antibiotics) compared to culture. The test was also found to be convenient and acceptable to patients and clinicians. A significant benefit of the test is that those children found positive are more likely to be treated with penicillin rather than a broad spectrum antimicrobial, which in turn will reduce the likelihood of resistant infections in the future.

Unusual protein-binding specificity and capacity of aza-arenophilic gels

A number of synthetic aza-arenophilic gels have been synthesized from Sepharose CL-4B, 3,5-dichloro-2,4,6-trifluoropyridine and 4-dimethylaminopyridine. These show high binding capacities for immunoglobulins and enzymes. Under high-salt buffer binding conditions, IgG can be effectively eluted, essentially free of contamination by BSA, using acidic conditions (pH 2.5) or phosphate buffers (pH 7.4) containing nucleophiles. Enzymes can also be readily adsorbed and desorbed. Thus these gels can be reused as supports for the immobilization of enzymes.

Interhemispheric switching mediates perceptual rivalry

BACKGROUND

Binocular rivalry refers to the alternating perceptual states that occur when the images seen by the two eyes are too different to be fused into a single percept. Logothetis and colleagues have challenged suggestions that this phenomenon occurs early in the visual pathway. They have shown that, in alert monkeys, neurons in the primary visual cortex continue to respond to their preferred stimulus despite the monkey reporting its absence. Moreover, they found that neural activity higher in the visual pathway is highly correlated with the monkey's reported percept. These and other findings suggest that the neural substrate of binocular rivalry must involve high levels, perhaps the same levels involved in reversible figure alternations.

RESULTS

We present evidence that activation or disruption of a single hemisphere in human subjects affects the perceptual alternations of binocular rivalry. Unilateral caloric vestibular stimulation changed the ratio of time spent in each competing perceptual state. Transcranial magnetic stimulation applied to one hemisphere disrupted normal perceptual alternations when the stimulation was timed to occur at one phase of the perceptual switch, but not at the other. Furthermore, activation of a single hemisphere by caloric stimulation affected the perceptual alternations of a reversible figure, the Necker cube.

CONCLUSIONS

Our findings suggest that interhemispheric switching mediates perceptual rivalry. Thus, competition for awareness in both binocular rivalry and reversible figures occurs between, rather than within, each hemisphere. This interhemispheric switch hypothesis has implications for understanding the neural mechanisms of conscious experience and also has clinical relevance as the rate of both types of perceptual rivalry is slow in bipolar disorder (manic depression).

Co-stimulation of promoter for low density lipoprotein receptor gene by sterol regulatory element-binding protein and Sp1 is specifically disrupted by the yin yang 1 protein

Sterol regulation of gene expression in mammalian cells is mediated by an interaction between the cholesterol-sensitive sterol regulatory element-binding proteins (SREBPs) and promoter-specific but generic co-regulatory transcription factors such as Sp1 and NF-Y/CBF. Thus, sterol-regulated promoters that require different co-regulatory factors could be regulated independently through targeting the specific interaction between the SREBPs and the individual co-regulatory proteins. In the present studies we demonstrate that transiently expressed yin yang 1 protein (YY1) inhibits the SREBP-mediated activation of the low density lipoprotein (LDL) receptor in a sensitive and dose-dependent manner. The inhibition is independent of YY1 binding directly to the LDL receptor promoter, and we show that the same region of YY1 that interacts in solution with Sp1 also interacts with SREBP. Furthermore, other SREBP-regulated genes that are not co-regulated by Sp1 are either not affected at all or are not as sensitive to the repression. Thus, the specific interaction that occurs between SREBPs and Sp1 to stimulate the LDL receptor promoter is a specific target for inhibition by the YY1 protein, and we provide evidence that the mechanism can be at least partially explained by the ability of YY1 to inhibit the interaction between SREBP and Sp1 in solution in vitro. The LDL receptor is the key gene of cholesterol uptake, and the rate-controlling genes of cholesterol synthesis are stimulated by the concerted action of SREBPs along with coregulators that are distinct from Sp1. Therefore, repression of gene expression through specifically targeting the interaction between SREBP and Sp1 would provide a molecular mechanism to explain how cholesterol uptake can be regulated independently from cholesterol biosynthesis in mammalian cells.

Patient selection may affect gene therapy success. Dominant negative effects observed for ornithine transcarbamylase in mouse and human hepatocytes

We have achieved significant improvement of ornithine transcarbamylase deficiency (OTCD) in a mouse model through adenoviral-mediated gene transfer of the human ornithine transcarbamylase cDNA. Substantial reduction in orotic aciduria was observed within 24 h of treatment. Metabolic correction was later associated with phenotypic correction and moderate increase in enzymatic activity. In an effort to identify the level of gene expression required to achieve wild-type levels of enzyme activity we uncovered a dominant negative effect of the endogenous mutant protein on the activity of the delivered recombinant wild-type protein. This phenomenon is relevant to homomultimeric protein defects such as OTCD, represent a challenging category of disorders for gene therapy. Thus, although our findings indicate that adenoviral-mediated gene transfer may have potential as a short-term treatment for OTCD in humans and may be effective especially during catabolic crisis, the observations in this study suggest that careful patient selection based on mutation class may be essential for initial OTCD gene therapy trials, and perhaps, for other homomultimeric enzyme deficiencies being considered as gene therapy targets.

Rapid purification of immunoglobulin G using aza-arenophilic chromatography: novel mode of protein-solid phase interactions

A derivative of aza-arenophilic gel having a dichlorosubstituent and an hydroxy ion as a capping nucleophile has been prepared. The properties of this gel in relation to IgG purification have been investigated in details. In the presence of high salt (1.5 M), albumin and some other serum proteins did not bind to the gel. IgG and some other minor proteins, however, were bound to the gel. The bound proteins can be eluted with an acidic buffer. SDS-PAGE showed that the fraction eluted with 0.1 M sodium acetate pH 4.2 consisted mainly of IgGs.

Avid AL, a synthetic ligand affinity gel mimicking immobilized bacterial antibody receptor for purification of immunoglobulin G

Avid AL is an affinity gel designed for the purification of immunoglobulin G (IgG). The gel was prepared by first reacting Sepharose with 3,5-dichloro-2,4,6-trifluoropyridine and 4-dimethylaminopyridine and then with 2-mercaptoethanol. The IgG purified by Avid AL is about 95% pure. The binding parameters of Avid AL for the whole IgG, Fab and Fc fragment and the stability of gel were investigated. The IgG bound to Avid AL can be eluted with an acidic buffer or with a novel neutral buffer containing electron donors. The development of such a mild neutral elution buffer is described. Application of Avid AL in a rapid gram-scale IgG purification was demonstrated. The possible mechanism of IgG binding is discussed.

Use of microwell plates carrying hydrazide groups to enhance antibody immobilization in enzyme immunoassays

Using microwell plates functionalized with surface hydrazide groups, we site-specifically immobilized antibodies to the surface of the wells. The procedure for site-specific, oriented immobilization of IgG to hydrazide surfaces is simple. It requires a brief, mild oxidation of the carbohydrate side chains of IgG with NaIO4 at a pH of approximately 5 and incubation of the oxidized IgG with the hydrazide surface. These oxidized immunoglobulins bind to the hydrazide groups of these plates preferentially by the Fc region of the molecule, resulting in improved specific activity. Enzyme immunoassays for horseradish peroxidase and human IgG were tested on both standard (hydrophobic) and hydrazide group-carrying surfaces. The improved antigen binding capacity of the hydrazide-modified plates results in greatly increased sensitivity (approximately 4 x) and improved linearity in both assays when compared to native, nonoxidized antibody used with standard microwell plates. Furthermore, the hydrazide functionalized plates exhibited lower non specific binding.

Rapid and simple isolation of multigram goat IgG from serum using Avid AL and radial flow column

Multigram quantities (2.5-10 g) of highly purified IgG were obtained within 4 h from serum by using Avid AL packed in a radial-flow column. Avid AL is an affinity gel containing a synthetic, low-mol-wt ligand capable of selectively binding IgG from serum of all animal species tested. By packing the gel in a radial-flow column up to 500 mL, a high flow rate of 50 mL/min can be achieved without adversely affecting the performance of the gel and the purity of the isolated antibody.

Flow injection analysis of lactose using covalently immobilized beta-galactosidase, mutarotase, and glucose oxidase/peroxidase on a 2-fluoro-1-methylpyridinium salt-activated Fractogel support

Milk samples were analyzed for their lactose content using flow injection analysis and incorporating immobilized beta-galactosidase or beta-galactosidase/mutarotase and glucose oxidase/peroxidase bioreactors. These enzymes were immobilized, under mild conditions, on to a 2-fluoro-1-methylpyridinium salt-activated Fractogel support. The use of a phosphate buffer (0.15 M) was found to facilitate the rapid mutarotation of alpha-D-glucose and hence could obviate the need for the more expensive mutarotase. The chromogenic agents of choice for monitoring the reaction were 3-methyl-2-benzothiazolinone hydrazone and 3-dimethylaminobenzoic acid. Linearity was observed over the concentration range 16-160 micrograms/ml using lactose standards (r = 0.996). Between 30 and 40 milk samples/h can be analyzed. Comparisons are made with existing HPLC and alkaline methylamine methods for a range of milk matrices. The FIA method consistently gives the lowest standard deviations and coefficient of variation for the various milk matrices analyzed.

Simple, quick and efficient site-directed antibody immobilization in a cartridge

A method is described for the simple, quick and efficient attachment of antibody within a cartridge for use as an immunoaffinity chromatography column. Antibodies are immobilized via their Fc regions through the use of periodate-oxidized carbohydrate functionalities of the immunoglobulin G. The method allows for the in situ coupling of the immunoglobulin G without prior removal of the oxidizing periodate solution. The entire procedure can be completed in 50 minutes. This method is especially useful for quick determinations of a particular monoclonal antibody's functionality or avidity towards a specific antigen. It may also be used in place of a conventional immunoaffinity column for the rapid isolation of small amounts of an antigen. This method will reduce the lengthy process of preparing an immunoaffinity column from several days to less than an hour.

Flow injection analysis of serum urea using urease covalently immobilized on 2-fluoro-1-methylpyridinium salt-activated fractogel and fluorescence detection

Serum samples were analyzed for their urea content using fluorescence flow injection analysis incorporating an immobilized urease bioreactor and a gas permeable separator. The urease was immobilized under mild and facile conditions to a hydrophilic 2-fluoro-1-methylpyridinium-activated support. The ammonia released as a result of urease-catalyzed urea hydrolysis diffused through a gas permeable membrane into a constant stream of o-phthaldehyde solution to form a highly fluorescent product with lambda ex at 340 nm and lambda em at 455 nm. Up to 25 serum samples can be analyzed per hour. The within-day coefficient of variation (CV) was 1.12% and the day-to-day CV was 1.25% for serum containing 10.50 mg urea nitrogen dl-1. The bioreactor shows excellent storage (at 4 degrees C) and operational stabilities (at 37 degrees C).

Chemistry and preparation of affinity ligands useful in immunoglobulin isolation and serum protein separation

A number of synthetic affinity gels having high affinity for immunoglobulins and albumin have been prepared by first reacting hydroxyl groups of a polymer with pentafluoropyridine and 4-dimethylaminopyridine in an anhydrous polar organic solvent and then reacting the gel further with nucleophiles such as ethyleneglycol or glycine in basic aqueous solutions. Immunoglobulins can be adsorbed to the gel in either high-salt or low-salt buffers, while albumin can only be adsorbed under low-salt conditions. The identity of the eluted proteins was analyzed by gradient polyacrylamide gel electrophoresis and enzyme-linked immunosorbent assay techniques. Human, goat, mouse and rabbit serum proteins were fractionated on these gels by using different adsorption and desorption conditions. The possible structures of the ligand are discussed. The results showed that the chromatographic behavior of these new gels with synthetic, low-molecular-weight ligands was remarkably similar to that of the more complex immunoglobulin binding gel such as immobilized Protein A or Protein G.

Spectrophotometric assay for ornithine decarboxylase

A rapid and sensitive spectrophotometric assay for ornithine decarboxylase is described. It is based on the observation that the product of ornithine decarboxylase, putrescine, reacts with 2,4,6-trinitrobenzenesulfonic acid to give a colored product soluble in 1-pentanol whereas ornithine does not. The amount of putrescine produced by the enzyme was determined by measuring the absorbance of the 1-pentanol extract of the reaction mixture at 420 nm, and by comparing the results to those obtained by the trapping of 14CO2 and by HPLC assays. The three assays were found to be equivalent in sensitivity, with the spectrophotometric assay having the advantages of being relatively rapid, requiring only common laboratory equipment, and not requiring the use of radioactive isotopes.

Single-enzyme-based amperometric assay for phosphate ion

An amperometric assay for phosphate ion, using a single enzymatic process, has been developed. The enzyme used was pyruvate oxidase, which catalyzes the oxidation of pyruvate in the presence of oxygen and phosphate ion. The products of the enzymatic reaction are acetyl phosphate, carbon dioxide, and hydrogen peroxide. The latter was monitored by means of a hydrogen peroxide electrode and an oxidase meter. Phosphate ion in the concentration range of 50-500 microM can be measured within 4 min. Anions, such as pyrophosphate, sulfate, nitrate, nitrite, and acetate, gave only marginal responses.

A simple spectrophotometric determination of solid supported amino groups

A simple spectrophotometric method for the quantitative determination of solid phase supported amino groups is described. The method involves reacting the solid support with an excess of activated acylating agent, N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) and an efficient acylation catalyst, 4-dimethylaminopyridine, and after thoroughly removing the unreacted SPDP, the solid support is reacted with an excess of dithiothreitol to quantitatively release pyridine-2-thione from the solid support to the solution. After an appropriate dilution, the released pyridine-2-thione which has a strong absorbance at 343 nm, is quantified by reading its absorbance in a spectrophotometer at 343 nm.

Identification of potential GABA-mimetics by their actions on brain GABA recognition sites

In an attempt to identify potential anticonvulsant compounds, 18 structural analogues of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) were tested for their ability to inhibit GABA receptor binding, sodium-dependent GABA binding and GABA aminotransferase activity in synaptic membranes from mouse brain. Nine inhibitors of receptor binding were found. The most potent was N-(thiocarbamoyl)glycine (Ki = 18 microM). However, this compound had no real effect on Na+ -dependent GABA binding nor on the activity of GABA aminotransferase. In addition, it was unable to enhance the binding of [3H]flunitrazepam as GABA agonists usually do. This could indicate that this inhibitor is, rather, a GABA receptor antagonist. Even though no particularly potent inhibitors of any of the GABA recognition sites were found, this technique nevertheless demonstrates how simple in vitro assays can be used to find drugs exhibiting potential GABA-mimetic activity.

Amperometric assay for collagenase. Amplification by the use of glucose oxidase conjugated to insoluble collagen

A sensitive and rapid amperometric assay for collagenase has been developed. The substrate for the assay is glucose oxidase covalently linked to insoluble collagen with dimethylsuberimidate. The collagenase cleaves the insoluble collagen--glucose oxidase conjugate into smaller, soluble fragments that have glucose oxidase activity. That activity is proportional to the collagenase activity hydrolyzing the insoluble conjugate. In the absence of collagenase, no glucose oxidase activity is found in the soluble phase. Glucose oxidase activity was assayed by measuring amperometrically the rate at which hydrogen peroxide is produced. The kinetics follow that proposed for a soluble enzyme acting on an insoluble substrate.

Antibody-induced conformational restriction as basis for new separation-free enzyme immunoassay

Under acid denaturing conditions, hologlucose oxidase labeled with 2,4-dinitrophenyl (DNP) was dissociated into flavin adenine dinucleotide (FAD) and DNP-labeled apoglucose oxidase (DNP-AG). Both lacked catalytic activity. The activity was restored by combining FAD and DNP-AG at about pH 7. If, on the other hand, anti-DNP serum was preincubated with the DNP-AG prior to the addition of FAD, activity was not restored. Furthermore, added DNP-aminocaproic acid counteracted the effects of the antibody in inhibiting the recombining of DNP-AG and FAD to form active enzyme. The anti-DNP serum probably prevented the DNP-AG from combining with FAD to form an active holoenzyme by restricting the mobility of the polypeptide chain of DNP-AG from folding into a catalytically active conformation. Based on such an antibody-induced conformational restriction of the DNP-AG, we developed a separation-free (homogeneous) enzyme immunoassay called AICREIA.

Tyrosine decarboxylase. Spectrophotometric assay and application in determining pyridoxal-5'-phosphate

We have developed a highly sensitive and rapid spectrophotometric assay for tyrosine decarboxylase that can be applied to determining pyridoxal-5'-phosphate. In the assay, tyramine, a product of tyrosine decarboxylation, reacts with 2,4,6-trinitrobenzenesulfonic acid to give a product soluble in toluene whereas tyrosine does not. We determined the amount of tyramine produced enzymatically by reading the absorbance at 340 nm of a toluene extract of the reaction mixture. This method is capable of detecting as low as 2.9 micrograms/mL of the enzyme. Using this method, we find the Km for tyrosine decarboxylase from Streptococcus faecalis to be 3.55 X 10(-4)M. We have also developed a specific and extremely sensitive method for determining pyridoxal-5'-phosphate, a cofactor of the enzyme, by using this spectrophotometric assay with apotyrosine decarboxylase.

Kinetics of rat brain soluble catechol-O-methyltransferase and its inhibition by substrate analogues

1. The initial rates and inhibition of rat brain catechol-O-methyltransferase were studied. Double reciprocal plots of initial rates versus either S-adenosyl-L-methionine or 3,4-dihydroxybenzoic acid, in the absence of product, gave a series of lines intersecting to the left of the ordinate. 2. Inhibition in the presence of S-adenosyl-L-homocysteine was competitive but in the presence of vanillic acid was non-competitive if S-adenosyl-L-methionine was the varied substrate. 3. When 3,4-dihydroxybenzoic acid was the varied substrate, both S-adenosyl-L-homocysteine and vanillic acid gave rise to a non-competitive inhibition. 4. The initial rate and product inhibition patterns were consistent with an ordered BiBi mechanism with S-adenosyl-L-methionine being the first substrate and 3,4-dihydroxybenzoic acid the second substrate to combine with the enzyme. 5. In addition, these results suggest that vanillic acid is the first product and S-adenosyl-L-homocysteine the second product to dissociate from the enzyme. 6. The substrate analogues salsolinol and 3-carboxysalsolinol were competitive inhibitors with respect to 3,4-dihydroxybenzoic acid but were non-competitive with respect to S-adenosyl-L-methionine. For enzymes with an ordered mechanism an uncompetitive inhibition would be expected. 7. A possible explanation is that both substrate analogues can combine with either free enzyme with lower affinity or with an intermediary enzyme form with much greater affinity. 8. A scheme which is consistent with the data is presented.

Enzyme modulator mediated immunoassay (EMMIA)

1. Enzyme modulator mediated immunoassay (EMMIA) is a separation-free (homogeneous) enzyme amplified immunoassay. 2. The assay is based on the ability of an analyte labeled enzyme modulator to modify the activity of an indicator enzyme and on ability of an anti-analyte antibody to abrogate the modifying action of the analyte-labeled enzyme modulator upon its binding to anti-analyte antibody. 3. The principle of EMMIA is elaborated in detail. The stages in the development of an EMMIA are described. 4. Criteria in selecting enzymes and modulators suitable for EMMIA are discussed. 5. Examples of EMMIA's using different kinds of modulators for different classes of analytes are presented.

Optimizing the o-phenylenediamine assay for horseradish peroxidase: effects of phosphate and pH, substrate and enzyme concentrations, and stopping reagents

Horseradish peroxidase, assayed with o-phenylenediamine, is irreversibly inactivated when incubated in phosphate buffer, 100 mmol/L, at pH 5. The inactivation depends on both duration and incubation and phosphate concentration. Phosphate was the most potent inactivator and citrate the least potent of a series of buffers tested. The inactivation is not attributable to ionic strength per se or to Na+ or K+. The observed inactivation did not occur at high concentrations (2500 nmol/L, 0.1 g/L) of enzyme; however, this "protective" effect could not be reproduced by adding bovine serum albumin or a surfactant (Tween 20) to lower concentrations of enzyme. The inactivation was independent of commercial source of the enzyme or the kind of chromogenic assay used. On the basis of this information, we optimized the assay so that it gave eightfold greater absorbance values than those reported by others. The improved assay was sensitive to as little as 0.4 pmol/L (16 ng/L) of peroxidase, and was linear over the range of 0.4 to 5 pmol/L (16-200 ng/L).

Optimizing the o-phenylenediamine assay for horseradish peroxidase: effects of phosphate and pH, substrate and enzyme concentrations, and stopping reagents

Horseradish peroxidase, assayed with o-phenylenediamine, is irreversibly inactivated when incubated in phosphate buffer, 100 mmol/L, at pH 5. The inactivation depends on both duration and incubation and phosphate concentration. Phosphate was the most potent inactivator and citrate the least potent of a series of buffers tested. The inactivation is not attributable to ionic strength per se or to Na+ or K+. The observed inactivation did not occur at high concentrations (2500 nmol/L, 0.1 g/L) of enzyme; however, this "protective" effect could not be reproduced by adding bovine serum albumin or a surfactant (Tween 20) to lower concentrations of enzyme. The inactivation was independent of commercial source of the enzyme or the kind of chromogenic assay used. On the basis of this information, we optimized the assay so that it gave eightfold greater absorbance values than those reported by others. The improved assay was sensitive to as little as 0.4 pmol/L (16 ng/L) of peroxidase, and was linear over the range of 0.4 to 5 pmol/L (16-200 ng/L).

Competitive inhibition of gamma-aminobutyric acid synaptosomal uptake by 4-(4'-azidobenzoimidylamino)butanoic acid

4-(4'-Azidobenzoimidylamino)butanoic acid (ABBA) is a potent inhibitor of rat brain synaptosomal [3H]gamma-aminobutyric acid uptake. Ki values were calculated to be 8 microM and 16 microM with respect to the high-affinity and the low-affinity uptake processes. These values are of the same order as those reported for nipecotic acid and guvacine, which until now have been the most potent uptake inhibitors available. Since ABBA contains a phenyl group, it might be capable of penetrating the blood-brain barrier, thus becoming a useful GABA mimetic.

Enzymes as versatile labels and signal amplifiers for monitoring immunochemical reactions

Enzymes have proven to be sensitive and versatile labels for immunochemical assays. The sensitivity of an enzyme label stems from its extraordinary catalytic power which in turn provides a great amplification of signals. Its versatility, however, stems from the fact that enzyme activity can be modulated by a number of substances. Enzyme labeled immunoassays can be divided into two categories: (a) heterogeneous and (b) homogeneous (non-separation). In the heterogeneous systems, the quantitation of the antibody bound and unbound fractions requires a physical separation of these two fractions, whereas the homogeneous or non-separation systems do not require such a separation. In the homogeneous systems, the unbound and antibody bound fractions can be distinguished functionally. A total of 11 unique principles used in the development of enzyme labeled immunoassays are described. The advantages, disadvantages and limitations of them are considered, as well as the future paths for research and developments.

p-Azidophenylglyoxal. A heterobifunctional photoactivable cross-linking reagent selective for arginyl residues

1. The synthesis described is of p-azidophenylglyoxal (p-APG) by diazotization of p-aminoacetophenone to an intermediate which when reacted with sodium azide gives p-azidoacetophenone; oxidation of the latter with selenium dioxide gives rise to p-APG (corrected melting point, 103-105 degrees C). The phenylglyoxal moiety was designed to react with arginine residues, whereas the p-azidoaryl function generates a reactive nitrene when activated with UV light; p-APG reacts most selectively with arginine and to a lesser extent with cystine and histidine. 2. p-APG has absorption peaks at 205 and 280 nm which decrease on photolysis. 3. Bovine heart lactic dehydrogenase, egg white lysozyme, horse liver alcohol dehydrogenase, and yeast alcohol dehydrogenase, all enzymes having arginyl residues at their active sites, are inhibited by p-APG in the dark. 4. Gel electrophoresis of oligomeric enzymes having arginyl residues at their active sites and exposed to p-APG and to UV irradiation gave varying proportions of monomers and photocross-linked dimers, trimers, tetramers, and larger molecular weight aggregates.

Homogeneous substrate-labeled fluorescent immunoassay for IgG in human serum

A homogeneous substrate-labeled fluorescent immunoassay for IgG has been developed. Purified IgG was covalently labeled with 6-(7-beta-galactosylcoumarin-3-carboxamido)-hexylamine to form a stable conjugate, GU-IgG. The galactosyl residue was hydrolyzed from GU-IgG by beta-galactosidase and the progress of the hydrolysis was monitored by the increase in fluorescence emission at 450 nm with excitation at 400 nm. Antibody to IgG diminished the activity of GU-IgG as a substrate for beta-galactosidase. Competitive binding immunoassays were conducted by allowing added IgG and GU-IgG to compete for a limited number of antibody binding sites. Hence, the fluorescence produced by enzymic hydrolysis increased with the level of added IgG. This method provides a simple and reliable immunoassay for IgG and is applicable to other proteins.

Inactivation of adenylate cyclase by phenylglyoxal and other dicarbonyls. Evidence for existence of essential arginyl residues

Rat brain adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) activity was markedly reduced when the enzyme was preincubated at 23 degrees C for periods up to 30 min with phenylglyoxyal (2.5-20 mM), an agent that binds specifically to arinyl residues. The kinetics indicated the interaction of phenylgloxal with one arginyl residue was responsible for the inactivation. Protection of inactivation of the enzyme by phenylglyoxal was attained in the presence of ATP and to a lesser extent by ADP and 5'-AMP but not by cyclic-AMP or Mg2+. In addition, 2,3-butanedione and 1,2-hexanedione, compounds that also react with arginyl residues, each inactivated adenylate cyclase to varying degrees. Furthermore, this inactivation was enhanced in the presence of borate ions. These observations strongly suggest that brain adenylate cyclase possesses essential arginyl residues.