beta-Lactamase production in experimental endocarditis due to aminoglycoside-resistant Streptococcus faecalis

We used a beta-lactamase-producing (beta L+) strain of Streptococcus faecalis that also had high levels of resistance to all aminoglycosides to induce experimental endocarditis in rats. The rats were treated for five or 10 days with procaine penicillin, vancomycin, gentamicin, rifampin, or ciprofloxacin (alone or in various combinations), or with penicillin plus clavulanic acid. The levels of penicillin in serum and vegetations declined rapidly in the beta L+-infected rats treated with procaine penicillin alone, unlike the sustained levels of penicillin in either beta L- -infected rats treated with procaine penicillin or beta L+-infected rats treated with penicillin plus clavulanic acid. For the beta L+-infected rats, the enterococcal counts in vegetations were significantly reduced (greater than 3 log10 cfu/g) only by vancomycin and by penicillin plus clavulanic acid. The efficacy of the latter regimen probably resulted from the inhibition of penicillin inactivation by clavulanic acid in vegetations infected with the beta L+ strain. Our in vivo findings document the biologic significance of beta-lactamase production.

Metabolism of cholesterol and triacylglycerol in cultured chick neuronal cells, glial cells, and fibroblasts: accumulation of esterified cholesterol in serum-free culture

Metabolism of free and esterified cholesterol and triacylglycerol was compared in cultured neuronal cells, glial cells, and fibroblasts grown from chick embryos. Cellular contents of free and esterified cholesterol were comparable in these cells and triacylglycerol content in the neuronal cells was about 40% of that in the other cell types. Cholesterol synthesis from [3H]acetate was high in all these cells and was not affected by fetal calf serum in the culture medium. Monensin, which has been shown to influence cholesterol metabolism through the inhibition of low-density lipoprotein receptor recycling in human fibroblasts, did not induce profound effects on cholesterol metabolism in these cells. Higher incorporation of [3H] oleic acid into esterified cholesterol was observed in the glial cells and fibroblasts when fetal calf serum was removed from the culture medium. Cellular content of the esterified cholesterol also increased in the glial cells under a serum-free arrangement. 25-Hydroxycholesterol induced higher incorporation of both [3H]acetic acid and [3H]oleic acid into esterified cholesterol in all of these cells. The results indicate that the active metabolism of cholesterol found in cultured chick neural cells and fibroblasts may not be regulated by an LDL receptor-mediated system and some factors in fetal calf serum inhibit cellular accumulation of esterified cholesterol.

Clinically occult breast lesions: localization and significance

From early 1974 through September 1985, 927 needle-guided breast biopsies were performed for clinically occult breast lesions. Two hundred and seventy (29%) of these lesions were malignant. This frequency of malignancy was comparable to a 20% frequency in biopsy samples obtained because of clinical (palpable) findings. Of 142 patients with nonpalpable invasive lesions who underwent axillary dissection, 42 (30%) had histologically confirmed axillary metastases. Although these invasive lesions may be clinically occult, they are not inconsequential and demand appropriate treatment. For those patients in this series undergoing mastectomy, the frequency of multicentric cancer in the same breast was 39%. The past 10 years have witnessed a trend in surgical management away from the standard radical or modified radical mastectomy toward limited surgery and radiation therapy for so-called early breast cancer. When planning treatment for these occult lesions, one must consider their biological potential to metastasize as well as their propensity for multicentricity.

Glycolipid sialosyltransferase activity in synaptosomes exhibits a product specificity for (2-8)disialosyl lactosyl ceramide (ganglioside GD3)

Intact synaptosomes prepared from 28-day-old rat brains were incubated with CMP-N-acetyl-(14C) neuraminic acid in Krebs-Henseleit buffer in an atmosphere of 95% O2: 5% CO2, at 37 degrees C. The activity of CMP-NANA:ganglioside sialosyltransferase using endogenous acceptors was 0.84 pmoles NANA transferred/mg synaptosomal protein/hr. Analysis of the distribution of labeled sialic acid revealed that GD3 ganglioside (alpha 2----8 disialosyl, alpha 2----3 galactosyl, beta 1----4 glucosyl, beta 1----1-ceramide) was the major product in the membrane carrying 32% of the total lipid bound label. Treatment of the reaction products with Clostridium neuraminidase liberated labeled sialic acid from GD3 and yielded labeled GM3, then unlabeled lactosyl ceramide. Lac-cer and GM3 are present in small amounts in synaptosomes, and GD3 represents less than 2% of the total ganglioside. Our findings indicate that the sialosyltransferase activity of synaptosomes exhibits a preferential product specificity for the small pool of synaptosomal membrane GD3 ganglioside that may be formed in situ, via sialosylation of its precursor (GM3 or lactosyl ceramide) which pre-exists in the synaptosomal plasma membrane. The second major labeled product quantitatively was GD1a whose precursor substrate, GM1, is quite abundant in the membrane, so that the conversion rate of GM1 to GD1a was low in comparison with GD3 formation. Sialosylation of other synaptosomal membrane gangliosides was negligible.

Extent of axillary dissection preceding irradiation for carcinoma of the breast

"Limited" surgery and irradiation have become more popular therapeutic options for women with stage I and stage II breast cancer, and surgical attention to the axilla is part of this approach. To understand the limitations of whatever axillary procedure is recommended, we undertook a retrospective analysis of the records of 277 women who had undergone radical or modified radical mastectomy. Of this group, 127 had metastases to at least one axillary or interpectoral lymph node. Skip metastases occurred in 13% of women with positive nodes; two women (1.6%) had metastases only to level III nodes, and two women had metastases only to interpectoral nodes. The extremely uncommon occurrence of metastases to level III alone or to interpectoral nodes alone, but the greater likelihood of skip metastases to level II, argues for both level I and level II axillary dissection preceding irradiation for patients with invasive carcinomas of the breast.

The effect of tri-N-acetylglucosamine on hydrogen exchange in hen egg white lysozyme

Tritium-hydrogen isotope exchange techniques have been employed to study the effect of tri-N-acetylglucosamine binding on the conformational dynamics of hen egg white lysozyme. Numerical Laplace inversion of the data provides exchange rate probability density functions that reveal three overlapping peaks for both the free enzyme and (GlcNAc)3-enzyme complex. Binding of (GlcNAc)3 decreases the exchange rates of all protons to some extent with by far the largest effect being observed for the slow exchanging protons. These have been located, by comparison with neutron diffraction results (Mason, S. A., Bentley, G. A., and McIntyre, G. J. (1984) in Neutrons in Biology (Schoenborn, B. P., ed) pp. 323-334, Plenum Press, New York), within the beta-sheet structure and on helices (8-13), (28-34), and (89-97), that define the edges of the so-called "hydrophobic box" in lysozyme. The regions of the protein that are most affected by binding (GlcNAc)3, as revealed by hydrogen exchange, are found to be quite distinct from the regions observed to undergo conformational changes by x-ray diffraction. Most of these segments of the protein are located at some distance from the (GlcNAc)3-binding site itself. Two segments (the beta-sheet and helix (28-34)) are closely associated with the two active-site carboxylate groups. These results suggest that exchange-stable regions having strong, highly organized hydrogen bonding may have an important role in catalytic function and the differential propagation of conformational and dynamic perturbations caused by ligand binding at distant sites on the protein.

Phosphoribosylpyrophosphate synthetase superactivity. A study of five patients with catalytic defects in the enzyme

Superactive phosphoribosylpyrophosphate (PRPP) synthetases were characterized in fibroblasts and erythrocytes from 5 unrelated men with gout and/or hyperuricemia and uric acid overproduction. The kinetic basis of enzyme superactivity in all patients was increased maximal reaction velocity. Affinities of the enzymes for substrates and activators and responsiveness to inhibitors were normal, and levels of immunoreactive enzyme in patient and control fibroblast and erythrocyte extracts were comparable. Enzymes purified to homogeneity from 2 patients confirmed the presence of isolated catalytic defects. Altered physical properties of certain of the superactive enzymes suggested the presence of several distinctive structural defects among the aberrant forms. Fibroblasts from each affected patient showed increased PRPP concentration and generation, as well as accelerated rates of all PRPP-requiring purine nucleotide synthetic pathways. These findings support the concept that enzyme superactivity results in uric acid overproduction as a consequence of increased rates of PRPP and purine nucleotide synthesis. Cultured cells from female relatives of 2 patients showed evidence for the heterozygous carrier state, as measured both by enzyme activities and by rates of PRPP and purine synthesis. The clinical phenotype in 4 patients was limited to early adult-onset gout and its consequences, whereas the fifth patient expressed a familial constellation of hyperuricemia, sensorineural deafness, ataxia, and renal insufficiency. The severity of the derangements in PRPP synthetase and in PRPP and purine synthesis in cells from the 5 patients, however, was comparable. The neurologic accompaniments of enzyme superactivity found in 1 family described here, and in 2 others described previously, thus may not necessarily be consequences of primary defects in PRPP synthetase.

Gated quenching of intrinsic fluorescence and phosphorescence of globular proteins. An extended model

We present a theoretical model to account for the quenching data of macromolecular fluorescence and phosphorescence when the accessibility to the quencher is gated by a dynamic mechanism coupled to the fluctuation of the macromolecular matrix. We show that the model currently in use to interpret gated quenching processes gives only approximate results in both qualitative and quantitative terms, and it can be regarded as a specific case of the presented model. We show that the gating dynamics affect both the apparent accessibility (alpha obs) and Ksv values obtained by the modified Stern-Volmer plot. The effect of gating on alpha obs and Ksv depends upon the relative rate of gating compared to the excited state lifetime. The model allows us to predict the effect of viscosity on quenching if it takes place by a gated mechanism. The prediction can and is, in this case, compared to the existing data on glycerol effects on acrylamide quenching of the tryptophan fluorescence in RNAse T1. The result shows that a simple gated model is not compatible with the observed quenching behavior.

Ulnar nerve involvement in carpal tunnel syndrome

This is a retrospective study of the involvement of the ulnar nerve in patients with electrodiagnostic evidence of carpal tunnel syndrome as defined by median sensory nerve action potential (SNAP) greater than 3.6msec at the wrist and/or motor distal latency in excess of 4.3msec. The study included 248 patients, 63 (25%) with unilateral and 185 (75%) with bilateral carpal tunnel syndrome. The electrodiagnostic criteria for ulnar nerve involvement was a SNAP peak latency greater than 3.7msec and/or motor distal latency in excess of 4.2msec. One hundred fourteen patients (46%) had delayed ulnar SNAP peak at the wrist; of these, 100 cases had bilateral ulnar nerve involvement and 14 had unilateral abnormalities. Slowing of the motor nerve conduction velocity for the elbow-wrist segment was noted in 24% and 15% of the study group for the median and ulnar nerves, respectively. An incidental finding was the presence of "double crush syndrome" in 35 patients (14%). The results of this study suggest the frequent association of ulnar nerve involvement at the wrist for sensory fibers and carpal tunnel syndrome.

The effects of monensin on membrane lipids of cultured human skin fibroblasts

We have investigated the effects of monensin, a monovalent cationophore, on the metabolism of neutral lipids, fatty acids, ceramide and phospholipids in cultured human skin fibroblasts. Treatment with 1 microM monensin for 18 h reduced the cellular cholesterol ester content to less than one-third of untreated cells, and incorporation of [3H]acetate into cholesterol ester was also reduced, to less than one-fifth. Concomitantly, a greater conversion of [3H]acetate into free cholesterol occurred. There was a moderate increase in free fatty acids, but no change in triacylglycerol content, although the content of the latter appeared to increase in the presence of fetal calf serum in the culture medium. Phosphatidylcholine decreased in content and phosphatidylserine increased among the phosphatides, but ceramide remained unchanged after monensin treatment. These findings suggest that monensin influences the metabolic interrelationships of structural lipids in fibroblasts.

The effects of phorbol ester on anabolism of lipids of cultured human skin fibroblasts

We have investigated the independent effects of phorbol ester (phorbol 12-myristate 13-acetate) on anabolism of the major lipid components in cultured diploid human skin fibroblasts. When we incubated these cells with [3H]acetate in serum-free medium for 18 h in the presence of 16 nM phorbol ester, [3H]acetate incorporation and the cellular content of cholesterol ester increased, and free cholesterol decreased. Enhancement of [3H]acetate incorporation into cholesterol ester was also observed when the cells were incubated with phorbol ester for 5 h in medium containing lipoprotein-deficient serum. Incorporation of [3H]galactose into glycosphingolipids increased many fold upon exposure of the cells either to fetal calf serum or separately to phorbol ester. Therefore, phorbol ester independently affects cholesterol and glycosphingolipid metabolism in a way that may be similar to that reported for serum low-density lipoproteins and unknown other factors in fetal calf serum. We have observed these effects of phorbol ester in the intact living cell. These findings should provide useful means for the study of metabolism of the plasma membrane lipid components in fibroblasts.

Metabolism of choline in brain of the aged CBF-1 mouse

In order to quantify the changes that occur in the cholinergic central nervous system with aging, we have compared acetylcholine (Ach) formation in brain cortex slice preparations from 2-year-old aged CBF-1 mouse brains and compared the findings with those in 2-4-month-old young adult mouse brain slices. Incorporation of exogenous radioactively labelled choline (31 nM [3H] choline) into acetyl choline in incubated brain slices was linear with time for 90 min. Percentage of total choline label distributed into Ach remained constant from 5 min after starting the incubation to 90 min. In contrast, distribution of label into intracellular free choline (Ch) and phosphorylcholine (Pch) changed continuously over this period suggesting that the Ch pool for Ach synthesis in brain cortex is different from that for Pch synthesis. Incorporation of radioactivity into Ach was not influenced by administration of 10 microM eserine, showing that the increment of radioactivity in Ach reflects rate of Ach formation, independently from degradation by acetylcholine esterases. Under our experimental conditions, slices from cortices of aged 24-month-old mouse brain showed a significantly greater (27%) incorporation of radioactivity into intracellular Ach than those from young, 2-4-month-old, brain cortices. Inhibitors of Ach release, 1 mM ATP or GABA, had no effect. Since concentration of radioactive precursor in the incubation medium was very low (31 nM), the Ch pool for Ach synthesis in slices was labelled without measurably changing the size of the endogenous pool. These data suggest a compensatory acceleration of Ach synthesis or else a smaller precursor pool specific for Ach synthesis into which labelled Ch migrated in aged brain.(ABSTRACT TRUNCATED AT 250 WORDS)

A double-quenching method for studying protein dynamics: separation of the fluorescence quenching parameters characteristic of solvent-exposed and solvent-masked fluorophors

A novel experimental method, suitable for separate analysis of the quenching parameters characteristic of solvent-exposed and solvent-masked fluorophors of macromolecules, is described. The method is based on the modified Stern-Volmer analysis and requires simultaneous application of two kinds of quencher: one that can selectively quench the emission of exposed fluorophors (e.g., ionic quenchers) and another that is nonselective (e.g., oxygen or, in many cases, acrylamide), capable of quenching the fluorescence of both exposed and masked groups. In order to examine the accuracy of the model, a computer simulation was performed. The results showed that the errors are comparable to those arising from the conventional quenching experiments. The method is applicable to phosphorescence quenching as well and is extendable to time-resolved measurements (by replacing fluorescence intensities with lifetimes). The method was applied to resolve the quenching parameters of lysozyme fluorescence by the use of iodide as selective and acrylamide as nonselective quenchers. The determination of the acrylamide quenching constant associated with the internal fluorophor, Trp-108 (Kq = 3.5 M-1), permits specific studies on the dynamics of internal regions of the protein. The quenching constant determined for the more exposed residue Trp-62 (Kq = 1.6 M-1) provides local information about the surface independent of the electrostatic effects observed when an ionic quencher is used.

Influence of monovalent cation transport on anabolism of glycosphingolipids in cultured human fibroblasts

We have reported [Saito, M., Saito, M., & Rosenberg, A. (1984) Biochemistry 23, 1043-1046] that the monovalent cationic ionophore monensin reduced the incorporation of labeled galactose into oligosaccharidyl glycosphingolipids (globotriaosylceramide, globotetraosylceramide, and gangliosides) and induced a cellular accumulation of glucosyl- and lactosylceramide in cultured diploid human fibroblasts. We have undertaken further studies on the effects of monensin and made comparison with the effects of related monovalent cation transporters on plasma membrane glycosphingolipid anabolism in human fibroblasts. Our results demonstrate that ionic flux can markedly influence glycosphingolipid synthesis, and they indicate that, like glycoprotein, the sites of glycosylation of the initial, precursor glycosphingolipids are different from the sites of higher glycosylation. At a concentration of 10(-7) M, monensin induced the maximum inhibition of incorporation of labeled galactose into polyglycosyl sphingolipids: globotriaosylceramide, globotetraosylceramide, and gangliosides; increased incorporation of labeled galactose into glucosyl- and lactosylceramide was clearly evident, and their content rose measurably in the cell at concentrations of monensin as low as 10(-8) M. These effects of monensin were reversible. Incorporation of labeled galactose into higher glycosylated neutral glycosphingolipids and gangliosides slowly resumed, and the accumulated glycosylceramide diminished after removal of monensin from the culture medium. Ouabain (plasma membrane Na+,K+-ATPase inhibitor) and A23187 (Ca2+ ionophore) also caused a rapid increase in incorporation of labeled hexose into glucosylceramide and decreased its incorporation into higher neutral glycosphingolipids and into gangliosides.(ABSTRACT TRUNCATED AT 250 WORDS)

The elasticity of spectrin-actin gels at high protein concentration

Human erythrocyte spectrin of high purity was studied alone and mixed with rabbit skeletal actin by dynamic rheometry as a function of protein concentration at pH 7.4 and 24 degrees C. Pure spectrin had a very low storage modulus, G', increasing slightly with increase in protein concentration (approximately 3 dynes/cm at 25 mg/ml). In contrast, unpurified cytoskeletal extracts containing spectrin, actin, and band 4.1 showed a marked concentration dependence for G', increasing to 150 dynes/cm at 20 mg/ml. Mixtures of purified spectrin and skeletal actin at a weight ratio of 4:1 also showed G' markedly dependent on concentration (approximately 150-200 dynes/cm at 20 mg/ml). Maximum elasticity of spectrin-actin gels occurred at a molar ratio of actin monomers to spectrin tetramers of 14:1. We conclude that the reconstituted in vitro spectrin-actin network consists of actin fibers cross-linked by spectrin tetramers at regular intervals. The gel is rapidly reformed after mechanical disruption or thermal collapse, indicating that the polymer fibers are in equilibrium with the constituent monomers.

The fate of glucosylceramide (glucocerebroside) in genetically impaired (lysosomal beta-glucosidase deficient) Gaucher disease diploid human fibroblasts

Diploid human infant skin fibroblasts cultured from normal infants and Gaucher disease infants, with genetically defective lysosomal glucosylceramide:beta-glucohydrolase activity, had a full range of homologous glycosphingolipids from the simplest (glucosylceramide) to higher neutral derivatives (lactosyl-, trihexosyl- and tetrahexosylceramide) and anionic sialo derivatives (gangliosides) (sialosyllactosyl-, disialosyllactosyl-, sialosylgangliotriaosyl-, and mono- and disialosylgangliotetraosylceramide). Although excessive storage of glucosylceramide in histiocytes is pathognomonic for Gaucher disease, we found that Gaucher disease fibroblasts contained 1.23 +/- 0.08 nmol of glucosylceramide/mg cell protein; normal infant cells, 1.11 +/- 0.48. When we aged infantile Gaucher disease fibroblasts for 20 days beyond their confluency state, we found no increased accumulation of glucosylceramide, but a 1.5-2-fold increase in trihexosylceramide, sialosylgangliotetraosylceramide, and disialosyllactosylceramide. Gaucher disease fibroblasts took up and could not degrade but, instead, effectively converted pulse-chase 3-O-[3H]glucosylceramide supplied in the growth medium in liposomes into higher glycosphingolipids, especially the plasma membrane ganglioside, sialosyllactosylceramide. When grown with extracellular particulate [3H]glucosylceramide, infantile Gaucher fibroblasts localized it and higher labeled homologues in the plasma membrane; glucosylceramide did not accumulate in the lysosomes. These findings indicate that fibroblasts that are genetically deficient in lysosomal glucosylceramide:beta-glucosidase avoid pathological lysosomal accumulation by relegating undegradable glucosylceramide to an anabolic compartment where glucosylceramide is converted into more highly glycosylated glycosphingolipids.