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Biomedical subjects

R D Knight

Publications and source records attributed to R D Knight.

51 records · Page 3Linked to original sources
PubMed1989

Abnormal responses of myeloid progenitor cells to granulocyte-macrophage colony-stimulating factor in human cyclic neutropenia.

Granulocyte-macrophage progenitors (CFU-GM) from four patients with childhood onset cyclic neutropenia demonstrated abnormal in vitro proliferative responses to purified, recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) when examined in detailed dose-response studies. Marrow aspirate specimens were obtained for these studies from cyclic neutropenia patients (both during neutropenic nadirs and during recovery phases of cycles), from leukemia patients in remission who had received myelosuppressive chemotherapy, and from healthy normal volunteers. Nucleated marrow cells were then isolated by density-gradient centrifugation and cryopreserved to permit studies of CFU-GM from patients and controls to be carried out at the same time and in replicate. Maximum clonal growth of CFU-GM from normal subjects and from individuals recovering from drug-induced myelosuppression was elicited by 20-100 pmol/liter rhGM-CSF, and the CSF concentrations that induced half-maximal responses (ED50) were between 1.0 and 3.0 pmol/liter. In contrast, maximum growth of CFU-GM from the cyclic neutropenia patients required greater than or equal to 1.0 nmol/liter rhGM-CSF and ED50's were greater than 30.0 pmol/liter. These abnormalities in the GM-CSF responsive growth of myeloid progenitors were independent of cycle time and were most apparent with the predominantly neutrophilic 7-d CFU-GM. Moreover, differences in the growth of 14-d CFU-GM could be attributed mostly if not entirely to differences in the generation of neutrophilic colonies. These findings indicate that childhood onset cyclic neutropenia is associated with an underlying disturbance in the GM-CSF responsive growth of myeloid progenitors committed to neutrophilic differentiation.

Adolescent↗
PubMed1988

Phase I and clinical pharmacology study of intravenous flavone acetic acid (NSC 347512).

We have conducted a Phase I and pharmacological study of flavone acetic acid, one of a series of novel flavonoids. The drug was administered i.v. weekly for 4 weeks, with a 2-week rest and then repeated. Flavone acetic acid was given initially in a 1-h infusion, but at the 3900-mg/m2 dose level, the infusion time was lengthened to 3 h. A total of 31 patients were treated with 9 different dose levels, ranging from 330 to 6400 mg/m2. Dose-limiting toxicity was acute hypotension that began after about one-third of each drug dose had been infused and rarely lasted more than a few minutes after the infusion was discontinued. In addition, subjective fatigue and asthenia causing unacceptable patient discomfort was dose limiting. A significant side effect noted that was not dose limiting was diarrhea during the infusion. This drug exhibited nonlinear pharmacokinetic behavior. Plasma levels exceeded 300 micrograms/ml during the infusion at the maximally tolerated dose. After the infusion ended the principal half-life was about 2 h. In 24-h urine collections 27% of the flavone acetic acid dose was recovered as intact drug and an additional 37% was recovered as a metabolite. The maximally tolerated dose determined in this study is 6400 mg/m2 given i.v. over 3 h.

Adult↗
PubMed1988

Clinical predictors of response in metastatic germ cell tumors.

Twenty-two patients with bulky, metastatic germ cell tumors were treated with cyclophosphamide, vinblastine, dactinomycin, bleomycin, and cisplatin (VAB) alternating with VP-16 and vincristine (VV). The overall complete response rate after chemotherapy with or without surgical excision of residual tissue was 63% (14 of 22 patients) with a median survival of 46 months. Five patients are dead of disease progression and three are alive beyond 3 years with only residual radiographic abnormalities. A retrospective analysis of prognostic variables (numbers of sites of disease, tumor marker levels) using two previously published prognosis formulas demonstrated a good correlation between prognostic variables (numbers of sites of disease, tumor marker levels) and the clinical assessment of prognosis based on tumor bulk and tumor marker level. Nevertheless, individual patients with other, unknown prognostic features may be incorrectly evaluated using either established formulas or clinical assessment of tumor bulk.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1988

Progressive loss of phenotypic proteins in mature granulocytes before the onset of blast crisis in human chronic myelogenous leukemia.

A combined high-performance liquid chromatography-sodium dodecyl sulfate-gel electrophoresis method for the study of the phenotypic protein patterns of mature blood granulocytes was previously described. With the use of this method in the present study, the progression of human chronic myelogenous leukemia (CML) from the stable to the blast crisis stage was shown to be accompanied by a progressive decrease in the amounts of cell membrane and granule phenotypic proteins in mature granulocytes. Survival time from the initial diagnosis was significantly shorter for CML patients whose levels of granulocyte phenotypic proteins were below the normal range compared with survival time for those patients whose levels were normal or higher than normal. The data suggest that these changes in mature granulocytes serve as useful diagnostic indicators of an impending blast crisis in CML patients.

Adolescent↗
PubMed1988

Extragonadal germ cell tumors. Clinicopathologic findings and treatment experience in 12 patients.

In patients with primary germ cell tumors, treatment with combination chemotherapy followed by surgical debulking of residual tissue usually produces favorable results. The best treatment for patients with extragonadal germ cell tumors (EGCT) remains a problem. In our series of 12 patients, important clinical features were related to the site of bulky tumor, and all patients exhibited sharply elevated levels of lactate dehydrogenase (LDH), beta subunit human chorionic gonadotropin (beta-HCG), and/or alpha-fetoprotein (AFP). Each patient was treated with systemic chemotherapy, and ten were treated with the same combination chemotherapy--cyclophosphamide, actinomycin, vinblastine, bleomycin, and cisplatin (VAB) alternating with VP-16 and vincristine (VV). Of these ten patients, five died of progressive disease, three of whom had brain metastases. The other five are alive and clinically free of disease. The addition of VP-16 and vincristine did not improve responses. Advanced disease at presentation contributes to the poorer prognosis for these patients. Earlier diagnosis and surgical debulking may improve the long-term survival of patients with this disease.

Adult↗
PubMed1987

Inosine monophosphate dehydrogenase and myeloid cell maturation.

In previous studies of purine ribonucleotide metabolism in the human myeloid leukemia cell line HL-60, we observed that there is a down-regulation of guanine ribonucleotide biosynthesis from the central intermediate, inosine monophosphate (IMP) and a depletion of intracellular guanosine triphosphate (GTP) and guanosine diphosphate (GDP) pools that occur during the induced maturation of these cells. We also found that inhibitors of IMP dehydrogenase, the enzyme that catalyzes the first step of guanylate synthesis from IMP, are potent inducers of HL-60 maturation. Because of these observations we specifically investigated the activity of IMP dehydrogenase in HL-60 cells and in a new inducible human myeloid leukemia cell line, RDFD2-25, both during maintenance culture and during induced maturation of the cells. Enzyme activity was examined directly in cell extracts with a radiometric assay that measures free 3H2O formed from [2-3H] IMP during the conversion of IMP to XMP. Uninduced HL-60 and RDFD2 cells in maintenance culture were found to have high levels of IMPD activity (5.2 to 5.7 pmol IMP metabolized/10(7) cells/min) compared with normal neutrophils and monocytes that had been purified from blood (less than 1.5 pmol IMP metabolized/10(7) cells/min). However, when HL-60 and RDFD2-25 cells were induced to mature with retinoic acid (10(-6) mol/L), dimethylformamide (6 X 10(-2) mol/L), or a known IMPD inhibitor, tiazofurin (10(-6) mol/L), IMPD activity in the cells fell by 51% to 80% within three to six hours. These changes in IMPD activity preceded detectable functional and antigenic maturation of the cells by at least 12 hours and were not temporally related to changes in cellular proliferation. These findings are consistent with the concept that the regulation of myeloid cell maturation may be influenced by intracellular concentrations of guanine ribonucleotides because IMP dehydrogenase activity is known to be rate limiting for the production of these nucleotides.

Cell Division↗
PubMed1985

Hereditary warfarin resistance. Investigation of a rare phenomenon.

A 57-year-old black woman required a daily dosage of 50 mg of warfarin sodium to maintain her prothrombin time in a therapeutic range. The central volume of distribution and clearance of warfarin were normal for this patient. These findings, combined with the patient's requirement for plasma warfarin levels four times greater than those usually required to achieve adequate anticoagulation, indicated that the relative resistance was due to altered pharmacodynamics of warfarin. The only child of the propositus, a daughter, showed a similar relative resistance, confirming that this family is the third to be reported with hereditary resistance to warfarin.

Adult↗
PubMed1983

Induced maturation of the human promyelocytic leukemia cell line, HL-60, by 2-beta-D-ribofuranosylselenazole-4-carboxamide.

The new synthetic nucleoside analogue, 2-beta-D-ribofuranosylselenazole-4-carboxamide, was evaluated for its effects upon the growth and maturation of the human promyelocytic leukemia cell line, HL-60. At a concentration of greater than or equal to 1 nm, this agent was found both to decrease HL-60 cell proliferation and to cause the cells to acquire an ability to phagocytose opsonized yeast and to reduce nitroblue tetrazolium dye, functions characteristic of mature myeloid cells. In addition, this agent at similar concentrations caused a marked depression of intracellular guanosine nucleotide pools and a reduction in the incorporation of [14C] hypoxanthine into guanylates. These results suggested that the selenazole nucleoside caused an inhibition of inosinate monophosphate dehydrogenase, a key enzyme of guanylate biosynthesis. We therefore measured the activity of this enzyme indirectly by simultaneous-UV-radioactivity HPLC as well as by a direct radiometric method and demonstrated markedly reduced enzyme activities by both assays in drug treated cells. Dose response studies indicated that concentrations of drug which caused greater than 30% inhibition of IMP dehydrogenase activity induced greater than 50% maturation of the cells. These observations with this new nucleoside analogue provide further support for the concept that production of guanosine nucleotides and the activity of IMP dehydrogenase have a role in regulating the terminal maturation of myeloid cells.

Carbon Radioisotopes↗
PubMed1982

Laboratory diagnosis of gonococcal infection by genetic transformation.

The transformation test for the detection of infection by Neisseria gonorrhoeae has been examined using pro gonococci as recipients and DNA preparations from 912 clinical isolates and from 240 direct swab specimens as donors. The reliability of the method was checked with DNA from clinical isolates; 82% of the N. meningitidis from throat swab specimens were capable of transforming the gonococcal recipients, but after identification of the meningococcus by the aminopeptidase profile, the transformation test was then 99.5% positive for the gonococcus with virtually no false-positives. The only other organism to give a positive reaction was N. lactamica, which occurred once in 912 specimens. When applied directly to swab specimens, the reliability of the test was reduced, but this may have been related to variability of the specimen itself. However, 7 of 15 specimens which were microscopically suspected to be gonococci but unculturable were positive; also, 9 out of 38 unculturable specimens that were not even suspected to be gonococci were positive. Hence the test was able to identify the presence of gonococci that were unculturable. The aminopeptidase activities were not sensitive enough to be detected in the direct swab specimens, and neither cys nor leu auxotrophs were suitable as recipients to give a differentiation between N. gonorrhoeae and N. meningitidis. Evidence was obtained which would support the proposition that the transfer of genetic material between N. gonorrhoeae and N. meningitidis may occur.

Aminopeptidases↗
PubMed1982

The effect of labor on the rheologic response of chorioamniotic membranes.

A study of chorioamniotic membranes was undertaken in 2 term populations. One group of women delivered vaginally after normal labor (N = 41), the other by elective cesarean section (N = 41). Rheologic properties were measured in an experimental environment. The membranes in each group responded similarly while intact. Those membranes subject to labor, however, ruptured earlier in cyclic testing. They also required more time to dissipate applied stress. This stress response pattern is similar to that seen with rupture of amorphous materials in which multiple flaws or cracks are aggravated by stress testing. The clinical problem of premature rupture of the membranes may occur by a phenomenon that produces flaws in their structure. The data suggest that these flaws may be aggravated by labor-like uterine activity.

Amnion↗
PubMed1981

Scanning X-ray microradiography of a section of a carious lesion in dental enamel.

A scanning X-ray microradiographic system is described with which it is possible to measure the X-ray absorption in a 1 mm X 1mm area of a section in about 27h at a resolution of 20 micrometers with a reproducibility of about +/- 1.5%. This system has advantages over photographic methods for certain quantitative investigations. The results can be presented in various forms including contour maps and half-tone pictures and this is illustrated with a radiograph of a section of a carious lesion in dental enamel.

Dental Caries↗
PubMedDate not supplied

How mitochondria redefine the code.

Annotated, complete DNA sequences are available for 213 mitochondrial genomes from 132 species. These provide an extensive sample of evolutionary adjustment of codon usage and meaning spanning the history of this organelle. Because most known coding changes are mitochondrial, such data bear on the general mechanism of codon reassignment. Coding changes have been attributed variously to loss of codons due to changes in directional mutation affecting the genome GC content (Osawa and Jukes 1988), to pressure to reduce the number of mitochondrial tRNAs to minimize the genome size (Anderson and Kurland 1991), and to the existence of transitional coding mechanisms in which translation is ambiguous (Schultz and Yarus 1994a). We find that a succession of such steps explains existing reassignments well. In particular, (1) Genomic variation in the prevalence of a codon's third-position nucleotide predicts relative mitochondrial codon usage well, though GC content does not. This is because A and T, and G and C, are uncorrelated in mitochondrial genomes. (2) Codons predicted to reach zero usage (disappear) do so more often than expected by chance, and codons that do disappear are disproportionately likely to be reassigned. However, codons predicted to disappear are not significantly more likely to be reassigned. Therefore, low codon frequencies can be related to codon reassignment, but appear to be neither necessary nor sufficient for reassignment. (3) Changes in the genetic code are not more likely to accompany smaller numbers of tRNA genes and are not more frequent in smaller genomes. Thus, mitochondrial codons are not reassigned during demonstrable selection for decreased genome size. Instead, the data suggest that both codon disappearance and codon reassignment depend on at least one other event. This mitochondrial event (leading to reassignment) occurs more frequently when a codon has disappeared, and produces only a small subset of possible reassignments. We suggest that coding ambiguity, the extension of a tRNA's decoding capacity beyond its original set of codons, is the second event. Ambiguity can act alone but often acts in concert with codon disappearance, which promotes codon reassignment.

Base Composition↗
PubMedDate not supplied

Replacement therapy for congenital Factor X deficiency.

We studied a young woman with severe (less than 1%) congenital factor X deficiency during a 2-year period in order to document the levels of factor X required to provide hemostasis for vaginal bleeding, epistaxis, and hemarthroses, as well as during surgery. Factor X levels of 9 to 17 percent, achieved with fresh-frozen plasma (FFP) were satisfactory for minor bleeding. Hemostasis was achieved during emergency surgery for hemoperitoneum by increasing the factor X level to 35 percent with a Factor IX concentrate, followed with infusions of FFP to maintain levels between 10 and 20 percent for 6 days postoperatively. These data suggest that factor X levels of 10 to 20 percent are sufficient for hemostasis in factor X-deficient patients even in the immediate postoperative period.

Adult↗