The effects of polyamines on the immunogenicity of polynucleotides

Calculating the etiology of systemic lupus erythematosus

Objective was to clarify the etiology and pathogenesis of systemic lupus erythematosus (SLE). Drug-induced lupus (DIL) and SLE are both found in humans, are exacerbated by the same viruses or drugs, and they are both more common in slow acetylators. Thus, DIL can be used as a model for SLE and the Adhami equation of DIL can be applied to SLE. Polyamines are the only possible link between the viral and amine hypotheses of SLE pathogenesis. Based on the Adhami equation, polyamines can explain the actual annual incidence of SLE in the general population. Putrescine is a very weak SLE-causing agent, while spermine and spermidine contribute equally in triggering SLE. The positively charged polyamines bind to negatively charged internucleosomal DNA and change its conformation from B (non-immunogenic) to Z (immunogenic). This is the major contribution of polyamines in triggering SLE. The other effects of polyamines are only secondary. Apoptosis is a necessary step in SLE pathogenesis, because it causes the internucleosomal fragmentation of DNA and exposes Z-DNA to the immune system (due to cell death). The next step is the production of anti-DNA antibodies, followed by other SLE phenomena. Polyamines not only cause SLE, but they are also important in sustaining the disease. Other endogenous and exogenous amines have additive effects with polyamines and may contribute in exacerbating SLE. When SLE is in the active phase, polyamine levels are higher as compared to remissions. Fluctuations in polyamine levels due to diet, metabolic factors, infections, intestinal flora, etc. or the presence of other amines may explain the course of SLE, characterized by remissions and exacerbations. Acetylcysteine is a drug that can be completely metabolized to acetyl groups. As such, this drug is proposed as the ideal acetyl donor for the acetylation of polyamines and other SLE-triggering compounds. Clinical trials will be necessary to test the role of acetylcysteine in the etiologic treatment of SLE.

CONCLUSIONS

Changes in DNA conformation by polyamines are the first step in SLE pathogenesis. Many genetic and environmental factors may increase or decrease the effects or levels of polyamines, causing SLE exacerbations or remissions. Viruses and other infectious agents may cause SLE by producing polyamines or by increasing the levels of endogenous polyamines. The major autoimmune diseases are characterized by remissions and exacerbations and not by a continuously progressive course, as commonly believed. Consequently, they are not sustained by internal vicious cycles, but by the initial triggering agent(s). While the conventional treatment of autoimmune disorders is important in minimizing tissue damage, the neutralization of their etiology may be important in curing and preventing autoimmunity.

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 andti-nuclear antibodies in patients as an adverse effect. We investigated the ability of hydralazine to promote/stabilize the triplex DNA form of poly(dA).2poly(dT). Under conditions of low ionic strength, the polynucleotide melted as a double helix with a melting temperature (Tm) of 55.3 degrees C. Hydralazine destabilized this duplex form by reducing its Tm to 52.5 degrees C. Spermidine (2.5 microM), a natural polyamine, provoked the triplex form of poly(dA)-.2poly(dT) with two melting transitions, Tm1 of 42.8 degrees C corresponding to triplex-->duplex+single-stranded DNA and Tm2 of 65.4 degrees C, corresponding to duplex melting. Triplex DNA thus formed in the presence of spermidine was further stabilized by hydralazine (250 microM) with a Tm1 of 53.6 degrees C. A similar stabilization effect of hydralazine was found on triplex 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-(triplex DNA) antibodies using an ELISA. Our results showed that 72% of sera from hydralazine-treated patients contained antibodies reacting toward the triplex DNA. In contrast, there was no significant binding of normal human sera to triplex 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 triplex DNA.

Polyamine induced Z-conformation of native calf thymus DNA

Conformational isomerization of native calf thymus DNA under the influence of spermine, spermidine and putrescine was monitored by UV absorption and immunospecific anti-Z-DNA antibodies. Immunological data indicated increased binding of anti-Z-DNA antibodies to polyamine-perturbed conformations of native DNA and double stranded poly(dG-dC). In the absence of polyamines, anti-Z-DNA antibodies did not bind to either polymers. Analysis of UV absorption studies indicates a left handed conformation of nDNA in the presence of polyamines. Moreover, we observed total aggregation of DNA in the presence of spermine on prolongued incubation. These perturbations in conformation were dependent on polyamine concentration. The results clearly suggest that certain regions of nDNA are sensitive to elevated levels of polyamines and are capable of undergoing B-->Z transition.

Polyamine-induced Z-DNA conformation in plasmids containing (dA-dC)n.(dG-dT)n inserts and increased binding of lupus autoantibodies to the Z-DNA form of plasmids

Blocks of potential Z-DNA-forming (dA-dC)n.(dG-dT)n sequences are ubiquitous in eukaryotic genomes. We examined whether naturally occurring polyamines, putrescine, spermidine and spermine, could provoke the Z-DNA conformation in plasmids pDHf2 and pDHf14 with 23 and 60 bp inserts respectively of (dA-dC)n.(dG-dT)n sequences using an e.l.i.s.a. Spermidine and spermine could provoke Z-DNA conformation in these plasmids, but putrescine was ineffective. For pDHf2 and pDHf14, the concentration of spermidine at the midpoint of B-DNA to Z-DNA transition was 25 microM, whereas that of spermine was 16 microM. Polyamine structural specificity was evident in the ability of spermidine homologues to induce Z-DNA. Inorganic cations, Co(NH3)6(3+) and Ru(NH3)6(3+), were ineffective. Our experiments also showed increased binding of anti-DNA autoantibodies from lupus patients as well as autoimmune MRL-lpr/lpr mice to pDHf2 and pDHf14 in the presence of polyamines. These data demonstrate that small blocks of (dA-dC)n.(dG-dT)n sequences could assume the Z-DNA conformation in the presence of natural polyamines. Increased concentrations of polyamines in the sera of lupus patients might facilitate immune complex-formation involving circulating DNA and anti-Z-DNA antibodies.

Hydralazine induces Z-DNA conformation in a polynucleotide and elicits anti(Z-DNA) antibodies in treated patients

We studied the effect of hydralazine, an antihypertensive drug with lupus-inducing side effects, on the conformation of poly(dG-m5dC).poly(dG-m5dC) and a plasmid with a 23 bp insert of (dG-dC)n.(dG-dC)n sequences. Using an e.l.i.s.a. with a monoclonal anti-(Z-DNA) antibody Z22, we found that hydralazine provoked the Z-DNA conformation in poly(dG-m5dC).poly(dG-m5dC) at 250-500 microM concentration. The supercoiled form of hydralazine-treated plasmid bound to Z22 in a gel-retardation assay. To examine further whether Z-DNA could act as an inciting agent in anti-nuclear antibody production in patients, we analysed 65 sera from 25 hypertensive patients taking hydralazine and found anti-(Z-DNA) antibodies in 82% of these sera. Sera from age-matched normal controls showed no binding to Z-DNA. Data on sera drawn sequentially from four hypertensive patients showed that antibodies were present after the drug treatment. These data demonstrate the presence of a high incidence of anti-(Z-DNA) antibodies in patients treated with hydralazine and suggest that a possible mechanism for the production of autoantibodies in drug-related lupus might involve the induction and stabilization of Z-DNA by drugs.