Hydrogen sulfide poisoning: clarification of some controversial issues.

BACKGROUND: Hydrogen sulfide is a toxic gas about which much has been written. We discuss here several issues we believe would benefit from further clarification. CONCLUSIONS: We conclude that: 1) Certain neurotoxic effects of exposure are probably due to a direct toxic effect on the brain, while others are almost certainly a result of hypoxia secondary to H2S-induced respiratory insufficiency; 2) pulmonary edema is a common consequence of poisoning and there is suggestive evidence of hyperactive airway responses in some individuals following brief H2S-induced unconsciousness (knockdown); 3) criteria for acceptable community levels are very different than those governing occupational standards; 4) urinary thiosulfate determinations can be useful for monitoring occupational exposure; and 5) determination of sulfide ion concentrations in blood or major organs can be useful in corroborating a diagnosis of fatal H2S toxicity, but there are many pitfalls in collecting, storing, and analyzing tissue and fluid samples.

Metal-catalyzed oxidation of histidine in human growth hormone. Mechanism, isotope effects, and inhibition by a mild denaturing alcohol.

Metal-catalyzed oxidation of proteins represents an important pathway of post-translational modification. We utilized human growth hormone (hGH), a protein with a well defined metal-binding site, to study the detailed mechanism of metal-catalyzed oxidation by ascorbate/Cu(II)/O2. Particularly His18 and His21 within the metal-binding site were oxidized, predominantly to 2-oxo-His with the incorporated oxygen originating from molecular oxygen, based on amino acid analysis, tryptic mapping, mass spectrometry, isotopic labeling, and 1H NMR. The anaerobic reduction of a hGH/Cu(II) mixture by ascorbate generated a hGH-Cu(I) complex with NMR spectral features different from those of native hGH and hGH/Cu(II). The anaerobic reaction of this hGH-Cu(I) complex with hydrogen peroxide resulted in the oxidation of His18 and His21, suggesting that a fraction of Cu(I) was bound at the metal-binding site of hGH. Site-specific oxidation of hGH required an intact metal-binding site and could largely (about 80%) be inhibited by the presence of >/=28% (v/v) 1-propanol which appears (i) to perturb the metal-binding site and (ii) to interact with a reactive oxygen species formed at the perturbed metal-binding site. The inhibition by 1-propanol-d7 (CD3CD2CD2OH) was significantly lower than that by 1-propanol-h7 with [residual hGH]1-propanol-h7/[residual hGH]1-propanol-d7 = 1.95 at 30% (v/v) 1-propanol, reflecting a kinetic isotope effect close to that for the reaction of a hydroxyl radical with Calpha-H/D bonds of methanol, suggesting the involvement of a hydroxyl radical-like species in the oxidation of His.

Metal-catalyzed photooxidation of histidine in human growth hormone.

Reports on nonenzymatic oxidation of human growth hormone (hGH) have been previously limited to methionyl residues (Met14 and Met125). We report on the oxidation of a histidyl residue in hGH treated with intense light. The photooxidation process is predominately site-specific to histidine at position 21, which forms a cation-binding site along with His18 and Glu174. This site binds metal ions and, under intense light, catalyzes the oxidation of His21. Products are formed by the addition of one, two, or three atoms of oxygen to the histidyl residue.

A turbidimetric method to determine visual appearance of protein solutions.

An instrumental method to analyze protein solutions for visual appearance is described which is based on spectrophotometric comparison to reference suspensions with varying degrees of turbidity. This method provides a useful substitute for visual inspection of uniform opalescent suspensions in that it is more convenient and less time-consuming and has the potential to be more reproducible, accurate and objective. Established categories of opalescence based on European Pharmacopoeial reference suspensions were determined using turbidity measured as optical density in the 340-360 nm range. A comparison of the mean optical density of a protein sample to those of the reference suspensions allowed a more reproducible assignment of the sample's category of opalescence than that of visual inspection.

Synthesis and biological evaluation of 4-fluoro-, 7-fluoro-, and 4,7-difluoro-5,6-dihydroxytryptamines.

The 5,6-dihydroxytryptamine (5,6-DHT) derivatives 4-fluoro- and 7-fluoro-5,6-DHTs (26a,b) and 4,7-difluoro-5,6-DHT (26c) were synthesized from 3-fluoroanisole (1) and 1,4-difluoro-2,3-dimethoxybenzene (13), respectively. Efficient methods were developed for the conversion of 1 to 4-fluoro- and 7-fluoro-5,6-bis(benzyloxy)indoles (12a,b, respectively), and 13 to 4,7-difluoro-5,6-[( diphenylmethylene)dioxy]indole (19) via reductive cyclization of 2-nitro-beta-(dialkylamino)styrenes prepared in situ from 2-nitrotoluenes. Indoles 12a,b and 19 were then converted to 26a-c via the corresponding indole-3-acetonitriles. The fluorine-substituted 5,6-DHTs displayed increased phenol acidities, determined spectrophotometrically, and decreased inherent potential to undergo oxidation as determined by cyclic voltammetry. Fluorine substitution did not have a significant adverse effect on the cytotoxic potential as judged from the IC50 values of 117, 125, 135, and 92 microM for 26a,c and 5,6-DHT, respectively, for the inhibition of incorporation of [3H]thymidine into the DNA of neuroblastoma clone N-2a cells in culture. Surprisingly, 26a-c exhibited 32-, 23-, and 13-fold higher affinities, respectively, compared to 5,6-DHT for the serotonergic uptake system of N-2a cells as measured by the ability of 26a-c and 5,6-DHT to antagonize the uptake of [3H]5-HT into the N-2a cells. These desirable chemical and biological properties of 26a-c should make them useful tools for the study of the molecular mechanism of neurodegenerative action of 5,6-DHT.

PCB-containing transformer fires: decontamination guidelines based on health considerations.

Realization that polychlorinated biphenyl-(PCB)-containing (askarel) transformer fires can produce toxic polychlorinated dibenzofuran (PCDF) and polychlorinated dibenzodioxin (PCDD) isomers has led to efforts to develop guidelines for cleanup of structures contaminated by soot from these fires. Two such fires have occurred in the United States in recent years, one in 1981 in Binghamton, N.Y., the other in 1983 in San Francisco. The phenomenon of PCB transformation to more toxic substances under conditions of uncontrolled combustion was studied in both locations, but much more extensively in New York. In terms of possible danger to human health, PCDFs comprise by far the most important PCB combustion products identified in the soot of both fires. PCDDs were not formed in sufficient quantity in either fire to constitute an important health hazard. The PCDF isomers of greatest health significance are the tetra-, penta-, and hexa- forms having all four lateral positions (2,3,7 and 8) chlorinated. Separate decontamination guidelines were established for each fire, based on different toxicity and exposure assumptions. One guideline was based on carcinogenic risk assessment of 2,3,7,8-TCDD and the other on experimental animal no-observed-effect level data for the same compound. More effort will be required to develop a generally accepted set of askarel fire decontamination guidelines.

The new biology and the question of personhood: implications for abortion.

Opposition to abortion is based in part on the assumption that personhood is achieved at or shortly after fertilization of the egg. This interpretation of personhood arises from a contemporary application of the ancient doctrine of preformationism, a doctrine which holds that there is a preformed individual, in an ontological sense, within the developing entity. The assumption that the fertilized egg is unique in its capacity to develop into a human being is at least in part responsible for the opinions of those opposed to abortion. Yet, the uniqueness of the zygote in its capacity to develop into an adult organism is qualified by the discovery that development may be possible in a number of other ways. Consideration of the phenomena of cloning, parthenogenesis and chimerism can relieve moral ambiguity about abortion and may reduce opposition to that practice.

Testicular function among epichlorohydrin workers.

Epichlorohydrin (1,2-epoxy-3-chloropropane) (ECH) is a colourless liquid used in the production of insecticides, agricultural chemicals, epoxy resins, and many other productions. It is highly reactive and an alkylating agent suspected of possessing carcinogenic properties in man. The results of a clinical-epidemiological investigation to ascertain whether exposure to ECH may be associated with sperm count suppression among ECH production workers at two chemical plants are presented. Medical histories and physical examinations with special emphasis on the genitourinary tract were completed on each participant. Blood samples and three semen specimens were also obtained. Since no internal control group were available, the data arising from this effort were analysed for each plant (plant A, 44 men; plant B, 84 men) using a control group of 90 chemical plants workers unexposed to any agents known to be toxic to the tests who were included in previous studies. This study provides no evidence that exposure to ECH at the concentrations existing at the two plants studied is responsible for sperm count suppression.

A method for monitoring the fertility of workers. 2. Validation of the method among workers exposed to dibromochloropropane.

A method has been developed for monitoring industrial workers and others exposed to environmental agents which may impair fertility. National birth probabilities specific for maternal birth cohort, age, parity, and race are used to derive expected fertility. Observed fertility is obtained by questionnaire. Standardized fertility ratios are computed for exposure and non-exposure periods and compared. The analytic techniques have been validated by applying the method to a group of 36 male factory employees working in an agricultural chemical division (ACD) where pesticides including the nematocide dibromochloropropane were formulated. Twelve of these employees in mid-1977 had been discovered to have severely depressed sperm counts related to occupational exposure. The standardized fertility ratio (SFR) computed from data available in mid-1977 for the period at risk from employment in the ACD (SFR = 0.75) was significantly lower than those derived for the entire not-at-risk period (SFR = 1.88) and the portion related to employment in other areas of the factory (SFR = 2.16). Similar differences also were evident from data available several years earlier, demonstrating that the surveillance technique would have been capable of detecting occupationally induced infertility among these workers in advance of the actual discovery date.

Testicular function of men occupationally exposed to para-tertiary butyl benzoic acid.

The possible testicular effects resulting from occupational exposure to para-tertiary butyl benzoic acid (p-TBBA) were studied in 90 male volunteers employed at the Martinez, California, facility of the Shell Chemical Company. The comparison data used were obtained from an external reference group of 103 male volunteers not exposed to any known testicular toxin. Exposure indices were based on the calendar years of employment in a given job category. Outcome variables included sperm count, history of fathering children, and gonadotropin levels. It was concluded that p-TBBA, at the levels of exposure experienced at this plant, does not have an apparent clinical or epidemiologic effect on testicular function.

Dibromochloropropane and its effect on testicular function in man.

This study represents the largest series to date documenting the gonadotoxic effect in humans of dibromochloropropane, a widely used pesticide. Three semen analyses, serum hormonal determinations (luteinizing hormone, follicle-stimulating hormone and testosterone) as well as genital examinations were completed for 228 workers at 2 chemical production sites and consisting of a dibromochloropropane-exposed and non-exposed cohort. Parameteric and non-parametric statistical analyses of the data sets of the sperm densities from the 2 subpopulations demonstrated statistical significance (p less than 0.10) at the short-term (1.5 years) manufacturing plant. Log transformation of the sperm count and hourly exposure data were necessary to develop meaningful statistical conclusions. The serum concentration of follicle-stimulating hormone as a group mean was significantly greater at both production sites for the exposed cohort when compared to the non-exposed participants but decreased by 10 levels of magnitude when the group demonstraing shorter but more recent exposure was compared to those from the plant with longer chemical production. Finally, a dose-response model suggested significant changes in sperm density at the short-term but more recently operated production site when more than 100 adjusted hours of exposure were exceeded, while the longer operated but longer closed facility demonstrated a significant impairment only when more than 1,000 adjusted hours of dibromochloropropane exposure were surpassed. This difference in exposure data may reflect regenerative changes in the tests once the gonadotoxic substance had been removed but exact nature of the dibromochloropropane effect and the possibility of a "no effect" concentration remain to be defined clearly.

Recovery of testicular function among DBCP workers.

Twenty-one men with DBCP-related sperm count suppression were re-examined one year after termination of exposure in July 1977. When examined initially, 12 of these men were azoospermic and nine oligospermic. By October 1978 the sperm count of eight of the nine oligospermic men had improved considerably, six having recovered to a normospermic state. None of the 12 azoospermic men had improved by August 1978. Eleven of the 12 men exposed for more than four years were azoospermic. Serum follicle-stimulating hormone (FSH) for these 11 men increased significantly between assessments. Four children were born to the wives of the nine oligospermic men; three of the children were normal and one had several defects. The significance of this observation cannot be interpreted in terms of DBCP exposure, since this study was not designed to examine pregnancy outcome.

Epidemiological assessment of occupationally related, chemically induced sperm count suppression.

Occupationally related, chemically induced sperm count suppression is a recently recognized problem, first brought to light in connection with the manufacture and formulation of dibromochloropropane (DBCP). The authors studied sperm count data from four occupational cohorts - two exposed to DBCP and two exposed to epichlorohydrin (ECH). In both DBCP cohorts there was a significant difference (alpha = 0.05) between sperm count distribution functions of the exposed group and of the non-exposed group. A much higher percentage of exposed men was oligospermic and the median sperm count for each exposed group was substantially lower than that for the respective non-exposed group. In the ECH cohorts there was no significant difference between sperm count data for the exposed group and for the non-exposed group. The authors concluded that exposure to DBCP, but not to ECH, was positively associated with detectable sperm count suppression. It is suggested that the key to identifying and assessing occupationally related sperm count suppression lies in the proper classification and interpretation of group sperm count data.

Testicular function among carbaryl-exposed exployees.

A cohort of 101 male carbaryl production workers with at least 1 yr experience in the carbaryl area was selected from employment records. Of these individuals, 47 provided satifactory semen samples for analysis; 36 of the 47 provided blood for hormone assay. There were no major age or employment-status differences between those who agreed to participate and those who did not. In the absence of sufficiently detailed industrial hygiene exposure data, a subjective exposure classification was developed. No apparent relationships were found between sperm count and exposure category or years worked in classifications based on carbaryl exposure. Also, no relationship was found between fathering children and exposure to carbaryl. When the sperm-count distribution of the carbaryl-exposed workers was compared with a distribution of sperm counts representing a nonexposed (control) population, no overall differences were observed that could be related to carbaryl exposure. There was a small excess in the number of sperm counts less than 20 million per milliliter among the carbaryl-exposed men, but the excess was not significant at alpha = 0.05.

Testicular function in DBCP exposed pesticide workers.

In mid-1977 a number of cases of infertility among male pesticide workers in California came to light. A description of this problem was published as a Preliminary Communication in The Lancet. A larger clinical-epidemiological study was undertaken to better understand the exposure-effect relationships involved. Of 142 non-vasectomized men providing semen samples, 107 had been exposed to 1,2-dibromo-3-chloropropane (DBCP) and 35 had not been exposed. There was a clearcut difference in both the distribution of sperm counts and the median counts between the exposed men and the not-exposed men, Of the exposed, 13.1% were azoospermic, 16.8% were severely oligospermic, and 15.8% were mildly oligospermic. Among the controls, 2.9% were azoospermic, none were severely oligospermic, and 5.7% were mildly oligospermic. Under workplace conditions, DBCP appears to have a selective effect on the seminiferous tubules.

Infertility in male pesticide workers.

A number of cases of infertility were discovered among men working in a California pesticide factory. The suspected cause was exposure to the chemical 1,2-dibromo-3-chloropropane (D.B.C.P.). The major effects, seen in 14 of 25 non-vasectomised men, were azoospermia or oligospermia and raised serum-levels of follicle-stimulating hormone and luteinising hormone. No other major abnormalities were detected, and testosterone levels were normal. Although a quantitative estimation of exposure could not be obtained, the observed effects appeared to be related to duration of exposure to D.B.C.P.