Evaluation of some fluorogenic substrates for continuous assay of aminopeptidase P

Three potential fluorogenic substrates for assay of aminopeptidase P (AP-P) have been prepared and evaluated, using enzyme purified from porcine kidney. They are based on internal quenching of the synthetic, fluorescent amino acid (R, S)-2-amino-3-(7-methoxy4-coumaryl)propanoic acid ((R,S)-Amp) by a 2, 4dinitrophenyl (DNP) group. The compounds are X-Pro-Pro-(R, S)-Amp-NH2, where X is H-Lys(epsilon-DNP), H-Orn(delta-DNP), or L-2-amino-3-(DNP)aminopropionic acid. The first two were found to be excellent substrates for AP-P, with respective Km values of 4.8 and 5.2 microM. An advantageous feature is that under the conditions of assay, using 4-mm2 cells, the substrates are without noticeable quenching effect on the fluorescence of Pro-Pro-(R,S)-Amp-NH2 (the product liberated by the action of AP-P). At concentrations greater than about 30-50 microM, both substrates appear to inhibit the enzyme, but this has little practical consequence since assays can be carried out at substrate concentrations, giving up to approximately 80% of Vmax without this inhibitory effect being noticeable. The Lys derivative was found to be a very useful substrate for a continuous assay for AP-P and equally good in a discontinuous assay of multiple samples using microtiter plates. The racemic center at the Amp residue did not prevent total hydrolysis of the Lys derivative, suggesting that subsite specificity in AP-P does not extend as far as the P3' position.

Transmembrane beta-barrel of staphylococcal alpha-toxin forms in sensitive but not in resistant cells

Staphylococcal alpha-toxin is a 293-residue, single-chain polypeptide that spontaneously assembles into a heptameric pore in target cell membranes. To identify the pore-forming domain, substitution mutants have been produced in which single cysteine residues were introduced throughout the toxin molecule. By attaching the environmentally sensitive dye acrylodan to the sulfhydryl groups, the environment of individual amino acid side chains could be probed. In liposomes, a single 23-amino acid sequence (residues 118-140) was found to move from a polar to a nonpolar environment, indicating that this sequence forms the walls of the pore. However, periodicity in side chain environmental polarity could not be detected in the liposomal system. In the present study, the fluorimetric analyses were extended to physiological target cells. With susceptible cells such as rabbit erythrocytes and human lymphocytes, the 23 central amino acids 118-140 were again found to insert into the membrane; in contrast to the previous study with liposomes, the expected periodicity was now detected. Thus, every other residue in the sequence 126-140 entered a nonpolar environment in a striking display of an amphipathic transmembrane beta-barrel. In contrast, human granulocytes were found to bind alpha-toxin to a similar extent as lymphocytes, but the heptamers forming on these cells failed to insert their pore-forming domain into the membrane. As a consequence, nonfunctional heptamers assembled and the cells remained viable. The data resolve the molecular organization of a pore-forming toxin domain in living cells and reveal that resistant cells can prevent insertion of the functional domain into the bilayer.

Adenosine A3 receptor stimulation inhibits migration of human eosinophils

Activation of adenosine A3 receptors (A3-R) produced a dose-dependent reduction in the chemotaxis of human eosinophils to platelet-activating factor (PAF), RANTES, and leukotriene B4 (LTB4) to a maximum of 58, 48, and 52%, respectively (P < 0.02). This effect was completely reversed by selective A3-R antagonists. In contrast, activation of A1 or A2a-R did not affect PAF-induced eosinophil chemotaxis. PAF up-regulated the expression of CDllb/CD18, down-regulated L-selectin, and also increased F-actin assembly in eosinophils. The expression of these activation markers was not influenced by A3-R, A2a, or A1-R stimulation. Activation of A3-R may play an important role in inflammation by inhibiting eosinophil migration.

Mechanisms of protection induced by attenuated simian immunodeficiency virus. I. Protection cannot be transferred with immune serum

To evaluate its role in protection, immune serum was collected from four macaques which were chronically infected with live attenuated simian immunodeficiency virus (SIVmacC8) and had resisted challenge with wild-type SIVmacJ5. The immune serum was transferred to two naive cynomolgus macaques by intraperitoneal injection (11 ml/kg). Four control macaques received an intraperitoneal injection of normal saline. One day later, all macaques were challenged with 10 MID50 of the J5M challenge stock of SIV. After challenge, all macaques became infected as determined by virus co-culture and diagnostic PCR. Virus loads in PBMC at 2 weeks post-challenge were indistinguishable between the two groups of macaques. Thus, the failure of passive immunization to transfer protection indicates that serum components alone are not sufficient to mediate the potent protection obtained using live attenuated vaccines. This is the first time that serum has been transferred from animals known to be protected against superinfection.

Public health in a managed care environment

As the health care system moves in a new direction, toward managed care, the critical role of public health in society's efforts to mitigate illness and the realization of health become more apparent. Indeed, the public health problems of this era will not yield to simple solutions. They require a multitude of resources, both human and material, and a myriad of services derived from these resources. Public health's role is to serve as the government's presence in assessing health status, developing policy, evaluating the effectiveness of policy implementation, and assuring access to and quality of comprehensive health services. Increasingly, public health must coordinate a wide array of systems in both the private and public sectors to fulfill its purpose.

Peptidyl inverse esters of p-methoxybenzoic acid: a novel class of potent inactivator of the serine proteases

A series of novel synthetic peptides, containing a C-terminal beta-amino alcohol linked to p-methoxybenzoic acid via an ester linkage, have been prepared and tested as inhibitors against typical members of the serine protease family. For example, the sequences Ac-Val-Pro-NH-CH-(CH2-C6H5)-CH2O-CO-C6H4-OCH3 (I) and Ac-Val-Pro-NH-CH-[CH-(CH3)2]-CH2O-CO-C6H4-OCH3 (II), which fulfil the known primary and secondary specificity requirements of chymotrypsin and elastase respectively, have been found to behave as exceptionally potent irreversible inactivators of their respective target protease. Thus I was found to inactivate chymotrypsin with an overall second-order rate constant (k2/Ki) of approx. 6.6x10(6) M-1. s-1, whereas II is an even more potent inactivator of human neutrophil elastase, exhibiting a second-order rate constant of inactivation of approx. 1.3x10(7) M-1.s-1. These values represent the largest rate constants ever reported for the inactivation of these proteases with synthetic peptide-based inactivators. On prolonged incubation in substrate-containing buffers, samples of the inactivated proteases were found to regain activity slowly. The first-order rate constants for the regeneration of enzymic activity from chymotrypsin and human neutrophil elastase inactivated by I and II respectively were determined to be approx. 5.8x10(-5) s-1 and approx. 4.3x10(-4) s-1. We believe that the most likely mechanism for the inactivation and regeneration of enzymic activity involves the formation and subsequent slow hydrolysis of long-lived acyl enzyme intermediates.

Evasion of cytotoxic T lymphocyte (CTL) responses by nef-dependent induction of Fas ligand (CD95L) expression on simian immunodeficiency virus-infected cells

Inoculation of macaques with live attenuated SIV strains has been shown to protect against subsequent challenge with wild-type SIV. The protective mechanism(s) remain obscure. To study the effect in more detail, we have investigated the role of virus-specific CTL responses in macaques infected with an attenuated SIV strain (pC8), which has a four-amino acid deletion in the nef gene, as compared with the wild-type SIVmac32H clone (pJ5). Cynomolgus macaques infected with pC8 were protected against subsequent challenge with pJ5 and did not develop any AIDS-like symptoms in the 12 months after infection. The pC8-induced protection was associated with high levels of virus-specific CTL responses to a variety of viral antigens. In contrast, pJ5-infected macaques had little, if any, detectable CTL response to the viral proteins after three months. The latter group of macaques also showed increased Fas expression and apoptotic cell death in both the CD4(+) and CD8(+) populations. In vitro, pJ5 but not pC8 leads to an increase in FasL expression on infected cells. Thus the expression of FasL may protect infected cells from CTL attack, killing viral-specific CTLs in the process, and providing a route for escaping the immune response, leading to the increased pathogenicity of pJ5. pC8, on the other hand does not induce FasL expression, allowing the development of a protective CTL response. Furthermore, interruption of the Fas-FasL interaction allows the regeneration of viral-specific CTL responses in pJ5-infected animals. This observation suggests an additional therapeutic approach to the treatment of AIDS.

Designed protein pores as components for biosensors

BACKGROUND

There is a pressing need for new sensors that can detect a variety of analytes, ranging from simple ions to complex compounds and even microorganisms. The devices should offer sensitivity, speed, reversibility and selectivity. Given these criteria, protein pores, remodeled so that their transmembrane conductances are modulated by the association of specific analytes, are excellent prospects as components of biosensors.

RESULTS

Structure-based design and a separation method that employs targeted chemical modification have been used to obtain a heteromeric form of the bacterial pore-forming protein staphylococcal alpha-hemolysin, in which one of the seven subunits contains a binding site for a divalent metal ion, M(II), which serves as a prototypic analyte. The single-channel current of the heteromer in planar bilayers is modulated by nanomolar Zn(II). Other M(II)s modulate the current and produce characteristic signatures. In addition, heteromers containing more than one mutant subunit exhibit distinct responses to M(II)s Hence, a large collection of responsive pores can be generated through subunit diversity and combinatorial assembly.

CONCLUSIONS

Engineered pores have several advantages as potential sensor elements: sensitivity is in the nanomolar range; analyte binding is rapid (diffusion limited in some cases) and reversible; strictly selective binding is not required because single-channel recordings are rich in information; and for a particular analyte, the dissociation rate constant, the extent of channel block and the voltage-dependence of these parameters are distinguishing, while the frequency of partial channel block reflects the analyte concentration. A single sensor element might, therefore, be used to quantitate more than one analyte at once. The approach described here can be generalized for additional analytes.

Founders-Sumner lecture

The revolution in patient care financing and in the structure and changing scope of the health service system calls for leaders in health care to address existing challenges in the health delivery system. Medical leadership cannot ignore, much less resist, the challenges inherent in the flux and dynamic changes going on in the medical care/health sciences environment. Some of these changes are fueled by fundamental advancements in science and technology. Other developments are fueled by political, demographic, economic and social forces. This article highlights some of these challenges and urges the medical leadership to assume the obligation to assure quality of health-care services and not allow it to be over-shadowed by market forces.

Mechanisms of protection induced by attenuated simian immunodeficiency virus. IV. Protection against challenge with virus grown in autologous simian cells

Attenuated simian immunodeficiency virus (SIV) induces potent protection against infection with wild-type virus, but the mechanism of this immunity remains obscure. Allogeneic antibodies, which arise within animals as a result of SIV infection, might protect against challenge with exogenous SIV grown in allogeneic cells. To test this hypothesis, eight macaques were infected with attenuated SIV and subsequently challenged with wild-type SIV grown in autologous cells or heterologous cells. The results clearly demonstrated that animals infected with attenuated SIV are protected against wild-type SIV grown in autologous or heterologous cells. Thus, the hypothesis that live attenuated SIV protects by the induction of allogeneic antibodies is not tenable.

Cancer risk assessment

Increasing efforts to reduce the burden of cancer have brought into sharp relief the relevance of cancer risk assessment in preventing the occurrence and, when that is not possible, preventing the progression of the disease. Methods for estimating human cancer risk have evolved steadily over the past few decades as more has been learned about molecular, genetic, and biological aspects of cancer. These methods have been applied with increasing frequency in community-based approaches to reduce the risk of environmentally provoked cancers. At the same time, patients are showing increased interest in estimates of their likelihood of developing cancer during the next 10, 20, or 30 years. This interest is involving more physicians in human cancer risk assessment in clinical counseling settings.

IL-4 and TNF-alpha-mediated proliferation of the human megakaryocytic line M-O7E is regulated by induced autocrine production of GM-CSF

In this study, the authors examined the effects of recombinant human interleukin 4 (rhIL-4) and recombinant human tumour necrosis factor alpha (rhTNF-alpha) alone or in combination on proliferation of the human cytokine dependent myeloid cell line, M-O7e. While rhIL-4 or rhTNF-alpha alone induced only a weak proliferative response, a synergistic proliferative signal was clearly evident on stimulation of cells with a combination of both cytokines. The stimulatory effect of rhTNF-alpha is mediated predominantly by the 55-kDa TNF receptor because the agonistic monoclonal antibody htr-9 and the Trp32 Thr86 TNF-alpha mutant protein specific for this receptor type produced similar results to rhTNF-alpha. In contrast, the Asn143 Arg145 TNF-alpha mutant protein specific for the 75-kDa TNF receptor produced only minimal proliferation of M-O7e cells. Using RT-PCR, we found that rhTNF-alpha rapidly and strongly induced granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA production, while rhIL-4 was a slow and less efficient inducer of GM-CSF mRNA. However, there was little evidence of the TNF-alpha/IL-4 combination acting synergistically on GM-CSF mRNA production as the levels of GM-CSF mRNA increased only marginally compared with IL-4 or TNF-alpha alone. Thus, the observed synergistic effect of TNF-alpha/IL-4 costimulation of M-O7e cells seems to be mediated via induction of GM-CSF secretion rather than an enhanced production of GM-CSF mRNA. Higher levels of GM-CSF were detectable in supernatants of cells treated with both rhIL-4 and rhTNF-alpha than in cells stimulated with either cytokine alone. Furthermore, addition of a neutralising antibody against GM-CSF abrogated the observed synergistic effect of rhIL-4 and rhTNF-alpha treatment, indicating that the rhIL-4/TNF-alpha combination acts to significantly increase GM-CSF release which then acts in an autocrine manner to enhance the proliferation of M-O7e cells.

Distal vessel atherosclerosis as a cause for false-positive renal scintigraphy

While captopril-enhanced renal scintigraphy is acknowledged to be a useful screening technique to detect clinically silent obstructive lesions of the main renal arteries, the presence of significant atherosclerosis of distal, smaller renal vessels as a cause of positive scintigraphy scans has not been reported extensively. In a retrospective 2-year analysis of 31 consecutive captopril-enhanced renal scintigrams, we found a total of 13 studies in 11 patients that were classified as "positive" for renal artery stenosis. Of these 11 patients with positive scintigraphic studies, 4 patients underwent 5 renal arteriography procedures; only 1 of these renal arteriograms showed significant stenosis of the main renal artery. In the other 4 cases, an angiographic pattern of diffuse intrarenal distal arterial disease correlated with scintigram lateralization. Angiography was also performed in 4 patients with negative captopril renal scintiscans. In each of these cases the arteriogram was also negative for significant renal artery stenosis, and only 1 patient had diffuse bilateral intrarenal arterial disease. We conclude that distal renal arterial narrowing should be considered in the differential diagnosis of lateralized renal scintigrams. A negative renal scintigraphic study may be more reliable for excluding significant main renal artery obstructive disease.

Murine epidermal growth factor peptide (33-42) binds to a YIGSR-specific laminin receptor on both tumor and endothelial cells

A laminin-antagonist peptide, comprising amino acids 33-42 of murine epidermal growth factor (mEGF-(33-42)), interacts with a breast cancer- and endothelial cell-associated receptor, which is specific for the laminin B1 chain sequence, CDPGYIGSR-NH2 (Lam.B1-(925-933)), and is immunologically similar to a previously described 67-kDa laminin receptor. In whole cell receptor assays, mEGF-(33-42), Lam. B1-(925-933), and laminin all have IC50 values for displacement of 125I-laminin in the range 1-5 nM. Cell attachment to solid-phase laminin is also blocked by all three ligands, but in contrast to the receptor assays, mEGF-(33-42) or Lam.B1-(925-933), while equipotent with each other, were less effective than laminin. The concentrations of the peptides required to produce half-maximal inhibition of attachment were in the range 230-390 nM, but those for laminin were 1000-fold lower, in the range 0.2-0.3 nM. Like laminin, solid-phase mEGF-(33-42) supports cell attachment, and this ability is blocked by anti-67-kDa receptor antibodies. Modeling studies suggest that both peptides present a tyrosyl and an arginyl residue on the same face of a right-handed helical fold with elliptical cross-section.

MMPI-2 patterns in African-American females

Researchers have reported conflicting conclusions about the relation of the MMPI (MMPI-2) clinical scale elevations and race. Consequently, this study examined the concurrent validity of the MMPI-2 in evaluating African-American females. Seventy-eight (78) African American college student volunteers were administered the MMPI-2, along with other measures of personality, achievement, and coping style. Scores revealed 76% of the sample had elevated profiles. Subjects were divided into three groups based on frequency of clinical scale code type. Subjects with the 5/9 profile elevations functioned as well as normals on measures of coping skills and mood disorders. Discussion emphasizes the importance of clinical interpretation of MMPI data in research programs and the relationship of the data to coping style.

Molecular architecture of a toxin pore: a 15-residue sequence lines the transmembrane channel of staphylococcal alpha-toxin

Staphylococcus aureus alpha-toxin is a hydrophilic polypeptide of 293 amino acids that produces heptameric transmembrane pores. During assembly, the formation of a pre-pore precedes membrane permeabilization; the latter is linked to a conformational change in the oligomer. Here, 41 single-cysteine replacement toxin mutants were thiol-specifically labelled with the polarity-sensitive fluorescent probe acrylodan. After oligomerization on membranes, only the mutants with acrylodan attached to residues in the sequence 118-140 exhibited a marked blue shift in the fluorescence emission maximum, indicative of movement of the fluorophore to a hydrophobic environment. Within this region, two functionally distinct parts could be identified. For mutants at positions 126-140, the shifts were partially reversed after membrane solubilization by detergents, indicating a direct interaction of the label with the membrane lipids. Membrane insertion of this sequence occurred together with the final pre-pore to pore transition of the heptamer. Thus residues 126-140 constitute a transmembrane sequence in the pore. With labelled residues 118-124, pre-pore assembly was the critical event to induce the spectral shifts, which persisted after the removal of membrane lipids and hence probably reflects protomer-protomer contacts within the heptamer. Finally, a derivative of the mutant N121C yielded occluded pores which could be opened by reductive reversal of the modification. Therefore this residue probably lines the lumen of the pore.

Aberration-free stretcher design for ultrashort-pulse amplification

A novel aberration-free pulse stretcher design is presented. This system permits the stretching of a 30-fs pulse to 300 ps and recompression to a duration of 33 fs, limited by the spectral clipping.

Staphylococcal alpha-toxin, streptolysin-O, and Escherichia coli hemolysin: prototypes of pore-forming bacterial cytolysins

Staphylococcal alpha-toxin, streptolysin-O, and Escherichia coli hemolysin are well-studied prototypes of pore-forming bacterial cytotoxins. Each is produced as a water-soluble single-chain polypeptide that inserts into target membranes to form aqueous transmembrane pores. This review will compare properties of the three toxin prototypes, highlighting the similarities and also the differences in their structure, mode of binding, mechanism of pore formation, and the responses they elicit in target cells. Pore-forming toxins represent the most potent and versatile weapons with which invading microbes damage the host macroorganism.

Assessment of urinary gonadotropin in solid carcinomas other than gynecological tumors

To the already long list of existing tumor markers, a new marker has been recently added, the urinary gonadotropin peptide (UGP). This marker is determined in the urine of cancer patients and is considered to be particularly specific for ovarian carcinomas. The purpose of our study was to assess the specificity of UGP in a variety of malignancies other than ovarian carcinomas, e.g., breast, colonic, lung, and urogenital tumors (n = 50 each). The tumors were compared with benign lesions of the same organs. Urine samples of 50 healthy donors served as controls. The 450 urine samples were tested in duplicate using the UGP EIA-kit from Ciba Corning Diagnostics. All tumors were staged and histologically classified. For normalization in all samples, creatinine levels were determined. UGP was found in all tested tumors, however, with very low sensitivity of 20% in urogenital tumors, 46% in lung, and 30% or 27% in colon and breast carcinomas, respectively. The specificity of UGP was comprised between 100% (breast) and 88%. Clearly elevated UGP-concentrations were seen in postmenopausal women. A comparison of UGP with the optimal markers for each tumor system showed that UGP is not superior to these markers. However, we can confirm UGP as being an optimal marker for gynecological carcinomas.

Early first-trimester ultrasound provides a window through which the chorionicity of twins can be diagnosed in an in vitro fertilization (IVF) population

PURPOSE

Early and accurate diagnosis of placentation alerts the obstetrician to potential clinical sequelae. The reproductive endocrinologist has a unique opportunity to sonographically evaluate the very early intrauterine pregnancy. We undertook this study to determine whether chorionicity could accurately be predicted using early first-trimester transvaginal ultrasound.

RESULTS

Of 47 sets of twins conceived through our IVF-ET program, all underwent detailed transvaginal sonography. These findings were then compared with results of placental pathology examination, after birth. Transvaginal sonography was performed 41 days following embryo transfer. All 3 monochorionic placentas were correctly predicted by ultrasound, while the remaining 44 placentas were dichorionic.

CONCLUSIONS

The significance of our findings lies both in our 100% accuracy in diagnosis and in the extremely early gestational age at which we were able to establish correctly the diagnosis of chorionicity. The errors in diagnosis made by previous investigators were often the result of not recognizing single placentae which were later histologically shown to be the result of placental fusion. The infertility specialist has a unique window of opportunity to evaluate placentation and should provide useful information regarding chorionicity to the obstetrical team.

Differences in cancer incidence, mortality, and survival between African Americans and whites

This report highlights selected evidence of different cancer patterns among African Americans and whites and considers potential risk factors associated with these cancers. During the years 1987 to 1991, African Americans experienced higher incidence and mortality rates than whites for multiple myeloma and for cancers of the oropharynx, colorectum, lung and bronchus, cervix, and prostate. African Americans had lower incidence and mortality for cancer of the urinary bladder. The incidence of breast cancer was higher among white women, but mortality was higher among African American women. Five-year relative survival for the period 1983 to 1990 was generally lower among African Americans than whites for cancers of the oropharynx, colorectum, cervix, prostate, and female breast but slightly higher for multiple myeloma. From 1973 to 1991, there were significant declines in cervical cancer incidence among women of both races, oropharyngeal cancer mortality among whites, and bladder cancer mortality for whites and African Americans. Risk factors for the more prominent cancers suggest that efforts aimed at changing lifestyles, achieving socioeconomic parity, and insuring environmental equity are likely to relieve African Americans of much of their disproportionate cancer burden.

Key residues for membrane binding, oligomerization, and pore forming activity of staphylococcal alpha-hemolysin identified by cysteine scanning mutagenesis and targeted chemical modification

The alpha-hemolysin (alpha HL) polypeptide is secreted by Staphylococcus aureus as a water-soluble monomer that assembles into lipid bilayers to form cylindrical heptameric pores 1-2 nm in effective internal diameter. We have individually replaced each charged residue (79 of 293 amino acids) and four neutral residues in alpha HL with cysteine, which is not found in the wild-type protein. The properties of these mutants have been examined before and after modification with the 450-Da dianionic sulfhydryl reagent 4-acetamido-4'-((iodoacetyl)amino)stilbene-2,2'-disulfonate (IASD). This modification was highly informative as 28 of 83 modified polypeptides showed substantially reduced pore forming activity on rabbit erythrocytes (rRBC), while only five of the unmodified cysteine mutants were markedly affected. Through detailed examination of the phenotypes of the mutant and modified hemolysins, we have pinpointed residues and regions in the alpha HL polypeptide chain that are important for binding to rRBC, oligomer formation and pore activity. Residues in both the N-terminal (Arg-66 and Glu-70) and C-terminal (Arg-200, Asp-254, Asp-255, and Asp-276) thirds of the protein are implicated in binding to cells. The His-35 replacement mutant modified with IASD was the only polypeptide in this study that failed to form SDS-resistant oligomers on rRBC. Altered hemolysins that formed oligomers but failed to lyse rRBC represented the most common defect. These alterations were clustered in the central glycine-rich loop, which has previously been implicated as a component of the lumen of the membrane-spanning channel, and in the regions flanking the loop. Alterations in mutant and modified hemolysins with the same defect were also scattered between the N terminus and His-48, in keeping with previous suggestions that an N-terminal segment and the central loop cooperate in the final step of pore assembly.

Substance P (NK1)- and neurokinin A (NK2)-receptor gene expression in inflammatory airway diseases

The tachykinin neuropeptides substance P and neurokinin (NK) A have been postulated to participate in the inflammatory reaction in airways of smokers and asthmatics. We have examined the hypothesis that the expression of one or more of the three cloned tachykinin receptors (NK1, NK2, and NK3) is increased in inflammatory airway disorders, which could result in augmentation of the effect of released tachykinin neuropeptides. NK1 receptor and NK2 receptor but not NK3-receptor mRNA were detected by ribonuclease protection assay in RNA from both cartilaginous and membranous bronchi and subpleural lung. In lung samples containing membranous airways, NK2-receptor mRNA expression was increased fourfold in asthmatics compared with nonsmoking controls, whereas NK1-receptor mRNA levels were similar in the two groups. NK1- and NK2-receptor mRNA expression was increased twofold in smokers without airflow obstruction compared with nonsmokers, whereas NK1-receptor mRNA expression was significantly lower in patients with chronic obstructive pulmonary disease compared with smoking controls. In situ hybridization indicated NK1-receptor mRNA was expressed in submucosal glands and airway epithelial cells, whereas NK2-receptor and NK3-receptor mRNA were not detected. These observations have implications for the pathophysiology and treatment of both asthma and tobacco smoke-induced airway inflammation.

Murine epidermal growth factor (EGF) fragment (33-42) inhibits both EGF- and laminin-dependent endothelial cell motility and angiogenesis

Laminin, murine epidermal growth factor (mEGF), and the synthetic laminin peptide Lam.B1(925-933) (a linear peptide from the B1 chain of murine laminin, CDPGY1GSR-amide) all stimulate endothelial cell motility above basal rates, whereas a synthetic mEGF fragment, mEGF33-42 (a linear peptide from the C-loop of mEGF, acetyl-C-[S-Acm]-VIGYSGDR-C-[S-Acm]-amide), inhibits motility. In both human SK HEP-1 and embryonic chick endothelial cells, mEGF33-42 blocks both EGF- and laminin-stimulated locomotion of endothelial cells. In vivo, mEGF33-42 also blocks both laminin- and mEGF-induced angiogenesis in the chick. In the human cell line. Lam.B1(925-933) has an additive effect in coincubation with either laminin or mEGF, but it blocks their effects in the chick cells. Lam.B1(925-933) alone stimulates angiogenesis in the chick but blocks laminin-induced angiogenesis. Thus, mEGF33-42 acts as a general laminin antagonist, whereas Lam.B1(925-933) acts as a laminin agonist in human cells, but in chick cells it acts as a partial antagonist. We propose that the presence of an anionic group at the eighth residue of mEGF33-42 may be the source of the antagonistic effects seen with this peptide as compared with the laminin fragment. These findings have important implications in the design of human antiangiogenic agents, and also in the use of chick models in the study of human disease.

Cytokine profile of circulating T cells of leprosy patients reflects both indiscriminate and polarized T-helper subsets: T-helper phenotype is stable and uninfluenced by related antigens of Mycobacterium leprae

Cytokine profiles of circulating mononuclear cells were studied with the aim of delineating T-cell subsets in leprosy patients with active disease. Using reverse transcriptase-polymerase chain reaction (RT-PCR) for cytokine mRNA and enzyme-linked immunoassay (ELISA) for the secreted products, interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) were studied. Three antigens, native Mycobacterium leprae, a recombinant antigen LSR/A15 of M. leprae and peptide 624 spanning 58-77 amino acids of the latter, were used to induce cytokine expression and release. Half of the subjects, irrespective of the clinical type or antigen used, showed a mixed T-helper type 0 (Th0)-like cytokine pattern, with evidence of the concomitant presence of IFN-gamma and IL-4. The remainder showed a polarized pattern based on the type of leprosy. Lepromatous patients with disseminated disease had Th2-type cytokines, with IL-4 but not IFN-gamma. In contrast, tuberculoid leprosy patients with localized disease showed a Th1-like profile, with the presence of IFN-gamma but not IL-4. Of interest was the stability of the Th phenotype for M. leprae-related antigens. Both the recombinant and the peptide antigens induced the same phenotype as the natural M. leprae bacillus in all except four of 45 leprosy patients.

Rate of growth of Pseudomonas fluorescens in donated blood

AIMS

To examine how delayed refrigeration of blood affects the growth of Pseudomonas fluorescens, one of the two most important causes of sepsis resulting from transfusion of contaminated blood.

METHODS

Two donations of whole blood were each divided into three aliquots and inoculated with 5-10 cfu/ml of a P fluorescens strain from a case of transfusion associated sepsis. From each donation, one aliquot was placed at 4 degrees C, one was held at 20 degrees C for six hours prior to refrigeration and the third was held at 20 degrees C for 24 hours prior to refrigeration. Samples were aseptically withdrawn over 17 days and bacterial counts were determined using a pour plate technique.

RESULTS

The rate of growth of P fluorescens in blood at 20 degrees C was increased compared with blood at 4 degrees C. At 24 hours the aliquots held at 20 degrees C for six and 24 hours had, respectively, 174 and 29,000 cfu/ml compared with 15 cfu/ml in aliquots held at 4 degrees C. There was no evidence of increased killing of P fluorescens at the higher temperature.

CONCLUSIONS

These results suggest that blood for transfusion should be refrigerated as soon as possible after collection.

A photogenerated pore-forming protein

BACKGROUND

The permeabilization of cells with bacterial pore-forming proteins is an important technique in cell biology that allows the exchange of small reagents into the cytoplasm of a cell. Another notable technology is the use of caged molecules whose activities are blocked by addition of photoremovable protecting groups. This allows the photogeneration of reagents on or in cells with spatial and temporal control. Here, we combine these approaches to produce a caged pore-forming protein for the controlled permeabilization of cells.

RESULTS

2-Bromo-2-(2-nitrophenyl)acetic acid (BNPA), a water-soluble cysteine-directed reagent for caging peptides and proteins with the alpha-carboxy-2-nitrobenzyl (CNB) protecting group, was synthesized. Glutathione (gamma-Glu-Cys-Gly) was released in high yield from gamma-Glu-CysCNB-Gly by irradiation at 300 nm. Based on this finding, scanning mutagenesis was used to find a single-cysteine mutant of the pore-forming protein staphylococcal alpha-hemolysin (alpha HL) suitable for caging. When alpha HL-R104C was derivatized with BNPA, pore-forming activity toward rabbit erythrocytes was lost. Near UV irradiation led to regeneration of the cysteine sulfhydryl group and the restoration of pore-forming activity.

CONCLUSIONS

Caged pore-forming proteins are potentially useful for permeabilizing one cell in a collection of cells or one region of the plasma membrane of a single cell. Therefore, alpha HL-R104C-CNB and other caged proteins designed to create pores of various diameters should be useful for many purposes. For example, the ability to introduce reagents into one cell of a network or into one region of a single cell could be used in studies of neuronal modulation. Further, BNPA should be generally useful for caging cysteine-containing peptides and single-cysteine mutant proteins to study, for example, cell signaling or structural changes in proteins.

Restoration of pore-forming activity in staphylococcal alpha-hemolysin by targeted covalent modification

In previous studies, the replacement of His35 in the pore-forming protein alpha-hemolysin (alpha HL) with Leu, Ile, Pro, Arg, Ser, Thr or Cys yielded inactive polypeptides. Here, we show that modification of the inactive single-cysteine mutant alpha HL-H35C with iodoacetamide, to form H35CamC, generates significant pore-forming activity. The closely related polypeptides H35N and H35Q have, respectively, essentially no activity and greatly reduced activity. The modified residue in H35CamC, S-carboxamidomethyl-cysteine, mimicks histidine in volume, polarity and hydrogen bonding potential, but is unable to ionize. Unmodified H35C is defective in the final step of pore formation: the conversion of an inactive heptameric membrane-bound assembly intermediate to a structure containing open channels. It is this step in assembly that is ameliorated in H35CamC.

An intermediate in the assembly of a pore-forming protein trapped with a genetically-engineered switch

BACKGROUND

Studies of the mechanisms by which certain water-soluble proteins can assemble into lipid bilayers are relevant to several areas of biology, including the biosynthesis of membrane and secreted proteins, virus membrane fusion and the action of immune proteins such as complement and perforin. The alpha-hemolysin (alpha HL) protein, an exotoxin secreted by Staphylococcus aureus that forms heptameric pores in lipid bilayers, is a useful model for studying membrane protein assembly. In addition, modified alpha HL might be useful as a component of biosensors or in drug delivery. We have therefore used protein engineering to produce variants of alpha HL that contain molecular triggers and switches with which pore-forming activity can be modulated at will. Previously, we showed that the conductance of pores formed by the mutant hemolysin alpha HL-H5, which contains a Zn(II)-binding pentahistidine sequence, is blocked by Zn(II) from either side of the lipid bilayer, suggesting that residues from the pentahistidine sequence line the lumen of the transmembrane channel.

RESULTS

Here we show that Zn(II) can arrest the assembly of alpha HL-H5 before pore formation by preventing an impermeable oligomeric prepore from proceeding to the fully assembled state. The prepore is a heptamer. Limited proteolysis shows that, unlike the functional pore, the prepore contains sites near the amino terminus of the polypeptide chain that are exposed to the aqueous phase. Upon removal of the bound Zn(II) with EDTA, pore formation is completed and the sites near the amino terminus become occluded. Conversion of the prepore to the active pore is the rate-determining step in assembly and cannot be reversed by the subsequent addition of excess Zn(II).

CONCLUSIONS

The introduction of a simple Zn(II)-binding motif into a pore-forming protein has allowed the isolation of a defined intermediate in assembly. Genetically-engineered switches for trapping and releasing intermediates that are actuated by metal coordination or other chemistries might be generally useful for analyzing the assembly of membrane proteins and other supramolecular structures.

Environmental health and African Americans: challenges and opportunities

Demographic shifts and other social and economic forces as well as the increasing concerns about environmental determinants of disease and dysfunction have focused more attention on the disproportionate burden of environmental risk on blacks and other minorities. This article reviews these developments and identifies related challenges and opportunities confronting the medical community in the prevention of environmentally provoked disease among black Americans.

Carboxyfluorescein and biotin neuromedin C analogues: synthesis and applications

Two neuromedin C (NC) analogues were constructed by Fmoc synthesis and in situ coupling of 4(5)-carboxyfluorescein or biotin to the N-terminus. Both displayed full agonism in an amylase release assay and cross-reacted fully with a NC-specific antiserum. Biotin NC functioned in a streptavidin-capture ELISA. Carboxyfluorescein NC was used to probe receptor localization in rat stomach. Specific NC binding sites, which did not interact with substance P, angiotensin I, or neurokinin A, were labeled in the antrum. Identity of NC binding sites was confirmed by microautoradiography. The specifically labeled cells were all found in the lamina propria and at least some of cells were identified as eosinophils.

Surface labeling of key residues during assembly of the transmembrane pore formed by staphylococcal alpha-hemolysin

Structural changes in staphylococcal alpha-hemolysin (alpha HL) that occur during oligomerization and pore formation on membranes have been examined by using a simple gel-shift assay to determine the rate of modification of key single-cysteine mutants with the hydrophilic sulfhydryl reagent, 4-acetamido-4'-((iodoacetyl)amino)stilbene-2,2'-disulfonate (IASD). The central glycine-rich loop of alpha HL lines the lumen of the transmembrane channel. A residue in the loop remains accessible to IASD after assembly, in keeping with the ability of the pore to pass molecules of approximately 1000 Da. By contrast, residues near the N-terminus, which are critical for pore function, become deeply buried during oligomerization, while a residue at the extreme C-terminus increases in reactivity after assembly, consistent with a location in the part of the pore that projects from the surface of the lipid bilayer.

Psychosocial needs of family caregivers of terminally ill patients

The primary caregivers (mean age = 63 yr.) of 28 terminally ill veterans (mean age = 67 yr.) who were living at home were surveyed for their concrete and psychosocial needs. The caregivers also completed the Beck Depression Inventory, the Life Satisfaction Index, the Provision of Social Relations scale, and the Burden Inventory. The rank order of concrete and psychosocial needs is reported for these caregivers. Increased scores on depression were associated with decreased life satisfaction as was low social support. Not surprisingly, higher numbers of concrete and psychosocial needs were associated with increases in depression.

Diabetes update

This article is a brief overview of the incidence, classification, and diagnosis of diabetes mellitus. Current concepts of diabetes management, including nutrition, exercise, and medication, are introduced.