Document Ra60wjQJ0XoQOD4DK6pqzo1eB

*f'* ri. k-, r i r . i" rV 4' h< c, yv It' Institut und Poliklinik fur Arbeits-und Sozialmedizin der Univorsitat zu Koln (Direktor: Prof. Dr. med. W. Bolt), Joseph-Stelzmannstr. 9, D-5000 Koln und Institut fur Toxikologic dor Universitat Tubingen (Direktor: Prof. Dr. med. H. Remmer) D-7400 Tubingen Summary. K.ics luvc been proircatc: with c nuro-l.,' e Ik u/imii.iJM/.idc which completely blocks me. of vinyl chlor idc, It ii.<, j minds arc c.\p</\cd i o atmospheric vmyl chlordc, formation of an etp.iht.nmn between the compound in ilie plu$e ami in the animal's uranism is obwrvcd I'nmcuboh/ed v myl chloride is concemr.iiL'il m adipose tissue 'I tie (list, mat ion y mem o: \ myi chloride in different organs of the r.n is constant over the concentration unye of 25 10.UU0 ppm of v iriv I chloride m rite e.\po:ure atni- sphere Distribution of met aboli res of vinyl chloi ide cont r asts to tint o' (tie o: i::in d (.omnium I, metabolites primarily are consent:,med m liver and in kidneys. Key words: Vinyl elilomle Dim i shutn n m o:y i m chloride metabolism In In h it on ci 1 \ nr, I Introduction Since the time that it was demonstrated that vinyl chloride has to be categorized in the series of careinogens, there has been an increased interest in questions of distribution and me tobo)ism of vinyl chloride in the organism. Many authors showed (Hefner et al., 1975; Green ft Hathway, 1975; Radwan ft Hcnschlcr, 1975; Kappas et al., 1975; liatanjbo et al . , 1 976 a,b; florpoth et al . , 1 976) that in vivo and ln._v_i_-:!\o R&S 026930 < } Ji J vinyl chloride metabolizes very quickly. The biotransformation leads to polar metabolites which leave the organism principally in the urine. Hefner et al. (1975) was able to show that in rats the consumption of vinyl chloride from the atmosphere is inhibited by substances which inhibit the metabolism of vinyl chloride. This means that after the initial setting up of an equilibrium between vinyl chloride in the air and vinyl chloride in the organism the substance can only be absorbed to the degree that it is metabolized. Recently we found that a pretreatment of rats using 6-ni tr.o-1.2.3-benzo-' thiadiazol, a potent inhibitor of oxidative drug metabolism, completely blocks the degradation of vinyl chloride in vivo (Bolt et al. , 1976). This puts us in a position of being able to study the precise tissue distri bution of nonmetabolized vinyl chloride under equilibrium conditions. Knowledge concerning tissue distribution and metabolism of vinyl chloride in an animal test is of interest in the establishing of a technical guide line concentration for vinyl chloride as well as for the evaluation of the health risk with varying vinyl chloride exposures. With regard to lipophilic properties of vinyl chloride, known from chcMiiistry, in the initial drafting of the trade union principles for occupational medicine, pre cautionary investigations, (section called) "danger due to vinyl chloride , as a precautionary measure overweight persons were designated as not suited". R&S 026931 The present article now shows in an animal test that, vinyl chloride has a very groat affinity for fatty tissue. This contrasts with the boiiavioi of metabolites which appear primarily in the liver and kidneys. Experimental Section Material 1,2-14C-vinyl chloride was synthesized by the radio chemistry department of Farbwerke Hoechst AG, Frankfurt. Financial support was cordially marie possible by the Dynamit Nobel AG, Troisdorf. (Inactive) vinyl chloride was cordially made available to us by the WackerChemie Company, Koln. 6-nitro-1.2.3.-benzothiadiazol was made made available by Dr. C.F. Wilkinson, Cornell University, Ithaca, N.Y. Exposing the Rats Male Wistar rats (170-200g) were exposed to 14 C-labeled vi.nyl chloride in a closed glass system (Bolt et al., 197G). Gas specimens could be taken at any desired time through a Teflon septum which were then investigated for their radioactivity. Using this method the consumption of vinyl chloride by the rats could be monitored. Pretreatment A complete blockage of the metabolism of vinyl chloride was achieved by means of a single injection (i.p.) of 50 mg/kg of 6-nitro-1.2.3.-benzo- R&s 026932 ! thiadiazol in O.G ml of DM SO which occurred one-half hour prior to the beginning of the exposure (Bolt ct al., 197G). Determination of the Radioactivity Concentration in the Organs The animals were sacrificed immediately after the exposure. The various organs were taken out and homogenized in a fourfold volume of water. An aliquot of 0.25 ml homogenate was dissolved in 0.5 ml of hyamin-hydroxide and then counted in 10 ml of scintillator (Bray, 1960). Determination of the Distribution of Unmodified Vinyl Chloride in the Rat Organs Along with blocking of the metabolism due to the 6-nitro-1.2.3-benzothiadiazol, the distribution of ^C-vinyl chloride was investigated with vinyl chloride concentrations in the air between 25 and 10,000 ppm. In order to make the given concentration of vinyl chloride obvious, after each injection of a trace dosage of '^C-vinyl chloride into the exposure system, the calculated amount of nonradioactive vinyl chloride was in jected into the system. After an exposure time of 5 hours the rats were sacrificed immediately after being removed from the closed system. The blood was collected in a vessel which contained heparin. Blood (1 ml) or organs (about 1 g) were then placed into a vessel with 5 ml toluene scintillator. The toluene scintillator contains 0.4'/. PPO and 0.01/ P0P0P in toluene. Homogenization, then centrifuging wore conducted in a "U1Lra-Turrax" and finally the toluene extract was put into a scintillation vessel. R&S 026933 t i Again 5 ml of toluene- scintillator wore added to ne extracted tissue and mixing, centrifuging again occurred witn tin; in-,; of trie "IJl tra-furrax" and this second extract was added Jo the first. The radioactivity of the toluene extract wa:, determined in a flerthold-EF 5000 liquid scintillation counter. Results and Discussion If the metabolism of vinyl chloride is blocked by 6-nitro-1.2.3-benzothiadiazol , then during exposure of a vinyl chloride-containing atmos phere, a stationary equilibrium sets up between vinyl chloride in the air and in the organism (Bolt et al., 197G). Table 1. Equilibrium distribution of 'C-vinyl chloride in various tissues of rats which were exposed to a ^C-vinyl chloride atmosphere. The metabolism of vinyl chloride in this experiment was blocked by 6-nitio1.2.3-benzothiadiazol (see experimental section). The values show the equilibria quotients between vinyl chloride in the tissue and vinyl chloride in the atmosphere. Tissue Blood Li ver Spleen Kidneys Muscle (M.psoas) Fatty tissue nMol vinyl _chl or i do in 1 q of tissue nMnl vfnyf chloride in I mi of air 0.65 1 0.13 0.62 1 0.10 0.59 - o.oa 0.59 0.16 0.68 * 0.13 8.30 *. 0.20 R&S 026934 The values indicate the average value standard deviation with 9 different atmospheric concentrations of vinyl chloride which were between 2s anti 10,000 ppm (see also Figure 1). roo ccooo> cn nmol of nonmetabolized VC 9 tissues ! Figure 1. Relationship of air concentration of vinyl chloride to the amount of nonmetabolized vinyl chloride in the tissue. Equilibria investigations in rats which were pretreated for the blocking of vinyl chloride metabolism using 6-nitro-1.2,3benzot'niadiazol (see experimental section). Organs: 9------- ------- 9 x-- -----x - ----- X O" - --0~ ---- 0 Fatty tissue Blood Liver * \ ; 10-1 '0*' ppm VC \r '1 i ]' Table 1 shows tiie situation of the equilibrium for various organs: in most organs vinyl chloride is found in an equilibrium with about equal amounts. The concentration (per g) of vinyl chloride is roughly 1/2 to 2/3 of the air concentration of vinyl chloride (per ml). Fatty tissue in which about 10 times higher concentrations of vinyl chloride were : i -7- found behaves completely differently. rigurc 1 shows that thin r,;lio throughout all of the investigated concentration range of 26 to 10,000 ppm of viny1 chi.Tide in the air remains constant. Table 2 contrasts the results which were obtained with equilibria conditions with the exclusion of metabolism and the contrast item is with the distri bution of radioactive metabolites of 1/lC-vinyl chloride as they are normally found (in intact metabolism) (see also Bolt et al., 1976). Here large amounts of radioactivity appear in the liver as the main metabolise! organ of vinyl chloride as well as in the kidneys which excrete the polar, metabolite. In contrast to this, the amount of radioactivity which is found in fatty tissue is very low. It must be taken into consideration here, however, that in the intact metabolism the concentration of vinyl chloride in the closed system used (Dolt et al., 1976) after about 5 hours of exposure has dropped to 1/10 of the initial value since the half-life of vinyl chloride in our system amounts to about 1 hour. The concentration of nonmetabolized ^'C-vinyl chloride present after 5 hours in the system, since it is in an equilibrium with the fatty tissue, in the present case must amount to about 3 to 4 nMol/g. The table shows that this is actually tne case. The fatty tissue, therefore, even with intact metabolism, does not contain significant amounts of vinyl chloride metabolites, rather nonrnetabol i zed vinyl chloride. R&S 026937 Table 2. Amounts of radioactivi t:y in the organs of rats which had been 14 exposed for 5 hours in a scaled system to a 1.2- 'C-vmyl chloride-confa in- intj atmosphere (initial vinyl chloride concentration - 100 ppm). The values are indicated as nMol of vinyl chloride or vinyl chloride metabolites per g of moist tissue. Organ Liver Spleen Kidneys Muscle (M.psoas) Fatty tissue Rats after pretreatment with 50 mg/kg of 6-nitro1,2.3-benzothiadiazol (average value from 2 tests) Rats without pre treatment (average value of 3 tests) With all due caution and skepticism concerning the transferring of animalexperimental findings to human conditions, on the basis of the present animal-experimental investigation results as well as on the basis of the physical-chemical lipophilic properties of vinyl chloride it must bo taken into account that even in human beings an accumulation of nonmetaboliced vinyl chloride can take place as a function of exposure. Along the lines of W.''\f preventative steps in occupational medicine it must, therefore, be main tained that persons who are heavily overweight are not suited for employment where there is vinyl chloride exposure. MTJ* tf'.. , ,<*' I " It' .CT* ' jn R&S 026938 lit>11, ! I.M , K.ppm, II . iu< liter, A , Iiu!r, \V the r,u Ait h, 'I'mLi>I 3> 15^ 1 n? U ) Bray. (i A , A s: tuple eft u u r.t lit pat J st int dlut* r f* > r liquid Seum!!ati*>n kuumer. Anal, BukIi.-ju a'p.- >\c.- m; ^ :u a Green, T,, II.ithu.iy. fJ K.: The Lni>lo<piaI tate m r.irs of vtiyl c!,!or.>]e jn :r! ri to it> o.'Uoycmeity Chcrn.-bioL Interaction-*, l I. 5*j 562 (1973) Hefner, K I; . Watan.the. I* Cl . Cohnup, \* J I'tehitittnry *>nnli\s of ti.v fate of u.hiied vinyl chloride monomer t rt ratv Ann \ V Ao.ni S*i 2**6. I 5 3 I * S f! 97 5 ) Knppus, H , Bob, ! I, M , Bur! iter, A,, B li. \V . K.tt live; mu,ruv)ir,es caul;. se * t;\ a!e::t binding of *'*CAmyl eh lot tde to madrono! ecu lev Nature 257, 2 3 r -- l 3 J (1975) Norpolh. K.. Muller, C.. Wtmng, 0\. CiOttschalk, 0., C.ottsLhalh. ! . Untcr.uehurjen iiber den StoMuevhiel dc* Vinyiehlonds upd iiher Wnkunpen tier Vm\ K `Air'd Inhalation auf K< yul.muMsniech.itWMr.en de\ l.eher.rofi'.veehv*!-. CfJiseh Cits. Arbeitsrncd.) Stuttgart: Centner 1976 Radw.m, 7.,. Hcn^chler, I) Uptake ;*nd r;u t iboliMn ul uts\! ch!i;r'.:e :n tuc r. dated perfumed rat liver prcpaiation A'aunyn Schtmedebery- Auh Phi*r'..:eo! . Suppl 2S7. R 100 (197 5) Watanabe. P.G., McGowan, C.K., Gehnn.;. 1* J Kite nl * C \.:\\ 1 de attt r 'onye oral adminiMraiion in rats 'Io\ico! Appl I'hunncol 56. >39 552 (1 976a) Wat ana be, I'.G , Mdlmv.in, C K,M adrul, f ,(.) , Cchr in.;, 1* J Fat e * >: * "C v :uv! chloride following inhalation exposure :n rats. To\nol App! FF :n:ia'o!, 37,^9-59 (1976b) Received on October 29, 1975/accei>tcd on November 19, 1975