Conjecture versus empirical data: a response to concerns raised about the National Preventive Dentistry Demonstration Program.
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Child↗
Biomedical subjects
R M Bell
Publications and source records attributed to R M Bell.
I.v. and intraarterial hybrid digital subtraction angiography: clinical evaluation.
Temporal/energy (hybrid) subtraction is a technique for removing soft-tissue motion artifact from digital subtraction angiograms. The diagnostic utility of hybrid subtraction for i.v. and intraarterial angiography was assessed in the first 9 months of operation of a dedicated production system. In i.v. carotid arteriography (N = 127), hybrid subtraction (H) provided a double-profile projection of the carotid bifurcation in an additional 14% of studies, compared with temporal subtraction (T) alone (H79:T48, p less than 0.001). However, a change in estimated percent stenosis or additional diagnostic information occurred in only 2% of studies. In i.v. abdominal arteriography (N = 23), hybrid subtraction, compared with temporal subtraction, provided a diagnostic examination in an additional 14% of studies (H20:T17); however, this difference is not statistically significant. An additional three i.v. abdominal angiograms were nondiagnostic. In intraarterial abdominal (N = 98) and pelvic (N = 60) angiography, hybrid subtraction provided a diagnostic examination in an additional 5% of studies (abdomen H94:T90, pelvis H58:T56); this difference was not statistically significant. An additional 5% of all intraarterial abdominal and pelvic digital subtraction angiographic studies were considered nondiagnostic. Hybrid subtraction provides a double-profile view of the carotid bifurcation in a significant number of patients. However, apart from some potential for improved i.v. abdominal arteriography, hybrid subtraction does not result in significant improvement in comparison to conventional temporal-subtraction techniques.
Adolescent↗
Mechanism of regulation of protein kinase C by lipid second messengers.
Protein kinase C (PKC), a Ca2+-and phospholipid-dependent protein kinase, is now known to be regulated by sn-1,2-diacylglycerol (DAG) second messengers and is the intracellular phorbol ester receptor. Models of transmembrane signaling events that elicit DAG production include receptor-mediated G protein-dependent activation of phospholipase C. Several products of oncogenes resemble transmembrane signaling elements; critical second-messenger levels may, therefore, be altered by genetic defects in these elements. We found that normal rat kidney cells transformed with ras and sis contained elevated levels of DAG, and cells transformed with temperature-sensitive K-ras had elevated DAG levels at the permissive but not the restrictive temperature. To study the mechanism of PKC activation by phosphatidylserine (PS), DAG, and Ca2+, we used mixed micelles of Triton X-100, and analogous methods to examine PS dependence on [3H]phorbol-dibutyrate binding and activation. PKC activation occurs at physiological mole fractions of PS and DAG and does not require a bilayer. Activation by PS, which was cooperative, required four or more molecules. Activation by DAG was not cooperative and one molecule was sufficient. Monomeric PKC is the active species. Our activation model suggests that PKC binds to Ca2+ and four PS carboxyl groups to form a surface-bound, "primed" but inactive complex. DAG binds to the complex of the four PS carboxyl groups, the Ca2+, and the PKC through three bonds, two to ester carbonyls and one to the 3-hydroxyl moiety. Collectively, these may cause a conformational change and activate the enzyme.
Animals↗
Pharmacy initiatives to reduce clindamycin use.
The effectiveness of clinical pharmacists and attending physicians in altering the prescribing of metronidazole and clindamycin by resident physicians was evaluated, and the effect of these changes on antibiotic costs was determined. In July 1983, clinical pharmacists and attending physicians educated resident physicians about the efficacy and cost-effectiveness of substituting metronidazole for clindamycin in the treatment of intraabdominal and pelvic infections. A three-month educational program was implemented, which included distribution of a newsletter and involvement of clinical pharmacists in patient rounds. The use patterns of these drugs were then monitored for a 12-month period. A total of 425 treatment periods for 414 patients were reviewed, representing 91% of all therapy with metronidazole and clindamycin. Metronidazole use increased from 18.2% one month after implementation of the educational program to a plateau of 50% by November. Clindamycin expenditures decreased by more than 50% from the previous fiscal year, resulting in a savings of $33,469 to the pharmacy. The prescribing patterns of resident physicians were altered and cost savings were realized as a result of a comprehensive educational program that focused on substituting metronidazole for clindamycin. The program's success was enhanced because an equally efficacious agent was available and because of the participation of clinical pharmacists in patient rounds.
Anti-Bacterial Agents↗
Pulmonary microembolism in the canine model: report of a pilot study.
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Animals↗
Effects of affirmative action in medical schools. A study of the class of 1975.
In the early 1970s, affirmative-action programs were introduced to accomplish a number of social goals, including increasing the supply of minority physicians and improving the health care of the poor. To assess the success of such programs, we analyzed data on people who graduated from U.S. medical schools in 1975 to determine how specialty choice, practice locations, patient populations served, and board-certification rates differ between minority and nonminority graduates. A larger proportion of minority graduates (55 per cent vs. 41 per cent, P less than 0.001) chose the primary-care specialties of family practice, general internal medicine, general pediatrics, and obstetrics-gynecology. Significantly more minority physicians (12 per cent vs. 6 per cent, P less than 0.01) practiced in locations designated as health-manpower shortage areas by the federal government and had more Medicaid recipients in their patient populations (31 per cent for blacks, 24 per cent for Hispanics, 14 per cent for whites; P less than 0.001). Physicians from each racial or ethnic group served disproportionately more patients of their own racial or ethnic group (P less than 0.001), but minority physicians did not serve significantly more persons from other racial or ethnic minority groups than did nonminority physicians. Many minority physicians served patient populations much like those of their nonminority colleagues, which indicates that substantial integration of the medical marketplace has taken place. Significantly fewer minority graduates had become board-certified by 1984 (48 per cent vs. 80 per cent, P less than 0.001), and most of this disparity was associated with differences in premedical-school characteristics and in the patient populations they served. Our analysis shows that minority graduates of the medical school class of 1975 are fulfilling many of the objectives of affirmative-action programs.
Certification↗
Activation of protein kinase C by Triton X-100 mixed micelles containing diacylglycerol and phosphatidylserine.
A mixed micellar assay for protein kinase C was developed to investigate the specificity and stoichiometry of activation by phospholipids and diacylglycerols. Triton X-100 mixed micelles containing 8 mol % phosphatidylserine (PS) and 2.5 mol % sn-1,2-dioleoylglycerol (diC18:1) activated rat brain protein kinase C in the presence of Ca2+ to the same degree as sonicated PS/diC18:1 did in the standard assay. However, protein kinase C activity was more responsive to diC18:1 in the mixed micellar assay than the standard assay. At 8 mol % PS and 100 microM Ca2+, diC18:1 stimulated maximally at 1 mol %. At 2.5 mol % diC18:1 and 100 microM Ca2+, PS did not activate until 3 mol % and then did so cooperatively with maximal stimulation occurring at 6-8 mol %. Direct evidence for a Ca2+-, PS-, and diC18:1-dependent interaction of protein kinase C with mixed micelles was obtained by molecular sieve chromatography on Sephacryl S-200. These data permit inferences pertaining to the number of diC18:1 and PS molecules/micelle which are required for activation. For diC18:1, a single molecule may be sufficient but no more than 2 molecules are required. For PS, greater than 4 but less than 10 molecules are required. These data establish that a phospholipid bilayer is not required for protein kinase C activation and that activation of monomeric protein kinase C occurs.
Animals↗
Structural requirements for diacylglycerols to mimic tumor-promoting phobol diester action on the epidermal growth factor receptor.
The structural requirements for diacylglycerols to mimic the action of tumor-promoting phorbol diesters on the epidermal growth factor (EGF) receptor of A431 human epidermoid carcinoma cells were investigated. Five biological effects were considered: inhibition of high affinity 125I-EGF binding, change in the phosphorylation state of the EGF receptor, inhibition of the EGF-dependent tyrosine phosphorylation of the EGF receptor, inhibition of [3H]phorbol 12 beta, 13 alpha-dibutyrate binding, and stimulation of calcium- and phospholipid-dependent protein kinase (C-kinase) in vitro. A marked effect of the acyl chain length, 3-10 carbons, of symmetric sn-1,2-diacylglycerols was observed on their ability to mimic the effect of 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). sn-1,2-Dipropanoylglycerol did not mimic the effects of PMA, but sn-1,2-didecanoylglycerol potently mimicked PMA action. A correlation was found between the ability of these diacylglycerols to stimulate the activity of C-kinase in vitro and to mimic the effects of PMA on the EGF receptor in intact cells. Analogues of sn-1,2-dioctanoylglycerol in which the 3' hydroxyl group was substituted with hydrogen, thio or chloro moieties were inactive when assayed for their ability to stimulate C-kinase in vitro and mimic PMA action in intact cells. We conclude that the hydroxyl group of a diacylglycerol is vital for the interaction with the phorbol diester receptor. The stringent correlation between the potency of the 11 diacylglycerol analogues tested to modulate C-kinase in vitro and to mimic PMA action in vivo provides strong evidence for the hypothesis that C-kinase plays a central role in the regulation of A431 cell EGF receptors by tumor-promoting phorbol diesters.
Animals↗
sn-1,2-Diacylglycerol kinase of Escherichia coli. Purification, reconstitution, and partial amino- and carboxyl-terminal analysis.
The sn-1,2-diacylglycerol kinase structural gene from Escherichia coli was demonstrated to be the dgkA locus previously sequenced (Lightner, V. A., Bell, R. M., and Modrich, P. (1983) J. Biol. Chem. 258, 10856-10861). The dgkA gene product was shown by maxicell analysis to be an Mr = 14,000 membrane-bound protein. When dgkA was placed on a hybrid plasmid under control of the lambda pL promoter, a 100-fold overproduction of diacylglycerol kinase activity was obtained. Diacylglycerol kinase was solubilized from membranes with 2-propanol/heptane/trifluoroacetic acid and purified to near homogeneity by high performance liquid chromatography. Activity was reconstituted in a mixed micellar assay containing beta-octylglucoside, cardiolipin, and sn-1,2-dioleoylglycerol. Amino acid analysis, partial NH2-terminal analysis and COOH-terminal analysis permitted alignment of the polypeptide on the sequenced gene. The data establish that dgkA is the structural gene for the diacylglycerol kinase and establish the primary structure of the enzyme of 122 residues, 13,245 daltons. Secondary structure analysis predicted a protein conformation consisting of three transmembrane alpha-helical segments, an amphipathic helix, and an alpha-helix. Taken together, the predicted helical segments comprise more than 75% of the polypeptide.
Amino Acid Sequence↗
sn-1,2-Dioctanoylglycerol. A cell-permeable diacylglycerol that mimics phorbol diester action on the epidermal growth factor receptor and mitogenesis.
The cell-permeable diacylglycerol, sn-1,2-dioctanoylglycerol (DiC8), is shown to mimic the effect of tumor promoting phorbol diesters on epidermal growth factor (EGF) binding and action in intact cells. DiC8 inhibited the binding of [3H]phorbol dibutyrate to A431 cell monolayers indicating that the diacylglycerol interacts with the phorbol diester receptor. At 0.3 microM, DiC8 half-maximally inhibited the high affinity binding of 125I-EGF to A431 human epidermoid carcinoma cells. Scatchard analysis indicated that the inhibition of 125I-EGF binding was very similar to that observed in the presence of 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). DiC8 also mimicked the action of PMA to increase the phosphorylation state of the EGF receptor in 32P-labeled cells. Phosphoamino acid analysis demonstrated that DiC8 and PMA caused an increase in the level of EGF-receptor phosphoserine and phosphothreonine, whereas EGF caused an increase in the level of phosphoserine, phosphothreonine, and phosphotyrosine. Phosphopeptide mapping of the EGF receptor showed that DiC8 and PMA enhanced the phosphorylation of the same tryptic peptides. DiC8 inhibited the EGF-dependent tyrosine phosphorylation of the EGF receptor in A431 cells in a similar manner to that observed with PMA. In further experiments with quiescent Swiss 3T3 fibroblasts, DiC8 mimicked the ability of PMA to stimulate the incorporation of [methyl-3H]thymidine synergistically with low concentrations of EGF. This result indicates that DiC8 will mimic the long-term effects of PMA to regulate mitogenesis and raises the possibility that it may be active in two stage carcinogenesis. As both DiC8 and PMA stimulate the Ca2+- and phospholipid-dependent protein kinase (C-kinase) in vitro, the results support the hypothesis that the activation of C-kinase is a critical component of phorbol diester action on EGF receptor modulation and cell proliferation.
Animals↗
Exogenous sn-1,2-diacylglycerols containing saturated fatty acids function as bioregulators of protein kinase C in human platelets.
The ability of exogenous sn-1,2-diacylglycerols and analogs to function as bioregulators of protein kinase C in human platelets was investigated. The activation of protein kinase C in platelets is indicated by specific phosphorylation of a 40,000-dalton protein. Dihexanoylglycerol, dioctanoylglycerol (diC8), didecanoylglycerol, and sn-1-oleoyl-2-acetylglycerol were active in stimulating 40,000-dalton protein phosphorylation. Only a trace of phosphorylation was elicited by dibutyrylglycerol. Phosphorylation was not induced by analogs of diC8 in which an -H, -SH, or -Cl group replaced the free -OH, nor by monoacylglycerols or long chain diacylglycerols. Maximum phosphorylation was induced by dihexanoylglycerol, diC8, and didecanoylglycerol at concentrations from 5 to 20 microM and between 5 and 30 S after exposure of platelets to these diacylglycerols. Under conditions of maximal phosphorylation of the 40,000-dalton protein, these diacylglycerols did not induce phosphatidylinositol turnover, or platelet aggregation, or stimulate release of ATP or serotonin. A small degree of aggregation was evident with platelets isolated in the absence of prostacyclin, and release of serotonin was observed when 1 mM Ca2+ or submaximal concentrations of ionophore A23187 were included. These results are consistent with a model in which platelet activation requires the simultaneous formation of two intracellular signals, diacylglycerols and Ca2+. These diacylglycerols and diacylglycerol analogs provide useful tools to investigate the function of diacylglycerols as bioregulators in intact cells.
Blood Platelets↗
Diacylglycerols release LH: structure-activity relations reveal a role for protein kinase C.
A series of diacylglycerols were synthesized with varying lengths and substituents in order to establish the structure-activity relationship between each with activation of protein kinase C and stimulation of a biological response system (pituitary luteinizing hormone release). This approach enables distinction between actions mediated by direct activation of protein kinase C and those due to other, presumably nonspecific, actions. The ability of diacylglycerols to function as regulators of a biological response system (pituitary luteinizing hormone release) and of protein kinase C was investigated with a series of sn-1,2 diacylglycerols containing fatty acids 4-10 carbons in length and with analogs in which the 3' hydroxyl was replaced with a chloro, hydrogen, or sulfhydryl moiety. Several diacylglycerols stimulated LH release in a saturable, time and dose dependent manner that was independent of extra-cellular calcium. Dioctanoylglycerol (diC8) was the most effective of the diacylglycerols tested; 3' analogs lacking the hydroxyl were inactive. The diacylglycerols activated protein kinase C in vitro whereas the 3' analogs did not. These data implicate protein kinase C in the mechanism of LH release, demonstrate that unsaturated fatty acyl moieties within the diacylglycerol are not required for protein kinase C activation, and establish diacylglycerol-protein kinase C structure-function relationships that should prove useful for investigations in other systems.
Animals↗
Assembly of the endoplasmic reticulum phospholipid bilayer: the phosphatidylcholine transporter.
Phospholipids are synthesized and concomitantly inserted on the cytoplasmic surface of the endoplasmic reticulum. Assembly of the phospholipid bilayer requires translocation to the lumenal monolayer. The hypothesis that rat liver microsomes contain a protein transporter, or "flippase," for phosphatidylcholine was tested by measuring the transport of sn-1,2,-dibutyroylphosphatidylcholine (diC4PC). This homolog retains the polar head group, the portion of the phospholipid unable to undergo spontaneous transmembrane movement in vesicles, and its water solubility permits application of standard transport methods. DiC4PC entered the lumenal compartment of microsomal vesicles. Transport was saturable and was dependent on time, amount of microsomes, and an intact permeability barrier. DiC4PC transport was inhibited by structural analogs (but not by sn-2,3-diC4PC) and by treatment of microsomes with proteases, N-ethylmaleimide, and trinitrobenzenesulfonic acid. These data suggest that the transmicrosomal movement of diC4PC is protein mediated. DiC4PC was not transported across PC vesicles or red cell membranes, where PC translocation is slow.
Androgen-Binding Protein↗
Diacylglycerols mimic phorbol diester induction of leukemic cell differentiation.
Activation of cellular protein kinase C appears to be involved in the mechanism by which phorbol diesters induce differentiation of human myeloid leukemia cells (HL-60). Protein kinase C is thought to be physiologically activated by diacylglycerol derived from receptor-mediated phosphatidylinositol hydrolysis. sn-1,2-diacylglycerols with short saturated acyl side chains (C4-C10) were synthesized and found to be potent activators of protein kinase C partially purified from HL-60 cells. These diacylglycerols were also competitive inhibitors of [3H]phorbol dibutyrate binding to the soluble phorbol diester receptor. The most potent diacylglycerol, sn-1,2-dioctanoylglycerol, displaced greater than 90% of [3H]phorbol dibutyrate from the phorbol diester receptor of intact HL-60 cells. Because of probable cellular metabolism of sn-1,2-dioctanoylglycerol, hourly doses were required to maintain persistent occupancy of the phorbol diester binding site. Treatment of HL-60 cells with either phorbol 12-myristate 13-acetate or sn-1,2-dioctanoylglycerol produced identical phosphoprotein changes. Finally, sn-1,2-dioctanoylglycerol induced differentiation of the HL-60 cells into cells with morphologic characteristics of macrophages. Substitution of the hydroxyl group at position 3 with a hydrogen, chloro, or sulfhydryl moiety inactivated sn-1,2-dioctanoylglycerol. These data strengthen the hypothesis that protein kinase C activation plays a role in macrophage differentiation.
Caenorhabditis elegans Proteins↗
Role of protein kinase C in diacylglycerol-mediated induction of ornithine decarboxylase and reduction of epidermal growth factor binding.
Tumor-promoting phorbol esters induce ornithine decarboxylase (ODCase) activity and reduce epidermal growth factor (EGF) binding in rat tracheal epithelial 2C5 cells. Phorbol esters activate protein kinase C by interacting at the same site as sn-1,2-diacylglycerols, the presumed physiological regulators. The effects of added sn-1,2-diacylglycerols and those generated by phospholipase C treatment of 2C5 cells on ODCase induction and EGF binding were investigated to establish a role for protein kinase C in these cellular responses. Treatment of 2C5 cells with phospholipase C induced ODCase activity and reduced EGF binding, whereas phospholipases A2 and D were inactive. When sn-1,2-diacylglycerols containing fatty acids 3-10 carbons in length were added to 2C5 cells, those diacylglycerols containing fatty acids 5-10 carbons in length caused ODCase induction and reduction in EGF binding. sn-1,2-Dioctanoylglycerol was one of the most active compounds tested. It induced ODCase in a dose- (50-500 microM) and time-dependent manner. The reduction of binding of 125I-labeled EGF by sn-1,2-dioctanoylglycerol was also time and dose dependent and appeared to result from a change in EGF affinity and not the number of receptor sites. This series of sn-1,2-diacylglycerols showed similar structure-function relationships in their ability to induce ODCase activity, to decrease EGF binding, to stimulate protein kinase C, and to inhibit [3H]phorbol dibutyrate binding to the phorbol ester receptor. These data demonstrate biological activities for a number of diacylglycerols and indicate that protein kinase C activation is implicated in ODCase induction and decreased EGF binding.
Animals↗
The cost and effectiveness of school-based preventive dental care.
The National Preventive Dentistry Demonstration Program assessed the cost and effectiveness of various types and combinations of school-based preventive dental care procedures. The program involved 20,052 first, second, and fifth graders from five fluoridated and five nonfluoridated communities. These children were examined at baseline and assigned to one of six treatment regimens. Four years later, 9,566 members of this group were examined again. Analyses of their dental examination data showed that dental health lessons, brushing and flossing, fluoride tablets and mouthrinsing, and professionally applied topical fluorides were not effective in reducing a substantial amount of dental decay, even when all of these procedures were used together. Occlusal sealants prevented one to two carious surfaces in four years. Children who were especially susceptible to decay did not benefit appreciably more from any of the preventive measures than did children in general. Annual direct per capita costs were $23 for sealant or fluoride prophy/gel applications and $3.29 for fluoride mouthrinsing. Communal water fluoridation was reaffirmed as the most cost-effective means of reducing tooth decay in children.
Child↗
A summary of the results of the National Preventive Dentistry Demonstration Program.
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Adolescent↗
Recurrent appendiceal colic.
From 1962 through 1983, 1,869 appendectomies were performed at our institution. Careful review disclosed 11 patients (0.6 per cent) who had an appendectomy for recurrent pain in the right lower abdominal quadrant not associated with other classical symptoms of appendicitis. Seven patients had an urgent diagnostic barium enema during the course of the episode of pain for which they had an appendectomy and six of the seven were abnormal. All of the patients exhibited gross abnormality of the appendix, such as fecalith (four), torsion or kinking of the appendix (three), narrowed lumen (three) and purulent material in the lumen (one). However, three specimens were thought to be histologically normal. In a follow-up study of ten of 11 patients for two weeks to 20 years, there has been no recurrence of the abdominal pain in all but one patient.
Adolescent↗