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Biomedical subjects

M Bronfman

Publications and source records attributed to M Bronfman.

At least 19 recordsLinked to original sources
PubMed2003

Activation of Wnt signaling rescues neurodegeneration and behavioral impairments induced by beta-amyloid fibrils.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, which is probably caused by the cytotoxic effect of the amyloid beta-peptide (Abeta). We report here molecular changes induced by Abeta, both in neuronal cells in culture and in rats injected in the dorsal hippocampus with preformed Abeta fibrils, as an in vivo model of the disease. Results indicate that in both systems, Abeta neurotoxicity resulted in the destabilization of endogenous levels of beta-catenin, a key transducer of the Wnt signaling pathway. Lithium chloride, which mimics Wnt signaling by inhibiting glycogen synthase kinase-3beta promoted the survival of post-mitotic neurons against Abeta neurotoxicity and recovered cytosolic beta-catenin to control levels. Moreover, the neurotoxic effect of Abeta fibrils was also modulated with protein kinase C agonists/inhibitors and reversed with conditioned medium containing the Wnt-3a ligand. We also examined the spatial memory performance of rats injected with preformed Abeta fibrils in the Morris water maze paradigm, and found that chronic lithium treatment protected neurodegeneration by rescuing beta-catenin levels and improved the deficit in spatial learning induced by Abeta. Our results are consistent with the idea that Abeta-dependent neurotoxicity induces a loss of function of Wnt signaling components and indicate that lithium or compounds that mimic this signaling cascade may be putative candidates for therapeutic intervention in Alzheimer's patients.

Alzheimer Disease↗
PubMed1999

High-affinity binding of fatty acyl-CoAs and peroxisome proliferator-CoA esters to glutathione S-transferases effect on enzymatic activity.

Acyl-CoAs are present at high concentrations within the cell, yet are strongly buffered by specific binding proteins in order to maintain a low intracellular unbound acyl-CoA concentration, compatible with their metabolic role, their importance in cell signaling, and as protection from their detergent properties. This intracellular regulation may be disrupted by nonmetabolizables acyl-CoA esters of xenobiotics, such as peroxisome proliferators, which are formed at relatively high concentration within the liver cell. The low molecular mass acyl-CoA binding protein (ACBP) and fatty acyl-CoA binding protein (FABP) have been proposed as the buffering system for fatty acyl-CoAs. Whether these proteins also bind xenobiotic-CoA is not known. Here we have identified new liver cytosolic fatty acyl-CoA and xenobiotic-CoA binding sites as glutathione S-transferase (GST), using fluorescent polarization and a acyl-etheno-CoA derivative of the peroxisome proliferator nafenopin as ligand. Rat liver GST and human liver recombinant GSTA1-1, GSTP1-1 and GSTM1-1 were used. Only class alpha rat liver GST and human GSTA1-1 bind xenobiotic-CoAs and fatty acyl-CoAs, with Kd values ranging from 200 nM to 5 microM. One mol of acyl-CoA is bound per mol of dimeric enzyme, and no metabolization or hydrolysis was observed. Binding results in strong inhibition of rat liver GST and human recombinant GSTA1-1 (IC50 at the nanomolar level for palmitoyl-CoA) but not GSTP1-1 and GSTM1-1. Acyl-CoAs do not interact with the GSTA1-1 substrate binding site, but probably with a different domain. Results suggest that under increased acyl-CoA concentration, as occurs after exposure to peroxisome proliferators, acyl-CoA binding to the abundant class alpha GSTs may result in strong inhibition of xenobiotic detoxification. Analysis of the binding properties of GSTs and other acyl-CoA binding proteins suggest that under increased acyl-CoA concentration GSTs would be responsible for xenobiotic-CoA binding whereas ACBP would preferentially bind fatty acyl-CoAs.

Acyl Coenzyme A↗
PubMed1999

Anti-proliferative effect of two novel palmitoyl-carnitine analogs, selective inhibitors of protein kinase C conventional isoenzymes.

Previous studies have shown that palmitoyl-carnitine is an anti-proliferative agent and a protein kinase C inhibitor. Two new palmitoyl-carnitine analogs were synthesized by replacing the ester bond with a metabolically more stable ether bond. An LD50 value in the nM range was found in anti-proliferative assays using HL-60 cells and was dependent on the alkyl-chain length. The inhibitory action of these water-soluble compounds on protein kinase C in vitro was greatly increased with respect to palmitoyl-carnitine and was dependent on the length of the alkyl chain. Its effect was mediated by an increase in the enzyme's requirement for phosphatidylserine. Inhibition of the in situ phosphorylation of a physiological platelet protein kinase C substrate and of phorbol ester-induced differentiation of HL-60 cells was also observed. Finally, to test for isoenzyme selectivity, several human recombinant protein kinase C isoforms were used. Only the Ca2+-dependent classic protein kinase Cs (alpha, betaIota, betaIotaIota and gamma) were inhibited by these compounds, yet the activities of casein kinase I, Ca2+/calmodulin-dependent kinase and cAMP-dependent protein kinase were unaffected. Thus, these novel inhibitors appear to be both protein kinase C and isozyme selective. They may be useful in assessing the individual roles of protein kinase C isoforms in cell proliferation and tumor development and may be rational candidates for anti-neoplasic drug design.

Animals↗
PubMed1999

How do researchers influence decision-makers? Case studies of Mexican policies.

Though the problems translating or applying research in policy-making are legion, solutions are rare. As developing countries increase their capacities to develop effective local solutions to their health problems, they confront the research/policy dilemma. Yet few descriptive studies of research-policy links can be found from developing countries, and the relevance of European and North American models and data is questionable. We report the results of a descriptive study from Mexico of the relationship between health research and policy in four vertical programmes (AIDS, cholera, family planning, immunization). We interviewed 67 researchers and policy-makers from different institutions and levels of responsibility. We analyzed interviewee responses looking for factors that promoted or impeded exchanges between researchers and policy-makers. These were, in turn, divided into emphases on content, actors, process, and context. Many of the promoting factors resembled findings from studies in industrialized countries. Some important differences across the four programmes, which also distinguish them from industrialized country programmes, included extent of reliance on formal communication channels, role of the mass media in building social consensus or creating discord, levels of social consensus, role of foreign donors, and extent of support for biomedical versus social research. We recommend various ways to increase the impact of research on health policy-making in Mexico. Some of the largest challenges include the fact that researchers are but one of many interest groups, and research but one input among many equally legitimate elements to be considered by policy-makers. Another important challenge in Mexico is the relatively small role played by the public in policy-making. Further democratic changes in Mexico may be the most important incentive to increase the use of research in policy-making.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Isolation of intact organelles by differential centrifugation of digitonin-treated hepatocytes using a table Eppendorf centrifuge.

A quick subcellular fractionation procedure using differential centrifugation, which is applicable to isolated and cultured cells, is presented. This technique was developed for studying the subcellular localization of phosphorylated proteins in isolated liver cells after various stimuli, but is also applicable to many other situations. The main difference with the usual techniques is that by including digitonin in the homogenization buffer, the procedure is greatly shortened. Furthermore, because the soluble fraction is separated from the particulate fraction very early in the fractionation procedure, subcellular organelles are not exposed to phosphatases and other soluble enzymes such as esterases and proteases during the fractionation. The entire procedure is carried out in an Eppendorf centrifuge, which allows isolation of the cytosolic fraction in less than 1 min, a washed nuclear fraction in about 4 min, a mitochondrial fraction in less than 10 min, and a washed light mitochondrial L fraction in about 40 min. Judging by the behavior of marker enzymes and the morphology of the fractions, the method is highly comparable to classical procedures.

Animals↗
PubMed1998

Enhanced differentiation of HL-60 leukemia cells to macrophages induced by ciprofibrate.

Ciprofibrate, an hypolipidaemic peroxisome proliferator, induced differentiation of HL-60 cells. The effect was greatly potentiated by phorbol 12-myristate 13-acetate at a concentration where neither phorbol ester nor ciprofibrate alone had any effect on these cells. As occurs for HL-60 cell differentiation induced by high phorbol ester concentration, the ciprofibrate-induced phorbol ester-dependent differentiation of HL-60 cells proceeded through the monocytic/macrophage pathway and induced the phosphorylation of proteins with similar molecular weights suggesting that increased protein kinase C activity may be involved in the effect. The peroxisome proliferator-activated receptor (PPARalpha) transcription factor is expressed in HL-60 cells, but no changes were observed in its expression upon HL-60 cell differentiation.

CD11 Antigens↗
PubMed1997

Overexpression of mdr2 gene by peroxisome proliferators in the mouse liver.

BACKGROUND: In mice, fibrates induce mdr2 gene expression, and its encoded P-glycoprotein in the canalicular domain of hepatocytes, as well as increasing biliary phospholipid output. It is not known whether this effect is restricted to fibrates or is a common property of peroxisome proliferators. AIMS: To test the effect of structurally unrelated peroxisome proliferators on mdr2 gene expression and biliary phospholipid output, and to explore the molecular mechanism(s) of mdr2 gene induction. METHODS: Male CFI mice were fed on a diet supplemented with several peroxisome proliferators: phenoxyacetic acid herbicides, plasticizers, acetylsalicylic acid and partially hydrogenated fish oil. RESULTS: Increased levels of mdr2 mRNAs, assessed by Northern blot analysis, were observed in the liver of mice treated with phenoxyacetic acid herbicides: 2,4,5-trichlorophenoxyacetic acid 570+/-133%, 2,4-dichlorophenoxyacetic acid 233+/-54% (p<0.005); plasticizers: di-(2-ethylhexyl)phthalate 282+/-78%, di-(isoheptyl)phthalate 163+/-40%, phthalic acid dinonyl ester 225+/-48% (p<0.01); and partially hydrogenated fish oil 372+/-138% (p<0.005). P-glycoprotein traffic ATPase content increased in the canalicular domain of hepatocyte of mice treated with the herbicide 2,4,5-trichlorophenoxyacetic acid and with partially hydrogenated fish oil (108% and 87%, respectively, p<0.05) as well as biliary phospholipid output (106% and 74%, respectively, p<0.05). In 2,4,5-trichlorophenoxyacetic acid-fed mice we found five-fold increase on mdr2 transcription rate, assessed by nuclear run-off assay. CONCLUSIONS: Peroxisome proliferators induce mdr2 gene, its encoded P-gp in the canalicular domain of hepatocytes and increase biliary phospholipid output. The modulation of mdr2 gene might be part of the pleiotrophic response of peroxisome proliferation in mice liver and seems to be regulated mainly at a transcriptional level.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1997

Development and evaluation of a health education intervention against Taenia solium in a rural community in Mexico.

A comprehensive study was undertaken in a rural community in the state of Morelos, Mexico to evaluate health education as an intervention measure against Taenia solium. An educational program was developed to promote recognition and knowledge of the transmission of the parasite and to improve hygienic behavior and sanitary conditions that foster transmission. The effects of educational intervention were evaluated by measuring changes in knowledge and practices and prevalence of human taeniasis and swine cysticercosis before and after the campaign. The health education strategy was implemented with the active participation of the population based on the information obtained from a sociologic study. A questionnaire was designed and used before, immediately after the intervention, and six months later. Statistically significant improvements occurred in knowledge of the parasite, its life cycle, and how it is acquired by humans; however, changes in behavior related to transmission were less dramatic and persistent. The prevalences of cysticercosis in pigs at the start of the education intervention were 2.6% and 5.2% by lingual examination and antibody detection (immunoblot assay), respectively, and approximately one year after the intervention they were 0% and 1.2% (P < 0.05). These changes were accompanied by significant reductions in the reported access of pigs to sources of infection and freedom to roam. We conclude that health education, developed along with community involvement, reduced opportunities for transmission of T. solium in the human-pig cycle.

Animals↗
PubMed1996

Species differences in the intracellular distribution of ciprofibroyl-CoA hydrolase. Implications for peroxisome proliferation.

Peroxisomal proliferators (HPP), such as ciprofibrate and clofibric acid, are species-specific drugs. Since HPP-coenzyme A derivatives might be involved in their action, we studied the subcellular distribution of liver ciprofibroyl-CoA hydrolase in rat and in two HPP-unresponsive species, humans and guinea pig. Total activity was similar in the three species and was not induced by clofibric acid treatment. In guinea pig, as in humans, the enzyme is localized in the mitochondrial and soluble fractions and no changes are observed after drug treatment. In the rat, the enzyme has a microsomal localization, but upon clofibric acid treatment it changes to a mitochondrial and soluble distribution, as in unresponsive species. These results raise the possibility that drug-induced hydrolases in rats might be normally expressed in humans and guinea pigs.

Animals↗
PubMed1996

Microbial removal of chlorinated phenols during aerobic treatment of effluents from radiata pine kraft pulps bleached with chlorine-based chemicals, with or without hemicellulases.

The removal of chlorophenolic compounds from kraft mill effluents bleached with chlorine (cBKME) or chlorine plus hemicellulases (bBKME) was studied in reactors of aerobic treatment lagoons. In these laboratory models, a stable microbial population removed biochemical oxygen demand at similar rates of the mill lagoon. Complete removal of nine chlorophenols and chloroguaiacols during microbial treatment of these effluents was detected by gas chromatography. Abiotic removal was only observed with 2,4-dichlorophenol and 2,4,5-trichlorophenol. There were no significant differences in degradative ability between microorganisms acclimated to grow in reactors fed with cBKME or bBKME. The latter had a lower content of adsorbable organic halogen and chlorophenols than cBKME. Microorganisms acclimated to cBKME or bBKME were only able to grow on phenol or guaiacol as sole carbon source. However, these microorganisms removed (0.1-0.5 mM) 4-chlorophenol, 2,4-dichlorophenol and 2,4-dichlorophenoxyacetate with BKME as primary carbon source. Under these conditions, 2,4,6- and 2,4,5-trichlorophenol, 4,5-dichloroguaiacol, 4,5,6-trichloroguaiacol and tetrachloroguaiacol were not removed. These results suggest that the microbial removal of bleaching chlorophenols and chloroguaiacols during aerobic treatment, probably takes place only because of their very low concentration (1-200 ppb) in BKME.

Bacteria, Aerobic↗
PubMed1995

Saturable binding sites for the coenzyme A ester of nafenopin, a peroxisome proliferator, in rat liver cytosol.

1. At least three different molecular weight binding sites exist in rat liver cytosol for nafenopin-CoA, the coenzyme A ester and metabolic product of the carcinogenic peroxisome proliferator nafenopin. No binding sites for the free drug were observed. 2. Polypeptides of 35-40 kDa molecular weight range where no acyl-CoA binding proteins have been previously described bind the highest proportion of nafenopin-CoA (60-70%). Binding is displaceable by the CoA esters of other peroxisome proliferators (ciprofibrate and tibric acid) and also by oleoyl-CoA but by palmitoyl-CoA. Direct binding studies show that 35-40-kDa polypeptides bind oleoyl-CoA but not oleic or palmitic acid, or palmitoyl-CoA. 3. Polypeptides of 10-14 and 65-70 kDa also bind nafenopin-CoA. However, in contrast with 35-40-kDa polypeptides they also bind oleic and palmitic acid as well as their correspondent acyl-CoA thioesters.

Acetyl Coenzyme A↗
PubMed1994

Changing physician prescribing patterns: evaluation of an educational strategy for acute diarrhea in Mexico City.

This paper presents the results of an intervention strategy designed to decrease drug prescription and increase the use of oral rehydration therapy (ORT) in the treatment of acute diarrhea aimed at family medicine practitioners in two primary health care units of the Mexican Social Security Institute. The intervention consisted of six successive stages: 1) Baseline study of prescribing practices by all 69 physicians in both clinics; 2) Training workshop attended by 36 physicians, including a critical analysis of relevant up-to-date literature, review of results of stage I, discussion of a previously designed treatment algorithm for acute diarrhea, and modification of it according to participant's experience; 3) Post-workshop evaluation; 4) Establishment of a peer review committee to discuss the treatment behavior of participating physicians; 5) Mid-term evaluation for 2 months after the committee stopped functioning; 6) Long-term evaluation at 6, 12 and 18 months, of 20 physicians who received the complete intervention (study group) and 20 physicians who received none (control group). The treatment behaviors of the study and control groups were similar on baseline, but differed significantly (P < 0.01) in the post-workshop evaluation. The study group showed a reduction in the use of antibiotics (from 78.8% to 39.3%) and restrictive diets (47.3% to 12.4%), and increased the use of ORT (31.4% to 58.4%) for children younger than 5 years old with acute diarrhea. In the mid-term evaluation, the use of antibiotics by the study group decreased to 27.6%, prescription of restrictive diets decreased to 6.4%, and use of ORT increased to 73.8% (P < 0.01, in all cases). In the long-term evaluation, persistent positive prescribing behavior was still present in the study group, with a significant difference (P < 0.05) compared to the control group, where no modification was found in the prescribing behavior throughout the study. The average proportion of cases treated according to the algorithm by the study group increased in 29.2% (31.3 to 60.5%) after the workshop, and 45.2% (31.3 to 76.5%) after peer review committee. This behavior was maintained during 18 months after the intervention (74%). The control group showed no significant modification in the average proportion of cases treated according to the algorithm during the study (2 years 7 months). The active participation of physicians in the workshop and in the peer review committee was identified as the key to the short and long-term success of the educational strategy.

Acute Disease↗
PubMed1993

Ciprofibrate, a carcinogenic peroxisome proliferator, increases the phosphorylation of epidermal-growth-factor receptor in isolated rat hepatocytes.

Ciprofibrate, a hypolipidaemic drug with carcinogenic and peroxisome-proliferation effects in rat liver, was found to increase the phosphorylation of epidermal-growth-factor receptor in 32P-labeled isolated rat hepatocytes. This effect was suppressed by protein-kinase-C inhibitors, and was accompanied by an almost complete inhibition of the receptor autophosphorylation normally induced by its ligand. However, in vitro experiments showed that protein-kinase-C phosphorylation of purified epidermal-growth-factor receptor was activated by ciprofibroyl-CoA, the acyl-CoA derivative of the drug, but not by the unmodified drug. Neither compound affected the ligand induction of epidermal-growth-factor-receptor autophosphorylation in isolated liver membranes. These results suggest that metabolically produced ciprofibroyl-CoA in liver cells would activate protein-kinase-C and produce changes in epidermal-growth-factor-receptor function.

Acyl Coenzyme A↗
PubMed1992

Subcellular distribution and characteristics of ciprofibroyl-CoA synthetase in rat liver. Its possible identity with long-chain acyl-CoA synthetase.

The subcellular distribution and characteristics of ciprofibroyl-CoA synthetase were studied in rat liver and compared with those of long-chain acyl-CoA synthetase (palmitate as substrate) which, as already known, is distributed among mitochondria, microsomes and peroxisomes. Upon differential centrifugation, the subcellular distribution of ciprofibroyl-CoA synthetase followed closely that of palmitoyl-CoA synthetase and was specifically inactivated in the mitochondrial fraction by freezing and thawing, a behaviour already described for palmitoyl-CoA synthetase. Both enzyme activities were found to co-purify through several steps from rat liver microsomes. By using a partially purified enzyme, the activation of ciprofibrate to its acyl-CoA ester followed Michaelis-Menten kinetics with an apparent Km of 0.63 +/- 0.1 mM. Ciprofibroyl-CoA synthetase was competitively inhibited by 25 and 50 microM-palmitic acid. Higher concentrations of the fatty acid resulted in a mixed type of inhibition. Conversely, ciprofibrate up to 0.5 mM was found to inhibit competitively palmitoyl-CoA synthetase, whereas higher concentrations also resulted in a mixed inhibition. The highest activity of ciprofibroyl-CoA synthetase was found in fat and liver homogenates. The distribution of the enzyme in different rat tissues was similar to that of palmitoyl-CoA synthetase. The present results suggest that long-chain acyl-CoA synthetase and ciprofibroyl-CoA synthetase activities reside in identical or closely related proteins.

Acyl Coenzyme A↗
PubMed1992

Hypolipidaemic drugs are activated to acyl-CoA esters in isolated rat hepatocytes. Detection of drug activation by human liver homogenates and by human platelets.

The formation of acyl-CoA esters of the hypolipidaemic peroxisome proliferators clofibric acid, ciprofibrate and nafenopin was studied in isolated rat hepatocytes. The concentration of ciprofibroyl-CoA in the liver of ciprofibrate-treated rats was in the range of 10-30 microM. The three drugs formed acyl-CoA esters when incubated with isolated hepatocytes. Their formation was saturable and reached a plateau after 30 min incubation. Maximal intracellular concentrations of ciprofibroyl-CoA and clofibroyl-CoA (100 microM and 55 microM respectively) were attained at 0.5 mM of the free drugs in the incubation medium, whereas for nafenopin-CoA, the maximal intracellular concentration (9 microM) was reached at 1 mM-nafenopin. At low concentrations of the hypolipidaemic compounds in the incubation medium a significant proportion of the total intracellular drug was present as its acyl-CoA ester (25-35% for ciprofibrate). When isolated hepatocytes were incubated with a ciprofibrate concentration comparable with that observed in the blood of drug-treated rats (0.1 mM), ciprofibroyl-CoA attained an intracellular concentration similar to that previously observed in the liver of treated rats. The formation of ciprofibroyl-CoA by isolated rat hepatocytes was stimulated by the addition of carnitine and partially inhibited by the addition of palmitate. Further, it was shown that human liver homogenates synthesized ciprofibroyl-CoA at a rate similar to that observed for rat liver homogenates. Solubilized human platelets also formed ciprofibroyl-CoA, although at a rate two orders of magnitude lower than that of liver. The results support the view that acyl-CoA esters of hypolipidaemic peroxisome proliferators may be the pharmacologically active species of the drugs.

Acyl Coenzyme A↗