TRIPLEX-DNA STABILIZATION BY HYDRALAZINE AND THE PRESENCE OF ANTI-(TRIPLEX DNA) ANTIBODIES IN PATIENTS TREATED WITH HYDRALAZINE

Hydralazine is an antihypertensive drug that elicits anti-nuclear antibodies in patients as an adverse effect. We investigated the ability of hydralazine to promote/stabilize the tripler DNA form of poly(dA). 2poly(dT). Under conditions of low ionic strength, the polynucleotide melted as a double helix with a melting temperature (T-m) of 55.3 degrees C. Hydralazine destabilized this duplex form by reducing its T-m to 52.5 degrees C. Spermidine (2.5 mu M), a natural polyamine, provoked the tripler form of poly(dA)-. 2poly(dT) with two melting transitions, T-m1 of 42.8 degrees C corresponding to tripler --> duplex + single-stranded DNA and T-m2 of 65.4 degrees C, corresponding to duplex melting. Tripler DNA thus formed in the presence of spermidine was further stabilized by hydralazine (250 mu M) with a T-m1 of 53.6 degrees C. A similar stabilization effect of hydralazine was found on tripler DNA formed in the presence of 5 mM Mg2+. CD spectra revealed conformational perturbations of DNA in the presence of spermidine and hydralazine. These results support the hypothesis that hydralazine is capable of stabilizing unusual forms of DNA. In contrast with the weak immunogenicity of DNA in its right-handed B-DNA conformation, these unusual forms are immunogenic and have the potential to elicit anti-DNA antibodies. To test this possibility, we analysed sera from a panel of 25 hydralazine-treated patients for anti-(tripler DNA) antibodies using an ELISA. Our results showed that 72% of sera from hydralazine-treated patients contained antibodies reacting toward the tripler DNA. In contrast, there was no significant binding of normal human sera to tripler DNA. Taken together our data indicate that hydralazine and related drugs might exert their action by interacting with DNA and stabilizing higher-order structures such as the tripler DNA.