Acetylcholinesterase in red blood cells

The multi-level effect of chlorpyrifos during clownfish metamorphosis

Chemical pollution in coastal waters, particularly from agricultural runoff organophosphates, poses a significant threat to marine ecosystems, including coral reefs. Pollutants such as chlorpyrifos (CPF) are widely used in agriculture and have adverse effects on marine life and humans. In this paper, we investigate the impact of CPF on the metamorphosis of a coral reef fish model, the clownfish Amphiprion ocellaris, focusing on the disruption of thyroid hormone (TH) signalling pathways. Our findings reveal that by reducing TH levels, CPF exposure impairs the formation of characteristic white bands in clownfish larvae, indicative of metamorphosis progression. Interestingly, TH treatment can rescue these effects, establishing a direct causal link between CPF effect and TH disruption. The body shape changes occurring during metamorphosis are also impacted by CPF exposure, shape changes are less advanced in CPF-treated larvae than in control conditions. Moreover, transcriptomic analysis elucidates CPF's effects on all components of the TH signalling pathway. Additionally, CPF induces systemic effects on cholesterol and vitamin D metabolism, DNA repair, and immunity, highlighting its broader TH-independent impacts. Pollutants are often overlooked in marine ecosystems, particularly in coral reefs. Developing and enhancing coral reef fish models, such as Amphiprion ocellaris (Cuvier, 1830), offers a more comprehensive understanding of how chemical pollution affects these ecosystems. This approach provides new insights into the complex mechanisms underlying CPF toxicity during fish metamorphosis, shedding light on the broader impact of environmental pollutants on marine organisms.

Heavy metal(loid) effect on multi-biomarker responses in apex predator: Novel assays in the monitoring of white stork nestlings

The goal of the present study was to investigate differences in biomarker responses related to metal(loid)s in white stork (Ciconia ciconia) nestling's blood from continental Croatia. To achieve this, a battery of biomarkers that can be affected by environmental pollutants, including metal(loid)s, was assessed (esterase activity, fluorescence-based oxidative stress biomarkers, metallothionein levels, glutathione-dependent enzyme activity). The research was conducted during the white stork breeding season in diverse areas (a landfill, industrial and agricultural sites, and an unpolluted area). White storks' nestlings near the landfill exhibited reduced carboxylesterase (CES) activity, elevated glutathione (GSH) concentration, as well as high Pb content in the blood. Increased As and Hg concentrations in blood were attributable to environmental contamination in agricultural area and an assumed unpolluted area, respectively. Furthermore, agricultural practices appeared to affect CES activity, as well as elevate Se levels. In addition to the successful implementation of biomarkers, present research showed that agricultural areas and a landfill are areas with increased metal(loid) levels possibly causing adverse effects on the white storks. This first-time heavy metal and metalloid analyses in the white stork nestlings from Croatia point to the necessary monitoring and future assessments of pollution impact to prevent irreversible adverse effects.

Selected Liver Markers in Predicting the Severity of Organophosphate and Carbamate Poisoning

Background

Intentional ingestion of organophosphate (OP) and carbamate is a significant health issue worldwide. It causes adverse health effects on the liver. This study aimed to determine liver transaminases (AST and ALT) and bilirubin levels to assess the severity of poisoning in patients with acute OP and carbamate poisoning.

Methods

A descriptive cross-sectional study was conducted on patients admitted to a selected hospital in Sri Lanka with acute OP and carbamate poisoning. The severity of poisoning was measured by RBC cholinesterase and Peradeniya Organophosphorus Poisoning scale (POP), where six clinical features were assessed based on a 3-point scale. A score of 0–3 was considered mild, 4–7 to be moderate, and 8–11 to be severe poisoning. Liver parameters such as AST, ALT, and total and direct bilirubin were measured.

Results

Among the 188 screened patients, 166 were recruited. Majority were males (112, 67.5%). Kruskal–Wallis test showed significant differences in AST and ALT on admission and AST on discharge, across POP groups ((χ² (2, n = 166) = 26.48, p ≤ 0.001), (χ² (2, n = 166) = 14.31, p=0.001), and (χ² (2, n = 157) = 11.34, p=0.003), respectively)). Mann–Whitney U test showed significantly higher AST and ALT in the moderate POP group compared to the mild POP group (AST: U = 1709, z = −4.50, p ≤ 0.001, r = 0.36; ALT: U = 2114, z = −3.04, p=0.002, r = 0.26) on admission. In addition, the treatment outcomes (duration of hospital stay and duration of ventilator assistance) were significantly correlated (p ≤ 0.001) with the severity of poisoning and serum AST and ALT at the time of admission.

Conclusion

AST and ALT levels on admission and AST level at discharge showed significant correlations with the severity of poisoning. Treatment outcomes significantly correlated with the severity of poisoning and serum AST and ALT levels.

Molecular therapeutics of Hemophilia A and B

INTRODUCTION

Hemophilia A (HA) or B (HB) is an X-linked recessive disorder caused by a defect in the factor VIII (FVIII) or factor IX (FIX) gene which leads to the dysfunction of blood coagulation. Protein replacement therapy (PRT) uses recombinant proteins and plasma-derived products, which incurs high cost and inconvenience requiring routine intravenous infusions and life-time treatment. Understanding of detailed molecular mechanisms on FVIII gene function could provide innovative solutions to amend this disorder. In recent decades, gene therapeutics have advanced rapidly and a one-time cure solution has been proposed.

AREAS COVERED

This review summarizes current understanding of molecular pathways involved in blood coagulation, with emphasis on FVIII's functional role. The existing knowledge and challenges on FVIII gene expression, from transcription, translation, post-translational modification including glycosylation to protein processing and secretion, and co-factor interactions are deciphered and potential molecular interventions discussed.

EXPERT OPINION

This article reviews the potential treatment targets for HA and HB, including antibodies, small molecules and gene therapeutics, based on molecular mechanisms of FVIII biosynthesis, and further, assessing the pros and cons of these various treatment strategies. Understanding detailed FVIII protein synthesis and secretory pathways could provide exciting opportunities in identifying novel therapeutics to ameliorate hemophilia state.

Correlation of Red Blood Cell Acetylcholinesterase Enzyme Activity with Various RBC Indices

Cholinesterases belongs to class hydrolases. There are two types acetylcholinesterase and butyryl cholinesterase. Acetylcholinesterase present in nerve endings and also in the RBC membrane. It helps to maintain the shape and size of RBCs. Any change in shape and size of RBCs may affect the activity of Acetylcholinesterase. Thus this study aimed to estimate RBCs Acetylcholinesterase enzyme activity in various types of anemias and correlate the RBCs Acetylcholinesterase enzyme activity with various hematological indices such as Erythrocyte Sedimentation Rate (ESR), Mean Corpuscular Hemoglobin (MCH), Mean Corpuscular Hemoglobin Concentration (MCHC), Mean Corpuscular Volume (MCV), Red cell Distribution Width (RDW) etc. After obtaining ethical approval from Institutional ethics committee total of 100 samples were collected from Clinical Biochemistry laboratory, Kasturba Medical College, Manipal, Manipal University. 25 were having normal RBC indices, 12 with hemolytic anemia, 26 with microcytic anemia and 26 with macrocytic anemia based on peripheral smear report and RBC indices. Acetylcholinesterase were measured using Ellman's method. RBC acetylcholinesterase activity was significantly increased in microcytic anemia (58.13 ± 5.4) and macrocytic anemia (76.87 ± 6.7) than normal group (37.62 ± 2.71). Also increased RBC acetylcholinesterase was seen in hemolytic anemia (48.11 ± 5.18) but the increase is not statistically significant. RBC acetylcholinesterase correlated negatively with hemoglobin (r = -0.356, p = 0.001) and positively with RDW (r = 0.31, p = 0.003). To conclude RBC acetylcholinesterase activity can be used as one of the potential marker for various types of anemia.

Erythrocyte acetylcholinesterase as biomarker of pesticide exposure: new and forgotten insights

Acetylcholinesterase (AChE) acts on the hydrolysis of acetylcholine, rapidly removing this neurotransmitter at cholinergic synapses and neuromuscular junctions as well as in neuronal growth and differentiation, modulation of cell adhesion ("electrotactins") and aryl-acylamidase activity (AAA). This enzyme is also found in erythrocyte, as 160 kDa dimer that anchors to the plasma membrane via glycophosphatidylinositol. The function of this enzyme in erythrocytes has not yet been elucidated; however, it is suspected to participate in cell-to-cell interactions. Here, a review on erythrocyte AChE characteristics and use as biomarker for organophosphorus and carbamate insecticides is presented since it is the first specific target/barrier of the action of these pesticides, besides plasma butyrylcholinesterase (BChE). However, some past and current methods have disadvantages: (a) not discriminating the activities of AChE and BChE; (b) low accuracy due to interference of hemoglobin in whole blood samples. On the other hand, extraction methods of hemoglobin-free erythrocyte AChE allows: (a) the freezing and transporting of samples; (b) samples free of colorimetric interference; (c) data from only erythrocyte AChE activity; (d) erythrocyte AChE specific activity presents higher correlation with the central nervous system AChE than other peripheral ChEs; (e) slow spontaneous regeneration against anti-ChEs agents of AChE in comparison to BChE, thus increasing the chances of detecting such compounds following longer interval after exposure. As monitoring perspectives, hemoglobin-free methodologies may be promising alternatives to assess the degree of exposure since they are not influenced by this interfering agent.

Erythrocyte Senescence in a Model of Rat Displaying Hutchinson-Gilford Progeria Syndrome

Background

Increased oxidative stress is a major cause of aging and age-related diseases. Erythrocytes serve as good model for aging studies. Dihydrotachysterol is known to induce premature aging feature in rats mimicking Hutchinson-Gilford progeria syndrome.

Aim

In the present study, attempts have been made to explore the differential response of young and senescent erythrocytes separated by density gradient centrifugation from accelerated senescence model of rats mimicking Hutchinson-Gilford progeria syndrome and naturally aged rats.

Methods

The erythrocytes of naturally aged and progeroid rats were separated into distinct, young and old cells on the basis of their differential densities. The parameters of oxidative stress and membrane transport systems were studied.

Discussion and Conclusion

Our study provides evidence that organismal aging negatively affects oxidative stress markers and membrane transport systems in both young and old erythrocytes. This study further substantiates that the changes in progeria model of rats resemble natural aging in terms of erythrocyte senescence.

Redox imbalance in a model of rat mimicking Hutchinson-Gilford progeria syndrome

Although several etiological factors contribute to the complexity of the aging process, the ultimate component of macromolecular damage and consequent cell death involves the altered redox balance inclined towards increased ROS production and/or decreased antioxidant protection. Given that, the chronic dihydrotachysterol (DHT) intoxication in rats induce Hutchinson Gilford progeria like syndrome, the present study provides the evidence for altered redox balance as evidenced by alteration in parameters of oxidative stress in blood plasma and erythrocytes including MDA, GSH, FRAP AOPP PMRS, AGEs, AChE and osmotic fragility which substantiate the suitability of the model for aging studies.

Effect of intensive lipid-lowering therapies on cholinesterase activity in patients with coronary artery disease

BACKGROUND

Many disease entities, including coronary artery disease (CAD), demonstrate abnormalities in the activity of cholinesterases. As CAD is characterized by an increase in cholesterol level, patients with this disease are treated with lipid-lowering drugs. The present study attempts to determine how statin or combined statin and ezetimibe therapy influences cholinesterase activity.

METHODS

Plasma and erythrocytes were isolated from the peripheral blood of CAD patients (n=61) and healthy subjects (n=63). The patients were randomized into three groups: 20mg/day rosuvastatin, 40mg/day atorvastatin, and combined 10mg/day atorvastatin with 10mg/day ezetimibe. The following parameters were studied: activity of acetylcholinesterase (AChE) and butyrylcholinoesterase (BChE) and lipid levels.

RESULTS

Patients with CAD demonstrated significant increase in AChE and BChE activity. We observed increase in the level of low-density lipoprotein cholesterol (LDL) and triglycerides (TG) level, and decrease in high density lipoprotein cholesterol (HDL) level. After atorvastatin monotherapy, the following decrease in activity were observed: 17% LDL, 43% total cholesterol (TC) level, 33% AChE and 17% BChE. The following decrease in activity were observed following rosuvastatin monotherapy: 26% LDL level, 26% AChE and 18% BChE. After combined atorvastatin+ezetimibe therapy, the following decrease in activity occurred: 27% of LDL level, 15% TC, 33% of AChE and 20% BChE.

CONCLUSIONS

Our results suggest that intensive lipid-lowering therapy has a beneficial effect on AChE and BChE activity and lipid levels. Combination atorvastatin+ezetimibe therapy was found to have similar effects on the tested parameters as statin monotherapy.

Biophysical Approaches for Oral Wound Healing: Emphasis on Photobiomodulation

Significance: Oral wounds can lead to significant pain and discomfort as well as affect overall general health due to poor diet and inadequate nutrition. Besides many biological and pharmaceutical methods being investigated, there is growing interest in exploring various biophysical devices that utilize electric, magnetic, ultrasound, pressure, and light energy. Recent Advances: Significant insight into mechanisms of these biophysical devices could provide a clear rationale for their clinical use. Preclinical studies are essential precursors in determining physiological mechanisms and elucidation of causal pathways. This will lead to development of safe and effective therapeutic protocols for clinical wound management. Critical Issues: Identification of precise events initiated by biophysical devices, specifically photobiomodulation-the major focus of this review, offers promising avenues in improving oral wound management. The primary phase responses initiated by the interventions that distinctly contribute to the therapeutic response must be clearly delineated from secondary phase responses. The latter events are a consequence of the wound healing process and must not be confused with causal mechanisms. Future Direction: Clinical adoption of these biophysical devices needs robust and efficacious protocols that can be developed by well-designed preclinical and clinical studies. Elucidation of the precise molecular mechanisms of these biophysical approaches could determine optimization of their applications for predictive oral wound care.

Upregulation of Acetylcholinesterase Mediated by p53 Contributes to Cisplatin-Induced Apoptosis in Human Breast Cancer Cell

BACKGROUND

The expression of acetylcholinesterase (AChE) could be induced during apoptosis in various cell types. And reduced AChE expression either by siRNA could prevent apoptosis. However, the detailed mechanisms underlying the AChE regulation are largely unknown in human breast cancer cell.

MATERIAL AND METHODS

MCF-7 cells were cultured and treated by cisplatin in the absence or presence of p53 siRNA.

RESULTS

In this study, the regulation of AChE expression during apoptosis induced by cisplatin, a current used anticancer drug, was investigated in human breast cancer cell line MCF-7. Exposure of MCF-7 cells to cisplatin resulted in apoptosis in a time- and concentration-dependent manner. Meanwhile, the upregulated AChE and p53 were also observed during apoptosis. Silencing interfering RNA directed against p53 blocked the expression of AChE.

CONCLUSION

Taken together, these results suggested that AChE expression could be upregulated by the activation of p53 during apoptosis induced by cisplatin in MCF-7 cells.

Design and Synthesis of New Dual Binding Site Cholinesterase Inhibitors: in vitro Inhibition Studies with in silico Docking

Cholinesterases (ChEs) play a vital role in the regulation of cholinergic transmission. The inhibition of ChEs is considered to be involved in increasing acetylcholine level in the brain and thus has been implicated in the treatment of Alzheimer’s disease. We have designed and synthesized a series of novel indole derivatives and screened them for inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Most of the tested compounds exhibited inhibitory activity against AChE and BChE. Among them 4f and 6e showed the highest AChE inhibitory activity with IC₅₀ 91.21±0.06 and 68.52±0.04 μM, respectively. However compound 5a exhibited the highest inhibitory activity against BChE (IC₅₀ 55.21±0.12 μM).

Effects of the organophosphate fenthion for control of the red-billed quelea Quelea quelea on cholinesterase and haemoglobin concentrations in the blood of target and non-target birds

The red-billed quelea bird Quelea quelea is one of sub-Saharan Africa's most damaging pests, attacking small-grain crops throughout semi-arid zones. It is routinely controlled by spraying its breeding colonies and roosts with organophosphate pesticides, actions often associated with detrimental effects on non-target organisms. Attributions of mortality and morbidity of non-targets to the sprays are difficult to confirm unequivocally but can be achieved by assessing depressions in cholinesterase activities since these are reduced by exposure to organophosphates. Here we report on surveys of birds caught before and after sprays that were examined for their blood cholinesterase activities to assess the extent to which these became depressed. Blood samples from birds were taken before and after sprays with fenthion against red-billed quelea in colonies or roosts, and at other unsprayed sites, in Botswana and Tanzania and analysed for levels of haemoglobin (Hb) and activities of whole blood acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Background activities of AChE, BChE and Hb concentrations varied with bird species, subspecies, mass, age and gender. Contrary to expectation, since avian erythrocytes are often reported to lack cholinesterases, acetylcholinesterase activities in pre-spray samples of adult birds were positively correlated with Hb concentrations. When these factors were taken into account there were highly significant declines (P < 0.0001) in AChE and BChE and increases in Hb after contact with fenthion in both target and non-target birds. BChE generally declined further (up to 87 % depression) from baseline levels than AChE (up to 83 % depression) but did so at a slower rate in a sample of quelea nestlings. Baseline activities of AChE and BChE and levels of Hb were higher in the East African subspecies of the red-billed quelea Q. q. aethiopica than in the southern African subspecies Q. q. lathamii, with the exception of BChE activities for adult males which were equivalent.

Choline acetyltransferase, acetylcholinesterase, and nicotinic acetylcholine receptors of human gingival and esophageal epithelia

A non-neuronal cholinergic system that includes neuronal-like nicotinic acetylcholine receptors (nAChRs) has recently been described in epithelial cells that line the skin and the upper respiratory tract. Since the use of nicotine-containing products is associated with morbidity in the upper digestive tract, and since nicotine may alter cellular functions directly via nAChRs, we sought to identify and characterize a non-neuronal cholinergic system in the gingival and esophageal epithelia. mRNA transcripts for alpha3, alpha5, alpha7, and beta2 nAChR subunits, choline acetyltransferase, and the asymmetric and globular forms of acetylcholinesterase were amplified from gingival keratinocytes (KC) by means of polymerase chain-reactions. These proteins were visualized in the gingival and esophageal epithelia by means of specific antibodies. Variations in distribution and intensity of immunostaining were found, indicating that the repertoire of cholinergic enzymes and receptors expressed by the cells changes during epithelial maturation, and that an upward concentration gradient of free acetylcholine exists. Blocking of the nAChRs with mecamylamine resulted in reversible loss of cell-to-cell adhesion, and shrinking and rounding of cultured gingival KC. Activation of the receptors with acetylcholine or carbachol caused stretching and peripheral ruffling of the cytoplasmic aprons, and formation of new intercellular contacts. These results demonstrate that both the keratinizing epithelium of attached gingiva and the non-keratinizing epithelium lining the upper two-thirds of the esophageal mucosa possess a non-neuronal cholinergic system. The nAChRs expressed by these epithelia are coupled to regulation of cell adhesion and motility, and may provide a target for the deleterious effects of nicotine.

Acetylcholinesterase activity in chronic renal failure

Twenty healthy subjects and 39 Chronic Renal Failure patients (CRF-patients) maintained on chronic hemodialysis were used in this investigation to study the changes in acetylcholinesterase (AChE) activity of red blood cells (RBCs). The CRF-patients were all undergoing hemodialysis treatment. AChE activity from the CRF-patients was determined before and after dialysis. An additional objective was to study the effect of chronic renal failure on human red blood cell aging. Blood samples were drawn from controls and CRF-patients in tubes containing EDTA or sodium heparin as an anticoagulant. Red blood cells were purified to avoid interference with monocytes, reticulocytes and leukocytes. The purified RBCs were subfractionated into young (y) (1.08-1.09), mid (m) (1.09-1.11) and old (o) (1.11-1.12) percoll density (g/mL) fractions using a discontinous percoll gradient. The mean +/- SD AChE per gram hemoglobin (U/g Hgb) activities in whole blood (WB), purified human red blood cells (PRBCs), young human red blood cells (y-RBCs), mid age human red blood cells (m-RBCs) and old human red blood cells (o-RBCs) in CRF-patients were 31.2+/-3.43, 29.3+/-3.26, 30.4+/-3.91, 25.1+/-5.25, 17.1+/-6.02 in females and 29.8+/-5.39, 28.8+/-5.29, 28.7+/-5.29, 23.7+/-5.39 and 16.0+/-5.60 in males. AChE activity from CRF-patients were higher than that found in the control subjects. The aging of human RBCs in both the controls and CRF-patients showed a progressive reduction in AChE activity. AChE activity of RBCs from female CRF-patients were significantly higher (p < 0.05) than that of the female control subjects. The RBCs isolated from male CRF-patients showed a higher AChE activity than control males, but a significant difference was only observed with the mid-age-cells. These studies further indicate that AChE activity remained insignificantly different in the various density based age subfractions of RBCs of both CRF-patients and controls.

Effects of exposure to lead on selected biochemical and haematological variables

Blood and urine samples were taken from 34 persons occupationally exposed to lead and from 56 non-exposed control persons and blood lead and haemoglobin concentrations, red blood cell count, erythrocyte glutathione peroxidase (GSH-peroxidase) and acetylcholinesterase (AChE), and urinary delta-aminolevulinic acid were determined. Blood lead concentrations of the lead-exposed subjects were within the range of generally accepted as safe for occupationally-exposed adults in many countries (i.e. below 50 micrograms Pb/dl blood). Yet, significant dose-dependent elevations were found in erythrocyte GSH-peroxidase and urinary delta-aminolevulinic acid. The urinary delta-aminolevulinic acid concentration of lead-exposed smokers was significantly elevated over that of lead-exposed non-smokers. Smoking did not effect the urinary delta-aminolevulinic acid concentration of control persons. In addition, a statistically significantly lower red blood cell count was observed in the lead-exposed group. Our results indicate that the above described safety standard for blood lead concentrations in occupationally exposed adults, although generally accepted, needs revision.

Kinetics for the inhibition of acetylcholinesterase from human erythrocyte by cisplatin

The antitumor drug cisplatin causes neurological side-effects in patients treated with this drug. Since acetylcholine plays a key role in human neurotransmission we characterized the inhibitory effect of cisplatin on the enzyme, acetylcholinesterase. Enzyme activity was monitored spectrophotometrically using Ellman's method. The time for 50% inhibition (t1/2) was inversely proportional to the concentration of the cisplatin. The reaction was therefore assessed to have a bimolecular rate constant of 36.5 (mM min)-1. The Km and Vmax were both decreased by 45 and 48%, respectively by 7.0 mM cisplatin during the reversible phase while the Km was increased 138% and Vmax was decreased up to 65% in the irreversible phase. The nature of the inhibition was uncompetitive and complex irreversible at the reversible and irreversible stages respectively. The inhibition constants for reversible and irreversible steps were estimated as 1.12 mM and 97.70 (mM min)-1 respectively. The dissociation constant for the irreversible complex was 2.62 mM. These studies show that cisplatin is an uncompetitive inhibitor of acetylcholinesterase. Such effects may contribute, at least in part, to the neurotoxic effects associated with the use of cisplatin.

Human keratinocytes synthesize, secrete, and degrade acetylcholine

We previously reported that normal human keratinocytes express muscarinic receptors, and that acetylcholine induces attachment of these cells to each other. We have now studied the ability of human keratinocytes to synthesize, secrete, and degrade acetylcholine. To detect and localize the synthesizing enzyme choline acetyltransferase and degrading enzyme acetylcholinesterase, cultured cells and cryostat sections of normal human skin were pre-incubated with specific monoclonal antibodies and stained with an avidin-biotin complex/alkaline phosphatase. The choline acetyltransferase activity was assessed by the conversion of [3H]acetyl CoA to [3H]acetylcholine, and newly synthesized [3H]acetylcholine was detected using thin-layer chromatography. The acetylcholinesterase activity was measured spectrophotometrically. Both cholinergic enzymes were present in cultured keratinocytes, and in basal, spinous and granular epidermal cell layers. Choline acetyltransferase was visualized in the vicinity of cell nuclei, and acetylcholinesterase was observed in or near cell membranes. Newly synthesized acetylcholine was detected in both cell homogenates and culture supernatants. The estimated Vmax of the synthesis of labeled acetylcholine by homogenized keratinocytes was about 20 pmoles acetylcholine produced/mg protein/min at 37 degrees C. A single keratinocyte synthesized a mean of 2 x 10(-17) moles, and released 7 x 10(-19) moles acetylcholine per minute. Both cell homogenates and culture supernatants exhibited similar acetylcholinesterase activities indicating that human keratinocytes secrete acetylcholinesterase, too. Thus, we have demonstrated that normal human keratinocytes possess choline acetyltransferase and acetylcholinesterase, and synthesize, store, release, and degrade acetylcholine. Because human keratinocytes can also respond to acetylcholine, we believe that keratinocyte acetylcholine works in the epidermis as a local hormone.

Investigation of the reversible inhibition of camel (Camelus dromedarius) acetylcholinesterase by tetracaine

1. The camel erythrocyte membrane bound acetylcholinesterase (AChE) was extracted with the non-ionic detergent Triton X-100 and some of its kinetics parameters were studied. In addition the effect of tetracaine hydrochloride on AChE was also investigated. 2. The Michaelis-Menten constant (KM) for the hydrolysis of acetylthiocholine iodide was found to be 7 x 10(-5) M and the Vmax was 21.2 mumol/hr/mg protein. 3. Tetracaine (0.025-0.80 mM) reversibly inhibited the AChE activity (25-82%) in a concentration-dependent manner, the IC50 being about 0.12 mM. 4. The Lineweaver-Burk plot and its secondary plots indicated that the nature of this inhibition is of the linear mixed type. This mixed type inhibition system is considered to be composed of partial competitive and pure non-competitive in nature. 5. The values of Ki(slope) and Kii(intercept) were estimated as 0.127 mM and 0.263 mM, respectively, by a secondary replot of primary double reciprocal plot of Lineweaver-Burk plot and Dixon plot. 6. Kii/Ki ratio shows that tetracaine has a greater affinity of binding to the active site than to a peripheral site.

[Histochemical investigations on the localization of acetylcholinesterase in the kidney of selected vertebrates]

The light and electron microscopical localization of AChE activity in the kidney of selected vertebrates was studied using the method of Karnovsky and Roots (1964) for light microscopy and the modification of the Koelle and Friedenwald's technique according to Tsuji (1974, 1984) for electron microscopy. AChE activity could be demonstrated light microscopically mainly within the glomeruli of some mammals (golden hamster, mouse, rat) and non-mammalian vertebrates (carp, frog). No activity was found in the glomeruli of guinea pig, of chicken and tortoise. In the mammalians, the strongest AChE activity could be demonstrated in the guinea pig, the lowest in the rat. A strong AChE enzyme activity was also detected within the interlobular arteries and the cells of Bowman's capsule. With the electron microscopical method AChE activity was demonstrated in mesangial cells and endothelial cells of the glomeruli (golden hamster and carp) and in the cells of Bowman's capsule (carp). Reaction product was localized within the cisterns of endoplasmic reticulum and the perinuclear space (nuclear envelope). A high amount of electron opaque material could be observed in the cells of Bowman's capsule and their lamina basalis. The functional significance of the localization of AChE activity in the glomeruli will be discussed.

Acetylcholinesterase in the human erythron. III. Regulation of differentiation

Acetylcholinesterase (AChE) is present in both primitive and mature erythroid cells, but a role for the enzyme in human hematopoiesis has not been defined. This prospect represented the primary objective of the following study. In clonal culture of normal human bone marrow cells, a "wave" of AChE activity was demonstrated, rising from undetectable levels to a peak (of 1.48 femto-moles per min per cell) at 10 days in the course of progressive erythroid clonogenesis. At concentrations of enzyme inhibitor that clearly reduced AChE activity in a dose-dependent fashion, there was no overall effect on erythropoiesis in vitro, but the clones were generally smaller and significantly more often multi-focal than in control cultures. Furthermore, in the presence of AChE inhibitors, a concentration-dependent increase in the myeloid-erythroid ratios of the culture harvests was observed. Likewise, a clear reduction in hemoglobination was revealed, in cells of 10 day cultures, from a mean hemoglobin concentration of 35.0 pg per cell in controls to 20.1 pg per cell in the presence of the maximal concentration of the inhibitor (10(-6) M eserine). These data point to a role for AChE in the regulation of differentiation in the human erythron.

Biochemical assays of hemoglobin in normal human erythroid clones

Quantitation of small amounts (2-3 micrograms) of hemoglobin (Hb) was achieved by each of three spectrophotometric techniques. An assay employing benzidine base consistently underestimated Hb at this level and gave a wide scatter of results at higher values. The cyanmethemoglobin method was at the limit of its sensitivity and suffers from the disadvantage of having high optical densities in the blank samples. By contrast, pyridine hemochromogen can be detected accurately with 200 ng of Hb (equivalent of 6,000 mature erythrocytes), and the regression line with this technique virtually passes through the origin. Furthermore, the extinction coefficient of pyridine hemochromogen in the Soret band is 13.5-fold greater than that of cyanmethemoglobin. In normal human erythroid clones, generated in vitro from bone marrow cells, mean cell hemoglobin (MCH) values were determined after various intervals of culture. The MCH after 5, 7, 10, and 14 days were 11.8, 15.8, 26.6, and 34.4 pg, respectively, by the pyridine hemochromogen method. Reaction product was also identified in granulocyte-macrophage clones, presumably reflecting the content of other heme proteins such as catalase and cytochromes. Account must be taken of this non-Hb material in computing true MCH values for erythroid cells.

Acetylcholinesterase in the human erythron. II. Biochemical assay

Acetylcholinesterase (AChE) is an integral erythrocyte membrane protein. A role for the enzyme in the developing human erythron is being explored. Assays of AchE by the standard Ellman technique overestimate the amount of enzyme by failing to account for the contribution of hemoglobin to the optical density of the reaction mixture. Furthermore, reliance on substrate selection alone for specificity is unsatisfactory. Incorporation of inhibitors of "true" AchE and of pseudocholinesterase confer greater ability to distinguish one enzyme from the other. In our experience, the inhibitor constant (Kl) for edrophonium, which is highly specific for AChE, is approximately 5 x 10(-5) M against adult human erythrocytes that contain significantly more total cholinesterase activity than do erythrocytes from umbilical cord blood. This consists of both "true" and "pseudo" enzyme, the former predominating and accounting for 0.75-1.65 (mean 1.02, median 0.87) femtomoles of substrate hydrolysed per min per cell in adult blood, with values of 0.15-1.04 (mean 0.71, median 0.73) obtained on cord blood. Moreover, the enzyme activity in neonatal erythrocytes has a rather different inhibitor profile from that of adult cells. AChE was also demonstrated in fresh (ALL) and cultured (K562 and HL60) human leukemic cells, as well as in primitive granulocyte-macrophage and erythroid cells cloned from normal human bone marrow. In the erythroid colonies the enzyme activity was 0-3.76 (mean 1.20, median 0.76) femtomoles per min per cell, apparently the first successful measurement of AChE in such cells.

Acetylcholinesterase in the human erythron. I. Cytochemistry

The successful demonstration and localisation of acetylcholinesterase (AChE), in cells by a cytochemical technique requires maximal expression of enzyme activity, minimal loss of AChE and precise, quantitative generation of reaction product at the actual site of the protein in vivo. These requirements are addressed in a standard technique that has been modified to avoid or optimise fixation and to exhibit enzyme activity under close-to-physiological conditions of osmolality, pH, and temperature. With these refinements and with the use of a variety of substrates and enzyme inhibitors of different specificities, true AChE was demonstrable on the membrane of erythrocytes and in the nucleus and cytoplasm of erythroblasts in bone marrow and of the constituent cells of erythroid clones in vitro. The activity in erythrocytes from umbilical cord blood was less than that in corresponding cells from the peripheral circulation of adults. AChE was observed also in human megakaryocytes and in leucocytes at all levels of differentiation, including the components of granulocyte-macrophage clones. Pseudocholinesterase was detected likewise across the spectrum of erythroid (and leucocyte) ontogeny, suggesting that these enzymes may exercise an important function in hematopoiesis.