all-trans-retinoyl-β-glucuronide is a potent teratogen in the mouse because of extensive metabolism...

TERATOLOGY 54150-156 (1996)

All-Trans-Retinoyl-P-Glucuronide Is a Potent Teratogen in the Mouse Because of Extensive Metabolism to All-Trans-Retinoic Acid H. NAU, M.M.A. ELMAZAR, R. ROHL, R. THIEL, AND J.O. SASS Znstitut fur Toxikologie und Embryopharmakologie, Fachbereich Humunmedizin, Freie Universitiit Berlin, 0-14195 Berlin, Germany (H.N., R.R., R.T.); King Suud University, College of Pharmacy, Riyudh 1145, Saudi Arabia M.M.A.E.); Universitatsklinik fur Kinder- und Jugendheilkunde, A-9020 Innsbruck, Austria (J.O.S.); Department of Food Toxicology, Veterinary Medical University of Hannover, 0-301 73 Hannover, Germany (H.N.)

ABSTRACT Al I - trans- retinoyl- p - D - g I ucu- ronide (all-trans-RAG) is a water-soluble derivative of all-frans-retinoic acid (all-frans-RA) and has been characterized as an endogenous metabolite of vitamin A in rat bile and kidney. All-frans-RAG was previously demonstrated to be a maior metabolite after application of all-trans-RA in several species (mouse, rat, rabbit, monkey); all-trans- RAG was described in these experiments to exhibit a very low placental transfer to the embryo. Be- cause retinoid-like activity has been found after application of all-frans-RAG in vivo as well as in several in vitro systems, and because of its low placental transfer, this glycoconjugate appeared to be an interesting retinoid with possible thera- peutic activity, but reduced teratogenicity. Here we investigated the teratogenic activity of all-trans- RAG in comparison to all-frans-RA in mice, and performed accompanying pharmacokinetic studies. Surprisingly,all-frans-RAGwas moreteratogen- ic than equimolar doses of all-frans-RA following subcutaneous application on day 11 of gestation in the mouse (20 prnol/kg body weight). Pharmaco- kinetic studies revealed that all-trans-RAG was ex- tensively hydrolyzed to all-trans-RA and that the plasma area under the concentration-time curve (AUC) of all-trans-RA following all-trans-RAG application exceeded the plasma AUC value of all- frans-RA following application of all-frans-RA. Ex- tensive hydrolysis of all-trans-RAG was also observed after intravenous application of this glycoconjugate. Transfer of all-frans-RAG to the embryo was low, but transfer was high to maternal organs such as the liver and kidney. These in vivo studies suggest that all-trans-RAG serves as a precursor of all-trans-RA by the intravenous and subcutaneous routes, and application of all-trans- RAG results in high and teratogenic in vivo exposure to all-frans-RA. o 1996 WiIey-Liss, Inc.

All-truns-retinoyl-p-D-glucuronide (all-truns-RAG) was first identified as an endogenous vitamin A me-

tabolite in rat bile, small intestine, and liver (Dunagin et al., '65; Zile e t al., '82; McCormick et al., '83). This glycoconjugate of all-truns-retinoic acid (all-truns-RA) was also purported to occur as an endogenous compo- nent in human plasma (Barua and Olson, '86). Subse- quently, all-truns-RAG was identified as a major metabolite after application of pharmacologic or toxic doses of retinol and all-truns-RA to mice (Creech Kraft et al., '91a), rats (Collins e t al., '95), rabbits (Tzimas et al., '94a), and monkeys (Eckhoff et al., '90, '91; Creech Kraft et al., '91b; for reviews see Nau, '93, '94). p-Glu- curonides of retinol, 13-cis-retinoic acid and 9-cis-retinoic acid (Eckhoff et al., '91; Creech &aft et al., '91a,b; Sass et al., '94, '95; Tzimas et al., '94b), were also identified and quantitated following administration of the respective aglycones.

All-truns-RAG attracted attention because it exerted retinoid-like biological activity in a variety of in vitro systems such as the cultured human promyelocytic leu- kemia cell line HL-60 (Zile et al., '87; Janick-Buckner et al., '91) and mammary gland in organ culture (Mehta et al., '91). In these systems, all-truns-RAG acted potently in regard to inhibition of proliferation and induction of differentiation. Administration of all- trans-RAG promoted the growth of vitamin A deficient rats. However, from those experiments it was not clear if all-truns-RAG acted directly or following hydrolysis to all-truns-RA. When analytical measurements were performed it became clear that a considerable portion of all-truns-RAG had been hydrolyzed in vitro and the resulting all-truns-RA was found in the medium as well as in the cultured tissue (Tzimas et al., '94c; Ruhl et al., '94; Foerster et al., '96). Considerable hydrolysis was also observed after intraperitoneal (i.p.) application of a tracer dose of 3H-all-truns-RAG in the rat

Received April 22, 1996; accepted July 29, 1996.

Address reprint requests to Dr. Heinz Nau, Dept. of Food Toxicology, Veterinary Medical University of Hannover, Biinteweg 15/115, D-30173 Hannover, Germany.

0 1996 WILEY-LISS, INC.

ALL-!l"S-RETINOYL-P-GLUCURONIDE 151

(Barua and Olson, '89). Retinoid glucuronides do not interact with cytosolic retinoid binding proteins (Mehta et al., '92) or retinoid receptors (Sani et al., '92), which could be taken as an argument against a direct action of these glycoconjugates.

Also further retinoid-glycoconjugates were shown to exert biological activity including all-truns-retinoyl-p- glucose (Barua and Olson, '91, '92), all-truns-retinyl-p- glucuronide (Barua and Olson, '871, all-truns-retinyl-p- glucose (Barua and Olson, ,921, the p-glucuronide of N-(4-hydroxypenyl)-retinamide (Bhatnagar et al., '91) and derivatives (Doepner et al., '92; Kaleagasioglu et al., '93; Panigot et al., '94; Robarge et al., '94).

Teratogenicity is an extremely serious side effect of essentially all active retinoids synthesized and tested up to now (Kochhar, 1967; for a review, cf. Nau et al., 1994). It is likely that the teratogenic activity is medi- ated by nuclear retinoid receptors which may also be crucially involved in the pharmacological effect of retinoid drugs in dermatology or oncology (Chambon, '93). A number of retinoid receptors have been shown to be expressed in embryonic tissue in a very specific spa- tial-temporal fashion, and it appears to be extremely difficult to develop novel retinoids which interact with the retinoid receptors in the desired target tissue of pharmacologic action, but do not interact with embryonic receptors.

We have been following another lead to retinoids with low teratogenic activity: retinoids exhibiting limited transfer to the embryo. We have demonstrated that all-truns-RAG, produced as metabolite of all- truns-RA, was transferred to the embryo to a very limited degree, and only a few percent of maternal plasma all-truns-RAG concentrations were found in the embryo of the mouse (Creech Kraft et al., '91a), rat (Col- lins et al., '94, '951, rabbit (Tzimas et al., '94a; Collins et al., '95), and monkey (Hummler et al., '94). Very low embryo/maternal plasma concentration ratios were also found for the p-glucuronides of 13-cis-retinoic acid (Creech-Kraft et al., '91a; Tzimas et al., '94a), 9 4 s - retinoic acid (Sass et al., '94; Tzimas et al., '94b) and retinol (Collins et al., '94).

The low placental transfer of retinoid-p-glucuronides, together with the biological activity of these glycoconjugates in vitro discussed above, prompted us to study the teratogenic activity of all-trans-RAG in vivo in mice. Gestational day (GD) 11 represents a suitable stage for treatment of mice, in order to assess teratogenic potencies of retinoids by morphologic eval- uation of near-term fetuses; resorption, growth retar- dation, cleft palate and limb reduction defects are re- liable end-points (Kochhar and Satre, '93). Parallel pharmacokinetic studies were performed for the ratio- nal interpretation of the results from our teratology study. Area under the concentration-time curve (AUC) values were used as exposure parameters because they have been previously shown to correlate well with teratogenic activity of retinoids (Nau, '90, '94).

MATERIALS AND METHODS Laboratory precautions

All work with retinoids was performed under dim amber light to avoid photodegradation. Retinoids and their solutions as well as biological samples for retinoid analysis were stored at -20°C.

Chemicals Retinoic acid isomers were provided by Hoffmann-La

Roche (Basel, Switzerland). All-truns-RAG was synthesized following a modification of the method of Barua and Olson ('87, '89) which has been reported recently (Foerster et al., '96). All chemicals for the synthesis were generously provided by BASF AG (Ludwigshafen, Germany). Organic solvents of highest purity and trifluoracetic acid were purchased from Merck (Darm- stadt, Germany). Water was purified with a Milli-Q water purification system (Millipore, Eschborn, Ger- many).

Animals NMRI mice (Han: NMRI; Zentralinstitut fiir Versuch-

stierzucht, Hannover, Germany, or Harlan-Winkel- mann, Borchen, Germany) were kept under specific pathogen free (spf) conditions and a 12-hr standard light-dark cycle. They received a standard pellet diet (Altromin 1324; Altromin, Lage, Germany) and tap water ad libitum. The animals were mated during 2-hr period in the morning. The following 24 hr interval was considered gestational day (GD) 0.

Teratologic study On GD 11, mice received a single subcutaneous (s.c.)

dose of 20 pmol all-truns-RAG or all-truns-RAkg body weight (b.wt.). The dosing volume was 1 mlkg; the vehicle was dimethyl sulfoxide (DMSO). A control group was administered the pure solvent. On GD 18, the dams were killed by cervical dislocation. Implan- tation sites, resorptions, and live fetuses were counted. Live fetuses were weighed individually and examined for external malformations. The fetuses were then pre- served in 5% formalin solution until examined for in- ternal malformations. Skeletal abnormalities were examined after staining with alizarin red S. Results are compared with those of the vehicle control group using Student's t-test (fetal weight) or chi-square test (others).

Toxicokinetic study Pregnant mice were treated with 20 pmol all-

truns-RA or all-trans-RAGlkg b.wt. on GD 11 as described for the teratologic study. To examine retinoid pharmacokinetics in the plasma of one group of mice, serial blood samples were collected under brief ether anesthesia from the retroorbital sinus into heparinized capillary tubes 0.25,0.5,1,2,4,8,16,24,32, and 48 hr after treatment. Plasma was prepared by centrifuga-

152 H. NAU ET AL. TABLE 1. Prenatal effects induced by all-trans-RA or all-trans-RAG (both

20 pmolkg, s.c.) in NMRI mice on GD 11

Control' (%) all-trans-RA (%) all-trans-RAG (%) No. of litters 9 9 12 Implantations 110 108 142 Resorptions 13 (11.8) 6 (5.6) 16 (11.3) Live fetuses 97 (88.2) 102 (94.4) 126 (88.7) Fetal weight (g k SD) 1.30 ? 0.11 1.24 f 0.13** 1.23 f 0.11** Exencephal y 0 (0) (0) 2 (1.6)

Full-length cleft palate' 0 (0) 4 (3.9)* 27 (21.4)** Dislocated hind limb 3 (3.1) 6 (5.9) 4 (3.2) Extra ribs' 10 (10.3) 15 (14.7) 62 (49.2)** Dislocated sternum2 9 (9.28) 14 (13.7) 40 (31.7)** Radius (bent)' (0) (0) 25 (19.8)**

Ulna (bent) (0) (0) 4 (3.2) Ulna (short) (0) (0) 3 (2.4) 'One ml DMSOkg b.wt. S.C. 'Significantly higher in the all-trans-RAG-treated group than in the all-tram-RA-treated group. *P < 0.05; **P < 0.01; compared with the control group using the Student's t-test (fetal weight) and chi-square test (others).

Kinked tail 0 (0) l(0.98) 0 (0)

Radius (short)' (0) (0) 12 (9.5)**

tion of the blood for 10 min at 1,500g and 4°C. Two other groups of mice were also administered all-trans- RAG as described. These animals were killed by cervical dislocation 2 and 6 hr after treatment, respectively, after blood had been collected. Plasma was prepared from this blood as described, and embryos, yolk sacs, placentas, and maternal livers, kidneys, and spleens were collected. To reduce their blood content, liver samples were rinsed with ice-cold 0.9% (w/v) aqueous NaCl solution. All tissues were weighed and immedi- ately frozen.

For examination of plasma retinoid concentrations at different time points after intravenous 6v.) administration, non-pregnant (female) mice were administered the all-trans-RAG solution or an equimolar solution of all-trans-RA in DMSO. They received a single i.v. dose (injected into the tail vein) of 5 kmol/kg (cor- responding to 10 p1 dosing solution per mouse).

Retinoid analysis Plasma, embryo, and yolk sac samples were ex-

tracted with a threefold volume of isopropanol, fol- lowed by solid phase extraction according to the method described by Collins et al. ('92). Analytes were enriched on AASP C2 solid phase extraction cartridges (silica modified with ethyl groups; ICT, Bad Homburg, Germany). Sample preparation of maternal tissues was based on this method. However, prior to extraction with isopropanol, the tissues-except livers-were homogenized in an equal volume of water. If necessary, tissues were minced with scissors before homogeniza- tion. Livers were homogenized with 9 volumes of ice- cold 0.9% (w/v) NaCl solution in a teflon-glass potter.

Following solid phase extraction, retinoid concentrations were determined with a reversed phase high performance liquid chromatographic (HPLC) method

(eluent A: water + 0.2% trifluoracetic acid; eluent B: acetonitrile + 0.2% trifluoracetic acid) which has been developed especially for separation of isomers of retinoyl-f3-D-glucuronide and retinoic acid (Sass and Nau, '94). Calibration was performed using solutions of bo- vine serum albumin spiked with defined concentrations of reference compounds. Plasma AUC values were calculated using the trapezoidal rule.

RESULTS Teratology

Both all- trans-RA and all-truns-RAG were administered on GD 11 in the NMRI mouse with a dose of 20 kmol/kg b.wt. As expected, this administration regimen was clearly teratogenic with all-trans-RA and a number of retinoid-specific malformations were observed such as limb defects, other skeletal defects, and cleft palate (Table 1). The fetal weight was slightly reduced by both drugs, and the embryolethality was not affected.

Surprisingly, all-trans-RAG exhibited a higher teratogenic potency compared to all-trans-RA: retinoid- specific malformations such as limb reduction defects and cleft palate were more pronounced after application of all-trans-RAG than after all-trans-RA (Table I).

Toxicokinetics I.v. administration. All-trans-RA as well as all-

trans-RAG, dissolved in DMSO, were administered to non-pregnant mice via the i.v. route. The concentrations observed in plasma are shown in Figure 1. Both drugs reached high initial concentrations. All- trans-RA was rapidly cleared, while the elimination of all-trans-RAG from mouse plasma proceeded much more slowly. Most importantly, considerable concen-

ALL-TRANS-RETINOYL-P-GLUCURONIDE 153

104,

103

102,

A all-trans-RAG i .v. B all-trans-RA i .v .

all-trans-RAG

100 I 0 1 2 3 4 5 6 0 1 2 3 4 5 6

Time [hours] Time [hours]

Fig. 1. Plasma concentrations of retinoids following i.v. administration of 5 pmoykg b.wt. all-trans- RAG (A) or all-trans-RA (B) in NMRI mice.

1 o3

1 o2

,RAG l o 3

10' I . I ' I ' I * I

0 2 4 6 8 Time [hours]

a I I - trans- R A

0 2 4 6 8 Time [hours]

10'

F5g. 2. Plasma concentrations of retinoids (mean ? SD, n = 3-6) following 8.c. administration of 20 pmol/kg b.wt. all-trans-RAG (A) or all-trans-RA (B) in NMRI mice; samples from retro-orbital sinuses. Kinetic analysis yields elimination half-lives for all-trans-RA and all-trans-RAG of 2.6 and 3.0 hr, respectively.

154 H. NAU ET AL.

TABLE 2. Plasma AUC values following administration of all-trans-RA or all-trans-RAG (both

20 pmolkg, s.c.) in NMRI mice on GD 11

AUC,-,h, (FMhr) Administration of All-trans-RA All-trans-RAG All-trans-RA (n = 6) 0.44 f 0.11 Trace All-trans-RAG (n = 3) 2.04 f 1.07* 8.84 f 1.48

*Significantly higher than the AUC of all-trans-RA following administration of all-trans-RA (P < 0.01; Student's two-tailed t-test).

trations of all-trans-RA were found in plasma after administration of all-trans-RAG. Some hemolysis of the blood was observed after i.v. application of the drug preparations as well as the pure vehicle (DMSO).

S.C. application. Plasma retinoid levels following S.C. application of all-trans-RA and all-trans-RAG to mice are shown in Figure 2. Again, high initial concentrations of all-trans-RAG (Fig. 2A) as well as all- trans-RA (Fig. 2B) were observed after application of the respective drugs. All-trans-RA was cleared rapidly after all-trans-RA administration, while all-trans-RAG was cleared more slowly. Again, considerable all- trans-RA levels were observed after all-trans-RAG application (Fig. 2A). The plasma concentrations of all- trans-RAG following all-trans-RA application were very low. Little hemolysis was observed after S.C. application of the DMSO preparations.

The plasma and tissue concentrations of retinoids found 2 and 6 hr after administration of all-trans-RAG to pregnant mice are shown in Tables 2 and 3. The plasma AUC values after administration of the drug conjugate (Table 2) were 8.84 p M h r all-trans-RAG and 2.04 pM/hr all-tram-RA. The elimination half-life of all-trans-RAG in maternal plasma, determined from the data displayed in Figure 2A, was 3.0 hr (r = 0.9999 for 2-8 hr). As expected, all-trans-RA exhibits good transfer to the embryo, while all-trans-RAG was

present in the embryo in minute concentrations only in spite of high maternal plasma levels (Table 3). In contrast, high concentrations of both all-trans-RA and all- trans-RAG were found in kidney, which even exceeded maternal plasma levels. Considerable levels of both all-trans-RA and all-trans-RAG were observed in liver, placenta, yolk sac, and spleen. Other isomers of RA and RAG were present in plasma and tissues in much lower concentrations.

DISCUSSION The most important finding of the present study was

the high teratogenicity observed in mice following administration of all-trans-RAG. The teratogenic potency of all-trans-RAG exceeded that of all-trans-RA in the experimental protocol of the present study. These results are readily explained by our toxicokinetic study: all-trans-RA levels and AUC values following administration of all-trans-RAG were high because of contin- uous hydrolysis of persistent all-trans-RAG levels. In contrast, all-trans-RA administration resulted in rapid clearance of this compound. Similar findings were observed after S.C. as well as i.v. administration regimens. It is thus clear that all-trans-RAG acts as a precursor for all-trans-RA, which is formed via hydrolysis in the maternal organism and can transfer to the embryonic compartment and act as a teratogen.

Previous studies showed that all-trans-RAG and its isomers-formed as metabolites from the respective retinoic acid-transfer to the embryo in small concentrations only: in several species (mouse, rat, rabbit, monkey) embryonic/maternal plasma ratios of all- trans-RAG were well below 0.1. It was therefore hoped that all-tram-RAG would be a n interesting retinoid with low teratogenic activity. Our present results dem- onstrate, however, that all-trans-RAG is readily hydrolyzed to the teratogenic all-trans-RA after S.C. as well as i.v. administration. All-trans-RAG is therefore a

TABLE 3. Plasma and tissue concentrations (nM) following S.C. administration of 20 pmoykg b.wt. all-trans-RAG to pregnant mice on GD 11

Time after Concentrations (nM) Plasma/ tissue administration (hr)' All-trans-RAG 13-cis-RAG 9-cis-RAG All-trans-RA 13-cis-RA 9-cis-RA Plasma 2

6 Embryo 2

6 Yolk sac 2

6 Placenta 2

6 Liver 2

6

6

6

Kidney 2

Spleen 2

1,703 f 674 854 * 193 18.5 * 4.2 37.2 f 15.2 465 2 199 482 f 227 634 t 256 883 -t 224

1,017 f 536 1,023 2 69.5 3,254 f 249 3,372 f 762

193 f 82.0 385 t 344

46.4 * 30.5 25.5 * 15.9 - -

2

2 - -

<20 20.9 L25.4

115 f 19.5 195 * 62.4 291 * 41.6 8.90 * 7.0 7.60 2 3.3

-

64.9 * 17.6 26.6 f22.7 - -

2 2 - - <20

21.1 k23.9 -

111 2 16.8 106 f 29.2 132 f 17.2

20.5 * 7.2 11.7 * 3.9

555 * 91.2 14.8 * 2.8 424 f 226 23.9 t 4.9 378 f 208 21.2 2 9.6 468 f 144

4,070 f 1,051 729 2 89.3

2,003 t 71 123 f 24.0 307 f 191

-

-

23.9 * 6.5

23.6 +. 10.9 27.5 f 14.9 27.9 f 17.7 18.3 k24.7

-

- 2 -

307 +. 220

58.1 2 15.4 34.1 ? 9.9

-

- -

9.73 * 7.3

4.02 2 2.7

18.2 ? 7.3

- -

- 2 2

- -

258 2 161 -

21.1 k23.4 - -

'N = 5 mice (2 hr); N = 4 mice (6 hr). 'Small peaks and/or overlapped by interfering fractions.

ALL-TRANS-RETINOYL-P-GLUCURONIDE 155

precursor for all-trans-RA after systemic application, and the hoped-for advantage of all-trans-RAG over all- trans-RA in regard to an improved safety ratio is not seen. The recent report that all-trans-RAG is of low teratogenicity after oral application in rats (Gunning et al., '93) must be interpreted with great caution: all- trans-RAG was only poorly absorbed under the experimental protocol used in that study (oral application). Our present study (s.c. application) clearly shows that all-trans-RAG, if absorbed, is a potent teratogen in vivo.

Further experiments need to be undertaken to show if all-trans-RAG has an advantage over all-trans-RA in other administration regimens. All-trans-RAG has been described to be less irritant to skin than all- trans-RA following topical application; however, much higher dosages of topical all-trans-RAG than topical all-trans-RA had to be used to exert a pharmacological effect (Gunning et al., '94). The possible systemic exposure to all-trans-RA following topical all-trans-RAG application has not yet been studied. The present results suggest that all-trans-RAG will be teratogenic if available systemically and that this retinoid should not be used in women of childbearing age until a formulation can be developed which exerts the desired pharmacological activity, but does not result in systemic retinoid exposure.

ACKNOWLEDGMENTS This work was supported by the European Commis-

sion (BIOTECH program BI02-CT93-047 1). The excel- lent technical assistance of C. Plum (HPLC) and I. Dill- mann (teratology) is gratefully acknowledged. U. Schwikowski prepared the glossy prints of the figures.

LITERATURE CITED Barua, A.B., and J.A. Olson (1986) Retinoyl p-glucuronide: An endog-

enous compound of human blood. Am. J. Clin. Nutr., 43:481-485. Barua, A.B., and J.A. Olson (1987) Chemical synthesis and growth-

promoting activity of all-trans-retinyl p-D-glucuronide. Biochem. J., 244:231-234.

Barua, A.B., and J.A. Olson (1989) Chemical synthesis of all-trans- [ll-3Hlretinoyl p-glucuronide and its metabolism in rats in vivo. Biochem. J . ,263:403 - 409.

Barua, A.B., and J.A. Olson (1991) All-trans retinoyl p-glucose: Chemical synthesis, growth-promoting activity, and metabolism in the rat. Int. J . Vit. Nutr. Res., 61 :258-263.

Barua, A.B., and J.A. Olson (1992) Chemical synthesis, growth-promoting activity, and metabolism of all-trans retinyl p-glucose in the rat. Int. J. Vit. Nutr. Res., 62:298-302.

Bhatnagar, R., H. Abou-Issa, R.W. Curley, Jr., A. Koolemans-Beynen, M.L. Moeschberger, and T.E. Webb (1991) Growth suppression of human breast carcinoma cells in culture by N-(4-hydroxyphenyD retinamide and its glucuronide and through synergism with glu- carate. Biochem. Pharmaml., 41:1471-1477.

Chambon, P. (1993) The molecular and genetic dissection of the retinoid signalling pathway. Gene, 135:223-228.

Collins, M.D., C. Eckhoff, I. Chahoud, G. Bochert, and H. Nau (1992) 4-Methylpyrazol partially ameliorated the teratogenicity of retinol and reduced the formation of all-trans-retinoic acid in the mouse. Arch. Toxicol., 66:652-659.

Collins, M.D., G. Tzimas, H. Hummler, H. Burgin, and H. Nau (1994)

Comparative teratology and transplacental pharmamkinetics of all-trans-retinoic acid, 13-cis-retinoic acid, and retinyl palmitate following daily administrations in rats. Toxicol. Appl. Pharmacol., 127:132-144.

Collins, M.D., G. Tzimas, H. Burgin, H. Hummler, and H. Nau (1995) Single versus multiple dose administration of all-trans-retinoic acid during organogenesis: Differential metabolism and transplacental kinetics in rat and rabbit. Toxicol. Appl. Pharmacol., 130:9-18.

Creech Kraft, J., C. Eckhoff, D.M. Kochhar, G. Bochert, I. Chahoud, and H. Nau (1991a) Isotretinoin (13-cis-retinoic acid) metabolism, cis-trans isomerization, glucuronidation and transfer to the mouse embryo: Consequences for teratogenicity. Teratogen. Carcinogen. Mutagen., 11:21-30.

Creech Kraft, J., W. Slikker, Jr., J.R. Bailey, L.G. Roberts, B. Fischer, W. Wittfoht, and H. Nau (1991b) Plasma pharmacokinetics and metabolism of 13-cis- and all-trans-retinoic acid in the cynomolgus monkey and the identification of 13-cis- and all-tmns-retinoyl-p- glucuronides. A comparison to one human case study with isotretinoin. Drug Metab. Dispos. 19:317-324.

Doepner, G., C.-D. Gerharz, U. v.Deessen, K. Kaiser, and H.K. Biesal- ski (1992) Effects of novel retinoids on growth and differentiation of a rhabdomyosareoma cell line. Arzneim. Forsch./Drug Res., 42fW: 1036-1040.

Dunagin, P.E., Jr., E.H. Meadows, Jr., and J.A. Olson (1965) Retinoyl beta-glucuronic acid A major metabolite of vitamin A in rat bile. Science, 148:86-87.

Eckhoff, C., W. Wittfoht, H. Nau, and W. Slikker, Jr . (1990) Charac- terization of oxidized and glucuronidated metabolites of retinol in monkey plasma by thermospray liquid chromatography/mass spec- trometry. Biomed. Environ. Mass Spectrom., 19:428-433.

Eckhoff, C., J.R. Bailey, M.D. Collins, W. Slikker, Jr., and H. Nau (1991) Influence of dose and pharmaceutical formulation of vitamin A on plasma levels of retinyl esters and retinol and metabolic gen- eration of retinoic acid compounds and p-glucuronides in the cynomolgus monkey. Toxicol. Appl. Pharmacol., 111:116-127.

Foerster, M., J.O. Sass, R. Ruhl, and H. Nau (1996) Comparative studies on effects of all-trans-retinoic acid and all-trans-retinoy1-P- glucuronide on the development of fetal mouse thymus in an organ culture system. Toxicol. In Vitro, 10:7-15.

Gunning, D.B., A.B. Barua, and J.A. Olson (1993) Comparative teratogenicity and metabolism of all-trans-retinoic acid, all-trans- retinoyl p-glucose, and all-tram-retinoyl p-glucuronide in pregnant Sprague-Dawley rats. Teratology, 47:29-36.

Gunning, D.B., A.B. Barua, R.A. Lloyd, and J.A. Olson (1994) Reti- noyl P-glucuronide: A nontoxic retinoid for the topical treatment of acne. J. Dermatol. Treat., 5:181-185.

Hummler, H., A.G. Hendrickx, and H. Nau (1994) Maternal toxicokinetics, metabolism and embryo exposure following a teratogenic dosing regimen with 13-cis-retinoic acid (isotretinoin) in the cynomolgus monkey. Teratology, 50:184-193.

Janick-Buckner, D., A.B. Barua, and J.A. Olson (1991) Induction of HL60 cell differentiation by water-soluble and nitrogen-containing conjugates of retinoic acid and retinol. FASEB J., 5:320-325.

Kaleagasioglu, F., G. Doepner, H.K. Biesalski, and M.R. Berger (1993) Antiproliferative activity of retinoic acid and some novel retinoid derivatives in breast and colorectal cancer cell lines of human origin. Anneim. ForschJDrug Res., 43fZ):487-490.

Kochhar, D.M. (1967) Teratogenic activity of retinoic acid. Acta Pathol. Microbiol. Sand., 70:398-404.

Kochhar, D.M., and M.A. Satre (1993) Retinoids and fetal malformations. In: Dietary Factors and Birth Defects. R.P. Sharma, ed. San Francisco: Pacific Division AAAS, pp. 134-229.

McCormick, A.M., K.D. Kroll, and J. Napoli (1983) 13-cis-retinoic acid metabolism in vivo. Biochemistry, 22:3933-3940.

Mehta, R.G., A.B. Barua, J.A. Olson, and R.C. Moon (1991) Effects of retinoid glucuronides on mammary gland development in organ culture. Oncology, 48:505-509.

Mehta, R.G., A.B. B a a , J.A. Olson, and R.C. Moon (1992) Retinoid glucuronides do not interact with retinoid binding proteins. Int. J. Vit. Nutr. Res., 62:143-147.

156 H. NAU ET AL. Nau, H. (1990) Correlation of transplacental and maternal pharma-

cokinetics of retinoids during organogenesis with teratogenicity. Methods Enzymol., 190:437-448.

Nau, H. (1993) Teratogenesis, transplacental pharmacokinetics, and metabolism of some retinoids in the mouse, monkey, and human. In: Retinoids: Progress in Research and Clinical Applications. M.A. Livrea and L. Packer, eds. New York: Marcel Dekker, pp. 599- 615.

Nau, H. (1994) Toxicokinetics and structure-activity relationships in retinoid teratogenesis. Ann. Oncol., 5(Suppl. 9):S39443.

Nau, H., I. Chahoud, L. Dencker, E. Lammer, and W.J. Scott (1994) Teratogenicity of vitamin A and retinoids. In: Vitamin A in Health and Disease. R. Blomhoff, ed. New York: Marcel Dekker, pp. 615- 664.

Panigot, M.J., K.A. Humphries, and R.W. Curley, Jr. (1994) Prepa- ration of 4-retinamidophenyl- and 4-retinamidobenzyl-C-glycosyl and C-glucuronosyl analogues of the glucuronide of 4-hydroxyphe- nyl-retinamide as potential stable cancer chemopreventive agents. J. Carbohydr. Chem., 13:303-321.

Fbbarge, M.J., J.J. Repa, K.K. Hanson, S. Seth, M. Clagett-Dame, H. Abou-Issa, and R.W. Curley (1994) N-linked analogs of retinoid 0-glucuronides: Potential cancer chemopreventivelchemotherapeu- tic agents. Bioorg. Med. Chem. Lett., 4:2117-2122.

Ruhl, R., D. Hofmann, H. Nau, and S. Klug (1994) Influence of all- trans-retinoyl-p-D-glucuronide on growth and differentiation in two in vitro systems of different biological complexity. Arch. Phar- m a d , 349(SupplJ:R108.

Sani, B.P., A.B. Barua, D.L. Hill, T.-W. Shih, and J.A. Olson (1992) Retinoyl p-glucuronides: Lack of binding to receptor proteins of retinoic acid as related to biological activity. Biochem. Pharmacol., 43:919-922.

Sass, J.O., and H. Nau (1994) Single-run analysis of isomers of retinoyl-p-D-glucuronide and retinoic acid by reversed-phase high-

performance liquid chromatography. J. Chromatogr., 685:182- 188.

Sass, J.O., G. Tzimas, and H. Nau (1994) 9-cis-retinoyl-p-D-glucuronide is a major metabolite of 9-cis-retinoic acid. Life Sci., 54:PL 69-74.

Sass, J.O., E. Masgrau, J.-H. Saurat, and H. Nau (1995) Metabolism of oral 9-cis-retinoic acid in the human: Identification of 9-cis-retinoyl-P-glucuronide and 9-cis-4-oxo-retinoyl-~-glucuronide as uri- nary metabolites. Drug Metab. Dispos., 23:887-891.

Tzimas, G., H. Biirgin, M.D. Collins, H. Hummler, and H. Nau (1994a) The high sensitivity of the rabbit to the teratogenic effects of 13-cis-retinoic acid (isotretinoin) is a consequence of prolonged exposure of the embryo to 13-cis-retinoic acid and 13-cis-4-0x0-retinoic acid, and not of isomerization to all-tmns-retinoic acid. Arch. Toxicol., 68: 119-128.

Tzimas, G., J.O. Sass, W. Wittfoht, M.M.A. Elmazar, K. Ehlers, and H. Nau (1994b) Identification of 9,13-dicis-retinoic acid as a major plasma metabolite of 9-cis-retinoic acid and limited transfer of 9-cis-retinoic acid and 9,13-dicis-retinoic acid to the mouse and rat embryos. Durg Metab. Dispos., 22:928-936.

Tzimas, G., J.O. Sass, R. Ruhl, S. Klug, M.D. Collins, and H. Nau (1994~) Proximate retinoid teratogens. In: From Basic Science to Clinical Applications. M.A. Livrea and G. Vidali, eds. Base1 Birkhauser Verlag, pp. 179-195.

Zile, M.G., R.C. Inhorn, and H.F. DeLuca (1982) Metabolism in vivo of all-trans-retinoic acid. Biosynthesis of 13-cis-retinoic acid and all- tmns- and 13-cis-retinoyl glucuronides in the intestinal rnucosa of the rat. J . Biol. Chem., 257:3544-3550.

Zile, M.H., M.E. Cullum, R.U. Simpson, A.B. Barua, and D.A. Swartz (1987) Induction of differentiation of human promyelocytic leuke- mia cell line HL-60 by retinoyl glucuronide, a biologically active metabolite of vitamin A. Roc. Natl. Acad. Sci. U.S.A., 84:2208- 2212.

all-trans-retinoyl-β-glucuronide is a potent teratogen in the mouse because of extensive metabolism...

Documents