Spontaneous oligomerization of a staphylococcal alpha-hemolysin conformationally constrained by removal of residues that form the transmembrane beta-barrel

Staphylococcal alpha-hemolysin is a water soluble, monomeric, bacterial exotoxin, which forms heptameric pores in membranes. The rate determining step in assembly is the conversion of a heptameric prepore to the fully assembled pore in which the central glycine-rich domain of each subunit inserts into the membrane to form a 14 strand beta barrel. Barrel formation is accompanied by a conformational change in which each N terminus latches onto an adjacent subunit. In the monomer in solution, the central domain is loosely organized and exposed to solvent. In this study, 25 amino acids of the central domain were removed and replaced with the sequence Asp-Gly, which favors the formation of a type I' beta-turn, to yield a mutant devoid of hemolytic activity. Within minutes after synthesis in the absence of membranes, the mutant polypeptide spontaneously assembled into heptamers, as demonstrated by atomic force microscopy. Limited proteolysis suggested that the N termini of the subunits in the heptamers were in the fully assembled pore conformation rather than the prepore conformation. Based on these findings, the deletion is proposed to constrain the central domain and thereby force the creation of a shortened beta barrel, which in turn induces the additional structural changes that normally accompany pore formation. The truncated pore might make a useful framework for the construction of designed membrane active macromolecules.      

The 1-hour advising session: helping students choose family practice

A case of chronic brucella endocarditis of a prosthetic valve is reported. The diagnosis of this infection was established by positive blood cultures and high brucella agglutination titre. The patient was successfully managed by combination of medical therapy (consisting of streptomycin, trimethoprim-sulphamethoxazole, rifampin and tetracycline) and surgery.     

Measuring the extent of abortion underreporting in the 1995 National Survey of Family Growth

CONTEXT: Induced abortions are often severely underreported in national surveys, hampering the estimation and analysis of unintended pregnancies. To improve the level of abortion reporting, the 1995 National Survey of Family Growth (NSFG) incorporated new interview and self-report procedures, as well as a monetary incentive to respondents. METHODS: The weighted numbers of abortions reported in the main interview of the 1995 NSFG (Cycle 5), in the self-report and in the two procedures combined are compared with abortion estimates from The Alan Guttmacher Institute. The Cycle 5 estimates are also compared with estimates from previous cycles of the NSFG. RESULTS: The self-report produces better reporting than the main interview, but combining data from the two procedures yields the highest count of abortions. For the period 1991-1994, the level of reporting is 45% in the main interview, 52% in the self-report and 59% when the two methods are combined. The level of abortion reporting in the combined data ranges from 40% for women with an income less than the federal poverty level to more than 75% among women who were older than 35, those who were married at the time of their abortion and those with an income above 200% of the poverty level. The completeness of abortion reporting in the main interview of Cycle 5, though indicating a remarkable improvement over reporting in Cycle 4, is comparable to the levels in Cycles 2 and 3. CONCLUSIONS: The usefulness of the NSFG remains extremely limited for analyses involving unintended pregnancy and abortion.     

Ischemic myelomalacia associated with fibrocartilaginous embolism in multiple finishing swine

Latin America generates a low proportion of the references quoted in Medline, the most popular health-related literature search database in the world. This paper explores references from and about Colombia in Medline during the period 1987-1996. Topics addressed, patterns of authorship and research locations are established. The number of Latin American journals indexed in Medline has been progressively reduced during this 10-year period, with Colombian journals completely excluded since 1991. During this 10-year period, the total output of Colombian research institutions in foreign journals consisted of 531 articles, 41% (219) of which come from the four leading universities. These figures are substantially lower than those from other countries of the region such as Venezuela or Chile. Despite some governmental efforts, Colombia continues to have a low scientific output and has yet to attract the interest of foreign researchers. Alternatives for development of Latin American research and publications are offered.     

Surgery of chest wall deformities

The effect of melatonin (MEL) on the nephropathy and the oxidative stress induced by a single and high dose of Adriamycin (AD) has been studied in Wistar male rats. MEL (50 microg/kg/day) was injected intraperitoneally 3 and 7 days, respectively, before and after AD injection (20 mg/kg i.p.). Trunk blood was drawn and triglycerides, total cholesterol, phospholipids, high-density lipoprotein cholesterol, urea, creatinine, total protein, lipoperoxides, and reduced glutathione (GSH) levels and catalase activity (CAT) were determined in serum. In kidney homogenates, lipoperoxides, GSH, and CAT were measured as well as total protein in urine. AD administration resulted in hyperlipidemia and high-grade proteinuria and a marked increase in serum lipoperoxides, urea, and creatinine. In the kidney, the increase in lipoperoxides was accompanied by a significant decrease of GSH and CAT. The efficiency of MEL was specially remarkable in restoring GSH, CAT, and proteinuria to the levels of controls. These results confirm the involvement of free radicals in the pathogenesis of nephrotoxicity induced by AD. Likewise, they show the high antioxidative power of MEL and its marked effect on the prevention and suppression of this nephropathy.     

Eprinomectin: a novel avermectin for control of lice in all classes of cattle

An early intensive anthracycline therapy can improve therapeutic outcome in adult acute lymphoblastic leukaemia (ALL) but is usually associated with marked myelosuppressive effects and significant morbidity by infections. To reduce this risk, we employed granulocyte colony-stimulating factor (G-CSF, filgrastim 5 microg/kg/d) as an adjunct to a myelotoxic, 14-day long induction regimen with idarubicin-vincristine-L-asparaginase-prednisone (IVAP). Owing to changes in study design, patients received 'late' (n = 28) or 'early' (n = 37) G-CSF from days 15 or 4 of IVAP, respectively, until resolution of severe neutropenia. Study endpoints included time to recovery from neutropenic nadir, duration of neutropenia <0.5 x 10(9)/l, incidence of infectious complications, assessment of variables affecting G-CSF response, clinical outcome and costs. Sixty-five consecutive cases were evaluable. Patients in early G-CSF group recovered significantly faster from the neutropenic nadir (p < 0.002), contracted less infectious complications (p = 0.007), and required less intravenous antibiotic (p = 0.008) and antifungal (p = 0.002) medications. Although these reductions did not compensate for the increased G-CSF treatment cost, the overall supportive care cost was not significantly increased by early G-CSF. Interestingly, T-ALL phenotype (p = 0.02) and higher neutrophil presentation count (p = 0.03) were associated with a shorter neutropenic course even with late G-CSF. Early G-CSF may be a valid approach to mitigate chemotherapy-induced neutropenia of IVAP and other similarly myelosuppressive adult ALL regimens.     

The cortical neuropeptide, cortistatin-14, impairs post-training memory processing

Cortistatin-14, a neuropeptide, is present primarily in the cortex and hippocampus. In the hippocampus, cortistatin-14 inhibits pyramidal cell firing and co-exists with GABA. To determine if cortistatin-14 would impair retention, saline or cortistatin-14 were injected intracerebroventricularly after footshock avoidance training in CD-1 mice. After 1 week, training was resumed to determine the effect of cortistatin-14 on retention. Cortistatin-14 was found to impair retention relative to the control group at doses of 0.5-5.0 micrograms.     

Immortalized cell lines from embryonic avian and murine otocysts: tools for molecular studies of the developing inner ear

Recently, our studies have focused on genes expressed at the earliest stages of inner ear development. Our aim is to identify and characterize genes that are involved in determining the axes of the semicircular canals, in otic crest delamination and in early innervation of the inner ear. Many elegant studies of auditory development have been done in animal models. However, the need for large amounts of well-characterized embryonic material for molecular studies makes the development of otocyst cell lines with different genetic repertoires attractive. We have therefore derived immortalized otocyst cells from two of the most widely used animal models of ear development: avians and mice. Avian cell isolates were produced from quail otocysts (embryonic stage 19) that were transformed with temperature-sensitive variants of the Rous sarcoma virus (RSV). Among the individual transformed cells are those that produce neuron-like derivatives in response to treatment with 10(-9) M retinoic acid. Mammalian cell isolates were derived from otocysts, of 9 day (post coitus) embryos of the H2kbtsA58 transgenic mouse (Immortomouse), which carries a temperature-sensitive variant of the Simian Virus 40 Tumor antigen. The vast majority of cells of the Immortomouse are capable of being immortalized at 33 degrees C, the permissive temperature for transgene expression, in the presence of gamma-interferon. Several putative clones et these cells differentiated into neuron-like cells after temperature shift and withdrawal of gamma-interferon; another isolate of cells assumed a neuron-like morphology on exposure to brain-derived neurotrophic factor even at the permissive temperature. We describe also a cell isolate that expresses the Pax-2 protein product and two putative cell lines that express the protein product of the chicken equivalent of the Drosophila segmentation gene engrailed. These genes and their protein products are expressed in specific subpopulation of otocyst cells at early stages. Both mouse and quail immortalized cell lines will be used to study inner ear development at the molecular level.     

Reference ranges for serum prostate-specific antigen in black and white men without cancer

OBJECTIVES: To determine the age- and race-specific prostate-specific antigen (PSA) distributions in healthy men in central South Carolina and to compare these to data from other studies. METHODS: Two thousand ninety-two black men aged 40 to 69 years and white men aged 50 to 69 years from the general population in 11 counties of central South Carolina participated in a prostate cancer educational program. Seventy-two percent of the participants were black-about double the proportion in the general population-and 63% of the men (1319 of 2092) subsequently obtained a PSA determination from their own physician. The distribution of serum PSA was compared with distributions from the Olmsted County study and from the Walter Reed Army Medical Center/Center for Prostate Disease Research study. RESULTS: Older men without cancer had higher PSA levels. Regression analyses yielded an associated increase of about 3.3% per year. Reference ranges for normal PSA in men without cancer (based on their sample 95th percentiles) were zero to 1.9, 3.8, and 5.7 ng/mL in black men aged 40 to 49, 50 to 59, and 60 to 69 years, and zero to 2.7 and 4.9 mg/mL in white men aged 50 to 59 and 60 to 69 years, respectively. CONCLUSIONS: Reference ranges for normal serum PSA levels should take into account the population from which they are derived and to which they will be applied. Reference ranges that are useful in the general population can differ from those that are appropriate in a hospital setting. For the general population in central South Carolina, reference ranges for serum PSA levels are lower than previously published reference ranges, particularly among black men.