Search PubMed⌕ Search

Biomedical subjects

R Pieters

Publications and source records attributed to R Pieters.

At least 163 records · Page 9Linked to original sources
PubMed1988

Adaptation of the rapid automated tetrazolium dye based (MTT) assay for chemosensitivity testing in childhood leukemia.

The reduction of the tetrazolium salt MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) to a blue-black formazan product by living but not by dead cells can be used to measure chemosensitivity of tumor cells. The main advantages of the MTT assay are its simplicity, rapidity, and the fact that the results are read automatically with a microplate spectrophotometer. Several reports on the use of the MTT assay in chemosensitivity testing have been published, but all these studies dealt with established cell lines and not with specimens obtained directly from patients. Here we present a study in which the MTT assay has been adapted to assess the effect of antineoplastic drugs on lymphoblasts of children with leukemia.

Antineoplastic Agents↗
PubMed1988

The role of 5'nucleotidase in therapy-resistance of childhood leukemia.

Purine nucleotides become available for a cell by two routes, namely purine de novo synthesis and the purine salvage pathway. 5'Nucleotidase is a purine pathway enzyme and is present in two forms. Cytoplasmic 5'nucleotidase (cyto 5'NT) catalyzes the intracellular degradation of purine nucleotides into their corresponding nucleosides. The plasma membrane bound form (ecto 5'NT) has its active site facing the external medium. Its function is the extracellular dephosphorylation of nucleotides, to which cells are generally impermeable, into nucleosides and the transport of these nucleosides through the cell membrane. Lymphoblastic 5'NT activity varies between different children with common-ALL. 5'NT positive cases have a higher relapse rate and thus a poorer prognosis than 5'NT negative cases. This can be explained by two hypotheses which are not mutually exclusive: 1. Rescue hypothesis. When purine de novo synthesis is blocked by methotrexate (MTX) and/or 6-mercaptopurine (6-MP), the malignant cell has to rely on the purine salvage pathway. This pathway depends on the ecto-5'NT activity. So, leukemic cells might be resistant to MTX and/or 6-MP because of ecto-5'NT activity. 2. Breakdown hypothesis. Leukemic cells are resistant to 6-MP because of the breakdown of the toxic nucleotide form of 6-MP into the nucleoside form by cyto-5'NT.

5'-Nucleotidase↗
PubMed1988

Nuclear magnetic resonance imaging of bone marrow in childhood leukaemia.

Bone marrow infarction is known to occur in childhood leukaemia. Although it may be suspected on clinical grounds, radiographic evidence is infrequent. We present three cases in which magnetic resonance imaging demonstrated unexpectedly extensive bone marrow lesions and discuss the evidence that these lesions were due to bone marrow infarction.

Adolescent↗
PubMed1988

Immunological phenotype of lymphoid cells in regenerating bone marrow of children after treatment for acute lymphoblastic leukemia.

Bone marrow samples from 8 children treated for acute lymphoblastic leukemia (ALL) were investigated at cessation of cytostatic treatment and during 18 months thereafter. The course of the percentage of lymphoid cells and characterization of these cells by means of monoclonal antibodies, peanut agglutinin (PNA) binding and S-phase determination are shown. The percentage of lymphocytes rises in the first 1.5 months, followed by a non-significant decline. The percentage of cells in S-phase is higher at 0 months than at 6, 15 and 18 months. The percentage of T-cells does not change significantly. In the first 1.5 months a sudden rise in the percentage of common-ALL-antigen (cALLA)-positive lymphocytes occurs. The number of B-cells rises to a peak at 6 months. PNA positively increases to a maximum at 3 months and is correlated with positivity for markers of the B-cell lineage. The percentages of B-cells, cALLA-positive, and PNA-positive lymphocytes do not change significantly after they reach their maximum values and are still high at 18 months. Our results show that after cessation of chemotherapy for ALL a lymphoid cell regeneration occurs in the bone marrow consisting of cells of the B-cell lineage; many of these are cALLA-positive, but are discernible from their malignant counterparts by PNA-positivity.

Antibodies, Monoclonal↗
PubMed1988

Consultation among peers in general practice; from no consultation to peer review.

The present study concerned several aspects of peer consultation by general practitioners, investigated in a group of 184 doctors (response rate: 83%) who had their vocational training in the department of general practice of the University of Utrecht and practised for at least three years at the time of the study. Questionnaire responses indicated that consultation during and outside surgery hours and participation in case-discussion groups generally extended over more than two years, occurred frequently, and usually pertained to diverse problems associated with diagnosis and treatment. Participation in study and peer review groups extended usually over a shorter time (1 to 1 1/2 years) and the problems dealt with were predominantly the same as for individual consultation. One-third of the general practitioners consulted colleagues frequently and continued to do so for long periods, dealing systematically with a variety of problems; one-third did so infrequently or unsystematically, and one-third did little or not at all. A relationship was found between the setting of the practice and consulting behaviour: 20% of those who practised alone never consulted peers, whereas those in group practices and health centres were accustomed to do so regularly.

Family Practice↗
PubMed1987

Bone marrow magnetic resonance studies in childhood leukemia. Evaluation of osteonecrosis.

In 25 patients under treatment or during follow-up for acute lymphoblastic leukemia magnetic resonance imaging (MRI) of both knees was compared to history and physical examination to detect osteonecrosis. Results of MRI were classified as: O, normal bone marrow (BM); 1, diffuse decrease in signal intensity; 2, circumscript lesions. Patients clinically suspected of osteonecrosis had a statistically significant increased incidence of Type 2 lesions. Three patients with a BM relapse also showed Type 2 lesions. Circumscript lesions of the epiphyses were seen exclusively in the four patients with clinical suspicion of osteonecrosis during BM remission and this may be a MR finding strongly indicative of osteonecrosis. Patients with Type 2 lesions during BM remission had received systemic chemotherapy for a statistically significant longer period than the other patients. Using MRI findings we suspect that at least four patients suffered osteonecrosis due to chemotherapy. MRI is a promising means of detecting this disorder.

Adolescent↗
PubMed1987

Prognostic significance of acid alpha-naphthyl acetate esterase and acid phosphatase in childhood acute lymphoblastic leukemia.

We studied the prognostic value of the enzymes acid alpha-naphthyl acetate esterase (ANAE) and acid phosphatase (AP) in 89 children with acute lymphoblastic leukemia (ALL). Follow-up data were available for 61 out of 67 cases of non T- non B-ALL, which were treated in different hospitals according to the same protocols. Sex, age, initial white blood cell count (WBC) and number of high risk patients (WBC above 25 X 10(9)/l) were comparable between enzyme-positive and -negative cases. The probabilities of complete continuous remission (CCR) were virtually identical in the AP+ and AP- group. For the ANAE+ group the probability of CCR was lower than for the ANAE- group, but this difference was not statistically significant (0.10 greater than p greater than 0.05). Within the common-ALL group (n = 32), no difference was found in probability of CCR between the AP+ and AP- group but ANAE+ cases had a significantly lower probability of CCR than ANAE- cases. This study is a contribution to the view that the cytochemical profile of ALL cells may have prognostic value.

Acid Phosphatase↗
PubMed1982

Rheumatoid arthritis associated with bronchiolitis obliterans and immunoblastic sarcoma.

A case is reported of a 72 year old man suffering from classical seropositive RA for 10 years. Two months before admission he experienced general illness, fever and itching. Lymph nodes enlargement and hepatosplenomegaly were found. Histologic features of lymph node biopsy were compatible with angioimmunoblastic lymphadenopathy and Lennert lymphoma. Rapidly progressive pulmonary deterioration followed with hilar invasion and honeycombing. Sternal punction, bone biopsy, bronchus biopsy and blind lung biopsy however, did not reveal lymphomatous invasion. On the contrary, lung biopsy, showed bronchiolitis obliterans, an often fatal, small airway disease whose connection with RA is discussed. Plasmapheresis induced a correction of leucopenia and thrombocytopenia. A fatal evolution evolved within six months. Autopsy revealed diffuse invasion by immunoblastic sarcoma. The clinicopathological entities angioimmunoblastic lymphadenopathy and Lennert lymphoma are referred to. The relationship with autoimmune disorders is stressed.

Aged↗
PubMed1981

Arteritis associated with hyperviscosity-like syndrome in rheumatoid arthritis, treated by intermittent plasma-exchange for 2.5 years.

A case is reported of a hyperviscosity-like syndrome in a 53-year-old male suffering from rheumatoid arthritis. The clinical presentation was an acute abdomen, peripheral neuritis, otovestibular areflexy, and central retinal vein thrombosis (papilloedema and retinopathy with venous engorgement, haemorrhages and exudates). Plasma viscosity was normal and whole blood viscosity, measured with an Oswald viscometer, was slightly elevated. The patient had markedly elevated rheumatoid factor tire and fibrinogen level. Histologically, there were no signs of arteritis in the mesentery. Intermittent plasma-exchange resulted in general improvement and no new vascular accidents after 2.5 years.

Arteritis↗
PubMed1981

The effect of plasma exchange on synovitis in rheumatoid arthritis.

Eight patients with a severe exacerbation of rheumatoid arthritis were treated by twice weekly plasma-exchange for 3 weeks in order to evaluate the effect of plasma-exchange on synovitis. During the plasma-exchange period, patients remained on the drug regimen they were on at admission to the hospital. Plasma was replaced isovolemically with human, purified plasma protein fraction. Improvement in clinical parameters of synovitis and serological parameters of inflammation occurred in almost all patients. After 6 months the clinical remissions were sustained. Three patients experienced a rebound synovitis and one patient a rebound vasculitis at the end of or just after the plasma-exchange period. The rebound phenomena were moderate and of short duration. Plasma-exchange may exert its beneficial effects by depleting important mediators of injury such a complement fibrinogen and circulating immune complexes, by improving reticuloendothelial function, and by increasing the drug response of the inflammatory target tissue. The role of depletion of circulating immune complexes was not so clear in this study. It is concluded that limited plasma-exchange is an effective means to induce a symptomatic improvement in an acute exacerbation of polyarthritis, without changing the basic therapy and thus avoiding corticosteroid dependency.

Adult↗
PubMedDate not supplied

Vasopressin-stimulated Ca2+ reabsorption in rabbit cortical collecting system: effects on cAMP and cytosolic Ca2+.

The effect of arginine vasopressin (AVP) on transepithelial Ca2+ transport in primary cultures of rabbit cortical collecting system cells was examined. Addition of AVP to the basolateral side of the monolayer dose-dependently (EC50 = 0.7 nM) increased active Ca2+ reabsorption from a basal value of 85 +/- 2 nmol.h-1.cm-2 to a maximum value of 124 +/- 3 nmol.h-1.cm-2. This was paralleled by a dose-dependent (EC50 = 1.1 nM) increase in cellular adenosine 3', 5'-cyclic monophosphate (cAMP) content. Both effects of AVP were mimicked by the V2 agonist deamino-Cys,D-Arg8-vasopressin (dDAVP) and forskolin. Addition of either AVP or dDAVP to the basolateral side evoked a sustained increase in cytosolic free Ca2+ concentration, which resulted from both Ca2+ entry and release from internal stores. Only the effect on Ca2+ entry was mimicked by forskolin, demonstrating that cAMP acts by activating a Ca2+ influx pathway. The present findings demonstrate that AVP stimulates transcellular Ca2+ transport in the cortical collecting system through activation of basolateral V2 receptors coupled to adenylyl cyclase to increase the cellular cAMP content.

Absorption↗
PubMedDate not supplied

Methods of in vitro toxicology.

In vitro methods are common and widely used for screening and ranking chemicals, and have also been taken into account sporadically for risk assessment purposes in the case of food additives. However, the range of food-associated compounds amenable to in vitro toxicology is considered much broader, comprising not only natural ingredients, including those from food preparation, but also compounds formed endogenously after exposure, permissible/authorised chemicals including additives, residues, supplements, chemicals from processing and packaging and contaminants. A major promise of in vitro systems is to obtain mechanism-derived information that is considered pivotal for adequate risk assessment. This paper critically reviews the entire process of risk assessment by in vitro toxicology, encompassing ongoing and future developments, with major emphasis on cytotoxicity, cellular responses, toxicokinetics, modelling, metabolism, cancer-related endpoints, developmental toxicity, prediction of allergenicity, and finally, development and application of biomarkers. It describes in depth the use of in vitro methods in strategies for characterising and predicting hazards to the human. Major weaknesses and strengths of these assay systems are addressed, together with some key issues concerning major research priorities to improve hazard identification and characterisation of food-associated chemicals.

Animal Testing Alternatives↗