Inhibitory Effects of Trientine, a Copper-Chelating Agent, on Induction of DNA Strand Breaks in Kidney Cells of Long-Evans Cinnamon (LEC) Rats.

The effects of treatment with trientine, a specific copper-chelating agent, on the accumulation of copper and induction of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson's disease. Copper accumulated in the kidneys of LEC rats in an age-dependent manner from 12 to 18 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, renal copper contents did not increase and were maintained at the same levels as those in 4-week-old LEC rats. Estimation of the amounts of DNA single-strand breaks (SSBs) by comet assay showed that SSBs of DNA were induced in a substantial population of LEC rat renal cortex cells around 12 weeks of age and that the amounts of SSBs increased in an age-dependent manner from 12 to 18 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, the observed number of cells with DNA damage decreased, suggesting that induction of SSBs of DNA was inhibited and/or SSBs were repaired during the period of treatment with trientine. The results show that SSBs of DNA in LEC rat kidney cells are induced prior to occurrence of clinical signs of hepatic injury and that treatment of LEC rats with trientine decreases the number of DNA strand breaks.     

Inhibitory effects of trientine, a copper-chelating agent, on induction of DNA strand breaks in hepatic cells of Long-Evans Cinnamon rats

Effects of treatment with trientine, a specific copper-chelating agent, on accumulation of copper and induction of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson's disease. Copper accumulated in the livers of LEC rats in an age-dependent manner from 4 to 13 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, hepatic copper contents did not increase and were maintained at the same levels as those in 10-week-old LEC rats. When the amounts of DNA single-strand breaks (SSBs) were estimated by a comet assay, SSBs of DNA were induced in a substantial population of LEC rat hepatic cells around 8 weeks of age and the amounts of SSBs increased in an age-dependent manner from 8 to 15 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, the observed number of cells with DNA damage decreased dramatically, suggesting that induction of SSBs of DNA was inhibited and/or SSBs were repaired during the period of treatment with trientine. The results show that treatment of LEC rats with trientine decreases the number of DNA strand breaks observed, although copper contents remain high in the liver.     

Abnormal hepatobiliary and circulating lipid metabolism in the Long-Evans Cinnamon rat model of Wilson's disease

Long-Evans Cinnamon (LEC) rats exhibit a genetic defect in Atp7b gene, which is homologous to the human Wilson's disease gene, resulting in an inability to mobilize copper from the liver. This study was undertaken to gain insight into the relationship between liver copper accumulation and plasma lipid profile, circulating lipoprotein composition, hepatic sterol metabolism and biliary lipid secretion rates in 12-week-old LEC rats compared to control Long-Evans rats. Concomitant with hepatic copper deposition, LEC rats displayed increased content of triglycerides (TGs), free cholesterol (FC) and cholesteryl ester (CE) in the liver. Hepatic concentrations of malondialdehyde (MDA), an index of lipid peroxidation were also significantly elevated in LEC rats (50%). This steatosis was associated with aberrant microsomal apolipoprotein (apo) B-100 and microsomal triglyceride transfer protein (MTP) content, hypotriglyceridemia, hypocholesterolemia and abnormalities in both circulating lipoprotein composition and size. Atypical hepatobiliary sterol metabolism was established by the assessment of the activity of key intracellular enzymes for cholesterol homeostasis, which demonstrated, with respect to controls, a 40% reduction in 3-hydroxy-3-methylglutaryl coenzyme A reductase, a 30% reduction in cholesterol 7alpha-hydroxylase, and a 54% reduction in acyl CoA:cholesterol acyltransferase. During a 6-h biliary drainage, a decline in the bile acid output was recorded and might be linked to the low protein expression of the bile salt export pump (BSEP or ABCB11). Our data emphasize the crucial role of copper balance in hepatic sterol homeostasis and lipoprotein metabolism in LEC rats. Additional studies are needed to delineate the mechanisms of these disorders.     

Iron depletion prevents adenine nucleotide decomposition and an increase of xanthine oxidase activity in the liver of the Long Evans Cinnamon (LEC) rat, an animal model of Wilson's disease.

The Long Evans Cinnamon (LEC) rat, which accumulates excess Cu in the liver as in patients with Wilson's disease, is a mutant strain displaying spontaneous hepatitis. It was reported that Fe, like Cu, increases in the liver and that the severity of hepatitis is modified by Fe in the diet. In this experiment, oxidative stress increased by Fe was investigated before the onset of hepatitis. To examine the effect of Fe on the progress into hepatitis, LEC female rats were fed an Fe-regular (Fe 214 microg/g; Fe(+) group) or an Fe-restricted (Fe 14 microg/g; Fe(-) group) diet from 53 days of age for 35 days. Fischer rats were also fed as control animals. Adenine nucleotide decomposition was determined as an index of oxidative stress based on xanthine oxidase activity. The size of the hepatic pool of adenine nucleotides (ATP+ADP+AMP) was significantly smaller in LEC rats than Fischer rats. The energy charge (ATP+0.5ADP)/(ATP+ADP+AMP) was smaller in Fe(+) groups than in Fe(-) groups. In the LEC rat liver, the Fe concentration in the Fe(+) group was 160% of that in Fe(-) group and the correlation coefficient between the hepatic Fe concentration and the energy charge was significant. In this strain, an increase of xanthine oxidase activity resulted in an increase of xanthine, an oxidized metabolite of hypoxanthine in the liver. The results suggest the involvement of the Fe in the progression into hepatitis in the LEC rat, even if the dietary Fe concentration is similar to that of commercial diet.     

Unusual accumulation of copper related to induction of metallothionein in the liver of LEC rats.

Copper (Cu), iron (Fe), zinc (Zn) and manganese (Mn) levels in organs of LEC rats (Long-Evans rats with a cinnamon-like coat color), which develop spontaneous jaundice with hereditary hepatitis, were determined by instrumental neutron activation analysis method. Unusual accumulations of Cu in the liver of LEC rats were found, depending on the age of the animals, the metal concentration being more than approximately 20-40 times those of normal LEA rats (Long-Evans rats with an agouti coat color). Fe and Zn were also accumulated, in addition to Cu, significantly in the LEC rats. The unusual Cu accumulations in the liver of LEC rats were associated with the induction of metallothionein, estimated by radioimmunoassay method, in the liver of LEC rats, rather than that of superoxide dismutase, estimated by electron spin resonance -spin trapping method. These findings suggest that the unusual Cu accumulation in LEC rats is involved in the development of jaundice, hepatic injury and hepatocellular carcinoma.     

Spontaneous cholangiofibrosis in Long-Evans Cinnamon rats: a rodent model for Wilson's disease

The Long-Evans Cinnamon (LEC) rat is a rodent model of Wilson's disease characterized by ceruloplasmin deficiency, hepatic copper accumulation, and hepatocellular injury. So far, the LEC rat appears to be the only strain in which cholangiofibrosis develops spontaneously. The aim of the study reported here was to characterize the time course of development and investigate the structural and ultrastructural features of cholangiofibrosis and their possible relationship to hepatic copper and iron content. The livers of 54 rats (22 males), ages 5 to 113 weeks, were examined by light microscopy and graded for statistical analysis, with respect to extent of replacement of liver tissue by cholangiofibrosis. The study was complemented by electron microscopy, and by measurements of copper and iron contents by atomic absorption spectroscopy. Cholangiofibrosis was present in LEC rats by 20 weeks of age. The hyperplastic biliary epithelial cells varied markedly in size and shape, ranging from flat to cuboidal or elongated. Epithelial cells did not exhibit characteristics of intestinal cells. Some basement membranes had splits, duplications, or multiplications. Cytoplasmic organelles within hyperplastic biliary cells appeared unremarkable in contrast to the characteristic mitochondrial abnormalities present in neighboring hepatocytes. There was a positive correlation between histologic grades of cholangiofibrosis and ages of the animals (r = 0.68, P < 0.001), but no significant correlation between histologic grade and hepatic copper or iron content. We conclude that cholangiofibrosis is the predominant pathologic response to chronic liver injury induced by excess copper in LEC rats. The pathogenic role of copper in the development of cholangiofibrosis requires clearer definition.     

In vivo evidence for accelerated generation of hydroxyl radicals in liver of Long-Evans Cinnamon (LEC) rats with acute hepatitis

The Long-Evans Cinnamon (LEC) rats accumulate excess copper (Cu) in the liver in a manner similar to patients with Wilson's disease (WD) and spontaneously develop acute hepatitis with severe jaundice. Although hydroxyl radicals (*OH) have been proposed to be a cause of hepatitis by the accumulation of Cu, it is not clear whether or not *OH can be produced in the liver of hepatitic LEC rats in vivo and also can be involved in the onset of hepatitis. In the present study, *OH production in plasma and liver of hepatitic LEC rats was quantified by trapping *OH with salicylic acid (SA) as 2, 3-dihydroxybenzoic acid (2, 3-DHBA). The ratios of 2, 3-DHBA/SA were significantly higher in plasma and liver of hepatitic LEC rats than those of Wistar rats and LEC rats showing no signs of hepatitis. Furthermore, the ratios of 2, 3-DHBA/SA in plasma and liver of hepatitic LEC rats were almost the same as those of Wistar rats treated orally with CuSO(4) (0.5 mmol/kg) 2 h before acetylsalicylic acid (ASA) injection. We also evaluated the protective effects of D-mannitol (a *OH scavenger) treatment against acute hepatitis in LEC rats. D-mannitol (500 mg/kg) was administered intraperitoneally to 10-week-old LEC rats for 3 weeks. D-mannitol treatment suppressed the increases in serum aspartate aminotransferase activity and total bilirubin concentration. In addition, D-mannitol treatment significantly reduced hepatic mitochondrial lipid peroxidation, which is thought to be important in the pathogenesis of Cu-induced hepatotoxicity. These observations suggest that accelerated generation of *OH catalyzed by free Cu in the liver may, at least in part, play a role in the pathogenesis of acute hepatitis in LEC rats.     

Copper-metallothionein induction in the liver of LEC rats.

Recently, copper (Cu) was found to be unusually accumulated, suggesting the induction of metallothionein (MT) in the liver of LEC rats (Long-Evans rats with a cinnamon-like coat color), which develop spontaneous jaundice with hereditary hepatitis. Thus, the direct relationship between the unusual Cu accumulation and the induction of Cu-MT was investigated by giving LEC rats Cu-overloaded or Cu-deficient diets. Results based on the determinations of Cu and MT levels in several organs, as well as the gel-filtration profiles of the cytosols of liver homogenates, showed that dietary Cu induced Cu-MT and development of hepatic injury associated with jaundice.     

Study of the origin of urinary porphyrins in experimental hexachlorobenzene-induced porphyria

The activity of the enzyme uroporphyrinogen decarboxylase was determined in the liver and the kidneys of C57BL/6 mice and Wistar albino rats with chronic hexachlorobenzene intoxication and the amount of the deposited uroporphyrin was measured in the both organs. In the control animals the activity of hepatic uroporphyrinogen decarboxylase was several times higher than the renal one. The administration of hexachlorobenzene led to an inhibition of the enzyme activity, which was equally expressed (about 2.5 times) in the liver and kidneys of the both species. The accumulation of uroporphyrin was more pronounced in the hepatic tissue than in the kidneys (about 9 times in mice and 5 times in rats on average). Taking into consideration the much higher uroporphyrin accumulation in the liver, the more active haem biosynthesis in this organ, as well as its larger size, one could accept that the predominant part of the urinary porphyrins in hexachlorobenzene porphyria has a hepatic and not a renal origin.     

Zinc supplementation decreases hepatic copper accumulation in LEC rat

The effect of dietary zinc (Zn) supplementation on copper (Cu)-induced liver damage was investigated in Long-Evans Cinnamon rats (LEC), a model for Wilson's disease (WD). Four-week-old LEC (N=64) and control Long-Evans (LE) (N=32) female rats were divided into two groups; one group was fed with a Zn-supplemented diet (group I) and the other was given a normal rodent diet (group II). LEC rats were killed at 6, 8, 10, 12, 18, and 20 wk of age; the LE control rats were killed at 6, 12, 18, and 20 wk of age. Cu concentration in the liver was reduced in LEC rats fed the Zn-supplemented diet compared with LEC rats on the normal diet between 6 and 18 wk of age. Metallothionein (MT) concentration in the livers of LEC rats in group I increased between 12 and 20 wk of age, whereas hepatic MT concentration in LEC rats from group II decreased after 12 wk. Hepatocyte apoptosis, as determined by TUNEL, was reduced in Zn-supplemented LEC rats at all ages. Cholangiocellular carcinoma was observed only in LEC rats in group II at wk 20. These results suggest that Zn supplementation can reduce hepatic Cu concentration and delay the onset of clinical and pathological changes of Cu toxicity in LEC rats. Although the actual mechanism of protection is unknown, it could be explained by sequestration of dietary Cu by intestinal MT, induced by high dietary Zn content.     

The antioxidant effect of DL-alpha-lipoic acid on copper-induced acute hepatitis in Long-Evans Cinnamon (LEC) rats

The Long-Evans Cinnamon (LEC) rats, due to a genetic defect, accumulate excess copper (Cu) in the liver in a manner similar to patients with Wilson's disease and spontaneously develop acute hepatitis with severe jaundice. In this study we examined the protective effect of DL-alpha-Lipoic acid (LA) against acute hepatitis in LEC rats. LA was administered to LEC rats by gavage in doses of 10, 30 and 100 mg/kg five times per week, starting at 8-weeks-old and continuing till 12-weeks-old. Although LA had little effect against the increases in serum transaminase activities, it suppressed the loss of body weight and prevented severe jaundice in a dose-dependent manner. Antioxidant system analyses in liver showed that LA treatment significantly suppressed the inactivations of catalase and glutathione peroxidase, and the induction of heme oxygenase-1, an enzyme which is inducible under oxidative stress. Furthermore, LA showed dose-dependent suppressive effect against increase in nonheme iron contents of both cytosolic and crude mitochondrial fractions in a dose-dependent manner. Although at the highest dose, LA slightly suppressed the accumulation of Cu in crude mitochondrial fraction, it had no effect on the accumulation of Cu in cytosolic fraction. While LA completely suppressed the increase in lipid peroxidation (LPO) in the microsomal fraction at the highest dose, the suppressive effect against LPO in crude mitochondrial fractions was slight. From these results, it is concluded that LA has antioxidant effects at the molecular level against the development of Cu-induced hepatitis in LEC rats. Moreover, mitochondrial oxidative damage might be involved in the development of acute hepatitis in LEC rats.     

Effects of diphenyl ether herbicides on porphyrin accumulation by cultured hepatocytes

Several diphenyl ether herbicides, such as acifluorfen methyl, have been previously shown to cause large accumulations of the heme and chlorophyll precursor, protoporphyrin, in plants. Lightinduced herbicidal damage is mediated by the photoactive porphyrin. Here we investigate whether diphenyl ether herbicides can affect porphyrin synthesis in rat and chick hepatocytes. In rat hepatocyte cultures, protoporphyrin, as well as coproporphyrin, accumulated after treatment with acifluorfen or acifluorfen methyl. Combination of acifluorfen methyl with an esterase inhibitor to prevent the conversion of acifluorfen methyl to acifluorfen resulted in a greater accumulation of porphyrins than caused by acifluorfen methyl or acifluorfen alone. In vitro enzyme studies of hepatic mitochondria isolated from rat and chick embryos demonstrated that protopor-phyrinogen oxidase, the penultimate enzyme of heme biosynthesis, was inhibited by low concentrations of acifluorfen, nitrofen, or acifluorfen methyl with the latter being the most potent inhibitor. These findings indicate that diphenyl ether treatment can cause protoporphyrin accumulation in rat hepatocyte cultures and suggest that this accumulation was associated with the inhibition of protoporphyrinogen oxidase. In cultured chick embryo hepatocytes, treatment with acifluorfen methyl plus an esterase inhibitor caused massive accumulation of uroporphyrin rather than protoporphyrin or coproporphyrin. Specific isozymes of cytochrome P450 were also induced in chick embryo hepatocytes. These effects were not observed in the absence of an esterase inhibitor. These results suggest that diphenyl ether herbicides can cause uroporphyrin accumulation similar to that induced by other cytochrome P450-inducing chemicals such as polyhalogenated aromatic hydrocarbons in the chick hepatocyte system.     

Porphyrin accumulation in mitochondria is mediated by 2-oxoglutarate carrier

Heme (Fe-protoporphyrin IX), an endogenous porphyrin derivative, is an essential molecule in living aerobic organisms and plays a role in a variety of physiological processes such as oxygen transport, respiration, and signal transduction. For the biosynthesis of heme or the mitochondrial heme proteins, heme or its biosynthetic precursor porphyrin must be transported into mitochondria from cytosol. The mechanism of porphyrin accumulation in the mitochondrial inner membrane is unclear. In the present study, we analyzed the mechanism of mitochondrial translocation of porphyrin derivatives. We showed that palladium meso-tetra(4-carboxyphenyl)porphyrin (PdTCPP), a phosphorescent porphyrin derivative, accumulated in the mitochondria of several cell lines. Using affinity latex beads, we showed that 2-oxoglutarate carrier (OGC), the mitochondrial transporter of 2-oxoglutarate, bound to PdTCPP, and in vitro PdTCPP inhibited 2-oxoglutarate uptake into mitochondria in a competitive manner (Ki = 15 microM). Interestingly, all types of porphyrin derivatives examined in this study competitively inhibited 2-oxoglutarate uptake into mitochondria, including protoporphyrin IX, coproporphyrin III, and hemin. Furthermore, mitochondrial accumulation of porphyrins was inhibited by 2-oxoglutarate or OGC inhibitor. These results suggested that porphyrin accumulation in mitochondria is mediated by OGC and that porphyrins are able to competitively inhibit 2-oxoglutarate uptake into mitochondria. This is the first report of a putative mechanism for accumulation of porphyrins in the mitochondrial inner membrane.     

Accumulation of Copper Induces DNA Strand Breaks in Brain Cells of Long-Evans Cinnamon (LEC) Rats, An Animal Model for Human Wilson Disease.

Copper accumulation and induction of DNA strand breaks were investigated in the brain of Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson disease that is a heritable disease of copper accumulation and copper toxicity in the liver, kidney and brain. Copper contents in the brain of LEC rats increased from 20 weeks of age and were approximately 3.5 to 6 folds higher than those in the brain of WKAH rats at 24 weeks of age. Hepatic copper contents in LEC rats increased from 4 to 12 weeks of age in an age-dependent manner, and then decreased from 16 to 20 weeks of age. Thus, we consider that copper accumulated in the liver was released from severely damaged hepatocytes and deposited in the brain, although copper contents in the brain were 1/20-fold lower than those in the liver. We also evaluated the amounts of DNA single-strand breaks (SSBs) in the brain by comet analysis. The proportions of nuclei in the cerebrum and cerebellum without DNA damage decreased, and nuclei with severe DNA damage appeared in LEC rats at 24 weeks of age. The comet scores of cerebrum and cerebellum cells significantly increased in LEC rats and were significantly higher than those in WKAH rats at 24 weeks of age. The results show that SSBs in LEC rat brain cells are induced at a lower concentration of copper than are SSBs in hepatic cells.     

Oxidative stress and pro-apoptotic conditions in a rodent model of Wilson's disease

Wilson's disease (WD) is an inherited disorder, characterized by selective copper deposition in liver and brain, chronic hepatitis and extra-pyramidal signs. In this study, we investigated changes of biochemical markers of oxidative stress and apoptosis in liver, striatum and cerebral cortex homogenates from Long-Evans Cinnamon (LEC) rats, a mutant strain isolated from Long Evans (LE) rats, in whom spontaneous hepatitis develops shortly after birth. LEC and control (LE) rats at 11 and 14 weeks of age were used. We determined tissue levels of glutathione (GSH/GSSG ratio), lipid peroxides, protein-thiols (P-SH), nitric oxide metabolites, activities of caspase-3 and total superoxide-dismutase (SOD), striatal levels of monoamines and serum levels of hepatic amino-transferases. We observed a decrease of protein-thiols, GSH/GSSG ratio and nitrogen species associated to increased lipid peroxidation in the liver and striatum - but not in the cerebral cortex - of LEC rats, accompanied by dramatic increase in serum amino-transferases and decrease of striatal catecholamines. Conversely, SOD and caspase-3 activity increased consistently only in the cortex of LEC rats. Hence, we assume that enhanced oxidative stress may play a central role in the cell degeneration in WD, at the main sites of copper deposition, with discrete pro-apoptotic conditions developing in distal areas.     

Cytochrome P-450 and chromosome damage by cyclophosphamide in LEC strain rats predisposed to hereditary hepatitis and liver cancer

LEC strain rats predisposed to hereditary hepatitis and liver cancer were examined for hepatic drug-metabolizing ability and the inducibility of chromosome damage by cyclophosphamide (CP) in somatic cells. Whereas the hepatic cytochrome P-450 contents and the activities of cytochrome P-450-catalyzed monooxygenases were lower in females than in males of both LEC and control LEA strains, male LEC rats exhibited significantly reduced cytochrome P-450 contents and monooxygenase activities compared with male LEA rats. When exposed to CP, a promutagen/procarcinogen requiring P-450-dependent metabolic activation, the frequencies of chromosome aberrations and sister-chromatid exchanges (SCEs) in bone marrow cells tended to be lower in females than in males of each strain and lower in LEC than in LEA rats of the same sex. In particular, the CP-induced SCEs were substantially lower in LEC rats. However, no such sex and strain differences were found in the SCE frequencies in regenerating hepatocytes of partially hepatectomized rats exposed to CP.     

Effects of starvation for heme on the synthesis of porphyrins in Escherichia coli

A study is described of the regulation of porphyrin synthesis in Escherichia coli using a heme-permeable, hemH deletion mutant, designated VS212. This strain utilizes only exogenous hemin that is supplied in the medium and accumulates porphyrins since the final step in the synthesis of heme is genetically blocked. It is possible, therefore, to monitor the rate of synthesis of heme by examining the accumulation of porphyrins. Using this system, we found that the rate of production of porphyrins depended on the availability of heme. The lower the concentration of hemin in the medium, the higher the level of porphyrins that accumulated. We next examined the mechanism responsible for the activation of porphyrin synthesis upon starvation for heme. The main activation occurred at the step that leads to the synthesis of 5-aminolevulinic acid (ALA). Starvation for heme induced the expression of a hemA-lacZ fusion gene, as previously reported, but an activation pathway that is independent of the hemA promoter was also identified. We found that starvation for heme caused the stringent response, and such starvation promoted the synthesis of porphyrins without having any effect on the expression of the hemA-lacZ fusion gene. We suggest a model for the regulation of porphyrin synthesis whereby the synthesis of porphyrins is coordinated with that of proteins.     

Porphyrogenic effects and induction of heme oxygenase in vivo by δ-aminolevulinic acid

The effects of single large doses of the porphyrin-heme precursor ?d-aminolevulinic acid on tissue porphyrins and on δ-aminolevulinate synthase and heme oxygenase, the rate-living enzymes of liver heme synthesis and degradation respectively, were studied in the chick embryo in ovo, in the mouse and in the rat. δ-Aminolevulinic acid treatment produced a distinctive pattern characterized by extensive tissue porphyrin accumulation and alterations in these rate-limiting enzymes in the liver. Repression of basal or allylisopropylacetamide-induced liver δ-aminolevulinate synthase was observed and, in the mouse and the rat, induction of liver heme oxygenase after δ-aminolevulinic acid treatment, in a manner similar to the known effects of hemin on these enzymes. In the chick embryo liver in ovo heme oxygenase was substantially higher than in rat and mouse liver, and was not significantly induced by δ-aminolevulinic acid or other compounds, including hemin, CS₂ and CoCl₂. Levulinic acid, an analogue of δ-aminolevulinic acid, did not induce heme oxygenase in mouse liver. δ-Aminolevunilic acid treatment did not impair ferrochelatase activity but was associated with slight and variable decreases in liver cytochrome P-450. Treatment of chick embryos with a small ‘priming’ dose of 1,4-dihydro-3,5-dicarbethoxycollidine, which impairs liver ferrochelatase activity, accentuated porphyrin accumulation after δ-aminolevulinic acid in the liver. These observations indicate that exogenous δ-aminolevulinic acid is metabolized to porphyrins in a number of tissues and, at least in the liver, to a physiologically significant amount of heme, thereby producing an increase in the size of one or more of the heme pools that regulate both heme systhesis and degradation. It is also possible than when δ-aminolevulinic acid is markedly overproduced in vivo it may be transported to many tissues and re-enter the heme pathway and alter porphyrin-heme metabolism in cells and tissues other than those in which its overproduction primarily occurs.     

Effects of starvation for heme on the synthesis of porphyrins in Escherichia coli

A study is described of the regulation of porphyrin synthesis in Escherichia coli using a heme-permeable, hemH deletion mutant, designated VS212. This strain utilizes only exogenous hemin that is supplied in the medium and accumulates porphyrins since the final step in the synthesis of heme is genetically blocked. It is possible, therefore, to monitor the rate of synthesis of heme by examining the accumulation of porphyrins. Using this system, we found that the rate of production of porphyrins depended on the availability of heme. The lower the concentration of hemin in the medium, the higher the level of porphyrins that accumulated. We next examined the mechanism responsible for the activation of porphyrin synthesis upon starvation for heme. The main activation occurred at the step that leads to the synthesis of 5-aminolevulinic acid (ALA). Starvation for heme induced the expression of a hemA-lacZ fusion gene, as previously reported, but an activation pathway that is independent of the hemA promoter was also identified. We found that starvation for heme caused the stringent response, and such starvation promoted the synthesis of porphyrins without having any effect on the expression of the hemA-lacZ fusion gene. We suggest a model for the regulation of porphyrin synthesis whereby the synthesis of porphyrins is coordinated with that of proteins. Received: 28 January 1997 / Accepted: 13 March 1997     

Development of liver regenerative therapy using glycoside-modified bone marrow cells

Several recent studies have reported that bone marrow cells (BMCs) have the ability to generate functional hepatocytes. However, the efficiency at which BMC transplantation generates functional hepatocytes is rather low. We assumed that if BMCs accumulated directly in liver, the functional BMC-derived hepatocytes should increase efficiently. We tried to increase the accumulation of BMCs directly in liver through the interaction between hepatic asialoglycoprotein receptor and desialylated BMCs. Desialylated BMCs were produced with treatment of neuraminidase. Desialylated BMCs that expressed green fluorescent protein (GFP) were injected into Long Evans Cinnamon (LEC) rats, a human Wilson's disease model, intravenously. At 3 and 5 months after transplantation, GFP-expressing hepatocyte nodules appeared in the liver of these BMC-transplanted LEC rats. These findings suggest that the functional BMC-derived hepatocytes can be generated by the direct accumulation of BMCs and that this strategy is new BMC therapy for liver regeneration.