In vitro cytotoxicity testing for prediction of acute human toxicity.

This study was designed to compare the cytotoxic concentrations of chemicals, determined with three independent in vitro cytotoxicity testing protocols, with each other and with established animal LD50 values, and against human toxic concentrations for the same chemicals. Ultimately, these comparisons allow us to evaluate the potential of in vitro cell culture methods for the ability to screen a variety of chemicals for prediction of human toxicity. Each laboratory independently tested 50 chemicals with known human lethal plasma concentrations and LD50 values. Two of the methods used monolayer cell cultures to measure the incorporation of radiolabeled amino acids into newly synthesized proteins and cellular protein content, while the third technique used the pollen tube growth test. The latter is based on the photometric quantification of pollen tube mass production in suspension culture. Experiments were performed in the absence or presence of increasing doses of the test chemical, during an 18- to 24-h incubation. Inhibitory concentrations were extrapolated from concentration-effect curves after linear regression analysis. Comparison of the cytotoxic concentrations confirms previous independent findings that the experimental IC50 values are more accurate predictors of human toxicity than equivalent toxic blood concentrations (HETC values) derived from rodent LD50s. In addition, there were no conclusive statistical differences among the methods. It is anticipated that, together, these procedures can be used as a battery of tests to supplement or replace currently used animal protocols for human risk assessment.

Tru-cut needle biopsy of subcutaneous fat in the diagnosis of secondary amyloidosis in rheumatoid arthritis

In order to investigate the presence of secondary amyloidosis in patients with rheumatoid artritis (RA), we performed and abdominal subcutaneous fat biopsy with a truc-cut needle in 50 patients. The tissue was stained with Congo red and was observed with polarized light microscopy. We found amyloid deposits in 78 percent of our patientas. We randomly selected ten patients with a positive biopsy and a second procedure was performed. Tissues were studied with electron microscopy. We found unbranced fibrils characteristic of amyloid in all of them. We found a direct correlation with rheumatoid factor titers: the more intense the amyloid deposit, the higher the rheumatoid factor titers (p< 0.001). We did not find any correlation betwen amyloid deposits and clinical manifestations of disease. Amyloid deposits in RA are more frequent than previously thought, and their clinical importance remains to be determined