Childhood lead poisoning in China

In China, comprehensive epidemiological data relating to the prevalence of childhood lead poisoning are not available. However, existing data suggest that this disease may be widely pervasive as a result of rapid industrialization and the use of leaded gasoline. Seventeen publications have reported elevated blood lead levels in children from different areas of the country. Children residing in industrial and busy traffic areas had average blood lead levels(BPb) of 21.8-67.9 mu g/dl. The percentages of BPb values above 10 mu g/dl, which is the definition of lead poisoning in children, ranged from 64.9% to 99.5%. Even for 'unexposed' children, about 50% of them had BPb values above 10 mu g/dl. Furthermore, several retrospective pilot studies were conducted in Shanghai, Shenyang, Fuzhou and Beijing to evaluate the health effects of lead at current degree of exposure. The link between low-level lead exposure and deficits in IQ, neurobehavioral development and physical growth is remarkably consistent without exception. In summary, the harmful health effects of childhood lead poisoning in limited studies of exposed and 'unexposed' children demonstrate that this totally preventable disease warrants considerable public health attention in China.

[A study on the effect of emodin on smooth muscle cell proliferation]

By using smooth muscle cell (SMC) culture in vitro and H3-TdR incorporation technique, we tested the effect of Emodin on SMC proliferation in three groups: (1) Normal rabbit iliac artery, (2) atherosclerotic rabbit iliac artery, (3) atherosclerotic rabbit iliac artery after PTA. These data indicated: Emodin has antiproliferative effect on SMC, which is dose dependent; it blocks the transition of SMC cycle from G0 to S. In PTA group it exerts a more significant proliferative effect than in the normal one. This is a the first report of Emodin's effect on SMC proliferation, it implies that the drug may be used clinically to prevent restenosis after PTCA.

The Myxococcus xanthus rfbABC operon encodes an ATP-binding cassette transporter homolog required for O-antigen biosynthesis and multicellular development

A wild-type sasA locus is critical for Myxococcus xanthus multicellular development. Mutations in the sasA locus cause defective fruiting body formation, reduce sporulation, and restore developmental expression of the early A-signal-dependent gene 4521 in the absence of A signal. The wild-type sasA locus has been located on a 14-kb cloned fragment of the M. xanthus chromosome. The nucleotide sequence of a 7-kb region containing the complete sasA locus was determined. Three open reading frames encoded by the genes, designated rfbA, B and C were identified. The deduced amino acid sequences of rfbA and rfbB show identity to the integral membrane domains and ATPase domains, respectively, of the ATP-binding cassette (ABC) transporter family. The highest identities are to a set of predicted ABC transporters required for the biosynthesis of lipopolysaccharide O-antigen in certain gram-negative bacteria. The rfbC gene encodes a predicted protein of 1,276 amino acids. This predicted protein contains a region of 358 amino acids that is 33.8% identical to the Yersinia enterocolitica O3 rfbH gene product, which is also required for O-antigen biosynthesis. Immunoblot analysis revealed that the sasA1 mutant, which was found to encode a nonsense codon in the beginning of rfbA, produced less O-antigen than sasA+ strains. These data indicate that the sasA locus is required for the biosynthesis of O-antigen and, when mutated, results in A-signal-independent expression of 4521.

[Clinical study on the effect of TCM treatment in decreasing frequency of peritoneal dialysis]

Traditional Chinese herbal medicine was used in combination with peritoneal dialysis (PD) in order to improve the renal function and reduce the frequency of PD. The results indicated that, after 3 months of PD+TCM, the serum BUN, creatinine and mean arterial pressure of therapeutic group lowered and the hemoglobin elevated as compared with those after 1 month of PD (P < 0.01), the difference of above-mentioned criteria between PD+TCM group and less frequent PD (LEPD) group was significant too, while there was no obvious difference in comparison of the PD+TCM group with regular PD group (P > 0.05). The effective rate and the edema cure rate of TCM+PD group were superior to the LFPD group, but had no evident difference as compared with the regular PD group. The results revealed that PD combined with TCM treatment might reduce the frequency of PD for the uremia patient deserved long-term PD therapy.

Tumor necrosis factor promotes phosphorylation and binding of insulin receptor substrate 1 to phosphatidylinositol 3-kinase in 3T3-L1 adipocytes

Chronic incubation of 3T3-L1 adipocytes with tumor necrosis factor (TNF) induces a state of insulin resistance characterized by a diminished ability of insulin to induce phosphorylation of the beta subunit of its own receptor and insulin receptor substrate 1 (IRS-1). When adipocytes are briefly pretreated with TNF and then stimulated with insulin, tyrosine phosphorylation of IRS-1 increases above the level induced by insulin alone. By itself, TNF induces the time-dependent tyrosine phosphorylation of proteins in 3T3-L1 adipocytes. Among these is IRS-1, a docking protein with tyrosine phosphorylation sites that bind cytoplasmic signaling molecules that contain Src homology 2 (SH2) domains. TNF stimulation of 3T3-L1 adipocytes also promotes the association of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase) with IRS-1 and also its tyrosine phosphorylation. In murine 3T3-L1 adipocytes, IRS-1 and PI 3-kinase phosphorylation and the association of these proteins are promoted by murine TNF, which interacts with the type 1 and type 2 TNF receptors. Human TNF, which binds to the murine type 1 TNF receptor selectively, also promotes IRS-1 phosphorylation and binding of IRS-1 to PI 3-kinase. This is the first demonstration that a member of the TNF/nerve growth factor receptor superfamily can use an IRS-1 signaling system as a component of its cellular response and provides a mechanism through which TNF receptors may engage downstream elements in signaling pathways.

Protection by chlorophyllin and indole-3-carbinol against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced DNA adducts and colonic aberrant crypts in the F344 rat

The most abundant heterocyclic amine in fried ground beef, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), induces colon carcinomas in the male F344 rat. The potential chemopreventive effects of two compounds, namely, the 'interceptor molecule' chlorophyllin (CHL) and a modulator of carcinogen activation, indole-3-carbinol (I3C), were examined in a PhIP colon carcinogenesis model. During weeks 3 and 4 of a 16-week study, F344 rats were given PhIP by oral gavage (50 mg/kg body weight, alternating days). Inhibitors were given either before and during PhIP exposure, after PhIP treatment, or continuously for 16 weeks. Treatment of rats with 0.1% CHL in the drinking water inhibited the formation of aberrant crypt foci (ACF) with > or = 4 crypts/focus, from 1.4 +/- 0.9 in controls to 0.7 +/- 0.3 following post-initiation CHL treatment, and to 0.3 +/- 0.5 in rats given CHL continuously for 16 weeks (mean +/- SD; P < 0.05). Potent inhibition of PhIP-induced ACF occurred following initiation, post-initiation and continuous exposure to 0.1% I3C in the diet. Using the initiation protocol, I3C completely inhibited the induction of the ACF with > or = 4 crypts/focus. In a separate experiment, rats were given 0.1% CHL in the drinking water or 0.1% I3C in the diet for 4 weeks. At the end of week 3, animals received 50 mg PhIP/kg body weight by single oral gavage and PhIP-DNA adducts were quantified in the colon and several other tissues by 32P-postlabeling analysis. In addition, the urine and feces were collected to study the effects of inhibitor treatment on PhIP metabolism and excretion. No significant protection against PhIP-DNA adduct formation was detected in the colon after CHL dosing, nor was a consistent pattern of CHL inhibition observed in several other tissues. In contrast, I3C shifted the time-course of adducts in all tissue; compared with controls, adducts were increased by I3C at 6 h but decreased at 24 h and 7 days following PhIP treatment. Analysis of urine metabolites revealed that I3C and CHL decreased the excretion of unmetabolized PhIP and 4'-hydroxy- << PhIP but increased the phase II detoxification products PhIP-4'-O-glucuronide and PhIP-4'- sulfate. In the feces, the elimination of unmetabolized PhIP was increased from 54.5% in controls to approximately 67% in CHL-treated rats and decreased to 28% in rats given I3C (P < 0.05). These results support a protective role for CHL and I3C against PhIP-induced colon carcinogenesis through mechanisms which alter the uptake or metabolism of the carcinogen, and by suppression in the post-initiation phase.

Paranodal structural abnormalities in rat CNS myelin developing in vivo in the presence of implanted O1 hybridoma cells

O1 hybridoma cells, which produce a monoclonal IgM antigalactocerebroside, were implanted into the spinal cords of immature and mature rats and the cords examined 5-24 days later. Study of the younger group, in which myelin was developing at the time of implantation, revealed examples of abnormal myelin sheaths in which the repeat period was markedly increased. The paranodal regions of these abnormal sheaths were superficially normal in configuration; i.e. myelin lamellae terminated one by one as 'terminal loops' that indented the axolemma and formed normal axoglial junctions displaying periodic 'transverse bands'. Neighbouring terminal loops are normally joined by tight junctions that block passage of tracers from the paranodal periaxonal space into the compact myelin, as seen after implantation of a control hybridoma. In the abnormal sheaths that developed after O1 implantation, in contrast, terminal loops were usually widely separated from each other. As a result, multiple pathways from the paranodal periaxonal space into the myelin sheath remained patent, forming potential routes for shunting nodal action currents. This subtle abnormality could thus compromise conduction, even though the sheaths might appear to be normally myelinated at the histological level. Equivalent abnormalities in human neurological diseases, including multiple sclerosis and paraproteinemic neuropathies, could underlie functional loss in the absence of frank demyelination.

Use of 'random-atom" phasing models to determine macromolecular heavy-atom replacement positions

A procedure is described by which the phase-invariant translation function may be used to provide starting set phases for the minimal function that are significantly better than those generated from random-atom coordinates. Applications to determine the heavy-atom positions for single isomorphous replacement data from macromolecular structures are very encouraging. In the case of chiral space groups, e.g. P4(1)2(1)2 versus P4(3)2(1)2, unlike Patterson functions, these methods provide the correct enantiomorph coordinates for the heavy-atom sites for whichever space group is chosen.

Inhibition by chlorophyllin of 2-amino-3-methylimidazo-[4,5-f]quinoline-induced tumorigenesis in the male F344 rat

This report describes a 1-year carcinogenicity bioassay in which male F344 rats received 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) by gavage 2-3 times per week throughout the first 35 weeks of study, while 0.1% sodium/copper chlorophyllin (CHL) was given concomitantly in the drinking water. The carcinogen dose was calculated to provide an average exposure of 4.2 mg IQ/rat per day, equivalent to that reported in previous carcinogenicity study in which rats were given 0.03% IQ in the diet. Adjusted for length of follow-up, inhibition was highly significant for total tumor burden (P < 0.001), and for specific sites was significant in the small intestine and Zymbal's gland (P < or = 0.1), and in the liver (P < 0.01). In rats given CHL, the first onset of tumors in the Zymbal's gland was delayed from week 20 to 36, but was shortened from week 31 to 26 in the skin (P < 0.05). These results support a chemopreventive role for CHL in several of the major target organs for IQ tumorigenesis in the rat, but raise concerns over possible deleterious effects in the skin.

TDSIR phasing: direct use of phase-invariant distributions in macromolecular crystallography

A new strategy for employing three phase triples invariant estimates from Hauptman's single isomorphous replacement (SIR) and anomalous dispersion (SAS) joint probability distribution formulae is outlined which produces a single unique phase-invariant solution in the case where the positions of the heavy-atom scatterers is known. A similar but non-identical result is obtained for the phase invariants of a structure for which a molecular-replacement solution has been obtained. It is important to note that the values of the individual native/derivative phases can be determined directly from the probability distribution formulae without having to utilize the phase-invariant estimates in an active way. Elimination of the multisolution aspect of utilizing phase-invariant estimates should have important repercussions with regard to phasing macromolecular sets of derivatized data. Trial calculations based on experimentally measured 2.5 A data for three derivatives of cytochrome c550 are encouraging. The average of the three SIR maps resolves a number of structural ambiguities seen in the published multiple isomorphous replacement (MIR) map obtained from eight derivatives.

Prunus necrotic ringspot ilarvirus: nucleotide sequence of RNA3 and the relationship to other ilarviruses based on coat protein comparison

The RNA3 of prunus necrotic ringspot ilarvirus (PNRSV) has been cloned and its entire sequence determined. The RNA3 consists of 1943 nucleotides (nt) and possesses two large open reading frames (ORFs) separated by an intergenic region of 74 nt. The 5' proximal ORF is 855 nt in length and codes for a protein of molecular mass 31.4 kDa which has homologies with the putative movement protein of other members of the Bromoviridae. The 3' proximal ORF of 675 nt is the cistron for the coat protein (CP) and has a predicted molecular mass of 24.9 kDa. The sequence of the 3' non-coding region (NCR) of PNRSV RNA3 showed a high degree of similarity with those of tobacco streak virus (TSV), prune dwarf virus (PDV), apple mosaic virus (ApMV) and also alfalfa mosaic virus (AIMV). In addition it contained potential stem-loop structures with interspersed AUGC motifs characteristic for ilar- and alfamoviruses. This conserved primary and secondary structure in all 3' NCRs may be responsible for the interaction with homologous and heterologous CPs and subsequent activation of genome replication. The CP gene of an ApMV isolate (ApMV-G) of 657 nt has also been cloned and sequenced. Although ApMV and PNRSV have a distant serological relationship, the deduced amino acid sequences of their CPs have an identity of only 51.8%. The N termini of PNRSV and ApMV CPs have in common a zinc-finger motif and the potential to form an amphipathic helix.

Differential regulation of angiotensin II receptor subtypes in rat kidney by low dietary sodium

This study was designed to determine whether expression of renal messenger RNA (mRNA) encoding the two known angiotensin II type 1 (AT1) receptor subtypes (AT1A and AT1B) can be regulated by dietary sodium. Seven-week-old male Wistar rats were fed a low-sodium diet (0.07%, n = 9) or a normal-sodium diet (0.5%, n = 9 [control]) for 14 days. A rat AT1 complementary DNA (cDNA) probe, which hybridizes to mRNA encoding both the AT1A and AT1B receptor subtypes, and cDNA probes, which are selective for AT1A or AT1B mRNA, were used in Northern blot or in situ hybridization analysis. By use of Northern blot analysis, renal mRNA levels for the AT1 and AT1A receptors in rats fed a low-sodium diet were found to be increased twofold (P < .05) compared with control. Because renal AT1B mRNA content was not detected by Northern blot analysis, quantitative image analysis of in situ hybridization with a digoxigenin-labeled cRNA probe made from AT1B cDNA was used. In situ hybridization analysis indicated that AT1B mRNA was expressed in the proximal and collecting tubules of the kidney in rats fed a normal-sodium diet. The low-sodium diet significantly decreased the percent positive staining area of AT1B mRNA in the renal cortex (5.51 +/- 0.77% versus 2.73 +/- 0.35%, P < .05) and medulla (4.76 +/- 0.70% versus 2.01 +/- 0.43%, P < .05) compared with the control diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular endothelial cell growth factor promotes tyrosine phosphorylation of mediators of signal transduction that contain SH2 domains. Association with endothelial cell proliferation

Vascular endothelial cell growth factor (VEGF), an endothelial cell-specific mitogen that plays an important role in angiogenesis, promotes the tyrosine phosphorylation of at least 11 proteins in bovine aortic endothelial cells (BAEC). Proteins immunoprecipitated from lysates of control- and VEGF-stimulated BAEC with antisera to phospholipase C-gamma (PLC-gamma) were fractionated by SDS-polyacrylamide gel electrophoresis and transferred to Immobilon-P. Evaluation of the Western blots with antisera to phosphotyrosine demonstrated that PLC-gamma and two proteins (100 and 85 kDa) that associate with PLC-gamma were phosphorylated in response to VEGF. By using antisera specific to other mediators of signal transduction that contain SH2 domains for immunoprecipitation, it was demonstrated that VEGF promotes phosphorylation of phosphatidylinositol 3-kinase, Ras GTPase activating protein (GAP), and the oncogenic adaptor protein NcK. Proteins of M(r) consistent with the VEGF receptors Flt-1 and Flk-1/KDR were also tyrosine phosphorylated in stimulated cells. Tyrosine-phosphorylated Nck, PLC-gamma, and two GAP-associated proteins, p190 and p62, were in GAP immunoprecipitates of VEGF-stimulated BAEC, and tyrosine-phosphorylated NcK was in phosphatidylinositol 3-kinase immunoprecipitates. These observations suggest that VEGF promotes formation of multimeric aggregates of VEGF receptors with proteins that contain SH2 domains and activate various signaling pathways. VEGF-promoted proliferation of endothelial cells and tyrosine phosphorylation of SH2 domain containing signaling molecules were inhibited by the tyrosine kinase inhibitor genistein.

Creation of a high cytotoxic active human tumor necrosis factor having the truncated and more basic amino terminus

In order to define the structure-functional relationship of tumor necrosis factor(TNF), a mutant TNF gene was created by site-specific mutagenesis based on the PCR technique. This gene was highly expressed in E.coli cells. The amount of the recombinant protein was up to about 80% of the total cellular proteins. Through one-step ion exchange chromatography, the mutant TNF could be purified to homogeneity. This mutein showed the molecular weight of a dimer but not a trimer. It bears the features of truncated amino terminus and increase of the basicity of amino terminal residues. Compared with the wild type TNF, the specific activity of mutant TNF was increased by fourfold.

Identification of a protein with homology to hsp90 that binds the type 1 tumor necrosis factor receptor

The yeast-based two hybrid has been used to identify a novel protein that binds to the intracellular domain of the type 1 receptor for tumor necrosis factor (TNFR-1IC). The TNF receptor-associated protein, TRAP-1, shows strong homology to members of the 90-kDa family of heat shock proteins. After in vitro transcription/translation and 35S labeling, TRAP-1 was precipitated using a fusion protein consisting of glutathione S-transferase and TNFR-1IC, showing that the two proteins directly interact. The ability of deletion mutants of TNFR-1 to interact with TRAP-1 was tested using the two hybrid system. This showed that the amino acid sequences that mediate binding are diffusely distributed outside of the domain in the C terminus of TNFR-1IC that signals cytotoxicity. The 2.4-kilobase TRAP-1 mRNA was variably expressed in skeletal muscle, liver, heart, brain, kidney, pancreas, lung, and placenta. TRAP-1 mRNA was also detected in each of eight different transformed cell lines. Identification of TRAP-1 may be an important step toward defining how TNFR-1, which does not contain protein tyrosine kinase activity, transmits its message to signal transduction pathways.

[Determination of psoralen and isopsoralen in tincture of fructus Psoraleae by HPLC]

A reversed-phase HPLC method was described for the determination of psoralen and isopsoralen in tincture of Fructus Psoraleae. After adding the internal standard and diluting the sample to a definite volume, the sample was injected and analysed. The RSDs were within 2% and the minimum working concentrations below 1 microgram/ml; the average recoveries of psoralen and isopsoralen 102.8% and 99.5% respectively and the linear ranges of psoralen and isopsoralen 12-200 micrograms/ml and 13-210 micrograms/ml (r = 0.999) respectively.

Enroute toward a computer based patient record: the ACIS project

The clinical arm of the University of Utah operates a 400 bed general hospital and 30 specialty and subspecialty clinics and with the advent of managed care will soon be linked to a much wider network of health care facilities throughout the state. Each of these patient care facilities maintains its own patient record. To provide common access to data on any patient needed to provide continuity to the care process where ever it occurs, the institution has embarked on the development of a completely electronic patient record. In this paper we will describe the route we have taken to achieve this goal in hopes of providing some sign posts along the way for others seeking the same destination.

Inhibition of CNS myelin development in vivo by implantation of anti-GalC hybridoma cells

Implantation of hybridoma cells that secrete a monoclonal antigalactocerebroside into the dorsal columns of < or = 9-day-old rat spinal cord results in failure of development of dorsal column myelin in the vicinity of the implant. Clusters of apparently undamaged amyelinated axons remain among the hybridoma cells. Ventral myelin is unaffected. These in vivo results support antibody-mediated inhibition of myelin formation as a potential mechanism underlying failure of remyelination in multiple sclerosis.

Mechanisms of the in vitro antimutagenic action of chlorophyllin against benzo[a]pyrene: studies of enzyme inhibition, molecular complex formation and degradation of the ultimate carcinogen

Mechanisms of the antimutagenic action of chlorophyllin (CHL) towards benzo[a]pyrene (BP) were studied in vitro. In the Salmonella assay, CHL inhibited the mutagenic activity of BP in the presence of an S9 activation system and was particularly effective against the direct-acting ultimate carcinogen, benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE). Spectral studies indicated that the time-dependent hydrolysis of BPDE to tetrols was augmented in the presence of CHL concentrations on the order of 5 microM. Dose-related inhibition of several cytochrome P450-dependent enzyme activities was observed upon addition of CHL to in vitro incubations. Spectral changes for the interaction between CHL and cytochrome P450 indicated that CHL does not bind to the active site of the enzyme, but exerts its inhibitory effect indirectly. This was achieved by inhibiting NADPH-cytochrome P450 reductase (Ki approximately 120 microM with cytochrome c as substrate), and did not involve lowering of the effective substrate concentration by complex formation with the procarcinogen. It is concluded that the in vitro antimutagenic activity of CHL towards BP involves accelerated degradation of the ultimate carcinogen, with inhibition of carcinogen activation occurring only at high CHL concentrations. The latter mechanism is unlikely to occur in vivo following p.o. administration due to the limited uptake of CHL from the gut, but tissue concentrations may be sufficiently high to cause degradation of BPDE.

Effects of cerebellar lesions on tonic seizures, tremor and lifespan in myelin-deficient rats

In common with other dysmyelinating mutants, the myelin-deficient rat displays an action tremor and tonic seizures culminating in the death of the animals at approximately 23-26 days. We find that deep lesions of the cerebellar vermis alleviate the manifestations of the myelin deficiency significantly. Such lesions introduced at 20 days or later eliminate both tremor and seizures for periods up to 10 days. Lifespan is prolonged to nearly 30 days, on average, and to 35 days in some cases. Shallow lesions of the vermis or lateral lobe lesions have relatively little effect. Based on these observations we suggest that the cerebellum contributes not only to the action tremor but also to the tonic seizures characteristic of central myelin deficiency. Spontaneous activity originating in myelin-deficient fiber tracts may be carried to the cerebellum and processed there to produce a highly amplified and/or synchronized output to broad areas of the neuraxis. Deep lesions of the vermis presumably interfere with cerebellar output and compromise the cerebellar contribution to the seizures. Tonic seizures and other 'paroxysmal attacks' also occur commonly in human demyelinating diseases including multiple sclerosis [11]. Manipulation of cerebellar output offers a potential approach to the control of such spontaneous activity.

Inhibition of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-DNA binding in rats given chlorophyllin: dose-response and time-course studies in the liver and colon

Chlorophyllin (CHL), a water-soluble salt of chlorophyll, has been shown to inhibit 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-DNA binding in vitro by a mechanism that involves molecular complex formation with the carcinogen. Based on this mechanism, rats weighing approximately 160 g were given 10 mumol (100 microCi) IQ or IQ plus 20, 200 or 1000 mumol CHL by single oral gavage. Six hours after dosing, CHL produced dose-related inhibition of IQ-DNA binding in three target organs for carcinogenesis, namely, the small intestine, large intestine and liver. In the latter tissues, > 80% inhibition was detected at the highest CHL dose tested, while IQ-DNA binding levels in the small intestine were reduced to below the limit of detection. Co-injection of CHL and IQ into ligated sections of small intestine inhibited the absorption of IQ in a dose-related manner, such that the highest dose of CHL almost completely blocked carcinogen uptake. Finally, rats given CHL by gavage at time 0 h were treated with IQ at various times thereafter and IQ-DNA binding levels were measured in the liver and colon 6 h after carcinogen exposure. Compared with controls given IQ alone, CHL inhibited binding by 79% at 0 h and 40% at 1 h in the liver, and by 63% at 0 h, 38% at 1 h and 58% at 24 h in the colon (P < 0.05 by Student's t-test). These results support a mechanism involving complex formation between CHL and IQ in vivo and suggest that the inhibitor is likely to be most effective when ingested simultaneously with the carcinogen.

Myelin formation by mouse glia in myelin-deficient rats treated with cyclosporine

Previous attempts to generate myelin in the myelin-deficient rat spinal cord by transplanting mouse glia were not successful. In order to determine whether this result was due to graft rejection or to interspecies mismatch of cellular or molecular components at the axoglial junction, we have repeated the experiment in cyclosporine-treated rats. Our results show that in the immunosuppressed hosts, foetal glial xenografts form an abundance of myelin within the dorsal columns at or near the injection site about two weeks after the operation. In some cases, myelination extends virtually across the entire width of the dorsal columns. Ultrastructurally, the myelin sheaths are normal in all respects, including the presence of the 'radial component'. The lateral edges of the myelin lamellae form typical paranodal axoglial junctions, some displaying periodic 'transverse bands'. We infer that previous mouse to rat xenograft failures reflect host immune response rather than mismatch of heterologous junctional components. We also compared foetal, early post-natal and adult xenografts. Foetal donor cells, containing an abundance of precursors but virtually no mature oligodendrocytes, are more effective than neonatal donor cells in forming myelin, and after adult grafts, we found no myelin formation. Thus, in xenografts, as in allografts, foetal precursor cells are far more suitable than glia from mature donors in generating significant amounts of myelin.

DNA sequence-selective binding of head-to-tail linked bis-lexitropsins: relation of phasing to cytotoxic potency

A series of polymethylene, -(CH2)n-tether-linked head-to-tail bislexitropsins (n = 1-7) have been synthesized in order to assess the effect on DNA binding of phasing, that arises because of lack of dimensional correspondence between oligopeptides and oligonucleotides. Binding constants to poly(dA-dT), estimated from ethidium displacement, are from 0.55 to 16.66 x 10(8) M-1. Comparable Ka values for calf thymus DNA and for poly(dG-dC) are approximately 10(6) and approximately 10(5) M-1, respectively reflecting the anticipated AT preference. Sequence-selective binding was examined by reflecting the anticipated AT preference. Sequence-selective binding was examined by methylethidium propyl ethylenediamine tetraacetic acid (MPE) complementary strand footprinting on an EcoRI/HindIII restriction fragment of pBR322 DNA with r = 0.08 and 0.32. Ligands bearing N-methylpyrrole dipeptide moieties linked by -(CH2)n, where n = 2, 4 or 6, give evidence of bidentate binding in (AT)n-rich sequences from footprinting at r = 0.32. By contrast, those ligands linked by (CH2)n, where n = 1, 3, 5 or 7, bind in a predominantly monodentate fashion. Cystostatic activity against KB human nasopharyngeal cancer cells has shown enhanced potency, compared with distamycin, for those linked bis-lexitropsins with n = 2, 4 and 6. That the increased potency may be attributed to more effective DNA binding in the latter cases is indicated by the fact that the n = 1, 3, 5 and 7 ligand homologues do not exhibit comparable enhanced cytotoxic potency.