Key Determinants of Phenotypic Heterogeneity of Hb E/β Thalassemia: A Comparative Study from Eastern India

HbE Beta thalassemia is phenotypically very diverse disease. We aim to study role of various genetic factors in determining severity of this disease. 243 diagnosed cases of HbE Beta thalassemia were included in this study. Patients were divided in two arms-transfusion dependent and non-transfusion dependent arms. Various factors (percentage of haemoglobin F, hemoglobin E, type of Beta mutation, Xmn1 polymorphism, alpha deletion, HPFH mutation) were evaluated in these patients. Xmn1 polymorphism (homozygous and heterozygous), presence of HPFH mutation and alpha deletion were more prevalent in NTDT arm versus TDT arm (p value < 0.001). Higher prevelance of severe beta mutation IVS 1-5 (G → C) mutation {64(61.54%) vs 38(27.34); p value < 0.001} was found in TDT arm when above factors were excluded from analysis. Higher mean haemoglobin F and mean Hemoglobin E percentage was associated with NTDT arm (p value < 0.001). Various factors (hemoglobin F and E percentage, Xmn1 polymorphism, HPFH mutation, alpha deletion and IVS 1-5 Beta mutation) were identified to affect severity of this cohort.

Genomic organization and tissue-specific expression of splice variants of mouse organic anion transporting polypeptide 2

cDNAs that code for mouse organic anion transporting polypeptide 2 (oatp2) have been cloned. At least three forms of mouse oatp2 cDNAs containing the same coding sequence were isolated. The common coding sequence is for a protein of 670 amino acids with 12 putative transmembrane domains. The deduced amino acid sequence of the mouse oatp2 shares 89% identity with the reported rat oatp2. Cloning and analysis of mouse oatp2 gene indicates that these isoforms are alternatively spliced products from the same gene. Heterogeneity was observed in the 5'-untranslated region of the cDNAs. Two of the three isoforms lacked the noncoding exon 3 sequence. Northern-blot hybridization analysis using the exon 3-specific probes demonstrated that mouse oatp2 mRNA containing exon 3 sequence is expressed in heart and lung, whereas exon 1-, 2-, and 17-specific probes detected mRNA only in brain and liver. The mouse oatp2 gene consists of 17 exons, including three noncoding exons, and 16 introns. All of the introns are flanked by GT-AG splice sequences except for intron 10 that is flanked by GC-AG splice sequence.

Cloning, expression, and ontogeny of mouse organic anion-transporting polypeptide-5, a kidney-specific organic anion transporter

The full-length coding sequence of mouse organic anion-transporting polypeptide (designated mouse Oatp-5) has been cloned from mouse kidney cDNA library. Analysis of the 5'-untranslated region (5'-UTR) of Oatp-5 cDNA through capsite cloning reveals two possible transcription start sites that are 4-bp apart. The 3'-untranslated region (3'-UTR) of Oatp-5 cDNA contains an early polyadenylation signal, indicating the possibility that mRNAs with different 3'-UTR lengths may coexist. Deduced amino acid sequence of mouse Oatp-5 protein contains 670 amino acids and has 10 putative transmembrane domains, multiple potential glycosylation and phosphorylation sites. Tissue-specific expression studies indicate that mouse Oatp-5 is expressed only in kidney. Studies on the developmental expression reveal that there is no significant expression of Oatp-5 mRNA in mouse kidney for at least 3 weeks after birth, and adult levels of Oatp-5 mRNA expression are attained more than 6 weeks after birth. Phylogenetic analysis reveals that mouse Oatp-5 is an ortholog of rat Oatp-5.

Cloning of the full-length coding sequence of rat liver-specific organic anion transporter-1 (rlst-1) and a splice variant and partial characterization of the rat lst-1 gene

The full-length coding sequence of rat liver-specific organic anion transporter-1 (lst-1) and its splice variant have been cloned. The full-length rat lst-1 (designated rlst-1a) encodes a protein containing 687 amino acids and has 12-putative transmembrane domains, multiple potential N-glycosylation and phosphorylation sites. Therefore, rat lst-1a has 35 additional amino acid residues compared to the previously reported rat lst-1. A splice variant (designated rlst-1c) reported in this communication encodes a protein containing 654 amino acids and has 10-putative transmembrane domains. PCR analysis suggests that rlst-1a is the most abundant form in liver. Phylogenetic analysis reveals that rat lst-1a is an ortholog of human LST-1 (hLST-1) and mouse lst-1 (mlst-1). The rlst-1 gene is composed of 15 exons and 14 introns. Analysis of exon-intron boundary reveals that the splice variant rlst-1c lacks the entire exon 7, while the previously reported rat lst-1 (designated herein as rlst-1b) lacks approximately half of exon 10, and the splicing has occurred through alternative usage of a splice donor site within exon 10.

Full-length cDNA cloning and genomic organization of the mouse liver-specific organic anion transporter-1 (lst-1)

We have cloned a cDNA that codes for mouse liver-specific transporter-1, mouse lst-1. The cDNA is comprised of 3296 base pairs and it contains a coding sequence for a protein of 689 amino acids with 12 putative transmembrane domains. The deduced amino acid sequence of the mouse lst-1 shares 64 and 77% identities with the reported human and rat lsts, respectively. Northern blot analysis demonstrates that mouse lst-1 mRNA is expressed exclusively in liver. We also report here the structural organization of the mouse lst-1 gene as the first evidence for the structure of a gene encoding an lst. The mouse lst-1 gene spans approximately 60 kbp in length and consists of 16 exons, including two noncoding exons. All the introns are flanked by GT-AG consensus splice sequences. 5'-Rapid Amplification of cDNA Ends (RACE) analyses demonstrate three splice variant mRNAs involving the noncoding exon 2 and exon 3. The 5'-flanking region of the gene contains consensus CAAT and TATA boxes and several potential binding sites for transcription factors for CAAT enhancer binding protein (C/EBP) and hepatocyte nuclear factors (HNF-3beta, HFH-1, and HFH-2), transcription factors important for liver-specific gene expression.

Induction of hepatic xenobiotic metabolizing enzymes in female Fischer-344 rats following repeated inhalation exposure to decamethylcyclopentasiloxane (D5)

Decamethylcyclopentasiloxane (D5) is a cyclic siloxane with a wide range of commercial applications. The present study was designed to investigate the effects of D5 on the expression and activity of selected rat hepatic phase I and phase II metabolizing enzymes. Female Fischer-344 rats were exposed to 160 ppm D5 vapors (6 h/day, 7 days/week, for 28 days) by whole-body inhalation. Changes in the activity and relative abundance of hepatic microsomal cytochromes P450 (CYP1A, CYP2B, CYP3A, and CYP4A), epoxide hydrolase, and UDP-glucuronosyltransferase (UDPGT) were measured. Repeated inhalation exposure of rats to D5 increased liver size by 16% relative to controls by day 28. During a 14-day post-exposure period, liver size in D5-exposed animals showed significant recovery. Exposure to D5 did not change total hepatic P450, but increased the activity of hepatic NADPH-cytochrome c reductase by 1.4-fold. An evaluation of cytochrome P450 (CYP) enzymes in hepatic microsomes prepared from D5-exposed rats revealed a slight (1.8-fold) increase in 7-ethoxyresorufin O-deethylase (EROD) activity, but no change in immunoreactive CYP1A1/2 protein. A moderate increase (4.2-fold) in both 7-pentoxyresorufin O-depentylase (PROD) activity and immunoreactive CYP2B1/2 protein (3.3-fold) was observed. Testosterone 6beta-hydroxylase activity was also increased (2.4-fold) as was CYP3A1/2 immunoreactive protein. Although a small increase in 11- and 12-hydroxylation of lauric acid was detected, no change in immunoreactive CYP4A levels was measured. Liver microsomal epoxide hydrolase activity and immunoreactive protein increased 1.7- and 1.4-fold, respectively, in the D5-exposed group. UDPGT activity toward chloramphenicol was induced 1.8-fold, while no change in UDPGT activity toward 4-nitrophenol was seen. These results suggest that the profile for enzyme induction following inhalation exposure of female Fischer-344 rats to D5 vapors is similar to that reported for phenobarbital, and therefore D5 may be described as a weak "phenobarbital-like" inducer.

Metallothionein: an intracellular protein to protect against cadmium toxicity

Metallothioneins (MT) are low-molecular-weight, cysteine-rich, metal-binding proteins. MT genes are readily induced by various physiologic and toxicologic stimuli. Because the cysteines in MT are absolutely conserved across species, it was suspected that the cysteines are necessary for function and MT is essential for life. In attempts to determine the function(s) of MT, studies have been performed using four different experimental paradigms: (a) animals injected with chemicals known to induce MT; (b) cells adapted to survive and grow in high concentrations of MT-inducing toxicants; (c) cells transfected with the MT gene; and (d) MT-transgenic and MT-null mice. Most often, results from studies using the first three approaches have indicated multiple functions of MT in cell biology: MT (a) is a "storehouse" for zinc, (b) is a free-radical scavenger, and (c) protects against cadmium (Cd) toxicity. However, studies using MT-transgenic and null mice have not strongly supported the first two proposed functions but strongly support its function in protecting against Cd toxicity. Repeated administration of Cd to MT-null mice results in nephrotoxicity at one tenth the dose that produces nephrotoxicity in control mice. Human studies indicate that 7% of the general population have renal dysfunction from Cd exposure. Therefore, if humans did not have MT, "normal" Cd exposure would be nephrotoxic to humans. Thus, it appears that during evolution, the ability of MT to protect against Cd toxicity might have taken a more pivotal role in the maintenance of life processes, as compared with its other proposed functions (i.e. storehouse for zinc and free radical scavenger).

ROLE OF ASCORBIC ACID ON TRANSAMINASE ACTIVITIES IN SOME METABOLICALLY ACTIVE TISSUES OF ASPIRIN TREATED RATS

Aspartate amino transferase (GOT) and alanine amino transferase (GPT) activities were studied in plasma, liver and kidney of aspirin treated and ascorbic acid supplemented groups for a period of seven days. GOT and GPT activities were increased in plasma but decreased significantly in liver and kidney in aspirin treated animals. Ascorbic acid supplemented groups showed no significant change of GOT and GPT in plasma and liver. In case of kidney, GOT activity remained unchange but GPT activity showed significant change in ascorbic acid supplemented group. The results clearly indicate that aspirin is a potent hepatotoxic and nephrotoxic drug but supplementation of ascorbic acid in High doses to rats fed aspirin can restore enzyme activities to the normal level.

Evaluation of octamethylcyclotetrasiloxane (D4) as an inducer of rat hepatic microsomal cytochrome P450, UDP-glucuronosyltransferase, and epoxide hydrolase: a 28-day inhalation study

Repeated inhalation exposure to octamethylcyclotetrasiloxane (D4) produces a reversible and dose-related hepatomegaly and proliferation of hepatic endoplasmic reticulum in rats. However, the effects of D4 on the expression of cytochrome P450 enzymes have not been evaluated. In the present study, the time course for changes in hepatic microsomal cytochrome P450 enzyme expression following repeated inhalation exposure to D4 vapors was determined in male and female Fischer 344 rats. Animals were exposed to D4 vapor at concentrations of 70 and 700 ppm, via whole body inhalation for 6 h/day, 5 days/week for 4 weeks. Specified animals were euthanized on exposure days 3, 7, 14, 21, and 28. Microsomal fractions were prepared from fresh liver by differential centrifugation. Enzyme activity as well as immunoreactive protein levels of several cytochrome P450 enzymes (CYP), epoxide hydrolase, and UDP-glucuronosyltransferase (UDPGT) were evaluated. The time course for enzyme induction was monitored by measuring 7-ethoxyresorufin O-deethylase (EROD) and 7-pentoxyresorufin O-depentylase (PROD) activities on days 3, 7, 14, 21, and 28. CYP1A1/2 activity, as determined by EROD activity, was increased approximately 2- to 3-fold over the exposure period. However, an examination of immunoreactive protein revealed no induction of CYP1A1 and a suppression of CYP1A2 in the 700 ppm D4 group. In comparison, CYP2B1/2 enzyme activity, as determined by PROD, was significantly increased as early as day 3 in both the 70 and 700 ppm D4 groups of male and female rats. Overall, PROD activity on day 28 was induced more than 10-fold in the 70 ppm D4 groups and more than 20-fold in the 700 ppm D4 groups. The increase in PROD activity was paralleled by a comparable increase in CYP2B1/2 immunoreactive protein. There was a modest (2- to 3-fold) increase in CYP3A1/2 activity and immunoreactive protein, as determined by 6 beta-hydroxylation of testosterone and Western blot analysis. Expression of CYP enzymes was at or near maximum by day 14 and remained relatively constant throughout the exposure period. On day 28, epoxide hydrolase activity and immunoreactive protein were induced (2- to 3-fold) in a dose-dependent manner. Only slight changes in the expression and activity of UDPGT were detected, and these did not appear to be dose related. Thus, repeated inhalation exposure to D4 induces CYP enzymes and epoxide hydrolase in a manner similar to that observed for phenobarbital (PB). Therefore, D4 can be described as a "PB-like" inducer of hepatic microsomal enzymes in the Fischer 344 rat.

Cadmium accumulation and metallothionein expression in brain of mice at different stages of development

Cadmium accumulation and metallothionein (MT) expression were studied in brains of adult mice as well as at different stages of development. MT expression was also studied in the eye of adult mice as well as at different stages of development. Using northern blot analysis with total RNA, MT mRNAs were not detected in day 16 through day 18 embryos or in postnatal animals up to day 14. Detectable expression of MT-I, -II, and -III mRNAs was obtained in brains of 30- and 60-day-old-mice. The expression of MT-III mRNA appeared to be much stronger in adults (12 weeks old or more) than in 30- and 60-day-old animals. In contrast, there was similar expression of MT-I and -II in 30- and 60-day-old mice. Cd distribution to brain was found to decrease with age; the brains of 7-day-old mice contained about 4-times more Cd than that of adult mice. Thus, an inverse correlation was observed between MT expression and Cd accumulation in brain.

Induction of metallothionein mRNA and protein in murine astrocyte cultures

Astrocytes are known to express metallothionein (MT) and were studied in culture to determine whether MT could be directly induced and which isoforms are induced. Primary astrocyte cultures were established from neonatal CF-1 mice. Both concentration-response and time-course analyses for MT induction at the protein level were determined. At the mRNA level, induction of MT-I, -II, and -III was examined 6 hr following the addition of the inducing agents. Dexamethasone (Dex), cadmium (Cd), mercury (Hg), or zinc (Zn) increased (three- to fourfold) MT protein in the astrocytes, whereas methyl mercury, lead, and interleukin-1 and -6 were ineffective. Cadmium was the most potent inducer, but was not more effective than Hg or Zn in inducing MT protein. All effective inducers increased MT protein by 24 hr. After 48 hr, Hg caused cell death, but all other effective inducers increased the MT protein examined over the 5 days. Cadmium induction of MT protein reached a peak at 96 hr, whereas the other effective inducers stimulated maximal MT protein at 24-48 hr. The effects of Dex, Cd, and Zn, on MT-I, -II, and -III mRNAs were also examined. Cadmium, Zn, and Dex stimulated increases in both MT-I and MT-II mRNA, with Dex producing the greatest effect (2.0- and 3.5-fold for MT-I and -II mRNA, respectively). Metallothionein-III mRNA was relatively unresponsive to induction. Therefore, Cd, Zn, and Dex induced MT-I and -II mRNA but not MT-III mRNA in astrocytes. These results demonstrate that MT-I and -II are directly induced in mouse astrocyte primary cultures.

Differential regulation of cytochrome P450 3A1 and P450 3A2 in rat liver following dexamethasone treatment

Induction of P450 3A1 and P450 3A2 was studied in adult rat liver following treatment with a single high dose of dexamethasone (DEX). The increase of both P450 3A1 and 3A2 occurred at the level of mRNA as well as protein. P450 3A isozymes thus induced were catalytically active. No constitutive expression of P450 3A1 mRNA or protein was observed in males or females. Constitutive expression of P450 3A2 mRNA and protein was observed in males but not in females. Additionally, in females, P450 3A2 was almost nondetectable compared to that in males, at any dose of DEX. A time course study following DEX treatment showed that P450 3A1 mRNA and protein were detectable in both sexes at 12 hours, increased until 48 hours, and then declined. The decline was more rapid in males. P450 3A2 mRNA and protein increased as early as 3 hours, increased further up to 48 hours, and slowly declined thereafter. A dose-response study indicated that P450 3A1 mRNA and protein progressively increased in both sexes from a dose of 30 mg/kg. In contrast, P450 3A2 mRNA and protein in males did not increase up to a dose of 30 mg/kg but increased at higher doses. Total P450 content and P450 3A catalytic activity were also found to increase with time and dose.

Induction of "male-specific" cytochrome P450 isozymes in female rats by oxandrolone

Oxandrolone (OXA) (5 alpha-androstan-2-oxa-17 alpha-methyl-17 beta-ol-3-one) is a clinically useful, synthetic, anabolic androgen steroid hormone. OXA was administered to rats orally twice daily for 3 days at 75 mg/kg to study the effect on hepatic cytochrome P450 (P450) isozymes. Western blots were performed on the hepatic microsomal fraction and probed with isozyme-specific monoclonal antibodies. Microsomes were also tested for catalytic activity in a testosterone metabolism assay. Data from Western blots revealed that, in female rats, there were increased levels of two male-specific isozymes, P4502C11 and P4503A2, as well as P4503A1. In contrast, male rats showed little or no change in expression of these P450 isozymes after OXA treatment. The 6 beta-hydroxylation of testosterone, which is catalyzed predominantly by P4503A1 and P4503A2, increased approximately 10-fold in female rats after treatment with OXA (from 0.05 +/- 0.01 to 0.52 +/- 0.05 nmol/min/mg protein), but only relatively small changes were seen in the male rats (from 1.02 +/- 0.05 to 1.38 +/- 0.07 nmol/min/mg protein). To investigate if the changes seen in P4503A1 and P4503A2 protein and activity were caused, at least in part, by an increase in mRNA levels, Northern blot analysis was performed. P4503A2 mRNA was increased dramatically in the female rat liver after OXA treatment, but only small increases in P4503A1 mRNA were seen. This data indicate that OXA induces P450 isozymes in the female but not in the male rat liver, probably through transcriptional activation, and some of these induced isozymes are male-specific.

Constitutive expression of metallothionein genes in mouse brain

Metallothioneins (MTs) are ubiquitous low-molecular-weight proteins that are induced by a variety of inducers, including metals, lipopolysaccharides (LPS), cytokines, oxidative stress, etc., and are thought to play a protective role against various toxic insults. The constitutive level of metallothionein is an important determinant of a tissue's susceptibility to toxic insults. In the present study, we report the constitutive expression of MT mRNAs in adult mouse brain. Analysis of total RNA from whole brain by Northern blot and solution hybridization showed that mRNAs for all three MT isoforms (I, II, III) were constitutively expressed in mouse brain, and there was no remarkable difference in their expression. However, in quantitative terms the order of expression was MT-I > MT-III > MT-II. The expression of MT-III and MT-II was about 70 and 50% of that of MT-I, respectively. Examination of their constitutive expression in different brain regions revealed that the three isoforms were expressed in all seven brain regions studied (olfactory bulb, cortex, caudate, hippocampus, thalamus, cerebellum, and brain stem), and there was only about a twofold difference in MT mRNA expression from one region of the brain to another. However, olfactory bulb had the highest mRNA expression for all three isoforms, as revealed by slot blot analysis. Constitutive expression of MT-I and -II mRNA, but not MT-III mRNA, was high in cerebellum. In order to study the cellular localization of MT mRNA, in situ hybridization of MT-I and MT-III mRNA was performed. For comparison, LPS was used to enhance MT-I mRNA signal because LPS is a good inducer of MT-I mRNA expression in mouse brain. In situ hybridization revealed that certain brain regions had distinctly localized high levels of expression of MT mRNAs. In brains of untreated mice, the constitutive expression of MT-I mRNA was high in the ependymal cell layer lining the lateral ventricles and in the Purkinje cell layer of cerebellum. The signal in the Purkinje cell layer was not on the Purkinje cells themselves, but was on locations consistent with that of glial cells. In LPS-treated mice, the signal in cerebellum was higher, and distinct signal appeared in the choroid plexus. However, signal in ependyma was similar to that in untreated mice. Pia mater in LPS-treated, but not in untreated, mouse brain showed enhanced signal for MT-I mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Species variation in hepatic metallothionein

Metallothionein (MT) is a low-molecular-weight protein involved in the homeostasis of endogenous metals and in the detoxication of heavy metals. In humans, the levels of hepatic MT have been shown to be up to 100 times the levels found in rat and mouse liver. In order to further investigate this species difference in hepatic MT levels, hepatic MT was quantified in 15 species (human, monkey, dog, cat, cow, pig, sheep, goat, rabbit, chicken, hamster, rat, mice, guinea pig, and frog). Fresh liver was obtained from each species and MT was quantified by 2 different metal-saturation assays. Results from the Cd-heme and Ag-heme assays showed that human, dog, cat, pig, and goat had the highest hepatic MT levels (400-700 micrograms/g liver). Monkey, cow, and sheep had moderate hepatic MT levels (about 200 micrograms/g liver), while rodents (mouse, rat, hamster, guinea pig, and rabbit) had low hepatic MT levels (2-10 micrograms/g liver). Hepatic MT levels in non-mammals (chick and frog) were slightly higher than rodents (about 20 micrograms/g liver). Sephadex G-75 column elution volumes ranged from 1.7 to 1.8, which implies that MT from all species had approximately the same molecular weight and similar structure. Copper and zinc concentration in the cytosols were measured by atomic absorption spectrophotometry. Dog and cat had the highest levels of Cu (86 and 50 micrograms/g liver, respectively), and pig and hamster were lowest (about 10 micrograms/g liver). Human, dog, cat, and goat had the highest levels of zinc (approximately 40-50 micrograms/g liver) while hamster and guinea pig were lowest (approximately 15 micrograms/g liver). The results show that there is a marked species difference in hepatic MT concentrations with dog, cat, and human having the highest levels.

In vitro and in vivo studies on the degradation of metallothionein

Degradation of metallothionein (MT) from rat liver was examined. Degradation of apo-MT by liver homogenate was greater than that by cytosol. At pH 5.5, degradation by homogenate was more than that at pH 7.2. These findings suggest that proteases that function at acidic pH are probably involved in MT degradation. Because lysosomes are the principal subcellular organelles that contain acid proteases (cathepsins), we compared the degradation of apo-MT by lysosomes and cytosol. Apo-MT was degraded about 400 times faster by lysosomal fraction than by cytosolic fraction. To determine the relative importance of different cathepsins, we used different inhibitors. Leupeptin, which inhibits cathepsins B and L, inhibited the degradation of apo-MT by 80%, implying that cathepsins B and/or L might be very important in the intracellular turnover of MT. Cathepsin D appeared to be the least significant, because apo-MT degradation was reduced by about 20% by inhibiting cathepsin D. When we extended this study with purified cathepsins, we obtained the same answer, i.e., the ability of different cathepsins to degrade apo-MT was in the following order: cathepsin B >> cathepsin C > cathepsin D. While apo-MT was susceptible to degradation, ZnMT and CdMT were highly resistant to degradation. Coincubation of ZnMT or CdMT with either lysosomal extract or purified cathepsins did not result in any appreciable degradation even after 16 hr. However, longer incubations did result in some degradation, especially by purified cathepsin B. Interestingly, CdMT degraded little faster than ZnMT by both lysosomal extract as well as purified cathepsin B.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of metallothionein by superantigenic bacterial exotoxin: probable involvement of the immune system

Metallothionein (MT) can be induced in mouse liver by a bacterial exotoxin, toxic shock syndrome toxin-1 (TSST-1). Hepatic MT was induced by TSST-1 in a dose-dependent manner from 100 micrograms/kg through 3 mg/kg in CF-1 mice, and by 6 h the induction was almost maximal. The increase of hepatic MT occurred at the mRNA level, also, and both MT-I and II mRNAs increased coordinately. Because TSST-1 is a superantigen, it was investigated whether TSST-1 induces MT through cytokines as a consequence of immunostimulation. In low-cytokine-producing mice (C3H/HeJ), up to a dose of 1 mg/kg of TSST-1, there was only 2- to 3-fold increase of hepatic MT. In contrast, in normal-cytokine-producing mice (C3Heb/FeJ), TSST-1 increased MT in a dose-dependent manner, and at a dose of 1 mg/kg, there was a 25-fold increase in hepatic MT. This suggests that activation of the immune system is probably involved in the induction of MT by TSST-1. Studies on the role of specific hepatic cytokines (IL-1, TNF-alpha, and IL-6) in TSST-mediated hepatic MT induction showed that TSST-1 did not increase hepatic IL-1 or TNF-alpha significantly over controls in any of the mouse strains studied. In contrast, TSST-1 induced hepatic IL-6 in all three strains of mice. However, in CF-1 and C3Heb/FeJ mice (normal-cytokine-producing) IL-6 induction preceded MT mRNA induction, but in C3H/HeJ mice (low-cytokine-producing), IL-6 induction did not precede MT mRNA induction.

Induction of metallothionein by alpha-hederin

alpha-Hederin (alpha-Hed) is a triterpenoid saponin that has been shown to protect against some hepatotoxicants. This study examined the protective effect of alpha-Hed against cadmium (Cd) hepatotoxicity and the mechanism of protection. alpha-Hed pretreatment (100 mumol/kg, sc) dramatically decreased Cd (3.7 mg/kg, iv) hepatotoxicity as indicated by a reduction of serum alanine aminotransferase and sorbitol dehydrogenase, as well as by histopathological examination. alpha-Hed did not produce protection by decreasing the distribution of Cd to the liver, as higher amounts of Cd were found in the liver of alpha-Hed-pretreated mice. However, there was a marked alteration in subcellular distribution of Cd in the alpha-Hed-pretreated mice, with much less Cd distributing to nuclei, mitochondria, and microsomes and more in the cytosol. The increased cytosolic Cd was found primarily bound to a low-molecular-weight protein, metallothionein (MT). alpha-Hed (10-300 mumol/kg, sc) produced a dose-dependent increase in hepatic MT with a 100-fold increase over controls 24 hr after a single injection of 100 mumol/kg, as determined by the Cd/hemoglobin assay. The hepatic MT increase produced by alpha-Hed is relatively long lasting, in that it is still eight times control values 6 days after a single administration. The induction of MT was also relatively specific for the liver, as little or no increase in MT was observed in other tissues. Furthermore, alpha-Hed increased both hepatic MT-I and MT-II levels. Northern blot analysis revealed that alpha-Hed rapidly increased MT mRNA levels. In conclusion, alpha-Hed decreases the hepatotoxicity of Cd by inducing MT, which binds Cd in the cytosol, and thus reduces the amount of Cd in the critical cellular organelles. alpha-Hed is an effective inducer of both MT-I and MT-II in liver, and this effect is associated with an increase in MT mRNA.

Oleanolic acid protects against cadmium hepatotoxicity by inducing metallothionein

Oleanolic acid (OA) is a triterpenoid compound that has been shown to protect against some hepatotoxicants and is used in China to treat hepatitis. This study was conducted to examine the protective effects of OA against cadmium (Cd)-induced liver injury in mice and the mechanism of protection. OA (100 mg/kg x 3 days) pretreatment dramatically decreased Cd (3.7 mg/kg i.v.)-induced liver injury as indicated by decreased serum activities of alanine aminotransferase and sorbitol dehydrogenase, as well as by histopathological observation. To examine the mechanism of protection, the distribution of Cd to major organs and the hepatic subcellular distribution of Cd were determined 2 hr after 109Cd injection (3.5 mg/kg of Cd and 10 microCi/mg of Cd i.v.). OA did not reduce the amount of Cd in liver, but significantly altered the hepatic subcellular distribution of Cd, with more Cd in hepatic cytosol bound to metallothionein (MT), and with less Cd in other organelles and proteins. OA produced an approximately 30-fold increase in hepatic MT, but had no appreciable effects on MT levels of five other organs. Furthermore, OA increased both hepatic MT-I and MT-II levels, as determined by high-performance liquid chromatography/atomic absorption spectrophotometry. Northern blot analysis revealed that OA increases MT mRNA expression. In summary, OA pretreatment protects against Cd-induced hepatotoxicity by inducing MT. MT bound Cd in the cytosol, and thus decreased the amount of Cd in other critical organelles and proteins. OA is a hepatic MT inducer for both MT-I and MT-II isoforms, and this effect is due, at least in part, to an increased MT mRNA accumulation.

Differential expression of the metallothionein gene in liver and brain of mice and rats

Expression of the metallothionein I (MT-I) gene was studied in liver and brain of control mice and rats, as well as following administration of Cd and lipopolysaccharide (LPS). Time-course studies revealed that MT mRNA reached a maximum in liver of both mice and rats 6 hr following treatment with Cd or LPS. MT mRNA from control and Cd- and LPS-treated rat brains could not be detected by Northern-blot analysis of total RNA, but Northern analysis with poly(A)-enriched RNA revealed that induction of MT mRNA in rat brain does occur with both Cd and LPS treatment. In contrast, mouse brain MT mRNA was easily detected by Northern-blot analysis of total RNA. It was also clear from Northern-blot analyses of both mouse and rat brain that LPS induced more MT mRNA than did Cd. Quantitation of MT mRNA by solution hybridization revealed that Cd and LPS induced similar amounts of MT mRNA in livers of mice (about 0.64 fmol/micrograms total RNA by Cd and 0.68 by LPS) and rats (about 0.23 fmol/micrograms total RNA by Cd and 0.21 by LPS). Therefore, both inducers increased MT mRNA about threefold more in mouse liver than in rat liver. In mouse and rat brain, LPS induced about twice as much MT mRNA as did Cd (about 0.08 fmol/micrograms total RNA by Cd and 0.16 by LPS in mice and about 0.006 fmol/micrograms total RNA by Cd and 0.008 by LPS in rats). However, the actual amount of MT mRNA induced in rat brain by either inducer was minimal compared to that in mouse brain. In fact, Cd induced 13 times more MT mRNA in mouse brain than in rat brain, and LPS induced about 20 times more MT mRNA in mouse brain than in rat brain. Cd distribution to liver was similar in both mice and rats, but the Cd concentration in mouse brain was about 60% more than that in rat brain. Distribution of LPS was also similar in mouse and rat livers, as well as in mouse and rat brains. Therefore, there exists a difference in the expression of MT gene in both liver and brain of mice and rats, the expression in mice being higher than that in rats. These findings suggest that such differential expression of the MT gene cannot be entirely accounted for by the difference in the tissue distribution of inducers. Other tissue-specific and species-specific factors controlling MT gene expression appear to be involved.

In vitro degradation of apo-, zinc-, and cadmium-metallothionein by cathepsins B, C, and D

Metallothionein (MT) has been extensively studied over the past several years because of its probable role in endogenous metal homeostasis and cellular protection. A large body of knowledge now exists describing the physicochemical properties of MT as well as the mechanisms involved in MT induction. It has been well established that MT protects tissues from metal toxicity by chelating metals that would otherwise be available to interact with and disrupt vital cell functions. Information on the degradation of metal-saturated MT and the fate of the metals associated with it would be extremely important in predicting metal toxicity. Lysosomes have been targeted as a possible subcellular site for the turnover of MT; however, the susceptibility of MT to degradation by specific acidic proteases (i.e., cathepsins) has not been described. Therefore, the purpose of the present study was to examine the relative abilities of cathepsins B, C, and D to degrade Zn7-MT, Cd7-MT, and apo-MT in vitro. In so doing, the effects of metal species, degree of metal saturation, and pH on the degradation processes were evaluated. Time course experiments revealed that apo-MT was rapidly degraded by all three cathepsins. Cathepsin B degraded apo-MT approximately 36-fold more rapidly than cathepsin C and 45-fold more rapidly than cathepsin D. Therefore, under the in vitro conditions used in this study, the relative potency of the cathepsins tested was cathepsin B much much greater than cathepsin C greater than cathepsin D. In comparison, metal-saturated MT was more than 1000-fold more resistant to degradation by the cathepsins tested. In order to determine how much metal was needed to protect MT against degradation, apo-MT was reconstituted with increasing molar equivalents of Zn2+. The results suggest that as metal to apo-MT ratios increase, less apo-MT substrate is available to the protease and degradation decreases.

Role of hepatic lysosomes in the degradation of metallothionein

The degradation of metallothionein (MT) by rat liver was examined. Degradation of MT by liver homogenate was greater than by cytosol. In addition, MT degradation by the homogenate at pH 5.5 was more than that at pH 7.2. Because lysosomal proteases function at acidic pH, these findings suggest the importance of lysosomes in MT degradation. The degradation by the lysosomal fraction was about 400-fold greater than that by the cytosol. Because cathepsins are the principal lysosomal proteases, we used cathepsin-specific inhibitors, such as leupeptin, E-64 and pepstatin, to determine the relative importance of different cathepsins in degrading MT. The study reveals that cathepsin B and/or L is (are) probably the most important enzyme(s) in degrading hepatic MT, because leupeptin, which blocks cathepsin B and L activity, inhibited the degradation of apo-MT by about 80%. Cathepsin D appears to be of least importance in MT degradation, because inhibition of this enzyme by pepstatin reduced degradation by only 20%. Studies on the degradation of apo-MT, ZnMT, and CdMT indicated that apo-MT is about 1500-fold more sensitive to degradation than ZnMT and CdMT. These data suggest that metals protect MT from degradation. This is further supported by a reconstitution experiment, which shows that with a progressive decrease of MT: metal ratio following titration of apo-MT by metals, there is a concomitant reduction in degradation. At a lysosomal pH of around 4.7, about 60% of Zn and 20% of Cd are displaced from MT, thereby making it susceptible to degradation. We propose, therefore, that lysosomes are probably important for MT degradation in vivo and that metal release is a prerequisite for degradation. With the release of metals, MT becomes susceptible to degradation, which is probably accomplished by the lysosomal cathepsins, in particular cathepsins B and L.