A novel strategy for in vivo expansion of transplanted hepatocytes using preparative hepatic irradiation and FasL-induced hepatocellular apoptosis

A strategy for inducing preferential proliferation of the engrafted hepatocytes over host liver cells should markedly increase the benefit of hepatocyte transplantation for the treatment of liver diseases and ex vivo gene therapy. We hypothesized that preparative hepatic irradiation (HIR) to inhibit host hepatocellular regeneration in combination with the mitotic stimulus of host hepatocellular apoptosis should permit repopulation of the liver by transplanted cells. To test this hypothesis, congeneic normal rat hepatocytes were transplanted into UDP-glucuronosyltransferase (UGT1A1)-deficient jaundiced Gunn rats (a model of Crigler-Najjar syndrome type I), following HIR and adenovirus-mediated FasL gene transfer. Progressive repopulation of the liver by engrafted UGT1A1-proficient hepatocytes over 5 months was demonstrated by the appearance of UGT1A1 protein and enzyme activity in the liver, biliary bilirubin glucuronides secretion, and long-term normalization of serum bilirubin levels. This is the first demonstration of massive hepatic repopulation by transplanted cells by HIR and FasL-induced controlled apoptosis of host liver cells.

Hepatocyte-based gene therapy

Hepatocyte-based gene therapy may be used to replace a missing gene product, confer proliferating ability to cultured hepatocytes, prevent allograft rejection, massively repopulate the host liver, or grow xenogeneic hepatocytes in mammalian liver. Gene transfer into isolated hepatocytes can be accomplished via nonviral or viral vectors, the viral vectors being more useful at this time. Common recombinant viruses that integrate into the host genome include murine leukemia retroviruses and lentiviruses, adenoassociated virus, and the T-antigen-deleted SV40 virus. Episomal viruses, such as adenoviruses, permit efficient gene transfer, but the transgene is lost upon proliferation of the transplanted hepatocyte in the host. Hybrid viruses that combine the high transduction efficiency of adenoviral vectors and the integrative capacity of other vectors, such as adenoassociated viruses, have been designed. Massive repopulation of the liver by transplanted hepatocytes can be achieved if a mitotic stimulus to the transplanted cells is combined with prevention of proliferation of the host hepatocytes. Treatment with a plant alkaloid or retrorsine, or preparative irradiation of the liver can be used to inhibit host hepatocellular proliferation, while partial hepatectomy, expression of Fas ligand, or thyroid hormone administration can be used as a mitotic stimulus to the transplanted cells.

Amplification of engrafted hepatocytes by preparative manipulation of the host liver

Scarcity of donor livers is a major obstacle to the general application of hepatocytes for the development of bioartificial liver assist devices as well as intracorporeal engraftment of hepatocytes for the treatment of inherited metabolic diseases. The number of hepatocytes that can be transplanted into the liver safely in a single sitting also limits the utility of this procedure. These limitations could be addressed by providing preferential proliferative advantage to the transplanted cells. Studies using transgenic mouse recipients or donors have indicated that massive repopulation of the host liver by engrafted hepatocytes requires that the transplanted cells are subjected to a proliferative stimulus to which the host hepatocytes cannot respond. Prevention of host hepatocyte proliferation has been achieved by treatment with a plant alkaloid, retrorsine. Because retrorsine is carcinogenic, we have evaluated preparative irradiation for this purpose. The proliferative stimulus may consist of the loss of hepatic mass (e.g., partial hepatectomy, reperfusion injury or induction of Fas-mediated apoptosis by gene transfer) or administration of stimulants of hepatocellular mitosis (e.g., growth factors or thyroid hormone). Potential applications of these preparative manipulations of the host liver include the treatment of inherited metabolic disorders by transplantation of allogeneic hepatocytes, hepatocyte-mediated ex vivo gene therapy, rescuing liver cancer patients from radiation-induced liver damage, and expansion of human hepatocytes in animal livers.

Liver irradiation: a potential preparative regimen for hepatocyte transplantation

Advances in the understanding of hepatocyte engraftment and repopulation of the host liver have already led to the use of hepatocyte transplantation (HT) with some success in the treatment of inherited and acquired liver diseases. Wider application of HT is severely limited by the unavailability of large number of transplantable hepatocytes and difficulties associated with transplanting an adequate number of cells for achieving therapeutically satisfactory levels of metabolic correction. Therefore, there is a need for preparative regimens that provide a growth advantage to the transplanted (healthy) hepatocytes over the host's own (diseased) hepatocytes so that the former can repopulate the host liver. We have recently shown that when the liver of recipient rats was subjected to radiotherapy and partial hepatectomy before HT, the transplanted hepatocytes engrafted in and massively repopulated the liver, and also ameliorated the adverse clinical and histopathological changes associated with hepatic irradiation. This protocol was then used as a preparative regimen for transplanting normal hepatocytes into jaundice mutant rats (Gunn strain), which lack hepatic bilirubin-uridinediphosphoglucuronate glucuronosyltransferase and is a model of Crigler-Najjar syndrome Type I. The results showed long-term correction of the metabolic abnormality, suggesting that the transplanted hepatocytes repopulated an irradiated liver and were metabolically functional. This strategy could be useful in the treatment of various genetic, metabolic, or malignant diseases of the liver.

Adenovirus-mediated antisense ATM gene transfer sensitizes prostate cancer cells to radiation

Treatment failure after radiation therapy of prostate cancer (PC) could be a significant problem. Our objective is to design genetic radiosensitizing strategies for the treatment of PC. Cells from individuals with the genetic disorder ataxia telangiectasia (AT) are hypersensitive to ionizing radiation. Therefore, we examined whether attenuation of the AT gene product, AT mutated (ATM), in PC cells could result in an increased intrinsic radiosensitivity. A p53-mutant PC cell line, PC-3 was infected with adenoviral vectors, expressing antisense ATM RNA to various domains of the ATM gene. Immunoblot analyses of cellular extracts from antisense ATM-transfected PC-3 cells showed attenuated expression of the ATM protein within 2 days of viral infection. Compared with cells infected with an adeno-beta-galactosidase vector, antisense ATM-transfected PC-3 cells showed aberrant control of S-phase cell-cycle checkpoints after exposure to ionizing radiation. Under these conditions, the intrinsic radiosensitivity of the PC-3 cells was enhanced. Consequently antisense ATM gene therapy could serve as a paradigm for strategies that target the cellular survival mechanisms of an irradiated tumor cell and may provide therapeutic benefit to patients undergoing radiation therapy for PC.

Antisense ATM gene therapy: a strategy to increase the radiosensitivity of human tumors

Atm, the gene mutated in ataxia-telangiectasia (AT) patients, is an essential component of the signal transduction pathway that responds to DNA damage due to ionizing radiation (IR). We attenuated ATM protein expression in human glioblastoma cells by expressing antisense RNA to a functional domain of the atm gene. While ATM expression decreased, constitutive expression of p53 and p21 increased. Irradiated ATM-attenuated cells failed to induce p53, demonstrated radioresistant DNA synthesis, and increased radiosensitivity. Antisense-ATM gene therapy in conjunction with radiation therapy may provide a novel strategy for the treatment of cancer.

Flt3-ligand administration after radiation therapy prolongs survival in a murine model of metastatic lung cancer

An ineffective tumor-specific immune response from inadequate/incompetent antigen presentation could contribute to the failure in tumor control and its dissemination. Dendritic cells (DCs) have been shown to present antigen from apoptotic cells. We hypothesized that Flt3-ligand (Flt3L) therapy, which expands DCs in vivo, in combination with local tumor radiotherapy (RT), should improve antigen presentation from dying, irradiated tumor cells. RT + Flt3L reduced pulmonary metastases in a murine model of Lewis lung carcinoma and significantly improved survival in C57Bl/6 mice with established footpad tumors. Mice treated with Flt3L alone showed delayed tumor growth but eventually succumbed to tumor progression. The combination therapy of RT + Flt3L failed to impact survival in immunodeficient athymic mice, implicating the role of T cells in prolonging survival. These results support an attractive strategy of sequential RT and immunotherapy with Flt3L to enhance tumor antigen presentation, which may produce therapeutic responses against disseminated cancer and improvement in survival.

Amelioration of radiation-induced liver damage in partially hepatectomized rats by hepatocyte transplantation

Hepatic tumors often recur in the liver after surgical resection. Postoperative radiotherapy (RT) could improve survival, but curative RT may induce delayed life-threatening radiation-induced liver damage. Because RT inhibits liver regeneration, we hypothesized that unirradiated, transplanted hepatocytes would proliferate preferentially in a partially resected and irradiated liver, providing metabolic support. We subjected F344 rats to hepatic RT and partial hepatectomy with/without a single intrasplenic, syngeneic hepatocyte transplantation. Hepatocyte transplantation ameliorated radiation-induced liver damage and improved survival of rats receiving RT after partial hepatectomy. We further demonstrated that transplanted hepatocytes extensively repopulate and function in a heavily irradiated rat liver.

Continuous primary sequence requirements in the 18-nucleotide promoter of dicot plant mitochondria

The nucleotide requirements of mitochondrial promoters of dicot plants were studied in detail in a pea in vitro transcription system. Deletions in the 5' regions of three different transcription initiation sites from pea, soybean, and Oenothera identified a crucial AT-rich sequence element (AT-Box) comprising nucleotide positions -14 to -9 relative to the first transcribed nucleotide. Transversion of the AT-Box sequence to comple- mentary nucleotide identities results in an almost complete loss of promoter activity, suggesting that primary structure rather than a simple accumulation of adenines and thymidines in this region is essential for promoter activity. This promoter segment thus appears to be involved in sequence specific binding of a respective protein factor(s) rather than merely loosening and melting the DNA helix during or for an initiation event. Manipulation of nucleotide identities in the 3' portion of the pea atp9 promoter and the respective 3'-flanking region revealed that essential sequences extend to positions +3/+4 beyond this transcription start site. Efficient transcription initiation at an 18-base pair promoter sequence ranging from nucleotide positions -14 to +4 integrated into different sequence contexts shows this element to be sufficient for autonomous promoter function independent of surrounding sequences.

Cotranscription of the rpl5-rps14-cob gene cluster in pea mitochondria

In pea mitochondria the rpl5, rpsl4 and cob ORFs are clustered in a unique genomic environment and are cotranscribed into a 4.7-kb primary transcript and several other polycistronic RNAs with sizes between 4.0 and 2.3 kb. All of the larger RNAs terminate at a common 3' end, 52 nucleotides downstream of the cob gene. Transcription is initiated at a promoter about 1.3 kb upstream of the rpl5 start codon. The promoter sequence 5'-AATAAGAGA-3' corresponds to the highly conserved 5'-CRTAAGAGA-3' motif often found in promoters in dicot plants. Functional analysis in a homologous in vitro transcription system showed the pea rpl5 promoter to be active, despite the presence of an altered base in first position of the promoter motif. In Oenothera, in contrast to pea, transcription of the rpl5 gene is driven by a promoter motif that conforms perfectly to the consensus sequence. Double inverted repeats located in the 3' flanking regions of the rpsl4 and cob ORFs in pea were investigated with respect to their possible role in defining transcript termini and their potential function in controlling exo- and endonucleolytic processing or transcript stabilization.

In plants a putative isovaleryl-CoA-dehydrogenase is located in mitochondria

In plants the degradation pathways of branched-chain amino acids have remained somewhat unclear with respect to both their biochemistry and their intracellular location. While biochemical evidence has localized some of the catabolic enzymes in peroxisomes/glyoxysomes, others cofractionate with mitochondria. We have now identified a candidate protein and corresponding cDNA for an enzyme of the leucine catabolic pathway, the isovaleryl-CoA-dehydrogenase (IVD). This polypeptide is a member of the acyl-CoA-dehydrogenase (ACDH) family and is encoded in the nuclear genome of Arabidopsis thaliana. Expression of the putative IVD gene in pea seedlings is documented by western blot analyses with an antibody against the mammalian IVD. Subcellular fractionation identifies the putative IVD enzyme in the mitochondrion. This localization suggests that in plants mitochondria contain at least part of the branched-chain amino acid degradation pathway(s).

Massive repopulation of rat liver by transplantation of hepatocytes into specific lobes of the liver and ligation of portal vein branches to other lobes

An important consideration in application of hepatocyte transplantation is whether the number of engrafted hepatocytes is sufficient to achieve the desired effect. Here we have evaluated the proliferative potential of transplanted primary hepatocytes during regeneration of hepatic lobes. Two million hepatocytes isolated from congeneic normal Wistar-RHA rats were injected into the main portal vein of deficient, jaundiced Gunn rats. The right branch of the portal vein was ligated 24 hr before hepatocyte transplantation (group A) or transiently clamped during hepatocyte injection (group B) or 24 hr after hepatocyte injection (group C). In these groups, the three lobes supplied by the right branch of the portal vein rapidly atrophied and disappeared in 4 days, whereas the remaining lobes proliferated, as shown by size increase and 5-bromo-2-deoxy-uridine uptake. Two control groups received 2 million (group D) or 20 million hepatocytes (group E) without ligation. Hepatocyte engraftment occurred in all groups. The greatest hypobilirubinemic effect was observed in group A, in which serum bilirubin concentrations were reduced to 1.7+/-0.45 mg/dl from pretransplantation levels of 6.9+/-1.2 mg/dl. This effect was even greater than that observed after transplantation of 20 times more hepatocytes without ligation (group E). Specific endonuclease digestion of a polymerase chain reaction-amplified segment of the ugt1 gene from hepatic DNA showed that up to 25% of the DNA was of donor origin. This paralleled the hepatic bilirubin-UDP-glucuronosyltransferase activity, which was above 50% of normal. The results indicate that the transplanted hepatocytes proliferate preferentially within the regenerating lobes, replacing more than 20% of the liver mass with the progeny of the transplanted phenotypically normal hepatocytes.

Thoracic spinal nerve and root conduction: a magnetic stimulation study

We describe a technique of magnetic coil (MC) stimulation of the thoracic spinal nerves and roots in 12 normal subjects and a patient with diabetes mellitus. We kept the MC flat against the vertebral column in the midline over T-7, T-8, and T-9 spinous processes and obtained compound muscle action potentials from the upper rectus abdominis, external oblique, and intercostal muscles. We obtained mean latencies to these muscles after stimulation in the posterior axillary line. We noted that the onset latencies remained fixed despite increasing the intensity of stimulation from 30% to 100% and on moving the coil up to 3 cm lateral to the spinous processes suggesting that the stimulation of the fastest conducting fibers was occurring at a fixed site, most likely at the intervertebral foramina. Prolonged latencies in the diabetic patient confirmed the diagnosis of radiculoneuropathy.

Regulation of human Gc (vitamin D--binding) protein levels: hormonal and cytokine control of gene expression in vitro

Studies were performed in Hep3B hepatocytes to better elucidate the mechanisms regulating circulating levels of human group-specific component (Gc). We measured changes in Gc messenger RNA (mRNA) synthesis and levels of secreted protein resulting from treatment of hepatocytes with cytokines and hormones known to influence synthesis of other proteins of hepatic origin. We particularly focused on compounds known to be prototypic stimulants during the acute phase response. Interleukin-6 (IL-6) and dexamethasone were shown to increase Gc mRNA approximately twofold while transforming growth factor beta (TGF beta) decreased Gc mRNA in a dose-dependent fashion by up to fivefold. The effects on secreted Gc protein levels were similar. These results indicate that Gc protein appears to be regulated differently than the other members of this gene family, albumin and alpha-fetoprotein (AFP), which are negative acute phase reactants. In addition, these contrasting effects on Gc synthesis of IL-6 and dexamethasone and of TGF beta suggest that high basal levels of Gc synthesis may be maintained during the acute phase response.

The vitamin D-binding protein gene: quantitation of amplified nucleic acids by ELISA

We have utilized enzyme-linked immunosorbent assay (ELISA) to quantitate PCR-amplified DNA. This method was used to measure mRNA for the vitamin D-binding protein (Gc), beta-actin and the transferrin receptor (TR) gene in the Hep3B cell line. Total RNA from Hep3B cells was reverse transcribed to obtain cDNA, which was amplified in the presence of digoxigenin-dUTP by PCR. The PCR products were then hybridized in liquid phase to a biotinylated, nested capture probe for the respective sequences. The hybridized products were bound to a streptavidin-coated ELISA plate and were detected by an alkaline-phosphatase-conjugated antibody to digoxigenin. ELISA standard curves for Gc and control genes, beta-actin and TR, were obtained after PCR amplification of serial dilutions of Hep3B total RNA. As an external standard, an ELISA standard curve for Gc was obtained after PCR amplification of serial dilutions of a full-length Gc cDNA insert obtained from a recombinant plasmid. Thus, we were able to develop a non-isotopic quantitation assay for PCR-amplified DNA that is highly sensitive and has the specificity of hybridization-based methods.

RNA synthesis and degradation during preferential inhibition of protein synthesis by cobalt chloride in Escherichia coli K-12

It has been observed that growth of Escherichia coli cells are inhibited when treated with cobalt chloride (300 microM). It has also been shown that CoCl2 preferentially inhibits translation without inhibiting the process of transcription (1, 2, 8). We report here, that during treatment of E. coli cells with CoCl2, both messenger RNA and stable RNA synthesis is slowed down about 2.5 folds. The rate of degradation of mRNA also decreases and both chemical and functional half-life of mRNA increases about 2.5 folds in Co-treated cells. This clearly shows that the process of transcription is also affected while translation is preferentially inhibited during CoCl2 treatment.

A ribonuclease-resistant cytoplasmic 10 S ribonucleoprotein of chick embryonic muscle. A potent inhibitor of cell-free protein synthesis

A ribonucleoprotein (RNP) particle sedimenting at 10 S in sucrose gradients had been isolated from the post-polysomal fraction of homogenates of 14-day-old chick embryonic leg and breast muscle by sucrose gradient fractionation and gel filtration. The 10 S RNP contains a 4 S RNA species (base composition: AMP, .3%; GMP, 22.2%; CMP, 24.2%; and UMP, 23.2%), and shows three major bands in the 70-90-nucleotide size range by polyacrylamide gel electrophoresis in 99% formamide. The 4 S RNA does not contain oligo(U)- and oligo(A)-rich tracts. The RNP has a characteristic buoyant density of 1.410 g/ml, which corresponds to an RNA/protein ratio of about 1:4. The UV absorption spectra of the RNP is very distinct from that of its RNA component. Both 4 S RNA and the 10 S RNP are potent inhibitors of translation of a variety of mRNAs such as chick muscle poly(A)+ mRNA, rabbit globin mRNA, EMC virus RNA, and poly(A)- and mRNA of rat liver in micrococcal nuclease-treated rabbit reticulocyte lysate. The inhibitory action of the RNA and the RNP on mRNA translation appears to involve the initiation process. The RNA and RNP do not have a nuclease activity associated with them. The hyperchromicity profile of the inhibitory RNA with increasing temperature indicates that it does not contain a significant amount of double-stranded structure. This is also supported by the complete loss of biological activity of the RNA by treatment with pancreatic RNase. In contrast, the inhibitory activity of the RNP was resistant to RNase. Electrophoresis of the protein moieties of the inhibitory RNP using both one- and two-dimensional gel techniques in the presence of sodium dodecyl sulfate shows a complex pattern of polypeptides of Mr = 12,000-150,000. The protein pattern of the 10 S particle is quite different from those of free and polysomal mRNP and poly(A)-protein complexes of chick embryonic muscles, indicating that most, if not all of the mRNA-associated proteins, are absent in the 19 S RNP. The properties of the inhibitory RNA indicate that it is different from the various low molecular weight RNA species which are involved in the modulation of protein synthesis in cell-free systems. It is concluded that the 10 S particle represents a novel class of RNP, which may be involved in posttranscriptional regulation of protein synthesis in embryonic muscles.

Non-coordinate regulation of RNA synthesis in Escherichia coli exposed to 0 degrees C

A non-coordinate mode of regulation of RNA synthesis is observed in Escherichia coli cells during exposure to 0 degrees C. The stable RNA synthesis is preferentially inhibited with simultaneous accumulation of messenger RNA. The species of RNA synthesized at 0 degrees C was determined by several criteria such as sedimentation value in sucrose gradients, DNA-RNA hybridization, half life measurements, protein synthesizing capacity and its functional rate of decay. The mode of regulation of RNA synthesis at 0 degrees C is unique and is distinct from the non-coordinate regulation observed during amino acid starvation under stringent control.