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Biomedical subjects

G D Luk

Publications and source records attributed to G D Luk.

At least 91 records · Page 5Linked to original sources
PubMed1986

Kinetic changes in mucosal ornithine decarboxylase activity during azoxymethane-induced colonic carcinogenesis in the rat.

In the azoxymethane (AOM)-treated rat model of colonic carcinogenesis, serial injections of the carcinogen lead to the eventual development of colonic tumors. However, the precise nature of carcinogenesis events in this commonly used model is not well defined, and the occurrence of classic initiation and promotion phases after serial injections is uncertain. Since increases in ornithine decarboxylase (ODC) activity have been associated with promotion in other tumor models, we measured mucosal ODC during AOM carcinogenesis in the rat. We gave male Fischer 344 rats ten weekly injections of AOM at a dose of 3 mg/kg (Wk 1-10) and measured colonic mucosal ODC activity during the entire 25-wk course. Colonic tumor incidence at Wk 25 was 0% in controls and 48% in AOM animals (15 of 31). Mucosal ODC in AOM animals was significantly increased over controls. The time course of changes in mucosal ODC was similar throughout the entire colon and differed generally in magnitude only. Distinct and prolonged increases in ODC activity occurred within 4 h of a single injection of carcinogen and persisted for at least 14 days. With a second AOM injection on Day 7, there was another distinct and prolonged increase in ODC over the persistently elevated activity. Over the entire 25 wk, the increase in ODC was distinctly biphasic, higher at Wk 2, 11, and 13 than at Wk 6, 17, 21, and 25. The findings indicate that AOM induces an increase in mucosal ODC during colonic carcinogenesis, and they suggest that this carcinogenesis model, with ten weekly injections of carcinogen, has the properties of a multistep process. The early peak in ODC might be associated with the early carcinogenesis (initiation) phase(s), and a subsequent second increase in ODC might be associated with late carcinogenesis (post-initiation or promotion) phase (s). These results strengthen the utility of the rat AOM colonic carcinogenesis model for further studies of the role of ODC and polyamine metabolism in neoplastic transformation.

Animals↗
PubMed1985

The effects of total parenteral nutrition on gastrointestinal growth and development.

Total parenteral nutrition (TPN) is vital for the nutritional support of infants with disorders of the gastrointestinal tract that prevent adequate enteral intake. Studies in adult rodents maintained on TPN have demonstrated intestinal atrophy and decreased activity of the brush border enzymes of the small bowel mucosa. We studied the effects of TPN during the phase of rapid intestinal growth and development in piglets. Matched groups of three 6-week-old weaned piglet littermates received a glucose (45 g/kg/d), amino acid (8 g/kg/d), and fat (2.5 g/kg/d) solution intravenously (IV) or by gastrostomy (GF), or were given hog chow (Chow) at an equivalent caloric value for three weeks. No differences were noted in the mean weight gain (13-15 g/kg/d), total serum protein (4.5-4.8 g/dL), BUN (9-12 mg/dL), or Hct (25% to 30%). The IV and GF animals, compared to the Chow animals, had decreased growth of the stomach, small bowel, and pancreas with decreased small bowel mucosal disaccharidase activity. The IV group, compared to Day 0 animal measurements, had decreased small bowel length and weight and pancreatic weight. Histology of the proximal small bowel mucosa in the IV animals showed decreased mucosal depth, villus height, crypt depth, and epithelial cell number from the crypt base to the midvillus. These findings suggest that stomach, small bowel, and pancreatic growth are dependent on the route of administration and/or the composition of the diet, the small bowel mucosa and the pancreas atrophies in young piglets maintained on TPN, the activity of some intestinal brush border disaccharidases are decreased in the small bowel in piglets maintained on either an intravenous or an intragastric infusion of a TPN solution.

Animals↗
PubMed1984

Ornithine decarboxylase as a biologic marker in familial colonic polyposis.

We investigated whether the activity of ornithine decarboxylase might serve as a diagnostic test for detecting the presence of the genotype for familial polyposis. This rate-limiting enzyme in the polyamine biosynthetic pathway is essential for intestinal mucosal proliferation. In colonic mucosa from 16 normal controls, ornithine decarboxylase activity was less than 2.5 nmol per milligram per hour. In contrast, it was higher than 2.5 nmol per milligram per hour in the normal-appearing areas of colonic mucosa from 11 of 13 patients with familial polyposis and in all polyps biopsied from these same subjects (P less than 0.05 for specimens from both sites, as compared with controls). Mucosa from dysplastic polyps showed higher mean ornithine decarboxylase activity than mucosa from polyps that were not dysplastic (P less than 0.05). In colonic mucosa from clinically unaffected, first-degree relatives of patients with familial polyposis, there was a bimodal distribution of ornithine decarboxylase activity, with one peak at the mean for normal controls and the other near the mean for normal-appearing mucosa from affected patients. Our study suggests that ornithine decarboxylase activity in colonic mucosa may reflect the abnormal proliferative state in familial polyposis and identify clinically normal family members who carry the genotype.

Clinical Enzyme Tests↗
PubMed1984

Polyamines and intestinal growth: absolute requirement for ODC activity in adaptation during lactation.

Ornithine decarboxylase (ODC), through the regulation of polyamine biosynthesis, is important in cell proliferation and differentiation. We followed intestinal mucosal ODC activity in lactating Lewis rats and correlated the ODC levels with the characteristic small intestinal adaptive changes accompanying lactation. During the first 14 days of lactation, mucosal ODC activity increased, with the maximal increase on day 5 corresponding to the time of maximal morphological intestinal adaptation. In animals given the specific inhibitor of ODC, alpha-difluoromethylornithine (DFMO), intestinal mucosal ODC activity was inhibited, and intestinal adaptation was suppressed, with marked diminution of the adaptive increase in mucosal weight and thickness especially in crypt depth. Our results suggest that ODC activity plays an essential role in mucosal hyperplasia during the intestinal adaptation accompanying lactation, possibly through the stimulation of crypt cell proliferation.

Adaptation, Physiological↗
PubMed1984

Inhibition of intestinal epithelial DNA synthesis and adaptive hyperplasia after jejunectomy in the rat by suppression of polyamine biosynthesis.

Transient increases in the activity of ornithine decarboxylase (ODC), the first and rate-limiting enzyme in polyamine biosynthesis, may be critical to initiation of cell growth. We previously reported such increases in ODC activity, and the polyamines, putrescine, and spermidine in rat ileal mucosa between days 1 and 4 after intestinal resection. During this time, there is initiation of mucosal cell hyperplasia, as measured morphologically and biochemically. Intestinal weight and mucosal thickness increase, as do mucosal DNA content and DNA synthesis. In the present study, we gave rats the specific irreversible ODC inhibitor, alpha-difluoromethyl ornithine (DFMO), beginning 3 d before jejunectomy. DFMO completely suppressed the increases in ODC activity and polyamine content in the intestinal mucosa. The suppression in ODC activity was associated with an 87% suppression of DNA synthesis, and resulted in a complete abolition of intestinal adaptation, as manifested by the absence of intestinal weight gain, increase in mucosal thickness, or increase in crypt cell production. Our results indicate that the increases in ODC activity and polyamine biosynthesis are critical for adaptive postresectional crypt cell proliferation in vivo, and that the critical step mediated by polyamines in this adaptive process is the onset of new DNA synthesis.

Animals↗
PubMed1984

Phase I trial and pharmacokinetic studies of alpha-difluoromethylornithine--an inhibitor of polyamine biosynthesis.

alpha-Difluoromethylornithine (DFMO), an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, blocks polyamine biosynthesis and has antitumor effects in animal tumor models as well as in athymic mice implanted with human small cell carcinoma. This study was designed to determine the maximally tolerated dose of oral DFMO administered every six hours for 28 days to patients with advanced solid tumors or lymphomas. DFMO levels were measured using an ion exchange chromatographic assay and pharmacokinetic studies were performed in patients treated at each dose level. Twenty-two patients received 24 courses of DFMO. The drug was generally well tolerated. Thrombocytopenia was the dose-limiting toxicity and gastrointestinal side effects were also seen. Thrombocytopenia developed in 11 of 16 patients who had received prior chemotherapy but the four patients who had no prior chemotherapy had no decrease in the platelet count. The steady state level of DFMO achieved at the highest dose (3 g/m2) were found to be within the range needed for inhibition of ornithine decarboxylase in cell-culture systems as well as for the inhibitory activity against various human tumors in vitro. A DFMO dose of 2.25 g/m2 every six hours is recommended for phase II studies in patients previously treated with cytotoxic drugs.

Adult↗
PubMed1983

Multiclonal origin of polyps in Gardner syndrome.

Electrophoretic analysis of glucose-6-phosphate dehydrogenase was performed on polyp tissue from three black female patients with Gardner syndrome and who are heterozygous for the A and B forms of this enzyme. Polyp tissues from the three patients displayed the AB phenotype. This finding suggests a multiclonal origin of polyps in Gardner syndrome. Studies of tumors originating from such polyps may provide information about the sequence of cellular events leading to malignant transformation.

Clone Cells↗
PubMed1983

Polyamine biosynthesis is required for the maintenance of peripheral blood cell elements in the rat.

The specific ornithine decarboxylase inhibitor alpha-difluoromethylornithine, when given to adult rats in vivo for 5 wk, resulted in a decrease in peripheral blood cell elements in normal rats and a marked suppression of marrow recovery in rats with chemotherapy-induced marrow hypoplasia. In normal rats, alpha-difluoromethylornithine resulted in a reduction of the leukocyte count to 73% of control, erythrocyte count to 61% of control, and platelet count to 24% of control. The bleeding time was increased to twice normal and 67% of the animals had epistaxis and 42% had melena. In rats treated with the S phase-specific chemotherapeutic agent 1-beta-D-arabinofuranosylcytosine, the simultaneous administration of alpha-difluoromethylornithine prevented the recovery of the bone marrow. The peripheral blood cell counts remained low--leukocyte count was 10% of control, and erythrocyte and platelet counts were 6% of control. All the animals developed epistaxis and melena and there was a 72% mortality. The administration of putrescine (4 mmol/kg, intraperitoneally, daily), the specific polyamine product of ornithine decarboxylase, reversed these hematologic effects in both normal and recovering marrow and resulted in rapid clinical improvement. Thus, the maintenance of normal, adult rat hematologic parameters, as with the proliferation of neoplastic and transformed cells in culture, is critically dependent on continued polyamine biosynthesis.

Animals↗
PubMed1983

Polyamines and intestinal growth--increased polyamine biosynthesis after jejunectomy.

Transient increases in the activities of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAM-DC), key enzymes in polyamine biosynthesis, may be critical to initiation of cell growth. We now report that such increases in ODC (X170) and SAM-DC (X83) activities, and their synthetic products putrescine (X4) and spermidine (X2), occur in rat ileal mucosa between days 1 and 4 after 50% intestinal resection. This is the time period of initiation of mucosal cell hyperplasia in intestinal adaptation after resection and is characterized by increased mucosal cell proliferation, as measured morphologically and biochemically. Intestinal weight increased by 76% and mucosal thickness by 48%. Mucosal DNA content increased by 67% and mucosal DNA synthesis by 104%. Increased intestinal crypt cell proliferation was manifested by a 120% increase in labeling per crypt and a 152% increase in crypt cell production rate (CCPR). The increase in ODC activity was closely associated with the increases in CCPR and rate of villus lengthening. Rates of mucosal cell proliferation, as measured by CCPR, and villus and crypt lengthening were significantly correlated with ODC activity (r = 0.97, 0.98, and 0.94, respectively; P less than 0.01 for all). Our results indicate that the increase in ODC activity, SAM-DC activity, and polyamine biosynthesis is closely associated with the process of adaptive postresectional crypt cell proliferation.

Animals↗
PubMed1983

Plasma postheparin diamine oxidase. Sensitive provocative test for quantitating length of acute intestinal mucosal injury in the rat.

Diamine oxidase (DAO; EC 1.4.3.6) is an enzyme found in high activity in the mature cells of the upper villus of rat small intestinal mucosa and in very much lower activity in all other tissues in the nonpregnant rat. This study was designed to determine whether a provocative test for increasing the level of plasma DAO activity by heparin administration could be used to monitor the extent and severity of acute, severe, small intestinal mucosal injury. In adult rats, small intestinal loops of varying lengths were perfused with 2,100 mosM sodium sulfate solution for 60 min to produce selective damage to villus epithelium. Plasma postheparin DAO (PHD) activity (180 min after 400 U/kg i.p. heparin) was measured 7 h after initiation of perfusion. With increasing length of intestinal mucosal injury, there was a progressive decrease in both basal and plasma PHD activity. The decrease in plasma PHD activity closely reflected the length of intestinal mucosa injured (n = 128, r = 0.86, P less than 0.001), and it was much more sensitive (threshold limit of detection = 13% of total length, range = 67 U/ml for 100% length of injury) than unstimulated basal levels of plasma DAO (threshold = 40%, range = 2.1 U/ml). Our previous data have suggested that DAO is unique among intestinal mucosal enzymes in that circulating levels can serve as a marker of mucosal injury; this study illustrates that the addition of a low-dose heparin administration enhances the use of DAO even further as a sensitive, quantitative, circulating marker for monitoring the extent of small intestinal mucosal injury in the rat.

Amine Oxidase (Copper-Containing)↗
PubMed1983

Regulation of hematopoiesis II: the role of polyamine inhibition on helper or suppressor influences of the thymus.

We have previously suggested in murine model systems, that two cell subpopulations with differing proliferative capacity, from the thymus, modify the growth of erythroid progenitor cells in vitro. In order to further characterize these populations, we have specifically inhibited polyamine biosynthesis; this pathway is essential for the process of cell replication. Thus, alpha-difluoromethyl ornithine (DFMO) was used to block the conversion of ornithine to putrescine, the first and rate-limiting step in polyamine biosynthesis. We observed a threefold increase in hematopoietic progenitors (CFU-S and CFU-E) from bone marrow in animals treated with DFMO. We further examined the effect of DFMO on accessory "helper" and "suppressor" cells from the thymus and observed an increase in helper activity with an elimination of suppressor activity. All of these effects of DFMO were specific for inhibition of polyamine biosynthesis, since simultaneous addition of the depleted biosynthetic product, putrescine, restored suppressor activity. We conclude that polyamine biosynthesis is required acutely for accessory cell regulation of hematopoiesis.

Animals↗
PubMed1983

Effects of dibutyryl cyclic adenosine 3':5'-monophosphate on the growth of cultured human small-cell lung carcinoma and the specific cellular activity of L-dopa decarboxylase.

High activity of L-dopa decarboxylase separates small (oat)-cell from non-small-cell lung cancer in cell culture. The present study investigates relationships between the specific cellular activity of this enzyme and: (a) cell growth kinetics of an established line (O-H-1) of human small cell lung carcinoma, and (b) responses of these cells to treatment with cyclic adenosine 3':5'-monophosphate and sodium butyrate. The O-H-1 cells, as for most other established small-cell lines, grow as suspended cell aggregates. During growth, the specific cellular activity of L-dopa decarboxylase parallels levels for [3H]thymidine labeling index and the ratio of cells in G2-M to those in G1-G0 phases of the cell cycle. Each of these parameters is 2- to 3-fold higher during exponential versus stationary growth. Continuous treatment with dibutyryl cyclic adenosine 3':5'-monophosphate (dcAMP; 0.1 or 1 mM) and 1 mM theophylline produces simultaneous cessation of cell growth and an increase in cellular L-dopa decarboxylase activity. During this period, analyses of DNA histograms reveal an increase in the number of cells in the G2-M phase; the rate of increase in the ratio of G2-M to G1-Go cells paralleled the rate of increase in specific activity of the enzyme. The effects of the dcAMP were promptly reversible; release of the apparent G2-M block preceded regrowth of the cells and was accompanied by a return of L-dopa decarboxylase activity to base-line levels. The changes in enzyme activity were specific for cyclic adenosine 3':5'-monophosphate; another cyclic adenosine 3':5'-monophosphate analogue, 8-bromo adenosine cyclic 3':5'-monophosphate yielded similar increases in L-dopa decarboxylase to those seen with dcAMP, while 0.01 to 1 mM butyrate alone produced the inhibition of cell growth but no changes in specific activity of L-dopa decarboxylase or percentage of cells in the different phases of the cell cycle. We conclude that the specific activity of L-dopa decarboxylase, a key neuroendocrine marker for cultured small-cell lung carcinoma, is highest during proliferative growth and/or when these cells are in the G2M phase of the cell cycle. The differential effects of dcAMP and sodium butyrate offer potential for exploring neuroendocrine differentiation in this important lung cancer and related endocrine neoplasms.

Aromatic-L-Amino-Acid Decarboxylases↗
PubMed1983

Successful treatment with DL-alpha-difluoromethylornithine in established human small cell variant lung carcinoma implants in athymic mice.

We report that p.o. administration of DL-alpha-difluoromethylornithine (DFMO), a specific inhibitor of polyamine biosynthesis, markedly inhibits the growth of established implants of cultured human small cell lung carcinoma (SCC) in athymic (nude) mice. Human SCC tumor cells, from a cell line which exhibited cell death in culture in the presence of DFMO, were inoculated s.c. into athymic mice. The tumors were permitted to grow until they became palpable (0.05 cu cm, 3- to 5-mm-diameter nodules). The animals were then randomized into control, and early (low tumor burden) and late (high tumor burden) treatment groups which received 3% DFMO in the drinking water (5.0 g/kg/day). The tumors in the untreated control group grew to a size of 29 cu cm by 9 weeks, and these animals had a median survival of 9 weeks. The late treatment group began DFMO treatment 3 weeks after clinical tumor engraftment, when mean tumor size was 1.5 cu cm (1.2- to 1.5-cm-diameter nodules). Tumor growth was inhibited by 60% (11.4 cu cm) by Week 9 and survival was prolonged, with 83% survival at 10 weeks and a 56% increase in median survival to 14 weeks (p less than 0.05). The early treatment group received the same dose of DFMO beginning 1 week after tumor engraftment, when their mean tumor size was 0.1 cu cm (4- to 6-mm-diameter nodules). The early DFMO group had a 99% inhibition in tumor growth (0.3 cu cm) (p less than 0.05). Survival was also prolonged compared to the untreated controls, with 83% survival at 10 weeks and a median survival of 15 weeks (p less than 0.05). In both the early- and late-DFMO-treatment groups, no significant clinical toxicities were observed in the first 10 weeks, during which antitumor therapeutic effects were seen. DFMO may have a potential role in the treatment of sensitive human tumors such as SCC. The data suggest that DFMO may be most useful clinically in patients with SCC who have a low tumor burden. Thus, DFMO might be an important tool to produce long-term maintenance of initial clinical remissions induced by combination chemotherapy.

Animals↗
PubMed1982

Ornithine decarboxylase: essential in proliferation but not differentiation of human promyelocytic leukemia cells.

The ornithine decarboxylase inhibitor DL-alpha-difluoromethyl ornithine inhibited a proliferation-associated increase in ornithine decarboxylase activity in cultured human promyelocytic leukemia cells, resulting in a marked suppression of cell proliferation and subsequent cell loss. It also inhibited increases in ornithine decarboxylase activity associated with the phorbol ester-induced conversion of promyelocytic HL-60 cells to monocyte-like cells and the retinoic acid-induced conversion to granulocyte-like cells. However, the inhibition of ornithine decarboxylase activity did not prevent cellular differentiation. These results suggest that polyamine biosynthesis has a specific role in cell proliferation rather than in inducing differentiation that is not accompanied by proliferation. The data also demonstrate that cessation of proliferation in HL-60 cells is not necessarily associated with differentiation.

Carboxy-Lyases↗
PubMed1981

Polyamines are necessary for the survival of human small-cell lung carcinoma in culture.

Many human small-cell lung carcinoma culture lines grow as multicellular aggregate spheroids, for which high L-dopa decarboxylase activity is a marker. During the initial cell aggregation and the exponential growth phase, there is a marked increase in ornithine decarboxylase activity and an accumulation of polyamines. alpha-Difluoromethylornithine, a specific enzyme-activated, irreversible ornithine decarboxylase inhibitor, blocks the increase in ornithine decarboxylase activity and in polyamines and inhibits human small-cell lung carcinoma cell growth. After the onset of a decreased proliferation rate, the multicellular spheroid aggregates become poorly formed, cell loss ensues, and there is a decrease in L-dopa decarboxylase activity. These findings support the hypothesis that ornithine decarboxylase and the polyamines play an essential role not only in the proliferative phase but also in the viability of human small-cell lung carcinoma cells in culture. The results suggest that alpha-difluoromethylornithine, a virtually nontoxic compound, may be potentially useful in the therapy of this human tumor.

Carcinoma, Small Cell↗
PubMed1981

Diamine oxidase as a plasma marker of rat intestinal mucosal injury and regeneration after administration of 1-beta-D-arabinofuranosylcytosine.

Diamine oxidase (DAO; EC 1.4.3.6) is an enzyme found in high activity in the mature upper villus cells of rat intestinal mucosa and only in very low activity in all other tissues except for the placenta in the pregnant rat. The present study was designed to investigate whether plasma and mucosal DAO could be used to monitor the timing and severity of injury and recovery of the intestinal mucosa after administration of the chemotherapeutic agent 1-beta-D-arabinofuranosylcytosine (ara-C). A dose of 0.3 g/kg s.c. every 8 hr for 6 doses was given to adult Lewis x Brown Norway rats. This resulted in death of the proliferating crypt cells, followed by regeneration of the mucosa from the surviving crypt cells, with recovery by Day 8. This mucosal damage and recovery was reflected by histological changes and a decrease in activity of mucosal disaccharidases and alkaline phosphatase. Both mucosal and plasma DAO levels also fell markedly to less than 10% of basal levels (N = 30, p less than 0.005) by Day 4 and recovered with a time course similar to the histological and biochemical changes indicative of injury and recovery. With increasing dosage and/or increasing duration of ara-C treatment, mucosal injury was progressive, with increasing loss of both plasma and mucosal DAO levels as compared to controls (N = 38, p less than 0.005). Plasma DAO levels in three patients with leukemia following ara-C chemotherapy decreased markedly to less than 30% of basal pretreatment levels (p less than 0.05) by Days 9 to 12, with a time course that was compatible with clinical intestinal mucosal injury. Our data document that plasma DAO levels reflect the mucosal injury and subsequent recovery after ara-C treatment in the rat and humans. Thus, plasma DAO may serve as a marker of the integrity of the intestinal mucosa after chemotherapy.

Alkaline Phosphatase↗