Biomedical subjects

E Gershonov

Publications and source records attributed to E Gershonov.

8 recordsLinked to original sources

PubMed2000

A novel approach for a water-soluble long-acting insulin prodrug: design, preparation, and analysis of [(2-sulfo)-9-fluorenylmethoxycarbonyl](3)-insulin.

In this study we designed, prepared, and analyzed a water-soluble, long-acting insulin derivative whose protracted action in vivo is based on a new principle rather than on slower absorption rates of suspended insulin formulations. To this end, we have prepared (9-fluorenylmethoxycarbonyl-SO(3)H)(3)-insulin ((FMS)(3)-insulin), a derivative having three 9-fluorenylmethoxycarbonyl-SO(3)H (FMS) moieties covalently linked to the three amino side chains of insulin. (FMS)(3)-insulin is soluble in aqueous buffers at neutral pH, at a concentration range of 0.15-0.60 mM, and has about 1% of both the biological potency and the receptor-binding affinity of the native hormone. Upon incubation at pH 7.4 and 37 degrees C, it undergoes a slow hydrolysis with linear regeneration of insulin possessing full biological potency. A single subcutaneous administration of (FMS)(3)-insulin to streptozocin-treated rats lowered circulating glucose levels for a prolonged period (t(1/2) = 30 h). Similarly, intraperitoneal administration of (FMS)(3)-insulin to healthy rats had a prolonged glucose-lowering effect. In this experimental system, recovery from hypoglycemia proceeded with a t(1/2) value of 14 +/- 1 h, as compared with t(1/2) = 8.0 +/- 1 h for native insulin and t(1/2) = 10.0 +/- 1 h for NPH-insulin. (FMS)(3)-insulin is more resistant to proteolysis and appears to be nonimmunogenic. On the whole, (FMS)(3)(-)insulin represents a prototype version of a water-soluble, long-acting preparation of insulin. It is nearly inactive at the time of administration, and therefore can be administered, at high dose, with no concern for hypoglycemia. Because of its decreased receptor-binding affinity, (FMS)(3)-insulin evades receptor-mediated endocytosis and degradation and, hence, persists for a long period in the circulation. The insulin constituent of the (FMS)(3)-insulin conjugate undergoes a slow, spontaneous activation in the circulatory system, manifesting a prolonged glucose-lowering action in vivo. According to the data presented here, (FMS)(3)-insulin represents a typical prodrug: a compound which by itself shows only marginal activity but over time it is chemically hydrolyzed to the fully active hormone.

Adipocytes↗

PubMed2000

Insulin-like effects of vanadium: basic and clinical implications.

Most mammalian cells contain vanadium at a concentration of about 20 nM, the bulk of which is probably in the reduced vanadyl (+4) form. Although this trace element is essential and should be present in the diet in minute quantities, no known physiological role for vanadium has been found thus far. In the late 1970s the vanadate ion was shown to act as an efficient inhibitor of Na+,K+-ATPase as well as of other related phosphohydrolases. In 1980 vanadium was reported to mimic the metabolic effects of insulin in rat adipocytes. During the last decade, vanadium has been found to act in an insulin-like manner in all three main target tissues of the hormone, namely skeletal muscles, adipose, and liver. Subsequent studies revealed that the action of vanadium salts is mediated through insulin-receptor independent alternative pathway(s). The investigation of the antidiabetic potency of vanadium soon ensued. Vanadium therapy was shown to normalize blood glucose levels in STZ-rats and to cure many hyperglycemia-related deficiencies. Therapeutic effects of vanadium were then demonstrated in type II diabetic rodents, which do not respond to exogenously administered insulin. Finally, clinical studies indicated encouraging beneficial effects. A major obstacle, however, is overcoming vanadium toxicity. Recently, several organically chelated vanadium compounds were found more potent and less toxic than vanadium salts in vivo. Such a newly discovered organic chelator of vanadium is described in this review.

Adipose Tissue↗

PubMed2000

Organic vanadium chelators potentiate vanadium-evoked glucose metabolism in vitro and in vivo: establishing criteria for optimal chelators.

Several ligands, when complexed with vanadium, potentiate its insulinomimetic activity both in vivo and in vitro. We have recently found that L-Glu-gamma-monohydroxamate (HXM) and L-Asp(beta)HXM were especially potent in this regard. In the present study, we used vanadium-enriched adipose cells and cell-free experimental systems to determine the features of L-Glu(gamma)HXM and L-Asp(beta)HXM that turn these ligands into optimal-synergizing vanadium chelators. We found that L-Glu(gamma)HXM and L-Asp(beta)(HXM) possess the following characteristics: 1) They associate with vanadium(+5) at pH 7.2 within a narrow range of an apparent formation constant of 1.3 to 1.9 x 10(2) M(-1); 2) they have nearly the same binding affinity for the vanadyl(+4) cation and the vanadate(+5) anion at physiological pH values; and 3) they form intense ultraviolet absorbing complexes upon associating with vanadium(+4) at 1 and 3 M stoichiometry, respectively, at pH 3.0. Vanadium ligands lacking any of these three defined criteria synergize less effectively with vanadium to activate glucose metabolism.

Adipocytes↗

PubMed2000

Vanadate restores glucose 6-phosphate in diabetic rats: a mechanism to enhance glucose metabolism.

Vanadate mimics the metabolic actions of insulin. In diabetic rodents, vanadate also sensitizes peripheral tissues to insulin. We have analyzed whether this latter effect is brought about by a mechanism other than the known insulinomimetic actions of vanadium in vitro. We report that the levels of glucose 6-phosphate (G-6-P) in adipose, liver, and muscle of streptozotocin-treated (STZ)-hyperglycemic rats are 77, 50, and 58% of those in healthy control rats, respectively. Normoglycemia was induced by vanadium or insulin therapy or by phlorizin. Vanadate fully restored G-6-P in all three insulin-responsive peripheral tissues. Insulin did not restore G-6-P in muscle, and phlorizin was ineffective in adipose and muscle. Incubation of diabetic adipose explants with glucose and vanadate in vitro increased lipogenic capacity three- to fourfold (half-maximally effective dose = 11 +/- 1 microM vanadate). Lipogenic capacity was elevated when a threshold level of approximately 7.5 +/- 0.3 nmol G-6-P/g tissue was reached. In summary, 1) chronic hyperglycemia largely reduces intracellular G-6-P in all three insulin-responsive tissues; 2) vanadate therapy restores this deficiency, but insulin therapy does not restore G-6-P in muscle tissue; 3) induction of normoglycemia per se (i.e., by phlorizin) restores G-6-P in liver only; and 4) glucose and vanadate together elevate G-6-P in adipose explants in vitro and significantly restore lipogenic capacity above the threshold of G-6-P level. We propose that hyperglycemia-associated decrease in peripheral G-6-P is a major factor responsible for peripheral resistance to insulin. The mechanism by which vanadate increases peripheral tissue capacity to metabolize glucose and to respond to the hormone involves elevation of this hexose phosphate metabolite and the cellular consequences of this elevated level of G-6-P.

Adipose Tissue↗

PubMed1999

L-Glutamic acid gamma-monohydroxamate. A potentiator of vanadium-evoked glucose metabolism in vitro and in vivo.

We report that the vanadium ligand L-Glu(gamma)HXM potentiates the capacity of free vanadium ions to activate glucose uptake and glucose metabolism in rat adipocytes in vitro (by 4-5-fold) and to lower blood glucose levels in hyperglycemic rats in vivo (by 5-7-fold). A molar ratio of two L-Glu(gamma)HXM molecules to one vanadium ion was most effective. Unlike other vanadium ligands that potentiate the insulinomimetic actions of vanadium, L-Glu(gamma)HXM partially activated lipogenesis in rat adipocytes in the absence of exogenous vanadium. This effect was not manifested by D-Glu(gamma)HXM. At 10-20 microM L-Glu(gamma)HXM, lipogenesis was activated 9-21%. This effect was approximately 9-fold higher (140 +/- 15% of maximal insulin response) in adipocytes derived from rats that had been treated with vanadium for several days. Titration of vanadium(IV) with L-Glu(gamma)HXM led to a rapid decrease in the absorbance of vanadium(IV) at 765 nm, and (51)V NMR spectroscopy revealed that the chemical shift of vanadium(IV) at -490 ppm disappeared with the appearance of a signal characteristic to vanadium(V) (-530 ppm) upon adding one equivalent of L-Glu(gamma)HXM. In summary, L-Glu(gamma)HXM is highly active in potentiating vanadium-activated glucose metabolism in vitro and in vivo and facilitating glucose metabolism in rat adipocytes in the absence of exogenous vanadium probably through conversion of trace intracellular vanadium into an active insulinomimetic compound. We propose that the active species is either a 1:1 or 2:1 L-Glu(gamma)HXM vanadium complex in which the endogenous vanadium(IV) has been altered to vanadium(V). Finally we demonstrate that L-Glu(gamma)HXM- and L-Glu(gamma)HXM.vanadium-evoked lipogenesis is arrested by wortmannin and that activation of glucose uptake in rat adipocytes is because of enhanced translocation of GLUT4 from low density microsomes to the plasma membrane.

Adipocytes↗

PubMed1999

New concept for long-acting insulin: spontaneous conversion of an inactive modified insulin to the active hormone in circulation: 9-fluorenylmethoxycarbonyl derivative of insulin.

Insulin is a short-lived species in the circulatory system. After binding to its receptor sites and transmission of its biological signals, bound insulin undergoes receptor-mediated endocytosis and consequent degradation. An inactive insulin derivative that is not recognized by the receptor has a longer circulation life, but obviously is biologically impotent. (Fmoc)2 insulin is an insulin derivative purified through high-performance liquid chromatography in which two 9-fluorenylmethoxycarbonyl (Fmoc) moieties are covalently linked to the (alpha-amino group of phenylalanine B1 and the epsilon-amino group of lysine B29. It has 1-2% of the biological potency and receptor binding capacity of the native hormone. After incubation, (Fmoc)2 insulin undergoes a time-dependent spontaneous conversion to fully active insulin in aqueous solution at 37 degrees C and a pH range of 7-8.5. At pH 7.4, the conversion proceeds slowly (t1/2 = 12 +/- 1 days) and biological activity is generated gradually. A single subcutaneous administration of (Fmoc)2 insulin to streptozocin-treated diabetic rats normalized their blood glucose levels and maintained the animals in an anabolic state over 2-3 days. A broad shallow peak of immunoreactive insulin was found to persist in circulation over this period. To confirm further that the long-acting effect of (Fmoc)2 insulin proceeds via slow release in the blood circulation itself, we administered native insulin, NPH insulin, or the (Fmoc)2 derivative intraperitoneally. The rats recovered from hypoglycemia at t1/2 = 8.0 +/- 0.3 and 10 +/- 0.4 h after administration of native and NPH insulin, respectively. In contrast, (Fmoc)2 insulin was active for a significantly longer time, with an extended onset of t1/2 = 26 +/- 1h, and a glucose-lowering effect even 40 h after administration. (Fmoc)2 insulin was also found to be more resistant to proteolysis. Finally, we found that (Fmoc)2 insulin does not induce antigenic effects. In summary, we present here a new concept for prolonging the half-life of insulin in the circulatory system, in which receptor-mediated endocytosis and degradation is delayed and accompanied by a time-dependent generation of basal insulin.

Animals↗

PubMed1996

1-Aminocyclobutanecarboxylic acid derivatives as novel structural elements in bioactive peptides: application to tuftsin analogs.

Four novel 2,4-methano amino acids (MAAs, 1-aminocyclobutane-1-carboxylic acids) were synthesized. These include the basic MAA analogs of lysine (16), ornithine (5), and arginine (6) and the neutral methanovaline (22), related to proline. The above MAAs, as well as the MAA analog of homothreonine (7), were incorporated into the peptide chain of the immunomodulatory peptide tuftsin, Thr-Lys-Pro-Arg, known to enhance several biological activities mediated by phagocytic cells. The synthetic methano tuftsin analogs were assayed for their ability to stimulate interleukin-6 (IL-6) secretion by mouse peritoneal macrophages and for their stability in human serum toward enzymatic degradation. It was found that, at 2 x 10(-7) M, [MThr1]tuftsin (24) and an isomer of [MVal3]tuftsin (27a) were considerably more active than the parent peptide in augmentation of cytokine release. [MOrn2]Tuftsin (25) was equally potent. The analogs [MThr1]tuftsin (24) and [MOrn2]tuftsin (25), both pertaining to the proteolytically sensitive Thr-Lys bond of tuftsin, exhibited high resistance to enzymatic hydrolysis as compared to tuftsin. Using specific rabbit anti-tuftsin antibodies in a competitive enzyme-linked immunosorbent assay (ELISA) revealed that none of the MAA analogs can cross-react with tuftsin. It may indicate that the peptides assume global structures different than that of tuftsin.

Amino Acids↗

PubMed1994

Novel psi-S-CH2 peptide-bond replacement and its utilization in the synthesis of nonpeptidic surrogates of the Leu-Asp-Val sequence that exhibit specific inhibitory activities on CD4+ T cell binding to fibronectin.

The Leu-Asp-Val-(LDV)-containing amino acid sequence, derived from the alternatively spliced first connecting segment region of fibronectin (FN), was shown to be recognized primarily by the alpha 4 beta 1-integrin receptor expressed on the surface of various cell types. This adhesion epitope may therefore inhibit integrin-mediated cell interactions with the extracellular matrix glycoprotein, including adhesion, migration, activation and differentiation. To probe the structural requirements for LDV recognition by integrins and examine the feasibility of inhibition of LDV-dependent cell-FN interactions, we have designed and constructed a novel psi-S-CH2 peptide bond surrogate that was employed in the formation of LDV surrogates. The synthesis of the psi-S-CH2 surrogates reported herein is based on Michael addition of 4-methylpentane thiol to an itaconic acid diester to form an S-CH2 bond. We have found that the LDV surrogates comprises of 4-methylpentanoate-Asp-i-butyl amide and 8-methyl-3-(2-methylpropylaminocarbonyl)-5-thianonanoic acid interfered with CD4+ human T-cell adhesion to FN in vitro, with an ED50 of 280 micrograms/mL. A control structural mimetic of the Leu-Glu-Val (LEV) peptide did not interfere with the T-cell-FN interaction. The specificity of the reaction was substantiated by the finding that the LDV mimetics did not interfere with T-cell adhesion to laminin, another major cell-adhesive glycoprotein of the extracellular matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

Amides↗