Cytochalasin B is a potent mitogen for chronic lymphocytic leukemia cells in vitro

Insulin sensitivity in prepubertal Caucasian normal weight children

BACKGROUND

Determining whether or not a child is insulin resistant is becoming a matter of fundamental interest even in childhood, as the incidence of metabolic complications of insulin resistance is rising. Thus reference values are needed.

AIM

To set percentiles for HOMA-IR and WBISI in Caucasian normal weight prepubertal children.

POPULATION

238 normal weight prepubertal Caucasian children (126 males/112 females).

METHODS

After physical examination including anthropometric measurements all children underwent an oral glucose tolerance test from which HOMA-IR and WBISI were calculated.

RESULTS

HOMA-IR values above the 95th percentile (2.03) and WBISI values below the 5th percentile (5.67) represent the cut-off values for the determination of insulin resistance.

CONCLUSION

These reference values are useful to easily detect insulin resistance within the prepubertal Caucasian population representing a helpful tool for clinicians to target such children in order to improve insulin sensitivity.

Synthesis of fluorescently tagged isoprenoid bisphosphonates that inhibit protein geranylgeranylation

Geminal bisphosphonates can be used for a variety of purposes in human disease including reduction of bone resorption in osteoporosis, treatment of fractures associated with malignancies of the prostate, breast, and lung, and direct anticancer activity against bone marrow derived malignancies. Previous research led to identification of some novel isoprenoid bisphosphonates that inhibit geranylgeranyl pyrophosphate (GGPP) synthesis and diminish protein geranylgeranylation. Described here is the synthesis of fluorescent anthranilate analogues of the most active isoprenoid bisphosphonates and examine their ability to impact post-translational processing of the small GTPases Ras, Rap1a, and Rab6. Similar to their non-fluorescent counterparts, some of these fluorescent isoprenoid bisphosphonates diminish protein geranylgeranylation. Their biological activity and fluorescent character suggest that they may be useful in studies of bisphosphonate localization both in cultured cells and in whole organisms.

Synthesis and biological activity of isoprenoid bisphosphonates

Bisphosphonates have been used in the clinic to treat osteoporosis and to reduce bone resorption and the accompanying pathological bone fractures that attend a number of malignancies including multiple myeloma and cancers of the prostate, breast, and lung. There is also evidence that some bisphosphonates have direct anticancer activity. Expansion of the current class of bisphosphonates may lead to compounds that more selectively and potently target these cancers through inhibition of the mevalonate pathway. To this end, a set of dialkyl bisphosphonates bearing isoprenoid chains of varying lengths has been synthesized. Some of these compounds were found to have biological activity on post-translational processing of the oncogenic small GTPases, Ras and Rap1a, in human-derived K562 leukemia cells. Most importantly, these compounds impair protein geranylgeranylation and not protein farnesylation.

Morphological modifications of apoptosis in HL-60 cells: effects of homocysteine and cytochalasins on apoptosis initiated by 3-deazaadenosine

Using electron microscopy, confocal laser scanning microscopy and measurements of intact DNA we have studied the morphology and DNA degradation of human leukaemia HL-60 cells undergoing drug initiated apoptosis. Apoptosis was initiated by 100 microM 3-deazaadenosine (c3Ado), 25 microM c3Ado plus 1 mM homocysteine thiolactone (Hcy) and 100 microM c3Ado plus 5 micrograms/ml cytochalasin B (CB). Two different phenotypes of apoptotic cells (APC), blebbed and non-blebbed, were present in the cultures. Blebbed APC dominated in cultures exposed to c3Ado, whereas most APC in cultures treated with c3Ado plus Hcy and all the APC in cultures treated with c3Ado plus CB displayed a non-blebbed phenotype. A more pronounced reduction of the chromatin/cytoplasm ratio, lower volume fractions of uncondensed chromatin and higher volume fractions of highly condensed chromatin (micronuclei) were found in cultures exposed to c3Ado and c3Ado plus Hcy when compared with cultures exposed to c3Ado plus CB. A partial inhibition of c3Ado apoptosis by CB was confirmed by measurements of intact DNA. The inhibitory effect of CB was not reproducible by CE, indicating that CB exerts its effect by an actin independent mechanism. Both blebbed and non-blebbed APC displayed nuclear fragmentation, segregation of organelles and cytoplasmic vesiculation, suggesting that the differences between the phenotypes were restricted to the cytoplasmic membrane. We were not able to demonstrate the presence of F-actin by fluorescein isothiocyanate-phalloidin staining in blebbed APC nor in non-blebbed APC in cultures treated with c3Ado plus Hcy. Non-blebbed APC in cultures treated with c3Ado plus CB displayed foci of F-actin at the internal part of the cytoplasmic membrane. This suggests that F-actin is preserved by the mechanism by which CB inhibits blebbing, and may indicate that blebbing of the cytoplasmic membrane during apoptosis is associated with F-actin deficiency rather than a result of actin-myosin interactions.

B-cell maturation in chronic lymphocytic leukaemia. IV. T-cell-dependent activation of leukaemic B cells by staphylococcal enterotoxin 'superantigens'

Staphylococcal enterotoxins (SE) are potent T-lymphocyte activators that stimulate T cells by directly cross-linking HLA-DR molecules on antigen-presenting cells with the V beta gene products of the T-cell receptor. The different SE activate all T cells expressing a given V beta, and, therefore, have been termed 'superantigens'. Here we show that SE are potent activators of leukaemic B cells from patients with chronic lymphocytic leukaemia (CLL). Purified B cells from seven of eight CLL patients with high WBC counts (greater than 80,000/microliters) responded to one or several of the tested SE (SEA, SEB, SEC1, SED, SEE) by proliferation ([3H]TdR incorporation) and/or Ig secretion. In several instances, the response of leukaemic B cells to SE was much stronger than was the response to other known B-cell activators including EBV, pokeweed mitogen (PWM), phorbolester (TPA), and Staphylococcus aureus Cowan I (SAC). The activation of leukaemic B cells by SE was strictly dependent on the addition of irradiated T cells isolated from healthy donors. FACS analysis of cultured cells ensured that the proliferating cells were indeed B cells. Taken together, these results demonstrate that SE are strong T-cell-dependent B-cell activators that, in some cases, can stimulate maturation of leukaemic B cells which are refractory to other activation signals.

Chromosome abnormalities in chronic lymphocytic leukemia revealed by cytochalasin B and Epstein-Barr virus

Peripheral blood lymphocytes from eight patients with chronic lymphocytic leukemia (CLL) were cultured with Epstein Barr virus (EBV) and cytochalasin B. All eight cytochalasin B cultures had analyzable metaphases whereas only six of the EBV cultures were successful. Furthermore, the number of abnormal metaphases and the mitotic indices were greater in the cytochalasin B cultures than in the EBV cultures. Trisomy 12, alone or in combination with other abnormalities, was the most frequent cytogenetic finding. Structural abnormalities of chromosomes #6 and #14 were also found. Cytochalasin B appears to be an effective mitogen for demonstrating abnormal metaphases in patients with CLL.

Long-term cultures of chronic lymphocytic leukemia B cells generate B suppressor cells

B suppressor cells (Bs) were generated by stimulation with PHA-P or concanavalin A of B cells from peripheral blood of B-cell chronic lymphocytic leukemia (B-CLL) patients. They suppressed well allogeneic mixed lymphocyte reactions. Long-term colonies of B cells from B-CLL were established for up to 6 weeks in liquid media, with B cells acquiring properties of suppressor cells while being cultured. Two types of cultures were observed: cells either grew in compact multicellular colonies or formed diffuse monolayers. Cells that remained alive in cultures for a number of weeks, but did not multiply, did not develop suppressive characteristics. Bs cells retained their phenotypic markers in cultures. Mitosis and lymphoblasts, but no differentiation into plasma cells, were observed. PHA-P-generated Bs were cultured in long-term colonies, retaining their suppressor properties. The establishment of long-term cultures of B-CLL cells may facilitate a better understanding of the nature and characteristics of normal and leukemic B cells.

Effects of anti-IgM on mitogen-induced proliferation of human B-lymphocyte malignancies

Therapeutic trials of anti-immunoglobulin antibody have produced a wide range of responses in attempts to control the growth of human B lymphoid neoplasms. This variability might reflect differences in intrinsic functional characteristics of malignant B lymphocytes that determine susceptibility to anti-immunoglobulin-mediated regulation of growth. To characterize B-lymphocyte malignancies, tissue samples from 24 patients were studied during short-term culture in vitro. Malignant B lymphocytes were stimulated to proliferate by the T-independent mitogens lipopolysaccharide, cytochalasin B, and Staphylococcus aureus that bears protein A. The effects of monoclonal mouse anti-human IgM on mitogen-induced malignant lymphocyte proliferation were then assessed. Mitogen-induced responses of malignant lymphocytes from three patients were abrogated by 2 micrograms/ml monoclonal anti-human IgM. Proliferation was also abrogated by polyclonal goat anti-IgM antiserum but proliferative responses were not affected by control monoclonal antibody. Further study showed that anti-immunoglobulin-mediated inhibition of proliferation was not dependent on Fc-determined interactions, nor was it dependent on the presence of T lymphocytes. These results indicate that a subset of human B-lymphocyte malignancies are susceptible to inhibition of proliferation mediated by anti-IgM.