Effect of germanium-132 on galactose cataracts and glycation in rats

Inhibitory effect of organogermanium compound 3-(trihydroxygermyl)propanoic acid on fructose-induced glycation of amino compounds

3-(Trihydroxygermyl)propanoic acid (THGP), a hydrolysate of poly-trans-[(2-carboxyethyl)germasesquioxane] (Ge-132, also known as repagermanium), can inhibit glycation between glucose/ribose and amino compounds. In addition, THGP may inhibit glycation by inhibiting reactions that occur after Amadori rearrangement and inducing the reversible solubilization of AGEs. In this study, we first investigated the effects and mechanisms on the glycation of fructose and amino compounds by THGP, as a greater reactivity was obtained with fructose than with glucose. Unlike other anti-glycation materials, THGP can form a complex with fructose, the initial compound of glycation. THGP also inhibited the production of AGEs and suppressed the reduction of fructose in a reaction between fructose and arginine. These results indicate that THGP forms a complex with cyclic fructose possessing a cis-diol structure at a reducing end, and that it suppresses the ring-opening of fructose and the progress of the initial glycation reaction. We next tried to evaluate the suppressive effect of glucosyl hesperidin (GHes) and THGP on the reaction of glycation between fructose and collagen. Both compounds effectively reduced the production of AGEs individually, and the combination of them led to a synergistic suppression. Therefore, through combination with other antiglycation materials, THGP may cooperatively exhibit glycation-inhibitory effects and be able to suppress the AGE production.

Quantitative assessment of the interactions between the organogermanium compound and saccharides using an NMR reporter molecule

Poly-trans-[(2-carboxyethyl)germasesquioxane], Ge-132, is a water-soluble organogermanium compound reported to have physiological effects such as immunostimulatory and antiviral effects. The hydrolysate of Ge-132, 3-(trihydroxygermyl)propanoic acid (THGP), can interact with diols; therefore, it likely can interact with diol-containing sugars in sugar chains, glycoproteins, and glycolipids, which have important physiological functions. In this study, we quantitatively assessed the ability of THGP to interact with saccharides using nuclear magnetic resonance (NMR) spectroscopy and THGP derivatives. THGP was complexed by binding its trihydroxy group with saccharides in aqueous solutions via the cis-diol group rather than the trans-diol group. The spectra of THGP and monosaccharides indicated that THGP has a higher affinity for ketose than aldose. Moreover, the complexation ability between THGP and saccharides was influenced by the number of cis-diol groups on the saccharide structure. Thus, interactions of THGP with important biological sugars might be involved in the physiological functions of Ge-132.

Emerging role of advanced glycation-end products (AGEs) in the pathobiology of eye diseases

Advanced glycation end products (AGEs) have been implicated in vision loss associated with macula degeneration, cataract formation, diabetic retinopathy and glaucoma. This pathogenic potential is mainly attributed to their accumulation in ocular tissues where they mediate aberrant crosslinking of extracellular matrix proteins and disruption of endothelial junctional complexes that affects cell permeability, mediates angiogenesis and breakdown of the inner blood-retinal barrier. Furthermore, AGEs severely affect cellular metabolism by disrupting ATP production, enhancing oxidative stress and modulating gene expression of anti-angiogenic and anti-inflammatory genes. Elucidation of AGE-induced mechanisms of action in different eye compartments will help in the understanding of the complex cellular and molecular processes associated with eye diseases. Several pharmaceutical agents with anti-glycating and anti-oxidant properties as well as AGE crosslink 'breakers' have been currently applied to eye diseases. The role of diet and the beneficial effects of certain nutriceuticals provide an alternative way to manage chronic visual disorders that affect the quality of life of millions of people.

Effect of germanium-132 on low-density lipoprotein oxidation and atherosclerosis in Kurosawa and Kusanagi hypercholesterolemic rabbits

Germanium-132 (Ge-132) was given at 200 mg/kg of body weight to 8-week-old Kurosawa and Kusanagi hypercholesterolemic (KHC) rabbits. Thirty-six weeks later, the susceptibility of plasma low-density lipoprotein to oxidation and the morphology of atherosclerosis in the aorta and coronary artery were investigated. Treatment with Ge-132 resulted in decreases in the oxidation rate and in the formation rate of thiobarbituric acid-reactive substances following copper-induced oxidation of LDL. Ge-132 is suggested to possess antioxidative properties, but this did not lead to any attenuation of atherosclerotic progression in the KHC rabbits.

Inhibitors of advanced glycation end product-associated protein cross-linking

The reaction of lens proteins with sugars over time results in the formation of protein-bound advanced glycation end products (AGEs). The most damaging element of AGE formation may be the synthesis of protein-protein cross-links in long-lived proteins, such as collagen or lens crystallins. A quantitative cross-linking assay, involving the sugar-dependent incorporation of [U-(14)C]lysine into protein, was employed to determine the efficacy of a variety of potential cross-linking inhibitors. Reaction mixtures contained 5.0 mM L-threose, 2.5 microCi [(14)C]lysine (1.0 mCi/mmole), 5.0 mg/ml bovine lens proteins, 0-10 mM inhibitor and 1.0 mM DTPA in 100 mM phosphate buffer, pH 7.0. Of 17 potential inhibitors tested, 11 showed 50% inhibition or less at 10 mM. The dicarbonyl-reactive compounds 2-aminoguanidine, semicarbazide and o-phenylenediamine inhibited 50% at 2.0 mM, whereas 10 mM dimethylguanidine had no effect. Several amino acids failed to compete effectively with [(14)C]lysine in the cross-linking assay; however, cysteine inhibited 50% at 1.0 mM. This was likely due to the sulfhydryl group of cysteine, because 3-mercaptopropionic acid and reduced glutathione exhibited similar activity. Sodium metabisulfite had the highest activity, inhibiting 50% at only 0.1-0.2 mM. Protein dimer formation, as determined by SDS-PAGE, was inhibited in a quantitatively similar manner. The dicarbonyl-reactive inhibitors and the sulfur-containing compounds produced similar inhibition curves for [(14)C]lysine incorporation over a 3 week assay with 250 mM glucose. A much lesser effect was observed on either the incorporation of [(14)C]glucose, or on fluorophore formation (360/420 nm), suggesting that non-cross-link fluorophores were also formed. The inhibitor data were consistent with cross-linking by a dicarbonyl intermediate. This was supported by the fact that the inhibitors were uniformly less effective when the 5.0 mM threose was replaced by either 3.0 mM 3-deoxythreosone or 3.0 mM threosone.

Effect of pretreatment of germanium-132 on Na(+)-K(+)-ATPase and galactose cataracts

PURPOSE

Recently, we reported that topical administration of 2-carboxyethyl germanium sesquioxide (Ge-132) concurrently with 50% galactose feeding delayed the establishment of mature cataracts and reduced advance glycation product. This study was to determine the effect of pretreatment of Ge-132 on galactose associated morphological changes and Na(+)-K(+)-ATPase activity.

METHODS

Young Sprague Dawley rats received topical eye drops four times a day of either saline or Ge-132 seven days prior to the 50% galactose diet and during galactose feeding. At desired intervals the lenses were extracted, photographed and processed for either light microscopy, scanning electron microscopy or the determination of Na(+)-K(+)-ATPase activity.

RESULTS

In Ge-132 pretreated lenses as compared to saline pretreated lenses the following results were observed: (a) the galactose-induced morphological alterations in the majority of lenses were delayed and (b) Na(+)-K(+)-ATPase activity was protected.

CONCLUSIONS

Our previous and current studies show that in addition to osmotic stress post-translational protein modification, such as glycation, including enzymes may play a role in initiating changes that lead to cataract development. The inhibition of protein glycation by antiglycating compounds, such as Ge-132, delays sugar cataract formation. Currently, we are investigating the status of protein glycation and advanced glycation end products following pretreatment with Ge-132 and the role of Ge-132 on the activities of enzymes such as aldose reductase and Na(+)-K(+)-ATPase.

Identification of hydrogen peroxide oxidation sites of alpha A- and alpha B-crystallins

The alpha-crystallins are the most abundant structural proteins of the lens and, because of their chaperone activity, contribute to the solubility of the other crystallins. With aging, the lens crystallins undergo a variety of modifications which correlate with a loss of solubility and the development of cataract. A recent study demonstrating that alpha-crystallins exposed in vitro to FeCl3 and H2O2 exhibit decreased chaperone activity, implicates metal catalyzed oxidations of alpha-crystallins in this loss of solubility. The present study has determined that alpha-crystallins incubated with FeCl3 and H2O2 are modified by the nearly complete oxidation of all methionine residues to methionine sulfoxide, with no other detectable reaction products. The modifications were identified from the molecular weights of peptides formed by enzymatic digestion of the alpha-crystallins and located by tandem mass spectrometric analysis of the fragmentation pattern of the mass spectra of the fragments from peptides with oxidized methionine is loss of 64 Da, which corresponds to loss of CH3SOH from the methionine sulfoxide. These fragments are useful in identifying peptides that include oxidized methionine residues.