Gene therapy: applications to the treatment of gastrointestinal and liver diseases

There has been much progress in our understanding of molecular mechanisms in the pathogenesis of inherited metabolic disorders. In addition, powerful new molecular techniques have made possible phenotypic alterations by delivery of foreign genes to target cells. As a result, concepts and methods that would have been considered purely science fiction 10 years ago can now be found in human clinical trials engaged in the treatment of these disorders. In this review, we have attempted to provide an introduction and survey of the topic of gene therapy, with specific examples of laboratory and clinical achievements to date, and highlights on potentials for applications in digestive diseases.

Effect of acetylcholine and NMDA on neurones of avian tectum and nucleus isthmi

In the present study the effects of microiontophoretically applied acetylcholine and NMDA were investigated on neurones of the avian nucleus isthmi. Whereas acetylcholine affected equally cell firing in the two parts of the nucleus, the magnocellular (Imc) and the parvocellular (Ipc) division, the effect of NMDA was predominantly confined to Ipc. The NMDA induced firing was specifically blocked by the antagonist CPP, while having no effect on acetylcholine. Our results support earlier findings that isthmo-tectal feedback loops can be modulated by distinct mechanisms in separate divisions of nucleus isthmi.

GABA as an inhibitory transmitter in the pigeon isthmo-tectal pathway

In the present investigation, the effects of inhibitory amino acids and their antagonists were tested on isthmo-tectal projection in the pigeon. The majority of superficial tectal cells are inhibited following stimulation of the parvocellular division of nucleus isthmi. A smaller portion of tectal cells showed excitatory responses followed by an inhibitory period. Both inhibitory mechanisms are blocked by the specific gamma-aminobutyric acid (GABA)-antagonist bicuculline but not by strychnine. Our results support the idea that GABA acts as an inhibitory neurotransmitter in the pigeon isthmo-tectal pathways.

[Quality control of xiaoqinglong mixture]

TLC was used to detect ephedrine, paeoniflorin, glycyrrhizic acid, cinnamic aldehyde and xixin volatile oils in Xiaoqinglong mixture. Paeoniflorin was determined by HPLC. The average recovery is 99.42%, and RSD 0.23%.

[Further studies on the depressor effect of erythrocytic antihypertensive factor]

We previously demonstrated the presence of a long-acting antihypertensive factor (AHF) in the erythrocytes of essential hypertensive subjects (EHS). The present investigation demonstrates further that the AHF is also capable of producing a rapid and transient blood pressure lowering effect in stroke prone spontaneously hypertensive rats (from 26.8 +/- 1.7 to 20.1 +/- 1.5 kPa by 10-30 s, P < 0.001). An even more stronger antihypertensive effect could be found if the AHF prepared from normal subjects or rats was used. We also found that some hypertensive factor was present in EHS plasma, but not in normal subjects. The results of the present paper suggest that AHF deficiency and higher level of pressor substance may play an important role in the development of essential hypertension.

Fate of DNA targeted to the liver by asialoglycoprotein receptor-mediated endocytosis in vivo. Prolonged persistence in cytoplasmic vesicles after partial hepatectomy

After intravenous injection, DNA complexed with asialoglycoprotein-polylysine conjugates is endocytosed by hepatocytes via asialoglycoprotein receptors and is expressed transiently. Long term persistence and expression occurs when partial hepatectomy is performed after gene delivery. To determine the intracellular location of the persisting DNA, we transferred a plasmid expressing bacterial chloramphenicol acetyltransferase into the liver of rats in vivo by asialoglycoprotein receptor-mediated endocytosis. The internalized DNA was measured by Southern blot. Twenty min after administration, 80-85% of the plasmid appeared in the liver, 80% of which was within hepatocytes (12,000-18,000 copies/hepatocyte). In sham-operated control rats, the transgene concentration decreased to 8-12 and 2-4% of the initial levels in 4 and 24 h, respectively, and became undetectable at 7 days. In rats subjected to 66% hepatectomy 20 min after DNA administration, 20, 9, and 7% of the plasmid in the residual liver persisted at 4 h, 24 h, and 7 days, respectively. Liver homogenates were fractionated by differential centrifugation and Percoll gradient centrifugation. In 66% hepatectomized rats, the plasmid persisted in an undegraded, transfection-competent form in plasma membrane/endosome-enriched fractions throughout the duration of the experiment (7 days), indicating that cytoplasmic vesicles are the main site of persistence of the endocytosed DNA.

Molecular characterization of a novel form of (A gamma delta beta)zero thalassemia deletion in a Chinese family

We have identified and molecularly characterized a novel deletion in the beta-globin gene cluster that is associated with elevated fetal hemoglobin in the adult. The propositus is a homozygote from the Yunnan province of China. The deletion spans about 90 kb of DNA and removes the A gamma, delta, and beta-globin genes. The 5' breakpoint of the deletion is located about 0.13 kb upstream from the A gamma-globin gene, whereas the 3' breakpoint is located about 66 kb downstream from the beta-globin gene, about 13 kb upstream from the breakpoint of the Chinese (A gamma delta beta)zero-thalassemia. Heterozygotes for this Yunnanese form of (A gamma delta beta)zero-thalassemia express between 9% and 17% of fetal hemoglobin, whereas the homozygote present with a mild anemia (Hb = 10.7 g/dl). Comparison of the sites of 3' breakpoints of the Yunnanese and the Chinese (A gamma delta beta)zero-thalassemia mutants is compatible with the hypothesis that an enhancer element is located between the 3' breakpoints of these two mutants. Juxta-position to the G gamma gene of this element may be responsible for the efficient gamma-gene expression in the Yunnanese mutant.

Postsynaptic potentials and morphological features of tectal cells in homing pigeons

In this study postsynaptic potentials responding to the electrical stimulation of the optic nerve and the nucleus isthmi pars parvocellularis (Ipc) were intracellularly recorded from 86 tectal cells in pigeons, 13 of which were marked with Lucifer yellow (LY). According to types of postsynaptic potentials and their succession, the postsynaptic responses could be classified into four types: excitatory postsynaptic potential (EPSP)-inhibitory postsynaptic potential (IPSP) sequence (EI type), E, I and IE types. Among them, E or EI responses were mainly produced to the optic nerve stimulation, while the electrical stimulation of the Ipc elicited I responses in more than half the recorded cells. LY-marked tectal cells included five ganglionic cells, four pyramidal cells, two bipolar cells and two stellate cells. The ganglionic cells were mainly located in tectal layers III and IV, whereas the others were in layer II. It appears from both intracellular recordings and fluorescent markings that there is some correlation between the morphological features and the postsynaptic response types of tectal cells.

Targeted transfection and expression of hepatitis B viral DNA in human hepatoma cells

A soluble DNA carrier system consisting of an asialoglycoprotein covalently linked to poly-L-lysine was used to bind DNA and deliver hepatitis B virus (HBV) DNA constructs to asialoglycoprotein receptor-positive human hepatoma cells. 4 d after transfection with surface or core gene expression constructs, HBsAg and HBeAg in the media were measured to be 16 ng/ml and 32 U/ml per 10(7) cells, respectively. Antigen production was completely inhibited by the addition of an excess of asialoorosomucoid. On the other hand, asialoglycoprotein receptor-negative human hepatoma cells, SK-Hep1, did not produce any viral antigens under identical conditions after incubation with HBV DNA complexed to a conjugate composed of asialoorosomucoid and poly-L-lysine. Using a complete HBV genome construct, HBsAg and HBeAg levels reached 16 ng/ml and 16 U/ml per 10(7) cells, respectively. Northern blots revealed characteristic HBV RNA transcripts including 3.5-, 2.4-, and 2.1-kb fragments. Intracellular and extracellular HBV DNA sequences including relaxed circular, linear and single stranded forms were detected by Southern blot hybridization. Finally, 42-nm Dane particles purified from the spent cultures medium were visualized by electron microscopy. This study demonstrates that a targetable DNA carrier system can transfect HBV DNA in vitro resulting in the production of complete HBV virions.

Lipocytes from fibrotic rat liver have an impaired feedback response to procollagen propeptides

Procollagen propeptides have been previously shown to be taken up by cultured fibroblasts and to inhibit collagen production at translational and transcriptional levels. In hepatic fibrosis, Ito cells are thought to be major contributors to collagen overproduction. We wondered whether an impaired response to procollagen propeptides by Ito cells from fibrotic liver could be a mechanism involved in collagen overproduction in hepatic fibrosis. In the presence of type I procollagen carboxy-terminal propeptide (200 nM), collagen production by Ito cells from normal rats was significantly decreased to 62.0% of control, whereas collagen production by Ito cells from two models of hepatic fibrosis in the rat, bile duct ligation and carbon tetrachloride treatment, was not significantly changed (102.4 and 102.6% of controls, respectively). By measurement of type I procollagen mRNA levels, this difference in response to procollagen carboxy-terminal propeptide was determined to occur at a pretranslational level. The rates of uptake, transfer to the nuclear compartment, and degradation of procollagen propeptide were not significantly different in Ito cells from normal and fibrotic liver.

Specific inhibition of hepatitis B viral gene expression in vitro by targeted antisense oligonucleotides

A 21-mer oligodeoxynucleotide complementary to the polyadenylation signal for human hepatitis B virus (HBV) was complexed to a soluble DNA-carrier system that is targetable to hepatocytes via asialoglycoprotein receptors present on those cells. A cell line, HepG2 (2.2.15) that possesses asialoglycoprotein receptors and is permanently transfected with hepatitis B virus (ayw subtype) was exposed to complexed antisense DNA or controls. In the presence of complexed antisense DNA, the concentration of hepatitis B surface antigen in medium was 80% lower than controls after 24 h. Furthermore, during the next 6 days, there was no significant increase in surface antigen concentration in the presence of complexed antisense DNA. The inhibition could be effectively blocked by competition with an excess of free asialoglycoprotein. Total protein synthesis remained unchanged by exposure to complexed antisense sequences under identical conditions. In addition, HBV DNA in the medium and cell layers after 24-h exposure to complexed antisense sequences was 80% lower than in controls. The data indicate that antisense oligonucleotides complexed by a soluble DNA-carrier system can be targeted to cells via asialoglycoprotein receptors resulting in specific inhibition of hepatitis B viral gene expression and replication.

A novel mechanism for achieving transgene persistence in vivo after somatic gene transfer into hepatocytes

Infusion of hepatocyte-specific DNA-protein complexes into rats leads to transient recombinant gene expression in liver. The eventual deterioration of gene expression is due in part to instability of the targeted DNA. In a previous report, we noted retention of transgene sequences in liver and persistent recombinant gene expression when the animals were subjected to partial hepatectomy following in vivo gene transfer. In an attempt to define the mechanism(s) responsible for persistent gene expression following partial hepatectomy, we characterized the molecular state of the retained, liver-associated transgenes. Southern blot analysis of DNA from liver tissues harvested various times after in vivo gene transfer and partial hepatectomy (10 min to 11 weeks) demonstrated high levels of transgene DNA (100-10,000 copies/cell). The predominant form of this DNA appeared to be episomal based on analyses of uncut DNA or DNA restricted by an endonuclease with one site in the plasmid. Livers from several animals contained a small proportion of transgene sequences of unknown structure. The existence of episomal DNA in liver was confirmed in experiments in which intact plasmid was rescued from total hepatocyte DNA by transformation of bacteria. Both strands of DNA in the liver-associated plasmid retained a bacterial pattern of methylation suggesting that the plasmid had not replicated in the eukaryotic cell. These results are consistent with the hypothesis that the majority of transgene sequences are retained as stabilized plasmids. The specific form of DNA which is transcriptionally active was not identified in these studies. This represents a new mechanism for retaining foreign DNA in eukaryotic cells in vivo and has implications both for the development of somatic gene therapies and the pathogenesis of viral diseases.

Evidence that an iron chelator regulates collagen synthesis by decreasing the stability of procollagen mRNA

Iron chelation has been shown previously to decrease collagen synthesis at a posttranslational level by inhibiting prolyl 4-hydroxylase, one of the key enzymes in collagen metabolism. On the other hand, recent in vivo studies of iron overload in rats suggest that iron could specifically activate collagen gene expression in liver tissues. These findings led us to investigate whether iron chelation might also affect collagen gene expression and posttranslational modification. Our data indicate that alpha,alpha'-dipyridyl, an iron chelator, at a concentration of 1 mmol/L, decreased steady-state levels of type I procollagen messenger RNA by 42% (p less than 0.001) without affecting beta-actin messenger RNA levels. Nuclear runoff studies demonstrated that transcription of the type I procollagen gene was unchanged by alpha,alpha'-dipyridyl. However, the turnover rate of type I procollagen messenger RNA was increased by 30%. This pretranslational inhibition of collagen synthesis was not due to decreased lipid peroxidation, because thiobarbituric acid-reactive substances were unchanged by alpha,alpha'-dipyridyl. However, cycloheximide totally abolished the effect, indicating that de novo protein synthesis was required.

Hepatocyte-directed gene transfer in vivo leads to transient improvement of hypercholesterolemia in low density lipoprotein receptor-deficient rabbits

Familial hypercholesterolemia is an inherited disease in humans, caused by a deficiency of low density lipoprotein (LDL) receptors, that we have used as a model for developing liver-directed gene therapies. Our strategy is to reconstitute hepatic LDL receptor expression in vivo by administering a DNA-protein complex that is capable of targeting the delivery of functional LDL receptor genes to hepatocytes. Infusion of this DNA-protein complex into the peripheral circulation of a rabbit animal model for familial hypercholesterolemia resulted in hepatocyte-specific gene transfer and a temporary amelioration of hypercholesterolemia. This noninvasive approach to gene therapy should have applications in the treatment of a wide spectrum of human diseases.

Macrophages can convert citrulline into arginine

Rat peritoneal macrophages were incubated in the presence of 0.05-1.0 mM-[14C]citrulline. The synthesis of [14C]arginine from 0.1 mM-[14C]citrulline was about 300 pmol/h per 10(6) cells in macrophages from saline-injected (control) rats. Both arginine synthesis from citrulline and nitrate production (an indicator of NO generation) were increased about 3-fold in the cells from lipopolysaccharide (LPS)-treated animals. The arginine synthesis was very sensitive to extracellular citrulline concentration in the range found in plasma (0.05-0.1 mM). The rate of arginine synthesis from citrulline was inhibited by about 20% by 0.5 mM-L-glutamine in both control and LPS-treated rat cells, but was inhibited by 0.5 mM-L-arginine only in control cells. Our results demonstrate that citrulline, produced by NO synthetase, can be recycled to arginine in macrophages. The citrulline-arginine cycle may contribute to the regulation of intracellular availability of arginine and thus the prolonged production of NO by macrophages.

Glucose and glutamine metabolism in rat macrophages: enhanced glycolysis and unaltered glutaminolysis in spontaneously diabetic BB rats

Metabolism of glutamine (Gln, 2 mM) and glucose (5 mM) was studied in vitro in isolated resident peritoneal macrophages from both normal (BBn) and spontaneously diabetic BB (BBd) rats. The major products from Gln were ammonia, glutamate, CO2 and to a lesser extent aspartate. Glucose decreased (P less than 0.01) the production of ammonia, CO2 and aspartate from Gln by 34-60%, but had no effect on the amount of glutamate accumulated. The major products from glucose were lactate and to a much lesser extent pyruvate and CO2. Gln decreased (P less than 0.01) 14CO2 production from [U-14C]glucose by 19-28%, increased (P less than 0.01) pyruvate production by 35-49%, but had no effect on lactate production. The fraction of glucose metabolized via the pentose phosphate pathway (PC) was less than 5%. There were no significant differences in Gln metabolism between BBn and BBd macrophages. The production of lactate and pyruvate and the flux from glucose into the PC were increased (P less than 0.01) by 2.4, 1.8 and 1.5-fold, respectively, in BBd cells. Increased macrophage glucose metabolism was also observed in diabetes-prone BB (BBdp) rats at 75-80 days but not at 50 days of age. In the presence of both Gln and glucose, potential ATP production from glucose was 2- and 4-times that from Gln, respectively, in BBn and BBd cells. Lactate production was the major pathway for glucose-derived ATP generation. These results demonstrate (a) glycolysis and flux from glucose through the pentose phosphate pathway are enhanced with no alteration in glutaminolysis in BBd macrophages; and (b) glucose may be a more important fuel than Gln for macrophages, particularly in BBd rats. The increased glucose metabolism may be associated with functional activation of the macrophages that have been proposed to be involved in beta-cell destruction and the development of diabetes.

Glutamine and glucose metabolism in thymocytes from normal and spontaneously diabetic BB rats

Metabolism of glutamine and glucose was studied in thymocytes from normal rats and BB rats with the spontaneous autoimmune diabetic syndrome to assess their potential roles as fuels. The major measured products from glucose were lactate and, to a lesser extent, CO2, and pyruvate. Glutamine had no effect on the rates of their production from glucose. Glutamine was metabolized to ammonia, aspartate, glutamate, and CO2, with aspartate being the major product of carbons from glutamine in the absence of glucose. Glucose markedly decreased the formation of ammonia, aspartate, and CO2 from glutamine, but increased that of glutamate, with an overall decrease in glutamine utilization by 55%. More glutamate than aspartate was produced from glutamine in the presence of glucose. The potential production of ATP from glucose was similar to that when glutamine was present alone. However, glucose markedly decreased production of ATP from glutamine, but not vice versa. This resulted in ATP production from glucose being 2.5 times that from glutamine when both substrates were present. The oxidation of glucose to CO2 via the Krebs cycle accounts for 75-80% of glucose-derived ATP production. Cellular ATP levels markedly decreased in the absence of exogenous substrates, but were constant throughout a 2-h incubation in the presence of glutamine, glucose, or both. There were no differences in thymocyte glucose or glutamine metabolism between normal and diabetic BB rats, in contrast to previous findings in peripheral lymphoid organs. Our results suggest that glucose is a more important fuel than glutamine for "resting" thymocytes, again in contrast to the cells of peripheral lymphoid organs in which glutamine is as important as glucose as a fuel.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical modification of an ecotropic murine leukemia virus results in redirection of its target cell specificity

An ecotropic virus was chemically modified in order to determine whether its target cell specificity could be altered. We hypothesized that chemical coupling of galactose residues to a virus might permit specific infection of hepatocytes mediated by asialoglycoprotein receptors unique to these cells. To test this hypothesis, we took advantage of the fact that: 1) artificial asialoglycoproteins can be created by chemical coupling of lactose to proteins; and 2) viruses that are ecotropic have a narrow species specificity. An ecotropic, rodent-specific, replication-defective murine leukemia virus containing the gene for beta-galactosidase was chemically modified with lactose to contain 5.9 mumol of lactose per mg of viral RNA. Modified and unmodified viruses were incubated for 5 days with HepG2, a human hepatoma line that possesses asialoglycoprotein receptors, and SK Hep1, a human cell line that does not. As expected from the ecotropism, unmodified virus did not produce beta-galactosidase activity in either cell type. Modified virus did not produce beta-galactosidase activity in SK Hep1 cells. However, modified virus did produce beta-galactosidase activity, 71.2 units/mg of cell protein, in the human receptor (+) HepG2 cells. Interestingly, modification of the virus also resulted in decreased enzyme activity in previously susceptible host rodent cells. Competition with modified virus by an excess of an asialoglycoprotein completely prevented development of enzymatic activity in HepG2 cells. Histochemical treatment of cells with 5-bromo-4-chloro-3-indoyl beta-D-galactoside to detect in situ beta-galactosidase activity demonstrated that only HepG2 cells treated with modified virus were positive and that 36% of these cells were stained after 5 days. These data indicate that chemical modification of a virus can result in a redirection of the infectivity of the virus toward hepatocyte-derived cells mediated by the presence of asialoglycoprotein receptors.

Receptor-mediated gene delivery in vivo. Partial correction of genetic analbuminemia in Nagase rats

A plasmid (palb3) was constructed containing the structural gene for human serum albumin driven by mouse albumin enhancer-rat albumin promoter elements. Using an asialoglycoprotein-polycation conjugate consisting of asialoorosomucoid coupled to poly-L-lysine, a soluble DNA complex was formed that was capable of targeting specifically to hepatocytes via asialoglycoprotein receptors present on these cells. Groups of Nagase analbuminemic rats were injected with complexed DNA or controls, followed by two-thirds partial hepatectomy to stimulate hepatocyte replication. Using a cDNA probe for the human albumin structural gene, hybridizable sequences were detected in analbuminemic rats treated with complex as determined by Southern blot analysis. Two weeks post-injection, the targeted DNA was found to exist primarily in plasmid form with an average copy number of 1000/diploid cell. Human albumin mRNA was detected by dot-blot hybridization with a specific oligonucleotide cDNA probe and confirmed by RNase protection assay using a vector-specific probe. Circulating human albumin was detected in the serum of palb3-treated Nagase analbuminemic rats by Western blots using an antibody specific for human serum albumin. A time course demonstrated that circulating human albumin was not detectable 24 h after injection, but became measurable at a level of 0.05 micrograms/ml within 48 h and increased in concentration to a maximum of 34 micrograms/ml by 2 weeks post-injection. This level of expression remained stable through 4 weeks after injection and partial hepatectomy.

Effects of extracellular pH, CO2, and HCO3- on ketogenesis in perfused rat liver

Effects of extracellular pH, CO2, and HCO3- on ketone body production from octanoate were studied in perfused livers from fasted rats. pH was adjusted to 7.1-7.5 by varying perfusate [HCO3-] and [CO2], where brackets denote concentration. At constant 25 mM [HCO3-], total production of beta-hydroxybutyrate (beta-OHB) + acetoacetate (AcAc) was constant from pH 7.1 to 7.5. However, the [beta-OHB]/[AcAc] ratio decreased from 1.60 to 1.00 when pH decreased from 7.3 to 7.1; there was no change at pH 7.4. At constant [CO2], decreasing pH from 7.4 to 7.1 did not alter either total ketogenesis or the [beta-OHB]/[AcAc] ratio. This suggests that high [CO2] rather than low pH was responsible for the alteration in the redox ratio. At constant pH of 7.4, variations in [HCO3-] between 15 and 25 mM did not influence total ketogenesis or the [beta-OHB]/[AcAc] ratio. However, increasing [HCO3-] from 25 to 35 mM decreased the [beta-OHB]/[AcAc] ratio from 1.76 to approximately 1, again without affecting total ketogenesis. At constant 1.75 mM [CO2], increasing [HCO3-] from 25 to 35 mM also reduced the [beta-OHB]/[AcAc] ratio from 1.63 to approximately 1, suggesting that the effect of high [HCO3-] on this redox ratio can be ascribed to HCO3- itself. It is concluded that high [CO2] or [HCO3-] decreases the mitochondrial [NADH]/[NAD+] ratio in hepatocytes, resulting in a decreased [beta-OHB]/[AcAc] ratio.

[Effects of antihypertensive factor from erythrocytes of essential hypertensive subjects on blood pressure in rats]

The effects of antihypertensive factor (AHF) from erythrocytes of essential hypertensive human subjects on the systolic blood pressure (SBP) and diastolic blood pressure (DBP) in spontaneously hypertensive rats (SHR), renal hypertensive rats (RHR), Wistar-Kyoto rats (WKY) and Wistar rats were examined. Single intraperitoneal injection of AHF (1.6 mg/kg body weight) resulted in a significant decrease in SBP of SHR and RHR. At 10 min postinjection, AHF lowered the SBP in SHR by 34.0 mmHg. SBP recovered to the original level at 3 h. The maximal decrease of SBP in RHR by 92.5 mmHg was at 24h postadministration and the SBP did not recover until the 9th day. When AHF was administered via femoral vein (0.8 mg/kg body weight), the maximal decrease values of the SBP and the DBP were 42.8 and 48.2 mmHg in SHR at 12 min and 38.3 and 42.5 mmHg in RHR at 25 min postinjection respectively. The DBP in Wistar rats decreased considerably (from 96.7 +/- 12.9 to 83.3 +/- 11.7 mmHg) at 5 min postadministration of AHF, but no effect on DBP in WKY rats was observed. The depressor effect of AHF on SBP in RHR was dose-dependent. AHF could also antagonize the pressor effect of norepinephrine in Wistar rats.

Effects of antihypertensive factor from erythrocyte of spontaneously hypertensive rats on the blood pressure and Ca2+ influx of arterial smooth muscle in rats

The effects of a partially purified antihypertensive factor (AHF) from erythrocytes of spontaneously hypertensive rats (SHR) on the blood pressure (BP) and Ca2+ influx of vascular smooth muscle (VSM) in rats were studied. The results indicated that AHF could produce a marked prolonged depressor effect and significantly inhibit the Ca2+ influx dose-dependently on both SHR and renal hypertensive rat (RHR) either in acute or in chronic experiments, but not on normotensive rats. It suggested that the inhibition of Ca2+ influx might be one of the important mechanisms for AHF as an endogenous depressor substance.

Glutamine metabolism in skeletal muscles from the broiler chick (Gallus domesticus) and the laboratory rat (Rattus norvegicus)

Oxidative decarboxylation of L-[1-14C]glutamine was studied in isolated chick and rat skeletal muscles incubated in the presence of glucose, insulin and plasma concentrations of amino acids. (1) The rate of oxidative decarboxylation of L-[1-14C]glutamine was high, and exceeded that of L-[1-14C]leucine in all muscles. (2) The rate of oxidative decarboxylation of L-[1-14C]glutamine increased with increasing intracellular concentrations of glutamine. (3) The activities of glutamine aminotransferases K and L were more than 10-fold greater in rat than in chick skeletal muscles. (4) Mitochondrial phosphate-activated glutaminase activity was approx. 10-fold greater in chick than in rat skeletal muscles and increased with increasing glutamine concentrations. (5) An inhibitor of glutaminase, 6-diazo-5-oxo-L-norleucine, inhibited the rate of glutamine decarboxylation in chick, but not in rat, skeletal muscle. These findings suggest that glutamine degradation in skeletal muscle may be substantial and may make an important contribution to the regulation of intramuscular glutamine concentrations. A species difference in the pathways and the subcellular location for the conversion of glutamine into 2-oxoglutarate in rat and chick skeletal muscles is implied by the relative activities of glutamine-degrading enzymes.

Elevated glutamine metabolism in splenocytes from spontaneously diabetic BB rats

To investigate the metabolic fates of glutamine in splenocytes from the BB rat with spontaneous immunologically mediated insulin-dependent diabetes, freshly isolated cells were incubated in Krebs-Ringer Hepes buffer with 1.0 mM-[U-14C]glutamine and 0, 4 mM- or 15 mM-glucose. (1) The major products of glutamine metabolism in splenocytes from normal and diabetic rats were ammonia, glutamate, aspartate and CO2. (2) The addition of glucose increased (P less than 0.01) glutamate production, but decreased (P less than 0.01) aspartate and CO2 production from glutamine, as compared with the values obtained in the absence of glucose. However, there were no differences in these metabolites of glutamine at 4 mM- and 15 mM-glucose. (3) At all glucose concentrations used, the productions of ammonia, glutamate, aspartate and CO2 from glutamine were all markedly increased (P less than 0.01) in splenocytes from diabetic rats. (4) Potential ATP production from glutamine in the splenocytes was similar to that from glucose, and was increased in cells from the diabetic rat. (5) ATP concentrations were increased (P less than 0.01) in diabetic-rat splenocytes in the presence of glutamine with or without glucose. (6) Our results demonstrate that glutamine is an important energy substrate for splenocytes and suggest that the increased glutamine metabolism may be associated with the activation of certain subsets of splenocytes in the immunologically mediated diabetic syndrome.

Propeptide-mediated regulation of procollagen synthesis in IMR-90 human lung fibroblast cell cultures. Evidence for transcriptional control

We have demonstrated previously that the carboxyl- and amino-terminal propeptides of type I procollagen can inhibit procollagen synthesis by specifically decreasing procollagen mRNA levels. The objective of the present experiments was to determine the mechanism by which propeptides cause these pretranslational effects. IMR-90 fibroblasts were exposed to medium containing carboxyl-terminal propeptide of type I procollagen, and nuclear run-off assays were performed by hybridization to a specific alpha 1 chain type I procollagen cDNA probe. Specific type I procollagen transcription rates were found to be decreased by 50% in the presence of 75 nM carboxyl-terminal propeptide compared with control (untreated) cells. Total cellular transcription rates as well as beta-actin mRNA rates were not affected significantly by any concentration of carboxyl-terminal propeptide. Propeptide radiolabeled with 125I was found to be taken up by cultured cells. Furthermore, exogenous carboxyl-terminal propeptide levels increased in the cytosolic compartment and eventually reached a steady-state level of 18 +/- 2 pmol/g cell protein by 30 min. Of particular interest was the finding that levels of radiolabeled carboxyl-terminal propeptide were also detected in the nuclear fraction and increased with time, reaching a plateau after 60 min of incubation. Incubation of nuclei from IMR-90 cells in medium containing varying concentrations of carboxyl-terminal propeptide resulted in nuclear transcription rates that were decreased by 40% compared with untreated controls. beta-Actin nuclear message levels remained unchanged under identical conditions. We conclude that carboxyl-terminal propeptide of type I procollagen can be internalized and become associated with the nuclear compartment. This suggests a feedback regulatory role on procollagen synthesis by a direct effect on procollagen gene transcription.

Glutamine and glucose metabolism in rat splenocytes and mesenteric lymph node lymphocytes

The metabolism of glutamine (2 mM) and glucose (5 mM) was studied in splenocytes and mesenteric lymph node lymphocytes of Wistar-Furth rats to assess their relative importance as energy substrates. The major products from glutamine were ammonia, glutamate, aspartate, and CO2, whereas those from glucose were lactate, pyruvate, and CO2 in cells from both lymphoid organs. The individual rates of glutamine and glucose metabolism were decreased in the presence of both substrates, compared with the rates when present separately. The rates of glucose and some (but not all) aspects of glutamine metabolism were higher (P less than 0.01) in splenocytes than in mesenteric lymphocytes. In cells from both lymphoid organs, glutamine and glucose could potentially contribute almost equal amounts of ATP in the presence of both substrates. Glutamine and glucose individually were able to provide sufficient amounts of ATP to maintain its concentrations in the cells throughout a 2-h incubation period at the same levels as with both substrates present. We also found that splenocyte concentration (3.3-100 x 10(6) cells/ml) in the incubations is an important determinant of rates of metabolite formation from glutamine when expressed per 10(6) cells. We conclude that glucose is not the only quantitatively significant energy substrate or even the major one for lymphocytes, because glutamine at near-physiological concentration can be readily utilized by these cells.

Delivery systems for gene therapy

Introduction of foreign genes into mammalian cells in vitro has been accomplished previously by a variety of methods. The few techniques that have been developed for transfection of mammalian cells in vivo, are technically difficult or lack cell specificity. We have developed a soluble, targetable DNA carrier system consisting of an asialoglycoprotein covalently coupled to a polycation. The strategy was based on: 1) the presence of unique receptors on hepatocytes which internalize galactose-terminal (asialo-)glycoproteins; 2) polycations can bind DNA in a non-covalent, non-damaging interaction. Using chloramphenicol acetyltransferase (CAT) as a marker gene, specific delivery and expression of CAT was demonstrated in vitro using asialoglycoprotein receptor (+) and (-) cell lines. Intravenous injection of conjugate-DNA complexes in rats resulted in detection of CAT DNA sequences in liver 10 min later by dot blots with a CAT cDNA probe. CAT enzyme activity 24 hrs later was found specifically in liver but no other tissues or control livers. Targeted hepatic CAT expression was transient, maximal at 24 hrs but declined to barely detectable levels by 96 hrs. Persistent foreign gene expression was achieved by injection of DNA complex followed by 67% partial hepatectomy. High levels of hepatic CAT activity were detected through 11 weeks post-hepatectomy. The data indicate that a targetable gene delivery system can permit in vivo expression of an exogenous gene after simple intravenous injection. The foreign gene expression can be enhanced and made to persist by induction of hepatocyte replication.

Targeted protection of hepatocytes from galactosamine toxicity in vivo

We present an in vivo model for specific protection of normal hepatocytes from damage by the highly specific hepatotoxin galactosamine. The idea is based on the fact that normal, unlike malignant, hepatocytes possess unique cell-surface receptors that can bind and internalize galactose terminal (asialo)glycoproteins by receptor-mediated endocytosis. A targetable carrier-antagonist conjugate was formed by coupling asialofetuin to the galactosamine antagonist uridine monophosphate. Intravenous injection of the antagonist conjugate resulted in specific uptake by the liver. Rats treated with carrier-antagonist conjugate together with a toxic dose of galactosamine developed significantly less hepatotoxicity than did controls. We conclude that a galactosamine antagonist can be targeted to liver, resulting in specific protection of hepatocytes from galactosamine toxicity in vivo. Because hepatoma cells lack asialoglycoprotein receptor activity, this "targeted rescue" may be of value in the differential protection of normal cells in the treatment of hepatocellular carcinoma.

Study on BcII/St14 RFLPs in Chinese for DNA diagnosis for hemophilia A

The BcII polymorphism within DXS52 (St14) was reported. It was composed of 4 allelic fragments, 4.0 kb, 3.3 kb, 3.0 kb and 2.3 kb. The frequency of these fragment were 0.09, 0.12, 0.44 and 0.35 respectively in the Chinese. The polymorphism provided the PIC of 0.66. DNA analysis of families with hemophilia A showed that the confidence of the RFLPs was the same as the TaqI/St14 RFLPs and for carrier detection the former is much better than that of the TaqI/St14 RFLPs.

The effect of glutamine on protein turnover in chick skeletal muscle in vitro

The effect of glutamine on the rates of protein synthesis and degradation was studied in isolated chick extensor digitorum communis muscles incubated in the presence of plasma concentrations of amino acids. Addition of 0.5-15 mM-glutamine increases (P less than 0.01) intracellular glutamine concentrations by 31-670%. There is a positive relationship (r = 0.975, P less than 0.01) between intracellular glutamine concentration and the rate of muscle protein synthesis measured by the incorporation of [3H]phenylalanine. The stimulating effect of 15 mM-glutamine on protein synthesis was decreased from 58 to 19% in muscles incubated in the absence of tyrosine. The rates of protein degradation, estimated from [3H]phenylalanine release from muscle proteins prelabelled in vivo, decreased (P less than 0.05) by 15-30% in the presence of 4-15 mM-glutamine when compared with muscles incubated in the presence of physiological concentrations of glutamine (0.5-1 mM). Glutamine concentrations ranging from 2 to 15 mM appear to have an overall anabolic effect on chick skeletal muscles incubated in vitro.

Targeting genes: delivery and persistent expression of a foreign gene driven by mammalian regulatory elements in vivo

We present evidence that a foreign gene driven by natural mammalian regulatory elements can be targeted to hepatocytes and the resultant gene expression made to persist. This was accomplished using a soluble DNA carrier system consisting of two covalently linked components: 1) a polycation, poly-L-lysine, that can bind DNA in a strong but non-damaging interaction, and 2) an asialoglycoprotein which can be targeted specifically to hepatocytes by cell surface asialoglycoprotein receptors unique to this cell type. A plasmid, palb-CAT, containing the gene for chloramphenicol acetyltransferase (CAT) driven by mouse albumin regulatory sequences was complexed to the carrier system. Intravenous injection of palb-CAT DNA in the form of a complex resulted in the presence of CAT enzyme activity in liver homogenates 24 h after injection. The targeted gene expression, however, was transient, reaching a maximum of 10 units/g liver at 24 h but was not detectable by 96 h. However, partial hepatectomy 30 min after injection resulted in persistent high levels of hepatic CAT activity (11.3 units/g) through 11 weeks post-injection. Southern analysis of livers 11 weeks after partial hepatectomy demonstrated that some of the targeted DNA had been integrated into the host genome. We conclude that a foreign gene driven by natural mammalian regulatory elements can be delivered to hepatocytes by intravenous injection in vivo using a soluble DNA carrier system. Foreign gene expression targeted in this manner can be made to persist by stimulation of hepatocyte replication.

A study of sex identification of trace, dried bloodstains using a Y-chromosome-specific deoxyribonucleic acid (DNA) probe

A new method is discussed which examines trace, dried bloodstains by gel in situ hybridization using a Y-chromosome-specific deoxyribonucleic acid (DNA) probe to determine the sex of the bloodstain for forensic medicine application. The complete DNA is transferred directly by electrophoresis onto the gel intact, bypassing the possibilities of impurities contaminating the sample and of DNA degradation. The method has proven accurate for small (2.5-mm-diameter) samples aged up to eight years and is quick, simple, and easily read.

Studies of beta-thalassemia mutations in families living in three provinces in southern China

beta-Thalassemia is a common disease in Southern China and 10 different mutations or frameshifts are responsible for most types of beta-thalassemia in this area. We studied 126 chromosomes of 80 beta-thalassemia patients from the Guangxi, Guangdong, and Sichuan Provinces using the polymerase chain reaction followed by dot-blot hybridization with specific oligonucleotide probes. The most common mutation in the three provinces is the frameshift at codons 41-42, followed by the A----T mutation at codon 17. The A----G mutation at nt -29 of the promoter is common in Sichuan but not in the other two provinces. Three mutations (T----C at nt -30; G----T at IVS-I-1, and G----C at IVS-I-5) were not observed. These data were used to initiate a prenatal diagnosis program using the same techniques for identification. Eleven fetuses at risk for beta-thalassemia have been diagnosed.

Is methionine transaminated in skeletal muscle?

Methionine transamination is extensive in rat and chick skeletal-muscle homogenates, but is barely detectable in intact rat, but not chick, skeletal muscles. Branched-chain amino acids essentially block methionine transamination in intact muscles and homogenates from both species. The physiological significance of methionine transamination in skeletal muscle is questioned.