Effects of poly-2-vinylpyridine-N-oxide (PVNO) were investigated in numerous in vivo and in vitro studies published in the nineteen sixties and seventies. These studies showed that PVNO inhibited development of
fibrosis from
quartz dust and improved lung clearance of
quartz after inhalation exposure. Ameliorating effects of PVNO were observed also for pulmonary damage from colloidal SiO2 and organic substances, and the fibrogenic
inflammation caused by
carrageenan. Although it is not proven that
silicosis is a precondition for
quartz-induced lung tumours, we investigated the hypothesis that PVNO could reduce the lung tumour risk from
quartz in rats. A carcinogenicity study was therefore started in rats with the main focus on the quantitative relationships among
pulmonary inflammation,
fibrosis and
neoplasia caused by intratracheal instillation of 3 mg
quartz DQ 12 with or without additional subcutaneous PVNO treatment. Other study groups were treated with multiple dust instillations, i.e. 30 instillations of 0.5 mg amorphous SiO2 at intervals of 2 weeks, 10 instillations of 0.5 mg of ultrafine
carbon black or 1 mg
coal at weekly intervals. The analyses of the bronchoalveolar lavage fluid (BALF) 9 months after start of the life-time study showed that the aim of producing similar levels of increased
enzyme concentrations in the four groups treated with
quartz/PVNO, amorphous SiO2,
carbon black and
coal was achieved. A 2.5- to 7.7-fold increase for
lactate dehydrogenase (LDH), total
protein,
alkaline phosphatase and gamma-glutamyl
transferase (gamma-GT) was found in these groups as compared to the control. In contrast,
quartz treatment without PVNO increased the LDH level up to 24-fold and of total
protein to 13-fold. However, the cell counts in the BALF were not so much different in all five groups, i.e.
quartz without PVNO (leukocytes: 480.000, PMN: 190.000),
quartz with PVNO (leukocytes: 300.000, PMN: 100.000), amorphous SiO2 (leukocytes: 570.000, PMN: 315.000),
carbon black (leukocytes: 390.000, PMN: 150.000) and
coal (leukocytes: 200.000, PMN: 65.000). Histopathological investigations after four weeks and three months revealed that the used PVNO sample was active in the
quartz and amorphous SiO2 groups and markedly reduced the incidences or severity of several pulmonary changes such as macrophage accumulation, inflammatory cell infiltration, interstitial
fibrosis, bronchiolo-alveolar
hyperplasia, alveolar
lipoproteinosis and amorphous SiO2 -induced granulomatous alveolitis/interstitial fibrotic
granulomas. Also in the lung-associated lymph nodes (LALN), PVNO treatment significantly reduced the incidence and severity of
inflammation in both
quartz and amorphous SiO2 groups as evidenced by the presence of well-circumscribed aggregates of intact particle-laden macrophages without signs of degeneration and accompanying granulocytic infiltration and
fibrosis. Immunological investigations at the 9 months timepoint on the in vitro production of reactive
nitrogen (RNI) or
oxygen (ROI) intermediates and tumour
necrosis factor (
TNF-alpha) from BALF-derived cells indicated a diminished responsiveness to LPS in all particle treatment groups. A diminished production of ROI was also found in the
quartz,
carbon black, and
coal dust groups, respectively, as compared to the values seen in the
quartz/PVNO- and amorphous SiO2 treated groups. Treatment with
quartz plus PVNO restored the capability of the cells to respond to LPS as compared to the treatment with
quartz alone.
TNF-alpha production was diminished in the groups treated with
quartz,
carbon black, and
coal dust alone whereas in the
quartz/PVNO- and amorphous SiO2-treated groups an elevated
TNF-alpha production was seen. These results led to the conclusion that only amorphous SiO2 did not affect the "normal" ability of the cells to respond to LPS and that PVNO protected the cells from a toxic effect of the
quartz particles.