Document 44o9RgaXgeMXwOQ2vDLrd282G

RESOLUTION OF DOSE-RESPONSE TOXICITY DATA FOR CHEMICALS REQUIRING METABOLIC ACTIVATION: EXAMPLE - VINYL CHLORIDE 1 12 P. J. Gehrmg , P. G. Watanabe and C. N. Park Abbreviated Title: Dose-response: Vinyl Chloride Manuscript # B600-176-77 Toxicology Research Laboratory 1803 Building Health and Environmental Research Dow Chemical, U.S.A. Midland, Michigan 48640 2 Physical Research Laboratory Math Applications, Bldg. 1707 Dow Chemical U.S.A. Midland, Michigan 48640 This study vac funded iy the companies supporting the vinyl chloride project:: being administered by the Mann fan tuning Chnmi i: in Association, Washington, 1>.C. Presented at the 17th Annual Meeting of the Society of Toxicology, March 12-16, 1978, San Francisco, Calif. Accepted for publication in Toxicology In Applied Pharmacology, 1978. DTH 000017427 Resolution of dose-response toxicity data for chemicals requiring metabolic activation: Example - vinyl chloride. Gehring, P. J. Watanabe, P. G. and Park, C. N. (1977). Toxicol. Appl. Pharmacol. ___, ___-___. The toxicity of many chemicals results from biotrans formation products formed from the chemical rather than from the chemical per -se. In such cases, the incremental response may become diminishingly smaller with increasing dose or exposure because activation of the chemical to the toxic form follov/s /it M i cb i<-) 1 x-rtcnt. imj r.liber Lb.in apparent. first-order kinetics. To illustrate Lb iconcept, rats were exposed to concentrations ranging from 1.4 to 4600 ppm vinyl chloride for 6 hours and the total amount metabolized determined. The amount metabolized followed apparent Michaelis-Menten kinetics. For rats, the logarithmic probability incidence of angiosarcoma versus the amount of vinyl chloride metabolized rather than the exposure concentration of vinyl chloride is linear. Assuming no threshold inspite of evidence to the contrary, extrapolation of the data below the range of doses causing experimentally observable responses predicted an incidence of 0.01 hepatic angiosarcoma in raLs exposed to 4.6 ppm vinyl chloride. Theoretical extention of the extrapolation to humans after adjusting for metabolic and body mass differences was under taken. The theoretical extrapolation for man exposed daily for 8 hours to 1 ppm suggests an incidence of 1.5 per 100,000,000. This theoretical incidence, although a likely DTH 000017428 -11- overestimate because of a less than predicted incidence in men exposed to 200 ppm and greater as well as evidence for a threshold in rats, is less than that expected to occur spontane ously. The concepts evolved from this analysis reveals why pharmacokinetics must be considered in designing toxicology experiments as well as in interpretation of the resulting data. DTH 000017429 There exists a great deal of uncertainty in predicting the potential response of exposure to chemicals at concentra tions below those producing an experimentally discernible response. This is particularly true when the response to the chemical in question is oncogenesis. Statistical projections recommended for assessing the risk of exposure to doses of oncogenic chemicals lower than those producing an observable response include those based on logarithm probability curves (probi L curves), .Logistic curves or linear curves (one-hit curves), (FDA Advisory Committee on Protocols for Safety Evaluation, 1971). One of the most commonly used statistical projections for risk assessment has been that promoted by Mantel and Bryan (1961) in which a logarithm probability projection with a slope of one is utilized. A flaw innate to all of these methods is that the dose-response information used to make the projection is based on the dose of chemical administered to the animal rather than the quantity of the administered dose giving rise to the response; the latter may either increase or decrease disproportionately as the administered dose is increased. The use of high doses to reveal the chronic toxicity incurred with exposure to a chemical is a common, scientifically DTH 000017430 -2defensible practice if judgment and scientific rationale are used in designing the experiments and in assessing the resulting data. However, such doses overwhelm frequently the enzymatic processes for activation of the chemical to the toxic form or for deactivation of the toxic form to an innocuous form. In this paper, it is demonstrated how the dose-dependent activation of vinyl chloride to an oncogenic product must be considered in resolving the dose-response of rats exposed via inhalation to vinyl chloride.' DTH 000017431 -J- METHODS Material. 14 i j Vinyl chloride ( C-labeled) v?.s synthesized from (1,2- C) 1,2-dichloroethane (Mew England Muclear, Lots #819-221 and 819-292, 5.0 and 4.8 mCi/nmcle, respectively) directly prior to use (Wagner et al., 1975). Ncn-labeled VC (f-latheson Gas Products) of 99.9% purity was mixed with the 14 C-material to obtain the desired specific activity. Animals. Male, Sprague-Dawley rats (Sparcan Research Laboratory) weighing 200-250 g were used throughout the study. Food and water were provided ad libitum except during the exposure. Exposures were conducted betv/een 9:00 a.m. and 3:00 p.n. (EST) . Groups of 3-6 rats were exposed to various concentrations of 14C-VC for 6 hours. Exposure and Procedure. The rats were exposed by inhalation under dynamic conditions in a 30 ?. glass inhalation chamber. The mean analytical concentrations of VC measured by gas chromatography were 1.440.3 (SD) , 9.3 + 0.2, 24.7:1.4, 5ir2, 109 + 23, 250 + 2, 511 + 11, 1020113, and 4600+311 ppm. Details of this exposure and the r.it hod of analytical He term -.nations nave been reported previously (Wa tana be et -yi . , 15 7 6 . -Immediately following DTH 00001743 the 6-hour exposure to various concentrations of ^C-VC (1.4-4600 ppm) the rats were killed by a blow to the head, and the carcass was analyzed for total radioactivity (Watanabe, et al., 1976b). Previous studies have shown that only a small percentage of radioactivity (<12%) is excreted as metabolites other than 14 C-VC during 72 hrs following a 6 hr inhalation exposure (Watanabe ejt al. , 1976a) . The large 14 proportion of the 12 is comprised of CO^ excretion 72 hrs it < < i / 1 '. I'm ; w t;:, vex y JiLLle ur l mu is excreted during the exposure period. Thus, the non-volatile radio activity determined immediately after exposure in the tissue and carcass is a good estimate of the total amount of metabolized VC. DTH 000017433 -0- RESULTS Consistent with the results of previous studies (Watanabe ot a]., I'JVG.t and 1 V/Git) , tie- i of VC by rats does not increase proport,ionaholy with increasing concentrations (jf VC being inh-il-d (Tiib 1 * I). The non I i n>-a i i I y of the amount, of VC metabolized during 6 hours of exposure to various concentrations of VC appeared to be i ri accordance with Michael in-Menton kinetic:: as described by the equation: V_ fa in this equation, v and v^, ara the velocity and maximum velocity respectively for the biotransformation of VC expressed as pg equivalents VC metabolized per 6 hours. S and K are the concentration of VC beinc inhaled and the m Michaelis constant expressed as eg VC/Z air, respectively. To ascertain whether Michaeiis-Menten kinetics were applicable, the data in Table 1 were analyzed in accordance with the ] jji'.'.ir Woo I f - /.M'ji]", v i mo;; bo: ".t oo trans form j t. i on of the M Lchae J i s-Men ton euu.tlioi (be.gel. , ll'VG), (2) DTH 000017434 -6- It can be seen from the plot (Fig. 1) that the data appear to lie along a straight line thus verifvina, at least visually, the Michaelis-Menton model. V and K can be estimated by the ordinate intercept and the slope of the line or they can be estimated directly by fitting the nonlinear Michaelis-Menten model. Both procedures yield similar parameter estimates. The estimates derived by fitting the model directly are 8558+1147 (SD) yq VC metabolized and 860+159 (SD) yg VC/Z air for V and respectively. Once a means is obtained to calculate the amount of VC metabolized by rats as a function of exposure, it is then possible to relate the untoward effects associated with vc exposure to the amount biotransformed rather than the exposure concentration of VC per se incurred by rats exposed to VC. Maltoni and Lefemine (1975) reported the incidence of hepatic angiosarcoma in rats exposed to different concentrations of VC, 4 hours/day, 5 dnys/week for 12 months and subsequently held for observation until de-urn (Tabic- 2). Before attempting to relate those data to the amount of VC biolrunstermed in accordance with the Michaelis-Menten equation using the n**evicuslv determined values of V and K , the value for V m m' m must be adjusted for the shorter exposure duration used by DTH 000017435 -7- amount of VC biotransformed daily by rats exposed to the various concentrations used in the experiment of Maltoni and Lefemine can be calculated from the equation: v (3) The resulting values for v are given in Table 2. Figure 2^depicts a logarithm probability plot (Drobit plot) of the incidence of hepatic angiosarcoma observed in rats by Maltoni and Lefemine (1975) versus the amount of VC biotransformed for 4 hours of exposure, v, or the exposure concentration, S. The incidence of hepatic angiosarcoma in rats is linear with respect co log v but not log S. The line drawn for log v versus tumor incidence (Figure 2) was deter mined by in; i n'i a g/ obi I. t ion an a) i s program, and the equation reJ a ting the incidunce of hepatic angiosarcoma to log v was: prebit rosoonse = -1.625 1.543 log v (4) DTH 000017436 -8- Using the foregoing equation, a projection below the levels of exposure producing an experimentally discernible response has been made (dashed line). Assuming no threshold for the induction of angiosarcoma in rats exposed to VC, the exposure concentration producing one angiosarcoma in 10,000 rats can be calculated. The probit: percent representing an incidence of 0.01% is 1.28. Substitution of this value into the equation (4) yields: Log v = 1.8827 v = 76.33 pg VC metabolized/4 hours Using equation 3, the concentration of exposure to VC needed to give this value for v is 11.66 pg/7, or 4.6 ppm (approximate 95% confidence limits obtained by substituting the upper and lower 95% confidence limits for v in equation 3 and solving for S are 0.03-9.7 ppm). Hence, exposure of rats to 4.6 ppm VC for 4 hours daily, 5 days/week for 1 year can be expected to produce one angiosarcoma per 10,000 rats if the dose-response curve remains valid at exposures less than those producing a discernible experimental response. DTH 0000]7437 -9- DISCUSSION For many chemicals, toxicity may not be a function of exposure to the chemical per se, but rather to a biotrans formation product of the chemical. Frequently, production of a toxic metabolite is dependent upon" enzymatically mediated reactions which are classically described by Michaelis-Menten kinetics. Since enzymatically mediated reactions are concentration-dependent and saturable, toxicity resulting from exposures to chemicals requiring activation to a toxic form cannot be related directly to the magnitude of exposure or dose. In such a case, it is necessary to determine the amount of the chemical undergoing biotrans formation as a function of dose or exposure before a meaning-' ful dose-response relationship can be established. There is considerable evidence that vinyl chloride requires bioactivation to produce curnors. Metabolic activation is required to induce nutations in bacteria exposed to VC (Bartsch et a_l . , 1975; Malavielle et aJU , 1975; Rannug ;i 1 . , 1574*. Covalent oi riding of 14 C to hepatic nacro- (,,o 1 <t;u I < s in fill:; (W. 11 a f i.'i jo _-jL aj_. , 1977) expensed to ^ ^C-VC also requires bioactivation. Covalent binding of electro phile:; to I >; ;/v has been as sex: i a ted with tumor i quncui s . DTH 000017438 -10- For vinyl chloride-induced hepatic angiosarcoma in rats, a logarithmic probability plot (probit plot) of the incidence versus the amount of vinyl chloride metabolized, v, over a range of exposures from r>0 Lo 10,000 ppm VC gives a classical I in", rig. ibi. Tie- dose-1 spouse relationship is not a straight line when plotted as a function of the exposure coiiceii I r a l j on, C (Tig. '/h) . Those results support, further the oonoia s j on the t. Vr r `.-gw i r1 hi otr a ns format i on to an active ;; e ! a bo I i V e I o , t uf si I ' / * 11' - . i . I'u Mi r mo r e , a more- reasonable evaluation of the dose-response data for vinyl chloride induced tumorigenesis requires knowledge of the amount of VC activated as a function of exposure. After arbitrarily excluding data acquired from rats exposed to concentrations of VC exceeding 500 ppm in the experiment of Maltoni and Lefemine (1975), Schneiderman et al^ (1975) extrapolated the remaining data to predict an incidence of 0.01% hepatic angiosarcoma in rats exposed to 1 ppm VC. This number is reasonably close to our prediction of 4.6 ppm VC for the same incidence. If Schneiderman e_t al had used all of the data, a dose-response curve with an unrealistically shallow slope would have resulted and the predicted level causing 0.01. noput. i o nog i osureemu would have been much smaller, on the order of 0.00001 ppm. DTH 000017439 -11- Thc concepts developed herein allow use of all of the data f-1 i .1 111 i'I \,/ M-1 ) t r,11 | .a),| ) i ) . jii j j11 ( ) ') 7 ; t ry r;r ,ii:, I r 11< t , i dr< - response curve on i ssierit ilic.illy dr1 < n:. i b 1s- basis. Assuim i ncj that the resulting dose-response curve can be projected beyond the range of the experimentally discernible responses, the i-/po.'.ii r < cono-'-n t r.i t ion r*'f.uir,,d I o produce tin incidence of: O.Ol'-t hepatic angiosarcoma in rats is 4.6 ppm. Aside from interpreting toxicity data for chemicals requiring activation to a toxic form, there are some practical implica tions of the concepts presented herein for designing experi ments to assess the toxicity, including carcinogenicity, of such chemicals. For these chemicals, increasing the concen tration above the apparent K will produce diminishinglv smaller increments in the response; no increase in the response is to be expected when the exposure concentration is 2 or 3 times K . Since total dose is a function of m exposure time as well as concentration, it is important to determine the effect of exposure time on the response. J shown in Equation 3, the only parameter influence^by As exposure tine is V , which is increased linearly with time. n Therefore, after the concentration to which the animals are exposed becomes 2 to 3 tines K , the amount metabolized, v, . i ] j i s,c re.i 1 in* i > 1 y wish i u< ; < m s i ng < exposu r> tine. For DTH 000017440 -12- this reason, the gradation of incidence of angiosarcoma in rats exposed to high concentrations of VC will become a function of exposure time rather than concentration. This reasoning makes it imperative that the duration of exposure as well as exposure concentration be considered in evaluating the results or epidemiological studies of people exposed to j, J j 11 C' i/1' ' (i I f . I I i on . 'll ye j (I l he '//<>[!'. e || 7 i I ' i) Illli Ml I. . i/n I ess the dose depes.dei. f , M i oh j e I j Men ten typo pharmaco kinetic parameters are resolved prior to designing the experiment, the results may be robbed of much of their value for characterizing the dose-response function for the untoward effects observed. Thus, the current approach using the maximum tolerated dose as defined presently and fractions thereof, may be scientifi cally unsound if the objective is to assess the potential toxicity of exposure to much lower doses or exposures. For some chemicals detoxification of the chemical per se or reactive metabolites formed from the chemical may also be dose-dependent and saturable leading to a build-up of toxic materials. In such cases, the incremental responses to increasing doses or exposures will become dispropor tion .1 t < 1 y ) -i r y ' r r 11 h' r rm xtri-i 1 ) < r ('.<< 0* 4i r i ng and Hi nil, ) ') 7 7 ) . DTH 000017441 -13- In the foregoing analysis, of the dose-response data for the induction of angiosarcoma in the rat, no threshold for the response was assumed. As indicated, extrapolation below the range of doses resulting in an observable response may over estimate the response in rats because there is evidence that detoxification of reactive metabolites of VC may occur more off ici e/t) y irat.:; expo:,.'] to concentration:; of VC he 1 ov/ 00 ppm (W*i I a tin be o* a I i 07 0-:) . Indeed , furthor analysis of the data reported by Multoni and Lefemine (1975) also provides an indication of a practical threshold. Jn a subsequent pf `-nl.nl i on of Lh'C.e dal i, it was revealed that t.ue latency for the development of hepatic angiosarcoma was respectively 64, 70, 78, 81, 79 and 135 weeks for rats exposed to 10,000, 6,000, 2,500, 500, 250 and 50 ppm VC (Maltoni, 1975). These results indicate that at some low levels of exposure the time required for induction may exceed considerably the life expectancy for rats. This is consistent with the work of others suggesting that multiples of a lifetime may be required for expression of cancer in response to low doses of a carcinogen (Druckrey, 1967 and Albert and Altshuler, 1973). Thus, extrapola tion of the data obtained for rats below the range of exposures causing a discernible response may be expected to overestimate the projected incidence. DTH 000017442 -14- The ultimate objective of a toxicological study is to develop data which can be used to assess the potential risk for man. It is worthwhile to utilize the concepts presented herein to achieve this objective realizing fully that such extrapolation is fraught with uncertainties. The basic assumptions made are: 1) Induction of angiosarcoma is related to the amount of reactive metabolite of VC per unit of mass. 2) Exposure of rats for 12 months approximates exposure of workers for their working life. 3) There is no threshold for the induction of angiosarcoma in either rats or man which likely overestimates the assumption of risk as discussed above. 4) The efficiency of the metabolic processes involved in the conversion of VC to the reactive form is propor tional to the body surface area. Since data for the biotransformation of VC by man are not available, the most logical basis for translation of the animal data to man would seem to oe on the basis of body surface area. DTH 000017443 -15- The last assumption deserves comment. There are considerable data in the literature shewing that metabolism in general and other physiological parameters as well are relatable directly to the surface area of the body (see Schmidt-NieIsen, 1970*, and Pinke], 1956). For this reason, administration of biolo- gica]ly active chemicals to various species frequently gives . i; i < ' [ 11 i /. i I < r 11 r > >i i v/ r i * n t J.1 i ,i 1m i n i :; t :; ed in proportion to the surface area of the body, that is dose per .vj'Mrr' m't'-j ol body :,ur i, c (Pinkol, 1951',). T)i i s reel a 1. ion- ship is gaining recognition in estimating the risk incurred by man from exposure tc chemicals in the environment (Committee on Safe Drinking Water, National Research Council, 1977). In utilizing this relationship it must, however, be recognized that the original relatior.shiD was developed for biologically active agents. Since metabolism and other physiological processes involved in detoxification are more active in smaller animals, the dose of a biologically active chemical per unit of mass required to produce a given effect increases as the body mass decreases, while the dose per unit surface area remains relatively constant. However, for a chemical : oeui ri ng <ic t. i /.- t: i on t.o tho bioloqj cal lv active toxic form, the total amount transformed will be roughlv proportional to the bodv surface area. Since toxicity is a function of mm concentration of the ictivo form in tissue, this total , ' r ; , ` . - r. :,< norm t) i x'-e for m.iss to . . ' ; .. I ' , i;, I I ; d ! : DTH 000017444 Using aforementioned rationale, the maximum velocity, V , for a 70 kg man can be estimated bv calculation using the V value obtained for a 0.250 kg3 rat. The Vm of man for VC will be : Vm (man) Vm (rat)( 1.85 0.045 sq m sq m or Vm (man) =- (8550 j.g/G hr) > = 351829 yg/6 hr wi.`-r < tii'.' yuJ J . i; 5 and 0.515 sq /; i a r t he body surf at;** areas of a 70 kg man and a 0.250 kg rat, respectively (Pinkel, 1958). For an 3 hour exposure, the value is 469105 yg/8 hr. In order to use this number to theoreti cally estimate the response in man using data collected in rats, the for man must be adjusted to a mass equivalent to that of rats since toxicity is a function of concentration in tissue. To do this, the number is divided by 70 kg/0.25 kg or 280. Vi if result inn V m J or man on a mass eq' uivalent, basis to that of rats is 1675 ug/3 hr. Using this value, the amount of VC transformed to a reactive form by man on a mass equiva lent basis to rat is given by the equation: V ug/8 hr 67 5 uq/8 hr . S ia/i>860 sg/'. + S ug/i (5) DTH 000017445 -17- Using this equation, the amount of VC transformed by man on a mass equivalent basis to rats was calculated as a function of exposure concentration ana the expected incidence of angio sarcoma estimated from ecuation 4 (Table 3). For men exposed to greater than 200 ppm VC, the incidence of angiosarcoma has been reported to be 0.02% (Fox and Collier, 1977). Hence, the theoretical calculated incidence using data from rats exceeds that currently detected by approximately 50 fold. This may indicate that people are less sensitive than rats to the induction of angiosarcoma or it may indicate that a practical' threshold for the ind action of ang i nnarco:;. a h - . si been a tf ai .nod , Cons is to.' it w i ! !i limn In! t'U J i b i J i L 7 ii t Ij.i l V on a oquiv.. i J on(. bas is to rats for men ex cos ed to 200 p pm is 625. This number J i < 1 ,< 1 ov/ l.li it ft y r rit:. ,od to 5 0 pOIII . As indicat ed previously, angiosarcoma observed in rats exposed to 50 ppm occurred only in a rat that lived 135 weeks (Maltoni 1975). Further, this rat did not die as a result of the angiosarcoma but was killed. Thus, as indicated previously, projection of the data collected in rats below the range of exposures producing an observable response ma / overestimate the incidence. DTH 000017446 -18- Inspite of the likelihood of overestimating the incidence of angiosarcoma in rats or man, the incidence predicted for people exposed to 1 ppm, the current OSHA (Occupational Safety and Health Act) standard, is very small (1.5 per 100 million)'. This value which is likely an overestimate is belov/ the expected incidence of spontaneous angiosarcoma rcpor ted to hi; ?.l) to /"> r,e;f in the IJ.H. annual Ly (Mnkk, et al, 1976) . In summary, it has been demonstrated that the incidence of VC induced angiosarcoma in rats is relatable not to the i oil' :< n 1 i 11 i on o 1 < /.\ < > a i; bn I r .it ; i i to I la allion n t of VC bio transformed. Ltiotransl ormution oi VC by rats is a dosedeoendent process characterised by Michaelis-Menten type kinetics. The concepts evolved from this analysis reveals why pharmacokinetics must be considered in designing toxicology experiments as well as in interpretation of the resulting data. Having characterized the dose-response for induction angiosarcoma in rats as a function of the amount t of VC biotransformed, a theoretical estimate of the incidence expected to occur in exposed men was undertaken using the data collected in rats. For daily 8 hr exposures to 1 ppm, th" ru' d id "d j no i danc' i : 1.5 in 100,000,000 which is loss than chat expected to occur spontaneously. This predicted DTH 00001744 - 19incidence is likely an over-estimate of that which will occur as a result of exposure to 1 ppm because there is some evidence for at least a practical threshold in both rats and man. There are no illusions that this estimate by extrapo lation of data outside the range of doses causing experi mentally observable responses and subsequently to man is without flaws. However, the rationale used represents a new approach which utilizes more logic than methods employed currently for such extrapolation. DTH 000017448 -20- REFERENCES Albert, R. E. and Altschuler, B. (1973). Considerations relating to the formulation of limits for unavailable population exposures to environmental carcinogens. (' i' I i o i. ' i I i' i' - r i r ': i r / ,1 . i , T r < >' '< -ed i ng'. of t. hf 12th Anmi.il Hanford Miolouy Symposium at Richland, Washington, 234-253. Bartsch, 1!., Malavielle, C . , and Montesano, R. (1975). Human rat and mouse liver mediated mutagenicity of vinyl chloride in 1: lore 1 la i yoh i mu r i 'i;i strain::. Trit. J. ru , l',, 4/9 4 : / . ,:;.m i It i < on Sale Ur inkin'? W-d`-r (1977). .`uimiiiry P'Mjort': Drinking Water and Health, Advisory Center on Toxicology, Assembly of Life Sciences, Washington, D.C. r Druckjpey, H. (1967). Quantitative aspects m chemical carcinogenesis. In Potential Carcinogenic Hazards From Drugs. Evaluation of Risks, R. Trubant, Ed., UICC Monograph Series, Vo.l . 7, Springer-Verlag, Berlin, 60-78. Food and Drug Administration Advisory Committee on Protocols for Safety Evaluation (1971) Panel on Carcinogenesis Report on Cancer Testing in Safety Evaluation of Food Additive:, .md I i '; d ,, Tex. Ar.rd . Pharmacol., 20: 4 19- ; i ?i . DTH 000017449 -21- Fox, A. J. and Collier, P. F. (1977). Mortality experience of workers exposed tc vinyl chloride monomer in the manufacture of polyvinyl chloride in Great Britain, Brit. J. Ind. Med., 34:]-30. Gehring, P. J. and Blau, G. (1977) . Mechanisms of carcino genesis: Dose-Response. J. Environ. Path. Toxicol., in press. Makk, L., Delmore, F., Creech, J. L., Ogden, L. L., Fadell, E. H., Songster, C. L., Clanton, J., Johnson, M. N. and Christopherson, W. H. (1976). Clinical and morphologic effects of hepatic angiosarcoma in vinyl chloride workers. Cancer, 37:149-163. Malavielle, C., Bartsch, H., Barbin, A., Camus, A. M., and Montesano, R. (1975) . Mutagenicity of vinyl chloride chloroethyleneoxide, chloroacetaldehyde and chloroethanol. Biochem, Biophys. Res. Comm., 63, 363-370. Maltoni, C. (1975). The value of predictive experimental environmental carcinogenesis. An example: vinyl chloride. Ambio, :18-23. Maltoni, C. and Lefeiuinc, C. (1975). Carcinogenicity assays of vinyl chloride: Current results. Ann. N.Y. Acad. Sci., 246, 195-224. DTH 000017450 -22- Mantel, N. and Bryan, W. R. (1961). "Safety" testing of carcinogenic agents. J. Mat. Cancer Inst., 27, 455-470. Pinkel, D. (1958). The use of body surface area as a criterion of drug dosage in cancer chemotherapy. Res., 18:853-856. Cancer Rannug, U., Johansson, A., P.amel, C. and Wachtmeister, C. A. (1974). The mutagenicity of vinyl chloride after metabolic activation, Ambio, 3, 194-197. Schmidt-Nielsen, K. (197C). Energy metabolism body size, and problems of scaling, Fed. Proc., 29:1524-1532. Schneiderman, M. A., Mantel, N. and Brown, C. C. (1975). From mouse to man - or how to get from the laboratory to Park Avenue and 59th Street. Ann. N.Y. Acad. Sci, 246, 237-248. Segel, I. H. (1976) . Bio chemical Calculations, 2nd Ed., pp. 236-237, John Wiley and Sons, Inc., New York. Wagner, E. R., Muelder, W. W., Watanabe, P. G., Hefner, R. E., Jr., Braun, W. H., and Gehring, P. J. (1975). Gas chromatographic method for the preparation of ^C-labeled vinyl chloride, J. Labeled Compounds, 11, 535-542. DTH 000017451 -23- VJatanabe, P. G., McGowan, G. R., Madrid, E. O. , and Gearing, 14 P. J. (1970a). Fate of C-vinyl chloride following inhalation exposure in rats. Toxicol. Appl. Pharmacol., 3_7 , 4 9-59. Watanabe, P. G., McGowan, G. R., and Gehring, P. J. (1976b). Fate of "^C-vinyl chloride after single oral administra tion in r a t s , To>: i no 1_. Aon 1. Pharmacol . , 3 0 , 339-352. Watanabe, P. G., Hefner, R. E., Jr., and Gehring, P. J. (1976c). Vinyl chloride induced depression of hepatic nonprotein sulfhydryl content and effects on broraosulphthalein (BSP) clearance in rats, Toxicology, 6, . 1-8. Watanabe, P. G., Zempel, J. H., Pegg, D. G., and Gehring, P. J. (1977). Hepatic macrc-nol ecular binding following exposure to vinyl chloride. Toxicol. Appl. Pharmacol., in press. DTH 000017452 -24- LEGENDS Figure 1. Metabolism of vinyl chloride analyzed in accordance with the Woolf-Augustinson-Hofstee linearized form of the Michael i -Merit en equation. Valuer; of V and v/S wore Laker from Table 1. The line was fit by linear r<q re:;: i on ana 1 /:; i . The.- co r re la ti on coeff icient, I , wan 0.88. Figure 2. (a) Metabolism of vinyl chloride expressed as 'log v ,uq VC metabolized, , . ., _ (' f-2------------t4-- ------------------) hr versus percent incidence of hepatic angiosarcoma (probability scale) . (b) Exposure concentration expressed as log S (ppm) versus the percent incidence of hepatic angio sarcoma. The probit equivalents of the percent incidence are shown on the right hand ordinant. The solid line is the best fit for experimentally observed responses while the dashed line represents extrapolation below those doses producing an observable response assuming no threshold. DTH 000017453 25FIGURE 1 DTH 000017454 -26FIGURE 2 DTH 000017455 Log S -27- TABLE 1 Parameters for Describing the Metabolism of Inhaled Vinyl Chloride (VC) Using Michaelis-Menten Kinetics Exposure Concentration S (ppm VC) 1.4 9 25 51 109 250 511 1020 4600 S (yg VC/2. air)a 3.6 23.0 64.0 13 0.6 270.0 640.0 1303.2 261L.2 11776.0 . yg VC metabolized13 _________6 hr___________ 303C 242+26 55742 1181+93 2406+173 3826+345 6263+355 4257+765 9255+1467 v/S 8.33 10.52 8.70 9.04 8.62 5.98 4.79 1.63 0.79 1 ppm VC = 2.56 yg VC/ air Determined from the total radioactivity in the carcass Mean + standard deviation DTH 000017456 C o rre la tio n B etw een E xposure C o n c e n tra tio n o f V in y l C h lo rid e M e ta b o lis m and In d u c tio n o f H e p a tic A n g ie se re .--a in H ats cm M a lto n i and L e fe m in e -28- o (0 oE 0) -H O p u -p o c c to p <U (1) d TO 013 0 i/i in <N cm tN <N f~~ (N -H <N P -H m O <U O -H Ch C ip cr. M0C < > A cm n m m CM O m m vo CD o> vo n t. ( r- in m cn <, \ i' i r , ti ro 01 N --( 0 xx M I--1 to p * CM -P -oin m o o m o m rH TT in cn nr ci m r- 01 w E vr O LO in LO m CN u > Cr >; n TO o O o o co X u > -VSluVO inn t-r-j vo m - in r--1 o nr vo CO CN * rH vr vo CN in c o-- p u 01 -P > p to np E V. u f- o o o o o o in O i^i O LTi rj O m o :: : n. n r xn i: /j o u ro 0) N *H C X rj P x: 01 E vr O > cn vo o i-' m vo -r u r.) 11 H i--i 0 XI to p P C 01 E vo U> Cr OP >H TO O' --VD m CM II u > f; ( n. r4 C3 CO in in co Cl J P rt Hi O. 1' \ o O' as*, in 01 cn p+ 3a 0 >p x: x: =>< tr x. vr O' P VO 0 in o r- o vo in 00 TO3 0) II P O> O P P o o ,. XI in (cr\ r-1 P (. O DTH 000017457 a g 03 W 1--1 0 p. XX wo 0 X G QJ p c dJ x g u E-* Xc G cr 33 x P o oc o * ... cr* G !" M H E G a g >. x d tn IS) a u< <D u P. in > X P wd E cx o Cr> pcc t. H H 33 'Or* TJ G o CJ E cj P p to o 0 o O' U, rl 1 f \ 11 C, t) (i u Ij rj '0 dj fO o -p p -M cz p. Cl (D *r0- E >do H P 4J W c oM (73 D TJ 0 0 CD (X -P 0 UH 00 *H o p CD tn 0 p 4J &L, C c d >n in o f--i d E in < dd 0 rH d o co u H p H 4J d JJ c tn OJ o o u CJ <H o CP OJ r: < r X C G OO pX d OJ G fX o Gu rH U p GC d O G in P 33 o X p H au a Pc G OM < CJ x fr- o G XW rl C XI o 0a p in (X G r\) o r--l 00 \D N > C"P f' f; fy ' J .1 X 03 G N r| rH 0 JC P d x; -P 0 CO E u > D > m rj U-> ,f <| r> J * y, r* 33 in 4J o v-- r' Vo C 0 u ''r l: (; r* j; O G r\j -29- 1 UO o1 r-H o *--i rH r--{ *X O r- m m r-H 00 OJ in in rH o o f. T CTi G rn m O . fj , i f; KD O' rrH CP 04 OJ fX. i.O aj . If 1 1 fJ . 1 r \ T4 O in rH tn G cc (3 o E p X pp 0 o in Q. -U 0d Xp u (3 C- E > in r4 IH 0 G 4J X X X (G G r- EX IT- > C0 *H cn X Xc <0 H X 1--1 E G 2GG G in i--1 ---1 in G (3 G > O P >- G P X O' GG XG X 'C in (0 G in EG cE o in -H G nJ X (3 0 G C' o Qi . 1 X X Xl i: G G rH in XG G c O rH G i--l X sGG 1 UG in -rn -H in 'C rH r( G GX ro >: X i--1 UX -P c X, in G XG G G cr XPG X in PX Cn O G c X in *H in nD 'O OGc c tn ra p GEG XpG GGP CH 1--1 X G \ GG o T1 G a t--t O G X r. 'Zj V rt i 1 r H p c ^- G CJ G tn a; G X II X X > X X 'O G E in 0X CJ <3 E X c XO G Poa r-H > X X to aX G X X >i rH X X *p cX Go Gp CD G in G X> G rH CO X o G a *--* in XG XP G XG X X ro E C0 Op P X X G 33 GG cr c G *H E Xp rH G XX oG p c f.'. W Fi G OS P XG E T3 O Gu Xp GG rP in Go O p --1 cn Gc oG in X G0 2 G GO tn c cG o 33 CP H in o Gc P rH X P P c X0 0 p o Ul o. CJ CJ 'O QJ r { 11 n uo G ^r^ 0. 4J Xo Gu o Gr* o f-- H -p O DTH 000017458 Chloroe thylene Vinyl chloride Cr. 1 M' t .iho] i r,iii Dose-response INDEX TERMS DTH 000017459