Modulation of porcine cytochrome P450 enzyme activities by surgical castration and immunocastration

The Reduction of the Combined Effects of Aflatoxin and Ochratoxin A in Piglet Livers and Kidneys by Dietary Antioxidants

The purpose of this study was to investigate the combined effects of aflatoxin B1 and ochratoxin A on protein expression and catalytic activities of CYP1A2, CYP2E1, CYP3A29 and GSTA1 and the preventive effect of dietary byproduct antioxidants administration against these mycotoxin damage. Three experimental groups (E1, E2, E3) and one control group (C) of piglets after weaning (TOPIGS-40 hybrid) were fed with experimental diets for 30 days. A basal diet containing normal compound feed for starter piglets was used as a control treatment and free of mycotoxin. The experimental groups were fed as follows: E1—basal diet plus a mixture (1:1) of two byproducts (grapeseed and sea buckthorn meal), E2—the basal diet experimentally contaminated with mycotoxins (479 ppb OTA and 62ppb AFB1) and E3—basal diet containing 5% of the mixture (1:1) of grapeseed and sea buckthorn meal and contaminated with the mix of OTA and AFB1. After 4 weeks, the animals were slaughtered, and tissue samples were taken from liver and kidney in order to perform microsomal fraction isolation, followed by protein expression and enzymatic analyses. The protein expressions of CYP2E1 and CYP3A29 were up-regulated in an insignificant manner in liver, whereas in kidney, those of CYP1A2, CYP2E1 and CYP3A29 were down-regulated. The enzymatic activities of CYP1A2, CYP2E1 and CYP3A29 decreased in liver, in a significant manner, whereas in kidney, these increased significantly. The co-presence of the two mycotoxins and the mixture of grape seed and sea buckthorn meal generated a tendency to return to the control values, which suggest that grapeseed and sea buckthorn meal waste represent a promising source in counteracting the harmful effect of ochratoxin A and aflatoxin B.

Perinatal exposure to a human relevant mixture of persistent organic pollutants: Effects on mammary gland development, ovarian folliculogenesis and liver in CD-1 mice

The ability of persistent organic pollutants (POPs) with endocrine disrupting properties to interfere with the developing reproductive system is of increasing concern. POPs are transferred from dams to offspring and the high sensitivity of neonates to endocrine disturbances may be caused by underdeveloped systems of metabolism and excretion. The present study aimed to characterize the effect of in utero and lactational exposure to a human relevant mixture of POPs on the female mammary gland, ovarian folliculogenesis and liver function in CD-1 offspring mice. Dams were exposed to the mixture through the diet at Control, Low or High doses (representing 0x, 5000x and 100 000x human estimated daily intake levels, respectively) from weaning and throughout mating, gestation, and lactation. Perinatally exposed female offspring exhibited altered mammary gland development and a suppressed ovarian follicle maturation. Increased hepatic cytochrome P450 enzymatic activities indirectly indicated activation of nuclear receptors and potential generation of reactive products. Hepatocellular hypertrophy was observed from weaning until 30 weeks of age and could potentially lead to hepatotoxicity. Further studies should investigate the effects of human relevant mixtures of POPs on several hormones combined with female reproductive ability and liver function.

Prenatal Exposure to Retrorsine Induces Developmental Toxicity and Hepatotoxicity of Fetal Rats in a Sex-Dependent Manner: The Role of Pregnane X Receptor Activation

Pyrrolizidine alkaloids (PAs) are a type of natural phytotoxin that contaminate food and feed and become an environmental health risk to humans and livestock. PAs exert toxicity that requires metabolic activation by cytochrome P450 (CYP) 3A, and case reports showed that fetuses are quite susceptible to PAs toxicity. The aim of this study was to explore the characteristics of developmental toxicity and fetal hepatotoxicity induced by retrorsine (RTS, a typcial toxic PA) and the underlying mechanism. Pregnant Wistar rats were intragastrically administered with 20 mg/(kg·day) RTS from gestation day (GD) 9 to 20. Results showed that prenatal RTS exposure lowered fetal bodyweights, reduced hepatocyte numbers, and potentiated hepatic apoptosis in fetuses, particularly females. Simutaneously, RTS increased CYP3A expression and pregnane X receptor (PXR) activation in female fetal liver. We further confirmed that RTS was a PXR agonist in LO2 and HepG2 cell lines. Furthermore, agonism or antagonism of androgen receptor (AR) either induced or blocked RTS-mediated PXR activation, respectively. As a PXR agonist, RTS toxicity was exacerbated in female fetus due to the increased CYP3A induction and self-metabolism, while the inhibitory effect of AR on PXR activation reduced the susceptibility of male fetus to RTS. Our findings indicated that PXR may be a potential therapeutic target for PA toxicity.

Expressions of cytochrome P450 aromatase and anti-Müllerian hormone in testes of fattening pigs by the timing of the first vaccination for immunocastration

In practice, two injections of gonadotropin-releasing hormone (GnRH) vaccine are recommended for pig immunocastration for effective outcomes. The present study aimed to investigate the expressions of cytochrome P450 aromatase (P450_arom ) and anti-Müllerian hormone (AMH) in testes, testicular length and testicular histomorphometry of the fattening pigs receiving the first injection of GnRH vaccine 6 weeks earlier than the standard protocol. Based on vaccination protocol, 24 pigs were equally divided into three groups: T1 was vaccinated at 15 and 19 weeks of age, T2 received vaccine at 9 and 19 weeks of age and C remained intact. P450_arom and AMH expressions were analysed using immunohistochemistry and Western blot. The results revealed that testicular length was highest in C pigs, but not different between T1 and T2 groups (6.5 ± 0.2 versus 6.9 ± 0.3 cm, p = .538). Histomorphometry demonstrated that the height of spermatogenic epithelia, the diameter of seminiferous tubules and the number of seminiferous tubules between T1 and T2 groups were not different (p > .05). For P450_arom , immunohistochemistry revealed that H-score of C group was significantly higher than that of both T1 and T2 groups. Western blot analysis showed that C group possessed the densest protein band. Moreover, H-score between T1 and T2 groups was not significantly different. Protein band intensity between both groups was not apparently different. As for AMH, C pigs had significantly lower H-score than both T1 and T2 pigs. Furthermore, T2 pigs possessed significantly higher H-score than T1 pigs. Western blot analysis showed that the most intense protein band was found in T2 group. In summary, GnRH vaccine affected testicular development and functions. The first injection could be performed either at 9 or 15 weeks of age since both protocols contributed to comparable results in aspect of testicular length, histomorphometry and expressions of P450_arom and AMH.

Monitoring of behavior, sex hormones and boar taint compounds during the vaccination program for immunocastration in three sire lines

Immunocastration (vaccination against boar taint) is an alternative method to prevent boar taint without the need for surgical castration. This study investigates the evolution of boar taint compounds in serum and fat, serum steroid compounds as well as behavior in immunocastrated pigs from 3 sire lines: 15 stress positive Belgian Piétrain (BP), 20 stress negative French Piétrain (FP), and 20 stress negative Canadian Duroc (CD). Hormone and boar taint compounds in serum were determined at 4 time points; boar taint compounds in fat were determined at 3 time points. Behavior, skin lesions, animal and pen fouling were also recorded before the first vaccination (<V1), between the first and second vaccination (<V2), and after the second vaccination (>V2). Aggressiveness, eating and drinking and general activity behavior declined from <V1 to <V2 and > V2 for all sire lines. Pigs from BP were cleaner than FP and CD pigs. Even though immunocastration was effective in general (reduced testosterone, estradiol as well as androstenone in serum) for all sire lines, some individual pigs showed either androstenone or skatole levels in fat above cutoff values. While the immunocastration mechanism works as intended for androstenone, and also for skatole for the three sire lines, the risk of carcasses with boar taint compounds above cutoff levels (respectively 1.9 and 3.7%) still remains to some extent.

Mechanistic insight into the role of immunocastration on eliminating skatole in boars

The accumulation of skatole in fat tissue is one of the predominant factors, causing boar taint. The present study was aimed to understand the mechanism whereby active immunization against GnRH (immunocastration) eliminates skatole in boars. Thirty-six boars were assigned within litter into three groups (n = 12): control, surgically castrated, or immunized against GnRH at 10 wk of age (with a booster 8 wk later). Faecal and blood samples (for skatole and skatole-regulatory hormone profiles) were collected at 4-wk intervals until boars were slaughtered (26 weeks). Immunocastration reduced (P < 0.05) serum levels of androstenone, 17β-estradiol and IGF1 especially after the booster immunization, and down-regulated (P < 0.05) mRNA expressions of both IGF1 and IGF1receptor (IGF1R) in mucosa of ileum as well as colon at slaughter. Compared to intact controls, immunocastration substantially decreased (P < 0.05) faecal skatole contents subsequent to the decrease of serum IGF1 levels, which persisted in boars after surgical castration. In parallel with the decreased formation of skatole in the intestine, levels of skatole in serum and then in fat tissue were also decreased (P < 0.05). On the other hand, deprivation of testicular steroids, especially androstenone and 17β-estradiol accelerated skatole degradation metabolism in the liver by increasing (P < 0.05) hepatic CYP2E1, CYP2A, CYP2C49 and CYB5A expressions. Collectively, our results suggested that immunocastration decreased skatole formation in the intestine and meanwhile accelerated skatole degradation metabolism in the liver, resultantly eliminating skatole accumulation in male pigs. Decreased intestinal skatole formation by immunocastration appeared to be associated with the attenuated actions of IGF1 on the turnover of both ileal and colon mucosa.

2-Aminoacetophenone Is the Main Volatile Phase I Skatole Metabolite in Pietrain × Baden-Württemberg Hybrid Type Boars

Skatole metabolites have been considered as putative contributors to boar taint. Recently, 2-aminoacetophenone, a volatile phase I skatole metabolite, was identified in back fat samples from boars of Pietrain × Baden-Württemberg hybrid type. This paper addresses the question of the physiological origin of the observed 2-aminoacetophenone in these pigs. Microsomal fractions from nine boars were isolated, and formation of skatole metabolites was subsequently analyzed by stable-isotope dilution analysis (SIDA) using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS). Significant breed-related differences in phase I skatole metabolism were observed, explaining the high levels of 2-aminoacetophenone in Pietrain × Baden-Württemberg hybrid type boars.

Hydrolysable tannin fed to entire male pigs affects intestinal production, tissue deposition and hepatic clearance of skatole

The effect of adding hydrolysable tannins to the diet of fattening boars was studied. Performance, reproductive organ weights, salivary gland morphology, boar taint compounds and skatole metabolism were evaluated. At 123 days of age and 52 ± 6 kg liveweight, 24 Landrace × Large White boars were assigned within a litter to four treatment groups: control (T0 fed mixture with 13.2 MJ/kg, 17.5% crude proteins) and three experimental diets for which the T0 diet was supplemented with 1%, 2% and 3% of hydrolysable tannin-rich extract (T1, T2 and T3, respectively). Pigs were kept individually with ad libitum access to feed and water and slaughtered at 193 days of age and 122 ± 10 kg liveweight. Adding hydrolysable tannins to the diet had no negative effect on growth performance at 1% and 2%, whereas the 3% inclusion reduced feed intake and resulted in an adaptive response of the salivary glands (particularly parotid gland hypertrophy). Relative to T0, fat tissue skatole concentration was increased in the T1 group, but was similar in T2 and T3. Across treatments tissue skatole concentrations were proportional to the activity of hepatic CYP450. The results indicate the potential of tannin supplementation to reduce boar taint although further investigations are needed in order to establishing optimal dosage.

Regulation of porcine hepatic cytochrome p450 - implication for boar taint

Cytochrome P450 (CYP450) is the major family of enzymes involved in the metabolism of several xenobiotic and endogenous compounds. Among substrates for CYP450 is the tryptophan metabolite skatole (3-methylindole), one of the major contributors to the off-odour associated with boar-tainted meat. The accumulation of skatole in pigs is highly dependent on the hepatic clearance by CYP450s. In recent years, the porcine CYP450 has attracted attention both in relation to meat quality and as a potential model for human CYP450. The molecular regulation of CYP450 mRNA expression is controlled by several nuclear receptors and transcription factors that are targets for numerous endogenously and exogenously produced agonists and antagonists. Moreover, CYP450 expression and activity are affected by factors such as age, gender and feeding. The regulation of porcine CYP450 has been suggested to have more similarities with human CYP450 than other animal models, including rodents. This article reviews the available data on porcine hepatic CYP450s and its implications for boar taint.

Skatole metabolism in the pigs with reduced testicular oestrogen synthesis

The objectives of the study were to investigate the involvement of oestrogens in the regulation of skatole levels in pigs. In total, 44 intact male pigs, siblings from 10 litters, were included in the study. Pigs were orally treated weekly with either 0.1 mg letrozole/kg body weight to reduce endogenous oestrogens or the canola oil vehicle. Fat and liver samples were collected at slaughter at 16, 20 and 40 weeks of age. Skatole and androstenone levels in fat and activities of hepatic cytochrome P4501A1, CYP1A2, CYP2A19 and CYP2E1 were analysed. Letrozole treatment did not significantly change either the levels of skatole or activities of skatole-metabolising enzymes, suggesting that oestrogens are not responsible for gender-related differences in skatole concentrations in porcine tissues.

The effect of rosmarinic acid on 1,2-dimethylhydrazine induced colon carcinogenesis

This study was carried out to investigate the chemopreventive potential of rosmarinic acid (RA) against 1,2-dimethylhydrazine (DMH) induced rat colon carcinogenesis by evaluating the effect of RA on tumour formation, antioxidant enzymes, cytochrome P450 content, p-nitrophenol hydroxylase and GST activities. Rats were divided into six groups and fed modified pellet diet for the entire experimental period. Group 1 served as control, group 2 received RA (10 mg/kgb.w.). Groups 3-6 were induced colon cancer by injecting DMH (20 mg/kgb.w.) subcutaneously once a week for the first four weeks (groups 3-6). In addition, RA was administered at the doses of 2.5, 5 and 10 mg/kgb.w. to groups 4-6 respectively. DMH treated rats showed large number of colonic tumours; decreased lipid peroxidation; decreased antioxidant status; elevated CYP450 content and PNPH activities; and decreased GST activity in the liver and colon. Supplementation with RA (5 mgkg/b.w.) to DMH treated rats significantly decreased the number of polyps (50%); reversed the markers of oxidative stress (21.0%); antioxidant status (38.55%); CYP450 content (29.41%); and PNPH activities (21.9%). RA at the dose of 5 mg/kgb.w. showed a most pronounced effect and could be used as a possible chemopreventive agent against colon cancer.

Modulation of cytochrome P450 enzymes in response to continuous or intermittent high-fat diet in pigs

1. To date, no information has been available on the modulation of cytochrome P450 enzymes (CYPs) following the administration of a hyperlipidemic diet in pigs. 2. We investigated the potential modulation of xenobiotic-metabolizing CYPs in liver, heart and duodenum of pigs subjected to a high-fat/high-cholesterol diet for 2 months continuously (C-HFD) or on alternate weeks (A-HFD). 3. The administration of the high-fat diet resulted in considerably increased plasma cholesterol levels although the animals were still able to manage the lipid overload efficiently, and no sign of effective tissue inflammation occurred in livers. Plasma lipid profile and liver histology indicated a better adaptive response of the A-HFD pigs compared to the C-HFD group. We showed a post-transcriptional induction of hepatic CYP2E1 activity in C-HFD pigs and a transcriptional induction of hepatic CYP3As - especially in the A-HFD group. No further CYP modulation was observed in either liver or extra-hepatic tissues. 4. In conclusion, the administration of a high-fat diet in pigs resulted in limited effects on the drug metabolism system. The better adaptive response of A-HFD pigs compared to C-HFD pigs is a very interesting observation since the intermittent administration of the diet reflects the mode of human behavior more closely.

Influence of sex and immunocastration on feed intake behavior, skatole and indole concentrations in adipose tissue of pigs

Feed intake behavior was studied between 9 weeks of age and slaughter in a total of 36 gilts, 32 immunocastrates, 33 surgically castrated barrows and 33 boars from 36 litters. Consequences for the concentration of substances contributing to off odor of pork (skatole, indole) were evaluated. Animals were kept in groups of 12 pigs of the same sex and treatment and fed ad libitum (13.4 MJ ME, 17% CP, 1.1% lysine). Individual feed intake behavior was recorded continuously by an electronic feeder. Immunocastration was carried out with two injections of Improvac with at least 4 weeks between both injections (1st: 12 to 17 weeks of age, 2nd: 19 to 21 weeks of age). Feed intake/day increased from an average of 0.91 ± 0.02 kg/day up to 3.15 ± 0.04 kg/day before slaughter. This increase was associated with a 50% reduction in the number of meals/day (from 15.8 ± 0.44 to 7.2 ± 0.29 meals/day). The larger meal sizes resulted from an increase in both, the duration of feed intake/meal and the feed intake rate (g/min). In addition, sex and treatment differences were observed: Feed intake in boars was lower than in all other groups due to a reduction in the number of meals/day and in the time spent feeding/day. In females, time spent feeding/day was quite similar to boars, but resulted from a higher number of meals of shorter duration. Barrows had a significantly higher feed intake because of a higher number of meals/day resulting in more time spent feeding/day. The feed intake rate was similar in boars, gilts and barrows and showed an increasing trend during the study, starting from about 15 g/min up to four times the amount. Immunocastration affected feed intake behavior severely, especially the meal size increased dramatically because of higher feed intake rate, which exceeded that of all other groups by 25% at the end of the study. The number of meals/day was not influenced by immunocastration and was almost identical to that of boars. Highest skatole concentrations were measured in fat of boars, whereas indole concentrations were higher in immunocastrates than in all other groups. In gilts and barrows, skatole concentrations were related to growth rate. Additionally, the feeding rate was an important factor explaining the variability in skatole/indole concentrations in adipose tissue. The physiological mechanisms however need further clarification.

Expression and activities of hepatic cytochrome P450 (CYP1A, CYP2A and CYP2E1) in entire and castrated male pigs

This study aimed to provide further insights into the mechanism of in vivo regulation of cytochrome P450 (CYP450) 1A, 2A and 2E1 activities in pigs with different levels of testicular steroids. Hepatic mRNA and protein expression and enzymatic activity of CYP1A, CYP2A and CYP2E1 were compared between entire male and castrated pigs. Castration was performed either surgically or immunologically. The pigs were divided into four groups. In the first group, piglets were surgically castrated without anaesthesia. Immunological castration was performed by vaccination with Improvac® (Pfizer Ltd). Vaccinated pigs were subdivided into two groups according to the vaccination regimen: early and standard vaccination. Pigs in the early vaccination group were vaccinated when aged 11 and 15 weeks. Pigs in the standard vaccination group were vaccinated when aged 17 and 21 weeks. In the control group, pigs remained intact throughout the study. Hepatic CYP450 mRNA expression, measured by real-time RT-PCR, differed significantly between groups for all isoforms measured: CYP1A2 (P = 0.002), 2A (P = 0.000) and 2E1 (P = 0.002). Lower CYP450 mRNA in entire male pigs suggests suppression of CYP1A2, CYP2A and CYP2E1 by testicular steroids at the transcriptional level. However, this suppression was not always reflected in decreased protein expression and activities of these isoforms, suggesting that at least some CYP450s (e.g. CYP2E1) are regulated by a post-transcriptional mechanism.

Nutritional Influences on Skatole Formation and Skatole Metabolism in the Pig

Skatole is a tryptophan (TRP) metabolite with fecal odor. Together with the testicular steroid androstenone it is regarded as a main determinant of boar taint, even if elevated concentrations of skatole occur occasionally in gilts and barrows. Skatole concentrations in adipose tissue result from a complex process, which includes the availability of TRP and the presence of specialized bacteria in the gut in need of TRP for energy production, as well as absorption, transport and accumulation of skatole in adipose tissue. Several steps of this process are influenced by diet and specific feed compounds. In the present paper the current knowledge about physiological mechanisms of skatole dynamics is summarized. Additionally mechanisms are discussed, by which effective feeding strategies and feed additives exert their influence in the prevention of high skatole concentrations in adipose pig tissue. It was concluded that the most effective measures are those which influence several steps of skatole formation. Despite the numerous studies carried out in the field of skatole physiology, interesting aspects still need clarification, such as the effect of adipose tissue turnover. Reliable control of skatole accretion in fat of boars is one of the main prerequisites for pork production with entire males.

Verapamil does not modify catalytic activity of CYP450 in rainbow trout after long-term exposure

Little is known about the effects of the cardiovascular drug verapamil (VRP) on metabolic processes in fish. Most calcium channel blockers including VRP are metabolized by cytochrome P450 (CYP450) enzymes. In this study we investigated the in vivo effect of VRP on some CYP450-mediated reactions in juvenile rainbow trout (Oncorhynchus mykiss). Fish were exposed to sublethal concentrations of VRP (0.5, 27 and 270 μg l(-1)) for 0, 21, and 42 day. The following CYP450-mediated reactions were studied in hepatic microsomes: O-dealkylation of ethoxyresorufin, methoxyresorufin, and pentoxyresorufin, hydroxylation of coumarin, tolbutamide, and p-nitrophenol, and O-debenzylation of 7-benzyloxy-4-trifluoromethylcoumarin. The amounts of products of these reactions did not differ among fish exposed to different levels of VRP and control fish. This suggests that the levels of VPR used did not alter catalytic activity of the selected CYP450 enzymes. In conclusion, none of the investigated CYP450-mediated reactions has potential as a biomarker to monitor VRP contamination of the aquatic environment.

Feeding dried chicory root to pigs decrease androstenone accumulation in fat by increasing hepatic 3β hydroxysteroid dehydrogenase expression

The present study investigated the in vivo effect of chicory root on testicular steroid concentrations and androstenone metabolizing enzymes in entire male pigs. Furthermore, the effect on skatole and indole concentrations in plasma and adipose tissue was investigated. The pigs were divided into two groups; one receiving experimental feed containing 10% dried chicory root for 16 days before slaughter, the control group was fed a standard diet. Plasma, adipose and liver tissue samples were collected at slaughter. Plasma was analyzed for the concentration of testosterone, estradiol, insulin-like growth factor 1 (IGF-1), skatole and indole. Adipose tissue was analyzed for the concentration of androstenone, skatole and indole, while the liver tissue was analyzed for mRNA and protein expressions of 3β-hydroxysteroid dehydrogenase (3β-HSD), sulfotransferase 2A1 and heat-shock protein 70 (HSP70). The results showed that the androstenone concentrations in the adipose tissue of chicory fed pigs were significantly (p<0.05) lower and indole concentrations were higher (p<0.05) compared to control fed pigs. Moreover the chicory root fed pigs had increased mRNA and protein expression of 3β-HSD and decreased HSP70 expression (p<0.05). Testosterone and IGF-1 concentrations in plasma as well as skatole concentrations in adipose tissue were not altered by dietary intake of chicory root. It is concluded that chicory root in the diet reduces the concentration of androstenone in adipose tissue via induction of 3β-HSD, and that these changes were not due to increased cellular stress.

In vitro and in vivo association of porcine hepatic cytochrome P450 3A and 2C activities with testicular steroids

The aim of this study was to screen the inhibitory potential of several testicular steroids on cytochrome P450 3A (CYP3A) and 2C (CYP2C) activities in porcine liver microsomes. The microsomes used in this study were obtained from pubertal male pigs of two breeds, Landrace and Duroc. For the in vitro inhibition study, porcine microsomes were incubated in the presence of 17β-estradiol, 17α-estradiol, androstenone, dehydroepiandrosterone and dihydrotestosterone. Both reversible and mechanism-based inhibitions were examined. 7-benzyloxyresorufin (BR) and 7-benzyloxy-4-trifluoromethylcoumarin (BFC) were used as substrates for CYP3A, and diclofenac and tolbutamide (TB) as substrates for CYP2C. 7-benzyloxyresorufin O-dealkylase (BROD) activity was inhibited by all tested steroids in the microsomes from Landrace pigs via mechanism-based mode, but in the microsomes from Duroc pigs, BROD activities were inhibited only in the presence of 17β-oestradiol. Mechanism-based inhibition of BFC metabolism by the tested steroids was observed in the microsomes from both breeds, but this inhibition was weak and did not exceed 20%. TB hydroxylase (TBOH) activity in the microsomes from Duroc pigs was inhibited by 17α-oestradiol through the mechanism-based mode of inhibition. None of the investigated steroids inhibited TBOH activity in Landrace pigs. For the in vivo study, male pigs were injected with a single dose of human chorionic gonadotropin (hCG) to stimulate testicular steroid production by the Leydig cells. In vivo stimulation with hGC did not alter BROD activity either in Landrace or in Duroc pigs. BFC metabolism was significantly induced by hCG stimulation in both breeds and TBOH activity only in Duroc pigs. Activity of diclofenac hydroxylase was not detected in either Landrace or Duroc pigs. Breed significantly affected BROD and TBOH activity with BROD being higher in Landrace and TBOH in Duroc pigs. This study improved our understanding of the role of testicular steroids in the regulation of porcine CYP450 activity.

Para-nitrophenol hydroxylation by fish liver microsomes: kinetics and effect of selective cytochrome P450 inhibitors

The study investigated the kinetics of p-nitrophenol hydroxylase (PNPH) in hepatic microsomes obtained from Atlantic salmon (Salmo salar). The selective inhibitors for some major mammalian cytochrome P450 (CYP450) were used to investigate the potential inhibitory effect on enzymes involved in p-nitrophenol hydroxylation. The following inhibitors were used: α-naphtoflavone (CYP1A), ellipticine (CYP1A1), furafylline (CYP1A2), 8-methoxypsoralen (8MOP, CYP2A6), 4-methylpyrazole (4MP, CYP2A6/2E1), diallyl sulfide (DAS, CYP2E1), and ketoconazole (CYP3A4). Additionally, the natural steroids 17-beta-oestraiol (E2) and testosterone were investigated as potential inhibitors of PNPH activity. It was found that formation of 4-nitrocatechol from p-nitrophenol followed monophasic kinetics with K(m) = 0.17 ± 0.03 mM and V(max) = 21.8 ± 1.05 pmol/min/mg. PNPH activity was competitively inhibited by diallyle sulfide with the K(i) value of 285.1 ± 94.2 μM μM and uncompetitively by ellipticine with K(i) value of 65.7 ± 7.8 μM. Moreover, E2 showed an ability to reduce PNPH activity through the mechanism-based inhibition mode. Our results suggest that hepatic microsomes from Atlantic salmon possess CYP2E1-like activity. However, specific isoform-mediated PNPH activity should be identified.

Early immunocastration of male pigs with Improvac(®) - effect on boar taint, hormones and reproductive organs

The aim of this study was to investigate the effect of a vaccine against gonadotropin-releasing hormone (GnRH), Improvac(®) (Pfizer Ltd), administered at a pre- or early pubertal stage on boar taint, hormonal status and reproductive organs. Crossbred male pigs (Swedish Yorkshire dams×Swedish Landrace sires or Swedish Yorkshire sires, n=192) were at birth randomly allocated to four groups: one group of pigs surgically castrated without anaesthesia before age 1 week, a second group of early vaccinated pigs given Improvac at ages 10 and 14 weeks, a third group of standard vaccinated pigs given Improvac at ages 16 and 20 weeks, and a fourth group of entire male pigs. Following the second vaccine injection, antibody titres increased rapidly, accompanied by a rapid decrease in testosterone and a slower decrease of skatole in plasma to the same low levels as for surgically castrated pigs. At slaughter, the levels of androstenone and skatole in adipose tissue were low in surgically castrated and vaccinated pigs, whereas entire male pigs had elevated levels (p<0.001). Similarly, oestradiol was at low levels for surgically castrated and vaccinated pigs, whereas entire male pigs had elevated levels (p<0.001). IGF-1 was lowest for surgically castrated pigs and highest for entire male pigs, with vaccinated pigs at an intermediate level (p<0.001). At slaughter, reproductive organs were small in pigs vaccinated with Improvac, and smaller in pigs vaccinated early (p<0.001). Under our experimental conditions, early vaccination with Improvac can be used as an alternative to the recommended schedule with maintained control of boar taint and testicular secretory activity.

Gender-related differences in cytochrome P450 in porcine liver--implication for activity, expression and inhibition by testicular steroids

In pigs, the hepatic cytochrome P450 (CYP) 1A2, 2A and 2E1 activity is important in the regulation of skatole accumulation in adipose tissue. This study investigated gender-related differences in CYP1A2, 2A and 2E1 dependent activity, protein and mRNA expression. This study also investigated the gonadal steroid dependent inhibition of CYP activity in relation to gender and dietary composition. Microsomes were prepared from the liver of female and entire male pigs (Landrace × Yorkshire sire and Duroc boars) reared under similar conditions and slaughtered at an age of 164 days. A group of entire male pigs fed dried chicory root for 16 days prior to slaughter were included in the study. CYP activities were assessed by the use of probe substrates, whilst mRNA and protein expression were analysed by RT-PCR and Western blotting. Furthermore inhibition of CYP dependent activity by gonadal steroids was assessed in vitro. Microsomes from female pigs had greater CYP1A2 and 2A activity, as well as mRNA expression compared to entire male pigs. The antibodies used did not detected differences in protein expression. In vitro inhibition by 17β-oestradiol, oestrone, androstenone and 3β-OH androstenol of CYP2E1 activity in microsomes from entire male pigs as well as inhibition of CYP1A activity in chicory fed entire male pigs was observed. Apart from that no effect of steroids was shown. In conclusion, female pigs show greater CYP activity and mRNA expression. Including chicory in the diet for 16 days changed the gonadal steroid dependent inhibition of CYP activity in entire male pigs.

In vitro inhibition of porcine cytochrome P450 by 17β -estradiol and 17α-estradiol

Sexually mature pigs are known to possess high concentrations of testicular steroids, which have been shown to change the activities of cytochrome P450 in vitro. The aim of the present study was to evaluate the regulation of CYP1A and CYP2E1 activity by the steroids dihydrotestosterone (DHT), 3β-androstenol, 17β-estradiol and 17α-estradiol. Catalytic activities of 7-ethoxyresorufin O-deethylase (EROD) and 7-methoxyresorufin O-demethylase (MROD) were used as markers of CYP1A activities, while p-nitrophenol hydroxylase (PNPH) was used as a marker of CYP2E1 activities. Of the steroids tested, only 17β-estradiol and 17α-estradiol inhibited EROD and MROD activities. This inhibition was observed when a steroid concentration of 100 µM was used, while lower concentrations showed no inhibitory effect. PNPH activities were inhibited only by 100 µM of 17β-estradiol. The significance of these results in vivo is unknown because inhibition was only found when concentrations of estrogens higher than physiological levels were used. Nevertheless, the results provided further evidence on the important role of estrogens in regulation of porcine cytochrome P450 activities.

Hepatic ethoxy-, methoxy- and pentoxyresorufin O-dealkylase activities in Landrace and Duroc pigs stimulated with HCG

The effect of human chorionic gonadotropin (hCG) stimulation on the activities of ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD) and pentoxyresorufin O-depentylase (PROD) was studied in intact male pigs of purebred Landrace and Duroc breeds. Pigs were divided into four groups: two control groups of each breed, without hCG stimulation (n = 20 for each breed), and two experimental groups (n = 18 for each breed), with hCG stimulation (Pregnyl(®); N.V. Organon, Oss, The Netherlands, 30 IU/kg live weight). Pigs were slaughtered 3 days after hCG stimulation and enzyme activities were measured in hepatic microsomes using two approaches. First, only one substrate concentration was used for the analysis of each enzyme activity. We found that EROD activity was suppressed by hCG-stimulation in Landrace (p = 0.004), but not Duroc pigs (p > 0.05). Generally, EROD activity was higher in Duroc pigs compared with Landrace (p = 0.017). Methoxyresorufin O-demethylase and PROD activities did not differ between groups (p > 0.05). To further characterize EROD, MROD and PROD, enzyme kinetic studies were performed. V(max) values for EROD and MROD in both breeds were lower after hCG stimulation (p < 0.001 for Landrace and p < 0.05 for Duroc). Additionally, V(max) values for EROD significantly differed between Landrace and Duroc pigs being higher in Duroc pigs (p < 0.05). We concluded that both hCG stimulation and breed differences may be important in the regulation of EROD and MROD activities. This study provides the first data on the effect of hCG stimulation and thus high testicular steroids, on EROD, MROD and PROD activities. Further studies are needed to investigate individual CYP450 enzymes and their regulation in porcine tissues.

Comparison of cytochrome P450 concentrations and metabolic activities in porcine hepatic microsomes prepared with two different methods

In the present study, porcine liver microsomes prepared by a conventional ultracentrifugation method were compared with microsomes prepared by a calcium aggregation method. Protein concentrations and activities of several cytochrome P450 enzymes were measured. It was concluded that using a calcium aggregation method for microsome preparation resulted in lower activities of porcine 7-ethoxyresorufin O-deethylase (EROD), 7-methoxyresorufin O-demethylase (MROD), 7-pentoxyresorufin O-depentylase (PROD) and p-nitrophenol hydroxylase (PNPH), compared to ultracentrifugation. Protein concentrations of CYP1A2 and CYP2E1, measured by Western blot, were similar in the microsomes prepared by the two methods, whereas CYP2A protein concentrations were significantly lower in the microsomes prepared by the calcium aggregation method. The choice of homogenization buffer (TRIS with addition of either 250 mM sucrose or 2mM EDTA) did not affect either individual CYP450 protein concentration or the rates of CYP450-mediated reactions. Freeze/thawing of microsomes did not affect the activities of EROD, MROD, COH and PNPH in the microsomes, indicating the stability of the measured isoforms following three cycles of freezing/thawing. A reduction in the activity of PROD was observed after the third freeze/thawing cycles of the microsomes prepared by both methods.

EROD and MROD as Markers of Cytochrome P450 1A Activities in Hepatic Microsomes from Entire and Castrated Male Pigs

In the present study, we characterized the kinetic parameters of 7-ethoxy-resorufin O-deethylation (EROD) and 7-methoxyresorufin O-demethylation (MROD) in hepatic microsomes from entire and castrated male pigs. Validation parameters of an HPLC-based method to analyse EROD and MROD activities are also described. Eadie-Hofstee plot analysis demonstrated a biphasic kinetic of EROD, indicating that at least two forms of cytochrome P450 are involved in this reaction. MROD followed monophasic kinetic, suggesting that a single enzyme, or enzymes with similar affinities, is responsible for the reaction. Inhibitory effects of α-naphthoflavone (ANF), ellipticine and furafylline were studied using microsomes from entire and castrated male pigs. ANF is a known inhibitor of both cytochrome P₄₅₀ 1A1 and 1A2 (CYP1A1 and CYP1A2); the presence of ANF in the incubations resulted in the inhibition of both EROD and MROD activities in porcine liver microsomes. EROD activities in porcine liver microsomes were also inhibited by selective CYP1A1 inhibitor ellipticine, but not by CYP1A2 inhibitor furafylline. MROD activities were strongly inhibited by ellipticine and to a much lesser extent by furafylline. Further studies are needed to evaluate substrate specificities of porcine CYP1A1 and CYP1A2.