An alpha-helical cationic antimicrobial peptide selectively modulates macrophage responses to lipopolysaccharide and directly alters macrophage gene expression

Certain cationic antimicrobial peptides block the binding of LPS to LPS-binding protein and reduce the ability of LPS to induce the production of inflammatory mediators by macrophages. To gain a more complete understanding of how LPS activates macrophages and how cationic peptides influence this process, we have used gene array technology to profile gene expression patterns in macrophages treated with LPS in the presence or the absence of the insect-derived cationic antimicrobial peptide CEMA (cecropin-melittin hybrid). We found that CEMA selectively blocked LPS-induced gene expression in the RAW 264.7 macrophage cell line. The ability of LPS to induce the expression of >40 genes was strongly inhibited by CEMA, while LPS-induced expression of another 16 genes was relatively unaffected. In addition, CEMA itself induced the expression of a distinct set of 35 genes, including genes involved in cell adhesion and apoptosis. Thus, CEMA, a synthetic alpha-helical peptide, selectively modulates the transcriptional response of macrophages to LPS and can alter gene expression in macrophages.

Bone lead concentrations assessed by in vivo X-ray fluorescence

The assessment of past chronic lead exposure is difficult. Chronic lead burden is not always correctly assessed using laboratory-based tests that are useful for acute or recent exposures. We describe a case of suspected chronic lead exposure that illustrated the need for improved and possibly noninvasive methods to determine cumulative lead body burden. X-Ray fluorescence (XRF) is discussed as a method to obtain in vivo bone lead measurements. We discuss the potential of such measurements as accurate biomarkers of cumulative exposure and whether XRF can be used for retroactive exposure assessment or to predict risk of future health problems.

An IgM lambda antibody to Escherichia coli produces false-positive results in multiple immunometric assays

BACKGROUND

Interferences in immunometric assays as a result of human anti-immunoglobulin antibodies frequently have been described in the literature. The etiology of these interfering antibodies is usually not known but has been associated with rheumatoid factors in some assays. It is known that microorganisms in experimental settings can induce anti-immunoglobulin antibodies.

METHODS

Following Escherichia coli septicemia, a 56-year-old male patient had increased immunoassay results for cardiac troponin I, thyrotropin, human chorionic gonadotropin, alpha-fetoprotein, and CA-125 that were consistent with myocardial infarction, hyperthyroidism, and pregnancy, and suggestive of an occult neoplasm such as hepatic or ovarian cancer. None of these diagnoses were consistent with the rest of his medical exam. In addition, the patient had a restricted IgM lambda paraprotein by immunofixation. Plasma from the patient was incubated with Sepharose-conjugated protein A, irrelevant murine monoclonal antibodies, and formalin-killed E. coli organisms from his infection to determine whether these immunoassay values were falsely increased.

RESULTS

Incubation of the patient's plasma with irrelevant murine monoclonal antibodies or the E. coli organism produced normal immunoassay values and removed the IgM lambda paraprotein.

CONCLUSIONS

The patient produced a very restricted IgM lambda antibody response to the E. coli infection that had anti-immunoglobulin activity and caused falsely increased values in numerous immunometric assays. Microorganism-induced anti-immunoglobulin antibodies are discussed in the context of this patient.

The role of antimicrobial peptides in animal defenses

It is becoming clear that the cationic antimicrobial peptides are an important component of the innate defenses of all species of life. Such peptides can be constitutively expressed or induced by bacteria or their products. The best peptides have good activities vs. a broad range of bacterial strains, including antibiotic-resistant isolates. They kill very rapidly, do not easily select resistant mutants, are synergistic with conventional antibiotics, other peptides, and lysozyme, and are able to kill bacteria in animal models. It is known that bacterial infections, especially when treated with antibiotics, can lead to the release of bacterial products such as lipopolysaccharide (LPS) and lipoteichoic acid, resulting in potentially lethal sepsis. In contrast to antibiotics, the peptides actually prevent cytokine induction by bacterial products in tissue culture and human blood, and they block the onset of sepsis in mouse models of endotoxemia. Consistent with this, transcriptional gene array experiments using a macrophage cell line demonstrated that a model peptide, CEMA, blocks the expression of many genes whose transcription was induced by LPS. The peptides do this in part by blocking LPS interaction with the serum protein LBP. In addition, CEMA itself has a direct effect on macrophage gene expression. Because cationic antimicrobial peptides are induced by LPS and are able to dampen the septic response of animal cells to LPS, we propose that, in addition to their role in direct and lysozyme-assisted killing of microbes, they have a role in feedback regulation of cytokine responses. We are currently developing variant peptides as therapeutics against antibiotic-resistant infections.

Salmonella typhimurium infection and lipopolysaccharide stimulation induce similar changes in macrophage gene expression

Changes in macrophage phenotype induced during infection result from the recognition of bacterial products as well as the action of bacterial virulence factors. We used the unprecedented opportunity provided by gene arrays to simultaneously study the expression of hundreds of genes during Salmonella typhimurium infection of macrophages and to assess the contribution of the bacterial virulence factor, LPS, in initiating the host responses to Salmonella. We found that S. typhimurium infection caused significant changes in the expression of numerous genes encoding chemokines, cell surface receptors, signaling molecules, and transcriptional activators at 4 h postinfection of the RAW 264.7 murine macrophage cell line. Our results revealed changes in the expression of several genes that had not been previously implicated in the host responses to S. typhimurium infection, as well as changes in the expression of several genes previously shown to be regulated by S. typhimurium infection. An overlapping spectrum of genes was expressed in response to virulent S. typhimurium and purified S. typhimurium LPS, reinforcing the major role of this surface molecule in stimulating the early response of macrophages to bacterial infection. The macrophage gene expression profile was further altered by activation with IFN-gamma, indicating that host cell responses depend on the activation state of the cell.

Clostridium difficile-associated diarrhoea in hospitalised patients

OBJECTIVE

The aim of the present study was to evaluate the incidence, risk factors and cost implications of Clostridium difficile-associated diarrhoea (CDAD) in hospitalized adult patients.

METHODS

Eighty-seven hospitalized adult patients, positively identified as having CDAD, were reviewed retrospectively to determine the risk factors and cost implications of CDAD.

RESULTS

The clinical manifestations, in addition to diarrhoea, included elevated temperature (= 37.8 degrees C; 42.5%), abdominal pain (63. 2%) and leucocytosis (=12 x 109 cells/l; 52.9%). Eight patients underwent endoscopy, and pseudomembranous colitis was confirmed in all of these patients. Nine patients died during their hospital stay. Cefotaxime and cefuroxime were the agents most commonly associated with CDAD. There was a significant difference (P < 0.001) between the sex distribution of CDAD patients and adult hospital patients (69% of CDAD patients were female vs. 52% of general adult hospital population). Significantly (P < 0.001) more patients with CDAD were admitted from the nursing home (NH) setting. The mean age of patients with CDAD admitted from NHs (n = 19) was older than those cases admitted from the community (n = 68) by 14 years (P < 0.001). The length of hospital stay was significantly (P < 0.001) longer for patients with CDAD (16.9 vs. 3.89 days). No differences (P = 0.306) were found in the response times for CDAD patients treated with either oral metronidazole (n = 39) or oral vancomycin (n = 48). The mean response time was, however, significantly longer in the CDAD patients admitted from NHs (4.2 days) compared with those admitted from the community (2.5 days), although the former patients were older and had significantly more comorbidity (P < 0.001). The mean cost per one treated-case of CDAD (bed, laboratory requests and treatment therapy) was calculated as pound2860.

CONCLUSION

Patients admitted from NHs are at increased risk of development of CDAD; receiving cefotaxime or cefuroxime axetil (oral form), being elderly and being female are risk factors for the development of CDAD. Treatment of CDAD with oral metronidazole or oral vancomycin gives rise to similar response times and efficacy.

The benefits of a hospital based community services liaison pharmacist

OBJECTIVE

To investigate the benefits of a community services liaison pharmacist in addressing medication misuse in elderly patients, which occur on both admission and discharge.

DESIGN

Completion of a medication history for each patient on admission by the community liaison pharmacist. On discharge updated medication record sheets were faxed to the patient's GP and community pharmacy; a survey of GPs' and community pharmacists' opinions who were involved in the study was carried out.

SUBJECTS AND SETTING

109 patients over the age of 60 on 4 or more medications admitted by the medical admissions unit of Antrim Area Hospital.

MAIN OUTCOME MEASURES

Medication related problems; GP and community pharmacist opinions of the service.

RESULTS

Of the 109 patients, 61% had an incomplete medication history on admission, 21% of patients who brought their own drugs were not dealt with appropriately in hospital and 33% of discharged patients had medication-related problems. The service was felt to be very useful by GPs (80%) and community pharmacists (100%). A reduction in readmission rate of 2.4% was seen in these patients compared to the average for this age group.

CONCLUSION

The community services liaison pharmacist produced benefits in terms of patient medication management, reduced readmission rates and wastage of patients' own drugs. A more detailed one-year study will now be carried out.

Use of a treatment protocol in the management of community-acquired lower respiratory tract infection

The aim of the present study was to examine the impact of an antimicrobial prescribing protocol on clinical and economic outcome measures in hospitalized patients with community-acquired lower respiratory tract infection (LRTI). The study was performed as a prospective controlled clinical trial within the medical wards at Antrim Area Hospital, Northern Ireland. Data were collected on all hospitalized adult patients with a primary diagnosis of LRTI during the period December 1994 to February 1995 (normal hospital practice; control group; n = 112). After an LRTI management protocol (medical, microbiological and pharmacy staff) had been developed, all hospitalized adult patients with a primary diagnosis of LRTI over the period December 1995 to February 1996 formed the intervention group (treated according to the protocol; n = 115). The results showed a statistically significant impact of the protocol in terms of clinical and economic outcome measures. Patients treated using the algorithmic prescribing protocol had significant reductions in length of hospital stay (geometric mean 4.5 versus 9.2 days), iv drug administration (34.8% versus 61.6%), duration of iv therapy (geometric mean 2.1 versus 5.7 days) and treatment failures (7.8% versus 31.3%). Healthcare costs were also significantly reduced. The use of the protocol was a major factor in streamlining the prescribing of antimicrobial therapy for community-acquired LRTI and led to more cost-effective patient management.

Cutting edge: cationic antimicrobial peptides block the binding of lipopolysaccharide (LPS) to LPS binding protein

We investigated the mechanism by which cationic antimicrobial peptides block the activation of macrophages by LPS. The initial step in LPS signaling is the transfer of LPS to CD14 by LPS binding protein (LBP). Because many cationic antimicrobial peptides bind LPS, we asked whether these peptides block the binding of LPS to LBP. Using an assay that measures the binding of LPS to immobilized LBP, we show for the first time that a variety of structurally diverse cationic antimicrobial peptides block the interaction of LPS with LBP. The relative ability of different cationic peptides to block the binding of LPS to LBP correlated with their ability to block LPS-induced TNF-alpha production by the RAW 264.7 macrophage cell line.

Interaction of cationic peptides with lipoteichoic acid and gram-positive bacteria

Compounds with antiendotoxin properties have been extensively studied for their potential as therapeutic agents for sepsis attributable to gram-negative bacteria. However, with the increasing incidence of gram-positive sepsis, there is interest in identifying compounds with a broad spectrum of action against both gram-positive and gram-negative bacteria. A series of synthetic alpha-helical cationic peptides related to bee melittin and silk moth cecropin have previously been shown to bind lipopolysaccharide (LPS) with high affinity, inhibit LPS-induced tumor necrosis factor alpha (TNF-alpha) production in vitro and in vivo, and kill gram-negative bacteria. In this study, we analyzed whether these peptides were active against gram-positive bacteria; whether they could bind to lipoteichoic acid (LTA), the major proinflammatory structure on gram-positive bacteria; and whether they could block the ability of LTA to promote the release of cytokines by the RAW 264.7 murine macrophage cell line. We found that the cationic peptides demonstrated moderate growth-inhibitory activity toward gram-positive bacteria. In addition, the peptides bound LTA with high affinity. This correlated with the ability of the peptides to block LTA-induced production of TNF and interleukin-6 by RAW 264.7 cells but did not correlate with their ability to kill the bacteria. The peptides also effectively inhibited LTA-induced TNF production in a whole human blood assay. The peptides were also able to partly block the ability of heat-killed Staphylococcus aureus, as well as soluble products of live S. aureus, to stimulate cytokine production by macrophages. Our results indicate that these cationic peptides may be useful to prevent sepsis and inflammation caused by both gram-negative and gram-positive bacteria.

Sequential antimicrobial therapy: treatment of severe lower respiratory tract infections in children

Although there have been a number of studies in adults, to date there has been little research into sequential antimicrobial therapy (SAT) in paediatric populations. The present study evaluates the impact of a SAT protocol for the treatment of severe lower respiratory tract infection in paediatric patients. The study involved 89 paediatric patients (44 control and 45 SAT). The SAT patients had a shorter length of hospital stay (4.0 versus 8.3 days), shorter duration of inpatient antimicrobial therapy (4.0 versus 7.9 days) with the period of iv therapy being reduced from a mean of 5.6 to 1.7 days. The total healthcare costs were reduced by 52%. The resolution of severe lower respiratory tract infection with a short course of iv antimicrobials, followed by conversion to oral therapy yielded clinical outcomes comparable to those achieved using longer term iv therapy. SAT proved to be an important cost-minimizing tool for realizing substantial healthcare costs savings.

Salt-resistant alpha-helical cationic antimicrobial peptides

Analogues based on the insect cecropin-bee melittin hybrid peptide (CEME) were studied and analyzed for activity and salt resistance. The new variants were designed to have an increase in amphipathic alpha-helical content (CP29 and CP26) and in overall positive charge (CP26). The alpha-helicity of these peptides was demonstrated by circular dichroism spectroscopy in the presence of liposomes. CP29 was shown to have activity against gram-negative bacteria that was similar to or better than those of the parent peptides, and CP26 had similar activity. CP29 had cytoplasmic membrane permeabilization activity, as assessed by the unmasking of cytoplasmic beta-galactosidase, similar to that of CEME and its more positively charged derivative named CEMA, whereas CP26 was substantially less effective. The activity of the peptides was not greatly attenuated by an uncoupler of membrane potential, carbonyl cyanide-m-chlorophenylhydrazone. The tryptophan residue in position 2 was shown to be necessary for interaction with cell membranes, as demonstrated by a complete lack of activity in the peptide CP208. Peptides CP29, CEME, and CEMA were resistant to antagonism by 0.1 to 0.3 M NaCl; however, CP26 was resistant to antagonism only by up to 160 mM NaCl. The peptides were generally more antagonized by 3 and 5 mM Mg2+ and by the polyanion alginate. It appeared that the positively charged C terminus in CP26 altered its ability to permeabilize the cytoplasmic membrane of Escherichia coli, although CP26 maintained its ability to kill gram-negative bacteria. These peptides are potential candidates for future therapeutic drugs.

Biological properties of structurally related alpha-helical cationic antimicrobial peptides

A series of alpha-helical cationic antimicrobial peptide variants with small amino acid changes was designed. Alterations in the charge, hydrophobicity, or length of the variant peptides did not improve the antimicrobial activity, and there was no statistically significant correlation between any of these factors and the MIC for Pseudomonas aeruginosa, Escherichia coli, or Salmonella typhimurium. Individual peptides demonstrated synergy with conventional antibiotics against antibiotic-resistant strains of P. aeruginosa. The peptides varied considerably in the ability to bind E. coli O111:B4 lipopolysaccharide (LPS), and this correlated significantly with their antimicrobial activity and ability to block LPS-stimulated tumor necrosis factor and interleukin-6 production. In general, the peptides studied here demonstrated a broad range of activities, including antimicrobial, antiendotoxin, and enhancer activities.

Modulation of human airway smooth muscle proliferation by type 3 phosphodiesterase inhibition

Elevation in cell cAMP content can inhibit mitogenic signaling in cultured human airway smooth muscle (HASM) cells. We studied the effects of the type 3-selective phosphodiesterase inhibitor siguazodan, the type 4-selective phosphodiesterase inhibitor rolipram, and the nonselective inhibitor 3-isobutyl-1-methylxanthine (IBMX) on proliferation of cultured HASM cells. At concentrations selective for the type 3 phosphodiesterase isoform, siguazodan inhibited both [3H]thymidine incorporation (IC50 2 microM) and the increase in cell number (10 microM; 64% reduction) induced by platelet-derived growth factor-BB (20 ng/ml). These effects were mimicked by IBMX. At concentrations selective for type 4 phosphodiesterase inhibition, rolipram was without effect. A 20-min exposure to siguazodan and rolipram did not increase whole cell cAMP levels. However, in HASM cells transfected with a cAMP-responsive luciferase reporter (p6CRE/Luc), increases in cAMP-driven luciferase expression were seen with siguazodan (3.9-fold) and IBMX (16.5-fold). These data suggest that inhibition of the type 3 phosphodiesterase isoform present in airway smooth muscle results in inhibition of mitogenic signaling, possibly through an increase in cAMP-driven gene expression.

Oxygen carriers as blood substitutes. Past, present, and future

Prospects for safe and effective blood substitutes are promising, based on clinical trial results of soluble hemoglobin solutions and emulsion of perfluorocarbins. Advantages of blood substitutes include sterilization of viral and bacterial contaminants, room temperature storage, a long shelf life, and absence of ABO and other red cell antigens. Projected arenas for their use include not only military applications but also trauma medicine and elective surgical settings, coupled with acute normovolemic hemodilution. Applications of perfluorocarbons are limited by the need for 100% FIO2. A significant challenge facing development of hemoglobin solutions is their effect on vascular tone through smooth muscle constriction. Development of second or third generation hemoglobin solutions may be necessary so that hemoglobin solutions more closely mimic cellular hemoglobin's nitric oxide binding properties. Optimizing O2 delivery to ischemic tissues and organs may lead to regulatory approval of these agents in this setting before their approval as blood substitutes.

Buccal absorption of enalapril and lisinopril

OBJECTIVE

The buccal absorption of captopril does not exhibit the classical pH/partition hypothesis, suggesting that mechanisms other than passive diffusion are involved in its absorption; animal studies have suggested that a peptide carrier-mediated transport system may be responsible for its absorption. The present study evaluated the effects of pH on octanol partitioning, and on the buccal absorption of enalapril and lisinopril, using in vitro techniques and buccal partitioning in human volunteer subjects.

METHODS

The partitioning of enalapril and lisinopril into n-octanol was examined over the pH range of 3 9 at room temperature.

RESULTS

Enalapril exhibited maximal partitioning into the organic phase at pH 4 5; minimal partitioning was recorded at pH values 8 and 9. The partitioning of lisinopril into n-octanol was found to be maximal at pH 9 and minimal at pH 3. Using the buccal absorption technique, the partitioning of enalapril and lisinopril (0.5 mg), was examined in six healthy male volunteers from buffered solutions (pH 3, 4, 5, 6, 7, 8 and 9). In the case of enalapril, lowest buccal partitioning occurred at pH 3, 8 and 9, while maximal partitioning occurred at pH 5; absorption of lisinopril was not extensive at any pH, but was greatest at pH 6. These results, in addition to the n-octanol partition coefficients, indicated that enalapril obeyed the normal lipid partition hypothesis with respect to buccal absorption. The buccal absorption of lisinopril also obeyed the lipid partition hypothesis over the pH range 3-7. These findings are in direct contrast to those for captopril. The buccal partitioning experiments were repeated at the maximal pH for absorption for each angiotensin converting enzyme (ACE) inhibitor, but with the addition of cephradine (0.05 mmol x l(-1)).

CONCLUSION

The data indicated that the presence of this peptide transport inhibitor had no effect on the buccal absorption of enalapril (0.06 mmol x l(-1)) and lisinopril (0.057 mmol x l(-1)), which suggests that both drugs do not share a common buccal absorption pathway with cephradine.

Correlation of plasma concentrations of cystatin C and creatinine to inulin clearance in a pediatric population

Measurement of blood concentrations of cystatin C (cysC), a cysteine protease inhibitor present in human plasma, has been suggested for use as an indicator of glomerular filtration rate (GFR) in a manner analogous to the use of plasma creatinine (SCR). In this study, cysC and SCR were measured in plasma from pediatric patients (4-19 years) with renal disease for whom a "gold standard" measurement of GFR via inulin clearance (C(IN)) was available. The data analyses were divided into two age groups: group A (4-12 years, n = 26) and group B (12-19 years, n = 34). For both age groups, the linear correlation coefficient of [cysC](-1) vs C(IN) (mL/min/1.73 m2) (r = 0.765 for group A and r = 0.869 for group B) was less than that of the linear correlation coefficient of [SCR](-1) vs C(IN) (r = 0.841 for group A and r = 0.892 for group B). As a single measurement for detection of abnormal GFR, however, the optimum receiver-operator characteristic point for cysC measurement (for group A at cysC >1.2 mg/L, sensitivity = 80%, specificity = 91%; and for group B at cysC >1.4 mg/L, sensitivity = 87%, specificity = 100%) was numerically superior to that for SCR measurement (for group A at SCR >8.0 mg/L, sensitivity = 67%, specificity = 100%; and for group B at SCR >9.0 mg/L, sensitivity = 91%, specificity = 91%), using a reference value for normal GFR of C(IN) > 90 mL/min/1.73 m2. However, these differences were not statistically significant. CysC measurement appears to be broadly equivalent to SCR measurement for estimation of GFR in pediatric patients.

Hemoglobin Raleigh as the cause of a falsely increased hemoglobin A1C in an automated ion-exchange HPLC method

Irreversible glycation of the hemoglobin A0 (HbA0) beta chain leads to the production of HbA1C, which can be used to monitor long-term blood glucose control in patients with diabetes mellitus. HbA1C is less positively charged than nonglycated HbA0, and this decrease in charge is the basis of ion-exchange and electrophoretic methods that measure HbA1C. We recently identified a sample that appeared to contain 46% HbA1C by an automated ion-exchange HPLC method (Bio-Rad Variant) but only 3.8% by an immunoinhibition latex agglutination method. A combination of traditional and mass spectrometric protein analysis and genomic DNA analysis of the Hb beta chain and genes revealed that the patient was heterozygotic for Hb-Raleigh, a variant containing a valine-->alanine substitution at position 1 of the beta chain. The amino-terminal alanine in this variant Hb is posttranslationally modified by acetylation, leading to a charge difference similar to glycation and making the behavior of HbA1C and Hb Raleigh virtually identical in the ion-exchange HPLC method. This observation suggests that it is important to confirm HbA1C values in excess of 15%, especially if they are not consistent with the clinical picture, by an independent HbA1C method such as immunoassay or boronic acid affinity chromatography. However, for this particular variant Hb, even these latter methods might be misleading, because the acetylated N-terminal amino acid of the Hb-Raleigh beta chain cannot be glycated.

Comparison between the CEDIA and EMIT II immunoassays for the determination of benzodiazepines

We evaluated a new, qualitative immunoassay for benzodiazepines in urine using CEDIA technology on the Hitachi 747 and compared its performance to an immunoassay using EMIT II methodology on the same instrument. A total of 500 urine samples received for routine drug screen analysis were prospectively examined for benzodiazepines by both methods. Samples producing positive results by either immunoassay method were analyzed by gas chromatography-mass spectrometry (GC-MS). Available medical records were reviewed for patients whose samples produced discrepant immunoassay results or that were positive in both immunoassays but negative by GC-MS. Samples that produced negative results in both immunoassays were not subjected to GC-MS analysis. Therefore, identification of an immunoassay result as a false negative only occurred when the sample produced a positive value in only one of the two immunoassays and was confirmed as positive by either GC-MS or medical record review. Following initial immunoassay screening and confirmation by GC-MS, a medical record review and reanalysis of GC-MS data was performed. After this in-depth analysis of the data, the CEDIA method produced 60 true-positives, 7 false positives and no false negatives. The EMIT II method produced 47 true positives, 1 fase positive and 13 false negatives. These differences appear to be due to the CEDIA assay being more sensitive for detection of lorazepam.

Coexpression of parathyroid hormone-related protein and its receptor in breast carcinoma: a potential autocrine effector system

Parathyroid hormone-related protein (PTHrP), the pathogenic factor in most cases of humoral hypercalcemia of malignancy, is also expressed by many normal tissues. Its diverse biologic activities in these tissues are mediated by the PTH/PTHrP receptor through autocrine and paracrine mechanisms. Recent data suggest that PTHrP and its receptor might also influence the growth and metastatic spread of some cancers through similar local actions. Accordingly, immunohistochemical studies using murine monoclonal antibodies to detect coexpression of PTHrP and the PTH/PTHrP receptor were performed on 52 invasive breast carcinomas to assess the existence of this potential autocrine effector system. All of the 52 invasive breast carcinomas expressed reactivity for PTHrP, and 50 (96%) of these tumors also expressed reactivity for the receptor. Although additional investigations are necessary for evaluation of the role of PTHrP and PTH/PTHrP receptor in tumor pathogenesis, our current study demonstrates the presence of this potential autocrine effector system in the great majority of invasive breast carcinomas.

Mechanisms of dopamine and dobutamine interference in biochemical tests that use peroxide and peroxidase to generate chromophore

Dopamine and dobutamine have recently been shown to produce a negative interference in several biochemical tests that use peroxide and peroxidase to generate a chromophore. To define the chemical mechanism of this interference, we examined the effects of dopamine and dobutamine in various peroxidase-based biochemical tests. Dopamine interfered stoichiometrically with peroxidase-based tests that use 4-aminophenazone to form chromophore but interfered little in those that use other compounds to generate chromophore. Dopamine reacts with 4-aminophenazone in the presence of peroxide and peroxidase to form a novel quinone-imine dye, with a smaller absorptivity than the chromophore formed in the absence of dopamine. The smaller absorptivity of this novel chromophore results in negative interference by reducing the total absorbance at the wavelength used to measure analyte. In contrast, dobutamine interfered stoichiometrically with all peroxidase-based tests studied, regardless of whether 4-aminophenazone was used to form the chromophore. Dobutamine was rapidly oxidized by peroxide in the presence of peroxidase, thus depleting the peroxide necessary to generate chromophore. Dopamine and dobutamine demonstrate two distinct general mechanisms of interference in peroxidase-based biochemical tests.