Howard H. Sussman

Plasma concentrations after rectal administration of acetaminophen in preterm neonates

Acetaminophen is frequently administered to infants and children for its antipyretic and analgesic properties. Oral administration is the route of choice in daily practice. In some circumstances this is impractical. Rectal administration of acetaminophen is an alternative route. This study measures plasma concentrations following rectal administration of acetaminophen 20 mg·kg−1 (10% Infants’ Tylenol Drops, McNeil Consumer Product Co., diluted with an equal volume of sterile water) in five preterm neonates. Serial arterial blood samples were obtained at 0, 15, 30, 60, 120, and 240 min. Pharmacokinetic parameters were (mean±sd): Cmax (maximum plasma concentration) of 8.38±3.92 μg·ml−1 and Tmax (time to reach maximum plasma concentration) of 78.0±40.2 min. Our results show that 20 mg·kg−1 of acetaminophen rectally results in low plasma levels in preterm neonates.

Relationship of ectopic placental alkaline phosphatase to ectopic chorionic gonadotropin and placental lactogen. Discordance of three "markers" for cancer.

The relationship of the ectopic presence of three placental proteins in the sera of patients with non‐trophoblastic neoplasms was investigated. The proteins chorionic gonadotropin, placental lactogen, and placental alkaline phosphatase were measured using radioimmune and immunochemical assays which enabled specific and quantitative measurement of each peptide. The results indicate that the presence of each peptide was independent of the others, and that when more than one peptide was found, the concentration of each was independent of the others. These results suggest that the regulation of synthesis of these proteins is not under coordinate control analogous to a single operon in bacterial systems. These findings also indicate that each of these peptides may be used as an independent cancer marker.

Human placental ferritin receptor

Brush-border membranes from human placenta were prepared and their purity was clarified by biochemical and morphological methods. Ferritin binding to these prepared membranes was examined using horse spleen 125I-apoferritin, and was found to be completed within 10 min at 37 degrees C and pH 7.5. The amount of ferritin bound to the membranes was found to be proportional to the amount of membrane added and saturable for a given amount of the membrane in the presence of excess ligand. The membranes exhibited specific ferritin binding with a Ka of 2.3 X 10(7) M-1 at pH 7.5. A competitive binding assay indicated that horse spleen 125I-apoferritin binding was inhibited by a 10-fold molar excess of horse spleen ferric ferritin and a 500-fold molar excess of human transferrin. These results suggest that human placental brush-border membranes have specific receptors for horse spleen apoferritin molecules.

Duration and magnitude of nerve growth factor signaling depend on the ratio of p75LNTR to TrkA.

The role of the low affinity neurotrophin receptor p75LNTR in neurotrophin signal transduction remains open. Recent reports show that this receptor generates intracellular signals independent of Trk activity, and others imply that it collaborates with Trk(s) to enhance cellular responses to low neurotrophin concentrations. We have used the Cytosensor microphysiometer as a direct marker of intracellular metabolic activity to address the physiologic role of p75LNTR in nerve growth factor (NGF) signal transduction. NGF treatment of PC12 or TrkA‐transfected Chinese hamster ovary (CHO) cells results in a rapid, transient increase in the extracellular acidification rate as measured by the Cytosensor; in both cell types, p75LNTR enhances this response. p75LNTR affects both the magnitude of and the duration of the extracellular acidification response to NGF. Moreover, it is not merely the presence of p75LNTR, but also the ratio of p75LNTR:TrkA which determines cellular responsiveness to NGF. In transiently transfected CHO cells, a 5:1 ratio of p75LNTR:trkA cDNAs produced the greatest change in NGF‐induced acid secretion. Pretreatment of PC12 cells with anti‐p75LNTR antibodies decreased the responsiveness to NGF. However, long‐term NGF exposure to PC12 cells in which p75LNTR expression was decreased to approximately 10% of wild‐type levels showed a longer duration of acid secretion compared to wild‐type PC12 cells. Together, these data suggest that p75LNTR may play a dual role in modulating NGF signal transduction by enhancing and extending cellular responses to short‐term ligand exposures while attenuating the metabolic response to long‐term ligand exposures. With regard to potential Trk‐independent p75LNTR signal transduction mechanisms, we detected no change in extracellular acidification response in 75LNTR‐transfected CHO cells, PCNA‐15 fibroblasts, or Schwann cells, all of which express large amounts of p75LNTR and no Trk. Thus, p75LNTR cannot produce any signal detected by microphysiometry in the absence of TrkA. J. Neurosci. Res. 51:442–453, 1998. © 1998 Wiley‐Liss, Inc.

Iron in Cancer

Iron participates in a range of reactions that are necessary for cell viability and cell proliferation. Iron is an essential component in DNA synthesis and in respiratory and oxidative metabolism. These functions relate to the properties of unremitting proliferation and a more anaerobic metabolism, that may contribute to a selective advantage of neoplastic cells over nonneoplastic cells. Clinical correlations have been made linking cellular iron content to the development of cancer in humans. The clinical entities include disease states in which there is abnormal accumulation of iron as part of the disease process, and cases in which neoplasms have developed as a result of administered iron preparations. The molecular mechanisms regulating cellular iron incorporation and the iron-dependent formation of reactive oxygen intermediates that can cause cell injury have been recently elucidated and provide a basis for better understanding the relationship of these processes to neoplastic development.

Characterization of transferrin binding and specificity of the placental transferrin receptor

This study systematically examined the characteristics of specific binding of adult diferric transferrin to its receptor using a Triton X-100 solubilized preparation from human placentas as the receptor source. The following information was obtained. The ionic strength for maximal binding is in the range of 0.1-0.3 M NaCl. The pH optimum for specific binding extends over the range, from pH 6.0-10.0. Specific binding of diferric transferrin is not affected by 2.5 approximately 50 mM CaCl2 or by 10 mM EDTA. Triton X-100 in the concentration range of 0.02-3.0% does not affect specific binding. Specific binding is saturated within 10 min at 25 or 37 degrees C in the presence of excess amounts of diferric transferrin. The binding is reversible and the dissociation of diferric transferrin from the transferrin receptor is complete within 40 min at 25 degrees C. Apotransferrin, both adult and fetal, showed less binding than the holotransferrin species by competitive binding assay in the presence of 10 mM EDTA independent of up to 20 mM CaCl2. A 1500-fold molar excess of adult and fetal apotransferrin is required to give 40% inhibition for 125I-labeled diferric transferrin binding. Since calcium ion is not a factor, and since apotransferrin has such high binding affinity for iron (Ka = 1 X 10(24], this experiment suggests that the EDTA was necessary to prevent conversion of apotransferrin to holotransferrin from available iron in the reaction system. The specificity of the transferrin receptor for transferrin was examined by competitive binding studies in which 125I-diferric transferrin binding was measured in the presence of a series of other proteins. The proteins tested in the competitive binding studies were classified into three groups; in the first group were human serum albumin and ovalbumin; in the second group were proteins containing iron ions, such as hemoglobin, hemoglobin-haptoglobin complex, heme-hemopexin complex, ferritin, and diferric lactoferrin; in the third group were the metal-binding serum proteins, ceruloplasmin and metallothionein. None of these proteins except ferritin showed inhibition of diferric transferrin binding to the receptor. The effect of ferritin was small since a 700- to 1500-fold molar excess of ferritin is required for 50% inhibition of binding of diferric transferrin to the receptor.

Differential expression of tubulin isotypes during the cell cycle

Microtubules play an essential role in cell division. Little is known about possible variations of total tubulin and tubulin isotype expression during the cell cycle. We analyzed the total tubulin content, tubulin polymerization status and tubulin isotype content in resting and dividing human K562 leukemic cells and human MES-SA sarcoma cells. Although the total cellular tubulin content increases as the cells progress toward mitosis, the total tubulin/total protein ratio is stable during the cell cycle. Reverse transcriptase-polymerase chain reaction was applied to analyze the levels of expression of alpha, beta, and gamma-tubulin isotypes. Whereas alpha-tubulin isotype and gamma-tubulin transcripts were found to be expressed at constant levels throughout the cell cycle, some of the beta-tubulin isotype transcripts were found to be more highly expressed in dividing then in resting cells. Both of the class IV beta-tubulin isotype transcripts (human 5 beta and beta 2, Class IVa and IVb, respectively) were expressed in dividing K562 and MES-SA cells at twice the levels found in resting cells. Increased expression of the class IV isotype proteins in dividing cells was confirmed by immunoblotting, both in K562 and in MES-SA cells. A larger fraction of total cell tubulin was found to be polymerized in dividing cells (36-40%) than in resting cells (27-30%). The degree of polymerization of class IV tubulin in dividing and resting cells was similar to that of total tubulin. These results show that total tubulin is expressed as constant levels throughout the cell cycle but that the degree of polymerization is increased as cells are committed to division. The relative overexpression of the two class IV beta-tubulin isotypes in dividing cells suggests functional specificity for these isotypes and a regulatory role of these isotypes on the microtubule network during mitosis.

Transferrin receptor is inversely correlated with estrogen receptor in breast cancer.

SummaryThe transferrin receptor (TfR) has been identified as a marker for proliferation in cells in culture and can be accurately quantitated by specific radioimmunoassay. This study directly quantifies levels of TfR and compares them to levels of estrogen receptor (ER) and progesterone receptor (PgR) in biopsy material obtained from patients with infiltrating ductal carcinoma of the breast. A comparison of ER and TfR levels displayed an exponential distribution which was log-normalized to yield a linear inverse relationship (r = −.44). Although ER was strongly correlated with PgR, there was no correlation pattern between TfR and PgR. Multiple regression analysis indicated that 73% of ER levels could be predicted by a combination of the other two markers, PgR (representing degree of differentiation) and TfR (representing growth rate). Transferrin receptor levels were also found to be correlated (p<.05) with menopausal status, with tumors from premenopausal patients exhibiting higher levels, whereas the opposite pattern was shown for estrogen receptor levels (p<.02). Neither steroid receptor nor transferrin receptor levels were correlated to stage of disease or presence of nodal involvement. Addition of TfR level as an independent marker for proliferation may facilitate the decision-making process in the treatment of individual cases of carcinoma of the breast.

Expression of human placental cell surface antigens on peripheral blood lymphocytes and lymphoblastoid cell lines.

The expression of human placental cell surface antigens was examined in cells of lymphoid origin, including peripheral blood lymphocytes and cultured lymphoblastoid cells of bone marrow or thymus derivation. A select group of this. defined set of surface antigens was detected on all three cell preparations. The most remarkable observation was the conspicuous absence of three subunits previously demonstrated to be present on all human cell surfaces examined to date. Antiserum directed against several placental components prevents adhesion and spreading of cell which grow attached to surfaces. These results suggest a role for these three glycoproteins in mediating cellular adhesion.

Modulation of the transferrin receptor during DMSO-induced differentiation in HL-60 cells

When HL-60 cells are induced to differentiate by dimethyl sulfoxide along a granulocytic pathway there is a fivefold decrease in the total number of transferrin receptors within 3 days, as compared to untreated cells. This decrease is due primarily to a rapid decline in the synthesis of the receptor rather than an increase in the degradation of the receptor. The decrease in transferrin receptor synthesis is a specific and early event that precedes the cessation of cell proliferation, differentiation, and the decrease in total protein synthesis.