Cytoreductive surgery combined with perioperative intraperitoneal chemotherapy for the management of peritoneal carcinomatosis from colorectal cancer: a multi-institutional study

PURPOSE

The three principal studies dedicated to the natural history of peritoneal carcinomatosis (PC) from colorectal cancer consistently showed median survival ranging between 6 and 8 months. New approaches combining cytoreductive surgery and perioperative intraperitoneal chemotherapy suggest improved survival.

PATIENTS AND METHODS

A retrospective multicenter study was performed to evaluate the international experience with this combined treatment and to identify the principal prognostic indicators. All patients had cytoreductive surgery and perioperative intraperitoneal chemotherapy (intraperitoneal chemohyperthermia and/or immediate postoperative intraperitoneal chemotherapy). PC from appendiceal origin was excluded.

RESULTS

The study included 506 patients from 28 institutions operated between May 1987 and December 2002. Their median age was 51 years. The median follow-up was 53 months. The morbidity and mortality rates were 22.9% and 4%, respectively. The overall median survival was 19.2 months. Patients in whom cytoreductive surgery was complete had a median survival of 32.4 months, compared with 8.4 months for patients in whom complete cytoreductive surgery was not possible (P <.001). Positive independent prognostic indicators by multivariate analysis were complete cytoreduction, treatment by a second procedure, limited extent of PC, age less than 65 years, and use of adjuvant chemotherapy. The use of neoadjuvant chemotherapy, lymph node involvement, presence of liver metastasis, and poor histologic differentiation were negative independent prognostic indicators.

CONCLUSION

The therapeutic approach combining cytoreductive surgery with perioperative intraperitoneal chemotherapy achieved long-term survival in a selected group of patients with PC from colorectal origin with acceptable morbidity and mortality. The complete cytoreductive surgery was the most important prognostic indicator.

Y chromosome sequence variation and the history of human populations

Binary polymorphisms associated with the non-recombining region of the human Y chromosome (NRY) preserve the paternal genetic legacy of our species that has persisted to the present, permitting inference of human evolution, population affinity and demographic history. We used denaturing high-performance liquid chromatography (DHPLC; ref. 2) to identify 160 of the 166 bi-allelic and 1 tri-allelic site that formed a parsimonious genealogy of 116 haplotypes, several of which display distinct population affinities based on the analysis of 1062 globally representative individuals. A minority of contemporary East Africans and Khoisan represent the descendants of the most ancestral patrilineages of anatomically modern humans that left Africa between 35,000 and 89,000 years ago.

The phylogeography of Y chromosome binary haplotypes and the origins of modern human populations

Although molecular genetic evidence continues to accumulate that is consistent with a recent common African ancestry of modern humans, its ability to illuminate regional histories remains incomplete. A set of unique event polymorphisms associated with the non-recombining portion of the Y-chromosome (NRY) addresses this issue by providing evidence concerning successful migrations originating from Africa, which can be interpreted as subsequent colonizations, differentiations and migrations overlaid upon previous population ranges. A total of 205 markers identified by denaturing high performance liquid chromatography (DHPLC), together with 13 taken from the literature, were used to construct a parsimonious genealogy. Ancestral allelic states were deduced from orthologous great ape sequences. A total of 131 unique haplotypes were defined which trace the microevolutionary trajectory of global modern human genetic diversification. The genealogy provides a detailed phylogeographic portrait of contemporary global population structure that is emblematic of human origins, divergence and population history that is consistent with climatic, paleoanthropological and other genetic knowledge.

Homologous recombination in Escherichia coli: dependence on substrate length and homology

We studied the in vivo recombination between homologous DNA sequences cloned in phage lambda and a pBR322-derived plasmid by assaying for the formation of phage-plasmid cointegrates by a single (or an odd number of) reciprocal exchange. (1) Recombination proceeds by the RecBC pathway in wild-type cells and by low levels of a RecF-dependent pathway in recBC- cells. The RecE pathway appears not to generate phage-plasmid cointegrates. (2) Recombination is linearly dependent on the length of the homologous sequences. In both RecBC and RecF-dependent pathways there is a minimal length, called the minimal efficient processing segment (MEPS), below which recombination becomes inefficient. The length of MEPS is between 23-27 base pairs (bp) and between 44-90 bp for the RecBC- and RecF-dependent pathways, respectively. A model, based on overlapping MEPS, of the correlation of genetic length with physical length is presented. The bases for the different MEPS length of the two pathways are discussed in relationship to the enzymes specific to each pathway. (3) The RecBC and the RecF-dependent pathways are each very sensitive to substrate homology. In wild-type E. coli, reduction of homology from 100% to 90% decreases recombinant frequency over 40-fold. The homology dependence of the RecBC and RecF-dependent pathways are similar. This suggests that a component common to both, probably recA, is responsible for the recognition of homology.

Sindbis virus: an efficient, broad host range vector for gene expression in animal cells

Sindbis virus, an enveloped virus with a single-stranded RNA genome, was engineered to express a bacterial protein, chloramphenicol acetyltransferase (CAT), in cultured insect, avian, and mammalian cells. The vectors were self-replicating and gene expression was efficient and rapid; up to 10(8) CAT polypeptides were produced per infected cell in 16 to 20 hours. CAT expression could be made temperature-sensitive by means of a derivative that incorporated a temperature-sensitive mutation in viral RNA synthesis. Vector genomic RNAs were packaged into infectious particles when Sindbis helper virus was used to supply virion structural proteins. The vector RNAs were stable to at least seven cycles of infection. The expression of CAT increased about 10(3)-fold, despite a 10(15)-fold dilution during the passaging. Sindbis virus vectors should prove useful for expressing large quantities of gene products in a variety of animal cells.

Recent common ancestry of human Y chromosomes: evidence from DNA sequence data

We consider a data set of DNA sequence variation at three Y chromosome genes (SMCY, DBY, and DFFRY) in a worldwide sample of human Y chromosomes. Between 53 and 70 chromosomes were fully screened for sequence variation at each locus by using the method of denaturing high-performance liquid chromatography. The sum of the lengths of the three genes is 64,120 bp. We have used these data to study the ancestral genealogy of human Y chromosomes. In particular, we focused on estimating the expected time to the most recent common ancestor and the expected ages of certain mutations with interesting geographic distributions. Although the geographic structure of the inferred haplotype tree is reminiscent of that obtained for other loci (the root is in Africa, and most of the oldest non-African lineages are Asian), the expected time to the most recent common ancestor is remarkably short, on the order of 50,000 years. Thus, although previous studies have noted that Y chromosome variation shows extreme geographic structure, we estimate that the spread of Y chromosomes out of Africa is much more recent than previously was thought. We also show that our data indicate substantial population growth in the effective number of human Y chromosomes.

Fluoride and casein phosphopeptide-amorphous calcium phosphate

Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) slows the progression of caries and remineralizes enamel subsurface lesions. The aim of this study was to determine the ability of CPP-ACP to increase the incorporation of fluoride into plaque and to promote enamel remineralization in situ. Randomized, double-blind, cross-over studies involved mouthrinses and dentifrices containing CPP-ACP and fluoride. The mouthrinses were used for 60 sec, three times/day for 5 days, and supragingival plaque was collected and analyzed for F. The dentifrices were rinsed as a water slurry for 60 sec four times/day for 14 days in an in situ model. The addition of 2% CPP-ACP to the 450-ppm-F mouthrinse significantly increased the incorporation of fluoride into plaque. The dentifrice containing 2% CPP-ACP produced a level of remineralization similar to that achieved with a dentifrice containing 2800 ppm F. The dentifrice containing 2% CPP-ACP plus 1100 ppm F was superior to all other formulations.

Retention in plaque and remineralization of enamel lesions by various forms of calcium in a mouthrinse or sugar-free chewing gum

Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) nanocomplexes incorporated into sugar-free chewing gum have been shown to remineralize enamel subsurface lesions in situ. The aim of this study was to compare the ability of CPP-ACP, with that of other forms of calcium, to be retained in supragingival plaque and remineralize enamel subsurface lesions in situ when delivered in a mouthrinse or sugar-free gum in randomized, double-blind trials. In the mouthrinse study, only the CPP-ACP-containing mouthrinse significantly increased plaque calcium and inorganic phosphate levels, and the CPP were immunolocalized to the surfaces of bacterial cells as well as the intercellular matrix. In the chewing gum studies, the gum containing the CPP-ACP, although not containing the most calcium per piece of gum, produced the highest level of enamel remineralization independent of gum-chewing frequency and duration. The CPP could be detected in plaque extracts 3 hrs after subjects chewed the CPP-ACP-containing gum. The results showed that CPP-ACP were superior to other forms of calcium in remineralizing enamel subsurface lesions.

Identification of a Drosophila brain-gut peptide related to the neuropeptide Y family

A neuropeptide F (NPF) was isolated from the fruit fly, Drosophila mellanogaster, based on a radioimmunoassay for a gut peptide from the corn earworm, Helicoverpa zea. A partial sequence was obtained from the fly peptide, and a genomic sequence coding for NPF was cloned after inverse polymerase chain reaction and shown to exist as a single genomic copy. The encoded, putative prepropeptide can be processed into an amidated NPF with 36 residues that is related to invertebrate NPF's and the neuropeptide Y family of vertebrates. In situ hybridization and immunocytochemistry showed that Drosophila NPF was expressed in the brain and midgut of fly larvae and adults.

Remineralization of enamel subsurface lesions by sugar-free chewing gum containing casein phosphopeptide-amorphous calcium phosphate

Casein phosphopeptide-amorphous calcium phosphate nanocomplexes (CPP-ACP) exhibit anticariogenic potential in laboratory, animal, and human in situ experiments. The aim of this study was to determine the ability of CPP-ACP in sugar-free chewing gum to remineralize enamel subsurface lesions in a human in situ model. Thirty subjects in randomized, cross-over, double-blind studies wore removable palatal appliances with six human-enamel half-slabs inset containing sub-surface demineralized lesions. The appliances were inserted immediately before gum-chewing for 20 min and then retained for another 20 min. This was performed four times per day for 14 days. At the completion of each treatment, the enamel half-slabs were paired with their respective demineralized control half-slabs, embedded, sectioned, and subjected to microradiography and densitometric image analysis, for measurement of the level of remineralization. The addition of CPP-ACP to either sorbitol- or xylitol-based gum resulted in a dose-related increase in enamel remineralization, with 0.19, 10.0, 18.8, and 56.4 mg of CPP-ACP producing an increase in enamel remineralization of 9, 63, 102, and 152%, respectively, relative to the control gum, independent of gum weight or type.

Population genetic implications from sequence variation in four Y chromosome genes

Some insight into human evolution has been gained from the sequencing of four Y chromosome genes. Primary genomic sequencing determined gene SMCY to be composed of 27 exons that comprise 4,620 bp of coding sequence. The unfinished sequencing of the 5' portion of gene UTY1 was completed by primer walking, and a total of 20 exons were found. By using denaturing HPLC, these two genes, as well as DBY and DFFRY, were screened for polymorphic sites in 53-72 representatives of the five continents. A total of 98 variants were found, yielding nucleotide diversity estimates of 2.45 x 10(-5), 5. 07 x 10(-5), and 8.54 x 10(-5) for the coding regions of SMCY, DFFRY, and UTY1, respectively, with no variant having been observed in DBY. In agreement with most autosomal genes, diversity estimates for the noncoding regions were about 2- to 3-fold higher and ranged from 9. 16 x 10(-5) to 14.2 x 10(-5) for the four genes. Analysis of the frequencies of derived alleles for all four genes showed that they more closely fit the expectation of a Luria-Delbrück distribution than a distribution expected under a constant population size model, providing evidence for exponential population growth. Pairwise nucleotide mismatch distributions date the occurrence of population expansion to approximately 28,000 years ago. This estimate is in accord with the spread of Aurignacian technology and the disappearance of the Neanderthals.

Consensus guidelines from The American Society of Peritoneal Surface Malignancies on standardizing the delivery of hyperthermic intraperitoneal chemotherapy (HIPEC) in colorectal cancer patients in the United States

BACKGROUND

The American Society of Peritoneal Surface Malignancies (ASPSM) is a consortium of cancer centers performing cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (HIPEC). This is a position paper from the ASPSM on the standardization of the delivery of HIPEC.

METHODS

A survey was conducted of all cancer centers performing HIPEC in the United States. We attempted to obtain consensus by the modified method of Delphi on seven key HIPEC parameters: (1) method, (2) inflow temperature, (3) perfusate volume, (4) drug, (5) dosage, (6) timing of drug delivery, and (7) total perfusion time. Statistical analysis was performed using nonparametric tests.

RESULTS

Response rates for ASPSM members (n = 45) and non-ASPSM members (n = 24) were 89 and 33 %, respectively. Of the responders from ASPSM members, 95 % agreed with implementing the proposal. Majority of the surgical oncologists favored the closed method of delivery with a standardized dual dose of mitomycin for a 90-min chemoperfusion for patients undergoing cytoreductive surgery for peritoneal carcinomatosis of colorectal origin.

CONCLUSIONS

This recommendation on a standardized delivery of HIPEC in patients with colorectal cancer represents an important first step in enhancing research in this field. Studies directed at maximizing the efficacy of each of the seven key elements will need to follow.

Effects of cis arrangement of chromatin insulators on enhancer-blocking activity

Chromatin boundary elements or insulators are believed to regulate gene activity in complex genetic loci by organizing specialized chromatin structures. Here, we report that the enhancer-blocking activity of the Drosophila suHw insulator is sensitive to insulator copy number and position. Two tandem copies of suHw were ineffective in blocking various enhancers from a downstream promoter. Moreover, an enhancer was blocked more effectively from a promoter by two flanking suHw insulators than by a single intervening one. Thus, insulators may modulate enhancer-promoter interactions by interacting with each other and facilitating the formation of chromatin loop domains.

An atlas of aromatase mRNA expression in the zebra finch brain

Neural conversion of androgen to estrogen by aromatase is an important step in the development and expression of masculine behavior in mammals and birds. In contrast to the low telencephalic levels of aromatase in adult mammals and nonsongbirds, the zebra finch telencephalon possesses high aromatase activity. This study maps, by in situ hybridization, cells that express aromatase mRNA in the adult zebra finch telencephalon, diencephalon, midbrain, and pons. High aromatase mRNA expression was observed in the caudal neostriatum, limbic archistriatum, and hypothalamus. The hippocampus, parahippocampal area, and hyperstriatum accessorium contained cells expressing moderate amounts of aromatase message. Weakly labeled cells were found in the rostral neostriatum, lobus parolfactorius, and mesencephalic reticular formation. These findings are consistent with aromatase activity measurements of zebra finch tissue and document with anatomical precision both the widespread expression of aromatase mRNA in the brain and novel sites of brain aromatase. This study identifies the caudal neostriatum as a major site of telencephalic aromatase. A previous survey (Gahr et al., 1993: J. Comp. Neurol. 327:112-122) of several avian species found that the presence of estrogen receptors in parts of the caudal neostriatum is unique to songbirds, which are the only birds to possess the elaborated telencephalic song system. Together, these findings suggest that the heightened estrogen synthesis and estrogen sensitivity of the passerine caudal neostriatum may have some functional relation with the telencephalic circuits responsible for song.

Gene amplification of the Menkes (MNK; ATP7A) P-type ATPase gene of CHO cells is associated with copper resistance and enhanced copper efflux

Three copper-resistant variants of cultured Chinese hamster ovary (CHO) cells were isolated and each was shown to accumulate less intracellular copper than the parental cells when grown in copper-supplemented media. The reduced copper accumulation was related to enhanced copper efflux. As cultured cells from patients with Menkes disease (mutations in MNK; ATP7A gene) accumulate copper, probably due to defective copper efflux, we investigated the possible role of the MNK gene in the molecular basis of copper resistance. We found increased MNK mRNA and MNK protein in all three resistant variants. The MNK protein, which has not been previously demonstrated experimentally in mammalian cells, was observed to have an apparent molecular weight of 178 kDa on SDS gels. The degree of increase in MNK mRNA and protein correlated well with the level of copper resistance and extent of copper efflux. By Southern blot and FISH analysis we determined that the molecular basis for overexpression of MNK was genomic amplification of the MNK gene. These data, combined with the clinical and cellular phenotype in Menkes disease, provide strong evidence that the MNK protein is involved in transmembrane copper efflux, and demonstrate a new system of gene amplification in mammalian cells.

Accuracy and clinical relevance of computed tomography scan interpretation of peritoneal cancer index in colorectal cancer peritoneal carcinomatosis: a multi-institutional study

BACKGROUND

Evaluation of peritoneal metastases by computed tomography (CT) scans is challenging and has been reported to be inaccurate.

METHODS

A multi-institutional prospective observational registry study of patients with peritoneal carcinomatosis from colorectal cancer was conducted and a subset analysis was performed to examine peritoneal cancer index (PCI) based on CT and intraoperative exploration.

RESULTS

Fifty-two patients (mean age 52.6 ± 12.4 years) from 16 institutions were included in this study. Inaccuracies of CT-based assessment of lesion sizes were observed in the RUQ (P = 0.004), LLQ (P < 0.0005), RLQ (P = 0.003), distal jejunum (P = 0.004), and distal ileum (P < 0.0005). When CT-PCI was classified based on the extent of carcinomatosis, 17 cases (33%) were underestimations, of which, 11 cases (21%) were upstaged from low to moderate, 4 cases (8%) were upstaged from low to severe, and 2 cases (4%) were upstaged from moderate to severe. Relevant clinical discordance where an upstage occurred to severe carcinomatosis constituted a true inaccuracy and was observed in six cases (12%).

CONCLUSIONS

The actual clinical impact of inaccuracies of CT-PCI was modest. CT-PCI will remain as a mandatory imaging tool and may be supplemented with other tools including positron emission tomography scan or diagnostic laparoscopy, in the patient selection for cytoreductive surgery and hyperthermic intraperitoneal chemotherapy.

Nanometer-size alpha-PbO(2)-type TiO(2) in garnet: A thermobarometer for ultrahigh-pressure metamorphism

A high-pressure phase of titanium dioxide (TiO(2)) with an alpha-PbO(2)-type structure has been identified in garnet of diamondiferous quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany. Analytical electron microscopy indicates that this alpha-PbO(2)-type TiO(2) occurred as an epitaxial nanometer-thick slab between twinned rutile bicrystals. Given a V-shaped curve for the equilibrium phase boundary of alpha-PbO(2)-type TiO(2) to rutile, the stabilization pressure of alpha-PbO(2)-type TiO(2) should be 4 to 5 gigapascals at 900 degrees to 1000 degrees C. This suggests a burial of continental crustal rocks to depths of at least 130 kilometers. The alpha-PbO(2)-type TiO(2) may be a useful pressure and temperature indicator in the diamond stability field.

Differential effects of isoflavones, from Astragalus membranaceus and Pueraria thomsonii, on the activation of PPARalpha, PPARgamma, and adipocyte differentiation in vitro

Compounds that target the peroxisome proliferator-activated receptors PPARalpha and PPARgamma are used to correct dyslipidemia and to restore glycemic balance, respectively. Because the majority of diabetic patients suffer from atherogenic lipid abnormalities, in addition to insulin resistance, ligands are required that can activate both PPARalpha and PPARgamma. In this study, we used chimeric PPARalpha/gamma reporter-gene bioassays to screen herbal extracts with purported antidiabetic properties. Extracts of Astragalus membranaceus and Pueraria thomsonii significantly activated PPARalpha and PPARgamma. Bioassay-guided fractionation resulted in the isolation of the isoflavones, formononetin, and calycosin from Astragalus membranaceus, and daidzein from Pueraria thomsonii as the PPAR-activating compounds. We investigated the effects of these and 2 common isoflavones, genistein and biochanin A, using chimeric and full-length PPAR constructs in vitro. Biochanin A and formononectin were potent activators of both PPAR receptors (EC50 = 1-4 micromol/L) with PPARalpha/PPARgamma activity ratios of 1:3 in the chimeric and almost 1:1 in the full-length assay, comparable to those observed for synthetic dual PPAR-activating compounds under pharmaceutical development. There was a subtle hierarchy of PPARalpha/gamma activities, indicating that biochanin A, formononetin, and genistein were more potent than calycosin and daidzein in chimeric as well as full-length receptor assays. At low doses, only biochanin A and formononetin, but not genistein, calycosin, or daidzein, activated PPARgamma-driven reporter-gene activity and induced differentiation of 3T3-L1 preadipocytes. Our data suggest the potential value of isoflavones, especially biochanin A and their parent botanicals, as antidiabetic agents and for use in regulating lipid metabolism.

Acid resistance of enamel subsurface lesions remineralized by a sugar-free chewing gum containing casein phosphopeptide-amorphous calcium phosphate

The aim of this clinical study was to investigate the acid resistance of enamel lesions remineralized in situ by a sugar-free chewing gum containing casein phosphopeptide-amorphous calcium phosphate nanocomplexes (CPP-ACP: Recaldent). The study utilized a double-blind, randomized, crossover design with two treatments: (i) sugar-free gum containing 18.8 mg of CPP-ACP, and (ii) sugar-free gum not containing CPP-ACP as control. Subjects wore removable palatal appliances with insets of human enamel containing demineralized subsurface lesions and chewed the gum for 20 min 4 times per day for 14 days. After each treatment the enamel slabs were removed and half of each lesion challenged with acid in vitro for 8 or 16 h. The level of remineralization was determined using microradiography. The gum containing CPP-ACP produced approximately twice the level of remineralization as the control sugar-free gum. The 8- and 16-hour acid challenge of the lesions remineralized with the control gum resulted in 65.4 and 88.0% reductions, respectively, of deposited mineral, while for the CPP-ACP-remineralized lesions the corresponding reductions were 30.5 and 41.8%. The acid challenge after in situ remineralization for both control and CPP-ACP-treated lesions resulted in demineralization underneath the remineralized zone, indicating that the remineralized mineral was more resistant to subsequent acid challenge. The results show that sugar-free gum containing CPP-ACP is superior to an equivalent gum not containing CPP-ACP in remineralization of enamel subsurface lesions in situ with mineral that is more resistant to subsequent acid challenge.

Isolation and characterization of a zebra finch aromatase cDNA: in situ hybridization reveals high aromatase expression in brain

The brain regions controlling song are much larger in male than in female zebra finches. This sex difference is thought to arise developmentally when the male's brain is exposed to higher levels of estrogen. The synthesis of estrogen from androgen is catalyzed by aromatase, a key enzyme implicated in song development in the zebra finch. To study the role of estrogen synthesis in the organization of brain regions responsible for song, a cDNA encoding aromatase was isolated from a zebra finch ovarian cDNA library. The 3188 bp cDNA contains a 1527 bp open reading frame with 5' and 3' untranslated regions of 116 bp and 1545 bp, respectively. The deduced polypeptide is 509 amino acids in length, and is highly homologous to aromatases reported for chicken (92%), human (72%), mouse (70%), rat (69%) and trout (53%). Northern blot analysis revealed 5.4 kb, 4.8 kb and 3.2 kb aromatase mRNAs in brain and ovary. In situ hybridization histochemistry revealed the expression of aromatase mRNA in ovarian thecal cells of some, but not all, follicles, suggesting that aromatase gene expression is regulated during follicular maturation. In the adult brain, the distribution of aromatase mRNA was surprisingly widespread, and included the preoptic area, hypothalamus, hippocampus and neostriatum. By contrast, little aromatase mRNA expression was noted in the song nuclei (HVC, RA, area X). This study, the first description of aromatase mRNA expression by in situ hybridization in the brain of any species, identifies a surprisingly large number of cells that express aromatase mRNA in the zebra finch telencephalon. This pattern may be a unique feature of all songbirds.

Drosophila neuropeptide F mediates integration of chemosensory stimulation and conditioning of the nervous system by food

The conserved neuropeptide Y (NPY) signaling pathway has been strongly implicated in the stimulation of food uptake in vertebrates as well as in the regulation of food conditioned foraging behaviors of Caenorhabditis elegans. Using in situ RNA hybridization and immunocytochemistry, we report the neuronal network of Drosophila neuropeptide F (dNPF), a human NPY homologue, in the larval central nervous system and its food-dependent modifications. We provide indications that gustatory stimulation by sugar, but not its ingestion or metabolism, is sufficient to trigger long-term, dose-dependent alterations of the dNPF neuronal circuit through both dnpf activation and increased synaptic transmission. Our results strongly suggest that the dNPF neuronal circuit is an integral part of the sensory system that mediates food signaling, providing the neural basis for understanding how invertebrate NPY regulates food response.

Remineralization of enamel subsurface lesions in situ by sugar-free lozenges containing casein phosphopeptideamorphous calcium phosphate

BACKGROUND

The anticariogenic potential of casein phosphopeptide-amorphous calcium phosphate nanocomplexes (CPP-ACP) has been demonstrated using laboratory, animal and human in situ caries models. The aim of this study was to determine the effect of CPP-ACP incorporation into a sugar-free lozenge (pressed mint tablet) on enamel remineralization in a human in situ model.

METHODS

The study utilized a double-blind, randomized, cross-over design with four treatments: (i) a lozenge containing 56.4mg (3 per cent w/w) CPP-ACP; (ii) a lozenge containing 18.8mg (1 per cent w/w) CPP-ACP; (iii) a lozenge not containing CPP-ACP; and (iv) a no lozenge nil-treatment control. Ten subjects wore removable palatal appliances with four, human-enamel, half-slab insets containing subsurface lesions. Lozenges were consumed, without chewing, four times per day for 14 days duration. After each treatment period the enamel slabs were removed, paired with their respective demineralized control, embedded, sectioned and subjected to microradiography and computer-assisted densitometric image analysis to determine the level of remineralization.

RESULTS

The incorporation of CPP-ACP into the lozenge significantly increased enamel subsurface lesion remineralization with 18.8 and 56.4mg of CPP-ACP increasing remineralization by 78 and 176 per cent respectively, relative to the control sugarfree lozenge.

CONCLUSION

This study demonstrates that lozenges are a suitable vehicle for the delivery of CPP-ACP to promote enamel remineralization.

Effect of base pair mismatches on recombination via the RecBCD pathway

The effect of base pair mismatches on recombination via the RecBCD pathway was studied in mutS and wild-type Escherichia coli, using substrates that contain single or multiple mismatches. Recombination between homologous DNA inserts in lambda phage and pBR322-derived plasmids forms phage-plasmid cointegrates that result from an odd numbers of crossovers. In the mutS host, when the sequence homology of a pair of 405 bp substrates decreased from 100% to 89%, the recombinant frequency decreased by about 9-fold, while in the wild-type host the decrease was about 240-fold. These results suggest that multiple mismatches can reduce recombinant frequencies by impeding the mechanism of recombination itself, and by provoking mismatch repair. Single mismatches in 31 bp substrates caused reductions in recombinant frequencies of 2- or 12-fold, depending on the location of the mismatch. However, unlike the reduction by multiple mismatches, the reduction of the recombinant frequencies by single mismatches was the same in both mutS and wild-type hosts. Thus a single mismatch is sufficient to impede recombination, and mismatch repair seems unable to act on single mismatches in very short homologies during recombination.

Nucleotide sequence and genomic organization of rice tungro spherical virus

Rice tungro disease is caused by a combination of two viruses: rice tungro spherical virus (RTSV) and rice tungro bacilliform virus (Jones et al. (1991) J. Gen. Virol. 72, 757-761.). The genome of RTSV is a single-stranded polyadenylated RNA. We present here the 12,433-nucleotide complete sequence of RTSV genomic RNA and its deduced coding regions. This sequence contains a large open reading frame (ORF) which initiates following a 514-nucleotide 5' leader sequence and is capable of encoding a viral polyprotein of 390.3 kDa. Two viral subgenomic RNAs of ca. 1.2 and 1.4 kb, respectively, were detected in RTSV-infected leaf tissues and mapped by S1 nuclease protection assay. These RNAs were determined to be congruent with the genomic RNA sequence proximal to the 3' terminus and could contain up to two small ORFs in their 5' to 3' orientation. There are at least three capsid protein subunit cistrons near the N-terminus of the large ORF. A computer-aided search of the C-terminal half of the large ORF revealed conserved protein sequence motifs for a viral RNA polymerase, proteinase, and a putative NTP-binding protein. These sequence motifs are arranged in a manner that resembles those of picorna-like viruses. Taken together, these data indicate that RTSV is a distinct type of positive-strand RNA virus. The evolutionary relationships between RTSV and other picorna-like plant viruses are discussed.