Interlaboratory validation of the in vitro eye irritation tests for cosmetic ingredients (9). Evaluation of cytotoxicity test on HeLa cells.

The cytotoxicity test using MTT on HeLa cells (HeLa-MTT) was evaluated as an alternative method to the Draize eye irritation test (Draize test) by six to eight laboratories. The 50% inhibition concentration (EC(50)) for MTT reduction was calculated. A total of thirty-nine test chemicals were examined. The average interlaboratory coefficient of variation (CV) of the present assay was 25%. Comparison of the in vitro test results with those of the Draize test revealed a correlation coefficient of -0.799 between the log(EC(50)) value and the maximum average total score (MAS) for a 10% solution or suspension. The following characteristics of HeLa-MTT have become apparent through this validation: (1) HeLa-MTT could be applied to all substances including water-insoluble substances, esters, a colour additive, and a substance which is known to directly reduce MTT; (2) there is good interlaboratory reproducibility and strong correlation between HeLa-MTT and Draize MAS; (3) results for strong acids, alkanolamines and alcohols (lower mono-ol) clearly deviate from other samples with respect to the correlation between HeLa-MTT and Draize MAS. These results suggest that HeLa-MTT may be useful for predicting the Draize MAS if definite criteria can be established for applicable compounds.

Interlaboratory validation of the in vitro eye irritation tests for cosmetic ingredients. (10) Evaluation of cytotoxicity test on CHL cells.

The present interlaboratory validation study was performed in order to evaluate the use of Chinese hamster lung cell lines that employs crystal violet staining (CHL-CVS) as an alternative cytotoxicity test to the Draize eye irritation test (Draize test) for cosmetic ingredients. Ten substances, nine of which were surfactants, were evaluated at seven laboratories in the first phase of the validation study; 15 substances including dyes and lipids were evaluated at seven laboratories in the second phase of the validation study; 14 substances including acids and alkalis were evaluated at four laboratories in the third phase of the validation study. The logEC(50) values obtained for CHL-CVS were compared with the maximal average Draize total score (MAS) for a 10% (w/v) solution of 38 cosmetic ingredients as well as isotonic sodium chloride solution. The interlaboratory coefficient of variation (CV) for EC(50)s was 35.6%, which was considered to be within a tolerable range. The correlation coefficient and the Spearman's rank correlation coefficient between the in vitro and in vivo tests were -0.729 and 0.709, respectively. The prediction ability of the proposed method was assessed from the linear regression line for a MAS cut-off point of 15. According to this analysis, four substances (two alcohols and two acids) were determined to be false negative. The present study revealed the following characteristic factors of this method: (1) CHL-CVS could be applied to all the test substances including dyes and lipids in this study; (2) The results for medium-insoluble substances varied according to the laboratory; (3) The correlation between the in vivo and in vitro data for acids and alcohols (lower mono-ol) differed from that of the other substances. These results suggested that the CHL-CVS might have a potential to predict the Draize MAS if definite criteria can be established for the compounds to be applicable.

Receptor-binding affinities of human epidermal growth factor variants having unnatural amino acid residues in position 23.

Ile-23 of human epidermal growth factor (hEGF) has been indicated, by mutagenesis and NMR studies, to be directly recognized by the receptor. In the present study, an unnatural phenylalanine analog, either 2-azaphenylalanine (2aF), 3-azaphenylalanine (3aF), 4-azaphenylalanine (4aF), or 4-fluorophenylalanine (4fF), was incorporated by an in vivo protein synthesis system into position 23 of [Phe23]hEGF, which retains appreciable receptor-binding affinity (about 20% of the wild type). We compared the receptor-binding affinities of the variants with that of [Phe23]hEGF and found that substitution of Phe-23 with 2aF or 3aF raised the affinity, while substitution with 4aF or 4fF remarkably reduced the affinity. The tertiary structure of [Phe23]hEGF was not significantly affected by the substitution of Phe-23 with 2aF, as shown by the two-dimensional nuclear magnetic resonance analysis. In addition, the substitution of residue 23 with His or Tyr produced an hEGF variant with a slightly higher receptor-binding affinity than that of [Phe23]hEGF. Our results suggest that the receptor has an asymmetric hydrophobic pocket for recognition of the side chain in position 23 of hEGF. Furthermore, on the receptor surface, this pocket seems to be adjacent to a less hydrophobic region with a hydrogen-bond acceptor and donor. Thus, the use of unnatural amino acids in addition to the 20 natural ones allows analyses of the structure-function relationship of a protein at a higher resolution than conventional site-directed substitution by only natural amino acid residues.

Recognition of an antiparallel beta-sheet structure of human epidermal growth factor by its receptor. Site-directed mutagenesis studies of Ala-30 and Asn-32.

The Ala-30 and Asn-32 residues involved in the major antiparallel beta-sheet structure of human epidermal growth factor (hEGF) were substituted with various amino acid residues, and the receptor-binding affinities of the nine variant hEGFs were determined by the use of human KB cells. The Ala-30----Arg, Ala-30----His and Ala-30----Phe substitutions drastically reduced the binding affinity, suggesting that the side chain in position 30 of Ala-30 of hEGF is required to be small for the receptor binding. The Asn-32----Asp substitution significantly reduced the binding affinity, while the Asn-32----His variant could bind to the receptor as well as to the wild-type hEGF. Therefore, it seems to be important for receptor binding that the side chain in position 32 does not have a negative charge but does have an NH group. Thus, we propose that, in the ligand-receptor complex, the receptor recognizes, on one side of the antiparallel beta-sheet structure of hEGF, a wider contact area than previously suggested.

A site-directed mutagenesis study on the role of isoleucine-23 of human epidermal growth factor in the receptor binding.

The isoleucine-23 residue of human epidermal growth factor (hEGF) was substituted by a variety of amino acid residues and the receptor-binding activities of variant hEGFs were determined by the use of human KB cell. Tight receptor binding was found of variants with hydrophobic amino acid residues in position 23. The size of the isoleucine residue was nearly optimum for the receptor binding as compared with other hydrophobic residues. The structure analysis by two-dimensional nuclear magnetic resonance spectroscopy showed that the substitution at position 23 only slightly affected the tertiary structure of hEGF. These indicate that the side chain of isoleucine residue in position 23, which is exposed on the protein surface, directly binds to a hydrophobic pocket of the receptor.

Stability of recombinant human epidermal growth factor in various solutions.

The stability of recombinant human epidermal growth factor (hEGF) in various solutions was examined. hEGF degraded spontaneously and temperature-dependently to several degradation products in phosphate buffered saline or in 0.1 N acetic acid. The enzymatic degradation was observed in human serum or in pepsin/HCl solution. The structure and biological activities of these compounds were examined. The results suggest that the Asp11 and Trp50 residues are important for the receptor binding.

Purification and characterization of high molecular weight human epidermal growth factor from human urine.

High molecular weight human epidermal growth factor (HMW-hEGF) was purified to homogeneity from human urine. The purification was achieved exclusively by the use of immunoaffinity chromatography and reverse phase high performance liquid chromatography (HPLC). The purified HMW-hEGF is composed of a single polypeptide chain with an apparent molecular weight of 30,000 and has pI of 4.0. Its N-terminal sequence was determined as Val-Ser-Asp-Gln-Asp-Asp-( )-Ala-Pro-Val-Gly-( )-Ser-Met-Tyr-Ala-Arg-( )-Ile- Ser-. The trypsin treatment of this protein gave hEGF like fragments. These results suggest that the obtained HMW-hEGF may play an important role in biosynthetic precursor of hEGF.

An inhibitor for post-proline cleaving enzyme; distribution and partial purification from porcine pancreas.

An inhibitor(s) for post-proline cleaving enzyme was checked by using a fluorogenic substrate, Z-Gly-Pro-4-methyl coumarinamide, and was found to be distributed widely in rat and porcine organs. The highest inhibitory activity on the enzyme was observed in pancreas and the inhibitor was partially purified from porcine pancreas extract by heat treatment, chromatographies on DEAE-Sephadex and Sephadex G-50 and affinity chromatography on trypsin-Sepharose. This inhibitor was very stable against temperature, pH and trichloroacetic acid treatment. The molecular weight was estimated to be 6500 by gel filtration. This inhibitor was highly specific for prolyl endopeptidases from mammals and Flavobacterium and inhibited the enzyme competitively. It acted neither on proline specific exopeptidases such as dipeptidyl aminopeptidase IV, proline aminopeptidase, prolidase, nor usual endopeptidases such as trypsin and alpha-chymotrypsin.