[Use of antimicrobials in a mother-child university hospital center in Canada: An observational study]

INTRODUCTION

The proper use of antimicrobials is a challenge in healthcare establishments.

OBJECTIVES

Describe the detailed antimicrobial consumption profile in 2021-2022. Describe the annual evolutionary profile of the use of antimicrobials in days of therapy/1000 patient days, antibiotic spectrum index/1000 patients days and according to the proportion of days of therapy administered by parenteral route from 2005-2006 to 2021-2022.

METHOD

Descriptive and retrospective study. All patients admitted to our mother-child hospital center between April 1, 2005 and March 31, 2022 were included. The study covers the consumption of all antimicrobials through the AWare classification of the World Health Organization and antibiotic spectrum index.

RESULTS

A total of 673.9 days of therapy/1000 patients days was calculated in 2021-2022, i.e. 550.8 for antibiotics, 46.5 for antivirals, 67.9 for antifungals and 8.7 for others. A total of 2436 ASI/1000 patient days was calculated in 2021-2021. According to the AWaRe classification, in 2021-2022, 52.1% (287/551) of days of therapy/1000 patients days referred to the "Access" group, 47.8% (263/551) to the "Watch" group and 0.2% (1/551) to the "Reserve" group.

CONCLUSION

This study aims to explore the use of antimicrobials in a mother-child hospital center. It puts into perspective a stable or even slightly decreasing use of a selection of antimicrobials and compares favorably with published data. Antibiotic governance is based in particular on the periodic evaluation of consumption. Our study illustrates different approaches to quantify and describe this use.

[Exploration of the evolution of antibiotic consumption according to the WHO AWaRe classification, in a mother-child university hospital]

BACKGROUND

Different measures of antimicrobial are used to ensure proper usage, as part of structured antimicrobial stewardship programs.

OBJECTIVE

The main objective of this study is to describe the consumption of antibiotics in a mother-child teaching hospital using the AWaRe classification over a period of 15 years.

METHODS

This descriptive and retrospective study included all the data on antibiotic consumption of patients admitted to mother-child University Hospital from April 1st 2005 to March 31st, 2021. Of the 180 international non-proprietary names of antibiotics proposed by the World Health Organization (WHO), 54 were used. The number of days of treatment (DOT) per 1000 patient-days (PD) was calculated per year, per patientele (e.g. surgery, pediatrics, oncology, intensive care, neonatal intensive care, nursery, psychiatry, rehabilitation and obstetrics and gynecology) and globally. The data was classified per the WHO AWaRe classification.

RESULTS

A total of 10,489 DOT/1000PD were used globally in 15 years, corresponding to 53.9% of the "Access" group, 45.2% of the "Watch" group and 0.9% of the "Reserve" group. A reduction in the use of antibiotics was noted. The ratios of antibiotic consumptions in DOT/1000PD of 2020-2021 to 2005-2006 were 0.84 globally (1713/5653), 0.79 for the "Access" group (286/361), 0.89 for the "Watch" group (270/302) and 0.88 for the "Reserve" group (2.1/2.4).

CONCLUSION

The AWaRe classification was used to describe the consumption of antibiotics in a mother-child center. Our consumption compared favorably with international data and is in line with the WHO targets. This position may be linked to the presence of a structured anti-biogovernance program that has been in place for several years within our hospital. More work is needed to more precisely identify the antibiotics that should benefit from better supervision.

Effect of chronic kidney disease on serum resistin level

BACKGROUND

Chronic Kidney Diseases (CKD) of all etiologies are usually associated with Insulin Resistance (IR). Resistin is also a protein associated with IR. Some studies conducted abroad have shown that resistin level is higher among CKD patients.

OBJECTIVE

To test if serum resistin level is significantly higher in CKD patients compared to normal individuals.

PATIENTS AND METHODS

96 CKD patients and 97 normal individuals were included in the study. Written informed consent was obtained from every individual.

RESULTS

Serum resistin level was higher in CKD patients compared to control subjects. The difference in serum resistin level between two groups was statistically significant.

CONCLUSION

Our study is probably the first study in India comparing serum resistin levels of CKD patients vis-à-vis control subjects. Further cellular research may be needed to explore this relation.

[Antibiotic consumption and bacterial sensitivity in a teaching hospital: A 5-year study]

INTRODUCTION

To reduce risks of antibiotic resistance, governmental and learned societies decreed the optimal use of antibiotics. The relation between antibiotic consumption and bacterial resistance increase has been clearly demonstrated over the last several years. Antibiotic consumption data and bacterial sensitivity data are regularly published, but very few publications have searched for a correlation between these two variables. This study focused on antibiotic use and consumption as well as bacterial sensitivity to these antibiotics.

OBJECTIVES

The main objective was to describe the changes in antibiotic consumption and bacterial sensitivity in a mother-child teaching hospital. The secondary objectives were to explore whether antibiotic use and bacterial sensitivity were correlated and to comment on the usefulness of these data for clinicians.

METHODS

This was a 5-year retrospective, descriptive, cross-sectional study. All samples from usually sterile biologic liquids of hospitalized pediatric patients were included in the study. The samples from outpatient clinics were excluded. All types of bacteria identified in more than 30 isolates were included in the study. The antibiotics usually used to treat these bacteria were included. To assess antibiotic consumption, we calculated the number of days of therapy per 1000 patient-days for hospitalized pediatric patients and we calculated the Pearson correlation coefficient between antibiotic consumption and sensitivity rates to these antibiotics. Two scenarios were explored: one with correlation by year and one with the next year for bacterial sensitivity.

RESULTS

During the study period (2010-2011 to 2014-2015), overall antibiotics consumption remained relatively stable. Concerning bacterial sensitivity, we noted important changes (sensitivity rates increased for 12 antibiotic-bacteria pairs, remained stable for five, and decreased for 15). We found three significant correlations for the first scenario: Pseudomonas aeruginos-ceftazidime (P=0.01), P. aeruginosa-ciprofloxacin and fluoroquinolone consumption (P=0.02), Enterococcus sp-ampicillin and penicillin consumption (P=0.04). For the second scenario, we found only two significant correlations: coagulase-negative Staphylococcus-oxacilline and penicillin consumption (P=0.02), P. aeruginosa/piperacillin (P=0.04).

CONCLUSION

This exploratory study allowed us to describe antibiotic consumption and bacterial sensitivity progression. To our knowledge, this is the first study exploring the correlation between antibiotic consumption and the bacterial sensitivity rate in pediatrics in Canada. It remains very difficult to show this correlation between these two variables because of the multiple sources of bacterial resistance. These data are particularly useful for the antimicrobial stewardship programs and for clinicians.

NATIONAL DOSE REGISTER IN FRANCE WITHIN THE NATIONAL INFORMATION SYSTEM SISERI

Over the past decade, France has developed an electronic dose register at national level called SISERI. Institute for Radiological Protection and Nuclear Safety is in charge of the management of this information system. Besides the main purpose of being a central register of any doses measured for the individual dosimetric monitoring of all exposed workers, SISERI has been developed so as to constitute a tool for occupational physicians and radiation protection officers allowing access in real-time to the results of the individual monitoring. The SISERI information system centralises, verifies and keeps the records of all personal dosimetric results of the 370 000 workers annually monitored in France. Moreover, since the publication of a new order in 2013, employers shall declare any new workers in SISERI before the beginning of their occupation and they shall upload data concerning in particular the activity field/sector and the occupation of each worker. The enforcement of this new order is going to enrich the individual dosimetric information stored in SISERI. Thus, it is expected that more precise and accurate statistics on occupational exposure to ionising radiation in France will be established in the next few years.

[Upgrading a pediatric pharmaceutical care service in Quebec]

INTRODUCTION

Clinical pharmacy has developed since the 1960s in North America, with large disparities in the presence of decentralized pharmacists in hospital units between healthcare programs. Decentralized pharmacists have been present in pediatrics since the 1970s. The main objective of this study was to describe the steps used to upgrade the pediatrics department's pharmaceutical care.

METHODS

A descriptive study was conducted to upgrade the pharmaceutical care provided by two full-time equivalents in two pediatric sectors including 81 beds of a tertiary mother-child hospital. The upgrade includes three steps: a structured literature review, a description of the department, and a description of the practice upgrades proposed by the research team, in consensus with the clinical pharmacy team.

RESULTS

Out of the 236 articles initially identified, 13 relevant articles were found on the role and impact of pharmacists in pediatrics. Nine pharmaceutical activities were supported by high-quality data. Following the literature review and concerted reflection, 15 improvements were identified as feasible without increasing the staff.

CONCLUSION

There are data on the impact of pharmacists in pediatrics. This descriptive study illustrates a method that was used to upgrade the pediatrics sector in a university mother-child health center.

Light-dependent assembly of ribulose-1,5-bisphosphate carboxylase

Ribulose-1,5-bisphosphate carboxylase [RuP(2)Case; 3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 4.1.1.39] is composed of eight small subunits (M(r), 14,000) and eight large subunits (M(r), 55,000). Newly synthesized large subunits are associated with two complexes having sedimentation coefficients of 7 and 29 S. Assembly of RuP(2)Case occurs in isolated intact chloroplasts in the light but not in the dark. When extracts of chloroplasts are treated with ATP or GTP, RuP(2)Case assembly is accelerated while the 29S large subunit complex is maintained. In the presence of Mg(2+), ATP brings about almost complete dissociation of the 29S complex, whereas GTP and a nonhydrolyzable analog of ATP are without effect. These results indicate the existence of a complex set of reactions involving nucleotides, Mg(2+), and several putative intermediates in RuP(2)Case assembly. It is postulated that these reactions at least partly account for the light dependence of RuP(2)Case assembly. In particular, ATP and GTP promote the assembly of large subunits into RuP(2)Case.

Synthesis and discharge of the coupling factor.adenosine diphosphate complex in spinach chloroplast lamellae

The formation of a coupling factor.ADP complex is shown to be dependent on photoinduced electron transport, AMP, and P(i), and sensitive to arsenate and sulfate. The stability of the complex is unaffected by subsequent addition of arsenate, but is quite markedly sensitive to the addition of ADP. The data are discussed in relation to possible models of photophosphorylation, and in particular, to one in which coupling factor-bound, photosynthetically generated, ADP serves as a phosphoryl donor to substrate ADP.

Low-coherence enhanced backscattering and its applications

The phenomenon of enhanced backscattering (EBS) of light, also known as coherent backscattering, has been the object of intensive investigation in non-biological media over the last two decades. However, there have been only a few attempts to explore EBS for tissue characterization and diagnosis. We have recently made progress in the EBS measurements in tissue by taking advantage of low spatial coherence illumination, which has led us to the development of low-coherence enhanced backscattering (LEBS) as a technique to characterize living tissue. In this paper, we review the current state of research on LEBS. In particular, we show that LEBS spectroscopy enables detection of early microarchitectural changes in tissue associated with carcinogenesis prior to the development of histologically-detectable alterations as well as any other known markers of neoplasia. Thus, LEBS may offer insights into initial events in carcinogenesis.

VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC) induced intimal hyperplasia in carotid arteries

BACKGROUND

The role of vascular endothelial growth factors (VEGFs) in intimal hyperplasia and atherogenesis remains unknown. Several studies have suggested that some members of the VEGF family reduce intimal hyperplasia, but others have proposed that VEGFs accelerate restenosis and atherosclerosis. This investigation conducted a comparative study with adenoviruses encoding different VEGFs in a rabbit carotid artery collar model of intimal hyperplasia in order to analyze the role of VEGFs in the formation of intimal hyperplasia.

MATERIALS AND METHODS

Intimal hyperplasia was induced in the carotid arteries of cholesterol fed New Zealand White rabbits using a silastic collar. Adenoviral vectors encoding VEGF-A, VEGF-B, VEGF-C, VEGF-C(DeltaNDeltaC), VEGF-D and VEGF-D(DeltaNDeltaC) were delivered to the adventitia using the collar as a gene delivery device. Adeno-LacZ was used as a control.

RESULTS

A significant (P < 0.01) increase in the intima/media ratio was observed in the arteries transduced with VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC). There was a significant increase in the number of proliferating cells in the adventitia, media and intima of the VEGF-A, VEGF-D and the VEGF-D(DeltaNDeltaC) transduced arteries. The majority of medial smooth muscle cells in these arteries had a synthetic phenotype. The presence of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the VEGF-A, VEGF-D and the VEGF-D(DeltaNDeltaC) transduced arteries was significantly increased. A significant positive correlation was observed between adventitial angiogenesis and intimal hyperplasia.

CONCLUSIONS

Adventitial delivery of adenoviruses encoding VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC) increased intimal hyperplasia in the rabbit collar model. Adventitial angiogenesis correlated positively with the intimal hyperplasia. These results indicated that efficient adventitial production of VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC) can cause thickening of the inner layer of the artery in rabbits.

Periadventitial angiopoietin-1 gene transfer induces angiogenesis in rabbit carotid arteries

This study was performed to evaluate angiogenic responses of angiopoietin-1 (Ang1) in vivo after adenovirus-mediated gene transfer in the periadventitial space of the rabbit carotid arteries using a collar technique. Adenoviruses encoding LacZ and vascular endothelial growth factor (VEGF) receptor-1-Ig fusion protein (VEGF-R1-Ig) adenoviruses were used as controls. Increased neovessel formation was seen in adventitia of the Ang1 transduced arteries 7 days after the gene transfer. Neovessels in the Ang1 transduced arteries were large in size and well perfused. Ang1 binds to Tie2 (tyrosine kinase with immunoglobulin and epidermal growth factor homology domain) receptors, which were expressed in the endothelium of the neovessels. When VEGF-R1-Ig was used with Ang1, it resulted in a decrease in the number of neovessels, which implies that VEGF-A or some other VEGF-R1 ligand(s) play a crucial role in angiogenesis occurring in response to Ang1. There were no significant differences in the total number of capillaries in the adventitia of the VEGF-R1-Ig transduced arteries as compared to LacZ controls. Neointima formation was not increased in the Ang1 transduced arteries as compared to the controls. We conclude that in the periadventitial space Ang1 shows angiogenic activity and is a potentially useful factor for the induction of therapeutic vascular growth in vivo.

Crystallization and preliminary X-ray diffraction data of the second and archaebacterial-type aspartyl-tRNA synthetase from Thermus thermophilus

The archaebacterial-type aspartyl-tRNA synthetase (AspRS2) from the thermophilic eubacterium Thermus thermophilus was crystallized using the hanging-drop vapour-diffusion method. Crystals grew at pH 9.5 in the presence of PEG 8000 and NaCl. A native diffraction data set has been collected at 2.5 A resolution using synchrotron radiation and cryocooling. Crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 57.3, b = 121.9, c = 166.9 A and V(M) = 3.03 A(3) Da(-1). There is one dimer of M(r) 96 000 per asymmetric unit. A molecular-replacement analysis gave solutions for the rotation and translation functions.

The heterotrimeric Thermus thermophilus Asp-tRNA(Asn) amidotransferase can also generate Gln-tRNA(Gln)

Thermus thermophilus strain HB8 is known to have a heterodimeric aspartyl-tRNA(Asn) amidotransferase (Asp-AdT) capable of forming Asn-tRNA(Asn) [Becker, H.D. and Kern, D. (1998) Proc. Natl. Acad. Sci. USA 95, 12832-12837]. Here we show that, like other bacteria, T. thermophilus possesses the canonical set of amidotransferase (AdT) genes (gatA, gatB and gatC). We cloned and sequenced these genes, and constructed an artificial operon for overexpression in Escherichia coli of the thermophilic holoenzyme. The overproduced T. thermophilus AdT can generate Gln-tRNA(Gln) as well as Asn-tRNA(Asn). Thus, the T. thermophilus tRNA-dependent AdT is a dual-specific Asp/Glu-AdT resembling other bacterial AdTs. In addition, we observed that removal of the 44 carboxy-terminal amino acids of the GatA subunit only inhibits the Asp-AdT activity, leaving the Glu-AdT activity of the mutant AdT unaltered; this shows that Asp-AdT and Glu-AdT activities can be mechanistically separated.

Concurrent physical activity increases fat oxidation during the shift to a high-fat diet

BACKGROUND

It takes several days to adapt to a high-fat diet. In an earlier study, we observed a large degree of interindividual variation in the capacity to adapt to a high-fat diet. We hypothesized that concurrent physical activity would accelerate fat oxidation during an isoenergetic high-fat diet.

OBJECTIVE

The objective of this study was to determine the effect of increased physical activity on the ability of young healthy men to increase fat oxidation during the shift to a high-fat diet.

DESIGN

Six young healthy men participated in a randomized, single-blind crossover study. The volunteers consumed a diet contributing 37% of energy as fat, 14% as protein, and 49% as carbohydrate for 4 d. Energy expenditure and macronutrient balance were then measured in a respiration chamber as the energy content of the isoenergetic diet was changed to 50% fat, 14% protein, and 36% carbohydrate. Treadmill walking, as the physical activity, was used to increase total daily energy expenditure to 1.8 times the resting metabolic rate during 1 of 2 stays in the metabolic chamber. Total daily energy expenditure was maintained at 1.4 times the resting metabolic rate for the other stay.

RESULTS

Energy balance was not significantly different between the 2 conditions. The 24-h respiratory quotient decreased more rapidly and to a greater extent under conditions of increased energy expenditure. Further, there was a decrease in the interindividual variability in the response of the respiratory quotient to a high-fat diet with increased energy expenditure (physical activity). Cumulative carbohydrate and protein balances were greater under conditions of increased physical activity. Conversely, cumulative fat balance was greater under sedentary conditions.

CONCLUSION

Concurrent physical activity increases fat oxidation during the shift to a high-fat diet.

Thermus thermophilus contains an eubacterial and an archaebacterial aspartyl-tRNA synthetase

Thermus thermophilus possesses two aspartyl-tRNA synthetases (AspRSs), AspRS1 and AspRS2, encoded by distinct genes. Alignment of the protein sequences with AspRSs of other origins reveals that AspRS1 possesses the structural features of eubacterial AspRSs, whereas AspRS2 is structurally related to the archaebacterial AspRSs. The structural dissimilarity between the two thermophilic AspRSs is correlated with functional divergences. AspRS1 aspartylates tRNA(Asp) whereas AspRS2 aspartylates tRNA(Asp), and tRNA(Asn) with similar efficiencies. Since Asp bound on tRNA(Asn) is converted into Asn by a tRNA-dependent aspartate amidotransferase, AspRS2 is involved in Asn-tRNA(Asn) formation. These properties relate functionally AspRS2 to archaebacterial AspRSs. The structural basis of the dual specificity of T. thermophilus tRNA(Asn) was investigated by comparing its sequence with those of tRNA(Asp) and tRNA(Asn) of strict specificity. It is shown that the thermophilic tRNA(Asn) contains the elements defining asparagine identity in Escherichia coli, part of which being also the major elements of aspartate identity, whereas minor elements of this identity are missing. The structural context that permits expression of aspartate and asparagine identities by tRNA(Asn) and how AspRS2 accommodates tRNA(Asp) and tRNA(Asn) will be discussed. This work establishes a distinct structure-function relationship of eubacterial and archaebacterial AspRSs. The structural and functional properties of the two thermophilic AspRSs will be discussed in the context of the modern and primitive pathways of tRNA aspartylation and asparaginylation and related to the phylogenetic connexion of T. thermophilus to eubacteria and archaebacteria.

Fat and carbohydrate balances during adaptation to a high-fat

BACKGROUND

Dietary fat contents are highly variable. Failure to compensate for the positive fat balance that occurs during the shift to a high-fat, low-carbohydrate diet by increasing energy expenditure or by decreasing food intake may result in the gain of fat mass.

OBJECTIVE

The objective of this study was to investigate the time course of fat oxidation during adaptation to an isoenergetic high-fat, low-carbohydrate diet.

DESIGN

After a 5-d control diet, dietary fat was increased from 37% of energy to 50% of energy for 4 d in 6 healthy, young lean men. Respiratory quotient and substrate macronutrient oxidation and balance were measured in a respiratory chamber. Fasting concentrations of insulin, glucose, and triacylglycerol; maximal oxygen consumption (f1.gif" BORDER="0">O(2)max) during treadmill exercise; and free-living energy expenditure were determined. Body fat was measured by dual-energy X-ray absorptiometry and visceral adipose tissue by computerized tomography.

RESULTS

Compared with the baseline diet, the high-fat, low-carbohydrate diet resulted in positive fat and protein balances and a negative carbohydrate balance. Insulin concentration and the postabsorptive respiratory quotient were positively correlated with the fat balance during the high-fat, low-carbohydrate diet, whereas f1.gif" BORDER="0">O(2)max during treadmill exercise was negatively related to fat balance. With use of stepwise regression, f1.gif" BORDER="0">O(2)max was the best predictor of fat balance. There was a negative correlation between fat balance and carbohydrate balance (r(2) = 0.88).

CONCLUSION

Both baseline insulin concentration and f1.gif" BORDER="0">O(2)max during treadmill exercise predict fat balance during the shift to a high-fat diet under isoenergetic conditions.

tRNA glycylation system from Thermus thermophilus. tRNAGly identity and functional interrelation with the glycylation systems from other phylae

The systems of tRNA glycylation belong to the most complex aminoacylation systems since neither the oligomeric structure of glycyl-tRNA synthetases (GlyRS) nor the discriminator bases in tRNAGly are conserved in the phylae. To better understand the structure-function relationship in glycylation systems of various origins and the functional peculiarities related to their structural divergences, the elements in tRNA conferring its glycine identity in Thermus thermophilus were characterized and compared to those of other systems. Thermophilic identity is conferred by the G1-C72, C2-G71, G3-C70, and C50-G64 pairs together with the G10, U16, C35, and C36 single residues. In contrast to most other aminoacylation systems, the discriminator base is not directly involved in identity. Transplantation of these elements in tRNAAsp and tRNAPhe converts specificity toward glycine albeit conservation of nucleotide 73. Analysis of the functional interrelation of the identity elements shows coupling in synthetase recognition of the elements from anticodon and G10 whereas those from acceptor arm are recognized independently. Despite nondirect implication in identity, the discriminator base contributes cooperatively with C36 in specificity of glycylation. The link between the structural heterogeneity and the functional divergence of the glycylation systems and the phylogenic interrelation of these systems were approached by comparing the ability of GlyRSs of various phylae to glycylate heterologous tRNAGly. Dimeric GlyRSs from mammalian and archaebacteria acylate efficiently only eukaryotic and archaebacterial tRNAGly with a discriminatory A73, whereas tetrameric Escherichia coli GlyRS acylates only eubacterial tRNAGly with a discriminatory U73. In contrast, dimeric yeast GlyRS acylates efficiently both eukaryotic and archaebacterial tRNAGly as well as peculiar prokaryotic isoacceptors. Species specificity is lost with the dimeric GlyRS from Thermus thermophilus that acylates efficiently eubacterial, archaebacterial, and eukaryotic tRNAGly. These features are discussed in the context of the evolution of the glycylation systems and the phylogenic interrelation of the organisms.

Chemoprevention of azoxymethane-induced colonic carcinogenesis by supplemental dietary ursodeoxycholic acid

The present studies were conducted at the Universities of Chicago and Arizona to examine and compare the effects of supplemental dietary ursodeoxycholic acid to cholic acid, a known tumor promoter, and to piroxicam, a known chemopreventive agent, in the azoxymethane (AOM) model of experimental colonic carcinogenesis. Male Fischer 344 rats were utilized in these experiments. All animals were fed a basal diet (AIN-76) supplemented with 0.2% or 0.4% cholic acid, 0.2% or 0.4% ursodeoxycholic acid, 0.2% ursodeoxycholic acid plus 0.2% cholic acid, or 75 ppm piroxicam. Rats were given s.c. injections once a week for 2 weeks with AOM (15 mg/kg body wt/week) or vehicle (saline) after being fed their respective diets for 2 weeks. The rats in each group were then maintained on their respective diets for approximately 28 weeks; after sacrifice, their colons were removed and examined macroscopically and microscopically for the presence of tumors. The results of these studies demonstrated that none of the control rats fed the various diets injected with AOM-vehicle developed tumors. In groups receiving AOM, the addition of cholic acid (0.4%) caused a significant increase in the incidence of tumors. In contrast, the addition of 0.2% ursodeoxycholic acid did not promote AOM-induced colonic tumors, and when it was added to a promoting dose of cholic acid (0.2%), 0.2% ursodeoxycholic acid prevented enhancement of tumor promotion. At higher doses (0.4%), supplemental dietary ursodeoxycholic acid significantly reduced the incidence of colon tumors and cancers. Moreover, the tumor suppressive effects of 0.4% ursodeoxycholic acid exceeded that of dietary piroxicam. Our results further emphasize the important role of bile salts in modulating colonic tumor development. These studies also demonstrate for the first time that supplemental dietary ursodeoxycholic acid is a chemopreventive agent in the AOM model of experimental colonic carcinogenesis.

Theory of chaperonin action: inertial model for enhancement of prokaryotic Rubisco assembly

We have performed a computational simulation of the aggregation and chaperonin-dependent reconstitution of dimeric prokaryotic ribulose bisphosphate carboxylase/oxygenase (Rubisco), based on the data of P. Goloubinoff et al. (1989, Nature 342, 884-889) and P. V. Viitanen et al. (1990, Biochemistry 29, 5665-5671). The aggregation is simulated by a set of 12 differential equations representing the aggregation of the Rubisco folding intermediate, Rubisco-I, with itself and with aggregates of Rubisco-I, leading up to dodecamers. Four rate constants, applying to forward or reverse steps in the aggregation process, were included. Optimal values for these constants were determined using the ellipsoid algorithm as implemented by one of us (Ecker, J.G. & Kupferschmid, M., 1988, Introduction to Operations Research, Wiley, New York, pp. 315-322). Intensive exploration of simpler aggregation models did not identify an alternative that could simulate the data as well as this one. The activity of the chaperonin in this system was simulated by using this aggregation model, combined with a model similar to that proposed by Goloubinoff et al. (1989). The model assumes that the chaperonin can bind the folding intermediate rapidly, and that the chaperonin complex releases the Rubisco molecule slowly, permitting time for its spontaneous folding while interacting with the chaperonin. This is followed by self-association of the folded Rubisco monomer to yield the active dimeric Rubisco. A modification of the model that simulates temperature effects was also constructed. The most important results we obtained indicate that the chaperonin-dependent reconstitution of Rubisco can be simulated adequately without invoking any catalysis of folding by the chaperonin. In addition, the simulations predict values for the association rate constant of Rubisco-I with the chaperonin, and other variables, that are subject to experimental verification.

Assembly of in vitro synthesized large subunits into ribulose-bisphosphate carboxylase/oxygenase. Formation and discharge of an L8-like species

Ribulose-bisphosphate carboxylase/oxygenase (Rubisco) from higher plants consists of eight approximately 53-kDa large subunits and eight approximately 14-kDa small subunits. Cytosolic ribosomes synthesize the small subunits as precursors, which enter the chloroplast, undergo proteolytic processing, and assemble with large subunits. Large subunits, synthesized in the chloroplast, first form a complex with the chloroplast chaperonin 60 (Cpn60(14)). In the presence of ATP, large subunits dissociate from Cpn60(14) and assemble into Rubisco. We now describe partial characterization of a new species, Z, containing radiotracer-labeled, newly synthesized pea Rubisco large subunits. Rubisco assembly occurs in low salt in the presence of small subunits and ATP. As with Rubisco assembly, the formation of Z is ATP-dependent and is inhibited by high chloride. Once formed, Z is stable except in high chloride. Z does not appear to interact directly with small subunits. However, after Z formation, Rubisco assembly occurs in an ATP-independent reaction that requires KCl and small subunits. These results are consistent with the hypothesis that Z is a large subunit containing structure that can contribute large subunits to Rubisco under appropriate conditions. Z shares some physical characteristics with reported cyanobacterial L8 core particles. However, formation of Rubisco from Z in the absence of ATP and the presence of small subunits appears to require conditions that otherwise destabilize Z.

Assembly of in Vitro-Synthesized Large Subunits into Ribulose Bisphosphate Carboxylase/Oxygenase Is Sensitive to CI-, Requires ATP, and Does Not Proceed When Large Subunits Are Synthesized at Temperatures [greater than or equal to]32[deg]C

In higher plants, ribulose bisphosphate carboxylase/oxygenase (Rubisco) consists of eight large "L" subunits, synthesized in chloroplasts, and eight small "S" subunits, synthesized as precursors in the cytosol. Assembly of these into holoenzyme occurs in the chloroplast stroma after import and processing of the S subunits. A chloroplast chaperonin interacts with the L subunits, which dissociate from the chaperonin before they assemble into holoenzyme. Our laboratory has reported L subunit assembly into Rubisco in chloroplast extracts after protein synthesis in leaves, intact chloroplasts, and most recently in membrane-free chloroplast extracts. We report here that the incorporation of in vitro-synthesized L subunits into holoenzyme depends on the conditions of L subunit synthesis. Rubisco assembly did not occur after L subunit synthesis at 160 mM KCI. When L subunit synthesis occurred at approximately 70 mM KCI, assembly depended on the temperature at which L subunit synthesis took place. These phenomena were the result of postsynthetic events taking place during incubation for protein synthesis. We separated these events from protein synthesis by lowering the temperature during protein synthesis. Lower temperatures supported the synthesis of full-length Rubisco L subunits. The assembly of these completed L subunits into Rubisco required intervening incubation with ATP, before addition of S subunits. ATP treatment mobilized L subunits from a complex with the chloroplast chaperonin 60 oligomer. Addition of 130 mM KCI at the beginning of the intervening incubation with ATP blocked the incorporation of L subunits into Rubisco. The inhibitory effect of high KCI was due to CI- and came after association of newly synthesized L subunits with chaperonin 60, but before S subunit addition. It is interesting that L subunits synthesized at [greater than or equal to]32[deg]C failed to assemble into Rubisco under any conditions. These results agree with previous results obtained in this laboratory using newly synthesized L subunits made in intact chloroplasts. They also show that assembly of in vitro-synthesized L subunits into Rubisco requires ATP, that CI- inhibits Rubisco assembly, and that synthesis temperature affects subsequent assembly competence of L subunits.

Synthesis and assembly of large subunits into ribulose bisphosphate carboxylase/oxygenase in chloroplast extracts

We have developed a new system for the in vitro synthesis of large subunits and their assembly into ribulose bisphosphate carboxylase oxygenase (Rubisco) holoenzyme in extracts of higher plant chloroplasts. This differs from previously described Rubisco assembly systems because the translation of the large subunits occurs in chloroplast extracts as opposed to isolated intact chloroplasts, and the subsequent assembly of large subunits into holoenzyme is completely dependent upon added small subunits. Amino acid incorporation in this system displayed the characteristics previously reported for chloroplast-based translation systems. Incorporation was sensitive to chloramphenicol or RNase but resistant to cycloheximide, required magnesium, and was stimulated by nucleotides. The primary product of this system was the large subunit of Rubisco. However, several lower molecular weight polypeptides were formed. These were structurally related to the Rubisco large subunit. The initiation inhibitor aurintricarboxylic acid (ATA) decreased the amount of lower molecular weight products accumulated. The accumulation of completed large subunits was only marginally reduced in the presence of ATA. The incorporation of newly synthesized large subunits into Rubisco holoenzyme occurred under conditions previously identified as optimal for the assembly of in organello-synthesized large subunits and required the addition of purified small subunits.