Mode of action of poly(vinylpyridine-N-oxide) in preventing silicosis: effective scavenging of carbonate anion radical

Small particles of crystalline silicon dioxide (crystallites) are exceptionally toxic. Inhalation of quartz crystallites causes silicosis, a devastating lung disease afflicting miners, particularly coal and stone workers. Poly(vinylpyridine-N-oxide)s (PVPNOs) have been applied in the prevention and treatment of silicosis, but their mode of action has been obscure. Recently, the sites of inducible *NO synthase activation and of nitrotyrosine formation were associated anatomically with the pathological quartz particle-caused lesions in the lungs. It has been suggested that the *NO formed combines rapidly with O2*- to yield ONOO-, a potential mediator of lung injury following silica exposure. Here, we show that PVPNOs do not react with peroxynitrite but scavenge exceptionally rapidly CO3*- radicals, which are produced in the decomposition of ONOO- in bicarbonate solutions. The rate constant for the reaction of CO3*- with PVPNO was found to be independent of the type and size of PVPNO, i.e., k = (1.9 +/- 0.2) x 10(5) M(-1) s(-1) per monomer. In contrast, the rate constant for the reaction of CO3*- with the small molecule 4-methylpyridine N-oxide did not exceed 1 x 10(4) M(-1) s(-1). The underlying reason for the difference is that, in the dissolved polymeric PVPNOs, the electrostatic repulsion between the N-oxide zwitterions destabilizes them, increasing dramatically their pKa. The protonated N-oxides at physiological pH have abstractable hydrogen atoms and are expected to react rapidly with CO3*-, just as cyclic hydroxylamines do. It is also shown that PVPNO inhibits tyrosine nitration by peroxynitrite at pH 7.6 in the presence of excess of CO2 in a concentration-dependent manner. Hence, binding of PVPNO to the quartz particles and eliminating CO3*- could prevent the killing of macrophages, the associated release of macrophage-recruiting cytokines, and the amplification of the local concentration of *NO by the recruited macrophages. The latter causes necrosis of the macrophage-infiltrated lung tissue and, upon repair of the necrotic lesion, results in the growth of the dysfunctional fibrotic tissue, which is the hallmark of silicosis.

[Trials of casual treatment of silicosis]

Silica-induced lung injury and the development of silicosis is one of the major occupational diseases. Accumulation and deposition of respirable dust containing silica mineral particles in the lung produces chronic lung disease characterized by granulomatous and fibrotic lesions. Knowledge of precise mechanisms, which induce this process is still limited, hence problems faced in the treatment of silicosis, especially the casual one. This article describes various trials of casual silicosis treatment with tetrandrine (Tet), isolated from the root of Stephania tetrandra, tumor necrosis factor (TNF) antagonists, polyvinyl-pyridine-N-oxide (PVNO), aluminum compounds, corticosteroids or bronchoalveolar lavage (BAL). The existing methods are not sufficient, which warrants further investigations. At present, prevention of the disease and treatment of its complications are most important.

[Application and analysis of biochemical indices for the evaluation of antisilicosis treatment. Study on anti-silicosis therapy and its evaluation research group]

The levels of serum Ceruloplasmin (Cp), Superoxide dismutase (SOD) and IgG of 296 silicosis patients treated by tetrandrine, polyvinylpridine-N-Oxide, hydroxypiperaquinoline phosphate and aluminium citrate were measured. Sera were collected before and after the 1st, 3rd and 6th therapy courses. 144 Silicosis patients without treatment were observed as controls. The levels of these three indices decreased by the end of treatment. The levels of SOD were fluctuated, which were increased after the 3rd course, but decreased after the 1st and 6th courses. The decrease of Cp, SOD and IgG consisted with the clinical effectiveness of the treatment, indicating that Cp, SOD and IgG were appropriate biochemical indicators for the evaluation of antisilicosis drugs. The quality control and the statistics standardization for data analysis are important.

A biochemical study on combined treatment of experimental silicosis with tetradrine-PVNO and tetradrine-QOHP in rats

A better understanding is needed to explain the mechanism of therapeutic effect of combined use of tetradrine-PVNO and tetradrine-QOHP which play very important roles in treatment of silicosis. Blood prolidase (PLD), monamine oxidase (MAO) and plasminogen (PLG) in silicotic rats after treatment with tetradrine-PVNO or tetradrine-QOHP were measured. The values obtained were compared with the untreated silicotic rats. It was found that the silicotic rats that received tetradrine-PVNO showed significant increase in PLD and decrease in PLG, but no significant change in MAO. The PLD in plasma of silicotic rats that received tetradrine-QOHP were elevated significantly, but PLG and MAO did not change appreciably. These findings suggest that the combined use of tetradrine-PVNO and tetradrine-QOHP can accelerate the degradation of collagen in silicotic rats.

The effects of tetrandrine (TT) and polyvinylpyridine-N-oxide (PVNO) on gene expression of type I and type III collagens during experimental silicosis

In the screening tests of drugs for silicosis in our laboratory, we found that TT, a type of alkaloid isolated from Stephania tetrandra, could inhibit the development of experimental silicosis of rats and the synthesis of collagen in rat lung. Chest X-rays of silicotic patients treated with TT for 1-3 years showed obvious changes. The silicotic nodules became smaller and shadows became clearer. PVNO was proved to have anti-silicotic effect on animal and clinically. This presentation reports the effect of them on collagen mRNA. Dot blot results showed that alpha 1 (I) and alpha 1 (III) mRNA levels increased significantly at 60 and 120 days after the rats were exposed to silica dust. The mRNA levels went down at 1 and 3 months after treated by TT and PVNO. In situ hybridization observation revealed that the silver grains of Type I and Type III collagen were scattered within the fibroblasts in cellular nodules and in thickened interstitium of silicosis tissue. The amounts of mRNA silver grains decreased in the lung tissue treated by TT and PVNO. It was suggested that TT and PVNO may inhibit the gene expression of collagen during silicosis.

[Studies on serum angiotensin-I-converting enzyme activity of experimental silicosis in rats]

The level of serum angiotensin-I-converting enzyme (SACE) activity on experimental silicosis in rats at different stages and under treatment with PVNO is reported. The results showed that levels of SACE in each dust groups begun to rise significantly higher than control groups as from the fifth day until 180th day (P less than 0.05). The levels of SACE of treatment groups with PVNO were significantly lower than the dust groups and similar to normal groups of the same age. It is suggested that SACE activity might be used as a reference index of silicosis.

[Polyvinylpyridine N-oxide (Bay 3504, P-204, PVNO) in the treatment of human silicosis]

After having demonstrated the therapeutic effectiveness of polyvinylpyridine-N-oxide (PVNO) for experimental silicosis in numerous animal studies, and after having finalized the toxicological examinations, a tolerance test was run in a controlled clinical assay with human subjects. After having shown that PVNO infusions did not result in toxic side-effects its therapeutic effectiveness was clinically studied in two different cohorts: matched pairs studies were conducted in 8 miners (group 1) and in 20 stone-cutters (group 2). The study demonstrates the therapeutic potency of PVNO for man as well, subject to certain moderating conditions as follows: the degree of silicosis, the age of the silicotic focus and the dust-type influenced the outcome of the treatment. The minimal dose should be between 300 and 400 mg per kg bodyweight and should be given in intervals of one to two years.

Protective effect of poly-2-vinylpyridine-N-oxide on susceptibility of silica-treated mice to experimental histoplasmosis

We have studied the ability of poly-2-vinylpyridine-N-oxide (PVNO), a lysosomal stabilizing agent, to abrogate the cytotoxic effects of silica on macrophages. Male C3H/HeN mice were pretreated with PVNO and inoculated intravenously with silica particles. At 24 h after silica injection, silica-treated and -untreated mice were challenged intravenously with varying doses of live yeast cells of Histoplasma capsulatum. All mice receiving silica died when challenged with 5 X 10(5) yeast cells of Histoplasma sp. compared with no deaths in PVNO-pretreated animals and 10% mortality in controls not receiving PVNO or silica. When animals were given 2.5 X 10(5) yeast cells (a sublethal dose), the protective effect of PVNO was seen by a reduction in splenomegaly and viable Histoplasma sp. present in the spleen. Furthermore, PVNO alone showed a significant protective effect (P less than 0.05) against a lethal challenge with Histoplasma sp. Prior treatment with PVNO also protected mouse peritoneal macrophages from the cytotoxic effects of silica particles in vitro. These results indicate that PVNO abrogates the cytotoxicity of silica particles on macrophages and also increases the resistance of mice to histoplasmosis.

Long-term follow-up observations of the therapeutic effect of PVNO on human silicosis

The effect of PVNO treatment on human silicosis was observed in 7 cases over a period of 9 years lasting from 1965 to 1974. The drug was given intramuscularly and by way of inhalation, respectively. The comparison of the radiographs taken before, during and 3 years after the administration of PVNO showed that during treatment the tendency of fibrotic progression was delayed in 4 cases while 2 cases were slightly progressive, and one was markedly progressive, 3 years after discontinuation of the PVNO treatment, only one case remained stable, two cases were slightly and 4 cases markedly progressive. These observations indicate that PVNO treatment may have an effect on the delay and control of silicosis progression in a portion of patients, but after discontinuation of the treatment further progression is possible.

[Antisilicotic action and side effects of polypyridylethyl-methacrylate iodomethylate]

Antisilicotic and side effects of a new polymer synthetized on the basis of polymethacrylic acid were studied. The polymer not only inhibited the development of silicotic sclerosis but also induced its partial reverse development. As regards the effect intensity it appeared to be equal to highly effective polyvinylpyridine-N-oxide. The data obtained indicate the necessity of a further study of the new antisilicotic polymer with a purpose of recommending it for clinical trials.

[Effect of inhalations of polyvinylpyridine-N-oxide on the development of experimental silicosis]

Experiments on albino rats showed that polyvinylpyridine-N-oxide (PVNO) inhalations (mol. mass 2000; 9.8 +/- 1.2 and 99 +/- 4 mg/m3 for 7 months) slowed down the course of silicosis developing with a gradual entrance and uniform distribution of dust in the lungs, but proved little effective with a one-time introduction of a large amount of "aggressive" dust because of the difficulty for the drug to reach and penetrate the sclerosed sections of the tissue. Considering low toxicity and an insignificant cumulative effect of PVNO, the electivity of its accumulation in the lungs during inhalation and marked protective action of low doses the authors hold it expedient to employ the inhalation method of administering the polymer for prevention of silicosis, while its use for curative purpose is not recommended.

Effects of Corynebacterium parvum on murine myeloid leukaemia

The effects of C. parvum on RFM/UN myeloid leukaemia were studied. Mice inoculated with 7.0 mg but not 0.7 mg C. parvum i.p. survived significantly longer than untreated leukaemic mice (P less than 0.001). Administration of silica abrogated the effects of C. parvum, whilst polyvinyl pyridine-N-oxide prevented the inhibitory effects of silica. These studies demonstrate that a single large dose of C. parvum, either before or after leukaemic-cell passage, can significantly prolong the survival of RFM mice bearing myeloid leukaemia. The effects of silica and PVNO on C. parvum suggest a critical role for macrophages in C. parvum effects on myeloid leukaemia.

[Antisilicotic properties of polyethylene-piperazine N-oxide--a new polymeric compound]

A high antisilicotic activity of a new polymeric compound--polyethylene-piperazine N-oxide (molecular mass 5000--8000, degree of exidation--80 per cent), synthetized on the basis of aliphatic amine, was shown as against polyvinylpyridine-N-oxide in experiments conducted on albino rats with silicosis.

[Possibilities of influencing experimental pneumoconiosis and experimental etching of respiratory organs by means of aerosol-inhalations (author's transl)]

The author presented the results of 7 experiments in which he followed with his co-workers the effect of preventively applied aerosol inhalations with rats and rabbits, dusted with quartz or coal dust. Aerosol inhalations of alkaline mineral water "Vincentka" and of salt mixtures, especially of calcium salts affected in some experiments favourably the development of lung dust changes, in other cases on the contrary they did not. The best effect was proved by polyvinylpyridin-N-oxide (PNO). The author described further his experience with aerosoltherapy in persons affected by inhalation of etching substances. Here the inhalation of 10% CaCl2 or Ca gluconicum and of 1% natrium bicarbonicum proved to be the best.

[Cytopharmacologic effect of using polyvinylpyridine-N-oxide in experimental silicosis]

Methods of scanning, transmission electron microscopy and cytochemistry were applied to the study of the development of experimental silicosis against the background of polyvinylpyridine-N-oxide administration. The majority of the macrophages retained their functional activity and realized quartz phagocytosis, eliminating it through the airway. Bringing the proteins on the cell surface in the fibroblasts was delayed, and formation of collagen fibers decreased. Application of the polymere prevented development of fibrosis of the lungs.

Pathogenicity to animals of fine dusts from Ruhr mines

Twelve different groups of fine mine dusts were examined for their in vivo aggressivity by intraperitoneal injection. Twelve months after injection of the dust, quantitative morphometric analysis of the lymph nodes was carried out to determine (a) the extent of the typical quartz reaction, (b) the in vivo cytotoxicity, (c) the size of the lymph nodes. Different fine dusts showed significant variations in parameter (a) and (c). In the second part of the investigation, the results of the lymph node tests and of in vitro cytotoxicity tests, and also the quartz contents of the dusts were fed into a data matrix and subjected to correlation analysis and principal component analysis. The following hypotheses were arrived at to explain the effect of the fine dust in vivo: (1) The amount of fine dust which penetrates into the lymph nodes is dependent on its in vitro cytotoxicity (Factor A). This is not related to the quartz content of the dust and is not inhibited by PVNO. (2) The specific fibrogenic activity of the fine dust within the lymph node is primarily dependent on its quartz content (Factor B). It appears that this effect is inhibited by PVNO. (3) The total fibrogenic activity depends on a combination of Factor A and B.

Long-term test on rhesus monkeys for the PVNO therapy of anthracosilicosis

In order to test the therapeutic efficiency of intravenous PVNO injections against anthracosilicotic changes, long-term inhalation tests were performed in which rhesus monkeys were exposed to coal-quartz dust. The exposures were given over a period of 48 months. PVNO treatment at a concentration of 300 or 600 mg/kg body weight began 8 months after the end of exposure. To determine the effect of PVNO injections, hydroxyproline examinations of the urine were made. After a total duration of 70 months the test was followed by an examination of respiration and circulation. In addition to histological check-ups the organ weights were determined. Under the influence of PVNO treatment neither a regression of anthracosilicotic changes in lungs and lung lymph nodes occurred nor was the progression of these changes retarded.