Effect of dexamethasone and cytochrome P 450 inhibitors on the formation of 7α-hydroxydehydroepiandrosterone by human adipose stromal cells

7α-Hydroxydehydroepiandrosterone (7α-OHDHA) is a major metabolite of dehydroepiandrosterone (DHA) using adipose stromal cells. To gain a better understanding of the factors regulating DHA metabolism, we examined the effect of dexamethasone and cytochrome P 450 inhibitors on the formation of 7α-OHDHA. Dexamethasone (10⁻⁹ to 10⁻⁷ M) stimulated 7α-OHDHA formation in a dose-dependent manner with a 2- to 5-fold stimulation at 10⁻⁷ M. The dexamethasone stimulated 7α-OHDHA formation was inhibited by RU486 in a dose-dependent manner with suppression to basal levels at 10⁻⁶ M. Progesterone (10⁻⁷ M) had no effect on 7α-OHDHA formation suggesting that the dexamethasone stimulation was acting through the glucocorticoid receptor. Conversion of DHA to 7α-OHDHA was inhibited by ketoconazole and metyrapone. An inhibition of 70–80% was obtained with ketoconazole and 25–60% with metyrapone at concentrations of 10⁻⁵ M. Aminoglutethimide phosphate was less effective than either ketoconazole or metyrapone in inhibiting 7α-OHDHA formation with <30% inhibition at 10⁻⁵ M. These studies indicate that 7-hydroxylation provides an alternative pathway for the metabolism of DHA in peripheral tissues. This pathway, which is regulated by glucocorticoids, may influence the amount of DHA available for conversion to androstenedione and its subsequent aromatization to estrone. The biological role of the 7-oxygenated metabolites and their effects on other steroidogenic pathways have not been established.     

Interleukin-1β-stimulated PGE2 production from early first trimester human decidual cells is inhibited by dexamethasone and progesterone

Cytokines are known to increase the production of prostaglandins by human decidual cells, but negative regulators have not been identified. We have examined the effects of dexamethasone and progesterone on prostaglandin (PG) E2 synthesis by cultured human first trimester decidual cells. The numbers of cyclooxygenase (COX) enzyme positive cells were visualised by immunocytochemistry, using antibodies specific for COX-1 and COX-2. Interleukin-1β stimulated the production of prostaglandins E2 and F2α dose-dependently, and this was associated with increased numbers of COX-2 positive cells. Progesterone (10⁻⁷−10⁻⁶ M) and dexamethasone (10⁻⁷−10⁻⁶ M) inhibited basal and interleukin-1β-stimulated prostaglandin production, and decreased the numbers of COX-2 positive cells. Neither interleukin-1β nor the steroids affected numbers of COX-1 positive cells. COX-2 seems to be the main enzyme controlling the synthesis of PGE2 by human decidual cells, and may be negatively regulated by progesterone.     

Prostacyclin and steroidogenesis in goat ovari cell types in vitro

Granulosa, theca and corpus luteum cells of the goat ovary were isolated and incubated separately for 6 hours, with or without various modulators. Arachidonic acid (AA, 10 ng to 100 μg/ml), the precursor for prostaglandin synthesis, produced a dose-dependent increase in progesterone (P₄) and estradiol-17β (E₂) productin by all the cell types. Prostaglandin synthetase inhibitors, aspirin (10⁻⁶−10⁻³M) and indomethacin (100 ng−1 mg/ml), produced a dose-dependent decrease in arachidonic acid-stimulated (100 μ/ml) steroid production. Prostacyclin synthetase stimulators, trapidil (1.6 μg− 1 mg/ml) and dipyridamole (10⁻⁶−10⁻³M), when added alone or along with AA, did not effect steroid production. Up to 100 μg/ml of U-51605 (9,11-azoprosta-5, 13-dienoic acid), a prostacyclin synthetase inhibitor, did not inhibit basal or AA-stimulated steroid production. Prostacyclin (PGl₂) and its stable analog 6βPGl₁(0.01–10μg/ml) produced a dose-dependent increase in P₄ and E₂ production in all three cell types. Increase at 1 and 10μg/ml was significant in all cases. 6-keto-PGE₁ (an active metabolite of PGl₂ in certain systems) produced an increase in steroid production which was significant in theca at 1μg/ml concentrations but had no significant effect on granulosa and corpus luteum cells at any dose level. 6-keto-PGf₁ alpha (stable metabolite of PGl₂) was without effect inthe present system. The lack of effect of PGl₂ at lower concentrations was not altered by either differentiation of the cells with FSH and testosterone or addition of steroid precursors, testosterone and pregnenolene. The present results indicate that AA- stimualted steroid production in the goat ovarian cell type is mediated by prostaglandins other than PGl₂ though PGl₂ itself can positively modulate the steroid production.     

Synthesis and evaluation of affinity adsorbents for glycoproteins: an artificial lectin

A combination of rational design based on mimicking natural protein–carbohydrate interactions and solid-phase combinatorial chemistry has led to the identification of an affinity ligand which displays selectivity for the mannose moiety of glycoproteins. The ligand, denoted 18/18 and comprising a triazine scaffold bis-substituted with 5-aminoindan, has been synthesised in solution, characterised by TLC, ¹H-NMR and MS. When immobilised to amine-derivatised agarose at concentrations >24 μmol/g moist weight gel, ligand 18/18 selectively binds glucose oxidase. The adsorbed enzyme was quantitatively eluted with 0.5 M α- -methyl-mannoside and to a lesser extent with the equivalent glucoside. An investigation of the comparative retention times of saccharidic solutes showed that significant retardation was observed for α- -mannose, mannobiose and mannan, with little or no evidence for selective retention of other saccharides, with the exception of α- -fucose. Interestingly, α- -fucose and α- -mannose share an identical configuration of the hydroxyl groups on C-2, C-3 and C-4. Analysis of Scatchard plots from partition equilibrium studies on the interaction of glucose oxidase and the p-nitrophenyl-glycosides of -mannose, -glucose, -fucose and -galactose with immobilised 18/18 establish that the affinity constants (K_AX) for the enzyme, the glycosides of mannose, glucose and fucose, and the p-nitrophenyl-galactoside are 4.3×10⁵ M⁻¹, 1.9×10⁴ M⁻¹ and 1.2×10⁴ M⁻¹ respectively. ¹H-NMR studies on the interaction of α- -methyl-mannoside with ligand 18/18 in solution confirm the involvement of the hydroxyl group in the C-2 position. Molecular modelling suggests the formation of four hydrogen bonds between the hydroxyl groups at positions C-2, C-3 and C-4 of α- -methyl-mannoside and the bridging and ring nitrogen atoms of the triazine scaffold, with aromatic stacking of a second ligand against the carbohydrate face. The greater specificity of ligand 18/18 for mannose and glucose than for galactose parallels that exhibited by concanavalin A.     

Main features of the oxidative metabolism in gills and liver of Odontesthes nigricans Richardson (Pisces, Atherinopsidae)

The aim of this work was to study comparatively the oxidative metabolism in gills and liver of a silverside, Odontesthes nigricans, in their natural environment, the Beagle Channel. Oxidative damage to lipids was evaluated by assessing TBARS and lipid radical content, in gills and liver. Gills showed a significantly higher degree of damage than liver. The content of α-tocopherol, β-carotene and catalase activity showed significantly higher values in the liver than in the gills. The ascorbyl radical (A^•) content showed no significant differences between gills and liver. The ascorbate (AH⁻) content was 12 ± 2 and 159 ± 28 nmol/mg FW in gills and liver, respectively. Oxidative metabolism at the hydrophilic level was assessed as the ratio A^•/AH⁻. The ratio A^•/AH⁻ was significantly different between organs, (6 ± 2)10^− 5 and (5 ± 2)10^− 6, for the gills and the liver, respectively. Both, lipid radical content/α-tocopherol content and lipid radical content/β-carotene content ratios were significantly higher in gills as compared to the values recorded for the liver, suggesting an increased situation of oxidative stress condition in the lipid phase of the gills. Taken as a whole, the O. nigricans liver exhibited a better control of oxidative damage than the gills, allowing minimization of intracellular damage when exposed to environmental stressing conditions.     

Different Inactivation Behaviors of MS-2 Phage and Escherichia coli in TiO2 Photocatalytic Disinfection

Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO₂ photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (·OH), which is generated on the surface of UV-illuminated TiO₂, plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H₂O₂ and O₂·⁻, etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe²⁺, were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O₂·⁻ and H₂O₂, according to the present results.     

ApoE −491A/T Promoter Polymorphism is not an Independent Risk Factor,but Associated with the ε4 Allele in Hungarian Alzheimer’s Dementia Population

Apolipoprotein E gene (Apoε) has three common alleles (ε2, ε3, and ε4), of which ε4 has been shown to be associated with an increased risk for Alzheimer’s disease (AD). Possible additional genetic factors, like the −491A variant of ApoE promoter may modify the development of AD, independently of the ApoE allele status. The objective of this study was to investigate whether A/T allelic polymorphism at site−491 of the ApoE promoter is associated with AD in a Hungarian population. The genomic DNA isolated from peripheral blood lymphocytes of 52 late-onset AD and 53 control individuals was used as a template for the two examined polymorphisms and PCR assay was applied. The ε4 allele was significantly over-represented in the AD group (28%) as compared with the control population (7%). No significant differences have been found between the control and the AD populations regarding the occurrence of the promoter A allele frequencies (control: 77%, AD: 70%). However, the AA genotype was more frequent in the AD group (48%) than in the control (10%) when the presence of ε4 allele was also considered. It is unlikely therefore that the −491A variant of the ApoE promoter gene is an independent risk factor in the Hungarian AD population, but a linkage disequilibrium exists between the two examined mutations.     

Potent constriction of cat coronary arteries by hydroperoxides of arachidonic acid and its blockade by anti-inflammatory agents

The ω-6 and ω-9 hydroperoxides of arachidonic acid caused dose-dependent constriction of cat coronary arteries in concentrations of 10⁻⁸ to 10⁻⁵M. Their potency was comparable to that of prostaglandin (PG) E₂, and PGF_2α and 100 times greater than that of arachidonic acid. The cyclooxygenase inhibitor, meclofenamate markedly reduced constriction caused by the hydroperoxides but potentiated constriction caused by the prostaglandins. The effects of the hydroperoxides were also reduced by indomethacin and dexamethasone but were unaffected by the thromboxane synthetase inhibitor imidazole. Since the hydroperoxides are not substrates for cyclooxygenase, it is suggested that they have a direct effect on the arteries which can be antagonized by anti-inflammatory drugs.     

Effect of pH and Oxalate on Hydroquinone-Derived Hydroxyl Radical Formation during Brown Rot Wood Degradation

The redox cycle of 2,5-dimethoxybenzoquinone (2,5-DMBQ) is proposed as a source of reducing equivalent for the regeneration of Fe²⁺ and H₂O₂ in brown rot fungal decay of wood. Oxalate has also been proposed to be the physiological iron reductant. We characterized the effect of pH and oxalate on the 2,5-DMBQ-driven Fenton chemistry and on Fe³⁺ reduction and oxidation. Hydroxyl radical formation was assessed by lipid peroxidation. We found that hydroquinone (2,5-DMHQ) is very stable in the absence of iron at pH 2 to 4, the pH of degraded wood. 2,5-DMHQ readily reduces Fe³⁺ at a rate constant of 4.5 × 10³ M⁻¹s⁻¹ at pH 4.0. Fe²⁺ is also very stable at a low pH. H₂O₂ generation results from the autoxidation of the semiquinone radical and was observed only when 2,5-DMHQ was incubated with Fe³⁺. Consistent with this conclusion, lipid peroxidation occurred only in incubation mixtures containing both 2,5-DMHQ and Fe³⁺. Catalase and hydroxyl radical scavengers were effective inhibitors of lipid peroxidation, whereas superoxide dismutase caused no inhibition. At a low concentration of oxalate (50 μM), ferric ion reduction and lipid peroxidation are enhanced. Thus, the enhancement of both ferric ion reduction and lipid peroxidation may be due to oxalate increasing the solubility of the ferric ion. Increasing the oxalate concentration such that the oxalate/ferric ion ratio favored formation of the 2:1 and 3:1 complexes resulted in inhibition of iron reduction and lipid peroxidation. Our results confirm that hydroxyl radical formation occurs via the 2,5-DMBQ redox cycle.     

IDPN-Induced Monoamine and Hydroxyl Radical Changes in the Rat Brain

--iminodipropionitrile (IDPN)-induced monoamine and hydroxyl radical changes in the rat brains were studied. IDPN caused decreases in 5-HT and 5-HIAA levels in all brain regions, strongly indicating that IDPN's neurotoxicity primarily affects 5-HT containing neurons. Dopamine and its metabolites' levels decreased in the some regions, most likely due to depression of dopamine metabolic turnover. Our results more clearly demonstrate IDPN-induced monoamine alterations in the rat brain more than previous reports. To clarify one of the pathogenesis of IDPN-induced neurological disorders, we measured hydroxyl radical levels. 2,3-DHBA increased at 1st day, and decreased in some regions at 7th days after discontinuing IDPN. We conclude, hydroxyl radical formation causes neuronal damage, and monoamine changes contribute to IDPN-induced neurological disorder.     

Macrophage responses to interferon-γ are dependent on cystatin C levels

The aim of the present investigation was to elucidate possible effects of cystatin C on inflammatory responses mediated by macrophages. Previously it has been shown that in vitro treatment of murine peritoneal macrophages with interferon-γ (IFN-γ) causes a down-regulation of cystatin C secretion. To investigate whether such changes in cystatin C expression in turn can affect inflammatory responses mediated by macrophages, we have compared effects of IFN-γ on macrophages isolated from wild-type (cysC^+/+) and cystatin C knockout (cysC^−/−) mice. It was shown that IFN-γ-primed cysC^−/− macrophages exhibit significantly higher interleukin-10 (IL-10) but lower tumor necrosis factor-α (TNF-α) expression, and reduced nuclear factor (NF)-κB p65 activation, compared to similarly primed cysC^+/+ cells. Exogenously added cystatin C enhanced IFN-γ-induced activation of NF-κB p65 and increased mRNA levels for inducible NO synthase (iNOS) in cysC^−/− macrophages as well as levels of nitric oxide and TNF-α in the cell culture medium, in agreement with an enhanced pro-inflammatory response. Accordingly, IFN-γ-induced IL-10 mRNA expression in cysC^−/− macrophages was down-regulated by exogenously added cystatin C. Taken together, our data provide evidence that changes in cystatin C levels alter macrophage responses to IFN-γ. The latter down-regulates the production of cystatin C, which leads to a suppressed inflammatory condition with enhanced IL-10 levels and down-regulated TNF-α and NF-κB. It is concluded that cystatin C through this effect can act as an immunomodulatory molecule.     

Lipid radical generation in polar (Laternula elliptica) and temperate (Mya arenaria) bivalves

Lipid peroxidation in Laternula elliptica was assessed by detecting lipid radicals by electronic paramagnetic resonance. The values were compared with data from the temperate mud clam Mya arenaria. Lipid radical content was higher in the Antarctic bivalve than in the temperate mud clam, even within the range of its habitat temperature. The rate of generation of lipid radicals was affected by the iron content in the samples. The iron content in individual samples of digestive glands in L. elliptica ranged from 3 to 6 nmol g⁻¹ fresh weight (fwt) and in M. arenaria from 0.6 to 2.7 nmol g⁻¹ fwt. Arrhenius plots, developed from the rates obtained in the presence of 25 μM iron, showed no significant differences between the activation energy calculated for digestive glands of L. elliptica and M. arenaria. The Fe³⁺ reduction rate in L. elliptica was higher than in M. arenaria (4.7±0.9 vs. 1.8±0.4 nmol mg⁻¹ protein min⁻¹, respectively). L. elliptica had a higher content of α-tocopherol and β-carotene than M. arenaria. Our data suggest that increased lipid radical content in the membranes of cold-adapted organisms could be related to iron content.     

The (+)- and (−)-gossypols potently inhibit human and rat 11β-hydroxysteroid dehydrogenase type 2

Gossypol has been proven to be a very effective male contraceptive. However, clinical trials showed that the major side effect of gossypol was hypokalemia. Gossypol occurs naturally as enantiomeric mixtures of (+)-gossypol and (−)-gossypol. The (−)-gossypol is found to be the active component of antifertility. 11β-Hydroxysteroid dehydrogenase 2 (11βHSD2) has been demonstrated to be a mineralocorticoid receptor (MR) protector by inactivating active glucocorticoids including corticosterone (CORT) in rats, and therefore mutation or suppression of 11βHSD2 causes hypokalemia and hypertension. In the present study, the potency of gossypol enantiomers was tested for the inhibition of 11βHSD1 and 2 in rat and human. Both (+) and (−)-gossypols showed a potent inhibition of 11βHSD2 with the half maximal inhibitory concentration (IC₅₀) of 0.61 and 1.33 μM for (+) and (−)-gossypols, respectively in rats and 1.05 and 1.90 μM for (+) and (−)-gossypols, respectively in human. The potency of gossypol to inhibit 11βHSD1 was far less; the IC₅₀ was ≥100 μM for racemic gossypol. The gossypol-induced hypokalemia is likely associated with its potent inhibition of kidney 11βHSD2.     

β-Endorphin and ACTH related peptides in primary cultures of rat anterior pituitary cells: evidence for different intracellular pools

Acid extracts of rat anterior pituitary cells and cell-derived culture media were shown to contain three forms of β-endorphin immunoreactive peptides, corresponding in molecular size to the prohormone pro-opiomelanocortin (POMC), β-lipotropin and 3.5 kDa β-endorphin, and essentially two forms of adrenocorticotropin (ACTH) immunoreactivity, representing a 20 kDa intermediate fragment and 4.5 kDa ACTH. Under basal conditions the intracellular peptides contained a high proportion of the bioactive forms of β-endorphin and ACTH whereas the extracellular peptides contained a higher proportion of the inactive precursors. When the cells were incubated for 3 h in the presence of 10⁻⁸ M CRF, the levels of intracellular β-endorphin and ACTH immunoreactivity were reduced by 15–30% and there was a 4–5-fold increase in the level of the secreted peptides; furthermore, unlike the peptides released under basal conditions, the peptides secreted under the influence of CRF contained much higher proportions of 4.5 kDa ACTH and 3.5 kDa β-endorphin, reflecting the intracellular patterns of these peptides. Similar results were obtained when secretion was stimulated by 10⁻⁷ M epinephrine, which produced a 2-fold increase in peptide release. In the presence of 10⁻⁶ M dexamethasone the basal secretion of ACTH and β-endorphin related peptides, and the intracellular levels of these peptides, remained unaltered. The results point to the existence of different intracellular compartments from which peptides at different states of maturation can be released selectively.β-EndorphinACTHPituitary cell cultureProcessingCRFEpinephrine     

The Granular Chloride Channel ClC-3 Is Permissive for Insulin Secretion

Insulin secretion from pancreatic β cells is dependent on maturation and acidification of the secretory granule, processes necessary for prohormone convertase cleavage of proinsulin. Previous studies in isolated β cells revealed that acidification may be dependent on the granule membrane chloride channel ClC-3, in a step permissive for a regulated secretory response. In this study, immuno-EM of β cells revealed colocalization of ClC-3 and insulin on secretory granules. Clcn3^−/− mice as well as isolated islets demonstrate impaired insulin secretion; Clcn3^−/− β cells are defective in regulated insulin exocytosis and granular acidification. Increased amounts of proinsulin were found in the majority of secretory granules in the Clcn3^−/− mice, while in Clcn3^+/+ cells, proinsulin was confined to the immature secretory granules. These results demonstrate that in pancreatic β cells, chloride channels, specifically ClC-3, are localized on insulin granules and play a role in insulin processing as well as insulin secretion through regulation of granular acidification.     

Biochemistry and pharmacology of 7α-substituted androstenediones as aromatase inhibitors

The inhibition of aromatase, the enzyme responsible for converting androgens to estrogens, is therapeutically useful for the endocrine treatment of hormone-dependent breast cancer. Research by our laboratory has focused on developing competitive and irreversible steroidal aromatase inhibitors, with an emphasis on synthesis and biochemistry of 7α-substituted androstenediones. Numerous 7α-thiosubstituted androst-4-ene-3,17-diones are potent competitive inhibitors, and several 1,4-diene analogs, such as 7α-(4′-aminophenylthio)-androsta-1,4-diene-3,17-dione (7α-APTADD), have demonstrated effective enzyme-activated irreversible inhibition of aromatase in microsomal enzyme assays. One focus of current research is to examine the effectiveness and biochemical pharmacology of 7α-APTADD in vivo. In the hormone-dependent 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary carcinoma model system, 7α-APTADD at a 50 mg/kg/day dose caused an initial decrease in mean tumor volume during the first week, and tumor volume remained unchanged throughout the remaining 5-week treatment period. This agent lowers serum estradiol levels and inhibits ovarian aromatase activity. A second research area has focused on the synthesis of more metabolically stable inhibitors by replacing the thioether linkage at the 7α position with a carbon-carbon linkage. Several 7α-arylaliphatic androst-4-ene-3,17-diones were synthesized by 1,6-conjugate additions of appropriate organocuprates to a protected androst-4,6-diene or by 1,4-conjugate additions to a seco-A-ring steroid intermediate. These compounds were all potent inhibitors of aromatase with apparent K_is ranging between 13 and 19 nM. Extension of the research on these 7α-arylaliphatic androgens includes the introduction of a C₁---C₂ double bond in the A-ring to provide enzyme-activated irreversible inhibitors. The desired 7α-arylaliphatic androsta-1,4-diene-3,17-diones were obtained from their corresponding 7α-arylaliphatic androst-4-ene-3,17-diones by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). These inhibitors demonstrated enzyme-mediated inactivation of aromatase with apparent k_inacts ranging from 4.4 × 10⁻⁴ to 1.90 x 10⁻³ s⁻¹. The best inactivator of the series was 7α-phenpropylandrosta-1,4-diene-3,17-dione, which exhibited a T_1/2 of 6.08 min. Aromatase inhibition was also observed in MCF-7 human mammary carcinoma cell cultures and in JAr human choriocarcinoma cell cultures, exhibiting IC₅₀ values of 64-328 nM. The 7α-arylaliphatic androgens thus demonstrate potent inhibition of aromatase in both microsomal incubations and in choriocarcinoma cell lines expressing aromatase enzymatic activity. Additionally, the results from these studies provide further evidence for the presence of a hydrophobic binding pocket existing near the 7α-position of the steroid in the active site of aromatase. The size of the 7α-substituent influences optimal binding of steroidal inhibitors to the active site and affects the extent of enzyme-mediated inactivation observed with androsta-1,4-diene-3,17-dione analogs.     

TGFbeta1 and TGFbeta3 are partially redundant effectors in brain vascular morphogenesis

Gene deletion experiments have shown that the three TGFβ isoforms regulate distinct developmental processes. Recent work by our group and others showed that the integrins αvβ6 and αvβ8 activate latent forms of TGFβ1 and TGFβ3. This raises the possibility that TGFβ1 and TGFβ3 act redundantly in developmental processes where both isoforms are expressed and activation is by integrins. To investigate this issue, we generated mice with defective integrin-mediated TGFβ1 activation (Tgfb1^RGE/RGE) that were also homozygous for a null mutation in the TGFβ3 gene. Tgfb1^RGE/RGE; Tgfb3^−/− mice have severely perturbed development of the brain vasculature that is highly similar to that in mice lacking αvβ8. Some Tgfb1^RGE/RGE; Tgfb3^+/− and Tgfb1^RGE/RGE; Tgfb3^+/+ mice have milder, background-dependent versions of the phenotype. In addition, we found that Tgfb3 gene status influences embryonic lethality due to TGFβ1 deficiency after limited backcrossing to the BALB/c background. Conversely, Tgfb1 gene status modifies the extent of palate fusion in Tgfb3^−/− mice after limited backcrossing to the ICR background. Our results are consistent with a functional connection between TGFβ1 and TGFβ3 during development based on a shared mechanism of activation.