Itzhak Goldwaser

Historic perspective and recent developments on the insulin-like actions of vanadium; toward developing vanadium-based drugs for diabetes

Abstract Intensive studies have been carried out during the last two decades, on the insulinomimetic effects of vanadium. Vanadium compounds mimic most of the metabolic effects of insulin on the main tissues of the hormone in vitro. Vanadium therapy induces normoglycemia and improves glucose homeostasis in insulin deficient and insulin resistant diabetic rodents. Improved sensitivity to insulin in liver and muscle tissues of Type II diabetic patients following vanadium therapy was observed as well. The key mechanisms involved are inhibition of protein–phosphotyrosine phosphatases and activation of nonreceptor protein–tyrosine kinases, in an insulin-receptor tyrosine kinase independent fashion. Vanadate activates glucose-metabolism in vitro at a site preceding activation of phosphatidylinositol-3-kinase (PI3-kinase). Regarding inhibition of lipolysis, vanadate (but not insulin) acts at a site downstream to the activation of PI3 kinase. Additional vanadium-dependent mechanism, operating in vivo, is the restoration of glucose-6-phosphate levels in liver, muscle and adipose tissue of hyperglycemic diabetic rats. This is attributed to vanadate-dependent inhibition of liver glucose-6-phosphatase, and of nonspecific hexose-6-phosphatases of the diabetic muscle and adipose tissues. Initial clinical studies were already performed. Several beneficial effects were documented. The potential usage of vanadium in the future care of diabetes in human, however, depends on manipulations that would elevate the insulinomimetic efficacy of vanadium without increasing its toxicity. Organically chelated vanadium compounds, in particular, the l -isomer of Glu(γ) monohydroxamate ( l -Glu(γ)HXM) are active in potentiating the capacity of free vanadium to activate glucose metabolism, in vitro and in diabetic rats in vivo. l -Glu(γ)HXM differs from other vanadium ligands in being an amino acid derivative that permeates into peripheral tissues through the amino acid transport system. In rat adipocytes, l -Glu(γ)HXM itself activates partially glucose metabolism, by permeating into cell interior, associating with the minute quantity of intracellular vanadium, and turning it into an insulinomimetic active species. l -Glu(γ)HXM, associates with the vanadyl (+4) cation, and the vanadate (+5) anion, at neutral pH with nearly the same binding affinity. Both these oxidation states of vanadium are insulinomimetic. The therapeutical potency of l -Glu(γ)HXM·vanadium complexes is actively studied. Preliminary results on this issue are to be presented.

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.

Immunogenicity, protective efficacy and mechanism of novel CCS adjuvanted influenza vaccine.

We optimized the immunogenicity of adjuvanted seasonal influenza vaccine based on commercial split influenza virus as an antigen (hemagglutinin = HA) and on a novel polycationic liposome as a potent adjuvant and efficient antigen carrier (CCS/C-HA vaccine). The vaccine was characterized physicochemically, and the mechanism of action of CCS/C as antigen carrier and adjuvant was studied. The optimized CCS/C-HA split virus vaccine, when administered intramuscularly (i.m.), is significantly more immunogenic in mice, rats and ferrets than split virus HA vaccine alone, and it provides for protective immunity in ferrets and mice against live virus challenge that exceeds the degree of efficacy of the split virus vaccine. Similar adjuvant effects of optimized CCS/C are also observed in mice for H1N1 swine influenza antigen. The CCS/C-HA vaccine enhances immune responses via the Th1 and Th2 pathways, and it increases both the humoral responses and the production of IL-2 and IFN-γ but not of the pro-inflammatory factor TNFα. In mice, levels of CD4(+) and CD8(+) T-cells and of MHC II and CD40 co-stimulatory molecules are also elevated. Structure-function relationship studies of the CCS molecule as an adjuvant/carrier show that replacing the saturated palmitoyl acyl chain with the mono-unsaturated oleoyl (C18:1) chain affects neither size distribution and zeta potential nor immune responses in mice. However, replacing the polyalkylamine head group spermine (having two secondary amines) with spermidine (having only one secondary amine) reduces the enhancement of the immune response by ∼ 50%, while polyalkylamines by themselves are ineffective in improving the immunogenicity over the commercial HA vaccine. This highlights the importance of the particulate nature of the carrier and the polyalkylamine secondary amines in the enhancement of the immune responses against seasonal influenza. Altogether, our results suggest that the CCS/C polycationic liposomes combine the activities of a potent adjuvant and efficient carrier of seasonal and swine flu vaccines and support further development of the CCS/C-HA vaccine.

Oral therapy of L-glutamic acid γ-monohydroxamate-vanadium (2:1) complex: Improvement of blood glucose profile in different types of diabetic rodents

We report that oral administration of vanadium (+5) combined with L-glutamic acid γ-monohydroxamate at 1:2 stoichiometry [L-Glu(γ)HXM.VO3-] is highly effective in reducing blood glucose levels (BGLs) in a wide variety of diabetic rodents. In streptozocin-treated rats, a single administration (0.28 mmol/kg body wt) decreased BGL from 490 to 360 mg/dl within 1 h of administration, keeping this reduced level for additional 22 h, and a daily dose of 0.14 mmol/kg was found optimal. In Zucker diabetic fatty (ZDF) rats, a single dose of 0.14 mmol/kg normalized BGL within 8 h of administration, and maintained normal value for additional two days. In db/db mice, a single L-Glu(γ)HXM.VO3- administration of 0.2 mmol/kg decreased BGL from 500 ± 50 to 240 ± 20 mg/dl at 2 h, but was less effective afterwards. In high-carbohydrate (CHO)-fed Psammomis obesus, a single oral dose (0.14 mmol/kg) normalized BGL over a period of two days, and a daily dose of 0.07 mmol/kg/d, at the time P. obesus was transferred from low- to high-CHO diet, fully arrested the development of hyperglycemia characterizing this diabetic rodent. Finally, we found that the index of toxicity of orally administered L-GLU(γ)HXM-vanadate in rodents is 5-7 times lower than that of free sodium vanadate.

Potentiating vanadium-evoked glucose metabolism by novel hydroxamate derivatives

L-glutamic acid (γ) monohydroxamate (L-Glu(γ)HXM) enhances the insulinomimetic activity of vanadium ions bothin vitro andin vivo. Based on this ligand as a lead compound, and in order to delineate molecular features relevant to its anti-diabetic potential, 14 related derivatives, including short peptides, were synthesized by solution as well as by solid phase methodologies. In addition, hydroxamate derivatives of (+) pantothenic acid and D-biotin were prepared. The vanadium binding, capacity of the hydroxamates synthesized was apparent, yet each had a different ligand-ions stoichiometry. Thein vitro lipogenic potency of several compounds toward rat adipocytes was demonstrated. Thus, vanadium complexes of L-Gln(α)HXM, L-Glu(γ)HXM-Gly, L-Aad(δ)HXM, di-Glu-γ,γ-HXM and of (+) pantothenic acid hydroxamate exhibited 82, 79, 76, 39 and 39% of maximal insulin activity, respectively. L-Aad (δ)HXM, L-Glu(γ)HXM-Gly and (+) pantothenic acid hydroxamate-by themselves —were found to possess 24, 14 and 10% of maximal insulin activity, respectively.In vivo potency, however, of L-Gln(α)HXM vanadium complex in streptozocin-treated rat diabetic model was less apparent.