Uptake and activation profile of murine dendritic cells in response to stimulation with functionalized iron oxide nanoparticles

Subunit vaccines typically have better safety profiles than live attenuated or killed whole-cell vaccines, but are often less immunogenic and less efficacious when deployed alone. Thus, immunological adjuvants are frequently formulated with subunit vaccines to improve efficacy. However, few vaccine adjuvants are FDA-approved; and for many adjuvants their mechanisms of action are poorly understood. We previously explored the use of iron oxide (IO) nanoparticles (NPs) in subunit vaccine delivery and show that the IO NPs also possess adjuvant-like qualities, eliminating the need for additional adjuvants in the vaccine formulation. This study further dissects the mode of action of IO NPs as immunological adjuvants by examining the relationship of particle size and uptake on the activation profile of murine bone marrow derived dendritic cells (BMDCs) in response to in vitro stimulation with functionalized IO NPs. Using IO NPs of sizes ranging 5 – 30 nm, we showed by flow cytometry immunophenotyping that only IOs of 20nm and 30nm could induce an activated BMDC subset. The level of NP uptake by BMDCs, as measured by Prussian Blue staining, also varied with particle size, with IO of 5nm being the most efficiently internalized. Intriguingly, the levels of BMDC activation did not correlate with the level of IO NP uptake. We hypothesize only IO NPs taken up via selective endocytic pathways will activate BMDCs. The production of cytokine/chemokines by these BMDCs as further characterizations of the adjuvant-like profiles of IO NPs in relation to particle size and cellular uptake is currently being examined. These studies begin to dissect the mode of action of IO NPs as a self-adjuvanted vaccine delivery system on the innate-adaptive immune interface.

The NIDDK High School Short-Term Research Experience for Underrepresented Persons

Background

Increasing the pipeline of aspiring minority biomedical/health professionals is a crucial component to diversifying the health science workforce. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) created the High School Short-Term Research Experience for Underrepresented Persons (HS-STEP-UP) to provide introductory biomedical/biobehavioral research experiences to promising high school students, who are traditionally underrepresented in the biomedical/biobehavioral sciences. The program reaches out to African American and Lationo/Hispanic students, as well as Native American students and students from the United States Territories.

Methods

HS-STEP-UP provides a stimulating, rigorous 8- to 10-week summer research experience for a national cohort of ~100 high school students each year; the experience is organized through four National Institutes of Health (NIH)-funded coordinating centers. Typically, the program receives about 300 applications a year and about 100 students are accepted. Applicants are reviewed and selected based upon their online application that includes: a high school transcript, list of classes and extracurricular activities, two recommendation letters and a personal statement. The program culminates with a symposium at the NIH where students present their research and attend workshops and seminars.

Results

For the 2017 and 2018 HS-STEP-UP programs, the classes included 193 students; 67% were females and 82% were underrepresented minorities. Forty eight percent of students reported a family income <$37,000/year, and 23% were from first generation college families. Ninety percent were very satisfied or satisfied with their research topic and 94% rated the end of the year symposium at NIH as excellent or very good. Only 65% were very satisfied or satisfied with their mentor matching, and 21% stated they were dissatisfied or very dissatisfied with their mentor. All the students successfully completed their summer research projects and presented their research abstracts at the symposium. All participating seniors reported attending college.

Conclusion

HS-STEP-UP has been highly successful in recruiting traditionally underrepresented students and supporting underrepresented HS students with a rewarding introductory experience to research. Students are overall satisfied with the program, but mentor matching needs more attention. Longer-term follow-up is needed to determine how participating in STEP UP impacts their decisions to participate in the biomedical workforce in the future.

Antibody and T cell responses in reciprocal prime-boost studies with full-length and truncated merozoite surface protein 1-42 vaccines

The P. falciparum Merozoite Surface Protein 1-42 (MSP1-42) is one of the most studied malaria subunit vaccine candidates. The N-terminal fragment of MSP1-42, MSP1-33, is primarily composed of allelic sequences, and has been shown to possess T helper epitopes that influence protective antibody responses toward the C-terminal region, MSP1-19. A truncated MSP1-42 vaccine, Construct 33-I, consisting of exclusively conserved T epitope regions of MSP1-33 expressed in tandem with MSP1-19, was previously shown to be a more effective immunogen than the full-length MSP1-42 vaccine. Here, by way of reciprocal priming/boosting immunization regimens, we studied the immunogenicity of Construct 33-I in the context of recognition by immune responses induced by the full-length native MSP1-42 protein, in order to gauge the effects of pre- and post-exposures to MSP1-42 on vaccine induced responses. Judging by immune responsiveness, antibody and T cell responses, Construct 33-I was effective as the priming antigen followed by full-length MSP1-42 boosting, as well as the boosting antigen following full-length MSP1-42 priming. In particular, Construct 33-I priming elicited the broadest responsiveness in immunized animals subsequently exposed to MSP1-42. Moreover, Construct 33-I, with its conserved MSP1-33 specific T cell epitopes, was equally well recognized by homologous and heterologous allelic forms of MSP1-42. Serum antibodies raised against Construct 33-I efficiently inhibited the growth of parasites carrying the heterologous MSP1-42 allele. These results suggest that Construct 33-I maintains and/or enhances its immunogenicity in an allelic or strain transcending fashion when deployed in populations having prior or subsequent exposures to native MSP1-42s.

Iron oxide nanoparticles as a clinically acceptable delivery platform for a recombinant blood-stage human malaria vaccine

This study explored the novel use of iron oxide (IO) nanoparticles (<20 nm) as a vaccine delivery platform without additional adjuvants. A recombinant malaria vaccine antigen, the merozoite surface protein 1 (rMSP1), was conjugated to IO nanoparticles (rMSP1-IO). Immunizations in outbred mice with rMSP1-IO achieved 100% responsiveness with antibody titers comparable to those obtained with rMSP1 formulated with a clinically acceptable adjuvant, Montanide ISA51 (2.7×10 vs. 1.6×10; respectively). Only rMSP1-1O could induce significant levels (80%) of parasite inhibitory antibodies. The rMSP1-IO was highly stable at 4°C and was amenable to lyophilization, maintaining its antigenicity, immunogenicity, and ability to induce inhibitory antibodies. Further testing in nonhuman primates, Aotus monkeys, also elicited 100% immune responsiveness and high levels of parasite inhibitory antibodies (55-100% inhibition). No apparent local or systemic toxicity was associated with IO immunizations. Murine macrophages and dendritic cells efficiently (>90%) internalized IO nanoparticles, but only the latter were significantly activated, with elevated expression/secretion of CD86, cytokines (IL-6, TNF-α, IL1-b, IFN-γ, and IL-12), and chemokines (CXCL1, CXCL2, CCL2, CCL3, CCL4, and CXCL10). Thus, the IO nanoparticles is a novel, safe, and effective vaccine platform, with built-in adjuvancy, that is highly stable and field deployable for cost-effective vaccine delivery.

The requirement of CD80, CD86, and ICAM-1 on the ability of adjuvant formulations to potentiate antibody responses to a Plasmodium falciparum blood-stage vaccine

Many adjuvants are known to enhance expression of co-stimulatory and adhesion molecules secondarily to the activation of immune cells. Whether interactions via these molecules are obligatory in adjuvants' ability to potentiation vaccine immunogenicity is less clear. We investigated the ability of eight adjuvant formulations to potentiate the immunogenicity of a malaria vaccine in mice deficient in the prominent co-stimulatory molecules, CD80 and CD86; and the adhesion ligand, ICAM-1. While no adjuvants could bypass co-stimulatory requirements, more formulations exhibited dependency for CD86 than for CD80. In CD80 or CD86 KO mice, formulations with the saponin derivative, QS21 could efficiently default to the other B7 molecule. This effect was dominant over other adjuvant constituents. The requirement for ICAM-1 could be readily bypassed using adjuvant formulations containing immunomodulators; whereas this was not the case with emulsion-type adjuvants in which reduction in adjuvanticity was associated with decreases in antigen-specific IFN-gamma responses. These studies may help to guide the formulation of vaccine adjuvants to maintain effectiveness in hosts with altered immunological environment that often result from infections.

Interleukin-6 has differential influence on the ability of adjuvant formulations to potentiate antibody responses to a Plasmodium falciparum blood-stage vaccine

The efficacy of vaccine adjuvants can be influenced by the immunological environment of the host, depending on the mechanism(s) by which they exert their immunopotentiating activities. Interleukin-6 is a pleiotropic cytokine that has a broad range of biological activities on immune and non-immune cells. We investigated the role of IL-6 on the ability of nine adjuvant formulations to induce antibody responses to the Plasmodium falciparum MSP1-19 malaria vaccine, using IL-6-/- (KO) mice. Results showed that some adjuvants, i.e. MPL-SE, CFA/IFA, ISA720/QS21/MPL, depended on IL-6 for their efficacy, while others exhibited increased potency in its absence. The efficacy of adjuvants in the IL-6 KO environment cannot be solely attributed to their ability to stimulate antigen-specific cellular responses, suggesting that other biological activities of IL-6 are also important. The results further suggest that two adjuvants utilized dissimilar pathways to potentiate the same type of immune response.

Plasmodium falciparum: immunization with MSP1-42 induced non-inhibitory antibodies that have no blocking activities but enhanced the potency of inhibitory anti-MSP1-42 antibodies

Hyperimmunization with Plasmodium falciparum MSP1-42 could induce antibodies that have little or no parasite growth inhibitory activities. These antisera had no blocking activities as determined by their ability to interfere with the in vitro activities of growth inhibitory anti-MSP1-42 sera. Equally important, they enhanced the potency of growth inhibitory anti-MSP1-42 sera.

Plasmodium falciparum anti-MSP1-19 antibodies induced by MSP1-42 and MSP1-19 based vaccines differed in specificity and parasite growth inhibition in terms of recognition of conserved versus variant epitopes

The C-terminal 42 kDa fragment (MSP1-42) and its smaller 19 kDa subfragment (MSP1-19) of the Plasmodium falciparum merozoite surface protein, MSP1, are leading candidate malaria vaccines. Since the targets of protective immunity lie within the MSP1-19, we compared the anti-MSP1-19 antibodies induced by vaccination with recombinant MSP1-42 and MSP1-19. The specificities of the antibody responses were analyzed using five recombinant MSP1-19s expressing different naturally occurring variant amino acid residues. We observed dramatic differences in the specificities of the anti-MSP1-19 antibodies induced by the two vaccines. MSP1-42 consistently induced crossreactive antibodies; whereas the antibodies induced by recombinant MSP1-19 were highly variable among animals in terms of recognition of conserved versus variant epitopes. Of the variant residues examined, only a subset significantly contributed as part of immunogenic B epitopes. MSP1-42 consistently induced potent growth inhibitory antibodies that recognized conserved epitopes, leading to efficient inhibition of heterologous parasites. In contrast, MSP1-19 induced strong inhibitory antibody responses in only a subset of animals studied. In some of the MSP1-19 immunized animals, inhibition of homologous parasites may be due to recognition of inhibitory epitopes associated with the homologous variant residues, and the induction of antibodies to conserved inhibitory epitopes may not be efficiently achieved. These data suggest an advantage of using MSP1-42 over MSP1-19 based vaccines.

Antigenicity and immunogenicity of the N-terminal 33-kDa processing fragment of the Plasmodium falciparum merozoite surface protein 1, MSP1: implications for vaccine development

The Plasmodium falciparum merozoite surface protein 1 (MSP1), MSP1-42 and MSP1-19 are protective malaria vaccines. MSP1-42 is cleaved to form MSP1-33 and MSP1-19. The role of MSP1-33 in immunity is unclear. We investigated the antibody responses to MSP1-33; and to MSP1-33Trunc, in which major conserved sequences were excised. While anti-MSP1-33 antibodies were subdominant in the anti-MSP1-42 responses, immunizations with MSP1-33 or MSP1-33Trunc induced high levels of antibodies reactive with MSP1-42 or whole merozoites. Anti-MSP1-33 and anti-MSP1-33Tunc antibodies crossreacted with both allelic forms of MSP1-42. Anti-MSP1-33 sera were ineffective in inhibiting parasite growth in vitro; but they significantly enhanced the activities of sub-optimal concentrations of the inhibitory anti-MSP1-42 sera. Thus, immunization strategies with MSP1-based vaccines may benefit from co-induction of anti-MSP1-33 responses to enhance efficacy and potency.

Expression of an immunologically reactive merozoite surface protein (MSP-1(42)) in E. coli

The 42-kDa carboxyl-terminal processing fragment of Plasmodium falciparum merozoite surface protein-1 (PfMSP-1(42)) is one of the anti-malarial vaccine candidate antigens. In the present study, recombinant MSP-1(42) was expressed as a fusion protein in a novel E. coli host. The average yield of the recombinant protein was 48 mg/l of bacterial culture. The antigenicity and immunogenicity of the purified protein were evaluated by comparing the results with those obtained from a well-characterized recombinant MSP-1(42) (Bmp42) expressed in the baculovirus expression system previously described from our laboratory. We observed that there is a high degree of similarities between the two recombinant proteins. Based on the results from T and B cell response, in vitro parasite growth inhibition, as well as cross-reactivities with several well-characterized MSP-1 specific Mabs, the bacterial expressed protein is apparently comparable to Bmp42 in terms of immunoreactivities. Our results suggest that the bacterial expression system could be employed to express immunologically active recombinant MSP-1(42) at elevated levels. This system may be an attractive alternative for producing a protective vaccine for human use at lower cost.

[Isolation and study of one novel full-length gene related to human glioma]

OBJECTIVES

To obtain differentially expressed genes related to human glioma using cDNA microarray and make a preliminary study of one novel full-length gene.

METHODS

Total RNA was extracted from human glioma tissues and normal brain tissues, and mRNA was used to make probes. After hybridization and washing procedure, the results of hybridization were scanned using computer system. One gene named 507E08 clone was subsequently analyzed by northern blotting, in situ hybridization, bioinformatics and radiation hybridization.

RESULTS

Fifteen differentially expressed novel genes related to human glioma were obtained through four times of hybridization and scanning. Northern blotting and in situ hybridization confirmed that 507E08 clone was lowly expressed in normal human brain tissue and over-expressed in human glioma tissue. BLASTn and BLASTx analysis showed that the clone 507E08 was a novel full-length gene with the length of 2002 bp. This gene, called human ribosomal protein 14.22 gene, codes 203 amino acids and is located on chromosome 14 between D14S1066 Marker and D14S265 Marker.

CONCLUSION

cDNA microarray technology can be successfully applied to identify differentially expressed genes with small amount of specimen, high quality, high speed, and high sensitivity. The novel full-length human ribosomal protein 14.22 gene may correlate with formation of human glioma.

Efficacy of two alternate vaccines based on Plasmodium falciparum merozoite surface protein 1 in an Aotus challenge trial

In an attempt to produce a more defined, clinical-grade version of a vaccine based on Plasmodium falciparum merozoite surface protein 1 (MSP1), we evaluated the efficacy of two recombinant forms of MSP1 in an Aotus nancymai challenge model system. One recombinant vaccine, bvMSP1(42), based on the 42-kDa C-terminal portion of MSP1, was expressed as a secreted protein in baculovirus-infected insect cells. A highly pure baculovirus product could be reproducibly expressed and purified at yields in excess of 8 mg of pure protein per liter of culture. This protein, when tested for efficacy in the Aotus challenge model, gave significant protection, with only one of seven monkeys requiring treatment for uncontrolled parasitemia after challenge with P. falciparum. The second recombinant protein, P30P2MSP1(19), has been used in previous studies and is based on the smaller, C-terminal 19-kDa portion of MSP1 expressed in Saccharomyces cerevisiae. Substantial changes were made in its production process to optimize expression. The optimum form of this vaccine antigen (as judged by in vitro and in vivo indicators) was then evaluated, along with bvMSP1(42), for efficacy in the A. nancymai system. The new formulation of P30P3MSP1(19) performed significantly worse than bvMSP1(42) and appeared to be less efficacious than we have found in the past, with four of seven monkeys in the vaccinated group requiring treatment for uncontrolled parasitemia. With both antigens, protection was seen only when high antibody levels were obtained by formulation of the vaccines in Freund's adjuvant. Vaccine formulation in an alternate adjuvant, MF59, resulted in significantly lower antibody titers and no protection.

Characterization of conserved T- and B-cell epitopes in Plasmodium falciparum major merozoite surface protein 1

Vaccines for P. falciparum will need to contain both T- and B-cell epitopes. Conserved epitopes are the most desirable, but they are often poorly immunogenic. The major merozoite surface protein 1 (MSP-1) is currently a leading vaccine candidate antigen. In this study, six peptides from conserved or partly conserved regions of MSP-1 were evaluated for immunogenicity in B10 congenic mice. Following immunization with the peptides, murine T cells were tested for the ability to proliferate in vitro and antibody responses to MSP-1 were evaluated in vivo. The results showed that one highly conserved sequence (MSP-1#1, VTHESYQELVKKLEALEDAV; located at amino acid positions 20 to 39) and one partly conserved sequence (MSP-1#23, GLFHKEKMILNEEEITTKGA; located at positions 44 to 63) contained both T- and B-cell epitopes. Immunization of mice with these peptides resulted in T-cell proliferation and enhanced production of antibody to MSP-1 upon exposure to merozoites. MSP-1#1 stimulated T-cell responses in three of the six strains of mice evaluated, whereas MSP-1#23 was immunogenic in only one strain. Immunization with the other four peptides resulted in T-cell responses to the peptides, but none of the resulting peptide-specific T cells recognized native MSP-1. These results demonstrate that two sequences located in the N terminus of MSP-1 can induce T- and B-cell responses following immunization in a murine model. Clearly, these sequences merit further consideration for inclusion in a vaccine for malaria.

[Supercritical-CO2 fluid extraction of natural VE and fatty oil from the oil foot of Brassica campestris and GC-MS analysis]

Natural VE and fatty oil from the oil foot of Brassica campestris are extracted by supercritical-CO2. After saponification and esterification these acidesters and natural VE in the extraction are analyzed by GC-MS. The results show that the fatty acids from SFE-CO2 contain 10 components which of oleic acid, linodeic acid and linolenic acid are main components, linodenic acid and linoleic acid of them are increased signifantly, at the same time, natural VE can be extracted from the materials and the rate of extraction gets to 95%.

[Experimental study on human glioma SHG44 treated by HSV-tk gene therapy]

The paper reports the construction of retroviral vector pLNTK carrying HSV-tk gene driven by PGK promoter and the successful transfer into human glioma cell SHG44. The in vitro study confirmed that ayclovir (ACV) sensitive level of the gene-transferred glioma cell (SHGLNTK) was 1,000 times that of SHG44. 3H-TdR incorporation confirmed that the DNA replication in SHGLNTK was considerably suppressed when treated with ACV. The in vivo study confirmed that ACV could suppress tumor formation of the SHGLNTK cells. In situ gene transfer treatment of nude mice carrying SHG44 tumor showed good therapeutic results. Such treatment may be used as an innovative method for brain tumor therapy.

Expression and antigenicity of Plasmodium falciparum major merozoite surface protein (MSP1(19)) variants secreted from Saccharomyces cerevisiae

Four antigenic variants of the 19-kDa carboxy terminal fragment of Plasmodium falciparum merozoite surface protein, MSP1 (MSP1(19)), were expressed in Saccharomyces cerevisiae as a histidine-tagged, secreted polypeptides (rMSP1(19)s). Structural analysis of the rMSP1(19)s indicated that a single amino acid change (E to Q) in the first EGF-like domain of the yeast-secreted rMSP1(19) proteins caused a significant change in their disulfide bond-dependent conformation. The antigenicity of the rMSP1(19)s were qualitatively and quantitatively analyzed by direct and competitive binding ELISAs. The data indicate that conserved and variant B cell determinants of MSP1(19), as well as epitopes that are known targets of protective antibodies, were recreated authentically in the rMSP1(19)s. Secretion of histidine-tagged rMSP1(19)s using the expression system described may be an efficient and effective means of producing a properly folded immunogen for a human vaccine against the blood stages of P. falciparum.

Oral 5-aminosalicylic acid for inflammatory bowel disease in pregnancy: safety and clinical course

BACKGROUND

Oral 5-aminosalicylic acid (5-ASA) has proven an effective maintenance therapy of ulcerative colitis and may also be useful in Crohn's disease, but its safety in pregnancy has not been established. The present study therefore examined the course and outcome of pregnancies in patients with inflammatory bowel disease who continued to take oral 5-ASA.

METHODS

Ten patients with ulcerative colitis and 7 patients with Crohn's disease with a total of 19 pregnancies were studied while they were receiving 5-ASA. All patients were previously in remission on 5-ASA, at a mean dose of 1.7 g/day (range, 0.8-2.4 g/day). They continued taking the drug without a change in dose and were followed up throughout their pregnancies and postpartum.

RESULTS

Eighteen pregnancies resulted in full-term delivery. No fetal abnormalities were found at delivery, and there were no clinical or biochemical abnormalities in the neonatal period. Four patients had a relapse. One patient required a colectomy but carried on to a full-term pregnancy. One patient had a miscarriage, but she had miscarried on four previous occasions before taking 5-ASA. She subsequently had a successful pregnancy on 5-ASA.

CONCLUSIONS

Oral 5-ASA appears to be safe for the management of inflammatory bowel disease during pregnancy.

Electron microscopic observations on alterations in cultured Plasmodium falciparum and infected erythrocytes after treatment with cyclic AMP in vitro

The fine structure of Plasmodium falciparum treated with cyclic AMP in vitro was studied. Cyclic AMP stimulated the appearance of membranous structures in P. falciparum-infected erythrocytes. Two types of membranous structures originating from the host cell were observed: multilaminate membranous structures and multistranded layer-like membranous structures. The multilaminate structures may play a role in gametocytogenesis and the maturation of the gametocyte. The multilaminate structures were either free in the cytoplasm of infected erythrocytes or present in association with the parasitophorous vacuole membrane surrounding immature gametocytes. These structures may originate from the erythrocyte plasma membrane and the parasitophorous vacuole membrane. Other notable findings in P. falciparum treated with cyclic AMP included the presence of loop-like membrane structures protruding from the plasma membrane of the parasite and termination of some plasma membranes of the parasite in dense granular structures.

63Nickel-constituents in renal cytosol of rats after injection of 63nickel chloride

Chromatographic and electrophoretic fractionations of 63Ni-constituents were performed upon renal cytosol samples from rats that were killed following administration of 63NiCl2. At 0.5 to one hr after i.v. injection of 63NiCl2 (0.1 to 0.5 mumole per kg body wt., N = 6), renal cytosol contained 11 percent (SE +/- 2 percent) of the 63Ni-dose. An average of 68 percent (SE +/- 4 percent) of 63Ni in these cytosol samples was associated with low molecular weight components (mol. wt. less than 2,000). The remainder was bound to five macromolecular constituents, with molecular weights of greater than 130,000 (Peak A), approximately 70,000 (Peak B), approximately 55,000 (Peak C), approximately 30,000 (Peak D), and approximately 10,000 (Peak E), based upon column chromatography on Sephadex G-200. The 63Ni that was present in Peaks A to E averaged, respectively, 1.8 percent, 10.7 percent, 7.5 percent, 10.0 percent and 1.6 percent of total 63Ni in renal cytosol. At one to fours hrs after i.m. injection of 63NiCl2 (100 mumol per kg body wt., N = 17), renal cytosol contained 2.2 percent (SE +/- 0.1 percent) of the 63Ni-dose; ultrafiltrable 63Ni averaged 57 percent (SE +/- 3 percent) of total 63Ni in renal cytosol. Macromolecular 63Ni-constituents in these samples were separated by electrophoresis in agarose gel and visualized by autoradiography. Peak D (mol. wt. approximately 30,000) was the most prominent of the five 63Ni-constituents. This study demonstrates that renal cytosol of 63NiCl2-treated rats contains five macromolecular 63Ni-constituents that may be involved in renal uptake, transport, storage, and excretion of 63Ni(II).

Effects of nickel compounds on incorporation of [3H] thymidine into DNA in rat liver and kidney

In vivo incorporation of [3H] thymidine into DNA was determined in rats at 28 h after partial hepatectomy. Administration of nickel carbonyl (Ni(CO)4) at 2 or 4 h before sacrifice inhibited [3H] thymidine uptake into liver and kidney DNA. For example, in rats killed 4 h after i.v. injection of Ni(CO)4 (2 mg Ni/100 g), [3H]-labelling of liver DNA averaged 54 (SE +/- 10)% of controls (p less than 0.05), and [3H]-labelling of kidney DNA averaged 53 (SE +/- 6)% of controls (p less than 0.01). Injection of NiCl2 (2 mg Ni/100 g, i.m.) 4 h before death did not significantly affect [3H] thymidine uptake into liver DNA, but did inhibit [3H] thymidine uptake into kidney DNA (65 +/- 6%, p less than 0.02). Binding of 63Ni to DNA in liver and kidney of rats killed 4 h after injection of 63Ni(CO)4 or 63NiCl2 ranged from 0.3 to 2.2 mol 63Ni/mol of DNA nucleotides. Ultracentrifugation of DNA on alkaline sucrose gradients did not reveal any differences between sedimentation profiles of hepatic DNA from Ni(CO)4-treated rats versus paired control rats.

Effect of hypophysectomy on persistence of methylated purines in rat liver deoxyribonucleic acid after administration of dimethylnitrosamine

The formation of methylated purines in DNA following dimethylnitrosamine administration was studied in control and hypophysectomized rats. When given the same dose of this carcinogen (in mg/kg body weight) the formation of the major product 7-methylguanine and of the minor products 1-, 3- and 7-methyladenine and 3-methylguanine was slightly greater in the livers of hypophysectomized rats than in controls. The rate of loss of these products from the DNA was not affected by hypophysectomy. O6-Methylguanine levels were significantly greater in the hepatic DNA of hypophysectomized rats compared to controls after doses of dimethylnitrosamine ranging from 1 to 20 mg/kg. This difference was due to a slower rate of loss of this purine from the DNA in the hypothysectomized rats. Growth hormone treatment increased the rate of removal of O6-methylguanine in the hypophysectomized rats but did not restore the activity to that found in controls. The possible significance of these results in the induction of tumors by dimethylnitrosamine is discussed.

Formation and subsequent removal of O6-methylguanine from deoxyribonucleic acid in rat liver and kidney after small doses of dimethylnitrosamine

1. The amounts of 7-methylguanine and O(6)-methylguanine present in the DNA of liver and kidney of rats 4h and 24h after administration of low doses of dimethylnitrosamine were measured. 2. O(6)-Methylguanine was rapidly removed from liver DNA so that less than 15% of the expected amount (on the basis of 7-methylguanine found) was present within 4h after doses of 0.25mg/kg body wt. or less. Within 24h of administration of dimethylnitrosamine at doses of 1mg/kg or below, more than 85% of the expected amount of O(6)-methylguanine was removed. Removal was most efficient (defined in terms of the percentage of the O(6)-methylguanine formed that was subsequently lost within 24h) after doses of 0.25-0.5mg/kg body wt. At doses greater or less than this the removal was less efficient, even though the absolute amount of O(6)-methylguanine lost during 24h increased with the dose of dimethylnitrosamine over the entire range of doses from 0.001 to 20mg/kg body wt. 3. Alkylation of kidney DNA after intraperitoneal injections of 1-50mug of dimethylnitrosamine/kg body wt. occurred at about one-tenth the extent of alkylation of liver DNA. Removal of O(6)-methylguanine from the DNA also took place in the kidney, but was slower than in the liver. 4. After oral administration of these doses of dimethylnitrosamine, the alkylation of kidney DNA was much less than after intraperitoneal administration and represented only 1-2% of that found in the liver. 5. Alkylation of liver and kidney DNA was readily detectable when measured 24h after the final injection in rats that received daily injections of 1mug of [(3)H]dimethylnitrosamine/kg for 2 or 3 weeks. After 3 weeks, O(6)-methylguanine contents in the liver DNA were about 1% of the 7-methylguanine contents. The amount of 7-methylguanine in the liver DNA was 10 times that in the kidney DNA, but liver O(6)-methylguanine contents were only twice those in the kidney. 6. Extracts able to catalyse the removal of O(6)-methylguanine from alkylated DNA in vitro were isolated from liver and kidney. These extracts did not lead to the loss of 7-methylguanine from DNA. 7. The possible relevance of the formation and removal of O(6)-methylguanine in DNA to the risk of tumour induction by exposure to low concentrations of dimethylnitrosamine is discussed.