Robert E. Corin

ANTI-FERTILITY AND OTHER ACTIONS OF GOSSYPOL ANALOGUES

From a series of gossypol derivatives studied, we conclude that the carbonyl groups of gossypol are needed for inhibition of erythrocyte anion transport and the hydroxy groups affect but are not essential to that inhibition. In an in vitro mouse erythroleukemia cytocidal assay, the most active compounds were gossypol and apogossypol. The latter was not active in the inhibition of erythrocyte anion transport or in a spermicidal assay. Of the more simple structures related to gossypol, those that were active in the cytocidal and spermicidal assays were bi-aromatic, linked by a 1- and not a 4-carbon chain and had free phenolic hydroxyl groups. These results are included in a discussion of the specificity and mechanism of action of gossypol.

Growth hormone-induced alteration of morphology and tubulin expression in 3T3 preadipose cells

Effects of growth hormone on morphology and cytoskeletal protein expression were examined in 3T3-F442A preadipocytes in serum-free medium. Between 2 and 5 days of culture 2 nM methionyl human growth hormone converted 3T3-F442A cells from a flat fibroblastic morphology to a rounded form with numerous membrane convolutions. Growth hormone treated cultures manifested a 30-40% reduction in cell volume. Growth hormone induced changes in morphology and volume preceded and were independent of lipogenesis. In cells treated with growth hormone, expression of alpha and beta-tubulin as determined by Western blotting was found to increase approximately 50% within 72 h as compared to untreated cells. After 7 days, tubulin levels in growth hormone treated cells were approximately 40% of control levels. This indicated that morphological changes and alteration of tubulin expression were signatures of growth hormone action on 3T3-F442A cells.

Activity of growth hormone peptides bGH 96–133 and hGH 95–133 in 3T3-F442A cells

Chemically synthesized bovine growth hormone (bGH) bGH 96-133 and its human homologue, hGH 95-133, have similar in vitro biological activities. Unlike native GH, bGH 96-133 and hGH 95-133 were completely without adipogenic or anti-insulin activity at doses up to 10 microM. bGH 96-133 had insulin-like activity, with a 100% increase in glucose uptake at 10 microM. bGH was anti-mitogenic and bGH 96-133 and hGH 95-133 were mitogenic (EC50 approximately 180 nM and maximal response at 1-2 microM). Only bGH 96-133 and hGH 95-133 displaced [125I]hGH 95-133 binding from 3T3-F442A fibroblasts with a Kd between 60-120 nM. bGH, hGH, insulin and IGF-I were without effect on [125I]hGH 95-133 binding. bGH 96-133 and hGH 95-133 did not significantly inhibit [125I]hGH or [125I]IGF-I binding. These experiments indicate that GH containing peptides bGH 96-133 and hGH 95-133 have mitogenic and insulin-like activity without the adipogenic, anti-insulin or anti-mitogenic activity of bGH. These peptides have a specific binding site which appears to be distinct from the GH, insulin and IGF-I receptors.

Binding and degradation of 125I-labeled insulin by a clonal line of rat pituitary tumor cells

Receptor sites for insulin on GH3 cells were characterized. Uptake of 125I-labeled insulin by the cells was dependent upon time and temperature, with apparent steady-states reached by 120, 20 and 10 min at 4, 23 and 37 degrees C, respectively. The binding sites were sensitive to trypsin, suggesting that the receptors contain protein. Insulin competed with 125I-labeled insulin for binding sites, with half-maximal competition observed at 5 nM insulin. Neither adrenocorticotropic hormone nor growth hormone competed for 125I-labeled insulin binding sites. 125I-labeled insulin binding was reversible, and saturable with respect to hormone concentration. 125I-labeled insulin was degraded at both 4 and 37 degrees C by GH3 cells, but not by medium conditioned by these cells. After a 5 min incubation at 37 degrees C, products of 125I-labeled insulin degradation could be recovered from the cells but were not detected extracellularly. Extending the time of incubation resulted in the recovery of fragments of 125I-labeled insulin from both cells and the medium. Native insulin inhibited most of the degradation of 125I-labeled insulin suggesting that degradation resulted, in part, from a saturable process. At steady-state, degradation products of 125I-labeled insulin, as well as intact hormone, were recovered from GH3 cells. After 30 min incubation at 37 degrees C, 80% of the cell-bound radioactivity was not extractable from GH3, cells with acetic acid.

Uptake of14C-Gossypol by Murine Erythroleukemia Cells: A Model of Unmediated Diffusion for Gossypol Uptake by a Nontesticular Cell

Gossypol (G) has been shown to be a highly efficacious oral male contraceptive [1, 2, 3]. G has potential for wide use as a contraceptive agent. Additionally, the study of G may provide a useful model for the development of new male oral contraceptives. The mechanism of contraceptive action and the pharmocokinetics of G are not well defined. At therapeutic (contraceptive) doses G is relatively non-toxic [2, 3]. Acutely toxic doses of G, in vivo, are ∿1000 fold greater than contraceptive doses of the drug [4, 5]. Thus, the in vivo pharmacology of G may be viewed as having two important facets. One involves the basis for selective toxicity to testicular tissues, i.e., what is the nature of the uptake system or target for drug action that accounts for testicular sensitivity to G? A second consideration is that contraceptive doses of G are not acutely toxic to most body tissues. We have approached the latter issues by studying the toxicity of G, in vitro, to an established cell line. Murine erythroleukemia cells (MELC) were chosen since they provide an easily handled model for non-testicular cells. Our preliminary studies [6] demonstrated the following: i) G is toxic and is irreversibly cytocidal to MELC after 24 h of exposure to G (30 µM). ii) G toxicity to MELC depends on the fetal calf serum (FCS) concentration of the growth medium, e.g., 5 µM G is not toxic when serum is 10% (v/v) but is toxic when the serum concentration of the medium is reduced to 5%. iii) FCS as well as bovine serum albumin (BSA) potently blocked the steady uptake of 14C-G by MELC and direct and indirect experiments demonstrated high affinity binding (KD < 1 µM) of G to BSA and FCS. iv) 14C-G uptake by MELC is saturable with a Km of ∿8 µM. High affinity binding of G to human serum albumin has been demonstrated by [7].