A novel progranulin mutation associated with variable clinical presentation and tau, TDP43 and alpha-synuclein pathology

Mutations in the progranulin (GRN) gene have recently been reported as a cause of the frontotemporal dementia (FTD) syndrome. We performed a clinical, neuropathological and molecular genetic study of two families with FTD and the same novel mutation in GRN. Age of onset ranged from 35 to 75 years and all individuals progressed to a severe dementia syndrome with a mean disease duration of approximately 6-10 years. Variable clinical presentations included language impairment, behaviour change or parkinsonism. Seven total autopsies in the families (five in Family 1, two in Family 2) showed gross and microscopic evidence of neuronal loss in the neocortex, striatum, hippocampus and substantia nigra. All cases with material available for immunohistochemistry had cytoplasmic and intranuclear ubiquitin positive, tau negative inclusions that stained best with an antibody to the TDP43 protein. In addition, all but one had evidence of distinctive tau pathology. Two cases in Family 1 also had alpha-synuclein (SNCA) pathology, one with diffuse neocortical inclusions and neurites and unusual striatal cytoplasmic inclusions. Affected persons in both families had the same mutation in GRN (c.709-2A>G). A minigene construct showed that this mutation alters splicing of exon 7 and results in reduced mRNA message in brain. A single GRN mutation in these two families was associated with variable clinical presentations consistent with the FTD syndrome. All cases had ubiquitin/TDP43 immuno-positive inclusions and most had additional tau pathology. Two cases had SNCA pathology. These findings suggest a link between mutations in GRN and aggregation of tau, TDP43 and SNCA.

Decreased mitochondrial hydrogen peroxide release in transgenic Drosophila melanogaster expressing intramitochondrial catalase

The objective of this study was to develop strategies for manipulating oxidative stress transgenically in a multicellular organism. Ectopic catalase was introduced into the mitochondrial matrix, which is the main intracellular site of H2O2 formation and where catalase is normally absent. Transgenic Drosophila melanogaster were generated by microinjection of a P element construct, containing the genomic catalase sequence of Drosophila, with the mitochondrial leader sequence of ornithine aminotransferase inserted upstream of the coding region. Total catalase activities in whole-body homogenates of 10-day-old flies from four transgenic lines were approximately 30-160% higher than those from the parental and four vector-only control lines. Expression of catalase in the mitochondrial matrix was confirmed by immunoblotting and catalase activity assays. Mitochondrial release of H2O2 was decreased by approximately 90% in the transgenic lines when compared to levels in vector-only controls. This in vivo system provides a novel model for examining the functional significance of decreased mitochondrial H2O2 release.

Age-related changes in activities of mitochondrial electron transport complexes in various tissues of the mouse

The purpose of the present study was to examine the role of mitochondria in the aging process by determining whether the activities of various electron transport chain oxidoreductases are deleteriously affected during aging and whether the hypothesized age-related alterations in different tissues follow a common pattern. Activities of respiratory complexes I, II, III, and IV were measured in mitochondria isolated from brain, heart, skeletal muscle, liver, and kidney of young (3.5 months), adult (12-14 months), and old (28-30 months) C57BL/6 mice. Activities of some individual complexes were decreased in old animals, but no common pattern can be discerned among various tissues. In general, activities of the complexes were more adversely affected in tissues such as brain, heart, and skeletal muscle, whose parenchyma is composed of postmitotic cells, than those in the liver and kidney, which are composed of slowly dividing cells. The main feature of age-related potentially dysfunctional alterations in tissues was the development of a shift in activity ratios among different complexes, such that it would tend to hinder the ability of mitochondria to effectively transfer electrons down the respiratory chain and thus adversely affect oxidative phosphorylation and/or autooxidizability of the respiratory components.

Effect of age and caloric restriction on bleomycin-chelatable and nonheme iron in different tissues of C57BL/6 mice

The objective of this study was to test the hypothesis that the widely observed age-associated increase in the amounts of macromolecular oxidative damage is due to an elevation in the availability of redox-active iron, that is believed to catalyze the scission of H2O2 to generate the highly reactive hydroxyl radical. Concentrations of bleomycin-chelatable iron and nonheme iron were measured in various tissues and different regions of the brain of mice fed on ad libitum (AL) or a calorically restricted (to 60% of AL) diet at different ages. The concentrations of these two pools of iron varied markedly as a function of tissue, age, and caloric intake. There was no consistent ratio between the amounts of nonheme and the bleomycin-chelatable iron pools across these conditions. Nonheme iron concentration increased with age in the liver, kidney, heart, striatum, hippocampus, midbrain and cerebellum of AL animals, whereas bleomycin-chelatable iron increased significantly with age only in the liver. Amounts of both nonheme and bleomycin-chelatable iron remained unaltered during aging in the cerebral cortex and hindbrain of AL mice. Caloric restriction had no effect on iron concentration in the brain or heart, but caused a marked increase in the concentration of both bleomycin-chelatable and nonheme iron in the liver and the kidney. The results do not support the hypothesis that accumulation of oxidative damage with age, or its attenuation by CR, are associated with corresponding variations in redox-active iron.

Substrate and site specificity of hydrogen peroxide generation in mouse mitochondria

The objective of this study was to elucidate the mechanisms of mitochondrial H2O2 generation in mouse organs by determining the nature of their differences in substrate utilization, inhibitor sensitivity, and the site specificity affecting H2O2 production. Mitochondria were isolated from heart, brain, and kidney and the rate of H2O2 generation was measured using the FADH-linked substrates succinate and alpha-glycerophosphate as well as the NADH-linked substrates pyruvate/malate, beta-hydroxybutyrate, and glutamate. Respiratory inhibitors, antimycin and rotenone, were added singly and sequentially to each substrate-supported H2O2 generation reaction mixture to determine the mitochondrial site(s) of generation and the optimal condition(s) for maximal rates of generation. Succinate supported the highest rate of mitochondrial H2O2 generation. Moreover, it was the preferred substrate for the heart mitochondria. alpha-Glycerophosphate is a poor substrate for H2O2 generation in heart mitochondria. Inhibitor studies showed that heart mitochondria were the most sensitive and responsive to antimycin, while brain was the most sensitive to rotenone. A surprising finding was that NADH-linked substrate-supported H2O2 generation in kidney mitochondria was not responsive to rotenone. The contribution from each of the three sites (ubiquinone, NADH dehydrogenase, and alpha-glycerophosphate dehydrogenase) of mitochondrial H2O2 generation to the total was both substrate and organ dependent. Results indicate that assay conditions must be considered before comparisons of sites and rates of mitochondrial H2O2 generation among different organs can be made.

Acute dyslipoproteinemia induced by interleukin-2: lecithin:cholesteryl acyltransferase, lipoprotein lipase, and hepatic lipase deficiencies

Recombinant human interleukin-2 (rIL-2) is used to treat refractory cancers. During such treatment, patients develop severe hypocholesterolemia along with striking alterations in the concentration and composition of the circulating lipoproteins. The present study was undertaken to gather information about the pathogenesis of these abnormalities. Patients were studied before-, during- and after a 5-day course of high dose i.v. rIL-2. Whole plasma cholesterol was markedly reduced by rIL-2 administration (52%; P < 0.001), whereas the triglyceride concentration did not change. Thus, the lipoproteins became triglyceride enriched (P = 0.004). Low density lipoprotein cholesterol, apolipoprotein B (apoB), high density lipoprotein cholesterol, and apoA-I concentrations all decreased. Esterified cholesterol levels were markedly reduced. Total plasma apoE increased markedly, and two kinds of abnormal particles appeared: 1) beta-migrating, very low density lipoproteins; and 2) discoidal, apoE- and phospholipid-containing particles with abnormal density and electrophoretic mobility. The activities of two lipoprotein triglyceride hydrolases, lipoprotein lipase and hepatic lipase, fell significantly during treatment and returned promptly to pretreatment levels after rIL-2 was discontinued. Lecithin:cholesteryl acyltransferase (LCAT) activity also decreased significantly (64%) during treatment, but in contrast to the lipases, remained low for at least 5 days after the last dose of rIL-2 (P < 0.001). High dose i.v. rIL-2 induces severe dyslipidemia with deficiencies of both postheparin lipases and acute LCAT deficiency. Most, if not all, of the lipoprotein changes observed are explained by the LCAT deficiency that follows IL-2-induced hepatocellular injury and cholestasis.

Molecular screening of the lipoprotein lipase gene in hypertriglyceridemic members of familial noninsulin-dependent diabetes mellitus families

Hypertriglyceridemia is common among individuals with noninsulin-dependent diabetes mellitus (NIDDM), and heterozygous lipoprotein lipase (LPL) mutations may result in the syndrome of familial hypertriglyceridemia and low levels of high density lipoprotein (HDL) cholesterol. To test the hypothesis that heterozygous LPL mutations predispose to the hypertriglyceridemia and low HDL cholesterol levels observed among members of familial NIDDM families, we examined 36 members and 3 unrelated spouses selected from members of 20 pedigrees for triglyceride levels exceeding the age- and sex-specific 95th percentile. Eighteen pedigree members and 2 spouses were diabetic. LPL exons 1-9 were screened by single strand conformation polymorphism analysis. Six different variants were detected in exons 2, 3, 4, 8, and 9, including 4 (exons 3, 4, and 8) silent nucleotide substitutions. A common nonsense mutation (exon 9; Ser-->Ter) was present in 2 pedigrees, and a missense mutation (exon 2; Asp-->Asn) was also present in members of 2 pedigrees. Analysis of members of these families suggested an association of the exon 2 variant with hypertriglyceridemia, although this trend was no longer significant when individuals with diabetes were excluded from the analysis. The variant enzyme was not present among 83 random control individuals, and when expressed in COS-1 cells, it was similar to the wild type with respect to specific activity, heparin binding, and heat stability. Our data suggest that coding region mutations of the LPL gene cannot account for the elevated triglyceride and low HDL levels noted in diabetic individuals and their relatives in most NIDDM pedigrees, but the exon 2 Asn variant may contribute to the hypertriglyceridemia in some families.

Diabetes increases hepatic hydroxymethyl glutaryl coenzyme A reductase protein and mRNA levels in the small intestine

Previous studies have shown that both cholesterol synthesis and the activity of hepatic hydroxymethyl glutaryl coenzyme A (HMG CoA) reductase, the rate-limiting enzyme in cholesterol synthesis, are increased in the small intestine of a wide variety of different animal models of diabetes. In the present study, we demonstrate that the mass of HMG CoA reductase protein is increased in the small intestine of both streptozocin-induced diabetic rats (2.5-fold) and streptozocin/alloxan-induced diabetic dogs (2.4-fold). These increases in HMG CoA reductase protein mass are of a magnitude similar to the previously observed increases in either HMG CoA reductase activity and/or cholesterol synthesis in the small intestine of diabetic animals. Furthermore, mRNA levels for HMG CoA reductase in the small intestine of diabetic rats and diabetic dogs are increased 2.1- and 1.7-fold, respectively. These results suggest that the increase in HMG CoA reductase protein levels in the small intestine of diabetic animals is due to an increase in mRNA levels. In contrast, mRNA levels for HMG CoA reductase in the liver of diabetic rats are not increased. Additionally, mRNA levels for the low-density lipoprotein (LDL) receptor are also increased in the small intestine of diabetic animals (rats, 43%; dogs, 59%). The increase in small-intestinal cholesterol synthesis has the potential for adversely affecting lipoprotein metabolism and increasing the risk of atherosclerosis in diabetes.

Mutations in exon 3 of the lipoprotein lipase gene segregating in a family with hypertriglyceridemia, pancreatitis, and non-insulin-dependent diabetes

A proband with chylomicronemia, pancreatitis, and non-insulin-dependent diabetes (NIDDM) bears two different mutations in exon 3 of the lipoprotein lipase (LPL) gene: a missense mutation, 75Arg-->Ser, inherited through the paternal line and a truncation, 73Tyr-->Ter, through the maternal line. NIDDM appeared to be independently segregating. The R75S mutant was studied in extracts and media from transfected COS-1 cells. Detectable amounts of catalytically competent R75S LPL suggested destabilization of the active homodimer as with exon 5 mutants (Hata et al. 1992. J. Biol. Chem. 267:20132-20139). Hydrolysis of a short-chain fatty acid ester indicated that R75S does not directly affect activation of LPL by apoC-II. Subjects with NIDDM and wild-type LPL, and nondiabetic middle-aged carriers of the 73Tyr-->Ter truncation had moderate hypertriglyceridemia (260-521 mg/dl) and reduced high density lipoprotein cholesterol. A maternal aunt with NIDDM carried the truncation. Her phenotype (triglycerides of 5,300 mg/dl, eruptive xanthomatosis, and recurrent pancreatitis) was as severe as that in homozygotes or compound heterozygotes. We conclude: (a) diabetic carriers of dysfunctional LPL alleles are at risk for severe lipemia; and (b) the physiologic defects in NIDDM may be additive or synergistic with heterozygous LPL deficiency.

Missense mutations in exon 5 of the human lipoprotein lipase gene. Inactivation correlates with loss of dimerization

Most missense mutations of the lipoprotein lipase (LPL) gene identified among LPL-deficient subjects cluster in a segment of the sequence that encodes the catalytic triad as well as functional elements involved in the activation of the lipase at lipid-water interfaces. Consequently, loss of activity may result either from direct alterations of such functional elements or from less specific effects on protein folding and stability. This issue was addressed by examining biochemical properties of four such variants (A176T, G188E, G195E, and S244T) in a heterologous expression system (COS-1 cells). Variant G195E (GGA----GAA) was previously unreported. In all instances, inactive enzyme was recovered in medium, albeit at reduced levels. Cellular synthesis and extracellular degradation were similar to those for wild type, suggesting that reduced secretion resulted from increased intracellular degradation. When cell extracts were subjected to heparin-Superose affinity chromatography followed by elution on a linear salt gradient, all variants exhibited a single, inactive, low affinity immunoreactive peak. By contrast, wild-type enzyme presented an additional, high affinity, active species, which we interpret as homodimeric enzyme. Substitution of the active-site serine (S132A) led to loss of activity but maintenance of the high affinity species. When large amounts of the G188E variant were applied to the column, small but significant amounts of high affinity, active enzyme were recovered. Systematic substitutions at residue 188 showed that only glycine could accommodate structural constraints at this position. We conclude that the mutations examined did not impart lipase deficiency by affecting specific functional elements of the enzyme. Rather, they appear to affect protein folding and stability, and thereby formation and maintenance of subunit assembly.

Mechanism of maturational decline of rat intestinal lactase-phlorizin hydrolase

The maturational decline in lactase-phlorizin hydrolase (LPH) activity was studied in groups of young rats ranging from suckling to early post-weaned states. Associated maturational increases in sucrase-isomaltase (SI) and maltase-glucoamylase (MG) activities were also examined as a comparison. Over this time period changes in cellular concentrations of the three enzymes were observed, reflecting corresponding changes in enzyme activities. Synthesis patterns accompanying these maturational changes in concentration were examined using labelled leucine as a marker. Synthesis of LPH was found to be maintained at constant rates independent of the maturation-associated decline in its concentration, whereas the increases in cellular concentrations of SI and MG were due to accelerated synthesis of the enzyme. Turnover of LPH, based on both the fractional synthesis rate and the disappearance rate of labelled leucine from prelabelled LPH pools, was increased in a quantitatively similar way to the decline in LPH concentration. These findings are consistent with our earlier proposal that the maturational decline of LPH occurs because of accelerated turnover, without a decrease in its rate of synthesis.

Maturation of jejunoileal gradients in rat intestine: the role of intraluminal nutrients

Jejunoileal gradients of intestinal function are thought to be established during the third week of life in the rat when postnatal intestinal maturation occurs. In order to investigate the normal development of jejunoileal gradients and whether either the absence of intraluminal nutrients or the form in which they are provided affected the development of jejunoileal gradients, gradients for mucosal DNA, protein, lactase and sucrase were studied in suckling rats undergoing normal weaning and compared to gradients in rats receiving no intraluminal nutrients or rats receiving nutrients in elemental form. In suckling animals, preexisting jejunoileal gradients for DNA and protein persisted through the weaning period, gradients for lactase formed by rapid decline of ileal function and sucrase gradients formed by rapid increase in jejunal activities. Intraluminal nutrients in elemental form resulted in the formation of jejunoileal gradients similar to those in intestines of normally weaned rats. The lack of intraluminal nutrients resulted in no qualitative differences in the expression of jejunoileal gradients for sucrase, but provision of elemental nutrients resulted in increased jejunoileal differences for this enzyme. The lack of intraluminal nutrients resulted in no gradients for DNA, less pronounced jejunoileal differences for protein and delayed maturational decline of ileal lactase which prevented development of jejunoileal gradients for the enzyme. These studies indicate that the formation of jejunoileal gradients in the maturing rat intestine for the parameters investigated require intraluminal nutrients regardless of the form in which they are provided for their normal expression.

Intestinal and hepatic cholesterogenesis in hypercholesterolemic dyslipidemia of experimental diabetes in dogs

We previously reported that dog diabetes results in hypercholesterolemia and the accumulation of a high-density lipoprotein (HDL) subclass, HDL1. Hypercholesterolemic diabetic rodents exhibit hyperphagia, intestinal hypertrophy, and increased intestinal cholesterol synthesis and absorption; intestinal 3-hydroxy-3-methylglutaryl (HMG) CoA reductase activity is increased, whereas hepatic activity is unchanged or reduced. To determine whether similar mechanisms operate in the hypercholesterolemic diabetic dog, we measured hepatic and intestinal cholesterologenesis. Streptozocin-alloxan-induced diabetic dogs allowed access to food ad libitum were hyperphagic and hypercholesterolemic (10.1 vs. 4.47 mM) but normotriglyceridemic. Plasma HDL1 concentrations were markedly increased. Differences in renal and hepatic function were not statistically significant, except serum alkaline phosphatase, which was elevated 4-fold (P = 0.0003). Urinary mevalonate, an index of whole-body cholesterol synthesis, was increased 6-fold. Intestinal and hepatic weights were both increased, and direct measurements showed crypt and villus thickening. The activity of HMG CoA reductase per gram organ weight was increased 1.7-fold in liver and 2.1-fold in intestine. Calculated whole-organ activity in intestine was nearly twice that in liver. These observations provide strong evidence that intestinal cholesterogenesis is involved in the pathogenesis of hypercholesterolemia in dog diabetes and support the conclusion that increased cholesterol synthesis plays a role in the hypercholesterolemia of diabetes.

Synthesis and accumulation of protein and carbohydrases along the rat villus column

Enterocytes of the intestinal mucosa of infant and adult rats continuously proliferate in the crypt, mature as they migrate along the villus column, and are discharged from the villus tip. We examined the synthesis patterns of total protein, lactase-phlorizin hydrolase, sucrase-isomaltase, and maltase-glucoamylase as well as the accumulation of these enzymes in cells during migration along the villus. Labeled leucine was administered intraperitoneally to suckling and young adult rats, and radioactivity was determined in protein and digestive carbohydrase pools of developing villus cells separated sequentially from tip to base of the villus column. The developing cells were found to continuously accumulate protein and carbohydrates as they ascended the villus column. In addition, incorporation of radioactivity into total protein and carbohydrase pools occurred at generally constant rates along the length of the villus. These studies showed that the differentiated enterocyte of both infant and young adult rat intestine exhibits a pattern of continuous growth while migrating the length of the villus column and maintains synthesis of protein and digestive carbohydrates at generally constant rates during this time.

Altered maturation of small intestinal function in the absence of intraluminal nutrients: rapid normalization with refeeding

The absence of intraluminal nutrients during weaning in rats was shown to result in altered intestinal growth and maturation. In this study intestinal length, mucosal weight, DNA, protein, and total disaccharidase activities were significantly lower in animals sustained by intravenous nutrients over the normal weaning age than were normally weaned controls but were greater than preweaning values. Absorptive capacity for sucrose (assessed by hydrogen-gas production) was diminished, directly linking incomplete maturation of sucrase to diminished intestinal function. To determine whether these alterations were permanent, rats previously deprived of intraluminal nutrients over the weaning period were refed. Eight days after refeeding, all variables except total lactase had attained values found in normally weaned age-matched controls, including absorptive capacity for sucrose. Although intestinal growth and maturation is abnormal in the absence of intraluminal nutrients during weaning, the abnormalities are not permanent and are rapidly corrected upon refeeding.

Intestinal lactase in the neonatal rat. Maturational changes in intracellular processing and brush-border degradation

The mechanism of decline in the catalytic activity of intestinal lactase during neonatal maturation has not been defined, but a shift in the lactase subunit synthesis from an active 130-kDa subunit to an inactive 100-kDa species has now been noted in the adult rat (Quan, R., Santiago, N. A., Tsuboi, K. K., and Gray, G. M. (1990) J. Biol. Chem. 265, 15882-15888). The subunit structure, synthesis, intracellular assembly, and subsequent degradation of lactase from the brush-border surface membrane was examined in 15-day-old pre-weaned and 30-day-old post-weaned intact rats. Lactase was labeled intraintestinally with [35S]methionine, isolated from Triton-solubilized membranes with monospecific polyclonal anti-lactase, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The protein-stained gel revealed subunits of 225 and 130 kDa, the latter species predominating in both the pre- and post-weaned state. The distinct adult-type 100-kDa moiety was present in post-weaned animals while only a trace of a slightly larger (approximately 110 kDa) species was observed in pre-weaned animals. Quantitation of radioactivity in newly synthesized lactase revealed an increasing prominence of the 100-kDa species in post-weaned rats (130/100 incorporation ratio: pre-weaned 6.2; post-weaned 3.3). Accumulation of newly labeled lactase in brush-border membranes after intraperitoneal [35S]methionine labeling was similar in both groups at 3 h. Despite these comparable rates of lactase synthesis, assembly and insertion in the pre- and post-weaned state, subsequent removal of the 130-kDa unit was more rapid in post-weaned animals (t1/2 = 11 h; pre-weaned t1/2 = 37 h). In intact rats, the neonatal maturational decline in lactase catalytic activities involves both a shift to production of the inactive 100-kDa subunit and increased membrane surface degradation of the active 130-kDa subunit.

Regulation of intestinal ontogeny by intraluminal nutrients

Major events in gastrointestinal ontogeny occur in the infant rat in association with weaning, resulting in striking alterations in small intestinal structure and function. Although the dietary changes attendant to weaning are not essential for the initiation of these events, dietary nutrients have been shown to participate in the maturation of some intestinal parameters. In order to define more precisely the role of intraluminal nutrients in the regulation of small intestinal ontogeny, a longitudinal study was conducted using a unique animal model in which intraluminal nutrients were excluded from the intact maturing intestine in vivo throughout the entire weaning period without major compromise in nutritional status. The absence of intraluminal nutrients over the weaning period resulted in diminished lengthening and accretion of mucosal mass, suggesting a slower rate of intestinal growth. Lower mucosal DNA, protein, and mitotic indices in intestines of animals receiving no intraluminal nutrients suggested that the lack of intraluminal nutrients resulted in the blunting of the striking increases in cellular proliferation normally exhibited by the developing intestinal mucosa at this time. Maturation of intestinal lactase-phlorizin hydrolase and maltase-glucoamylase was not affected by the absence of intraluminal nutrients. Although the appearance of sucrase-isomaltase was not altered by the absence of intraluminal nutrients, activity levels rose to only 50% of control levels. These data suggest that during this period of rapid intestinal maturation, intestinal growth is more dependent upon intraluminal nutrients than are the characteristic enzymic alterations normally expressed during this period.(ABSTRACT TRUNCATED AT 250 WORDS)

Human intestinal lactase-phlorizin hydrolase: isolation and preparation of a specific antiserum

Human intestinal lactase-phlorizin hydrolase (lactase) was selectively isolated with monospecific polyclonal antibodies to rat lactase. In addition to their immunologic similarities indicated by this isolation, human and rat lactase have similar kinetic characteristics but different subunit structure when analyzed by gel electrophoresis under reducing conditions. Rabbits immunized by injecting human lactase complexed with anti-rat lactase produced specific antibodies to human lactase that exhibited little cross-reactivity to the rat enzyme. The simple single-step procedure allows isolation of human lactase in high purity from small biologic samples and preparation of specific antisera to the human enzyme.

Dietary CHO and stimulation of carbohydrases along villus column of fasted rat jejunum

Adult rats when fed a high carbohydrate diet of 70% sucrose or glucose for 24 h following a 4-day fast showed increased concentrations of intestinal sucrase-isomaltase (EC 3.2.1.48, EC 3.2.1.10) and maltase-glucoamylase (EC 3.2.1.20) but not lactase-phlorizin hydrolase (EC 3.2.1.23, EC 3.2.1.62). The concentration increases of these enzymes were accompanied by corresponding acceleration of their synthesis rates. Contrary to earlier studies by others, suggesting that upper villus cells in the fasted intestine are unresponsive to stimulation of sucrase activity by refeeding a high-sucrose diet, the concentration increases of both sucrase-isomaltase and maltase-glucoamylase were seen to occur in cells all along the length of the villus column. The earlier studies differed from the present study by basing enzyme assays relative to protein rather than the DNA content of villus cell fractions. We have shown that villus cells increase their protein content severalfold while migrating to villus tip, providing the basis for the difference between earlier and the present findings. Further evidence that stimulation of sucrase-isomaltase and maltase-glucoamylase by high carbohydrate is not restricted to the crypt and lower villus region was obtained by the finding that their synthesis rates appeared to be equally stimulated along the length of the villus column.

Maturational patterns of carbohydrases in the ileal remnant of rats after jejunectomy at infancy

The enteric epithelium of suckling rat undergoes dramatic functional and cytokinetic changes (redifferentiation) with maturation. Ileal epithelial maturation was studied in infant rats subjected to 60% proximal enterectomy at age 10 d in an effort to examine redifferentiation mechanisms. Two months after resection the residual ileal remnant was increased in diameter, weight, total protein, and DNA per unit length compared with ileal segments from control littermates that had laparotomy without resection. The residual ileum demonstrated increased sucrase activity per unit length but was indistinguishable from control ileal segments in activity per unit DNA or villus distribution. Lactase activity was negligible in all segments of the residual intestine. Villus height and crypt depth were increased in the residual ileum with slight increases in cell turnover and cell-migration rates. These results show the presence of an intrinsic program for regulation of ileal epithelial maturation and its resistance to alteration by a major stimulus applied before its expression.

Recovery of exogenous heme as carbon monoxide and biliary heme in adult rats after tin protoporphyrin treatment

We studied the effect of tin protoporphyrin (TP) on bilirubin production in adult Wistar rats by quantifying in vivo carbon monoxide (CO) excretion and the simultaneous excretion of biliary heme after common bile duct cannulation. A known amount of heme was injected intravenously as red blood cells (RBC) damaged with a sulfhydryl inhibitor, N-ethylmaleimide. The recovery of heme as CO or biliary heme in the cannulated animals was calculated as the molar percent of heme recovered over heme injected. For cannulated controls (n = 4), the recovery was 89 +/- 6% SD, and no heme appeared in bile. Cannulated rats treated with TP (n = 4) had 64 +/- 11% recovered as CO and 30 +/- 11% as heme in bile. Our findings suggest that TP is an effective in vivo inhibitor of exogenous heme catabolism and bilirubin production in adult rats. Furthermore, this inhibition results in increased excretion of heme into the bile proportional to the degree of inhibition.

Growth and differentiative maturation of the rat enterocyte

Cells of the intestinal mucosa of the infant and adult rat maintain a pattern of continuous growth, accumulating structural and functional proteins and lipids while migrating the length of the villus column. Cells of jejunal and ileal segments were fractionated sequentially from villus tip to inner crypt and distribution patterns were determined for DNA, total protein, cholesterol, phospholipid, and disaccharidases. Patterns of increasing ratios of protein, lipids, and disaccharidases to DNA were maintained to villus tips, with only slight fall-off of enzymes observed. Distribution profiles of disaccharidases, when computed relative to protein (as seen in previous reports), show distortion of the true cellular distribution pattern of these enzymes as determined by the DNA content of the fractions. Wide variation in cell protein concentrations was evident between jejunal and ileal segments in pre- and postweaned rats. Ileal cells of the suckling rat contained particularly high protein concentrations, which appeared to be largely transitory in nature and related to food intake. Cholesterol and phospholipids were found to be concentrated in the microvillus membrane and account for a significantly large fraction of the cellular content of these lipids.

Red cell destruction and bilirubin production in adult rats with short-term biliary obstruction

The rate of total bilirubin production and the concomitant relative rate of early-labeled bilirubin (ELB) formation were studied in adult Wistar rats with short-term common bile duct ligation. The pulmonary excretion rate of CO (VeCO), an index of total bilirubin production, was measured preoperatively and postoperatively on day 3 and on day 5 or 6. While the VeCO measurements of control and experimental animals were similar preoperatively, the postoperative VeCO measurements of the experimental animals averaged 30% higher than those of control animals. On postoperative day 3, the relative rate of ELB formation was measured by the recovery of excreted 14CO after the administration of 14C-labeled delta-aminolevulinic acid (ALA) or glycine as nonerythropoietic or total heme synthesis precursor, respectively. No significant differences were found in the 14CO recovered from either compound during the study period between the experimental and control animals. The half-life of 51Cr-labeled transfused red blood cells was decreased by nearly 50% in bile duct ligated rats compared to that in the sham operated ones. We conclude that hemolysis is a major factor contributing to the increase in total bilirubin production even after short-term biliary obstruction in the rat.

Effects of hydrocortisone on carbohydrase concentrations, de novo synthesis and turnover patterns in immature rat intestine

Hydrocortisone administration to infant rats enhanced cellobiase and maltase activities and induced precocious expression of sucrase and trehalase activities along the length of the small intestine. These activity changes reflected proportional concentration increases in the enzymes lactase (EC 3.2.1.23), maltase/glucoamylase (EC 3.2.1.20) and sucrase-isomaltase (EC 3.2.1.48/10). Administration of an equivalent tracer dose of [3H]leucine (by body weight) to control and hydrocortisone-treated infant rats resulted in greater accumulation of label in the carbohydrase pools of the treated rats, suggesting their increased de novo synthesis. The increased concentrations of lactase and maltase/glucoamylase induced by exogenous hydrocortisone were matched by the presence of corresponding greater amounts of label in their brush border pools. Accumulation of label in each of the lactase, maltase/glucoamylase and sucrase-isomaltase pools was generally similar in the hydrocortisone-treated rats, suggesting equivalent stimulation of their synthesis as a group by the humoral agent. The turnover rates of the carbohydrases as a group were found to be similar and did not appear to differ in control and hydrocortisone-treated rats. Total protein synthesis rates were slightly greater in the intestine of the hydrocortisone-treated group of rats.

Suppression of carbon monoxide excretion rate by tin protoporphyrin

The effect of a single prophylactic dose of tin protoporphyrin on the carbon monoxide (CO) excretion rate of antibiotic-treated neonatal rats before and after hematoma formation was evaluated. The CO excretion rate, reflecting the rate of bilirubin production, of tin protoporphyrin-treated (TP-H) rats 24 hours after injection of 65 mole of tin protoporphyrin per kilogram (time [t] = 0 hours) was approximately 18% lower than those of the saline-control (S-C) and saline-hematoma (S-H) rats, but this difference was no longer evident at t = 43 hours. After hematoma formation at t = 44 hours, the CO excretion rate of the S-H rats increased rapidly; this increase was delayed and lessened in the TP-H rats. At eight hours posthematoma (t = 52 hours), the CO excretion rate of the TP-H rats was significantly lower than that of the S-H rats, 53 +/- 2 vs 73 +/- 3 microL/kg/hr, respectively. A maximal rate of 89 +/- 5 microL/kg/hr was reached 25 hours posthematoma in the S-H rats (t = 69 hours), as compared with 80 +/- 3 microL/kg/hr at 44 hours posthematoma in the TP-H rats (t = 88 hours). The recovery of injected blood as CO over a 68-hour study period was approximately 90% for the S-H rats and approximately 65% for the TP-H rats. At t = 112 hours, hepatic heme oxygenase activity of the TP-H rats was still significantly lower than that of the S-H and S-C rats; however, plasma bilirubin concentrations of all three groups were similar. These studies demonstrate that tin protoporphyrin is an effective in vivo inhibitor of endogenous heme catabolism as measured by the CO excretion rate in antibiotic-treated neonatal rats with and without artificially created hematomas.

Nature of elevated rat intestinal carbohydrase activities after high-carbohydrate diet feeding

Adult rats that were maintained on a low-carbohydrate intake showed rapid increase in the activities of sucrase, maltase, and lactase along the length of the small intestine when they were fed a high-starch diet. In the present study, we have identified these activity increases, and showed that they reflect proportional accumulations in enzyme-protein of sucrase-isomaltase (EC 3.2.1.10, 3.2.1.48), maltase-glucoamylase (EC 3.2.1.20), and neutral lactase (EC 3.2.1.23). It was determined that each of these enzymes exists in adult rat intestine in single immunoreactive form and accounts as a group for all sucrase, cellobiase, and most maltase and lactase activities. Dietary change from low to high carbohydrate (starch) resulted in an increase in [3H]leucine accumulation in each of the enzymes, without a change in the amount of label accumulation in total intestinal proteins. The increase in label accumulation in the brush-border carbohydrase pools was matched generally by proportional elevation in the pool concentrations of sucrase-isomaltase and lactase but not maltase. These studies suggest that the elevation of intestinal carbohydrase concentrations induced by high-carbohydrate feeding may involve selective stimulation of their synthesis.

Effect of tin protoporphyrin on the excretion rate of carbon monoxide in newborn rats after hematoma formation

This study evaluated the efficacy of tin protoporphyrin (TP), a competitive inhibitor of heme oxygenase, in suppressing the total body excretion rate of carbon monoxide (CO), an index of total bilirubin formation, in neonatal rats with artificially created hematomas. Wistar rat litters less than 12 h old were each divided into three groups of similar weight and treated as follows: (a) saline control (S); (b) hematoma, 80 microliter blood (H); (c) TP, 65 mumol/kg, and hematoma (TP-H). CO excretion of the H group increased rapidly after hematoma formation, reaching a maximum value of 79 +/- 4 SE microliter/kg/h 25 h later. Treatment with TP did not affect the pattern of CO excretion or its magnitude (78 +/- 2 SE microliter/kg/h, 25 h posthematoma). The S group showed no increase in CO excretion at this time (40 +/- 2 SE microliter/kg/h). At the conclusion of the experiment (45 h posthematoma), the plasma total bilirubin levels were slightly lower in the TP-H rats (1.0 +/- 0.1 SE mg/dl) than in H rats (1.2 +/- 0.1 SE mg/dl). The S rats had a plasma total bilirubin concentration of 0.8 +/- 0.1 SE mg/dl. The hepatic and splenic heme oxygenase activities were decreased by 61% (p less than 0.001) and 48% (p less than 0.05), respectively, in the TP-H rats as compared to the H rats. The S and H rats had similar enzyme activities. The results of this study suggest that though single-dose TP decreased tissue heme oxygenase activity, it did not significantly affect total bilirubin formation.

The nature of maturational decline of intestinal lactase activity

We have examined the nature of the decline of lactase (EC 3.2.1.23) activity in the maturing rat intestine. It was established in an initial study that the activity decline reflected a proportional reduction in the concentration of the enzyme protein. Accumulation patterns of label into lactase, total intestinal proteins and sucrase (EC 3.2.1.48)-isomaltase (EC 3.2.1.10) were compared, 4 h following administration of a tracer dose of [3H]leucine to weanling rats exhibiting a wide range of lactase decline. Accumulation of increasing amounts of label in total intestinal proteins and sucrase-isomaltase pools was found to accompany the lactase decline, in contrast to accumulation of a constant amount of label in the declining lactase pools. The pattern of increased label accumulation in total intestinal proteins was shown in a corollary study to reflect a corresponding acceleration of total protein synthesis. On this basis, the finding of a constant amount of label in the declining lactase pools suggested a constant synthesis of lactase. We proposed earlier that associated reductions in enterocyte life-span (leading to correspondingly less lactase accumulation) rather than suppressed synthesis may provide the primary causal basis of lactase decline in the postweaned mammal.

Pulmonary excretion rate of carbon monoxide as an index of total bilirubin formation in adult male Wistar rats with common bile duct ligation

Total bilirubin formation (TBF) in the rat after a short period of common bile duct ligation was studied by measuring the pulmonary excretion rate of CO (VECO). At postoperative day 3, the VECO of experimental animals was higher when compared with the preoperative VECO (p less than 0.005); whereas the VECO of control animals did not change. Also, on the 3rd postoperative day, the relative rate of early labeling of bilirubin following the administration of delta-aminolevulinic acid-5-14C, a preferential hepatic heme synthesis precursor, was similar between the experimental and control animals; only the experimental animals had an abnormal peroxide hemolysis test. We conclude that common bile duct ligation in the rat is associated with elevations in the VECO, indicating significant increases in TBF, and the source of the increase is probably of erythropoietic origin. This finding may be relevant to the understanding of the pathophysiology of obstructive jaundice in human neonates.

Hydrogen gas excretion after sucrose gavage in the fasted rat

The effect of a 3-day fast on the functional ability of the adult rat to hydrolyze and absorb sucrose was determined. The evaluation was based on previous studies which have shown the total amount of hydrogen gas (H2) excreted by the animal to reflect the extent of undigested carbohydrate entering the colon from the small intestine. H2 excretion was measured using a gas chromatographic technique in experimental (72 h fasted) and control (12 h fasted) animals after administration of sucrose by gastric gavage. Total H2 excretion was 3-fold higher in the experimental animals (n = 5) than in the controls (n = 5) (p less than 0.005) indicating a significant increase of sucrose malabsorption in the experimental animals. Administration of a second dose of sucrose 8 to 9 h after the first dose (refeeding) resulted in markedly decreased malabsorption relative to the first administration in both experimental (n = 2) and control (n = 2) animals. These results suggest that a 3-day fast markedly impairs the ability of the intestine to hydrolyze and absorb sucrose and that refeeding rapidly restores the ability to utilize this substrate. H2 excretion was similar between experimental and control animals after the administration of lactulose, a nonabsorbed and nondigested carbohydrate, suggesting that the observed results of the sucrose studies were independent of any possible changes in the intestinal microflora.

The role of bilirubin production in breast-fed infants with elevated serum bilirubin concentrations at 2 weeks of life

The carboxyhemoglobin level (COHb), an accepted qualitative index of bilirubin production, was measured in normal, full-term, breast-fed (n = 9) or formula-fed (n = 11) infants at 2 days and 2 weeks of life. The mean COHb did not differ significantly at 2 days and 2 weeks in either of the groups, nor did the mean COHb differ between the groups at 2 weeks. The mean serum bilirubin concentration was lower in the formula-fed infants compared to the breast-fed infants at 2 weeks (p less than 0.05). The mean serum bilirubin concentration decreased by only 14 percent among the breast-fed infants, and actually increased in three infants by 2 weeks. In comparison, the mean serum bilirubin concentration of the formula-fed infants decreased by 61 percent (p less than 0.05), with the serum bilirubin concentration decreasing in each infant by 2 weeks. These findings are consistent with the generally held belief that bilirubin production is not the primary etiology of elevated serum bilirubin concentrations associated with breast-feeding in the second week of life. However, continued high bilirubin production at 2 weeks may contribute to the potential for significant jaundice in some infants with impaired hepatic function or increased enterohepatic circulation of bilirubin.

Carbon monoxide in blood: an improved microliter blood-sample collection system, with rapid analysis by gas chromatography

We examined the sensitive assay for carboxyhemoglobin based on reaction with K3Fe(CN)6 and gas chromatography of the liberated CO. Our improvements included increased baseline stability, shorter analysis time, and simpler standardization. EDTA-containing Vacutainer Tubes (lavender-stoppered) increase the carboxyhemoglobin content of blood stored in them. The carboxyhemoglobin content of blood stored in capillary tubes containing solid heparin and saponin remained stable for two weeks. Using our improved procedures, we measured the carboxyhemoglobin content of blood from adults and neonates collected via venipuncture or heel or fingersticks. We observed no significant difference in carboxyhemoglobin content of blood obtained by venipuncture or heel stick for premature infants, 0.19 +/- 0.04 vs 0.18 +/- 0.03 mL of CO per 100 mL of blood, respectively (mean +/- SD). Nonsmoking adults (n = 19) had CO values (mean +/- SD) of 0.19 +/- 0.03 and 0.17 +/- 0.04 mL per 100 mL of blood, and smoking adults (n = 7) gave CO values of 0.96 +/- 0.49 and 0.91 +/- 0.49 mL/dL, for venipuncture and fingerstick, respectively.

Carbon monoxide in blood: an improved microliter blood-sample collection system, with rapid analysis by gas chromatography

We examined the sensitive assay for carboxyhemoglobin based on reaction with K3Fe(CN)6 and gas chromatography of the liberated CO. Our improvements included increased baseline stability, shorter analysis time, and simpler standardization. EDTA-containing Vacutainer Tubes (lavender-stoppered) increase the carboxyhemoglobin content of blood stored in them. The carboxyhemoglobin content of blood stored in capillary tubes containing solid heparin and saponin remained stable for two weeks. Using our improved procedures, we measured the carboxyhemoglobin content of blood from adults and neonates collected via venipuncture or heel or fingersticks. We observed no significant difference in carboxyhemoglobin content of blood obtained by venipuncture or heel stick for premature infants, 0.19 +/- 0.04 vs 0.18 +/- 0.03 mL of CO per 100 mL of blood, respectively (mean +/- SD). Nonsmoking adults (n = 19) had CO values (mean +/- SD) of 0.19 +/- 0.03 and 0.17 +/- 0.04 mL per 100 mL of blood, and smoking adults (n = 7) gave CO values of 0.96 +/- 0.49 and 0.91 +/- 0.49 mL/dL, for venipuncture and fingerstick, respectively.

Detection of gastric contents in tracheal fluid of infants by lactose assay

We designed an in vitro assay to detect the presence of lactose in the tracheal aspirates of premature, ventilator-dependent infants. This method was employed to identify recurrent, unrecognized aspiration, which could prolong the requirements for ventilator support and contribute to the development of chronic lung disease. One hundred five determinations of lactose were performed on the tracheal fluid obtained from 42 ventilator-dependent infants who were receiving enteral feedings. There was a wide range of lactose levels (0 to 3,270 nmol lactose/ml tracheal aspirate). Six infants had samples that were highly suggestive of aspiration (greater than 200 nmol lactose/ml tracheal aspirate). Twenty infants had questionably positive samples (25 to 200 nmol lactose/ml tracheal aspirate), and 16 infants had samples that were considered negative for aspiration (less than 25 nmol lactose/ml tracheal aspirate).

Delayed ontogenic development in the bypassed ileum of the infant rat

Ontogenic development continues after birth in mammalian enteric epithelium as an adaptive mechanism to extrauterine life. In the rat, particularly significant developmental changes in enteric structure, function, and cytokinetic properties occur over a short critical period (usually between 16 and 20 days of age), preparatory to dietary change with weaning. Surgical bypass of ileal segments was performed on suckling rats of 12-14 days of age, and the effect on subsequent intestinal development was studied in both the bypassed and the shortened segment remaining in continuity. The bypassed segment, although achieving normal maturational patterns of active sucrase appearance and maltase accumulation, continued to maintain coincident immature patterns of high lactose activity and low cell turnover times. The intestine in continuity showed precocious appearance of active sucrase and accumulation along with maltase to greater than control levels, accompanied by a normal coincident decline in lactase activity and enterocyte life-span. Involvement of intraluminal influences on various parameters of enteric ontogenic development is thus indicated with the effects expressed by a delay in the excluded (bypassed) segment and by stimulation in the shortened segment in continuity. Data are presented in further support of the hypothesis that the life-span of the enterocyte serves postnatally as a primary determinant of enteric lactase levels.

Sugar hydrolases and their arrangement on the rat intestinal microvillus membrane

The arrangement of the sugar hydrolases, sucrase-isomaltase, maltase, and lactase on the microvillus membrane of rat intestine was investigated by immunological technique. The enzymes were purified essentially free of each other to near homogeneity and antisera of high specificity were obtained against each. Microvillus membranes were prepared routinely in high purity from rat intestine and contained an average 61% protein, 20% lipid, and 19% carbohydrate, with the sugar hydrolases comprising an estimated 20--25% of the membrane protein. The immunoreactivity of membrane-bound sucrase-isomaltase, maltase, and lactase was investigated with antisera demostrating specific reactivity to each, when tested in the presence of other membrane extractives. The membrane-bound enzymes were found in each case to combine with antibody in amounts equivalent to that required to effect precipitation of comparable units of the free enzymes from solution. Preloading membrane vesicles with antibodies to any two of the enzymes did not affect either the immunoreactivity or extractability (by papain or Triton X-100) of the third. The antibody-binding studies indicated an arrangement of these enzymes independent of each other on the membrane surface, in a manner allowing each to maintain a high degree of molecular freedom.

Sugar hydrolases of the infant rat intestine and their arrangement of the brush border membrane

Lactase and maltase, the predominant sugar hydrolases associated with the intestinal brush bordermembrane of the suckling rat, were purified essentially free of the other to near homogeneity (lactase at specific activity 23, maltase at specific activity 58), and their specific physiocochemical properties determined. Antisera prepared to each showed by immunodiffusion a single common precipitin line with pure enzyme and solubilized proteins of the brush border membrane. Brush border membranes were purified 26--35-fold from infant rat intestine. Membranes prepared from 10-day-old rats contained 32% protein, 43% lipid and 25% carbohydrate with lactase and maltase estimated to comprise in excess of 10% and 2%, respectively, of the membrane protein. Immunotitration curves of lactase and maltase showed equivalent antibody binding by the membrane-bound and free enzyme forms. Furthermore, antibody binding to one enzyme did not affect the immunotitration curve or the extractability (by papain or Triton X-100) of the other membrane-bound enzyme. It was concluded that the lactase and maltase molecules are attached singly on the external membrane surface in a spatially independent manner with their antigenic sites as freely available to antibody binding as exhibited by their papain-solubilized counterparts.

Antiproliferative agents and differential survival between normal and cancer cells

A basic difference in response between normal cells (primate fibroblasts) and colonic cancer cells (human and rodent) to the antiproliferative action of both N-(phosphonacetyl)-L-aspartate and thymidine is described in this report. Both normal and colonic cancer cells, when cultured in the presence of these agents, cease to increase their cell numbers. Evidence is presented to show that the normal cells respond to deprivation of pyrimidine nucleotide induced by these agents by simple growth arrest, in which a quiescent state may be maintained for prolonged periods without cell death. Cancer cells are shown to respond in a characteristically different manner in which cell division continues accompanied by limited cell survival, with the surviving population representing a balance of these opposing processes. The extent to which these in vitro findings, based on a limited number of comparisons under restrictive artificial conditions, relate to the in vivo state remains to be established.

Pseudouridine-deficient transfer RNAs from Escherichia coli B and their use as substrates for pseudouridine synthetase

Transfer RNAs isolated from Escherichia coli B grown in the presence of 2-thiouracil are deficient in pseudouridine. Much of this deficiency is from the T psi C region, which has only about 50% of its normal pseudouridine content. The other modified nucleoside from this region, ribothymidine, is reduced by only about 10%. Studies showed that 2-thiouracil is incoproated into the RNA of E. coli during growth in the presence of the analog. This incorporation appears to result from the replacement of uracil, occur in a random manner, and involve all RNA species. The extent of incorporation varies from 1 to 3 mol %, depending upon the preparation and RNA species examined. Electrophoresis on polyacrylamide gels and chromatography on Sephadex G-75 and reverse phase (Systen 5) columns of normal and 2-thiouracil-containing tRNAs revealed no profile differences. No accumulation of any precursor tRNA in the thiopyrimidine-treated cells is found. A partial recovery of the pseudouridine content of 2-thiouracil-containing tRNAs can be achieved in vivo by removal of the 2-thiouracil from the culture media. These transfer RNAs have also been used as substrates to study the properties of a partially purified preparation of pseudouridine synthetase II invitro and should be useful as substrates in the further purification of this enzyme.

Selective inhibition of pyrimidine biosynthesis and effect on proliferative growth of colonic cancer cells

A highly selective inhibition of de novo pyrimidine synthesis in the intact cell has been demonstrated by the action of N-(phosphonacetyl)-L-aspartate (PALA), a transition-state analog inhibitor of the reaction catalyzed by asparate transcarbamylase. The effect of pyrimidine deprivation induced by this agent on the viability and survival of human normal (WI-38) and colonic cancer cells (HT-29) was examined. The PALA-treated, pyrimidine-deprived cells failed to grow but demonstrated a normal rate of glucose utilization with impaired glycogen synthesis. Pyrimidine deprivation and lack of cell growth were maintained long after PALA removal. Growth inhibition of HT-29 cells by PALA was found to reflect an apparent steady state between newly formed and dying cells induced by limited pyrimidine availability. The highly selective nature of PALA action was confirmed by the ability of an exogenous source of pyrimidine to restore the normal growth pattern of the cell. Significant antitumor activity of PALA was found against a transplantable colonic tumor (line 26) carried in mice.