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PubMed1977

Thermodynamics of binding to native alpha-chymotrypsin and to forms of alpha-chymotrypsin in which catalytically essential residues are modified; a study of "productive" and "nonproductive" associations.

The standard free energy (deltaG degrees), enthalpy (deltaH degrees), and entropy (deltaS degrees) of association for proflavin and D- and L-N-AcTrp have been obtained at pH 7.8 for native alpha-chymotrypsin (Cht) and for forms of Cht in which essential catalytic residues of the active site are modified. The modified Cht forms studied are dehydroalaninyl-195-alpha-Cht and N-methylhistidinyl-57-alpha-Cht. Associations to native Cht (pH 7.8) are characterized by negative deltaH degrees and deltaS degrees values (i.e., for L-AcTrp deltaH degrees = -9.1 kcal/mol and deltaS degrees = -21 eu at T = 25 degreesC). In contrast, we found associations to modified Chts to be characterized by an enthalpy near zero and a positive entropy of association, the values of the deltaH degrees and deltaS degrees for association to the modified Cht forms being similar to those expected for transfer of small aromatic molecules from water to a nonpolar solvent phase. Differences in deltaH degrees and deltaS degrees observed for binding of substrate analogues and inhibitors to modified and native Cht (pH 7.8) are approximately + 10 kcal/mol and +30 eu, respectively. Data from D. D. F. Shiao ((1970), Biochemistry 9, 1083) similarly show differences of comparable magnitude between binding of substrate analogues to active alpha-Cht (pH 7.8) and the His-57 protonated form of alpha-Cht (pH 5.6). The negative deltaH degrees and deltaS degrees values of associations for binding to active alpha-Cht indicate that a substrate-induced conformational change occurs on substrate association with the primary binding site (S1), which does not occur in Ser-195 and His-57 modified Cht. From these differences we infer a linkage between binding of substrate into S1 and the catalytic residues in the nucleophilic subsite (S1-S1'). Our data also show that associations of substrate analogues into potentially productive Michaelis complexes S1 cannot be easily differentiated from associations that are nonproductive (i.e., nonactivated) from their deltaG degrees obsd, but may be differentiated by their respective deltaH degrees obsd and deltaS degrees obsd for association. Accordingly, it is indicated that the probable substrate association-activation process, characterized thermodynamically in this work, occurs in the substrate binding step and leads to lowered free energies of activation in catalytic steps succeeding binding however, the process does not influence the observed strength of substrate binding.

Binding Sites↗
PubMed1977

Conformation of DNA modified with a dihydrodiol epoxide derivative of benzo[a]pyrene.

The conformation of calf thymus DNA modified by reaction with (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy7,8,9,10-tetrahydrobenzo[a]pyrene, which binds covalently mainly to the 2-amino group of guanosine residues, was studied. With samples in which 1.5 or 2.2% of the bases were modified, there was a slight decrease in Tm during heat denaturation and a slight increase in susceptibility to the single strand specific nuclease S1. In a DNA sample in which 4.5% of the bases were modified, there was an appreciable decrease in Tm and a marked increase in susceptibility to S1 nuclease. The kinetics of the reaction of the modified DNAs with formaldehyde provided evidence for locally destabilized regions ranging from 1 to 7 base plates, depending on the extent of modification. Alkaline and neutral sucrose gradient analyses revealed no evidence for strand breakage in the 1.5 and 2.2% modified samples, although single-strand breaks were found in the 4.5% modified samples. Taken together, these results suggest that DNA molecules containing a covalently bound benzo[a]pyrene derivative have an altered conformation characterized by small localized regions which are destabilized and easily denatured. The conformational changes associated with the covalent binding of the benzo[a]pyrene derivative to native DNA appear to be different from, and less marked, than those associated with the covalent binding of N-2-acetylaminofluorene to native DNA.

Animals↗
PubMed1997

Activation of regulated actin by SH1-modified myosin subfragment 1.

The reactive SH1 (Cys-707) group of the myosin subfragment 1 (S1) has been used frequently as an attachment site for fluorescent and spin probes in solution and muscle fiber experiments. In this study we examined (i) the motor function of SH1 spin-labeled heavy meromyosin (HMM) in the in vitro motility assays and (ii) the effect of SH1-modified S1 on the motility of regulated actin, i.e., actin complexed with tropomyosin and troponin. N-ethylmaleimide (NEM), N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)-iodacetamide (IASL), N-[[(iodoacetyl)amino]ethyl]1-sulfo-5-naphthylamine (IAEDANS), and iodoacetamide (IAA) were used to selectively modify the SH1 group on S1; the SH1 group on HMM was labeled with IASL. In the in vitro motility assays, 10-20% of unregulated actin filaments moved at a speed of approximately 1 microm/s over a surface coated with 90-95% modified IASL-HMM. Actin sliding was not observed with 95-98% modified IASL-HMM. The sliding of regulated actin over unmodified HMM was activated by the addition of S1 modified with any of the SH1 reagents to the in vitro motility assay solutions; both the speeds and the percentage of the moving filaments increased at pCa 5, 7, and 8. To shed light on the activation of regulated actin sliding by SH1-modifed S1, acto-S1 ATPase and the binding to actin were determined for IASL-S1. While the binding affinities to actin were similar for IASL-S1 and unmodified S1 in the presence and absence of ADP and ATP, the Km and Vmax values were approximately 10-fold lower for the modified protein. It is concluded that the activation of regulated actin by SH1-modifed S1 facilitates the interaction of unmodified HMM heads with actin and thus can increase the sliding speeds and the percentage of regulated actin filaments that move in the in vitro motility assays.

Actins↗
PubMed2001

Sorption of nonpolar aromatic contaminants by chlorosilane surface modified natural minerals.

The efficacy of the surface modification of natural diatomite and zeolite material by chlorosilanes is demonstrated. Chlorosilanes used were trimethylchlorosilane (TMSCI), tert-butyldimethylchlorosilane (TBDMSCI), dimethyloctadecylchlorosilane (DMODSCI), and diphenyldichlorosilane (DPDSCI) possessing different headgroups and chemical properties. Silanol groups of the diatomite and zeolite were modified by chemical reaction with the chlorosilanes resulting in a stable covalent attachment of the organosilanes to the mineral surface. The alteration of surface properties of the modified material was proved by measurements of water adsorption capacity, total organic carbon (TOC) content, and thermoanalytical data. The surface modified material showed great stability even when exposed to extremes in ionic strength, pH, and to pure organic solvents. Sorption of toluene, o-xylene, and naphthalene from water was greatly enhanced by the surface modification compared to the untreated materials which showed no measurable sorption of these compounds. The enhanced sorption was dependent on the organic carbon content as well as on chemical characteristics of the chlorosilanes used. Batch sorption experiments showed that the phenyl headgroups of DPDSCI have the best affinity for aromatic compounds. Removal from an aqueous solution of 10 mg/L of naphthalene, o-xylene, and toluene was 71%, 60%, and 30% for surface modified diatomite and 51%, 30%, and 16% for modified clinoptilolite, respectively. Sorption data were well described by the Freundlich isotherm equation, which indicated physical adsorption onto the lipophilic surface rather than partitioning into the surface organic phase. The chlorosilane modified materials have an apparent potential for application in environmental technologies such as permeable reactive barriers (PRB) or wastewater treatment.

Adsorption↗
PubMed1993

Uniformly modified 2'-deoxy-2'-fluoro phosphorothioate oligonucleotides as nuclease-resistant antisense compounds with high affinity and specificity for RNA targets.

"Uniformly" modified phosphodiester or phosphorothioate oligonucleotides incorporating 2'-deoxy-2'-fluoroadenosine, -guanosine, -uridine, and -cytidine, reported herein for the first time, when hybridized with RNA afforded consistent additive enhancement of duplex stability without compromising base-pair specificity. CD spectra of the 2'-deoxy-2'-fluoro-modified oligonucleotides hybridized with RNA indicated that the duplex adopts a fully A-form conformation. The 2'-deoxy-2'-fluoro-modified oligonucleotides in phosphodiester form were not resistant to nucleases; however, the modified phosphorothioate oligonucleotides were highly nuclease resistant and retained exceptional binding affinity to the RNA targets. The stabilizing effects of the 2'-deoxy-2'-fluoro modifications on RNA-DNA duplexes were shown to be superior to those of the 2'-O-methylribo substitutions. RNA hybrid duplexes with uniformly 2'-deoxy-2'-fluoro-modified oligonucleotides did not support HeLa RNase H activity; however, incorporation of the modifications into "chimeric" oligonucleotides has been shown to activate mammalian RNase H. "Uniformly" modified 2'-deoxy-2'-fluoro phosphorothioate oligonucleotides afforded antisense molecules with (1) high binding affinity and selectivity for the RNA target and (2) stability toward nucleases.

Base Sequence↗
PubMedDate not supplied

Synthesis, characterization, and solution properties of ras sequences modified by arylamine carcinogens at the first base of codon 61.

The complementary pentadecamers d(5'-TACTCTTCTTGACCT) (strand A) and d(5'-AGGTCAAGAAGAGTA) (strand B), which span a portion of the mouse c-Ha-ras protooncogene centered around codon 61, were synthesized by using standard beta-cyanoethyl phosphoramidite chemistry and characterized by sequence analysis. Strand A, containing a sole guanine at the position corresponding to the first base of codon 61, was modified with N-acetoxy-N-(trifluoroacetyl)-2-aminofluorene or its 4-aminobiphenyl analogue. In both cases only the corresponding N-(deoxyguanosin-8-yl)arylamine adduct was formed, as judged from HPLC and UV analyses conducted after enzymatic hydrolysis of the modified oligomers. Nonmodified and modified pentadecamers were annealed with strand B. Cooperative melting transitions were observed with all samples, thus indicating the formation of stable duplexes. Melting temperatures decreased in the order nonmodified duplex greater than 2-aminofluorene-modified duplex greater than 4-aminobiphenyl-modified duplex, which indicated destabilization of the helical structure upon incorporation of the adducts, with 4-aminobiphenyl having the greatest effect. Circular dichroism spectra of all duplexes were characteristic of an overall right-handed B-type conformation, with no major conformational differences being detected between the two arylamine-modified oligomers.

Aminobiphenyl Compounds↗
PubMedDate not supplied

Major and minor groove conformations of DNA trimers modified on guanine or adenine by 4-aminobiphenyl: adenine adducts favor the minor groove.

We have studied the conformational effects of 4-aminobiphenyl modification at C-8 of guanine or adenine on double-stranded DNA trimers. We used sequences with the modified purine at the central base pair and all 16 possible neighboring sequences at the outer pairs. Minimized potential energy calculations were carried out using the molecular mechanics program DUPLEX to survey the conformation space of these adducts, using a total of 1280 starting structures both in the modified guanine series and in the modified adenine series. Conformer families in which the bound 4-aminobiphenyl was located in the DNA major groove, and in the minor groove, were located for both adenine and guanine modification. In the modified guanine series, the major and minor groove families were roughly comparable in energy, and the sequence context determined which was more stable in a particular case. In the modified adenine series, however, the minor groove structure was more than 10 kcal/mol more stable than the major groove structure for all sequences. As a result, minor groove adducts provided most of the global minima in the adenine-modified series. This result may be relevant to a previous mutagenesis study [Lasko et al. (1988) J. Biol. Chem. 263, 15429-15435] in which the hot spot of most frequent occurrence was located at an adenine, in the sequence GAT.

Adenine↗
PubMed1999

Peroxide-modified titanium dioxide: a chemical analog of putative Martian soil oxidants.

Hydrogen peroxide chemisorbed on titanium dioxide (peroxide-modified titanium dioxide) is investigated as a chemical analog to the putative soil oxidants responsible for the chemical reactivity seen in the Viking biology experiments. When peroxide-modified titanium dioxide (anatase) was exposed to a solution similar to the Viking labeled release (LR) experiment organic medium, CO2 gas was released into the sample cell headspace. Storage of these samples at 10 degrees C for 48 hr prior to exposure to organics resulted in a positive response while storage for 7 days did not. In the Viking LR experiment, storage of the Martian surface samples for 2 sols (approximately 49 hr) resulted in a positive response while storage for 141 sols essentially eliminated the initial rapid release of CO2. Heating the peroxide-modified titanium dioxide to 50 degrees C prior to exposure to organics resulted in a negative response. This is similar to, but not identical to, the Viking samples where heating to approximately 46 degrees C diminished the response by 54-80% and heating to 51.5 apparently eliminated the response. When exposed to water vapor, the peroxide-modified titanium dioxide samples release O2 in a manner similar to the release seen in the Viking gas exchange experiment (GEx). Reactivity is retained upon heating at 50 degrees C for three hours, distinguishing this active agent from the one responsible for the release of CO2 from aqueous organics. The release of CO2 by the peroxide-modified titanium dioxide is attributed to the decomposition of organics by outer-sphere peroxide complexes associated with surface hydroxyl groups, while the release of O2 upon humidification is attributed to more stable inner-sphere peroxide complexes associated with Ti4+ cations. Heating the peroxide-modified titanium dioxide to 145 degrees C inhibited the release of O2, while in the Viking experiments heating to this temperature diminished but did not eliminated the response. Although the thermal stability of the titanium-peroxide complexes in this work is lower than the stability seen in the Viking experiments, it is expected that similar types of complexes will form in titanium containing minerals other than anatase and the stability of these complexes will vary with surface hydroxylation and mineralogy.

Carbon Dioxide↗
PubMed2002

A modified coumarinic acid-based cyclic prodrug of an opioid peptide: its enzymatic and chemical stability and cell permeation characteristics.

PURPOSE: To evaluate the chemical/enzymatic stability and the cell permeation characteristics of the modified coumarinic acid-based cyclic prodrug 2 of DADLE (H-Tyr-D-Ala-Gly-Phe-D-Leu-OH), which has an aldehyde equivalent (oxymethyl) inserted between the phenolic group of the promoiety and the carboxylic acid group of the peptide. METHODS: The rates of the chemical/enzymatic conversion of the oxymethyl-modified prodrug 2 to DADLE were measured by HPLC. The cellular permeation characteristics of DADLE and its oxymethyl-modified prodrug 2 were measured by HPLC using Caco-2 cells, wild type Madin-Darby Canine Kidney cells (MDCK-WT), MDCK cells transfected with human MDR1 gene (MDCK-MDR1), and MDCK cells transfected with human MRP2 gene (MDCK-MRP2) grown onto microporous membranes. RESULTS: The oxymethyl-modified coumarinic acid-based cyclic prodrug 2 degraded chemically to DADLE in a pH-dependent manner, i.e., rates of conversion increased with increasing pH. The prodrug 2 degraded rapidly in rat plasma (t1/2 = 39 min) and rat liver homogenate (t1/2 = 59.2 min), but much slower in Caco-2 cell homogenate (t1/2 = 678.7 min) and human plasma (t1/2 = 264.3 min). In all four cell lines used for transport studies, the flux rates of the oxymethyl prodrug 2 in the basolateral (BL)-to-apical (AP) direction (Papp BL-to-AP) were significantly greater than the flux rates in the AP-to-BL direction (Papp AP-to-BL). The Papp BB-to-AP/Papp AP-to-BL ratios were >116, 35.1, 21.2, and 12.6 in Caco-2, MDCK-MDR1, MDCK-MRP2, and MDCK-WT cells, respectively. The efflux of the modified prodrug could be inhibited by GF120918 (an inhibitor for P-gp) and cyclosporin A (an inhibitor for P-gp and MRP2). CONCLUSIONS: The oxymethyl-modified coumarinic acid-based cyclic prodrug 2 of DADLE could be converted to DADLE in both chemical and enzymatic media. However, the prodrug was a good substrate for both P-gp and MRP2 suggesting that its permeation across intestinal mucosa and blood-brain barrier would be significantly restricted.

Acids↗
PubMed2003

Antigen-specific targeting of CD8+ T cells with receptor-modified T lymphocytes.

Chimeric receptors that link ligand recognition domains, such as antibody Fv fragments, with TCR signaling domains can redirect T lymphocytes against MHC-unrestricted targets. Such receptor-modified T lymphocytes have shown promise in the treatment of infectious diseases and cancer. We hypothesized that receptor-modified T lymphocytes may also be designed to target antigen-specific T cells. We synthesized chimeric receptors consisting of the extracellular and transmembrane domains of the class I MHC H-2K(b) molecule linked to the signaling domains of either TCR-zeta, CD28 and zeta, or CD28, zeta, and lck. T lymphocytes modified to express these receptors and pulsed with antigenic peptide specifically killed precursor CTL. Cytolysis was efficient, even at effector:target ratios of less than one, and specific, selectively killing antigen-specific precursor CTL among a mixed population of T cells. Cytolysis required activation of the receptor-modified T cells, and did not occur with a signaling-deficient chimeric receptor. In contrast to precursor CTL, differentiated CTL proved resistant to lysis by the receptor-modified T cells. These data demonstrate the feasibility of redirecting T lymphocytes against antigen-specific T cells. Receptor-modified T cells expressing chimeric MHC receptors have potential application in autoimmune and alloimmune diseases.

Animals↗
PubMed1990

Comparative study of chemical modifiers for the determination of molybdenum in milk by electrothermal atomisation atomic absorption spectrometry.

A comparative study of various chemical modifiers for the determination of molybdenum in milk by electrothermal atomisation atomic absorption spectrometry was carried out. Methods with nitric acid or barium difluoride as the chemical modifier and in the absence of a chemical modifier were studied by introducing the milk samples directly into the graphite furnace with octyl alcohol. The graphite furnace programme, amount of modifier and the calibration and additions graphs were studied in all instances. The characteristic masses were 17.82, 18.64 and 12.08 pg of molybdenum in the absence of a chemical modifier and with nitric acid or barium difluoride as the chemical modifier, respectively. The precision, accuracy and interferences of the method were also investigated.

Animals↗
PubMed2002

Cultivation of Acetobacter xylinum for bacterial cellulose production in a modified airlift reactor.

Acetobacter xylinum for bacterial cellulose production was cultivated in a modified airlift reactor. Better results were obtained from the modified reactor than from a conventional bubble column. After 72 h of cultivation, the final concentration of bacterial cellulose was 7.72 g/l and the productivity was 0.107 g/l per h in the modified airlift reactor. The concentration of bacterial cellulose was about three times higher than that produced in the conventional bubble column. Moreover, the bacterial cellulose produced using the modified reactor formed a unique elliptical pellet (the average diameter was 10 mm), which is different from the fibrous form produced using the stirred-tank reactor. The modified airlift reactor with the suspended bacterial cellulose in pellet form had a higher volumetric oxygen-transfer coefficient and mixing capability than that with bacterial cellulose in fibrous form. The dissolved oxygen in the modified airlift reactor could be maintained above 35% throughout the cultivation.

Bioreactors↗
PubMed1984

The low-density-lipoprotein pathway of native and chemically modified low-density lipoproteins isolated from plasma incubated in vitro.

Normal fasting human plasma was incubated for 24 h at 37 degrees C in the presence or absence of lecithin:cholesterol acyltransferase (LCAT) inhibitors. The low-density lipoprotein (LDL) fractions of incubated plasma (control LDL and LCAT-modified LDL) were studied with respect to their chemical and functional properties. LCAT-modified LDL differed from control LDL by a decreased phospholipid and free-cholesterol content, but increased cholesteryl esters. Furthermore, an increase of the relative protein content in LDL by 16-20% was found. Apolipoproteins of LCAT-modified LDL exhibited a 10-fold increase of apo AI, a 4-5-fold increase of apo E, and a 2-fold increase of apo C. All these apolipoproteins resided together with apo B on the same particles. LCAT-modified LDL displayed a higher electrophoretic mobility, a higher hydrated density, a decreased flotation constant and a smaller diameter. Cultured human fibroblasts bound and internalized LCAT-modified LDL to a lower extent than control LDL. The degradation, however, was faster. Modified LDL suppressed 3-hydroxy-3-methylglutaryl-CoA reductase activity to a lower extent than did control LDL. Our results demonstrate that LCAT action, together with lipid transfer and exchange processes, markedly alters the chemical and physiochemical properties of LDL. This in turn significantly influences LDL catabolism in vitro.

Cells, Cultured↗
PubMed1987

Some electron-transfer reactions involving carbodi-imide-modified cytochrome c.

The reaction kinetics of native and carbodi-imide-modified tuna and horse heart cytochromes c with both a strong (dithionite) and a relatively weak (ascorbate) reducing agent were studied over a wide range of conditions. In their reactions with dithionite both the native and modified cytochromes exhibit single exponential time courses. The effects of dithionite concentration and ionic strength on the rate of the reduction are complex and can best be explained in terms of the model proposed by Lambeth & Palmer [(1973) J. Biol. Chem. 248, 6095-6103]. According to this model, at low ionic strength the native proteins are reduced almost exclusively by S2O4(2-) whereas the modified proteins showed reactivity towards both S2O4(2-) and SO2.-. These findings are interpreted in terms of the different charge characteristics of the carbodi-imide-modified proteins relative to the native proteins. The findings that the modified proteins react with ascorbate in a biphasic manner are explained as arising from ascorbate binding to a reducible form of the protein, before electron transfer, with an equilibrium between the ascorbate-reducible form of the protein and a non-reducible form. Estimates were obtained for both the ascorbate equilibrium binding constant and the rate constant for the internal electron transfer for both the native and modified horse and tuna proteins. The effect of pH on the reactions indicates that the active reductant in all cases is ascorbate2-. The studies of ascorbate reactivity yield important information concerning the proposed correlation between ascorbate reducibility and the presence of a 695 nm-absorption band, and the study of dithionite reactivity illustrates the effect of protein charge and solution ionic strength on the relative contributions made by the species SO2.- and S2O4(2-) to the reduction of ferricytochrome c.

Animals↗
PubMed1990

Kinetic analysis of regeneration by dilution of a covalently modified protein.

An analysis of regeneration by dilution of a covalently modified protein is presented. It is shown that, when protein regeneration is realized through the intermediacy of a protein-modifying agent adsorptive complex, the reaction is described by a summation of two exponential functions of reaction time plus a constant-term equation. The conditions whereby this equation reduces to a single-exponential equation are delineated. It is shown that, when protein regeneration is described by a single-exponential function of reaction time, the first-order protein-regeneration rate constant is a function of modifying-agent concentration and also of the microscopic reaction rate constants. Accordingly, the protein-modifying agent dissociation constant (Ki), as well as the protein-covalent-modification and -regeneration, rate constants (k+2 and K-2), may be determined by an analysis of dilution-induced protein-regeneration (or enzyme-reactivation) data obtained at different dilutions of the covalently modified protein-modifying agent preparation.

Adsorption↗
PubMed1990

Utilization of the free energy of the reversible binding of protein and modifying agent towards the rate-enhancement of protein covalent modification.

An analysis is presented of the catalytic factors responsible for the rate-enhancement that may be observed when a protein modification reaction is compared with a reaction of the same modifying agent with a model micromolecular compound exhibiting the same reactive group as the protein under study. It is seen that affinity-mediated rate-enhancement of protein modification is realized by the loss of activation entropy. On the assumption that attainment of maximal affinity-mediated rate-enhancement presents with an activation entropy of the protein modification reaction equal to zero, whereas the activation enthalpy of the reaction remains unchanged, it is shown that the value for maximal affinity-mediated rate-enhancement is equal to e-delta s++/R. Accordingly, protein modification reactions may be differentiated into (i) reactions the rate-enhancement of which (relative to the reaction of the same modifying agent with a model compound) is primarily entropy-controlled and (ii) reactions the rate-enhancement of which is primarily enthalpy-controlled. It is seen that modifying agents of low reactivity towards model compounds, but with a high, i.e. highly negative, activation entropy are better suited as prospective affinity-based protein-modifying agents, since the potential affinity-mediated rate-enhancement, and hence the selectivity, of these compounds is necessarily high. Kinetic and thermodynamic constants of the reaction of modifying agents with proteins, and with model compounds, and values of maximal affinity-mediated rate-enhancement, based on published data of the reaction of several modifying agents with model compounds, are presented and discussed.

Kinetics↗
PubMed1999

Monocyte proliferation induced by modified serum is associated with endogenous M-CSF production: evidence for involvement of a signalling pathway via scavenger receptors.

It was found that human serum stored for 2 months at 4 degrees C (modified serum) induced monocyte proliferation and simultaneous macrophage colony stimulating factor (M-CSF) production by these cells in vitro. Cell number, estimated by DNA content, doubled after 10 days in culture in the presence of modified serum, while it decreased in culture with freshly thawed control serum. As the addition of more than 2.5 ng/ml of recombinant M-CSF significantly supported monocyte survival/proliferation, cells were cultured for 10 days in medium supplemented with control serum, and endogenous M-CSF production was investigated by enzyme-linked immunosorbent assay. M-CSF concentration in the supernatants was 15-30 ng/ml after 10 day in culture with modified serum, a level that might be sufficient for monocyte proliferation. The modified serum induced M-CSF from freshly isolated monocytes, while M-CSF was hardly detected in cultures supplemented with control serum. Assay for peroxidized lipid and agarose gel electrophoresis demonstrated that the modified serum contained more oxidized low density lipoproteins (LDL) than the control serum. Ligands of scavenger receptors, which are receptors for oxidized LDL, such as dextran sulphate, polyinosinic acid, heparin and acetylated LDL also significantly induced M-CSF production from human monocytes, although this was at levels below 2 ng/ml. These results indicate that serum modified by oxidation stimulates monocytes to produce M-CSF resulting in their proliferation, and that signalling via scavenger receptors is one of the mechanisms responsible for this induction of M-CSF.

Acetylation↗
PubMed2002

Antibacterial and physical properties of resin modified glass-ionomers combined with chlorhexidine.

The purpose of this study was to determine the effect on mechanical properties and antimicrobial activity of the addition of chlorhexidine (CHX) to a resin modified glass-ionomer (Photac-fil, ESPE, Norristown, PA, USA). Chlorhexidine diacetate was combined with a resin modified glass-ionomer material at a concentration of 5%. The samples were tested for hardness, tensile strength and erosion at 24 h and 6-week intervals and for elution of CHX and antimicrobial activity weekly for 6 weeks. At 24 h there was no significant difference in hardness between the two groups, but at 6 weeks the resin modified glass-ionomer group was significantly harder than the CHX groups (P < 0.05). The diametral tensile strength test indicated no difference between the control and CHX groups at 24 h or at 6 weeks. The jet erosion test demonstrated significantly less erosion with the CHX group at 24 h but at 6 weeks the CHX group showed significantly more erosion than the control group. The chemical assay data demonstrated a peak elution of CHX at week 1 with residual amounts at weeks 2 and 3. The microbial data demonstrated that the CHX group had a significant reduction in Streptococcus mutans numbers for weeks 1-3, but after week 4 there was no difference between the glass-ionomer with and without CHX. The addition of CHX to resin modified glass-ionomer altered hardness and erosion of the resin-modified glass-ionomer, but because there are no material specifications, it is difficult to determine clinical implications. Chlorhexidine did significantly improve the antimicrobial effect of the glass-ionomer which was consistent with the chemical assay data. The results indicated that the addition of CHX to resin modified glass-ionomer material (Photac-fil) did not seriously degrade the physical properties during the time period tested and that the addition of CHX resulted in a greater reduction in S. mutans when compared with glass-ionomer alone.

Analysis of Variance↗