Hepatic expression of polymerase beta, Ref-1, PCNA, and Bax in WY 14,643-exposed rats and hamsters

The hepatic levels of three protein markers of oxidative stress, polymerase beta, Ref-1, and PCNA, and of the pro-apoptotic protein, Bax, were quantitated after exposure to WY 14,643 (500 ppm in the feed) for 6 or 34 days in a rodent that is susceptible peroxisome proliferator (PP)-induced liver tumors (the Sprague Dawley rat) and in a rodent that is relatively resistant PP-induced liver tumors (the Syrian hamster). The analysis of detergent-extracted whole liver homogenates by immunoblotting showed a marked increase in the abundance of a 45-kDa variant of polymerase beta immunoreactivity and significant increases in the expression of Ref-1 and PCNA in WY 14,643-exposed rats. In contrast. WY 14,643-exposed hamsters expressed only trace levels of the polymerase beta variant and showed significant decreases in the expression of Ref-1 and PCNA. Long-term WY 14,643 exposure was associated with marked decreases in Bax expression in both species. Dose-response studies in the rat showed that the hepatic expression of the polymerase beta and Ref-1 were significantly increased after 6 days of exposure to WY 14,643 at levels of 5 and 50 ppm, respectively. The analysis of subcellular fractions of rat liver showed that the pathological increases in the levels of polymerase beta, Ref-1, and PCNA were especially prominent in mitochondria-enriched particulate liver subfractions. These results indicate that WY 14,643 exposure is associated with an increase in oxidative stress to the liver and that liver mitochondria are a major target of WY 14,643-associated liver damage. Our data are consistent with the hypothesis that the chronic overexpression of mutagenic or oncogenic effectors like polymerase beta and Ref-1 in a setting of increased hepatocyte proliferation and decreased apoptosis may facilitate peroxisome proliferator-induced hepatocellular carcinoma in the rat.

Preventing gut leakiness by oats supplementation ameliorates alcohol-induced liver damage in rats

Only 30% of alcoholics develop liver disease (ALD) suggesting that additional factors are needed. Endotoxin is one such factor, but its etiology is unclear. Since the gut is the main source of endotoxin, we sought to determine whether an increase in intestinal permeability (leaky gut) is required for alcohol-induced endotoxemia and liver injury and whether the gut leakiness is preventable. For 10 weeks, rats received by gavage increasing alcohol doses (to 8 g/kg/day) and either oats (10 g/kg) or chow b.i.d. Intestinal permeability was then assessed by urinary excretion of lactulose and mannitol. Liver injury was evaluated histologically, biochemically (liver fat content), and by serum aminotransferase. Alcohol caused gut leakiness that was associated with both endotoxemia and liver injury. Oats prevented these changes. We conclude that chronic gavage of alcohol in rats is a simple experimental model that mimics key aspects of ALD, including endotoxemia and liver injury, and can be useful to study possible mechanisms of endotoxemia in ALD. Since preventing the gut leakiness by oats also prevented the endotoxemia and ameliorated liver damage in rat, our results suggest that alcohol-induced gut leakiness 1) may cause alcohol-induced endotoxemia and liver injury and 2) may be the critical cofactor in the 30% of alcoholics who develop ALD. Further studies are needed to determine whether ALD in humans can be prevented by preventing alcohol-induced gut leakiness, studies that should lead to the development of useful therapeutic agents for the prevention of ALD.

A novel bipartite intronic splicing enhancer promotes the inclusion of a mini-exon in the AMP deaminase 1 gene

Alternative splicing of the 12-base exon 2 of the adenosine monophosphate deaminase (AMPD) gene is subject to regulation by both cis- and trans-regulatory signals. The extent of exon 2 inclusion is stage- and cell type-specific and is subject to the physiological state of the cell. In adult skeletal muscle, a cell type that regulates the activity of this allosteric enzyme at several levels, the exon 2-plus form of AMPD, predominates. We have performed a systematic analysis of the cis-acting regulatory sequences that reside in the intron immediately downstream of this mini-exon. A complex element comprising sequences that enhance exon 2 inclusion and sequences that counteract this effect resides in the middle of this intron. We demonstrate that the enhancing component is bipartite, with more than a kilobase of sequence separating the two functional sites. The presence of even minimal levels the mini-exon in the fully processed AMPD mRNA requires both of these sites, neither of which appears in any other published splicing enhancer. An RNA binding activity derived from a muscle cell line requires both of the enhancing sites. Mutations in either of the sites that eliminate exon 2 inclusion abrogate this binding activity.

Circadian rhythm of serum total homocysteine in men

Serum homocysteine levels were examined in a 24-hour study of 7 healthy and 5 diabetic men, revealing a statistically significant circadian rhythm (p = 0.030), normal concentrations of 11.83 +/- 1.2 vs 12.99 +/- 1.2 micromol/L, with peak values occurring during the evening (10:37 P.M.) and lowest levels occurring during the morning. These findings imply that increased atherosclerotic risk in insulin-resistant diabetics during morning hours does not appear to be explained by differences in homocysteine levels in the normal population.

Exacerbation of alcoholic liver injury by enteral endotoxin in rats

Increased gut permeability (leaky gut) and endotoxin-mediated Kupffer cell activation are proposed as the mechanisms of alcoholic liver injury. Although ethanol feeding is shown to sensitize the liver for injury induced by parental administration of lipopolysaccharide (LPS), how enteral LPS loading affects alcoholic liver injury is yet to be tested. The present study provides direct evidence for enhanced entrance to portal circulation of LPS enterally administered to the intragastric ethanol infusion model. Portal and systemic blood endotoxin levels increased to 43.0 +/- 4.1 and 6.2 +/- 4.3 pg/mL at 2 hours following enteral LPS administration (5 mg/kg) in alcohol-fed animals, while no such increases were observed in pair-fed controls. However, endotoxin levels in systemic blood of alcohol-fed rats were reduced to 0 to 1. 5 pg/mL 16 hours after LPS administration. Weekly enteral administration of LPS to the model for 9 weeks exacerbated an increase in plasma alanine transaminase (ALT) levels (227 +/- 75 vs. 140 +/- 70; P <.01), mononuclear infiltration (25 +/- 22 vs. 6.4 +/- 4.4/10 mm(2); P =.02), sinusoidal congestion, and spotty necrosis, and induced diffuse coagulative necrosis and centrilobular fibrosis in some animals. Reverse-transcription polymerase chain reaction (RT-PCR) analysis confirmed the LPS effect at the tissue level by demonstrating accentuated induction of tumor necrosis factor alpha (TNF-alpha) and Cox-2 mRNA. In conclusion, enteral LPS administration potentiates alcoholic liver necrosis, inflammation, and fibrosis despite efficient endotoxin clearance by the liver and mild systemic endotoxemia that occurs episodically following enteral LPS challenge.

Positive and negative elements mediate control of alternative splicing in the AMPD1 gene

The second exon of the AMP deaminase (AMPD) 1 gene is alternatively spliced in response to stage-specific signals elaborated during myocyte differentiation. Since inheritance of the mutation in exon 2 of the AMPD1 gene has been recently shown to be associated with a better prognosis of congestive heart failure and the alternative splicing of exon 2 modulates the residual activity of AMPD1 in individuals with this mutant allele, the regulatory mechanism of alternative splicing in the AMPD1 gene is clinically intriguing. Retention or exclusion of exon 2 results from the interplay between negative and positive elements in the primary transcript. Exon 2 is intrinsically defective and difficult to recognize. Herein, we show that this property of exon 2 is the consequence of three defects; a suboptimal 3' splice acceptor site, a suboptimal 5' splice donor site and the small size of the exon. An improvement in any one of these defects relieves the masking of this exon. Further, this defective exon can only be identified in the presence of the adjacent downstream intron.

Measuring contributions to the research mission of medical schools

The authors of this article, who were the members and staff of a research panel formed by the AAMC as part of its mission-based management initiative, reflect on the growing interest in quantitative information in the management of the research mission of medical schools. They note the serious limitations of any such system of measures for research, particularly its inability to represent directly the quality of the research effort. Despite these concerns, the authors acknowledge that leaders in academic medicine have always used quantitative measures in one form or another to compare performance or assess progress. Two factors appear to be driving increases in this practice: (1) the need to demonstrate to institutional stakeholders that resources are being used wisely and that the school's performance justifies continued investment in the research mission; and (2) the need to fashion an economic strategy to manage precious institutional resources, particularly research space. Given these realities, the authors offer guidelines for the proper development and use of measures to assess contributions by faculty, departments, and institutions to the research mission. They also comment on the measures most commonly used in four areas: grants and other revenue-generating activities; publications; faculty members' research reputation and contributions to the national research enterprise; and support to the general research mission of the school. The authors conclude that quantitative information can help institutional leaders in important management decisions. However, the potential for misuse is great. The key is always to regard this information as an aid to judgment, not a substitute for it.

Altered purine and glycogen metabolism in skeletal muscle during exercise in patients with heart failure

Plasma levels of ammonia and hypoxanthine (HX) can be indices of purine nucleotide degradation. The present study determined if patients with heart failure (HF) have altered exercise plasma ammonia and HX levels relative to the peak work rate performed. Blood lactate, plasma ammonia, and plasma HX levels were measured in 59 patients with HF (New York Heart Association [NYHA] classes I:20, II:21, and III:18) and 21 controls at rest and after a maximal cardiopulmonary exercise test. The peak work rate (normal and NYHA I, II, and III, 163+/-11, 152+/-9, 94+/-5, and 69+/-5 W) and peak oxygen uptake ([VO2] 32.3+/-1.7, 25.1+/-0.9, 18.6+/-0.5, and 14.1+/-0.6 mL/min/kg) decreased as the NYHA functional class increased. The increment from rest to peak exercise (delta) for lactate ([(delta)lactate] 6.1+/-0.3, 4.8+/-0.4, 4.6+/-0.3, and 2.9+/-0.3 mmol/L), (delta)ammonia (132+/-14, 119+/-20, 94+/-13, and 32+/-6 microg/dL), and (delta)HX (33.5+/-3.4, 24.9+/-4.7, 20.6+/-3.0, and 9.9+/-1.2 micromol/L) was progressively smaller as HF worsened. The ratio for (delta)lactate to peak work rate (0.037+/-0.003, 0.032+/-0.004, 0.049+/-0.003, and 0.042+/-0.005) was higher in classes II to III HF, while the ratio for (delta)ammonia to peak work rate (0.81+/-0.14, 0.78+/-0.16, 0.99+/-0.11, and 0.47+/-0.11) was significantly lower in class III HF. In summary, patients with HF exhibited a smaller ammonia response with a higher lactate response to exercise when normalized with the peak work rate. These results suggest there may be an altered purine and glycogen metabolism during exercise in skeletal muscle in patients with HF.

Common variant in AMPD1 gene predicts improved clinical outcome in patients with heart failure

BACKGROUND

This study was undertaken to identify gene(s) that may be associated with improved clinical outcome in patients with congestive heart failure (CHF). The adenosine monophosphate deaminase locus (AMPD1) was selected for study. We hypothesized that inheritance of the mutant AMPD1 allele is associated with increased probability of survival without cardiac transplantation in patients with CHF.

METHODS AND RESULTS

AMPD1 genotype was determined in 132 patients with advanced CHF and 91 control reference subjects by use of a polymerase chain reaction-based, allele-specific oligonucleotide detection assay. In patients with CHF, those heterozygous (n=20) or homozygous (n=1) for the mutant AMPD1 allele (AMPD1 +/- or -/-, respectively) experienced a significantly longer duration of heart failure symptoms before referral for transplantation evaluation than CHF patients homozygous for the wild-type allele (AMPD1 +/+; n=111; 7.6+/-6.5 versus 3.2+/-3.6 years; P<0.001). The OR of surviving without cardiac transplantation >/=5 years after initial hospitalization for CHF symptoms was 8.6 times greater (95% CI: 3.05, 23.87) in those patients carrying >/=1 mutant AMPD1 allele than in those carrying 2 wild-type AMPD1 +/+ alleles.

CONCLUSIONS

After the onset of CHF symptoms, the mutant AMPD1 allele is associated with prolonged probability of survival without cardiac transplantation. The mechanism by which the presence of the mutant AMPD1 allele may modify the clinical phenotype of heart failure remains to be determined.

Analysis of risk factors for the development of bronchiolitis obliterans syndrome

Chronic rejection after lung transplantation, manifesting as bronchiolitis obliterans syndrome (BOS), has become the dominant challenge to long-term patient and graft survival. In order to elucidate risk factors for development of BOS we utilized the 1995 revision of the working formulation for the classification of lung allograft rejection (), and devised a quantitative method to retrospectively study lung transplant biopsies from all patients who survived at least 90 d. All transbronchial biopsies were regraded 0 to 4 for acute perivascular rejection and lymphocytic bronchitis/bronchiolitis (LBB), and the grades were totaled over a period of time to give two scores, respectively, for each patient. Also examined were timing of acute rejection and LBB episodes and decreased immunosuppression defined as two or more cyclosporine A levels < 200 ng/ml. Sixty-six patients with BOS and 68 with no BOS (NBOS) satisfied our criteria for inclusion in the study. Demographics including age, sex, and primary diagnoses were similar. The mean perivascular score for BOS was 6.2 over a mean follow-up of 822 d (range, 113 to 2,146) compared with 3.2 for NBOS over 550 d (range, 97 to 1,734) mean follow-up. Airway scores were 5.3 and 1.7, respectively, for the same follow-up periods. There was no correlation between length of follow-up and rejection or LBB scores, although mean length of follow-up for the two groups was significantly different. Late acute rejection and LBB were significantly associated with BOS as was decreased immunosuppression. In addition to perivascular rejection, LBB, late acute rejection, and decreased immunosuppression are significant risk factors for the development of BOS. Analysis of the current data leads us to believe that LBB, in the absence of infection, is in fact a manifestation of acute rejection, with similar implications for graft function as acute perivascular rejection.

Leaky gut in alcoholic cirrhosis: a possible mechanism for alcohol-induced liver damage

OBJECTIVE

Only 30% of alcoholics develop cirrhosis, suggesting that the development of alcohol-induced liver injury requires one or more additional factors. Animal studies have shown that gut-derived endotoxin is one such factor. Because increased intestinal permeability has been shown to cause endotoxemia, we hypothesized that increased gastrointestinal permeability contributes to the pathogenesis of alcoholic liver disease. This study aimed to measure gastroduodenal and intestinal permeability in alcoholics with and without chronic liver disease and in nonalcoholic subjects with chronic liver disease.

METHODS

Gastroduodenal permeability was assessed by measurement of urinary excretion of sucrose after oral administration. Intestinal permeability was assessed by measurement of urinary lactulose and mannitol after oral administration of these sugars.

RESULTS

Alcoholics with no liver disease showed a small but significant increase in sucrose excretion. Alcoholics with chronic liver disease demonstrated a marked and highly significant increase in urinary sucrose excretion relative to the controls, to the alcoholics with no liver disease, and to the nonalcoholics with liver disease. Alcoholics with chronic liver disease demonstrated a marked and highly significant increase in both lactulose absorption and in the urinary lactulose/mannitol ratio (alcoholics 0.703 vs controls 0.019, p = 0.01). In contrast, alcoholics with no liver disease and nonalcoholics with liver disease showed normal lactulose absorption and normal lactulose/mannitol ratio.

CONCLUSION

Because only the alcoholics with chronic liver disease had increased intestinal permeability, we conclude that a "leaky" gut may be a necessary cofactor for the development of chronic liver injury in heavy drinkers.

Determination of protein carbonyl groups by immunoblotting

Free radical-mediated oxidation of proteins results in the formation of carbonyl groups in quantities that reflect the intensity of the oxidative stress. We have developed an immunochemical technique for the quantification of carbonyl groups in protein samples prepared from small tissue samples and cell cultures. Protein samples were slot-blotted onto a polyvinylidene difluoride membrane, which was sequentially treated with 2,4-dinitrophenylhydrazine (DNPH), a primary antibody specific for the 2,4-dinitrophenol group, and a peroxidase-labeled second antibody. After the blots were developed with a chemiluminescent substrate and exposed to X-ray film, the level of immunostaining was quantitated by densitometry. Using oxidized bovine serum albumin as a standard and loading 5 microg of protein per slot, the minimum detectable carbonyl content was approximately 60 pmol carbonyl/mg protein. When necessary, nonspecific staining by noncarbonyl constituents in complex sample matrices was accounted for by using sodium borohydride-treated blanks. Results by the new method were highly correlated (r = 0.932, P < 0.0001) with those of the standard DNPH-based spectrophotometric technique. The coefficient of variation at a carbonyl level of 1.5 nmol/mg protein was 9.7%. The utility of this new method was demonstrated by measuring protein oxidation in cultured human colon cells (SW620) that were briefly exposed to H2O2.

Control of AMP deaminase 1 binding to myosin heavy chain

AMP deaminase (AMPD) plays a central role in preserving the adenylate energy charge in myocytes following exercise and in producing intermediates for the citric acid cycle in muscle. Prior studies have demonstrated that AMPD1 binds to myosin heavy chain (MHC) in vitro; binding to the myofibril varies with the state of muscle contraction in vivo, and binding of AMPD1 to MHC is required for activation of this enzyme in myocytes. The present study has identified three domains in AMPD1 that influence binding of this enzyme to MHC using a cotransfection model that permits assessment of mutations introduced into the AMPD1 peptide. One domain that encompasses residues 178-333 of this 727-amino acid peptide is essential for binding of AMPD1 to MHC. This region of AMPD1 shares sequence similarity with several regions of titin, another MHC binding protein. Two additional domains regulate binding of this peptide to MHC in response to intracellular and extracellular signals. A nucleotide binding site, which is located at residues 660-674, controls binding of AMPD1 to MHC in response to changes in intracellular ATP concentration. Deletion analyses demonstrate that the amino-terminal 65 residues of AMPD1 play a critical role in modulating the sensitivity to ATP-induced inhibition of MHC binding. Alternative splicing of the AMPD1 gene product, which alters the sequence of residues 8-12, produces two AMPD1 isoforms that exhibit different MHC binding properties in the presence of ATP. These findings are discussed in the context of the various roles proposed for AMPD in energy production in the myocyte.

Expression and regulation of interferon-gamma-induced tryptophan catabolism in cultured skin fibroblasts

Interferon-gamma (IFN-gamma)-induced, indoleamine dioxygenase-catalyzed tryptophan catabolism was studied in cultured human foreskin fibroblasts using the increase in cellular kynurenine synthesis as an index of gene expression. The time courses of the inhibition of IFN-gamma-induced kynurenine synthesis by actinomycin D and cycloheximide showed that the indoleamine dioxygenase gene was transcribed as early as 2 h and translated as early as 5 h after initiation of IFN treatment. Expression was completely inhibited by the Ser/Thr kinase inhibitor, H-7 (66 microM), during the first 2 h after IFN-gamma treatment. Prolonged pretreatment of cells with high concentrations of staurosporine (380 nM) or genestein (610 microM) inhibited expression by 38% and 53%, respectively. Genestein also inhibited expression when it was added to cultures between 8 and 24 h after IFN-gamma treatment. The expression of kynurenine synthesis was inhibited by A23817 during the first 4 h after IFN treatment by mechanisms that were independent of cyclooxygenase, calmodulin, and calcineurin. Exogenous gangliosides (bovine brain gangliosides and purified GM1) inhibited IDO expression throughout the first 24 h after IFN-gamma treatment by mechanisms that did not involve effects on Ca2+ channels. Other biologic response modifiers, including phorbol myristic acetate, arachidonic acid, lipopolysaccharide, analogs of cAMP and cGMP, W-7, and sphingosine, did not induce IDO in the absence of IFN-gamma, nor did they modulate IFN-gamma-induced expression. These results indicate that the expression of kynurenine synthesis is modulated at the transcriptional and posttranscriptional levels by protein tyrosine kinase and by a Ser/Thr kinase with properties distinctly different from those of conventional protein kinase C. The capacity for attenuation of this IFN-gamma-induced response over its entire time course by many effectors and through multiple cellular signaling pathways may represent a mechanism for fine-tuning the level of oxidative tryptophan metabolism to meet the needs of a particular cytostatic or antiproliferative response.

Glutathione content of colonic mucosa: evidence for oxidative damage in active ulcerative colitis

Oxidative stress appears to play a role in the tissue damage of active ulcerative colitis, and it has been suggested that a defect in mucosal antioxidant defenses is a etiological factor in the disease. This study was undertaken to investigate the mucosal content and oxidation state of glutathione in ulcerative colitis in the active and inactive states and to examine the relationship between glutathione content and disease activity in this patient population. Endoscopic biopsies of colon mucosa were collected from normal subjects, from macroscopically normal tissue of patients with inactive and active ulcerative colitis, and from inflamed tissue of patients with active ulcerative colitis. The mucosal contents of GSH and GSSG were determined by liquid chromatography. We found no significant differences in tissue contents of reduced glutathione among the four groups. The median tissue level of oxidized glutathione in inflamed mucosa from patients with active ulcerative colitis was increased 1.7-fold (P = 0.017) over that of patients with inactive disease. The oxidized glutathione content of the mucosa also showed significant positive correlations with clinical and histological indices of disease severity among ulcerative colitis patients. In conclusion, a change in the redox status of mucosal glutathione is associated with inflammation and disease activity in ulcerative colitis. This change appears to be a consequence of inflammation rather than a pathogenic factor for the disease.

Modulatory effects of the colonic milieu on neutrophil oxidative burst: a possible pathogenic mechanism of ulcerative colitis

An important hallmark of ulcerative colitis (UC) is mucosal neutrophil (PMN) infiltration associated with mucosal damage. This suggests that colonic chemoattractants such as bacterial products (e.g., N-formyl-methionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide (LPS)) reach systemic circulation and attract PMNs to the colon. PMNs are then activated in the colonic mucosa and release their toxic oxidative metabolites. However, bacterial products are also present in the systemic circulation of healthy subjects. Thus we hypothesized that PMNs develop tolerance to colonic factors in the normal state and that this tolerance is absent in UC. We evaluated the PMN respiratory burst in response to stimulation with fMLP, LPS, or phorbol 12-myristate 13-acetate (PMA) by measuring the production of reactive oxygen species (ROS) with both luminol-enhanced chemiluminescence and a cytochrome C reduction assay. PMNs were obtained from control subjects, inactive UC patients, patients with UC who had undergone colectomies, and non-UC patients with colectomies. All three stimuli induced a significant rise in ROS. PMNs from non-UC colectomy subjects produced significantly higher ROS than PMNs from control subjects with intact colons in response to both fMLP and LPS. In contrast, PMNs from UC colectomy patients produced levels of ROS similar to those produced by PMNs from UC patients with intact colons in response to fMLP and LPS. Colectomy had no effect on PMA-induced ROS production in controls. The observed difference in fMLP-induced ROS production in control subjects with intact colons was not due to fMLP receptor down-regulation because a competition assay performed with the fMLP blocker BMLP showed a similar receptor apparent affinity in all four groups. We conclude the following: (1) the normal colonic milieu modulates the PMN respiratory burst, resulting in hyporesponsiveness of PMNs to "physiologic" but not "pharmacologic" stimulation. This effect is not due to receptor down-regulation. (2) UC colonic milieu does not appear to modulate PMN respiratory burst. This loss of PMN "tolerance" to colonic factors may have a pathogenic role in the sustained inflammation and tissue damage in UC.

Coupled enzymatic assay for the determination of sucrose

An enzymatic spectrophotometric assay for the determination of sucrose in unextracted samples of serum and urine was developed. The method entailed the coupling of invertase-catalyzed sucrose hydrolysis with a fructose dehydrogenase-catalyzed oxidation of the liberated fructose. The latter reaction generated reducing equivalents that were transferred to a tetrazolium salt with a concomitant increase in absorbance at 570 nm. The assay, which was carried out in microtiter plates, had a minimum detectable sucrose concentration of 0.03 mmol/liter and run-to-run and within-run coefficients of variation of 7.5 and 6.7%, respectively, and showed a good correlation with urine sucrose determination by GLC (r = 0.92). The assay range of 0.03-2.10 mmol/liter is suitable for the quantitation of serum sucrose following iv administration and for the quantitation of urine sucrose at basal levels and following the consumption of an oral test dose of sucrose. This method was used to analyze urine samples from a group of human subjects who consumed 20 g of sucrose for the assessment of gastroduodenal permeability. This convenient assay provides for the rapid and specific estimation of sucrose and has the potential to be used in a variety of manual, semiautomated, or automated formats.

Subunit composition of AMPD varies in response to changes in AMPD1 and AMPD3 gene expression in skeletal muscle

Adenosine monophosphate deaminase (AMPD), a central enzyme in energy metabolism in skeletal muscle, is encoded by a multigene family in higher eukaryotes. Denervation was used as a stimulus to induce a change in fiber type composition of rat gastrocnemius muscle and, consequently, gene expression. Specific antisera and nucleic acid probes were used to assess changes in expression of the AMPD1 and AMPD3 genes. Total AMPD activity in denervated skeletal muscle increased by 34%. The composition of the AMPD tetrameric holoenzyme was altered in two ways: The percentage of AMPD holoenzyme molecules consisting of one or more AMPD3 subunits increased three-fold, and the percentage of AMPD1 mRNA that excludes exon 2-encoded sequences doubled. These results suggest that expression of the AMPD1 and AMPD3 genes may be coordinated in myocytes to effect production of an AMPD holoenzyme of varying subunit composition.

Gene therapy: socioeconomic and ethical issues. A roundtable discussion

Gene therapy research has the potential to revolutionize the way in which many human diseases are treated. Despite its enormous potential, roundtable panelists concluded that the field needs time to mature scientifically without pressure to develop a marketable therapeutic product. In addition, health care decision makers, physicians, and the lay public need to be educated on the future medical, economic, and ethical ramifications of gene therapy.

Incidence of post-transplant malignancy among 674 solid-organ-transplant recipients at a single center

We evaluated the post-transplant course of the entire solid-organ-transplant population at our institution to determine the frequency, incidence and specific type of post-transplant malignancies which occurred at a single center. Of 674 solid-organ-transplant recipients (305 renal, 307 heart, 54 lung, 8 heart/lung), we detected 79 malignancies (48 heart, 28 renal, 2 lung, 1 heart/lung), representing an overall cancer frequency of 11.7%, 15.6% for heart and 9.2% for renal transplant recipients. The frequency in both transplant groups was higher than that reported previously in the multicenter data in the literature (about 6%); we also noted a shorter interval to malignancy (27 vs. 61 months). The most common malignancies overall were skin/lip carcinomas and post-transplant lymphoproliferative disorder (PTLD). The frequency of PTLD was higher in non-renal (6.5%) than renal (0.7%) transplant recipients and statistical analysis confirmed a significant higher incidence of all malignancies (p = 0.0032) and of PTLD (p = 0.0001) in heart and lung recipients as opposed to renal transplant recipients. The frequency of total skin/lip carcinomas was essentially equal in the heart and renal transplant groups (6%), and statistical analysis showed no significant difference in incidence of this general type of malignancy; however, there was a marked disparity in interval to squamous cell carcinoma (SCC) between renal and heart transplant recipients (27 versus 59 months). This was associated with an apparent increase in the rate of occurence of SCC after 60 months in heart transplant recipients, a finding not previously reported in the multicenter data in the literature. We did not demonstrate a significant effect of the withdrawal of prophylactic OKT3 from the immunosuppression regimen of heart transplant recipients on the incidence of all tumors, PTLD or skin/lip tumors.

Identification of functional domains in AMPD1 by mutational analysis

AMP deaminase (AMPD) is a complex allosteric enzyme encoded by a multigene family in higher eukaryotes. The amino terminus of each AMPD gene is unique, while the mild and carboxy termini have been highly conserved among all the AMPD genes. Mutational analyses of the AMPD1 gene demonstrate that the catalytic site and a regulatory site, likely an ATP binding site, are located in the highly conserved carboxy terminus. Deletion mutants and a normal splice variant of AMPD1 demonstrate that the amino terminus has a profound influence on catalytic activity of AMPD and by inference from prior studies this region also influences binding of AMPD1 to myosin. Results of these studies suggest a regulatory model in which alternative splicing in the amino terminal region of AMPD1 generates isoforms of AMPD that exhibit differential sensitivity to effector molecules such as ATP.

Verification of reference ranges by using a Monte Carlo sampling technique

We have investigated the application of Monte Carlo significance tests to the verification of reference ranges in the context of the transfer of an established range from one laboratory to another. Here we present an introduction to the Monte Carlo technique, outline a procedure for performing these tests using a commercially available software program, and demonstrate some of the operating characteristics of the tests when they are used to compare samples of different sizes and variances.

The differing effects of acute and chronic alcohol on gastric and intestinal permeability

OBJECTIVE

Acute and chronic alcohol intake cause GI symptoms because of either alcohol-induced structural or functional abnormalities. In theory, the disruption of the integrity of the gut mucosa should be reflected by changes in the absorption of molecular probes, such as lactulose, mannitol, and sucrose. Accordingly, we investigated the effects of acute and chronic ethanol on the permeability of the gastric and small intestinal mucosa.

METHODS

We measured the absorption of sucrose, mannitol, and lactulose in 20 controls and 18 alcoholics within 3 days after their last drink. We evaluated the reversibility of the abnormalities in alcoholics by repeat testing after 7 to 14 days of sobriety. The acute effects of ethanol in normal controls and abstinent alcoholics were also studied after the administration of ethanol by both the oral and IV routes.

RESULTS

The absorptions of lactulose and sucrose in chronic alcoholics were normal. However, the alcoholics demonstrated a significant decrease in mannitol absorption and a corresponding increase in the lactulose/mannitol ratio. Both parameters returned to normal after a period of sobriety. Acute ethanol did not significantly affect mannitol or lactulose absorption, whereas oral ethanol significantly increased sucrose absorption.

CONCLUSIONS

Chronic ethanol reversibly affects the integrity of small intestinal villi without significantly affecting gastrointestinal permeability. In contrast, a single oral dose of ethanol increases gastroduodenal permeability but has no effect on the lactulose or mannitol permeability of the small intestine. These regional changes in gut permeabilities may contribute to alcohol-induced GI symptoms.

Verification of reference ranges by using a Monte Carlo sampling technique

We have investigated the application of Monte Carlo significance tests to the verification of reference ranges in the context of the transfer of an established range from one laboratory to another. Here we present an introduction to the Monte Carlo technique, outline a procedure for performing these tests using a commercially available software program, and demonstrate some of the operating characteristics of the tests when they are used to compare samples of different sizes and variances.

Inflammation-associated changes in the cellular availability of tryptophan and kynurenine in renal transplant recipients

In the course of evaluating the hypothesis that tryptophan or tryptophan metabolites mediate some of the physiological or pathological aspects of the inflammatory response, we assessed the bioavailability of tryptophan and kynurenine in renal allograft recipients during periods of stable graft function, acute rejection and OKT3 therapy. In normal controls and patients with stable function, approximately 8% of the tryptophan and less than 5% of the kynurenine in serum were present in the freely diffusable form. The free tryptophan concentration was significantly increased during acute rejection, while free tryptophan as well as total and free kynurenine concentrations were significantly increased during OKT3 therapy. In each case the ratio of free indole to the sum of the plasma concentrations of large neutral amino acids was also increased. In vitro studies of indole binding to human serum proteins demonstrated the parallel displacement of bound tryptophan and kynurenine by physiological changes in pH, serum albumin concentration and free fatty acid concentration. The results suggest that inflammation associated increases in the oxidative metabolism of tryptophan are accompanied by the increased availability of serum indoles for intracellular metabolism in the tissues.

Functionally distinct elements are required for expression of the AMPD1 gene in myocytes

AMP deaminase (AMPD) is an enzyme found in all eukaryotic cells. Tissue-specific and stage-specific isoforms of this enzyme are found in vertebrates, and expression of these different isoforms is determined by selective expression of the multiple genes. The AMPD1 gene is expressed predominantly in skeletal muscle, in which transcript abundance is controlled by stage-specific and fiber type-specific signals. This enzyme activity is presumed to be important in skeletal muscle because a metabolic myopathy develops in individuals with an inherited deficiency of AMPD1. In the present study, cis- and trans-acting factors that control expression of AMPD1 have been identified. Two cis-acting elements located within 100 nucleotides of the transcriptional start site are required for muscle-specific expression of AMPD1. One element (-100 to -79) behaves like a tissue-specific enhancer, and it interacts with protein(s) found predominantly in nuclei of myoblasts and myotubes. This element is similar in sequence to an MEF2 binding motif, and it contains an A/T core that is essential for enhancer activity and binding of a nuclear protein(s). The second element (-60 to -40) has properties of a stage-specific promoter in that it is essential for muscle-specific expression of the AMPD1 promoter, does not confer muscle-specific expression on a heterologous promoter construct, and interacts with a protein(s) restricted to nuclei of differentiated myotubes. Interaction between these functionally distinct elements may be required for regulating the expression of AMPD1 during myocyte differentiation and in different muscle fiber types.

Alternative splicing: a mechanism for phenotypic rescue of a common inherited defect

Approximately 2% of Caucasians and African-Americans are homozygous for a nonsense mutation in exon 2 of the AMPD1 (AMP deaminase) gene. These individuals have a high grade deficiency of AMPD activity in their skeletal muscle. More than 100 patients with AMPD1 deficiency have been reported to have symptoms of a metabolic myopathy, but it is apparent many individuals with this inherited defect are asymptomatic given the prevalence of this mutant. Results of the present study provide a potential molecular explanation for "correction" of this genetic defect. Alternative splicing eliminates exon 2 in 0.6-2% of AMPD1 mRNA transcripts in adult skeletal muscle. Expression studies document that AMPD1 mRNA, which has exon 2 deleted, encodes a functional AMPD peptide. A much higher percentage of alternatively spliced transcripts are found during differentiation of human myocytes in vitro. Transfection studies with human minigene constructs demonstrate that alternative splicing of the primary transcript of human AMPD1 is controlled by tissue-specific and stage-specific signals. Alternative splicing of exon 2 in individuals who have inherited this defect provides a mechanism for phenotypic rescue and variations in splicing patterns may contribute to the variability in clinical symptoms.

Immunologic evidence for three isoforms of AMP deaminase (AMPD) in mature skeletal muscle

Four rabbit polyclonal antisera to purified AMP deaminase (AMPD) isozymes were used to precipitate homogenate AMPD activity from dissected gracilis, soleus and gastrocnemius muscles of the cat, rabbit, rat, mouse, Rhesus monkey, human and toad. The antisera were also tested against other unusual muscles: autonomically innervated striated muscle of the upper esophagus (UEM), skeletal muscle of patients with myo-AMPD deficiency and extraocular muscles (EOM) of humans and Rhesus monkeys. The reference antiserum, M, prepared against human psoas muscle AMPD, precipitated > 90% AMPD from all primate skeletal muscles tested, and from type-2 muscles of all mammals tested, but < 75% from cat and rodent soleus, toad gastrocnemius and primate UEM, EOM and myo-AMPD deficient muscles. Thus, a second isozyme was clearly indicated. Antibody B, against rat liver and kidney AMPD, had no effect with any muscle specimen. Antibody C, against rat heart AMPD, produced additive precipitation of AMPD from soleus of rat and mouse, while antibody E1, against human red cell (and heart) AMPD, produced additive AMPD precipitation from toad gastrocnemius, cat soleus and muscles of several AMPD-deficient humans. A second AMPD isozyme thus accounted for as much as 25% of total activity in some animal red muscles, but no more than 5% in human mixed muscles. At least one more isozyme is needed to account for muscle AMPD unreactive with all antibodies tested in rabbit soleus, toad gastrocnemius and primate UEM and EOM. A list is appended of the approximate AMPD activity in various human cells and tissues.

Molecular cloning of human amidophosphoribosyltransferase

The cDNA of human amidophosphoribosyltransferase (EC 2.4.2.14, ATase), which is the supposed regulatory allosteric enzyme of de novo purine nucleotide biosynthesis, has been cloned from human hepatoma (HepG2) cDNA library. The predicted open reading frame encodes a protein of 517 amino acids with a deduced molecular weight (Mr) of 57,398, which is consistent with the molecular mass of 56 kDa on SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of the ATase subunit purified from human placenta. The derived amino acid sequence exhibits 93, 82, 41, 37, and 33% identity with the sequences of rat, chicken, Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae ATases, respectively. Southern blot analysis suggested that the ATase gene exists as multiple copies. ATase mRNA (3.5 kb) is ubiquitously expressed in various human tissues. Comparison with rat and chicken ATases showed that two cysteine residues for an iron-sulfur cluster were conserved. Four consensus phosphorylation sites for cAMP-dependent protein kinase were found.

Toxicity and pharmacokinetics of ciprofloxacin

Ciprofloxacin is a fluorinated quinolone antibiotic with a broad spectrum of activity against both gram positive and gram negative organisms. Previous studies have indicated that oral or parenteral preparations of ciprofloxacin resulted in therapeutic concentrations in the aqueous humor but intravitreal levels were found to be only marginally higher than the MIC90 for gram positive cocci. Toxicity was evaluated following intravitreal doses of ciprofloxacin injected into the mid-vitreous cavity of one eye of pigmented rabbits. As a control, an identical volume of normal saline was injected into the fellow eye. Four doses of ciprofloxacin were studied, 100 micrograms, 250 micrograms, 500 micrograms and 1000 micrograms. Electroretinograms (ERGs) were recorded prior to injection and 1, 7 and 14 days after injection. These were analyzed as b-wave amplitude ratios between treated and untreated eyes. On ophthalmoscopic examination focal areas of retinitis were observed following injection of both 500 micrograms and 1000 micrograms of ciprofloxacin but not at 250 micrograms. Additionally, ERG amplitude ratios were significantly reduced following the 1000 micrograms dose. At the 100 or 250 micrograms ciprofloxacin dose histological sections are comparable with control eyes and appear normal; ERG ratios were unchanged from the baseline level and careful indirect ophthalmoscopic examination revealed no alterations. Pharmacokinetic analysis after single intravitreal injection of 250 micrograms of ciprofloxacin (N = 3 rabbits/dose) disclosed vitreous fluid levels (microgram/ml) of 146 at 0 hr, 77 at 4 hr, 32 at 8 hr, 0.49 at 24 hr and 0.24 at 48 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal and hepatic output of glutathione in plasma and whole blood

Measurement of glutathione (GSH) output by the rat kidney and liver demonstrated a substantial net release into red cells across both tissues. The results suggest important roles for kidney and liver in the maintenance of GSH concentrations in red cells and a significant role for the red cell in the interorgan transport of GSH.

Point mutations in the DNA polymerase gene of human cytomegalovirus that result in resistance to antiviral agents

Three independently isolated mutants of human cytomegalovirus strain AD169 were found to be resistant to ganciclovir at a 50% effective dose of 200 microM. Phosphorylation of ganciclovir was reduced 10-fold in mutant-infected cells compared with AD169-infected cells. All three mutants were also determined to be resistant to the nucleotide analogs (S)-1-[(3-hydroxy-2- phosphonylmethoxy)propyl]adenine (HPMPA) and (S)-1-[(3-hydroxy-2-phosphonylmethoxy)propyl]cytosine (HPMPC) and hypersensitive to thymine-1-D-arabinofuranoside (AraT). Single base changes resulting in amino acid substitutions were demonstrated in the nucleotide sequence of the DNA polymerase gene of each mutant. The polymerase mutation contained in one of the mutants was transferred to the wild-type AD169 background. Ganciclovir phosphorylation in cells infected with the recombinant virus produced by this transfer was found to be equivalent to that of AD169-infected cells. The ganciclovir resistance of the recombinant was reduced fourfold compared with that of the parental mutant; however, the recombinant remained resistant to HPMPA and HPMPC and hypersensitive to AraT. The ganciclovir resistance of the mutants therefore appears to result from mutations in two genes: (i) a kinase which phosphorylates ganciclovir and (ii) the viral DNA polymerase.

Mitomycin C-induced colitis in rats: a new animal model of acute colonic inflammation implicating reactive oxygen species

The mechanism of the tissue damage induced by colonic inflammation in ulcerative colitis is not established. We therefore developed and characterized a simple new rat model of acute colonic inflammation induced by a single systemic injection of mitomycin C. After an intraperitoneal injection of mitomycin-C, colon histologic examination revealed transient (3 to 14 days) diffuse, colonic inflammation and injury that, like human ulcerative colitis, was limited to the mucosal layer. The rest of the gastrointestinal tract was spared. Gut permeability, as measured by urinary excretion of orally administered lactulose and mannitol, was unchanged 3 days after injection, when inflammation was already present; permeability was increased at 7 days, when inflammation was maximal. Mitomycin C did not produce inflammation in experimentally bypassed segments of small bowel despite the presence of colonic-type bacteria, suggesting that lack of intraluminal bacteria was not responsible for the absence of inflammation in the small intestine. Chemiluminescence, a means of estimating levels of reactive oxygen species, was greater in the intact, inflamed colon of mitomycin C-treated rats than in bypassed segments. Moreover, inflamed mucosal scrapings produced more in vitro luminol-enhanced chemiluminescence. Furthermore, the reactive oxygen species scavengers allopurinol, catalase, and WR-2721 decreased inflammation severity. We therefore conclude: (1) the mitomycin C-treated rat is a novel, easy to prepare animal model of acute inflammation of colonic mucosa, with morphologic similarities to the acute phase of ulcerative colitis in human beings; (2) increased gut permeability in mitomycin C-treated rats is the result, not the cause, of the inflammation; and (3) reactive oxygen species play an important role in colonic inflammation and tissue injury in this model, and possibly in human ulcerative colitis.

Molecular basis of AMP deaminase deficiency in skeletal muscle

AMP deaminase (AMPD; EC 3.5.4.6) is encoded by a multigene family in mammals. The AMPD1 gene is expressed at high levels in skeletal muscle, where this enzyme is thought to play an important role in energy metabolism. Deficiency of AMPD activity in skeletal muscle is associated with symptoms of a metabolic myopathy. Eleven unrelated individuals with AMPD deficiency were studied, and each was shown to be homozygous for a mutant allele characterized by a C----T transition at nucleotide 34 (codon 12 in exon 2) and at nucleotide 143 (codon 48 in exon 3). The C----T transition at codon 12 results in a nonsense mutation predicting a severely truncated AMPD peptide. Consistent with this prediction, no immunoreactive AMPD1 peptide is detectable in skeletal muscle of these patients. This mutant allele is found in 12% of Caucasians and 19% of African-Americans, whereas none of the 106 Japanese subjects surveyed has this mutant allele. We conclude from these studies that this mutant allele is present at a sufficiently high frequency to account for the 2% reported incidence of AMPD deficiency in muscle biopsies. The restricted distribution and high frequency of this doubly mutated allele suggest it arose in a remote ancestor of individuals of Western European descent.

Oxidative tryptophan metabolism in renal allograft recipients: increased kynurenine synthesis is associated with inflammation and OKT3 therapy

Serum concentrations of tryptophan (TRP) and kynurenine (KYN) were determined in renal allograft recipients (RAR) as an index of interferon-gamma-induced, indoleamine-dioxygenase-catalysed TRP degradation. Serum TRP and KYN in RAR during periods of stable graft function were typically within the normal range, however, the median values for serum KYN demonstrated significant increases 5-7 days prior to biopsy-confirmed acute rejection (1.6-fold, P less than 0.01) and on the day of biopsy (1.7-fold, P less than 0.001). Serum KYN was also markedly elevated in patients who contracted viral or Gram-negative bacterial infections in the absence of graft rejection. Serum KYN was not correlated with serum creatinine in RAR nor were serum TRP or KYN affected by antirejection therapy with high dose steroids. Retrospective analysis of intra-patient changes in serum KYN demonstrated that KYN monitoring was a useful adjunct to serum creatinine in the early detection of first acute rejection episodes. The first course of OKT3 therapy was associated with low serum TRP and significant increases in serum KYN (two- to three-fold) following the first three doses. The time course of these abnormalities corresponded to that over which many of the side effects of the OKT3 'first dose reaction' have been reported to occur. Significant changes in serum KYN were not observed in patients receiving repeat courses of OKT3 therapy. Significant decreases in serum TRP and significant increases in serum KYN were both prevalent and frequent in RAR during the first two postoperative months.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular analysis of the myoadenylate deaminase deficiencies

Myoadenylate deaminase (mAMPD) deficiency is a clinically heterogeneous metabolic myopathy consisting of primary (inherited) and secondary (acquired) forms based on a variety of clinical and laboratory findings. To provide a basis for delineating the underlying molecular defects in mAMPD deficiency, and as a means to test the proposal for multiple forms of the resulting disease, Northern blot analyses were performed with RNA isolated from individual patients with classified primary and secondary deficiency utilizing human mAMPD cDNA probes isolated from adult skeletal muscle libraries. Analysis of nine patients with primary mAMPD deficiency indicates normal abundance of mAMPD transcript. No immunoreactive mAMPD polypeptide is detected in Western blot analyses of skeletal muscle extracts prepared from these patients. Specificity to mAMPD is demonstrated by normal creatine kinase (CK) activities and M-creatine kinase (M-CK) transcript abundance. Similar analyses of four individuals with secondary mAMPD deficiency reveal heterogeneity in this subgroup of patients. Whereas two of these patients exhibit normal mAMPD transcript abundance, two others associated with inflammatory myopathy display reductions in mAMPD and M-CK transcript abundance. Examination of tissue sections derived from the same biopsies utilized in the isolation of RNA demonstrates the integrity of the skeletal muscle in those patients with associated inflammatory myopathy. Combined, these data support the proposal for multiple forms of mAMPD deficiency, and indicate that the primary condition is most commonly characterized by specific point mutations or small deletions/rearrangements in the ampd 1 gene, whereas some patients with secondary mAMPD deficiency display more generalized aberrations in gene expression.

Exon recognition and nucleocytoplasmic partitioning determine AMPD1 alternative transcript production

Two mature transcripts are produced from the rat AMP deaminase 1 (AMPD1) gene, one that retains exon 2 and one from which exon 2 has been removed. The ratio of these two transcripts is controlled by stage-specific and tissue-specific signals (I. Mineo, P. R. H. Clarke, R. L. Sabina, and E. W. Holmes, Mol. Cell. Biol. 10:5271-5278, 1990; R. L. Sabina, N. Ogasawara, and E. W. Holmes, Mol. Cell. Biol. 9:2244-2246, 1989). By using transfection studies with native, mutant, and chimeric minigene constructs, two steps in RNA processing that determine the ratio of these two transcripts have been identified. The first step is recognition of this exon in the primary transcript. The primary transcript is subject to alternative splicing in which exon 2 is either recognized and thereby included in the mature mRNA or is ignored and retained in a composite intron containing intron 1-exon 2-intron 2. The following properties of the primary transcript influence exon recognition. (i) Exon 2 is intrinsically difficult to recognize, possibly because of its small size (only 12 bases) and/or a suboptimal 5' donor site at the exon 2-intron 2 boundary. (ii) Intron 2 plays a permissive role in recognition of exon 2 because it is removed at a relatively slow rate, presumably because of the suboptimal polypyrimidine tract in the putative 3' branch site. The second step in RNA processing that influences the ratio of mature transcripts produced from the AMPD1 gene occurs subsequent to the ligation of exon 2 to exon 1. An RNA intermediate, composed of exon 1-exon 2-intron 2-exon 3, is produced in the first processing step, but it is variably retained in the nucleus. Retention of this intermediate in the nucleus is associated with accumulation of the mature mRNA containing exon 2, while cytoplasmic escape of this intermediate is reactions, exon recognition and nucleocytoplasmic partitioning, determine the relative abundance of alternative mRNAs derived from the AMPD1 gene.

Free amino acids during chronic cyclosporine A toxicity in intact and partially nephrectomized rats

The effects of 40 days of treatment with Cyclosporine A (CSA) on plasma and urine free amino acids were investigated in sham-operated (C) and partially nephrectomized (Pnx) female Fischer 344 rats. High Dose CSA (30 mg/kg/day ip) was associated with reduced weight gain, increased plasma urea nitrogen, and hypoproteinemia in C and Pnx animals. These animals also demonstrated increased plasma levels of alanine, markedly reduced levels of tryptophan, and an increase in urinary excretion of methylhistidines. C but not Pnx animals also showed a significant increase in plasma serine and a decrease in plasma taurine. CSA treatment of group C resulted in a progressive aminoaciduria involving substrates of the neutral and acidic renal amino acid transport systems; however, the renal excretion of taurine and beta-alanine by these animals was markedly reduced as compared to vehicle treated controls. High dose CSA exacerbated aminoaciduria in Pnx animals, but in this group, the excretion of beta amino acids was also increased. Our findings demonstrate that chronic CSA toxicity in rodents with normal renal function is characterized by increased muscle protein catabolism, significant reductions in plasma tryptophan, and an apparent decrease in whole body taurine pools. With the exception of the taurine abnormalities. CSA treatment had similar effects on Pnx animals; however, in this group, CSA-induced pathological changes were superimposed on the changes due to renal insufficiency per se. CSA toxicity as identified by the parameters investigated in this study was no more severe in Pnx animals with moderate chronic renal insufficiency than in controls with intact renal function.

The effect of chronic renal insufficiency on cyclosporine nephrotoxicity

Despite cyclosporine's efficacy in preventing rejection, its use has been hampered by nephrotoxicity. Questions remain concerning its application in patients with decreased renal function. The purpose of this study was to 1) establish a reliable animal model with chronic renal insufficiency (CRI) to study cyclosporine (CyA) nephrotoxicity, and 2) compare the long-term (50 day) severity of CyA nephrotoxicity in CRI versus normal animals. Fischer 344 rats were divided into six groups (15 to 22 each). In three groups, CRI was induced by a 5/6th nephrectomy (three groups were sham operated). After three wks., daily i.p. injections of olive oil, CyA at five mg./kg., or CyA at 30 mg./kg. daily were administered. Serum and urine were collected at 10 day intervals for the determination of biochemical indices of renal function. Animals were sacrificed after 50 days of treatment and renal histology was evaluated by light and electron microscopy. Chronic CyA treatment was well tolerated by both intact and CRI rats, suggesting that this is a reliable model for long-term CyA toxicity studies. CyA decreased renal function at day 50 in both CRI and intact animals. CRI of mild to moderate degree had little effect on the biochemical and histological indices of CyA induced nephrotoxicity. CRI does appear to potentiate the metabolic toxicity that occurs after chronic treatment with high dose CyA.

Adenylate deaminase deficiency in a mutant murine T cell lymphoma cell line

From a population of wild type S49 cells, a clone, DTB6, was isolated in a single step from selective medium containing thymidine and dibutyryl cyclic AMP that exhibited a 60% deficiency in AMP deaminase (AMP-D) activity. The AMP-D deficiency conferred to the DTB6 cells a striking susceptibility to killing by low concentrations of either adenine or adenosine, the latter in the presence of an inhibitor of adenosine deaminase activity. This growth supersensitivity of DTB6 cells toward adenine could be ameliorated by the addition of hypoxanthine to the culture medium. Immunoprecipitation of AMP-D from wild type and mutant cells revealed that the DTB6 cell line contained markedly diminished amounts of the AMP-D isozyme which reacts with antisera to the predominant isoform expressed in adult kidney. The quantities of the AMP-D isozyme immunoprecipitated by antisera raised to the predominant isoform prepared from adult heart were equivalent in the two cell lines. Although Northern blot analyses revealed no alterations in mRNA sizes or levels encoded by either of the AMP-D genes, Southern blots of genomic DNA hybridized to a cDNA specific for the ampd2 gene revealed the presence of a new BamHI restriction fragment in the DNA of DTB6 cells. These data suggested that a point mutation has occurred in the ampd2 gene of DTB6 cells which encodes the AMP-D isozyme recognized by the kidney antisera. The DTB6 cells also possessed a virtual complete deficiency in thymidine kinase activity. The two enzyme deficiencies were distinguishable. The ability to isolate single step mutants with two seemingly independent biochemical abnormalities raises the speculation that there may be some link between cellular functions responsible for purine nucleotide and thymidine metabolism.

Adenylate deaminase. A multigene family in humans and rats

Multiple AMP deaminase (AMP-D) isoforms have been found in vertebrates, and tissue-specific inherited deficiencies of AMP-D have been described in two unrelated clinical syndromes suggesting there may be more than one AMP-D gene in higher eukaryotes. Using a newly isolated cDNA cloned from an adult rat brain library and a previously reported cDNA cloned from adult rat skeletal muscle, two linked AMP-D genes have been identified in rat and man. ampd1 is expressed at high levels in skeletal muscle of the adult rat. ampd2 is the predominant gene expressed in non-muscle tissues and smooth muscle of the adult rat, and it is also the predominant gene expressed in embryonic muscle and undifferentiated myoblasts. Both genes are expressed in cardiac muscle of the adult rat. The peptides encoded by these two genes have distinct immunological properties. The conservation of nucleotide sequence and exon/intron boundaries in these two genes suggests they arose by duplication of a common primordial gene around 150 million years ago.

Characterization of the human and rat myoadenylate deaminase genes

AMP deaminase is an ubiquitous enzyme in eukaryotic cells, and tissue-specific isoforms are produced in mammals by differential expression of the two genes which encode this enzyme activity as well as by alternative splicing of the primary transcript of one of these genes. Deficiency of this enzyme activity is one of the most common causes of metabolic myopathy in man. To provide a framework for understanding the molecular basis of this inherited disorder and the mechanisms responsible for regulating the expression of this enzyme activity, both the human and rat muscle-specific genes for AMP deaminase have been cloned and partially sequenced. Comparison of the two genes shows a high degree of conservation of sequence and structural organization. The two genes share the following characteristics: 1) both are approximately 20 kilobases in size, have identical exon/intron boundaries, and exhibit similar intron/exon structural organization; 2) the transcription start site is located at the same position in both genes, and comparison of 5'-flanking sequences reveals four highly conserved domains that together contain the information necessary for muscle-specific expression of a receptor cDNA; 3) coding sequences are 88% identical and the 5'-untranslated regions are 67% identical; 4) both genes have extremely short 3'-untranslated regions (13-17 nucleotides); 5) highly conserved intervening sequences of several hundred nucleotides surround most exon/intron boundaries. In situ hybridization and analysis of human-mouse somatic cell hybrids have localized the human gene (designated AMPD1) to chromosome 1 in the region p13-p21. The implications of these structural properties for identifying functional domains in the AMP deaminase peptide, regulation of expression of this gene, and inheritance of AMP deaminase deficiency are discussed.

Reversal of creatine kinase translational repression by 3' untranslated sequences

A subline of U937 cells (U937D) was obtained in which creatine kinase B (CK-B) messenger RNA was present and bound to ribosomes, but CK activity was undetectable. Transformation of U937D cells with retrovirus vectors that contain the 3' untranslated region (3' UTR) of CK-B messenger RNA exhibited CK activity with no change in abundance of CK-B mRNA. The 3' UTR formed a complex in vitro with a component of S100 extracts from wild-type cells. This binding activity was not detectable in S100 extracts from cells that expressed CK activity after transformation with the 3' UTR-containing vector. These results suggest that translation of CK-B is repressed by binding of a soluble factor or factors to the 3' UTR.