Biomedical subjects

Min Dong

Publications and source records attributed to Min Dong.

22 records · Page 2Linked to original sources

PubMed2003

Stability of 2'-deoxyxanthosine in DNA.

The deamination of nucleobases in DNA occurs by a variety of mechanisms and results in the formation of hypoxanthine from adenine, uracil from cytosine, and xanthine and oxanine from guanine. 2'-Deoxyxanthosine (dX) has been assumed to be an unstable lesion in cells, yet no study has been performed under biological conditions. We now report that dX is a relatively stable lesion at pH 7, 37 degrees C and 110 mM ionic strength, with a half-life (t(1/2)) of 2.4 years in double-stranded DNA. The stability of dX as a 2'-deoxynucleoside (t(1/2) = 3.7 min at pH 2; 1104 h at pH 6) was increased substantially upon incorporation into a single-stranded oligodeoxynucleotide, in which the half-life of dX at different pH values was found to range from 7.7 h at pH 2 to 17 700 h at pH 7. Incorporation of dX into a double-stranded oligodeoxynucleotide resulted in a statistically insignificant increase in the half-life to 20 900 h at pH 7. Data for the pH dependence of the stability of dX in single-stranded DNA were used to determine the rate constants for the acid-catalyzed (2.6 x 10(-5) x s(-1)) and pH-independent (1.4 x 10(-8) x s(-1)) depurination reactions for dX as well as the dissociation constant for the N7 position of dX (6.1 x 10(-4) M). We conclude that dX is a relatively stable lesion that could play a role in deamination-induced mutagenesis.

Amination↗

PubMed2003

Absence of 2'-deoxyoxanosine and presence of abasic sites in DNA exposed to nitric oxide at controlled physiological concentrations.

Nitric oxide (NO(*)) is a physiologically important molecule at low concentrations, while high levels have been implicated in the pathophysiology of diseases associated with chronic inflammation, such as cancer. While an extensive study in vitro suggests that oxidative and nitrosative reactions dominate the complicated chemistry of NO(*)-mediated genotoxicity, neither the spectrum of DNA lesions nor their consequences in vivo have been rigorously defined. We have approached this problem with a major effort to define the spectrum of nitrosative DNA lesions produced by NO(*)-derived reactive nitrogen species under biological conditions. Plasmid pUC19 DNA was exposed to steady state concentrations of 1.3 microM NO(*) and 190 microM O(2) (calculated steady state concentrations of 40 fM N(2)O(3) and 3 pM NO(2)(*) in the bulk solution) in a recently developed reactor that avoids the undesired gas phase chemistry of NO(*) and approximates the conditions at sites of inflammation in tissues. The resulting spectrum of nitrosatively induced abasic sites and nucleobase deamination products was defined using plasmid topoisomer analysis and a novel LC/MS assay, respectively. With a limit of detection of 100 fmol and a sensitivity of 6 lesions per 10(7) nt in 50 microg of DNA, the LC/MS analysis revealed that 2'-deoxyxanthosine (dX), 2'-deoxyinosine (dI), and 2'-deoxyuridine (dU) were formed at nearly identical rates (k = 1.2 x 10(5) M(-1) s(-1)) to the extent of approximately 80 lesions per 10(6) nt after 12 h exposure to NO(*) in the reactor. While reactions with HNO(2) resulted in the formation of high levels of 2'-deoxyoxanosine (dO), one of two products arising from deamination of dG, dO, was not detected in 500 microg of DNA exposed to NO(*) in the reactor for up to 24 h (<6 lesions per 10(8) nt). This result leads to the prediction that dO will not be present at significant levels in inflamed tissues. Another important observation was the NO(*)-induced production of abasic sites, which likely arise by nitrosative depurination reactions, to the extent of approximately 10 per 10(6) nt after 12 h of exposure to NO(*) in the reactor. In conjunction with other studies of nitrosatively induced dG-dG cross-links, these results lead to the prediction of the following spectrum of nitrosative DNA lesions in inflamed tissues: approximately 2% dG-dG cross-links, 4-6% abasic sites, and 25-35% each of dX, dI, and dU.

DNA Damage↗

PubMed2003

Cross-binding between Plasmodium falciparum CTL epitopes and HLA class I molecules.

Plasmodium falciparum CTL epitope minigenes containing HLA-A2 and HLA-B7 subtype supermotifs were cloned into a plasmid expression vector; this expression was measured in eight human HLA class I molecule specific cell lines. Three assays for in vitro antigen presentation analysis were developed to examine the cross-binding between CTL epitopes and HLA class I molecules, including cell surface peptide-MHC class I binding assay, binding stabilization assay and MHC class I assembling assay. The results demonstrated that the HLA-B51 restricted CTL epitope of Plasmodium falciparum could be presented by other HLA class I molecules; however, no other presentation was found for HLA-A2.1 CTL epitope. This work suggests the possibility for improved vaccine-coverage rates by development of a CTL vaccine which contains epitopes capable of cross-binding among different MHC class I alleles.

Animals↗

PubMed2003

[Effect of Citrus aurantium extract on L-type calcium currents in ventricular myocytes of single guinea pigs].

OBJECTIVE: To determine the effect of citrus aurantium extract (CAE) on L-type calcium currents (ICa-L) in ventricular myocytes of guinea pigs. METHODS: Single myocytes were dissociated by enzymatic dissociation method. The whole-cell patch-clamp recording technique was used to record the change of calcium current after the administration of CAE. RESULTS: 1. CAE 4 x 10(-3), 2 x 10(-2), 4 x 10(-2), and 1 x 10(-1) g/ml increased the ICa-L by 15.89%, 29.01%, 52.03% and 59.76% (P < 0.05), respectively. 2. CAE 2 x 10(-1) and 4 x 10(-1) g/ml decreased the ICa-L by 16.61% and 30.87% (P < 0.05), respectively. CAE changed the ICa-L significantly, but did not change the shape of I-V curves. CONCLUSIONS: CAE 4 x 10(-3)-1 x 10(-1) g/ml can increase the L-type calcium current in guinea pig ventricular myocytes significantly in a concentration-dependent manner, and promote the opening of calcium channel. CAE 2 x 10(-1)-4 x 10(-1) g/ml may inhibit the L-type calcium channels of ventricular myocytes, and depress the opening of calcium channel.

Animals↗