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 anti bodies in patients as an adverse effect. We investigated the ability o f hydralazine to promote/stabilize the tripler DNA form of poly(dA). 2 poly(dT). Under conditions of low ionic strength, the polynucleotide m elted as a double helix with a melting temperature (T-m) of 55.3 degre es 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-s tranded DNA and T-m2 of 65.4 degrees C, corresponding to duplex meltin g. Tripler DNA thus formed in the presence of spermidine was further s tabilized by hydralazine (250 mu M) with a T-m1 of 53.6 degrees C. A s imilar stabilization effect of hydralazine was found on tripler DNA fo rmed in the presence of 5 mM Mg2+. CD spectra revealed conformational perturbations of DNA in the presence of spermidine and hydralazine. Th ese results support the hypothesis that hydralazine is capable of stab ilizing unusual forms of DNA. In contrast with the weak immunogenicity of DNA in its right-handed B-DNA conformation, these unusual forms ar e immunogenic and have the potential to elicit anti-DNA antibodies. To test this possibility, we analysed sera from a panel of 25 hydralazin e-treated patients for anti-(tripler DNA) antibodies using an ELISA. O ur results showed that 72% of sera from hydralazine-treated patients c ontained antibodies reacting toward the tripler DNA. In contrast, ther e was no significant binding of normal human sera to tripler DNA. Take n together our data indicate that hydralazine and related drugs might exert their action by interacting with DNA and stabilizing higher-orde r structures such as the tripler DNA.