Clinicopathologic analysis of renal and extrarenal angiomyolipomas: report of 44 cases

BACKGROUND

Angiomyolipoma (AML) is a rare soft tissue tumor involving the kidneys, liver and other visceral organs. It is composed of smooth muscle cells, adipocytes and small- to medium-sized hyalinized vessels. The purpose of this study was to investigate the characteristic clinicopathologic manifestations of AML in different tissues.

METHODS

We collected 37 renal, four hepatic, one lymph node, one subcutaneous and one uterine cervical AML to analyze the clinical, histologic, histochemical and immunohistochemical variations of AML in different tissues.

RESULTS

Clinically, renal and hepatic AML were associated with tuberous sclerosis complex and predominate in women. There were several prominent pathologic differences between renal and extrarenal AML. First, none of the tumors were encapsulated except for the subcutaneous AML, which had a pseudocapsule. Secondly, the smooth muscle cells were usually epithelioid shaped in hepatic AML and occasionally in renal AML, but not in subcutaneous or uterine AML. Furthermore, hepatic AML characteristically showed extramedullary hematopoiesis and eosinophilic hyaline granules. Finally, only the tumor cells of renal, lymph node and hepatic AML had periodic acid-Schiff (PAS), PAS-D (after diastase digestion) positive granules and monoclonal mouse anti-human melanosome clone (HMB-45) immunoreactivity.

CONCLUSIONS

By combining the clinical, histologic, histochemical and immunohistochemical features, some discrepancies between the renal and extrarenal AML were observed, such as female predominance, association with tuberous sclerosis complex, morphology of the smooth muscle cells, presence of PAS, PAS-D positive granules and HMB-45 immunoreactivity in tumor cells. Extramedullary hematopoiesis and hyaline globules are unique to hepatic AMLs. These specific pathologic manifestations not only implicate the histogenesis of AML from different organs, but also assist in making a correct diagnosis.

Effects of isoflavones containing soy protein isolate compared with fish protein on serum lipids and susceptibility of low density lipoprotein and liver lipids to in vitro oxidation in hamsters

The effects of dietary soy protein isolate (SPI), ethanol-extracted SPI (E-SPI) low in isoflavones, and fish protein (FP) on the concentration of blood lipids and the susceptibility of low density lipoprotein (LDL) to copper-induced oxidation were compared in male golden Syrian hamsters fed a moderate hypercholesterolemic semi-purified diet for 10 weeks. SPI, E-SPI, and FP were incorporated into the isonitrogenous experimental diets as protein sources. The SPI group exhibited significantly lower serum total cholesterol concentration compared with the E-SPI group (P < 0.05) and the FP group (P < 0.01). Both the SPI and E-SPI groups showed lower LDL cholesterol (P < 0.001 and P < 0.05, respectively) and less LDL apolipoprotein B (P < 0.01) compared with the FP group. The distribution pattern of serum lipoprotein cholesterol fractions of the SPI and E-SPI groups were similar to each other, but different from that of the FP group. The lysine/arginine ratio of the three diets was significantly correlated with serum total cholesterol concentration (r = 0.462, P = 0.023). The resistance of LDL to copper-induced oxidation was greater in the SPI group than in the E-SPI and FP groups as assessed by the lower concentrations of thiobarbituric acid-reactive substances (TBARS) and the longer lag time required for the formation of conjugated dienes (P < 0.01). Livers of hamsters fed the FP diet had a higher amount of TBARS than those of hamsters fed SPI (P < 0.01) and E-SPI (P < 0.05) diets. The SPI diet showed sparing effects on alpha-tocopherol contents in both serum and liver. It seems likely that soy isoflavones protect the circulating and membrane lipids by sparing alpha-tocopherol and endogenous antioxidants.

Circadian variations in plasma and erythrocyte concentrations of glutamate, glutamine, and alanine in men on a diet without and with added monosodium glutamate

Variations in plasma and erythrocyte concentrations of glutamate, glutamine, and alanine during the day were studied in 10 healthy men fed ordinary Taiwanese meals, first without and, 1 week later, with monosodium glutamate (MSG) added. MSG at a level of 15, 40, and 45 mg/kg (total, 100 mg/kg/d) was added, respectively, to the breakfast, lunch, and dinner meals. Heparinized blood samples were collected over 24 hours with 1- to 3-hour intervals. In both trials, plasma glutamate concentrations increased significantly after lunch and dinner. Although the circadian variations of plasma glutamate were small (between 32 and 53 micromol/L), the levels nevertheless varied significantly as a function of the time of day in both trials. Considering that the dietary intake of glutamate was high when MSG was added, the low plasma glutamate concentration over 24 hours indicates that glutamate is actively metabolized. On the other hand, the concentrations of erythrocyte glutamate (507 to 631 micromol/L) and glutamine (427 to 613 micromol/L) did not show a significant postprandial increase or circadian variation. Nevertheless, the concentration of plasma glutamine (539 to 657 micromol/L) varied significantly as a function of time in both trials. The plasma concentration of alanine (274 to 494 micromol/L) increased significantly after each meal and decreased significantly from 2:00 to 5:00 AM in both trials. Both plasma and erythrocyte alanine concentrations varied significantly as a function of time. These results show that the substantial amount of MSG intake had no apparent effect on the circadian variation profiles of blood glutamate, glutamine, and alanine.

Why reversing the sequence of the alpha domain of human metallothionein-2 does not change its metal-binding and folding characteristics

A novel peptide, the backward reading sequence of human metallothionein-2 alpha domain, was synthesized and its chemical and spectroscopic properties analyzed. This folded retro-alpha domain was able to bind Cd(II) in identical stoichiometries with the chemically synthesized alpha domain of metallothionein-2. Nearly identical to the alpha domain, Cd-binding retro-alpha domain showed a characteristic ultraviolet absorption spectrum with a shoulder at 245-250 nm (due to cadmium-thiolate charge transfer), and the absorption shoulder was abolished by acidification [suggesting mercaptide bonding between Cd(II) and the cysteine residues]. Similar metal-binding capabilities between alpha domain and retro-alpha domain were observed also by pH titration and in the reaction with the sulfhydryl reagent 5,5'-dithiobis(2-nitrobenzoic acid). A two-state cooperativity of the metal-cluster formation was observed spectroscopically in the titration of the retro-alpha domain, indicating that the retro-protein is foldable. In contrast to other proteins, our results indicate that the reversion of the amino acid sequence for the alpha domain does not change its foldability and metal-binding capacity, suggesting that the order of its sequence is not critical to the formation of a critical metal-tetrathiolate nucleus. However, CD spectra of the Cd-binding alpha domain and retro-alpha domain showed that the reversal direction of the domain sequence backbone significantly affects the formation of structure even when it is foldable.

Neonatal intestinal perforation caused by congenital defect of the small intestinal musculature: report of one case

Congenital defect of the small intestinal musculature is a rare cause of neonatal spontaneous intestinal obstruction or perforation. Its etiology and pathogenesis are still controversial. A male infant presented with intestinal obstruction at two days of age and rapidly progressed to perforation and septic shock. He died at seven days of age. Autopsy finding revealed a perforation hole at twenty-five cm proximal to ileocecal valve. Histology examination demonstrates multifocal deficiency of the inner circular muscle layer three cm around the perforation site. The clinical and histological characteristics are reviewed and discussed. We propose that the muscle defect of small intestine, especially ileum, is secondary to ischemic injury rather than an embryological malformation.

Term pregnancy in a noncommunicating rudimentary horn of an unicornuate uterus: a case report

A case of full-term pregnancy in the noncommunicating rudimentary horn of unicornuate uterus is presented. A healthy female infant weighing 2,985 g was delivered by cesarean section at 37 weeks' gestation. The diagnosis was missed by prenatal ultrasonography and was made only at laparotomy. A retrospective analysis of our ultrasound studies revealed that the echo pattern of the nongravid uterus resembled a soft pelvic mass. Color Doppler imaging revealed prominent low-impedance uterine arcuate-radial arterial blood flow surrounding the periphery of the pelvic mass, as well as multiple areas of placental implantation with a pulsatile lacunar flow pattern. A high index of suspicion of rudimentary horn pregnancy should be borne in mind whenever late-pregnancy ultrasonography shows the above-mentioned characteristic ultrasonic findings.

Endoscopic management of lateral pharyngeal pouch

A patient with dysphagia including symptoms of regurgitation of food and worsening pulmonary symptoms was found to have a lateral pharyngeal pouch. The diagnosis was made by barium swallow study and confirmed by endoscopy. The characteristic barium swallow findings include retention of barium in a sac or diverticulum. Endoscopy showed a pouch in the left lateral pharynx, adjacent to the vallecula. Surgical therapy consisting of endoscopic stapling of the mucosal band separating the pouch from the pharynx was performed successfully, and the patient improved dramatically.

Function and sequence analyses of tumor suppressor gene p53 of CHO.K1 cells

The tumor suppressor gene p53 plays an important role in guarding genomic integrity. When induced in response to environmental results, the gene product of p53 functions as a transcription factor to transactivate genes involved in arresting the cell cycle and as a facilitator of DNA repair. In contrast, the status of p53 in Chinese hamster ovary (CHO) cells, commonly used as a model system for various studies including those involving the cell cycle and transformation, remains an enigma. In this study, the function and sequence of p53 in CHO.K1 cells were investigated. The level of p53 proteins was elevated on ultraviolet (UV) irradiation of the cells, and the proteins formed specific complexes as probed with DNA containing p53-binding sequences. Its activities toward responsive promoters were inducible by UV in a dose-dependent manner. Although p53 in CHO.K1 contained a single missense mutation at codon 211, the mutation apparently had no effect on the functional properties of the protein. The CHO.K1 cells on X-ray irradiation failed to arrest at G1 phase even when the cells were transfected with a wildtype human p53 gene, indicating that the failure probably was not caused by dysfunction of its p53, but by some other mechanism. This result is consistent with the finding that p21(Waf1/Cip1) is undetectable in UV-treated CHO.K1 cells, whereas Gadd45 is induced by UV light in the cells.

Comparative effects of polyunsaturated- to saturated fatty acid ratio versus polyunsaturated- and monounsaturated fatty acids to saturated fatty acid ratio on lipid metabolism in rats

This study examined the effects of various polyunsaturated fatty acid (PUFA, P)/saturated fatty acid (SFA, S) ratio versus PUFA + monounsaturated fatty acid (MUFA, M)/SFA ratio on lipid metabolism. The P/S ratio of dietary fat was fixed at a certain level (0.5, 1, 2, or 4, respectively) for each of four pairs of rat groups respectively, and then the P + M/S ratio was changed for the four pairs of rat groups. When the P/S ratio was fixed at 0.5, 1, 2, or 4, the plasma total cholesterol, LDL-cholesterol (C), and HDL-C levels did not show any significant difference in each pair of groups with different P + M/S ratios. However, when the P/S ratio was fixed at 1.0, the higher P + M/S ratio of 5.7 (M/S=4.7, P/M=0.2) resulted in significantly higher plasma total triacylglycerol (TAG), VLDL-TAG, VLDL-C, and VLDL-phospholipid (PL) than the lower P + M/S ratio of 1.4 (M/S=0.4, P/M=2.4). Whereas when SFA was fixed at a similar level, it therefore had approximately the same P + M/S ratio(5.3, 5.6, 5.7), and by increasing the P/S ratio from 1, 2 to 4 (70.4, 52.7 and 23.2% of the total fatty acids as MUFA respectively), the plasma VLDL-C, VLDL-TAG, and VLDL-PL concentrations decreased progressively. When PUFA or MUFA was kept on a similar level (14.9 or 53% respectively), the higher P + M/S ratio (5.7 or 5.3, respectively) resulted in significantly greater accumulation of liver cholesterol than the lower P + M/S ratio of 2.2. When the P/S ratio was fixed at 1 or 4, the diet of higher P + M/S ratio in a pair of the groups also resulted in greater accumulation of liver cholesterol. The results of the study suggests that if the P + M/S ratio was below 3, the change in the P/S ratios (0.5, 1 or 2) did not affect the levels of plasma total and lipoprotein cholesterol and TAG. Increases in the plasma VLDL-C and VLDL-TAG were related to increased MUFA content in the diet. And high MUFA content resulted in greater accumulation of liver cholesterol. It seems that the prerequisites for keeping low plasma and liver cholesterol are (a) low M/S ratio and (b) high P/M ratio and (c) P + M/S ratio not to exceed 3.

Effects of the ratio of polyunsaturated and monounsaturated fatty acid to saturated fatty acid on rat plasma and liver lipid concentrations

The effects of dietary monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid + MUFA/saturated fatty acid (PUFA + MUFA/SFA) ratio on plasma and liver lipid concentrations were studied. In experiment I, when rats were fed with 40% fat (energy%, PUFA/SFA ratio 1.0) and 1% (w/w) cholesterol (C) diets for 21 d, a large amount of MUFA (28.1 energy%, PUFA + MUFA/SFA = 5.7) in the diet was found to increase the plasma total C, triacylglycerol (TAG), and phospholipid (PL) as compared with the low-MUFA diet (7.0 energy%, PUFA + MUFA/SFA = 1.4). The plasma very low density lipoprotein (VLDL)-C, VLDL-TAG, VLDL-PL, and low density lipoprotein (LDL)-C increased significantly in the high-MUFA diet group, but high density lipoprotein (HDL)-C did not change significantly. The high-MUFA diet resulted in greater accumulation of liver C but lesser accumulation of TAG. In experiment II, when dietary SFA was fixed at a certain level (13.2 energy%; PUFA + MUFA/SFA = 2.0), rats given a larger amount of MUFA (23.1 energy%; PUFA/MUFA = 0.2; MUFA/SFA = 1.8) showed higher plasma and liver C levels than did the low-MUFA diet (7.7 energy%; PUFA/MUFA = 2.5; MUFA/SFA = 0.6). When PUFA was fixed at a certain level (24.4 energy%), there was not a significant difference in the plasma C level between the high- and low-MUFA dietary groups (PUFA + MUFA/SFA = 4.8 and 8.4), but the higher PUFA + MUFA/SFA diet, which was high in MUFA/SFA ratio, significantly decreased the plasma HDL-C and TAG levels. However, when MUFA content was fixed at a certain level (16.4 energy%), no significant difference was observed between the two groups with different PUFA/SFA ratios of 0.2 and 4.1, but liver C level was raised in the higher PUFA/SFA diet. It appears that the PUFA/SFA ratio alone is unsuitable to predict the change of plasma C level, because a large amount of dietary MUFA may lead to an increase of plasma and liver lipids in rats. It seems that the prerequisites for keeping low plasma and liver C are (i) low MUFA/SFA ratio, (ii) high PUFA/MUFA ratio, and (iii) PUFA + MUFA/SFA ratio not to exceed 2.

Multiple isoforms of metallothionein are expressed in the porcine liver

Isogenes are highly homologous to each other and are often difficult to ascertain, as has been the case with metallothionein, a metal-binding protein rich in cysteines. Conventional separation of metallothionein isoforms relied on ion exchange chromatography of the proteins, or screening for the sequences from gene libraries. In this study, a combination of RT-PCR and partial protein sequencing is used in the identification of metallothionein isogenes expressed in porcine liver. By this approach, we have identified expressed coding sequences which constitute 10 new isogenes. Of the four known groups of metallothioneins (MT), phylogenetic analyses place these pig isogenes in the MT-1 group, except two which are identified as being closely related to MT-2, and none in groups 3 and 4. The isogenes are thus namedpMT-1a to -1g, andpMT-2a and -2b. While each of the isogene sequences is unique, two isogenes,pMT-1e1 andpMT-1e2, share an identical amino acid sequence, differing only in specific codons. Two others,pMT-1b andpMT-1g, have a cysteine substituted by arginine, the first such sequence ever detected in MT.pMT-2a andpMT-2b are closely aligned with the MT-2 group of vertebrates, in spite of the absence of a characteristic acidic amino acid at position 10 or 11, common in other mammalian metallothioneins.

Promoter structure and activity of type 1 rice metallothionein-like gene

A novel stress-inducible metallothionein-like gene from rice, designated as rgMT-1 (rice genomic metallothionein-like gene-1), was isolated and sequenced. From the sequence analysis of its 5'-flanking region, two putative TATA boxes, one CAAT box, and several short sequences homologous to regulatory cis-elements previously reported were identified. Two direct repeats, one 10 bp in length (CAAAATCAAA) and the other 11 bp (GTGAAAATACT), respectively, were also found. By transient GUS (beta-glucuronidase) assay, the expression of GUS, in vitro, was enhanced by the presence of the rgMT-1 intron. The critical region which controls the basal transcription was shown to lie between -73 and -36 upstream of rgMT-1, in which one of the two putative TATA boxes was located. The promoter activity was lost completely when both putative TATA boxes were deleted. This is the first report describing the genomic structure and regulation of a monocotyledonous metallothionein-like gene critical to the response of stress.

Type 2 rice metallothionein-like gene has two introns

A type 2 rice metallothionein-like gene was isolated from root by PCR and sequenced. The PCR fragment was designated as pcr1460, which overlaps with OsMT-2, a cDNA sequence previously characterized, with the presence of two additional segments, 583 and 613 bp in length. These segments are recognized as introns which divide the coding sequence into three exons, 65, 78 and 106 base pairs in length. The sequences flanking the introns conform with the GT/AG rule for splice junctions, and one exonic open reading frame can be identified in each of the introns. The observation that MT-like gene has two introns is the first of such a finding obtained from monocotyledonous plants.

Cysteine contributions to metal binding preference for Zn/Cd in the beta-domain of metallothionein

Previous studies showed that metals in the beta-domain of metallothionein (MT) are more readily exchangeable and the level of avidity is site specific. This is reflected by energy differences computed with a series of simulated structures derived from X-ray crystallography. In this study, we examined further the contribution of each of the nine cysteines in the beta-domain. By semi-empirical MNDO calculations, we observed that the relative average binding strength is the strongest for Cys21 to Cd[M4] and for Cys26 to Zn[M3], except for the bridging cysteines. These results suggest that binding site preference for Zn/Cd is determined by binding strength between specific cysteines and metal ion species.

Flat adenoma of the colon: two cases

Flat adenoma has been frequently reported to have a higher potential for malignant change than other polypoid adenomas. It is an endoscopically visible sessile lesion that consists histologically of an adenomatous change of the colonic mucosa. Detection, diagnosis, and treatment of flat adenoma has not previously been reported in Taiwan. We found such lesions in two patients during colonoscopic examinations as patches of discolored and irregular mucosa. Histopathologic studies revealed adenomas with mild to moderate dysplasia. Patient 1 underwent segmental colectomy; patient 2 underwent an endoscopic strip biopsy. Focal malignant changes were noted in patient 1. Both patients received close follow-up at the outpatient clinic. No recurrence has been seen in patient 1. Patient 2 developed an enlarged sessile lesion with a histologic picture showing a tubular adenoma without malignancy but refused further surgical treatment. This paper outlines the endoscopic and pathologic characteristics of flat adenoma in two patients, and should alert physicians to the importance of early detection and treatment of this lesion.

Chylothorax as a complication of anterior thoracic interbody fusion: a case report

A case is reported of chylothorax following an uneventful anterior thoracic interbody spinal fusion. To present knowledge, this complication is reported to occur in 0.2% of intrathoracic operations, and may give rise to 50% mortality unless stress properly recognized and managed.

Effects of n-3 and n-6 fatty acids on plasma eicosanoids and liver antioxidant enzymes in rats receiving total parenteral nutrition

The effect of total parenteral nutrition (TPN) enriched with n-3 or n-6 fatty acids on the concentration of plasma eicosanoids was evaluated in rats. Rats were divided into three groups: the control group (n = 6) was fed a chow diet and infused with saline only. Two experimental groups (n = 11, 13) received TPN solutions at an energy level of 30 kcal/100g body weight with 40% energy provided as fat. The experimental groups were maintained on TPN for a period of 7 d. The basal TPN solutions were isonitrogenous and identical in nutrient composition except for differences in lipid source. One experimental group received a safflower oil emulsion, whereas the other group received a fish oil emulsion. At the end of the experimental period, plasma 6-keto prostaglandin F1 alpha, thromboxane B2, bleeding time, lipid peroxidation products, and antioxidant enzymes of liver were analyzed. The results demonstrated that the fish oil group had lower 6-keto prostaglandin F1 alpha concentration than the safflower oil group. Also, plasma thromboxane B2 was the lowest in the fish oil group among the three groups. There was no difference in bleeding time among the groups. With regard to liver lipid peroxidation products, malondialdehyde concentration was not higher in the fish oil group, whereas superoxide dismutase and glutathione peroxidase activities were lower in the fish oil group compared with the control and safflower oil groups. The results suggest that TPN prepared with fish oil fat emulsion causes less accumulation of lipid peroxidation products in the liver of rats, and may be beneficial in preventing platelet aggregation.

Semi-empirical simulation of Zn/Cd binding site preference in the metal binding domains of mammalian metallothionein

Metallothionein, a two-domain protein, naturally binds seven gram atoms of divalent ions such as Zn and Cd. Four of the metals (M1, M5, M6 and M7) are found in the alpha-domain and three (M2, M3 and M4) in the beta-domain. Previous studies have shown that metals in the beta-domain are more readily exchangeable, and the level of avidity is site specific. By semi-empirical MNDO modified neglect of diatomic overlap calculations, we found the tendency of binding energy for Cd to be M4 > M2 > M3 [corrected] in the beta-cluster and M5 > M7 > M1, M6 in the alpha-cluster. Thus, the replacement of Zn by Cd can be expected to follow the order M4-->M2-->M3 in the beta-domain and M5-->M7-->M1 or M6 in the alpha-domain. This is reflected by energy differences computed with a series of simulated structures derived from either X-ray crystallography or NMR coordinates.

RNA expression patterns of a type 2 metallothionein-like gene from rice

A type 2 metallothionein-like gene from rice, OsMT-2 (Oryza sativa metallothionein-like gene-2), was isolated in its cDNA form and sequenced. By northern analyses OsMT-2 expression was shown to be induced under stress by sucrose starvation, heat shock and, to a lesser extent, abscisic acid, but not excess metals, including copper. Its response to sucrose starvation was transient and different from OsMT-1, a type 1 metallothionein-like gene of rice inducible by copper. These results suggest that while OsMT-2 is also involved in cellular response to stress, its function may be complementary to that of OsMT-1.

A high cholesterol, (n-3) polyunsaturated fatty acid diet induces hypercholesterolemia more than a high cholesterol (n-6) polyunsaturated fatty acid diet in hamsters

This study was designed to study the effects of (n-3) polyunsaturated fatty acids (PUFA) on plasma and liver lipids, particularly lipoprotein cholesterol concentrations, in hamsters. Diets rich in (n-3) PUFA (21 g/100 g fatty acid) or (n-6) PUFA (37.4 g/ 100 g fatty acid) with or without 5 g/kg cholesterol (C) supplements were given for 4 wk to male hamsters weighing 70-90 g. The VLDL- and (IDL + LDL)-cholesterol concentrations were 114 and 128% higher in hamsters fed the (n-3) PUFA + C diet than in those fed the (n-6) PUFA + C diet. However, these differences were not observed when cholesterol was not supplemented. Hamsters fed the (n-3) PUFA diet had significantly lower plasma and hepatic triglyceride concentrations than those fed the (n-6) PUFA diet. Concentrations were comparable in hamsters fed (n-6) PUFA + C and (n-3) PUFA + C. Hepatic cholesteryl esters were significantly lower, while hepatic microsomal acyl-CoA:cholesterol acyltransferase activity and VLDL cholesteryl esters were significantly higher in hamsters fed the (n-3) PUFA + C diet than in those fed the (n-6) PUFA + C diet. Our results demonstrate that elevation of VLDL- and (IDL + LDL)-cholesterol in hamsters by (n-3) PUFA, compared with (n-6) PUFA, is dependent on dietary cholesterol supplementation and may be due to decreased catabolism of these lipoproteins.

Effects of fish oil and safflower oil emulsions on diet-inducedhepatic steatosis in rats receiving total parenteral nutrition

This study was conducted to investigate the effects of fish oil and safflower oil emulsions in total parenteral nutrition (TPN) solutions on diet-induced hepatic steatosis. Rats were divided into a control group (C, n = 6) and four experimental groups (A, B, S, F, n = 11 approximately 14). The control group was fed a chow diet whereas the experimental groups received a high fat (15%, w/w) diet containing 0.1% (w/w) cholesterol. Group A received the high fat diet for 4 weeks, and was killed at the end of the fourth week to ensure that hepatic steatosis had occurred. Groups S and group F received TPN with safflower oil or fish oil emulsions, respectively, for 1 week following experimental diet feeding for 4 weeks. Group B was fed a limited amount of the high fat diet, without cholesterol, for 1 week following 4 weeks of experimental diet in order to maintain the same body weight and cholesterol intake as the TPN groups. Diet-induced hepatic steatosis was observed in the experimental groups. Fat deposition was reversed when the total caloric and cholesterol intake was reduced. Fish oil infusion ameliorated the severity of hepatic steatosis, whereas safflower oil had no effect on liver fat deposition. These results suggest that TPN with fish oil emulsions may be beneficial to patients with diet-induced hepatic steatosis.

Effects of fat emulsions with different fatty acid composition on plasma and hepatic lipids in rats receiving total parenteral nutrition

Effects of different fatty acids on the development of hepatic steatosis were studied in rats receiving total parenteral nutrition (TPN). 65 rats, with internal jugular catheters, were divided into one control group (n = 8), and four experimental groups (n = 13-15 each). The control group was fed a chow diet and all experimental groups received TPN. TPN provided 300 kcal/kg/day with 40% of the non-protein energy provided as fat. All TPN solutions were isonitrogenous and identical in nutrient composition except for the fatty acid composition of the fat emulsion. Four kinds of fat emulsions rich in: 1) medium chain fatty acids (C8:0,C10:0), 2) oleic acid (C18:1 n-9), 3) linoleic acid (C18:2 n-6), 4) eicosapentaenoic acid (C20:5 n-3)/docosahexaenoic acid (C22:6 n-3), were used. These fat emulsions were prepared with: 1) a mixture of medium chain triglycerides (MCT) and soybean oil (9:1), 2) olive oil, 3) safflower oil, 4) fish oil, respectively. The results of the study demonstrated a higher hepatic lipid content in the olive oil and safflower oil groups than in the control group, whereas no significant difference was seen between the MCT and control groups. Also, no difference was observed between the fish oil and control groups. With regard to the plasma lipids, the MCT group and olive oil group produced hyperlipidaemia. The plasma of the safflower oil and fish oil groups, however, had a low lipid concentration comparable to the control group. These results suggest that TPN with a fat emulsion prepared with fish oil does not cause hyperlipidaemia nor induce hepatic steatosis in normal rats.

Lipoprotein responses to fish, coconut and soybean oil diets with and without cholesterol in the Syrian hamster

Thirty-six young male Syrian hamsters were fed with test diets containing coconut oil, soybean oil or fish oil with and without 0.5% cholesterol for 6 weeks. Without dietary cholesterol supplementation, animals on the fish oil diet had significantly lower plasma total triglyceride (TG) and total cholesterol than those on the coconut oil or soybean oil diet. The decrease of TG was seen mainly in the very low density lipoprotein (VLDL) fraction. The degree of decrease in cholesterol was similar in all of the lipoprotein fractions. With 0.5% dietary cholesterol supplementation, there was no significant difference in plasma TG level among the three dietary groups. However, the fish oil group had significantly higher plasma cholesterol than the coconut oil and soybean oil groups. The increase of cholesterol was mainly in the VLDL and low density lipoprotein (LDL) fractions. In contrast to the plasma cholesterol level, the hepatic cholesteryl ester content was significantly lower in the cholesterol-supplemented fish oil group than in the coconut oil and soybean oil counterparts. The cholesterol-supplemented fish oil group showed higher liver microsomal acyl-coenzyme A:cholesterol acyltransferase activity than the other two groups, while there was no significant difference in the excretion of fecal neutral and acidic sterols among the three dietary groups.

Effects of L-glutamine on induced hepatosteatosis in rats receiving total parenteral nutrition

Glutamine (Gln) supplementation in total parenteral nutrition (TPN) has been shown to have a preventive effect on high glucose induced hepatic steatosis. This animal study was undertaken to evaluate whether Gln could prevent hepatic steatosis induced by high fat or high glucose infusion. After placement of internal jugular catheters, rats were divided into three groups: control (n = 8), high fat (n = 13) and high glucose (n = 14) groups. The control group was fed with a chow diet and infused with saline alone. The experimental groups were infused with either a high fat (65% of nonprotein calories) or high glucose (83% of total kilocalories) solution. Energy intake was 35 kcal/100 g body weight per day. TPN solutions were isocaloric, isonitrogenous and isovolemic. Each experimental group was divided into two subgroups, with one receiving a Gln supplement to replace 40% of total amino acid nitrogen. The results demonstrated obvious fatty infiltration in the experimental groups, mainly from triglyceride (TG) accumulation. Plasma very low density lipoprotein-triglyceride (VLDL-TG) was significantly lower in the experimental groups than in the control group, suggesting that liver secretion of TG may have been inhibited in the experimental groups. Liver fatty acid synthetase (FAS) activity and plasma free fatty acid were lower in the high fat group than in the control and high glucose groups. There was no difference in hepatic lipids content, FAS activity, VLDL-TG, hepatic uptake of fatty acids and liver histologic change in the subgroups with and without Gln supplementation. Thus, Gln supplementation in a TPN solution has no effect in preventing hepatic steatosis induced by either high glucose or high fat infusion in rats under these experimental conditions.

Sources of triacylglycerol accumulation in livers of rats fed a cholesterol-supplemented diet

The source of free fatty acids (FFA) and the pathways contributing to the accumulation of neutral fats in livers of rats fed a cholesterol-enriched diet were investigated in this report. Supplementation with 1% cholesterol in the diet for four weeks resulted in hepatomegaly in the rats. The contents of cholesterol and triacylglycerols (TG) per gram liver measured in rats fasted overnight increased by 48 mg (approximately tenfold) and 66 mg (approximately fourfold), respectively. The activities of glycerophosphate acyltransferase and diacylglycerol acyltransferase, the two key enzymes for TG synthesis in liver microsomes, were found to increase by 23 and 19%, respectively, in the cholesterol-fed rats. The secretion of plasma TG present predominantly in very low density lipoprotein was found to decrease by approximately 30%. The incorporation of tritium from tritiated water in liver FFA increased by twofold in rats fed the cholesterol-supplemented diet, whereas the activity of CPT I in liver mitochondria decreased by 23%. The uptake of plasma FFA in vivo in livers of fasted rats maintained on the cholesterol-supplemented diet decreased by 60%. Our data thus indicate that the excess TG accumulated in livers of rats fed the cholesterol-enriched diet resulted from increased synthesis and decreased secretion of TG. To meet the demand of fatty acids for this purpose, de novo lipogenesis increased, whereas beta-oxidation decreased. Although difference in the uptake of extrahepatic FFA may be discounted, a difference in the uptake of chylomicron remnants between the control and cholesterol-fed rats may not be ruled out.

A novel stress-inducible metallothionein-like gene from rice

A novel rice genomic sequence encoding coding segments homologous to other metallothionein-like genes was isolated from Oryza sativa genomic library. This sequence, hereby designated as rgMT (rice genomic metallothionein-like gene), consists of two exons and one intron. From the coding sequence, it is predicted that rgMT encodes one protein of 74 amino acids. Differential expression of rgMT in rice plants was observed as mature transcripts were more abundant in roots than in leaves and sheaths. Under different stress conditions, such as excess heavy metals and heat shock, expression of rgMT was significantly elevated. This was especially noticeable with 250 microM CuCl2 for 16 h, 40 degrees C heat for 2 h and 0.06% DMSO for 1 h. Under sucrose starvation, rgMT transcripts also increased with time up to 72 h. During recovery from sucrose starvation, the transcripts declined slightly within 12 h of recovery. rgMT transcripts were also seen to have increased expression in senescent leaves. These results support the notion that rgMT is a stress-inducible gene in rice heretofore unreported.

The effects of apolipoprotein E polymorphism on the distribution of lipids and lipoproteins in the Chinese population

The effects of apolipoprotein E (apo E) polymorphism on the distribution of serum levels of total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) were studied in 546 unrelated Chinese in Taiwan. By isoelectric focusing and immunoblotting, three common alleles were demonstrated. The frequencies of the epsilon 2, epsilon 3 and epsilon 4 alleles were 0.076, 0.875 and 0.049, respectively. The relative frequency of the epsilon 3 allele was higher than that in Caucasians, whereas the frequency of epsilon 4 was lower in the Chinese population. Individuals with apo E4/4 phenotype had the highest serum TC and LDL-C concentrations, while the lowest levels were associated with apo E2/2 phenotype. There was a trend for individuals carrying the epsilon 2 allele to have a higher HDL-C level. No relationship between apo E phenotype and TG level was observed in this study. These data indicated that a given apo E allele acted in a relatively similar way in determining individual differences between Chinese and Caucasian populations in serum lipid and lipoprotein.

Transcripts of metallothionein genes in Arabidopsis thaliana

Using oligonucleotides with highly conserved cysteine-rich codons as probes, we isolated from a lambda YES Arabidopsis thaliana cDNA library two different sequences, each encodes an unique protein. These proteins, hereby designated as AtMT-q (AtMT-2) and AtMT-k (AtMT-1), are characteristic of metallothionein, carrying 13 and 14 cysteines in a total of 45 and 81 amino acids, respectively.

Replacement of all alpha-domain lysines with glutamates reduces metallothionein detoxification function

Mammalian metallothioneins (MTs) possess eight highly conserved lysine residues, including three in each of two metal binding domains. We used site-directed mutagenesis to replace these intradomain lysines in Chinese hamster ovary MT2 with glutamic acid and/or glutamine. These mutant MTs were expressed in a metal sensitive yeast host. One mutant which had all three lysines in the alpha-domain replaced by glutamates (K43,51,56E) exhibited a reduced ability, relative to native MT, to protect yeast transformants against otherwise toxic levels of cadmium. This triply substituted mutant also exhibited anomalous migration on a non-denaturing gel relative to wild type MT and other MT lysine mutants, suggesting that the intradomain lysines are important in maintaining the conformational integrity of MT.

Substitution of glutamic acids for the conserved lysines in the alpha domain affects metal binding in both the alpha and beta domains of mammalian metallothionein

Lysine residues are highly conserved in mammalian metallothioneins (MTs). Recombinant mutant Chinese hamster MT2 in which all of the lysines (K) in the alpha-domain were substituted by glutamic acids (E) was assayed with, expressed in and purified from a cadmium sensitive strain of yeast Saccharomyces cerevisiae. Circular dichroism analyses of the mutated protein, mutein K43,51,56E, revealed that the overall structure remained unchanged. However, a 1-D 113Cd NMR study detected significant differences in the chemical shifts of the corresponding resonances between wild type protein and the recombinant mutein. Reduction of integrated intensity in the NMR spectra was also observed for resonances from the four-metal cluster (I and V-VII) in the alpha-domain of the mutein. At various temperatures, facile intermolecular exchange of metals in the beta-domain of the mutein was also observed, which was unexpected and was different from wild type. Our results thus demonstrate that replacing all three lysines by glutamic acids in the alpha-domain changed metal-thiolate interactions in both domains of the recombinant mutein. This may explain the reduced ability of the mutein to convey cadmium resistance. We propose that while the lysine residues in the alpha-domain of wild type MT are not critical for maintaining protein structure, they play a role in regulating the microenvironment and stability of both metal-binding clusters, a feature critical to metal detoxification.

Effect of L-glutamine on hepatic lipids at different energy levels in rats receiving total parenteral nutrition

The effect of glutamine on hepatic steatosis and serum amino acid pattern was studied in rats receiving total parenteral nutrition (TPN) with different levels of caloric intake. Rats were divided into four groups; a control group (n = 10) was fed a chow diet and infused with saline only. Three experimental groups (n = 8 to 10) received TPN solutions at energy levels of 25 kcal, 30 kcal, and 35 kcal/100 g body weight, respectively. The experimental groups were maintained with TPN for a period of 6 days. Each experimental group was divided into two subgroups, one of which was supplemented with glutamine, replacing 40% of the total amino acid nitrogen. All of the basal TPN solutions were isonitrogenous and identical in nutrient composition, except for the difference in energy level, which was adjusted with glucose. The results demonstrated that liver fat increased in accordance with the increase of glucose supply, and this increase was mainly due to triglyceride accumulation. Very-low-density lipoprotein-triglyceride and serum free fatty acid were significantly higher in the 30-kcal groups. There were no differences in hepatic lipid content, very-low-density lipoprotein-triglyceride secretion, or hepatic uptake of fatty acids between subgroups with and without glutamine supplementation. It was concluded that glutamine enrichment of a TPN solution did not have any effect on hepatic steatosis in normal rats.

Cellular interactions implicated in the mechanism of photoreceptor degeneration in transgenic mice expressing a mutant rhodopsin gene

Photoreceptors of transgenic mice expressing a mutant rhodopsin gene (Pro347-->Ser) slowly degenerate. The mechanism of degeneration was studied by aggregation of embryos of normal and transgenic mice to form chimeras. In these chimeras, mosaicism was observed in the coat color, retinal pigment epithelium, and retina. In the retina, the genotype of adjacent patches of normal and transgenic photoreceptors was determined by in situ hybridization with a transgene-specific RNA probe. Photoreceptors in the chimeric retina degenerated uniformly, independent of the genotype and similar to the photoreceptors in transgenic mice. However, the chimeric retinas showed varying proportions of normal and transgenic cells. The chimeric retina with a nearly even proportion of normal and transgenic photoreceptors displayed uniform but slower degeneration than that observed in a transgenic mouse of the same age. Our results demonstrate non-autonomy of gene action for the mutated rhodopsin gene and imply that cellular interactions between photoreceptors in the retina probably play a role in degeneration.

Metallothionein detoxification function is impaired by replacement of both conserved lysines with glutamines in the hinge between the two domains

Mammalian metallothioneins (MTs) possess eight highly conserved lysine residues, two of which constitute the hinge between two metal binding domains. By site-directed mutagenesis and recombinant DNA techniques, we replaced the interdomain lysines in Chinese hamster ovary MT2 with all possible combinations of glutamic acid and/or glutamine. The resultant MTs were expressed and assayed for detoxification function in a transformed yeast system. Results showed that these mutant MTs, like the native protein, bound seven atoms of divalent metal per molecule and conferred cadmium resistance to a metal-sensitive yeast host. Replacement of one or both of the lysines in the interdomain region was inconsequential to the structure and function of MT, unless both substituted residues were uncharged. When both lysines were replaced by glutamine (K30,31Q), a reduction in the ability of MT to protect yeast transformants against otherwise toxic levels of cadmium was observed. This diminished metal detoxification capacity was due to a decrease in the steady-state level of MT. These results suggest that at least one charged amino acid must be present in the hinge for the proper expression of MT.

[Change and effect of Epstein Barr virus (EBV) antigen induced T8 cells in nasopharyngeal carcinoma patients and EBV seropositive individuals]

T8 cells from peripheral blood mononuclear cells (PBMC) of nasopharyngeal carcinoma (N PC) patients, IgA/VCA positive and negative normal individuals were induced by Epstein Barr virus (EBV) antigen, and their effects on the EBV infected auto-PBMC were observed. The data showed: after PBMC were induced by EBV antigen for 5 days, the T8 cells increased in the all three groups, but less remarkably in NPC group than in the other two groups. The T8 cells induced by EBV antigen could inhibit the activation, proliferation and differentiation of EBV infected auto-B cells in IgA/VCA positive and negative groups. But they had an enhancing effect in NPC group. The results suggest that the production of these cells was reduced and their function altered in NPC patients. Therefore it may be related to the enhancement of EBV activated B cells.

Foods predictive of nutrient intake in Chinese diet in Taiwan: I. Total calories, protein, fat and fatty acids

Dietary consumption data obtained by food weighing for 539 households in Taiwan in 1980-1981 were used to search for foods predictive of nutrient intake. The average per capita nutrient intake in each household was calculated for total calories, protein, fat and fatty acids (saturated fatty acids, oleic acid and unsaturated fatty acids). Stepwise multiple regression analysis was carried out to reveal the relative importance of each of 405 food items in the dietary survey data for predicting nutrient intake. We found that as few as seven to 20 food items could account for a large proportion of the variability of macronutrient intake in this population. These lists of foods were the minimum needed to categorize an individual's nutrient intake for epidemiological studies in Taiwan. The types and amounts of cooking oils (important predictors of fat and calories) added to the dishes were found to vary from family to family, and should be considered in designing dietary questionnaires for Chinese in other societies.

Foods predictive of nutrient intake in Chinese diet in Taiwan: II. Vitamin A, vitamin B1, vitamin B2, vitamin C and calcium

Dietary consumption data obtained by food weighing for 539 households in Taiwan in 1980-1981 were used to search for predictor foods of individual intake of several vitamins and calcium. Stepwise multiple regression analysis was carried out on food items that were univariately and significantly associated with nutrient intakes, to screen for the important predictors. Less than ten foods were enough to explain more than 90% of the interperson variation for vitamin A, vitamin B1, and vitamin B2. For vitamin C and calcium, 20 food items could explain only 87% of the variation. Salt, brown sugar, and soy bean sauce were selected among calcium predictors. The information on foods predictive of nutrient intake is useful in designing food frequency questionnaires and materials for nutrition education. Although this paper provides such information for Chinese living in Taiwan, some issues described (such as the need to assess spices) may have been overlooked and could be generalized to populations using stir-frying as a major cooking method.

The complete nucleotide sequence of the Crossostoma lacustre mitochondrial genome: conservation and variations among vertebrates

The complete mitochondrial (mt) genome of Crossostoma lacustre, a freshwater loach from mountain stream of Taiwan, has been cloned and sequenced. This fish mt genome, consisting of 16558 base-pairs, encodes genes for 13 proteins, two rRNAs, and 22 tRNAs, in addition to a regulatory sequence for replication and transcription (D-loop), is similar to those of the other vertebrates in both the order and orientation of these genes. The protein-coding and ribosomal RNA genes are highly homologous both in size and composition, to their counterparts in mammals, birds, amphibians, and invertebrates, and using essentially the same set of codons, including both the initiation and termination signals, and the tRNAs. Differences do exist, however, in the lengths and sequences of the D-loop regions, and in space between genes, which account for the variations in total lengths of the genomes. Our observations provide evidence for the first time for the conservation of genetic information in the fish mitochondrial genome, especially among the vertebrates.

Effects of dietary supplementation with fish oil on prostanoid metabolism during acute coronary occlusion with or without reperfusion in diet-induced hypercholesterolemic rabbits

We studied the changes in myocardial and aortic concentrations of prostacyclin and thromboxane A2 during acute coronary occlusion with or without reperfusion in rabbits fed with a cholesterol-enriched diet with or without fish oil supplementation for a short (5 days) or long period (6 weeks). New Zealand white male rabbits were divided into 5 groups: Group I, 15 control rabbits fed with a laboratory standard rabbit chow. In addition to the standard chow, the 4 study groups were treated with cholesterol or fish oil. Group II, 17 rabbits fed with a 1% high cholesterol diet for 5 days. Group III, 16 rabbits fed with a diet containing 1% cholesterol and 10% fish oil for 5 days. Group IV, 17 rabbits fed with the same diet as group II for 6 weeks. Group V, 18 rabbits fed with the same diet as group III for 6 weeks. Each group of rabbits was randomly divided into the coronary occlusion or occlusion-reperfusion mode of experiment. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h. Subsequent reperfusion for 4 h was performed in the occlusion-reperfusion rabbits. The aortic tissue above the aortic valve and the ischemic and normal (nonischemic) areas of the left ventricle were excised for the measurement of 6-keto-PGF1 alpha and thromboxane B2 levels by radioimmunoassay. Both during coronary occlusion and occlusion-reperfusion, rabbits showed higher myocardial concentrations of 6-keto-PGF1 alpha and thromboxane B2 in the ischemic area than in the normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy requirements in response to high protein feeding in young male adults

Two experiments were conducted to investigate the effects of moderate (MPI) and high (HPI) levels of protein intake on energy utilization in 12 healthy young male adults who were confined to a metabolic unit for 56 days. The amount of energy supplied was adjusted so that the subjects could maintain a relatively constant body weight, which was used as the criterion to see whether the body was under an energy balance. All foods were supplied in conventional style. In the first experiment, six young men were given a diet of 1.18 g (MPI) and 1.74 g (HPI) protein/kg of body weight/day in consecutive periods. In the second experiment, another six young men were studied at a protein intake of 1.08 g (MPI) and 2.00 g (HPI)/kg/day. The results indicate that both energy intake and energy expenditure are independent of protein intake. The average gross energy intake of the subjects was between 2,300 to 3,240 kcal/day, corresponding to a light-to-moderate grade of energy expenditure. The efficiency of energy utilization did not differ significantly between the moderate and high levels of protein intake in adults.

Effects of excess protein intake on nitrogen utilization in young men

The efficiency of nitrogen (N) utilization was studied in 12 young male subjects. Protein intake levels were adjusted from moderate (1.08 and 1.18 g protein/kg/day) to high (1.74 and 2.00 g protein/kg/day). All of the food was supplied in the form of a normal mixed Chinese diet. Six subjects were admitted to a metabolic unit at a time for 56 days, in two consecutive periods. The results indicate that a higher protein intake causes more N excretion in urine and feces. Biologic value (BV) and net protein utilization (NPU) were markedly decreased during the high protein intake (HPI) period. However, a significant increase in the N balance was found in the presence of excessive protein intake. Digestibility of protein seemed to increase during the HPI period, with the apparent digestibility of the dietary protein being about 83% to 90%. We conclude from this study that excessive N intake reduces the efficiency of N utilization, but still results in a positive N balance in adult human subjects.

Effects of dietary supplementation with fish oil on atherosclerosis and myocardial injury during acute coronary occlusion-reperfusion in diet-induced hypercholesterolemic rabbits

We studied myocardial injury during acute coronary occlusion-reperfusion and atherosclerosis in rabbits fed a high cholesterol diet with or without fish oil supplementation. New Zealand white male rabbits were divided into 3 groups. Eight control rabbits fed with laboratory standard rabbit chow were group I. In addition to the standard chow, 15 rabbits fed with a 1% cholesterol-enriched diet for 6 weeks were group II, and 10 rabbits fed with a 1% cholesterol-enriched and 10% fish oil supplemented diet for 6 weeks were group III. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h, followed by reperfusion for 4 h. Myocardial injury was assessed by tissue creatine kinase activities and amino-nitrogen concentrations from the ischemic (infarct) and nonischemic (normal) myocardium, and the infarct area/risk area ratios of the left ventricle. The surface area of the atherosclerotic lesions of the aorta and pulmonary artery was measured by planimeter. There was significantly more myocardial loss of creatine kinase and amino-nitrogen in the cholesterol-fed rabbits than the controls (p less than 0.01 and 0.02, respectively). The cholesterol and fish oil-treated rabbits had a nonsignificant reduction in myocardial loss of both agents as compared to their corresponding cholesterol-fed ones. The same trend was also found in the infarct area/risk area ratio. Fish oil treated rabbits had a good effect on the reduction of atherosclerotic lesions and tissue cholesterol levels in the aorta and pulmonary artery, but not in the left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effect of adrenalectomy on rat liver metallothionein mRNA levels in basal and stress conditions

Liver metallothionein (MT) mRNA and serum MT levels of adrenalectomized (ADX) and sham-ADX rats in basal and stress (1, 3 or 6 h of restraint) conditions have been measured. Serum MT levels were overall lower in ADX than in sham-ADX rats. Basal liver MT mRNA levels were increased in ADX rats, suggesting that glucocorticoids have an inhibitory role on the regulation of liver MT synthesis. In contrast, liver MT mRNA levels were increased by stress in sham-ADX but not in ADX rats, suggesting a stimulatory role for glucocorticoids. These results suggest that glucocorticoids have a different role in liver MT regulation depending on the physiological situation.

Mutation of invariant cysteines of mammalian metallothionein alters metal binding capacity, cadmium resistance, and 113Cd NMR spectrum

Using a yeast expression vector system, we have expressed both wild type and six mutated Chinese hamster metallothionein coding sequences in a metal-sensitive yeast strain in which the endogenous metallothionein gene has been deleted. The mutant proteins have single or double cysteine to tyrosine replacements (C13Y, C50Y, and C13,50Y), single cysteine to serine replacements (C13S and C50S), or a single cysteine to alanine replacement (C50A). These proteins function in their yeast host in cadmium detoxification to differing extents. Metallothioneins which contain a cysteine mutation at position 50 (C50Y, C50S, C50A, and C13,50Y) conferred markedly less cadmium resistance than wild type metallothionein, or metallothionein with a single cysteine mutation at position 13 (C13Y and C13S). Wild type and three of the mutant Chinese hamster metallothioneins (C13Y, C50Y, and C13,50Y) were purified from yeast grown in subtoxic levels of either CdCl2 or 113CdCl2. All three of the mutant proteins bound less cadmium than the wild type protein when metal-binding stoichiometries were determined. The one-dimensional 113Cd NMR spectrum of the recombinant wild type Chinese hamster metallothionein was compared to the spectra of native rat and rabbit liver metallothioneins. The close correspondence between the 113Cd chemical shifts in these metallothioneins is consistent with the presence of two separate metal clusters, A and B, corresponding, respectively, to the alpha- and beta-domains, in the recombinant metallothionein. The one-dimensional 113Cd NMR spectra recorded on each of the three mutant metallothioneins, on the other hand, provide some indication as to the structural basis for the reduced, by one, metal stoichiometry of each of the mutant metallothioneins. For the C13Y mutant, it appears that the beta-domain now binds a total of two metal ions whereas with the C50Y mutant, the alpha-domain appears metal-deficient. For the double mutant, C13,50Y, the 113Cd resonances are indicative of major structural reorganizations in both domains.

Molecular cloning of Chinese hamster metallothionein II gene and its 5' flanking region

A genomic DNA clone containing Chinese hamster metallothionein II (MTII) gene and its 5' flanking region was isolated from Cd resistant Chinese hamster ovary (CHO) cells. DNA sequence analysis showed that there are three exons and two introns in the structure of the MTII gene. Further characterization of the 5' flanking region reveals the possible transcription initiation site, metal responsive element and basal-level enhancer sequence. Putatively, this is the promoter region of CHO MTII gene.

Effect of cysteine replacements at positions 13 and 50 on metallothionein structure

Recombinant wild-type and mutant Chinese hamster metallothioneins, purified from the yeast Saccharomyces cerevisiae, were analyzed for their chemical and spectroscopic properties. The mutant proteins contain cysteine to tyrosine replacements at positions 13 and 50. Wild-type and mutant metallothioneins, in their cadmium-bound forms, all showed characteristic ultraviolet absorption spectra with shoulders at 245-250 nm due to cadmium-thiolate charge transfer. Upon acidification, these absorption shoulders were abolished. In all cases, two distinct titrations were seen, presumably corresponding to two independent cadmium binding domains in each of the proteins. Analysis of domain structures was performed both with the sulfhydryl reagent 5,5'-dithiobis(2-nitrobenzoic acid) and with the protease subtilisin. These studies indicated that both mutations affected domain structure by disrupting the normally tight protein clusters. Circular dichroism spectra obtained for wild-type and mutant metallothioneins showed unique structural rearrangements in mutants containing a cysteine-50 to tyrosine alteration. These data, along with previously obtained 113Cd NMR data, were incorporated into a model which can account for the in vivo and in vitro properties of these mutant proteins.

Differential effect of cysteine-to-serine substitutions in metallothionein on cadmium resistance

A set of mutant coding sequences for Chinese hamster metallothionein (MT) 2 in which codons for individual cysteines were replaced by serine codons was cloned into a yeast expression system. MT gene expression was placed under control of a constitutive promoter on a multicopy Escherichia coli-yeast shuttle vector. MTs were expressed in a metal-sensitive host that lacks the endogenous MT gene. The expressed MTs conferred increased metal resistance to the yeast host. A sensitive assay for cadmium resistance was developed in which population doubling times were monitored in rich liquid medium supplemented with a sublethal dose of CdCl2. Measurements on mutants with single cysteine replacements at 12 positions revealed two mutant classes. One class (Cys----Ser at position 5, 13, 19, or 33) did not affect the detoxification capacity of MT. A second class (Cys----Ser at position 7, 15, 26, 29, 44, 48, 50, or 60) conferred to the host markedly less resistance to cadmium. Bridging cysteines were more critical to cadmium resistance. All five bridging cysteine mutants studied (at positions 7, 15, 44, 50, and 60) conferred lower cadmium resistance. In contrast, mutation of four out of seven terminal cysteines (at position 5, 13, 19, or 33) was shown to be inconsequential. Mutations tend to be more detrimental in the alpha domain than in the beta domain in conveying cadmium resistance, suggesting that the contribution of individual cysteine to the detoxification function of MT is site specific.