Dose-Dependent Neuroprotective Effect of Standardized Bee Venom Phospholipase A2 Against MPTP-Induced Parkinson's Disease in Mice

Parkinson’s disease (PD) is a chronic progressive neurodegenerative movement disorder characterized by the selective loss of dopaminergic neurons within the substantia nigra (SN). While the precise etiology of dopaminergic neuronal demise is elusive, multiple lines of evidence indicate that neuroinflammation is involved in the pathogenesis of PD. We have previously demonstrated that subcutaneous administration of bee venom (BV) phospholipase A₂ (bvPLA₂) suppresses dopaminergic neuronal cell death in a PD mouse model. In the present study, we established standardized methods for producing bvPLA₂ agent isolated from crude BV at good manufacturing practice (GMP) facility. The therapeutic efficacy of purified bvPLA2 agent was examined in MPTP-induced PD mice. Importantly, administration of purified bvPLA₂ in a dose-dependent manner reversed motor deficits in PD mice as well as inhibited loss of dopaminergic neurons within the SN of PD mice. The concentration-dependent action of standardized bvPLA₂ appeared to be related to the induction of CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs), which, in part, inhibits T helper 1 (Th1) and Th17 polarization and suppresses microglial activation in PD mice. Taken together, these results suggest that standardized bvPLA₂ purified from BV shows a neuroprotective effect against PD and thus has a potential target for treatment of PD.

A novel class of phosphonate nucleosides. 9-[(1-phosphonomethoxycyclopropyl)methyl]guanine as a potent and selective anti-HBV agent

9-[1-(Phosphonomethoxycyclopropyl)methyl]guanine (PMCG, 1), representative of a novel class of phosphonate nucleosides, blocks HBV replication with excellent potency (EC(50) = 0.5 microM) in a primary culture of HepG2 2.2.15 cells. It exhibits no significant cytotoxicity in several human cell lines up to 1.0 mM. It does not inhibit replication of human immunodeficiency virus (HIV-1) or herpes simplex virus (HSV-1) at 30 microM. Many purine base analogues of 1 also exhibit inhibitory activity against HBV, but at 30 microM, pyrimidine analogues do not. 1 is 4 times more potent than 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), which was used as a positive control (EC(50) = 2.0 microM). The characteristic cyclopropyl moiety at the 2'-position of 1 was prepared by titanium-mediated Kulinkovich cyclopropanation. 1 was modified to give the orally available drug candidate, PMCDG Dipivoxil (2). Compound 2 exhibited excellent efficacy when administered at 5 mg per kg per day in a study with woodchucks infected with woodchuck hepatitis B virus (WHBV). Drug candidate 2 has successfully completed phase I clinical trials and is currently undergoing phase II clinical studies for evaluation of efficacy.

Transcription inhibition using modified pentanucleotides

Inhibition of gene expression was recently achieved by targeting the transcriptionally competent open complex using relatively short, pentameric modified oligonucleotides at approximately 60 microM. Corroborative affinity cleavage experiments using the copper complex of a phenanthroline conjugate provided the impetus to synthesize additional analogues containing substituents at the 2'-position of uridine in a derivative of 5'-GUGGA (-4 to +1), with the purpose of inhibiting transcription at lower concentrations. Conjugates of 5'-GUGGA modified at the 2'-position of uridine were convergently synthesized using a recently reported method. Seven analogues based upon the 5'-GUGGA scaffold were tested for their ability to inhibit transcription of the lac UV-5 operon. The conjugate containing a tethered pyrene showed 70% inhibition at 20 microM, and modest inhibition at as low as 5 microM. This is a significant improvement over previously tested pentanucleotides and provides direction for the preparation of a next generation of inhibitors.

Covalent trapping of human DNA polymerase beta by the oxidative DNA lesion 2-deoxyribonolactone

Oxidized abasic residues in DNA constitute a major class of radiation and oxidative damage. Free radical attack on the nucleotidyl C-1' carbon yields 2-deoxyribonolactone (dL) as a significant lesion. Although dL residues are efficiently incised by the main human abasic endonuclease enzyme Ape1, we show here that subsequent excision by human DNA polymerase beta is impaired at dL compared with unmodified abasic sites. This inhibition is accompanied by accumulation of a protein-DNA cross-link not observed in reactions of polymerase beta with unmodified abasic sites, although a similar form can be trapped by reduction with sodium borohydride. The formation of the stably cross-linked species with dL depends on the polymerase lysine 72 residue, which forms a Schiff base with the C-1 aldehyde during excision of an unmodified abasic site. In the case of a dL residue, attack on the lactone C-1 by lysine 72 proceeds more slowly and evidently produces an amide linkage, which resists further processing. Consequently dL residues may not be readily repaired by "short-patch" base excision repair but instead function as suicide substrates in the formation of protein-DNA cross-links that may require alternative modes of repair.

Synthesis of 2'-modified oligodeoxynucleotides via on-column conjugation

Oligodeoxynucleotides modified at the 2'-position of 2'-amino-2'-deoxyuridine or uridine were prepared in high yield and purity using phosphoramidites 2 and 3, respectively. Oligodeoxynucleotide conjugates were prepared on the solid-phase synthesis support following selective unmasking of the nucleophile incorporated in these phosphoramidites. Synthesis of oligodeoxynucleotides modified at the 2'-position of an internal nucleotide provides molecules that are complementary to those previously prepared via a similar approach using C5-substituted pyrimidines. The efficiency of functionalization of the 2'-O-alkylamino-uridine derived from 3 in a protected oligodeoxynucleotide was less susceptible to steric hindrance than the 2'-amino-2'-deoxyuridine in the same polymeric substrate. However, the greater reactivity of the 2'-O-alkylamine containing nucleotide gave rise to undesired acetamide formation resulting from nucleophilic attack on the 5'-terminal acetate in capped failure sequences. This problem was overcome by using 2,2,2-trimethylacetyl anhydride as a capping agent during the automated synthesis cycles. Finally, the efficiency of the photochemical unmasking of the support bound alkylamine on a 1 mumole scale was improved by using two 20 min photolysis cycles, coupled with removing reaction byproducts between cycles.

Independent generation and reactivity of 2-deoxy-5-methyleneuridin-5-yl, a significant reactive intermediate produced from thymidine as a result of oxidative stress

2'-Deoxy-5-methyleneuridin-5-yl (1) is produced in a variety of DNA damage processes and is believed to result in the formation of lesions that are mutagenic and refractory to enzymatic repair. 2'-Deoxy-5-methyleneuridin-5-yl (1) was independently generated under anaerobic conditions via Norrish Type I photocleavage during Pyrex filtered photolysis of the benzyl ketone 7. The radical (1) exhibits behavior consistent with that of a resonance-stabilized radical. The KIE for hydrogen atom transfer from t-BuSH was found to be 7.3 +/- 1.7. Competition studies between radical recombination and hydrogen atom donors (2,5-dimethyltetrahydrofuran, kTrap = 46.1 +/- 15.4 M(-1) s(-1); propan-2-ol, kTrap = 13.6 +/- 3.5 M(-1) s(-1)) chosen to mimic the carbohydrate components of 2'-deoxyribonucleotides suggest that 2'-deoxy-5-methyleneuridin-5-yl (1) may be able to transfer damage from the nucleobase to the deoxyribose of an adjacent nucleotide in DNA under hypoxic conditions.

Synthesis of modified oligodeoxyribonucleotides on a solid-phase support via derivatization of a selectively revealed 2'-amino-2'-deoxyuridine

[formula: see text] High yields of oligodeoxyribonucleotides modified at the C2'-position of site specifically incorporated 2'-amino-2'-deoxyuridine are obtained by photolytically unmasking the nucleophile in an otherwise protected solid-phase support-bound biopolymer.

Photosensitization of guanine-specific DNA damage by a cyano-substituted quinoxaline di-N-oxide

The cyano-substituted quinoxaline di-N-oxide (2) is a potential antitumor agent, which selectively kills hypoxic cells. While investigating this drug's potential ability to act as a surrogate for O(2) in DNA damage processes, we discovered that 2 produces alkali-labile lesions selectively at 2'-deoxyguanosine positions upon irradiation in the UV-A (lambda(max) = 350 nm) region. Strand damage is induced in single-stranded and double-stranded substrates, with the latter being slightly more susceptible to lesion formation. Alkaline-labile lesions are formed under aerobic and anaerobic conditions. The efficient formation of alkali-labile lesions by 2 suggests that this molecule may exhibit phototoxicity. Subsequent investigation of this process suggests that photoexcited 2 damages DNA via a type I process. The results of experiments aimed at determining the involvement of singlet O(2) are ambiguous and indicate that commonly used experimental tests for this species may be less definitive than often thought. The involvement of other reactive oxygen species in strand damage, such as hydroxyl radical, is ruled out.

Reaction of the hypoxia-selective antitumor agent tirapazamine with a C1'-radical in single-stranded and double-stranded DNA: the drug and its metabolites can serve as surrogates for molecular oxygen in radical-mediated DNA damage reactions

The compound 3-amino-1,2,4-benzotriazine 1,4-dioxide (1, tirapazamine; also known as SR4233, WIN 59075, and tirazone) is a clinically promising anticancer agent that selectively kills the oxygen-poor (hypoxic) cells found in tumors. When activated by one-electron enzymatic reduction, tirapazamine induces radical-mediated oxidative DNA strand cleavage. Using the ability to generate a single deoxyribose radical at a defined site in an oligonucleotide, we recently provided direct evidence that, in addition to initiating the formation of DNA radicals, tirapazamine can react with these radicals and convert them into base-labile lesions [Daniels et al. (1998) Chem. Res. Toxicol. 11, 1254-1257]. The rate constant for trapping of a C1'-radical in single-stranded DNA by tirapazamine was shown to be approximately 2 x 10(8) M(-1) s(-1), demonstrating that tirapazamine can substitute for molecular oxygen in radical-mediated DNA strand damage reactions. Because reactions of tirapazamine with DNA radicals may play an important role in its ability to damage DNA, we have further characterized the ability of the drug and its metabolites to convert a C1'-DNA radical into a base-labile lesion. We find that tirapazamine reacts with a C1'-radical in double-stranded DNA with a rate constant of 4.6 x 10(6) M(-1) s(-1). The mono-N-oxide (3) stemming from bioreductive metabolism of tirapazamine converts the C1'-radical to an alkaline-labile lesion more effectively than the parent drug. Compound 3 traps a C1'-radical in single-stranded DNA with a rate constant of 4.6 x 10(8) M(-1) s(-1) and in double-stranded DNA with a rate constant of 1.4 x 10(7) M(-)(1) s(-)(1). We have also examined the rate and mechanism of reactions between the C1'-radical and representatives from two known classes of "oxygen mimetic" agents: the nitroxyl radical 2,2,6, 6-tetramethylpiperidin-N-oxyl (4, TEMPO) and the nitroimidazole misonidazole (5). TEMPO traps the C1'-radical in single-stranded DNA (7.2 x 10(7) M(-1) s(-1)) approximately 3 times less effectively than tirapazamine, but 2 times as fast in double-stranded DNA (9.1 x 10(6) M(-1) s(-1)). Misonidazole traps the radical in single- (6. 9 x 10(8) M(-1) s(-1)) and double-stranded DNA (2.9 x 10(7) M(-1) s(-1)) with rate constants that are roughly comparable to those measured for the mono-N-oxide metabolite of tirapazamine. Finally, information regarding the chemical mechanism by which these compounds oxidize a monomeric C1'-nucleoside radical has been provided by product analysis and isotopic labeling studies.

The reactivity of the 2-deoxyribonolactone lesion in single-stranded DNA and its implication in reaction mechanisms of DNA damage and repair

The formal C1'-oxidation product, 2-deoxyribonolactone, is formed as a result of DNA damage induced via a variety of agents, including gamma-radiolysis and the enediyne antitumor antibiotics. This alkaline labile lesion may also be an intermediate during DNA damage induced by copper-phenanthroline. Oligo-nucleotides containing this lesion at a defined site were formed via aerobic photolysis of oligonucleotides containing a photolabile ketone, and were characterized by gel electrophoresis and electrospray mass spectrometry (ESI-MS). Treatment of oligo-nucleotides containing the lesion with secondary amines produces strand breaks consisting of 3'-phosphate termini, and products which migrate more slowly in polyacrylamide gels. MALDI-TOF mass spectrometry analysis indicates that the slower moving products are formal adducts of the beta-elimination product resulting from 2-deoxyribonolactone and one molecule of amine. The addition of beta-mercapto-ethanol to the reaction mixture produces thiol adducts as well. The stability of these adducts suggests that they cannot be the labile species characterized by gel electrophoresis in copper-phenanthroline-mediated strand scission. The characterization of these adducts by mass spectrometry also provides, by analogy, affirmation of proposals regarding the reactivity of nucleophiles with the beta-elimination product of abasic sites. Finally, the effects of this lesion and the various adducts on DNA repair enzymes are unknown, but their facile generation from oligonucleotides containing a photolabile ketone suggests that such issues could be addressed.

Diverging Effects of Steric Congestion on the Reaction of Tributylstannyl Radicals with Areneselenols and Aryl Bromides and Their Mechanistic Implications

The effects of bulky ortho,ortho' groups on the reactions of aryl bromides and areneselenols with tributylstannane have been studied. Bulky ortho,ortho' groups accelerate the reaction of the bromides with the stannane but retard the reactions of the selenols. On the other hand, ab initio and force field calculations show that introducing bulky ortho substituents into selenols causes a greater increase in strain than in the corresponding bromides. Two possible explanations for the divergent reactivity patterns are advanced. On one hand, it is possible that bromine abstraction by stannyl radicals from aryl bromides proceeds in a single step through a linear transition state whereas the abstraction of SeH from the selenols involves a T-shaped, hypervalent intermediate. Alternatively, it may be that both reactions are concerted with the bromine abstraction having a late transition state and the SeH abstraction an early one. Approximate second-order rate constants for the reaction of tributylstannane with a range of hindered aryl bromides are derived from competition reactions. 2,4,6-Tri-tert-butylbenzeneselenol is able to function moderately well as a catalyst for the stannane-mediated reactions of vinyl bromides. The X-ray crystal structure of bis(2,4,6-triisopropylphenyl) diselenide is presented.

Chemistry of 1-Alkoxy-1-glycosyl Radicals: Formation of beta-Mannopyranosides by Radical Decarboxylation and Decarbonylation of manno-Heptulosonic Acid Glycoside Derivatives

A method for the preparation of highly enriched beta-mannopyranosides is described. A glycosyl donor 28 is prepared from tetraallyl mannonolactone by standard means and coupled to a number of primary carbohydrate alcohols, resulting in the isolation in excellent yields of axial disaccharides. Following exchange of the allyl groups for acetyl esters, the furan is oxidatively cleaved with catalytic RuO(2) and NaIO(4) and the resulting acid subjected to the Barton decarboxylation. Coupling of 28 to a secondary alcohol, methyl 2,3-isopropylidene-alpha-L-rhamnopyranoside, resulted in an apparent inversion of anomeric stereochemistry and isolation of an equatorial disaccharide.

Effects of moxibustion on cellular immunocompetence of gamma-irradiated mice

The effects of moxibustion on cellular immunocompetence of gamma-irradiated mice were investigated in this study. A total of 240 male young mice (ICR strain), 6-8 weeks of age, were chosen and divided into three groups. Group A was the normal control. Group B, the experimental control, was treated with 400 rad whole body gamma-irradiation. Group C, the experimental group, was treated with moxibustion (MT) after being exposed to gamma-irradiation. Six to eight mice from each group were sacrificed on days 1, 5, 12, 19, 26 and 33 post-irradiation. The body and splenic weights of mice in each group were measured. The cellular immunocompetence was measured by 3H-thymidine uptake in each experimental mouse. The results revealed that 400 rad of gamma-ray irradiation inhibited the increase of body and splenic weights, and exerted a pronounced inhibitory effect on the incorporative rates of 3H-thymidine after being stimulated by mitogens such as PHA, PWM, Con A and LPS in the splenic lymphoid cells. MT seemed to help the recovery of the cellular immunocompetence in the gamma-ray irradiated mice.